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Revision 1.35 by root, Fri Nov 23 19:35:09 2007 UTC vs.
Revision 1.195 by root, Mon Oct 20 17:50:48 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_ struct 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_ struct 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	struct 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<struct 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);
…		…
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<struct 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		284
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
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
194	This will initialise the default event loop if it hasn't been initialised	289	This will initialise the default event loop if it hasn't been initialised
…		…
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	struct 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, struct 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	struct 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
571	problem. You best act on it by reporting the problem and somehow coping	899	problem. You best act on it by reporting the problem and somehow coping
572	with the watcher being stopped.	900	with the watcher being stopped.
573		901
574	Libev will usually signal a few "dummy" events together with an error,	902	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	903	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	904	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	905	the error from read() or write(). This will not work in multi-threaded
578	programs, though, so beware.	906	programs, though, as the fd could already be closed and reused for another
		907	thing, so beware.
579		908
580	=back	909	=back
581		910
		911	=head2 GENERIC WATCHER FUNCTIONS
		912
		913	In the following description, C<TYPE> stands for the watcher type,
		914	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
		915
		916	=over 4
		917
		918	=item C<ev_init> (ev_TYPE *watcher, callback)
		919
		920	This macro initialises the generic portion of a watcher. The contents
		921	of the watcher object can be arbitrary (so C<malloc> will do). Only
		922	the generic parts of the watcher are initialised, you I<need> to call
		923	the type-specific C<ev_TYPE_set> macro afterwards to initialise the
		924	type-specific parts. For each type there is also a C<ev_TYPE_init> macro
		925	which rolls both calls into one.
		926
		927	You can reinitialise a watcher at any time as long as it has been stopped
		928	(or never started) and there are no pending events outstanding.
		929
		930	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,
		931	int revents)>.
		932
		933	Example: Initialise an C<ev_io> watcher in two steps.
		934
		935	ev_io w;
		936	ev_init (&w, my_cb);
		937	ev_io_set (&w, STDIN_FILENO, EV_READ);
		938
		939	=item C<ev_TYPE_set> (ev_TYPE *, [args])
		940
		941	This macro initialises the type-specific parts of a watcher. You need to
		942	call C<ev_init> at least once before you call this macro, but you can
		943	call C<ev_TYPE_set> any number of times. You must not, however, call this
		944	macro on a watcher that is active (it can be pending, however, which is a
		945	difference to the C<ev_init> macro).
		946
		947	Although some watcher types do not have type-specific arguments
		948	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
		949
		950	See C<ev_init>, above, for an example.
		951
		952	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
		953
		954	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
		955	calls into a single call. This is the most convenient method to initialise
		956	a watcher. The same limitations apply, of course.
		957
		958	Example: Initialise and set an C<ev_io> watcher in one step.
		959
		960	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		961
		962	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)
		963
		964	Starts (activates) the given watcher. Only active watchers will receive
		965	events. If the watcher is already active nothing will happen.
		966
		967	Example: Start the C<ev_io> watcher that is being abused as example in this
		968	whole section.
		969
		970	ev_io_start (EV_DEFAULT_UC, &w);
		971
		972	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)
		973
		974	Stops the given watcher if active, and clears the pending status (whether
		975	the watcher was active or not).
		976
		977	It is possible that stopped watchers are pending - for example,
		978	non-repeating timers are being stopped when they become pending - but
		979	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
		980	pending. If you want to free or reuse the memory used by the watcher it is
		981	therefore a good idea to always call its C<ev_TYPE_stop> function.
		982
		983	=item bool ev_is_active (ev_TYPE *watcher)
		984
		985	Returns a true value iff the watcher is active (i.e. it has been started
		986	and not yet been stopped). As long as a watcher is active you must not modify
		987	it.
		988
		989	=item bool ev_is_pending (ev_TYPE *watcher)
		990
		991	Returns a true value iff the watcher is pending, (i.e. it has outstanding
		992	events but its callback has not yet been invoked). As long as a watcher
		993	is pending (but not active) you must not call an init function on it (but
		994	C<ev_TYPE_set> is safe), you must not change its priority, and you must
		995	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		996	it).
		997
		998	=item callback ev_cb (ev_TYPE *watcher)
		999
		1000	Returns the callback currently set on the watcher.
		1001
		1002	=item ev_cb_set (ev_TYPE *watcher, callback)
		1003
		1004	Change the callback. You can change the callback at virtually any time
		1005	(modulo threads).
		1006
		1007	=item ev_set_priority (ev_TYPE *watcher, priority)
		1008
		1009	=item int ev_priority (ev_TYPE *watcher)
		1010
		1011	Set and query the priority of the watcher. The priority is a small
		1012	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
		1013	(default: C<-2>). Pending watchers with higher priority will be invoked
		1014	before watchers with lower priority, but priority will not keep watchers
		1015	from being executed (except for C<ev_idle> watchers).
		1016
		1017	This means that priorities are I<only> used for ordering callback
		1018	invocation after new events have been received. This is useful, for
		1019	example, to reduce latency after idling, or more often, to bind two
		1020	watchers on the same event and make sure one is called first.
		1021
		1022	If you need to suppress invocation when higher priority events are pending
		1023	you need to look at C<ev_idle> watchers, which provide this functionality.
		1024
		1025	You I<must not> change the priority of a watcher as long as it is active or
		1026	pending.
		1027
		1028	The default priority used by watchers when no priority has been set is
		1029	always C<0>, which is supposed to not be too high and not be too low :).
		1030
		1031	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1032	fine, as long as you do not mind that the priority value you query might
		1033	or might not have been adjusted to be within valid range.
		1034
		1035	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		1036
		1037	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		1038	C<loop> nor C<revents> need to be valid as long as the watcher callback
		1039	can deal with that fact, as both are simply passed through to the
		1040	callback.
		1041
		1042	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		1043
		1044	If the watcher is pending, this function clears its pending status and
		1045	returns its C<revents> bitset (as if its callback was invoked). If the
		1046	watcher isn't pending it does nothing and returns C<0>.
		1047
		1048	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1049	callback to be invoked, which can be accomplished with this function.
		1050
		1051	=back
		1052
		1053
582	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1054	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
583		1055
584	Each watcher has, by default, a member C<void *data> that you can change	1056	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	1057	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	1058	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	1059	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	1060	member, you can also "subclass" the watcher type and provide your own
589	data:	1061	data:
590		1062
591	struct my_io	1063	struct my_io
592	{	1064	{
593	struct ev_io io;	1065	struct ev_io io;
594	int otherfd;	1066	int otherfd;
595	void *somedata;	1067	void *somedata;
596	struct whatever *mostinteresting;	1068	struct whatever *mostinteresting;
597	}	1069	};
		1070
		1071	...
		1072	struct my_io w;
		1073	ev_io_init (&w.io, my_cb, fd, EV_READ);
598		1074
599	And since your callback will be called with a pointer to the watcher, you	1075	And since your callback will be called with a pointer to the watcher, you
600	can cast it back to your own type:	1076	can cast it back to your own type:
601		1077
602	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1078	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)
603	{	1079	{
604	struct my_io *w = (struct my_io *)w_;	1080	struct my_io *w = (struct my_io *)w_;
605	...	1081	...
606	}	1082	}
607		1083
608	More interesting and less C-conformant ways of catsing your callback type	1084	More interesting and less C-conformant ways of casting your callback type
609	have been omitted....	1085	instead have been omitted.
		1086
		1087	Another common scenario is to use some data structure with multiple
		1088	embedded watchers:
		1089
		1090	struct my_biggy
		1091	{
		1092	int some_data;
		1093	ev_timer t1;
		1094	ev_timer t2;
		1095	}
		1096
		1097	In this case getting the pointer to C<my_biggy> is a bit more
		1098	complicated: Either you store the address of your C<my_biggy> struct
		1099	in the C<data> member of the watcher (for woozies), or you need to use
		1100	some pointer arithmetic using C<offsetof> inside your watchers (for real
		1101	programmers):
		1102
		1103	#include <stddef.h>
		1104
		1105	static void
		1106	t1_cb (EV_P_ struct ev_timer *w, int revents)
		1107	{
		1108	struct my_biggy big = (struct my_biggy *
		1109	(((char *)w) - offsetof (struct my_biggy, t1));
		1110	}
		1111
		1112	static void
		1113	t2_cb (EV_P_ struct ev_timer *w, int revents)
		1114	{
		1115	struct my_biggy big = (struct my_biggy *
		1116	(((char *)w) - offsetof (struct my_biggy, t2));
		1117	}
610		1118
611		1119
612	=head1 WATCHER TYPES	1120	=head1 WATCHER TYPES
613		1121
614	This section describes each watcher in detail, but will not repeat	1122	This section describes each watcher in detail, but will not repeat
615	information given in the last section.	1123	information given in the last section. Any initialisation/set macros,
		1124	functions and members specific to the watcher type are explained.
616		1125
		1126	Members are additionally marked with either I<[read-only]>, meaning that,
		1127	while the watcher is active, you can look at the member and expect some
		1128	sensible content, but you must not modify it (you can modify it while the
		1129	watcher is stopped to your hearts content), or I<[read-write]>, which
		1130	means you can expect it to have some sensible content while the watcher
		1131	is active, but you can also modify it. Modifying it may not do something
		1132	sensible or take immediate effect (or do anything at all), but libev will
		1133	not crash or malfunction in any way.
617		1134
		1135
618	=head2 C<ev_io> - is this file descriptor readable or writable	1136	=head2 C<ev_io> - is this file descriptor readable or writable?
619		1137
620	I/O watchers check whether a file descriptor is readable or writable	1138	I/O watchers check whether a file descriptor is readable or writable
621	in each iteration of the event loop (This behaviour is called	1139	in each iteration of the event loop, or, more precisely, when reading
622	level-triggering because you keep receiving events as long as the	1140	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	1141	some data. This behaviour is called level-triggering because you keep
624	act on the event and neither want to receive future events).	1142	receiving events as long as the condition persists. Remember you can stop
		1143	the watcher if you don't want to act on the event and neither want to
		1144	receive future events.
625		1145
626	In general you can register as many read and/or write event watchers per	1146	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	1147	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	1148	descriptors to non-blocking mode is also usually a good idea (but not
629	required if you know what you are doing).	1149	required if you know what you are doing).
630		1150
631	You have to be careful with dup'ed file descriptors, though. Some backends	1151	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	1152	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	1153	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		1154
637	If you must do this, then force the use of a known-to-be-good backend	1155	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	1156	receive "spurious" readiness notifications, that is your callback might
		1157	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
		1158	because there is no data. Not only are some backends known to create a
		1159	lot of those (for example Solaris ports), it is very easy to get into
		1160	this situation even with a relatively standard program structure. Thus
		1161	it is best to always use non-blocking I/O: An extra C<read>(2) returning
		1162	C<EAGAIN> is far preferable to a program hanging until some data arrives.
		1163
		1164	If you cannot run the fd in non-blocking mode (for example you should
		1165	not play around with an Xlib connection), then you have to separately
		1166	re-test whether a file descriptor is really ready with a known-to-be good
		1167	interface such as poll (fortunately in our Xlib example, Xlib already
		1168	does this on its own, so its quite safe to use). Some people additionally
		1169	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1170	indefinitely.
		1171
		1172	But really, best use non-blocking mode.
		1173
		1174	=head3 The special problem of disappearing file descriptors
		1175
		1176	Some backends (e.g. kqueue, epoll) need to be told about closing a file
		1177	descriptor (either due to calling C<close> explicitly or any other means,
		1178	such as C<dup2>). The reason is that you register interest in some file
		1179	descriptor, but when it goes away, the operating system will silently drop
		1180	this interest. If another file descriptor with the same number then is
		1181	registered with libev, there is no efficient way to see that this is, in
		1182	fact, a different file descriptor.
		1183
		1184	To avoid having to explicitly tell libev about such cases, libev follows
		1185	the following policy: Each time C<ev_io_set> is being called, libev
		1186	will assume that this is potentially a new file descriptor, otherwise
		1187	it is assumed that the file descriptor stays the same. That means that
		1188	you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the
		1189	descriptor even if the file descriptor number itself did not change.
		1190
		1191	This is how one would do it normally anyway, the important point is that
		1192	the libev application should not optimise around libev but should leave
		1193	optimisations to libev.
		1194
		1195	=head3 The special problem of dup'ed file descriptors
		1196
		1197	Some backends (e.g. epoll), cannot register events for file descriptors,
		1198	but only events for the underlying file descriptions. That means when you
		1199	have C<dup ()>'ed file descriptors or weirder constellations, and register
		1200	events for them, only one file descriptor might actually receive events.
		1201
		1202	There is no workaround possible except not registering events
		1203	for potentially C<dup ()>'ed file descriptors, or to resort to
		1204	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1205
		1206	=head3 The special problem of fork
		1207
		1208	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
		1209	useless behaviour. Libev fully supports fork, but needs to be told about
		1210	it in the child.
		1211
		1212	To support fork in your programs, you either have to call
		1213	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
		1214	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
639	C<EVBACKEND_POLL>).	1215	C<EVBACKEND_POLL>.
		1216
		1217	=head3 The special problem of SIGPIPE
		1218
		1219	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1220	when writing to a pipe whose other end has been closed, your program gets
		1221	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1222	this is sensible behaviour, for daemons, this is usually undesirable.
		1223
		1224	So when you encounter spurious, unexplained daemon exits, make sure you
		1225	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1226	somewhere, as that would have given you a big clue).
		1227
		1228
		1229	=head3 Watcher-Specific Functions
640		1230
641	=over 4	1231	=over 4
642		1232
643	=item ev_io_init (ev_io *, callback, int fd, int events)	1233	=item ev_io_init (ev_io *, callback, int fd, int events)
644		1234
645	=item ev_io_set (ev_io *, int fd, int events)	1235	=item ev_io_set (ev_io *, int fd, int events)
646		1236
647	Configures an C<ev_io> watcher. The fd is the file descriptor to rceeive	1237	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 |	1238	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
649	EV_WRITE> to receive the given events.	1239	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
650		1240
651	Please note that most of the more scalable backend mechanisms (for example	1241	=item int fd [read-only]
652	epoll and solaris ports) can result in spurious readyness notifications	1242
653	for file descriptors, so you practically need to use non-blocking I/O (and	1243	The file descriptor being watched.
654	treat callback invocation as hint only), or retest separately with a safe	1244
655	interface before doing I/O (XLib can do this), or force the use of either	1245	=item int events [read-only]
656	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>, which don't suffer from this	1246
657	problem. Also note that it is quite easy to have your callback invoked	1247	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		1248
662	=back	1249	=back
663		1250
		1251	=head3 Examples
		1252
664	Example: call C<stdin_readable_cb> when STDIN_FILENO has become, well	1253	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	1254	readable, but only once. Since it is likely line-buffered, you could
666	attempt to read a whole line in the callback:	1255	attempt to read a whole line in the callback.
667		1256
668	static void	1257	static void
669	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1258	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)
670	{	1259	{
671	ev_io_stop (loop, w);	1260	ev_io_stop (loop, w);
672	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1261	.. read from stdin here (or from w->fd) and handle any I/O errors
673	}	1262	}
674		1263
675	...	1264	...
676	struct ev_loop *loop = ev_default_init (0);	1265	struct ev_loop *loop = ev_default_init (0);
677	struct ev_io stdin_readable;	1266	struct ev_io stdin_readable;
678	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1267	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
679	ev_io_start (loop, &stdin_readable);	1268	ev_io_start (loop, &stdin_readable);
680	ev_loop (loop, 0);	1269	ev_loop (loop, 0);
681		1270
682		1271
683	=head2 C<ev_timer> - relative and optionally recurring timeouts	1272	=head2 C<ev_timer> - relative and optionally repeating timeouts
684		1273
685	Timer watchers are simple relative timers that generate an event after a	1274	Timer watchers are simple relative timers that generate an event after a
686	given time, and optionally repeating in regular intervals after that.	1275	given time, and optionally repeating in regular intervals after that.
687		1276
688	The timers are based on real time, that is, if you register an event that	1277	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	1278	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	1279	year, it will still time out after (roughly) one hour. "Roughly" because
691	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1280	detecting time jumps is hard, and some inaccuracies are unavoidable (the
692	monotonic clock option helps a lot here).	1281	monotonic clock option helps a lot here).
		1282
		1283	The callback is guaranteed to be invoked only I<after> its timeout has
		1284	passed, but if multiple timers become ready during the same loop iteration
		1285	then order of execution is undefined.
		1286
		1287	=head3 The special problem of time updates
		1288
		1289	Establishing the current time is a costly operation (it usually takes at
		1290	least two system calls): EV therefore updates its idea of the current
		1291	time only before and after C<ev_loop> collects new events, which causes a
		1292	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		1293	lots of events in one iteration.
693		1294
694	The relative timeouts are calculated relative to the C<ev_now ()>	1295	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	1296	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	1297	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	1298	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:	1299	timeout on the current time, use something like this to adjust for this:
699		1300
700	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1301	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
701		1302
702	The callback is guarenteed to be invoked only when its timeout has passed,	1303	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	1304	update of the time returned by C<ev_now ()> by calling C<ev_now_update
704	order of execution is undefined.	1305	()>.
		1306
		1307	=head3 Watcher-Specific Functions and Data Members
705		1308
706	=over 4	1309	=over 4
707		1310
708	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1311	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
709		1312
710	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	1313	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
711		1314
712	Configure the timer to trigger after C<after> seconds. If C<repeat> is	1315	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	1316	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	1317	reached. If it is positive, then the timer will automatically be
715	later, again, and again, until stopped manually.	1318	configured to trigger again C<repeat> seconds later, again, and again,
		1319	until stopped manually.
716		1320
717	The timer itself will do a best-effort at avoiding drift, that is, if you	1321	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	1322	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	1323	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	1324	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.	1325	do stuff) the timer will not fire more than once per event loop iteration.
722		1326
723	=item ev_timer_again (loop)	1327	=item ev_timer_again (loop, ev_timer *)
724		1328
725	This will act as if the timer timed out and restart it again if it is	1329	This will act as if the timer timed out and restart it again if it is
726	repeating. The exact semantics are:	1330	repeating. The exact semantics are:
727		1331
		1332	If the timer is pending, its pending status is cleared.
		1333
728	If the timer is started but nonrepeating, stop it.	1334	If the timer is started but non-repeating, stop it (as if it timed out).
729		1335
730	If the timer is repeating, either start it if necessary (with the repeat	1336	If the timer is repeating, either start it if necessary (with the
731	value), or reset the running timer to the repeat value.	1337	C<repeat> value), or reset the running timer to the C<repeat> value.
732		1338
733	This sounds a bit complicated, but here is a useful and typical	1339	This sounds a bit complicated, but here is a useful and typical
734	example: Imagine you have a tcp connection and you want a so-called idle	1340	example: Imagine you have a TCP connection and you want a so-called idle
735	timeout, that is, you want to be called when there have been, say, 60	1341	timeout, that is, you want to be called when there have been, say, 60
736	seconds of inactivity on the socket. The easiest way to do this is to	1342	seconds of inactivity on the socket. The easiest way to do this is to
737	configure an C<ev_timer> with after=repeat=60 and calling ev_timer_again each	1343	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
738	time you successfully read or write some data. If you go into an idle	1344	C<ev_timer_again> each time you successfully read or write some data. If
739	state where you do not expect data to travel on the socket, you can stop	1345	you go into an idle state where you do not expect data to travel on the
740	the timer, and again will automatically restart it if need be.	1346	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
		1347	automatically restart it if need be.
		1348
		1349	That means you can ignore the C<after> value and C<ev_timer_start>
		1350	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
		1351
		1352	ev_timer_init (timer, callback, 0., 5.);
		1353	ev_timer_again (loop, timer);
		1354	...
		1355	timer->again = 17.;
		1356	ev_timer_again (loop, timer);
		1357	...
		1358	timer->again = 10.;
		1359	ev_timer_again (loop, timer);
		1360
		1361	This is more slightly efficient then stopping/starting the timer each time
		1362	you want to modify its timeout value.
		1363
		1364	Note, however, that it is often even more efficient to remember the
		1365	time of the last activity and let the timer time-out naturally. In the
		1366	callback, you then check whether the time-out is real, or, if there was
		1367	some activity, you reschedule the watcher to time-out in "last_activity +
		1368	timeout - ev_now ()" seconds.
		1369
		1370	=item ev_tstamp repeat [read-write]
		1371
		1372	The current C<repeat> value. Will be used each time the watcher times out
		1373	or C<ev_timer_again> is called, and determines the next timeout (if any),
		1374	which is also when any modifications are taken into account.
741		1375
742	=back	1376	=back
743		1377
		1378	=head3 Examples
		1379
744	Example: create a timer that fires after 60 seconds.	1380	Example: Create a timer that fires after 60 seconds.
745		1381
746	static void	1382	static void
747	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1383	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
748	{	1384	{
749	.. one minute over, w is actually stopped right here	1385	.. one minute over, w is actually stopped right here
750	}	1386	}
751		1387
752	struct ev_timer mytimer;	1388	struct ev_timer mytimer;
753	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	1389	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
754	ev_timer_start (loop, &mytimer);	1390	ev_timer_start (loop, &mytimer);
755		1391
756	Example: create a timeout timer that times out after 10 seconds of	1392	Example: Create a timeout timer that times out after 10 seconds of
757	inactivity.	1393	inactivity.
758		1394
759	static void	1395	static void
760	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1396	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
761	{	1397	{
762	.. ten seconds without any activity	1398	.. ten seconds without any activity
763	}	1399	}
764		1400
765	struct ev_timer mytimer;	1401	struct ev_timer mytimer;
766	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	1402	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
767	ev_timer_again (&mytimer); /* start timer */	1403	ev_timer_again (&mytimer); /* start timer */
768	ev_loop (loop, 0);	1404	ev_loop (loop, 0);
769		1405
770	// and in some piece of code that gets executed on any "activity":	1406	// and in some piece of code that gets executed on any "activity":
771	// reset the timeout to start ticking again at 10 seconds	1407	// reset the timeout to start ticking again at 10 seconds
772	ev_timer_again (&mytimer);	1408	ev_timer_again (&mytimer);
773		1409
774		1410
775	=head2 C<ev_periodic> - to cron or not to cron	1411	=head2 C<ev_periodic> - to cron or not to cron?
776		1412
777	Periodic watchers are also timers of a kind, but they are very versatile	1413	Periodic watchers are also timers of a kind, but they are very versatile
778	(and unfortunately a bit complex).	1414	(and unfortunately a bit complex).
779		1415
780	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1416	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	1417	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	1418	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 ()	1419	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	1420	+ 10.>, that is, an absolute time not a delay) and then reset your system
		1421	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	1422	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	1423	roughly 10 seconds later as it uses a relative timeout).
787	again).
788		1424
789	They can also be used to implement vastly more complex timers, such as	1425	C<ev_periodic>s can also be used to implement vastly more complex timers,
790	triggering an event on eahc midnight, local time.	1426	such as triggering an event on each "midnight, local time", or other
		1427	complicated rules.
791		1428
792	As with timers, the callback is guarenteed to be invoked only when the	1429	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	1430	time (C<at>) has passed, but if multiple periodic timers become ready
794	during the same loop iteration then order of execution is undefined.	1431	during the same loop iteration, then order of execution is undefined.
		1432
		1433	=head3 Watcher-Specific Functions and Data Members
795		1434
796	=over 4	1435	=over 4
797		1436
798	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1437	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)
799		1438
800	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1439	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)
801		1440
802	Lots of arguments, lets sort it out... There are basically three modes of	1441	Lots of arguments, lets sort it out... There are basically three modes of
803	operation, and we will explain them from simplest to complex:	1442	operation, and we will explain them from simplest to most complex:
804		1443
805	=over 4	1444	=over 4
806		1445
807	=item * absolute timer (interval = reschedule_cb = 0)	1446	=item * absolute timer (at = time, interval = reschedule_cb = 0)
808		1447
809	In this configuration the watcher triggers an event at the wallclock time	1448	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,	1449	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	1450	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.	1451	only run when the system clock reaches or surpasses this time.
813		1452
814	=item * non-repeating interval timer (interval > 0, reschedule_cb = 0)	1453	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)
815		1454
816	In this mode the watcher will always be scheduled to time out at the next	1455	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	1456	C<at + N * interval> time (for some integer N, which can also be negative)
818	of any time jumps.	1457	and then repeat, regardless of any time jumps.
819		1458
820	This can be used to create timers that do not drift with respect to system	1459	This can be used to create timers that do not drift with respect to the
821	time:	1460	system clock, for example, here is a C<ev_periodic> that triggers each
		1461	hour, on the hour:
822		1462
823	ev_periodic_set (&periodic, 0., 3600., 0);	1463	ev_periodic_set (&periodic, 0., 3600., 0);
824		1464
825	This doesn't mean there will always be 3600 seconds in between triggers,	1465	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	1466	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	1467	full hour (UTC), or more correctly, when the system time is evenly divisible
828	by 3600.	1468	by 3600.
829		1469
830	Another way to think about it (for the mathematically inclined) is that	1470	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	1471	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.	1472	time where C<time = at (mod interval)>, regardless of any time jumps.
833		1473
		1474	For numerical stability it is preferable that the C<at> value is near
		1475	C<ev_now ()> (the current time), but there is no range requirement for
		1476	this value, and in fact is often specified as zero.
		1477
		1478	Note also that there is an upper limit to how often a timer can fire (CPU
		1479	speed for example), so if C<interval> is very small then timing stability
		1480	will of course deteriorate. Libev itself tries to be exact to be about one
		1481	millisecond (if the OS supports it and the machine is fast enough).
		1482
834	=item * manual reschedule mode (reschedule_cb = callback)	1483	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)
835		1484
836	In this mode the values for C<interval> and C<at> are both being	1485	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	1486	ignored. Instead, each time the periodic watcher gets scheduled, the
838	reschedule callback will be called with the watcher as first, and the	1487	reschedule callback will be called with the watcher as first, and the
839	current time as second argument.	1488	current time as second argument.
840		1489
841	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	1490	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,	1491	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		1492
		1493	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		1494	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		1495	only event loop modification you are allowed to do).
		1496
846	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	1497	The callback prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic
847	ev_tstamp now)>, e.g.:	1498	*w, ev_tstamp now)>, e.g.:
848		1499
849	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1500	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)
850	{	1501	{
851	return now + 60.;	1502	return now + 60.;
852	}	1503	}
…		…
854	It must return the next time to trigger, based on the passed time value	1505	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	1506	(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	1507	will usually be called just before the callback will be triggered, but
857	might be called at other times, too.	1508	might be called at other times, too.
858		1509
859	NOTE: I<< This callback must always return a time that is later than the	1510	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.	1511	equal to the passed C<now> value >>.
861		1512
862	This can be used to create very complex timers, such as a timer that	1513	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	1514	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	1515	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	1516	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).	1517	reason I omitted it as an example).
867		1518
868	=back	1519	=back
…		…
872	Simply stops and restarts the periodic watcher again. This is only useful	1523	Simply stops and restarts the periodic watcher again. This is only useful
873	when you changed some parameters or the reschedule callback would return	1524	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	1525	a different time than the last time it was called (e.g. in a crond like
875	program when the crontabs have changed).	1526	program when the crontabs have changed).
876		1527
		1528	=item ev_tstamp ev_periodic_at (ev_periodic *)
		1529
		1530	When active, returns the absolute time that the watcher is supposed to
		1531	trigger next.
		1532
		1533	=item ev_tstamp offset [read-write]
		1534
		1535	When repeating, this contains the offset value, otherwise this is the
		1536	absolute point in time (the C<at> value passed to C<ev_periodic_set>).
		1537
		1538	Can be modified any time, but changes only take effect when the periodic
		1539	timer fires or C<ev_periodic_again> is being called.
		1540
		1541	=item ev_tstamp interval [read-write]
		1542
		1543	The current interval value. Can be modified any time, but changes only
		1544	take effect when the periodic timer fires or C<ev_periodic_again> is being
		1545	called.
		1546
		1547	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]
		1548
		1549	The current reschedule callback, or C<0>, if this functionality is
		1550	switched off. Can be changed any time, but changes only take effect when
		1551	the periodic timer fires or C<ev_periodic_again> is being called.
		1552
877	=back	1553	=back
878		1554
		1555	=head3 Examples
		1556
879	Example: call a callback every hour, or, more precisely, whenever the	1557	Example: Call a callback every hour, or, more precisely, whenever the
880	system clock is divisible by 3600. The callback invocation times have	1558	system time is divisible by 3600. The callback invocation times have
881	potentially a lot of jittering, but good long-term stability.	1559	potentially a lot of jitter, but good long-term stability.
882		1560
883	static void	1561	static void
884	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1562	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)
885	{	1563	{
886	... its now a full hour (UTC, or TAI or whatever your clock follows)	1564	... its now a full hour (UTC, or TAI or whatever your clock follows)
887	}	1565	}
888		1566
889	struct ev_periodic hourly_tick;	1567	struct ev_periodic hourly_tick;
890	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	1568	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
891	ev_periodic_start (loop, &hourly_tick);	1569	ev_periodic_start (loop, &hourly_tick);
892		1570
893	Example: the same as above, but use a reschedule callback to do it:	1571	Example: The same as above, but use a reschedule callback to do it:
894		1572
895	#include <math.h>	1573	#include <math.h>
896		1574
897	static ev_tstamp	1575	static ev_tstamp
898	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	1576	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)
899	{	1577	{
900	return fmod (now, 3600.) + 3600.;	1578	return now + (3600. - fmod (now, 3600.));
901	}	1579	}
902		1580
903	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	1581	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
904		1582
905	Example: call a callback every hour, starting now:	1583	Example: Call a callback every hour, starting now:
906		1584
907	struct ev_periodic hourly_tick;	1585	struct ev_periodic hourly_tick;
908	ev_periodic_init (&hourly_tick, clock_cb,	1586	ev_periodic_init (&hourly_tick, clock_cb,
909	fmod (ev_now (loop), 3600.), 3600., 0);	1587	fmod (ev_now (loop), 3600.), 3600., 0);
910	ev_periodic_start (loop, &hourly_tick);	1588	ev_periodic_start (loop, &hourly_tick);
911		1589
912		1590
913	=head2 C<ev_signal> - signal me when a signal gets signalled	1591	=head2 C<ev_signal> - signal me when a signal gets signalled!
914		1592
915	Signal watchers will trigger an event when the process receives a specific	1593	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	1594	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	1595	will try it's best to deliver signals synchronously, i.e. as part of the
918	normal event processing, like any other event.	1596	normal event processing, like any other event.
919		1597
		1598	If you want signals asynchronously, just use C<sigaction> as you would
		1599	do without libev and forget about sharing the signal. You can even use
		1600	C<ev_async> from a signal handler to synchronously wake up an event loop.
		1601
920	You can configure as many watchers as you like per signal. Only when the	1602	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	1603	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	1604	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	1605	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	1606	the last signal watcher for a signal is stopped, libev will reset the
925	SIG_DFL (regardless of what it was set to before).	1607	signal handler to SIG_DFL (regardless of what it was set to before).
		1608
		1609	If possible and supported, libev will install its handlers with
		1610	C<SA_RESTART> behaviour enabled, so system calls should not be unduly
		1611	interrupted. If you have a problem with system calls getting interrupted by
		1612	signals you can block all signals in an C<ev_check> watcher and unblock
		1613	them in an C<ev_prepare> watcher.
		1614
		1615	=head3 Watcher-Specific Functions and Data Members
926		1616
927	=over 4	1617	=over 4
928		1618
929	=item ev_signal_init (ev_signal *, callback, int signum)	1619	=item ev_signal_init (ev_signal *, callback, int signum)
930		1620
931	=item ev_signal_set (ev_signal *, int signum)	1621	=item ev_signal_set (ev_signal *, int signum)
932		1622
933	Configures the watcher to trigger on the given signal number (usually one	1623	Configures the watcher to trigger on the given signal number (usually one
934	of the C<SIGxxx> constants).	1624	of the C<SIGxxx> constants).
935		1625
		1626	=item int signum [read-only]
		1627
		1628	The signal the watcher watches out for.
		1629
936	=back	1630	=back
937		1631
		1632	=head3 Examples
938		1633
		1634	Example: Try to exit cleanly on SIGINT.
		1635
		1636	static void
		1637	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)
		1638	{
		1639	ev_unloop (loop, EVUNLOOP_ALL);
		1640	}
		1641
		1642	struct ev_signal signal_watcher;
		1643	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		1644	ev_signal_start (loop, &signal_watcher);
		1645
		1646
939	=head2 C<ev_child> - wait for pid status changes	1647	=head2 C<ev_child> - watch out for process status changes
940		1648
941	Child watchers trigger when your process receives a SIGCHLD in response to	1649	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).	1650	some child status changes (most typically when a child of yours dies or
		1651	exits). It is permissible to install a child watcher I<after> the child
		1652	has been forked (which implies it might have already exited), as long
		1653	as the event loop isn't entered (or is continued from a watcher), i.e.,
		1654	forking and then immediately registering a watcher for the child is fine,
		1655	but forking and registering a watcher a few event loop iterations later is
		1656	not.
		1657
		1658	Only the default event loop is capable of handling signals, and therefore
		1659	you can only register child watchers in the default event loop.
		1660
		1661	=head3 Process Interaction
		1662
		1663	Libev grabs C<SIGCHLD> as soon as the default event loop is
		1664	initialised. This is necessary to guarantee proper behaviour even if
		1665	the first child watcher is started after the child exits. The occurrence
		1666	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		1667	synchronously as part of the event loop processing. Libev always reaps all
		1668	children, even ones not watched.
		1669
		1670	=head3 Overriding the Built-In Processing
		1671
		1672	Libev offers no special support for overriding the built-in child
		1673	processing, but if your application collides with libev's default child
		1674	handler, you can override it easily by installing your own handler for
		1675	C<SIGCHLD> after initialising the default loop, and making sure the
		1676	default loop never gets destroyed. You are encouraged, however, to use an
		1677	event-based approach to child reaping and thus use libev's support for
		1678	that, so other libev users can use C<ev_child> watchers freely.
		1679
		1680	=head3 Stopping the Child Watcher
		1681
		1682	Currently, the child watcher never gets stopped, even when the
		1683	child terminates, so normally one needs to stop the watcher in the
		1684	callback. Future versions of libev might stop the watcher automatically
		1685	when a child exit is detected.
		1686
		1687	=head3 Watcher-Specific Functions and Data Members
943		1688
944	=over 4	1689	=over 4
945		1690
946	=item ev_child_init (ev_child *, callback, int pid)	1691	=item ev_child_init (ev_child *, callback, int pid, int trace)
947		1692
948	=item ev_child_set (ev_child *, int pid)	1693	=item ev_child_set (ev_child *, int pid, int trace)
949		1694
950	Configures the watcher to wait for status changes of process C<pid> (or	1695	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	1696	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	1697	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	1698	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	1699	C<waitpid> documentation). The C<rpid> member contains the pid of the
955	process causing the status change.	1700	process causing the status change. C<trace> must be either C<0> (only
		1701	activate the watcher when the process terminates) or C<1> (additionally
		1702	activate the watcher when the process is stopped or continued).
		1703
		1704	=item int pid [read-only]
		1705
		1706	The process id this watcher watches out for, or C<0>, meaning any process id.
		1707
		1708	=item int rpid [read-write]
		1709
		1710	The process id that detected a status change.
		1711
		1712	=item int rstatus [read-write]
		1713
		1714	The process exit/trace status caused by C<rpid> (see your systems
		1715	C<waitpid> and C<sys/wait.h> documentation for details).
956		1716
957	=back	1717	=back
958		1718
959	Example: try to exit cleanly on SIGINT and SIGTERM.	1719	=head3 Examples
960		1720
		1721	Example: C<fork()> a new process and install a child handler to wait for
		1722	its completion.
		1723
		1724	ev_child cw;
		1725
961	static void	1726	static void
962	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	1727	child_cb (EV_P_ struct ev_child *w, int revents)
963	{	1728	{
964	ev_unloop (loop, EVUNLOOP_ALL);	1729	ev_child_stop (EV_A_ w);
		1730	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
965	}	1731	}
966		1732
967	struct ev_signal signal_watcher;	1733	pid_t pid = fork ();
968	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
969	ev_signal_start (loop, &sigint_cb);
970		1734
		1735	if (pid < 0)
		1736	// error
		1737	else if (pid == 0)
		1738	{
		1739	// the forked child executes here
		1740	exit (1);
		1741	}
		1742	else
		1743	{
		1744	ev_child_init (&cw, child_cb, pid, 0);
		1745	ev_child_start (EV_DEFAULT_ &cw);
		1746	}
971		1747
		1748
		1749	=head2 C<ev_stat> - did the file attributes just change?
		1750
		1751	This watches a file system path for attribute changes. That is, it calls
		1752	C<stat> regularly (or when the OS says it changed) and sees if it changed
		1753	compared to the last time, invoking the callback if it did.
		1754
		1755	The path does not need to exist: changing from "path exists" to "path does
		1756	not exist" is a status change like any other. The condition "path does
		1757	not exist" is signified by the C<st_nlink> field being zero (which is
		1758	otherwise always forced to be at least one) and all the other fields of
		1759	the stat buffer having unspecified contents.
		1760
		1761	The path I<should> be absolute and I<must not> end in a slash. If it is
		1762	relative and your working directory changes, the behaviour is undefined.
		1763
		1764	Since there is no standard kernel interface to do this, the portable
		1765	implementation simply calls C<stat (2)> regularly on the path to see if
		1766	it changed somehow. You can specify a recommended polling interval for
		1767	this case. If you specify a polling interval of C<0> (highly recommended!)
		1768	then a I<suitable, unspecified default> value will be used (which
		1769	you can expect to be around five seconds, although this might change
		1770	dynamically). Libev will also impose a minimum interval which is currently
		1771	around C<0.1>, but thats usually overkill.
		1772
		1773	This watcher type is not meant for massive numbers of stat watchers,
		1774	as even with OS-supported change notifications, this can be
		1775	resource-intensive.
		1776
		1777	At the time of this writing, the only OS-specific interface implemented
		1778	is the Linux inotify interface (implementing kqueue support is left as
		1779	an exercise for the reader. Note, however, that the author sees no way
		1780	of implementing C<ev_stat> semantics with kqueue).
		1781
		1782	=head3 ABI Issues (Largefile Support)
		1783
		1784	Libev by default (unless the user overrides this) uses the default
		1785	compilation environment, which means that on systems with large file
		1786	support disabled by default, you get the 32 bit version of the stat
		1787	structure. When using the library from programs that change the ABI to
		1788	use 64 bit file offsets the programs will fail. In that case you have to
		1789	compile libev with the same flags to get binary compatibility. This is
		1790	obviously the case with any flags that change the ABI, but the problem is
		1791	most noticeably disabled with ev_stat and large file support.
		1792
		1793	The solution for this is to lobby your distribution maker to make large
		1794	file interfaces available by default (as e.g. FreeBSD does) and not
		1795	optional. Libev cannot simply switch on large file support because it has
		1796	to exchange stat structures with application programs compiled using the
		1797	default compilation environment.
		1798
		1799	=head3 Inotify and Kqueue
		1800
		1801	When C<inotify (7)> support has been compiled into libev (generally only
		1802	available with Linux) and present at runtime, it will be used to speed up
		1803	change detection where possible. The inotify descriptor will be created lazily
		1804	when the first C<ev_stat> watcher is being started.
		1805
		1806	Inotify presence does not change the semantics of C<ev_stat> watchers
		1807	except that changes might be detected earlier, and in some cases, to avoid
		1808	making regular C<stat> calls. Even in the presence of inotify support
		1809	there are many cases where libev has to resort to regular C<stat> polling,
		1810	but as long as the path exists, libev usually gets away without polling.
		1811
		1812	There is no support for kqueue, as apparently it cannot be used to
		1813	implement this functionality, due to the requirement of having a file
		1814	descriptor open on the object at all times, and detecting renames, unlinks
		1815	etc. is difficult.
		1816
		1817	=head3 The special problem of stat time resolution
		1818
		1819	The C<stat ()> system call only supports full-second resolution portably, and
		1820	even on systems where the resolution is higher, most file systems still
		1821	only support whole seconds.
		1822
		1823	That means that, if the time is the only thing that changes, you can
		1824	easily miss updates: on the first update, C<ev_stat> detects a change and
		1825	calls your callback, which does something. When there is another update
		1826	within the same second, C<ev_stat> will be unable to detect unless the
		1827	stat data does change in other ways (e.g. file size).
		1828
		1829	The solution to this is to delay acting on a change for slightly more
		1830	than a second (or till slightly after the next full second boundary), using
		1831	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		1832	ev_timer_again (loop, w)>).
		1833
		1834	The C<.02> offset is added to work around small timing inconsistencies
		1835	of some operating systems (where the second counter of the current time
		1836	might be be delayed. One such system is the Linux kernel, where a call to
		1837	C<gettimeofday> might return a timestamp with a full second later than
		1838	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		1839	update file times then there will be a small window where the kernel uses
		1840	the previous second to update file times but libev might already execute
		1841	the timer callback).
		1842
		1843	=head3 Watcher-Specific Functions and Data Members
		1844
		1845	=over 4
		1846
		1847	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
		1848
		1849	=item ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)
		1850
		1851	Configures the watcher to wait for status changes of the given
		1852	C<path>. The C<interval> is a hint on how quickly a change is expected to
		1853	be detected and should normally be specified as C<0> to let libev choose
		1854	a suitable value. The memory pointed to by C<path> must point to the same
		1855	path for as long as the watcher is active.
		1856
		1857	The callback will receive an C<EV_STAT> event when a change was detected,
		1858	relative to the attributes at the time the watcher was started (or the
		1859	last change was detected).
		1860
		1861	=item ev_stat_stat (loop, ev_stat *)
		1862
		1863	Updates the stat buffer immediately with new values. If you change the
		1864	watched path in your callback, you could call this function to avoid
		1865	detecting this change (while introducing a race condition if you are not
		1866	the only one changing the path). Can also be useful simply to find out the
		1867	new values.
		1868
		1869	=item ev_statdata attr [read-only]
		1870
		1871	The most-recently detected attributes of the file. Although the type is
		1872	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
		1873	suitable for your system, but you can only rely on the POSIX-standardised
		1874	members to be present. If the C<st_nlink> member is C<0>, then there was
		1875	some error while C<stat>ing the file.
		1876
		1877	=item ev_statdata prev [read-only]
		1878
		1879	The previous attributes of the file. The callback gets invoked whenever
		1880	C<prev> != C<attr>, or, more precisely, one or more of these members
		1881	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		1882	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
		1883
		1884	=item ev_tstamp interval [read-only]
		1885
		1886	The specified interval.
		1887
		1888	=item const char *path [read-only]
		1889
		1890	The file system path that is being watched.
		1891
		1892	=back
		1893
		1894	=head3 Examples
		1895
		1896	Example: Watch C</etc/passwd> for attribute changes.
		1897
		1898	static void
		1899	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
		1900	{
		1901	/* /etc/passwd changed in some way */
		1902	if (w->attr.st_nlink)
		1903	{
		1904	printf ("passwd current size %ld\n", (long)w->attr.st_size);
		1905	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
		1906	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
		1907	}
		1908	else
		1909	/* you shalt not abuse printf for puts */
		1910	puts ("wow, /etc/passwd is not there, expect problems. "
		1911	"if this is windows, they already arrived\n");
		1912	}
		1913
		1914	...
		1915	ev_stat passwd;
		1916
		1917	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
		1918	ev_stat_start (loop, &passwd);
		1919
		1920	Example: Like above, but additionally use a one-second delay so we do not
		1921	miss updates (however, frequent updates will delay processing, too, so
		1922	one might do the work both on C<ev_stat> callback invocation I<and> on
		1923	C<ev_timer> callback invocation).
		1924
		1925	static ev_stat passwd;
		1926	static ev_timer timer;
		1927
		1928	static void
		1929	timer_cb (EV_P_ ev_timer *w, int revents)
		1930	{
		1931	ev_timer_stop (EV_A_ w);
		1932
		1933	/* now it's one second after the most recent passwd change */
		1934	}
		1935
		1936	static void
		1937	stat_cb (EV_P_ ev_stat *w, int revents)
		1938	{
		1939	/* reset the one-second timer */
		1940	ev_timer_again (EV_A_ &timer);
		1941	}
		1942
		1943	...
		1944	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		1945	ev_stat_start (loop, &passwd);
		1946	ev_timer_init (&timer, timer_cb, 0., 1.02);
		1947
		1948
972	=head2 C<ev_idle> - when you've got nothing better to do	1949	=head2 C<ev_idle> - when you've got nothing better to do...
973		1950
974	Idle watchers trigger events when there are no other events are pending	1951	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	1952	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,	1953	as receiving "events").
977	imagine) it will not be triggered. But when your process is idle all idle	1954
978	watchers are being called again and again, once per event loop iteration -	1955	That is, as long as your process is busy handling sockets or timeouts
		1956	(or even signals, imagine) of the same or higher priority it will not be
		1957	triggered. But when your process is idle (or only lower-priority watchers
		1958	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	1959	iteration - until stopped, that is, or your process receives more events
980	busy.	1960	and becomes busy again with higher priority stuff.
981		1961
982	The most noteworthy effect is that as long as any idle watchers are	1962	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.	1963	active, the process will not block when waiting for new events.
984		1964
985	Apart from keeping your process non-blocking (which is a useful	1965	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	1966	effect on its own sometimes), idle watchers are a good place to do
987	"pseudo-background processing", or delay processing stuff to after the	1967	"pseudo-background processing", or delay processing stuff to after the
988	event loop has handled all outstanding events.	1968	event loop has handled all outstanding events.
989		1969
		1970	=head3 Watcher-Specific Functions and Data Members
		1971
990	=over 4	1972	=over 4
991		1973
992	=item ev_idle_init (ev_signal *, callback)	1974	=item ev_idle_init (ev_signal *, callback)
993		1975
994	Initialises and configures the idle watcher - it has no parameters of any	1976	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,	1977	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
996	believe me.	1978	believe me.
997		1979
998	=back	1980	=back
999		1981
		1982	=head3 Examples
		1983
1000	Example: dynamically allocate an C<ev_idle>, start it, and in the	1984	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1001	callback, free it. Alos, use no error checking, as usual.	1985	callback, free it. Also, use no error checking, as usual.
1002		1986
1003	static void	1987	static void
1004	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	1988	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)
1005	{	1989	{
1006	free (w);	1990	free (w);
1007	// now do something you wanted to do when the program has	1991	// now do something you wanted to do when the program has
1008	// no longer asnything immediate to do.	1992	// no longer anything immediate to do.
1009	}	1993	}
1010		1994
1011	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	1995	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));
1012	ev_idle_init (idle_watcher, idle_cb);	1996	ev_idle_init (idle_watcher, idle_cb);
1013	ev_idle_start (loop, idle_cb);	1997	ev_idle_start (loop, idle_cb);
1014		1998
1015		1999
1016	=head2 C<ev_prepare> and C<ev_check> - customise your event loop	2000	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1017		2001
1018	Prepare and check watchers are usually (but not always) used in tandem:	2002	Prepare and check watchers are usually (but not always) used in pairs:
1019	prepare watchers get invoked before the process blocks and check watchers	2003	prepare watchers get invoked before the process blocks and check watchers
1020	afterwards.	2004	afterwards.
1021		2005
		2006	You I<must not> call C<ev_loop> or similar functions that enter
		2007	the current event loop from either C<ev_prepare> or C<ev_check>
		2008	watchers. Other loops than the current one are fine, however. The
		2009	rationale behind this is that you do not need to check for recursion in
		2010	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
		2011	C<ev_check> so if you have one watcher of each kind they will always be
		2012	called in pairs bracketing the blocking call.
		2013
1022	Their main purpose is to integrate other event mechanisms into libev and	2014	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	2015	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	2016	variable changes, implement your own watchers, integrate net-snmp or a
1025	coroutine library and lots more.	2017	coroutine library and lots more. They are also occasionally useful if
		2018	you cache some data and want to flush it before blocking (for example,
		2019	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
		2020	watcher).
1026		2021
1027	This is done by examining in each prepare call which file descriptors need	2022	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	2023	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	2024	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	2025	libraries provide exactly this functionality). Then, in the check watcher,
1031	any events that occured (by checking the pending status of all watchers	2026	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	2027	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,	2028	I/O and timer callbacks will never actually be called (but must be valid
1034	because you never know, you know?).	2029	nevertheless, because you never know, you know?).
1035		2030
1036	As another example, the Perl Coro module uses these hooks to integrate	2031	As another example, the Perl Coro module uses these hooks to integrate
1037	coroutines into libev programs, by yielding to other active coroutines	2032	coroutines into libev programs, by yielding to other active coroutines
1038	during each prepare and only letting the process block if no coroutines	2033	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	2034	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	2035	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	2036	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	2037	loop from blocking if lower-priority coroutines are active, thus mapping
1043	low-priority coroutines to idle/background tasks).	2038	low-priority coroutines to idle/background tasks).
1044		2039
		2040	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
		2041	priority, to ensure that they are being run before any other watchers
		2042	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2043
		2044	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
		2045	activate ("feed") events into libev. While libev fully supports this, they
		2046	might get executed before other C<ev_check> watchers did their job. As
		2047	C<ev_check> watchers are often used to embed other (non-libev) event
		2048	loops those other event loops might be in an unusable state until their
		2049	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
		2050	others).
		2051
		2052	=head3 Watcher-Specific Functions and Data Members
		2053
1045	=over 4	2054	=over 4
1046		2055
1047	=item ev_prepare_init (ev_prepare *, callback)	2056	=item ev_prepare_init (ev_prepare *, callback)
1048		2057
1049	=item ev_check_init (ev_check *, callback)	2058	=item ev_check_init (ev_check *, callback)
1050		2059
1051	Initialises and configures the prepare or check watcher - they have no	2060	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>	2061	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.	2062	macros, but using them is utterly, utterly, utterly and completely
		2063	pointless.
1054		2064
1055	=back	2065	=back
1056		2066
1057	Example: *TODO*.	2067	=head3 Examples
1058		2068
		2069	There are a number of principal ways to embed other event loops or modules
		2070	into libev. Here are some ideas on how to include libadns into libev
		2071	(there is a Perl module named C<EV::ADNS> that does this, which you could
		2072	use as a working example. Another Perl module named C<EV::Glib> embeds a
		2073	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
		2074	Glib event loop).
1059		2075
		2076	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
		2077	and in a check watcher, destroy them and call into libadns. What follows
		2078	is pseudo-code only of course. This requires you to either use a low
		2079	priority for the check watcher or use C<ev_clear_pending> explicitly, as
		2080	the callbacks for the IO/timeout watchers might not have been called yet.
		2081
		2082	static ev_io iow [nfd];
		2083	static ev_timer tw;
		2084
		2085	static void
		2086	io_cb (ev_loop *loop, ev_io *w, int revents)
		2087	{
		2088	}
		2089
		2090	// create io watchers for each fd and a timer before blocking
		2091	static void
		2092	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)
		2093	{
		2094	int timeout = 3600000;
		2095	struct pollfd fds [nfd];
		2096	// actual code will need to loop here and realloc etc.
		2097	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
		2098
		2099	/* the callback is illegal, but won't be called as we stop during check */
		2100	ev_timer_init (&tw, 0, timeout * 1e-3);
		2101	ev_timer_start (loop, &tw);
		2102
		2103	// create one ev_io per pollfd
		2104	for (int i = 0; i < nfd; ++i)
		2105	{
		2106	ev_io_init (iow + i, io_cb, fds [i].fd,
		2107	((fds [i].events & POLLIN ? EV_READ : 0)
		2108	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
		2109
		2110	fds [i].revents = 0;
		2111	ev_io_start (loop, iow + i);
		2112	}
		2113	}
		2114
		2115	// stop all watchers after blocking
		2116	static void
		2117	adns_check_cb (ev_loop *loop, ev_check *w, int revents)
		2118	{
		2119	ev_timer_stop (loop, &tw);
		2120
		2121	for (int i = 0; i < nfd; ++i)
		2122	{
		2123	// set the relevant poll flags
		2124	// could also call adns_processreadable etc. here
		2125	struct pollfd *fd = fds + i;
		2126	int revents = ev_clear_pending (iow + i);
		2127	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
		2128	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
		2129
		2130	// now stop the watcher
		2131	ev_io_stop (loop, iow + i);
		2132	}
		2133
		2134	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
		2135	}
		2136
		2137	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
		2138	in the prepare watcher and would dispose of the check watcher.
		2139
		2140	Method 3: If the module to be embedded supports explicit event
		2141	notification (libadns does), you can also make use of the actual watcher
		2142	callbacks, and only destroy/create the watchers in the prepare watcher.
		2143
		2144	static void
		2145	timer_cb (EV_P_ ev_timer *w, int revents)
		2146	{
		2147	adns_state ads = (adns_state)w->data;
		2148	update_now (EV_A);
		2149
		2150	adns_processtimeouts (ads, &tv_now);
		2151	}
		2152
		2153	static void
		2154	io_cb (EV_P_ ev_io *w, int revents)
		2155	{
		2156	adns_state ads = (adns_state)w->data;
		2157	update_now (EV_A);
		2158
		2159	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
		2160	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
		2161	}
		2162
		2163	// do not ever call adns_afterpoll
		2164
		2165	Method 4: Do not use a prepare or check watcher because the module you
		2166	want to embed is not flexible enough to support it. Instead, you can
		2167	override their poll function. The drawback with this solution is that the
		2168	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
		2169	this approach, effectively embedding EV as a client into the horrible
		2170	libglib event loop.
		2171
		2172	static gint
		2173	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
		2174	{
		2175	int got_events = 0;
		2176
		2177	for (n = 0; n < nfds; ++n)
		2178	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
		2179
		2180	if (timeout >= 0)
		2181	// create/start timer
		2182
		2183	// poll
		2184	ev_loop (EV_A_ 0);
		2185
		2186	// stop timer again
		2187	if (timeout >= 0)
		2188	ev_timer_stop (EV_A_ &to);
		2189
		2190	// stop io watchers again - their callbacks should have set
		2191	for (n = 0; n < nfds; ++n)
		2192	ev_io_stop (EV_A_ iow [n]);
		2193
		2194	return got_events;
		2195	}
		2196
		2197
1060	=head2 C<ev_embed> - when one backend isn't enough	2198	=head2 C<ev_embed> - when one backend isn't enough...
1061		2199
1062	This is a rather advanced watcher type that lets you embed one event loop	2200	This is a rather advanced watcher type that lets you embed one event loop
1063	into another.	2201	into another (currently only C<ev_io> events are supported in the embedded
		2202	loop, other types of watchers might be handled in a delayed or incorrect
		2203	fashion and must not be used).
1064		2204
1065	There are primarily two reasons you would want that: work around bugs and	2205	There are primarily two reasons you would want that: work around bugs and
1066	prioritise I/O.	2206	prioritise I/O.
1067		2207
1068	As an example for a bug workaround, the kqueue backend might only support	2208	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	2209	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	2210	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	2211	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	2212	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	2213	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.	2214	C<kevent>, but at least you can use both mechanisms for what they are
		2215	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
1075		2216
1076	As for prioritising I/O: rarely you have the case where some fds have	2217	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	2218	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	2219	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	2220	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.	2221	the rest in a second one, and embed the second one in the first.
		2222
		2223	As long as the watcher is active, the callback will be invoked every time
		2224	there might be events pending in the embedded loop. The callback must then
		2225	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke
		2226	their callbacks (you could also start an idle watcher to give the embedded
		2227	loop strictly lower priority for example). You can also set the callback
		2228	to C<0>, in which case the embed watcher will automatically execute the
		2229	embedded loop sweep.
1081		2230
1082	As long as the watcher is started it will automatically handle events. The	2231	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	2232	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	2233	set the callback to C<0> to avoid having to specify one if you are not
1085	interested in that.	2234	interested in that.
1086		2235
1087	Also, there have not currently been made special provisions for forking:	2236	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,	2237	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	2238	but you will also have to stop and restart any C<ev_embed> watchers
1090	yourself.	2239	yourself - but you can use a fork watcher to handle this automatically,
		2240	and future versions of libev might do just that.
1091		2241
1092	Unfortunately, not all backends are embeddable, only the ones returned by	2242	Unfortunately, not all backends are embeddable: only the ones returned by
1093	C<ev_embeddable_backends> are, which, unfortunately, does not include any	2243	C<ev_embeddable_backends> are, which, unfortunately, does not include any
1094	portable one.	2244	portable one.
1095		2245
1096	So when you want to use this feature you will always have to be prepared	2246	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	2247	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	2248	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:	2249	create it, and if that fails, use the normal loop for everything.
1100		2250
1101	struct ev_loop *loop_hi = ev_default_init (0);	2251	=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		2252
1111	// if we got one, then embed it, otherwise default to loop_hi	2253	While the C<ev_embed> watcher is running, forks in the embedding loop will
1112	if (loop_lo)	2254	automatically be applied to the embedded loop as well, so no special
1113	{	2255	fork handling is required in that case. When the watcher is not running,
1114	ev_embed_init (&embed, 0, loop_lo);	2256	however, it is still the task of the libev user to call C<ev_loop_fork ()>
1115	ev_embed_start (loop_hi, &embed);	2257	as applicable.
1116	}	2258
1117	else	2259	=head3 Watcher-Specific Functions and Data Members
1118	loop_lo = loop_hi;
1119		2260
1120	=over 4	2261	=over 4
1121		2262
1122	=item ev_embed_init (ev_embed *, callback, struct ev_loop *loop)	2263	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
1123		2264
1124	=item ev_embed_set (ev_embed *, callback, struct ev_loop *loop)	2265	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)
1125		2266
1126	Configures the watcher to embed the given loop, which must be embeddable.	2267	Configures the watcher to embed the given loop, which must be
		2268	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
		2269	invoked automatically, otherwise it is the responsibility of the callback
		2270	to invoke it (it will continue to be called until the sweep has been done,
		2271	if you do not want that, you need to temporarily stop the embed watcher).
		2272
		2273	=item ev_embed_sweep (loop, ev_embed *)
		2274
		2275	Make a single, non-blocking sweep over the embedded loop. This works
		2276	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
		2277	appropriate way for embedded loops.
		2278
		2279	=item struct ev_loop *other [read-only]
		2280
		2281	The embedded event loop.
1127		2282
1128	=back	2283	=back
1129		2284
		2285	=head3 Examples
		2286
		2287	Example: Try to get an embeddable event loop and embed it into the default
		2288	event loop. If that is not possible, use the default loop. The default
		2289	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		2290	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		2291	used).
		2292
		2293	struct ev_loop *loop_hi = ev_default_init (0);
		2294	struct ev_loop *loop_lo = 0;
		2295	struct ev_embed embed;
		2296
		2297	// see if there is a chance of getting one that works
		2298	// (remember that a flags value of 0 means autodetection)
		2299	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		2300	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		2301	: 0;
		2302
		2303	// if we got one, then embed it, otherwise default to loop_hi
		2304	if (loop_lo)
		2305	{
		2306	ev_embed_init (&embed, 0, loop_lo);
		2307	ev_embed_start (loop_hi, &embed);
		2308	}
		2309	else
		2310	loop_lo = loop_hi;
		2311
		2312	Example: Check if kqueue is available but not recommended and create
		2313	a kqueue backend for use with sockets (which usually work with any
		2314	kqueue implementation). Store the kqueue/socket-only event loop in
		2315	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		2316
		2317	struct ev_loop *loop = ev_default_init (0);
		2318	struct ev_loop *loop_socket = 0;
		2319	struct ev_embed embed;
		2320
		2321	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		2322	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		2323	{
		2324	ev_embed_init (&embed, 0, loop_socket);
		2325	ev_embed_start (loop, &embed);
		2326	}
		2327
		2328	if (!loop_socket)
		2329	loop_socket = loop;
		2330
		2331	// now use loop_socket for all sockets, and loop for everything else
		2332
		2333
		2334	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
		2335
		2336	Fork watchers are called when a C<fork ()> was detected (usually because
		2337	whoever is a good citizen cared to tell libev about it by calling
		2338	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the
		2339	event loop blocks next and before C<ev_check> watchers are being called,
		2340	and only in the child after the fork. If whoever good citizen calling
		2341	C<ev_default_fork> cheats and calls it in the wrong process, the fork
		2342	handlers will be invoked, too, of course.
		2343
		2344	=head3 Watcher-Specific Functions and Data Members
		2345
		2346	=over 4
		2347
		2348	=item ev_fork_init (ev_signal *, callback)
		2349
		2350	Initialises and configures the fork watcher - it has no parameters of any
		2351	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
		2352	believe me.
		2353
		2354	=back
		2355
		2356
		2357	=head2 C<ev_async> - how to wake up another event loop
		2358
		2359	In general, you cannot use an C<ev_loop> from multiple threads or other
		2360	asynchronous sources such as signal handlers (as opposed to multiple event
		2361	loops - those are of course safe to use in different threads).
		2362
		2363	Sometimes, however, you need to wake up another event loop you do not
		2364	control, for example because it belongs to another thread. This is what
		2365	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you
		2366	can signal it by calling C<ev_async_send>, which is thread- and signal
		2367	safe.
		2368
		2369	This functionality is very similar to C<ev_signal> watchers, as signals,
		2370	too, are asynchronous in nature, and signals, too, will be compressed
		2371	(i.e. the number of callback invocations may be less than the number of
		2372	C<ev_async_sent> calls).
		2373
		2374	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		2375	just the default loop.
		2376
		2377	=head3 Queueing
		2378
		2379	C<ev_async> does not support queueing of data in any way. The reason
		2380	is that the author does not know of a simple (or any) algorithm for a
		2381	multiple-writer-single-reader queue that works in all cases and doesn't
		2382	need elaborate support such as pthreads.
		2383
		2384	That means that if you want to queue data, you have to provide your own
		2385	queue. But at least I can tell you how to implement locking around your
		2386	queue:
		2387
		2388	=over 4
		2389
		2390	=item queueing from a signal handler context
		2391
		2392	To implement race-free queueing, you simply add to the queue in the signal
		2393	handler but you block the signal handler in the watcher callback. Here is
		2394	an example that does that for some fictitious SIGUSR1 handler:
		2395
		2396	static ev_async mysig;
		2397
		2398	static void
		2399	sigusr1_handler (void)
		2400	{
		2401	sometype data;
		2402
		2403	// no locking etc.
		2404	queue_put (data);
		2405	ev_async_send (EV_DEFAULT_ &mysig);
		2406	}
		2407
		2408	static void
		2409	mysig_cb (EV_P_ ev_async *w, int revents)
		2410	{
		2411	sometype data;
		2412	sigset_t block, prev;
		2413
		2414	sigemptyset (&block);
		2415	sigaddset (&block, SIGUSR1);
		2416	sigprocmask (SIG_BLOCK, &block, &prev);
		2417
		2418	while (queue_get (&data))
		2419	process (data);
		2420
		2421	if (sigismember (&prev, SIGUSR1)
		2422	sigprocmask (SIG_UNBLOCK, &block, 0);
		2423	}
		2424
		2425	(Note: pthreads in theory requires you to use C<pthread_setmask>
		2426	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		2427	either...).
		2428
		2429	=item queueing from a thread context
		2430
		2431	The strategy for threads is different, as you cannot (easily) block
		2432	threads but you can easily preempt them, so to queue safely you need to
		2433	employ a traditional mutex lock, such as in this pthread example:
		2434
		2435	static ev_async mysig;
		2436	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		2437
		2438	static void
		2439	otherthread (void)
		2440	{
		2441	// only need to lock the actual queueing operation
		2442	pthread_mutex_lock (&mymutex);
		2443	queue_put (data);
		2444	pthread_mutex_unlock (&mymutex);
		2445
		2446	ev_async_send (EV_DEFAULT_ &mysig);
		2447	}
		2448
		2449	static void
		2450	mysig_cb (EV_P_ ev_async *w, int revents)
		2451	{
		2452	pthread_mutex_lock (&mymutex);
		2453
		2454	while (queue_get (&data))
		2455	process (data);
		2456
		2457	pthread_mutex_unlock (&mymutex);
		2458	}
		2459
		2460	=back
		2461
		2462
		2463	=head3 Watcher-Specific Functions and Data Members
		2464
		2465	=over 4
		2466
		2467	=item ev_async_init (ev_async *, callback)
		2468
		2469	Initialises and configures the async watcher - it has no parameters of any
		2470	kind. There is a C<ev_asynd_set> macro, but using it is utterly pointless,
		2471	trust me.
		2472
		2473	=item ev_async_send (loop, ev_async *)
		2474
		2475	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		2476	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		2477	C<ev_feed_event>, this call is safe to do from other threads, signal or
		2478	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
		2479	section below on what exactly this means).
		2480
		2481	This call incurs the overhead of a system call only once per loop iteration,
		2482	so while the overhead might be noticeable, it doesn't apply to repeated
		2483	calls to C<ev_async_send>.
		2484
		2485	=item bool = ev_async_pending (ev_async *)
		2486
		2487	Returns a non-zero value when C<ev_async_send> has been called on the
		2488	watcher but the event has not yet been processed (or even noted) by the
		2489	event loop.
		2490
		2491	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		2492	the loop iterates next and checks for the watcher to have become active,
		2493	it will reset the flag again. C<ev_async_pending> can be used to very
		2494	quickly check whether invoking the loop might be a good idea.
		2495
		2496	Not that this does I<not> check whether the watcher itself is pending, only
		2497	whether it has been requested to make this watcher pending.
		2498
		2499	=back
		2500
1130		2501
1131	=head1 OTHER FUNCTIONS	2502	=head1 OTHER FUNCTIONS
1132		2503
1133	There are some other functions of possible interest. Described. Here. Now.	2504	There are some other functions of possible interest. Described. Here. Now.
1134		2505
1135	=over 4	2506	=over 4
1136		2507
1137	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	2508	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
1138		2509
1139	This function combines a simple timer and an I/O watcher, calls your	2510	This function combines a simple timer and an I/O watcher, calls your
1140	callback on whichever event happens first and automatically stop both	2511	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	2512	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	2513	or timeout without having to allocate/configure/start/stop/free one or
1143	more watchers yourself.	2514	more watchers yourself.
1144		2515
1145	If C<fd> is less than 0, then no I/O watcher will be started and events	2516	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	2517	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
1147	C<events> set will be craeted and started.	2518	the given C<fd> and C<events> set will be created and started.
1148		2519
1149	If C<timeout> is less than 0, then no timeout watcher will be	2520	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	2521	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	2522	repeat = 0) will be started. C<0> is a valid timeout.
1152	dubious value.
1153		2523
1154	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	2524	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	2525	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>	2526	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
1157	value passed to C<ev_once>:	2527	value passed to C<ev_once>. Note that it is possible to receive I<both>
		2528	a timeout and an io event at the same time - you probably should give io
		2529	events precedence.
1158		2530
		2531	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		2532
1159	static void stdin_ready (int revents, void *arg)	2533	static void stdin_ready (int revents, void *arg)
1160	{	2534	{
1161	if (revents & EV_TIMEOUT)
1162	/* doh, nothing entered */;
1163	else if (revents & EV_READ)	2535	if (revents & EV_READ)
1164	/* stdin might have data for us, joy! */;	2536	/* stdin might have data for us, joy! */;
		2537	else if (revents & EV_TIMEOUT)
		2538	/* doh, nothing entered */;
1165	}	2539	}
1166		2540
1167	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	2541	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
1168		2542
1169	=item ev_feed_event (loop, watcher, int events)	2543	=item ev_feed_event (ev_loop *, watcher *, int revents)
1170		2544
1171	Feeds the given event set into the event loop, as if the specified event	2545	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	2546	had happened for the specified watcher (which must be a pointer to an
1173	initialised but not necessarily started event watcher).	2547	initialised but not necessarily started event watcher).
1174		2548
1175	=item ev_feed_fd_event (loop, int fd, int revents)	2549	=item ev_feed_fd_event (ev_loop *, int fd, int revents)
1176		2550
1177	Feed an event on the given fd, as if a file descriptor backend detected	2551	Feed an event on the given fd, as if a file descriptor backend detected
1178	the given events it.	2552	the given events it.
1179		2553
1180	=item ev_feed_signal_event (loop, int signum)	2554	=item ev_feed_signal_event (ev_loop *loop, int signum)
1181		2555
1182	Feed an event as if the given signal occured (loop must be the default loop!).	2556	Feed an event as if the given signal occurred (C<loop> must be the default
		2557	loop!).
1183		2558
1184	=back	2559	=back
1185		2560
1186		2561
1187	=head1 LIBEVENT EMULATION	2562	=head1 LIBEVENT EMULATION
…		…
1202		2577
1203	=item * Priorities are not currently supported. Initialising priorities	2578	=item * Priorities are not currently supported. Initialising priorities
1204	will fail and all watchers will have the same priority, even though there	2579	will fail and all watchers will have the same priority, even though there
1205	is an ev_pri field.	2580	is an ev_pri field.
1206		2581
		2582	=item * In libevent, the last base created gets the signals, in libev, the
		2583	first base created (== the default loop) gets the signals.
		2584
1207	=item * Other members are not supported.	2585	=item * Other members are not supported.
1208		2586
1209	=item * The libev emulation is I<not> ABI compatible to libevent, you need	2587	=item * The libev emulation is I<not> ABI compatible to libevent, you need
1210	to use the libev header file and library.	2588	to use the libev header file and library.
1211		2589
1212	=back	2590	=back
1213		2591
1214	=head1 C++ SUPPORT	2592	=head1 C++ SUPPORT
1215		2593
1216	TBD.	2594	Libev comes with some simplistic wrapper classes for C++ that mainly allow
		2595	you to use some convenience methods to start/stop watchers and also change
		2596	the callback model to a model using method callbacks on objects.
		2597
		2598	To use it,
		2599
		2600	#include <ev++.h>
		2601
		2602	This automatically includes F<ev.h> and puts all of its definitions (many
		2603	of them macros) into the global namespace. All C++ specific things are
		2604	put into the C<ev> namespace. It should support all the same embedding
		2605	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
		2606
		2607	Care has been taken to keep the overhead low. The only data member the C++
		2608	classes add (compared to plain C-style watchers) is the event loop pointer
		2609	that the watcher is associated with (or no additional members at all if
		2610	you disable C<EV_MULTIPLICITY> when embedding libev).
		2611
		2612	Currently, functions, and static and non-static member functions can be
		2613	used as callbacks. Other types should be easy to add as long as they only
		2614	need one additional pointer for context. If you need support for other
		2615	types of functors please contact the author (preferably after implementing
		2616	it).
		2617
		2618	Here is a list of things available in the C<ev> namespace:
		2619
		2620	=over 4
		2621
		2622	=item C<ev::READ>, C<ev::WRITE> etc.
		2623
		2624	These are just enum values with the same values as the C<EV_READ> etc.
		2625	macros from F<ev.h>.
		2626
		2627	=item C<ev::tstamp>, C<ev::now>
		2628
		2629	Aliases to the same types/functions as with the C<ev_> prefix.
		2630
		2631	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
		2632
		2633	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
		2634	the same name in the C<ev> namespace, with the exception of C<ev_signal>
		2635	which is called C<ev::sig> to avoid clashes with the C<signal> macro
		2636	defines by many implementations.
		2637
		2638	All of those classes have these methods:
		2639
		2640	=over 4
		2641
		2642	=item ev::TYPE::TYPE ()
		2643
		2644	=item ev::TYPE::TYPE (struct ev_loop *)
		2645
		2646	=item ev::TYPE::~TYPE
		2647
		2648	The constructor (optionally) takes an event loop to associate the watcher
		2649	with. If it is omitted, it will use C<EV_DEFAULT>.
		2650
		2651	The constructor calls C<ev_init> for you, which means you have to call the
		2652	C<set> method before starting it.
		2653
		2654	It will not set a callback, however: You have to call the templated C<set>
		2655	method to set a callback before you can start the watcher.
		2656
		2657	(The reason why you have to use a method is a limitation in C++ which does
		2658	not allow explicit template arguments for constructors).
		2659
		2660	The destructor automatically stops the watcher if it is active.
		2661
		2662	=item w->set<class, &class::method> (object *)
		2663
		2664	This method sets the callback method to call. The method has to have a
		2665	signature of C<void (*)(ev_TYPE &, int)>, it receives the watcher as
		2666	first argument and the C<revents> as second. The object must be given as
		2667	parameter and is stored in the C<data> member of the watcher.
		2668
		2669	This method synthesizes efficient thunking code to call your method from
		2670	the C callback that libev requires. If your compiler can inline your
		2671	callback (i.e. it is visible to it at the place of the C<set> call and
		2672	your compiler is good :), then the method will be fully inlined into the
		2673	thunking function, making it as fast as a direct C callback.
		2674
		2675	Example: simple class declaration and watcher initialisation
		2676
		2677	struct myclass
		2678	{
		2679	void io_cb (ev::io &w, int revents) { }
		2680	}
		2681
		2682	myclass obj;
		2683	ev::io iow;
		2684	iow.set <myclass, &myclass::io_cb> (&obj);
		2685
		2686	=item w->set<function> (void *data = 0)
		2687
		2688	Also sets a callback, but uses a static method or plain function as
		2689	callback. The optional C<data> argument will be stored in the watcher's
		2690	C<data> member and is free for you to use.
		2691
		2692	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
		2693
		2694	See the method-C<set> above for more details.
		2695
		2696	Example: Use a plain function as callback.
		2697
		2698	static void io_cb (ev::io &w, int revents) { }
		2699	iow.set <io_cb> ();
		2700
		2701	=item w->set (struct ev_loop *)
		2702
		2703	Associates a different C<struct ev_loop> with this watcher. You can only
		2704	do this when the watcher is inactive (and not pending either).
		2705
		2706	=item w->set ([arguments])
		2707
		2708	Basically the same as C<ev_TYPE_set>, with the same arguments. Must be
		2709	called at least once. Unlike the C counterpart, an active watcher gets
		2710	automatically stopped and restarted when reconfiguring it with this
		2711	method.
		2712
		2713	=item w->start ()
		2714
		2715	Starts the watcher. Note that there is no C<loop> argument, as the
		2716	constructor already stores the event loop.
		2717
		2718	=item w->stop ()
		2719
		2720	Stops the watcher if it is active. Again, no C<loop> argument.
		2721
		2722	=item w->again () (C<ev::timer>, C<ev::periodic> only)
		2723
		2724	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
		2725	C<ev_TYPE_again> function.
		2726
		2727	=item w->sweep () (C<ev::embed> only)
		2728
		2729	Invokes C<ev_embed_sweep>.
		2730
		2731	=item w->update () (C<ev::stat> only)
		2732
		2733	Invokes C<ev_stat_stat>.
		2734
		2735	=back
		2736
		2737	=back
		2738
		2739	Example: Define a class with an IO and idle watcher, start one of them in
		2740	the constructor.
		2741
		2742	class myclass
		2743	{
		2744	ev::io io ; void io_cb (ev::io &w, int revents);
		2745	ev::idle idle; void idle_cb (ev::idle &w, int revents);
		2746
		2747	myclass (int fd)
		2748	{
		2749	io .set <myclass, &myclass::io_cb > (this);
		2750	idle.set <myclass, &myclass::idle_cb> (this);
		2751
		2752	io.start (fd, ev::READ);
		2753	}
		2754	};
		2755
		2756
		2757	=head1 OTHER LANGUAGE BINDINGS
		2758
		2759	Libev does not offer other language bindings itself, but bindings for a
		2760	number of languages exist in the form of third-party packages. If you know
		2761	any interesting language binding in addition to the ones listed here, drop
		2762	me a note.
		2763
		2764	=over 4
		2765
		2766	=item Perl
		2767
		2768	The EV module implements the full libev API and is actually used to test
		2769	libev. EV is developed together with libev. Apart from the EV core module,
		2770	there are additional modules that implement libev-compatible interfaces
		2771	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		2772	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		2773	and C<EV::Glib>).
		2774
		2775	It can be found and installed via CPAN, its homepage is at
		2776	L<http://software.schmorp.de/pkg/EV>.
		2777
		2778	=item Python
		2779
		2780	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		2781	seems to be quite complete and well-documented. Note, however, that the
		2782	patch they require for libev is outright dangerous as it breaks the ABI
		2783	for everybody else, and therefore, should never be applied in an installed
		2784	libev (if python requires an incompatible ABI then it needs to embed
		2785	libev).
		2786
		2787	=item Ruby
		2788
		2789	Tony Arcieri has written a ruby extension that offers access to a subset
		2790	of the libev API and adds file handle abstractions, asynchronous DNS and
		2791	more on top of it. It can be found via gem servers. Its homepage is at
		2792	L<http://rev.rubyforge.org/>.
		2793
		2794	=item D
		2795
		2796	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		2797	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		2798
		2799	=back
		2800
		2801
		2802	=head1 MACRO MAGIC
		2803
		2804	Libev can be compiled with a variety of options, the most fundamental
		2805	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
		2806	functions and callbacks have an initial C<struct ev_loop *> argument.
		2807
		2808	To make it easier to write programs that cope with either variant, the
		2809	following macros are defined:
		2810
		2811	=over 4
		2812
		2813	=item C<EV_A>, C<EV_A_>
		2814
		2815	This provides the loop I<argument> for functions, if one is required ("ev
		2816	loop argument"). The C<EV_A> form is used when this is the sole argument,
		2817	C<EV_A_> is used when other arguments are following. Example:
		2818
		2819	ev_unref (EV_A);
		2820	ev_timer_add (EV_A_ watcher);
		2821	ev_loop (EV_A_ 0);
		2822
		2823	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
		2824	which is often provided by the following macro.
		2825
		2826	=item C<EV_P>, C<EV_P_>
		2827
		2828	This provides the loop I<parameter> for functions, if one is required ("ev
		2829	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
		2830	C<EV_P_> is used when other parameters are following. Example:
		2831
		2832	// this is how ev_unref is being declared
		2833	static void ev_unref (EV_P);
		2834
		2835	// this is how you can declare your typical callback
		2836	static void cb (EV_P_ ev_timer *w, int revents)
		2837
		2838	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
		2839	suitable for use with C<EV_A>.
		2840
		2841	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
		2842
		2843	Similar to the other two macros, this gives you the value of the default
		2844	loop, if multiple loops are supported ("ev loop default").
		2845
		2846	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		2847
		2848	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		2849	default loop has been initialised (C<UC> == unchecked). Their behaviour
		2850	is undefined when the default loop has not been initialised by a previous
		2851	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		2852
		2853	It is often prudent to use C<EV_DEFAULT> when initialising the first
		2854	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
		2855
		2856	=back
		2857
		2858	Example: Declare and initialise a check watcher, utilising the above
		2859	macros so it will work regardless of whether multiple loops are supported
		2860	or not.
		2861
		2862	static void
		2863	check_cb (EV_P_ ev_timer *w, int revents)
		2864	{
		2865	ev_check_stop (EV_A_ w);
		2866	}
		2867
		2868	ev_check check;
		2869	ev_check_init (&check, check_cb);
		2870	ev_check_start (EV_DEFAULT_ &check);
		2871	ev_loop (EV_DEFAULT_ 0);
		2872
		2873	=head1 EMBEDDING
		2874
		2875	Libev can (and often is) directly embedded into host
		2876	applications. Examples of applications that embed it include the Deliantra
		2877	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
		2878	and rxvt-unicode.
		2879
		2880	The goal is to enable you to just copy the necessary files into your
		2881	source directory without having to change even a single line in them, so
		2882	you can easily upgrade by simply copying (or having a checked-out copy of
		2883	libev somewhere in your source tree).
		2884
		2885	=head2 FILESETS
		2886
		2887	Depending on what features you need you need to include one or more sets of files
		2888	in your application.
		2889
		2890	=head3 CORE EVENT LOOP
		2891
		2892	To include only the libev core (all the C<ev_*> functions), with manual
		2893	configuration (no autoconf):
		2894
		2895	#define EV_STANDALONE 1
		2896	#include "ev.c"
		2897
		2898	This will automatically include F<ev.h>, too, and should be done in a
		2899	single C source file only to provide the function implementations. To use
		2900	it, do the same for F<ev.h> in all files wishing to use this API (best
		2901	done by writing a wrapper around F<ev.h> that you can include instead and
		2902	where you can put other configuration options):
		2903
		2904	#define EV_STANDALONE 1
		2905	#include "ev.h"
		2906
		2907	Both header files and implementation files can be compiled with a C++
		2908	compiler (at least, thats a stated goal, and breakage will be treated
		2909	as a bug).
		2910
		2911	You need the following files in your source tree, or in a directory
		2912	in your include path (e.g. in libev/ when using -Ilibev):
		2913
		2914	ev.h
		2915	ev.c
		2916	ev_vars.h
		2917	ev_wrap.h
		2918
		2919	ev_win32.c required on win32 platforms only
		2920
		2921	ev_select.c only when select backend is enabled (which is enabled by default)
		2922	ev_poll.c only when poll backend is enabled (disabled by default)
		2923	ev_epoll.c only when the epoll backend is enabled (disabled by default)
		2924	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
		2925	ev_port.c only when the solaris port backend is enabled (disabled by default)
		2926
		2927	F<ev.c> includes the backend files directly when enabled, so you only need
		2928	to compile this single file.
		2929
		2930	=head3 LIBEVENT COMPATIBILITY API
		2931
		2932	To include the libevent compatibility API, also include:
		2933
		2934	#include "event.c"
		2935
		2936	in the file including F<ev.c>, and:
		2937
		2938	#include "event.h"
		2939
		2940	in the files that want to use the libevent API. This also includes F<ev.h>.
		2941
		2942	You need the following additional files for this:
		2943
		2944	event.h
		2945	event.c
		2946
		2947	=head3 AUTOCONF SUPPORT
		2948
		2949	Instead of using C<EV_STANDALONE=1> and providing your configuration in
		2950	whatever way you want, you can also C<m4_include([libev.m4])> in your
		2951	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
		2952	include F<config.h> and configure itself accordingly.
		2953
		2954	For this of course you need the m4 file:
		2955
		2956	libev.m4
		2957
		2958	=head2 PREPROCESSOR SYMBOLS/MACROS
		2959
		2960	Libev can be configured via a variety of preprocessor symbols you have to
		2961	define before including any of its files. The default in the absence of
		2962	autoconf is documented for every option.
		2963
		2964	=over 4
		2965
		2966	=item EV_STANDALONE
		2967
		2968	Must always be C<1> if you do not use autoconf configuration, which
		2969	keeps libev from including F<config.h>, and it also defines dummy
		2970	implementations for some libevent functions (such as logging, which is not
		2971	supported). It will also not define any of the structs usually found in
		2972	F<event.h> that are not directly supported by the libev core alone.
		2973
		2974	=item EV_USE_MONOTONIC
		2975
		2976	If defined to be C<1>, libev will try to detect the availability of the
		2977	monotonic clock option at both compile time and runtime. Otherwise no use
		2978	of the monotonic clock option will be attempted. If you enable this, you
		2979	usually have to link against librt or something similar. Enabling it when
		2980	the functionality isn't available is safe, though, although you have
		2981	to make sure you link against any libraries where the C<clock_gettime>
		2982	function is hiding in (often F<-lrt>).
		2983
		2984	=item EV_USE_REALTIME
		2985
		2986	If defined to be C<1>, libev will try to detect the availability of the
		2987	real-time clock option at compile time (and assume its availability at
		2988	runtime if successful). Otherwise no use of the real-time clock option will
		2989	be attempted. This effectively replaces C<gettimeofday> by C<clock_get
		2990	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the
		2991	note about libraries in the description of C<EV_USE_MONOTONIC>, though.
		2992
		2993	=item EV_USE_NANOSLEEP
		2994
		2995	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		2996	and will use it for delays. Otherwise it will use C<select ()>.
		2997
		2998	=item EV_USE_EVENTFD
		2999
		3000	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		3001	available and will probe for kernel support at runtime. This will improve
		3002	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		3003	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		3004	2.7 or newer, otherwise disabled.
		3005
		3006	=item EV_USE_SELECT
		3007
		3008	If undefined or defined to be C<1>, libev will compile in support for the
		3009	C<select>(2) backend. No attempt at auto-detection will be done: if no
		3010	other method takes over, select will be it. Otherwise the select backend
		3011	will not be compiled in.
		3012
		3013	=item EV_SELECT_USE_FD_SET
		3014
		3015	If defined to C<1>, then the select backend will use the system C<fd_set>
		3016	structure. This is useful if libev doesn't compile due to a missing
		3017	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout on
		3018	exotic systems. This usually limits the range of file descriptors to some
		3019	low limit such as 1024 or might have other limitations (winsocket only
		3020	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might
		3021	influence the size of the C<fd_set> used.
		3022
		3023	=item EV_SELECT_IS_WINSOCKET
		3024
		3025	When defined to C<1>, the select backend will assume that
		3026	select/socket/connect etc. don't understand file descriptors but
		3027	wants osf handles on win32 (this is the case when the select to
		3028	be used is the winsock select). This means that it will call
		3029	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
		3030	it is assumed that all these functions actually work on fds, even
		3031	on win32. Should not be defined on non-win32 platforms.
		3032
		3033	=item EV_FD_TO_WIN32_HANDLE
		3034
		3035	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		3036	file descriptors to socket handles. When not defining this symbol (the
		3037	default), then libev will call C<_get_osfhandle>, which is usually
		3038	correct. In some cases, programs use their own file descriptor management,
		3039	in which case they can provide this function to map fds to socket handles.
		3040
		3041	=item EV_USE_POLL
		3042
		3043	If defined to be C<1>, libev will compile in support for the C<poll>(2)
		3044	backend. Otherwise it will be enabled on non-win32 platforms. It
		3045	takes precedence over select.
		3046
		3047	=item EV_USE_EPOLL
		3048
		3049	If defined to be C<1>, libev will compile in support for the Linux
		3050	C<epoll>(7) backend. Its availability will be detected at runtime,
		3051	otherwise another method will be used as fallback. This is the preferred
		3052	backend for GNU/Linux systems. If undefined, it will be enabled if the
		3053	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		3054
		3055	=item EV_USE_KQUEUE
		3056
		3057	If defined to be C<1>, libev will compile in support for the BSD style
		3058	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
		3059	otherwise another method will be used as fallback. This is the preferred
		3060	backend for BSD and BSD-like systems, although on most BSDs kqueue only
		3061	supports some types of fds correctly (the only platform we found that
		3062	supports ptys for example was NetBSD), so kqueue might be compiled in, but
		3063	not be used unless explicitly requested. The best way to use it is to find
		3064	out whether kqueue supports your type of fd properly and use an embedded
		3065	kqueue loop.
		3066
		3067	=item EV_USE_PORT
		3068
		3069	If defined to be C<1>, libev will compile in support for the Solaris
		3070	10 port style backend. Its availability will be detected at runtime,
		3071	otherwise another method will be used as fallback. This is the preferred
		3072	backend for Solaris 10 systems.
		3073
		3074	=item EV_USE_DEVPOLL
		3075
		3076	Reserved for future expansion, works like the USE symbols above.
		3077
		3078	=item EV_USE_INOTIFY
		3079
		3080	If defined to be C<1>, libev will compile in support for the Linux inotify
		3081	interface to speed up C<ev_stat> watchers. Its actual availability will
		3082	be detected at runtime. If undefined, it will be enabled if the headers
		3083	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		3084
		3085	=item EV_ATOMIC_T
		3086
		3087	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		3088	access is atomic with respect to other threads or signal contexts. No such
		3089	type is easily found in the C language, so you can provide your own type
		3090	that you know is safe for your purposes. It is used both for signal handler "locking"
		3091	as well as for signal and thread safety in C<ev_async> watchers.
		3092
		3093	In the absence of this define, libev will use C<sig_atomic_t volatile>
		3094	(from F<signal.h>), which is usually good enough on most platforms.
		3095
		3096	=item EV_H
		3097
		3098	The name of the F<ev.h> header file used to include it. The default if
		3099	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
		3100	used to virtually rename the F<ev.h> header file in case of conflicts.
		3101
		3102	=item EV_CONFIG_H
		3103
		3104	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
		3105	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
		3106	C<EV_H>, above.
		3107
		3108	=item EV_EVENT_H
		3109
		3110	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
		3111	of how the F<event.h> header can be found, the default is C<"event.h">.
		3112
		3113	=item EV_PROTOTYPES
		3114
		3115	If defined to be C<0>, then F<ev.h> will not define any function
		3116	prototypes, but still define all the structs and other symbols. This is
		3117	occasionally useful if you want to provide your own wrapper functions
		3118	around libev functions.
		3119
		3120	=item EV_MULTIPLICITY
		3121
		3122	If undefined or defined to C<1>, then all event-loop-specific functions
		3123	will have the C<struct ev_loop *> as first argument, and you can create
		3124	additional independent event loops. Otherwise there will be no support
		3125	for multiple event loops and there is no first event loop pointer
		3126	argument. Instead, all functions act on the single default loop.
		3127
		3128	=item EV_MINPRI
		3129
		3130	=item EV_MAXPRI
		3131
		3132	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
		3133	C<EV_MAXPRI>, but otherwise there are no non-obvious limitations. You can
		3134	provide for more priorities by overriding those symbols (usually defined
		3135	to be C<-2> and C<2>, respectively).
		3136
		3137	When doing priority-based operations, libev usually has to linearly search
		3138	all the priorities, so having many of them (hundreds) uses a lot of space
		3139	and time, so using the defaults of five priorities (-2 .. +2) is usually
		3140	fine.
		3141
		3142	If your embedding application does not need any priorities, defining these
		3143	both to C<0> will save some memory and CPU.
		3144
		3145	=item EV_PERIODIC_ENABLE
		3146
		3147	If undefined or defined to be C<1>, then periodic timers are supported. If
		3148	defined to be C<0>, then they are not. Disabling them saves a few kB of
		3149	code.
		3150
		3151	=item EV_IDLE_ENABLE
		3152
		3153	If undefined or defined to be C<1>, then idle watchers are supported. If
		3154	defined to be C<0>, then they are not. Disabling them saves a few kB of
		3155	code.
		3156
		3157	=item EV_EMBED_ENABLE
		3158
		3159	If undefined or defined to be C<1>, then embed watchers are supported. If
		3160	defined to be C<0>, then they are not. Embed watchers rely on most other
		3161	watcher types, which therefore must not be disabled.
		3162
		3163	=item EV_STAT_ENABLE
		3164
		3165	If undefined or defined to be C<1>, then stat watchers are supported. If
		3166	defined to be C<0>, then they are not.
		3167
		3168	=item EV_FORK_ENABLE
		3169
		3170	If undefined or defined to be C<1>, then fork watchers are supported. If
		3171	defined to be C<0>, then they are not.
		3172
		3173	=item EV_ASYNC_ENABLE
		3174
		3175	If undefined or defined to be C<1>, then async watchers are supported. If
		3176	defined to be C<0>, then they are not.
		3177
		3178	=item EV_MINIMAL
		3179
		3180	If you need to shave off some kilobytes of code at the expense of some
		3181	speed, define this symbol to C<1>. Currently this is used to override some
		3182	inlining decisions, saves roughly 30% code size on amd64. It also selects a
		3183	much smaller 2-heap for timer management over the default 4-heap.
		3184
		3185	=item EV_PID_HASHSIZE
		3186
		3187	C<ev_child> watchers use a small hash table to distribute workload by
		3188	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
		3189	than enough. If you need to manage thousands of children you might want to
		3190	increase this value (I<must> be a power of two).
		3191
		3192	=item EV_INOTIFY_HASHSIZE
		3193
		3194	C<ev_stat> watchers use a small hash table to distribute workload by
		3195	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
		3196	usually more than enough. If you need to manage thousands of C<ev_stat>
		3197	watchers you might want to increase this value (I<must> be a power of
		3198	two).
		3199
		3200	=item EV_USE_4HEAP
		3201
		3202	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3203	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		3204	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		3205	faster performance with many (thousands) of watchers.
		3206
		3207	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3208	(disabled).
		3209
		3210	=item EV_HEAP_CACHE_AT
		3211
		3212	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3213	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		3214	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		3215	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		3216	but avoids random read accesses on heap changes. This improves performance
		3217	noticeably with many (hundreds) of watchers.
		3218
		3219	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3220	(disabled).
		3221
		3222	=item EV_VERIFY
		3223
		3224	Controls how much internal verification (see C<ev_loop_verify ()>) will
		3225	be done: If set to C<0>, no internal verification code will be compiled
		3226	in. If set to C<1>, then verification code will be compiled in, but not
		3227	called. If set to C<2>, then the internal verification code will be
		3228	called once per loop, which can slow down libev. If set to C<3>, then the
		3229	verification code will be called very frequently, which will slow down
		3230	libev considerably.
		3231
		3232	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be
		3233	C<0>.
		3234
		3235	=item EV_COMMON
		3236
		3237	By default, all watchers have a C<void *data> member. By redefining
		3238	this macro to a something else you can include more and other types of
		3239	members. You have to define it each time you include one of the files,
		3240	though, and it must be identical each time.
		3241
		3242	For example, the perl EV module uses something like this:
		3243
		3244	#define EV_COMMON \
		3245	SV *self; /* contains this struct */ \
		3246	SV *cb_sv, *fh /* note no trailing ";" */
		3247
		3248	=item EV_CB_DECLARE (type)
		3249
		3250	=item EV_CB_INVOKE (watcher, revents)
		3251
		3252	=item ev_set_cb (ev, cb)
		3253
		3254	Can be used to change the callback member declaration in each watcher,
		3255	and the way callbacks are invoked and set. Must expand to a struct member
		3256	definition and a statement, respectively. See the F<ev.h> header file for
		3257	their default definitions. One possible use for overriding these is to
		3258	avoid the C<struct ev_loop *> as first argument in all cases, or to use
		3259	method calls instead of plain function calls in C++.
		3260
		3261	=back
		3262
		3263	=head2 EXPORTED API SYMBOLS
		3264
		3265	If you need to re-export the API (e.g. via a DLL) and you need a list of
		3266	exported symbols, you can use the provided F<Symbol.*> files which list
		3267	all public symbols, one per line:
		3268
		3269	Symbols.ev for libev proper
		3270	Symbols.event for the libevent emulation
		3271
		3272	This can also be used to rename all public symbols to avoid clashes with
		3273	multiple versions of libev linked together (which is obviously bad in
		3274	itself, but sometimes it is inconvenient to avoid this).
		3275
		3276	A sed command like this will create wrapper C<#define>'s that you need to
		3277	include before including F<ev.h>:
		3278
		3279	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		3280
		3281	This would create a file F<wrap.h> which essentially looks like this:
		3282
		3283	#define ev_backend myprefix_ev_backend
		3284	#define ev_check_start myprefix_ev_check_start
		3285	#define ev_check_stop myprefix_ev_check_stop
		3286	...
		3287
		3288	=head2 EXAMPLES
		3289
		3290	For a real-world example of a program the includes libev
		3291	verbatim, you can have a look at the EV perl module
		3292	(L<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
		3293	the F<libev/> subdirectory and includes them in the F<EV/EVAPI.h> (public
		3294	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file
		3295	will be compiled. It is pretty complex because it provides its own header
		3296	file.
		3297
		3298	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
		3299	that everybody includes and which overrides some configure choices:
		3300
		3301	#define EV_MINIMAL 1
		3302	#define EV_USE_POLL 0
		3303	#define EV_MULTIPLICITY 0
		3304	#define EV_PERIODIC_ENABLE 0
		3305	#define EV_STAT_ENABLE 0
		3306	#define EV_FORK_ENABLE 0
		3307	#define EV_CONFIG_H <config.h>
		3308	#define EV_MINPRI 0
		3309	#define EV_MAXPRI 0
		3310
		3311	#include "ev++.h"
		3312
		3313	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
		3314
		3315	#include "ev_cpp.h"
		3316	#include "ev.c"
		3317
		3318	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
		3319
		3320	=head2 THREADS AND COROUTINES
		3321
		3322	=head3 THREADS
		3323
		3324	All libev functions are reentrant and thread-safe unless explicitly
		3325	documented otherwise, but libev implements no locking itself. This means
		3326	that you can use as many loops as you want in parallel, as long as there
		3327	are no concurrent calls into any libev function with the same loop
		3328	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		3329	of course): libev guarantees that different event loops share no data
		3330	structures that need any locking.
		3331
		3332	Or to put it differently: calls with different loop parameters can be done
		3333	concurrently from multiple threads, calls with the same loop parameter
		3334	must be done serially (but can be done from different threads, as long as
		3335	only one thread ever is inside a call at any point in time, e.g. by using
		3336	a mutex per loop).
		3337
		3338	Specifically to support threads (and signal handlers), libev implements
		3339	so-called C<ev_async> watchers, which allow some limited form of
		3340	concurrency on the same event loop, namely waking it up "from the
		3341	outside".
		3342
		3343	If you want to know which design (one loop, locking, or multiple loops
		3344	without or something else still) is best for your problem, then I cannot
		3345	help you, but here is some generic advice:
		3346
		3347	=over 4
		3348
		3349	=item * most applications have a main thread: use the default libev loop
		3350	in that thread, or create a separate thread running only the default loop.
		3351
		3352	This helps integrating other libraries or software modules that use libev
		3353	themselves and don't care/know about threading.
		3354
		3355	=item * one loop per thread is usually a good model.
		3356
		3357	Doing this is almost never wrong, sometimes a better-performance model
		3358	exists, but it is always a good start.
		3359
		3360	=item * other models exist, such as the leader/follower pattern, where one
		3361	loop is handed through multiple threads in a kind of round-robin fashion.
		3362
		3363	Choosing a model is hard - look around, learn, know that usually you can do
		3364	better than you currently do :-)
		3365
		3366	=item * often you need to talk to some other thread which blocks in the
		3367	event loop.
		3368
		3369	C<ev_async> watchers can be used to wake them up from other threads safely
		3370	(or from signal contexts...).
		3371
		3372	An example use would be to communicate signals or other events that only
		3373	work in the default loop by registering the signal watcher with the
		3374	default loop and triggering an C<ev_async> watcher from the default loop
		3375	watcher callback into the event loop interested in the signal.
		3376
		3377	=back
		3378
		3379	=head3 COROUTINES
		3380
		3381	Libev is very accommodating to coroutines ("cooperative threads"):
		3382	libev fully supports nesting calls to its functions from different
		3383	coroutines (e.g. you can call C<ev_loop> on the same loop from two
		3384	different coroutines, and switch freely between both coroutines running the
		3385	loop, as long as you don't confuse yourself). The only exception is that
		3386	you must not do this from C<ev_periodic> reschedule callbacks.
		3387
		3388	Care has been taken to ensure that libev does not keep local state inside
		3389	C<ev_loop>, and other calls do not usually allow for coroutine switches as
		3390	they do not clal any callbacks.
		3391
		3392	=head2 COMPILER WARNINGS
		3393
		3394	Depending on your compiler and compiler settings, you might get no or a
		3395	lot of warnings when compiling libev code. Some people are apparently
		3396	scared by this.
		3397
		3398	However, these are unavoidable for many reasons. For one, each compiler
		3399	has different warnings, and each user has different tastes regarding
		3400	warning options. "Warn-free" code therefore cannot be a goal except when
		3401	targeting a specific compiler and compiler-version.
		3402
		3403	Another reason is that some compiler warnings require elaborate
		3404	workarounds, or other changes to the code that make it less clear and less
		3405	maintainable.
		3406
		3407	And of course, some compiler warnings are just plain stupid, or simply
		3408	wrong (because they don't actually warn about the condition their message
		3409	seems to warn about). For example, certain older gcc versions had some
		3410	warnings that resulted an extreme number of false positives. These have
		3411	been fixed, but some people still insist on making code warn-free with
		3412	such buggy versions.
		3413
		3414	While libev is written to generate as few warnings as possible,
		3415	"warn-free" code is not a goal, and it is recommended not to build libev
		3416	with any compiler warnings enabled unless you are prepared to cope with
		3417	them (e.g. by ignoring them). Remember that warnings are just that:
		3418	warnings, not errors, or proof of bugs.
		3419
		3420
		3421	=head2 VALGRIND
		3422
		3423	Valgrind has a special section here because it is a popular tool that is
		3424	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		3425
		3426	If you think you found a bug (memory leak, uninitialised data access etc.)
		3427	in libev, then check twice: If valgrind reports something like:
		3428
		3429	==2274== definitely lost: 0 bytes in 0 blocks.
		3430	==2274== possibly lost: 0 bytes in 0 blocks.
		3431	==2274== still reachable: 256 bytes in 1 blocks.
		3432
		3433	Then there is no memory leak, just as memory accounted to global variables
		3434	is not a memleak - the memory is still being refernced, and didn't leak.
		3435
		3436	Similarly, under some circumstances, valgrind might report kernel bugs
		3437	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		3438	although an acceptable workaround has been found here), or it might be
		3439	confused.
		3440
		3441	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		3442	make it into some kind of religion.
		3443
		3444	If you are unsure about something, feel free to contact the mailing list
		3445	with the full valgrind report and an explanation on why you think this
		3446	is a bug in libev (best check the archives, too :). However, don't be
		3447	annoyed when you get a brisk "this is no bug" answer and take the chance
		3448	of learning how to interpret valgrind properly.
		3449
		3450	If you need, for some reason, empty reports from valgrind for your project
		3451	I suggest using suppression lists.
		3452
		3453
		3454	=head1 PORTABILITY NOTES
		3455
		3456	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		3457
		3458	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		3459	requires, and its I/O model is fundamentally incompatible with the POSIX
		3460	model. Libev still offers limited functionality on this platform in
		3461	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		3462	descriptors. This only applies when using Win32 natively, not when using
		3463	e.g. cygwin.
		3464
		3465	Lifting these limitations would basically require the full
		3466	re-implementation of the I/O system. If you are into these kinds of
		3467	things, then note that glib does exactly that for you in a very portable
		3468	way (note also that glib is the slowest event library known to man).
		3469
		3470	There is no supported compilation method available on windows except
		3471	embedding it into other applications.
		3472
		3473	Not a libev limitation but worth mentioning: windows apparently doesn't
		3474	accept large writes: instead of resulting in a partial write, windows will
		3475	either accept everything or return C<ENOBUFS> if the buffer is too large,
		3476	so make sure you only write small amounts into your sockets (less than a
		3477	megabyte seems safe, but this apparently depends on the amount of memory
		3478	available).
		3479
		3480	Due to the many, low, and arbitrary limits on the win32 platform and
		3481	the abysmal performance of winsockets, using a large number of sockets
		3482	is not recommended (and not reasonable). If your program needs to use
		3483	more than a hundred or so sockets, then likely it needs to use a totally
		3484	different implementation for windows, as libev offers the POSIX readiness
		3485	notification model, which cannot be implemented efficiently on windows
		3486	(Microsoft monopoly games).
		3487
		3488	A typical way to use libev under windows is to embed it (see the embedding
		3489	section for details) and use the following F<evwrap.h> header file instead
		3490	of F<ev.h>:
		3491
		3492	#define EV_STANDALONE /* keeps ev from requiring config.h */
		3493	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		3494
		3495	#include "ev.h"
		3496
		3497	And compile the following F<evwrap.c> file into your project (make sure
		3498	you do I<not> compile the F<ev.c> or any other embedded source files!):
		3499
		3500	#include "evwrap.h"
		3501	#include "ev.c"
		3502
		3503	=over 4
		3504
		3505	=item The winsocket select function
		3506
		3507	The winsocket C<select> function doesn't follow POSIX in that it
		3508	requires socket I<handles> and not socket I<file descriptors> (it is
		3509	also extremely buggy). This makes select very inefficient, and also
		3510	requires a mapping from file descriptors to socket handles (the Microsoft
		3511	C runtime provides the function C<_open_osfhandle> for this). See the
		3512	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		3513	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		3514
		3515	The configuration for a "naked" win32 using the Microsoft runtime
		3516	libraries and raw winsocket select is:
		3517
		3518	#define EV_USE_SELECT 1
		3519	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		3520
		3521	Note that winsockets handling of fd sets is O(n), so you can easily get a
		3522	complexity in the O(n²) range when using win32.
		3523
		3524	=item Limited number of file descriptors
		3525
		3526	Windows has numerous arbitrary (and low) limits on things.
		3527
		3528	Early versions of winsocket's select only supported waiting for a maximum
		3529	of C<64> handles (probably owning to the fact that all windows kernels
		3530	can only wait for C<64> things at the same time internally; Microsoft
		3531	recommends spawning a chain of threads and wait for 63 handles and the
		3532	previous thread in each. Great).
		3533
		3534	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		3535	to some high number (e.g. C<2048>) before compiling the winsocket select
		3536	call (which might be in libev or elsewhere, for example, perl does its own
		3537	select emulation on windows).
		3538
		3539	Another limit is the number of file descriptors in the Microsoft runtime
		3540	libraries, which by default is C<64> (there must be a hidden I<64> fetish
		3541	or something like this inside Microsoft). You can increase this by calling
		3542	C<_setmaxstdio>, which can increase this limit to C<2048> (another
		3543	arbitrary limit), but is broken in many versions of the Microsoft runtime
		3544	libraries.
		3545
		3546	This might get you to about C<512> or C<2048> sockets (depending on
		3547	windows version and/or the phase of the moon). To get more, you need to
		3548	wrap all I/O functions and provide your own fd management, but the cost of
		3549	calling select (O(n²)) will likely make this unworkable.
		3550
		3551	=back
		3552
		3553	=head2 PORTABILITY REQUIREMENTS
		3554
		3555	In addition to a working ISO-C implementation and of course the
		3556	backend-specific APIs, libev relies on a few additional extensions:
		3557
		3558	=over 4
		3559
		3560	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		3561	calling conventions regardless of C<ev_watcher_type *>.
		3562
		3563	Libev assumes not only that all watcher pointers have the same internal
		3564	structure (guaranteed by POSIX but not by ISO C for example), but it also
		3565	assumes that the same (machine) code can be used to call any watcher
		3566	callback: The watcher callbacks have different type signatures, but libev
		3567	calls them using an C<ev_watcher *> internally.
		3568
		3569	=item C<sig_atomic_t volatile> must be thread-atomic as well
		3570
		3571	The type C<sig_atomic_t volatile> (or whatever is defined as
		3572	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		3573	threads. This is not part of the specification for C<sig_atomic_t>, but is
		3574	believed to be sufficiently portable.
		3575
		3576	=item C<sigprocmask> must work in a threaded environment
		3577
		3578	Libev uses C<sigprocmask> to temporarily block signals. This is not
		3579	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		3580	pthread implementations will either allow C<sigprocmask> in the "main
		3581	thread" or will block signals process-wide, both behaviours would
		3582	be compatible with libev. Interaction between C<sigprocmask> and
		3583	C<pthread_sigmask> could complicate things, however.
		3584
		3585	The most portable way to handle signals is to block signals in all threads
		3586	except the initial one, and run the default loop in the initial thread as
		3587	well.
		3588
		3589	=item C<long> must be large enough for common memory allocation sizes
		3590
		3591	To improve portability and simplify its API, libev uses C<long> internally
		3592	instead of C<size_t> when allocating its data structures. On non-POSIX
		3593	systems (Microsoft...) this might be unexpectedly low, but is still at
		3594	least 31 bits everywhere, which is enough for hundreds of millions of
		3595	watchers.
		3596
		3597	=item C<double> must hold a time value in seconds with enough accuracy
		3598
		3599	The type C<double> is used to represent timestamps. It is required to
		3600	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
		3601	enough for at least into the year 4000. This requirement is fulfilled by
		3602	implementations implementing IEEE 754 (basically all existing ones).
		3603
		3604	=back
		3605
		3606	If you know of other additional requirements drop me a note.
		3607
		3608
		3609	=head1 ALGORITHMIC COMPLEXITIES
		3610
		3611	In this section the complexities of (many of) the algorithms used inside
		3612	libev will be documented. For complexity discussions about backends see
		3613	the documentation for C<ev_default_init>.
		3614
		3615	All of the following are about amortised time: If an array needs to be
		3616	extended, libev needs to realloc and move the whole array, but this
		3617	happens asymptotically rarer with higher number of elements, so O(1) might
		3618	mean that libev does a lengthy realloc operation in rare cases, but on
		3619	average it is much faster and asymptotically approaches constant time.
		3620
		3621	=over 4
		3622
		3623	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
		3624
		3625	This means that, when you have a watcher that triggers in one hour and
		3626	there are 100 watchers that would trigger before that, then inserting will
		3627	have to skip roughly seven (C<ld 100>) of these watchers.
		3628
		3629	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
		3630
		3631	That means that changing a timer costs less than removing/adding them,
		3632	as only the relative motion in the event queue has to be paid for.
		3633
		3634	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
		3635
		3636	These just add the watcher into an array or at the head of a list.
		3637
		3638	=item Stopping check/prepare/idle/fork/async watchers: O(1)
		3639
		3640	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
		3641
		3642	These watchers are stored in lists, so they need to be walked to find the
		3643	correct watcher to remove. The lists are usually short (you don't usually
		3644	have many watchers waiting for the same fd or signal: one is typical, two
		3645	is rare).
		3646
		3647	=item Finding the next timer in each loop iteration: O(1)
		3648
		3649	By virtue of using a binary or 4-heap, the next timer is always found at a
		3650	fixed position in the storage array.
		3651
		3652	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		3653
		3654	A change means an I/O watcher gets started or stopped, which requires
		3655	libev to recalculate its status (and possibly tell the kernel, depending
		3656	on backend and whether C<ev_io_set> was used).
		3657
		3658	=item Activating one watcher (putting it into the pending state): O(1)
		3659
		3660	=item Priority handling: O(number_of_priorities)
		3661
		3662	Priorities are implemented by allocating some space for each
		3663	priority. When doing priority-based operations, libev usually has to
		3664	linearly search all the priorities, but starting/stopping and activating
		3665	watchers becomes O(1) with respect to priority handling.
		3666
		3667	=item Sending an ev_async: O(1)
		3668
		3669	=item Processing ev_async_send: O(number_of_async_watchers)
		3670
		3671	=item Processing signals: O(max_signal_number)
		3672
		3673	Sending involves a system call I<iff> there were no other C<ev_async_send>
		3674	calls in the current loop iteration. Checking for async and signal events
		3675	involves iterating over all running async watchers or all signal numbers.
		3676
		3677	=back
		3678
1217		3679
1218	=head1 AUTHOR	3680	=head1 AUTHOR
1219		3681
1220	Marc Lehmann <libev@schmorp.de>.	3682	Marc Lehmann <libev@schmorp.de>.
1221		3683

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