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Revision 1.48 by root, Tue Nov 27 08:11:52 2007 UTC vs.
Revision 1.170 by root, Sat Jul 5 02:25:40 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
…		…
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))
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
…		…
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));
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);
…		…
177	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	279	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
178		280
179	An event loop is described by a C<struct ev_loop *>. The library knows two	281	An event loop is described by a C<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
183	If you use threads, a common model is to run the default event loop
184	in your main thread (or in a separate thread) and for each thread you
185	create, you also create another event loop. Libev itself does no locking
186	whatsoever, so if you mix calls to the same event loop in different
187	threads, make sure you lock (this is usually a bad idea, though, even if
188	done correctly, because it's hideous and inefficient).
189		284
190	=over 4	285	=over 4
191		286
192	=item struct ev_loop *ev_default_loop (unsigned int flags)	287	=item struct ev_loop *ev_default_loop (unsigned int flags)
193		288
…		…
197	flags. If that is troubling you, check C<ev_backend ()> afterwards).	292	flags. If that is troubling you, check C<ev_backend ()> afterwards).
198		293
199	If you don't know what event loop to use, use the one returned from this	294	If you don't know what event loop to use, use the one returned from this
200	function.	295	function.
201		296
		297	Note that this function is I<not> thread-safe, so if you want to use it
		298	from multiple threads, you have to lock (note also that this is unlikely,
		299	as loops cannot bes hared easily between threads anyway).
		300
		301	The default loop is the only loop that can handle C<ev_signal> and
		302	C<ev_child> watchers, and to do this, it always registers a handler
		303	for C<SIGCHLD>. If this is a problem for your application you can either
		304	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you
		305	can simply overwrite the C<SIGCHLD> signal handler I<after> calling
		306	C<ev_default_init>.
		307
202	The flags argument can be used to specify special behaviour or specific	308	The flags argument can be used to specify special behaviour or specific
203	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).	309	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
204		310
205	The following flags are supported:	311	The following flags are supported:
206		312
…		…
211	The default flags value. Use this if you have no clue (it's the right	317	The default flags value. Use this if you have no clue (it's the right
212	thing, believe me).	318	thing, believe me).
213		319
214	=item C<EVFLAG_NOENV>	320	=item C<EVFLAG_NOENV>
215		321
216	If this flag bit is ored into the flag value (or the program runs setuid	322	If this flag bit is or'ed into the flag value (or the program runs setuid
217	or setgid) then libev will I<not> look at the environment variable	323	or setgid) then libev will I<not> look at the environment variable
218	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	324	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
219	override the flags completely if it is found in the environment. This is	325	override the flags completely if it is found in the environment. This is
220	useful to try out specific backends to test their performance, or to work	326	useful to try out specific backends to test their performance, or to work
221	around bugs.	327	around bugs.
222		328
		329	=item C<EVFLAG_FORKCHECK>
		330
		331	Instead of calling C<ev_default_fork> or C<ev_loop_fork> manually after
		332	a fork, you can also make libev check for a fork in each iteration by
		333	enabling this flag.
		334
		335	This works by calling C<getpid ()> on every iteration of the loop,
		336	and thus this might slow down your event loop if you do a lot of loop
		337	iterations and little real work, but is usually not noticeable (on my
		338	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence
		339	without a system call and thus I<very> fast, but my GNU/Linux system also has
		340	C<pthread_atfork> which is even faster).
		341
		342	The big advantage of this flag is that you can forget about fork (and
		343	forget about forgetting to tell libev about forking) when you use this
		344	flag.
		345
		346	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
		347	environment variable.
		348
223	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	349	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
224		350
225	This is your standard select(2) backend. Not I<completely> standard, as	351	This is your standard select(2) backend. Not I<completely> standard, as
226	libev tries to roll its own fd_set with no limits on the number of fds,	352	libev tries to roll its own fd_set with no limits on the number of fds,
227	but if that fails, expect a fairly low limit on the number of fds when	353	but if that fails, expect a fairly low limit on the number of fds when
228	using this backend. It doesn't scale too well (O(highest_fd)), but its usually	354	using this backend. It doesn't scale too well (O(highest_fd)), but its
229	the fastest backend for a low number of fds.	355	usually the fastest backend for a low number of (low-numbered :) fds.
		356
		357	To get good performance out of this backend you need a high amount of
		358	parallelism (most of the file descriptors should be busy). If you are
		359	writing a server, you should C<accept ()> in a loop to accept as many
		360	connections as possible during one iteration. You might also want to have
		361	a look at C<ev_set_io_collect_interval ()> to increase the amount of
		362	readiness notifications you get per iteration.
230		363
231	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)	364	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
232		365
233	And this is your standard poll(2) backend. It's more complicated than	366	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	367	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	368	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).	369	considerably with a lot of inactive fds). It scales similarly to select,
		370	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
		371	performance tips.
237		372
238	=item C<EVBACKEND_EPOLL> (value 4, Linux)	373	=item C<EVBACKEND_EPOLL> (value 4, Linux)
239		374
240	For few fds, this backend is a bit little slower than poll and select,	375	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	376	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	377	like O(total_fds) where n is the total number of fds (or the highest fd),
243	either O(1) or O(active_fds).	378	epoll scales either O(1) or O(active_fds). The epoll design has a number
		379	of shortcomings, such as silently dropping events in some hard-to-detect
		380	cases and requiring a system call per fd change, no fork support and bad
		381	support for dup.
244		382
245	While stopping and starting an I/O watcher in the same iteration will	383	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	384	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	385	(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	386	best to avoid that. Also, C<dup ()>'ed file descriptors might not work
249	well if you register events for both fds.	387	very well if you register events for both fds.
250		388
251	Please note that epoll sometimes generates spurious notifications, so you	389	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	390	need to use non-blocking I/O or other means to avoid blocking when no data
253	(or space) is available.	391	(or space) is available.
254		392
		393	Best performance from this backend is achieved by not unregistering all
		394	watchers for a file descriptor until it has been closed, if possible, i.e.
		395	keep at least one watcher active per fd at all times.
		396
		397	While nominally embeddable in other event loops, this feature is broken in
		398	all kernel versions tested so far.
		399
255	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	400	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
256		401
257	Kqueue deserves special mention, as at the time of this writing, it	402	Kqueue deserves special mention, as at the time of this writing, it
258	was broken on all BSDs except NetBSD (usually it doesn't work with	403	was broken on all BSDs except NetBSD (usually it doesn't work reliably
259	anything but sockets and pipes, except on Darwin, where of course its	404	with anything but sockets and pipes, except on Darwin, where of course
260	completely useless). For this reason its not being "autodetected"	405	it's completely useless). For this reason it's not being "auto-detected"
261	unless you explicitly specify it explicitly in the flags (i.e. using	406	unless you explicitly specify it explicitly in the flags (i.e. using
262	C<EVBACKEND_KQUEUE>).	407	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
		408	system like NetBSD.
		409
		410	You still can embed kqueue into a normal poll or select backend and use it
		411	only for sockets (after having made sure that sockets work with kqueue on
		412	the target platform). See C<ev_embed> watchers for more info.
263		413
264	It scales in the same way as the epoll backend, but the interface to the	414	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	415	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	416	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	417	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
268	incident, so its best to avoid that.	418	two event changes per incident, support for C<fork ()> is very bad and it
		419	drops fds silently in similarly hard-to-detect cases.
		420
		421	This backend usually performs well under most conditions.
		422
		423	While nominally embeddable in other event loops, this doesn't work
		424	everywhere, so you might need to test for this. And since it is broken
		425	almost everywhere, you should only use it when you have a lot of sockets
		426	(for which it usually works), by embedding it into another event loop
		427	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>) and using it only for
		428	sockets.
269		429
270	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	430	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
271		431
272	This is not implemented yet (and might never be).	432	This is not implemented yet (and might never be, unless you send me an
		433	implementation). According to reports, C</dev/poll> only supports sockets
		434	and is not embeddable, which would limit the usefulness of this backend
		435	immensely.
273		436
274	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	437	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
275		438
276	This uses the Solaris 10 port mechanism. As with everything on Solaris,	439	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)).	440	it's really slow, but it still scales very well (O(active_fds)).
278		441
279	Please note that solaris ports can result in a lot of spurious	442	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	443	notifications, so you need to use non-blocking I/O or other means to avoid
281	blocking when no data (or space) is available.	444	blocking when no data (or space) is available.
		445
		446	While this backend scales well, it requires one system call per active
		447	file descriptor per loop iteration. For small and medium numbers of file
		448	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
		449	might perform better.
		450
		451	On the positive side, ignoring the spurious readiness notifications, this
		452	backend actually performed to specification in all tests and is fully
		453	embeddable, which is a rare feat among the OS-specific backends.
282		454
283	=item C<EVBACKEND_ALL>	455	=item C<EVBACKEND_ALL>
284		456
285	Try all backends (even potentially broken ones that wouldn't be tried	457	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	458	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
287	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	459	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
288		460
		461	It is definitely not recommended to use this flag.
		462
289	=back	463	=back
290		464
291	If one or more of these are ored into the flags value, then only these	465	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	466	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	467	specified, all backends in C<ev_recommended_backends ()> will be tried.
294	order of their flag values :)
295		468
296	The most typical usage is like this:	469	The most typical usage is like this:
297		470
298	if (!ev_default_loop (0))	471	if (!ev_default_loop (0))
299	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");	472	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
300		473
301	Restrict libev to the select and poll backends, and do not allow	474	Restrict libev to the select and poll backends, and do not allow
302	environment settings to be taken into account:	475	environment settings to be taken into account:
303		476
304	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);	477	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
305		478
306	Use whatever libev has to offer, but make sure that kqueue is used if	479	Use whatever libev has to offer, but make sure that kqueue is used if
307	available (warning, breaks stuff, best use only with your own private	480	available (warning, breaks stuff, best use only with your own private
308	event loop and only if you know the OS supports your types of fds):	481	event loop and only if you know the OS supports your types of fds):
309		482
310	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);	483	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
311		484
312	=item struct ev_loop *ev_loop_new (unsigned int flags)	485	=item struct ev_loop *ev_loop_new (unsigned int flags)
313		486
314	Similar to C<ev_default_loop>, but always creates a new event loop that is	487	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	488	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	489	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).	490	undefined behaviour (or a failed assertion if assertions are enabled).
318		491
		492	Note that this function I<is> thread-safe, and the recommended way to use
		493	libev with threads is indeed to create one loop per thread, and using the
		494	default loop in the "main" or "initial" thread.
		495
319	Example: try to create a event loop that uses epoll and nothing else.	496	Example: Try to create a event loop that uses epoll and nothing else.
320		497
321	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	498	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
322	if (!epoller)	499	if (!epoller)
323	fatal ("no epoll found here, maybe it hides under your chair");	500	fatal ("no epoll found here, maybe it hides under your chair");
324		501
325	=item ev_default_destroy ()	502	=item ev_default_destroy ()
326		503
327	Destroys the default loop again (frees all memory and kernel state	504	Destroys the default loop again (frees all memory and kernel state
328	etc.). None of the active event watchers will be stopped in the normal	505	etc.). None of the active event watchers will be stopped in the normal
329	sense, so e.g. C<ev_is_active> might still return true. It is your	506	sense, so e.g. C<ev_is_active> might still return true. It is your
330	responsibility to either stop all watchers cleanly yoursef I<before>	507	responsibility to either stop all watchers cleanly yourself I<before>
331	calling this function, or cope with the fact afterwards (which is usually	508	calling this function, or cope with the fact afterwards (which is usually
332	the easiest thing, youc na just ignore the watchers and/or C<free ()> them	509	the easiest thing, you can just ignore the watchers and/or C<free ()> them
333	for example).	510	for example).
		511
		512	Note that certain global state, such as signal state, will not be freed by
		513	this function, and related watchers (such as signal and child watchers)
		514	would need to be stopped manually.
		515
		516	In general it is not advisable to call this function except in the
		517	rare occasion where you really need to free e.g. the signal handling
		518	pipe fds. If you need dynamically allocated loops it is better to use
		519	C<ev_loop_new> and C<ev_loop_destroy>).
334		520
335	=item ev_loop_destroy (loop)	521	=item ev_loop_destroy (loop)
336		522
337	Like C<ev_default_destroy>, but destroys an event loop created by an	523	Like C<ev_default_destroy>, but destroys an event loop created by an
338	earlier call to C<ev_loop_new>.	524	earlier call to C<ev_loop_new>.
339		525
340	=item ev_default_fork ()	526	=item ev_default_fork ()
341		527
		528	This function sets a flag that causes subsequent C<ev_loop> iterations
342	This function reinitialises the kernel state for backends that have	529	to reinitialise the kernel state for backends that have one. Despite the
343	one. Despite the name, you can call it anytime, but it makes most sense	530	name, you can call it anytime, but it makes most sense after forking, in
344	after forking, in either the parent or child process (or both, but that	531	the child process (or both child and parent, but that again makes little
345	again makes little sense).	532	sense). You I<must> call it in the child before using any of the libev
		533	functions, and it will only take effect at the next C<ev_loop> iteration.
346		534
347	You I<must> call this function in the child process after forking if and	535	On the other hand, you only need to call this function in the child
348	only if you want to use the event library in both processes. If you just	536	process if and only if you want to use the event library in the child. If
349	fork+exec, you don't have to call it.	537	you just fork+exec, you don't have to call it at all.
350		538
351	The function itself is quite fast and it's usually not a problem to call	539	The function itself is quite fast and it's usually not a problem to call
352	it just in case after a fork. To make this easy, the function will fit in	540	it just in case after a fork. To make this easy, the function will fit in
353	quite nicely into a call to C<pthread_atfork>:	541	quite nicely into a call to C<pthread_atfork>:
354		542
355	pthread_atfork (0, 0, ev_default_fork);	543	pthread_atfork (0, 0, ev_default_fork);
356		544
357	At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> are safe to use
358	without calling this function, so if you force one of those backends you
359	do not need to care.
360
361	=item ev_loop_fork (loop)	545	=item ev_loop_fork (loop)
362		546
363	Like C<ev_default_fork>, but acts on an event loop created by	547	Like C<ev_default_fork>, but acts on an event loop created by
364	C<ev_loop_new>. Yes, you have to call this on every allocated event loop	548	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
365	after fork, and how you do this is entirely your own problem.	549	after fork, and how you do this is entirely your own problem.
		550
		551	=item int ev_is_default_loop (loop)
		552
		553	Returns true when the given loop actually is the default loop, false otherwise.
		554
		555	=item unsigned int ev_loop_count (loop)
		556
		557	Returns the count of loop iterations for the loop, which is identical to
		558	the number of times libev did poll for new events. It starts at C<0> and
		559	happily wraps around with enough iterations.
		560
		561	This value can sometimes be useful as a generation counter of sorts (it
		562	"ticks" the number of loop iterations), as it roughly corresponds with
		563	C<ev_prepare> and C<ev_check> calls.
366		564
367	=item unsigned int ev_backend (loop)	565	=item unsigned int ev_backend (loop)
368		566
369	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	567	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
370	use.	568	use.
…		…
373		571
374	Returns the current "event loop time", which is the time the event loop	572	Returns the current "event loop time", which is the time the event loop
375	received events and started processing them. This timestamp does not	573	received events and started processing them. This timestamp does not
376	change as long as callbacks are being processed, and this is also the base	574	change as long as callbacks are being processed, and this is also the base
377	time used for relative timers. You can treat it as the timestamp of the	575	time used for relative timers. You can treat it as the timestamp of the
378	event occuring (or more correctly, libev finding out about it).	576	event occurring (or more correctly, libev finding out about it).
379		577
380	=item ev_loop (loop, int flags)	578	=item ev_loop (loop, int flags)
381		579
382	Finally, this is it, the event handler. This function usually is called	580	Finally, this is it, the event handler. This function usually is called
383	after you initialised all your watchers and you want to start handling	581	after you initialised all your watchers and you want to start handling
…		…
395	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	593	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle
396	those events and any outstanding ones, but will not block your process in	594	those events and any outstanding ones, but will not block your process in
397	case there are no events and will return after one iteration of the loop.	595	case there are no events and will return after one iteration of the loop.
398		596
399	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	597	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if
400	neccessary) and will handle those and any outstanding ones. It will block	598	necessary) and will handle those and any outstanding ones. It will block
401	your process until at least one new event arrives, and will return after	599	your process until at least one new event arrives, and will return after
402	one iteration of the loop. This is useful if you are waiting for some	600	one iteration of the loop. This is useful if you are waiting for some
403	external event in conjunction with something not expressible using other	601	external event in conjunction with something not expressible using other
404	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is	602	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is
405	usually a better approach for this kind of thing.	603	usually a better approach for this kind of thing.
406		604
407	Here are the gory details of what C<ev_loop> does:	605	Here are the gory details of what C<ev_loop> does:
408		606
409	* If there are no active watchers (reference count is zero), return.	607	- Before the first iteration, call any pending watchers.
410	- Queue prepare watchers and then call all outstanding watchers.	608	* If EVFLAG_FORKCHECK was used, check for a fork.
		609	- If a fork was detected, queue and call all fork watchers.
		610	- Queue and call all prepare watchers.
411	- If we have been forked, recreate the kernel state.	611	- If we have been forked, recreate the kernel state.
412	- Update the kernel state with all outstanding changes.	612	- Update the kernel state with all outstanding changes.
413	- Update the "event loop time".	613	- Update the "event loop time".
414	- Calculate for how long to block.	614	- Calculate for how long to sleep or block, if at all
		615	(active idle watchers, EVLOOP_NONBLOCK or not having
		616	any active watchers at all will result in not sleeping).
		617	- Sleep if the I/O and timer collect interval say so.
415	- Block the process, waiting for any events.	618	- Block the process, waiting for any events.
416	- Queue all outstanding I/O (fd) events.	619	- Queue all outstanding I/O (fd) events.
417	- Update the "event loop time" and do time jump handling.	620	- Update the "event loop time" and do time jump handling.
418	- Queue all outstanding timers.	621	- Queue all outstanding timers.
419	- Queue all outstanding periodics.	622	- Queue all outstanding periodics.
420	- If no events are pending now, queue all idle watchers.	623	- If no events are pending now, queue all idle watchers.
421	- Queue all check watchers.	624	- Queue all check watchers.
422	- Call all queued watchers in reverse order (i.e. check watchers first).	625	- Call all queued watchers in reverse order (i.e. check watchers first).
423	Signals and child watchers are implemented as I/O watchers, and will	626	Signals and child watchers are implemented as I/O watchers, and will
424	be handled here by queueing them when their watcher gets executed.	627	be handled here by queueing them when their watcher gets executed.
425	- If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	628	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
426	were used, return, otherwise continue with step *.	629	were used, or there are no active watchers, return, otherwise
		630	continue with step *.
427		631
428	Example: queue some jobs and then loop until no events are outsanding	632	Example: Queue some jobs and then loop until no events are outstanding
429	anymore.	633	anymore.
430		634
431	... queue jobs here, make sure they register event watchers as long	635	... queue jobs here, make sure they register event watchers as long
432	... as they still have work to do (even an idle watcher will do..)	636	... as they still have work to do (even an idle watcher will do..)
433	ev_loop (my_loop, 0);	637	ev_loop (my_loop, 0);
…		…
437		641
438	Can be used to make a call to C<ev_loop> return early (but only after it	642	Can be used to make a call to C<ev_loop> return early (but only after it
439	has processed all outstanding events). The C<how> argument must be either	643	has processed all outstanding events). The C<how> argument must be either
440	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	644	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
441	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	645	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
		646
		647	This "unloop state" will be cleared when entering C<ev_loop> again.
442		648
443	=item ev_ref (loop)	649	=item ev_ref (loop)
444		650
445	=item ev_unref (loop)	651	=item ev_unref (loop)
446		652
…		…
451	returning, ev_unref() after starting, and ev_ref() before stopping it. For	657	returning, ev_unref() after starting, and ev_ref() before stopping it. For
452	example, libev itself uses this for its internal signal pipe: It is not	658	example, libev itself uses this for its internal signal pipe: It is not
453	visible to the libev user and should not keep C<ev_loop> from exiting if	659	visible to the libev user and should not keep C<ev_loop> from exiting if
454	no event watchers registered by it are active. It is also an excellent	660	no event watchers registered by it are active. It is also an excellent
455	way to do this for generic recurring timers or from within third-party	661	way to do this for generic recurring timers or from within third-party
456	libraries. Just remember to I<unref after start> and I<ref before stop>.	662	libraries. Just remember to I<unref after start> and I<ref before stop>
		663	(but only if the watcher wasn't active before, or was active before,
		664	respectively).
457		665
458	Example: create a signal watcher, but keep it from keeping C<ev_loop>	666	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
459	running when nothing else is active.	667	running when nothing else is active.
460		668
461	struct dv_signal exitsig;	669	struct ev_signal exitsig;
462	ev_signal_init (&exitsig, sig_cb, SIGINT);	670	ev_signal_init (&exitsig, sig_cb, SIGINT);
463	ev_signal_start (myloop, &exitsig);	671	ev_signal_start (loop, &exitsig);
464	evf_unref (myloop);	672	evf_unref (loop);
465		673
466	Example: for some weird reason, unregister the above signal handler again.	674	Example: For some weird reason, unregister the above signal handler again.
467		675
468	ev_ref (myloop);	676	ev_ref (loop);
469	ev_signal_stop (myloop, &exitsig);	677	ev_signal_stop (loop, &exitsig);
		678
		679	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
		680
		681	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
		682
		683	These advanced functions influence the time that libev will spend waiting
		684	for events. Both are by default C<0>, meaning that libev will try to
		685	invoke timer/periodic callbacks and I/O callbacks with minimum latency.
		686
		687	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
		688	allows libev to delay invocation of I/O and timer/periodic callbacks to
		689	increase efficiency of loop iterations.
		690
		691	The background is that sometimes your program runs just fast enough to
		692	handle one (or very few) event(s) per loop iteration. While this makes
		693	the program responsive, it also wastes a lot of CPU time to poll for new
		694	events, especially with backends like C<select ()> which have a high
		695	overhead for the actual polling but can deliver many events at once.
		696
		697	By setting a higher I<io collect interval> you allow libev to spend more
		698	time collecting I/O events, so you can handle more events per iteration,
		699	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
		700	C<ev_timer>) will be not affected. Setting this to a non-null value will
		701	introduce an additional C<ev_sleep ()> call into most loop iterations.
		702
		703	Likewise, by setting a higher I<timeout collect interval> you allow libev
		704	to spend more time collecting timeouts, at the expense of increased
		705	latency (the watcher callback will be called later). C<ev_io> watchers
		706	will not be affected. Setting this to a non-null value will not introduce
		707	any overhead in libev.
		708
		709	Many (busy) programs can usually benefit by setting the I/O collect
		710	interval to a value near C<0.1> or so, which is often enough for
		711	interactive servers (of course not for games), likewise for timeouts. It
		712	usually doesn't make much sense to set it to a lower value than C<0.01>,
		713	as this approaches the timing granularity of most systems.
		714
		715	=item ev_loop_verify (loop)
		716
		717	This function only does something when C<EV_VERIFY> support has been
		718	compiled in. It tries to go through all internal structures and checks
		719	them for validity. If anything is found to be inconsistent, it will print
		720	an error message to standard error and call C<abort ()>.
		721
		722	This can be used to catch bugs inside libev itself: under normal
		723	circumstances, this function will never abort as of course libev keeps its
		724	data structures consistent.
470		725
471	=back	726	=back
472		727
473		728
474	=head1 ANATOMY OF A WATCHER	729	=head1 ANATOMY OF A WATCHER
475		730
476	A watcher is a structure that you create and register to record your	731	A watcher is a structure that you create and register to record your
477	interest in some event. For instance, if you want to wait for STDIN to	732	interest in some event. For instance, if you want to wait for STDIN to
478	become readable, you would create an C<ev_io> watcher for that:	733	become readable, you would create an C<ev_io> watcher for that:
479		734
480	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	735	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)
481	{	736	{
482	ev_io_stop (w);	737	ev_io_stop (w);
483	ev_unloop (loop, EVUNLOOP_ALL);	738	ev_unloop (loop, EVUNLOOP_ALL);
484	}	739	}
485		740
486	struct ev_loop *loop = ev_default_loop (0);	741	struct ev_loop *loop = ev_default_loop (0);
487	struct ev_io stdin_watcher;	742	struct ev_io stdin_watcher;
488	ev_init (&stdin_watcher, my_cb);	743	ev_init (&stdin_watcher, my_cb);
489	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	744	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
490	ev_io_start (loop, &stdin_watcher);	745	ev_io_start (loop, &stdin_watcher);
491	ev_loop (loop, 0);	746	ev_loop (loop, 0);
492		747
493	As you can see, you are responsible for allocating the memory for your	748	As you can see, you are responsible for allocating the memory for your
494	watcher structures (and it is usually a bad idea to do this on the stack,	749	watcher structures (and it is usually a bad idea to do this on the stack,
495	although this can sometimes be quite valid).	750	although this can sometimes be quite valid).
496		751
497	Each watcher structure must be initialised by a call to C<ev_init	752	Each watcher structure must be initialised by a call to C<ev_init
498	(watcher *, callback)>, which expects a callback to be provided. This	753	(watcher *, callback)>, which expects a callback to be provided. This
499	callback gets invoked each time the event occurs (or, in the case of io	754	callback gets invoked each time the event occurs (or, in the case of I/O
500	watchers, each time the event loop detects that the file descriptor given	755	watchers, each time the event loop detects that the file descriptor given
501	is readable and/or writable).	756	is readable and/or writable).
502		757
503	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	758	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro
504	with arguments specific to this watcher type. There is also a macro	759	with arguments specific to this watcher type. There is also a macro
…		…
565	received events. Callbacks of both watcher types can start and stop as	820	received events. Callbacks of both watcher types can start and stop as
566	many watchers as they want, and all of them will be taken into account	821	many watchers as they want, and all of them will be taken into account
567	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	822	(for example, a C<ev_prepare> watcher might start an idle watcher to keep
568	C<ev_loop> from blocking).	823	C<ev_loop> from blocking).
569		824
		825	=item C<EV_EMBED>
		826
		827	The embedded event loop specified in the C<ev_embed> watcher needs attention.
		828
		829	=item C<EV_FORK>
		830
		831	The event loop has been resumed in the child process after fork (see
		832	C<ev_fork>).
		833
		834	=item C<EV_ASYNC>
		835
		836	The given async watcher has been asynchronously notified (see C<ev_async>).
		837
570	=item C<EV_ERROR>	838	=item C<EV_ERROR>
571		839
572	An unspecified error has occured, the watcher has been stopped. This might	840	An unspecified error has occurred, the watcher has been stopped. This might
573	happen because the watcher could not be properly started because libev	841	happen because the watcher could not be properly started because libev
574	ran out of memory, a file descriptor was found to be closed or any other	842	ran out of memory, a file descriptor was found to be closed or any other
575	problem. You best act on it by reporting the problem and somehow coping	843	problem. You best act on it by reporting the problem and somehow coping
576	with the watcher being stopped.	844	with the watcher being stopped.
577		845
578	Libev will usually signal a few "dummy" events together with an error,	846	Libev will usually signal a few "dummy" events together with an error,
579	for example it might indicate that a fd is readable or writable, and if	847	for example it might indicate that a fd is readable or writable, and if
580	your callbacks is well-written it can just attempt the operation and cope	848	your callbacks is well-written it can just attempt the operation and cope
581	with the error from read() or write(). This will not work in multithreaded	849	with the error from read() or write(). This will not work in multi-threaded
582	programs, though, so beware.	850	programs, though, so beware.
583		851
584	=back	852	=back
585		853
586	=head2 GENERIC WATCHER FUNCTIONS	854	=head2 GENERIC WATCHER FUNCTIONS
…		…
616	Although some watcher types do not have type-specific arguments	884	Although some watcher types do not have type-specific arguments
617	(e.g. C<ev_prepare>) you still need to call its C<set> macro.	885	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
618		886
619	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	887	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
620		888
621	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	889	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
622	calls into a single call. This is the most convinient method to initialise	890	calls into a single call. This is the most convenient method to initialise
623	a watcher. The same limitations apply, of course.	891	a watcher. The same limitations apply, of course.
624		892
625	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	893	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)
626		894
627	Starts (activates) the given watcher. Only active watchers will receive	895	Starts (activates) the given watcher. Only active watchers will receive
…		…
645	=item bool ev_is_pending (ev_TYPE *watcher)	913	=item bool ev_is_pending (ev_TYPE *watcher)
646		914
647	Returns a true value iff the watcher is pending, (i.e. it has outstanding	915	Returns a true value iff the watcher is pending, (i.e. it has outstanding
648	events but its callback has not yet been invoked). As long as a watcher	916	events but its callback has not yet been invoked). As long as a watcher
649	is pending (but not active) you must not call an init function on it (but	917	is pending (but not active) you must not call an init function on it (but
650	C<ev_TYPE_set> is safe) and you must make sure the watcher is available to	918	C<ev_TYPE_set> is safe), you must not change its priority, and you must
651	libev (e.g. you cnanot C<free ()> it).	919	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		920	it).
652		921
653	=item callback = ev_cb (ev_TYPE *watcher)	922	=item callback ev_cb (ev_TYPE *watcher)
654		923
655	Returns the callback currently set on the watcher.	924	Returns the callback currently set on the watcher.
656		925
657	=item ev_cb_set (ev_TYPE *watcher, callback)	926	=item ev_cb_set (ev_TYPE *watcher, callback)
658		927
659	Change the callback. You can change the callback at virtually any time	928	Change the callback. You can change the callback at virtually any time
660	(modulo threads).	929	(modulo threads).
		930
		931	=item ev_set_priority (ev_TYPE *watcher, priority)
		932
		933	=item int ev_priority (ev_TYPE *watcher)
		934
		935	Set and query the priority of the watcher. The priority is a small
		936	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
		937	(default: C<-2>). Pending watchers with higher priority will be invoked
		938	before watchers with lower priority, but priority will not keep watchers
		939	from being executed (except for C<ev_idle> watchers).
		940
		941	This means that priorities are I<only> used for ordering callback
		942	invocation after new events have been received. This is useful, for
		943	example, to reduce latency after idling, or more often, to bind two
		944	watchers on the same event and make sure one is called first.
		945
		946	If you need to suppress invocation when higher priority events are pending
		947	you need to look at C<ev_idle> watchers, which provide this functionality.
		948
		949	You I<must not> change the priority of a watcher as long as it is active or
		950	pending.
		951
		952	The default priority used by watchers when no priority has been set is
		953	always C<0>, which is supposed to not be too high and not be too low :).
		954
		955	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		956	fine, as long as you do not mind that the priority value you query might
		957	or might not have been adjusted to be within valid range.
		958
		959	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		960
		961	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		962	C<loop> nor C<revents> need to be valid as long as the watcher callback
		963	can deal with that fact.
		964
		965	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		966
		967	If the watcher is pending, this function returns clears its pending status
		968	and returns its C<revents> bitset (as if its callback was invoked). If the
		969	watcher isn't pending it does nothing and returns C<0>.
661		970
662	=back	971	=back
663		972
664		973
665	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	974	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
…		…
669	to associate arbitrary data with your watcher. If you need more data and	978	to associate arbitrary data with your watcher. If you need more data and
670	don't want to allocate memory and store a pointer to it in that data	979	don't want to allocate memory and store a pointer to it in that data
671	member, you can also "subclass" the watcher type and provide your own	980	member, you can also "subclass" the watcher type and provide your own
672	data:	981	data:
673		982
674	struct my_io	983	struct my_io
675	{	984	{
676	struct ev_io io;	985	struct ev_io io;
677	int otherfd;	986	int otherfd;
678	void *somedata;	987	void *somedata;
679	struct whatever *mostinteresting;	988	struct whatever *mostinteresting;
680	}	989	}
681		990
682	And since your callback will be called with a pointer to the watcher, you	991	And since your callback will be called with a pointer to the watcher, you
683	can cast it back to your own type:	992	can cast it back to your own type:
684		993
685	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	994	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)
686	{	995	{
687	struct my_io *w = (struct my_io *)w_;	996	struct my_io *w = (struct my_io *)w_;
688	...	997	...
689	}	998	}
690		999
691	More interesting and less C-conformant ways of catsing your callback type	1000	More interesting and less C-conformant ways of casting your callback type
692	have been omitted....	1001	instead have been omitted.
		1002
		1003	Another common scenario is having some data structure with multiple
		1004	watchers:
		1005
		1006	struct my_biggy
		1007	{
		1008	int some_data;
		1009	ev_timer t1;
		1010	ev_timer t2;
		1011	}
		1012
		1013	In this case getting the pointer to C<my_biggy> is a bit more complicated,
		1014	you need to use C<offsetof>:
		1015
		1016	#include <stddef.h>
		1017
		1018	static void
		1019	t1_cb (EV_P_ struct ev_timer *w, int revents)
		1020	{
		1021	struct my_biggy big = (struct my_biggy *
		1022	(((char *)w) - offsetof (struct my_biggy, t1));
		1023	}
		1024
		1025	static void
		1026	t2_cb (EV_P_ struct ev_timer *w, int revents)
		1027	{
		1028	struct my_biggy big = (struct my_biggy *
		1029	(((char *)w) - offsetof (struct my_biggy, t2));
		1030	}
693		1031
694		1032
695	=head1 WATCHER TYPES	1033	=head1 WATCHER TYPES
696		1034
697	This section describes each watcher in detail, but will not repeat	1035	This section describes each watcher in detail, but will not repeat
…		…
721	In general you can register as many read and/or write event watchers per	1059	In general you can register as many read and/or write event watchers per
722	fd as you want (as long as you don't confuse yourself). Setting all file	1060	fd as you want (as long as you don't confuse yourself). Setting all file
723	descriptors to non-blocking mode is also usually a good idea (but not	1061	descriptors to non-blocking mode is also usually a good idea (but not
724	required if you know what you are doing).	1062	required if you know what you are doing).
725		1063
726	You have to be careful with dup'ed file descriptors, though. Some backends
727	(the linux epoll backend is a notable example) cannot handle dup'ed file
728	descriptors correctly if you register interest in two or more fds pointing
729	to the same underlying file/socket/etc. description (that is, they share
730	the same underlying "file open").
731
732	If you must do this, then force the use of a known-to-be-good backend	1064	If you must do this, then force the use of a known-to-be-good backend
733	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and	1065	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
734	C<EVBACKEND_POLL>).	1066	C<EVBACKEND_POLL>).
735		1067
736	Another thing you have to watch out for is that it is quite easy to	1068	Another thing you have to watch out for is that it is quite easy to
737	receive "spurious" readyness notifications, that is your callback might	1069	receive "spurious" readiness notifications, that is your callback might
738	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1070	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
739	because there is no data. Not only are some backends known to create a	1071	because there is no data. Not only are some backends known to create a
740	lot of those (for example solaris ports), it is very easy to get into	1072	lot of those (for example Solaris ports), it is very easy to get into
741	this situation even with a relatively standard program structure. Thus	1073	this situation even with a relatively standard program structure. Thus
742	it is best to always use non-blocking I/O: An extra C<read>(2) returning	1074	it is best to always use non-blocking I/O: An extra C<read>(2) returning
743	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1075	C<EAGAIN> is far preferable to a program hanging until some data arrives.
744		1076
745	If you cannot run the fd in non-blocking mode (for example you should not	1077	If you cannot run the fd in non-blocking mode (for example you should not
746	play around with an Xlib connection), then you have to seperately re-test	1078	play around with an Xlib connection), then you have to separately re-test
747	wether a file descriptor is really ready with a known-to-be good interface	1079	whether a file descriptor is really ready with a known-to-be good interface
748	such as poll (fortunately in our Xlib example, Xlib already does this on	1080	such as poll (fortunately in our Xlib example, Xlib already does this on
749	its own, so its quite safe to use).	1081	its own, so its quite safe to use).
750		1082
		1083	=head3 The special problem of disappearing file descriptors
		1084
		1085	Some backends (e.g. kqueue, epoll) need to be told about closing a file
		1086	descriptor (either by calling C<close> explicitly or by any other means,
		1087	such as C<dup>). The reason is that you register interest in some file
		1088	descriptor, but when it goes away, the operating system will silently drop
		1089	this interest. If another file descriptor with the same number then is
		1090	registered with libev, there is no efficient way to see that this is, in
		1091	fact, a different file descriptor.
		1092
		1093	To avoid having to explicitly tell libev about such cases, libev follows
		1094	the following policy: Each time C<ev_io_set> is being called, libev
		1095	will assume that this is potentially a new file descriptor, otherwise
		1096	it is assumed that the file descriptor stays the same. That means that
		1097	you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the
		1098	descriptor even if the file descriptor number itself did not change.
		1099
		1100	This is how one would do it normally anyway, the important point is that
		1101	the libev application should not optimise around libev but should leave
		1102	optimisations to libev.
		1103
		1104	=head3 The special problem of dup'ed file descriptors
		1105
		1106	Some backends (e.g. epoll), cannot register events for file descriptors,
		1107	but only events for the underlying file descriptions. That means when you
		1108	have C<dup ()>'ed file descriptors or weirder constellations, and register
		1109	events for them, only one file descriptor might actually receive events.
		1110
		1111	There is no workaround possible except not registering events
		1112	for potentially C<dup ()>'ed file descriptors, or to resort to
		1113	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1114
		1115	=head3 The special problem of fork
		1116
		1117	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
		1118	useless behaviour. Libev fully supports fork, but needs to be told about
		1119	it in the child.
		1120
		1121	To support fork in your programs, you either have to call
		1122	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
		1123	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
		1124	C<EVBACKEND_POLL>.
		1125
		1126	=head3 The special problem of SIGPIPE
		1127
		1128	While not really specific to libev, it is easy to forget about SIGPIPE:
		1129	when reading from a pipe whose other end has been closed, your program
		1130	gets send a SIGPIPE, which, by default, aborts your program. For most
		1131	programs this is sensible behaviour, for daemons, this is usually
		1132	undesirable.
		1133
		1134	So when you encounter spurious, unexplained daemon exits, make sure you
		1135	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1136	somewhere, as that would have given you a big clue).
		1137
		1138
		1139	=head3 Watcher-Specific Functions
		1140
751	=over 4	1141	=over 4
752		1142
753	=item ev_io_init (ev_io *, callback, int fd, int events)	1143	=item ev_io_init (ev_io *, callback, int fd, int events)
754		1144
755	=item ev_io_set (ev_io *, int fd, int events)	1145	=item ev_io_set (ev_io *, int fd, int events)
756		1146
757	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1147	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
758	rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or	1148	receive events for and events is either C<EV_READ>, C<EV_WRITE> or
759	C<EV_READ | EV_WRITE> to receive the given events.	1149	C<EV_READ | EV_WRITE> to receive the given events.
760		1150
761	=item int fd [read-only]	1151	=item int fd [read-only]
762		1152
763	The file descriptor being watched.	1153	The file descriptor being watched.
…		…
766		1156
767	The events being watched.	1157	The events being watched.
768		1158
769	=back	1159	=back
770		1160
		1161	=head3 Examples
		1162
771	Example: call C<stdin_readable_cb> when STDIN_FILENO has become, well	1163	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
772	readable, but only once. Since it is likely line-buffered, you could	1164	readable, but only once. Since it is likely line-buffered, you could
773	attempt to read a whole line in the callback:	1165	attempt to read a whole line in the callback.
774		1166
775	static void	1167	static void
776	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1168	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)
777	{	1169	{
778	ev_io_stop (loop, w);	1170	ev_io_stop (loop, w);
779	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1171	.. read from stdin here (or from w->fd) and haqndle any I/O errors
780	}	1172	}
781		1173
782	...	1174	...
783	struct ev_loop *loop = ev_default_init (0);	1175	struct ev_loop *loop = ev_default_init (0);
784	struct ev_io stdin_readable;	1176	struct ev_io stdin_readable;
785	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1177	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
786	ev_io_start (loop, &stdin_readable);	1178	ev_io_start (loop, &stdin_readable);
787	ev_loop (loop, 0);	1179	ev_loop (loop, 0);
788		1180
789		1181
790	=head2 C<ev_timer> - relative and optionally repeating timeouts	1182	=head2 C<ev_timer> - relative and optionally repeating timeouts
791		1183
792	Timer watchers are simple relative timers that generate an event after a	1184	Timer watchers are simple relative timers that generate an event after a
793	given time, and optionally repeating in regular intervals after that.	1185	given time, and optionally repeating in regular intervals after that.
794		1186
795	The timers are based on real time, that is, if you register an event that	1187	The timers are based on real time, that is, if you register an event that
796	times out after an hour and you reset your system clock to last years	1188	times out after an hour and you reset your system clock to January last
797	time, it will still time out after (roughly) and hour. "Roughly" because	1189	year, it will still time out after (roughly) and hour. "Roughly" because
798	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1190	detecting time jumps is hard, and some inaccuracies are unavoidable (the
799	monotonic clock option helps a lot here).	1191	monotonic clock option helps a lot here).
800		1192
801	The relative timeouts are calculated relative to the C<ev_now ()>	1193	The relative timeouts are calculated relative to the C<ev_now ()>
802	time. This is usually the right thing as this timestamp refers to the time	1194	time. This is usually the right thing as this timestamp refers to the time
…		…
804	you suspect event processing to be delayed and you I<need> to base the timeout	1196	you suspect event processing to be delayed and you I<need> to base the timeout
805	on the current time, use something like this to adjust for this:	1197	on the current time, use something like this to adjust for this:
806		1198
807	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1199	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
808		1200
809	The callback is guarenteed to be invoked only when its timeout has passed,	1201	The callback is guaranteed to be invoked only after its timeout has passed,
810	but if multiple timers become ready during the same loop iteration then	1202	but if multiple timers become ready during the same loop iteration then
811	order of execution is undefined.	1203	order of execution is undefined.
812		1204
		1205	=head3 Watcher-Specific Functions and Data Members
		1206
813	=over 4	1207	=over 4
814		1208
815	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1209	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
816		1210
817	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	1211	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
818		1212
819	Configure the timer to trigger after C<after> seconds. If C<repeat> is	1213	Configure the timer to trigger after C<after> seconds. If C<repeat>
820	C<0.>, then it will automatically be stopped. If it is positive, then the	1214	is C<0.>, then it will automatically be stopped once the timeout is
821	timer will automatically be configured to trigger again C<repeat> seconds	1215	reached. If it is positive, then the timer will automatically be
822	later, again, and again, until stopped manually.	1216	configured to trigger again C<repeat> seconds later, again, and again,
		1217	until stopped manually.
823		1218
824	The timer itself will do a best-effort at avoiding drift, that is, if you	1219	The timer itself will do a best-effort at avoiding drift, that is, if
825	configure a timer to trigger every 10 seconds, then it will trigger at	1220	you configure a timer to trigger every 10 seconds, then it will normally
826	exactly 10 second intervals. If, however, your program cannot keep up with	1221	trigger at exactly 10 second intervals. If, however, your program cannot
827	the timer (because it takes longer than those 10 seconds to do stuff) the	1222	keep up with the timer (because it takes longer than those 10 seconds to
828	timer will not fire more than once per event loop iteration.	1223	do stuff) the timer will not fire more than once per event loop iteration.
829		1224
830	=item ev_timer_again (loop)	1225	=item ev_timer_again (loop, ev_timer *)
831		1226
832	This will act as if the timer timed out and restart it again if it is	1227	This will act as if the timer timed out and restart it again if it is
833	repeating. The exact semantics are:	1228	repeating. The exact semantics are:
834		1229
		1230	If the timer is pending, its pending status is cleared.
		1231
835	If the timer is started but nonrepeating, stop it.	1232	If the timer is started but non-repeating, stop it (as if it timed out).
836		1233
837	If the timer is repeating, either start it if necessary (with the repeat	1234	If the timer is repeating, either start it if necessary (with the
838	value), or reset the running timer to the repeat value.	1235	C<repeat> value), or reset the running timer to the C<repeat> value.
839		1236
840	This sounds a bit complicated, but here is a useful and typical	1237	This sounds a bit complicated, but here is a useful and typical
841	example: Imagine you have a tcp connection and you want a so-called	1238	example: Imagine you have a TCP connection and you want a so-called idle
842	idle timeout, that is, you want to be called when there have been,	1239	timeout, that is, you want to be called when there have been, say, 60
843	say, 60 seconds of inactivity on the socket. The easiest way to do	1240	seconds of inactivity on the socket. The easiest way to do this is to
844	this is to configure an C<ev_timer> with C<after>=C<repeat>=C<60> and calling	1241	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
845	C<ev_timer_again> each time you successfully read or write some data. If	1242	C<ev_timer_again> each time you successfully read or write some data. If
846	you go into an idle state where you do not expect data to travel on the	1243	you go into an idle state where you do not expect data to travel on the
847	socket, you can stop the timer, and again will automatically restart it if	1244	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
848	need be.	1245	automatically restart it if need be.
849		1246
850	You can also ignore the C<after> value and C<ev_timer_start> altogether	1247	That means you can ignore the C<after> value and C<ev_timer_start>
851	and only ever use the C<repeat> value:	1248	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
852		1249
853	ev_timer_init (timer, callback, 0., 5.);	1250	ev_timer_init (timer, callback, 0., 5.);
854	ev_timer_again (loop, timer);	1251	ev_timer_again (loop, timer);
855	...	1252	...
856	timer->again = 17.;	1253	timer->again = 17.;
857	ev_timer_again (loop, timer);	1254	ev_timer_again (loop, timer);
858	...	1255	...
859	timer->again = 10.;	1256	timer->again = 10.;
860	ev_timer_again (loop, timer);	1257	ev_timer_again (loop, timer);
861		1258
862	This is more efficient then stopping/starting the timer eahc time you want	1259	This is more slightly efficient then stopping/starting the timer each time
863	to modify its timeout value.	1260	you want to modify its timeout value.
864		1261
865	=item ev_tstamp repeat [read-write]	1262	=item ev_tstamp repeat [read-write]
866		1263
867	The current C<repeat> value. Will be used each time the watcher times out	1264	The current C<repeat> value. Will be used each time the watcher times out
868	or C<ev_timer_again> is called and determines the next timeout (if any),	1265	or C<ev_timer_again> is called and determines the next timeout (if any),
869	which is also when any modifications are taken into account.	1266	which is also when any modifications are taken into account.
870		1267
871	=back	1268	=back
872		1269
		1270	=head3 Examples
		1271
873	Example: create a timer that fires after 60 seconds.	1272	Example: Create a timer that fires after 60 seconds.
874		1273
875	static void	1274	static void
876	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1275	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
877	{	1276	{
878	.. one minute over, w is actually stopped right here	1277	.. one minute over, w is actually stopped right here
879	}	1278	}
880		1279
881	struct ev_timer mytimer;	1280	struct ev_timer mytimer;
882	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	1281	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
883	ev_timer_start (loop, &mytimer);	1282	ev_timer_start (loop, &mytimer);
884		1283
885	Example: create a timeout timer that times out after 10 seconds of	1284	Example: Create a timeout timer that times out after 10 seconds of
886	inactivity.	1285	inactivity.
887		1286
888	static void	1287	static void
889	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1288	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
890	{	1289	{
891	.. ten seconds without any activity	1290	.. ten seconds without any activity
892	}	1291	}
893		1292
894	struct ev_timer mytimer;	1293	struct ev_timer mytimer;
895	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	1294	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
896	ev_timer_again (&mytimer); /* start timer */	1295	ev_timer_again (&mytimer); /* start timer */
897	ev_loop (loop, 0);	1296	ev_loop (loop, 0);
898		1297
899	// and in some piece of code that gets executed on any "activity":	1298	// and in some piece of code that gets executed on any "activity":
900	// reset the timeout to start ticking again at 10 seconds	1299	// reset the timeout to start ticking again at 10 seconds
901	ev_timer_again (&mytimer);	1300	ev_timer_again (&mytimer);
902		1301
903		1302
904	=head2 C<ev_periodic> - to cron or not to cron?	1303	=head2 C<ev_periodic> - to cron or not to cron?
905		1304
906	Periodic watchers are also timers of a kind, but they are very versatile	1305	Periodic watchers are also timers of a kind, but they are very versatile
907	(and unfortunately a bit complex).	1306	(and unfortunately a bit complex).
908		1307
909	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1308	Unlike C<ev_timer>'s, they are not based on real time (or relative time)
910	but on wallclock time (absolute time). You can tell a periodic watcher	1309	but on wall clock time (absolute time). You can tell a periodic watcher
911	to trigger "at" some specific point in time. For example, if you tell a	1310	to trigger after some specific point in time. For example, if you tell a
912	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()	1311	periodic watcher to trigger in 10 seconds (by specifying e.g. C<ev_now ()
913	+ 10.>) and then reset your system clock to the last year, then it will	1312	+ 10.>, that is, an absolute time not a delay) and then reset your system
		1313	clock to January of the previous year, then it will take more than year
914	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	1314	to trigger the event (unlike an C<ev_timer>, which would still trigger
915	roughly 10 seconds later and of course not if you reset your system time	1315	roughly 10 seconds later as it uses a relative timeout).
916	again).
917		1316
918	They can also be used to implement vastly more complex timers, such as	1317	C<ev_periodic>s can also be used to implement vastly more complex timers,
919	triggering an event on eahc midnight, local time.	1318	such as triggering an event on each "midnight, local time", or other
		1319	complicated, rules.
920		1320
921	As with timers, the callback is guarenteed to be invoked only when the	1321	As with timers, the callback is guaranteed to be invoked only when the
922	time (C<at>) has been passed, but if multiple periodic timers become ready	1322	time (C<at>) has passed, but if multiple periodic timers become ready
923	during the same loop iteration then order of execution is undefined.	1323	during the same loop iteration then order of execution is undefined.
		1324
		1325	=head3 Watcher-Specific Functions and Data Members
924		1326
925	=over 4	1327	=over 4
926		1328
927	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1329	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)
928		1330
…		…
931	Lots of arguments, lets sort it out... There are basically three modes of	1333	Lots of arguments, lets sort it out... There are basically three modes of
932	operation, and we will explain them from simplest to complex:	1334	operation, and we will explain them from simplest to complex:
933		1335
934	=over 4	1336	=over 4
935		1337
936	=item * absolute timer (interval = reschedule_cb = 0)	1338	=item * absolute timer (at = time, interval = reschedule_cb = 0)
937		1339
938	In this configuration the watcher triggers an event at the wallclock time	1340	In this configuration the watcher triggers an event after the wall clock
939	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	1341	time C<at> has passed and doesn't repeat. It will not adjust when a time
940	that is, if it is to be run at January 1st 2011 then it will run when the	1342	jump occurs, that is, if it is to be run at January 1st 2011 then it will
941	system time reaches or surpasses this time.	1343	run when the system time reaches or surpasses this time.
942		1344
943	=item * non-repeating interval timer (interval > 0, reschedule_cb = 0)	1345	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)
944		1346
945	In this mode the watcher will always be scheduled to time out at the next	1347	In this mode the watcher will always be scheduled to time out at the next
946	C<at + N * interval> time (for some integer N) and then repeat, regardless	1348	C<at + N * interval> time (for some integer N, which can also be negative)
947	of any time jumps.	1349	and then repeat, regardless of any time jumps.
948		1350
949	This can be used to create timers that do not drift with respect to system	1351	This can be used to create timers that do not drift with respect to system
950	time:	1352	time, for example, here is a C<ev_periodic> that triggers each hour, on
		1353	the hour:
951		1354
952	ev_periodic_set (&periodic, 0., 3600., 0);	1355	ev_periodic_set (&periodic, 0., 3600., 0);
953		1356
954	This doesn't mean there will always be 3600 seconds in between triggers,	1357	This doesn't mean there will always be 3600 seconds in between triggers,
955	but only that the the callback will be called when the system time shows a	1358	but only that the callback will be called when the system time shows a
956	full hour (UTC), or more correctly, when the system time is evenly divisible	1359	full hour (UTC), or more correctly, when the system time is evenly divisible
957	by 3600.	1360	by 3600.
958		1361
959	Another way to think about it (for the mathematically inclined) is that	1362	Another way to think about it (for the mathematically inclined) is that
960	C<ev_periodic> will try to run the callback in this mode at the next possible	1363	C<ev_periodic> will try to run the callback in this mode at the next possible
961	time where C<time = at (mod interval)>, regardless of any time jumps.	1364	time where C<time = at (mod interval)>, regardless of any time jumps.
962		1365
		1366	For numerical stability it is preferable that the C<at> value is near
		1367	C<ev_now ()> (the current time), but there is no range requirement for
		1368	this value, and in fact is often specified as zero.
		1369
		1370	Note also that there is an upper limit to how often a timer can fire (CPU
		1371	speed for example), so if C<interval> is very small then timing stability
		1372	will of course deteriorate. Libev itself tries to be exact to be about one
		1373	millisecond (if the OS supports it and the machine is fast enough).
		1374
963	=item * manual reschedule mode (reschedule_cb = callback)	1375	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)
964		1376
965	In this mode the values for C<interval> and C<at> are both being	1377	In this mode the values for C<interval> and C<at> are both being
966	ignored. Instead, each time the periodic watcher gets scheduled, the	1378	ignored. Instead, each time the periodic watcher gets scheduled, the
967	reschedule callback will be called with the watcher as first, and the	1379	reschedule callback will be called with the watcher as first, and the
968	current time as second argument.	1380	current time as second argument.
969		1381
970	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	1382	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,
971	ever, or make any event loop modifications>. If you need to stop it,	1383	ever, or make ANY event loop modifications whatsoever>.
972	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by
973	starting a prepare watcher).
974		1384
		1385	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		1386	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		1387	only event loop modification you are allowed to do).
		1388
975	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	1389	The callback prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic
976	ev_tstamp now)>, e.g.:	1390	*w, ev_tstamp now)>, e.g.:
977		1391
978	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1392	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)
979	{	1393	{
980	return now + 60.;	1394	return now + 60.;
981	}	1395	}
…		…
983	It must return the next time to trigger, based on the passed time value	1397	It must return the next time to trigger, based on the passed time value
984	(that is, the lowest time value larger than to the second argument). It	1398	(that is, the lowest time value larger than to the second argument). It
985	will usually be called just before the callback will be triggered, but	1399	will usually be called just before the callback will be triggered, but
986	might be called at other times, too.	1400	might be called at other times, too.
987		1401
988	NOTE: I<< This callback must always return a time that is later than the	1402	NOTE: I<< This callback must always return a time that is higher than or
989	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	1403	equal to the passed C<now> value >>.
990		1404
991	This can be used to create very complex timers, such as a timer that	1405	This can be used to create very complex timers, such as a timer that
992	triggers on each midnight, local time. To do this, you would calculate the	1406	triggers on "next midnight, local time". To do this, you would calculate the
993	next midnight after C<now> and return the timestamp value for this. How	1407	next midnight after C<now> and return the timestamp value for this. How
994	you do this is, again, up to you (but it is not trivial, which is the main	1408	you do this is, again, up to you (but it is not trivial, which is the main
995	reason I omitted it as an example).	1409	reason I omitted it as an example).
996		1410
997	=back	1411	=back
…		…
1001	Simply stops and restarts the periodic watcher again. This is only useful	1415	Simply stops and restarts the periodic watcher again. This is only useful
1002	when you changed some parameters or the reschedule callback would return	1416	when you changed some parameters or the reschedule callback would return
1003	a different time than the last time it was called (e.g. in a crond like	1417	a different time than the last time it was called (e.g. in a crond like
1004	program when the crontabs have changed).	1418	program when the crontabs have changed).
1005		1419
		1420	=item ev_tstamp ev_periodic_at (ev_periodic *)
		1421
		1422	When active, returns the absolute time that the watcher is supposed to
		1423	trigger next.
		1424
		1425	=item ev_tstamp offset [read-write]
		1426
		1427	When repeating, this contains the offset value, otherwise this is the
		1428	absolute point in time (the C<at> value passed to C<ev_periodic_set>).
		1429
		1430	Can be modified any time, but changes only take effect when the periodic
		1431	timer fires or C<ev_periodic_again> is being called.
		1432
1006	=item ev_tstamp interval [read-write]	1433	=item ev_tstamp interval [read-write]
1007		1434
1008	The current interval value. Can be modified any time, but changes only	1435	The current interval value. Can be modified any time, but changes only
1009	take effect when the periodic timer fires or C<ev_periodic_again> is being	1436	take effect when the periodic timer fires or C<ev_periodic_again> is being
1010	called.	1437	called.
…		…
1015	switched off. Can be changed any time, but changes only take effect when	1442	switched off. Can be changed any time, but changes only take effect when
1016	the periodic timer fires or C<ev_periodic_again> is being called.	1443	the periodic timer fires or C<ev_periodic_again> is being called.
1017		1444
1018	=back	1445	=back
1019		1446
		1447	=head3 Examples
		1448
1020	Example: call a callback every hour, or, more precisely, whenever the	1449	Example: Call a callback every hour, or, more precisely, whenever the
1021	system clock is divisible by 3600. The callback invocation times have	1450	system clock is divisible by 3600. The callback invocation times have
1022	potentially a lot of jittering, but good long-term stability.	1451	potentially a lot of jitter, but good long-term stability.
1023		1452
1024	static void	1453	static void
1025	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1454	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)
1026	{	1455	{
1027	... its now a full hour (UTC, or TAI or whatever your clock follows)	1456	... its now a full hour (UTC, or TAI or whatever your clock follows)
1028	}	1457	}
1029		1458
1030	struct ev_periodic hourly_tick;	1459	struct ev_periodic hourly_tick;
1031	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	1460	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1032	ev_periodic_start (loop, &hourly_tick);	1461	ev_periodic_start (loop, &hourly_tick);
1033		1462
1034	Example: the same as above, but use a reschedule callback to do it:	1463	Example: The same as above, but use a reschedule callback to do it:
1035		1464
1036	#include <math.h>	1465	#include <math.h>
1037		1466
1038	static ev_tstamp	1467	static ev_tstamp
1039	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	1468	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)
1040	{	1469	{
1041	return fmod (now, 3600.) + 3600.;	1470	return fmod (now, 3600.) + 3600.;
1042	}	1471	}
1043		1472
1044	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	1473	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1045		1474
1046	Example: call a callback every hour, starting now:	1475	Example: Call a callback every hour, starting now:
1047		1476
1048	struct ev_periodic hourly_tick;	1477	struct ev_periodic hourly_tick;
1049	ev_periodic_init (&hourly_tick, clock_cb,	1478	ev_periodic_init (&hourly_tick, clock_cb,
1050	fmod (ev_now (loop), 3600.), 3600., 0);	1479	fmod (ev_now (loop), 3600.), 3600., 0);
1051	ev_periodic_start (loop, &hourly_tick);	1480	ev_periodic_start (loop, &hourly_tick);
1052		1481
1053		1482
1054	=head2 C<ev_signal> - signal me when a signal gets signalled!	1483	=head2 C<ev_signal> - signal me when a signal gets signalled!
1055		1484
1056	Signal watchers will trigger an event when the process receives a specific	1485	Signal watchers will trigger an event when the process receives a specific
…		…
1063	with the kernel (thus it coexists with your own signal handlers as long	1492	with the kernel (thus it coexists with your own signal handlers as long
1064	as you don't register any with libev). Similarly, when the last signal	1493	as you don't register any with libev). Similarly, when the last signal
1065	watcher for a signal is stopped libev will reset the signal handler to	1494	watcher for a signal is stopped libev will reset the signal handler to
1066	SIG_DFL (regardless of what it was set to before).	1495	SIG_DFL (regardless of what it was set to before).
1067		1496
		1497	If possible and supported, libev will install its handlers with
		1498	C<SA_RESTART> behaviour enabled, so system calls should not be unduly
		1499	interrupted. If you have a problem with system calls getting interrupted by
		1500	signals you can block all signals in an C<ev_check> watcher and unblock
		1501	them in an C<ev_prepare> watcher.
		1502
		1503	=head3 Watcher-Specific Functions and Data Members
		1504
1068	=over 4	1505	=over 4
1069		1506
1070	=item ev_signal_init (ev_signal *, callback, int signum)	1507	=item ev_signal_init (ev_signal *, callback, int signum)
1071		1508
1072	=item ev_signal_set (ev_signal *, int signum)	1509	=item ev_signal_set (ev_signal *, int signum)
…		…
1078		1515
1079	The signal the watcher watches out for.	1516	The signal the watcher watches out for.
1080		1517
1081	=back	1518	=back
1082		1519
		1520	=head3 Examples
		1521
		1522	Example: Try to exit cleanly on SIGINT and SIGTERM.
		1523
		1524	static void
		1525	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)
		1526	{
		1527	ev_unloop (loop, EVUNLOOP_ALL);
		1528	}
		1529
		1530	struct ev_signal signal_watcher;
		1531	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		1532	ev_signal_start (loop, &sigint_cb);
		1533
1083		1534
1084	=head2 C<ev_child> - watch out for process status changes	1535	=head2 C<ev_child> - watch out for process status changes
1085		1536
1086	Child watchers trigger when your process receives a SIGCHLD in response to	1537	Child watchers trigger when your process receives a SIGCHLD in response to
1087	some child status changes (most typically when a child of yours dies).	1538	some child status changes (most typically when a child of yours dies). It
		1539	is permissible to install a child watcher I<after> the child has been
		1540	forked (which implies it might have already exited), as long as the event
		1541	loop isn't entered (or is continued from a watcher).
		1542
		1543	Only the default event loop is capable of handling signals, and therefore
		1544	you can only register child watchers in the default event loop.
		1545
		1546	=head3 Process Interaction
		1547
		1548	Libev grabs C<SIGCHLD> as soon as the default event loop is
		1549	initialised. This is necessary to guarantee proper behaviour even if
		1550	the first child watcher is started after the child exits. The occurrence
		1551	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		1552	synchronously as part of the event loop processing. Libev always reaps all
		1553	children, even ones not watched.
		1554
		1555	=head3 Overriding the Built-In Processing
		1556
		1557	Libev offers no special support for overriding the built-in child
		1558	processing, but if your application collides with libev's default child
		1559	handler, you can override it easily by installing your own handler for
		1560	C<SIGCHLD> after initialising the default loop, and making sure the
		1561	default loop never gets destroyed. You are encouraged, however, to use an
		1562	event-based approach to child reaping and thus use libev's support for
		1563	that, so other libev users can use C<ev_child> watchers freely.
		1564
		1565	=head3 Watcher-Specific Functions and Data Members
1088		1566
1089	=over 4	1567	=over 4
1090		1568
1091	=item ev_child_init (ev_child *, callback, int pid)	1569	=item ev_child_init (ev_child *, callback, int pid, int trace)
1092		1570
1093	=item ev_child_set (ev_child *, int pid)	1571	=item ev_child_set (ev_child *, int pid, int trace)
1094		1572
1095	Configures the watcher to wait for status changes of process C<pid> (or	1573	Configures the watcher to wait for status changes of process C<pid> (or
1096	I<any> process if C<pid> is specified as C<0>). The callback can look	1574	I<any> process if C<pid> is specified as C<0>). The callback can look
1097	at the C<rstatus> member of the C<ev_child> watcher structure to see	1575	at the C<rstatus> member of the C<ev_child> watcher structure to see
1098	the status word (use the macros from C<sys/wait.h> and see your systems	1576	the status word (use the macros from C<sys/wait.h> and see your systems
1099	C<waitpid> documentation). The C<rpid> member contains the pid of the	1577	C<waitpid> documentation). The C<rpid> member contains the pid of the
1100	process causing the status change.	1578	process causing the status change. C<trace> must be either C<0> (only
		1579	activate the watcher when the process terminates) or C<1> (additionally
		1580	activate the watcher when the process is stopped or continued).
1101		1581
1102	=item int pid [read-only]	1582	=item int pid [read-only]
1103		1583
1104	The process id this watcher watches out for, or C<0>, meaning any process id.	1584	The process id this watcher watches out for, or C<0>, meaning any process id.
1105		1585
…		…
1112	The process exit/trace status caused by C<rpid> (see your systems	1592	The process exit/trace status caused by C<rpid> (see your systems
1113	C<waitpid> and C<sys/wait.h> documentation for details).	1593	C<waitpid> and C<sys/wait.h> documentation for details).
1114		1594
1115	=back	1595	=back
1116		1596
1117	Example: try to exit cleanly on SIGINT and SIGTERM.	1597	=head3 Examples
1118		1598
		1599	Example: C<fork()> a new process and install a child handler to wait for
		1600	its completion.
		1601
		1602	ev_child cw;
		1603
1119	static void	1604	static void
1120	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	1605	child_cb (EV_P_ struct ev_child *w, int revents)
1121	{	1606	{
1122	ev_unloop (loop, EVUNLOOP_ALL);	1607	ev_child_stop (EV_A_ w);
		1608	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1123	}	1609	}
1124		1610
1125	struct ev_signal signal_watcher;	1611	pid_t pid = fork ();
1126	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	1612
1127	ev_signal_start (loop, &sigint_cb);	1613	if (pid < 0)
		1614	// error
		1615	else if (pid == 0)
		1616	{
		1617	// the forked child executes here
		1618	exit (1);
		1619	}
		1620	else
		1621	{
		1622	ev_child_init (&cw, child_cb, pid, 0);
		1623	ev_child_start (EV_DEFAULT_ &cw);
		1624	}
1128		1625
1129		1626
1130	=head2 C<ev_stat> - did the file attributes just change?	1627	=head2 C<ev_stat> - did the file attributes just change?
1131		1628
1132	This watches a filesystem path for attribute changes. That is, it calls	1629	This watches a file system path for attribute changes. That is, it calls
1133	C<stat> regularly (or when the OS says it changed) and sees if it changed	1630	C<stat> regularly (or when the OS says it changed) and sees if it changed
1134	compared to the last time, invoking the callback if it did.	1631	compared to the last time, invoking the callback if it did.
1135		1632
1136	The path does not need to exist: changing from "path exists" to "path does	1633	The path does not need to exist: changing from "path exists" to "path does
1137	not exist" is a status change like any other. The condition "path does	1634	not exist" is a status change like any other. The condition "path does
1138	not exist" is signified by the C<st_nlink> field being zero (which is	1635	not exist" is signified by the C<st_nlink> field being zero (which is
1139	otherwise always forced to be at least one) and all the other fields of	1636	otherwise always forced to be at least one) and all the other fields of
1140	the stat buffer having unspecified contents.	1637	the stat buffer having unspecified contents.
1141		1638
		1639	The path I<should> be absolute and I<must not> end in a slash. If it is
		1640	relative and your working directory changes, the behaviour is undefined.
		1641
1142	Since there is no standard to do this, the portable implementation simply	1642	Since there is no standard to do this, the portable implementation simply
1143	calls C<stat (2)> regulalry on the path to see if it changed somehow. You	1643	calls C<stat (2)> regularly on the path to see if it changed somehow. You
1144	can specify a recommended polling interval for this case. If you specify	1644	can specify a recommended polling interval for this case. If you specify
1145	a polling interval of C<0> (highly recommended!) then a I<suitable,	1645	a polling interval of C<0> (highly recommended!) then a I<suitable,
1146	unspecified default> value will be used (which you can expect to be around	1646	unspecified default> value will be used (which you can expect to be around
1147	five seconds, although this might change dynamically). Libev will also	1647	five seconds, although this might change dynamically). Libev will also
1148	impose a minimum interval which is currently around C<0.1>, but thats	1648	impose a minimum interval which is currently around C<0.1>, but thats
…		…
1150		1650
1151	This watcher type is not meant for massive numbers of stat watchers,	1651	This watcher type is not meant for massive numbers of stat watchers,
1152	as even with OS-supported change notifications, this can be	1652	as even with OS-supported change notifications, this can be
1153	resource-intensive.	1653	resource-intensive.
1154		1654
1155	At the time of this writing, no specific OS backends are implemented, but	1655	At the time of this writing, only the Linux inotify interface is
1156	if demand increases, at least a kqueue and inotify backend will be added.	1656	implemented (implementing kqueue support is left as an exercise for the
		1657	reader, note, however, that the author sees no way of implementing ev_stat
		1658	semantics with kqueue). Inotify will be used to give hints only and should
		1659	not change the semantics of C<ev_stat> watchers, which means that libev
		1660	sometimes needs to fall back to regular polling again even with inotify,
		1661	but changes are usually detected immediately, and if the file exists there
		1662	will be no polling.
		1663
		1664	=head3 ABI Issues (Largefile Support)
		1665
		1666	Libev by default (unless the user overrides this) uses the default
		1667	compilation environment, which means that on systems with large file
		1668	support disabled by default, you get the 32 bit version of the stat
		1669	structure. When using the library from programs that change the ABI to
		1670	use 64 bit file offsets the programs will fail. In that case you have to
		1671	compile libev with the same flags to get binary compatibility. This is
		1672	obviously the case with any flags that change the ABI, but the problem is
		1673	most noticeably disabled with ev_stat and large file support.
		1674
		1675	The solution for this is to lobby your distribution maker to make large
		1676	file interfaces available by default (as e.g. FreeBSD does) and not
		1677	optional. Libev cannot simply switch on large file support because it has
		1678	to exchange stat structures with application programs compiled using the
		1679	default compilation environment.
		1680
		1681	=head3 Inotify
		1682
		1683	When C<inotify (7)> support has been compiled into libev (generally only
		1684	available on Linux) and present at runtime, it will be used to speed up
		1685	change detection where possible. The inotify descriptor will be created lazily
		1686	when the first C<ev_stat> watcher is being started.
		1687
		1688	Inotify presence does not change the semantics of C<ev_stat> watchers
		1689	except that changes might be detected earlier, and in some cases, to avoid
		1690	making regular C<stat> calls. Even in the presence of inotify support
		1691	there are many cases where libev has to resort to regular C<stat> polling.
		1692
		1693	(There is no support for kqueue, as apparently it cannot be used to
		1694	implement this functionality, due to the requirement of having a file
		1695	descriptor open on the object at all times).
		1696
		1697	=head3 The special problem of stat time resolution
		1698
		1699	The C<stat ()> system call only supports full-second resolution portably, and
		1700	even on systems where the resolution is higher, many file systems still
		1701	only support whole seconds.
		1702
		1703	That means that, if the time is the only thing that changes, you can
		1704	easily miss updates: on the first update, C<ev_stat> detects a change and
		1705	calls your callback, which does something. When there is another update
		1706	within the same second, C<ev_stat> will be unable to detect it as the stat
		1707	data does not change.
		1708
		1709	The solution to this is to delay acting on a change for slightly more
		1710	than a second (or till slightly after the next full second boundary), using
		1711	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		1712	ev_timer_again (loop, w)>).
		1713
		1714	The C<.02> offset is added to work around small timing inconsistencies
		1715	of some operating systems (where the second counter of the current time
		1716	might be be delayed. One such system is the Linux kernel, where a call to
		1717	C<gettimeofday> might return a timestamp with a full second later than
		1718	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		1719	update file times then there will be a small window where the kernel uses
		1720	the previous second to update file times but libev might already execute
		1721	the timer callback).
		1722
		1723	=head3 Watcher-Specific Functions and Data Members
1157		1724
1158	=over 4	1725	=over 4
1159		1726
1160	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)	1727	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
1161		1728
…		…
1165	C<path>. The C<interval> is a hint on how quickly a change is expected to	1732	C<path>. The C<interval> is a hint on how quickly a change is expected to
1166	be detected and should normally be specified as C<0> to let libev choose	1733	be detected and should normally be specified as C<0> to let libev choose
1167	a suitable value. The memory pointed to by C<path> must point to the same	1734	a suitable value. The memory pointed to by C<path> must point to the same
1168	path for as long as the watcher is active.	1735	path for as long as the watcher is active.
1169		1736
1170	The callback will be receive C<EV_STAT> when a change was detected,	1737	The callback will receive C<EV_STAT> when a change was detected, relative
1171	relative to the attributes at the time the watcher was started (or the	1738	to the attributes at the time the watcher was started (or the last change
1172	last change was detected).	1739	was detected).
1173		1740
1174	=item ev_stat_stat (ev_stat *)	1741	=item ev_stat_stat (loop, ev_stat *)
1175		1742
1176	Updates the stat buffer immediately with new values. If you change the	1743	Updates the stat buffer immediately with new values. If you change the
1177	watched path in your callback, you could call this fucntion to avoid	1744	watched path in your callback, you could call this function to avoid
1178	detecting this change (while introducing a race condition). Can also be	1745	detecting this change (while introducing a race condition if you are not
1179	useful simply to find out the new values.	1746	the only one changing the path). Can also be useful simply to find out the
		1747	new values.
1180		1748
1181	=item ev_statdata attr [read-only]	1749	=item ev_statdata attr [read-only]
1182		1750
1183	The most-recently detected attributes of the file. Although the type is of	1751	The most-recently detected attributes of the file. Although the type is
1184	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types	1752	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
1185	suitable for your system. If the C<st_nlink> member is C<0>, then there	1753	suitable for your system, but you can only rely on the POSIX-standardised
		1754	members to be present. If the C<st_nlink> member is C<0>, then there was
1186	was some error while C<stat>ing the file.	1755	some error while C<stat>ing the file.
1187		1756
1188	=item ev_statdata prev [read-only]	1757	=item ev_statdata prev [read-only]
1189		1758
1190	The previous attributes of the file. The callback gets invoked whenever	1759	The previous attributes of the file. The callback gets invoked whenever
1191	C<prev> != C<attr>.	1760	C<prev> != C<attr>, or, more precisely, one or more of these members
		1761	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		1762	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
1192		1763
1193	=item ev_tstamp interval [read-only]	1764	=item ev_tstamp interval [read-only]
1194		1765
1195	The specified interval.	1766	The specified interval.
1196		1767
1197	=item const char *path [read-only]	1768	=item const char *path [read-only]
1198		1769
1199	The filesystem path that is being watched.	1770	The file system path that is being watched.
1200		1771
1201	=back	1772	=back
1202		1773
		1774	=head3 Examples
		1775
1203	Example: Watch C</etc/passwd> for attribute changes.	1776	Example: Watch C</etc/passwd> for attribute changes.
1204		1777
1205	static void	1778	static void
1206	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)	1779	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1207	{	1780	{
1208	/* /etc/passwd changed in some way */	1781	/* /etc/passwd changed in some way */
1209	if (w->attr.st_nlink)	1782	if (w->attr.st_nlink)
1210	{	1783	{
1211	printf ("passwd current size %ld\n", (long)w->attr.st_size);	1784	printf ("passwd current size %ld\n", (long)w->attr.st_size);
1212	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);	1785	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
1213	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);	1786	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
1214	}	1787	}
1215	else	1788	else
1216	/* you shalt not abuse printf for puts */	1789	/* you shalt not abuse printf for puts */
1217	puts ("wow, /etc/passwd is not there, expect problems. "	1790	puts ("wow, /etc/passwd is not there, expect problems. "
1218	"if this is windows, they already arrived\n");	1791	"if this is windows, they already arrived\n");
1219	}	1792	}
1220		1793
1221	...	1794	...
1222	ev_stat passwd;	1795	ev_stat passwd;
1223		1796
1224	ev_stat_init (&passwd, passwd_cb, "/etc/passwd");	1797	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1225	ev_stat_start (loop, &passwd);	1798	ev_stat_start (loop, &passwd);
		1799
		1800	Example: Like above, but additionally use a one-second delay so we do not
		1801	miss updates (however, frequent updates will delay processing, too, so
		1802	one might do the work both on C<ev_stat> callback invocation I<and> on
		1803	C<ev_timer> callback invocation).
		1804
		1805	static ev_stat passwd;
		1806	static ev_timer timer;
		1807
		1808	static void
		1809	timer_cb (EV_P_ ev_timer *w, int revents)
		1810	{
		1811	ev_timer_stop (EV_A_ w);
		1812
		1813	/* now it's one second after the most recent passwd change */
		1814	}
		1815
		1816	static void
		1817	stat_cb (EV_P_ ev_stat *w, int revents)
		1818	{
		1819	/* reset the one-second timer */
		1820	ev_timer_again (EV_A_ &timer);
		1821	}
		1822
		1823	...
		1824	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		1825	ev_stat_start (loop, &passwd);
		1826	ev_timer_init (&timer, timer_cb, 0., 1.02);
1226		1827
1227		1828
1228	=head2 C<ev_idle> - when you've got nothing better to do...	1829	=head2 C<ev_idle> - when you've got nothing better to do...
1229		1830
1230	Idle watchers trigger events when there are no other events are pending	1831	Idle watchers trigger events when no other events of the same or higher
1231	(prepare, check and other idle watchers do not count). That is, as long	1832	priority are pending (prepare, check and other idle watchers do not
1232	as your process is busy handling sockets or timeouts (or even signals,	1833	count).
1233	imagine) it will not be triggered. But when your process is idle all idle	1834
1234	watchers are being called again and again, once per event loop iteration -	1835	That is, as long as your process is busy handling sockets or timeouts
		1836	(or even signals, imagine) of the same or higher priority it will not be
		1837	triggered. But when your process is idle (or only lower-priority watchers
		1838	are pending), the idle watchers are being called once per event loop
1235	until stopped, that is, or your process receives more events and becomes	1839	iteration - until stopped, that is, or your process receives more events
1236	busy.	1840	and becomes busy again with higher priority stuff.
1237		1841
1238	The most noteworthy effect is that as long as any idle watchers are	1842	The most noteworthy effect is that as long as any idle watchers are
1239	active, the process will not block when waiting for new events.	1843	active, the process will not block when waiting for new events.
1240		1844
1241	Apart from keeping your process non-blocking (which is a useful	1845	Apart from keeping your process non-blocking (which is a useful
1242	effect on its own sometimes), idle watchers are a good place to do	1846	effect on its own sometimes), idle watchers are a good place to do
1243	"pseudo-background processing", or delay processing stuff to after the	1847	"pseudo-background processing", or delay processing stuff to after the
1244	event loop has handled all outstanding events.	1848	event loop has handled all outstanding events.
1245		1849
		1850	=head3 Watcher-Specific Functions and Data Members
		1851
1246	=over 4	1852	=over 4
1247		1853
1248	=item ev_idle_init (ev_signal *, callback)	1854	=item ev_idle_init (ev_signal *, callback)
1249		1855
1250	Initialises and configures the idle watcher - it has no parameters of any	1856	Initialises and configures the idle watcher - it has no parameters of any
1251	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	1857	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1252	believe me.	1858	believe me.
1253		1859
1254	=back	1860	=back
1255		1861
		1862	=head3 Examples
		1863
1256	Example: dynamically allocate an C<ev_idle>, start it, and in the	1864	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1257	callback, free it. Alos, use no error checking, as usual.	1865	callback, free it. Also, use no error checking, as usual.
1258		1866
1259	static void	1867	static void
1260	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	1868	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)
1261	{	1869	{
1262	free (w);	1870	free (w);
1263	// now do something you wanted to do when the program has	1871	// now do something you wanted to do when the program has
1264	// no longer asnything immediate to do.	1872	// no longer anything immediate to do.
1265	}	1873	}
1266		1874
1267	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	1875	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));
1268	ev_idle_init (idle_watcher, idle_cb);	1876	ev_idle_init (idle_watcher, idle_cb);
1269	ev_idle_start (loop, idle_cb);	1877	ev_idle_start (loop, idle_cb);
1270		1878
1271		1879
1272	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	1880	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1273		1881
1274	Prepare and check watchers are usually (but not always) used in tandem:	1882	Prepare and check watchers are usually (but not always) used in tandem:
…		…
1293		1901
1294	This is done by examining in each prepare call which file descriptors need	1902	This is done by examining in each prepare call which file descriptors need
1295	to be watched by the other library, registering C<ev_io> watchers for	1903	to be watched by the other library, registering C<ev_io> watchers for
1296	them and starting an C<ev_timer> watcher for any timeouts (many libraries	1904	them and starting an C<ev_timer> watcher for any timeouts (many libraries
1297	provide just this functionality). Then, in the check watcher you check for	1905	provide just this functionality). Then, in the check watcher you check for
1298	any events that occured (by checking the pending status of all watchers	1906	any events that occurred (by checking the pending status of all watchers
1299	and stopping them) and call back into the library. The I/O and timer	1907	and stopping them) and call back into the library. The I/O and timer
1300	callbacks will never actually be called (but must be valid nevertheless,	1908	callbacks will never actually be called (but must be valid nevertheless,
1301	because you never know, you know?).	1909	because you never know, you know?).
1302		1910
1303	As another example, the Perl Coro module uses these hooks to integrate	1911	As another example, the Perl Coro module uses these hooks to integrate
…		…
1307	with priority higher than or equal to the event loop and one coroutine	1915	with priority higher than or equal to the event loop and one coroutine
1308	of lower priority, but only once, using idle watchers to keep the event	1916	of lower priority, but only once, using idle watchers to keep the event
1309	loop from blocking if lower-priority coroutines are active, thus mapping	1917	loop from blocking if lower-priority coroutines are active, thus mapping
1310	low-priority coroutines to idle/background tasks).	1918	low-priority coroutines to idle/background tasks).
1311		1919
		1920	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
		1921	priority, to ensure that they are being run before any other watchers
		1922	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,
		1923	too) should not activate ("feed") events into libev. While libev fully
		1924	supports this, they might get executed before other C<ev_check> watchers
		1925	did their job. As C<ev_check> watchers are often used to embed other
		1926	(non-libev) event loops those other event loops might be in an unusable
		1927	state until their C<ev_check> watcher ran (always remind yourself to
		1928	coexist peacefully with others).
		1929
		1930	=head3 Watcher-Specific Functions and Data Members
		1931
1312	=over 4	1932	=over 4
1313		1933
1314	=item ev_prepare_init (ev_prepare *, callback)	1934	=item ev_prepare_init (ev_prepare *, callback)
1315		1935
1316	=item ev_check_init (ev_check *, callback)	1936	=item ev_check_init (ev_check *, callback)
…		…
1319	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	1939	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1320	macros, but using them is utterly, utterly and completely pointless.	1940	macros, but using them is utterly, utterly and completely pointless.
1321		1941
1322	=back	1942	=back
1323		1943
1324	Example: To include a library such as adns, you would add IO watchers	1944	=head3 Examples
1325	and a timeout watcher in a prepare handler, as required by libadns, and	1945
		1946	There are a number of principal ways to embed other event loops or modules
		1947	into libev. Here are some ideas on how to include libadns into libev
		1948	(there is a Perl module named C<EV::ADNS> that does this, which you could
		1949	use as a working example. Another Perl module named C<EV::Glib> embeds a
		1950	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
		1951	Glib event loop).
		1952
		1953	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
1326	in a check watcher, destroy them and call into libadns. What follows is	1954	and in a check watcher, destroy them and call into libadns. What follows
1327	pseudo-code only of course:	1955	is pseudo-code only of course. This requires you to either use a low
		1956	priority for the check watcher or use C<ev_clear_pending> explicitly, as
		1957	the callbacks for the IO/timeout watchers might not have been called yet.
1328		1958
1329	static ev_io iow [nfd];	1959	static ev_io iow [nfd];
1330	static ev_timer tw;	1960	static ev_timer tw;
1331		1961
1332	static void	1962	static void
1333	io_cb (ev_loop *loop, ev_io *w, int revents)	1963	io_cb (ev_loop *loop, ev_io *w, int revents)
1334	{	1964	{
1335	// set the relevant poll flags
1336	// could also call adns_processreadable etc. here
1337	struct pollfd *fd = (struct pollfd *)w->data;
1338	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1339	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1340	}	1965	}
1341		1966
1342	// create io watchers for each fd and a timer before blocking	1967	// create io watchers for each fd and a timer before blocking
1343	static void	1968	static void
1344	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	1969	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)
1345	{	1970	{
1346	int timeout = 3600000;truct pollfd fds [nfd];	1971	int timeout = 3600000;
		1972	struct pollfd fds [nfd];
1347	// actual code will need to loop here and realloc etc.	1973	// actual code will need to loop here and realloc etc.
1348	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	1974	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1349		1975
1350	/* the callback is illegal, but won't be called as we stop during check */	1976	/* the callback is illegal, but won't be called as we stop during check */
1351	ev_timer_init (&tw, 0, timeout * 1e-3);	1977	ev_timer_init (&tw, 0, timeout * 1e-3);
1352	ev_timer_start (loop, &tw);	1978	ev_timer_start (loop, &tw);
1353		1979
1354	// create on ev_io per pollfd	1980	// create one ev_io per pollfd
1355	for (int i = 0; i < nfd; ++i)	1981	for (int i = 0; i < nfd; ++i)
1356	{	1982	{
1357	ev_io_init (iow + i, io_cb, fds [i].fd,	1983	ev_io_init (iow + i, io_cb, fds [i].fd,
1358	((fds [i].events & POLLIN ? EV_READ : 0)	1984	((fds [i].events & POLLIN ? EV_READ : 0)
1359	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));	1985	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1360		1986
1361	fds [i].revents = 0;	1987	fds [i].revents = 0;
1362	iow [i].data = fds + i;
1363	ev_io_start (loop, iow + i);	1988	ev_io_start (loop, iow + i);
1364	}	1989	}
1365	}	1990	}
1366		1991
1367	// stop all watchers after blocking	1992	// stop all watchers after blocking
1368	static void	1993	static void
1369	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	1994	adns_check_cb (ev_loop *loop, ev_check *w, int revents)
1370	{	1995	{
1371	ev_timer_stop (loop, &tw);	1996	ev_timer_stop (loop, &tw);
1372		1997
1373	for (int i = 0; i < nfd; ++i)	1998	for (int i = 0; i < nfd; ++i)
		1999	{
		2000	// set the relevant poll flags
		2001	// could also call adns_processreadable etc. here
		2002	struct pollfd *fd = fds + i;
		2003	int revents = ev_clear_pending (iow + i);
		2004	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
		2005	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
		2006
		2007	// now stop the watcher
1374	ev_io_stop (loop, iow + i);	2008	ev_io_stop (loop, iow + i);
		2009	}
1375		2010
1376	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));	2011	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1377	}	2012	}
		2013
		2014	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
		2015	in the prepare watcher and would dispose of the check watcher.
		2016
		2017	Method 3: If the module to be embedded supports explicit event
		2018	notification (libadns does), you can also make use of the actual watcher
		2019	callbacks, and only destroy/create the watchers in the prepare watcher.
		2020
		2021	static void
		2022	timer_cb (EV_P_ ev_timer *w, int revents)
		2023	{
		2024	adns_state ads = (adns_state)w->data;
		2025	update_now (EV_A);
		2026
		2027	adns_processtimeouts (ads, &tv_now);
		2028	}
		2029
		2030	static void
		2031	io_cb (EV_P_ ev_io *w, int revents)
		2032	{
		2033	adns_state ads = (adns_state)w->data;
		2034	update_now (EV_A);
		2035
		2036	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
		2037	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
		2038	}
		2039
		2040	// do not ever call adns_afterpoll
		2041
		2042	Method 4: Do not use a prepare or check watcher because the module you
		2043	want to embed is too inflexible to support it. Instead, you can override
		2044	their poll function. The drawback with this solution is that the main
		2045	loop is now no longer controllable by EV. The C<Glib::EV> module does
		2046	this.
		2047
		2048	static gint
		2049	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
		2050	{
		2051	int got_events = 0;
		2052
		2053	for (n = 0; n < nfds; ++n)
		2054	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
		2055
		2056	if (timeout >= 0)
		2057	// create/start timer
		2058
		2059	// poll
		2060	ev_loop (EV_A_ 0);
		2061
		2062	// stop timer again
		2063	if (timeout >= 0)
		2064	ev_timer_stop (EV_A_ &to);
		2065
		2066	// stop io watchers again - their callbacks should have set
		2067	for (n = 0; n < nfds; ++n)
		2068	ev_io_stop (EV_A_ iow [n]);
		2069
		2070	return got_events;
		2071	}
1378		2072
1379		2073
1380	=head2 C<ev_embed> - when one backend isn't enough...	2074	=head2 C<ev_embed> - when one backend isn't enough...
1381		2075
1382	This is a rather advanced watcher type that lets you embed one event loop	2076	This is a rather advanced watcher type that lets you embed one event loop
…		…
1424	portable one.	2118	portable one.
1425		2119
1426	So when you want to use this feature you will always have to be prepared	2120	So when you want to use this feature you will always have to be prepared
1427	that you cannot get an embeddable loop. The recommended way to get around	2121	that you cannot get an embeddable loop. The recommended way to get around
1428	this is to have a separate variables for your embeddable loop, try to	2122	this is to have a separate variables for your embeddable loop, try to
1429	create it, and if that fails, use the normal loop for everything:	2123	create it, and if that fails, use the normal loop for everything.
1430		2124
1431	struct ev_loop *loop_hi = ev_default_init (0);	2125	=head3 Watcher-Specific Functions and Data Members
1432	struct ev_loop *loop_lo = 0;
1433	struct ev_embed embed;
1434
1435	// see if there is a chance of getting one that works
1436	// (remember that a flags value of 0 means autodetection)
1437	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
1438	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
1439	: 0;
1440
1441	// if we got one, then embed it, otherwise default to loop_hi
1442	if (loop_lo)
1443	{
1444	ev_embed_init (&embed, 0, loop_lo);
1445	ev_embed_start (loop_hi, &embed);
1446	}
1447	else
1448	loop_lo = loop_hi;
1449		2126
1450	=over 4	2127	=over 4
1451		2128
1452	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	2129	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
1453		2130
…		…
1455		2132
1456	Configures the watcher to embed the given loop, which must be	2133	Configures the watcher to embed the given loop, which must be
1457	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	2134	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
1458	invoked automatically, otherwise it is the responsibility of the callback	2135	invoked automatically, otherwise it is the responsibility of the callback
1459	to invoke it (it will continue to be called until the sweep has been done,	2136	to invoke it (it will continue to be called until the sweep has been done,
1460	if you do not want thta, you need to temporarily stop the embed watcher).	2137	if you do not want that, you need to temporarily stop the embed watcher).
1461		2138
1462	=item ev_embed_sweep (loop, ev_embed *)	2139	=item ev_embed_sweep (loop, ev_embed *)
1463		2140
1464	Make a single, non-blocking sweep over the embedded loop. This works	2141	Make a single, non-blocking sweep over the embedded loop. This works
1465	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most	2142	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
1466	apropriate way for embedded loops.	2143	appropriate way for embedded loops.
1467		2144
1468	=item struct ev_loop *loop [read-only]	2145	=item struct ev_loop *other [read-only]
1469		2146
1470	The embedded event loop.	2147	The embedded event loop.
		2148
		2149	=back
		2150
		2151	=head3 Examples
		2152
		2153	Example: Try to get an embeddable event loop and embed it into the default
		2154	event loop. If that is not possible, use the default loop. The default
		2155	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		2156	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		2157	used).
		2158
		2159	struct ev_loop *loop_hi = ev_default_init (0);
		2160	struct ev_loop *loop_lo = 0;
		2161	struct ev_embed embed;
		2162
		2163	// see if there is a chance of getting one that works
		2164	// (remember that a flags value of 0 means autodetection)
		2165	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		2166	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		2167	: 0;
		2168
		2169	// if we got one, then embed it, otherwise default to loop_hi
		2170	if (loop_lo)
		2171	{
		2172	ev_embed_init (&embed, 0, loop_lo);
		2173	ev_embed_start (loop_hi, &embed);
		2174	}
		2175	else
		2176	loop_lo = loop_hi;
		2177
		2178	Example: Check if kqueue is available but not recommended and create
		2179	a kqueue backend for use with sockets (which usually work with any
		2180	kqueue implementation). Store the kqueue/socket-only event loop in
		2181	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		2182
		2183	struct ev_loop *loop = ev_default_init (0);
		2184	struct ev_loop *loop_socket = 0;
		2185	struct ev_embed embed;
		2186
		2187	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		2188	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		2189	{
		2190	ev_embed_init (&embed, 0, loop_socket);
		2191	ev_embed_start (loop, &embed);
		2192	}
		2193
		2194	if (!loop_socket)
		2195	loop_socket = loop;
		2196
		2197	// now use loop_socket for all sockets, and loop for everything else
		2198
		2199
		2200	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
		2201
		2202	Fork watchers are called when a C<fork ()> was detected (usually because
		2203	whoever is a good citizen cared to tell libev about it by calling
		2204	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the
		2205	event loop blocks next and before C<ev_check> watchers are being called,
		2206	and only in the child after the fork. If whoever good citizen calling
		2207	C<ev_default_fork> cheats and calls it in the wrong process, the fork
		2208	handlers will be invoked, too, of course.
		2209
		2210	=head3 Watcher-Specific Functions and Data Members
		2211
		2212	=over 4
		2213
		2214	=item ev_fork_init (ev_signal *, callback)
		2215
		2216	Initialises and configures the fork watcher - it has no parameters of any
		2217	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
		2218	believe me.
		2219
		2220	=back
		2221
		2222
		2223	=head2 C<ev_async> - how to wake up another event loop
		2224
		2225	In general, you cannot use an C<ev_loop> from multiple threads or other
		2226	asynchronous sources such as signal handlers (as opposed to multiple event
		2227	loops - those are of course safe to use in different threads).
		2228
		2229	Sometimes, however, you need to wake up another event loop you do not
		2230	control, for example because it belongs to another thread. This is what
		2231	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you
		2232	can signal it by calling C<ev_async_send>, which is thread- and signal
		2233	safe.
		2234
		2235	This functionality is very similar to C<ev_signal> watchers, as signals,
		2236	too, are asynchronous in nature, and signals, too, will be compressed
		2237	(i.e. the number of callback invocations may be less than the number of
		2238	C<ev_async_sent> calls).
		2239
		2240	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		2241	just the default loop.
		2242
		2243	=head3 Queueing
		2244
		2245	C<ev_async> does not support queueing of data in any way. The reason
		2246	is that the author does not know of a simple (or any) algorithm for a
		2247	multiple-writer-single-reader queue that works in all cases and doesn't
		2248	need elaborate support such as pthreads.
		2249
		2250	That means that if you want to queue data, you have to provide your own
		2251	queue. But at least I can tell you would implement locking around your
		2252	queue:
		2253
		2254	=over 4
		2255
		2256	=item queueing from a signal handler context
		2257
		2258	To implement race-free queueing, you simply add to the queue in the signal
		2259	handler but you block the signal handler in the watcher callback. Here is an example that does that for
		2260	some fictitious SIGUSR1 handler:
		2261
		2262	static ev_async mysig;
		2263
		2264	static void
		2265	sigusr1_handler (void)
		2266	{
		2267	sometype data;
		2268
		2269	// no locking etc.
		2270	queue_put (data);
		2271	ev_async_send (EV_DEFAULT_ &mysig);
		2272	}
		2273
		2274	static void
		2275	mysig_cb (EV_P_ ev_async *w, int revents)
		2276	{
		2277	sometype data;
		2278	sigset_t block, prev;
		2279
		2280	sigemptyset (&block);
		2281	sigaddset (&block, SIGUSR1);
		2282	sigprocmask (SIG_BLOCK, &block, &prev);
		2283
		2284	while (queue_get (&data))
		2285	process (data);
		2286
		2287	if (sigismember (&prev, SIGUSR1)
		2288	sigprocmask (SIG_UNBLOCK, &block, 0);
		2289	}
		2290
		2291	(Note: pthreads in theory requires you to use C<pthread_setmask>
		2292	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		2293	either...).
		2294
		2295	=item queueing from a thread context
		2296
		2297	The strategy for threads is different, as you cannot (easily) block
		2298	threads but you can easily preempt them, so to queue safely you need to
		2299	employ a traditional mutex lock, such as in this pthread example:
		2300
		2301	static ev_async mysig;
		2302	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		2303
		2304	static void
		2305	otherthread (void)
		2306	{
		2307	// only need to lock the actual queueing operation
		2308	pthread_mutex_lock (&mymutex);
		2309	queue_put (data);
		2310	pthread_mutex_unlock (&mymutex);
		2311
		2312	ev_async_send (EV_DEFAULT_ &mysig);
		2313	}
		2314
		2315	static void
		2316	mysig_cb (EV_P_ ev_async *w, int revents)
		2317	{
		2318	pthread_mutex_lock (&mymutex);
		2319
		2320	while (queue_get (&data))
		2321	process (data);
		2322
		2323	pthread_mutex_unlock (&mymutex);
		2324	}
		2325
		2326	=back
		2327
		2328
		2329	=head3 Watcher-Specific Functions and Data Members
		2330
		2331	=over 4
		2332
		2333	=item ev_async_init (ev_async *, callback)
		2334
		2335	Initialises and configures the async watcher - it has no parameters of any
		2336	kind. There is a C<ev_asynd_set> macro, but using it is utterly pointless,
		2337	believe me.
		2338
		2339	=item ev_async_send (loop, ev_async *)
		2340
		2341	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		2342	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		2343	C<ev_feed_event>, this call is safe to do in other threads, signal or
		2344	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
		2345	section below on what exactly this means).
		2346
		2347	This call incurs the overhead of a system call only once per loop iteration,
		2348	so while the overhead might be noticeable, it doesn't apply to repeated
		2349	calls to C<ev_async_send>.
		2350
		2351	=item bool = ev_async_pending (ev_async *)
		2352
		2353	Returns a non-zero value when C<ev_async_send> has been called on the
		2354	watcher but the event has not yet been processed (or even noted) by the
		2355	event loop.
		2356
		2357	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		2358	the loop iterates next and checks for the watcher to have become active,
		2359	it will reset the flag again. C<ev_async_pending> can be used to very
		2360	quickly check whether invoking the loop might be a good idea.
		2361
		2362	Not that this does I<not> check whether the watcher itself is pending, only
		2363	whether it has been requested to make this watcher pending.
1471		2364
1472	=back	2365	=back
1473		2366
1474		2367
1475	=head1 OTHER FUNCTIONS	2368	=head1 OTHER FUNCTIONS
…		…
1486	or timeout without having to allocate/configure/start/stop/free one or	2379	or timeout without having to allocate/configure/start/stop/free one or
1487	more watchers yourself.	2380	more watchers yourself.
1488		2381
1489	If C<fd> is less than 0, then no I/O watcher will be started and events	2382	If C<fd> is less than 0, then no I/O watcher will be started and events
1490	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	2383	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and
1491	C<events> set will be craeted and started.	2384	C<events> set will be created and started.
1492		2385
1493	If C<timeout> is less than 0, then no timeout watcher will be	2386	If C<timeout> is less than 0, then no timeout watcher will be
1494	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	2387	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
1495	repeat = 0) will be started. While C<0> is a valid timeout, it is of	2388	repeat = 0) will be started. While C<0> is a valid timeout, it is of
1496	dubious value.	2389	dubious value.
…		…
1498	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	2391	The callback has the type C<void (*cb)(int revents, void *arg)> and gets
1499	passed an C<revents> set like normal event callbacks (a combination of	2392	passed an C<revents> set like normal event callbacks (a combination of
1500	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	2393	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
1501	value passed to C<ev_once>:	2394	value passed to C<ev_once>:
1502		2395
1503	static void stdin_ready (int revents, void *arg)	2396	static void stdin_ready (int revents, void *arg)
1504	{	2397	{
1505	if (revents & EV_TIMEOUT)	2398	if (revents & EV_TIMEOUT)
1506	/* doh, nothing entered */;	2399	/* doh, nothing entered */;
1507	else if (revents & EV_READ)	2400	else if (revents & EV_READ)
1508	/* stdin might have data for us, joy! */;	2401	/* stdin might have data for us, joy! */;
1509	}	2402	}
1510		2403
1511	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	2404	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
1512		2405
1513	=item ev_feed_event (ev_loop *, watcher *, int revents)	2406	=item ev_feed_event (ev_loop *, watcher *, int revents)
1514		2407
1515	Feeds the given event set into the event loop, as if the specified event	2408	Feeds the given event set into the event loop, as if the specified event
1516	had happened for the specified watcher (which must be a pointer to an	2409	had happened for the specified watcher (which must be a pointer to an
…		…
1521	Feed an event on the given fd, as if a file descriptor backend detected	2414	Feed an event on the given fd, as if a file descriptor backend detected
1522	the given events it.	2415	the given events it.
1523		2416
1524	=item ev_feed_signal_event (ev_loop *loop, int signum)	2417	=item ev_feed_signal_event (ev_loop *loop, int signum)
1525		2418
1526	Feed an event as if the given signal occured (C<loop> must be the default	2419	Feed an event as if the given signal occurred (C<loop> must be the default
1527	loop!).	2420	loop!).
1528		2421
1529	=back	2422	=back
1530		2423
1531		2424
…		…
1547		2440
1548	=item * Priorities are not currently supported. Initialising priorities	2441	=item * Priorities are not currently supported. Initialising priorities
1549	will fail and all watchers will have the same priority, even though there	2442	will fail and all watchers will have the same priority, even though there
1550	is an ev_pri field.	2443	is an ev_pri field.
1551		2444
		2445	=item * In libevent, the last base created gets the signals, in libev, the
		2446	first base created (== the default loop) gets the signals.
		2447
1552	=item * Other members are not supported.	2448	=item * Other members are not supported.
1553		2449
1554	=item * The libev emulation is I<not> ABI compatible to libevent, you need	2450	=item * The libev emulation is I<not> ABI compatible to libevent, you need
1555	to use the libev header file and library.	2451	to use the libev header file and library.
1556		2452
1557	=back	2453	=back
1558		2454
1559	=head1 C++ SUPPORT	2455	=head1 C++ SUPPORT
1560		2456
1561	Libev comes with some simplistic wrapper classes for C++ that mainly allow	2457	Libev comes with some simplistic wrapper classes for C++ that mainly allow
1562	you to use some convinience methods to start/stop watchers and also change	2458	you to use some convenience methods to start/stop watchers and also change
1563	the callback model to a model using method callbacks on objects.	2459	the callback model to a model using method callbacks on objects.
1564		2460
1565	To use it,	2461	To use it,
1566		2462
1567	#include <ev++.h>	2463	#include <ev++.h>
1568		2464
1569	(it is not installed by default). This automatically includes F<ev.h>	2465	This automatically includes F<ev.h> and puts all of its definitions (many
1570	and puts all of its definitions (many of them macros) into the global	2466	of them macros) into the global namespace. All C++ specific things are
1571	namespace. All C++ specific things are put into the C<ev> namespace.	2467	put into the C<ev> namespace. It should support all the same embedding
		2468	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
1572		2469
1573	It should support all the same embedding options as F<ev.h>, most notably	2470	Care has been taken to keep the overhead low. The only data member the C++
1574	C<EV_MULTIPLICITY>.	2471	classes add (compared to plain C-style watchers) is the event loop pointer
		2472	that the watcher is associated with (or no additional members at all if
		2473	you disable C<EV_MULTIPLICITY> when embedding libev).
		2474
		2475	Currently, functions, and static and non-static member functions can be
		2476	used as callbacks. Other types should be easy to add as long as they only
		2477	need one additional pointer for context. If you need support for other
		2478	types of functors please contact the author (preferably after implementing
		2479	it).
1575		2480
1576	Here is a list of things available in the C<ev> namespace:	2481	Here is a list of things available in the C<ev> namespace:
1577		2482
1578	=over 4	2483	=over 4
1579		2484
…		…
1595		2500
1596	All of those classes have these methods:	2501	All of those classes have these methods:
1597		2502
1598	=over 4	2503	=over 4
1599		2504
1600	=item ev::TYPE::TYPE (object *, object::method *)	2505	=item ev::TYPE::TYPE ()
1601		2506
1602	=item ev::TYPE::TYPE (object *, object::method *, struct ev_loop *)	2507	=item ev::TYPE::TYPE (struct ev_loop *)
1603		2508
1604	=item ev::TYPE::~TYPE	2509	=item ev::TYPE::~TYPE
1605		2510
1606	The constructor takes a pointer to an object and a method pointer to	2511	The constructor (optionally) takes an event loop to associate the watcher
1607	the event handler callback to call in this class. The constructor calls	2512	with. If it is omitted, it will use C<EV_DEFAULT>.
1608	C<ev_init> for you, which means you have to call the C<set> method	2513
1609	before starting it. If you do not specify a loop then the constructor	2514	The constructor calls C<ev_init> for you, which means you have to call the
1610	automatically associates the default loop with this watcher.	2515	C<set> method before starting it.
		2516
		2517	It will not set a callback, however: You have to call the templated C<set>
		2518	method to set a callback before you can start the watcher.
		2519
		2520	(The reason why you have to use a method is a limitation in C++ which does
		2521	not allow explicit template arguments for constructors).
1611		2522
1612	The destructor automatically stops the watcher if it is active.	2523	The destructor automatically stops the watcher if it is active.
		2524
		2525	=item w->set<class, &class::method> (object *)
		2526
		2527	This method sets the callback method to call. The method has to have a
		2528	signature of C<void (*)(ev_TYPE &, int)>, it receives the watcher as
		2529	first argument and the C<revents> as second. The object must be given as
		2530	parameter and is stored in the C<data> member of the watcher.
		2531
		2532	This method synthesizes efficient thunking code to call your method from
		2533	the C callback that libev requires. If your compiler can inline your
		2534	callback (i.e. it is visible to it at the place of the C<set> call and
		2535	your compiler is good :), then the method will be fully inlined into the
		2536	thunking function, making it as fast as a direct C callback.
		2537
		2538	Example: simple class declaration and watcher initialisation
		2539
		2540	struct myclass
		2541	{
		2542	void io_cb (ev::io &w, int revents) { }
		2543	}
		2544
		2545	myclass obj;
		2546	ev::io iow;
		2547	iow.set <myclass, &myclass::io_cb> (&obj);
		2548
		2549	=item w->set<function> (void *data = 0)
		2550
		2551	Also sets a callback, but uses a static method or plain function as
		2552	callback. The optional C<data> argument will be stored in the watcher's
		2553	C<data> member and is free for you to use.
		2554
		2555	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
		2556
		2557	See the method-C<set> above for more details.
		2558
		2559	Example:
		2560
		2561	static void io_cb (ev::io &w, int revents) { }
		2562	iow.set <io_cb> ();
1613		2563
1614	=item w->set (struct ev_loop *)	2564	=item w->set (struct ev_loop *)
1615		2565
1616	Associates a different C<struct ev_loop> with this watcher. You can only	2566	Associates a different C<struct ev_loop> with this watcher. You can only
1617	do this when the watcher is inactive (and not pending either).	2567	do this when the watcher is inactive (and not pending either).
1618		2568
1619	=item w->set ([args])	2569	=item w->set ([arguments])
1620		2570
1621	Basically the same as C<ev_TYPE_set>, with the same args. Must be	2571	Basically the same as C<ev_TYPE_set>, with the same arguments. Must be
1622	called at least once. Unlike the C counterpart, an active watcher gets	2572	called at least once. Unlike the C counterpart, an active watcher gets
1623	automatically stopped and restarted.	2573	automatically stopped and restarted when reconfiguring it with this
		2574	method.
1624		2575
1625	=item w->start ()	2576	=item w->start ()
1626		2577
1627	Starts the watcher. Note that there is no C<loop> argument as the	2578	Starts the watcher. Note that there is no C<loop> argument, as the
1628	constructor already takes the loop.	2579	constructor already stores the event loop.
1629		2580
1630	=item w->stop ()	2581	=item w->stop ()
1631		2582
1632	Stops the watcher if it is active. Again, no C<loop> argument.	2583	Stops the watcher if it is active. Again, no C<loop> argument.
1633		2584
1634	=item w->again () C<ev::timer>, C<ev::periodic> only	2585	=item w->again () (C<ev::timer>, C<ev::periodic> only)
1635		2586
1636	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding	2587	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
1637	C<ev_TYPE_again> function.	2588	C<ev_TYPE_again> function.
1638		2589
1639	=item w->sweep () C<ev::embed> only	2590	=item w->sweep () (C<ev::embed> only)
1640		2591
1641	Invokes C<ev_embed_sweep>.	2592	Invokes C<ev_embed_sweep>.
		2593
		2594	=item w->update () (C<ev::stat> only)
		2595
		2596	Invokes C<ev_stat_stat>.
1642		2597
1643	=back	2598	=back
1644		2599
1645	=back	2600	=back
1646		2601
1647	Example: Define a class with an IO and idle watcher, start one of them in	2602	Example: Define a class with an IO and idle watcher, start one of them in
1648	the constructor.	2603	the constructor.
1649		2604
1650	class myclass	2605	class myclass
1651	{	2606	{
1652	ev_io io; void io_cb (ev::io &w, int revents);	2607	ev::io io; void io_cb (ev::io &w, int revents);
1653	ev_idle idle void idle_cb (ev::idle &w, int revents);	2608	ev:idle idle void idle_cb (ev::idle &w, int revents);
1654		2609
1655	myclass ();	2610	myclass (int fd)
1656	}	2611	{
		2612	io .set <myclass, &myclass::io_cb > (this);
		2613	idle.set <myclass, &myclass::idle_cb> (this);
1657		2614
1658	myclass::myclass (int fd)
1659	: io (this, &myclass::io_cb),
1660	idle (this, &myclass::idle_cb)
1661	{
1662	io.start (fd, ev::READ);	2615	io.start (fd, ev::READ);
		2616	}
		2617	};
		2618
		2619
		2620	=head1 OTHER LANGUAGE BINDINGS
		2621
		2622	Libev does not offer other language bindings itself, but bindings for a
		2623	number of languages exist in the form of third-party packages. If you know
		2624	any interesting language binding in addition to the ones listed here, drop
		2625	me a note.
		2626
		2627	=over 4
		2628
		2629	=item Perl
		2630
		2631	The EV module implements the full libev API and is actually used to test
		2632	libev. EV is developed together with libev. Apart from the EV core module,
		2633	there are additional modules that implement libev-compatible interfaces
		2634	to C<libadns> (C<EV::ADNS>), C<Net::SNMP> (C<Net::SNMP::EV>) and the
		2635	C<libglib> event core (C<Glib::EV> and C<EV::Glib>).
		2636
		2637	It can be found and installed via CPAN, its homepage is at
		2638	L<http://software.schmorp.de/pkg/EV>.
		2639
		2640	=item Python
		2641
		2642	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		2643	seems to be quite complete and well-documented. Note, however, that the
		2644	patch they require for libev is outright dangerous as it breaks the ABI
		2645	for everybody else, and therefore, should never be applied in an installed
		2646	libev (if python requires an incompatible ABI then it needs to embed
		2647	libev).
		2648
		2649	=item Ruby
		2650
		2651	Tony Arcieri has written a ruby extension that offers access to a subset
		2652	of the libev API and adds file handle abstractions, asynchronous DNS and
		2653	more on top of it. It can be found via gem servers. Its homepage is at
		2654	L<http://rev.rubyforge.org/>.
		2655
		2656	=item D
		2657
		2658	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		2659	be found at L<http://git.llucax.com.ar/?p=software/ev.d.git;a=summary>.
		2660
		2661	=back
		2662
		2663
		2664	=head1 MACRO MAGIC
		2665
		2666	Libev can be compiled with a variety of options, the most fundamental
		2667	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
		2668	functions and callbacks have an initial C<struct ev_loop *> argument.
		2669
		2670	To make it easier to write programs that cope with either variant, the
		2671	following macros are defined:
		2672
		2673	=over 4
		2674
		2675	=item C<EV_A>, C<EV_A_>
		2676
		2677	This provides the loop I<argument> for functions, if one is required ("ev
		2678	loop argument"). The C<EV_A> form is used when this is the sole argument,
		2679	C<EV_A_> is used when other arguments are following. Example:
		2680
		2681	ev_unref (EV_A);
		2682	ev_timer_add (EV_A_ watcher);
		2683	ev_loop (EV_A_ 0);
		2684
		2685	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
		2686	which is often provided by the following macro.
		2687
		2688	=item C<EV_P>, C<EV_P_>
		2689
		2690	This provides the loop I<parameter> for functions, if one is required ("ev
		2691	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
		2692	C<EV_P_> is used when other parameters are following. Example:
		2693
		2694	// this is how ev_unref is being declared
		2695	static void ev_unref (EV_P);
		2696
		2697	// this is how you can declare your typical callback
		2698	static void cb (EV_P_ ev_timer *w, int revents)
		2699
		2700	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
		2701	suitable for use with C<EV_A>.
		2702
		2703	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
		2704
		2705	Similar to the other two macros, this gives you the value of the default
		2706	loop, if multiple loops are supported ("ev loop default").
		2707
		2708	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		2709
		2710	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		2711	default loop has been initialised (C<UC> == unchecked). Their behaviour
		2712	is undefined when the default loop has not been initialised by a previous
		2713	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		2714
		2715	It is often prudent to use C<EV_DEFAULT> when initialising the first
		2716	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
		2717
		2718	=back
		2719
		2720	Example: Declare and initialise a check watcher, utilising the above
		2721	macros so it will work regardless of whether multiple loops are supported
		2722	or not.
		2723
		2724	static void
		2725	check_cb (EV_P_ ev_timer *w, int revents)
		2726	{
		2727	ev_check_stop (EV_A_ w);
1663	}	2728	}
		2729
		2730	ev_check check;
		2731	ev_check_init (&check, check_cb);
		2732	ev_check_start (EV_DEFAULT_ &check);
		2733	ev_loop (EV_DEFAULT_ 0);
1664		2734
1665	=head1 EMBEDDING	2735	=head1 EMBEDDING
1666		2736
1667	Libev can (and often is) directly embedded into host	2737	Libev can (and often is) directly embedded into host
1668	applications. Examples of applications that embed it include the Deliantra	2738	applications. Examples of applications that embed it include the Deliantra
1669	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)	2739	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
1670	and rxvt-unicode.	2740	and rxvt-unicode.
1671		2741
1672	The goal is to enable you to just copy the neecssary files into your	2742	The goal is to enable you to just copy the necessary files into your
1673	source directory without having to change even a single line in them, so	2743	source directory without having to change even a single line in them, so
1674	you can easily upgrade by simply copying (or having a checked-out copy of	2744	you can easily upgrade by simply copying (or having a checked-out copy of
1675	libev somewhere in your source tree).	2745	libev somewhere in your source tree).
1676		2746
1677	=head2 FILESETS	2747	=head2 FILESETS
1678		2748
1679	Depending on what features you need you need to include one or more sets of files	2749	Depending on what features you need you need to include one or more sets of files
1680	in your app.	2750	in your application.
1681		2751
1682	=head3 CORE EVENT LOOP	2752	=head3 CORE EVENT LOOP
1683		2753
1684	To include only the libev core (all the C<ev_*> functions), with manual	2754	To include only the libev core (all the C<ev_*> functions), with manual
1685	configuration (no autoconf):	2755	configuration (no autoconf):
1686		2756
1687	#define EV_STANDALONE 1	2757	#define EV_STANDALONE 1
1688	#include "ev.c"	2758	#include "ev.c"
1689		2759
1690	This will automatically include F<ev.h>, too, and should be done in a	2760	This will automatically include F<ev.h>, too, and should be done in a
1691	single C source file only to provide the function implementations. To use	2761	single C source file only to provide the function implementations. To use
1692	it, do the same for F<ev.h> in all files wishing to use this API (best	2762	it, do the same for F<ev.h> in all files wishing to use this API (best
1693	done by writing a wrapper around F<ev.h> that you can include instead and	2763	done by writing a wrapper around F<ev.h> that you can include instead and
1694	where you can put other configuration options):	2764	where you can put other configuration options):
1695		2765
1696	#define EV_STANDALONE 1	2766	#define EV_STANDALONE 1
1697	#include "ev.h"	2767	#include "ev.h"
1698		2768
1699	Both header files and implementation files can be compiled with a C++	2769	Both header files and implementation files can be compiled with a C++
1700	compiler (at least, thats a stated goal, and breakage will be treated	2770	compiler (at least, thats a stated goal, and breakage will be treated
1701	as a bug).	2771	as a bug).
1702		2772
1703	You need the following files in your source tree, or in a directory	2773	You need the following files in your source tree, or in a directory
1704	in your include path (e.g. in libev/ when using -Ilibev):	2774	in your include path (e.g. in libev/ when using -Ilibev):
1705		2775
1706	ev.h	2776	ev.h
1707	ev.c	2777	ev.c
1708	ev_vars.h	2778	ev_vars.h
1709	ev_wrap.h	2779	ev_wrap.h
1710		2780
1711	ev_win32.c required on win32 platforms only	2781	ev_win32.c required on win32 platforms only
1712		2782
1713	ev_select.c only when select backend is enabled (which is by default)	2783	ev_select.c only when select backend is enabled (which is enabled by default)
1714	ev_poll.c only when poll backend is enabled (disabled by default)	2784	ev_poll.c only when poll backend is enabled (disabled by default)
1715	ev_epoll.c only when the epoll backend is enabled (disabled by default)	2785	ev_epoll.c only when the epoll backend is enabled (disabled by default)
1716	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	2786	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
1717	ev_port.c only when the solaris port backend is enabled (disabled by default)	2787	ev_port.c only when the solaris port backend is enabled (disabled by default)
1718		2788
1719	F<ev.c> includes the backend files directly when enabled, so you only need	2789	F<ev.c> includes the backend files directly when enabled, so you only need
1720	to compile this single file.	2790	to compile this single file.
1721		2791
1722	=head3 LIBEVENT COMPATIBILITY API	2792	=head3 LIBEVENT COMPATIBILITY API
1723		2793
1724	To include the libevent compatibility API, also include:	2794	To include the libevent compatibility API, also include:
1725		2795
1726	#include "event.c"	2796	#include "event.c"
1727		2797
1728	in the file including F<ev.c>, and:	2798	in the file including F<ev.c>, and:
1729		2799
1730	#include "event.h"	2800	#include "event.h"
1731		2801
1732	in the files that want to use the libevent API. This also includes F<ev.h>.	2802	in the files that want to use the libevent API. This also includes F<ev.h>.
1733		2803
1734	You need the following additional files for this:	2804	You need the following additional files for this:
1735		2805
1736	event.h	2806	event.h
1737	event.c	2807	event.c
1738		2808
1739	=head3 AUTOCONF SUPPORT	2809	=head3 AUTOCONF SUPPORT
1740		2810
1741	Instead of using C<EV_STANDALONE=1> and providing your config in	2811	Instead of using C<EV_STANDALONE=1> and providing your configuration in
1742	whatever way you want, you can also C<m4_include([libev.m4])> in your	2812	whatever way you want, you can also C<m4_include([libev.m4])> in your
1743	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then	2813	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
1744	include F<config.h> and configure itself accordingly.	2814	include F<config.h> and configure itself accordingly.
1745		2815
1746	For this of course you need the m4 file:	2816	For this of course you need the m4 file:
1747		2817
1748	libev.m4	2818	libev.m4
1749		2819
1750	=head2 PREPROCESSOR SYMBOLS/MACROS	2820	=head2 PREPROCESSOR SYMBOLS/MACROS
1751		2821
1752	Libev can be configured via a variety of preprocessor symbols you have to define	2822	Libev can be configured via a variety of preprocessor symbols you have to
1753	before including any of its files. The default is not to build for multiplicity	2823	define before including any of its files. The default in the absence of
1754	and only include the select backend.	2824	autoconf is noted for every option.
1755		2825
1756	=over 4	2826	=over 4
1757		2827
1758	=item EV_STANDALONE	2828	=item EV_STANDALONE
1759		2829
…		…
1764	F<event.h> that are not directly supported by the libev core alone.	2834	F<event.h> that are not directly supported by the libev core alone.
1765		2835
1766	=item EV_USE_MONOTONIC	2836	=item EV_USE_MONOTONIC
1767		2837
1768	If defined to be C<1>, libev will try to detect the availability of the	2838	If defined to be C<1>, libev will try to detect the availability of the
1769	monotonic clock option at both compiletime and runtime. Otherwise no use	2839	monotonic clock option at both compile time and runtime. Otherwise no use
1770	of the monotonic clock option will be attempted. If you enable this, you	2840	of the monotonic clock option will be attempted. If you enable this, you
1771	usually have to link against librt or something similar. Enabling it when	2841	usually have to link against librt or something similar. Enabling it when
1772	the functionality isn't available is safe, though, althoguh you have	2842	the functionality isn't available is safe, though, although you have
1773	to make sure you link against any libraries where the C<clock_gettime>	2843	to make sure you link against any libraries where the C<clock_gettime>
1774	function is hiding in (often F<-lrt>).	2844	function is hiding in (often F<-lrt>).
1775		2845
1776	=item EV_USE_REALTIME	2846	=item EV_USE_REALTIME
1777		2847
1778	If defined to be C<1>, libev will try to detect the availability of the	2848	If defined to be C<1>, libev will try to detect the availability of the
1779	realtime clock option at compiletime (and assume its availability at	2849	real-time clock option at compile time (and assume its availability at
1780	runtime if successful). Otherwise no use of the realtime clock option will	2850	runtime if successful). Otherwise no use of the real-time clock option will
1781	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	2851	be attempted. This effectively replaces C<gettimeofday> by C<clock_get
1782	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See tzhe note about libraries	2852	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the
1783	in the description of C<EV_USE_MONOTONIC>, though.	2853	note about libraries in the description of C<EV_USE_MONOTONIC>, though.
		2854
		2855	=item EV_USE_NANOSLEEP
		2856
		2857	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		2858	and will use it for delays. Otherwise it will use C<select ()>.
		2859
		2860	=item EV_USE_EVENTFD
		2861
		2862	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		2863	available and will probe for kernel support at runtime. This will improve
		2864	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		2865	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		2866	2.7 or newer, otherwise disabled.
1784		2867
1785	=item EV_USE_SELECT	2868	=item EV_USE_SELECT
1786		2869
1787	If undefined or defined to be C<1>, libev will compile in support for the	2870	If undefined or defined to be C<1>, libev will compile in support for the
1788	C<select>(2) backend. No attempt at autodetection will be done: if no	2871	C<select>(2) backend. No attempt at auto-detection will be done: if no
1789	other method takes over, select will be it. Otherwise the select backend	2872	other method takes over, select will be it. Otherwise the select backend
1790	will not be compiled in.	2873	will not be compiled in.
1791		2874
1792	=item EV_SELECT_USE_FD_SET	2875	=item EV_SELECT_USE_FD_SET
1793		2876
1794	If defined to C<1>, then the select backend will use the system C<fd_set>	2877	If defined to C<1>, then the select backend will use the system C<fd_set>
1795	structure. This is useful if libev doesn't compile due to a missing	2878	structure. This is useful if libev doesn't compile due to a missing
1796	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on	2879	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout on
1797	exotic systems. This usually limits the range of file descriptors to some	2880	exotic systems. This usually limits the range of file descriptors to some
1798	low limit such as 1024 or might have other limitations (winsocket only	2881	low limit such as 1024 or might have other limitations (winsocket only
1799	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	2882	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might
1800	influence the size of the C<fd_set> used.	2883	influence the size of the C<fd_set> used.
1801		2884
…		…
1807	be used is the winsock select). This means that it will call	2890	be used is the winsock select). This means that it will call
1808	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	2891	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
1809	it is assumed that all these functions actually work on fds, even	2892	it is assumed that all these functions actually work on fds, even
1810	on win32. Should not be defined on non-win32 platforms.	2893	on win32. Should not be defined on non-win32 platforms.
1811		2894
		2895	=item EV_FD_TO_WIN32_HANDLE
		2896
		2897	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		2898	file descriptors to socket handles. When not defining this symbol (the
		2899	default), then libev will call C<_get_osfhandle>, which is usually
		2900	correct. In some cases, programs use their own file descriptor management,
		2901	in which case they can provide this function to map fds to socket handles.
		2902
1812	=item EV_USE_POLL	2903	=item EV_USE_POLL
1813		2904
1814	If defined to be C<1>, libev will compile in support for the C<poll>(2)	2905	If defined to be C<1>, libev will compile in support for the C<poll>(2)
1815	backend. Otherwise it will be enabled on non-win32 platforms. It	2906	backend. Otherwise it will be enabled on non-win32 platforms. It
1816	takes precedence over select.	2907	takes precedence over select.
1817		2908
1818	=item EV_USE_EPOLL	2909	=item EV_USE_EPOLL
1819		2910
1820	If defined to be C<1>, libev will compile in support for the Linux	2911	If defined to be C<1>, libev will compile in support for the Linux
1821	C<epoll>(7) backend. Its availability will be detected at runtime,	2912	C<epoll>(7) backend. Its availability will be detected at runtime,
1822	otherwise another method will be used as fallback. This is the	2913	otherwise another method will be used as fallback. This is the preferred
1823	preferred backend for GNU/Linux systems.	2914	backend for GNU/Linux systems. If undefined, it will be enabled if the
		2915	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
1824		2916
1825	=item EV_USE_KQUEUE	2917	=item EV_USE_KQUEUE
1826		2918
1827	If defined to be C<1>, libev will compile in support for the BSD style	2919	If defined to be C<1>, libev will compile in support for the BSD style
1828	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	2920	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
1841	otherwise another method will be used as fallback. This is the preferred	2933	otherwise another method will be used as fallback. This is the preferred
1842	backend for Solaris 10 systems.	2934	backend for Solaris 10 systems.
1843		2935
1844	=item EV_USE_DEVPOLL	2936	=item EV_USE_DEVPOLL
1845		2937
1846	reserved for future expansion, works like the USE symbols above.	2938	Reserved for future expansion, works like the USE symbols above.
		2939
		2940	=item EV_USE_INOTIFY
		2941
		2942	If defined to be C<1>, libev will compile in support for the Linux inotify
		2943	interface to speed up C<ev_stat> watchers. Its actual availability will
		2944	be detected at runtime. If undefined, it will be enabled if the headers
		2945	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		2946
		2947	=item EV_ATOMIC_T
		2948
		2949	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		2950	access is atomic with respect to other threads or signal contexts. No such
		2951	type is easily found in the C language, so you can provide your own type
		2952	that you know is safe for your purposes. It is used both for signal handler "locking"
		2953	as well as for signal and thread safety in C<ev_async> watchers.
		2954
		2955	In the absence of this define, libev will use C<sig_atomic_t volatile>
		2956	(from F<signal.h>), which is usually good enough on most platforms.
1847		2957
1848	=item EV_H	2958	=item EV_H
1849		2959
1850	The name of the F<ev.h> header file used to include it. The default if	2960	The name of the F<ev.h> header file used to include it. The default if
1851	undefined is C<< <ev.h> >> in F<event.h> and C<"ev.h"> in F<ev.c>. This	2961	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
1852	can be used to virtually rename the F<ev.h> header file in case of conflicts.	2962	used to virtually rename the F<ev.h> header file in case of conflicts.
1853		2963
1854	=item EV_CONFIG_H	2964	=item EV_CONFIG_H
1855		2965
1856	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	2966	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
1857	F<ev.c>'s idea of where to find the F<config.h> file, similarly to	2967	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
1858	C<EV_H>, above.	2968	C<EV_H>, above.
1859		2969
1860	=item EV_EVENT_H	2970	=item EV_EVENT_H
1861		2971
1862	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	2972	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
1863	of how the F<event.h> header can be found.	2973	of how the F<event.h> header can be found, the default is C<"event.h">.
1864		2974
1865	=item EV_PROTOTYPES	2975	=item EV_PROTOTYPES
1866		2976
1867	If defined to be C<0>, then F<ev.h> will not define any function	2977	If defined to be C<0>, then F<ev.h> will not define any function
1868	prototypes, but still define all the structs and other symbols. This is	2978	prototypes, but still define all the structs and other symbols. This is
…		…
1875	will have the C<struct ev_loop *> as first argument, and you can create	2985	will have the C<struct ev_loop *> as first argument, and you can create
1876	additional independent event loops. Otherwise there will be no support	2986	additional independent event loops. Otherwise there will be no support
1877	for multiple event loops and there is no first event loop pointer	2987	for multiple event loops and there is no first event loop pointer
1878	argument. Instead, all functions act on the single default loop.	2988	argument. Instead, all functions act on the single default loop.
1879		2989
		2990	=item EV_MINPRI
		2991
		2992	=item EV_MAXPRI
		2993
		2994	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
		2995	C<EV_MAXPRI>, but otherwise there are no non-obvious limitations. You can
		2996	provide for more priorities by overriding those symbols (usually defined
		2997	to be C<-2> and C<2>, respectively).
		2998
		2999	When doing priority-based operations, libev usually has to linearly search
		3000	all the priorities, so having many of them (hundreds) uses a lot of space
		3001	and time, so using the defaults of five priorities (-2 .. +2) is usually
		3002	fine.
		3003
		3004	If your embedding application does not need any priorities, defining these both to
		3005	C<0> will save some memory and CPU.
		3006
1880	=item EV_PERIODIC_ENABLE	3007	=item EV_PERIODIC_ENABLE
1881		3008
1882	If undefined or defined to be C<1>, then periodic timers are supported. If	3009	If undefined or defined to be C<1>, then periodic timers are supported. If
1883	defined to be C<0>, then they are not. Disabling them saves a few kB of	3010	defined to be C<0>, then they are not. Disabling them saves a few kB of
1884	code.	3011	code.
1885		3012
		3013	=item EV_IDLE_ENABLE
		3014
		3015	If undefined or defined to be C<1>, then idle watchers are supported. If
		3016	defined to be C<0>, then they are not. Disabling them saves a few kB of
		3017	code.
		3018
1886	=item EV_EMBED_ENABLE	3019	=item EV_EMBED_ENABLE
1887		3020
1888	If undefined or defined to be C<1>, then embed watchers are supported. If	3021	If undefined or defined to be C<1>, then embed watchers are supported. If
1889	defined to be C<0>, then they are not.	3022	defined to be C<0>, then they are not.
1890		3023
1891	=item EV_STAT_ENABLE	3024	=item EV_STAT_ENABLE
1892		3025
1893	If undefined or defined to be C<1>, then stat watchers are supported. If	3026	If undefined or defined to be C<1>, then stat watchers are supported. If
1894	defined to be C<0>, then they are not.	3027	defined to be C<0>, then they are not.
1895		3028
		3029	=item EV_FORK_ENABLE
		3030
		3031	If undefined or defined to be C<1>, then fork watchers are supported. If
		3032	defined to be C<0>, then they are not.
		3033
		3034	=item EV_ASYNC_ENABLE
		3035
		3036	If undefined or defined to be C<1>, then async watchers are supported. If
		3037	defined to be C<0>, then they are not.
		3038
1896	=item EV_MINIMAL	3039	=item EV_MINIMAL
1897		3040
1898	If you need to shave off some kilobytes of code at the expense of some	3041	If you need to shave off some kilobytes of code at the expense of some
1899	speed, define this symbol to C<1>. Currently only used for gcc to override	3042	speed, define this symbol to C<1>. Currently this is used to override some
1900	some inlining decisions, saves roughly 30% codesize of amd64.	3043	inlining decisions, saves roughly 30% code size on amd64. It also selects a
		3044	much smaller 2-heap for timer management over the default 4-heap.
		3045
		3046	=item EV_PID_HASHSIZE
		3047
		3048	C<ev_child> watchers use a small hash table to distribute workload by
		3049	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
		3050	than enough. If you need to manage thousands of children you might want to
		3051	increase this value (I<must> be a power of two).
		3052
		3053	=item EV_INOTIFY_HASHSIZE
		3054
		3055	C<ev_stat> watchers use a small hash table to distribute workload by
		3056	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
		3057	usually more than enough. If you need to manage thousands of C<ev_stat>
		3058	watchers you might want to increase this value (I<must> be a power of
		3059	two).
		3060
		3061	=item EV_USE_4HEAP
		3062
		3063	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3064	timer and periodics heap, libev uses a 4-heap when this symbol is defined
		3065	to C<1>. The 4-heap uses more complicated (longer) code but has
		3066	noticeably faster performance with many (thousands) of watchers.
		3067
		3068	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3069	(disabled).
		3070
		3071	=item EV_HEAP_CACHE_AT
		3072
		3073	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3074	timer and periodics heap, libev can cache the timestamp (I<at>) within
		3075	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		3076	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		3077	but avoids random read accesses on heap changes. This improves performance
		3078	noticeably with with many (hundreds) of watchers.
		3079
		3080	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3081	(disabled).
		3082
		3083	=item EV_VERIFY
		3084
		3085	Controls how much internal verification (see C<ev_loop_verify ()>) will
		3086	be done: If set to C<0>, no internal verification code will be compiled
		3087	in. If set to C<1>, then verification code will be compiled in, but not
		3088	called. If set to C<2>, then the internal verification code will be
		3089	called once per loop, which can slow down libev. If set to C<3>, then the
		3090	verification code will be called very frequently, which will slow down
		3091	libev considerably.
		3092
		3093	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be
		3094	C<0.>
1901		3095
1902	=item EV_COMMON	3096	=item EV_COMMON
1903		3097
1904	By default, all watchers have a C<void *data> member. By redefining	3098	By default, all watchers have a C<void *data> member. By redefining
1905	this macro to a something else you can include more and other types of	3099	this macro to a something else you can include more and other types of
1906	members. You have to define it each time you include one of the files,	3100	members. You have to define it each time you include one of the files,
1907	though, and it must be identical each time.	3101	though, and it must be identical each time.
1908		3102
1909	For example, the perl EV module uses something like this:	3103	For example, the perl EV module uses something like this:
1910		3104
1911	#define EV_COMMON \	3105	#define EV_COMMON \
1912	SV *self; /* contains this struct */ \	3106	SV *self; /* contains this struct */ \
1913	SV *cb_sv, *fh /* note no trailing ";" */	3107	SV *cb_sv, *fh /* note no trailing ";" */
1914		3108
1915	=item EV_CB_DECLARE (type)	3109	=item EV_CB_DECLARE (type)
1916		3110
1917	=item EV_CB_INVOKE (watcher, revents)	3111	=item EV_CB_INVOKE (watcher, revents)
1918		3112
1919	=item ev_set_cb (ev, cb)	3113	=item ev_set_cb (ev, cb)
1920		3114
1921	Can be used to change the callback member declaration in each watcher,	3115	Can be used to change the callback member declaration in each watcher,
1922	and the way callbacks are invoked and set. Must expand to a struct member	3116	and the way callbacks are invoked and set. Must expand to a struct member
1923	definition and a statement, respectively. See the F<ev.v> header file for	3117	definition and a statement, respectively. See the F<ev.h> header file for
1924	their default definitions. One possible use for overriding these is to	3118	their default definitions. One possible use for overriding these is to
1925	avoid the C<struct ev_loop *> as first argument in all cases, or to use	3119	avoid the C<struct ev_loop *> as first argument in all cases, or to use
1926	method calls instead of plain function calls in C++.	3120	method calls instead of plain function calls in C++.
		3121
		3122	=head2 EXPORTED API SYMBOLS
		3123
		3124	If you need to re-export the API (e.g. via a DLL) and you need a list of
		3125	exported symbols, you can use the provided F<Symbol.*> files which list
		3126	all public symbols, one per line:
		3127
		3128	Symbols.ev for libev proper
		3129	Symbols.event for the libevent emulation
		3130
		3131	This can also be used to rename all public symbols to avoid clashes with
		3132	multiple versions of libev linked together (which is obviously bad in
		3133	itself, but sometimes it is inconvenient to avoid this).
		3134
		3135	A sed command like this will create wrapper C<#define>'s that you need to
		3136	include before including F<ev.h>:
		3137
		3138	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		3139
		3140	This would create a file F<wrap.h> which essentially looks like this:
		3141
		3142	#define ev_backend myprefix_ev_backend
		3143	#define ev_check_start myprefix_ev_check_start
		3144	#define ev_check_stop myprefix_ev_check_stop
		3145	...
1927		3146
1928	=head2 EXAMPLES	3147	=head2 EXAMPLES
1929		3148
1930	For a real-world example of a program the includes libev	3149	For a real-world example of a program the includes libev
1931	verbatim, you can have a look at the EV perl module	3150	verbatim, you can have a look at the EV perl module
…		…
1934	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file	3153	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file
1935	will be compiled. It is pretty complex because it provides its own header	3154	will be compiled. It is pretty complex because it provides its own header
1936	file.	3155	file.
1937		3156
1938	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	3157	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
1939	that everybody includes and which overrides some autoconf choices:	3158	that everybody includes and which overrides some configure choices:
1940		3159
		3160	#define EV_MINIMAL 1
1941	#define EV_USE_POLL 0	3161	#define EV_USE_POLL 0
1942	#define EV_MULTIPLICITY 0	3162	#define EV_MULTIPLICITY 0
1943	#define EV_PERIODICS 0	3163	#define EV_PERIODIC_ENABLE 0
		3164	#define EV_STAT_ENABLE 0
		3165	#define EV_FORK_ENABLE 0
1944	#define EV_CONFIG_H <config.h>	3166	#define EV_CONFIG_H <config.h>
		3167	#define EV_MINPRI 0
		3168	#define EV_MAXPRI 0
1945		3169
1946	#include "ev++.h"	3170	#include "ev++.h"
1947		3171
1948	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	3172	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
1949		3173
1950	#include "ev_cpp.h"	3174	#include "ev_cpp.h"
1951	#include "ev.c"	3175	#include "ev.c"
		3176
		3177
		3178	=head1 THREADS AND COROUTINES
		3179
		3180	=head2 THREADS
		3181
		3182	Libev itself is completely thread-safe, but it uses no locking. This
		3183	means that you can use as many loops as you want in parallel, as long as
		3184	only one thread ever calls into one libev function with the same loop
		3185	parameter.
		3186
		3187	Or put differently: calls with different loop parameters can be done in
		3188	parallel from multiple threads, calls with the same loop parameter must be
		3189	done serially (but can be done from different threads, as long as only one
		3190	thread ever is inside a call at any point in time, e.g. by using a mutex
		3191	per loop).
		3192
		3193	If you want to know which design (one loop, locking, or multiple loops
		3194	without or something else still) is best for your problem, then I cannot
		3195	help you. I can give some generic advice however:
		3196
		3197	=over 4
		3198
		3199	=item * most applications have a main thread: use the default libev loop
		3200	in that thread, or create a separate thread running only the default loop.
		3201
		3202	This helps integrating other libraries or software modules that use libev
		3203	themselves and don't care/know about threading.
		3204
		3205	=item * one loop per thread is usually a good model.
		3206
		3207	Doing this is almost never wrong, sometimes a better-performance model
		3208	exists, but it is always a good start.
		3209
		3210	=item * other models exist, such as the leader/follower pattern, where one
		3211	loop is handed through multiple threads in a kind of round-robin fashion.
		3212
		3213	Choosing a model is hard - look around, learn, know that usually you can do
		3214	better than you currently do :-)
		3215
		3216	=item * often you need to talk to some other thread which blocks in the
		3217	event loop - C<ev_async> watchers can be used to wake them up from other
		3218	threads safely (or from signal contexts...).
		3219
		3220	=back
		3221
		3222	=head2 COROUTINES
		3223
		3224	Libev is much more accommodating to coroutines ("cooperative threads"):
		3225	libev fully supports nesting calls to it's functions from different
		3226	coroutines (e.g. you can call C<ev_loop> on the same loop from two
		3227	different coroutines and switch freely between both coroutines running the
		3228	loop, as long as you don't confuse yourself). The only exception is that
		3229	you must not do this from C<ev_periodic> reschedule callbacks.
		3230
		3231	Care has been invested into making sure that libev does not keep local
		3232	state inside C<ev_loop>, and other calls do not usually allow coroutine
		3233	switches.
1952		3234
1953		3235
1954	=head1 COMPLEXITIES	3236	=head1 COMPLEXITIES
1955		3237
1956	In this section the complexities of (many of) the algorithms used inside	3238	In this section the complexities of (many of) the algorithms used inside
1957	libev will be explained. For complexity discussions about backends see the	3239	libev will be explained. For complexity discussions about backends see the
1958	documentation for C<ev_default_init>.	3240	documentation for C<ev_default_init>.
1959		3241
		3242	All of the following are about amortised time: If an array needs to be
		3243	extended, libev needs to realloc and move the whole array, but this
		3244	happens asymptotically never with higher number of elements, so O(1) might
		3245	mean it might do a lengthy realloc operation in rare cases, but on average
		3246	it is much faster and asymptotically approaches constant time.
		3247
1960	=over 4	3248	=over 4
1961		3249
1962	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	3250	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
1963		3251
		3252	This means that, when you have a watcher that triggers in one hour and
		3253	there are 100 watchers that would trigger before that then inserting will
		3254	have to skip roughly seven (C<ld 100>) of these watchers.
		3255
1964	=item Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)	3256	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
1965		3257
		3258	That means that changing a timer costs less than removing/adding them
		3259	as only the relative motion in the event queue has to be paid for.
		3260
1966	=item Starting io/check/prepare/idle/signal/child watchers: O(1)	3261	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
1967		3262
		3263	These just add the watcher into an array or at the head of a list.
		3264
1968	=item Stopping check/prepare/idle watchers: O(1)	3265	=item Stopping check/prepare/idle/fork/async watchers: O(1)
1969		3266
1970	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % 16))	3267	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
1971		3268
		3269	These watchers are stored in lists then need to be walked to find the
		3270	correct watcher to remove. The lists are usually short (you don't usually
		3271	have many watchers waiting for the same fd or signal).
		3272
1972	=item Finding the next timer per loop iteration: O(1)	3273	=item Finding the next timer in each loop iteration: O(1)
		3274
		3275	By virtue of using a binary or 4-heap, the next timer is always found at a
		3276	fixed position in the storage array.
1973		3277
1974	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)	3278	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
1975		3279
1976	=item Activating one watcher: O(1)	3280	A change means an I/O watcher gets started or stopped, which requires
		3281	libev to recalculate its status (and possibly tell the kernel, depending
		3282	on backend and whether C<ev_io_set> was used).
		3283
		3284	=item Activating one watcher (putting it into the pending state): O(1)
		3285
		3286	=item Priority handling: O(number_of_priorities)
		3287
		3288	Priorities are implemented by allocating some space for each
		3289	priority. When doing priority-based operations, libev usually has to
		3290	linearly search all the priorities, but starting/stopping and activating
		3291	watchers becomes O(1) w.r.t. priority handling.
		3292
		3293	=item Sending an ev_async: O(1)
		3294
		3295	=item Processing ev_async_send: O(number_of_async_watchers)
		3296
		3297	=item Processing signals: O(max_signal_number)
		3298
		3299	Sending involves a system call I<iff> there were no other C<ev_async_send>
		3300	calls in the current loop iteration. Checking for async and signal events
		3301	involves iterating over all running async watchers or all signal numbers.
1977		3302
1978	=back	3303	=back
1979		3304
1980		3305
		3306	=head1 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		3307
		3308	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		3309	requires, and its I/O model is fundamentally incompatible with the POSIX
		3310	model. Libev still offers limited functionality on this platform in
		3311	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		3312	descriptors. This only applies when using Win32 natively, not when using
		3313	e.g. cygwin.
		3314
		3315	Lifting these limitations would basically require the full
		3316	re-implementation of the I/O system. If you are into these kinds of
		3317	things, then note that glib does exactly that for you in a very portable
		3318	way (note also that glib is the slowest event library known to man).
		3319
		3320	There is no supported compilation method available on windows except
		3321	embedding it into other applications.
		3322
		3323	Not a libev limitation but worth mentioning: windows apparently doesn't
		3324	accept large writes: instead of resulting in a partial write, windows will
		3325	either accept everything or return C<ENOBUFS> if the buffer is too large,
		3326	so make sure you only write small amounts into your sockets (less than a
		3327	megabyte seems safe, but thsi apparently depends on the amount of memory
		3328	available).
		3329
		3330	Due to the many, low, and arbitrary limits on the win32 platform and
		3331	the abysmal performance of winsockets, using a large number of sockets
		3332	is not recommended (and not reasonable). If your program needs to use
		3333	more than a hundred or so sockets, then likely it needs to use a totally
		3334	different implementation for windows, as libev offers the POSIX readiness
		3335	notification model, which cannot be implemented efficiently on windows
		3336	(Microsoft monopoly games).
		3337
		3338	A typical way to use libev under windows is to embed it (see the embedding
		3339	section for details) and use the following F<evwrap.h> header file instead
		3340	of F<ev.h>:
		3341
		3342	#define EV_STANDALONE /* keeps ev from requiring config.h */
		3343	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		3344
		3345	#include "ev.h"
		3346
		3347	And compile the following F<evwrap.c> file into your project (make sure
		3348	you do I<not> compile the F<ev.c> or any other embedded soruce files!):
		3349
		3350	#include "evwrap.h"
		3351	#include "ev.c"
		3352
		3353	=over 4
		3354
		3355	=item The winsocket select function
		3356
		3357	The winsocket C<select> function doesn't follow POSIX in that it
		3358	requires socket I<handles> and not socket I<file descriptors> (it is
		3359	also extremely buggy). This makes select very inefficient, and also
		3360	requires a mapping from file descriptors to socket handles (the Microsoft
		3361	C runtime provides the function C<_open_osfhandle> for this). See the
		3362	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		3363	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		3364
		3365	The configuration for a "naked" win32 using the Microsoft runtime
		3366	libraries and raw winsocket select is:
		3367
		3368	#define EV_USE_SELECT 1
		3369	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		3370
		3371	Note that winsockets handling of fd sets is O(n), so you can easily get a
		3372	complexity in the O(n²) range when using win32.
		3373
		3374	=item Limited number of file descriptors
		3375
		3376	Windows has numerous arbitrary (and low) limits on things.
		3377
		3378	Early versions of winsocket's select only supported waiting for a maximum
		3379	of C<64> handles (probably owning to the fact that all windows kernels
		3380	can only wait for C<64> things at the same time internally; Microsoft
		3381	recommends spawning a chain of threads and wait for 63 handles and the
		3382	previous thread in each. Great).
		3383
		3384	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		3385	to some high number (e.g. C<2048>) before compiling the winsocket select
		3386	call (which might be in libev or elsewhere, for example, perl does its own
		3387	select emulation on windows).
		3388
		3389	Another limit is the number of file descriptors in the Microsoft runtime
		3390	libraries, which by default is C<64> (there must be a hidden I<64> fetish
		3391	or something like this inside Microsoft). You can increase this by calling
		3392	C<_setmaxstdio>, which can increase this limit to C<2048> (another
		3393	arbitrary limit), but is broken in many versions of the Microsoft runtime
		3394	libraries.
		3395
		3396	This might get you to about C<512> or C<2048> sockets (depending on
		3397	windows version and/or the phase of the moon). To get more, you need to
		3398	wrap all I/O functions and provide your own fd management, but the cost of
		3399	calling select (O(n²)) will likely make this unworkable.
		3400
		3401	=back
		3402
		3403
		3404	=head1 PORTABILITY REQUIREMENTS
		3405
		3406	In addition to a working ISO-C implementation, libev relies on a few
		3407	additional extensions:
		3408
		3409	=over 4
		3410
		3411	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		3412	calling conventions regardless of C<ev_watcher_type *>.
		3413
		3414	Libev assumes not only that all watcher pointers have the same internal
		3415	structure (guaranteed by POSIX but not by ISO C for example), but it also
		3416	assumes that the same (machine) code can be used to call any watcher
		3417	callback: The watcher callbacks have different type signatures, but libev
		3418	calls them using an C<ev_watcher *> internally.
		3419
		3420	=item C<sig_atomic_t volatile> must be thread-atomic as well
		3421
		3422	The type C<sig_atomic_t volatile> (or whatever is defined as
		3423	C<EV_ATOMIC_T>) must be atomic w.r.t. accesses from different
		3424	threads. This is not part of the specification for C<sig_atomic_t>, but is
		3425	believed to be sufficiently portable.
		3426
		3427	=item C<sigprocmask> must work in a threaded environment
		3428
		3429	Libev uses C<sigprocmask> to temporarily block signals. This is not
		3430	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		3431	pthread implementations will either allow C<sigprocmask> in the "main
		3432	thread" or will block signals process-wide, both behaviours would
		3433	be compatible with libev. Interaction between C<sigprocmask> and
		3434	C<pthread_sigmask> could complicate things, however.
		3435
		3436	The most portable way to handle signals is to block signals in all threads
		3437	except the initial one, and run the default loop in the initial thread as
		3438	well.
		3439
		3440	=item C<long> must be large enough for common memory allocation sizes
		3441
		3442	To improve portability and simplify using libev, libev uses C<long>
		3443	internally instead of C<size_t> when allocating its data structures. On
		3444	non-POSIX systems (Microsoft...) this might be unexpectedly low, but
		3445	is still at least 31 bits everywhere, which is enough for hundreds of
		3446	millions of watchers.
		3447
		3448	=item C<double> must hold a time value in seconds with enough accuracy
		3449
		3450	The type C<double> is used to represent timestamps. It is required to
		3451	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
		3452	enough for at least into the year 4000. This requirement is fulfilled by
		3453	implementations implementing IEEE 754 (basically all existing ones).
		3454
		3455	=back
		3456
		3457	If you know of other additional requirements drop me a note.
		3458
		3459
		3460	=head1 COMPILER WARNINGS
		3461
		3462	Depending on your compiler and compiler settings, you might get no or a
		3463	lot of warnings when compiling libev code. Some people are apparently
		3464	scared by this.
		3465
		3466	However, these are unavoidable for many reasons. For one, each compiler
		3467	has different warnings, and each user has different tastes regarding
		3468	warning options. "Warn-free" code therefore cannot be a goal except when
		3469	targeting a specific compiler and compiler-version.
		3470
		3471	Another reason is that some compiler warnings require elaborate
		3472	workarounds, or other changes to the code that make it less clear and less
		3473	maintainable.
		3474
		3475	And of course, some compiler warnings are just plain stupid, or simply
		3476	wrong (because they don't actually warn about the condition their message
		3477	seems to warn about).
		3478
		3479	While libev is written to generate as few warnings as possible,
		3480	"warn-free" code is not a goal, and it is recommended not to build libev
		3481	with any compiler warnings enabled unless you are prepared to cope with
		3482	them (e.g. by ignoring them). Remember that warnings are just that:
		3483	warnings, not errors, or proof of bugs.
		3484
		3485
		3486	=head1 VALGRIND
		3487
		3488	Valgrind has a special section here because it is a popular tool that is
		3489	highly useful, but valgrind reports are very hard to interpret.
		3490
		3491	If you think you found a bug (memory leak, uninitialised data access etc.)
		3492	in libev, then check twice: If valgrind reports something like:
		3493
		3494	==2274== definitely lost: 0 bytes in 0 blocks.
		3495	==2274== possibly lost: 0 bytes in 0 blocks.
		3496	==2274== still reachable: 256 bytes in 1 blocks.
		3497
		3498	Then there is no memory leak. Similarly, under some circumstances,
		3499	valgrind might report kernel bugs as if it were a bug in libev, or it
		3500	might be confused (it is a very good tool, but only a tool).
		3501
		3502	If you are unsure about something, feel free to contact the mailing list
		3503	with the full valgrind report and an explanation on why you think this is
		3504	a bug in libev. However, don't be annoyed when you get a brisk "this is
		3505	no bug" answer and take the chance of learning how to interpret valgrind
		3506	properly.
		3507
		3508	If you need, for some reason, empty reports from valgrind for your project
		3509	I suggest using suppression lists.
		3510
		3511
1981	=head1 AUTHOR	3512	=head1 AUTHOR
1982		3513
1983	Marc Lehmann <libev@schmorp.de>.	3514	Marc Lehmann <libev@schmorp.de>.
1984		3515

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