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…		…
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	#include <ev.h>	7	#include <ev.h>
8		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	}
		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://cvs.schmorp.de/libev/ev.html>.
		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 floatingpoint value. Unlike the name
52		119	component C<stamp> might indicate, it is also used for time differences
		120	throughout libev.
53		121
54	=head1 GLOBAL FUNCTIONS	122	=head1 GLOBAL FUNCTIONS
55		123
56	These functions can be called anytime, even before initialising the	124	These functions can be called anytime, even before initialising the
57	library in any way.	125	library in any way.
…		…
62		130
63	Returns the current time as libev would use it. Please note that the	131	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	132	C<ev_now> function is usually faster and also often returns the timestamp
65	you actually want to know.	133	you actually want to know.
66		134
		135	=item ev_sleep (ev_tstamp interval)
		136
		137	Sleep for the given interval: The current thread will be blocked until
		138	either it is interrupted or the given time interval has passed. Basically
		139	this is a subsecond-resolution C<sleep ()>.
		140
67	=item int ev_version_major ()	141	=item int ev_version_major ()
68		142
69	=item int ev_version_minor ()	143	=item int ev_version_minor ()
70		144
71	You can find out the major and minor version numbers of the library	145	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	146	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	147	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	148	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the
75	version of the library your program was compiled against.	149	version of the library your program was compiled against.
76		150
		151	These version numbers refer to the ABI version of the library, not the
		152	release version.
		153
77	Usually, it's a good idea to terminate if the major versions mismatch,	154	Usually, it's a good idea to terminate if the major versions mismatch,
78	as this indicates an incompatible change. Minor versions are usually	155	as this indicates an incompatible change. Minor versions are usually
79	compatible to older versions, so a larger minor version alone is usually	156	compatible to older versions, so a larger minor version alone is usually
80	not a problem.	157	not a problem.
81		158
82	Example: make sure we haven't accidentally been linked against the wrong	159	Example: Make sure we haven't accidentally been linked against the wrong
83	version:	160	version.
84		161
85	assert (("libev version mismatch",	162	assert (("libev version mismatch",
86	ev_version_major () == EV_VERSION_MAJOR	163	ev_version_major () == EV_VERSION_MAJOR
87	&& ev_version_minor () >= EV_VERSION_MINOR));	164	&& ev_version_minor () >= EV_VERSION_MINOR));
88		165
…		…
118		195
119	See the description of C<ev_embed> watchers for more info.	196	See the description of C<ev_embed> watchers for more info.
120		197
121	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	198	=item ev_set_allocator (void *(*cb)(void *ptr, long size))
122		199
123	Sets the allocation function to use (the prototype is similar to the	200	Sets the allocation function to use (the prototype is similar - the
124	realloc C function, the semantics are identical). It is used to allocate	201	semantics is identical - to the realloc C function). It is used to
125	and free memory (no surprises here). If it returns zero when memory	202	allocate and free memory (no surprises here). If it returns zero when
126	needs to be allocated, the library might abort or take some potentially	203	memory needs to be allocated, the library might abort or take some
127	destructive action. The default is your system realloc function.	204	potentially destructive action. The default is your system realloc
		205	function.
128		206
129	You could override this function in high-availability programs to, say,	207	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,	208	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.	209	or even to sleep a while and retry until some memory is available.
132		210
133	Example: replace the libev allocator with one that waits a bit and then	211	Example: Replace the libev allocator with one that waits a bit and then
134	retries: better than mine).	212	retries).
135		213
136	static void *	214	static void *
137	persistent_realloc (void *ptr, long size)	215	persistent_realloc (void *ptr, size_t size)
138	{	216	{
139	for (;;)	217	for (;;)
140	{	218	{
141	void *newptr = realloc (ptr, size);	219	void *newptr = realloc (ptr, size);
142		220
…		…
158	callback is set, then libev will expect it to remedy the sitution, no	236	callback is set, then libev will expect it to remedy the sitution, no
159	matter what, when it returns. That is, libev will generally retry the	237	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	238	requested operation, or, if the condition doesn't go away, do bad stuff
161	(such as abort).	239	(such as abort).
162		240
163	Example: do the same thing as libev does internally:	241	Example: This is basically the same thing that libev does internally, too.
164		242
165	static void	243	static void
166	fatal_error (const char *msg)	244	fatal_error (const char *msg)
167	{	245	{
168	perror (msg);	246	perror (msg);
…		…
197	flags. If that is troubling you, check C<ev_backend ()> afterwards).	275	flags. If that is troubling you, check C<ev_backend ()> afterwards).
198		276
199	If you don't know what event loop to use, use the one returned from this	277	If you don't know what event loop to use, use the one returned from this
200	function.	278	function.
201		279
		280	The default loop is the only loop that can handle C<ev_signal> and
		281	C<ev_child> watchers, and to do this, it always registers a handler
		282	for C<SIGCHLD>. If this is a problem for your app you can either
		283	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you
		284	can simply overwrite the C<SIGCHLD> signal handler I<after> calling
		285	C<ev_default_init>.
		286
202	The flags argument can be used to specify special behaviour or specific	287	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>).	288	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
204		289
205	The following flags are supported:	290	The following flags are supported:
206		291
…		…
218	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	303	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
219	override the flags completely if it is found in the environment. This is	304	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	305	useful to try out specific backends to test their performance, or to work
221	around bugs.	306	around bugs.
222		307
		308	=item C<EVFLAG_FORKCHECK>
		309
		310	Instead of calling C<ev_default_fork> or C<ev_loop_fork> manually after
		311	a fork, you can also make libev check for a fork in each iteration by
		312	enabling this flag.
		313
		314	This works by calling C<getpid ()> on every iteration of the loop,
		315	and thus this might slow down your event loop if you do a lot of loop
		316	iterations and little real work, but is usually not noticeable (on my
		317	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence
		318	without a syscall and thus I<very> fast, but my GNU/Linux system also has
		319	C<pthread_atfork> which is even faster).
		320
		321	The big advantage of this flag is that you can forget about fork (and
		322	forget about forgetting to tell libev about forking) when you use this
		323	flag.
		324
		325	This flag setting cannot be overriden or specified in the C<LIBEV_FLAGS>
		326	environment variable.
		327
223	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	328	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
224		329
225	This is your standard select(2) backend. Not I<completely> standard, as	330	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,	331	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	332	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	333	using this backend. It doesn't scale too well (O(highest_fd)), but its
229	the fastest backend for a low number of fds.	334	usually the fastest backend for a low number of (low-numbered :) fds.
		335
		336	To get good performance out of this backend you need a high amount of
		337	parallelity (most of the file descriptors should be busy). If you are
		338	writing a server, you should C<accept ()> in a loop to accept as many
		339	connections as possible during one iteration. You might also want to have
		340	a look at C<ev_set_io_collect_interval ()> to increase the amount of
		341	readyness notifications you get per iteration.
230		342
231	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)	343	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
232		344
233	And this is your standard poll(2) backend. It's more complicated than	345	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	346	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	347	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).	348	considerably with a lot of inactive fds). It scales similarly to select,
		349	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
		350	performance tips.
237		351
238	=item C<EVBACKEND_EPOLL> (value 4, Linux)	352	=item C<EVBACKEND_EPOLL> (value 4, Linux)
239		353
240	For few fds, this backend is a bit little slower than poll and select,	354	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	355	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	356	like O(total_fds) where n is the total number of fds (or the highest fd),
243	either O(1) or O(active_fds).	357	epoll scales either O(1) or O(active_fds). The epoll design has a number
		358	of shortcomings, such as silently dropping events in some hard-to-detect
		359	cases and rewiring a syscall per fd change, no fork support and bad
		360	support for dup.
244		361
245	While stopping and starting an I/O watcher in the same iteration will	362	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	363	will result in some caching, there is still a syscall per such incident
247	(because the fd could point to a different file description now), so its	364	(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	365	best to avoid that. Also, C<dup ()>'ed file descriptors might not work
249	well if you register events for both fds.	366	very well if you register events for both fds.
250		367
251	Please note that epoll sometimes generates spurious notifications, so you	368	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	369	need to use non-blocking I/O or other means to avoid blocking when no data
253	(or space) is available.	370	(or space) is available.
254		371
		372	Best performance from this backend is achieved by not unregistering all
		373	watchers for a file descriptor until it has been closed, if possible, i.e.
		374	keep at least one watcher active per fd at all times.
		375
		376	While nominally embeddeble in other event loops, this feature is broken in
		377	all kernel versions tested so far.
		378
255	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	379	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
256		380
257	Kqueue deserves special mention, as at the time of this writing, it	381	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	382	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	383	with anything but sockets and pipes, except on Darwin, where of course
260	completely useless). For this reason its not being "autodetected"	384	it's completely useless). For this reason it's not being "autodetected"
261	unless you explicitly specify it explicitly in the flags (i.e. using	385	unless you explicitly specify it explicitly in the flags (i.e. using
262	C<EVBACKEND_KQUEUE>).	386	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
		387	system like NetBSD.
		388
		389	You still can embed kqueue into a normal poll or select backend and use it
		390	only for sockets (after having made sure that sockets work with kqueue on
		391	the target platform). See C<ev_embed> watchers for more info.
263		392
264	It scales in the same way as the epoll backend, but the interface to the	393	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	394	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	395	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	396	cause an extra syscall as with C<EVBACKEND_EPOLL>, it still adds up to
268	incident, so its best to avoid that.	397	two event changes per incident, support for C<fork ()> is very bad and it
		398	drops fds silently in similarly hard-to-detect cases.
		399
		400	This backend usually performs well under most conditions.
		401
		402	While nominally embeddable in other event loops, this doesn't work
		403	everywhere, so you might need to test for this. And since it is broken
		404	almost everywhere, you should only use it when you have a lot of sockets
		405	(for which it usually works), by embedding it into another event loop
		406	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>) and using it only for
		407	sockets.
269		408
270	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	409	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
271		410
272	This is not implemented yet (and might never be).	411	This is not implemented yet (and might never be, unless you send me an
		412	implementation). According to reports, C</dev/poll> only supports sockets
		413	and is not embeddable, which would limit the usefulness of this backend
		414	immensely.
273		415
274	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	416	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
275		417
276	This uses the Solaris 10 port mechanism. As with everything on Solaris,	418	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)).	419	it's really slow, but it still scales very well (O(active_fds)).
278		420
279	Please note that solaris ports can result in a lot of spurious	421	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	422	notifications, so you need to use non-blocking I/O or other means to avoid
281	blocking when no data (or space) is available.	423	blocking when no data (or space) is available.
		424
		425	While this backend scales well, it requires one system call per active
		426	file descriptor per loop iteration. For small and medium numbers of file
		427	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
		428	might perform better.
		429
		430	On the positive side, ignoring the spurious readyness notifications, this
		431	backend actually performed to specification in all tests and is fully
		432	embeddable, which is a rare feat among the OS-specific backends.
282		433
283	=item C<EVBACKEND_ALL>	434	=item C<EVBACKEND_ALL>
284		435
285	Try all backends (even potentially broken ones that wouldn't be tried	436	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	437	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
287	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	438	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
288		439
		440	It is definitely not recommended to use this flag.
		441
289	=back	442	=back
290		443
291	If one or more of these are ored into the flags value, then only these	444	If one or more of these are ored into the flags value, then only these
292	backends will be tried (in the reverse order as given here). If none are	445	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	446	specified, all backends in C<ev_recommended_backends ()> will be tried.
294	order of their flag values :)
295		447
296	The most typical usage is like this:	448	The most typical usage is like this:
297		449
298	if (!ev_default_loop (0))	450	if (!ev_default_loop (0))
299	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");	451	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
…		…
314	Similar to C<ev_default_loop>, but always creates a new event loop that is	466	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	467	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	468	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).	469	undefined behaviour (or a failed assertion if assertions are enabled).
318		470
319	Example: try to create a event loop that uses epoll and nothing else.	471	Example: Try to create a event loop that uses epoll and nothing else.
320		472
321	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	473	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
322	if (!epoller)	474	if (!epoller)
323	fatal ("no epoll found here, maybe it hides under your chair");	475	fatal ("no epoll found here, maybe it hides under your chair");
324		476
325	=item ev_default_destroy ()	477	=item ev_default_destroy ()
326		478
327	Destroys the default loop again (frees all memory and kernel state	479	Destroys the default loop again (frees all memory and kernel state
328	etc.). This stops all registered event watchers (by not touching them in	480	etc.). None of the active event watchers will be stopped in the normal
329	any way whatsoever, although you cannot rely on this :).	481	sense, so e.g. C<ev_is_active> might still return true. It is your
		482	responsibility to either stop all watchers cleanly yoursef I<before>
		483	calling this function, or cope with the fact afterwards (which is usually
		484	the easiest thing, you can just ignore the watchers and/or C<free ()> them
		485	for example).
		486
		487	Note that certain global state, such as signal state, will not be freed by
		488	this function, and related watchers (such as signal and child watchers)
		489	would need to be stopped manually.
		490
		491	In general it is not advisable to call this function except in the
		492	rare occasion where you really need to free e.g. the signal handling
		493	pipe fds. If you need dynamically allocated loops it is better to use
		494	C<ev_loop_new> and C<ev_loop_destroy>).
330		495
331	=item ev_loop_destroy (loop)	496	=item ev_loop_destroy (loop)
332		497
333	Like C<ev_default_destroy>, but destroys an event loop created by an	498	Like C<ev_default_destroy>, but destroys an event loop created by an
334	earlier call to C<ev_loop_new>.	499	earlier call to C<ev_loop_new>.
335		500
336	=item ev_default_fork ()	501	=item ev_default_fork ()
337		502
		503	This function sets a flag that causes subsequent C<ev_loop> iterations
338	This function reinitialises the kernel state for backends that have	504	to reinitialise the kernel state for backends that have one. Despite the
339	one. Despite the name, you can call it anytime, but it makes most sense	505	name, you can call it anytime, but it makes most sense after forking, in
340	after forking, in either the parent or child process (or both, but that	506	the child process (or both child and parent, but that again makes little
341	again makes little sense).	507	sense). You I<must> call it in the child before using any of the libev
		508	functions, and it will only take effect at the next C<ev_loop> iteration.
342		509
343	You I<must> call this function in the child process after forking if and	510	On the other hand, you only need to call this function in the child
344	only if you want to use the event library in both processes. If you just	511	process if and only if you want to use the event library in the child. If
345	fork+exec, you don't have to call it.	512	you just fork+exec, you don't have to call it at all.
346		513
347	The function itself is quite fast and it's usually not a problem to call	514	The function itself is quite fast and it's usually not a problem to call
348	it just in case after a fork. To make this easy, the function will fit in	515	it just in case after a fork. To make this easy, the function will fit in
349	quite nicely into a call to C<pthread_atfork>:	516	quite nicely into a call to C<pthread_atfork>:
350		517
351	pthread_atfork (0, 0, ev_default_fork);	518	pthread_atfork (0, 0, ev_default_fork);
352		519
353	At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> are safe to use
354	without calling this function, so if you force one of those backends you
355	do not need to care.
356
357	=item ev_loop_fork (loop)	520	=item ev_loop_fork (loop)
358		521
359	Like C<ev_default_fork>, but acts on an event loop created by	522	Like C<ev_default_fork>, but acts on an event loop created by
360	C<ev_loop_new>. Yes, you have to call this on every allocated event loop	523	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
361	after fork, and how you do this is entirely your own problem.	524	after fork, and how you do this is entirely your own problem.
		525
		526	=item int ev_is_default_loop (loop)
		527
		528	Returns true when the given loop actually is the default loop, false otherwise.
		529
		530	=item unsigned int ev_loop_count (loop)
		531
		532	Returns the count of loop iterations for the loop, which is identical to
		533	the number of times libev did poll for new events. It starts at C<0> and
		534	happily wraps around with enough iterations.
		535
		536	This value can sometimes be useful as a generation counter of sorts (it
		537	"ticks" the number of loop iterations), as it roughly corresponds with
		538	C<ev_prepare> and C<ev_check> calls.
362		539
363	=item unsigned int ev_backend (loop)	540	=item unsigned int ev_backend (loop)
364		541
365	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	542	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
366	use.	543	use.
…		…
369		546
370	Returns the current "event loop time", which is the time the event loop	547	Returns the current "event loop time", which is the time the event loop
371	received events and started processing them. This timestamp does not	548	received events and started processing them. This timestamp does not
372	change as long as callbacks are being processed, and this is also the base	549	change as long as callbacks are being processed, and this is also the base
373	time used for relative timers. You can treat it as the timestamp of the	550	time used for relative timers. You can treat it as the timestamp of the
374	event occuring (or more correctly, libev finding out about it).	551	event occurring (or more correctly, libev finding out about it).
375		552
376	=item ev_loop (loop, int flags)	553	=item ev_loop (loop, int flags)
377		554
378	Finally, this is it, the event handler. This function usually is called	555	Finally, this is it, the event handler. This function usually is called
379	after you initialised all your watchers and you want to start handling	556	after you initialised all your watchers and you want to start handling
…		…
400	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is	577	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is
401	usually a better approach for this kind of thing.	578	usually a better approach for this kind of thing.
402		579
403	Here are the gory details of what C<ev_loop> does:	580	Here are the gory details of what C<ev_loop> does:
404		581
405	* If there are no active watchers (reference count is zero), return.	582	- Before the first iteration, call any pending watchers.
406	- Queue prepare watchers and then call all outstanding watchers.	583	* If EVFLAG_FORKCHECK was used, check for a fork.
		584	- If a fork was detected, queue and call all fork watchers.
		585	- Queue and call all prepare watchers.
407	- If we have been forked, recreate the kernel state.	586	- If we have been forked, recreate the kernel state.
408	- Update the kernel state with all outstanding changes.	587	- Update the kernel state with all outstanding changes.
409	- Update the "event loop time".	588	- Update the "event loop time".
410	- Calculate for how long to block.	589	- Calculate for how long to sleep or block, if at all
		590	(active idle watchers, EVLOOP_NONBLOCK or not having
		591	any active watchers at all will result in not sleeping).
		592	- Sleep if the I/O and timer collect interval say so.
411	- Block the process, waiting for any events.	593	- Block the process, waiting for any events.
412	- Queue all outstanding I/O (fd) events.	594	- Queue all outstanding I/O (fd) events.
413	- Update the "event loop time" and do time jump handling.	595	- Update the "event loop time" and do time jump handling.
414	- Queue all outstanding timers.	596	- Queue all outstanding timers.
415	- Queue all outstanding periodics.	597	- Queue all outstanding periodics.
416	- If no events are pending now, queue all idle watchers.	598	- If no events are pending now, queue all idle watchers.
417	- Queue all check watchers.	599	- Queue all check watchers.
418	- Call all queued watchers in reverse order (i.e. check watchers first).	600	- Call all queued watchers in reverse order (i.e. check watchers first).
419	Signals and child watchers are implemented as I/O watchers, and will	601	Signals and child watchers are implemented as I/O watchers, and will
420	be handled here by queueing them when their watcher gets executed.	602	be handled here by queueing them when their watcher gets executed.
421	- If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	603	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
422	were used, return, otherwise continue with step *.	604	were used, or there are no active watchers, return, otherwise
		605	continue with step *.
423		606
424	Example: queue some jobs and then loop until no events are outsanding	607	Example: Queue some jobs and then loop until no events are outstanding
425	anymore.	608	anymore.
426		609
427	... queue jobs here, make sure they register event watchers as long	610	... queue jobs here, make sure they register event watchers as long
428	... as they still have work to do (even an idle watcher will do..)	611	... as they still have work to do (even an idle watcher will do..)
429	ev_loop (my_loop, 0);	612	ev_loop (my_loop, 0);
…		…
433		616
434	Can be used to make a call to C<ev_loop> return early (but only after it	617	Can be used to make a call to C<ev_loop> return early (but only after it
435	has processed all outstanding events). The C<how> argument must be either	618	has processed all outstanding events). The C<how> argument must be either
436	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	619	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
437	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	620	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
		621
		622	This "unloop state" will be cleared when entering C<ev_loop> again.
438		623
439	=item ev_ref (loop)	624	=item ev_ref (loop)
440		625
441	=item ev_unref (loop)	626	=item ev_unref (loop)
442		627
…		…
447	returning, ev_unref() after starting, and ev_ref() before stopping it. For	632	returning, ev_unref() after starting, and ev_ref() before stopping it. For
448	example, libev itself uses this for its internal signal pipe: It is not	633	example, libev itself uses this for its internal signal pipe: It is not
449	visible to the libev user and should not keep C<ev_loop> from exiting if	634	visible to the libev user and should not keep C<ev_loop> from exiting if
450	no event watchers registered by it are active. It is also an excellent	635	no event watchers registered by it are active. It is also an excellent
451	way to do this for generic recurring timers or from within third-party	636	way to do this for generic recurring timers or from within third-party
452	libraries. Just remember to I<unref after start> and I<ref before stop>.	637	libraries. Just remember to I<unref after start> and I<ref before stop>
		638	(but only if the watcher wasn't active before, or was active before,
		639	respectively).
453		640
454	Example: create a signal watcher, but keep it from keeping C<ev_loop>	641	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
455	running when nothing else is active.	642	running when nothing else is active.
456		643
457	struct dv_signal exitsig;	644	struct ev_signal exitsig;
458	ev_signal_init (&exitsig, sig_cb, SIGINT);	645	ev_signal_init (&exitsig, sig_cb, SIGINT);
459	ev_signal_start (myloop, &exitsig);	646	ev_signal_start (loop, &exitsig);
460	evf_unref (myloop);	647	evf_unref (loop);
461		648
462	Example: for some weird reason, unregister the above signal handler again.	649	Example: For some weird reason, unregister the above signal handler again.
463		650
464	ev_ref (myloop);	651	ev_ref (loop);
465	ev_signal_stop (myloop, &exitsig);	652	ev_signal_stop (loop, &exitsig);
		653
		654	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
		655
		656	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
		657
		658	These advanced functions influence the time that libev will spend waiting
		659	for events. Both are by default C<0>, meaning that libev will try to
		660	invoke timer/periodic callbacks and I/O callbacks with minimum latency.
		661
		662	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
		663	allows libev to delay invocation of I/O and timer/periodic callbacks to
		664	increase efficiency of loop iterations.
		665
		666	The background is that sometimes your program runs just fast enough to
		667	handle one (or very few) event(s) per loop iteration. While this makes
		668	the program responsive, it also wastes a lot of CPU time to poll for new
		669	events, especially with backends like C<select ()> which have a high
		670	overhead for the actual polling but can deliver many events at once.
		671
		672	By setting a higher I<io collect interval> you allow libev to spend more
		673	time collecting I/O events, so you can handle more events per iteration,
		674	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
		675	C<ev_timer>) will be not affected. Setting this to a non-null value will
		676	introduce an additional C<ev_sleep ()> call into most loop iterations.
		677
		678	Likewise, by setting a higher I<timeout collect interval> you allow libev
		679	to spend more time collecting timeouts, at the expense of increased
		680	latency (the watcher callback will be called later). C<ev_io> watchers
		681	will not be affected. Setting this to a non-null value will not introduce
		682	any overhead in libev.
		683
		684	Many (busy) programs can usually benefit by setting the io collect
		685	interval to a value near C<0.1> or so, which is often enough for
		686	interactive servers (of course not for games), likewise for timeouts. It
		687	usually doesn't make much sense to set it to a lower value than C<0.01>,
		688	as this approsaches the timing granularity of most systems.
466		689
467	=back	690	=back
		691
468		692
469	=head1 ANATOMY OF A WATCHER	693	=head1 ANATOMY OF A WATCHER
470		694
471	A watcher is a structure that you create and register to record your	695	A watcher is a structure that you create and register to record your
472	interest in some event. For instance, if you want to wait for STDIN to	696	interest in some event. For instance, if you want to wait for STDIN to
…		…
505	*) >>), and you can stop watching for events at any time by calling the	729	*) >>), and you can stop watching for events at any time by calling the
506	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	730	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.
507		731
508	As long as your watcher is active (has been started but not stopped) you	732	As long as your watcher is active (has been started but not stopped) you
509	must not touch the values stored in it. Most specifically you must never	733	must not touch the values stored in it. Most specifically you must never
510	reinitialise it or call its set macro.	734	reinitialise it or call its C<set> macro.
511
512	You can check whether an event is active by calling the C<ev_is_active
513	(watcher *)> macro. To see whether an event is outstanding (but the
514	callback for it has not been called yet) you can use the C<ev_is_pending
515	(watcher *)> macro.
516		735
517	Each and every callback receives the event loop pointer as first, the	736	Each and every callback receives the event loop pointer as first, the
518	registered watcher structure as second, and a bitset of received events as	737	registered watcher structure as second, and a bitset of received events as
519	third argument.	738	third argument.
520		739
…		…
544	The signal specified in the C<ev_signal> watcher has been received by a thread.	763	The signal specified in the C<ev_signal> watcher has been received by a thread.
545		764
546	=item C<EV_CHILD>	765	=item C<EV_CHILD>
547		766
548	The pid specified in the C<ev_child> watcher has received a status change.	767	The pid specified in the C<ev_child> watcher has received a status change.
		768
		769	=item C<EV_STAT>
		770
		771	The path specified in the C<ev_stat> watcher changed its attributes somehow.
549		772
550	=item C<EV_IDLE>	773	=item C<EV_IDLE>
551		774
552	The C<ev_idle> watcher has determined that you have nothing better to do.	775	The C<ev_idle> watcher has determined that you have nothing better to do.
553		776
…		…
561	received events. Callbacks of both watcher types can start and stop as	784	received events. Callbacks of both watcher types can start and stop as
562	many watchers as they want, and all of them will be taken into account	785	many watchers as they want, and all of them will be taken into account
563	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	786	(for example, a C<ev_prepare> watcher might start an idle watcher to keep
564	C<ev_loop> from blocking).	787	C<ev_loop> from blocking).
565		788
		789	=item C<EV_EMBED>
		790
		791	The embedded event loop specified in the C<ev_embed> watcher needs attention.
		792
		793	=item C<EV_FORK>
		794
		795	The event loop has been resumed in the child process after fork (see
		796	C<ev_fork>).
		797
		798	=item C<EV_ASYNC>
		799
		800	The given async watcher has been asynchronously notified (see C<ev_async>).
		801
566	=item C<EV_ERROR>	802	=item C<EV_ERROR>
567		803
568	An unspecified error has occured, the watcher has been stopped. This might	804	An unspecified error has occured, the watcher has been stopped. This might
569	happen because the watcher could not be properly started because libev	805	happen because the watcher could not be properly started because libev
570	ran out of memory, a file descriptor was found to be closed or any other	806	ran out of memory, a file descriptor was found to be closed or any other
…		…
576	your callbacks is well-written it can just attempt the operation and cope	812	your callbacks is well-written it can just attempt the operation and cope
577	with the error from read() or write(). This will not work in multithreaded	813	with the error from read() or write(). This will not work in multithreaded
578	programs, though, so beware.	814	programs, though, so beware.
579		815
580	=back	816	=back
		817
		818	=head2 GENERIC WATCHER FUNCTIONS
		819
		820	In the following description, C<TYPE> stands for the watcher type,
		821	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
		822
		823	=over 4
		824
		825	=item C<ev_init> (ev_TYPE *watcher, callback)
		826
		827	This macro initialises the generic portion of a watcher. The contents
		828	of the watcher object can be arbitrary (so C<malloc> will do). Only
		829	the generic parts of the watcher are initialised, you I<need> to call
		830	the type-specific C<ev_TYPE_set> macro afterwards to initialise the
		831	type-specific parts. For each type there is also a C<ev_TYPE_init> macro
		832	which rolls both calls into one.
		833
		834	You can reinitialise a watcher at any time as long as it has been stopped
		835	(or never started) and there are no pending events outstanding.
		836
		837	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,
		838	int revents)>.
		839
		840	=item C<ev_TYPE_set> (ev_TYPE *, [args])
		841
		842	This macro initialises the type-specific parts of a watcher. You need to
		843	call C<ev_init> at least once before you call this macro, but you can
		844	call C<ev_TYPE_set> any number of times. You must not, however, call this
		845	macro on a watcher that is active (it can be pending, however, which is a
		846	difference to the C<ev_init> macro).
		847
		848	Although some watcher types do not have type-specific arguments
		849	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
		850
		851	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
		852
		853	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
		854	calls into a single call. This is the most convinient method to initialise
		855	a watcher. The same limitations apply, of course.
		856
		857	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)
		858
		859	Starts (activates) the given watcher. Only active watchers will receive
		860	events. If the watcher is already active nothing will happen.
		861
		862	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)
		863
		864	Stops the given watcher again (if active) and clears the pending
		865	status. It is possible that stopped watchers are pending (for example,
		866	non-repeating timers are being stopped when they become pending), but
		867	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If
		868	you want to free or reuse the memory used by the watcher it is therefore a
		869	good idea to always call its C<ev_TYPE_stop> function.
		870
		871	=item bool ev_is_active (ev_TYPE *watcher)
		872
		873	Returns a true value iff the watcher is active (i.e. it has been started
		874	and not yet been stopped). As long as a watcher is active you must not modify
		875	it.
		876
		877	=item bool ev_is_pending (ev_TYPE *watcher)
		878
		879	Returns a true value iff the watcher is pending, (i.e. it has outstanding
		880	events but its callback has not yet been invoked). As long as a watcher
		881	is pending (but not active) you must not call an init function on it (but
		882	C<ev_TYPE_set> is safe), you must not change its priority, and you must
		883	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		884	it).
		885
		886	=item callback ev_cb (ev_TYPE *watcher)
		887
		888	Returns the callback currently set on the watcher.
		889
		890	=item ev_cb_set (ev_TYPE *watcher, callback)
		891
		892	Change the callback. You can change the callback at virtually any time
		893	(modulo threads).
		894
		895	=item ev_set_priority (ev_TYPE *watcher, priority)
		896
		897	=item int ev_priority (ev_TYPE *watcher)
		898
		899	Set and query the priority of the watcher. The priority is a small
		900	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
		901	(default: C<-2>). Pending watchers with higher priority will be invoked
		902	before watchers with lower priority, but priority will not keep watchers
		903	from being executed (except for C<ev_idle> watchers).
		904
		905	This means that priorities are I<only> used for ordering callback
		906	invocation after new events have been received. This is useful, for
		907	example, to reduce latency after idling, or more often, to bind two
		908	watchers on the same event and make sure one is called first.
		909
		910	If you need to suppress invocation when higher priority events are pending
		911	you need to look at C<ev_idle> watchers, which provide this functionality.
		912
		913	You I<must not> change the priority of a watcher as long as it is active or
		914	pending.
		915
		916	The default priority used by watchers when no priority has been set is
		917	always C<0>, which is supposed to not be too high and not be too low :).
		918
		919	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		920	fine, as long as you do not mind that the priority value you query might
		921	or might not have been adjusted to be within valid range.
		922
		923	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		924
		925	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		926	C<loop> nor C<revents> need to be valid as long as the watcher callback
		927	can deal with that fact.
		928
		929	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		930
		931	If the watcher is pending, this function returns clears its pending status
		932	and returns its C<revents> bitset (as if its callback was invoked). If the
		933	watcher isn't pending it does nothing and returns C<0>.
		934
		935	=back
		936
581		937
582	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	938	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
583		939
584	Each watcher has, by default, a member C<void *data> that you can change	940	Each watcher has, by default, a member C<void *data> that you can change
585	and read at any time, libev will completely ignore it. This can be used	941	and read at any time, libev will completely ignore it. This can be used
…		…
603	{	959	{
604	struct my_io *w = (struct my_io *)w_;	960	struct my_io *w = (struct my_io *)w_;
605	...	961	...
606	}	962	}
607		963
608	More interesting and less C-conformant ways of catsing your callback type	964	More interesting and less C-conformant ways of casting your callback type
609	have been omitted....	965	instead have been omitted.
		966
		967	Another common scenario is having some data structure with multiple
		968	watchers:
		969
		970	struct my_biggy
		971	{
		972	int some_data;
		973	ev_timer t1;
		974	ev_timer t2;
		975	}
		976
		977	In this case getting the pointer to C<my_biggy> is a bit more complicated,
		978	you need to use C<offsetof>:
		979
		980	#include <stddef.h>
		981
		982	static void
		983	t1_cb (EV_P_ struct ev_timer *w, int revents)
		984	{
		985	struct my_biggy big = (struct my_biggy *
		986	(((char *)w) - offsetof (struct my_biggy, t1));
		987	}
		988
		989	static void
		990	t2_cb (EV_P_ struct ev_timer *w, int revents)
		991	{
		992	struct my_biggy big = (struct my_biggy *
		993	(((char *)w) - offsetof (struct my_biggy, t2));
		994	}
610		995
611		996
612	=head1 WATCHER TYPES	997	=head1 WATCHER TYPES
613		998
614	This section describes each watcher in detail, but will not repeat	999	This section describes each watcher in detail, but will not repeat
615	information given in the last section.	1000	information given in the last section. Any initialisation/set macros,
		1001	functions and members specific to the watcher type are explained.
616		1002
		1003	Members are additionally marked with either I<[read-only]>, meaning that,
		1004	while the watcher is active, you can look at the member and expect some
		1005	sensible content, but you must not modify it (you can modify it while the
		1006	watcher is stopped to your hearts content), or I<[read-write]>, which
		1007	means you can expect it to have some sensible content while the watcher
		1008	is active, but you can also modify it. Modifying it may not do something
		1009	sensible or take immediate effect (or do anything at all), but libev will
		1010	not crash or malfunction in any way.
617		1011
		1012
618	=head2 C<ev_io> - is this file descriptor readable or writable	1013	=head2 C<ev_io> - is this file descriptor readable or writable?
619		1014
620	I/O watchers check whether a file descriptor is readable or writable	1015	I/O watchers check whether a file descriptor is readable or writable
621	in each iteration of the event loop (This behaviour is called	1016	in each iteration of the event loop, or, more precisely, when reading
622	level-triggering because you keep receiving events as long as the	1017	would not block the process and writing would at least be able to write
623	condition persists. Remember you can stop the watcher if you don't want to	1018	some data. This behaviour is called level-triggering because you keep
624	act on the event and neither want to receive future events).	1019	receiving events as long as the condition persists. Remember you can stop
		1020	the watcher if you don't want to act on the event and neither want to
		1021	receive future events.
625		1022
626	In general you can register as many read and/or write event watchers per	1023	In general you can register as many read and/or write event watchers per
627	fd as you want (as long as you don't confuse yourself). Setting all file	1024	fd as you want (as long as you don't confuse yourself). Setting all file
628	descriptors to non-blocking mode is also usually a good idea (but not	1025	descriptors to non-blocking mode is also usually a good idea (but not
629	required if you know what you are doing).	1026	required if you know what you are doing).
630		1027
631	You have to be careful with dup'ed file descriptors, though. Some backends
632	(the linux epoll backend is a notable example) cannot handle dup'ed file
633	descriptors correctly if you register interest in two or more fds pointing
634	to the same underlying file/socket etc. description (that is, they share
635	the same underlying "file open").
636
637	If you must do this, then force the use of a known-to-be-good backend	1028	If you must do this, then force the use of a known-to-be-good backend
638	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and	1029	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
639	C<EVBACKEND_POLL>).	1030	C<EVBACKEND_POLL>).
640		1031
		1032	Another thing you have to watch out for is that it is quite easy to
		1033	receive "spurious" readyness notifications, that is your callback might
		1034	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
		1035	because there is no data. Not only are some backends known to create a
		1036	lot of those (for example solaris ports), it is very easy to get into
		1037	this situation even with a relatively standard program structure. Thus
		1038	it is best to always use non-blocking I/O: An extra C<read>(2) returning
		1039	C<EAGAIN> is far preferable to a program hanging until some data arrives.
		1040
		1041	If you cannot run the fd in non-blocking mode (for example you should not
		1042	play around with an Xlib connection), then you have to seperately re-test
		1043	whether a file descriptor is really ready with a known-to-be good interface
		1044	such as poll (fortunately in our Xlib example, Xlib already does this on
		1045	its own, so its quite safe to use).
		1046
		1047	=head3 The special problem of disappearing file descriptors
		1048
		1049	Some backends (e.g. kqueue, epoll) need to be told about closing a file
		1050	descriptor (either by calling C<close> explicitly or by any other means,
		1051	such as C<dup>). The reason is that you register interest in some file
		1052	descriptor, but when it goes away, the operating system will silently drop
		1053	this interest. If another file descriptor with the same number then is
		1054	registered with libev, there is no efficient way to see that this is, in
		1055	fact, a different file descriptor.
		1056
		1057	To avoid having to explicitly tell libev about such cases, libev follows
		1058	the following policy: Each time C<ev_io_set> is being called, libev
		1059	will assume that this is potentially a new file descriptor, otherwise
		1060	it is assumed that the file descriptor stays the same. That means that
		1061	you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the
		1062	descriptor even if the file descriptor number itself did not change.
		1063
		1064	This is how one would do it normally anyway, the important point is that
		1065	the libev application should not optimise around libev but should leave
		1066	optimisations to libev.
		1067
		1068	=head3 The special problem of dup'ed file descriptors
		1069
		1070	Some backends (e.g. epoll), cannot register events for file descriptors,
		1071	but only events for the underlying file descriptions. That means when you
		1072	have C<dup ()>'ed file descriptors or weirder constellations, and register
		1073	events for them, only one file descriptor might actually receive events.
		1074
		1075	There is no workaround possible except not registering events
		1076	for potentially C<dup ()>'ed file descriptors, or to resort to
		1077	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1078
		1079	=head3 The special problem of fork
		1080
		1081	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
		1082	useless behaviour. Libev fully supports fork, but needs to be told about
		1083	it in the child.
		1084
		1085	To support fork in your programs, you either have to call
		1086	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
		1087	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
		1088	C<EVBACKEND_POLL>.
		1089
		1090
		1091	=head3 Watcher-Specific Functions
		1092
641	=over 4	1093	=over 4
642		1094
643	=item ev_io_init (ev_io *, callback, int fd, int events)	1095	=item ev_io_init (ev_io *, callback, int fd, int events)
644		1096
645	=item ev_io_set (ev_io *, int fd, int events)	1097	=item ev_io_set (ev_io *, int fd, int events)
646		1098
647	Configures an C<ev_io> watcher. The fd is the file descriptor to rceeive	1099	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
648	events for and events is either C<EV_READ>, C<EV_WRITE> or C<EV_READ |	1100	rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or
649	EV_WRITE> to receive the given events.	1101	C<EV_READ | EV_WRITE> to receive the given events.
650		1102
651	Please note that most of the more scalable backend mechanisms (for example	1103	=item int fd [read-only]
652	epoll and solaris ports) can result in spurious readyness notifications	1104
653	for file descriptors, so you practically need to use non-blocking I/O (and	1105	The file descriptor being watched.
654	treat callback invocation as hint only), or retest separately with a safe	1106
655	interface before doing I/O (XLib can do this), or force the use of either	1107	=item int events [read-only]
656	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>, which don't suffer from this	1108
657	problem. Also note that it is quite easy to have your callback invoked	1109	The events being watched.
658	when the readyness condition is no longer valid even when employing
659	typical ways of handling events, so its a good idea to use non-blocking
660	I/O unconditionally.
661		1110
662	=back	1111	=back
663		1112
		1113	=head3 Examples
		1114
664	Example: call C<stdin_readable_cb> when STDIN_FILENO has become, well	1115	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
665	readable, but only once. Since it is likely line-buffered, you could	1116	readable, but only once. Since it is likely line-buffered, you could
666	attempt to read a whole line in the callback:	1117	attempt to read a whole line in the callback.
667		1118
668	static void	1119	static void
669	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1120	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)
670	{	1121	{
671	ev_io_stop (loop, w);	1122	ev_io_stop (loop, w);
…		…
678	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1129	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
679	ev_io_start (loop, &stdin_readable);	1130	ev_io_start (loop, &stdin_readable);
680	ev_loop (loop, 0);	1131	ev_loop (loop, 0);
681		1132
682		1133
683	=head2 C<ev_timer> - relative and optionally recurring timeouts	1134	=head2 C<ev_timer> - relative and optionally repeating timeouts
684		1135
685	Timer watchers are simple relative timers that generate an event after a	1136	Timer watchers are simple relative timers that generate an event after a
686	given time, and optionally repeating in regular intervals after that.	1137	given time, and optionally repeating in regular intervals after that.
687		1138
688	The timers are based on real time, that is, if you register an event that	1139	The timers are based on real time, that is, if you register an event that
…		…
701		1152
702	The callback is guarenteed to be invoked only when its timeout has passed,	1153	The callback is guarenteed to be invoked only when its timeout has passed,
703	but if multiple timers become ready during the same loop iteration then	1154	but if multiple timers become ready during the same loop iteration then
704	order of execution is undefined.	1155	order of execution is undefined.
705		1156
		1157	=head3 Watcher-Specific Functions and Data Members
		1158
706	=over 4	1159	=over 4
707		1160
708	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1161	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
709		1162
710	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	1163	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
…		…
718	configure a timer to trigger every 10 seconds, then it will trigger at	1171	configure a timer to trigger every 10 seconds, then it will trigger at
719	exactly 10 second intervals. If, however, your program cannot keep up with	1172	exactly 10 second intervals. If, however, your program cannot keep up with
720	the timer (because it takes longer than those 10 seconds to do stuff) the	1173	the timer (because it takes longer than those 10 seconds to do stuff) the
721	timer will not fire more than once per event loop iteration.	1174	timer will not fire more than once per event loop iteration.
722		1175
723	=item ev_timer_again (loop)	1176	=item ev_timer_again (loop, ev_timer *)
724		1177
725	This will act as if the timer timed out and restart it again if it is	1178	This will act as if the timer timed out and restart it again if it is
726	repeating. The exact semantics are:	1179	repeating. The exact semantics are:
727		1180
		1181	If the timer is pending, its pending status is cleared.
		1182
728	If the timer is started but nonrepeating, stop it.	1183	If the timer is started but nonrepeating, stop it (as if it timed out).
729		1184
730	If the timer is repeating, either start it if necessary (with the repeat	1185	If the timer is repeating, either start it if necessary (with the
731	value), or reset the running timer to the repeat value.	1186	C<repeat> value), or reset the running timer to the C<repeat> value.
732		1187
733	This sounds a bit complicated, but here is a useful and typical	1188	This sounds a bit complicated, but here is a useful and typical
734	example: Imagine you have a tcp connection and you want a so-called idle	1189	example: Imagine you have a tcp connection and you want a so-called idle
735	timeout, that is, you want to be called when there have been, say, 60	1190	timeout, that is, you want to be called when there have been, say, 60
736	seconds of inactivity on the socket. The easiest way to do this is to	1191	seconds of inactivity on the socket. The easiest way to do this is to
737	configure an C<ev_timer> with after=repeat=60 and calling ev_timer_again each	1192	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
738	time you successfully read or write some data. If you go into an idle	1193	C<ev_timer_again> each time you successfully read or write some data. If
739	state where you do not expect data to travel on the socket, you can stop	1194	you go into an idle state where you do not expect data to travel on the
740	the timer, and again will automatically restart it if need be.	1195	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
		1196	automatically restart it if need be.
		1197
		1198	That means you can ignore the C<after> value and C<ev_timer_start>
		1199	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
		1200
		1201	ev_timer_init (timer, callback, 0., 5.);
		1202	ev_timer_again (loop, timer);
		1203	...
		1204	timer->again = 17.;
		1205	ev_timer_again (loop, timer);
		1206	...
		1207	timer->again = 10.;
		1208	ev_timer_again (loop, timer);
		1209
		1210	This is more slightly efficient then stopping/starting the timer each time
		1211	you want to modify its timeout value.
		1212
		1213	=item ev_tstamp repeat [read-write]
		1214
		1215	The current C<repeat> value. Will be used each time the watcher times out
		1216	or C<ev_timer_again> is called and determines the next timeout (if any),
		1217	which is also when any modifications are taken into account.
741		1218
742	=back	1219	=back
743		1220
		1221	=head3 Examples
		1222
744	Example: create a timer that fires after 60 seconds.	1223	Example: Create a timer that fires after 60 seconds.
745		1224
746	static void	1225	static void
747	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1226	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
748	{	1227	{
749	.. one minute over, w is actually stopped right here	1228	.. one minute over, w is actually stopped right here
…		…
751		1230
752	struct ev_timer mytimer;	1231	struct ev_timer mytimer;
753	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	1232	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
754	ev_timer_start (loop, &mytimer);	1233	ev_timer_start (loop, &mytimer);
755		1234
756	Example: create a timeout timer that times out after 10 seconds of	1235	Example: Create a timeout timer that times out after 10 seconds of
757	inactivity.	1236	inactivity.
758		1237
759	static void	1238	static void
760	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1239	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
761	{	1240	{
…		…
770	// and in some piece of code that gets executed on any "activity":	1249	// and in some piece of code that gets executed on any "activity":
771	// reset the timeout to start ticking again at 10 seconds	1250	// reset the timeout to start ticking again at 10 seconds
772	ev_timer_again (&mytimer);	1251	ev_timer_again (&mytimer);
773		1252
774		1253
775	=head2 C<ev_periodic> - to cron or not to cron	1254	=head2 C<ev_periodic> - to cron or not to cron?
776		1255
777	Periodic watchers are also timers of a kind, but they are very versatile	1256	Periodic watchers are also timers of a kind, but they are very versatile
778	(and unfortunately a bit complex).	1257	(and unfortunately a bit complex).
779		1258
780	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1259	Unlike C<ev_timer>'s, they are not based on real time (or relative time)
781	but on wallclock time (absolute time). You can tell a periodic watcher	1260	but on wallclock time (absolute time). You can tell a periodic watcher
782	to trigger "at" some specific point in time. For example, if you tell a	1261	to trigger "at" some specific point in time. For example, if you tell a
783	periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now ()	1262	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()
784	+ 10.>) and then reset your system clock to the last year, then it will	1263	+ 10.>) and then reset your system clock to the last year, then it will
785	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	1264	take a year to trigger the event (unlike an C<ev_timer>, which would trigger
786	roughly 10 seconds later and of course not if you reset your system time	1265	roughly 10 seconds later).
787	again).
788		1266
789	They can also be used to implement vastly more complex timers, such as	1267	They can also be used to implement vastly more complex timers, such as
790	triggering an event on eahc midnight, local time.	1268	triggering an event on each midnight, local time or other, complicated,
		1269	rules.
791		1270
792	As with timers, the callback is guarenteed to be invoked only when the	1271	As with timers, the callback is guarenteed to be invoked only when the
793	time (C<at>) has been passed, but if multiple periodic timers become ready	1272	time (C<at>) has been passed, but if multiple periodic timers become ready
794	during the same loop iteration then order of execution is undefined.	1273	during the same loop iteration then order of execution is undefined.
795		1274
		1275	=head3 Watcher-Specific Functions and Data Members
		1276
796	=over 4	1277	=over 4
797		1278
798	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1279	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)
799		1280
800	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1281	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)
…		…
802	Lots of arguments, lets sort it out... There are basically three modes of	1283	Lots of arguments, lets sort it out... There are basically three modes of
803	operation, and we will explain them from simplest to complex:	1284	operation, and we will explain them from simplest to complex:
804		1285
805	=over 4	1286	=over 4
806		1287
807	=item * absolute timer (interval = reschedule_cb = 0)	1288	=item * absolute timer (at = time, interval = reschedule_cb = 0)
808		1289
809	In this configuration the watcher triggers an event at the wallclock time	1290	In this configuration the watcher triggers an event at the wallclock time
810	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	1291	C<at> and doesn't repeat. It will not adjust when a time jump occurs,
811	that is, if it is to be run at January 1st 2011 then it will run when the	1292	that is, if it is to be run at January 1st 2011 then it will run when the
812	system time reaches or surpasses this time.	1293	system time reaches or surpasses this time.
813		1294
814	=item * non-repeating interval timer (interval > 0, reschedule_cb = 0)	1295	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)
815		1296
816	In this mode the watcher will always be scheduled to time out at the next	1297	In this mode the watcher will always be scheduled to time out at the next
817	C<at + N * interval> time (for some integer N) and then repeat, regardless	1298	C<at + N * interval> time (for some integer N, which can also be negative)
818	of any time jumps.	1299	and then repeat, regardless of any time jumps.
819		1300
820	This can be used to create timers that do not drift with respect to system	1301	This can be used to create timers that do not drift with respect to system
821	time:	1302	time:
822		1303
823	ev_periodic_set (&periodic, 0., 3600., 0);	1304	ev_periodic_set (&periodic, 0., 3600., 0);
…		…
829		1310
830	Another way to think about it (for the mathematically inclined) is that	1311	Another way to think about it (for the mathematically inclined) is that
831	C<ev_periodic> will try to run the callback in this mode at the next possible	1312	C<ev_periodic> will try to run the callback in this mode at the next possible
832	time where C<time = at (mod interval)>, regardless of any time jumps.	1313	time where C<time = at (mod interval)>, regardless of any time jumps.
833		1314
		1315	For numerical stability it is preferable that the C<at> value is near
		1316	C<ev_now ()> (the current time), but there is no range requirement for
		1317	this value.
		1318
834	=item * manual reschedule mode (reschedule_cb = callback)	1319	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)
835		1320
836	In this mode the values for C<interval> and C<at> are both being	1321	In this mode the values for C<interval> and C<at> are both being
837	ignored. Instead, each time the periodic watcher gets scheduled, the	1322	ignored. Instead, each time the periodic watcher gets scheduled, the
838	reschedule callback will be called with the watcher as first, and the	1323	reschedule callback will be called with the watcher as first, and the
839	current time as second argument.	1324	current time as second argument.
840		1325
841	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	1326	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,
842	ever, or make any event loop modifications>. If you need to stop it,	1327	ever, or make any event loop modifications>. If you need to stop it,
843	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by	1328	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by
844	starting a prepare watcher).	1329	starting an C<ev_prepare> watcher, which is legal).
845		1330
846	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	1331	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,
847	ev_tstamp now)>, e.g.:	1332	ev_tstamp now)>, e.g.:
848		1333
849	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1334	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)
…		…
872	Simply stops and restarts the periodic watcher again. This is only useful	1357	Simply stops and restarts the periodic watcher again. This is only useful
873	when you changed some parameters or the reschedule callback would return	1358	when you changed some parameters or the reschedule callback would return
874	a different time than the last time it was called (e.g. in a crond like	1359	a different time than the last time it was called (e.g. in a crond like
875	program when the crontabs have changed).	1360	program when the crontabs have changed).
876		1361
		1362	=item ev_tstamp offset [read-write]
		1363
		1364	When repeating, this contains the offset value, otherwise this is the
		1365	absolute point in time (the C<at> value passed to C<ev_periodic_set>).
		1366
		1367	Can be modified any time, but changes only take effect when the periodic
		1368	timer fires or C<ev_periodic_again> is being called.
		1369
		1370	=item ev_tstamp interval [read-write]
		1371
		1372	The current interval value. Can be modified any time, but changes only
		1373	take effect when the periodic timer fires or C<ev_periodic_again> is being
		1374	called.
		1375
		1376	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]
		1377
		1378	The current reschedule callback, or C<0>, if this functionality is
		1379	switched off. Can be changed any time, but changes only take effect when
		1380	the periodic timer fires or C<ev_periodic_again> is being called.
		1381
		1382	=item ev_tstamp at [read-only]
		1383
		1384	When active, contains the absolute time that the watcher is supposed to
		1385	trigger next.
		1386
877	=back	1387	=back
878		1388
		1389	=head3 Examples
		1390
879	Example: call a callback every hour, or, more precisely, whenever the	1391	Example: Call a callback every hour, or, more precisely, whenever the
880	system clock is divisible by 3600. The callback invocation times have	1392	system clock is divisible by 3600. The callback invocation times have
881	potentially a lot of jittering, but good long-term stability.	1393	potentially a lot of jittering, but good long-term stability.
882		1394
883	static void	1395	static void
884	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1396	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)
…		…
888		1400
889	struct ev_periodic hourly_tick;	1401	struct ev_periodic hourly_tick;
890	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	1402	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
891	ev_periodic_start (loop, &hourly_tick);	1403	ev_periodic_start (loop, &hourly_tick);
892		1404
893	Example: the same as above, but use a reschedule callback to do it:	1405	Example: The same as above, but use a reschedule callback to do it:
894		1406
895	#include <math.h>	1407	#include <math.h>
896		1408
897	static ev_tstamp	1409	static ev_tstamp
898	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	1410	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)
…		…
900	return fmod (now, 3600.) + 3600.;	1412	return fmod (now, 3600.) + 3600.;
901	}	1413	}
902		1414
903	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	1415	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
904		1416
905	Example: call a callback every hour, starting now:	1417	Example: Call a callback every hour, starting now:
906		1418
907	struct ev_periodic hourly_tick;	1419	struct ev_periodic hourly_tick;
908	ev_periodic_init (&hourly_tick, clock_cb,	1420	ev_periodic_init (&hourly_tick, clock_cb,
909	fmod (ev_now (loop), 3600.), 3600., 0);	1421	fmod (ev_now (loop), 3600.), 3600., 0);
910	ev_periodic_start (loop, &hourly_tick);	1422	ev_periodic_start (loop, &hourly_tick);
911		1423
912		1424
913	=head2 C<ev_signal> - signal me when a signal gets signalled	1425	=head2 C<ev_signal> - signal me when a signal gets signalled!
914		1426
915	Signal watchers will trigger an event when the process receives a specific	1427	Signal watchers will trigger an event when the process receives a specific
916	signal one or more times. Even though signals are very asynchronous, libev	1428	signal one or more times. Even though signals are very asynchronous, libev
917	will try it's best to deliver signals synchronously, i.e. as part of the	1429	will try it's best to deliver signals synchronously, i.e. as part of the
918	normal event processing, like any other event.	1430	normal event processing, like any other event.
…		…
922	with the kernel (thus it coexists with your own signal handlers as long	1434	with the kernel (thus it coexists with your own signal handlers as long
923	as you don't register any with libev). Similarly, when the last signal	1435	as you don't register any with libev). Similarly, when the last signal
924	watcher for a signal is stopped libev will reset the signal handler to	1436	watcher for a signal is stopped libev will reset the signal handler to
925	SIG_DFL (regardless of what it was set to before).	1437	SIG_DFL (regardless of what it was set to before).
926		1438
		1439	If possible and supported, libev will install its handlers with
		1440	C<SA_RESTART> behaviour enabled, so syscalls should not be unduly
		1441	interrupted. If you have a problem with syscalls getting interrupted by
		1442	signals you can block all signals in an C<ev_check> watcher and unblock
		1443	them in an C<ev_prepare> watcher.
		1444
		1445	=head3 Watcher-Specific Functions and Data Members
		1446
927	=over 4	1447	=over 4
928		1448
929	=item ev_signal_init (ev_signal *, callback, int signum)	1449	=item ev_signal_init (ev_signal *, callback, int signum)
930		1450
931	=item ev_signal_set (ev_signal *, int signum)	1451	=item ev_signal_set (ev_signal *, int signum)
932		1452
933	Configures the watcher to trigger on the given signal number (usually one	1453	Configures the watcher to trigger on the given signal number (usually one
934	of the C<SIGxxx> constants).	1454	of the C<SIGxxx> constants).
935		1455
		1456	=item int signum [read-only]
		1457
		1458	The signal the watcher watches out for.
		1459
936	=back	1460	=back
937		1461
		1462	=head3 Examples
938		1463
		1464	Example: Try to exit cleanly on SIGINT and SIGTERM.
		1465
		1466	static void
		1467	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)
		1468	{
		1469	ev_unloop (loop, EVUNLOOP_ALL);
		1470	}
		1471
		1472	struct ev_signal signal_watcher;
		1473	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		1474	ev_signal_start (loop, &sigint_cb);
		1475
		1476
939	=head2 C<ev_child> - wait for pid status changes	1477	=head2 C<ev_child> - watch out for process status changes
940		1478
941	Child watchers trigger when your process receives a SIGCHLD in response to	1479	Child watchers trigger when your process receives a SIGCHLD in response to
942	some child status changes (most typically when a child of yours dies).	1480	some child status changes (most typically when a child of yours dies). It
		1481	is permissible to install a child watcher I<after> the child has been
		1482	forked (which implies it might have already exited), as long as the event
		1483	loop isn't entered (or is continued from a watcher).
		1484
		1485	Only the default event loop is capable of handling signals, and therefore
		1486	you can only rgeister child watchers in the default event loop.
		1487
		1488	=head3 Process Interaction
		1489
		1490	Libev grabs C<SIGCHLD> as soon as the default event loop is
		1491	initialised. This is necessary to guarantee proper behaviour even if
		1492	the first child watcher is started after the child exits. The occurance
		1493	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		1494	synchronously as part of the event loop processing. Libev always reaps all
		1495	children, even ones not watched.
		1496
		1497	=head3 Overriding the Built-In Processing
		1498
		1499	Libev offers no special support for overriding the built-in child
		1500	processing, but if your application collides with libev's default child
		1501	handler, you can override it easily by installing your own handler for
		1502	C<SIGCHLD> after initialising the default loop, and making sure the
		1503	default loop never gets destroyed. You are encouraged, however, to use an
		1504	event-based approach to child reaping and thus use libev's support for
		1505	that, so other libev users can use C<ev_child> watchers freely.
		1506
		1507	=head3 Watcher-Specific Functions and Data Members
943		1508
944	=over 4	1509	=over 4
945		1510
946	=item ev_child_init (ev_child *, callback, int pid)	1511	=item ev_child_init (ev_child *, callback, int pid, int trace)
947		1512
948	=item ev_child_set (ev_child *, int pid)	1513	=item ev_child_set (ev_child *, int pid, int trace)
949		1514
950	Configures the watcher to wait for status changes of process C<pid> (or	1515	Configures the watcher to wait for status changes of process C<pid> (or
951	I<any> process if C<pid> is specified as C<0>). The callback can look	1516	I<any> process if C<pid> is specified as C<0>). The callback can look
952	at the C<rstatus> member of the C<ev_child> watcher structure to see	1517	at the C<rstatus> member of the C<ev_child> watcher structure to see
953	the status word (use the macros from C<sys/wait.h> and see your systems	1518	the status word (use the macros from C<sys/wait.h> and see your systems
954	C<waitpid> documentation). The C<rpid> member contains the pid of the	1519	C<waitpid> documentation). The C<rpid> member contains the pid of the
955	process causing the status change.	1520	process causing the status change. C<trace> must be either C<0> (only
		1521	activate the watcher when the process terminates) or C<1> (additionally
		1522	activate the watcher when the process is stopped or continued).
		1523
		1524	=item int pid [read-only]
		1525
		1526	The process id this watcher watches out for, or C<0>, meaning any process id.
		1527
		1528	=item int rpid [read-write]
		1529
		1530	The process id that detected a status change.
		1531
		1532	=item int rstatus [read-write]
		1533
		1534	The process exit/trace status caused by C<rpid> (see your systems
		1535	C<waitpid> and C<sys/wait.h> documentation for details).
956		1536
957	=back	1537	=back
958		1538
959	Example: try to exit cleanly on SIGINT and SIGTERM.	1539	=head3 Examples
		1540
		1541	Example: C<fork()> a new process and install a child handler to wait for
		1542	its completion.
		1543
		1544	ev_child cw;
960		1545
961	static void	1546	static void
962	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	1547	child_cb (EV_P_ struct ev_child *w, int revents)
963	{	1548	{
964	ev_unloop (loop, EVUNLOOP_ALL);	1549	ev_child_stop (EV_A_ w);
		1550	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
965	}	1551	}
966		1552
967	struct ev_signal signal_watcher;	1553	pid_t pid = fork ();
968	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
969	ev_signal_start (loop, &sigint_cb);
970		1554
		1555	if (pid < 0)
		1556	// error
		1557	else if (pid == 0)
		1558	{
		1559	// the forked child executes here
		1560	exit (1);
		1561	}
		1562	else
		1563	{
		1564	ev_child_init (&cw, child_cb, pid, 0);
		1565	ev_child_start (EV_DEFAULT_ &cw);
		1566	}
971		1567
		1568
		1569	=head2 C<ev_stat> - did the file attributes just change?
		1570
		1571	This watches a filesystem path for attribute changes. That is, it calls
		1572	C<stat> regularly (or when the OS says it changed) and sees if it changed
		1573	compared to the last time, invoking the callback if it did.
		1574
		1575	The path does not need to exist: changing from "path exists" to "path does
		1576	not exist" is a status change like any other. The condition "path does
		1577	not exist" is signified by the C<st_nlink> field being zero (which is
		1578	otherwise always forced to be at least one) and all the other fields of
		1579	the stat buffer having unspecified contents.
		1580
		1581	The path I<should> be absolute and I<must not> end in a slash. If it is
		1582	relative and your working directory changes, the behaviour is undefined.
		1583
		1584	Since there is no standard to do this, the portable implementation simply
		1585	calls C<stat (2)> regularly on the path to see if it changed somehow. You
		1586	can specify a recommended polling interval for this case. If you specify
		1587	a polling interval of C<0> (highly recommended!) then a I<suitable,
		1588	unspecified default> value will be used (which you can expect to be around
		1589	five seconds, although this might change dynamically). Libev will also
		1590	impose a minimum interval which is currently around C<0.1>, but thats
		1591	usually overkill.
		1592
		1593	This watcher type is not meant for massive numbers of stat watchers,
		1594	as even with OS-supported change notifications, this can be
		1595	resource-intensive.
		1596
		1597	At the time of this writing, only the Linux inotify interface is
		1598	implemented (implementing kqueue support is left as an exercise for the
		1599	reader). Inotify will be used to give hints only and should not change the
		1600	semantics of C<ev_stat> watchers, which means that libev sometimes needs
		1601	to fall back to regular polling again even with inotify, but changes are
		1602	usually detected immediately, and if the file exists there will be no
		1603	polling.
		1604
		1605	=head3 ABI Issues (Largefile Support)
		1606
		1607	Libev by default (unless the user overrides this) uses the default
		1608	compilation environment, which means that on systems with optionally
		1609	disabled large file support, you get the 32 bit version of the stat
		1610	structure. When using the library from programs that change the ABI to
		1611	use 64 bit file offsets the programs will fail. In that case you have to
		1612	compile libev with the same flags to get binary compatibility. This is
		1613	obviously the case with any flags that change the ABI, but the problem is
		1614	most noticably with ev_stat and largefile support.
		1615
		1616	=head3 Inotify
		1617
		1618	When C<inotify (7)> support has been compiled into libev (generally only
		1619	available on Linux) and present at runtime, it will be used to speed up
		1620	change detection where possible. The inotify descriptor will be created lazily
		1621	when the first C<ev_stat> watcher is being started.
		1622
		1623	Inotify presense does not change the semantics of C<ev_stat> watchers
		1624	except that changes might be detected earlier, and in some cases, to avoid
		1625	making regular C<stat> calls. Even in the presense of inotify support
		1626	there are many cases where libev has to resort to regular C<stat> polling.
		1627
		1628	(There is no support for kqueue, as apparently it cannot be used to
		1629	implement this functionality, due to the requirement of having a file
		1630	descriptor open on the object at all times).
		1631
		1632	=head3 The special problem of stat time resolution
		1633
		1634	The C<stat ()> syscall only supports full-second resolution portably, and
		1635	even on systems where the resolution is higher, many filesystems still
		1636	only support whole seconds.
		1637
		1638	That means that, if the time is the only thing that changes, you might
		1639	miss updates: on the first update, C<ev_stat> detects a change and calls
		1640	your callback, which does something. When there is another update within
		1641	the same second, C<ev_stat> will be unable to detect it.
		1642
		1643	The solution to this is to delay acting on a change for a second (or till
		1644	the next second boundary), using a roughly one-second delay C<ev_timer>
		1645	(C<ev_timer_set (w, 0., 1.01); ev_timer_again (loop, w)>). The C<.01>
		1646	is added to work around small timing inconsistencies of some operating
		1647	systems.
		1648
		1649	=head3 Watcher-Specific Functions and Data Members
		1650
		1651	=over 4
		1652
		1653	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
		1654
		1655	=item ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)
		1656
		1657	Configures the watcher to wait for status changes of the given
		1658	C<path>. The C<interval> is a hint on how quickly a change is expected to
		1659	be detected and should normally be specified as C<0> to let libev choose
		1660	a suitable value. The memory pointed to by C<path> must point to the same
		1661	path for as long as the watcher is active.
		1662
		1663	The callback will be receive C<EV_STAT> when a change was detected,
		1664	relative to the attributes at the time the watcher was started (or the
		1665	last change was detected).
		1666
		1667	=item ev_stat_stat (loop, ev_stat *)
		1668
		1669	Updates the stat buffer immediately with new values. If you change the
		1670	watched path in your callback, you could call this fucntion to avoid
		1671	detecting this change (while introducing a race condition). Can also be
		1672	useful simply to find out the new values.
		1673
		1674	=item ev_statdata attr [read-only]
		1675
		1676	The most-recently detected attributes of the file. Although the type is of
		1677	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
		1678	suitable for your system. If the C<st_nlink> member is C<0>, then there
		1679	was some error while C<stat>ing the file.
		1680
		1681	=item ev_statdata prev [read-only]
		1682
		1683	The previous attributes of the file. The callback gets invoked whenever
		1684	C<prev> != C<attr>.
		1685
		1686	=item ev_tstamp interval [read-only]
		1687
		1688	The specified interval.
		1689
		1690	=item const char *path [read-only]
		1691
		1692	The filesystem path that is being watched.
		1693
		1694	=back
		1695
		1696	=head3 Examples
		1697
		1698	Example: Watch C</etc/passwd> for attribute changes.
		1699
		1700	static void
		1701	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
		1702	{
		1703	/* /etc/passwd changed in some way */
		1704	if (w->attr.st_nlink)
		1705	{
		1706	printf ("passwd current size %ld\n", (long)w->attr.st_size);
		1707	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
		1708	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
		1709	}
		1710	else
		1711	/* you shalt not abuse printf for puts */
		1712	puts ("wow, /etc/passwd is not there, expect problems. "
		1713	"if this is windows, they already arrived\n");
		1714	}
		1715
		1716	...
		1717	ev_stat passwd;
		1718
		1719	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
		1720	ev_stat_start (loop, &passwd);
		1721
		1722	Example: Like above, but additionally use a one-second delay so we do not
		1723	miss updates (however, frequent updates will delay processing, too, so
		1724	one might do the work both on C<ev_stat> callback invocation I<and> on
		1725	C<ev_timer> callback invocation).
		1726
		1727	static ev_stat passwd;
		1728	static ev_timer timer;
		1729
		1730	static void
		1731	timer_cb (EV_P_ ev_timer *w, int revents)
		1732	{
		1733	ev_timer_stop (EV_A_ w);
		1734
		1735	/* now it's one second after the most recent passwd change */
		1736	}
		1737
		1738	static void
		1739	stat_cb (EV_P_ ev_stat *w, int revents)
		1740	{
		1741	/* reset the one-second timer */
		1742	ev_timer_again (EV_A_ &timer);
		1743	}
		1744
		1745	...
		1746	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		1747	ev_stat_start (loop, &passwd);
		1748	ev_timer_init (&timer, timer_cb, 0., 1.01);
		1749
		1750
972	=head2 C<ev_idle> - when you've got nothing better to do	1751	=head2 C<ev_idle> - when you've got nothing better to do...
973		1752
974	Idle watchers trigger events when there are no other events are pending	1753	Idle watchers trigger events when no other events of the same or higher
975	(prepare, check and other idle watchers do not count). That is, as long	1754	priority are pending (prepare, check and other idle watchers do not
976	as your process is busy handling sockets or timeouts (or even signals,	1755	count).
977	imagine) it will not be triggered. But when your process is idle all idle	1756
978	watchers are being called again and again, once per event loop iteration -	1757	That is, as long as your process is busy handling sockets or timeouts
		1758	(or even signals, imagine) of the same or higher priority it will not be
		1759	triggered. But when your process is idle (or only lower-priority watchers
		1760	are pending), the idle watchers are being called once per event loop
979	until stopped, that is, or your process receives more events and becomes	1761	iteration - until stopped, that is, or your process receives more events
980	busy.	1762	and becomes busy again with higher priority stuff.
981		1763
982	The most noteworthy effect is that as long as any idle watchers are	1764	The most noteworthy effect is that as long as any idle watchers are
983	active, the process will not block when waiting for new events.	1765	active, the process will not block when waiting for new events.
984		1766
985	Apart from keeping your process non-blocking (which is a useful	1767	Apart from keeping your process non-blocking (which is a useful
986	effect on its own sometimes), idle watchers are a good place to do	1768	effect on its own sometimes), idle watchers are a good place to do
987	"pseudo-background processing", or delay processing stuff to after the	1769	"pseudo-background processing", or delay processing stuff to after the
988	event loop has handled all outstanding events.	1770	event loop has handled all outstanding events.
989		1771
		1772	=head3 Watcher-Specific Functions and Data Members
		1773
990	=over 4	1774	=over 4
991		1775
992	=item ev_idle_init (ev_signal *, callback)	1776	=item ev_idle_init (ev_signal *, callback)
993		1777
994	Initialises and configures the idle watcher - it has no parameters of any	1778	Initialises and configures the idle watcher - it has no parameters of any
995	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	1779	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
996	believe me.	1780	believe me.
997		1781
998	=back	1782	=back
999		1783
		1784	=head3 Examples
		1785
1000	Example: dynamically allocate an C<ev_idle>, start it, and in the	1786	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1001	callback, free it. Alos, use no error checking, as usual.	1787	callback, free it. Also, use no error checking, as usual.
1002		1788
1003	static void	1789	static void
1004	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	1790	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)
1005	{	1791	{
1006	free (w);	1792	free (w);
1007	// now do something you wanted to do when the program has	1793	// now do something you wanted to do when the program has
1008	// no longer asnything immediate to do.	1794	// no longer anything immediate to do.
1009	}	1795	}
1010		1796
1011	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	1797	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));
1012	ev_idle_init (idle_watcher, idle_cb);	1798	ev_idle_init (idle_watcher, idle_cb);
1013	ev_idle_start (loop, idle_cb);	1799	ev_idle_start (loop, idle_cb);
1014		1800
1015		1801
1016	=head2 C<ev_prepare> and C<ev_check> - customise your event loop	1802	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1017		1803
1018	Prepare and check watchers are usually (but not always) used in tandem:	1804	Prepare and check watchers are usually (but not always) used in tandem:
1019	prepare watchers get invoked before the process blocks and check watchers	1805	prepare watchers get invoked before the process blocks and check watchers
1020	afterwards.	1806	afterwards.
1021		1807
		1808	You I<must not> call C<ev_loop> or similar functions that enter
		1809	the current event loop from either C<ev_prepare> or C<ev_check>
		1810	watchers. Other loops than the current one are fine, however. The
		1811	rationale behind this is that you do not need to check for recursion in
		1812	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
		1813	C<ev_check> so if you have one watcher of each kind they will always be
		1814	called in pairs bracketing the blocking call.
		1815
1022	Their main purpose is to integrate other event mechanisms into libev and	1816	Their main purpose is to integrate other event mechanisms into libev and
1023	their use is somewhat advanced. This could be used, for example, to track	1817	their use is somewhat advanced. This could be used, for example, to track
1024	variable changes, implement your own watchers, integrate net-snmp or a	1818	variable changes, implement your own watchers, integrate net-snmp or a
1025	coroutine library and lots more.	1819	coroutine library and lots more. They are also occasionally useful if
		1820	you cache some data and want to flush it before blocking (for example,
		1821	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
		1822	watcher).
1026		1823
1027	This is done by examining in each prepare call which file descriptors need	1824	This is done by examining in each prepare call which file descriptors need
1028	to be watched by the other library, registering C<ev_io> watchers for	1825	to be watched by the other library, registering C<ev_io> watchers for
1029	them and starting an C<ev_timer> watcher for any timeouts (many libraries	1826	them and starting an C<ev_timer> watcher for any timeouts (many libraries
1030	provide just this functionality). Then, in the check watcher you check for	1827	provide just this functionality). Then, in the check watcher you check for
…		…
1040	with priority higher than or equal to the event loop and one coroutine	1837	with priority higher than or equal to the event loop and one coroutine
1041	of lower priority, but only once, using idle watchers to keep the event	1838	of lower priority, but only once, using idle watchers to keep the event
1042	loop from blocking if lower-priority coroutines are active, thus mapping	1839	loop from blocking if lower-priority coroutines are active, thus mapping
1043	low-priority coroutines to idle/background tasks).	1840	low-priority coroutines to idle/background tasks).
1044		1841
		1842	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
		1843	priority, to ensure that they are being run before any other watchers
		1844	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,
		1845	too) should not activate ("feed") events into libev. While libev fully
		1846	supports this, they will be called before other C<ev_check> watchers
		1847	did their job. As C<ev_check> watchers are often used to embed other
		1848	(non-libev) event loops those other event loops might be in an unusable
		1849	state until their C<ev_check> watcher ran (always remind yourself to
		1850	coexist peacefully with others).
		1851
		1852	=head3 Watcher-Specific Functions and Data Members
		1853
1045	=over 4	1854	=over 4
1046		1855
1047	=item ev_prepare_init (ev_prepare *, callback)	1856	=item ev_prepare_init (ev_prepare *, callback)
1048		1857
1049	=item ev_check_init (ev_check *, callback)	1858	=item ev_check_init (ev_check *, callback)
…		…
1052	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	1861	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1053	macros, but using them is utterly, utterly and completely pointless.	1862	macros, but using them is utterly, utterly and completely pointless.
1054		1863
1055	=back	1864	=back
1056		1865
1057	Example: *TODO*.	1866	=head3 Examples
1058		1867
		1868	There are a number of principal ways to embed other event loops or modules
		1869	into libev. Here are some ideas on how to include libadns into libev
		1870	(there is a Perl module named C<EV::ADNS> that does this, which you could
		1871	use for an actually working example. Another Perl module named C<EV::Glib>
		1872	embeds a Glib main context into libev, and finally, C<Glib::EV> embeds EV
		1873	into the Glib event loop).
1059		1874
		1875	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
		1876	and in a check watcher, destroy them and call into libadns. What follows
		1877	is pseudo-code only of course. This requires you to either use a low
		1878	priority for the check watcher or use C<ev_clear_pending> explicitly, as
		1879	the callbacks for the IO/timeout watchers might not have been called yet.
		1880
		1881	static ev_io iow [nfd];
		1882	static ev_timer tw;
		1883
		1884	static void
		1885	io_cb (ev_loop *loop, ev_io *w, int revents)
		1886	{
		1887	}
		1888
		1889	// create io watchers for each fd and a timer before blocking
		1890	static void
		1891	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)
		1892	{
		1893	int timeout = 3600000;
		1894	struct pollfd fds [nfd];
		1895	// actual code will need to loop here and realloc etc.
		1896	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
		1897
		1898	/* the callback is illegal, but won't be called as we stop during check */
		1899	ev_timer_init (&tw, 0, timeout * 1e-3);
		1900	ev_timer_start (loop, &tw);
		1901
		1902	// create one ev_io per pollfd
		1903	for (int i = 0; i < nfd; ++i)
		1904	{
		1905	ev_io_init (iow + i, io_cb, fds [i].fd,
		1906	((fds [i].events & POLLIN ? EV_READ : 0)
		1907	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
		1908
		1909	fds [i].revents = 0;
		1910	ev_io_start (loop, iow + i);
		1911	}
		1912	}
		1913
		1914	// stop all watchers after blocking
		1915	static void
		1916	adns_check_cb (ev_loop *loop, ev_check *w, int revents)
		1917	{
		1918	ev_timer_stop (loop, &tw);
		1919
		1920	for (int i = 0; i < nfd; ++i)
		1921	{
		1922	// set the relevant poll flags
		1923	// could also call adns_processreadable etc. here
		1924	struct pollfd *fd = fds + i;
		1925	int revents = ev_clear_pending (iow + i);
		1926	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
		1927	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
		1928
		1929	// now stop the watcher
		1930	ev_io_stop (loop, iow + i);
		1931	}
		1932
		1933	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
		1934	}
		1935
		1936	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
		1937	in the prepare watcher and would dispose of the check watcher.
		1938
		1939	Method 3: If the module to be embedded supports explicit event
		1940	notification (adns does), you can also make use of the actual watcher
		1941	callbacks, and only destroy/create the watchers in the prepare watcher.
		1942
		1943	static void
		1944	timer_cb (EV_P_ ev_timer *w, int revents)
		1945	{
		1946	adns_state ads = (adns_state)w->data;
		1947	update_now (EV_A);
		1948
		1949	adns_processtimeouts (ads, &tv_now);
		1950	}
		1951
		1952	static void
		1953	io_cb (EV_P_ ev_io *w, int revents)
		1954	{
		1955	adns_state ads = (adns_state)w->data;
		1956	update_now (EV_A);
		1957
		1958	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
		1959	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
		1960	}
		1961
		1962	// do not ever call adns_afterpoll
		1963
		1964	Method 4: Do not use a prepare or check watcher because the module you
		1965	want to embed is too inflexible to support it. Instead, youc na override
		1966	their poll function. The drawback with this solution is that the main
		1967	loop is now no longer controllable by EV. The C<Glib::EV> module does
		1968	this.
		1969
		1970	static gint
		1971	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
		1972	{
		1973	int got_events = 0;
		1974
		1975	for (n = 0; n < nfds; ++n)
		1976	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
		1977
		1978	if (timeout >= 0)
		1979	// create/start timer
		1980
		1981	// poll
		1982	ev_loop (EV_A_ 0);
		1983
		1984	// stop timer again
		1985	if (timeout >= 0)
		1986	ev_timer_stop (EV_A_ &to);
		1987
		1988	// stop io watchers again - their callbacks should have set
		1989	for (n = 0; n < nfds; ++n)
		1990	ev_io_stop (EV_A_ iow [n]);
		1991
		1992	return got_events;
		1993	}
		1994
		1995
1060	=head2 C<ev_embed> - when one backend isn't enough	1996	=head2 C<ev_embed> - when one backend isn't enough...
1061		1997
1062	This is a rather advanced watcher type that lets you embed one event loop	1998	This is a rather advanced watcher type that lets you embed one event loop
1063	into another.	1999	into another (currently only C<ev_io> events are supported in the embedded
		2000	loop, other types of watchers might be handled in a delayed or incorrect
		2001	fashion and must not be used).
1064		2002
1065	There are primarily two reasons you would want that: work around bugs and	2003	There are primarily two reasons you would want that: work around bugs and
1066	prioritise I/O.	2004	prioritise I/O.
1067		2005
1068	As an example for a bug workaround, the kqueue backend might only support	2006	As an example for a bug workaround, the kqueue backend might only support
…		…
1077	to be watched and handled very quickly (with low latency), and even	2015	to be watched and handled very quickly (with low latency), and even
1078	priorities and idle watchers might have too much overhead. In this case	2016	priorities and idle watchers might have too much overhead. In this case
1079	you would put all the high priority stuff in one loop and all the rest in	2017	you would put all the high priority stuff in one loop and all the rest in
1080	a second one, and embed the second one in the first.	2018	a second one, and embed the second one in the first.
1081		2019
		2020	As long as the watcher is active, the callback will be invoked every time
		2021	there might be events pending in the embedded loop. The callback must then
		2022	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke
		2023	their callbacks (you could also start an idle watcher to give the embedded
		2024	loop strictly lower priority for example). You can also set the callback
		2025	to C<0>, in which case the embed watcher will automatically execute the
		2026	embedded loop sweep.
		2027
1082	As long as the watcher is started it will automatically handle events. The	2028	As long as the watcher is started it will automatically handle events. The
1083	callback will be invoked whenever some events have been handled. You can	2029	callback will be invoked whenever some events have been handled. You can
1084	set the callback to C<0> to avoid having to specify one if you are not	2030	set the callback to C<0> to avoid having to specify one if you are not
1085	interested in that.	2031	interested in that.
1086		2032
…		…
1094	portable one.	2040	portable one.
1095		2041
1096	So when you want to use this feature you will always have to be prepared	2042	So when you want to use this feature you will always have to be prepared
1097	that you cannot get an embeddable loop. The recommended way to get around	2043	that you cannot get an embeddable loop. The recommended way to get around
1098	this is to have a separate variables for your embeddable loop, try to	2044	this is to have a separate variables for your embeddable loop, try to
1099	create it, and if that fails, use the normal loop for everything:	2045	create it, and if that fails, use the normal loop for everything.
		2046
		2047	=head3 Watcher-Specific Functions and Data Members
		2048
		2049	=over 4
		2050
		2051	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
		2052
		2053	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)
		2054
		2055	Configures the watcher to embed the given loop, which must be
		2056	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
		2057	invoked automatically, otherwise it is the responsibility of the callback
		2058	to invoke it (it will continue to be called until the sweep has been done,
		2059	if you do not want thta, you need to temporarily stop the embed watcher).
		2060
		2061	=item ev_embed_sweep (loop, ev_embed *)
		2062
		2063	Make a single, non-blocking sweep over the embedded loop. This works
		2064	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
		2065	apropriate way for embedded loops.
		2066
		2067	=item struct ev_loop *other [read-only]
		2068
		2069	The embedded event loop.
		2070
		2071	=back
		2072
		2073	=head3 Examples
		2074
		2075	Example: Try to get an embeddable event loop and embed it into the default
		2076	event loop. If that is not possible, use the default loop. The default
		2077	loop is stored in C<loop_hi>, while the mebeddable loop is stored in
		2078	C<loop_lo> (which is C<loop_hi> in the acse no embeddable loop can be
		2079	used).
1100		2080
1101	struct ev_loop *loop_hi = ev_default_init (0);	2081	struct ev_loop *loop_hi = ev_default_init (0);
1102	struct ev_loop *loop_lo = 0;	2082	struct ev_loop *loop_lo = 0;
1103	struct ev_embed embed;	2083	struct ev_embed embed;
1104		2084
…		…
1115	ev_embed_start (loop_hi, &embed);	2095	ev_embed_start (loop_hi, &embed);
1116	}	2096	}
1117	else	2097	else
1118	loop_lo = loop_hi;	2098	loop_lo = loop_hi;
1119		2099
		2100	Example: Check if kqueue is available but not recommended and create
		2101	a kqueue backend for use with sockets (which usually work with any
		2102	kqueue implementation). Store the kqueue/socket-only event loop in
		2103	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		2104
		2105	struct ev_loop *loop = ev_default_init (0);
		2106	struct ev_loop *loop_socket = 0;
		2107	struct ev_embed embed;
		2108
		2109	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		2110	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		2111	{
		2112	ev_embed_init (&embed, 0, loop_socket);
		2113	ev_embed_start (loop, &embed);
		2114	}
		2115
		2116	if (!loop_socket)
		2117	loop_socket = loop;
		2118
		2119	// now use loop_socket for all sockets, and loop for everything else
		2120
		2121
		2122	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
		2123
		2124	Fork watchers are called when a C<fork ()> was detected (usually because
		2125	whoever is a good citizen cared to tell libev about it by calling
		2126	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the
		2127	event loop blocks next and before C<ev_check> watchers are being called,
		2128	and only in the child after the fork. If whoever good citizen calling
		2129	C<ev_default_fork> cheats and calls it in the wrong process, the fork
		2130	handlers will be invoked, too, of course.
		2131
		2132	=head3 Watcher-Specific Functions and Data Members
		2133
1120	=over 4	2134	=over 4
1121		2135
1122	=item ev_embed_init (ev_embed *, callback, struct ev_loop *loop)	2136	=item ev_fork_init (ev_signal *, callback)
1123		2137
1124	=item ev_embed_set (ev_embed *, callback, struct ev_loop *loop)	2138	Initialises and configures the fork watcher - it has no parameters of any
		2139	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
		2140	believe me.
1125		2141
1126	Configures the watcher to embed the given loop, which must be embeddable.	2142	=back
		2143
		2144
		2145	=head2 C<ev_async> - how to wake up another event loop
		2146
		2147	In general, you cannot use an C<ev_loop> from multiple threads or other
		2148	asynchronous sources such as signal handlers (as opposed to multiple event
		2149	loops - those are of course safe to use in different threads).
		2150
		2151	Sometimes, however, you need to wake up another event loop you do not
		2152	control, for example because it belongs to another thread. This is what
		2153	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you
		2154	can signal it by calling C<ev_async_send>, which is thread- and signal
		2155	safe.
		2156
		2157	This functionality is very similar to C<ev_signal> watchers, as signals,
		2158	too, are asynchronous in nature, and signals, too, will be compressed
		2159	(i.e. the number of callback invocations may be less than the number of
		2160	C<ev_async_sent> calls).
		2161
		2162	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		2163	just the default loop.
		2164
		2165	=head3 Queueing
		2166
		2167	C<ev_async> does not support queueing of data in any way. The reason
		2168	is that the author does not know of a simple (or any) algorithm for a
		2169	multiple-writer-single-reader queue that works in all cases and doesn't
		2170	need elaborate support such as pthreads.
		2171
		2172	That means that if you want to queue data, you have to provide your own
		2173	queue. But at least I can tell you would implement locking around your
		2174	queue:
		2175
		2176	=over 4
		2177
		2178	=item queueing from a signal handler context
		2179
		2180	To implement race-free queueing, you simply add to the queue in the signal
		2181	handler but you block the signal handler in the watcher callback. Here is an example that does that for
		2182	some fictitiuous SIGUSR1 handler:
		2183
		2184	static ev_async mysig;
		2185
		2186	static void
		2187	sigusr1_handler (void)
		2188	{
		2189	sometype data;
		2190
		2191	// no locking etc.
		2192	queue_put (data);
		2193	ev_async_send (EV_DEFAULT_ &mysig);
		2194	}
		2195
		2196	static void
		2197	mysig_cb (EV_P_ ev_async *w, int revents)
		2198	{
		2199	sometype data;
		2200	sigset_t block, prev;
		2201
		2202	sigemptyset (&block);
		2203	sigaddset (&block, SIGUSR1);
		2204	sigprocmask (SIG_BLOCK, &block, &prev);
		2205
		2206	while (queue_get (&data))
		2207	process (data);
		2208
		2209	if (sigismember (&prev, SIGUSR1)
		2210	sigprocmask (SIG_UNBLOCK, &block, 0);
		2211	}
		2212
		2213	(Note: pthreads in theory requires you to use C<pthread_setmask>
		2214	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		2215	either...).
		2216
		2217	=item queueing from a thread context
		2218
		2219	The strategy for threads is different, as you cannot (easily) block
		2220	threads but you can easily preempt them, so to queue safely you need to
		2221	employ a traditional mutex lock, such as in this pthread example:
		2222
		2223	static ev_async mysig;
		2224	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		2225
		2226	static void
		2227	otherthread (void)
		2228	{
		2229	// only need to lock the actual queueing operation
		2230	pthread_mutex_lock (&mymutex);
		2231	queue_put (data);
		2232	pthread_mutex_unlock (&mymutex);
		2233
		2234	ev_async_send (EV_DEFAULT_ &mysig);
		2235	}
		2236
		2237	static void
		2238	mysig_cb (EV_P_ ev_async *w, int revents)
		2239	{
		2240	pthread_mutex_lock (&mymutex);
		2241
		2242	while (queue_get (&data))
		2243	process (data);
		2244
		2245	pthread_mutex_unlock (&mymutex);
		2246	}
		2247
		2248	=back
		2249
		2250
		2251	=head3 Watcher-Specific Functions and Data Members
		2252
		2253	=over 4
		2254
		2255	=item ev_async_init (ev_async *, callback)
		2256
		2257	Initialises and configures the async watcher - it has no parameters of any
		2258	kind. There is a C<ev_asynd_set> macro, but using it is utterly pointless,
		2259	believe me.
		2260
		2261	=item ev_async_send (loop, ev_async *)
		2262
		2263	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		2264	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		2265	C<ev_feed_event>, this call is safe to do in other threads, signal or
		2266	similar contexts (see the dicusssion of C<EV_ATOMIC_T> in the embedding
		2267	section below on what exactly this means).
		2268
		2269	This call incurs the overhead of a syscall only once per loop iteration,
		2270	so while the overhead might be noticable, it doesn't apply to repeated
		2271	calls to C<ev_async_send>.
1127		2272
1128	=back	2273	=back
1129		2274
1130		2275
1131	=head1 OTHER FUNCTIONS	2276	=head1 OTHER FUNCTIONS
…		…
1164	/* stdin might have data for us, joy! */;	2309	/* stdin might have data for us, joy! */;
1165	}	2310	}
1166		2311
1167	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	2312	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
1168		2313
1169	=item ev_feed_event (loop, watcher, int events)	2314	=item ev_feed_event (ev_loop *, watcher *, int revents)
1170		2315
1171	Feeds the given event set into the event loop, as if the specified event	2316	Feeds the given event set into the event loop, as if the specified event
1172	had happened for the specified watcher (which must be a pointer to an	2317	had happened for the specified watcher (which must be a pointer to an
1173	initialised but not necessarily started event watcher).	2318	initialised but not necessarily started event watcher).
1174		2319
1175	=item ev_feed_fd_event (loop, int fd, int revents)	2320	=item ev_feed_fd_event (ev_loop *, int fd, int revents)
1176		2321
1177	Feed an event on the given fd, as if a file descriptor backend detected	2322	Feed an event on the given fd, as if a file descriptor backend detected
1178	the given events it.	2323	the given events it.
1179		2324
1180	=item ev_feed_signal_event (loop, int signum)	2325	=item ev_feed_signal_event (ev_loop *loop, int signum)
1181		2326
1182	Feed an event as if the given signal occured (loop must be the default loop!).	2327	Feed an event as if the given signal occured (C<loop> must be the default
		2328	loop!).
1183		2329
1184	=back	2330	=back
1185		2331
1186		2332
1187	=head1 LIBEVENT EMULATION	2333	=head1 LIBEVENT EMULATION
…		…
1211		2357
1212	=back	2358	=back
1213		2359
1214	=head1 C++ SUPPORT	2360	=head1 C++ SUPPORT
1215		2361
1216	TBD.	2362	Libev comes with some simplistic wrapper classes for C++ that mainly allow
		2363	you to use some convinience methods to start/stop watchers and also change
		2364	the callback model to a model using method callbacks on objects.
		2365
		2366	To use it,
		2367
		2368	#include <ev++.h>
		2369
		2370	This automatically includes F<ev.h> and puts all of its definitions (many
		2371	of them macros) into the global namespace. All C++ specific things are
		2372	put into the C<ev> namespace. It should support all the same embedding
		2373	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
		2374
		2375	Care has been taken to keep the overhead low. The only data member the C++
		2376	classes add (compared to plain C-style watchers) is the event loop pointer
		2377	that the watcher is associated with (or no additional members at all if
		2378	you disable C<EV_MULTIPLICITY> when embedding libev).
		2379
		2380	Currently, functions, and static and non-static member functions can be
		2381	used as callbacks. Other types should be easy to add as long as they only
		2382	need one additional pointer for context. If you need support for other
		2383	types of functors please contact the author (preferably after implementing
		2384	it).
		2385
		2386	Here is a list of things available in the C<ev> namespace:
		2387
		2388	=over 4
		2389
		2390	=item C<ev::READ>, C<ev::WRITE> etc.
		2391
		2392	These are just enum values with the same values as the C<EV_READ> etc.
		2393	macros from F<ev.h>.
		2394
		2395	=item C<ev::tstamp>, C<ev::now>
		2396
		2397	Aliases to the same types/functions as with the C<ev_> prefix.
		2398
		2399	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
		2400
		2401	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
		2402	the same name in the C<ev> namespace, with the exception of C<ev_signal>
		2403	which is called C<ev::sig> to avoid clashes with the C<signal> macro
		2404	defines by many implementations.
		2405
		2406	All of those classes have these methods:
		2407
		2408	=over 4
		2409
		2410	=item ev::TYPE::TYPE ()
		2411
		2412	=item ev::TYPE::TYPE (struct ev_loop *)
		2413
		2414	=item ev::TYPE::~TYPE
		2415
		2416	The constructor (optionally) takes an event loop to associate the watcher
		2417	with. If it is omitted, it will use C<EV_DEFAULT>.
		2418
		2419	The constructor calls C<ev_init> for you, which means you have to call the
		2420	C<set> method before starting it.
		2421
		2422	It will not set a callback, however: You have to call the templated C<set>
		2423	method to set a callback before you can start the watcher.
		2424
		2425	(The reason why you have to use a method is a limitation in C++ which does
		2426	not allow explicit template arguments for constructors).
		2427
		2428	The destructor automatically stops the watcher if it is active.
		2429
		2430	=item w->set<class, &class::method> (object *)
		2431
		2432	This method sets the callback method to call. The method has to have a
		2433	signature of C<void (*)(ev_TYPE &, int)>, it receives the watcher as
		2434	first argument and the C<revents> as second. The object must be given as
		2435	parameter and is stored in the C<data> member of the watcher.
		2436
		2437	This method synthesizes efficient thunking code to call your method from
		2438	the C callback that libev requires. If your compiler can inline your
		2439	callback (i.e. it is visible to it at the place of the C<set> call and
		2440	your compiler is good :), then the method will be fully inlined into the
		2441	thunking function, making it as fast as a direct C callback.
		2442
		2443	Example: simple class declaration and watcher initialisation
		2444
		2445	struct myclass
		2446	{
		2447	void io_cb (ev::io &w, int revents) { }
		2448	}
		2449
		2450	myclass obj;
		2451	ev::io iow;
		2452	iow.set <myclass, &myclass::io_cb> (&obj);
		2453
		2454	=item w->set<function> (void *data = 0)
		2455
		2456	Also sets a callback, but uses a static method or plain function as
		2457	callback. The optional C<data> argument will be stored in the watcher's
		2458	C<data> member and is free for you to use.
		2459
		2460	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
		2461
		2462	See the method-C<set> above for more details.
		2463
		2464	Example:
		2465
		2466	static void io_cb (ev::io &w, int revents) { }
		2467	iow.set <io_cb> ();
		2468
		2469	=item w->set (struct ev_loop *)
		2470
		2471	Associates a different C<struct ev_loop> with this watcher. You can only
		2472	do this when the watcher is inactive (and not pending either).
		2473
		2474	=item w->set ([args])
		2475
		2476	Basically the same as C<ev_TYPE_set>, with the same args. Must be
		2477	called at least once. Unlike the C counterpart, an active watcher gets
		2478	automatically stopped and restarted when reconfiguring it with this
		2479	method.
		2480
		2481	=item w->start ()
		2482
		2483	Starts the watcher. Note that there is no C<loop> argument, as the
		2484	constructor already stores the event loop.
		2485
		2486	=item w->stop ()
		2487
		2488	Stops the watcher if it is active. Again, no C<loop> argument.
		2489
		2490	=item w->again () (C<ev::timer>, C<ev::periodic> only)
		2491
		2492	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
		2493	C<ev_TYPE_again> function.
		2494
		2495	=item w->sweep () (C<ev::embed> only)
		2496
		2497	Invokes C<ev_embed_sweep>.
		2498
		2499	=item w->update () (C<ev::stat> only)
		2500
		2501	Invokes C<ev_stat_stat>.
		2502
		2503	=back
		2504
		2505	=back
		2506
		2507	Example: Define a class with an IO and idle watcher, start one of them in
		2508	the constructor.
		2509
		2510	class myclass
		2511	{
		2512	ev::io io; void io_cb (ev::io &w, int revents);
		2513	ev:idle idle void idle_cb (ev::idle &w, int revents);
		2514
		2515	myclass (int fd)
		2516	{
		2517	io .set <myclass, &myclass::io_cb > (this);
		2518	idle.set <myclass, &myclass::idle_cb> (this);
		2519
		2520	io.start (fd, ev::READ);
		2521	}
		2522	};
		2523
		2524
		2525	=head1 OTHER LANGUAGE BINDINGS
		2526
		2527	Libev does not offer other language bindings itself, but bindings for a
		2528	numbe rof languages exist in the form of third-party packages. If you know
		2529	any interesting language binding in addition to the ones listed here, drop
		2530	me a note.
		2531
		2532	=over 4
		2533
		2534	=item Perl
		2535
		2536	The EV module implements the full libev API and is actually used to test
		2537	libev. EV is developed together with libev. Apart from the EV core module,
		2538	there are additional modules that implement libev-compatible interfaces
		2539	to C<libadns> (C<EV::ADNS>), C<Net::SNMP> (C<Net::SNMP::EV>) and the
		2540	C<libglib> event core (C<Glib::EV> and C<EV::Glib>).
		2541
		2542	It can be found and installed via CPAN, its homepage is found at
		2543	L<http://software.schmorp.de/pkg/EV>.
		2544
		2545	=item Ruby
		2546
		2547	Tony Arcieri has written a ruby extension that offers access to a subset
		2548	of the libev API and adds filehandle abstractions, asynchronous DNS and
		2549	more on top of it. It can be found via gem servers. Its homepage is at
		2550	L<http://rev.rubyforge.org/>.
		2551
		2552	=item D
		2553
		2554	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		2555	be found at L<http://git.llucax.com.ar/?p=software/ev.d.git;a=summary>.
		2556
		2557	=back
		2558
		2559
		2560	=head1 MACRO MAGIC
		2561
		2562	Libev can be compiled with a variety of options, the most fundamantal
		2563	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
		2564	functions and callbacks have an initial C<struct ev_loop *> argument.
		2565
		2566	To make it easier to write programs that cope with either variant, the
		2567	following macros are defined:
		2568
		2569	=over 4
		2570
		2571	=item C<EV_A>, C<EV_A_>
		2572
		2573	This provides the loop I<argument> for functions, if one is required ("ev
		2574	loop argument"). The C<EV_A> form is used when this is the sole argument,
		2575	C<EV_A_> is used when other arguments are following. Example:
		2576
		2577	ev_unref (EV_A);
		2578	ev_timer_add (EV_A_ watcher);
		2579	ev_loop (EV_A_ 0);
		2580
		2581	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
		2582	which is often provided by the following macro.
		2583
		2584	=item C<EV_P>, C<EV_P_>
		2585
		2586	This provides the loop I<parameter> for functions, if one is required ("ev
		2587	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
		2588	C<EV_P_> is used when other parameters are following. Example:
		2589
		2590	// this is how ev_unref is being declared
		2591	static void ev_unref (EV_P);
		2592
		2593	// this is how you can declare your typical callback
		2594	static void cb (EV_P_ ev_timer *w, int revents)
		2595
		2596	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
		2597	suitable for use with C<EV_A>.
		2598
		2599	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
		2600
		2601	Similar to the other two macros, this gives you the value of the default
		2602	loop, if multiple loops are supported ("ev loop default").
		2603
		2604	=back
		2605
		2606	Example: Declare and initialise a check watcher, utilising the above
		2607	macros so it will work regardless of whether multiple loops are supported
		2608	or not.
		2609
		2610	static void
		2611	check_cb (EV_P_ ev_timer *w, int revents)
		2612	{
		2613	ev_check_stop (EV_A_ w);
		2614	}
		2615
		2616	ev_check check;
		2617	ev_check_init (&check, check_cb);
		2618	ev_check_start (EV_DEFAULT_ &check);
		2619	ev_loop (EV_DEFAULT_ 0);
		2620
		2621	=head1 EMBEDDING
		2622
		2623	Libev can (and often is) directly embedded into host
		2624	applications. Examples of applications that embed it include the Deliantra
		2625	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
		2626	and rxvt-unicode.
		2627
		2628	The goal is to enable you to just copy the necessary files into your
		2629	source directory without having to change even a single line in them, so
		2630	you can easily upgrade by simply copying (or having a checked-out copy of
		2631	libev somewhere in your source tree).
		2632
		2633	=head2 FILESETS
		2634
		2635	Depending on what features you need you need to include one or more sets of files
		2636	in your app.
		2637
		2638	=head3 CORE EVENT LOOP
		2639
		2640	To include only the libev core (all the C<ev_*> functions), with manual
		2641	configuration (no autoconf):
		2642
		2643	#define EV_STANDALONE 1
		2644	#include "ev.c"
		2645
		2646	This will automatically include F<ev.h>, too, and should be done in a
		2647	single C source file only to provide the function implementations. To use
		2648	it, do the same for F<ev.h> in all files wishing to use this API (best
		2649	done by writing a wrapper around F<ev.h> that you can include instead and
		2650	where you can put other configuration options):
		2651
		2652	#define EV_STANDALONE 1
		2653	#include "ev.h"
		2654
		2655	Both header files and implementation files can be compiled with a C++
		2656	compiler (at least, thats a stated goal, and breakage will be treated
		2657	as a bug).
		2658
		2659	You need the following files in your source tree, or in a directory
		2660	in your include path (e.g. in libev/ when using -Ilibev):
		2661
		2662	ev.h
		2663	ev.c
		2664	ev_vars.h
		2665	ev_wrap.h
		2666
		2667	ev_win32.c required on win32 platforms only
		2668
		2669	ev_select.c only when select backend is enabled (which is enabled by default)
		2670	ev_poll.c only when poll backend is enabled (disabled by default)
		2671	ev_epoll.c only when the epoll backend is enabled (disabled by default)
		2672	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
		2673	ev_port.c only when the solaris port backend is enabled (disabled by default)
		2674
		2675	F<ev.c> includes the backend files directly when enabled, so you only need
		2676	to compile this single file.
		2677
		2678	=head3 LIBEVENT COMPATIBILITY API
		2679
		2680	To include the libevent compatibility API, also include:
		2681
		2682	#include "event.c"
		2683
		2684	in the file including F<ev.c>, and:
		2685
		2686	#include "event.h"
		2687
		2688	in the files that want to use the libevent API. This also includes F<ev.h>.
		2689
		2690	You need the following additional files for this:
		2691
		2692	event.h
		2693	event.c
		2694
		2695	=head3 AUTOCONF SUPPORT
		2696
		2697	Instead of using C<EV_STANDALONE=1> and providing your config in
		2698	whatever way you want, you can also C<m4_include([libev.m4])> in your
		2699	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
		2700	include F<config.h> and configure itself accordingly.
		2701
		2702	For this of course you need the m4 file:
		2703
		2704	libev.m4
		2705
		2706	=head2 PREPROCESSOR SYMBOLS/MACROS
		2707
		2708	Libev can be configured via a variety of preprocessor symbols you have to define
		2709	before including any of its files. The default is not to build for multiplicity
		2710	and only include the select backend.
		2711
		2712	=over 4
		2713
		2714	=item EV_STANDALONE
		2715
		2716	Must always be C<1> if you do not use autoconf configuration, which
		2717	keeps libev from including F<config.h>, and it also defines dummy
		2718	implementations for some libevent functions (such as logging, which is not
		2719	supported). It will also not define any of the structs usually found in
		2720	F<event.h> that are not directly supported by the libev core alone.
		2721
		2722	=item EV_USE_MONOTONIC
		2723
		2724	If defined to be C<1>, libev will try to detect the availability of the
		2725	monotonic clock option at both compiletime and runtime. Otherwise no use
		2726	of the monotonic clock option will be attempted. If you enable this, you
		2727	usually have to link against librt or something similar. Enabling it when
		2728	the functionality isn't available is safe, though, although you have
		2729	to make sure you link against any libraries where the C<clock_gettime>
		2730	function is hiding in (often F<-lrt>).
		2731
		2732	=item EV_USE_REALTIME
		2733
		2734	If defined to be C<1>, libev will try to detect the availability of the
		2735	realtime clock option at compiletime (and assume its availability at
		2736	runtime if successful). Otherwise no use of the realtime clock option will
		2737	be attempted. This effectively replaces C<gettimeofday> by C<clock_get
		2738	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the
		2739	note about libraries in the description of C<EV_USE_MONOTONIC>, though.
		2740
		2741	=item EV_USE_NANOSLEEP
		2742
		2743	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		2744	and will use it for delays. Otherwise it will use C<select ()>.
		2745
		2746	=item EV_USE_SELECT
		2747
		2748	If undefined or defined to be C<1>, libev will compile in support for the
		2749	C<select>(2) backend. No attempt at autodetection will be done: if no
		2750	other method takes over, select will be it. Otherwise the select backend
		2751	will not be compiled in.
		2752
		2753	=item EV_SELECT_USE_FD_SET
		2754
		2755	If defined to C<1>, then the select backend will use the system C<fd_set>
		2756	structure. This is useful if libev doesn't compile due to a missing
		2757	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on
		2758	exotic systems. This usually limits the range of file descriptors to some
		2759	low limit such as 1024 or might have other limitations (winsocket only
		2760	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might
		2761	influence the size of the C<fd_set> used.
		2762
		2763	=item EV_SELECT_IS_WINSOCKET
		2764
		2765	When defined to C<1>, the select backend will assume that
		2766	select/socket/connect etc. don't understand file descriptors but
		2767	wants osf handles on win32 (this is the case when the select to
		2768	be used is the winsock select). This means that it will call
		2769	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
		2770	it is assumed that all these functions actually work on fds, even
		2771	on win32. Should not be defined on non-win32 platforms.
		2772
		2773	=item EV_FD_TO_WIN32_HANDLE
		2774
		2775	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		2776	file descriptors to socket handles. When not defining this symbol (the
		2777	default), then libev will call C<_get_osfhandle>, which is usually
		2778	correct. In some cases, programs use their own file descriptor management,
		2779	in which case they can provide this function to map fds to socket handles.
		2780
		2781	=item EV_USE_POLL
		2782
		2783	If defined to be C<1>, libev will compile in support for the C<poll>(2)
		2784	backend. Otherwise it will be enabled on non-win32 platforms. It
		2785	takes precedence over select.
		2786
		2787	=item EV_USE_EPOLL
		2788
		2789	If defined to be C<1>, libev will compile in support for the Linux
		2790	C<epoll>(7) backend. Its availability will be detected at runtime,
		2791	otherwise another method will be used as fallback. This is the
		2792	preferred backend for GNU/Linux systems.
		2793
		2794	=item EV_USE_KQUEUE
		2795
		2796	If defined to be C<1>, libev will compile in support for the BSD style
		2797	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
		2798	otherwise another method will be used as fallback. This is the preferred
		2799	backend for BSD and BSD-like systems, although on most BSDs kqueue only
		2800	supports some types of fds correctly (the only platform we found that
		2801	supports ptys for example was NetBSD), so kqueue might be compiled in, but
		2802	not be used unless explicitly requested. The best way to use it is to find
		2803	out whether kqueue supports your type of fd properly and use an embedded
		2804	kqueue loop.
		2805
		2806	=item EV_USE_PORT
		2807
		2808	If defined to be C<1>, libev will compile in support for the Solaris
		2809	10 port style backend. Its availability will be detected at runtime,
		2810	otherwise another method will be used as fallback. This is the preferred
		2811	backend for Solaris 10 systems.
		2812
		2813	=item EV_USE_DEVPOLL
		2814
		2815	reserved for future expansion, works like the USE symbols above.
		2816
		2817	=item EV_USE_INOTIFY
		2818
		2819	If defined to be C<1>, libev will compile in support for the Linux inotify
		2820	interface to speed up C<ev_stat> watchers. Its actual availability will
		2821	be detected at runtime.
		2822
		2823	=item EV_ATOMIC_T
		2824
		2825	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		2826	access is atomic with respect to other threads or signal contexts. No such
		2827	type is easily found in the C language, so you can provide your own type
		2828	that you know is safe for your purposes. It is used both for signal handler "locking"
		2829	as well as for signal and thread safety in C<ev_async> watchers.
		2830
		2831	In the absense of this define, libev will use C<sig_atomic_t volatile>
		2832	(from F<signal.h>), which is usually good enough on most platforms.
		2833
		2834	=item EV_H
		2835
		2836	The name of the F<ev.h> header file used to include it. The default if
		2837	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
		2838	used to virtually rename the F<ev.h> header file in case of conflicts.
		2839
		2840	=item EV_CONFIG_H
		2841
		2842	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
		2843	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
		2844	C<EV_H>, above.
		2845
		2846	=item EV_EVENT_H
		2847
		2848	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
		2849	of how the F<event.h> header can be found, the default is C<"event.h">.
		2850
		2851	=item EV_PROTOTYPES
		2852
		2853	If defined to be C<0>, then F<ev.h> will not define any function
		2854	prototypes, but still define all the structs and other symbols. This is
		2855	occasionally useful if you want to provide your own wrapper functions
		2856	around libev functions.
		2857
		2858	=item EV_MULTIPLICITY
		2859
		2860	If undefined or defined to C<1>, then all event-loop-specific functions
		2861	will have the C<struct ev_loop *> as first argument, and you can create
		2862	additional independent event loops. Otherwise there will be no support
		2863	for multiple event loops and there is no first event loop pointer
		2864	argument. Instead, all functions act on the single default loop.
		2865
		2866	=item EV_MINPRI
		2867
		2868	=item EV_MAXPRI
		2869
		2870	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
		2871	C<EV_MAXPRI>, but otherwise there are no non-obvious limitations. You can
		2872	provide for more priorities by overriding those symbols (usually defined
		2873	to be C<-2> and C<2>, respectively).
		2874
		2875	When doing priority-based operations, libev usually has to linearly search
		2876	all the priorities, so having many of them (hundreds) uses a lot of space
		2877	and time, so using the defaults of five priorities (-2 .. +2) is usually
		2878	fine.
		2879
		2880	If your embedding app does not need any priorities, defining these both to
		2881	C<0> will save some memory and cpu.
		2882
		2883	=item EV_PERIODIC_ENABLE
		2884
		2885	If undefined or defined to be C<1>, then periodic timers are supported. If
		2886	defined to be C<0>, then they are not. Disabling them saves a few kB of
		2887	code.
		2888
		2889	=item EV_IDLE_ENABLE
		2890
		2891	If undefined or defined to be C<1>, then idle watchers are supported. If
		2892	defined to be C<0>, then they are not. Disabling them saves a few kB of
		2893	code.
		2894
		2895	=item EV_EMBED_ENABLE
		2896
		2897	If undefined or defined to be C<1>, then embed watchers are supported. If
		2898	defined to be C<0>, then they are not.
		2899
		2900	=item EV_STAT_ENABLE
		2901
		2902	If undefined or defined to be C<1>, then stat watchers are supported. If
		2903	defined to be C<0>, then they are not.
		2904
		2905	=item EV_FORK_ENABLE
		2906
		2907	If undefined or defined to be C<1>, then fork watchers are supported. If
		2908	defined to be C<0>, then they are not.
		2909
		2910	=item EV_ASYNC_ENABLE
		2911
		2912	If undefined or defined to be C<1>, then async watchers are supported. If
		2913	defined to be C<0>, then they are not.
		2914
		2915	=item EV_MINIMAL
		2916
		2917	If you need to shave off some kilobytes of code at the expense of some
		2918	speed, define this symbol to C<1>. Currently only used for gcc to override
		2919	some inlining decisions, saves roughly 30% codesize of amd64.
		2920
		2921	=item EV_PID_HASHSIZE
		2922
		2923	C<ev_child> watchers use a small hash table to distribute workload by
		2924	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
		2925	than enough. If you need to manage thousands of children you might want to
		2926	increase this value (I<must> be a power of two).
		2927
		2928	=item EV_INOTIFY_HASHSIZE
		2929
		2930	C<ev_stat> watchers use a small hash table to distribute workload by
		2931	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
		2932	usually more than enough. If you need to manage thousands of C<ev_stat>
		2933	watchers you might want to increase this value (I<must> be a power of
		2934	two).
		2935
		2936	=item EV_COMMON
		2937
		2938	By default, all watchers have a C<void *data> member. By redefining
		2939	this macro to a something else you can include more and other types of
		2940	members. You have to define it each time you include one of the files,
		2941	though, and it must be identical each time.
		2942
		2943	For example, the perl EV module uses something like this:
		2944
		2945	#define EV_COMMON \
		2946	SV *self; /* contains this struct */ \
		2947	SV *cb_sv, *fh /* note no trailing ";" */
		2948
		2949	=item EV_CB_DECLARE (type)
		2950
		2951	=item EV_CB_INVOKE (watcher, revents)
		2952
		2953	=item ev_set_cb (ev, cb)
		2954
		2955	Can be used to change the callback member declaration in each watcher,
		2956	and the way callbacks are invoked and set. Must expand to a struct member
		2957	definition and a statement, respectively. See the F<ev.h> header file for
		2958	their default definitions. One possible use for overriding these is to
		2959	avoid the C<struct ev_loop *> as first argument in all cases, or to use
		2960	method calls instead of plain function calls in C++.
		2961
		2962	=head2 EXPORTED API SYMBOLS
		2963
		2964	If you need to re-export the API (e.g. via a dll) and you need a list of
		2965	exported symbols, you can use the provided F<Symbol.*> files which list
		2966	all public symbols, one per line:
		2967
		2968	Symbols.ev for libev proper
		2969	Symbols.event for the libevent emulation
		2970
		2971	This can also be used to rename all public symbols to avoid clashes with
		2972	multiple versions of libev linked together (which is obviously bad in
		2973	itself, but sometimes it is inconvinient to avoid this).
		2974
		2975	A sed command like this will create wrapper C<#define>'s that you need to
		2976	include before including F<ev.h>:
		2977
		2978	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		2979
		2980	This would create a file F<wrap.h> which essentially looks like this:
		2981
		2982	#define ev_backend myprefix_ev_backend
		2983	#define ev_check_start myprefix_ev_check_start
		2984	#define ev_check_stop myprefix_ev_check_stop
		2985	...
		2986
		2987	=head2 EXAMPLES
		2988
		2989	For a real-world example of a program the includes libev
		2990	verbatim, you can have a look at the EV perl module
		2991	(L<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
		2992	the F<libev/> subdirectory and includes them in the F<EV/EVAPI.h> (public
		2993	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file
		2994	will be compiled. It is pretty complex because it provides its own header
		2995	file.
		2996
		2997	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
		2998	that everybody includes and which overrides some configure choices:
		2999
		3000	#define EV_MINIMAL 1
		3001	#define EV_USE_POLL 0
		3002	#define EV_MULTIPLICITY 0
		3003	#define EV_PERIODIC_ENABLE 0
		3004	#define EV_STAT_ENABLE 0
		3005	#define EV_FORK_ENABLE 0
		3006	#define EV_CONFIG_H <config.h>
		3007	#define EV_MINPRI 0
		3008	#define EV_MAXPRI 0
		3009
		3010	#include "ev++.h"
		3011
		3012	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
		3013
		3014	#include "ev_cpp.h"
		3015	#include "ev.c"
		3016
		3017
		3018	=head1 COMPLEXITIES
		3019
		3020	In this section the complexities of (many of) the algorithms used inside
		3021	libev will be explained. For complexity discussions about backends see the
		3022	documentation for C<ev_default_init>.
		3023
		3024	All of the following are about amortised time: If an array needs to be
		3025	extended, libev needs to realloc and move the whole array, but this
		3026	happens asymptotically never with higher number of elements, so O(1) might
		3027	mean it might do a lengthy realloc operation in rare cases, but on average
		3028	it is much faster and asymptotically approaches constant time.
		3029
		3030	=over 4
		3031
		3032	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
		3033
		3034	This means that, when you have a watcher that triggers in one hour and
		3035	there are 100 watchers that would trigger before that then inserting will
		3036	have to skip roughly seven (C<ld 100>) of these watchers.
		3037
		3038	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
		3039
		3040	That means that changing a timer costs less than removing/adding them
		3041	as only the relative motion in the event queue has to be paid for.
		3042
		3043	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
		3044
		3045	These just add the watcher into an array or at the head of a list.
		3046
		3047	=item Stopping check/prepare/idle/fork/async watchers: O(1)
		3048
		3049	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
		3050
		3051	These watchers are stored in lists then need to be walked to find the
		3052	correct watcher to remove. The lists are usually short (you don't usually
		3053	have many watchers waiting for the same fd or signal).
		3054
		3055	=item Finding the next timer in each loop iteration: O(1)
		3056
		3057	By virtue of using a binary heap, the next timer is always found at the
		3058	beginning of the storage array.
		3059
		3060	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		3061
		3062	A change means an I/O watcher gets started or stopped, which requires
		3063	libev to recalculate its status (and possibly tell the kernel, depending
		3064	on backend and wether C<ev_io_set> was used).
		3065
		3066	=item Activating one watcher (putting it into the pending state): O(1)
		3067
		3068	=item Priority handling: O(number_of_priorities)
		3069
		3070	Priorities are implemented by allocating some space for each
		3071	priority. When doing priority-based operations, libev usually has to
		3072	linearly search all the priorities, but starting/stopping and activating
		3073	watchers becomes O(1) w.r.t. priority handling.
		3074
		3075	=item Sending an ev_async: O(1)
		3076
		3077	=item Processing ev_async_send: O(number_of_async_watchers)
		3078
		3079	=item Processing signals: O(max_signal_number)
		3080
		3081	Sending involves a syscall I<iff> there were no other C<ev_async_send>
		3082	calls in the current loop iteration. Checking for async and signal events
		3083	involves iterating over all running async watchers or all signal numbers.
		3084
		3085	=back
		3086
		3087
		3088	=head1 Win32 platform limitations and workarounds
		3089
		3090	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		3091	requires, and its I/O model is fundamentally incompatible with the POSIX
		3092	model. Libev still offers limited functionality on this platform in
		3093	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		3094	descriptors. This only applies when using Win32 natively, not when using
		3095	e.g. cygwin.
		3096
		3097	There is no supported compilation method available on windows except
		3098	embedding it into other applications.
		3099
		3100	Due to the many, low, and arbitrary limits on the win32 platform and the
		3101	abysmal performance of winsockets, using a large number of sockets is not
		3102	recommended (and not reasonable). If your program needs to use more than
		3103	a hundred or so sockets, then likely it needs to use a totally different
		3104	implementation for windows, as libev offers the POSIX model, which cannot
		3105	be implemented efficiently on windows (microsoft monopoly games).
		3106
		3107	=over 4
		3108
		3109	=item The winsocket select function
		3110
		3111	The winsocket C<select> function doesn't follow POSIX in that it requires
		3112	socket I<handles> and not socket I<file descriptors>. This makes select
		3113	very inefficient, and also requires a mapping from file descriptors
		3114	to socket handles. See the discussion of the C<EV_SELECT_USE_FD_SET>,
		3115	C<EV_SELECT_IS_WINSOCKET> and C<EV_FD_TO_WIN32_HANDLE> preprocessor
		3116	symbols for more info.
		3117
		3118	The configuration for a "naked" win32 using the microsoft runtime
		3119	libraries and raw winsocket select is:
		3120
		3121	#define EV_USE_SELECT 1
		3122	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		3123
		3124	Note that winsockets handling of fd sets is O(n), so you can easily get a
		3125	complexity in the O(n²) range when using win32.
		3126
		3127	=item Limited number of file descriptors
		3128
		3129	Windows has numerous arbitrary (and low) limits on things. Early versions
		3130	of winsocket's select only supported waiting for a max. of C<64> handles
		3131	(probably owning to the fact that all windows kernels can only wait for
		3132	C<64> things at the same time internally; microsoft recommends spawning a
		3133	chain of threads and wait for 63 handles and the previous thread in each).
		3134
		3135	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		3136	to some high number (e.g. C<2048>) before compiling the winsocket select
		3137	call (which might be in libev or elsewhere, for example, perl does its own
		3138	select emulation on windows).
		3139
		3140	Another limit is the number of file descriptors in the microsoft runtime
		3141	libraries, which by default is C<64> (there must be a hidden I<64> fetish
		3142	or something like this inside microsoft). You can increase this by calling
		3143	C<_setmaxstdio>, which can increase this limit to C<2048> (another
		3144	arbitrary limit), but is broken in many versions of the microsoft runtime
		3145	libraries.
		3146
		3147	This might get you to about C<512> or C<2048> sockets (depending on
		3148	windows version and/or the phase of the moon). To get more, you need to
		3149	wrap all I/O functions and provide your own fd management, but the cost of
		3150	calling select (O(n²)) will likely make this unworkable.
		3151
		3152	=back
		3153
1217		3154
1218	=head1 AUTHOR	3155	=head1 AUTHOR
1219		3156
1220	Marc Lehmann <libev@schmorp.de>.	3157	Marc Lehmann <libev@schmorp.de>.
1221		3158

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