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Revision 1.35 by root, Fri Nov 23 19:35:09 2007 UTC vs.
Revision 1.168 by root, Mon Jun 9 14:31:36 2008 UTC

…		…
2		2
3	libev - a high performance full-featured event loop written in C	3	libev - a high performance full-featured event loop written in C
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	#include <ev.h>	7	#include <ev.h>
		8
		9	=head2 EXAMPLE PROGRAM
		10
		11	// a single header file is required
		12	#include <ev.h>
		13
		14	// every watcher type has its own typedef'd struct
		15	// with the name ev_<type>
		16	ev_io stdin_watcher;
		17	ev_timer timeout_watcher;
		18
		19	// all watcher callbacks have a similar signature
		20	// this callback is called when data is readable on stdin
		21	static void
		22	stdin_cb (EV_P_ struct ev_io *w, int revents)
		23	{
		24	puts ("stdin ready");
		25	// for one-shot events, one must manually stop the watcher
		26	// with its corresponding stop function.
		27	ev_io_stop (EV_A_ w);
		28
		29	// this causes all nested ev_loop's to stop iterating
		30	ev_unloop (EV_A_ EVUNLOOP_ALL);
		31	}
		32
		33	// another callback, this time for a time-out
		34	static void
		35	timeout_cb (EV_P_ struct ev_timer *w, int revents)
		36	{
		37	puts ("timeout");
		38	// this causes the innermost ev_loop to stop iterating
		39	ev_unloop (EV_A_ EVUNLOOP_ONE);
		40	}
		41
		42	int
		43	main (void)
		44	{
		45	// use the default event loop unless you have special needs
		46	struct ev_loop *loop = ev_default_loop (0);
		47
		48	// initialise an io watcher, then start it
		49	// this one will watch for stdin to become readable
		50	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
		51	ev_io_start (loop, &stdin_watcher);
		52
		53	// initialise a timer watcher, then start it
		54	// simple non-repeating 5.5 second timeout
		55	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		56	ev_timer_start (loop, &timeout_watcher);
		57
		58	// now wait for events to arrive
		59	ev_loop (loop, 0);
		60
		61	// unloop was called, so exit
		62	return 0;
		63	}
8		64
9	=head1 DESCRIPTION	65	=head1 DESCRIPTION
10		66
		67	The newest version of this document is also available as an html-formatted
		68	web page you might find easier to navigate when reading it for the first
		69	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
		70
11	Libev is an event loop: you register interest in certain events (such as a	71	Libev is an event loop: you register interest in certain events (such as a
12	file descriptor being readable or a timeout occuring), and it will manage	72	file descriptor being readable or a timeout occurring), and it will manage
13	these event sources and provide your program with events.	73	these event sources and provide your program with events.
14		74
15	To do this, it must take more or less complete control over your process	75	To do this, it must take more or less complete control over your process
16	(or thread) by executing the I<event loop> handler, and will then	76	(or thread) by executing the I<event loop> handler, and will then
17	communicate events via a callback mechanism.	77	communicate events via a callback mechanism.
…		…
19	You register interest in certain events by registering so-called I<event	79	You register interest in certain events by registering so-called I<event
20	watchers>, which are relatively small C structures you initialise with the	80	watchers>, which are relatively small C structures you initialise with the
21	details of the event, and then hand it over to libev by I<starting> the	81	details of the event, and then hand it over to libev by I<starting> the
22	watcher.	82	watcher.
23		83
24	=head1 FEATURES	84	=head2 FEATURES
25		85
26	Libev supports select, poll, the linux-specific epoll and the bsd-specific	86	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
27	kqueue mechanisms for file descriptor events, relative timers, absolute	87	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
28	timers with customised rescheduling, signal events, process status change	88	for file descriptor events (C<ev_io>), the Linux C<inotify> interface
29	events (related to SIGCHLD), and event watchers dealing with the event	89	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers
30	loop mechanism itself (idle, prepare and check watchers). It also is quite	90	with customised rescheduling (C<ev_periodic>), synchronous signals
		91	(C<ev_signal>), process status change events (C<ev_child>), and event
		92	watchers dealing with the event loop mechanism itself (C<ev_idle>,
		93	C<ev_embed>, C<ev_prepare> and C<ev_check> watchers) as well as
		94	file watchers (C<ev_stat>) and even limited support for fork events
		95	(C<ev_fork>).
		96
		97	It also is quite fast (see this
31	fast (see this L<benchmark|http://libev.schmorp.de/bench.html> comparing	98	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
32	it to libevent for example).	99	for example).
33		100
34	=head1 CONVENTIONS	101	=head2 CONVENTIONS
35		102
36	Libev is very configurable. In this manual the default configuration	103	Libev is very configurable. In this manual the default (and most common)
37	will be described, which supports multiple event loops. For more info	104	configuration will be described, which supports multiple event loops. For
38	about various configuration options please have a look at the file	105	more info about various configuration options please have a look at
39	F<README.embed> in the libev distribution. If libev was configured without	106	B<EMBED> section in this manual. If libev was configured without support
40	support for multiple event loops, then all functions taking an initial	107	for multiple event loops, then all functions taking an initial argument of
41	argument of name C<loop> (which is always of type C<struct ev_loop *>)	108	name C<loop> (which is always of type C<struct ev_loop *>) will not have
42	will not have this argument.	109	this argument.
43		110
44	=head1 TIME REPRESENTATION	111	=head2 TIME REPRESENTATION
45		112
46	Libev represents time as a single floating point number, representing the	113	Libev represents time as a single floating point number, representing the
47	(fractional) number of seconds since the (POSIX) epoch (somewhere near	114	(fractional) number of seconds since the (POSIX) epoch (somewhere near
48	the beginning of 1970, details are complicated, don't ask). This type is	115	the beginning of 1970, details are complicated, don't ask). This type is
49	called C<ev_tstamp>, which is what you should use too. It usually aliases	116	called C<ev_tstamp>, which is what you should use too. It usually aliases
50	to the C<double> type in C, and when you need to do any calculations on	117	to the C<double> type in C, and when you need to do any calculations on
51	it, you should treat it as such.	118	it, you should treat it as some floating point value. Unlike the name
		119	component C<stamp> might indicate, it is also used for time differences
		120	throughout libev.
		121
		122	=head1 ERROR HANDLING
		123
		124	Libev knows three classes of errors: operating system errors, usage errors
		125	and internal errors (bugs).
		126
		127	When libev catches an operating system error it cannot handle (for example
		128	a system call indicating a condition libev cannot fix), it calls the callback
		129	set via C<ev_set_syserr_cb>, which is supposed to fix the problem or
		130	abort. The default is to print a diagnostic message and to call C<abort
		131	()>.
		132
		133	When libev detects a usage error such as a negative timer interval, then
		134	it will print a diagnostic message and abort (via the C<assert> mechanism,
		135	so C<NDEBUG> will disable this checking): these are programming errors in
		136	the libev caller and need to be fixed there.
		137
		138	Libev also has a few internal error-checking C<assert>ions, and also has
		139	extensive consistency checking code. These do not trigger under normal
		140	circumstances, as they indicate either a bug in libev or worse.
52		141
53		142
54	=head1 GLOBAL FUNCTIONS	143	=head1 GLOBAL FUNCTIONS
55		144
56	These functions can be called anytime, even before initialising the	145	These functions can be called anytime, even before initialising the
…		…
62		151
63	Returns the current time as libev would use it. Please note that the	152	Returns the current time as libev would use it. Please note that the
64	C<ev_now> function is usually faster and also often returns the timestamp	153	C<ev_now> function is usually faster and also often returns the timestamp
65	you actually want to know.	154	you actually want to know.
66		155
		156	=item ev_sleep (ev_tstamp interval)
		157
		158	Sleep for the given interval: The current thread will be blocked until
		159	either it is interrupted or the given time interval has passed. Basically
		160	this is a sub-second-resolution C<sleep ()>.
		161
67	=item int ev_version_major ()	162	=item int ev_version_major ()
68		163
69	=item int ev_version_minor ()	164	=item int ev_version_minor ()
70		165
71	You can find out the major and minor version numbers of the library	166	You can find out the major and minor ABI version numbers of the library
72	you linked against by calling the functions C<ev_version_major> and	167	you linked against by calling the functions C<ev_version_major> and
73	C<ev_version_minor>. If you want, you can compare against the global	168	C<ev_version_minor>. If you want, you can compare against the global
74	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the	169	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the
75	version of the library your program was compiled against.	170	version of the library your program was compiled against.
76		171
		172	These version numbers refer to the ABI version of the library, not the
		173	release version.
		174
77	Usually, it's a good idea to terminate if the major versions mismatch,	175	Usually, it's a good idea to terminate if the major versions mismatch,
78	as this indicates an incompatible change. Minor versions are usually	176	as this indicates an incompatible change. Minor versions are usually
79	compatible to older versions, so a larger minor version alone is usually	177	compatible to older versions, so a larger minor version alone is usually
80	not a problem.	178	not a problem.
81		179
82	Example: make sure we haven't accidentally been linked against the wrong	180	Example: Make sure we haven't accidentally been linked against the wrong
83	version:	181	version.
84		182
85	assert (("libev version mismatch",	183	assert (("libev version mismatch",
86	ev_version_major () == EV_VERSION_MAJOR	184	ev_version_major () == EV_VERSION_MAJOR
87	&& ev_version_minor () >= EV_VERSION_MINOR));	185	&& ev_version_minor () >= EV_VERSION_MINOR));
88		186
89	=item unsigned int ev_supported_backends ()	187	=item unsigned int ev_supported_backends ()
90		188
91	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>	189	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
92	value) compiled into this binary of libev (independent of their	190	value) compiled into this binary of libev (independent of their
…		…
94	a description of the set values.	192	a description of the set values.
95		193
96	Example: make sure we have the epoll method, because yeah this is cool and	194	Example: make sure we have the epoll method, because yeah this is cool and
97	a must have and can we have a torrent of it please!!!11	195	a must have and can we have a torrent of it please!!!11
98		196
99	assert (("sorry, no epoll, no sex",	197	assert (("sorry, no epoll, no sex",
100	ev_supported_backends () & EVBACKEND_EPOLL));	198	ev_supported_backends () & EVBACKEND_EPOLL));
101		199
102	=item unsigned int ev_recommended_backends ()	200	=item unsigned int ev_recommended_backends ()
103		201
104	Return the set of all backends compiled into this binary of libev and also	202	Return the set of all backends compiled into this binary of libev and also
105	recommended for this platform. This set is often smaller than the one	203	recommended for this platform. This set is often smaller than the one
106	returned by C<ev_supported_backends>, as for example kqueue is broken on	204	returned by C<ev_supported_backends>, as for example kqueue is broken on
107	most BSDs and will not be autodetected unless you explicitly request it	205	most BSDs and will not be auto-detected unless you explicitly request it
108	(assuming you know what you are doing). This is the set of backends that	206	(assuming you know what you are doing). This is the set of backends that
109	libev will probe for if you specify no backends explicitly.	207	libev will probe for if you specify no backends explicitly.
110		208
111	=item unsigned int ev_embeddable_backends ()	209	=item unsigned int ev_embeddable_backends ()
112		210
…		…
118		216
119	See the description of C<ev_embed> watchers for more info.	217	See the description of C<ev_embed> watchers for more info.
120		218
121	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	219	=item ev_set_allocator (void *(*cb)(void *ptr, long size))
122		220
123	Sets the allocation function to use (the prototype is similar to the	221	Sets the allocation function to use (the prototype is similar - the
124	realloc C function, the semantics are identical). It is used to allocate	222	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
125	and free memory (no surprises here). If it returns zero when memory	223	used to allocate and free memory (no surprises here). If it returns zero
126	needs to be allocated, the library might abort or take some potentially	224	when memory needs to be allocated (C<size != 0>), the library might abort
127	destructive action. The default is your system realloc function.	225	or take some potentially destructive action.
		226
		227	Since some systems (at least OpenBSD and Darwin) fail to implement
		228	correct C<realloc> semantics, libev will use a wrapper around the system
		229	C<realloc> and C<free> functions by default.
128		230
129	You could override this function in high-availability programs to, say,	231	You could override this function in high-availability programs to, say,
130	free some memory if it cannot allocate memory, to use a special allocator,	232	free some memory if it cannot allocate memory, to use a special allocator,
131	or even to sleep a while and retry until some memory is available.	233	or even to sleep a while and retry until some memory is available.
132		234
133	Example: replace the libev allocator with one that waits a bit and then	235	Example: Replace the libev allocator with one that waits a bit and then
134	retries: better than mine).	236	retries (example requires a standards-compliant C<realloc>).
135		237
136	static void *	238	static void *
137	persistent_realloc (void *ptr, long size)	239	persistent_realloc (void *ptr, size_t size)
138	{	240	{
139	for (;;)	241	for (;;)
140	{	242	{
141	void *newptr = realloc (ptr, size);	243	void *newptr = realloc (ptr, size);
142		244
…		…
150	...	252	...
151	ev_set_allocator (persistent_realloc);	253	ev_set_allocator (persistent_realloc);
152		254
153	=item ev_set_syserr_cb (void (*cb)(const char *msg));	255	=item ev_set_syserr_cb (void (*cb)(const char *msg));
154		256
155	Set the callback function to call on a retryable syscall error (such	257	Set the callback function to call on a retryable system call error (such
156	as failed select, poll, epoll_wait). The message is a printable string	258	as failed select, poll, epoll_wait). The message is a printable string
157	indicating the system call or subsystem causing the problem. If this	259	indicating the system call or subsystem causing the problem. If this
158	callback is set, then libev will expect it to remedy the sitution, no	260	callback is set, then libev will expect it to remedy the situation, no
159	matter what, when it returns. That is, libev will generally retry the	261	matter what, when it returns. That is, libev will generally retry the
160	requested operation, or, if the condition doesn't go away, do bad stuff	262	requested operation, or, if the condition doesn't go away, do bad stuff
161	(such as abort).	263	(such as abort).
162		264
163	Example: do the same thing as libev does internally:	265	Example: This is basically the same thing that libev does internally, too.
164		266
165	static void	267	static void
166	fatal_error (const char *msg)	268	fatal_error (const char *msg)
167	{	269	{
168	perror (msg);	270	perror (msg);
…		…
177	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	279	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
178		280
179	An event loop is described by a C<struct ev_loop *>. The library knows two	281	An event loop is described by a C<struct ev_loop *>. The library knows two
180	types of such loops, the I<default> loop, which supports signals and child	282	types of such loops, the I<default> loop, which supports signals and child
181	events, and dynamically created loops which do not.	283	events, and dynamically created loops which do not.
182
183	If you use threads, a common model is to run the default event loop
184	in your main thread (or in a separate thread) and for each thread you
185	create, you also create another event loop. Libev itself does no locking
186	whatsoever, so if you mix calls to the same event loop in different
187	threads, make sure you lock (this is usually a bad idea, though, even if
188	done correctly, because it's hideous and inefficient).
189		284
190	=over 4	285	=over 4
191		286
192	=item struct ev_loop *ev_default_loop (unsigned int flags)	287	=item struct ev_loop *ev_default_loop (unsigned int flags)
193		288
…		…
197	flags. If that is troubling you, check C<ev_backend ()> afterwards).	292	flags. If that is troubling you, check C<ev_backend ()> afterwards).
198		293
199	If you don't know what event loop to use, use the one returned from this	294	If you don't know what event loop to use, use the one returned from this
200	function.	295	function.
201		296
		297	Note that this function is I<not> thread-safe, so if you want to use it
		298	from multiple threads, you have to lock (note also that this is unlikely,
		299	as loops cannot bes hared easily between threads anyway).
		300
		301	The default loop is the only loop that can handle C<ev_signal> and
		302	C<ev_child> watchers, and to do this, it always registers a handler
		303	for C<SIGCHLD>. If this is a problem for your application you can either
		304	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you
		305	can simply overwrite the C<SIGCHLD> signal handler I<after> calling
		306	C<ev_default_init>.
		307
202	The flags argument can be used to specify special behaviour or specific	308	The flags argument can be used to specify special behaviour or specific
203	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).	309	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
204		310
205	The following flags are supported:	311	The following flags are supported:
206		312
…		…
211	The default flags value. Use this if you have no clue (it's the right	317	The default flags value. Use this if you have no clue (it's the right
212	thing, believe me).	318	thing, believe me).
213		319
214	=item C<EVFLAG_NOENV>	320	=item C<EVFLAG_NOENV>
215		321
216	If this flag bit is ored into the flag value (or the program runs setuid	322	If this flag bit is or'ed into the flag value (or the program runs setuid
217	or setgid) then libev will I<not> look at the environment variable	323	or setgid) then libev will I<not> look at the environment variable
218	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	324	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
219	override the flags completely if it is found in the environment. This is	325	override the flags completely if it is found in the environment. This is
220	useful to try out specific backends to test their performance, or to work	326	useful to try out specific backends to test their performance, or to work
221	around bugs.	327	around bugs.
222		328
		329	=item C<EVFLAG_FORKCHECK>
		330
		331	Instead of calling C<ev_default_fork> or C<ev_loop_fork> manually after
		332	a fork, you can also make libev check for a fork in each iteration by
		333	enabling this flag.
		334
		335	This works by calling C<getpid ()> on every iteration of the loop,
		336	and thus this might slow down your event loop if you do a lot of loop
		337	iterations and little real work, but is usually not noticeable (on my
		338	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence
		339	without a system call and thus I<very> fast, but my GNU/Linux system also has
		340	C<pthread_atfork> which is even faster).
		341
		342	The big advantage of this flag is that you can forget about fork (and
		343	forget about forgetting to tell libev about forking) when you use this
		344	flag.
		345
		346	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
		347	environment variable.
		348
223	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	349	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
224		350
225	This is your standard select(2) backend. Not I<completely> standard, as	351	This is your standard select(2) backend. Not I<completely> standard, as
226	libev tries to roll its own fd_set with no limits on the number of fds,	352	libev tries to roll its own fd_set with no limits on the number of fds,
227	but if that fails, expect a fairly low limit on the number of fds when	353	but if that fails, expect a fairly low limit on the number of fds when
228	using this backend. It doesn't scale too well (O(highest_fd)), but its usually	354	using this backend. It doesn't scale too well (O(highest_fd)), but its
229	the fastest backend for a low number of fds.	355	usually the fastest backend for a low number of (low-numbered :) fds.
		356
		357	To get good performance out of this backend you need a high amount of
		358	parallelism (most of the file descriptors should be busy). If you are
		359	writing a server, you should C<accept ()> in a loop to accept as many
		360	connections as possible during one iteration. You might also want to have
		361	a look at C<ev_set_io_collect_interval ()> to increase the amount of
		362	readiness notifications you get per iteration.
230		363
231	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)	364	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
232		365
233	And this is your standard poll(2) backend. It's more complicated than	366	And this is your standard poll(2) backend. It's more complicated
234	select, but handles sparse fds better and has no artificial limit on the	367	than select, but handles sparse fds better and has no artificial
235	number of fds you can use (except it will slow down considerably with a	368	limit on the number of fds you can use (except it will slow down
236	lot of inactive fds). It scales similarly to select, i.e. O(total_fds).	369	considerably with a lot of inactive fds). It scales similarly to select,
		370	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
		371	performance tips.
237		372
238	=item C<EVBACKEND_EPOLL> (value 4, Linux)	373	=item C<EVBACKEND_EPOLL> (value 4, Linux)
239		374
240	For few fds, this backend is a bit little slower than poll and select,	375	For few fds, this backend is a bit little slower than poll and select,
241	but it scales phenomenally better. While poll and select usually scale like	376	but it scales phenomenally better. While poll and select usually scale
242	O(total_fds) where n is the total number of fds (or the highest fd), epoll scales	377	like O(total_fds) where n is the total number of fds (or the highest fd),
243	either O(1) or O(active_fds).	378	epoll scales either O(1) or O(active_fds). The epoll design has a number
		379	of shortcomings, such as silently dropping events in some hard-to-detect
		380	cases and requiring a system call per fd change, no fork support and bad
		381	support for dup.
244		382
245	While stopping and starting an I/O watcher in the same iteration will	383	While stopping, setting and starting an I/O watcher in the same iteration
246	result in some caching, there is still a syscall per such incident	384	will result in some caching, there is still a system call per such incident
247	(because the fd could point to a different file description now), so its	385	(because the fd could point to a different file description now), so its
248	best to avoid that. Also, dup()ed file descriptors might not work very	386	best to avoid that. Also, C<dup ()>'ed file descriptors might not work
249	well if you register events for both fds.	387	very well if you register events for both fds.
250		388
251	Please note that epoll sometimes generates spurious notifications, so you	389	Please note that epoll sometimes generates spurious notifications, so you
252	need to use non-blocking I/O or other means to avoid blocking when no data	390	need to use non-blocking I/O or other means to avoid blocking when no data
253	(or space) is available.	391	(or space) is available.
254		392
		393	Best performance from this backend is achieved by not unregistering all
		394	watchers for a file descriptor until it has been closed, if possible, i.e.
		395	keep at least one watcher active per fd at all times.
		396
		397	While nominally embeddable in other event loops, this feature is broken in
		398	all kernel versions tested so far.
		399
255	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	400	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
256		401
257	Kqueue deserves special mention, as at the time of this writing, it	402	Kqueue deserves special mention, as at the time of this writing, it
258	was broken on all BSDs except NetBSD (usually it doesn't work with	403	was broken on all BSDs except NetBSD (usually it doesn't work reliably
259	anything but sockets and pipes, except on Darwin, where of course its	404	with anything but sockets and pipes, except on Darwin, where of course
260	completely useless). For this reason its not being "autodetected"	405	it's completely useless). For this reason it's not being "auto-detected"
261	unless you explicitly specify it explicitly in the flags (i.e. using	406	unless you explicitly specify it explicitly in the flags (i.e. using
262	C<EVBACKEND_KQUEUE>).	407	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
		408	system like NetBSD.
		409
		410	You still can embed kqueue into a normal poll or select backend and use it
		411	only for sockets (after having made sure that sockets work with kqueue on
		412	the target platform). See C<ev_embed> watchers for more info.
263		413
264	It scales in the same way as the epoll backend, but the interface to the	414	It scales in the same way as the epoll backend, but the interface to the
265	kernel is more efficient (which says nothing about its actual speed, of	415	kernel is more efficient (which says nothing about its actual speed, of
266	course). While starting and stopping an I/O watcher does not cause an	416	course). While stopping, setting and starting an I/O watcher does never
267	extra syscall as with epoll, it still adds up to four event changes per	417	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
268	incident, so its best to avoid that.	418	two event changes per incident, support for C<fork ()> is very bad and it
		419	drops fds silently in similarly hard-to-detect cases.
		420
		421	This backend usually performs well under most conditions.
		422
		423	While nominally embeddable in other event loops, this doesn't work
		424	everywhere, so you might need to test for this. And since it is broken
		425	almost everywhere, you should only use it when you have a lot of sockets
		426	(for which it usually works), by embedding it into another event loop
		427	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>) and using it only for
		428	sockets.
269		429
270	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	430	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
271		431
272	This is not implemented yet (and might never be).	432	This is not implemented yet (and might never be, unless you send me an
		433	implementation). According to reports, C</dev/poll> only supports sockets
		434	and is not embeddable, which would limit the usefulness of this backend
		435	immensely.
273		436
274	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	437	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
275		438
276	This uses the Solaris 10 port mechanism. As with everything on Solaris,	439	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
277	it's really slow, but it still scales very well (O(active_fds)).	440	it's really slow, but it still scales very well (O(active_fds)).
278		441
279	Please note that solaris ports can result in a lot of spurious	442	Please note that Solaris event ports can deliver a lot of spurious
280	notifications, so you need to use non-blocking I/O or other means to avoid	443	notifications, so you need to use non-blocking I/O or other means to avoid
281	blocking when no data (or space) is available.	444	blocking when no data (or space) is available.
		445
		446	While this backend scales well, it requires one system call per active
		447	file descriptor per loop iteration. For small and medium numbers of file
		448	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
		449	might perform better.
		450
		451	On the positive side, ignoring the spurious readiness notifications, this
		452	backend actually performed to specification in all tests and is fully
		453	embeddable, which is a rare feat among the OS-specific backends.
282		454
283	=item C<EVBACKEND_ALL>	455	=item C<EVBACKEND_ALL>
284		456
285	Try all backends (even potentially broken ones that wouldn't be tried	457	Try all backends (even potentially broken ones that wouldn't be tried
286	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	458	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
287	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	459	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
288		460
		461	It is definitely not recommended to use this flag.
		462
289	=back	463	=back
290		464
291	If one or more of these are ored into the flags value, then only these	465	If one or more of these are or'ed into the flags value, then only these
292	backends will be tried (in the reverse order as given here). If none are	466	backends will be tried (in the reverse order as listed here). If none are
293	specified, most compiled-in backend will be tried, usually in reverse	467	specified, all backends in C<ev_recommended_backends ()> will be tried.
294	order of their flag values :)
295		468
296	The most typical usage is like this:	469	The most typical usage is like this:
297		470
298	if (!ev_default_loop (0))	471	if (!ev_default_loop (0))
299	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");	472	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
300		473
301	Restrict libev to the select and poll backends, and do not allow	474	Restrict libev to the select and poll backends, and do not allow
302	environment settings to be taken into account:	475	environment settings to be taken into account:
303		476
304	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);	477	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
305		478
306	Use whatever libev has to offer, but make sure that kqueue is used if	479	Use whatever libev has to offer, but make sure that kqueue is used if
307	available (warning, breaks stuff, best use only with your own private	480	available (warning, breaks stuff, best use only with your own private
308	event loop and only if you know the OS supports your types of fds):	481	event loop and only if you know the OS supports your types of fds):
309		482
310	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);	483	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
311		484
312	=item struct ev_loop *ev_loop_new (unsigned int flags)	485	=item struct ev_loop *ev_loop_new (unsigned int flags)
313		486
314	Similar to C<ev_default_loop>, but always creates a new event loop that is	487	Similar to C<ev_default_loop>, but always creates a new event loop that is
315	always distinct from the default loop. Unlike the default loop, it cannot	488	always distinct from the default loop. Unlike the default loop, it cannot
316	handle signal and child watchers, and attempts to do so will be greeted by	489	handle signal and child watchers, and attempts to do so will be greeted by
317	undefined behaviour (or a failed assertion if assertions are enabled).	490	undefined behaviour (or a failed assertion if assertions are enabled).
318		491
		492	Note that this function I<is> thread-safe, and the recommended way to use
		493	libev with threads is indeed to create one loop per thread, and using the
		494	default loop in the "main" or "initial" thread.
		495
319	Example: try to create a event loop that uses epoll and nothing else.	496	Example: Try to create a event loop that uses epoll and nothing else.
320		497
321	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	498	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
322	if (!epoller)	499	if (!epoller)
323	fatal ("no epoll found here, maybe it hides under your chair");	500	fatal ("no epoll found here, maybe it hides under your chair");
324		501
325	=item ev_default_destroy ()	502	=item ev_default_destroy ()
326		503
327	Destroys the default loop again (frees all memory and kernel state	504	Destroys the default loop again (frees all memory and kernel state
328	etc.). This stops all registered event watchers (by not touching them in	505	etc.). None of the active event watchers will be stopped in the normal
329	any way whatsoever, although you cannot rely on this :).	506	sense, so e.g. C<ev_is_active> might still return true. It is your
		507	responsibility to either stop all watchers cleanly yourself I<before>
		508	calling this function, or cope with the fact afterwards (which is usually
		509	the easiest thing, you can just ignore the watchers and/or C<free ()> them
		510	for example).
		511
		512	Note that certain global state, such as signal state, will not be freed by
		513	this function, and related watchers (such as signal and child watchers)
		514	would need to be stopped manually.
		515
		516	In general it is not advisable to call this function except in the
		517	rare occasion where you really need to free e.g. the signal handling
		518	pipe fds. If you need dynamically allocated loops it is better to use
		519	C<ev_loop_new> and C<ev_loop_destroy>).
330		520
331	=item ev_loop_destroy (loop)	521	=item ev_loop_destroy (loop)
332		522
333	Like C<ev_default_destroy>, but destroys an event loop created by an	523	Like C<ev_default_destroy>, but destroys an event loop created by an
334	earlier call to C<ev_loop_new>.	524	earlier call to C<ev_loop_new>.
335		525
336	=item ev_default_fork ()	526	=item ev_default_fork ()
337		527
		528	This function sets a flag that causes subsequent C<ev_loop> iterations
338	This function reinitialises the kernel state for backends that have	529	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	530	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	531	the child process (or both child and parent, but that again makes little
341	again makes little sense).	532	sense). You I<must> call it in the child before using any of the libev
		533	functions, and it will only take effect at the next C<ev_loop> iteration.
342		534
343	You I<must> call this function in the child process after forking if and	535	On the other hand, you only need to call this function in the child
344	only if you want to use the event library in both processes. If you just	536	process if and only if you want to use the event library in the child. If
345	fork+exec, you don't have to call it.	537	you just fork+exec, you don't have to call it at all.
346		538
347	The function itself is quite fast and it's usually not a problem to call	539	The function itself is quite fast and it's usually not a problem to call
348	it just in case after a fork. To make this easy, the function will fit in	540	it just in case after a fork. To make this easy, the function will fit in
349	quite nicely into a call to C<pthread_atfork>:	541	quite nicely into a call to C<pthread_atfork>:
350		542
351	pthread_atfork (0, 0, ev_default_fork);	543	pthread_atfork (0, 0, ev_default_fork);
352		544
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)	545	=item ev_loop_fork (loop)
358		546
359	Like C<ev_default_fork>, but acts on an event loop created by	547	Like C<ev_default_fork>, but acts on an event loop created by
360	C<ev_loop_new>. Yes, you have to call this on every allocated event loop	548	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
361	after fork, and how you do this is entirely your own problem.	549	after fork, and how you do this is entirely your own problem.
		550
		551	=item int ev_is_default_loop (loop)
		552
		553	Returns true when the given loop actually is the default loop, false otherwise.
		554
		555	=item unsigned int ev_loop_count (loop)
		556
		557	Returns the count of loop iterations for the loop, which is identical to
		558	the number of times libev did poll for new events. It starts at C<0> and
		559	happily wraps around with enough iterations.
		560
		561	This value can sometimes be useful as a generation counter of sorts (it
		562	"ticks" the number of loop iterations), as it roughly corresponds with
		563	C<ev_prepare> and C<ev_check> calls.
362		564
363	=item unsigned int ev_backend (loop)	565	=item unsigned int ev_backend (loop)
364		566
365	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	567	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
366	use.	568	use.
…		…
369		571
370	Returns the current "event loop time", which is the time the event loop	572	Returns the current "event loop time", which is the time the event loop
371	received events and started processing them. This timestamp does not	573	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	574	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	575	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).	576	event occurring (or more correctly, libev finding out about it).
375		577
376	=item ev_loop (loop, int flags)	578	=item ev_loop (loop, int flags)
377		579
378	Finally, this is it, the event handler. This function usually is called	580	Finally, this is it, the event handler. This function usually is called
379	after you initialised all your watchers and you want to start handling	581	after you initialised all your watchers and you want to start handling
…		…
391	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	593	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle
392	those events and any outstanding ones, but will not block your process in	594	those events and any outstanding ones, but will not block your process in
393	case there are no events and will return after one iteration of the loop.	595	case there are no events and will return after one iteration of the loop.
394		596
395	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	597	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if
396	neccessary) and will handle those and any outstanding ones. It will block	598	necessary) and will handle those and any outstanding ones. It will block
397	your process until at least one new event arrives, and will return after	599	your process until at least one new event arrives, and will return after
398	one iteration of the loop. This is useful if you are waiting for some	600	one iteration of the loop. This is useful if you are waiting for some
399	external event in conjunction with something not expressible using other	601	external event in conjunction with something not expressible using other
400	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is	602	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is
401	usually a better approach for this kind of thing.	603	usually a better approach for this kind of thing.
402		604
403	Here are the gory details of what C<ev_loop> does:	605	Here are the gory details of what C<ev_loop> does:
404		606
405	* If there are no active watchers (reference count is zero), return.	607	- Before the first iteration, call any pending watchers.
406	- Queue prepare watchers and then call all outstanding watchers.	608	* If EVFLAG_FORKCHECK was used, check for a fork.
		609	- If a fork was detected, queue and call all fork watchers.
		610	- Queue and call all prepare watchers.
407	- If we have been forked, recreate the kernel state.	611	- If we have been forked, recreate the kernel state.
408	- Update the kernel state with all outstanding changes.	612	- Update the kernel state with all outstanding changes.
409	- Update the "event loop time".	613	- Update the "event loop time".
410	- Calculate for how long to block.	614	- Calculate for how long to sleep or block, if at all
		615	(active idle watchers, EVLOOP_NONBLOCK or not having
		616	any active watchers at all will result in not sleeping).
		617	- Sleep if the I/O and timer collect interval say so.
411	- Block the process, waiting for any events.	618	- Block the process, waiting for any events.
412	- Queue all outstanding I/O (fd) events.	619	- Queue all outstanding I/O (fd) events.
413	- Update the "event loop time" and do time jump handling.	620	- Update the "event loop time" and do time jump handling.
414	- Queue all outstanding timers.	621	- Queue all outstanding timers.
415	- Queue all outstanding periodics.	622	- Queue all outstanding periodics.
416	- If no events are pending now, queue all idle watchers.	623	- If no events are pending now, queue all idle watchers.
417	- Queue all check watchers.	624	- Queue all check watchers.
418	- Call all queued watchers in reverse order (i.e. check watchers first).	625	- Call all queued watchers in reverse order (i.e. check watchers first).
419	Signals and child watchers are implemented as I/O watchers, and will	626	Signals and child watchers are implemented as I/O watchers, and will
420	be handled here by queueing them when their watcher gets executed.	627	be handled here by queueing them when their watcher gets executed.
421	- If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	628	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
422	were used, return, otherwise continue with step *.	629	were used, or there are no active watchers, return, otherwise
		630	continue with step *.
423		631
424	Example: queue some jobs and then loop until no events are outsanding	632	Example: Queue some jobs and then loop until no events are outstanding
425	anymore.	633	anymore.
426		634
427	... queue jobs here, make sure they register event watchers as long	635	... 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..)	636	... as they still have work to do (even an idle watcher will do..)
429	ev_loop (my_loop, 0);	637	ev_loop (my_loop, 0);
…		…
433		641
434	Can be used to make a call to C<ev_loop> return early (but only after it	642	Can be used to make a call to C<ev_loop> return early (but only after it
435	has processed all outstanding events). The C<how> argument must be either	643	has processed all outstanding events). The C<how> argument must be either
436	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	644	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
437	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	645	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
		646
		647	This "unloop state" will be cleared when entering C<ev_loop> again.
438		648
439	=item ev_ref (loop)	649	=item ev_ref (loop)
440		650
441	=item ev_unref (loop)	651	=item ev_unref (loop)
442		652
…		…
447	returning, ev_unref() after starting, and ev_ref() before stopping it. For	657	returning, ev_unref() after starting, and ev_ref() before stopping it. For
448	example, libev itself uses this for its internal signal pipe: It is not	658	example, libev itself uses this for its internal signal pipe: It is not
449	visible to the libev user and should not keep C<ev_loop> from exiting if	659	visible to the libev user and should not keep C<ev_loop> from exiting if
450	no event watchers registered by it are active. It is also an excellent	660	no event watchers registered by it are active. It is also an excellent
451	way to do this for generic recurring timers or from within third-party	661	way to do this for generic recurring timers or from within third-party
452	libraries. Just remember to I<unref after start> and I<ref before stop>.	662	libraries. Just remember to I<unref after start> and I<ref before stop>
		663	(but only if the watcher wasn't active before, or was active before,
		664	respectively).
453		665
454	Example: create a signal watcher, but keep it from keeping C<ev_loop>	666	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
455	running when nothing else is active.	667	running when nothing else is active.
456		668
457	struct dv_signal exitsig;	669	struct ev_signal exitsig;
458	ev_signal_init (&exitsig, sig_cb, SIGINT);	670	ev_signal_init (&exitsig, sig_cb, SIGINT);
459	ev_signal_start (myloop, &exitsig);	671	ev_signal_start (loop, &exitsig);
460	evf_unref (myloop);	672	evf_unref (loop);
461		673
462	Example: for some weird reason, unregister the above signal handler again.	674	Example: For some weird reason, unregister the above signal handler again.
463		675
464	ev_ref (myloop);	676	ev_ref (loop);
465	ev_signal_stop (myloop, &exitsig);	677	ev_signal_stop (loop, &exitsig);
		678
		679	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
		680
		681	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
		682
		683	These advanced functions influence the time that libev will spend waiting
		684	for events. Both are by default C<0>, meaning that libev will try to
		685	invoke timer/periodic callbacks and I/O callbacks with minimum latency.
		686
		687	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
		688	allows libev to delay invocation of I/O and timer/periodic callbacks to
		689	increase efficiency of loop iterations.
		690
		691	The background is that sometimes your program runs just fast enough to
		692	handle one (or very few) event(s) per loop iteration. While this makes
		693	the program responsive, it also wastes a lot of CPU time to poll for new
		694	events, especially with backends like C<select ()> which have a high
		695	overhead for the actual polling but can deliver many events at once.
		696
		697	By setting a higher I<io collect interval> you allow libev to spend more
		698	time collecting I/O events, so you can handle more events per iteration,
		699	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
		700	C<ev_timer>) will be not affected. Setting this to a non-null value will
		701	introduce an additional C<ev_sleep ()> call into most loop iterations.
		702
		703	Likewise, by setting a higher I<timeout collect interval> you allow libev
		704	to spend more time collecting timeouts, at the expense of increased
		705	latency (the watcher callback will be called later). C<ev_io> watchers
		706	will not be affected. Setting this to a non-null value will not introduce
		707	any overhead in libev.
		708
		709	Many (busy) programs can usually benefit by setting the I/O collect
		710	interval to a value near C<0.1> or so, which is often enough for
		711	interactive servers (of course not for games), likewise for timeouts. It
		712	usually doesn't make much sense to set it to a lower value than C<0.01>,
		713	as this approaches the timing granularity of most systems.
		714
		715	=item ev_loop_verify (loop)
		716
		717	This function only does something when C<EV_VERIFY> support has been
		718	compiled in. It tries to go through all internal structures and checks
		719	them for validity. If anything is found to be inconsistent, it will print
		720	an error message to standard error and call C<abort ()>.
		721
		722	This can be used to catch bugs inside libev itself: under normal
		723	circumstances, this function will never abort as of course libev keeps its
		724	data structures consistent.
466		725
467	=back	726	=back
		727
468		728
469	=head1 ANATOMY OF A WATCHER	729	=head1 ANATOMY OF A WATCHER
470		730
471	A watcher is a structure that you create and register to record your	731	A watcher is a structure that you create and register to record your
472	interest in some event. For instance, if you want to wait for STDIN to	732	interest in some event. For instance, if you want to wait for STDIN to
473	become readable, you would create an C<ev_io> watcher for that:	733	become readable, you would create an C<ev_io> watcher for that:
474		734
475	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	735	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)
476	{	736	{
477	ev_io_stop (w);	737	ev_io_stop (w);
478	ev_unloop (loop, EVUNLOOP_ALL);	738	ev_unloop (loop, EVUNLOOP_ALL);
479	}	739	}
480		740
481	struct ev_loop *loop = ev_default_loop (0);	741	struct ev_loop *loop = ev_default_loop (0);
482	struct ev_io stdin_watcher;	742	struct ev_io stdin_watcher;
483	ev_init (&stdin_watcher, my_cb);	743	ev_init (&stdin_watcher, my_cb);
484	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	744	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
485	ev_io_start (loop, &stdin_watcher);	745	ev_io_start (loop, &stdin_watcher);
486	ev_loop (loop, 0);	746	ev_loop (loop, 0);
487		747
488	As you can see, you are responsible for allocating the memory for your	748	As you can see, you are responsible for allocating the memory for your
489	watcher structures (and it is usually a bad idea to do this on the stack,	749	watcher structures (and it is usually a bad idea to do this on the stack,
490	although this can sometimes be quite valid).	750	although this can sometimes be quite valid).
491		751
492	Each watcher structure must be initialised by a call to C<ev_init	752	Each watcher structure must be initialised by a call to C<ev_init
493	(watcher *, callback)>, which expects a callback to be provided. This	753	(watcher *, callback)>, which expects a callback to be provided. This
494	callback gets invoked each time the event occurs (or, in the case of io	754	callback gets invoked each time the event occurs (or, in the case of I/O
495	watchers, each time the event loop detects that the file descriptor given	755	watchers, each time the event loop detects that the file descriptor given
496	is readable and/or writable).	756	is readable and/or writable).
497		757
498	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	758	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro
499	with arguments specific to this watcher type. There is also a macro	759	with arguments specific to this watcher type. There is also a macro
…		…
505	*) >>), and you can stop watching for events at any time by calling the	765	*) >>), and you can stop watching for events at any time by calling the
506	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	766	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.
507		767
508	As long as your watcher is active (has been started but not stopped) you	768	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	769	must not touch the values stored in it. Most specifically you must never
510	reinitialise it or call its set macro.	770	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		771
517	Each and every callback receives the event loop pointer as first, the	772	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	773	registered watcher structure as second, and a bitset of received events as
519	third argument.	774	third argument.
520		775
…		…
544	The signal specified in the C<ev_signal> watcher has been received by a thread.	799	The signal specified in the C<ev_signal> watcher has been received by a thread.
545		800
546	=item C<EV_CHILD>	801	=item C<EV_CHILD>
547		802
548	The pid specified in the C<ev_child> watcher has received a status change.	803	The pid specified in the C<ev_child> watcher has received a status change.
		804
		805	=item C<EV_STAT>
		806
		807	The path specified in the C<ev_stat> watcher changed its attributes somehow.
549		808
550	=item C<EV_IDLE>	809	=item C<EV_IDLE>
551		810
552	The C<ev_idle> watcher has determined that you have nothing better to do.	811	The C<ev_idle> watcher has determined that you have nothing better to do.
553		812
…		…
561	received events. Callbacks of both watcher types can start and stop as	820	received events. Callbacks of both watcher types can start and stop as
562	many watchers as they want, and all of them will be taken into account	821	many watchers as they want, and all of them will be taken into account
563	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	822	(for example, a C<ev_prepare> watcher might start an idle watcher to keep
564	C<ev_loop> from blocking).	823	C<ev_loop> from blocking).
565		824
		825	=item C<EV_EMBED>
		826
		827	The embedded event loop specified in the C<ev_embed> watcher needs attention.
		828
		829	=item C<EV_FORK>
		830
		831	The event loop has been resumed in the child process after fork (see
		832	C<ev_fork>).
		833
		834	=item C<EV_ASYNC>
		835
		836	The given async watcher has been asynchronously notified (see C<ev_async>).
		837
566	=item C<EV_ERROR>	838	=item C<EV_ERROR>
567		839
568	An unspecified error has occured, the watcher has been stopped. This might	840	An unspecified error has occurred, the watcher has been stopped. This might
569	happen because the watcher could not be properly started because libev	841	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	842	ran out of memory, a file descriptor was found to be closed or any other
571	problem. You best act on it by reporting the problem and somehow coping	843	problem. You best act on it by reporting the problem and somehow coping
572	with the watcher being stopped.	844	with the watcher being stopped.
573		845
574	Libev will usually signal a few "dummy" events together with an error,	846	Libev will usually signal a few "dummy" events together with an error,
575	for example it might indicate that a fd is readable or writable, and if	847	for example it might indicate that a fd is readable or writable, and if
576	your callbacks is well-written it can just attempt the operation and cope	848	your callbacks is well-written it can just attempt the operation and cope
577	with the error from read() or write(). This will not work in multithreaded	849	with the error from read() or write(). This will not work in multi-threaded
578	programs, though, so beware.	850	programs, though, so beware.
579		851
580	=back	852	=back
		853
		854	=head2 GENERIC WATCHER FUNCTIONS
		855
		856	In the following description, C<TYPE> stands for the watcher type,
		857	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
		858
		859	=over 4
		860
		861	=item C<ev_init> (ev_TYPE *watcher, callback)
		862
		863	This macro initialises the generic portion of a watcher. The contents
		864	of the watcher object can be arbitrary (so C<malloc> will do). Only
		865	the generic parts of the watcher are initialised, you I<need> to call
		866	the type-specific C<ev_TYPE_set> macro afterwards to initialise the
		867	type-specific parts. For each type there is also a C<ev_TYPE_init> macro
		868	which rolls both calls into one.
		869
		870	You can reinitialise a watcher at any time as long as it has been stopped
		871	(or never started) and there are no pending events outstanding.
		872
		873	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,
		874	int revents)>.
		875
		876	=item C<ev_TYPE_set> (ev_TYPE *, [args])
		877
		878	This macro initialises the type-specific parts of a watcher. You need to
		879	call C<ev_init> at least once before you call this macro, but you can
		880	call C<ev_TYPE_set> any number of times. You must not, however, call this
		881	macro on a watcher that is active (it can be pending, however, which is a
		882	difference to the C<ev_init> macro).
		883
		884	Although some watcher types do not have type-specific arguments
		885	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
		886
		887	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
		888
		889	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
		890	calls into a single call. This is the most convenient method to initialise
		891	a watcher. The same limitations apply, of course.
		892
		893	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)
		894
		895	Starts (activates) the given watcher. Only active watchers will receive
		896	events. If the watcher is already active nothing will happen.
		897
		898	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)
		899
		900	Stops the given watcher again (if active) and clears the pending
		901	status. It is possible that stopped watchers are pending (for example,
		902	non-repeating timers are being stopped when they become pending), but
		903	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If
		904	you want to free or reuse the memory used by the watcher it is therefore a
		905	good idea to always call its C<ev_TYPE_stop> function.
		906
		907	=item bool ev_is_active (ev_TYPE *watcher)
		908
		909	Returns a true value iff the watcher is active (i.e. it has been started
		910	and not yet been stopped). As long as a watcher is active you must not modify
		911	it.
		912
		913	=item bool ev_is_pending (ev_TYPE *watcher)
		914
		915	Returns a true value iff the watcher is pending, (i.e. it has outstanding
		916	events but its callback has not yet been invoked). As long as a watcher
		917	is pending (but not active) you must not call an init function on it (but
		918	C<ev_TYPE_set> is safe), you must not change its priority, and you must
		919	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		920	it).
		921
		922	=item callback ev_cb (ev_TYPE *watcher)
		923
		924	Returns the callback currently set on the watcher.
		925
		926	=item ev_cb_set (ev_TYPE *watcher, callback)
		927
		928	Change the callback. You can change the callback at virtually any time
		929	(modulo threads).
		930
		931	=item ev_set_priority (ev_TYPE *watcher, priority)
		932
		933	=item int ev_priority (ev_TYPE *watcher)
		934
		935	Set and query the priority of the watcher. The priority is a small
		936	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
		937	(default: C<-2>). Pending watchers with higher priority will be invoked
		938	before watchers with lower priority, but priority will not keep watchers
		939	from being executed (except for C<ev_idle> watchers).
		940
		941	This means that priorities are I<only> used for ordering callback
		942	invocation after new events have been received. This is useful, for
		943	example, to reduce latency after idling, or more often, to bind two
		944	watchers on the same event and make sure one is called first.
		945
		946	If you need to suppress invocation when higher priority events are pending
		947	you need to look at C<ev_idle> watchers, which provide this functionality.
		948
		949	You I<must not> change the priority of a watcher as long as it is active or
		950	pending.
		951
		952	The default priority used by watchers when no priority has been set is
		953	always C<0>, which is supposed to not be too high and not be too low :).
		954
		955	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		956	fine, as long as you do not mind that the priority value you query might
		957	or might not have been adjusted to be within valid range.
		958
		959	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		960
		961	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		962	C<loop> nor C<revents> need to be valid as long as the watcher callback
		963	can deal with that fact.
		964
		965	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		966
		967	If the watcher is pending, this function returns clears its pending status
		968	and returns its C<revents> bitset (as if its callback was invoked). If the
		969	watcher isn't pending it does nothing and returns C<0>.
		970
		971	=back
		972
581		973
582	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	974	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
583		975
584	Each watcher has, by default, a member C<void *data> that you can change	976	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	977	and read at any time, libev will completely ignore it. This can be used
586	to associate arbitrary data with your watcher. If you need more data and	978	to associate arbitrary data with your watcher. If you need more data and
587	don't want to allocate memory and store a pointer to it in that data	979	don't want to allocate memory and store a pointer to it in that data
588	member, you can also "subclass" the watcher type and provide your own	980	member, you can also "subclass" the watcher type and provide your own
589	data:	981	data:
590		982
591	struct my_io	983	struct my_io
592	{	984	{
593	struct ev_io io;	985	struct ev_io io;
594	int otherfd;	986	int otherfd;
595	void *somedata;	987	void *somedata;
596	struct whatever *mostinteresting;	988	struct whatever *mostinteresting;
597	}	989	}
598		990
599	And since your callback will be called with a pointer to the watcher, you	991	And since your callback will be called with a pointer to the watcher, you
600	can cast it back to your own type:	992	can cast it back to your own type:
601		993
602	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	994	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)
603	{	995	{
604	struct my_io *w = (struct my_io *)w_;	996	struct my_io *w = (struct my_io *)w_;
605	...	997	...
606	}	998	}
607		999
608	More interesting and less C-conformant ways of catsing your callback type	1000	More interesting and less C-conformant ways of casting your callback type
609	have been omitted....	1001	instead have been omitted.
		1002
		1003	Another common scenario is having some data structure with multiple
		1004	watchers:
		1005
		1006	struct my_biggy
		1007	{
		1008	int some_data;
		1009	ev_timer t1;
		1010	ev_timer t2;
		1011	}
		1012
		1013	In this case getting the pointer to C<my_biggy> is a bit more complicated,
		1014	you need to use C<offsetof>:
		1015
		1016	#include <stddef.h>
		1017
		1018	static void
		1019	t1_cb (EV_P_ struct ev_timer *w, int revents)
		1020	{
		1021	struct my_biggy big = (struct my_biggy *
		1022	(((char *)w) - offsetof (struct my_biggy, t1));
		1023	}
		1024
		1025	static void
		1026	t2_cb (EV_P_ struct ev_timer *w, int revents)
		1027	{
		1028	struct my_biggy big = (struct my_biggy *
		1029	(((char *)w) - offsetof (struct my_biggy, t2));
		1030	}
610		1031
611		1032
612	=head1 WATCHER TYPES	1033	=head1 WATCHER TYPES
613		1034
614	This section describes each watcher in detail, but will not repeat	1035	This section describes each watcher in detail, but will not repeat
615	information given in the last section.	1036	information given in the last section. Any initialisation/set macros,
		1037	functions and members specific to the watcher type are explained.
616		1038
		1039	Members are additionally marked with either I<[read-only]>, meaning that,
		1040	while the watcher is active, you can look at the member and expect some
		1041	sensible content, but you must not modify it (you can modify it while the
		1042	watcher is stopped to your hearts content), or I<[read-write]>, which
		1043	means you can expect it to have some sensible content while the watcher
		1044	is active, but you can also modify it. Modifying it may not do something
		1045	sensible or take immediate effect (or do anything at all), but libev will
		1046	not crash or malfunction in any way.
617		1047
		1048
618	=head2 C<ev_io> - is this file descriptor readable or writable	1049	=head2 C<ev_io> - is this file descriptor readable or writable?
619		1050
620	I/O watchers check whether a file descriptor is readable or writable	1051	I/O watchers check whether a file descriptor is readable or writable
621	in each iteration of the event loop (This behaviour is called	1052	in each iteration of the event loop, or, more precisely, when reading
622	level-triggering because you keep receiving events as long as the	1053	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	1054	some data. This behaviour is called level-triggering because you keep
624	act on the event and neither want to receive future events).	1055	receiving events as long as the condition persists. Remember you can stop
		1056	the watcher if you don't want to act on the event and neither want to
		1057	receive future events.
625		1058
626	In general you can register as many read and/or write event watchers per	1059	In general you can register as many read and/or write event watchers per
627	fd as you want (as long as you don't confuse yourself). Setting all file	1060	fd as you want (as long as you don't confuse yourself). Setting all file
628	descriptors to non-blocking mode is also usually a good idea (but not	1061	descriptors to non-blocking mode is also usually a good idea (but not
629	required if you know what you are doing).	1062	required if you know what you are doing).
630		1063
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	1064	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	1065	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
639	C<EVBACKEND_POLL>).	1066	C<EVBACKEND_POLL>).
640		1067
		1068	Another thing you have to watch out for is that it is quite easy to
		1069	receive "spurious" readiness notifications, that is your callback might
		1070	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
		1071	because there is no data. Not only are some backends known to create a
		1072	lot of those (for example Solaris ports), it is very easy to get into
		1073	this situation even with a relatively standard program structure. Thus
		1074	it is best to always use non-blocking I/O: An extra C<read>(2) returning
		1075	C<EAGAIN> is far preferable to a program hanging until some data arrives.
		1076
		1077	If you cannot run the fd in non-blocking mode (for example you should not
		1078	play around with an Xlib connection), then you have to separately re-test
		1079	whether a file descriptor is really ready with a known-to-be good interface
		1080	such as poll (fortunately in our Xlib example, Xlib already does this on
		1081	its own, so its quite safe to use).
		1082
		1083	=head3 The special problem of disappearing file descriptors
		1084
		1085	Some backends (e.g. kqueue, epoll) need to be told about closing a file
		1086	descriptor (either by calling C<close> explicitly or by any other means,
		1087	such as C<dup>). The reason is that you register interest in some file
		1088	descriptor, but when it goes away, the operating system will silently drop
		1089	this interest. If another file descriptor with the same number then is
		1090	registered with libev, there is no efficient way to see that this is, in
		1091	fact, a different file descriptor.
		1092
		1093	To avoid having to explicitly tell libev about such cases, libev follows
		1094	the following policy: Each time C<ev_io_set> is being called, libev
		1095	will assume that this is potentially a new file descriptor, otherwise
		1096	it is assumed that the file descriptor stays the same. That means that
		1097	you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the
		1098	descriptor even if the file descriptor number itself did not change.
		1099
		1100	This is how one would do it normally anyway, the important point is that
		1101	the libev application should not optimise around libev but should leave
		1102	optimisations to libev.
		1103
		1104	=head3 The special problem of dup'ed file descriptors
		1105
		1106	Some backends (e.g. epoll), cannot register events for file descriptors,
		1107	but only events for the underlying file descriptions. That means when you
		1108	have C<dup ()>'ed file descriptors or weirder constellations, and register
		1109	events for them, only one file descriptor might actually receive events.
		1110
		1111	There is no workaround possible except not registering events
		1112	for potentially C<dup ()>'ed file descriptors, or to resort to
		1113	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1114
		1115	=head3 The special problem of fork
		1116
		1117	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
		1118	useless behaviour. Libev fully supports fork, but needs to be told about
		1119	it in the child.
		1120
		1121	To support fork in your programs, you either have to call
		1122	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
		1123	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
		1124	C<EVBACKEND_POLL>.
		1125
		1126	=head3 The special problem of SIGPIPE
		1127
		1128	While not really specific to libev, it is easy to forget about SIGPIPE:
		1129	when reading from a pipe whose other end has been closed, your program
		1130	gets send a SIGPIPE, which, by default, aborts your program. For most
		1131	programs this is sensible behaviour, for daemons, this is usually
		1132	undesirable.
		1133
		1134	So when you encounter spurious, unexplained daemon exits, make sure you
		1135	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1136	somewhere, as that would have given you a big clue).
		1137
		1138
		1139	=head3 Watcher-Specific Functions
		1140
641	=over 4	1141	=over 4
642		1142
643	=item ev_io_init (ev_io *, callback, int fd, int events)	1143	=item ev_io_init (ev_io *, callback, int fd, int events)
644		1144
645	=item ev_io_set (ev_io *, int fd, int events)	1145	=item ev_io_set (ev_io *, int fd, int events)
646		1146
647	Configures an C<ev_io> watcher. The fd is the file descriptor to rceeive	1147	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 |	1148	receive events for and events is either C<EV_READ>, C<EV_WRITE> or
649	EV_WRITE> to receive the given events.	1149	C<EV_READ | EV_WRITE> to receive the given events.
650		1150
651	Please note that most of the more scalable backend mechanisms (for example	1151	=item int fd [read-only]
652	epoll and solaris ports) can result in spurious readyness notifications	1152
653	for file descriptors, so you practically need to use non-blocking I/O (and	1153	The file descriptor being watched.
654	treat callback invocation as hint only), or retest separately with a safe	1154
655	interface before doing I/O (XLib can do this), or force the use of either	1155	=item int events [read-only]
656	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>, which don't suffer from this	1156
657	problem. Also note that it is quite easy to have your callback invoked	1157	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		1158
662	=back	1159	=back
663		1160
		1161	=head3 Examples
		1162
664	Example: call C<stdin_readable_cb> when STDIN_FILENO has become, well	1163	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
665	readable, but only once. Since it is likely line-buffered, you could	1164	readable, but only once. Since it is likely line-buffered, you could
666	attempt to read a whole line in the callback:	1165	attempt to read a whole line in the callback.
667		1166
668	static void	1167	static void
669	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1168	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)
670	{	1169	{
671	ev_io_stop (loop, w);	1170	ev_io_stop (loop, w);
672	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1171	.. read from stdin here (or from w->fd) and haqndle any I/O errors
673	}	1172	}
674		1173
675	...	1174	...
676	struct ev_loop *loop = ev_default_init (0);	1175	struct ev_loop *loop = ev_default_init (0);
677	struct ev_io stdin_readable;	1176	struct ev_io stdin_readable;
678	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1177	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
679	ev_io_start (loop, &stdin_readable);	1178	ev_io_start (loop, &stdin_readable);
680	ev_loop (loop, 0);	1179	ev_loop (loop, 0);
681		1180
682		1181
683	=head2 C<ev_timer> - relative and optionally recurring timeouts	1182	=head2 C<ev_timer> - relative and optionally repeating timeouts
684		1183
685	Timer watchers are simple relative timers that generate an event after a	1184	Timer watchers are simple relative timers that generate an event after a
686	given time, and optionally repeating in regular intervals after that.	1185	given time, and optionally repeating in regular intervals after that.
687		1186
688	The timers are based on real time, that is, if you register an event that	1187	The timers are based on real time, that is, if you register an event that
689	times out after an hour and you reset your system clock to last years	1188	times out after an hour and you reset your system clock to January last
690	time, it will still time out after (roughly) and hour. "Roughly" because	1189	year, it will still time out after (roughly) and hour. "Roughly" because
691	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1190	detecting time jumps is hard, and some inaccuracies are unavoidable (the
692	monotonic clock option helps a lot here).	1191	monotonic clock option helps a lot here).
693		1192
694	The relative timeouts are calculated relative to the C<ev_now ()>	1193	The relative timeouts are calculated relative to the C<ev_now ()>
695	time. This is usually the right thing as this timestamp refers to the time	1194	time. This is usually the right thing as this timestamp refers to the time
…		…
697	you suspect event processing to be delayed and you I<need> to base the timeout	1196	you suspect event processing to be delayed and you I<need> to base the timeout
698	on the current time, use something like this to adjust for this:	1197	on the current time, use something like this to adjust for this:
699		1198
700	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1199	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
701		1200
702	The callback is guarenteed to be invoked only when its timeout has passed,	1201	The callback is guaranteed to be invoked only after its timeout has passed,
703	but if multiple timers become ready during the same loop iteration then	1202	but if multiple timers become ready during the same loop iteration then
704	order of execution is undefined.	1203	order of execution is undefined.
705		1204
		1205	=head3 Watcher-Specific Functions and Data Members
		1206
706	=over 4	1207	=over 4
707		1208
708	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1209	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
709		1210
710	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	1211	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
711		1212
712	Configure the timer to trigger after C<after> seconds. If C<repeat> is	1213	Configure the timer to trigger after C<after> seconds. If C<repeat>
713	C<0.>, then it will automatically be stopped. If it is positive, then the	1214	is C<0.>, then it will automatically be stopped once the timeout is
714	timer will automatically be configured to trigger again C<repeat> seconds	1215	reached. If it is positive, then the timer will automatically be
715	later, again, and again, until stopped manually.	1216	configured to trigger again C<repeat> seconds later, again, and again,
		1217	until stopped manually.
716		1218
717	The timer itself will do a best-effort at avoiding drift, that is, if you	1219	The timer itself will do a best-effort at avoiding drift, that is, if
718	configure a timer to trigger every 10 seconds, then it will trigger at	1220	you configure a timer to trigger every 10 seconds, then it will normally
719	exactly 10 second intervals. If, however, your program cannot keep up with	1221	trigger at exactly 10 second intervals. If, however, your program cannot
720	the timer (because it takes longer than those 10 seconds to do stuff) the	1222	keep up with the timer (because it takes longer than those 10 seconds to
721	timer will not fire more than once per event loop iteration.	1223	do stuff) the timer will not fire more than once per event loop iteration.
722		1224
723	=item ev_timer_again (loop)	1225	=item ev_timer_again (loop, ev_timer *)
724		1226
725	This will act as if the timer timed out and restart it again if it is	1227	This will act as if the timer timed out and restart it again if it is
726	repeating. The exact semantics are:	1228	repeating. The exact semantics are:
727		1229
		1230	If the timer is pending, its pending status is cleared.
		1231
728	If the timer is started but nonrepeating, stop it.	1232	If the timer is started but non-repeating, stop it (as if it timed out).
729		1233
730	If the timer is repeating, either start it if necessary (with the repeat	1234	If the timer is repeating, either start it if necessary (with the
731	value), or reset the running timer to the repeat value.	1235	C<repeat> value), or reset the running timer to the C<repeat> value.
732		1236
733	This sounds a bit complicated, but here is a useful and typical	1237	This sounds a bit complicated, but here is a useful and typical
734	example: Imagine you have a tcp connection and you want a so-called idle	1238	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	1239	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	1240	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	1241	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	1242	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	1243	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.	1244	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
		1245	automatically restart it if need be.
		1246
		1247	That means you can ignore the C<after> value and C<ev_timer_start>
		1248	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
		1249
		1250	ev_timer_init (timer, callback, 0., 5.);
		1251	ev_timer_again (loop, timer);
		1252	...
		1253	timer->again = 17.;
		1254	ev_timer_again (loop, timer);
		1255	...
		1256	timer->again = 10.;
		1257	ev_timer_again (loop, timer);
		1258
		1259	This is more slightly efficient then stopping/starting the timer each time
		1260	you want to modify its timeout value.
		1261
		1262	=item ev_tstamp repeat [read-write]
		1263
		1264	The current C<repeat> value. Will be used each time the watcher times out
		1265	or C<ev_timer_again> is called and determines the next timeout (if any),
		1266	which is also when any modifications are taken into account.
741		1267
742	=back	1268	=back
743		1269
		1270	=head3 Examples
		1271
744	Example: create a timer that fires after 60 seconds.	1272	Example: Create a timer that fires after 60 seconds.
745		1273
746	static void	1274	static void
747	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1275	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
748	{	1276	{
749	.. one minute over, w is actually stopped right here	1277	.. one minute over, w is actually stopped right here
750	}	1278	}
751		1279
752	struct ev_timer mytimer;	1280	struct ev_timer mytimer;
753	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	1281	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
754	ev_timer_start (loop, &mytimer);	1282	ev_timer_start (loop, &mytimer);
755		1283
756	Example: create a timeout timer that times out after 10 seconds of	1284	Example: Create a timeout timer that times out after 10 seconds of
757	inactivity.	1285	inactivity.
758		1286
759	static void	1287	static void
760	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1288	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
761	{	1289	{
762	.. ten seconds without any activity	1290	.. ten seconds without any activity
763	}	1291	}
764		1292
765	struct ev_timer mytimer;	1293	struct ev_timer mytimer;
766	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	1294	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
767	ev_timer_again (&mytimer); /* start timer */	1295	ev_timer_again (&mytimer); /* start timer */
768	ev_loop (loop, 0);	1296	ev_loop (loop, 0);
769		1297
770	// and in some piece of code that gets executed on any "activity":	1298	// and in some piece of code that gets executed on any "activity":
771	// reset the timeout to start ticking again at 10 seconds	1299	// reset the timeout to start ticking again at 10 seconds
772	ev_timer_again (&mytimer);	1300	ev_timer_again (&mytimer);
773		1301
774		1302
775	=head2 C<ev_periodic> - to cron or not to cron	1303	=head2 C<ev_periodic> - to cron or not to cron?
776		1304
777	Periodic watchers are also timers of a kind, but they are very versatile	1305	Periodic watchers are also timers of a kind, but they are very versatile
778	(and unfortunately a bit complex).	1306	(and unfortunately a bit complex).
779		1307
780	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1308	Unlike C<ev_timer>'s, they are not based on real time (or relative time)
781	but on wallclock time (absolute time). You can tell a periodic watcher	1309	but on wall clock time (absolute time). You can tell a periodic watcher
782	to trigger "at" some specific point in time. For example, if you tell a	1310	to trigger after some specific point in time. For example, if you tell a
783	periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now ()	1311	periodic watcher to trigger in 10 seconds (by specifying e.g. C<ev_now ()
784	+ 10.>) and then reset your system clock to the last year, then it will	1312	+ 10.>, that is, an absolute time not a delay) and then reset your system
		1313	clock to January of the previous year, then it will take more than year
785	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	1314	to trigger the event (unlike an C<ev_timer>, which would still trigger
786	roughly 10 seconds later and of course not if you reset your system time	1315	roughly 10 seconds later as it uses a relative timeout).
787	again).
788		1316
789	They can also be used to implement vastly more complex timers, such as	1317	C<ev_periodic>s can also be used to implement vastly more complex timers,
790	triggering an event on eahc midnight, local time.	1318	such as triggering an event on each "midnight, local time", or other
		1319	complicated, rules.
791		1320
792	As with timers, the callback is guarenteed to be invoked only when the	1321	As with timers, the callback is guaranteed to be invoked only when the
793	time (C<at>) has been passed, but if multiple periodic timers become ready	1322	time (C<at>) has passed, but if multiple periodic timers become ready
794	during the same loop iteration then order of execution is undefined.	1323	during the same loop iteration then order of execution is undefined.
		1324
		1325	=head3 Watcher-Specific Functions and Data Members
795		1326
796	=over 4	1327	=over 4
797		1328
798	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1329	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)
799		1330
…		…
802	Lots of arguments, lets sort it out... There are basically three modes of	1333	Lots of arguments, lets sort it out... There are basically three modes of
803	operation, and we will explain them from simplest to complex:	1334	operation, and we will explain them from simplest to complex:
804		1335
805	=over 4	1336	=over 4
806		1337
807	=item * absolute timer (interval = reschedule_cb = 0)	1338	=item * absolute timer (at = time, interval = reschedule_cb = 0)
808		1339
809	In this configuration the watcher triggers an event at the wallclock time	1340	In this configuration the watcher triggers an event after the wall clock
810	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	1341	time C<at> has passed and doesn't repeat. It will not adjust when a time
811	that is, if it is to be run at January 1st 2011 then it will run when the	1342	jump occurs, that is, if it is to be run at January 1st 2011 then it will
812	system time reaches or surpasses this time.	1343	run when the system time reaches or surpasses this time.
813		1344
814	=item * non-repeating interval timer (interval > 0, reschedule_cb = 0)	1345	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)
815		1346
816	In this mode the watcher will always be scheduled to time out at the next	1347	In this mode the watcher will always be scheduled to time out at the next
817	C<at + N * interval> time (for some integer N) and then repeat, regardless	1348	C<at + N * interval> time (for some integer N, which can also be negative)
818	of any time jumps.	1349	and then repeat, regardless of any time jumps.
819		1350
820	This can be used to create timers that do not drift with respect to system	1351	This can be used to create timers that do not drift with respect to system
821	time:	1352	time, for example, here is a C<ev_periodic> that triggers each hour, on
		1353	the hour:
822		1354
823	ev_periodic_set (&periodic, 0., 3600., 0);	1355	ev_periodic_set (&periodic, 0., 3600., 0);
824		1356
825	This doesn't mean there will always be 3600 seconds in between triggers,	1357	This doesn't mean there will always be 3600 seconds in between triggers,
826	but only that the the callback will be called when the system time shows a	1358	but only that the callback will be called when the system time shows a
827	full hour (UTC), or more correctly, when the system time is evenly divisible	1359	full hour (UTC), or more correctly, when the system time is evenly divisible
828	by 3600.	1360	by 3600.
829		1361
830	Another way to think about it (for the mathematically inclined) is that	1362	Another way to think about it (for the mathematically inclined) is that
831	C<ev_periodic> will try to run the callback in this mode at the next possible	1363	C<ev_periodic> will try to run the callback in this mode at the next possible
832	time where C<time = at (mod interval)>, regardless of any time jumps.	1364	time where C<time = at (mod interval)>, regardless of any time jumps.
833		1365
		1366	For numerical stability it is preferable that the C<at> value is near
		1367	C<ev_now ()> (the current time), but there is no range requirement for
		1368	this value, and in fact is often specified as zero.
		1369
		1370	Note also that there is an upper limit to how often a timer can fire (CPU
		1371	speed for example), so if C<interval> is very small then timing stability
		1372	will of course deteriorate. Libev itself tries to be exact to be about one
		1373	millisecond (if the OS supports it and the machine is fast enough).
		1374
834	=item * manual reschedule mode (reschedule_cb = callback)	1375	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)
835		1376
836	In this mode the values for C<interval> and C<at> are both being	1377	In this mode the values for C<interval> and C<at> are both being
837	ignored. Instead, each time the periodic watcher gets scheduled, the	1378	ignored. Instead, each time the periodic watcher gets scheduled, the
838	reschedule callback will be called with the watcher as first, and the	1379	reschedule callback will be called with the watcher as first, and the
839	current time as second argument.	1380	current time as second argument.
840		1381
841	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	1382	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,
842	ever, or make any event loop modifications>. If you need to stop it,	1383	ever, or make ANY event loop modifications whatsoever>.
843	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by
844	starting a prepare watcher).
845		1384
		1385	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		1386	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		1387	only event loop modification you are allowed to do).
		1388
846	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	1389	The callback prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic
847	ev_tstamp now)>, e.g.:	1390	*w, ev_tstamp now)>, e.g.:
848		1391
849	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1392	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)
850	{	1393	{
851	return now + 60.;	1394	return now + 60.;
852	}	1395	}
…		…
854	It must return the next time to trigger, based on the passed time value	1397	It must return the next time to trigger, based on the passed time value
855	(that is, the lowest time value larger than to the second argument). It	1398	(that is, the lowest time value larger than to the second argument). It
856	will usually be called just before the callback will be triggered, but	1399	will usually be called just before the callback will be triggered, but
857	might be called at other times, too.	1400	might be called at other times, too.
858		1401
859	NOTE: I<< This callback must always return a time that is later than the	1402	NOTE: I<< This callback must always return a time that is higher than or
860	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	1403	equal to the passed C<now> value >>.
861		1404
862	This can be used to create very complex timers, such as a timer that	1405	This can be used to create very complex timers, such as a timer that
863	triggers on each midnight, local time. To do this, you would calculate the	1406	triggers on "next midnight, local time". To do this, you would calculate the
864	next midnight after C<now> and return the timestamp value for this. How	1407	next midnight after C<now> and return the timestamp value for this. How
865	you do this is, again, up to you (but it is not trivial, which is the main	1408	you do this is, again, up to you (but it is not trivial, which is the main
866	reason I omitted it as an example).	1409	reason I omitted it as an example).
867		1410
868	=back	1411	=back
…		…
872	Simply stops and restarts the periodic watcher again. This is only useful	1415	Simply stops and restarts the periodic watcher again. This is only useful
873	when you changed some parameters or the reschedule callback would return	1416	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	1417	a different time than the last time it was called (e.g. in a crond like
875	program when the crontabs have changed).	1418	program when the crontabs have changed).
876		1419
		1420	=item ev_tstamp ev_periodic_at (ev_periodic *)
		1421
		1422	When active, returns the absolute time that the watcher is supposed to
		1423	trigger next.
		1424
		1425	=item ev_tstamp offset [read-write]
		1426
		1427	When repeating, this contains the offset value, otherwise this is the
		1428	absolute point in time (the C<at> value passed to C<ev_periodic_set>).
		1429
		1430	Can be modified any time, but changes only take effect when the periodic
		1431	timer fires or C<ev_periodic_again> is being called.
		1432
		1433	=item ev_tstamp interval [read-write]
		1434
		1435	The current interval value. Can be modified any time, but changes only
		1436	take effect when the periodic timer fires or C<ev_periodic_again> is being
		1437	called.
		1438
		1439	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]
		1440
		1441	The current reschedule callback, or C<0>, if this functionality is
		1442	switched off. Can be changed any time, but changes only take effect when
		1443	the periodic timer fires or C<ev_periodic_again> is being called.
		1444
877	=back	1445	=back
878		1446
		1447	=head3 Examples
		1448
879	Example: call a callback every hour, or, more precisely, whenever the	1449	Example: Call a callback every hour, or, more precisely, whenever the
880	system clock is divisible by 3600. The callback invocation times have	1450	system clock is divisible by 3600. The callback invocation times have
881	potentially a lot of jittering, but good long-term stability.	1451	potentially a lot of jitter, but good long-term stability.
882		1452
883	static void	1453	static void
884	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1454	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)
885	{	1455	{
886	... its now a full hour (UTC, or TAI or whatever your clock follows)	1456	... its now a full hour (UTC, or TAI or whatever your clock follows)
887	}	1457	}
888		1458
889	struct ev_periodic hourly_tick;	1459	struct ev_periodic hourly_tick;
890	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	1460	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
891	ev_periodic_start (loop, &hourly_tick);	1461	ev_periodic_start (loop, &hourly_tick);
892		1462
893	Example: the same as above, but use a reschedule callback to do it:	1463	Example: The same as above, but use a reschedule callback to do it:
894		1464
895	#include <math.h>	1465	#include <math.h>
896		1466
897	static ev_tstamp	1467	static ev_tstamp
898	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	1468	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)
899	{	1469	{
900	return fmod (now, 3600.) + 3600.;	1470	return fmod (now, 3600.) + 3600.;
901	}	1471	}
902		1472
903	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	1473	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
904		1474
905	Example: call a callback every hour, starting now:	1475	Example: Call a callback every hour, starting now:
906		1476
907	struct ev_periodic hourly_tick;	1477	struct ev_periodic hourly_tick;
908	ev_periodic_init (&hourly_tick, clock_cb,	1478	ev_periodic_init (&hourly_tick, clock_cb,
909	fmod (ev_now (loop), 3600.), 3600., 0);	1479	fmod (ev_now (loop), 3600.), 3600., 0);
910	ev_periodic_start (loop, &hourly_tick);	1480	ev_periodic_start (loop, &hourly_tick);
911		1481
912		1482
913	=head2 C<ev_signal> - signal me when a signal gets signalled	1483	=head2 C<ev_signal> - signal me when a signal gets signalled!
914		1484
915	Signal watchers will trigger an event when the process receives a specific	1485	Signal watchers will trigger an event when the process receives a specific
916	signal one or more times. Even though signals are very asynchronous, libev	1486	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	1487	will try it's best to deliver signals synchronously, i.e. as part of the
918	normal event processing, like any other event.	1488	normal event processing, like any other event.
…		…
922	with the kernel (thus it coexists with your own signal handlers as long	1492	with the kernel (thus it coexists with your own signal handlers as long
923	as you don't register any with libev). Similarly, when the last signal	1493	as you don't register any with libev). Similarly, when the last signal
924	watcher for a signal is stopped libev will reset the signal handler to	1494	watcher for a signal is stopped libev will reset the signal handler to
925	SIG_DFL (regardless of what it was set to before).	1495	SIG_DFL (regardless of what it was set to before).
926		1496
		1497	If possible and supported, libev will install its handlers with
		1498	C<SA_RESTART> behaviour enabled, so system calls should not be unduly
		1499	interrupted. If you have a problem with system calls getting interrupted by
		1500	signals you can block all signals in an C<ev_check> watcher and unblock
		1501	them in an C<ev_prepare> watcher.
		1502
		1503	=head3 Watcher-Specific Functions and Data Members
		1504
927	=over 4	1505	=over 4
928		1506
929	=item ev_signal_init (ev_signal *, callback, int signum)	1507	=item ev_signal_init (ev_signal *, callback, int signum)
930		1508
931	=item ev_signal_set (ev_signal *, int signum)	1509	=item ev_signal_set (ev_signal *, int signum)
932		1510
933	Configures the watcher to trigger on the given signal number (usually one	1511	Configures the watcher to trigger on the given signal number (usually one
934	of the C<SIGxxx> constants).	1512	of the C<SIGxxx> constants).
935		1513
		1514	=item int signum [read-only]
		1515
		1516	The signal the watcher watches out for.
		1517
936	=back	1518	=back
937		1519
		1520	=head3 Examples
938		1521
		1522	Example: Try to exit cleanly on SIGINT and SIGTERM.
		1523
		1524	static void
		1525	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)
		1526	{
		1527	ev_unloop (loop, EVUNLOOP_ALL);
		1528	}
		1529
		1530	struct ev_signal signal_watcher;
		1531	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		1532	ev_signal_start (loop, &sigint_cb);
		1533
		1534
939	=head2 C<ev_child> - wait for pid status changes	1535	=head2 C<ev_child> - watch out for process status changes
940		1536
941	Child watchers trigger when your process receives a SIGCHLD in response to	1537	Child watchers trigger when your process receives a SIGCHLD in response to
942	some child status changes (most typically when a child of yours dies).	1538	some child status changes (most typically when a child of yours dies). It
		1539	is permissible to install a child watcher I<after> the child has been
		1540	forked (which implies it might have already exited), as long as the event
		1541	loop isn't entered (or is continued from a watcher).
		1542
		1543	Only the default event loop is capable of handling signals, and therefore
		1544	you can only register child watchers in the default event loop.
		1545
		1546	=head3 Process Interaction
		1547
		1548	Libev grabs C<SIGCHLD> as soon as the default event loop is
		1549	initialised. This is necessary to guarantee proper behaviour even if
		1550	the first child watcher is started after the child exits. The occurrence
		1551	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		1552	synchronously as part of the event loop processing. Libev always reaps all
		1553	children, even ones not watched.
		1554
		1555	=head3 Overriding the Built-In Processing
		1556
		1557	Libev offers no special support for overriding the built-in child
		1558	processing, but if your application collides with libev's default child
		1559	handler, you can override it easily by installing your own handler for
		1560	C<SIGCHLD> after initialising the default loop, and making sure the
		1561	default loop never gets destroyed. You are encouraged, however, to use an
		1562	event-based approach to child reaping and thus use libev's support for
		1563	that, so other libev users can use C<ev_child> watchers freely.
		1564
		1565	=head3 Watcher-Specific Functions and Data Members
943		1566
944	=over 4	1567	=over 4
945		1568
946	=item ev_child_init (ev_child *, callback, int pid)	1569	=item ev_child_init (ev_child *, callback, int pid, int trace)
947		1570
948	=item ev_child_set (ev_child *, int pid)	1571	=item ev_child_set (ev_child *, int pid, int trace)
949		1572
950	Configures the watcher to wait for status changes of process C<pid> (or	1573	Configures the watcher to wait for status changes of process C<pid> (or
951	I<any> process if C<pid> is specified as C<0>). The callback can look	1574	I<any> process if C<pid> is specified as C<0>). The callback can look
952	at the C<rstatus> member of the C<ev_child> watcher structure to see	1575	at the C<rstatus> member of the C<ev_child> watcher structure to see
953	the status word (use the macros from C<sys/wait.h> and see your systems	1576	the status word (use the macros from C<sys/wait.h> and see your systems
954	C<waitpid> documentation). The C<rpid> member contains the pid of the	1577	C<waitpid> documentation). The C<rpid> member contains the pid of the
955	process causing the status change.	1578	process causing the status change. C<trace> must be either C<0> (only
		1579	activate the watcher when the process terminates) or C<1> (additionally
		1580	activate the watcher when the process is stopped or continued).
		1581
		1582	=item int pid [read-only]
		1583
		1584	The process id this watcher watches out for, or C<0>, meaning any process id.
		1585
		1586	=item int rpid [read-write]
		1587
		1588	The process id that detected a status change.
		1589
		1590	=item int rstatus [read-write]
		1591
		1592	The process exit/trace status caused by C<rpid> (see your systems
		1593	C<waitpid> and C<sys/wait.h> documentation for details).
956		1594
957	=back	1595	=back
958		1596
959	Example: try to exit cleanly on SIGINT and SIGTERM.	1597	=head3 Examples
960		1598
		1599	Example: C<fork()> a new process and install a child handler to wait for
		1600	its completion.
		1601
		1602	ev_child cw;
		1603
961	static void	1604	static void
962	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	1605	child_cb (EV_P_ struct ev_child *w, int revents)
963	{	1606	{
964	ev_unloop (loop, EVUNLOOP_ALL);	1607	ev_child_stop (EV_A_ w);
		1608	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
965	}	1609	}
966		1610
967	struct ev_signal signal_watcher;	1611	pid_t pid = fork ();
968	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
969	ev_signal_start (loop, &sigint_cb);
970		1612
		1613	if (pid < 0)
		1614	// error
		1615	else if (pid == 0)
		1616	{
		1617	// the forked child executes here
		1618	exit (1);
		1619	}
		1620	else
		1621	{
		1622	ev_child_init (&cw, child_cb, pid, 0);
		1623	ev_child_start (EV_DEFAULT_ &cw);
		1624	}
971		1625
		1626
		1627	=head2 C<ev_stat> - did the file attributes just change?
		1628
		1629	This watches a file system path for attribute changes. That is, it calls
		1630	C<stat> regularly (or when the OS says it changed) and sees if it changed
		1631	compared to the last time, invoking the callback if it did.
		1632
		1633	The path does not need to exist: changing from "path exists" to "path does
		1634	not exist" is a status change like any other. The condition "path does
		1635	not exist" is signified by the C<st_nlink> field being zero (which is
		1636	otherwise always forced to be at least one) and all the other fields of
		1637	the stat buffer having unspecified contents.
		1638
		1639	The path I<should> be absolute and I<must not> end in a slash. If it is
		1640	relative and your working directory changes, the behaviour is undefined.
		1641
		1642	Since there is no standard to do this, the portable implementation simply
		1643	calls C<stat (2)> regularly on the path to see if it changed somehow. You
		1644	can specify a recommended polling interval for this case. If you specify
		1645	a polling interval of C<0> (highly recommended!) then a I<suitable,
		1646	unspecified default> value will be used (which you can expect to be around
		1647	five seconds, although this might change dynamically). Libev will also
		1648	impose a minimum interval which is currently around C<0.1>, but thats
		1649	usually overkill.
		1650
		1651	This watcher type is not meant for massive numbers of stat watchers,
		1652	as even with OS-supported change notifications, this can be
		1653	resource-intensive.
		1654
		1655	At the time of this writing, only the Linux inotify interface is
		1656	implemented (implementing kqueue support is left as an exercise for the
		1657	reader, note, however, that the author sees no way of implementing ev_stat
		1658	semantics with kqueue). Inotify will be used to give hints only and should
		1659	not change the semantics of C<ev_stat> watchers, which means that libev
		1660	sometimes needs to fall back to regular polling again even with inotify,
		1661	but changes are usually detected immediately, and if the file exists there
		1662	will be no polling.
		1663
		1664	=head3 ABI Issues (Largefile Support)
		1665
		1666	Libev by default (unless the user overrides this) uses the default
		1667	compilation environment, which means that on systems with optionally
		1668	disabled large file support, you get the 32 bit version of the stat
		1669	structure. When using the library from programs that change the ABI to
		1670	use 64 bit file offsets the programs will fail. In that case you have to
		1671	compile libev with the same flags to get binary compatibility. This is
		1672	obviously the case with any flags that change the ABI, but the problem is
		1673	most noticeably with ev_stat and large file support.
		1674
		1675	=head3 Inotify
		1676
		1677	When C<inotify (7)> support has been compiled into libev (generally only
		1678	available on Linux) and present at runtime, it will be used to speed up
		1679	change detection where possible. The inotify descriptor will be created lazily
		1680	when the first C<ev_stat> watcher is being started.
		1681
		1682	Inotify presence does not change the semantics of C<ev_stat> watchers
		1683	except that changes might be detected earlier, and in some cases, to avoid
		1684	making regular C<stat> calls. Even in the presence of inotify support
		1685	there are many cases where libev has to resort to regular C<stat> polling.
		1686
		1687	(There is no support for kqueue, as apparently it cannot be used to
		1688	implement this functionality, due to the requirement of having a file
		1689	descriptor open on the object at all times).
		1690
		1691	=head3 The special problem of stat time resolution
		1692
		1693	The C<stat ()> system call only supports full-second resolution portably, and
		1694	even on systems where the resolution is higher, many file systems still
		1695	only support whole seconds.
		1696
		1697	That means that, if the time is the only thing that changes, you can
		1698	easily miss updates: on the first update, C<ev_stat> detects a change and
		1699	calls your callback, which does something. When there is another update
		1700	within the same second, C<ev_stat> will be unable to detect it as the stat
		1701	data does not change.
		1702
		1703	The solution to this is to delay acting on a change for slightly more
		1704	than a second (or till slightly after the next full second boundary), using
		1705	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		1706	ev_timer_again (loop, w)>).
		1707
		1708	The C<.02> offset is added to work around small timing inconsistencies
		1709	of some operating systems (where the second counter of the current time
		1710	might be be delayed. One such system is the Linux kernel, where a call to
		1711	C<gettimeofday> might return a timestamp with a full second later than
		1712	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		1713	update file times then there will be a small window where the kernel uses
		1714	the previous second to update file times but libev might already execute
		1715	the timer callback).
		1716
		1717	=head3 Watcher-Specific Functions and Data Members
		1718
		1719	=over 4
		1720
		1721	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
		1722
		1723	=item ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)
		1724
		1725	Configures the watcher to wait for status changes of the given
		1726	C<path>. The C<interval> is a hint on how quickly a change is expected to
		1727	be detected and should normally be specified as C<0> to let libev choose
		1728	a suitable value. The memory pointed to by C<path> must point to the same
		1729	path for as long as the watcher is active.
		1730
		1731	The callback will receive C<EV_STAT> when a change was detected, relative
		1732	to the attributes at the time the watcher was started (or the last change
		1733	was detected).
		1734
		1735	=item ev_stat_stat (loop, ev_stat *)
		1736
		1737	Updates the stat buffer immediately with new values. If you change the
		1738	watched path in your callback, you could call this function to avoid
		1739	detecting this change (while introducing a race condition if you are not
		1740	the only one changing the path). Can also be useful simply to find out the
		1741	new values.
		1742
		1743	=item ev_statdata attr [read-only]
		1744
		1745	The most-recently detected attributes of the file. Although the type is
		1746	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
		1747	suitable for your system, but you can only rely on the POSIX-standardised
		1748	members to be present. If the C<st_nlink> member is C<0>, then there was
		1749	some error while C<stat>ing the file.
		1750
		1751	=item ev_statdata prev [read-only]
		1752
		1753	The previous attributes of the file. The callback gets invoked whenever
		1754	C<prev> != C<attr>, or, more precisely, one or more of these members
		1755	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		1756	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
		1757
		1758	=item ev_tstamp interval [read-only]
		1759
		1760	The specified interval.
		1761
		1762	=item const char *path [read-only]
		1763
		1764	The file system path that is being watched.
		1765
		1766	=back
		1767
		1768	=head3 Examples
		1769
		1770	Example: Watch C</etc/passwd> for attribute changes.
		1771
		1772	static void
		1773	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
		1774	{
		1775	/* /etc/passwd changed in some way */
		1776	if (w->attr.st_nlink)
		1777	{
		1778	printf ("passwd current size %ld\n", (long)w->attr.st_size);
		1779	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
		1780	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
		1781	}
		1782	else
		1783	/* you shalt not abuse printf for puts */
		1784	puts ("wow, /etc/passwd is not there, expect problems. "
		1785	"if this is windows, they already arrived\n");
		1786	}
		1787
		1788	...
		1789	ev_stat passwd;
		1790
		1791	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
		1792	ev_stat_start (loop, &passwd);
		1793
		1794	Example: Like above, but additionally use a one-second delay so we do not
		1795	miss updates (however, frequent updates will delay processing, too, so
		1796	one might do the work both on C<ev_stat> callback invocation I<and> on
		1797	C<ev_timer> callback invocation).
		1798
		1799	static ev_stat passwd;
		1800	static ev_timer timer;
		1801
		1802	static void
		1803	timer_cb (EV_P_ ev_timer *w, int revents)
		1804	{
		1805	ev_timer_stop (EV_A_ w);
		1806
		1807	/* now it's one second after the most recent passwd change */
		1808	}
		1809
		1810	static void
		1811	stat_cb (EV_P_ ev_stat *w, int revents)
		1812	{
		1813	/* reset the one-second timer */
		1814	ev_timer_again (EV_A_ &timer);
		1815	}
		1816
		1817	...
		1818	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		1819	ev_stat_start (loop, &passwd);
		1820	ev_timer_init (&timer, timer_cb, 0., 1.02);
		1821
		1822
972	=head2 C<ev_idle> - when you've got nothing better to do	1823	=head2 C<ev_idle> - when you've got nothing better to do...
973		1824
974	Idle watchers trigger events when there are no other events are pending	1825	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	1826	priority are pending (prepare, check and other idle watchers do not
976	as your process is busy handling sockets or timeouts (or even signals,	1827	count).
977	imagine) it will not be triggered. But when your process is idle all idle	1828
978	watchers are being called again and again, once per event loop iteration -	1829	That is, as long as your process is busy handling sockets or timeouts
		1830	(or even signals, imagine) of the same or higher priority it will not be
		1831	triggered. But when your process is idle (or only lower-priority watchers
		1832	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	1833	iteration - until stopped, that is, or your process receives more events
980	busy.	1834	and becomes busy again with higher priority stuff.
981		1835
982	The most noteworthy effect is that as long as any idle watchers are	1836	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.	1837	active, the process will not block when waiting for new events.
984		1838
985	Apart from keeping your process non-blocking (which is a useful	1839	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	1840	effect on its own sometimes), idle watchers are a good place to do
987	"pseudo-background processing", or delay processing stuff to after the	1841	"pseudo-background processing", or delay processing stuff to after the
988	event loop has handled all outstanding events.	1842	event loop has handled all outstanding events.
989		1843
		1844	=head3 Watcher-Specific Functions and Data Members
		1845
990	=over 4	1846	=over 4
991		1847
992	=item ev_idle_init (ev_signal *, callback)	1848	=item ev_idle_init (ev_signal *, callback)
993		1849
994	Initialises and configures the idle watcher - it has no parameters of any	1850	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,	1851	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
996	believe me.	1852	believe me.
997		1853
998	=back	1854	=back
999		1855
		1856	=head3 Examples
		1857
1000	Example: dynamically allocate an C<ev_idle>, start it, and in the	1858	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1001	callback, free it. Alos, use no error checking, as usual.	1859	callback, free it. Also, use no error checking, as usual.
1002		1860
1003	static void	1861	static void
1004	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	1862	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)
1005	{	1863	{
1006	free (w);	1864	free (w);
1007	// now do something you wanted to do when the program has	1865	// now do something you wanted to do when the program has
1008	// no longer asnything immediate to do.	1866	// no longer anything immediate to do.
1009	}	1867	}
1010		1868
1011	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	1869	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));
1012	ev_idle_init (idle_watcher, idle_cb);	1870	ev_idle_init (idle_watcher, idle_cb);
1013	ev_idle_start (loop, idle_cb);	1871	ev_idle_start (loop, idle_cb);
1014		1872
1015		1873
1016	=head2 C<ev_prepare> and C<ev_check> - customise your event loop	1874	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1017		1875
1018	Prepare and check watchers are usually (but not always) used in tandem:	1876	Prepare and check watchers are usually (but not always) used in tandem:
1019	prepare watchers get invoked before the process blocks and check watchers	1877	prepare watchers get invoked before the process blocks and check watchers
1020	afterwards.	1878	afterwards.
1021		1879
		1880	You I<must not> call C<ev_loop> or similar functions that enter
		1881	the current event loop from either C<ev_prepare> or C<ev_check>
		1882	watchers. Other loops than the current one are fine, however. The
		1883	rationale behind this is that you do not need to check for recursion in
		1884	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
		1885	C<ev_check> so if you have one watcher of each kind they will always be
		1886	called in pairs bracketing the blocking call.
		1887
1022	Their main purpose is to integrate other event mechanisms into libev and	1888	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	1889	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	1890	variable changes, implement your own watchers, integrate net-snmp or a
1025	coroutine library and lots more.	1891	coroutine library and lots more. They are also occasionally useful if
		1892	you cache some data and want to flush it before blocking (for example,
		1893	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
		1894	watcher).
1026		1895
1027	This is done by examining in each prepare call which file descriptors need	1896	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	1897	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	1898	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	1899	provide just this functionality). Then, in the check watcher you check for
1031	any events that occured (by checking the pending status of all watchers	1900	any events that occurred (by checking the pending status of all watchers
1032	and stopping them) and call back into the library. The I/O and timer	1901	and stopping them) and call back into the library. The I/O and timer
1033	callbacks will never actually be called (but must be valid nevertheless,	1902	callbacks will never actually be called (but must be valid nevertheless,
1034	because you never know, you know?).	1903	because you never know, you know?).
1035		1904
1036	As another example, the Perl Coro module uses these hooks to integrate	1905	As another example, the Perl Coro module uses these hooks to integrate
…		…
1040	with priority higher than or equal to the event loop and one coroutine	1909	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	1910	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	1911	loop from blocking if lower-priority coroutines are active, thus mapping
1043	low-priority coroutines to idle/background tasks).	1912	low-priority coroutines to idle/background tasks).
1044		1913
		1914	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
		1915	priority, to ensure that they are being run before any other watchers
		1916	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,
		1917	too) should not activate ("feed") events into libev. While libev fully
		1918	supports this, they might get executed before other C<ev_check> watchers
		1919	did their job. As C<ev_check> watchers are often used to embed other
		1920	(non-libev) event loops those other event loops might be in an unusable
		1921	state until their C<ev_check> watcher ran (always remind yourself to
		1922	coexist peacefully with others).
		1923
		1924	=head3 Watcher-Specific Functions and Data Members
		1925
1045	=over 4	1926	=over 4
1046		1927
1047	=item ev_prepare_init (ev_prepare *, callback)	1928	=item ev_prepare_init (ev_prepare *, callback)
1048		1929
1049	=item ev_check_init (ev_check *, callback)	1930	=item ev_check_init (ev_check *, callback)
…		…
1052	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	1933	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.	1934	macros, but using them is utterly, utterly and completely pointless.
1054		1935
1055	=back	1936	=back
1056		1937
1057	Example: *TODO*.	1938	=head3 Examples
1058		1939
		1940	There are a number of principal ways to embed other event loops or modules
		1941	into libev. Here are some ideas on how to include libadns into libev
		1942	(there is a Perl module named C<EV::ADNS> that does this, which you could
		1943	use as a working example. Another Perl module named C<EV::Glib> embeds a
		1944	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
		1945	Glib event loop).
1059		1946
		1947	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
		1948	and in a check watcher, destroy them and call into libadns. What follows
		1949	is pseudo-code only of course. This requires you to either use a low
		1950	priority for the check watcher or use C<ev_clear_pending> explicitly, as
		1951	the callbacks for the IO/timeout watchers might not have been called yet.
		1952
		1953	static ev_io iow [nfd];
		1954	static ev_timer tw;
		1955
		1956	static void
		1957	io_cb (ev_loop *loop, ev_io *w, int revents)
		1958	{
		1959	}
		1960
		1961	// create io watchers for each fd and a timer before blocking
		1962	static void
		1963	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)
		1964	{
		1965	int timeout = 3600000;
		1966	struct pollfd fds [nfd];
		1967	// actual code will need to loop here and realloc etc.
		1968	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
		1969
		1970	/* the callback is illegal, but won't be called as we stop during check */
		1971	ev_timer_init (&tw, 0, timeout * 1e-3);
		1972	ev_timer_start (loop, &tw);
		1973
		1974	// create one ev_io per pollfd
		1975	for (int i = 0; i < nfd; ++i)
		1976	{
		1977	ev_io_init (iow + i, io_cb, fds [i].fd,
		1978	((fds [i].events & POLLIN ? EV_READ : 0)
		1979	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
		1980
		1981	fds [i].revents = 0;
		1982	ev_io_start (loop, iow + i);
		1983	}
		1984	}
		1985
		1986	// stop all watchers after blocking
		1987	static void
		1988	adns_check_cb (ev_loop *loop, ev_check *w, int revents)
		1989	{
		1990	ev_timer_stop (loop, &tw);
		1991
		1992	for (int i = 0; i < nfd; ++i)
		1993	{
		1994	// set the relevant poll flags
		1995	// could also call adns_processreadable etc. here
		1996	struct pollfd *fd = fds + i;
		1997	int revents = ev_clear_pending (iow + i);
		1998	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
		1999	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
		2000
		2001	// now stop the watcher
		2002	ev_io_stop (loop, iow + i);
		2003	}
		2004
		2005	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
		2006	}
		2007
		2008	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
		2009	in the prepare watcher and would dispose of the check watcher.
		2010
		2011	Method 3: If the module to be embedded supports explicit event
		2012	notification (libadns does), you can also make use of the actual watcher
		2013	callbacks, and only destroy/create the watchers in the prepare watcher.
		2014
		2015	static void
		2016	timer_cb (EV_P_ ev_timer *w, int revents)
		2017	{
		2018	adns_state ads = (adns_state)w->data;
		2019	update_now (EV_A);
		2020
		2021	adns_processtimeouts (ads, &tv_now);
		2022	}
		2023
		2024	static void
		2025	io_cb (EV_P_ ev_io *w, int revents)
		2026	{
		2027	adns_state ads = (adns_state)w->data;
		2028	update_now (EV_A);
		2029
		2030	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
		2031	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
		2032	}
		2033
		2034	// do not ever call adns_afterpoll
		2035
		2036	Method 4: Do not use a prepare or check watcher because the module you
		2037	want to embed is too inflexible to support it. Instead, you can override
		2038	their poll function. The drawback with this solution is that the main
		2039	loop is now no longer controllable by EV. The C<Glib::EV> module does
		2040	this.
		2041
		2042	static gint
		2043	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
		2044	{
		2045	int got_events = 0;
		2046
		2047	for (n = 0; n < nfds; ++n)
		2048	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
		2049
		2050	if (timeout >= 0)
		2051	// create/start timer
		2052
		2053	// poll
		2054	ev_loop (EV_A_ 0);
		2055
		2056	// stop timer again
		2057	if (timeout >= 0)
		2058	ev_timer_stop (EV_A_ &to);
		2059
		2060	// stop io watchers again - their callbacks should have set
		2061	for (n = 0; n < nfds; ++n)
		2062	ev_io_stop (EV_A_ iow [n]);
		2063
		2064	return got_events;
		2065	}
		2066
		2067
1060	=head2 C<ev_embed> - when one backend isn't enough	2068	=head2 C<ev_embed> - when one backend isn't enough...
1061		2069
1062	This is a rather advanced watcher type that lets you embed one event loop	2070	This is a rather advanced watcher type that lets you embed one event loop
1063	into another.	2071	into another (currently only C<ev_io> events are supported in the embedded
		2072	loop, other types of watchers might be handled in a delayed or incorrect
		2073	fashion and must not be used).
1064		2074
1065	There are primarily two reasons you would want that: work around bugs and	2075	There are primarily two reasons you would want that: work around bugs and
1066	prioritise I/O.	2076	prioritise I/O.
1067		2077
1068	As an example for a bug workaround, the kqueue backend might only support	2078	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	2087	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	2088	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	2089	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.	2090	a second one, and embed the second one in the first.
1081		2091
		2092	As long as the watcher is active, the callback will be invoked every time
		2093	there might be events pending in the embedded loop. The callback must then
		2094	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke
		2095	their callbacks (you could also start an idle watcher to give the embedded
		2096	loop strictly lower priority for example). You can also set the callback
		2097	to C<0>, in which case the embed watcher will automatically execute the
		2098	embedded loop sweep.
		2099
1082	As long as the watcher is started it will automatically handle events. The	2100	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	2101	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	2102	set the callback to C<0> to avoid having to specify one if you are not
1085	interested in that.	2103	interested in that.
1086		2104
…		…
1094	portable one.	2112	portable one.
1095		2113
1096	So when you want to use this feature you will always have to be prepared	2114	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	2115	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	2116	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:	2117	create it, and if that fails, use the normal loop for everything.
1100		2118
1101	struct ev_loop *loop_hi = ev_default_init (0);	2119	=head3 Watcher-Specific Functions and Data Members
1102	struct ev_loop *loop_lo = 0;
1103	struct ev_embed embed;
1104
1105	// see if there is a chance of getting one that works
1106	// (remember that a flags value of 0 means autodetection)
1107	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
1108	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
1109	: 0;
1110
1111	// if we got one, then embed it, otherwise default to loop_hi
1112	if (loop_lo)
1113	{
1114	ev_embed_init (&embed, 0, loop_lo);
1115	ev_embed_start (loop_hi, &embed);
1116	}
1117	else
1118	loop_lo = loop_hi;
1119		2120
1120	=over 4	2121	=over 4
1121		2122
1122	=item ev_embed_init (ev_embed *, callback, struct ev_loop *loop)	2123	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
1123		2124
1124	=item ev_embed_set (ev_embed *, callback, struct ev_loop *loop)	2125	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)
1125		2126
1126	Configures the watcher to embed the given loop, which must be embeddable.	2127	Configures the watcher to embed the given loop, which must be
		2128	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
		2129	invoked automatically, otherwise it is the responsibility of the callback
		2130	to invoke it (it will continue to be called until the sweep has been done,
		2131	if you do not want that, you need to temporarily stop the embed watcher).
		2132
		2133	=item ev_embed_sweep (loop, ev_embed *)
		2134
		2135	Make a single, non-blocking sweep over the embedded loop. This works
		2136	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
		2137	appropriate way for embedded loops.
		2138
		2139	=item struct ev_loop *other [read-only]
		2140
		2141	The embedded event loop.
		2142
		2143	=back
		2144
		2145	=head3 Examples
		2146
		2147	Example: Try to get an embeddable event loop and embed it into the default
		2148	event loop. If that is not possible, use the default loop. The default
		2149	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		2150	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		2151	used).
		2152
		2153	struct ev_loop *loop_hi = ev_default_init (0);
		2154	struct ev_loop *loop_lo = 0;
		2155	struct ev_embed embed;
		2156
		2157	// see if there is a chance of getting one that works
		2158	// (remember that a flags value of 0 means autodetection)
		2159	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		2160	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		2161	: 0;
		2162
		2163	// if we got one, then embed it, otherwise default to loop_hi
		2164	if (loop_lo)
		2165	{
		2166	ev_embed_init (&embed, 0, loop_lo);
		2167	ev_embed_start (loop_hi, &embed);
		2168	}
		2169	else
		2170	loop_lo = loop_hi;
		2171
		2172	Example: Check if kqueue is available but not recommended and create
		2173	a kqueue backend for use with sockets (which usually work with any
		2174	kqueue implementation). Store the kqueue/socket-only event loop in
		2175	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		2176
		2177	struct ev_loop *loop = ev_default_init (0);
		2178	struct ev_loop *loop_socket = 0;
		2179	struct ev_embed embed;
		2180
		2181	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		2182	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		2183	{
		2184	ev_embed_init (&embed, 0, loop_socket);
		2185	ev_embed_start (loop, &embed);
		2186	}
		2187
		2188	if (!loop_socket)
		2189	loop_socket = loop;
		2190
		2191	// now use loop_socket for all sockets, and loop for everything else
		2192
		2193
		2194	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
		2195
		2196	Fork watchers are called when a C<fork ()> was detected (usually because
		2197	whoever is a good citizen cared to tell libev about it by calling
		2198	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the
		2199	event loop blocks next and before C<ev_check> watchers are being called,
		2200	and only in the child after the fork. If whoever good citizen calling
		2201	C<ev_default_fork> cheats and calls it in the wrong process, the fork
		2202	handlers will be invoked, too, of course.
		2203
		2204	=head3 Watcher-Specific Functions and Data Members
		2205
		2206	=over 4
		2207
		2208	=item ev_fork_init (ev_signal *, callback)
		2209
		2210	Initialises and configures the fork watcher - it has no parameters of any
		2211	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
		2212	believe me.
		2213
		2214	=back
		2215
		2216
		2217	=head2 C<ev_async> - how to wake up another event loop
		2218
		2219	In general, you cannot use an C<ev_loop> from multiple threads or other
		2220	asynchronous sources such as signal handlers (as opposed to multiple event
		2221	loops - those are of course safe to use in different threads).
		2222
		2223	Sometimes, however, you need to wake up another event loop you do not
		2224	control, for example because it belongs to another thread. This is what
		2225	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you
		2226	can signal it by calling C<ev_async_send>, which is thread- and signal
		2227	safe.
		2228
		2229	This functionality is very similar to C<ev_signal> watchers, as signals,
		2230	too, are asynchronous in nature, and signals, too, will be compressed
		2231	(i.e. the number of callback invocations may be less than the number of
		2232	C<ev_async_sent> calls).
		2233
		2234	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		2235	just the default loop.
		2236
		2237	=head3 Queueing
		2238
		2239	C<ev_async> does not support queueing of data in any way. The reason
		2240	is that the author does not know of a simple (or any) algorithm for a
		2241	multiple-writer-single-reader queue that works in all cases and doesn't
		2242	need elaborate support such as pthreads.
		2243
		2244	That means that if you want to queue data, you have to provide your own
		2245	queue. But at least I can tell you would implement locking around your
		2246	queue:
		2247
		2248	=over 4
		2249
		2250	=item queueing from a signal handler context
		2251
		2252	To implement race-free queueing, you simply add to the queue in the signal
		2253	handler but you block the signal handler in the watcher callback. Here is an example that does that for
		2254	some fictitious SIGUSR1 handler:
		2255
		2256	static ev_async mysig;
		2257
		2258	static void
		2259	sigusr1_handler (void)
		2260	{
		2261	sometype data;
		2262
		2263	// no locking etc.
		2264	queue_put (data);
		2265	ev_async_send (EV_DEFAULT_ &mysig);
		2266	}
		2267
		2268	static void
		2269	mysig_cb (EV_P_ ev_async *w, int revents)
		2270	{
		2271	sometype data;
		2272	sigset_t block, prev;
		2273
		2274	sigemptyset (&block);
		2275	sigaddset (&block, SIGUSR1);
		2276	sigprocmask (SIG_BLOCK, &block, &prev);
		2277
		2278	while (queue_get (&data))
		2279	process (data);
		2280
		2281	if (sigismember (&prev, SIGUSR1)
		2282	sigprocmask (SIG_UNBLOCK, &block, 0);
		2283	}
		2284
		2285	(Note: pthreads in theory requires you to use C<pthread_setmask>
		2286	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		2287	either...).
		2288
		2289	=item queueing from a thread context
		2290
		2291	The strategy for threads is different, as you cannot (easily) block
		2292	threads but you can easily preempt them, so to queue safely you need to
		2293	employ a traditional mutex lock, such as in this pthread example:
		2294
		2295	static ev_async mysig;
		2296	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		2297
		2298	static void
		2299	otherthread (void)
		2300	{
		2301	// only need to lock the actual queueing operation
		2302	pthread_mutex_lock (&mymutex);
		2303	queue_put (data);
		2304	pthread_mutex_unlock (&mymutex);
		2305
		2306	ev_async_send (EV_DEFAULT_ &mysig);
		2307	}
		2308
		2309	static void
		2310	mysig_cb (EV_P_ ev_async *w, int revents)
		2311	{
		2312	pthread_mutex_lock (&mymutex);
		2313
		2314	while (queue_get (&data))
		2315	process (data);
		2316
		2317	pthread_mutex_unlock (&mymutex);
		2318	}
		2319
		2320	=back
		2321
		2322
		2323	=head3 Watcher-Specific Functions and Data Members
		2324
		2325	=over 4
		2326
		2327	=item ev_async_init (ev_async *, callback)
		2328
		2329	Initialises and configures the async watcher - it has no parameters of any
		2330	kind. There is a C<ev_asynd_set> macro, but using it is utterly pointless,
		2331	believe me.
		2332
		2333	=item ev_async_send (loop, ev_async *)
		2334
		2335	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		2336	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		2337	C<ev_feed_event>, this call is safe to do in other threads, signal or
		2338	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
		2339	section below on what exactly this means).
		2340
		2341	This call incurs the overhead of a system call only once per loop iteration,
		2342	so while the overhead might be noticeable, it doesn't apply to repeated
		2343	calls to C<ev_async_send>.
		2344
		2345	=item bool = ev_async_pending (ev_async *)
		2346
		2347	Returns a non-zero value when C<ev_async_send> has been called on the
		2348	watcher but the event has not yet been processed (or even noted) by the
		2349	event loop.
		2350
		2351	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		2352	the loop iterates next and checks for the watcher to have become active,
		2353	it will reset the flag again. C<ev_async_pending> can be used to very
		2354	quickly check whether invoking the loop might be a good idea.
		2355
		2356	Not that this does I<not> check whether the watcher itself is pending, only
		2357	whether it has been requested to make this watcher pending.
1127		2358
1128	=back	2359	=back
1129		2360
1130		2361
1131	=head1 OTHER FUNCTIONS	2362	=head1 OTHER FUNCTIONS
…		…
1142	or timeout without having to allocate/configure/start/stop/free one or	2373	or timeout without having to allocate/configure/start/stop/free one or
1143	more watchers yourself.	2374	more watchers yourself.
1144		2375
1145	If C<fd> is less than 0, then no I/O watcher will be started and events	2376	If C<fd> is less than 0, then no I/O watcher will be started and events
1146	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	2377	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and
1147	C<events> set will be craeted and started.	2378	C<events> set will be created and started.
1148		2379
1149	If C<timeout> is less than 0, then no timeout watcher will be	2380	If C<timeout> is less than 0, then no timeout watcher will be
1150	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	2381	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
1151	repeat = 0) will be started. While C<0> is a valid timeout, it is of	2382	repeat = 0) will be started. While C<0> is a valid timeout, it is of
1152	dubious value.	2383	dubious value.
…		…
1154	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	2385	The callback has the type C<void (*cb)(int revents, void *arg)> and gets
1155	passed an C<revents> set like normal event callbacks (a combination of	2386	passed an C<revents> set like normal event callbacks (a combination of
1156	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	2387	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
1157	value passed to C<ev_once>:	2388	value passed to C<ev_once>:
1158		2389
1159	static void stdin_ready (int revents, void *arg)	2390	static void stdin_ready (int revents, void *arg)
1160	{	2391	{
1161	if (revents & EV_TIMEOUT)	2392	if (revents & EV_TIMEOUT)
1162	/* doh, nothing entered */;	2393	/* doh, nothing entered */;
1163	else if (revents & EV_READ)	2394	else if (revents & EV_READ)
1164	/* stdin might have data for us, joy! */;	2395	/* stdin might have data for us, joy! */;
1165	}	2396	}
1166		2397
1167	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	2398	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
1168		2399
1169	=item ev_feed_event (loop, watcher, int events)	2400	=item ev_feed_event (ev_loop *, watcher *, int revents)
1170		2401
1171	Feeds the given event set into the event loop, as if the specified event	2402	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	2403	had happened for the specified watcher (which must be a pointer to an
1173	initialised but not necessarily started event watcher).	2404	initialised but not necessarily started event watcher).
1174		2405
1175	=item ev_feed_fd_event (loop, int fd, int revents)	2406	=item ev_feed_fd_event (ev_loop *, int fd, int revents)
1176		2407
1177	Feed an event on the given fd, as if a file descriptor backend detected	2408	Feed an event on the given fd, as if a file descriptor backend detected
1178	the given events it.	2409	the given events it.
1179		2410
1180	=item ev_feed_signal_event (loop, int signum)	2411	=item ev_feed_signal_event (ev_loop *loop, int signum)
1181		2412
1182	Feed an event as if the given signal occured (loop must be the default loop!).	2413	Feed an event as if the given signal occurred (C<loop> must be the default
		2414	loop!).
1183		2415
1184	=back	2416	=back
1185		2417
1186		2418
1187	=head1 LIBEVENT EMULATION	2419	=head1 LIBEVENT EMULATION
…		…
1202		2434
1203	=item * Priorities are not currently supported. Initialising priorities	2435	=item * Priorities are not currently supported. Initialising priorities
1204	will fail and all watchers will have the same priority, even though there	2436	will fail and all watchers will have the same priority, even though there
1205	is an ev_pri field.	2437	is an ev_pri field.
1206		2438
		2439	=item * In libevent, the last base created gets the signals, in libev, the
		2440	first base created (== the default loop) gets the signals.
		2441
1207	=item * Other members are not supported.	2442	=item * Other members are not supported.
1208		2443
1209	=item * The libev emulation is I<not> ABI compatible to libevent, you need	2444	=item * The libev emulation is I<not> ABI compatible to libevent, you need
1210	to use the libev header file and library.	2445	to use the libev header file and library.
1211		2446
1212	=back	2447	=back
1213		2448
1214	=head1 C++ SUPPORT	2449	=head1 C++ SUPPORT
1215		2450
1216	TBD.	2451	Libev comes with some simplistic wrapper classes for C++ that mainly allow
		2452	you to use some convenience methods to start/stop watchers and also change
		2453	the callback model to a model using method callbacks on objects.
		2454
		2455	To use it,
		2456
		2457	#include <ev++.h>
		2458
		2459	This automatically includes F<ev.h> and puts all of its definitions (many
		2460	of them macros) into the global namespace. All C++ specific things are
		2461	put into the C<ev> namespace. It should support all the same embedding
		2462	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
		2463
		2464	Care has been taken to keep the overhead low. The only data member the C++
		2465	classes add (compared to plain C-style watchers) is the event loop pointer
		2466	that the watcher is associated with (or no additional members at all if
		2467	you disable C<EV_MULTIPLICITY> when embedding libev).
		2468
		2469	Currently, functions, and static and non-static member functions can be
		2470	used as callbacks. Other types should be easy to add as long as they only
		2471	need one additional pointer for context. If you need support for other
		2472	types of functors please contact the author (preferably after implementing
		2473	it).
		2474
		2475	Here is a list of things available in the C<ev> namespace:
		2476
		2477	=over 4
		2478
		2479	=item C<ev::READ>, C<ev::WRITE> etc.
		2480
		2481	These are just enum values with the same values as the C<EV_READ> etc.
		2482	macros from F<ev.h>.
		2483
		2484	=item C<ev::tstamp>, C<ev::now>
		2485
		2486	Aliases to the same types/functions as with the C<ev_> prefix.
		2487
		2488	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
		2489
		2490	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
		2491	the same name in the C<ev> namespace, with the exception of C<ev_signal>
		2492	which is called C<ev::sig> to avoid clashes with the C<signal> macro
		2493	defines by many implementations.
		2494
		2495	All of those classes have these methods:
		2496
		2497	=over 4
		2498
		2499	=item ev::TYPE::TYPE ()
		2500
		2501	=item ev::TYPE::TYPE (struct ev_loop *)
		2502
		2503	=item ev::TYPE::~TYPE
		2504
		2505	The constructor (optionally) takes an event loop to associate the watcher
		2506	with. If it is omitted, it will use C<EV_DEFAULT>.
		2507
		2508	The constructor calls C<ev_init> for you, which means you have to call the
		2509	C<set> method before starting it.
		2510
		2511	It will not set a callback, however: You have to call the templated C<set>
		2512	method to set a callback before you can start the watcher.
		2513
		2514	(The reason why you have to use a method is a limitation in C++ which does
		2515	not allow explicit template arguments for constructors).
		2516
		2517	The destructor automatically stops the watcher if it is active.
		2518
		2519	=item w->set<class, &class::method> (object *)
		2520
		2521	This method sets the callback method to call. The method has to have a
		2522	signature of C<void (*)(ev_TYPE &, int)>, it receives the watcher as
		2523	first argument and the C<revents> as second. The object must be given as
		2524	parameter and is stored in the C<data> member of the watcher.
		2525
		2526	This method synthesizes efficient thunking code to call your method from
		2527	the C callback that libev requires. If your compiler can inline your
		2528	callback (i.e. it is visible to it at the place of the C<set> call and
		2529	your compiler is good :), then the method will be fully inlined into the
		2530	thunking function, making it as fast as a direct C callback.
		2531
		2532	Example: simple class declaration and watcher initialisation
		2533
		2534	struct myclass
		2535	{
		2536	void io_cb (ev::io &w, int revents) { }
		2537	}
		2538
		2539	myclass obj;
		2540	ev::io iow;
		2541	iow.set <myclass, &myclass::io_cb> (&obj);
		2542
		2543	=item w->set<function> (void *data = 0)
		2544
		2545	Also sets a callback, but uses a static method or plain function as
		2546	callback. The optional C<data> argument will be stored in the watcher's
		2547	C<data> member and is free for you to use.
		2548
		2549	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
		2550
		2551	See the method-C<set> above for more details.
		2552
		2553	Example:
		2554
		2555	static void io_cb (ev::io &w, int revents) { }
		2556	iow.set <io_cb> ();
		2557
		2558	=item w->set (struct ev_loop *)
		2559
		2560	Associates a different C<struct ev_loop> with this watcher. You can only
		2561	do this when the watcher is inactive (and not pending either).
		2562
		2563	=item w->set ([arguments])
		2564
		2565	Basically the same as C<ev_TYPE_set>, with the same arguments. Must be
		2566	called at least once. Unlike the C counterpart, an active watcher gets
		2567	automatically stopped and restarted when reconfiguring it with this
		2568	method.
		2569
		2570	=item w->start ()
		2571
		2572	Starts the watcher. Note that there is no C<loop> argument, as the
		2573	constructor already stores the event loop.
		2574
		2575	=item w->stop ()
		2576
		2577	Stops the watcher if it is active. Again, no C<loop> argument.
		2578
		2579	=item w->again () (C<ev::timer>, C<ev::periodic> only)
		2580
		2581	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
		2582	C<ev_TYPE_again> function.
		2583
		2584	=item w->sweep () (C<ev::embed> only)
		2585
		2586	Invokes C<ev_embed_sweep>.
		2587
		2588	=item w->update () (C<ev::stat> only)
		2589
		2590	Invokes C<ev_stat_stat>.
		2591
		2592	=back
		2593
		2594	=back
		2595
		2596	Example: Define a class with an IO and idle watcher, start one of them in
		2597	the constructor.
		2598
		2599	class myclass
		2600	{
		2601	ev::io io; void io_cb (ev::io &w, int revents);
		2602	ev:idle idle void idle_cb (ev::idle &w, int revents);
		2603
		2604	myclass (int fd)
		2605	{
		2606	io .set <myclass, &myclass::io_cb > (this);
		2607	idle.set <myclass, &myclass::idle_cb> (this);
		2608
		2609	io.start (fd, ev::READ);
		2610	}
		2611	};
		2612
		2613
		2614	=head1 OTHER LANGUAGE BINDINGS
		2615
		2616	Libev does not offer other language bindings itself, but bindings for a
		2617	number of languages exist in the form of third-party packages. If you know
		2618	any interesting language binding in addition to the ones listed here, drop
		2619	me a note.
		2620
		2621	=over 4
		2622
		2623	=item Perl
		2624
		2625	The EV module implements the full libev API and is actually used to test
		2626	libev. EV is developed together with libev. Apart from the EV core module,
		2627	there are additional modules that implement libev-compatible interfaces
		2628	to C<libadns> (C<EV::ADNS>), C<Net::SNMP> (C<Net::SNMP::EV>) and the
		2629	C<libglib> event core (C<Glib::EV> and C<EV::Glib>).
		2630
		2631	It can be found and installed via CPAN, its homepage is at
		2632	L<http://software.schmorp.de/pkg/EV>.
		2633
		2634	=item Python
		2635
		2636	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		2637	seems to be quite complete and well-documented. Note, however, that the
		2638	patch they require for libev is outright dangerous as it breaks the ABI
		2639	for everybody else, and therefore, should never be applied in an installed
		2640	libev (if python requires an incompatible ABI then it needs to embed
		2641	libev).
		2642
		2643	=item Ruby
		2644
		2645	Tony Arcieri has written a ruby extension that offers access to a subset
		2646	of the libev API and adds file handle abstractions, asynchronous DNS and
		2647	more on top of it. It can be found via gem servers. Its homepage is at
		2648	L<http://rev.rubyforge.org/>.
		2649
		2650	=item D
		2651
		2652	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		2653	be found at L<http://git.llucax.com.ar/?p=software/ev.d.git;a=summary>.
		2654
		2655	=back
		2656
		2657
		2658	=head1 MACRO MAGIC
		2659
		2660	Libev can be compiled with a variety of options, the most fundamental
		2661	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
		2662	functions and callbacks have an initial C<struct ev_loop *> argument.
		2663
		2664	To make it easier to write programs that cope with either variant, the
		2665	following macros are defined:
		2666
		2667	=over 4
		2668
		2669	=item C<EV_A>, C<EV_A_>
		2670
		2671	This provides the loop I<argument> for functions, if one is required ("ev
		2672	loop argument"). The C<EV_A> form is used when this is the sole argument,
		2673	C<EV_A_> is used when other arguments are following. Example:
		2674
		2675	ev_unref (EV_A);
		2676	ev_timer_add (EV_A_ watcher);
		2677	ev_loop (EV_A_ 0);
		2678
		2679	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
		2680	which is often provided by the following macro.
		2681
		2682	=item C<EV_P>, C<EV_P_>
		2683
		2684	This provides the loop I<parameter> for functions, if one is required ("ev
		2685	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
		2686	C<EV_P_> is used when other parameters are following. Example:
		2687
		2688	// this is how ev_unref is being declared
		2689	static void ev_unref (EV_P);
		2690
		2691	// this is how you can declare your typical callback
		2692	static void cb (EV_P_ ev_timer *w, int revents)
		2693
		2694	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
		2695	suitable for use with C<EV_A>.
		2696
		2697	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
		2698
		2699	Similar to the other two macros, this gives you the value of the default
		2700	loop, if multiple loops are supported ("ev loop default").
		2701
		2702	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		2703
		2704	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		2705	default loop has been initialised (C<UC> == unchecked). Their behaviour
		2706	is undefined when the default loop has not been initialised by a previous
		2707	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		2708
		2709	It is often prudent to use C<EV_DEFAULT> when initialising the first
		2710	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
		2711
		2712	=back
		2713
		2714	Example: Declare and initialise a check watcher, utilising the above
		2715	macros so it will work regardless of whether multiple loops are supported
		2716	or not.
		2717
		2718	static void
		2719	check_cb (EV_P_ ev_timer *w, int revents)
		2720	{
		2721	ev_check_stop (EV_A_ w);
		2722	}
		2723
		2724	ev_check check;
		2725	ev_check_init (&check, check_cb);
		2726	ev_check_start (EV_DEFAULT_ &check);
		2727	ev_loop (EV_DEFAULT_ 0);
		2728
		2729	=head1 EMBEDDING
		2730
		2731	Libev can (and often is) directly embedded into host
		2732	applications. Examples of applications that embed it include the Deliantra
		2733	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
		2734	and rxvt-unicode.
		2735
		2736	The goal is to enable you to just copy the necessary files into your
		2737	source directory without having to change even a single line in them, so
		2738	you can easily upgrade by simply copying (or having a checked-out copy of
		2739	libev somewhere in your source tree).
		2740
		2741	=head2 FILESETS
		2742
		2743	Depending on what features you need you need to include one or more sets of files
		2744	in your application.
		2745
		2746	=head3 CORE EVENT LOOP
		2747
		2748	To include only the libev core (all the C<ev_*> functions), with manual
		2749	configuration (no autoconf):
		2750
		2751	#define EV_STANDALONE 1
		2752	#include "ev.c"
		2753
		2754	This will automatically include F<ev.h>, too, and should be done in a
		2755	single C source file only to provide the function implementations. To use
		2756	it, do the same for F<ev.h> in all files wishing to use this API (best
		2757	done by writing a wrapper around F<ev.h> that you can include instead and
		2758	where you can put other configuration options):
		2759
		2760	#define EV_STANDALONE 1
		2761	#include "ev.h"
		2762
		2763	Both header files and implementation files can be compiled with a C++
		2764	compiler (at least, thats a stated goal, and breakage will be treated
		2765	as a bug).
		2766
		2767	You need the following files in your source tree, or in a directory
		2768	in your include path (e.g. in libev/ when using -Ilibev):
		2769
		2770	ev.h
		2771	ev.c
		2772	ev_vars.h
		2773	ev_wrap.h
		2774
		2775	ev_win32.c required on win32 platforms only
		2776
		2777	ev_select.c only when select backend is enabled (which is enabled by default)
		2778	ev_poll.c only when poll backend is enabled (disabled by default)
		2779	ev_epoll.c only when the epoll backend is enabled (disabled by default)
		2780	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
		2781	ev_port.c only when the solaris port backend is enabled (disabled by default)
		2782
		2783	F<ev.c> includes the backend files directly when enabled, so you only need
		2784	to compile this single file.
		2785
		2786	=head3 LIBEVENT COMPATIBILITY API
		2787
		2788	To include the libevent compatibility API, also include:
		2789
		2790	#include "event.c"
		2791
		2792	in the file including F<ev.c>, and:
		2793
		2794	#include "event.h"
		2795
		2796	in the files that want to use the libevent API. This also includes F<ev.h>.
		2797
		2798	You need the following additional files for this:
		2799
		2800	event.h
		2801	event.c
		2802
		2803	=head3 AUTOCONF SUPPORT
		2804
		2805	Instead of using C<EV_STANDALONE=1> and providing your configuration in
		2806	whatever way you want, you can also C<m4_include([libev.m4])> in your
		2807	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
		2808	include F<config.h> and configure itself accordingly.
		2809
		2810	For this of course you need the m4 file:
		2811
		2812	libev.m4
		2813
		2814	=head2 PREPROCESSOR SYMBOLS/MACROS
		2815
		2816	Libev can be configured via a variety of preprocessor symbols you have to
		2817	define before including any of its files. The default in the absence of
		2818	autoconf is noted for every option.
		2819
		2820	=over 4
		2821
		2822	=item EV_STANDALONE
		2823
		2824	Must always be C<1> if you do not use autoconf configuration, which
		2825	keeps libev from including F<config.h>, and it also defines dummy
		2826	implementations for some libevent functions (such as logging, which is not
		2827	supported). It will also not define any of the structs usually found in
		2828	F<event.h> that are not directly supported by the libev core alone.
		2829
		2830	=item EV_USE_MONOTONIC
		2831
		2832	If defined to be C<1>, libev will try to detect the availability of the
		2833	monotonic clock option at both compile time and runtime. Otherwise no use
		2834	of the monotonic clock option will be attempted. If you enable this, you
		2835	usually have to link against librt or something similar. Enabling it when
		2836	the functionality isn't available is safe, though, although you have
		2837	to make sure you link against any libraries where the C<clock_gettime>
		2838	function is hiding in (often F<-lrt>).
		2839
		2840	=item EV_USE_REALTIME
		2841
		2842	If defined to be C<1>, libev will try to detect the availability of the
		2843	real-time clock option at compile time (and assume its availability at
		2844	runtime if successful). Otherwise no use of the real-time clock option will
		2845	be attempted. This effectively replaces C<gettimeofday> by C<clock_get
		2846	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the
		2847	note about libraries in the description of C<EV_USE_MONOTONIC>, though.
		2848
		2849	=item EV_USE_NANOSLEEP
		2850
		2851	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		2852	and will use it for delays. Otherwise it will use C<select ()>.
		2853
		2854	=item EV_USE_EVENTFD
		2855
		2856	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		2857	available and will probe for kernel support at runtime. This will improve
		2858	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		2859	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		2860	2.7 or newer, otherwise disabled.
		2861
		2862	=item EV_USE_SELECT
		2863
		2864	If undefined or defined to be C<1>, libev will compile in support for the
		2865	C<select>(2) backend. No attempt at auto-detection will be done: if no
		2866	other method takes over, select will be it. Otherwise the select backend
		2867	will not be compiled in.
		2868
		2869	=item EV_SELECT_USE_FD_SET
		2870
		2871	If defined to C<1>, then the select backend will use the system C<fd_set>
		2872	structure. This is useful if libev doesn't compile due to a missing
		2873	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout on
		2874	exotic systems. This usually limits the range of file descriptors to some
		2875	low limit such as 1024 or might have other limitations (winsocket only
		2876	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might
		2877	influence the size of the C<fd_set> used.
		2878
		2879	=item EV_SELECT_IS_WINSOCKET
		2880
		2881	When defined to C<1>, the select backend will assume that
		2882	select/socket/connect etc. don't understand file descriptors but
		2883	wants osf handles on win32 (this is the case when the select to
		2884	be used is the winsock select). This means that it will call
		2885	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
		2886	it is assumed that all these functions actually work on fds, even
		2887	on win32. Should not be defined on non-win32 platforms.
		2888
		2889	=item EV_FD_TO_WIN32_HANDLE
		2890
		2891	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		2892	file descriptors to socket handles. When not defining this symbol (the
		2893	default), then libev will call C<_get_osfhandle>, which is usually
		2894	correct. In some cases, programs use their own file descriptor management,
		2895	in which case they can provide this function to map fds to socket handles.
		2896
		2897	=item EV_USE_POLL
		2898
		2899	If defined to be C<1>, libev will compile in support for the C<poll>(2)
		2900	backend. Otherwise it will be enabled on non-win32 platforms. It
		2901	takes precedence over select.
		2902
		2903	=item EV_USE_EPOLL
		2904
		2905	If defined to be C<1>, libev will compile in support for the Linux
		2906	C<epoll>(7) backend. Its availability will be detected at runtime,
		2907	otherwise another method will be used as fallback. This is the preferred
		2908	backend for GNU/Linux systems. If undefined, it will be enabled if the
		2909	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		2910
		2911	=item EV_USE_KQUEUE
		2912
		2913	If defined to be C<1>, libev will compile in support for the BSD style
		2914	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
		2915	otherwise another method will be used as fallback. This is the preferred
		2916	backend for BSD and BSD-like systems, although on most BSDs kqueue only
		2917	supports some types of fds correctly (the only platform we found that
		2918	supports ptys for example was NetBSD), so kqueue might be compiled in, but
		2919	not be used unless explicitly requested. The best way to use it is to find
		2920	out whether kqueue supports your type of fd properly and use an embedded
		2921	kqueue loop.
		2922
		2923	=item EV_USE_PORT
		2924
		2925	If defined to be C<1>, libev will compile in support for the Solaris
		2926	10 port style backend. Its availability will be detected at runtime,
		2927	otherwise another method will be used as fallback. This is the preferred
		2928	backend for Solaris 10 systems.
		2929
		2930	=item EV_USE_DEVPOLL
		2931
		2932	Reserved for future expansion, works like the USE symbols above.
		2933
		2934	=item EV_USE_INOTIFY
		2935
		2936	If defined to be C<1>, libev will compile in support for the Linux inotify
		2937	interface to speed up C<ev_stat> watchers. Its actual availability will
		2938	be detected at runtime. If undefined, it will be enabled if the headers
		2939	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		2940
		2941	=item EV_ATOMIC_T
		2942
		2943	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		2944	access is atomic with respect to other threads or signal contexts. No such
		2945	type is easily found in the C language, so you can provide your own type
		2946	that you know is safe for your purposes. It is used both for signal handler "locking"
		2947	as well as for signal and thread safety in C<ev_async> watchers.
		2948
		2949	In the absence of this define, libev will use C<sig_atomic_t volatile>
		2950	(from F<signal.h>), which is usually good enough on most platforms.
		2951
		2952	=item EV_H
		2953
		2954	The name of the F<ev.h> header file used to include it. The default if
		2955	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
		2956	used to virtually rename the F<ev.h> header file in case of conflicts.
		2957
		2958	=item EV_CONFIG_H
		2959
		2960	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
		2961	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
		2962	C<EV_H>, above.
		2963
		2964	=item EV_EVENT_H
		2965
		2966	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
		2967	of how the F<event.h> header can be found, the default is C<"event.h">.
		2968
		2969	=item EV_PROTOTYPES
		2970
		2971	If defined to be C<0>, then F<ev.h> will not define any function
		2972	prototypes, but still define all the structs and other symbols. This is
		2973	occasionally useful if you want to provide your own wrapper functions
		2974	around libev functions.
		2975
		2976	=item EV_MULTIPLICITY
		2977
		2978	If undefined or defined to C<1>, then all event-loop-specific functions
		2979	will have the C<struct ev_loop *> as first argument, and you can create
		2980	additional independent event loops. Otherwise there will be no support
		2981	for multiple event loops and there is no first event loop pointer
		2982	argument. Instead, all functions act on the single default loop.
		2983
		2984	=item EV_MINPRI
		2985
		2986	=item EV_MAXPRI
		2987
		2988	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
		2989	C<EV_MAXPRI>, but otherwise there are no non-obvious limitations. You can
		2990	provide for more priorities by overriding those symbols (usually defined
		2991	to be C<-2> and C<2>, respectively).
		2992
		2993	When doing priority-based operations, libev usually has to linearly search
		2994	all the priorities, so having many of them (hundreds) uses a lot of space
		2995	and time, so using the defaults of five priorities (-2 .. +2) is usually
		2996	fine.
		2997
		2998	If your embedding application does not need any priorities, defining these both to
		2999	C<0> will save some memory and CPU.
		3000
		3001	=item EV_PERIODIC_ENABLE
		3002
		3003	If undefined or defined to be C<1>, then periodic timers are supported. If
		3004	defined to be C<0>, then they are not. Disabling them saves a few kB of
		3005	code.
		3006
		3007	=item EV_IDLE_ENABLE
		3008
		3009	If undefined or defined to be C<1>, then idle watchers are supported. If
		3010	defined to be C<0>, then they are not. Disabling them saves a few kB of
		3011	code.
		3012
		3013	=item EV_EMBED_ENABLE
		3014
		3015	If undefined or defined to be C<1>, then embed watchers are supported. If
		3016	defined to be C<0>, then they are not.
		3017
		3018	=item EV_STAT_ENABLE
		3019
		3020	If undefined or defined to be C<1>, then stat watchers are supported. If
		3021	defined to be C<0>, then they are not.
		3022
		3023	=item EV_FORK_ENABLE
		3024
		3025	If undefined or defined to be C<1>, then fork watchers are supported. If
		3026	defined to be C<0>, then they are not.
		3027
		3028	=item EV_ASYNC_ENABLE
		3029
		3030	If undefined or defined to be C<1>, then async watchers are supported. If
		3031	defined to be C<0>, then they are not.
		3032
		3033	=item EV_MINIMAL
		3034
		3035	If you need to shave off some kilobytes of code at the expense of some
		3036	speed, define this symbol to C<1>. Currently this is used to override some
		3037	inlining decisions, saves roughly 30% code size on amd64. It also selects a
		3038	much smaller 2-heap for timer management over the default 4-heap.
		3039
		3040	=item EV_PID_HASHSIZE
		3041
		3042	C<ev_child> watchers use a small hash table to distribute workload by
		3043	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
		3044	than enough. If you need to manage thousands of children you might want to
		3045	increase this value (I<must> be a power of two).
		3046
		3047	=item EV_INOTIFY_HASHSIZE
		3048
		3049	C<ev_stat> watchers use a small hash table to distribute workload by
		3050	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
		3051	usually more than enough. If you need to manage thousands of C<ev_stat>
		3052	watchers you might want to increase this value (I<must> be a power of
		3053	two).
		3054
		3055	=item EV_USE_4HEAP
		3056
		3057	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3058	timer and periodics heap, libev uses a 4-heap when this symbol is defined
		3059	to C<1>. The 4-heap uses more complicated (longer) code but has
		3060	noticeably faster performance with many (thousands) of watchers.
		3061
		3062	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3063	(disabled).
		3064
		3065	=item EV_HEAP_CACHE_AT
		3066
		3067	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3068	timer and periodics heap, libev can cache the timestamp (I<at>) within
		3069	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		3070	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		3071	but avoids random read accesses on heap changes. This improves performance
		3072	noticeably with with many (hundreds) of watchers.
		3073
		3074	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3075	(disabled).
		3076
		3077	=item EV_VERIFY
		3078
		3079	Controls how much internal verification (see C<ev_loop_verify ()>) will
		3080	be done: If set to C<0>, no internal verification code will be compiled
		3081	in. If set to C<1>, then verification code will be compiled in, but not
		3082	called. If set to C<2>, then the internal verification code will be
		3083	called once per loop, which can slow down libev. If set to C<3>, then the
		3084	verification code will be called very frequently, which will slow down
		3085	libev considerably.
		3086
		3087	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be
		3088	C<0.>
		3089
		3090	=item EV_COMMON
		3091
		3092	By default, all watchers have a C<void *data> member. By redefining
		3093	this macro to a something else you can include more and other types of
		3094	members. You have to define it each time you include one of the files,
		3095	though, and it must be identical each time.
		3096
		3097	For example, the perl EV module uses something like this:
		3098
		3099	#define EV_COMMON \
		3100	SV *self; /* contains this struct */ \
		3101	SV *cb_sv, *fh /* note no trailing ";" */
		3102
		3103	=item EV_CB_DECLARE (type)
		3104
		3105	=item EV_CB_INVOKE (watcher, revents)
		3106
		3107	=item ev_set_cb (ev, cb)
		3108
		3109	Can be used to change the callback member declaration in each watcher,
		3110	and the way callbacks are invoked and set. Must expand to a struct member
		3111	definition and a statement, respectively. See the F<ev.h> header file for
		3112	their default definitions. One possible use for overriding these is to
		3113	avoid the C<struct ev_loop *> as first argument in all cases, or to use
		3114	method calls instead of plain function calls in C++.
		3115
		3116	=head2 EXPORTED API SYMBOLS
		3117
		3118	If you need to re-export the API (e.g. via a DLL) and you need a list of
		3119	exported symbols, you can use the provided F<Symbol.*> files which list
		3120	all public symbols, one per line:
		3121
		3122	Symbols.ev for libev proper
		3123	Symbols.event for the libevent emulation
		3124
		3125	This can also be used to rename all public symbols to avoid clashes with
		3126	multiple versions of libev linked together (which is obviously bad in
		3127	itself, but sometimes it is inconvenient to avoid this).
		3128
		3129	A sed command like this will create wrapper C<#define>'s that you need to
		3130	include before including F<ev.h>:
		3131
		3132	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		3133
		3134	This would create a file F<wrap.h> which essentially looks like this:
		3135
		3136	#define ev_backend myprefix_ev_backend
		3137	#define ev_check_start myprefix_ev_check_start
		3138	#define ev_check_stop myprefix_ev_check_stop
		3139	...
		3140
		3141	=head2 EXAMPLES
		3142
		3143	For a real-world example of a program the includes libev
		3144	verbatim, you can have a look at the EV perl module
		3145	(L<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
		3146	the F<libev/> subdirectory and includes them in the F<EV/EVAPI.h> (public
		3147	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file
		3148	will be compiled. It is pretty complex because it provides its own header
		3149	file.
		3150
		3151	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
		3152	that everybody includes and which overrides some configure choices:
		3153
		3154	#define EV_MINIMAL 1
		3155	#define EV_USE_POLL 0
		3156	#define EV_MULTIPLICITY 0
		3157	#define EV_PERIODIC_ENABLE 0
		3158	#define EV_STAT_ENABLE 0
		3159	#define EV_FORK_ENABLE 0
		3160	#define EV_CONFIG_H <config.h>
		3161	#define EV_MINPRI 0
		3162	#define EV_MAXPRI 0
		3163
		3164	#include "ev++.h"
		3165
		3166	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
		3167
		3168	#include "ev_cpp.h"
		3169	#include "ev.c"
		3170
		3171
		3172	=head1 THREADS AND COROUTINES
		3173
		3174	=head2 THREADS
		3175
		3176	Libev itself is completely thread-safe, but it uses no locking. This
		3177	means that you can use as many loops as you want in parallel, as long as
		3178	only one thread ever calls into one libev function with the same loop
		3179	parameter.
		3180
		3181	Or put differently: calls with different loop parameters can be done in
		3182	parallel from multiple threads, calls with the same loop parameter must be
		3183	done serially (but can be done from different threads, as long as only one
		3184	thread ever is inside a call at any point in time, e.g. by using a mutex
		3185	per loop).
		3186
		3187	If you want to know which design is best for your problem, then I cannot
		3188	help you but by giving some generic advice:
		3189
		3190	=over 4
		3191
		3192	=item * most applications have a main thread: use the default libev loop
		3193	in that thread, or create a separate thread running only the default loop.
		3194
		3195	This helps integrating other libraries or software modules that use libev
		3196	themselves and don't care/know about threading.
		3197
		3198	=item * one loop per thread is usually a good model.
		3199
		3200	Doing this is almost never wrong, sometimes a better-performance model
		3201	exists, but it is always a good start.
		3202
		3203	=item * other models exist, such as the leader/follower pattern, where one
		3204	loop is handed through multiple threads in a kind of round-robin fashion.
		3205
		3206	Choosing a model is hard - look around, learn, know that usually you can do
		3207	better than you currently do :-)
		3208
		3209	=item * often you need to talk to some other thread which blocks in the
		3210	event loop - C<ev_async> watchers can be used to wake them up from other
		3211	threads safely (or from signal contexts...).
		3212
		3213	=back
		3214
		3215	=head2 COROUTINES
		3216
		3217	Libev is much more accommodating to coroutines ("cooperative threads"):
		3218	libev fully supports nesting calls to it's functions from different
		3219	coroutines (e.g. you can call C<ev_loop> on the same loop from two
		3220	different coroutines and switch freely between both coroutines running the
		3221	loop, as long as you don't confuse yourself). The only exception is that
		3222	you must not do this from C<ev_periodic> reschedule callbacks.
		3223
		3224	Care has been invested into making sure that libev does not keep local
		3225	state inside C<ev_loop>, and other calls do not usually allow coroutine
		3226	switches.
		3227
		3228
		3229	=head1 COMPLEXITIES
		3230
		3231	In this section the complexities of (many of) the algorithms used inside
		3232	libev will be explained. For complexity discussions about backends see the
		3233	documentation for C<ev_default_init>.
		3234
		3235	All of the following are about amortised time: If an array needs to be
		3236	extended, libev needs to realloc and move the whole array, but this
		3237	happens asymptotically never with higher number of elements, so O(1) might
		3238	mean it might do a lengthy realloc operation in rare cases, but on average
		3239	it is much faster and asymptotically approaches constant time.
		3240
		3241	=over 4
		3242
		3243	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
		3244
		3245	This means that, when you have a watcher that triggers in one hour and
		3246	there are 100 watchers that would trigger before that then inserting will
		3247	have to skip roughly seven (C<ld 100>) of these watchers.
		3248
		3249	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
		3250
		3251	That means that changing a timer costs less than removing/adding them
		3252	as only the relative motion in the event queue has to be paid for.
		3253
		3254	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
		3255
		3256	These just add the watcher into an array or at the head of a list.
		3257
		3258	=item Stopping check/prepare/idle/fork/async watchers: O(1)
		3259
		3260	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
		3261
		3262	These watchers are stored in lists then need to be walked to find the
		3263	correct watcher to remove. The lists are usually short (you don't usually
		3264	have many watchers waiting for the same fd or signal).
		3265
		3266	=item Finding the next timer in each loop iteration: O(1)
		3267
		3268	By virtue of using a binary or 4-heap, the next timer is always found at a
		3269	fixed position in the storage array.
		3270
		3271	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		3272
		3273	A change means an I/O watcher gets started or stopped, which requires
		3274	libev to recalculate its status (and possibly tell the kernel, depending
		3275	on backend and whether C<ev_io_set> was used).
		3276
		3277	=item Activating one watcher (putting it into the pending state): O(1)
		3278
		3279	=item Priority handling: O(number_of_priorities)
		3280
		3281	Priorities are implemented by allocating some space for each
		3282	priority. When doing priority-based operations, libev usually has to
		3283	linearly search all the priorities, but starting/stopping and activating
		3284	watchers becomes O(1) w.r.t. priority handling.
		3285
		3286	=item Sending an ev_async: O(1)
		3287
		3288	=item Processing ev_async_send: O(number_of_async_watchers)
		3289
		3290	=item Processing signals: O(max_signal_number)
		3291
		3292	Sending involves a system call I<iff> there were no other C<ev_async_send>
		3293	calls in the current loop iteration. Checking for async and signal events
		3294	involves iterating over all running async watchers or all signal numbers.
		3295
		3296	=back
		3297
		3298
		3299	=head1 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		3300
		3301	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		3302	requires, and its I/O model is fundamentally incompatible with the POSIX
		3303	model. Libev still offers limited functionality on this platform in
		3304	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		3305	descriptors. This only applies when using Win32 natively, not when using
		3306	e.g. cygwin.
		3307
		3308	Lifting these limitations would basically require the full
		3309	re-implementation of the I/O system. If you are into these kinds of
		3310	things, then note that glib does exactly that for you in a very portable
		3311	way (note also that glib is the slowest event library known to man).
		3312
		3313	There is no supported compilation method available on windows except
		3314	embedding it into other applications.
		3315
		3316	Not a libev limitation but worth mentioning: windows apparently doesn't
		3317	accept large writes: instead of resulting in a partial write, windows will
		3318	either accept everything or return C<ENOBUFS> if the buffer is too large,
		3319	so make sure you only write small amounts into your sockets (less than a
		3320	megabyte seems safe, but thsi apparently depends on the amount of memory
		3321	available).
		3322
		3323	Due to the many, low, and arbitrary limits on the win32 platform and
		3324	the abysmal performance of winsockets, using a large number of sockets
		3325	is not recommended (and not reasonable). If your program needs to use
		3326	more than a hundred or so sockets, then likely it needs to use a totally
		3327	different implementation for windows, as libev offers the POSIX readiness
		3328	notification model, which cannot be implemented efficiently on windows
		3329	(Microsoft monopoly games).
		3330
		3331	A typical way to use libev under windows is to embed it (see the embedding
		3332	section for details) and use the following F<evwrap.h> header file instead
		3333	of F<ev.h>:
		3334
		3335	#define EV_STANDALONE /* keeps ev from requiring config.h */
		3336	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		3337
		3338	#include "ev.h"
		3339
		3340	And compile the following F<evwrap.c> file into your project (make sure
		3341	you do I<not> compile the F<ev.c> or any other embedded soruce files!):
		3342
		3343	#include "evwrap.h"
		3344	#include "ev.c"
		3345
		3346	=over 4
		3347
		3348	=item The winsocket select function
		3349
		3350	The winsocket C<select> function doesn't follow POSIX in that it
		3351	requires socket I<handles> and not socket I<file descriptors> (it is
		3352	also extremely buggy). This makes select very inefficient, and also
		3353	requires a mapping from file descriptors to socket handles (the Microsoft
		3354	C runtime provides the function C<_open_osfhandle> for this). See the
		3355	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		3356	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		3357
		3358	The configuration for a "naked" win32 using the Microsoft runtime
		3359	libraries and raw winsocket select is:
		3360
		3361	#define EV_USE_SELECT 1
		3362	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		3363
		3364	Note that winsockets handling of fd sets is O(n), so you can easily get a
		3365	complexity in the O(n²) range when using win32.
		3366
		3367	=item Limited number of file descriptors
		3368
		3369	Windows has numerous arbitrary (and low) limits on things.
		3370
		3371	Early versions of winsocket's select only supported waiting for a maximum
		3372	of C<64> handles (probably owning to the fact that all windows kernels
		3373	can only wait for C<64> things at the same time internally; Microsoft
		3374	recommends spawning a chain of threads and wait for 63 handles and the
		3375	previous thread in each. Great).
		3376
		3377	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		3378	to some high number (e.g. C<2048>) before compiling the winsocket select
		3379	call (which might be in libev or elsewhere, for example, perl does its own
		3380	select emulation on windows).
		3381
		3382	Another limit is the number of file descriptors in the Microsoft runtime
		3383	libraries, which by default is C<64> (there must be a hidden I<64> fetish
		3384	or something like this inside Microsoft). You can increase this by calling
		3385	C<_setmaxstdio>, which can increase this limit to C<2048> (another
		3386	arbitrary limit), but is broken in many versions of the Microsoft runtime
		3387	libraries.
		3388
		3389	This might get you to about C<512> or C<2048> sockets (depending on
		3390	windows version and/or the phase of the moon). To get more, you need to
		3391	wrap all I/O functions and provide your own fd management, but the cost of
		3392	calling select (O(n²)) will likely make this unworkable.
		3393
		3394	=back
		3395
		3396
		3397	=head1 PORTABILITY REQUIREMENTS
		3398
		3399	In addition to a working ISO-C implementation, libev relies on a few
		3400	additional extensions:
		3401
		3402	=over 4
		3403
		3404	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		3405	calling conventions regardless of C<ev_watcher_type *>.
		3406
		3407	Libev assumes not only that all watcher pointers have the same internal
		3408	structure (guaranteed by POSIX but not by ISO C for example), but it also
		3409	assumes that the same (machine) code can be used to call any watcher
		3410	callback: The watcher callbacks have different type signatures, but libev
		3411	calls them using an C<ev_watcher *> internally.
		3412
		3413	=item C<sig_atomic_t volatile> must be thread-atomic as well
		3414
		3415	The type C<sig_atomic_t volatile> (or whatever is defined as
		3416	C<EV_ATOMIC_T>) must be atomic w.r.t. accesses from different
		3417	threads. This is not part of the specification for C<sig_atomic_t>, but is
		3418	believed to be sufficiently portable.
		3419
		3420	=item C<sigprocmask> must work in a threaded environment
		3421
		3422	Libev uses C<sigprocmask> to temporarily block signals. This is not
		3423	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		3424	pthread implementations will either allow C<sigprocmask> in the "main
		3425	thread" or will block signals process-wide, both behaviours would
		3426	be compatible with libev. Interaction between C<sigprocmask> and
		3427	C<pthread_sigmask> could complicate things, however.
		3428
		3429	The most portable way to handle signals is to block signals in all threads
		3430	except the initial one, and run the default loop in the initial thread as
		3431	well.
		3432
		3433	=item C<long> must be large enough for common memory allocation sizes
		3434
		3435	To improve portability and simplify using libev, libev uses C<long>
		3436	internally instead of C<size_t> when allocating its data structures. On
		3437	non-POSIX systems (Microsoft...) this might be unexpectedly low, but
		3438	is still at least 31 bits everywhere, which is enough for hundreds of
		3439	millions of watchers.
		3440
		3441	=item C<double> must hold a time value in seconds with enough accuracy
		3442
		3443	The type C<double> is used to represent timestamps. It is required to
		3444	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
		3445	enough for at least into the year 4000. This requirement is fulfilled by
		3446	implementations implementing IEEE 754 (basically all existing ones).
		3447
		3448	=back
		3449
		3450	If you know of other additional requirements drop me a note.
		3451
		3452
		3453	=head1 COMPILER WARNINGS
		3454
		3455	Depending on your compiler and compiler settings, you might get no or a
		3456	lot of warnings when compiling libev code. Some people are apparently
		3457	scared by this.
		3458
		3459	However, these are unavoidable for many reasons. For one, each compiler
		3460	has different warnings, and each user has different tastes regarding
		3461	warning options. "Warn-free" code therefore cannot be a goal except when
		3462	targeting a specific compiler and compiler-version.
		3463
		3464	Another reason is that some compiler warnings require elaborate
		3465	workarounds, or other changes to the code that make it less clear and less
		3466	maintainable.
		3467
		3468	And of course, some compiler warnings are just plain stupid, or simply
		3469	wrong (because they don't actually warn about the condition their message
		3470	seems to warn about).
		3471
		3472	While libev is written to generate as few warnings as possible,
		3473	"warn-free" code is not a goal, and it is recommended not to build libev
		3474	with any compiler warnings enabled unless you are prepared to cope with
		3475	them (e.g. by ignoring them). Remember that warnings are just that:
		3476	warnings, not errors, or proof of bugs.
		3477
		3478
		3479	=head1 VALGRIND
		3480
		3481	Valgrind has a special section here because it is a popular tool that is
		3482	highly useful, but valgrind reports are very hard to interpret.
		3483
		3484	If you think you found a bug (memory leak, uninitialised data access etc.)
		3485	in libev, then check twice: If valgrind reports something like:
		3486
		3487	==2274== definitely lost: 0 bytes in 0 blocks.
		3488	==2274== possibly lost: 0 bytes in 0 blocks.
		3489	==2274== still reachable: 256 bytes in 1 blocks.
		3490
		3491	Then there is no memory leak. Similarly, under some circumstances,
		3492	valgrind might report kernel bugs as if it were a bug in libev, or it
		3493	might be confused (it is a very good tool, but only a tool).
		3494
		3495	If you are unsure about something, feel free to contact the mailing list
		3496	with the full valgrind report and an explanation on why you think this is
		3497	a bug in libev. However, don't be annoyed when you get a brisk "this is
		3498	no bug" answer and take the chance of learning how to interpret valgrind
		3499	properly.
		3500
		3501	If you need, for some reason, empty reports from valgrind for your project
		3502	I suggest using suppression lists.
		3503
1217		3504
1218	=head1 AUTHOR	3505	=head1 AUTHOR
1219		3506
1220	Marc Lehmann <libev@schmorp.de>.	3507	Marc Lehmann <libev@schmorp.de>.
1221		3508

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