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Revision 1.37 by root, Sat Nov 24 07:20:43 2007 UTC vs.
Revision 1.175 by root, Mon Sep 8 16:36:14 2008 UTC

…		…
2		2
3	libev - a high performance full-featured event loop written in C	3	libev - a high performance full-featured event loop written in C
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	#include <ev.h>	7	#include <ev.h>
		8
		9	=head2 EXAMPLE PROGRAM
		10
		11	// a single header file is required
		12	#include <ev.h>
		13
		14	// every watcher type has its own typedef'd struct
		15	// with the name ev_<type>
		16	ev_io stdin_watcher;
		17	ev_timer timeout_watcher;
		18
		19	// all watcher callbacks have a similar signature
		20	// this callback is called when data is readable on stdin
		21	static void
		22	stdin_cb (EV_P_ struct ev_io *w, int revents)
		23	{
		24	puts ("stdin ready");
		25	// for one-shot events, one must manually stop the watcher
		26	// with its corresponding stop function.
		27	ev_io_stop (EV_A_ w);
		28
		29	// this causes all nested ev_loop's to stop iterating
		30	ev_unloop (EV_A_ EVUNLOOP_ALL);
		31	}
		32
		33	// another callback, this time for a time-out
		34	static void
		35	timeout_cb (EV_P_ struct ev_timer *w, int revents)
		36	{
		37	puts ("timeout");
		38	// this causes the innermost ev_loop to stop iterating
		39	ev_unloop (EV_A_ EVUNLOOP_ONE);
		40	}
		41
		42	int
		43	main (void)
		44	{
		45	// use the default event loop unless you have special needs
		46	struct ev_loop *loop = ev_default_loop (0);
		47
		48	// initialise an io watcher, then start it
		49	// this one will watch for stdin to become readable
		50	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
		51	ev_io_start (loop, &stdin_watcher);
		52
		53	// initialise a timer watcher, then start it
		54	// simple non-repeating 5.5 second timeout
		55	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		56	ev_timer_start (loop, &timeout_watcher);
		57
		58	// now wait for events to arrive
		59	ev_loop (loop, 0);
		60
		61	// unloop was called, so exit
		62	return 0;
		63	}
8		64
9	=head1 DESCRIPTION	65	=head1 DESCRIPTION
10		66
		67	The newest version of this document is also available as an html-formatted
		68	web page you might find easier to navigate when reading it for the first
		69	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
		70
11	Libev is an event loop: you register interest in certain events (such as a	71	Libev is an event loop: you register interest in certain events (such as a
12	file descriptor being readable or a timeout occuring), and it will manage	72	file descriptor being readable or a timeout occurring), and it will manage
13	these event sources and provide your program with events.	73	these event sources and provide your program with events.
14		74
15	To do this, it must take more or less complete control over your process	75	To do this, it must take more or less complete control over your process
16	(or thread) by executing the I<event loop> handler, and will then	76	(or thread) by executing the I<event loop> handler, and will then
17	communicate events via a callback mechanism.	77	communicate events via a callback mechanism.
…		…
19	You register interest in certain events by registering so-called I<event	79	You register interest in certain events by registering so-called I<event
20	watchers>, which are relatively small C structures you initialise with the	80	watchers>, which are relatively small C structures you initialise with the
21	details of the event, and then hand it over to libev by I<starting> the	81	details of the event, and then hand it over to libev by I<starting> the
22	watcher.	82	watcher.
23		83
24	=head1 FEATURES	84	=head2 FEATURES
25		85
26	Libev supports select, poll, the linux-specific epoll and the bsd-specific	86	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
27	kqueue mechanisms for file descriptor events, relative timers, absolute	87	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
28	timers with customised rescheduling, signal events, process status change	88	for file descriptor events (C<ev_io>), the Linux C<inotify> interface
29	events (related to SIGCHLD), and event watchers dealing with the event	89	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers
30	loop mechanism itself (idle, prepare and check watchers). It also is quite	90	with customised rescheduling (C<ev_periodic>), synchronous signals
		91	(C<ev_signal>), process status change events (C<ev_child>), and event
		92	watchers dealing with the event loop mechanism itself (C<ev_idle>,
		93	C<ev_embed>, C<ev_prepare> and C<ev_check> watchers) as well as
		94	file watchers (C<ev_stat>) and even limited support for fork events
		95	(C<ev_fork>).
		96
		97	It also is quite fast (see this
31	fast (see this L<benchmark|http://libev.schmorp.de/bench.html> comparing	98	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
32	it to libevent for example).	99	for example).
33		100
34	=head1 CONVENTIONS	101	=head2 CONVENTIONS
35		102
36	Libev is very configurable. In this manual the default configuration	103	Libev is very configurable. In this manual the default (and most common)
37	will be described, which supports multiple event loops. For more info	104	configuration will be described, which supports multiple event loops. For
38	about various configuration options please have a look at the file	105	more info about various configuration options please have a look at
39	F<README.embed> in the libev distribution. If libev was configured without	106	B<EMBED> section in this manual. If libev was configured without support
40	support for multiple event loops, then all functions taking an initial	107	for multiple event loops, then all functions taking an initial argument of
41	argument of name C<loop> (which is always of type C<struct ev_loop *>)	108	name C<loop> (which is always of type C<struct ev_loop *>) will not have
42	will not have this argument.	109	this argument.
43		110
44	=head1 TIME REPRESENTATION	111	=head2 TIME REPRESENTATION
45		112
46	Libev represents time as a single floating point number, representing the	113	Libev represents time as a single floating point number, representing the
47	(fractional) number of seconds since the (POSIX) epoch (somewhere near	114	(fractional) number of seconds since the (POSIX) epoch (somewhere near
48	the beginning of 1970, details are complicated, don't ask). This type is	115	the beginning of 1970, details are complicated, don't ask). This type is
49	called C<ev_tstamp>, which is what you should use too. It usually aliases	116	called C<ev_tstamp>, which is what you should use too. It usually aliases
50	to the C<double> type in C, and when you need to do any calculations on	117	to the C<double> type in C, and when you need to do any calculations on
51	it, you should treat it as such.	118	it, you should treat it as some floating point value. Unlike the name
		119	component C<stamp> might indicate, it is also used for time differences
		120	throughout libev.
		121
		122	=head1 ERROR HANDLING
		123
		124	Libev knows three classes of errors: operating system errors, usage errors
		125	and internal errors (bugs).
		126
		127	When libev catches an operating system error it cannot handle (for example
		128	a system call indicating a condition libev cannot fix), it calls the callback
		129	set via C<ev_set_syserr_cb>, which is supposed to fix the problem or
		130	abort. The default is to print a diagnostic message and to call C<abort
		131	()>.
		132
		133	When libev detects a usage error such as a negative timer interval, then
		134	it will print a diagnostic message and abort (via the C<assert> mechanism,
		135	so C<NDEBUG> will disable this checking): these are programming errors in
		136	the libev caller and need to be fixed there.
		137
		138	Libev also has a few internal error-checking C<assert>ions, and also has
		139	extensive consistency checking code. These do not trigger under normal
		140	circumstances, as they indicate either a bug in libev or worse.
52		141
53		142
54	=head1 GLOBAL FUNCTIONS	143	=head1 GLOBAL FUNCTIONS
55		144
56	These functions can be called anytime, even before initialising the	145	These functions can be called anytime, even before initialising the
…		…
62		151
63	Returns the current time as libev would use it. Please note that the	152	Returns the current time as libev would use it. Please note that the
64	C<ev_now> function is usually faster and also often returns the timestamp	153	C<ev_now> function is usually faster and also often returns the timestamp
65	you actually want to know.	154	you actually want to know.
66		155
		156	=item ev_sleep (ev_tstamp interval)
		157
		158	Sleep for the given interval: The current thread will be blocked until
		159	either it is interrupted or the given time interval has passed. Basically
		160	this is a sub-second-resolution C<sleep ()>.
		161
67	=item int ev_version_major ()	162	=item int ev_version_major ()
68		163
69	=item int ev_version_minor ()	164	=item int ev_version_minor ()
70		165
71	You can find out the major and minor version numbers of the library	166	You can find out the major and minor ABI version numbers of the library
72	you linked against by calling the functions C<ev_version_major> and	167	you linked against by calling the functions C<ev_version_major> and
73	C<ev_version_minor>. If you want, you can compare against the global	168	C<ev_version_minor>. If you want, you can compare against the global
74	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the	169	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the
75	version of the library your program was compiled against.	170	version of the library your program was compiled against.
76		171
		172	These version numbers refer to the ABI version of the library, not the
		173	release version.
		174
77	Usually, it's a good idea to terminate if the major versions mismatch,	175	Usually, it's a good idea to terminate if the major versions mismatch,
78	as this indicates an incompatible change. Minor versions are usually	176	as this indicates an incompatible change. Minor versions are usually
79	compatible to older versions, so a larger minor version alone is usually	177	compatible to older versions, so a larger minor version alone is usually
80	not a problem.	178	not a problem.
81		179
82	Example: make sure we haven't accidentally been linked against the wrong	180	Example: Make sure we haven't accidentally been linked against the wrong
83	version:	181	version.
84		182
85	assert (("libev version mismatch",	183	assert (("libev version mismatch",
86	ev_version_major () == EV_VERSION_MAJOR	184	ev_version_major () == EV_VERSION_MAJOR
87	&& ev_version_minor () >= EV_VERSION_MINOR));	185	&& ev_version_minor () >= EV_VERSION_MINOR));
88		186
89	=item unsigned int ev_supported_backends ()	187	=item unsigned int ev_supported_backends ()
90		188
91	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>	189	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
92	value) compiled into this binary of libev (independent of their	190	value) compiled into this binary of libev (independent of their
…		…
94	a description of the set values.	192	a description of the set values.
95		193
96	Example: make sure we have the epoll method, because yeah this is cool and	194	Example: make sure we have the epoll method, because yeah this is cool and
97	a must have and can we have a torrent of it please!!!11	195	a must have and can we have a torrent of it please!!!11
98		196
99	assert (("sorry, no epoll, no sex",	197	assert (("sorry, no epoll, no sex",
100	ev_supported_backends () & EVBACKEND_EPOLL));	198	ev_supported_backends () & EVBACKEND_EPOLL));
101		199
102	=item unsigned int ev_recommended_backends ()	200	=item unsigned int ev_recommended_backends ()
103		201
104	Return the set of all backends compiled into this binary of libev and also	202	Return the set of all backends compiled into this binary of libev and also
105	recommended for this platform. This set is often smaller than the one	203	recommended for this platform. This set is often smaller than the one
106	returned by C<ev_supported_backends>, as for example kqueue is broken on	204	returned by C<ev_supported_backends>, as for example kqueue is broken on
107	most BSDs and will not be autodetected unless you explicitly request it	205	most BSDs and will not be auto-detected unless you explicitly request it
108	(assuming you know what you are doing). This is the set of backends that	206	(assuming you know what you are doing). This is the set of backends that
109	libev will probe for if you specify no backends explicitly.	207	libev will probe for if you specify no backends explicitly.
110		208
111	=item unsigned int ev_embeddable_backends ()	209	=item unsigned int ev_embeddable_backends ()
112		210
…		…
118		216
119	See the description of C<ev_embed> watchers for more info.	217	See the description of C<ev_embed> watchers for more info.
120		218
121	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	219	=item ev_set_allocator (void *(*cb)(void *ptr, long size))
122		220
123	Sets the allocation function to use (the prototype is similar to the	221	Sets the allocation function to use (the prototype is similar - the
124	realloc C function, the semantics are identical). It is used to allocate	222	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
125	and free memory (no surprises here). If it returns zero when memory	223	used to allocate and free memory (no surprises here). If it returns zero
126	needs to be allocated, the library might abort or take some potentially	224	when memory needs to be allocated (C<size != 0>), the library might abort
127	destructive action. The default is your system realloc function.	225	or take some potentially destructive action.
		226
		227	Since some systems (at least OpenBSD and Darwin) fail to implement
		228	correct C<realloc> semantics, libev will use a wrapper around the system
		229	C<realloc> and C<free> functions by default.
128		230
129	You could override this function in high-availability programs to, say,	231	You could override this function in high-availability programs to, say,
130	free some memory if it cannot allocate memory, to use a special allocator,	232	free some memory if it cannot allocate memory, to use a special allocator,
131	or even to sleep a while and retry until some memory is available.	233	or even to sleep a while and retry until some memory is available.
132		234
133	Example: replace the libev allocator with one that waits a bit and then	235	Example: Replace the libev allocator with one that waits a bit and then
134	retries: better than mine).	236	retries (example requires a standards-compliant C<realloc>).
135		237
136	static void *	238	static void *
137	persistent_realloc (void *ptr, long size)	239	persistent_realloc (void *ptr, size_t size)
138	{	240	{
139	for (;;)	241	for (;;)
140	{	242	{
141	void *newptr = realloc (ptr, size);	243	void *newptr = realloc (ptr, size);
142		244
…		…
150	...	252	...
151	ev_set_allocator (persistent_realloc);	253	ev_set_allocator (persistent_realloc);
152		254
153	=item ev_set_syserr_cb (void (*cb)(const char *msg));	255	=item ev_set_syserr_cb (void (*cb)(const char *msg));
154		256
155	Set the callback function to call on a retryable syscall error (such	257	Set the callback function to call on a retryable system call error (such
156	as failed select, poll, epoll_wait). The message is a printable string	258	as failed select, poll, epoll_wait). The message is a printable string
157	indicating the system call or subsystem causing the problem. If this	259	indicating the system call or subsystem causing the problem. If this
158	callback is set, then libev will expect it to remedy the sitution, no	260	callback is set, then libev will expect it to remedy the situation, no
159	matter what, when it returns. That is, libev will generally retry the	261	matter what, when it returns. That is, libev will generally retry the
160	requested operation, or, if the condition doesn't go away, do bad stuff	262	requested operation, or, if the condition doesn't go away, do bad stuff
161	(such as abort).	263	(such as abort).
162		264
163	Example: do the same thing as libev does internally:	265	Example: This is basically the same thing that libev does internally, too.
164		266
165	static void	267	static void
166	fatal_error (const char *msg)	268	fatal_error (const char *msg)
167	{	269	{
168	perror (msg);	270	perror (msg);
…		…
177	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	279	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
178		280
179	An event loop is described by a C<struct ev_loop *>. The library knows two	281	An event loop is described by a C<struct ev_loop *>. The library knows two
180	types of such loops, the I<default> loop, which supports signals and child	282	types of such loops, the I<default> loop, which supports signals and child
181	events, and dynamically created loops which do not.	283	events, and dynamically created loops which do not.
182
183	If you use threads, a common model is to run the default event loop
184	in your main thread (or in a separate thread) and for each thread you
185	create, you also create another event loop. Libev itself does no locking
186	whatsoever, so if you mix calls to the same event loop in different
187	threads, make sure you lock (this is usually a bad idea, though, even if
188	done correctly, because it's hideous and inefficient).
189		284
190	=over 4	285	=over 4
191		286
192	=item struct ev_loop *ev_default_loop (unsigned int flags)	287	=item struct ev_loop *ev_default_loop (unsigned int flags)
193		288
…		…
197	flags. If that is troubling you, check C<ev_backend ()> afterwards).	292	flags. If that is troubling you, check C<ev_backend ()> afterwards).
198		293
199	If you don't know what event loop to use, use the one returned from this	294	If you don't know what event loop to use, use the one returned from this
200	function.	295	function.
201		296
		297	Note that this function is I<not> thread-safe, so if you want to use it
		298	from multiple threads, you have to lock (note also that this is unlikely,
		299	as loops cannot bes hared easily between threads anyway).
		300
		301	The default loop is the only loop that can handle C<ev_signal> and
		302	C<ev_child> watchers, and to do this, it always registers a handler
		303	for C<SIGCHLD>. If this is a problem for your application you can either
		304	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you
		305	can simply overwrite the C<SIGCHLD> signal handler I<after> calling
		306	C<ev_default_init>.
		307
202	The flags argument can be used to specify special behaviour or specific	308	The flags argument can be used to specify special behaviour or specific
203	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).	309	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
204		310
205	The following flags are supported:	311	The following flags are supported:
206		312
…		…
211	The default flags value. Use this if you have no clue (it's the right	317	The default flags value. Use this if you have no clue (it's the right
212	thing, believe me).	318	thing, believe me).
213		319
214	=item C<EVFLAG_NOENV>	320	=item C<EVFLAG_NOENV>
215		321
216	If this flag bit is ored into the flag value (or the program runs setuid	322	If this flag bit is or'ed into the flag value (or the program runs setuid
217	or setgid) then libev will I<not> look at the environment variable	323	or setgid) then libev will I<not> look at the environment variable
218	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	324	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
219	override the flags completely if it is found in the environment. This is	325	override the flags completely if it is found in the environment. This is
220	useful to try out specific backends to test their performance, or to work	326	useful to try out specific backends to test their performance, or to work
221	around bugs.	327	around bugs.
222		328
		329	=item C<EVFLAG_FORKCHECK>
		330
		331	Instead of calling C<ev_default_fork> or C<ev_loop_fork> manually after
		332	a fork, you can also make libev check for a fork in each iteration by
		333	enabling this flag.
		334
		335	This works by calling C<getpid ()> on every iteration of the loop,
		336	and thus this might slow down your event loop if you do a lot of loop
		337	iterations and little real work, but is usually not noticeable (on my
		338	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence
		339	without a system call and thus I<very> fast, but my GNU/Linux system also has
		340	C<pthread_atfork> which is even faster).
		341
		342	The big advantage of this flag is that you can forget about fork (and
		343	forget about forgetting to tell libev about forking) when you use this
		344	flag.
		345
		346	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
		347	environment variable.
		348
223	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	349	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
224		350
225	This is your standard select(2) backend. Not I<completely> standard, as	351	This is your standard select(2) backend. Not I<completely> standard, as
226	libev tries to roll its own fd_set with no limits on the number of fds,	352	libev tries to roll its own fd_set with no limits on the number of fds,
227	but if that fails, expect a fairly low limit on the number of fds when	353	but if that fails, expect a fairly low limit on the number of fds when
228	using this backend. It doesn't scale too well (O(highest_fd)), but its usually	354	using this backend. It doesn't scale too well (O(highest_fd)), but its
229	the fastest backend for a low number of fds.	355	usually the fastest backend for a low number of (low-numbered :) fds.
		356
		357	To get good performance out of this backend you need a high amount of
		358	parallelism (most of the file descriptors should be busy). If you are
		359	writing a server, you should C<accept ()> in a loop to accept as many
		360	connections as possible during one iteration. You might also want to have
		361	a look at C<ev_set_io_collect_interval ()> to increase the amount of
		362	readiness notifications you get per iteration.
230		363
231	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)	364	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
232		365
233	And this is your standard poll(2) backend. It's more complicated than	366	And this is your standard poll(2) backend. It's more complicated
234	select, but handles sparse fds better and has no artificial limit on the	367	than select, but handles sparse fds better and has no artificial
235	number of fds you can use (except it will slow down considerably with a	368	limit on the number of fds you can use (except it will slow down
236	lot of inactive fds). It scales similarly to select, i.e. O(total_fds).	369	considerably with a lot of inactive fds). It scales similarly to select,
		370	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
		371	performance tips.
237		372
238	=item C<EVBACKEND_EPOLL> (value 4, Linux)	373	=item C<EVBACKEND_EPOLL> (value 4, Linux)
239		374
240	For few fds, this backend is a bit little slower than poll and select,	375	For few fds, this backend is a bit little slower than poll and select,
241	but it scales phenomenally better. While poll and select usually scale like	376	but it scales phenomenally better. While poll and select usually scale
242	O(total_fds) where n is the total number of fds (or the highest fd), epoll scales	377	like O(total_fds) where n is the total number of fds (or the highest fd),
243	either O(1) or O(active_fds).	378	epoll scales either O(1) or O(active_fds). The epoll design has a number
		379	of shortcomings, such as silently dropping events in some hard-to-detect
		380	cases and requiring a system call per fd change, no fork support and bad
		381	support for dup.
244		382
245	While stopping and starting an I/O watcher in the same iteration will	383	While stopping, setting and starting an I/O watcher in the same iteration
246	result in some caching, there is still a syscall per such incident	384	will result in some caching, there is still a system call per such incident
247	(because the fd could point to a different file description now), so its	385	(because the fd could point to a different file description now), so its
248	best to avoid that. Also, dup()ed file descriptors might not work very	386	best to avoid that. Also, C<dup ()>'ed file descriptors might not work
249	well if you register events for both fds.	387	very well if you register events for both fds.
250		388
251	Please note that epoll sometimes generates spurious notifications, so you	389	Please note that epoll sometimes generates spurious notifications, so you
252	need to use non-blocking I/O or other means to avoid blocking when no data	390	need to use non-blocking I/O or other means to avoid blocking when no data
253	(or space) is available.	391	(or space) is available.
254		392
		393	Best performance from this backend is achieved by not unregistering all
		394	watchers for a file descriptor until it has been closed, if possible, i.e.
		395	keep at least one watcher active per fd at all times.
		396
		397	While nominally embeddable in other event loops, this feature is broken in
		398	all kernel versions tested so far.
		399
255	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	400	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
256		401
257	Kqueue deserves special mention, as at the time of this writing, it	402	Kqueue deserves special mention, as at the time of this writing, it
258	was broken on all BSDs except NetBSD (usually it doesn't work with	403	was broken on all BSDs except NetBSD (usually it doesn't work reliably
259	anything but sockets and pipes, except on Darwin, where of course its	404	with anything but sockets and pipes, except on Darwin, where of course
260	completely useless). For this reason its not being "autodetected"	405	it's completely useless). For this reason it's not being "auto-detected"
261	unless you explicitly specify it explicitly in the flags (i.e. using	406	unless you explicitly specify it explicitly in the flags (i.e. using
262	C<EVBACKEND_KQUEUE>).	407	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
		408	system like NetBSD.
		409
		410	You still can embed kqueue into a normal poll or select backend and use it
		411	only for sockets (after having made sure that sockets work with kqueue on
		412	the target platform). See C<ev_embed> watchers for more info.
263		413
264	It scales in the same way as the epoll backend, but the interface to the	414	It scales in the same way as the epoll backend, but the interface to the
265	kernel is more efficient (which says nothing about its actual speed, of	415	kernel is more efficient (which says nothing about its actual speed, of
266	course). While starting and stopping an I/O watcher does not cause an	416	course). While stopping, setting and starting an I/O watcher does never
267	extra syscall as with epoll, it still adds up to four event changes per	417	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
268	incident, so its best to avoid that.	418	two event changes per incident, support for C<fork ()> is very bad and it
		419	drops fds silently in similarly hard-to-detect cases.
		420
		421	This backend usually performs well under most conditions.
		422
		423	While nominally embeddable in other event loops, this doesn't work
		424	everywhere, so you might need to test for this. And since it is broken
		425	almost everywhere, you should only use it when you have a lot of sockets
		426	(for which it usually works), by embedding it into another event loop
		427	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>) and using it only for
		428	sockets.
269		429
270	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	430	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
271		431
272	This is not implemented yet (and might never be).	432	This is not implemented yet (and might never be, unless you send me an
		433	implementation). According to reports, C</dev/poll> only supports sockets
		434	and is not embeddable, which would limit the usefulness of this backend
		435	immensely.
273		436
274	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	437	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
275		438
276	This uses the Solaris 10 port mechanism. As with everything on Solaris,	439	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
277	it's really slow, but it still scales very well (O(active_fds)).	440	it's really slow, but it still scales very well (O(active_fds)).
278		441
279	Please note that solaris ports can result in a lot of spurious	442	Please note that Solaris event ports can deliver a lot of spurious
280	notifications, so you need to use non-blocking I/O or other means to avoid	443	notifications, so you need to use non-blocking I/O or other means to avoid
281	blocking when no data (or space) is available.	444	blocking when no data (or space) is available.
		445
		446	While this backend scales well, it requires one system call per active
		447	file descriptor per loop iteration. For small and medium numbers of file
		448	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
		449	might perform better.
		450
		451	On the positive side, ignoring the spurious readiness notifications, this
		452	backend actually performed to specification in all tests and is fully
		453	embeddable, which is a rare feat among the OS-specific backends.
282		454
283	=item C<EVBACKEND_ALL>	455	=item C<EVBACKEND_ALL>
284		456
285	Try all backends (even potentially broken ones that wouldn't be tried	457	Try all backends (even potentially broken ones that wouldn't be tried
286	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	458	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
287	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	459	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
288		460
		461	It is definitely not recommended to use this flag.
		462
289	=back	463	=back
290		464
291	If one or more of these are ored into the flags value, then only these	465	If one or more of these are or'ed into the flags value, then only these
292	backends will be tried (in the reverse order as given here). If none are	466	backends will be tried (in the reverse order as listed here). If none are
293	specified, most compiled-in backend will be tried, usually in reverse	467	specified, all backends in C<ev_recommended_backends ()> will be tried.
294	order of their flag values :)
295		468
296	The most typical usage is like this:	469	The most typical usage is like this:
297		470
298	if (!ev_default_loop (0))	471	if (!ev_default_loop (0))
299	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");	472	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
300		473
301	Restrict libev to the select and poll backends, and do not allow	474	Restrict libev to the select and poll backends, and do not allow
302	environment settings to be taken into account:	475	environment settings to be taken into account:
303		476
304	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);	477	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
305		478
306	Use whatever libev has to offer, but make sure that kqueue is used if	479	Use whatever libev has to offer, but make sure that kqueue is used if
307	available (warning, breaks stuff, best use only with your own private	480	available (warning, breaks stuff, best use only with your own private
308	event loop and only if you know the OS supports your types of fds):	481	event loop and only if you know the OS supports your types of fds):
309		482
310	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);	483	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
311		484
312	=item struct ev_loop *ev_loop_new (unsigned int flags)	485	=item struct ev_loop *ev_loop_new (unsigned int flags)
313		486
314	Similar to C<ev_default_loop>, but always creates a new event loop that is	487	Similar to C<ev_default_loop>, but always creates a new event loop that is
315	always distinct from the default loop. Unlike the default loop, it cannot	488	always distinct from the default loop. Unlike the default loop, it cannot
316	handle signal and child watchers, and attempts to do so will be greeted by	489	handle signal and child watchers, and attempts to do so will be greeted by
317	undefined behaviour (or a failed assertion if assertions are enabled).	490	undefined behaviour (or a failed assertion if assertions are enabled).
318		491
		492	Note that this function I<is> thread-safe, and the recommended way to use
		493	libev with threads is indeed to create one loop per thread, and using the
		494	default loop in the "main" or "initial" thread.
		495
319	Example: try to create a event loop that uses epoll and nothing else.	496	Example: Try to create a event loop that uses epoll and nothing else.
320		497
321	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	498	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
322	if (!epoller)	499	if (!epoller)
323	fatal ("no epoll found here, maybe it hides under your chair");	500	fatal ("no epoll found here, maybe it hides under your chair");
324		501
325	=item ev_default_destroy ()	502	=item ev_default_destroy ()
326		503
327	Destroys the default loop again (frees all memory and kernel state	504	Destroys the default loop again (frees all memory and kernel state
328	etc.). None of the active event watchers will be stopped in the normal	505	etc.). None of the active event watchers will be stopped in the normal
329	sense, so e.g. C<ev_is_active> might still return true. It is your	506	sense, so e.g. C<ev_is_active> might still return true. It is your
330	responsibility to either stop all watchers cleanly yoursef I<before>	507	responsibility to either stop all watchers cleanly yourself I<before>
331	calling this function, or cope with the fact afterwards (which is usually	508	calling this function, or cope with the fact afterwards (which is usually
332	the easiest thing, youc na just ignore the watchers and/or C<free ()> them	509	the easiest thing, you can just ignore the watchers and/or C<free ()> them
333	for example).	510	for example).
		511
		512	Note that certain global state, such as signal state, will not be freed by
		513	this function, and related watchers (such as signal and child watchers)
		514	would need to be stopped manually.
		515
		516	In general it is not advisable to call this function except in the
		517	rare occasion where you really need to free e.g. the signal handling
		518	pipe fds. If you need dynamically allocated loops it is better to use
		519	C<ev_loop_new> and C<ev_loop_destroy>).
334		520
335	=item ev_loop_destroy (loop)	521	=item ev_loop_destroy (loop)
336		522
337	Like C<ev_default_destroy>, but destroys an event loop created by an	523	Like C<ev_default_destroy>, but destroys an event loop created by an
338	earlier call to C<ev_loop_new>.	524	earlier call to C<ev_loop_new>.
339		525
340	=item ev_default_fork ()	526	=item ev_default_fork ()
341		527
		528	This function sets a flag that causes subsequent C<ev_loop> iterations
342	This function reinitialises the kernel state for backends that have	529	to reinitialise the kernel state for backends that have one. Despite the
343	one. Despite the name, you can call it anytime, but it makes most sense	530	name, you can call it anytime, but it makes most sense after forking, in
344	after forking, in either the parent or child process (or both, but that	531	the child process (or both child and parent, but that again makes little
345	again makes little sense).	532	sense). You I<must> call it in the child before using any of the libev
		533	functions, and it will only take effect at the next C<ev_loop> iteration.
346		534
347	You I<must> call this function in the child process after forking if and	535	On the other hand, you only need to call this function in the child
348	only if you want to use the event library in both processes. If you just	536	process if and only if you want to use the event library in the child. If
349	fork+exec, you don't have to call it.	537	you just fork+exec, you don't have to call it at all.
350		538
351	The function itself is quite fast and it's usually not a problem to call	539	The function itself is quite fast and it's usually not a problem to call
352	it just in case after a fork. To make this easy, the function will fit in	540	it just in case after a fork. To make this easy, the function will fit in
353	quite nicely into a call to C<pthread_atfork>:	541	quite nicely into a call to C<pthread_atfork>:
354		542
355	pthread_atfork (0, 0, ev_default_fork);	543	pthread_atfork (0, 0, ev_default_fork);
356		544
357	At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> are safe to use
358	without calling this function, so if you force one of those backends you
359	do not need to care.
360
361	=item ev_loop_fork (loop)	545	=item ev_loop_fork (loop)
362		546
363	Like C<ev_default_fork>, but acts on an event loop created by	547	Like C<ev_default_fork>, but acts on an event loop created by
364	C<ev_loop_new>. Yes, you have to call this on every allocated event loop	548	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
365	after fork, and how you do this is entirely your own problem.	549	after fork, and how you do this is entirely your own problem.
		550
		551	=item int ev_is_default_loop (loop)
		552
		553	Returns true when the given loop actually is the default loop, false otherwise.
		554
		555	=item unsigned int ev_loop_count (loop)
		556
		557	Returns the count of loop iterations for the loop, which is identical to
		558	the number of times libev did poll for new events. It starts at C<0> and
		559	happily wraps around with enough iterations.
		560
		561	This value can sometimes be useful as a generation counter of sorts (it
		562	"ticks" the number of loop iterations), as it roughly corresponds with
		563	C<ev_prepare> and C<ev_check> calls.
366		564
367	=item unsigned int ev_backend (loop)	565	=item unsigned int ev_backend (loop)
368		566
369	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	567	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
370	use.	568	use.
…		…
373		571
374	Returns the current "event loop time", which is the time the event loop	572	Returns the current "event loop time", which is the time the event loop
375	received events and started processing them. This timestamp does not	573	received events and started processing them. This timestamp does not
376	change as long as callbacks are being processed, and this is also the base	574	change as long as callbacks are being processed, and this is also the base
377	time used for relative timers. You can treat it as the timestamp of the	575	time used for relative timers. You can treat it as the timestamp of the
378	event occuring (or more correctly, libev finding out about it).	576	event occurring (or more correctly, libev finding out about it).
379		577
380	=item ev_loop (loop, int flags)	578	=item ev_loop (loop, int flags)
381		579
382	Finally, this is it, the event handler. This function usually is called	580	Finally, this is it, the event handler. This function usually is called
383	after you initialised all your watchers and you want to start handling	581	after you initialised all your watchers and you want to start handling
…		…
395	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	593	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle
396	those events and any outstanding ones, but will not block your process in	594	those events and any outstanding ones, but will not block your process in
397	case there are no events and will return after one iteration of the loop.	595	case there are no events and will return after one iteration of the loop.
398		596
399	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	597	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if
400	neccessary) and will handle those and any outstanding ones. It will block	598	necessary) and will handle those and any outstanding ones. It will block
401	your process until at least one new event arrives, and will return after	599	your process until at least one new event arrives, and will return after
402	one iteration of the loop. This is useful if you are waiting for some	600	one iteration of the loop. This is useful if you are waiting for some
403	external event in conjunction with something not expressible using other	601	external event in conjunction with something not expressible using other
404	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is	602	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is
405	usually a better approach for this kind of thing.	603	usually a better approach for this kind of thing.
406		604
407	Here are the gory details of what C<ev_loop> does:	605	Here are the gory details of what C<ev_loop> does:
408		606
409	* If there are no active watchers (reference count is zero), return.	607	- Before the first iteration, call any pending watchers.
410	- Queue prepare watchers and then call all outstanding watchers.	608	* If EVFLAG_FORKCHECK was used, check for a fork.
		609	- If a fork was detected (by any means), queue and call all fork watchers.
		610	- Queue and call all prepare watchers.
411	- If we have been forked, recreate the kernel state.	611	- If we have been forked, detach and recreate the kernel state
		612	as to not disturb the other process.
412	- Update the kernel state with all outstanding changes.	613	- Update the kernel state with all outstanding changes.
413	- Update the "event loop time".	614	- Update the "event loop time" (ev_now ()).
414	- Calculate for how long to block.	615	- Calculate for how long to sleep or block, if at all
		616	(active idle watchers, EVLOOP_NONBLOCK or not having
		617	any active watchers at all will result in not sleeping).
		618	- Sleep if the I/O and timer collect interval say so.
415	- Block the process, waiting for any events.	619	- Block the process, waiting for any events.
416	- Queue all outstanding I/O (fd) events.	620	- Queue all outstanding I/O (fd) events.
417	- Update the "event loop time" and do time jump handling.	621	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
418	- Queue all outstanding timers.	622	- Queue all outstanding timers.
419	- Queue all outstanding periodics.	623	- Queue all outstanding periodics.
420	- If no events are pending now, queue all idle watchers.	624	- Unless any events are pending now, queue all idle watchers.
421	- Queue all check watchers.	625	- Queue all check watchers.
422	- Call all queued watchers in reverse order (i.e. check watchers first).	626	- Call all queued watchers in reverse order (i.e. check watchers first).
423	Signals and child watchers are implemented as I/O watchers, and will	627	Signals and child watchers are implemented as I/O watchers, and will
424	be handled here by queueing them when their watcher gets executed.	628	be handled here by queueing them when their watcher gets executed.
425	- If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	629	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
426	were used, return, otherwise continue with step *.	630	were used, or there are no active watchers, return, otherwise
		631	continue with step *.
427		632
428	Example: queue some jobs and then loop until no events are outsanding	633	Example: Queue some jobs and then loop until no events are outstanding
429	anymore.	634	anymore.
430		635
431	... queue jobs here, make sure they register event watchers as long	636	... queue jobs here, make sure they register event watchers as long
432	... as they still have work to do (even an idle watcher will do..)	637	... as they still have work to do (even an idle watcher will do..)
433	ev_loop (my_loop, 0);	638	ev_loop (my_loop, 0);
434	... jobs done. yeah!	639	... jobs done or somebody called unloop. yeah!
435		640
436	=item ev_unloop (loop, how)	641	=item ev_unloop (loop, how)
437		642
438	Can be used to make a call to C<ev_loop> return early (but only after it	643	Can be used to make a call to C<ev_loop> return early (but only after it
439	has processed all outstanding events). The C<how> argument must be either	644	has processed all outstanding events). The C<how> argument must be either
440	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	645	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
441	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	646	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
		647
		648	This "unloop state" will be cleared when entering C<ev_loop> again.
442		649
443	=item ev_ref (loop)	650	=item ev_ref (loop)
444		651
445	=item ev_unref (loop)	652	=item ev_unref (loop)
446		653
…		…
451	returning, ev_unref() after starting, and ev_ref() before stopping it. For	658	returning, ev_unref() after starting, and ev_ref() before stopping it. For
452	example, libev itself uses this for its internal signal pipe: It is not	659	example, libev itself uses this for its internal signal pipe: It is not
453	visible to the libev user and should not keep C<ev_loop> from exiting if	660	visible to the libev user and should not keep C<ev_loop> from exiting if
454	no event watchers registered by it are active. It is also an excellent	661	no event watchers registered by it are active. It is also an excellent
455	way to do this for generic recurring timers or from within third-party	662	way to do this for generic recurring timers or from within third-party
456	libraries. Just remember to I<unref after start> and I<ref before stop>.	663	libraries. Just remember to I<unref after start> and I<ref before stop>
		664	(but only if the watcher wasn't active before, or was active before,
		665	respectively).
457		666
458	Example: create a signal watcher, but keep it from keeping C<ev_loop>	667	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
459	running when nothing else is active.	668	running when nothing else is active.
460		669
461	struct dv_signal exitsig;	670	struct ev_signal exitsig;
462	ev_signal_init (&exitsig, sig_cb, SIGINT);	671	ev_signal_init (&exitsig, sig_cb, SIGINT);
463	ev_signal_start (myloop, &exitsig);	672	ev_signal_start (loop, &exitsig);
464	evf_unref (myloop);	673	evf_unref (loop);
465		674
466	Example: for some weird reason, unregister the above signal handler again.	675	Example: For some weird reason, unregister the above signal handler again.
467		676
468	ev_ref (myloop);	677	ev_ref (loop);
469	ev_signal_stop (myloop, &exitsig);	678	ev_signal_stop (loop, &exitsig);
		679
		680	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
		681
		682	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
		683
		684	These advanced functions influence the time that libev will spend waiting
		685	for events. Both time intervals are by default C<0>, meaning that libev
		686	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		687	latency.
		688
		689	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
		690	allows libev to delay invocation of I/O and timer/periodic callbacks
		691	to increase efficiency of loop iterations (or to increase power-saving
		692	opportunities).
		693
		694	The background is that sometimes your program runs just fast enough to
		695	handle one (or very few) event(s) per loop iteration. While this makes
		696	the program responsive, it also wastes a lot of CPU time to poll for new
		697	events, especially with backends like C<select ()> which have a high
		698	overhead for the actual polling but can deliver many events at once.
		699
		700	By setting a higher I<io collect interval> you allow libev to spend more
		701	time collecting I/O events, so you can handle more events per iteration,
		702	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
		703	C<ev_timer>) will be not affected. Setting this to a non-null value will
		704	introduce an additional C<ev_sleep ()> call into most loop iterations.
		705
		706	Likewise, by setting a higher I<timeout collect interval> you allow libev
		707	to spend more time collecting timeouts, at the expense of increased
		708	latency (the watcher callback will be called later). C<ev_io> watchers
		709	will not be affected. Setting this to a non-null value will not introduce
		710	any overhead in libev.
		711
		712	Many (busy) programs can usually benefit by setting the I/O collect
		713	interval to a value near C<0.1> or so, which is often enough for
		714	interactive servers (of course not for games), likewise for timeouts. It
		715	usually doesn't make much sense to set it to a lower value than C<0.01>,
		716	as this approaches the timing granularity of most systems.
		717
		718	Setting the I<timeout collect interval> can improve the opportunity for
		719	saving power, as the program will "bundle" timer callback invocations that
		720	are "near" in time together, by delaying some, thus reducing the number of
		721	times the process sleeps and wakes up again. Another useful technique to
		722	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		723	they fire on, say, one-second boundaries only.
		724
		725	=item ev_loop_verify (loop)
		726
		727	This function only does something when C<EV_VERIFY> support has been
		728	compiled in. It tries to go through all internal structures and checks
		729	them for validity. If anything is found to be inconsistent, it will print
		730	an error message to standard error and call C<abort ()>.
		731
		732	This can be used to catch bugs inside libev itself: under normal
		733	circumstances, this function will never abort as of course libev keeps its
		734	data structures consistent.
470		735
471	=back	736	=back
		737
472		738
473	=head1 ANATOMY OF A WATCHER	739	=head1 ANATOMY OF A WATCHER
474		740
475	A watcher is a structure that you create and register to record your	741	A watcher is a structure that you create and register to record your
476	interest in some event. For instance, if you want to wait for STDIN to	742	interest in some event. For instance, if you want to wait for STDIN to
477	become readable, you would create an C<ev_io> watcher for that:	743	become readable, you would create an C<ev_io> watcher for that:
478		744
479	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	745	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)
480	{	746	{
481	ev_io_stop (w);	747	ev_io_stop (w);
482	ev_unloop (loop, EVUNLOOP_ALL);	748	ev_unloop (loop, EVUNLOOP_ALL);
483	}	749	}
484		750
485	struct ev_loop *loop = ev_default_loop (0);	751	struct ev_loop *loop = ev_default_loop (0);
486	struct ev_io stdin_watcher;	752	struct ev_io stdin_watcher;
487	ev_init (&stdin_watcher, my_cb);	753	ev_init (&stdin_watcher, my_cb);
488	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	754	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
489	ev_io_start (loop, &stdin_watcher);	755	ev_io_start (loop, &stdin_watcher);
490	ev_loop (loop, 0);	756	ev_loop (loop, 0);
491		757
492	As you can see, you are responsible for allocating the memory for your	758	As you can see, you are responsible for allocating the memory for your
493	watcher structures (and it is usually a bad idea to do this on the stack,	759	watcher structures (and it is usually a bad idea to do this on the stack,
494	although this can sometimes be quite valid).	760	although this can sometimes be quite valid).
495		761
496	Each watcher structure must be initialised by a call to C<ev_init	762	Each watcher structure must be initialised by a call to C<ev_init
497	(watcher *, callback)>, which expects a callback to be provided. This	763	(watcher *, callback)>, which expects a callback to be provided. This
498	callback gets invoked each time the event occurs (or, in the case of io	764	callback gets invoked each time the event occurs (or, in the case of I/O
499	watchers, each time the event loop detects that the file descriptor given	765	watchers, each time the event loop detects that the file descriptor given
500	is readable and/or writable).	766	is readable and/or writable).
501		767
502	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	768	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro
503	with arguments specific to this watcher type. There is also a macro	769	with arguments specific to this watcher type. There is also a macro
…		…
543	The signal specified in the C<ev_signal> watcher has been received by a thread.	809	The signal specified in the C<ev_signal> watcher has been received by a thread.
544		810
545	=item C<EV_CHILD>	811	=item C<EV_CHILD>
546		812
547	The pid specified in the C<ev_child> watcher has received a status change.	813	The pid specified in the C<ev_child> watcher has received a status change.
		814
		815	=item C<EV_STAT>
		816
		817	The path specified in the C<ev_stat> watcher changed its attributes somehow.
548		818
549	=item C<EV_IDLE>	819	=item C<EV_IDLE>
550		820
551	The C<ev_idle> watcher has determined that you have nothing better to do.	821	The C<ev_idle> watcher has determined that you have nothing better to do.
552		822
…		…
560	received events. Callbacks of both watcher types can start and stop as	830	received events. Callbacks of both watcher types can start and stop as
561	many watchers as they want, and all of them will be taken into account	831	many watchers as they want, and all of them will be taken into account
562	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	832	(for example, a C<ev_prepare> watcher might start an idle watcher to keep
563	C<ev_loop> from blocking).	833	C<ev_loop> from blocking).
564		834
		835	=item C<EV_EMBED>
		836
		837	The embedded event loop specified in the C<ev_embed> watcher needs attention.
		838
		839	=item C<EV_FORK>
		840
		841	The event loop has been resumed in the child process after fork (see
		842	C<ev_fork>).
		843
		844	=item C<EV_ASYNC>
		845
		846	The given async watcher has been asynchronously notified (see C<ev_async>).
		847
565	=item C<EV_ERROR>	848	=item C<EV_ERROR>
566		849
567	An unspecified error has occured, the watcher has been stopped. This might	850	An unspecified error has occurred, the watcher has been stopped. This might
568	happen because the watcher could not be properly started because libev	851	happen because the watcher could not be properly started because libev
569	ran out of memory, a file descriptor was found to be closed or any other	852	ran out of memory, a file descriptor was found to be closed or any other
570	problem. You best act on it by reporting the problem and somehow coping	853	problem. You best act on it by reporting the problem and somehow coping
571	with the watcher being stopped.	854	with the watcher being stopped.
572		855
573	Libev will usually signal a few "dummy" events together with an error,	856	Libev will usually signal a few "dummy" events together with an error,
574	for example it might indicate that a fd is readable or writable, and if	857	for example it might indicate that a fd is readable or writable, and if
575	your callbacks is well-written it can just attempt the operation and cope	858	your callbacks is well-written it can just attempt the operation and cope
576	with the error from read() or write(). This will not work in multithreaded	859	with the error from read() or write(). This will not work in multi-threaded
577	programs, though, so beware.	860	programs, though, so beware.
578		861
579	=back	862	=back
580		863
581	=head2 SUMMARY OF GENERIC WATCHER FUNCTIONS	864	=head2 GENERIC WATCHER FUNCTIONS
582		865
583	In the following description, C<TYPE> stands for the watcher type,	866	In the following description, C<TYPE> stands for the watcher type,
584	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.	867	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
585		868
586	=over 4	869	=over 4
…		…
595	which rolls both calls into one.	878	which rolls both calls into one.
596		879
597	You can reinitialise a watcher at any time as long as it has been stopped	880	You can reinitialise a watcher at any time as long as it has been stopped
598	(or never started) and there are no pending events outstanding.	881	(or never started) and there are no pending events outstanding.
599		882
600	The callbakc is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	883	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,
601	int revents)>.	884	int revents)>.
602		885
603	=item C<ev_TYPE_set> (ev_TYPE *, [args])	886	=item C<ev_TYPE_set> (ev_TYPE *, [args])
604		887
605	This macro initialises the type-specific parts of a watcher. You need to	888	This macro initialises the type-specific parts of a watcher. You need to
…		…
611	Although some watcher types do not have type-specific arguments	894	Although some watcher types do not have type-specific arguments
612	(e.g. C<ev_prepare>) you still need to call its C<set> macro.	895	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
613		896
614	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	897	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
615		898
616	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	899	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
617	calls into a single call. This is the most convinient method to initialise	900	calls into a single call. This is the most convenient method to initialise
618	a watcher. The same limitations apply, of course.	901	a watcher. The same limitations apply, of course.
619		902
620	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	903	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)
621		904
622	Starts (activates) the given watcher. Only active watchers will receive	905	Starts (activates) the given watcher. Only active watchers will receive
…		…
640	=item bool ev_is_pending (ev_TYPE *watcher)	923	=item bool ev_is_pending (ev_TYPE *watcher)
641		924
642	Returns a true value iff the watcher is pending, (i.e. it has outstanding	925	Returns a true value iff the watcher is pending, (i.e. it has outstanding
643	events but its callback has not yet been invoked). As long as a watcher	926	events but its callback has not yet been invoked). As long as a watcher
644	is pending (but not active) you must not call an init function on it (but	927	is pending (but not active) you must not call an init function on it (but
645	C<ev_TYPE_set> is safe) and you must make sure the watcher is available to	928	C<ev_TYPE_set> is safe), you must not change its priority, and you must
646	libev (e.g. you cnanot C<free ()> it).	929	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		930	it).
647		931
648	=item callback = ev_cb (ev_TYPE *watcher)	932	=item callback ev_cb (ev_TYPE *watcher)
649		933
650	Returns the callback currently set on the watcher.	934	Returns the callback currently set on the watcher.
651		935
652	=item ev_cb_set (ev_TYPE *watcher, callback)	936	=item ev_cb_set (ev_TYPE *watcher, callback)
653		937
654	Change the callback. You can change the callback at virtually any time	938	Change the callback. You can change the callback at virtually any time
655	(modulo threads).	939	(modulo threads).
		940
		941	=item ev_set_priority (ev_TYPE *watcher, priority)
		942
		943	=item int ev_priority (ev_TYPE *watcher)
		944
		945	Set and query the priority of the watcher. The priority is a small
		946	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
		947	(default: C<-2>). Pending watchers with higher priority will be invoked
		948	before watchers with lower priority, but priority will not keep watchers
		949	from being executed (except for C<ev_idle> watchers).
		950
		951	This means that priorities are I<only> used for ordering callback
		952	invocation after new events have been received. This is useful, for
		953	example, to reduce latency after idling, or more often, to bind two
		954	watchers on the same event and make sure one is called first.
		955
		956	If you need to suppress invocation when higher priority events are pending
		957	you need to look at C<ev_idle> watchers, which provide this functionality.
		958
		959	You I<must not> change the priority of a watcher as long as it is active or
		960	pending.
		961
		962	The default priority used by watchers when no priority has been set is
		963	always C<0>, which is supposed to not be too high and not be too low :).
		964
		965	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		966	fine, as long as you do not mind that the priority value you query might
		967	or might not have been adjusted to be within valid range.
		968
		969	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		970
		971	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		972	C<loop> nor C<revents> need to be valid as long as the watcher callback
		973	can deal with that fact.
		974
		975	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		976
		977	If the watcher is pending, this function returns clears its pending status
		978	and returns its C<revents> bitset (as if its callback was invoked). If the
		979	watcher isn't pending it does nothing and returns C<0>.
656		980
657	=back	981	=back
658		982
659		983
660	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	984	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
…		…
664	to associate arbitrary data with your watcher. If you need more data and	988	to associate arbitrary data with your watcher. If you need more data and
665	don't want to allocate memory and store a pointer to it in that data	989	don't want to allocate memory and store a pointer to it in that data
666	member, you can also "subclass" the watcher type and provide your own	990	member, you can also "subclass" the watcher type and provide your own
667	data:	991	data:
668		992
669	struct my_io	993	struct my_io
670	{	994	{
671	struct ev_io io;	995	struct ev_io io;
672	int otherfd;	996	int otherfd;
673	void *somedata;	997	void *somedata;
674	struct whatever *mostinteresting;	998	struct whatever *mostinteresting;
675	}	999	}
676		1000
677	And since your callback will be called with a pointer to the watcher, you	1001	And since your callback will be called with a pointer to the watcher, you
678	can cast it back to your own type:	1002	can cast it back to your own type:
679		1003
680	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1004	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)
681	{	1005	{
682	struct my_io *w = (struct my_io *)w_;	1006	struct my_io *w = (struct my_io *)w_;
683	...	1007	...
684	}	1008	}
685		1009
686	More interesting and less C-conformant ways of catsing your callback type	1010	More interesting and less C-conformant ways of casting your callback type
687	have been omitted....	1011	instead have been omitted.
		1012
		1013	Another common scenario is having some data structure with multiple
		1014	watchers:
		1015
		1016	struct my_biggy
		1017	{
		1018	int some_data;
		1019	ev_timer t1;
		1020	ev_timer t2;
		1021	}
		1022
		1023	In this case getting the pointer to C<my_biggy> is a bit more complicated,
		1024	you need to use C<offsetof>:
		1025
		1026	#include <stddef.h>
		1027
		1028	static void
		1029	t1_cb (EV_P_ struct ev_timer *w, int revents)
		1030	{
		1031	struct my_biggy big = (struct my_biggy *
		1032	(((char *)w) - offsetof (struct my_biggy, t1));
		1033	}
		1034
		1035	static void
		1036	t2_cb (EV_P_ struct ev_timer *w, int revents)
		1037	{
		1038	struct my_biggy big = (struct my_biggy *
		1039	(((char *)w) - offsetof (struct my_biggy, t2));
		1040	}
688		1041
689		1042
690	=head1 WATCHER TYPES	1043	=head1 WATCHER TYPES
691		1044
692	This section describes each watcher in detail, but will not repeat	1045	This section describes each watcher in detail, but will not repeat
693	information given in the last section.	1046	information given in the last section. Any initialisation/set macros,
		1047	functions and members specific to the watcher type are explained.
694		1048
		1049	Members are additionally marked with either I<[read-only]>, meaning that,
		1050	while the watcher is active, you can look at the member and expect some
		1051	sensible content, but you must not modify it (you can modify it while the
		1052	watcher is stopped to your hearts content), or I<[read-write]>, which
		1053	means you can expect it to have some sensible content while the watcher
		1054	is active, but you can also modify it. Modifying it may not do something
		1055	sensible or take immediate effect (or do anything at all), but libev will
		1056	not crash or malfunction in any way.
695		1057
		1058
696	=head2 C<ev_io> - is this file descriptor readable or writable	1059	=head2 C<ev_io> - is this file descriptor readable or writable?
697		1060
698	I/O watchers check whether a file descriptor is readable or writable	1061	I/O watchers check whether a file descriptor is readable or writable
699	in each iteration of the event loop (This behaviour is called	1062	in each iteration of the event loop, or, more precisely, when reading
700	level-triggering because you keep receiving events as long as the	1063	would not block the process and writing would at least be able to write
701	condition persists. Remember you can stop the watcher if you don't want to	1064	some data. This behaviour is called level-triggering because you keep
702	act on the event and neither want to receive future events).	1065	receiving events as long as the condition persists. Remember you can stop
		1066	the watcher if you don't want to act on the event and neither want to
		1067	receive future events.
703		1068
704	In general you can register as many read and/or write event watchers per	1069	In general you can register as many read and/or write event watchers per
705	fd as you want (as long as you don't confuse yourself). Setting all file	1070	fd as you want (as long as you don't confuse yourself). Setting all file
706	descriptors to non-blocking mode is also usually a good idea (but not	1071	descriptors to non-blocking mode is also usually a good idea (but not
707	required if you know what you are doing).	1072	required if you know what you are doing).
708		1073
709	You have to be careful with dup'ed file descriptors, though. Some backends
710	(the linux epoll backend is a notable example) cannot handle dup'ed file
711	descriptors correctly if you register interest in two or more fds pointing
712	to the same underlying file/socket etc. description (that is, they share
713	the same underlying "file open").
714
715	If you must do this, then force the use of a known-to-be-good backend	1074	If you must do this, then force the use of a known-to-be-good backend
716	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and	1075	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
717	C<EVBACKEND_POLL>).	1076	C<EVBACKEND_POLL>).
718		1077
		1078	Another thing you have to watch out for is that it is quite easy to
		1079	receive "spurious" readiness notifications, that is your callback might
		1080	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
		1081	because there is no data. Not only are some backends known to create a
		1082	lot of those (for example Solaris ports), it is very easy to get into
		1083	this situation even with a relatively standard program structure. Thus
		1084	it is best to always use non-blocking I/O: An extra C<read>(2) returning
		1085	C<EAGAIN> is far preferable to a program hanging until some data arrives.
		1086
		1087	If you cannot run the fd in non-blocking mode (for example you should not
		1088	play around with an Xlib connection), then you have to separately re-test
		1089	whether a file descriptor is really ready with a known-to-be good interface
		1090	such as poll (fortunately in our Xlib example, Xlib already does this on
		1091	its own, so its quite safe to use).
		1092
		1093	=head3 The special problem of disappearing file descriptors
		1094
		1095	Some backends (e.g. kqueue, epoll) need to be told about closing a file
		1096	descriptor (either by calling C<close> explicitly or by any other means,
		1097	such as C<dup>). The reason is that you register interest in some file
		1098	descriptor, but when it goes away, the operating system will silently drop
		1099	this interest. If another file descriptor with the same number then is
		1100	registered with libev, there is no efficient way to see that this is, in
		1101	fact, a different file descriptor.
		1102
		1103	To avoid having to explicitly tell libev about such cases, libev follows
		1104	the following policy: Each time C<ev_io_set> is being called, libev
		1105	will assume that this is potentially a new file descriptor, otherwise
		1106	it is assumed that the file descriptor stays the same. That means that
		1107	you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the
		1108	descriptor even if the file descriptor number itself did not change.
		1109
		1110	This is how one would do it normally anyway, the important point is that
		1111	the libev application should not optimise around libev but should leave
		1112	optimisations to libev.
		1113
		1114	=head3 The special problem of dup'ed file descriptors
		1115
		1116	Some backends (e.g. epoll), cannot register events for file descriptors,
		1117	but only events for the underlying file descriptions. That means when you
		1118	have C<dup ()>'ed file descriptors or weirder constellations, and register
		1119	events for them, only one file descriptor might actually receive events.
		1120
		1121	There is no workaround possible except not registering events
		1122	for potentially C<dup ()>'ed file descriptors, or to resort to
		1123	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1124
		1125	=head3 The special problem of fork
		1126
		1127	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
		1128	useless behaviour. Libev fully supports fork, but needs to be told about
		1129	it in the child.
		1130
		1131	To support fork in your programs, you either have to call
		1132	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
		1133	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
		1134	C<EVBACKEND_POLL>.
		1135
		1136	=head3 The special problem of SIGPIPE
		1137
		1138	While not really specific to libev, it is easy to forget about SIGPIPE:
		1139	when writing to a pipe whose other end has been closed, your program gets
		1140	send a SIGPIPE, which, by default, aborts your program. For most programs
		1141	this is sensible behaviour, for daemons, this is usually undesirable.
		1142
		1143	So when you encounter spurious, unexplained daemon exits, make sure you
		1144	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1145	somewhere, as that would have given you a big clue).
		1146
		1147
		1148	=head3 Watcher-Specific Functions
		1149
719	=over 4	1150	=over 4
720		1151
721	=item ev_io_init (ev_io *, callback, int fd, int events)	1152	=item ev_io_init (ev_io *, callback, int fd, int events)
722		1153
723	=item ev_io_set (ev_io *, int fd, int events)	1154	=item ev_io_set (ev_io *, int fd, int events)
724		1155
725	Configures an C<ev_io> watcher. The fd is the file descriptor to rceeive	1156	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
726	events for and events is either C<EV_READ>, C<EV_WRITE> or C<EV_READ |	1157	receive events for and events is either C<EV_READ>, C<EV_WRITE> or
727	EV_WRITE> to receive the given events.	1158	C<EV_READ | EV_WRITE> to receive the given events.
728		1159
729	Please note that most of the more scalable backend mechanisms (for example	1160	=item int fd [read-only]
730	epoll and solaris ports) can result in spurious readyness notifications	1161
731	for file descriptors, so you practically need to use non-blocking I/O (and	1162	The file descriptor being watched.
732	treat callback invocation as hint only), or retest separately with a safe	1163
733	interface before doing I/O (XLib can do this), or force the use of either	1164	=item int events [read-only]
734	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>, which don't suffer from this	1165
735	problem. Also note that it is quite easy to have your callback invoked	1166	The events being watched.
736	when the readyness condition is no longer valid even when employing
737	typical ways of handling events, so its a good idea to use non-blocking
738	I/O unconditionally.
739		1167
740	=back	1168	=back
741		1169
		1170	=head3 Examples
		1171
742	Example: call C<stdin_readable_cb> when STDIN_FILENO has become, well	1172	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
743	readable, but only once. Since it is likely line-buffered, you could	1173	readable, but only once. Since it is likely line-buffered, you could
744	attempt to read a whole line in the callback:	1174	attempt to read a whole line in the callback.
745		1175
746	static void	1176	static void
747	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1177	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)
748	{	1178	{
749	ev_io_stop (loop, w);	1179	ev_io_stop (loop, w);
750	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1180	.. read from stdin here (or from w->fd) and haqndle any I/O errors
751	}	1181	}
752		1182
753	...	1183	...
754	struct ev_loop *loop = ev_default_init (0);	1184	struct ev_loop *loop = ev_default_init (0);
755	struct ev_io stdin_readable;	1185	struct ev_io stdin_readable;
756	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1186	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
757	ev_io_start (loop, &stdin_readable);	1187	ev_io_start (loop, &stdin_readable);
758	ev_loop (loop, 0);	1188	ev_loop (loop, 0);
759		1189
760		1190
761	=head2 C<ev_timer> - relative and optionally recurring timeouts	1191	=head2 C<ev_timer> - relative and optionally repeating timeouts
762		1192
763	Timer watchers are simple relative timers that generate an event after a	1193	Timer watchers are simple relative timers that generate an event after a
764	given time, and optionally repeating in regular intervals after that.	1194	given time, and optionally repeating in regular intervals after that.
765		1195
766	The timers are based on real time, that is, if you register an event that	1196	The timers are based on real time, that is, if you register an event that
767	times out after an hour and you reset your system clock to last years	1197	times out after an hour and you reset your system clock to January last
768	time, it will still time out after (roughly) and hour. "Roughly" because	1198	year, it will still time out after (roughly) and hour. "Roughly" because
769	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1199	detecting time jumps is hard, and some inaccuracies are unavoidable (the
770	monotonic clock option helps a lot here).	1200	monotonic clock option helps a lot here).
		1201
		1202	The callback is guaranteed to be invoked only after its timeout has passed,
		1203	but if multiple timers become ready during the same loop iteration then
		1204	order of execution is undefined.
		1205
		1206	=head3 The special problem of time updates
		1207
		1208	Requesting the current time is a costly operation (it usually takes at
		1209	least two syscalls): EV therefore updates it's idea of the current time
		1210	only before and after C<ev_loop> polls for new events, which causes the
		1211	difference between C<ev_now ()> and C<ev_time ()>.
771		1212
772	The relative timeouts are calculated relative to the C<ev_now ()>	1213	The relative timeouts are calculated relative to the C<ev_now ()>
773	time. This is usually the right thing as this timestamp refers to the time	1214	time. This is usually the right thing as this timestamp refers to the time
774	of the event triggering whatever timeout you are modifying/starting. If	1215	of the event triggering whatever timeout you are modifying/starting. If
775	you suspect event processing to be delayed and you I<need> to base the timeout	1216	you suspect event processing to be delayed and you I<need> to base the
776	on the current time, use something like this to adjust for this:	1217	timeout on the current time, use something like this to adjust for this:
777		1218
778	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1219	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
779		1220
780	The callback is guarenteed to be invoked only when its timeout has passed,	1221	=head3 Watcher-Specific Functions and Data Members
781	but if multiple timers become ready during the same loop iteration then
782	order of execution is undefined.
783		1222
784	=over 4	1223	=over 4
785		1224
786	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1225	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
787		1226
788	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	1227	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
789		1228
790	Configure the timer to trigger after C<after> seconds. If C<repeat> is	1229	Configure the timer to trigger after C<after> seconds. If C<repeat>
791	C<0.>, then it will automatically be stopped. If it is positive, then the	1230	is C<0.>, then it will automatically be stopped once the timeout is
792	timer will automatically be configured to trigger again C<repeat> seconds	1231	reached. If it is positive, then the timer will automatically be
793	later, again, and again, until stopped manually.	1232	configured to trigger again C<repeat> seconds later, again, and again,
		1233	until stopped manually.
794		1234
795	The timer itself will do a best-effort at avoiding drift, that is, if you	1235	The timer itself will do a best-effort at avoiding drift, that is, if
796	configure a timer to trigger every 10 seconds, then it will trigger at	1236	you configure a timer to trigger every 10 seconds, then it will normally
797	exactly 10 second intervals. If, however, your program cannot keep up with	1237	trigger at exactly 10 second intervals. If, however, your program cannot
798	the timer (because it takes longer than those 10 seconds to do stuff) the	1238	keep up with the timer (because it takes longer than those 10 seconds to
799	timer will not fire more than once per event loop iteration.	1239	do stuff) the timer will not fire more than once per event loop iteration.
800		1240
801	=item ev_timer_again (loop)	1241	=item ev_timer_again (loop, ev_timer *)
802		1242
803	This will act as if the timer timed out and restart it again if it is	1243	This will act as if the timer timed out and restart it again if it is
804	repeating. The exact semantics are:	1244	repeating. The exact semantics are:
805		1245
		1246	If the timer is pending, its pending status is cleared.
		1247
806	If the timer is started but nonrepeating, stop it.	1248	If the timer is started but non-repeating, stop it (as if it timed out).
807		1249
808	If the timer is repeating, either start it if necessary (with the repeat	1250	If the timer is repeating, either start it if necessary (with the
809	value), or reset the running timer to the repeat value.	1251	C<repeat> value), or reset the running timer to the C<repeat> value.
810		1252
811	This sounds a bit complicated, but here is a useful and typical	1253	This sounds a bit complicated, but here is a useful and typical
812	example: Imagine you have a tcp connection and you want a so-called idle	1254	example: Imagine you have a TCP connection and you want a so-called idle
813	timeout, that is, you want to be called when there have been, say, 60	1255	timeout, that is, you want to be called when there have been, say, 60
814	seconds of inactivity on the socket. The easiest way to do this is to	1256	seconds of inactivity on the socket. The easiest way to do this is to
815	configure an C<ev_timer> with after=repeat=60 and calling ev_timer_again each	1257	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
816	time you successfully read or write some data. If you go into an idle	1258	C<ev_timer_again> each time you successfully read or write some data. If
817	state where you do not expect data to travel on the socket, you can stop	1259	you go into an idle state where you do not expect data to travel on the
818	the timer, and again will automatically restart it if need be.	1260	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
		1261	automatically restart it if need be.
		1262
		1263	That means you can ignore the C<after> value and C<ev_timer_start>
		1264	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
		1265
		1266	ev_timer_init (timer, callback, 0., 5.);
		1267	ev_timer_again (loop, timer);
		1268	...
		1269	timer->again = 17.;
		1270	ev_timer_again (loop, timer);
		1271	...
		1272	timer->again = 10.;
		1273	ev_timer_again (loop, timer);
		1274
		1275	This is more slightly efficient then stopping/starting the timer each time
		1276	you want to modify its timeout value.
		1277
		1278	=item ev_tstamp repeat [read-write]
		1279
		1280	The current C<repeat> value. Will be used each time the watcher times out
		1281	or C<ev_timer_again> is called and determines the next timeout (if any),
		1282	which is also when any modifications are taken into account.
819		1283
820	=back	1284	=back
821		1285
		1286	=head3 Examples
		1287
822	Example: create a timer that fires after 60 seconds.	1288	Example: Create a timer that fires after 60 seconds.
823		1289
824	static void	1290	static void
825	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1291	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
826	{	1292	{
827	.. one minute over, w is actually stopped right here	1293	.. one minute over, w is actually stopped right here
828	}	1294	}
829		1295
830	struct ev_timer mytimer;	1296	struct ev_timer mytimer;
831	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	1297	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
832	ev_timer_start (loop, &mytimer);	1298	ev_timer_start (loop, &mytimer);
833		1299
834	Example: create a timeout timer that times out after 10 seconds of	1300	Example: Create a timeout timer that times out after 10 seconds of
835	inactivity.	1301	inactivity.
836		1302
837	static void	1303	static void
838	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1304	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
839	{	1305	{
840	.. ten seconds without any activity	1306	.. ten seconds without any activity
841	}	1307	}
842		1308
843	struct ev_timer mytimer;	1309	struct ev_timer mytimer;
844	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	1310	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
845	ev_timer_again (&mytimer); /* start timer */	1311	ev_timer_again (&mytimer); /* start timer */
846	ev_loop (loop, 0);	1312	ev_loop (loop, 0);
847		1313
848	// and in some piece of code that gets executed on any "activity":	1314	// and in some piece of code that gets executed on any "activity":
849	// reset the timeout to start ticking again at 10 seconds	1315	// reset the timeout to start ticking again at 10 seconds
850	ev_timer_again (&mytimer);	1316	ev_timer_again (&mytimer);
851		1317
852		1318
853	=head2 C<ev_periodic> - to cron or not to cron	1319	=head2 C<ev_periodic> - to cron or not to cron?
854		1320
855	Periodic watchers are also timers of a kind, but they are very versatile	1321	Periodic watchers are also timers of a kind, but they are very versatile
856	(and unfortunately a bit complex).	1322	(and unfortunately a bit complex).
857		1323
858	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1324	Unlike C<ev_timer>'s, they are not based on real time (or relative time)
859	but on wallclock time (absolute time). You can tell a periodic watcher	1325	but on wall clock time (absolute time). You can tell a periodic watcher
860	to trigger "at" some specific point in time. For example, if you tell a	1326	to trigger after some specific point in time. For example, if you tell a
861	periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now ()	1327	periodic watcher to trigger in 10 seconds (by specifying e.g. C<ev_now ()
862	+ 10.>) and then reset your system clock to the last year, then it will	1328	+ 10.>, that is, an absolute time not a delay) and then reset your system
		1329	clock to January of the previous year, then it will take more than year
863	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	1330	to trigger the event (unlike an C<ev_timer>, which would still trigger
864	roughly 10 seconds later and of course not if you reset your system time	1331	roughly 10 seconds later as it uses a relative timeout).
865	again).
866		1332
867	They can also be used to implement vastly more complex timers, such as	1333	C<ev_periodic>s can also be used to implement vastly more complex timers,
868	triggering an event on eahc midnight, local time.	1334	such as triggering an event on each "midnight, local time", or other
		1335	complicated, rules.
869		1336
870	As with timers, the callback is guarenteed to be invoked only when the	1337	As with timers, the callback is guaranteed to be invoked only when the
871	time (C<at>) has been passed, but if multiple periodic timers become ready	1338	time (C<at>) has passed, but if multiple periodic timers become ready
872	during the same loop iteration then order of execution is undefined.	1339	during the same loop iteration then order of execution is undefined.
		1340
		1341	=head3 Watcher-Specific Functions and Data Members
873		1342
874	=over 4	1343	=over 4
875		1344
876	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1345	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)
877		1346
…		…
880	Lots of arguments, lets sort it out... There are basically three modes of	1349	Lots of arguments, lets sort it out... There are basically three modes of
881	operation, and we will explain them from simplest to complex:	1350	operation, and we will explain them from simplest to complex:
882		1351
883	=over 4	1352	=over 4
884		1353
885	=item * absolute timer (interval = reschedule_cb = 0)	1354	=item * absolute timer (at = time, interval = reschedule_cb = 0)
886		1355
887	In this configuration the watcher triggers an event at the wallclock time	1356	In this configuration the watcher triggers an event after the wall clock
888	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	1357	time C<at> has passed and doesn't repeat. It will not adjust when a time
889	that is, if it is to be run at January 1st 2011 then it will run when the	1358	jump occurs, that is, if it is to be run at January 1st 2011 then it will
890	system time reaches or surpasses this time.	1359	run when the system time reaches or surpasses this time.
891		1360
892	=item * non-repeating interval timer (interval > 0, reschedule_cb = 0)	1361	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)
893		1362
894	In this mode the watcher will always be scheduled to time out at the next	1363	In this mode the watcher will always be scheduled to time out at the next
895	C<at + N * interval> time (for some integer N) and then repeat, regardless	1364	C<at + N * interval> time (for some integer N, which can also be negative)
896	of any time jumps.	1365	and then repeat, regardless of any time jumps.
897		1366
898	This can be used to create timers that do not drift with respect to system	1367	This can be used to create timers that do not drift with respect to system
899	time:	1368	time, for example, here is a C<ev_periodic> that triggers each hour, on
		1369	the hour:
900		1370
901	ev_periodic_set (&periodic, 0., 3600., 0);	1371	ev_periodic_set (&periodic, 0., 3600., 0);
902		1372
903	This doesn't mean there will always be 3600 seconds in between triggers,	1373	This doesn't mean there will always be 3600 seconds in between triggers,
904	but only that the the callback will be called when the system time shows a	1374	but only that the callback will be called when the system time shows a
905	full hour (UTC), or more correctly, when the system time is evenly divisible	1375	full hour (UTC), or more correctly, when the system time is evenly divisible
906	by 3600.	1376	by 3600.
907		1377
908	Another way to think about it (for the mathematically inclined) is that	1378	Another way to think about it (for the mathematically inclined) is that
909	C<ev_periodic> will try to run the callback in this mode at the next possible	1379	C<ev_periodic> will try to run the callback in this mode at the next possible
910	time where C<time = at (mod interval)>, regardless of any time jumps.	1380	time where C<time = at (mod interval)>, regardless of any time jumps.
911		1381
		1382	For numerical stability it is preferable that the C<at> value is near
		1383	C<ev_now ()> (the current time), but there is no range requirement for
		1384	this value, and in fact is often specified as zero.
		1385
		1386	Note also that there is an upper limit to how often a timer can fire (CPU
		1387	speed for example), so if C<interval> is very small then timing stability
		1388	will of course deteriorate. Libev itself tries to be exact to be about one
		1389	millisecond (if the OS supports it and the machine is fast enough).
		1390
912	=item * manual reschedule mode (reschedule_cb = callback)	1391	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)
913		1392
914	In this mode the values for C<interval> and C<at> are both being	1393	In this mode the values for C<interval> and C<at> are both being
915	ignored. Instead, each time the periodic watcher gets scheduled, the	1394	ignored. Instead, each time the periodic watcher gets scheduled, the
916	reschedule callback will be called with the watcher as first, and the	1395	reschedule callback will be called with the watcher as first, and the
917	current time as second argument.	1396	current time as second argument.
918		1397
919	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	1398	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,
920	ever, or make any event loop modifications>. If you need to stop it,	1399	ever, or make ANY event loop modifications whatsoever>.
921	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by
922	starting a prepare watcher).
923		1400
		1401	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		1402	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		1403	only event loop modification you are allowed to do).
		1404
924	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	1405	The callback prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic
925	ev_tstamp now)>, e.g.:	1406	*w, ev_tstamp now)>, e.g.:
926		1407
927	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1408	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)
928	{	1409	{
929	return now + 60.;	1410	return now + 60.;
930	}	1411	}
…		…
932	It must return the next time to trigger, based on the passed time value	1413	It must return the next time to trigger, based on the passed time value
933	(that is, the lowest time value larger than to the second argument). It	1414	(that is, the lowest time value larger than to the second argument). It
934	will usually be called just before the callback will be triggered, but	1415	will usually be called just before the callback will be triggered, but
935	might be called at other times, too.	1416	might be called at other times, too.
936		1417
937	NOTE: I<< This callback must always return a time that is later than the	1418	NOTE: I<< This callback must always return a time that is higher than or
938	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	1419	equal to the passed C<now> value >>.
939		1420
940	This can be used to create very complex timers, such as a timer that	1421	This can be used to create very complex timers, such as a timer that
941	triggers on each midnight, local time. To do this, you would calculate the	1422	triggers on "next midnight, local time". To do this, you would calculate the
942	next midnight after C<now> and return the timestamp value for this. How	1423	next midnight after C<now> and return the timestamp value for this. How
943	you do this is, again, up to you (but it is not trivial, which is the main	1424	you do this is, again, up to you (but it is not trivial, which is the main
944	reason I omitted it as an example).	1425	reason I omitted it as an example).
945		1426
946	=back	1427	=back
…		…
950	Simply stops and restarts the periodic watcher again. This is only useful	1431	Simply stops and restarts the periodic watcher again. This is only useful
951	when you changed some parameters or the reschedule callback would return	1432	when you changed some parameters or the reschedule callback would return
952	a different time than the last time it was called (e.g. in a crond like	1433	a different time than the last time it was called (e.g. in a crond like
953	program when the crontabs have changed).	1434	program when the crontabs have changed).
954		1435
		1436	=item ev_tstamp ev_periodic_at (ev_periodic *)
		1437
		1438	When active, returns the absolute time that the watcher is supposed to
		1439	trigger next.
		1440
		1441	=item ev_tstamp offset [read-write]
		1442
		1443	When repeating, this contains the offset value, otherwise this is the
		1444	absolute point in time (the C<at> value passed to C<ev_periodic_set>).
		1445
		1446	Can be modified any time, but changes only take effect when the periodic
		1447	timer fires or C<ev_periodic_again> is being called.
		1448
		1449	=item ev_tstamp interval [read-write]
		1450
		1451	The current interval value. Can be modified any time, but changes only
		1452	take effect when the periodic timer fires or C<ev_periodic_again> is being
		1453	called.
		1454
		1455	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]
		1456
		1457	The current reschedule callback, or C<0>, if this functionality is
		1458	switched off. Can be changed any time, but changes only take effect when
		1459	the periodic timer fires or C<ev_periodic_again> is being called.
		1460
955	=back	1461	=back
956		1462
		1463	=head3 Examples
		1464
957	Example: call a callback every hour, or, more precisely, whenever the	1465	Example: Call a callback every hour, or, more precisely, whenever the
958	system clock is divisible by 3600. The callback invocation times have	1466	system clock is divisible by 3600. The callback invocation times have
959	potentially a lot of jittering, but good long-term stability.	1467	potentially a lot of jitter, but good long-term stability.
960		1468
961	static void	1469	static void
962	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1470	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)
963	{	1471	{
964	... its now a full hour (UTC, or TAI or whatever your clock follows)	1472	... its now a full hour (UTC, or TAI or whatever your clock follows)
965	}	1473	}
966		1474
967	struct ev_periodic hourly_tick;	1475	struct ev_periodic hourly_tick;
968	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	1476	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
969	ev_periodic_start (loop, &hourly_tick);	1477	ev_periodic_start (loop, &hourly_tick);
970		1478
971	Example: the same as above, but use a reschedule callback to do it:	1479	Example: The same as above, but use a reschedule callback to do it:
972		1480
973	#include <math.h>	1481	#include <math.h>
974		1482
975	static ev_tstamp	1483	static ev_tstamp
976	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	1484	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)
977	{	1485	{
978	return fmod (now, 3600.) + 3600.;	1486	return fmod (now, 3600.) + 3600.;
979	}	1487	}
980		1488
981	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	1489	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
982		1490
983	Example: call a callback every hour, starting now:	1491	Example: Call a callback every hour, starting now:
984		1492
985	struct ev_periodic hourly_tick;	1493	struct ev_periodic hourly_tick;
986	ev_periodic_init (&hourly_tick, clock_cb,	1494	ev_periodic_init (&hourly_tick, clock_cb,
987	fmod (ev_now (loop), 3600.), 3600., 0);	1495	fmod (ev_now (loop), 3600.), 3600., 0);
988	ev_periodic_start (loop, &hourly_tick);	1496	ev_periodic_start (loop, &hourly_tick);
989		1497
990		1498
991	=head2 C<ev_signal> - signal me when a signal gets signalled	1499	=head2 C<ev_signal> - signal me when a signal gets signalled!
992		1500
993	Signal watchers will trigger an event when the process receives a specific	1501	Signal watchers will trigger an event when the process receives a specific
994	signal one or more times. Even though signals are very asynchronous, libev	1502	signal one or more times. Even though signals are very asynchronous, libev
995	will try it's best to deliver signals synchronously, i.e. as part of the	1503	will try it's best to deliver signals synchronously, i.e. as part of the
996	normal event processing, like any other event.	1504	normal event processing, like any other event.
…		…
1000	with the kernel (thus it coexists with your own signal handlers as long	1508	with the kernel (thus it coexists with your own signal handlers as long
1001	as you don't register any with libev). Similarly, when the last signal	1509	as you don't register any with libev). Similarly, when the last signal
1002	watcher for a signal is stopped libev will reset the signal handler to	1510	watcher for a signal is stopped libev will reset the signal handler to
1003	SIG_DFL (regardless of what it was set to before).	1511	SIG_DFL (regardless of what it was set to before).
1004		1512
		1513	If possible and supported, libev will install its handlers with
		1514	C<SA_RESTART> behaviour enabled, so system calls should not be unduly
		1515	interrupted. If you have a problem with system calls getting interrupted by
		1516	signals you can block all signals in an C<ev_check> watcher and unblock
		1517	them in an C<ev_prepare> watcher.
		1518
		1519	=head3 Watcher-Specific Functions and Data Members
		1520
1005	=over 4	1521	=over 4
1006		1522
1007	=item ev_signal_init (ev_signal *, callback, int signum)	1523	=item ev_signal_init (ev_signal *, callback, int signum)
1008		1524
1009	=item ev_signal_set (ev_signal *, int signum)	1525	=item ev_signal_set (ev_signal *, int signum)
1010		1526
1011	Configures the watcher to trigger on the given signal number (usually one	1527	Configures the watcher to trigger on the given signal number (usually one
1012	of the C<SIGxxx> constants).	1528	of the C<SIGxxx> constants).
1013		1529
		1530	=item int signum [read-only]
		1531
		1532	The signal the watcher watches out for.
		1533
1014	=back	1534	=back
1015		1535
		1536	=head3 Examples
1016		1537
		1538	Example: Try to exit cleanly on SIGINT and SIGTERM.
		1539
		1540	static void
		1541	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)
		1542	{
		1543	ev_unloop (loop, EVUNLOOP_ALL);
		1544	}
		1545
		1546	struct ev_signal signal_watcher;
		1547	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		1548	ev_signal_start (loop, &sigint_cb);
		1549
		1550
1017	=head2 C<ev_child> - wait for pid status changes	1551	=head2 C<ev_child> - watch out for process status changes
1018		1552
1019	Child watchers trigger when your process receives a SIGCHLD in response to	1553	Child watchers trigger when your process receives a SIGCHLD in response to
1020	some child status changes (most typically when a child of yours dies).	1554	some child status changes (most typically when a child of yours dies). It
		1555	is permissible to install a child watcher I<after> the child has been
		1556	forked (which implies it might have already exited), as long as the event
		1557	loop isn't entered (or is continued from a watcher).
		1558
		1559	Only the default event loop is capable of handling signals, and therefore
		1560	you can only register child watchers in the default event loop.
		1561
		1562	=head3 Process Interaction
		1563
		1564	Libev grabs C<SIGCHLD> as soon as the default event loop is
		1565	initialised. This is necessary to guarantee proper behaviour even if
		1566	the first child watcher is started after the child exits. The occurrence
		1567	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		1568	synchronously as part of the event loop processing. Libev always reaps all
		1569	children, even ones not watched.
		1570
		1571	=head3 Overriding the Built-In Processing
		1572
		1573	Libev offers no special support for overriding the built-in child
		1574	processing, but if your application collides with libev's default child
		1575	handler, you can override it easily by installing your own handler for
		1576	C<SIGCHLD> after initialising the default loop, and making sure the
		1577	default loop never gets destroyed. You are encouraged, however, to use an
		1578	event-based approach to child reaping and thus use libev's support for
		1579	that, so other libev users can use C<ev_child> watchers freely.
		1580
		1581	=head3 Stopping the Child Watcher
		1582
		1583	Currently, the child watcher never gets stopped, even when the
		1584	child terminates, so normally one needs to stop the watcher in the
		1585	callback. Future versions of libev might stop the watcher automatically
		1586	when a child exit is detected.
		1587
		1588	=head3 Watcher-Specific Functions and Data Members
1021		1589
1022	=over 4	1590	=over 4
1023		1591
1024	=item ev_child_init (ev_child *, callback, int pid)	1592	=item ev_child_init (ev_child *, callback, int pid, int trace)
1025		1593
1026	=item ev_child_set (ev_child *, int pid)	1594	=item ev_child_set (ev_child *, int pid, int trace)
1027		1595
1028	Configures the watcher to wait for status changes of process C<pid> (or	1596	Configures the watcher to wait for status changes of process C<pid> (or
1029	I<any> process if C<pid> is specified as C<0>). The callback can look	1597	I<any> process if C<pid> is specified as C<0>). The callback can look
1030	at the C<rstatus> member of the C<ev_child> watcher structure to see	1598	at the C<rstatus> member of the C<ev_child> watcher structure to see
1031	the status word (use the macros from C<sys/wait.h> and see your systems	1599	the status word (use the macros from C<sys/wait.h> and see your systems
1032	C<waitpid> documentation). The C<rpid> member contains the pid of the	1600	C<waitpid> documentation). The C<rpid> member contains the pid of the
1033	process causing the status change.	1601	process causing the status change. C<trace> must be either C<0> (only
		1602	activate the watcher when the process terminates) or C<1> (additionally
		1603	activate the watcher when the process is stopped or continued).
		1604
		1605	=item int pid [read-only]
		1606
		1607	The process id this watcher watches out for, or C<0>, meaning any process id.
		1608
		1609	=item int rpid [read-write]
		1610
		1611	The process id that detected a status change.
		1612
		1613	=item int rstatus [read-write]
		1614
		1615	The process exit/trace status caused by C<rpid> (see your systems
		1616	C<waitpid> and C<sys/wait.h> documentation for details).
1034		1617
1035	=back	1618	=back
1036		1619
1037	Example: try to exit cleanly on SIGINT and SIGTERM.	1620	=head3 Examples
1038		1621
		1622	Example: C<fork()> a new process and install a child handler to wait for
		1623	its completion.
		1624
		1625	ev_child cw;
		1626
1039	static void	1627	static void
1040	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	1628	child_cb (EV_P_ struct ev_child *w, int revents)
1041	{	1629	{
1042	ev_unloop (loop, EVUNLOOP_ALL);	1630	ev_child_stop (EV_A_ w);
		1631	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1043	}	1632	}
1044		1633
1045	struct ev_signal signal_watcher;	1634	pid_t pid = fork ();
1046	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
1047	ev_signal_start (loop, &sigint_cb);
1048		1635
		1636	if (pid < 0)
		1637	// error
		1638	else if (pid == 0)
		1639	{
		1640	// the forked child executes here
		1641	exit (1);
		1642	}
		1643	else
		1644	{
		1645	ev_child_init (&cw, child_cb, pid, 0);
		1646	ev_child_start (EV_DEFAULT_ &cw);
		1647	}
1049		1648
		1649
		1650	=head2 C<ev_stat> - did the file attributes just change?
		1651
		1652	This watches a file system path for attribute changes. That is, it calls
		1653	C<stat> regularly (or when the OS says it changed) and sees if it changed
		1654	compared to the last time, invoking the callback if it did.
		1655
		1656	The path does not need to exist: changing from "path exists" to "path does
		1657	not exist" is a status change like any other. The condition "path does
		1658	not exist" is signified by the C<st_nlink> field being zero (which is
		1659	otherwise always forced to be at least one) and all the other fields of
		1660	the stat buffer having unspecified contents.
		1661
		1662	The path I<should> be absolute and I<must not> end in a slash. If it is
		1663	relative and your working directory changes, the behaviour is undefined.
		1664
		1665	Since there is no standard to do this, the portable implementation simply
		1666	calls C<stat (2)> regularly on the path to see if it changed somehow. You
		1667	can specify a recommended polling interval for this case. If you specify
		1668	a polling interval of C<0> (highly recommended!) then a I<suitable,
		1669	unspecified default> value will be used (which you can expect to be around
		1670	five seconds, although this might change dynamically). Libev will also
		1671	impose a minimum interval which is currently around C<0.1>, but thats
		1672	usually overkill.
		1673
		1674	This watcher type is not meant for massive numbers of stat watchers,
		1675	as even with OS-supported change notifications, this can be
		1676	resource-intensive.
		1677
		1678	At the time of this writing, only the Linux inotify interface is
		1679	implemented (implementing kqueue support is left as an exercise for the
		1680	reader, note, however, that the author sees no way of implementing ev_stat
		1681	semantics with kqueue). Inotify will be used to give hints only and should
		1682	not change the semantics of C<ev_stat> watchers, which means that libev
		1683	sometimes needs to fall back to regular polling again even with inotify,
		1684	but changes are usually detected immediately, and if the file exists there
		1685	will be no polling.
		1686
		1687	=head3 ABI Issues (Largefile Support)
		1688
		1689	Libev by default (unless the user overrides this) uses the default
		1690	compilation environment, which means that on systems with large file
		1691	support disabled by default, you get the 32 bit version of the stat
		1692	structure. When using the library from programs that change the ABI to
		1693	use 64 bit file offsets the programs will fail. In that case you have to
		1694	compile libev with the same flags to get binary compatibility. This is
		1695	obviously the case with any flags that change the ABI, but the problem is
		1696	most noticeably disabled with ev_stat and large file support.
		1697
		1698	The solution for this is to lobby your distribution maker to make large
		1699	file interfaces available by default (as e.g. FreeBSD does) and not
		1700	optional. Libev cannot simply switch on large file support because it has
		1701	to exchange stat structures with application programs compiled using the
		1702	default compilation environment.
		1703
		1704	=head3 Inotify
		1705
		1706	When C<inotify (7)> support has been compiled into libev (generally only
		1707	available on Linux) and present at runtime, it will be used to speed up
		1708	change detection where possible. The inotify descriptor will be created lazily
		1709	when the first C<ev_stat> watcher is being started.
		1710
		1711	Inotify presence does not change the semantics of C<ev_stat> watchers
		1712	except that changes might be detected earlier, and in some cases, to avoid
		1713	making regular C<stat> calls. Even in the presence of inotify support
		1714	there are many cases where libev has to resort to regular C<stat> polling.
		1715
		1716	(There is no support for kqueue, as apparently it cannot be used to
		1717	implement this functionality, due to the requirement of having a file
		1718	descriptor open on the object at all times).
		1719
		1720	=head3 The special problem of stat time resolution
		1721
		1722	The C<stat ()> system call only supports full-second resolution portably, and
		1723	even on systems where the resolution is higher, many file systems still
		1724	only support whole seconds.
		1725
		1726	That means that, if the time is the only thing that changes, you can
		1727	easily miss updates: on the first update, C<ev_stat> detects a change and
		1728	calls your callback, which does something. When there is another update
		1729	within the same second, C<ev_stat> will be unable to detect it as the stat
		1730	data does not change.
		1731
		1732	The solution to this is to delay acting on a change for slightly more
		1733	than a second (or till slightly after the next full second boundary), using
		1734	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		1735	ev_timer_again (loop, w)>).
		1736
		1737	The C<.02> offset is added to work around small timing inconsistencies
		1738	of some operating systems (where the second counter of the current time
		1739	might be be delayed. One such system is the Linux kernel, where a call to
		1740	C<gettimeofday> might return a timestamp with a full second later than
		1741	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		1742	update file times then there will be a small window where the kernel uses
		1743	the previous second to update file times but libev might already execute
		1744	the timer callback).
		1745
		1746	=head3 Watcher-Specific Functions and Data Members
		1747
		1748	=over 4
		1749
		1750	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
		1751
		1752	=item ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)
		1753
		1754	Configures the watcher to wait for status changes of the given
		1755	C<path>. The C<interval> is a hint on how quickly a change is expected to
		1756	be detected and should normally be specified as C<0> to let libev choose
		1757	a suitable value. The memory pointed to by C<path> must point to the same
		1758	path for as long as the watcher is active.
		1759
		1760	The callback will receive C<EV_STAT> when a change was detected, relative
		1761	to the attributes at the time the watcher was started (or the last change
		1762	was detected).
		1763
		1764	=item ev_stat_stat (loop, ev_stat *)
		1765
		1766	Updates the stat buffer immediately with new values. If you change the
		1767	watched path in your callback, you could call this function to avoid
		1768	detecting this change (while introducing a race condition if you are not
		1769	the only one changing the path). Can also be useful simply to find out the
		1770	new values.
		1771
		1772	=item ev_statdata attr [read-only]
		1773
		1774	The most-recently detected attributes of the file. Although the type is
		1775	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
		1776	suitable for your system, but you can only rely on the POSIX-standardised
		1777	members to be present. If the C<st_nlink> member is C<0>, then there was
		1778	some error while C<stat>ing the file.
		1779
		1780	=item ev_statdata prev [read-only]
		1781
		1782	The previous attributes of the file. The callback gets invoked whenever
		1783	C<prev> != C<attr>, or, more precisely, one or more of these members
		1784	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		1785	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
		1786
		1787	=item ev_tstamp interval [read-only]
		1788
		1789	The specified interval.
		1790
		1791	=item const char *path [read-only]
		1792
		1793	The file system path that is being watched.
		1794
		1795	=back
		1796
		1797	=head3 Examples
		1798
		1799	Example: Watch C</etc/passwd> for attribute changes.
		1800
		1801	static void
		1802	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
		1803	{
		1804	/* /etc/passwd changed in some way */
		1805	if (w->attr.st_nlink)
		1806	{
		1807	printf ("passwd current size %ld\n", (long)w->attr.st_size);
		1808	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
		1809	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
		1810	}
		1811	else
		1812	/* you shalt not abuse printf for puts */
		1813	puts ("wow, /etc/passwd is not there, expect problems. "
		1814	"if this is windows, they already arrived\n");
		1815	}
		1816
		1817	...
		1818	ev_stat passwd;
		1819
		1820	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
		1821	ev_stat_start (loop, &passwd);
		1822
		1823	Example: Like above, but additionally use a one-second delay so we do not
		1824	miss updates (however, frequent updates will delay processing, too, so
		1825	one might do the work both on C<ev_stat> callback invocation I<and> on
		1826	C<ev_timer> callback invocation).
		1827
		1828	static ev_stat passwd;
		1829	static ev_timer timer;
		1830
		1831	static void
		1832	timer_cb (EV_P_ ev_timer *w, int revents)
		1833	{
		1834	ev_timer_stop (EV_A_ w);
		1835
		1836	/* now it's one second after the most recent passwd change */
		1837	}
		1838
		1839	static void
		1840	stat_cb (EV_P_ ev_stat *w, int revents)
		1841	{
		1842	/* reset the one-second timer */
		1843	ev_timer_again (EV_A_ &timer);
		1844	}
		1845
		1846	...
		1847	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		1848	ev_stat_start (loop, &passwd);
		1849	ev_timer_init (&timer, timer_cb, 0., 1.02);
		1850
		1851
1050	=head2 C<ev_idle> - when you've got nothing better to do	1852	=head2 C<ev_idle> - when you've got nothing better to do...
1051		1853
1052	Idle watchers trigger events when there are no other events are pending	1854	Idle watchers trigger events when no other events of the same or higher
1053	(prepare, check and other idle watchers do not count). That is, as long	1855	priority are pending (prepare, check and other idle watchers do not
1054	as your process is busy handling sockets or timeouts (or even signals,	1856	count).
1055	imagine) it will not be triggered. But when your process is idle all idle	1857
1056	watchers are being called again and again, once per event loop iteration -	1858	That is, as long as your process is busy handling sockets or timeouts
		1859	(or even signals, imagine) of the same or higher priority it will not be
		1860	triggered. But when your process is idle (or only lower-priority watchers
		1861	are pending), the idle watchers are being called once per event loop
1057	until stopped, that is, or your process receives more events and becomes	1862	iteration - until stopped, that is, or your process receives more events
1058	busy.	1863	and becomes busy again with higher priority stuff.
1059		1864
1060	The most noteworthy effect is that as long as any idle watchers are	1865	The most noteworthy effect is that as long as any idle watchers are
1061	active, the process will not block when waiting for new events.	1866	active, the process will not block when waiting for new events.
1062		1867
1063	Apart from keeping your process non-blocking (which is a useful	1868	Apart from keeping your process non-blocking (which is a useful
1064	effect on its own sometimes), idle watchers are a good place to do	1869	effect on its own sometimes), idle watchers are a good place to do
1065	"pseudo-background processing", or delay processing stuff to after the	1870	"pseudo-background processing", or delay processing stuff to after the
1066	event loop has handled all outstanding events.	1871	event loop has handled all outstanding events.
1067		1872
		1873	=head3 Watcher-Specific Functions and Data Members
		1874
1068	=over 4	1875	=over 4
1069		1876
1070	=item ev_idle_init (ev_signal *, callback)	1877	=item ev_idle_init (ev_signal *, callback)
1071		1878
1072	Initialises and configures the idle watcher - it has no parameters of any	1879	Initialises and configures the idle watcher - it has no parameters of any
1073	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	1880	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1074	believe me.	1881	believe me.
1075		1882
1076	=back	1883	=back
1077		1884
		1885	=head3 Examples
		1886
1078	Example: dynamically allocate an C<ev_idle>, start it, and in the	1887	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1079	callback, free it. Alos, use no error checking, as usual.	1888	callback, free it. Also, use no error checking, as usual.
1080		1889
1081	static void	1890	static void
1082	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	1891	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)
1083	{	1892	{
1084	free (w);	1893	free (w);
1085	// now do something you wanted to do when the program has	1894	// now do something you wanted to do when the program has
1086	// no longer asnything immediate to do.	1895	// no longer anything immediate to do.
1087	}	1896	}
1088		1897
1089	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	1898	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));
1090	ev_idle_init (idle_watcher, idle_cb);	1899	ev_idle_init (idle_watcher, idle_cb);
1091	ev_idle_start (loop, idle_cb);	1900	ev_idle_start (loop, idle_cb);
1092		1901
1093		1902
1094	=head2 C<ev_prepare> and C<ev_check> - customise your event loop	1903	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1095		1904
1096	Prepare and check watchers are usually (but not always) used in tandem:	1905	Prepare and check watchers are usually (but not always) used in tandem:
1097	prepare watchers get invoked before the process blocks and check watchers	1906	prepare watchers get invoked before the process blocks and check watchers
1098	afterwards.	1907	afterwards.
1099		1908
		1909	You I<must not> call C<ev_loop> or similar functions that enter
		1910	the current event loop from either C<ev_prepare> or C<ev_check>
		1911	watchers. Other loops than the current one are fine, however. The
		1912	rationale behind this is that you do not need to check for recursion in
		1913	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
		1914	C<ev_check> so if you have one watcher of each kind they will always be
		1915	called in pairs bracketing the blocking call.
		1916
1100	Their main purpose is to integrate other event mechanisms into libev and	1917	Their main purpose is to integrate other event mechanisms into libev and
1101	their use is somewhat advanced. This could be used, for example, to track	1918	their use is somewhat advanced. This could be used, for example, to track
1102	variable changes, implement your own watchers, integrate net-snmp or a	1919	variable changes, implement your own watchers, integrate net-snmp or a
1103	coroutine library and lots more.	1920	coroutine library and lots more. They are also occasionally useful if
		1921	you cache some data and want to flush it before blocking (for example,
		1922	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
		1923	watcher).
1104		1924
1105	This is done by examining in each prepare call which file descriptors need	1925	This is done by examining in each prepare call which file descriptors need
1106	to be watched by the other library, registering C<ev_io> watchers for	1926	to be watched by the other library, registering C<ev_io> watchers for
1107	them and starting an C<ev_timer> watcher for any timeouts (many libraries	1927	them and starting an C<ev_timer> watcher for any timeouts (many libraries
1108	provide just this functionality). Then, in the check watcher you check for	1928	provide just this functionality). Then, in the check watcher you check for
1109	any events that occured (by checking the pending status of all watchers	1929	any events that occurred (by checking the pending status of all watchers
1110	and stopping them) and call back into the library. The I/O and timer	1930	and stopping them) and call back into the library. The I/O and timer
1111	callbacks will never actually be called (but must be valid nevertheless,	1931	callbacks will never actually be called (but must be valid nevertheless,
1112	because you never know, you know?).	1932	because you never know, you know?).
1113		1933
1114	As another example, the Perl Coro module uses these hooks to integrate	1934	As another example, the Perl Coro module uses these hooks to integrate
…		…
1118	with priority higher than or equal to the event loop and one coroutine	1938	with priority higher than or equal to the event loop and one coroutine
1119	of lower priority, but only once, using idle watchers to keep the event	1939	of lower priority, but only once, using idle watchers to keep the event
1120	loop from blocking if lower-priority coroutines are active, thus mapping	1940	loop from blocking if lower-priority coroutines are active, thus mapping
1121	low-priority coroutines to idle/background tasks).	1941	low-priority coroutines to idle/background tasks).
1122		1942
		1943	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
		1944	priority, to ensure that they are being run before any other watchers
		1945	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,
		1946	too) should not activate ("feed") events into libev. While libev fully
		1947	supports this, they might get executed before other C<ev_check> watchers
		1948	did their job. As C<ev_check> watchers are often used to embed other
		1949	(non-libev) event loops those other event loops might be in an unusable
		1950	state until their C<ev_check> watcher ran (always remind yourself to
		1951	coexist peacefully with others).
		1952
		1953	=head3 Watcher-Specific Functions and Data Members
		1954
1123	=over 4	1955	=over 4
1124		1956
1125	=item ev_prepare_init (ev_prepare *, callback)	1957	=item ev_prepare_init (ev_prepare *, callback)
1126		1958
1127	=item ev_check_init (ev_check *, callback)	1959	=item ev_check_init (ev_check *, callback)
…		…
1130	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	1962	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1131	macros, but using them is utterly, utterly and completely pointless.	1963	macros, but using them is utterly, utterly and completely pointless.
1132		1964
1133	=back	1965	=back
1134		1966
1135	Example: *TODO*.	1967	=head3 Examples
1136		1968
		1969	There are a number of principal ways to embed other event loops or modules
		1970	into libev. Here are some ideas on how to include libadns into libev
		1971	(there is a Perl module named C<EV::ADNS> that does this, which you could
		1972	use as a working example. Another Perl module named C<EV::Glib> embeds a
		1973	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
		1974	Glib event loop).
1137		1975
		1976	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
		1977	and in a check watcher, destroy them and call into libadns. What follows
		1978	is pseudo-code only of course. This requires you to either use a low
		1979	priority for the check watcher or use C<ev_clear_pending> explicitly, as
		1980	the callbacks for the IO/timeout watchers might not have been called yet.
		1981
		1982	static ev_io iow [nfd];
		1983	static ev_timer tw;
		1984
		1985	static void
		1986	io_cb (ev_loop *loop, ev_io *w, int revents)
		1987	{
		1988	}
		1989
		1990	// create io watchers for each fd and a timer before blocking
		1991	static void
		1992	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)
		1993	{
		1994	int timeout = 3600000;
		1995	struct pollfd fds [nfd];
		1996	// actual code will need to loop here and realloc etc.
		1997	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
		1998
		1999	/* the callback is illegal, but won't be called as we stop during check */
		2000	ev_timer_init (&tw, 0, timeout * 1e-3);
		2001	ev_timer_start (loop, &tw);
		2002
		2003	// create one ev_io per pollfd
		2004	for (int i = 0; i < nfd; ++i)
		2005	{
		2006	ev_io_init (iow + i, io_cb, fds [i].fd,
		2007	((fds [i].events & POLLIN ? EV_READ : 0)
		2008	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
		2009
		2010	fds [i].revents = 0;
		2011	ev_io_start (loop, iow + i);
		2012	}
		2013	}
		2014
		2015	// stop all watchers after blocking
		2016	static void
		2017	adns_check_cb (ev_loop *loop, ev_check *w, int revents)
		2018	{
		2019	ev_timer_stop (loop, &tw);
		2020
		2021	for (int i = 0; i < nfd; ++i)
		2022	{
		2023	// set the relevant poll flags
		2024	// could also call adns_processreadable etc. here
		2025	struct pollfd *fd = fds + i;
		2026	int revents = ev_clear_pending (iow + i);
		2027	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
		2028	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
		2029
		2030	// now stop the watcher
		2031	ev_io_stop (loop, iow + i);
		2032	}
		2033
		2034	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
		2035	}
		2036
		2037	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
		2038	in the prepare watcher and would dispose of the check watcher.
		2039
		2040	Method 3: If the module to be embedded supports explicit event
		2041	notification (libadns does), you can also make use of the actual watcher
		2042	callbacks, and only destroy/create the watchers in the prepare watcher.
		2043
		2044	static void
		2045	timer_cb (EV_P_ ev_timer *w, int revents)
		2046	{
		2047	adns_state ads = (adns_state)w->data;
		2048	update_now (EV_A);
		2049
		2050	adns_processtimeouts (ads, &tv_now);
		2051	}
		2052
		2053	static void
		2054	io_cb (EV_P_ ev_io *w, int revents)
		2055	{
		2056	adns_state ads = (adns_state)w->data;
		2057	update_now (EV_A);
		2058
		2059	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
		2060	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
		2061	}
		2062
		2063	// do not ever call adns_afterpoll
		2064
		2065	Method 4: Do not use a prepare or check watcher because the module you
		2066	want to embed is too inflexible to support it. Instead, you can override
		2067	their poll function. The drawback with this solution is that the main
		2068	loop is now no longer controllable by EV. The C<Glib::EV> module does
		2069	this.
		2070
		2071	static gint
		2072	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
		2073	{
		2074	int got_events = 0;
		2075
		2076	for (n = 0; n < nfds; ++n)
		2077	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
		2078
		2079	if (timeout >= 0)
		2080	// create/start timer
		2081
		2082	// poll
		2083	ev_loop (EV_A_ 0);
		2084
		2085	// stop timer again
		2086	if (timeout >= 0)
		2087	ev_timer_stop (EV_A_ &to);
		2088
		2089	// stop io watchers again - their callbacks should have set
		2090	for (n = 0; n < nfds; ++n)
		2091	ev_io_stop (EV_A_ iow [n]);
		2092
		2093	return got_events;
		2094	}
		2095
		2096
1138	=head2 C<ev_embed> - when one backend isn't enough	2097	=head2 C<ev_embed> - when one backend isn't enough...
1139		2098
1140	This is a rather advanced watcher type that lets you embed one event loop	2099	This is a rather advanced watcher type that lets you embed one event loop
1141	into another (currently only C<ev_io> events are supported in the embedded	2100	into another (currently only C<ev_io> events are supported in the embedded
1142	loop, other types of watchers might be handled in a delayed or incorrect	2101	loop, other types of watchers might be handled in a delayed or incorrect
1143	fashion and must not be used).	2102	fashion and must not be used).
…		…
1182	portable one.	2141	portable one.
1183		2142
1184	So when you want to use this feature you will always have to be prepared	2143	So when you want to use this feature you will always have to be prepared
1185	that you cannot get an embeddable loop. The recommended way to get around	2144	that you cannot get an embeddable loop. The recommended way to get around
1186	this is to have a separate variables for your embeddable loop, try to	2145	this is to have a separate variables for your embeddable loop, try to
1187	create it, and if that fails, use the normal loop for everything:	2146	create it, and if that fails, use the normal loop for everything.
1188		2147
1189	struct ev_loop *loop_hi = ev_default_init (0);	2148	=head3 Watcher-Specific Functions and Data Members
1190	struct ev_loop *loop_lo = 0;
1191	struct ev_embed embed;
1192
1193	// see if there is a chance of getting one that works
1194	// (remember that a flags value of 0 means autodetection)
1195	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
1196	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
1197	: 0;
1198
1199	// if we got one, then embed it, otherwise default to loop_hi
1200	if (loop_lo)
1201	{
1202	ev_embed_init (&embed, 0, loop_lo);
1203	ev_embed_start (loop_hi, &embed);
1204	}
1205	else
1206	loop_lo = loop_hi;
1207		2149
1208	=over 4	2150	=over 4
1209		2151
1210	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	2152	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
1211		2153
…		…
1213		2155
1214	Configures the watcher to embed the given loop, which must be	2156	Configures the watcher to embed the given loop, which must be
1215	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	2157	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
1216	invoked automatically, otherwise it is the responsibility of the callback	2158	invoked automatically, otherwise it is the responsibility of the callback
1217	to invoke it (it will continue to be called until the sweep has been done,	2159	to invoke it (it will continue to be called until the sweep has been done,
1218	if you do not want thta, you need to temporarily stop the embed watcher).	2160	if you do not want that, you need to temporarily stop the embed watcher).
1219		2161
1220	=item ev_embed_sweep (loop, ev_embed *)	2162	=item ev_embed_sweep (loop, ev_embed *)
1221		2163
1222	Make a single, non-blocking sweep over the embedded loop. This works	2164	Make a single, non-blocking sweep over the embedded loop. This works
1223	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most	2165	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
1224	apropriate way for embedded loops.	2166	appropriate way for embedded loops.
		2167
		2168	=item struct ev_loop *other [read-only]
		2169
		2170	The embedded event loop.
		2171
		2172	=back
		2173
		2174	=head3 Examples
		2175
		2176	Example: Try to get an embeddable event loop and embed it into the default
		2177	event loop. If that is not possible, use the default loop. The default
		2178	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		2179	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		2180	used).
		2181
		2182	struct ev_loop *loop_hi = ev_default_init (0);
		2183	struct ev_loop *loop_lo = 0;
		2184	struct ev_embed embed;
		2185
		2186	// see if there is a chance of getting one that works
		2187	// (remember that a flags value of 0 means autodetection)
		2188	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		2189	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		2190	: 0;
		2191
		2192	// if we got one, then embed it, otherwise default to loop_hi
		2193	if (loop_lo)
		2194	{
		2195	ev_embed_init (&embed, 0, loop_lo);
		2196	ev_embed_start (loop_hi, &embed);
		2197	}
		2198	else
		2199	loop_lo = loop_hi;
		2200
		2201	Example: Check if kqueue is available but not recommended and create
		2202	a kqueue backend for use with sockets (which usually work with any
		2203	kqueue implementation). Store the kqueue/socket-only event loop in
		2204	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		2205
		2206	struct ev_loop *loop = ev_default_init (0);
		2207	struct ev_loop *loop_socket = 0;
		2208	struct ev_embed embed;
		2209
		2210	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		2211	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		2212	{
		2213	ev_embed_init (&embed, 0, loop_socket);
		2214	ev_embed_start (loop, &embed);
		2215	}
		2216
		2217	if (!loop_socket)
		2218	loop_socket = loop;
		2219
		2220	// now use loop_socket for all sockets, and loop for everything else
		2221
		2222
		2223	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
		2224
		2225	Fork watchers are called when a C<fork ()> was detected (usually because
		2226	whoever is a good citizen cared to tell libev about it by calling
		2227	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the
		2228	event loop blocks next and before C<ev_check> watchers are being called,
		2229	and only in the child after the fork. If whoever good citizen calling
		2230	C<ev_default_fork> cheats and calls it in the wrong process, the fork
		2231	handlers will be invoked, too, of course.
		2232
		2233	=head3 Watcher-Specific Functions and Data Members
		2234
		2235	=over 4
		2236
		2237	=item ev_fork_init (ev_signal *, callback)
		2238
		2239	Initialises and configures the fork watcher - it has no parameters of any
		2240	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
		2241	believe me.
		2242
		2243	=back
		2244
		2245
		2246	=head2 C<ev_async> - how to wake up another event loop
		2247
		2248	In general, you cannot use an C<ev_loop> from multiple threads or other
		2249	asynchronous sources such as signal handlers (as opposed to multiple event
		2250	loops - those are of course safe to use in different threads).
		2251
		2252	Sometimes, however, you need to wake up another event loop you do not
		2253	control, for example because it belongs to another thread. This is what
		2254	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you
		2255	can signal it by calling C<ev_async_send>, which is thread- and signal
		2256	safe.
		2257
		2258	This functionality is very similar to C<ev_signal> watchers, as signals,
		2259	too, are asynchronous in nature, and signals, too, will be compressed
		2260	(i.e. the number of callback invocations may be less than the number of
		2261	C<ev_async_sent> calls).
		2262
		2263	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		2264	just the default loop.
		2265
		2266	=head3 Queueing
		2267
		2268	C<ev_async> does not support queueing of data in any way. The reason
		2269	is that the author does not know of a simple (or any) algorithm for a
		2270	multiple-writer-single-reader queue that works in all cases and doesn't
		2271	need elaborate support such as pthreads.
		2272
		2273	That means that if you want to queue data, you have to provide your own
		2274	queue. But at least I can tell you would implement locking around your
		2275	queue:
		2276
		2277	=over 4
		2278
		2279	=item queueing from a signal handler context
		2280
		2281	To implement race-free queueing, you simply add to the queue in the signal
		2282	handler but you block the signal handler in the watcher callback. Here is an example that does that for
		2283	some fictitious SIGUSR1 handler:
		2284
		2285	static ev_async mysig;
		2286
		2287	static void
		2288	sigusr1_handler (void)
		2289	{
		2290	sometype data;
		2291
		2292	// no locking etc.
		2293	queue_put (data);
		2294	ev_async_send (EV_DEFAULT_ &mysig);
		2295	}
		2296
		2297	static void
		2298	mysig_cb (EV_P_ ev_async *w, int revents)
		2299	{
		2300	sometype data;
		2301	sigset_t block, prev;
		2302
		2303	sigemptyset (&block);
		2304	sigaddset (&block, SIGUSR1);
		2305	sigprocmask (SIG_BLOCK, &block, &prev);
		2306
		2307	while (queue_get (&data))
		2308	process (data);
		2309
		2310	if (sigismember (&prev, SIGUSR1)
		2311	sigprocmask (SIG_UNBLOCK, &block, 0);
		2312	}
		2313
		2314	(Note: pthreads in theory requires you to use C<pthread_setmask>
		2315	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		2316	either...).
		2317
		2318	=item queueing from a thread context
		2319
		2320	The strategy for threads is different, as you cannot (easily) block
		2321	threads but you can easily preempt them, so to queue safely you need to
		2322	employ a traditional mutex lock, such as in this pthread example:
		2323
		2324	static ev_async mysig;
		2325	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		2326
		2327	static void
		2328	otherthread (void)
		2329	{
		2330	// only need to lock the actual queueing operation
		2331	pthread_mutex_lock (&mymutex);
		2332	queue_put (data);
		2333	pthread_mutex_unlock (&mymutex);
		2334
		2335	ev_async_send (EV_DEFAULT_ &mysig);
		2336	}
		2337
		2338	static void
		2339	mysig_cb (EV_P_ ev_async *w, int revents)
		2340	{
		2341	pthread_mutex_lock (&mymutex);
		2342
		2343	while (queue_get (&data))
		2344	process (data);
		2345
		2346	pthread_mutex_unlock (&mymutex);
		2347	}
		2348
		2349	=back
		2350
		2351
		2352	=head3 Watcher-Specific Functions and Data Members
		2353
		2354	=over 4
		2355
		2356	=item ev_async_init (ev_async *, callback)
		2357
		2358	Initialises and configures the async watcher - it has no parameters of any
		2359	kind. There is a C<ev_asynd_set> macro, but using it is utterly pointless,
		2360	believe me.
		2361
		2362	=item ev_async_send (loop, ev_async *)
		2363
		2364	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		2365	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		2366	C<ev_feed_event>, this call is safe to do in other threads, signal or
		2367	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
		2368	section below on what exactly this means).
		2369
		2370	This call incurs the overhead of a system call only once per loop iteration,
		2371	so while the overhead might be noticeable, it doesn't apply to repeated
		2372	calls to C<ev_async_send>.
		2373
		2374	=item bool = ev_async_pending (ev_async *)
		2375
		2376	Returns a non-zero value when C<ev_async_send> has been called on the
		2377	watcher but the event has not yet been processed (or even noted) by the
		2378	event loop.
		2379
		2380	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		2381	the loop iterates next and checks for the watcher to have become active,
		2382	it will reset the flag again. C<ev_async_pending> can be used to very
		2383	quickly check whether invoking the loop might be a good idea.
		2384
		2385	Not that this does I<not> check whether the watcher itself is pending, only
		2386	whether it has been requested to make this watcher pending.
1225		2387
1226	=back	2388	=back
1227		2389
1228		2390
1229	=head1 OTHER FUNCTIONS	2391	=head1 OTHER FUNCTIONS
…		…
1240	or timeout without having to allocate/configure/start/stop/free one or	2402	or timeout without having to allocate/configure/start/stop/free one or
1241	more watchers yourself.	2403	more watchers yourself.
1242		2404
1243	If C<fd> is less than 0, then no I/O watcher will be started and events	2405	If C<fd> is less than 0, then no I/O watcher will be started and events
1244	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	2406	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and
1245	C<events> set will be craeted and started.	2407	C<events> set will be created and started.
1246		2408
1247	If C<timeout> is less than 0, then no timeout watcher will be	2409	If C<timeout> is less than 0, then no timeout watcher will be
1248	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	2410	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
1249	repeat = 0) will be started. While C<0> is a valid timeout, it is of	2411	repeat = 0) will be started. While C<0> is a valid timeout, it is of
1250	dubious value.	2412	dubious value.
…		…
1252	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	2414	The callback has the type C<void (*cb)(int revents, void *arg)> and gets
1253	passed an C<revents> set like normal event callbacks (a combination of	2415	passed an C<revents> set like normal event callbacks (a combination of
1254	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	2416	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
1255	value passed to C<ev_once>:	2417	value passed to C<ev_once>:
1256		2418
1257	static void stdin_ready (int revents, void *arg)	2419	static void stdin_ready (int revents, void *arg)
1258	{	2420	{
1259	if (revents & EV_TIMEOUT)	2421	if (revents & EV_TIMEOUT)
1260	/* doh, nothing entered */;	2422	/* doh, nothing entered */;
1261	else if (revents & EV_READ)	2423	else if (revents & EV_READ)
1262	/* stdin might have data for us, joy! */;	2424	/* stdin might have data for us, joy! */;
1263	}	2425	}
1264		2426
1265	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	2427	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
1266		2428
1267	=item ev_feed_event (ev_loop *, watcher *, int revents)	2429	=item ev_feed_event (ev_loop *, watcher *, int revents)
1268		2430
1269	Feeds the given event set into the event loop, as if the specified event	2431	Feeds the given event set into the event loop, as if the specified event
1270	had happened for the specified watcher (which must be a pointer to an	2432	had happened for the specified watcher (which must be a pointer to an
…		…
1275	Feed an event on the given fd, as if a file descriptor backend detected	2437	Feed an event on the given fd, as if a file descriptor backend detected
1276	the given events it.	2438	the given events it.
1277		2439
1278	=item ev_feed_signal_event (ev_loop *loop, int signum)	2440	=item ev_feed_signal_event (ev_loop *loop, int signum)
1279		2441
1280	Feed an event as if the given signal occured (C<loop> must be the default	2442	Feed an event as if the given signal occurred (C<loop> must be the default
1281	loop!).	2443	loop!).
1282		2444
1283	=back	2445	=back
1284		2446
1285		2447
…		…
1301		2463
1302	=item * Priorities are not currently supported. Initialising priorities	2464	=item * Priorities are not currently supported. Initialising priorities
1303	will fail and all watchers will have the same priority, even though there	2465	will fail and all watchers will have the same priority, even though there
1304	is an ev_pri field.	2466	is an ev_pri field.
1305		2467
		2468	=item * In libevent, the last base created gets the signals, in libev, the
		2469	first base created (== the default loop) gets the signals.
		2470
1306	=item * Other members are not supported.	2471	=item * Other members are not supported.
1307		2472
1308	=item * The libev emulation is I<not> ABI compatible to libevent, you need	2473	=item * The libev emulation is I<not> ABI compatible to libevent, you need
1309	to use the libev header file and library.	2474	to use the libev header file and library.
1310		2475
1311	=back	2476	=back
1312		2477
1313	=head1 C++ SUPPORT	2478	=head1 C++ SUPPORT
1314		2479
1315	TBD.	2480	Libev comes with some simplistic wrapper classes for C++ that mainly allow
		2481	you to use some convenience methods to start/stop watchers and also change
		2482	the callback model to a model using method callbacks on objects.
		2483
		2484	To use it,
		2485
		2486	#include <ev++.h>
		2487
		2488	This automatically includes F<ev.h> and puts all of its definitions (many
		2489	of them macros) into the global namespace. All C++ specific things are
		2490	put into the C<ev> namespace. It should support all the same embedding
		2491	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
		2492
		2493	Care has been taken to keep the overhead low. The only data member the C++
		2494	classes add (compared to plain C-style watchers) is the event loop pointer
		2495	that the watcher is associated with (or no additional members at all if
		2496	you disable C<EV_MULTIPLICITY> when embedding libev).
		2497
		2498	Currently, functions, and static and non-static member functions can be
		2499	used as callbacks. Other types should be easy to add as long as they only
		2500	need one additional pointer for context. If you need support for other
		2501	types of functors please contact the author (preferably after implementing
		2502	it).
		2503
		2504	Here is a list of things available in the C<ev> namespace:
		2505
		2506	=over 4
		2507
		2508	=item C<ev::READ>, C<ev::WRITE> etc.
		2509
		2510	These are just enum values with the same values as the C<EV_READ> etc.
		2511	macros from F<ev.h>.
		2512
		2513	=item C<ev::tstamp>, C<ev::now>
		2514
		2515	Aliases to the same types/functions as with the C<ev_> prefix.
		2516
		2517	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
		2518
		2519	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
		2520	the same name in the C<ev> namespace, with the exception of C<ev_signal>
		2521	which is called C<ev::sig> to avoid clashes with the C<signal> macro
		2522	defines by many implementations.
		2523
		2524	All of those classes have these methods:
		2525
		2526	=over 4
		2527
		2528	=item ev::TYPE::TYPE ()
		2529
		2530	=item ev::TYPE::TYPE (struct ev_loop *)
		2531
		2532	=item ev::TYPE::~TYPE
		2533
		2534	The constructor (optionally) takes an event loop to associate the watcher
		2535	with. If it is omitted, it will use C<EV_DEFAULT>.
		2536
		2537	The constructor calls C<ev_init> for you, which means you have to call the
		2538	C<set> method before starting it.
		2539
		2540	It will not set a callback, however: You have to call the templated C<set>
		2541	method to set a callback before you can start the watcher.
		2542
		2543	(The reason why you have to use a method is a limitation in C++ which does
		2544	not allow explicit template arguments for constructors).
		2545
		2546	The destructor automatically stops the watcher if it is active.
		2547
		2548	=item w->set<class, &class::method> (object *)
		2549
		2550	This method sets the callback method to call. The method has to have a
		2551	signature of C<void (*)(ev_TYPE &, int)>, it receives the watcher as
		2552	first argument and the C<revents> as second. The object must be given as
		2553	parameter and is stored in the C<data> member of the watcher.
		2554
		2555	This method synthesizes efficient thunking code to call your method from
		2556	the C callback that libev requires. If your compiler can inline your
		2557	callback (i.e. it is visible to it at the place of the C<set> call and
		2558	your compiler is good :), then the method will be fully inlined into the
		2559	thunking function, making it as fast as a direct C callback.
		2560
		2561	Example: simple class declaration and watcher initialisation
		2562
		2563	struct myclass
		2564	{
		2565	void io_cb (ev::io &w, int revents) { }
		2566	}
		2567
		2568	myclass obj;
		2569	ev::io iow;
		2570	iow.set <myclass, &myclass::io_cb> (&obj);
		2571
		2572	=item w->set<function> (void *data = 0)
		2573
		2574	Also sets a callback, but uses a static method or plain function as
		2575	callback. The optional C<data> argument will be stored in the watcher's
		2576	C<data> member and is free for you to use.
		2577
		2578	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
		2579
		2580	See the method-C<set> above for more details.
		2581
		2582	Example:
		2583
		2584	static void io_cb (ev::io &w, int revents) { }
		2585	iow.set <io_cb> ();
		2586
		2587	=item w->set (struct ev_loop *)
		2588
		2589	Associates a different C<struct ev_loop> with this watcher. You can only
		2590	do this when the watcher is inactive (and not pending either).
		2591
		2592	=item w->set ([arguments])
		2593
		2594	Basically the same as C<ev_TYPE_set>, with the same arguments. Must be
		2595	called at least once. Unlike the C counterpart, an active watcher gets
		2596	automatically stopped and restarted when reconfiguring it with this
		2597	method.
		2598
		2599	=item w->start ()
		2600
		2601	Starts the watcher. Note that there is no C<loop> argument, as the
		2602	constructor already stores the event loop.
		2603
		2604	=item w->stop ()
		2605
		2606	Stops the watcher if it is active. Again, no C<loop> argument.
		2607
		2608	=item w->again () (C<ev::timer>, C<ev::periodic> only)
		2609
		2610	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
		2611	C<ev_TYPE_again> function.
		2612
		2613	=item w->sweep () (C<ev::embed> only)
		2614
		2615	Invokes C<ev_embed_sweep>.
		2616
		2617	=item w->update () (C<ev::stat> only)
		2618
		2619	Invokes C<ev_stat_stat>.
		2620
		2621	=back
		2622
		2623	=back
		2624
		2625	Example: Define a class with an IO and idle watcher, start one of them in
		2626	the constructor.
		2627
		2628	class myclass
		2629	{
		2630	ev::io io; void io_cb (ev::io &w, int revents);
		2631	ev:idle idle void idle_cb (ev::idle &w, int revents);
		2632
		2633	myclass (int fd)
		2634	{
		2635	io .set <myclass, &myclass::io_cb > (this);
		2636	idle.set <myclass, &myclass::idle_cb> (this);
		2637
		2638	io.start (fd, ev::READ);
		2639	}
		2640	};
		2641
		2642
		2643	=head1 OTHER LANGUAGE BINDINGS
		2644
		2645	Libev does not offer other language bindings itself, but bindings for a
		2646	number of languages exist in the form of third-party packages. If you know
		2647	any interesting language binding in addition to the ones listed here, drop
		2648	me a note.
		2649
		2650	=over 4
		2651
		2652	=item Perl
		2653
		2654	The EV module implements the full libev API and is actually used to test
		2655	libev. EV is developed together with libev. Apart from the EV core module,
		2656	there are additional modules that implement libev-compatible interfaces
		2657	to C<libadns> (C<EV::ADNS>), C<Net::SNMP> (C<Net::SNMP::EV>) and the
		2658	C<libglib> event core (C<Glib::EV> and C<EV::Glib>).
		2659
		2660	It can be found and installed via CPAN, its homepage is at
		2661	L<http://software.schmorp.de/pkg/EV>.
		2662
		2663	=item Python
		2664
		2665	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		2666	seems to be quite complete and well-documented. Note, however, that the
		2667	patch they require for libev is outright dangerous as it breaks the ABI
		2668	for everybody else, and therefore, should never be applied in an installed
		2669	libev (if python requires an incompatible ABI then it needs to embed
		2670	libev).
		2671
		2672	=item Ruby
		2673
		2674	Tony Arcieri has written a ruby extension that offers access to a subset
		2675	of the libev API and adds file handle abstractions, asynchronous DNS and
		2676	more on top of it. It can be found via gem servers. Its homepage is at
		2677	L<http://rev.rubyforge.org/>.
		2678
		2679	=item D
		2680
		2681	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		2682	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		2683
		2684	=back
		2685
		2686
		2687	=head1 MACRO MAGIC
		2688
		2689	Libev can be compiled with a variety of options, the most fundamental
		2690	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
		2691	functions and callbacks have an initial C<struct ev_loop *> argument.
		2692
		2693	To make it easier to write programs that cope with either variant, the
		2694	following macros are defined:
		2695
		2696	=over 4
		2697
		2698	=item C<EV_A>, C<EV_A_>
		2699
		2700	This provides the loop I<argument> for functions, if one is required ("ev
		2701	loop argument"). The C<EV_A> form is used when this is the sole argument,
		2702	C<EV_A_> is used when other arguments are following. Example:
		2703
		2704	ev_unref (EV_A);
		2705	ev_timer_add (EV_A_ watcher);
		2706	ev_loop (EV_A_ 0);
		2707
		2708	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
		2709	which is often provided by the following macro.
		2710
		2711	=item C<EV_P>, C<EV_P_>
		2712
		2713	This provides the loop I<parameter> for functions, if one is required ("ev
		2714	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
		2715	C<EV_P_> is used when other parameters are following. Example:
		2716
		2717	// this is how ev_unref is being declared
		2718	static void ev_unref (EV_P);
		2719
		2720	// this is how you can declare your typical callback
		2721	static void cb (EV_P_ ev_timer *w, int revents)
		2722
		2723	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
		2724	suitable for use with C<EV_A>.
		2725
		2726	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
		2727
		2728	Similar to the other two macros, this gives you the value of the default
		2729	loop, if multiple loops are supported ("ev loop default").
		2730
		2731	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		2732
		2733	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		2734	default loop has been initialised (C<UC> == unchecked). Their behaviour
		2735	is undefined when the default loop has not been initialised by a previous
		2736	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		2737
		2738	It is often prudent to use C<EV_DEFAULT> when initialising the first
		2739	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
		2740
		2741	=back
		2742
		2743	Example: Declare and initialise a check watcher, utilising the above
		2744	macros so it will work regardless of whether multiple loops are supported
		2745	or not.
		2746
		2747	static void
		2748	check_cb (EV_P_ ev_timer *w, int revents)
		2749	{
		2750	ev_check_stop (EV_A_ w);
		2751	}
		2752
		2753	ev_check check;
		2754	ev_check_init (&check, check_cb);
		2755	ev_check_start (EV_DEFAULT_ &check);
		2756	ev_loop (EV_DEFAULT_ 0);
		2757
		2758	=head1 EMBEDDING
		2759
		2760	Libev can (and often is) directly embedded into host
		2761	applications. Examples of applications that embed it include the Deliantra
		2762	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
		2763	and rxvt-unicode.
		2764
		2765	The goal is to enable you to just copy the necessary files into your
		2766	source directory without having to change even a single line in them, so
		2767	you can easily upgrade by simply copying (or having a checked-out copy of
		2768	libev somewhere in your source tree).
		2769
		2770	=head2 FILESETS
		2771
		2772	Depending on what features you need you need to include one or more sets of files
		2773	in your application.
		2774
		2775	=head3 CORE EVENT LOOP
		2776
		2777	To include only the libev core (all the C<ev_*> functions), with manual
		2778	configuration (no autoconf):
		2779
		2780	#define EV_STANDALONE 1
		2781	#include "ev.c"
		2782
		2783	This will automatically include F<ev.h>, too, and should be done in a
		2784	single C source file only to provide the function implementations. To use
		2785	it, do the same for F<ev.h> in all files wishing to use this API (best
		2786	done by writing a wrapper around F<ev.h> that you can include instead and
		2787	where you can put other configuration options):
		2788
		2789	#define EV_STANDALONE 1
		2790	#include "ev.h"
		2791
		2792	Both header files and implementation files can be compiled with a C++
		2793	compiler (at least, thats a stated goal, and breakage will be treated
		2794	as a bug).
		2795
		2796	You need the following files in your source tree, or in a directory
		2797	in your include path (e.g. in libev/ when using -Ilibev):
		2798
		2799	ev.h
		2800	ev.c
		2801	ev_vars.h
		2802	ev_wrap.h
		2803
		2804	ev_win32.c required on win32 platforms only
		2805
		2806	ev_select.c only when select backend is enabled (which is enabled by default)
		2807	ev_poll.c only when poll backend is enabled (disabled by default)
		2808	ev_epoll.c only when the epoll backend is enabled (disabled by default)
		2809	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
		2810	ev_port.c only when the solaris port backend is enabled (disabled by default)
		2811
		2812	F<ev.c> includes the backend files directly when enabled, so you only need
		2813	to compile this single file.
		2814
		2815	=head3 LIBEVENT COMPATIBILITY API
		2816
		2817	To include the libevent compatibility API, also include:
		2818
		2819	#include "event.c"
		2820
		2821	in the file including F<ev.c>, and:
		2822
		2823	#include "event.h"
		2824
		2825	in the files that want to use the libevent API. This also includes F<ev.h>.
		2826
		2827	You need the following additional files for this:
		2828
		2829	event.h
		2830	event.c
		2831
		2832	=head3 AUTOCONF SUPPORT
		2833
		2834	Instead of using C<EV_STANDALONE=1> and providing your configuration in
		2835	whatever way you want, you can also C<m4_include([libev.m4])> in your
		2836	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
		2837	include F<config.h> and configure itself accordingly.
		2838
		2839	For this of course you need the m4 file:
		2840
		2841	libev.m4
		2842
		2843	=head2 PREPROCESSOR SYMBOLS/MACROS
		2844
		2845	Libev can be configured via a variety of preprocessor symbols you have to
		2846	define before including any of its files. The default in the absence of
		2847	autoconf is noted for every option.
		2848
		2849	=over 4
		2850
		2851	=item EV_STANDALONE
		2852
		2853	Must always be C<1> if you do not use autoconf configuration, which
		2854	keeps libev from including F<config.h>, and it also defines dummy
		2855	implementations for some libevent functions (such as logging, which is not
		2856	supported). It will also not define any of the structs usually found in
		2857	F<event.h> that are not directly supported by the libev core alone.
		2858
		2859	=item EV_USE_MONOTONIC
		2860
		2861	If defined to be C<1>, libev will try to detect the availability of the
		2862	monotonic clock option at both compile time and runtime. Otherwise no use
		2863	of the monotonic clock option will be attempted. If you enable this, you
		2864	usually have to link against librt or something similar. Enabling it when
		2865	the functionality isn't available is safe, though, although you have
		2866	to make sure you link against any libraries where the C<clock_gettime>
		2867	function is hiding in (often F<-lrt>).
		2868
		2869	=item EV_USE_REALTIME
		2870
		2871	If defined to be C<1>, libev will try to detect the availability of the
		2872	real-time clock option at compile time (and assume its availability at
		2873	runtime if successful). Otherwise no use of the real-time clock option will
		2874	be attempted. This effectively replaces C<gettimeofday> by C<clock_get
		2875	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the
		2876	note about libraries in the description of C<EV_USE_MONOTONIC>, though.
		2877
		2878	=item EV_USE_NANOSLEEP
		2879
		2880	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		2881	and will use it for delays. Otherwise it will use C<select ()>.
		2882
		2883	=item EV_USE_EVENTFD
		2884
		2885	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		2886	available and will probe for kernel support at runtime. This will improve
		2887	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		2888	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		2889	2.7 or newer, otherwise disabled.
		2890
		2891	=item EV_USE_SELECT
		2892
		2893	If undefined or defined to be C<1>, libev will compile in support for the
		2894	C<select>(2) backend. No attempt at auto-detection will be done: if no
		2895	other method takes over, select will be it. Otherwise the select backend
		2896	will not be compiled in.
		2897
		2898	=item EV_SELECT_USE_FD_SET
		2899
		2900	If defined to C<1>, then the select backend will use the system C<fd_set>
		2901	structure. This is useful if libev doesn't compile due to a missing
		2902	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout on
		2903	exotic systems. This usually limits the range of file descriptors to some
		2904	low limit such as 1024 or might have other limitations (winsocket only
		2905	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might
		2906	influence the size of the C<fd_set> used.
		2907
		2908	=item EV_SELECT_IS_WINSOCKET
		2909
		2910	When defined to C<1>, the select backend will assume that
		2911	select/socket/connect etc. don't understand file descriptors but
		2912	wants osf handles on win32 (this is the case when the select to
		2913	be used is the winsock select). This means that it will call
		2914	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
		2915	it is assumed that all these functions actually work on fds, even
		2916	on win32. Should not be defined on non-win32 platforms.
		2917
		2918	=item EV_FD_TO_WIN32_HANDLE
		2919
		2920	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		2921	file descriptors to socket handles. When not defining this symbol (the
		2922	default), then libev will call C<_get_osfhandle>, which is usually
		2923	correct. In some cases, programs use their own file descriptor management,
		2924	in which case they can provide this function to map fds to socket handles.
		2925
		2926	=item EV_USE_POLL
		2927
		2928	If defined to be C<1>, libev will compile in support for the C<poll>(2)
		2929	backend. Otherwise it will be enabled on non-win32 platforms. It
		2930	takes precedence over select.
		2931
		2932	=item EV_USE_EPOLL
		2933
		2934	If defined to be C<1>, libev will compile in support for the Linux
		2935	C<epoll>(7) backend. Its availability will be detected at runtime,
		2936	otherwise another method will be used as fallback. This is the preferred
		2937	backend for GNU/Linux systems. If undefined, it will be enabled if the
		2938	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		2939
		2940	=item EV_USE_KQUEUE
		2941
		2942	If defined to be C<1>, libev will compile in support for the BSD style
		2943	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
		2944	otherwise another method will be used as fallback. This is the preferred
		2945	backend for BSD and BSD-like systems, although on most BSDs kqueue only
		2946	supports some types of fds correctly (the only platform we found that
		2947	supports ptys for example was NetBSD), so kqueue might be compiled in, but
		2948	not be used unless explicitly requested. The best way to use it is to find
		2949	out whether kqueue supports your type of fd properly and use an embedded
		2950	kqueue loop.
		2951
		2952	=item EV_USE_PORT
		2953
		2954	If defined to be C<1>, libev will compile in support for the Solaris
		2955	10 port style backend. Its availability will be detected at runtime,
		2956	otherwise another method will be used as fallback. This is the preferred
		2957	backend for Solaris 10 systems.
		2958
		2959	=item EV_USE_DEVPOLL
		2960
		2961	Reserved for future expansion, works like the USE symbols above.
		2962
		2963	=item EV_USE_INOTIFY
		2964
		2965	If defined to be C<1>, libev will compile in support for the Linux inotify
		2966	interface to speed up C<ev_stat> watchers. Its actual availability will
		2967	be detected at runtime. If undefined, it will be enabled if the headers
		2968	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		2969
		2970	=item EV_ATOMIC_T
		2971
		2972	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		2973	access is atomic with respect to other threads or signal contexts. No such
		2974	type is easily found in the C language, so you can provide your own type
		2975	that you know is safe for your purposes. It is used both for signal handler "locking"
		2976	as well as for signal and thread safety in C<ev_async> watchers.
		2977
		2978	In the absence of this define, libev will use C<sig_atomic_t volatile>
		2979	(from F<signal.h>), which is usually good enough on most platforms.
		2980
		2981	=item EV_H
		2982
		2983	The name of the F<ev.h> header file used to include it. The default if
		2984	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
		2985	used to virtually rename the F<ev.h> header file in case of conflicts.
		2986
		2987	=item EV_CONFIG_H
		2988
		2989	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
		2990	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
		2991	C<EV_H>, above.
		2992
		2993	=item EV_EVENT_H
		2994
		2995	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
		2996	of how the F<event.h> header can be found, the default is C<"event.h">.
		2997
		2998	=item EV_PROTOTYPES
		2999
		3000	If defined to be C<0>, then F<ev.h> will not define any function
		3001	prototypes, but still define all the structs and other symbols. This is
		3002	occasionally useful if you want to provide your own wrapper functions
		3003	around libev functions.
		3004
		3005	=item EV_MULTIPLICITY
		3006
		3007	If undefined or defined to C<1>, then all event-loop-specific functions
		3008	will have the C<struct ev_loop *> as first argument, and you can create
		3009	additional independent event loops. Otherwise there will be no support
		3010	for multiple event loops and there is no first event loop pointer
		3011	argument. Instead, all functions act on the single default loop.
		3012
		3013	=item EV_MINPRI
		3014
		3015	=item EV_MAXPRI
		3016
		3017	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
		3018	C<EV_MAXPRI>, but otherwise there are no non-obvious limitations. You can
		3019	provide for more priorities by overriding those symbols (usually defined
		3020	to be C<-2> and C<2>, respectively).
		3021
		3022	When doing priority-based operations, libev usually has to linearly search
		3023	all the priorities, so having many of them (hundreds) uses a lot of space
		3024	and time, so using the defaults of five priorities (-2 .. +2) is usually
		3025	fine.
		3026
		3027	If your embedding application does not need any priorities, defining these both to
		3028	C<0> will save some memory and CPU.
		3029
		3030	=item EV_PERIODIC_ENABLE
		3031
		3032	If undefined or defined to be C<1>, then periodic timers are supported. If
		3033	defined to be C<0>, then they are not. Disabling them saves a few kB of
		3034	code.
		3035
		3036	=item EV_IDLE_ENABLE
		3037
		3038	If undefined or defined to be C<1>, then idle watchers are supported. If
		3039	defined to be C<0>, then they are not. Disabling them saves a few kB of
		3040	code.
		3041
		3042	=item EV_EMBED_ENABLE
		3043
		3044	If undefined or defined to be C<1>, then embed watchers are supported. If
		3045	defined to be C<0>, then they are not.
		3046
		3047	=item EV_STAT_ENABLE
		3048
		3049	If undefined or defined to be C<1>, then stat watchers are supported. If
		3050	defined to be C<0>, then they are not.
		3051
		3052	=item EV_FORK_ENABLE
		3053
		3054	If undefined or defined to be C<1>, then fork watchers are supported. If
		3055	defined to be C<0>, then they are not.
		3056
		3057	=item EV_ASYNC_ENABLE
		3058
		3059	If undefined or defined to be C<1>, then async watchers are supported. If
		3060	defined to be C<0>, then they are not.
		3061
		3062	=item EV_MINIMAL
		3063
		3064	If you need to shave off some kilobytes of code at the expense of some
		3065	speed, define this symbol to C<1>. Currently this is used to override some
		3066	inlining decisions, saves roughly 30% code size on amd64. It also selects a
		3067	much smaller 2-heap for timer management over the default 4-heap.
		3068
		3069	=item EV_PID_HASHSIZE
		3070
		3071	C<ev_child> watchers use a small hash table to distribute workload by
		3072	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
		3073	than enough. If you need to manage thousands of children you might want to
		3074	increase this value (I<must> be a power of two).
		3075
		3076	=item EV_INOTIFY_HASHSIZE
		3077
		3078	C<ev_stat> watchers use a small hash table to distribute workload by
		3079	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
		3080	usually more than enough. If you need to manage thousands of C<ev_stat>
		3081	watchers you might want to increase this value (I<must> be a power of
		3082	two).
		3083
		3084	=item EV_USE_4HEAP
		3085
		3086	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3087	timer and periodics heap, libev uses a 4-heap when this symbol is defined
		3088	to C<1>. The 4-heap uses more complicated (longer) code but has
		3089	noticeably faster performance with many (thousands) of watchers.
		3090
		3091	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3092	(disabled).
		3093
		3094	=item EV_HEAP_CACHE_AT
		3095
		3096	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3097	timer and periodics heap, libev can cache the timestamp (I<at>) within
		3098	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		3099	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		3100	but avoids random read accesses on heap changes. This improves performance
		3101	noticeably with with many (hundreds) of watchers.
		3102
		3103	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3104	(disabled).
		3105
		3106	=item EV_VERIFY
		3107
		3108	Controls how much internal verification (see C<ev_loop_verify ()>) will
		3109	be done: If set to C<0>, no internal verification code will be compiled
		3110	in. If set to C<1>, then verification code will be compiled in, but not
		3111	called. If set to C<2>, then the internal verification code will be
		3112	called once per loop, which can slow down libev. If set to C<3>, then the
		3113	verification code will be called very frequently, which will slow down
		3114	libev considerably.
		3115
		3116	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be
		3117	C<0.>
		3118
		3119	=item EV_COMMON
		3120
		3121	By default, all watchers have a C<void *data> member. By redefining
		3122	this macro to a something else you can include more and other types of
		3123	members. You have to define it each time you include one of the files,
		3124	though, and it must be identical each time.
		3125
		3126	For example, the perl EV module uses something like this:
		3127
		3128	#define EV_COMMON \
		3129	SV *self; /* contains this struct */ \
		3130	SV *cb_sv, *fh /* note no trailing ";" */
		3131
		3132	=item EV_CB_DECLARE (type)
		3133
		3134	=item EV_CB_INVOKE (watcher, revents)
		3135
		3136	=item ev_set_cb (ev, cb)
		3137
		3138	Can be used to change the callback member declaration in each watcher,
		3139	and the way callbacks are invoked and set. Must expand to a struct member
		3140	definition and a statement, respectively. See the F<ev.h> header file for
		3141	their default definitions. One possible use for overriding these is to
		3142	avoid the C<struct ev_loop *> as first argument in all cases, or to use
		3143	method calls instead of plain function calls in C++.
		3144
		3145	=head2 EXPORTED API SYMBOLS
		3146
		3147	If you need to re-export the API (e.g. via a DLL) and you need a list of
		3148	exported symbols, you can use the provided F<Symbol.*> files which list
		3149	all public symbols, one per line:
		3150
		3151	Symbols.ev for libev proper
		3152	Symbols.event for the libevent emulation
		3153
		3154	This can also be used to rename all public symbols to avoid clashes with
		3155	multiple versions of libev linked together (which is obviously bad in
		3156	itself, but sometimes it is inconvenient to avoid this).
		3157
		3158	A sed command like this will create wrapper C<#define>'s that you need to
		3159	include before including F<ev.h>:
		3160
		3161	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		3162
		3163	This would create a file F<wrap.h> which essentially looks like this:
		3164
		3165	#define ev_backend myprefix_ev_backend
		3166	#define ev_check_start myprefix_ev_check_start
		3167	#define ev_check_stop myprefix_ev_check_stop
		3168	...
		3169
		3170	=head2 EXAMPLES
		3171
		3172	For a real-world example of a program the includes libev
		3173	verbatim, you can have a look at the EV perl module
		3174	(L<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
		3175	the F<libev/> subdirectory and includes them in the F<EV/EVAPI.h> (public
		3176	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file
		3177	will be compiled. It is pretty complex because it provides its own header
		3178	file.
		3179
		3180	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
		3181	that everybody includes and which overrides some configure choices:
		3182
		3183	#define EV_MINIMAL 1
		3184	#define EV_USE_POLL 0
		3185	#define EV_MULTIPLICITY 0
		3186	#define EV_PERIODIC_ENABLE 0
		3187	#define EV_STAT_ENABLE 0
		3188	#define EV_FORK_ENABLE 0
		3189	#define EV_CONFIG_H <config.h>
		3190	#define EV_MINPRI 0
		3191	#define EV_MAXPRI 0
		3192
		3193	#include "ev++.h"
		3194
		3195	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
		3196
		3197	#include "ev_cpp.h"
		3198	#include "ev.c"
		3199
		3200
		3201	=head1 THREADS AND COROUTINES
		3202
		3203	=head2 THREADS
		3204
		3205	Libev itself is completely thread-safe, but it uses no locking. This
		3206	means that you can use as many loops as you want in parallel, as long as
		3207	only one thread ever calls into one libev function with the same loop
		3208	parameter.
		3209
		3210	Or put differently: calls with different loop parameters can be done in
		3211	parallel from multiple threads, calls with the same loop parameter must be
		3212	done serially (but can be done from different threads, as long as only one
		3213	thread ever is inside a call at any point in time, e.g. by using a mutex
		3214	per loop).
		3215
		3216	If you want to know which design (one loop, locking, or multiple loops
		3217	without or something else still) is best for your problem, then I cannot
		3218	help you. I can give some generic advice however:
		3219
		3220	=over 4
		3221
		3222	=item * most applications have a main thread: use the default libev loop
		3223	in that thread, or create a separate thread running only the default loop.
		3224
		3225	This helps integrating other libraries or software modules that use libev
		3226	themselves and don't care/know about threading.
		3227
		3228	=item * one loop per thread is usually a good model.
		3229
		3230	Doing this is almost never wrong, sometimes a better-performance model
		3231	exists, but it is always a good start.
		3232
		3233	=item * other models exist, such as the leader/follower pattern, where one
		3234	loop is handed through multiple threads in a kind of round-robin fashion.
		3235
		3236	Choosing a model is hard - look around, learn, know that usually you can do
		3237	better than you currently do :-)
		3238
		3239	=item * often you need to talk to some other thread which blocks in the
		3240	event loop - C<ev_async> watchers can be used to wake them up from other
		3241	threads safely (or from signal contexts...).
		3242
		3243	=back
		3244
		3245	=head2 COROUTINES
		3246
		3247	Libev is much more accommodating to coroutines ("cooperative threads"):
		3248	libev fully supports nesting calls to it's functions from different
		3249	coroutines (e.g. you can call C<ev_loop> on the same loop from two
		3250	different coroutines and switch freely between both coroutines running the
		3251	loop, as long as you don't confuse yourself). The only exception is that
		3252	you must not do this from C<ev_periodic> reschedule callbacks.
		3253
		3254	Care has been invested into making sure that libev does not keep local
		3255	state inside C<ev_loop>, and other calls do not usually allow coroutine
		3256	switches.
		3257
		3258
		3259	=head1 COMPLEXITIES
		3260
		3261	In this section the complexities of (many of) the algorithms used inside
		3262	libev will be explained. For complexity discussions about backends see the
		3263	documentation for C<ev_default_init>.
		3264
		3265	All of the following are about amortised time: If an array needs to be
		3266	extended, libev needs to realloc and move the whole array, but this
		3267	happens asymptotically never with higher number of elements, so O(1) might
		3268	mean it might do a lengthy realloc operation in rare cases, but on average
		3269	it is much faster and asymptotically approaches constant time.
		3270
		3271	=over 4
		3272
		3273	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
		3274
		3275	This means that, when you have a watcher that triggers in one hour and
		3276	there are 100 watchers that would trigger before that then inserting will
		3277	have to skip roughly seven (C<ld 100>) of these watchers.
		3278
		3279	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
		3280
		3281	That means that changing a timer costs less than removing/adding them
		3282	as only the relative motion in the event queue has to be paid for.
		3283
		3284	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
		3285
		3286	These just add the watcher into an array or at the head of a list.
		3287
		3288	=item Stopping check/prepare/idle/fork/async watchers: O(1)
		3289
		3290	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
		3291
		3292	These watchers are stored in lists then need to be walked to find the
		3293	correct watcher to remove. The lists are usually short (you don't usually
		3294	have many watchers waiting for the same fd or signal).
		3295
		3296	=item Finding the next timer in each loop iteration: O(1)
		3297
		3298	By virtue of using a binary or 4-heap, the next timer is always found at a
		3299	fixed position in the storage array.
		3300
		3301	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		3302
		3303	A change means an I/O watcher gets started or stopped, which requires
		3304	libev to recalculate its status (and possibly tell the kernel, depending
		3305	on backend and whether C<ev_io_set> was used).
		3306
		3307	=item Activating one watcher (putting it into the pending state): O(1)
		3308
		3309	=item Priority handling: O(number_of_priorities)
		3310
		3311	Priorities are implemented by allocating some space for each
		3312	priority. When doing priority-based operations, libev usually has to
		3313	linearly search all the priorities, but starting/stopping and activating
		3314	watchers becomes O(1) w.r.t. priority handling.
		3315
		3316	=item Sending an ev_async: O(1)
		3317
		3318	=item Processing ev_async_send: O(number_of_async_watchers)
		3319
		3320	=item Processing signals: O(max_signal_number)
		3321
		3322	Sending involves a system call I<iff> there were no other C<ev_async_send>
		3323	calls in the current loop iteration. Checking for async and signal events
		3324	involves iterating over all running async watchers or all signal numbers.
		3325
		3326	=back
		3327
		3328
		3329	=head1 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		3330
		3331	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		3332	requires, and its I/O model is fundamentally incompatible with the POSIX
		3333	model. Libev still offers limited functionality on this platform in
		3334	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		3335	descriptors. This only applies when using Win32 natively, not when using
		3336	e.g. cygwin.
		3337
		3338	Lifting these limitations would basically require the full
		3339	re-implementation of the I/O system. If you are into these kinds of
		3340	things, then note that glib does exactly that for you in a very portable
		3341	way (note also that glib is the slowest event library known to man).
		3342
		3343	There is no supported compilation method available on windows except
		3344	embedding it into other applications.
		3345
		3346	Not a libev limitation but worth mentioning: windows apparently doesn't
		3347	accept large writes: instead of resulting in a partial write, windows will
		3348	either accept everything or return C<ENOBUFS> if the buffer is too large,
		3349	so make sure you only write small amounts into your sockets (less than a
		3350	megabyte seems safe, but thsi apparently depends on the amount of memory
		3351	available).
		3352
		3353	Due to the many, low, and arbitrary limits on the win32 platform and
		3354	the abysmal performance of winsockets, using a large number of sockets
		3355	is not recommended (and not reasonable). If your program needs to use
		3356	more than a hundred or so sockets, then likely it needs to use a totally
		3357	different implementation for windows, as libev offers the POSIX readiness
		3358	notification model, which cannot be implemented efficiently on windows
		3359	(Microsoft monopoly games).
		3360
		3361	A typical way to use libev under windows is to embed it (see the embedding
		3362	section for details) and use the following F<evwrap.h> header file instead
		3363	of F<ev.h>:
		3364
		3365	#define EV_STANDALONE /* keeps ev from requiring config.h */
		3366	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		3367
		3368	#include "ev.h"
		3369
		3370	And compile the following F<evwrap.c> file into your project (make sure
		3371	you do I<not> compile the F<ev.c> or any other embedded soruce files!):
		3372
		3373	#include "evwrap.h"
		3374	#include "ev.c"
		3375
		3376	=over 4
		3377
		3378	=item The winsocket select function
		3379
		3380	The winsocket C<select> function doesn't follow POSIX in that it
		3381	requires socket I<handles> and not socket I<file descriptors> (it is
		3382	also extremely buggy). This makes select very inefficient, and also
		3383	requires a mapping from file descriptors to socket handles (the Microsoft
		3384	C runtime provides the function C<_open_osfhandle> for this). See the
		3385	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		3386	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		3387
		3388	The configuration for a "naked" win32 using the Microsoft runtime
		3389	libraries and raw winsocket select is:
		3390
		3391	#define EV_USE_SELECT 1
		3392	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		3393
		3394	Note that winsockets handling of fd sets is O(n), so you can easily get a
		3395	complexity in the O(n²) range when using win32.
		3396
		3397	=item Limited number of file descriptors
		3398
		3399	Windows has numerous arbitrary (and low) limits on things.
		3400
		3401	Early versions of winsocket's select only supported waiting for a maximum
		3402	of C<64> handles (probably owning to the fact that all windows kernels
		3403	can only wait for C<64> things at the same time internally; Microsoft
		3404	recommends spawning a chain of threads and wait for 63 handles and the
		3405	previous thread in each. Great).
		3406
		3407	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		3408	to some high number (e.g. C<2048>) before compiling the winsocket select
		3409	call (which might be in libev or elsewhere, for example, perl does its own
		3410	select emulation on windows).
		3411
		3412	Another limit is the number of file descriptors in the Microsoft runtime
		3413	libraries, which by default is C<64> (there must be a hidden I<64> fetish
		3414	or something like this inside Microsoft). You can increase this by calling
		3415	C<_setmaxstdio>, which can increase this limit to C<2048> (another
		3416	arbitrary limit), but is broken in many versions of the Microsoft runtime
		3417	libraries.
		3418
		3419	This might get you to about C<512> or C<2048> sockets (depending on
		3420	windows version and/or the phase of the moon). To get more, you need to
		3421	wrap all I/O functions and provide your own fd management, but the cost of
		3422	calling select (O(n²)) will likely make this unworkable.
		3423
		3424	=back
		3425
		3426
		3427	=head1 PORTABILITY REQUIREMENTS
		3428
		3429	In addition to a working ISO-C implementation, libev relies on a few
		3430	additional extensions:
		3431
		3432	=over 4
		3433
		3434	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		3435	calling conventions regardless of C<ev_watcher_type *>.
		3436
		3437	Libev assumes not only that all watcher pointers have the same internal
		3438	structure (guaranteed by POSIX but not by ISO C for example), but it also
		3439	assumes that the same (machine) code can be used to call any watcher
		3440	callback: The watcher callbacks have different type signatures, but libev
		3441	calls them using an C<ev_watcher *> internally.
		3442
		3443	=item C<sig_atomic_t volatile> must be thread-atomic as well
		3444
		3445	The type C<sig_atomic_t volatile> (or whatever is defined as
		3446	C<EV_ATOMIC_T>) must be atomic w.r.t. accesses from different
		3447	threads. This is not part of the specification for C<sig_atomic_t>, but is
		3448	believed to be sufficiently portable.
		3449
		3450	=item C<sigprocmask> must work in a threaded environment
		3451
		3452	Libev uses C<sigprocmask> to temporarily block signals. This is not
		3453	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		3454	pthread implementations will either allow C<sigprocmask> in the "main
		3455	thread" or will block signals process-wide, both behaviours would
		3456	be compatible with libev. Interaction between C<sigprocmask> and
		3457	C<pthread_sigmask> could complicate things, however.
		3458
		3459	The most portable way to handle signals is to block signals in all threads
		3460	except the initial one, and run the default loop in the initial thread as
		3461	well.
		3462
		3463	=item C<long> must be large enough for common memory allocation sizes
		3464
		3465	To improve portability and simplify using libev, libev uses C<long>
		3466	internally instead of C<size_t> when allocating its data structures. On
		3467	non-POSIX systems (Microsoft...) this might be unexpectedly low, but
		3468	is still at least 31 bits everywhere, which is enough for hundreds of
		3469	millions of watchers.
		3470
		3471	=item C<double> must hold a time value in seconds with enough accuracy
		3472
		3473	The type C<double> is used to represent timestamps. It is required to
		3474	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
		3475	enough for at least into the year 4000. This requirement is fulfilled by
		3476	implementations implementing IEEE 754 (basically all existing ones).
		3477
		3478	=back
		3479
		3480	If you know of other additional requirements drop me a note.
		3481
		3482
		3483	=head1 COMPILER WARNINGS
		3484
		3485	Depending on your compiler and compiler settings, you might get no or a
		3486	lot of warnings when compiling libev code. Some people are apparently
		3487	scared by this.
		3488
		3489	However, these are unavoidable for many reasons. For one, each compiler
		3490	has different warnings, and each user has different tastes regarding
		3491	warning options. "Warn-free" code therefore cannot be a goal except when
		3492	targeting a specific compiler and compiler-version.
		3493
		3494	Another reason is that some compiler warnings require elaborate
		3495	workarounds, or other changes to the code that make it less clear and less
		3496	maintainable.
		3497
		3498	And of course, some compiler warnings are just plain stupid, or simply
		3499	wrong (because they don't actually warn about the condition their message
		3500	seems to warn about).
		3501
		3502	While libev is written to generate as few warnings as possible,
		3503	"warn-free" code is not a goal, and it is recommended not to build libev
		3504	with any compiler warnings enabled unless you are prepared to cope with
		3505	them (e.g. by ignoring them). Remember that warnings are just that:
		3506	warnings, not errors, or proof of bugs.
		3507
		3508
		3509	=head1 VALGRIND
		3510
		3511	Valgrind has a special section here because it is a popular tool that is
		3512	highly useful, but valgrind reports are very hard to interpret.
		3513
		3514	If you think you found a bug (memory leak, uninitialised data access etc.)
		3515	in libev, then check twice: If valgrind reports something like:
		3516
		3517	==2274== definitely lost: 0 bytes in 0 blocks.
		3518	==2274== possibly lost: 0 bytes in 0 blocks.
		3519	==2274== still reachable: 256 bytes in 1 blocks.
		3520
		3521	Then there is no memory leak. Similarly, under some circumstances,
		3522	valgrind might report kernel bugs as if it were a bug in libev, or it
		3523	might be confused (it is a very good tool, but only a tool).
		3524
		3525	If you are unsure about something, feel free to contact the mailing list
		3526	with the full valgrind report and an explanation on why you think this is
		3527	a bug in libev. However, don't be annoyed when you get a brisk "this is
		3528	no bug" answer and take the chance of learning how to interpret valgrind
		3529	properly.
		3530
		3531	If you need, for some reason, empty reports from valgrind for your project
		3532	I suggest using suppression lists.
		3533
1316		3534
1317	=head1 AUTHOR	3535	=head1 AUTHOR
1318		3536
1319	Marc Lehmann <libev@schmorp.de>.	3537	Marc Lehmann <libev@schmorp.de>.
1320		3538

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