ViewVC Help

View File | Revision Log | Show Annotations | Download File

/cvs/libev/ev.pod

Comparing libev/ev.pod (file contents):
Revision 1.116 by root, Mon Dec 31 01:34:09 2007 UTC vs.
Revision 1.211 by root, Mon Nov 3 14:34:16 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		8
9	=head2 EXAMPLE PROGRAM	9	=head2 EXAMPLE PROGRAM
10		10
		11	// a single header file is required
11	#include <ev.h>	12	#include <ev.h>
12		13
		14	// every watcher type has its own typedef'd struct
		15	// with the name ev_TYPE
13	ev_io stdin_watcher;	16	ev_io stdin_watcher;
14	ev_timer timeout_watcher;	17	ev_timer timeout_watcher;
15		18
16	/* called when data readable on stdin */	19	// all watcher callbacks have a similar signature
		20	// this callback is called when data is readable on stdin
17	static void	21	static void
18	stdin_cb (EV_P_ struct ev_io *w, int revents)	22	stdin_cb (EV_P_ ev_io *w, int revents)
19	{	23	{
20	/* puts ("stdin ready"); */	24	puts ("stdin ready");
21	ev_io_stop (EV_A_ w); /* just a syntax example */	25	// for one-shot events, one must manually stop the watcher
22	ev_unloop (EV_A_ EVUNLOOP_ALL); /* leave all loop calls */	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);
23	}	31	}
24		32
		33	// another callback, this time for a time-out
25	static void	34	static void
26	timeout_cb (EV_P_ struct ev_timer *w, int revents)	35	timeout_cb (EV_P_ ev_timer *w, int revents)
27	{	36	{
28	/* puts ("timeout"); */	37	puts ("timeout");
29	ev_unloop (EV_A_ EVUNLOOP_ONE); /* leave one loop call */	38	// this causes the innermost ev_loop to stop iterating
		39	ev_unloop (EV_A_ EVUNLOOP_ONE);
30	}	40	}
31		41
32	int	42	int
33	main (void)	43	main (void)
34	{	44	{
		45	// use the default event loop unless you have special needs
35	struct ev_loop *loop = ev_default_loop (0);	46	ev_loop *loop = ev_default_loop (0);
36		47
37	/* initialise an io watcher, then start it */	48	// initialise an io watcher, then start it
		49	// this one will watch for stdin to become readable
38	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);	50	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
39	ev_io_start (loop, &stdin_watcher);	51	ev_io_start (loop, &stdin_watcher);
40		52
		53	// initialise a timer watcher, then start it
41	/* simple non-repeating 5.5 second timeout */	54	// simple non-repeating 5.5 second timeout
42	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);	55	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
43	ev_timer_start (loop, &timeout_watcher);	56	ev_timer_start (loop, &timeout_watcher);
44		57
45	/* loop till timeout or data ready */	58	// now wait for events to arrive
46	ev_loop (loop, 0);	59	ev_loop (loop, 0);
47		60
		61	// unloop was called, so exit
48	return 0;	62	return 0;
49	}	63	}
50		64
51	=head1 DESCRIPTION	65	=head1 DESCRIPTION
52		66
53	The newest version of this document is also available as a html-formatted	67	The newest version of this document is also available as an html-formatted
54	web page you might find easier to navigate when reading it for the first	68	web page you might find easier to navigate when reading it for the first
55	time: L<http://cvs.schmorp.de/libev/ev.html>.	69	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
56		70
57	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
58	file descriptor being readable or a timeout occurring), and it will manage	72	file descriptor being readable or a timeout occurring), and it will manage
59	these event sources and provide your program with events.	73	these event sources and provide your program with events.
60		74
…		…
84	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent	98	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
85	for example).	99	for example).
86		100
87	=head2 CONVENTIONS	101	=head2 CONVENTIONS
88		102
89	Libev is very configurable. In this manual the default configuration will	103	Libev is very configurable. In this manual the default (and most common)
90	be described, which supports multiple event loops. For more info about	104	configuration will be described, which supports multiple event loops. For
91	various configuration options please have a look at B<EMBED> section in	105	more info about various configuration options please have a look at
92	this manual. If libev was configured without support for multiple event	106	B<EMBED> section in this manual. If libev was configured without support
93	loops, then all functions taking an initial argument of name C<loop>	107	for multiple event loops, then all functions taking an initial argument of
94	(which is always of type C<struct ev_loop *>) will not have this argument.	108	name C<loop> (which is always of type C<ev_loop *>) will not have
		109	this argument.
95		110
96	=head2 TIME REPRESENTATION	111	=head2 TIME REPRESENTATION
97		112
98	Libev represents time as a single floating point number, representing the	113	Libev represents time as a single floating point number, representing the
99	(fractional) number of seconds since the (POSIX) epoch (somewhere near	114	(fractional) number of seconds since the (POSIX) epoch (somewhere near
100	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
101	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
102	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
103	it, you should treat it as some floatingpoint value. Unlike the name	118	it, you should treat it as some floating point value. Unlike the name
104	component C<stamp> might indicate, it is also used for time differences	119	component C<stamp> might indicate, it is also used for time differences
105	throughout libev.	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.
		141
106		142
107	=head1 GLOBAL FUNCTIONS	143	=head1 GLOBAL FUNCTIONS
108		144
109	These functions can be called anytime, even before initialising the	145	These functions can be called anytime, even before initialising the
110	library in any way.	146	library in any way.
…		…
119		155
120	=item ev_sleep (ev_tstamp interval)	156	=item ev_sleep (ev_tstamp interval)
121		157
122	Sleep for the given interval: The current thread will be blocked until	158	Sleep for the given interval: The current thread will be blocked until
123	either it is interrupted or the given time interval has passed. Basically	159	either it is interrupted or the given time interval has passed. Basically
124	this is a subsecond-resolution C<sleep ()>.	160	this is a sub-second-resolution C<sleep ()>.
125		161
126	=item int ev_version_major ()	162	=item int ev_version_major ()
127		163
128	=item int ev_version_minor ()	164	=item int ev_version_minor ()
129		165
…		…
142	not a problem.	178	not a problem.
143		179
144	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
145	version.	181	version.
146		182
147	assert (("libev version mismatch",	183	assert (("libev version mismatch",
148	ev_version_major () == EV_VERSION_MAJOR	184	ev_version_major () == EV_VERSION_MAJOR
149	&& ev_version_minor () >= EV_VERSION_MINOR));	185	&& ev_version_minor () >= EV_VERSION_MINOR));
150		186
151	=item unsigned int ev_supported_backends ()	187	=item unsigned int ev_supported_backends ()
152		188
153	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_*>
154	value) compiled into this binary of libev (independent of their	190	value) compiled into this binary of libev (independent of their
…		…
156	a description of the set values.	192	a description of the set values.
157		193
158	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
159	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
160		196
161	assert (("sorry, no epoll, no sex",	197	assert (("sorry, no epoll, no sex",
162	ev_supported_backends () & EVBACKEND_EPOLL));	198	ev_supported_backends () & EVBACKEND_EPOLL));
163		199
164	=item unsigned int ev_recommended_backends ()	200	=item unsigned int ev_recommended_backends ()
165		201
166	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
167	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
168	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
169	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
170	(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
171	libev will probe for if you specify no backends explicitly.	207	libev will probe for if you specify no backends explicitly.
172		208
173	=item unsigned int ev_embeddable_backends ()	209	=item unsigned int ev_embeddable_backends ()
174		210
…		…
178	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	214	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for
179	recommended ones.	215	recommended ones.
180		216
181	See the description of C<ev_embed> watchers for more info.	217	See the description of C<ev_embed> watchers for more info.
182		218
183	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	219	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]
184		220
185	Sets the allocation function to use (the prototype is similar - the	221	Sets the allocation function to use (the prototype is similar - the
186	semantics is identical - to the realloc C function). It is used to	222	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
187	allocate and free memory (no surprises here). If it returns zero when	223	used to allocate and free memory (no surprises here). If it returns zero
188	memory needs to be allocated, the library might abort or take some	224	when memory needs to be allocated (C<size != 0>), the library might abort
189	potentially destructive action. The default is your system realloc	225	or take some potentially destructive action.
190	function.	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.
191		230
192	You could override this function in high-availability programs to, say,	231	You could override this function in high-availability programs to, say,
193	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,
194	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.
195		234
196	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
197	retries).	236	retries (example requires a standards-compliant C<realloc>).
198		237
199	static void *	238	static void *
200	persistent_realloc (void *ptr, size_t size)	239	persistent_realloc (void *ptr, size_t size)
201	{	240	{
202	for (;;)	241	for (;;)
…		…
211	}	250	}
212		251
213	...	252	...
214	ev_set_allocator (persistent_realloc);	253	ev_set_allocator (persistent_realloc);
215		254
216	=item ev_set_syserr_cb (void (*cb)(const char *msg));	255	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]
217		256
218	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
219	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
220	indicating the system call or subsystem causing the problem. If this	259	indicating the system call or subsystem causing the problem. If this
221	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
222	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
223	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
224	(such as abort).	263	(such as abort).
225		264
226	Example: This is basically the same thing that libev does internally, too.	265	Example: This is basically the same thing that libev does internally, too.
…		…
237		276
238	=back	277	=back
239		278
240	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	279	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
241		280
242	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 C<struct>
243	types of such loops, the I<default> loop, which supports signals and child	282	is I<not> optional in this case, as there is also an C<ev_loop>
244	events, and dynamically created loops which do not.	283	I<function>).
245		284
246	If you use threads, a common model is to run the default event loop	285	The library knows two types of such loops, the I<default> loop, which
247	in your main thread (or in a separate thread) and for each thread you	286	supports signals and child events, and dynamically created loops which do
248	create, you also create another event loop. Libev itself does no locking	287	not.
249	whatsoever, so if you mix calls to the same event loop in different
250	threads, make sure you lock (this is usually a bad idea, though, even if
251	done correctly, because it's hideous and inefficient).
252		288
253	=over 4	289	=over 4
254		290
255	=item struct ev_loop *ev_default_loop (unsigned int flags)	291	=item struct ev_loop *ev_default_loop (unsigned int flags)
256		292
…		…
260	flags. If that is troubling you, check C<ev_backend ()> afterwards).	296	flags. If that is troubling you, check C<ev_backend ()> afterwards).
261		297
262	If you don't know what event loop to use, use the one returned from this	298	If you don't know what event loop to use, use the one returned from this
263	function.	299	function.
264		300
		301	Note that this function is I<not> thread-safe, so if you want to use it
		302	from multiple threads, you have to lock (note also that this is unlikely,
		303	as loops cannot be shared easily between threads anyway).
		304
		305	The default loop is the only loop that can handle C<ev_signal> and
		306	C<ev_child> watchers, and to do this, it always registers a handler
		307	for C<SIGCHLD>. If this is a problem for your application you can either
		308	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you
		309	can simply overwrite the C<SIGCHLD> signal handler I<after> calling
		310	C<ev_default_init>.
		311
265	The flags argument can be used to specify special behaviour or specific	312	The flags argument can be used to specify special behaviour or specific
266	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).	313	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
267		314
268	The following flags are supported:	315	The following flags are supported:
269		316
…		…
274	The default flags value. Use this if you have no clue (it's the right	321	The default flags value. Use this if you have no clue (it's the right
275	thing, believe me).	322	thing, believe me).
276		323
277	=item C<EVFLAG_NOENV>	324	=item C<EVFLAG_NOENV>
278		325
279	If this flag bit is ored into the flag value (or the program runs setuid	326	If this flag bit is or'ed into the flag value (or the program runs setuid
280	or setgid) then libev will I<not> look at the environment variable	327	or setgid) then libev will I<not> look at the environment variable
281	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	328	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
282	override the flags completely if it is found in the environment. This is	329	override the flags completely if it is found in the environment. This is
283	useful to try out specific backends to test their performance, or to work	330	useful to try out specific backends to test their performance, or to work
284	around bugs.	331	around bugs.
…		…
290	enabling this flag.	337	enabling this flag.
291		338
292	This works by calling C<getpid ()> on every iteration of the loop,	339	This works by calling C<getpid ()> on every iteration of the loop,
293	and thus this might slow down your event loop if you do a lot of loop	340	and thus this might slow down your event loop if you do a lot of loop
294	iterations and little real work, but is usually not noticeable (on my	341	iterations and little real work, but is usually not noticeable (on my
295	Linux system for example, C<getpid> is actually a simple 5-insn sequence	342	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence
296	without a syscall and thus I<very> fast, but my Linux system also has	343	without a system call and thus I<very> fast, but my GNU/Linux system also has
297	C<pthread_atfork> which is even faster).	344	C<pthread_atfork> which is even faster).
298		345
299	The big advantage of this flag is that you can forget about fork (and	346	The big advantage of this flag is that you can forget about fork (and
300	forget about forgetting to tell libev about forking) when you use this	347	forget about forgetting to tell libev about forking) when you use this
301	flag.	348	flag.
302		349
303	This flag setting cannot be overriden or specified in the C<LIBEV_FLAGS>	350	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
304	environment variable.	351	environment variable.
305		352
306	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	353	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
307		354
308	This is your standard select(2) backend. Not I<completely> standard, as	355	This is your standard select(2) backend. Not I<completely> standard, as
…		…
310	but if that fails, expect a fairly low limit on the number of fds when	357	but if that fails, expect a fairly low limit on the number of fds when
311	using this backend. It doesn't scale too well (O(highest_fd)), but its	358	using this backend. It doesn't scale too well (O(highest_fd)), but its
312	usually the fastest backend for a low number of (low-numbered :) fds.	359	usually the fastest backend for a low number of (low-numbered :) fds.
313		360
314	To get good performance out of this backend you need a high amount of	361	To get good performance out of this backend you need a high amount of
315	parallelity (most of the file descriptors should be busy). If you are	362	parallelism (most of the file descriptors should be busy). If you are
316	writing a server, you should C<accept ()> in a loop to accept as many	363	writing a server, you should C<accept ()> in a loop to accept as many
317	connections as possible during one iteration. You might also want to have	364	connections as possible during one iteration. You might also want to have
318	a look at C<ev_set_io_collect_interval ()> to increase the amount of	365	a look at C<ev_set_io_collect_interval ()> to increase the amount of
319	readyness notifications you get per iteration.	366	readiness notifications you get per iteration.
		367
		368	This backend maps C<EV_READ> to the C<readfds> set and C<EV_WRITE> to the
		369	C<writefds> set (and to work around Microsoft Windows bugs, also onto the
		370	C<exceptfds> set on that platform).
320		371
321	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)	372	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
322		373
323	And this is your standard poll(2) backend. It's more complicated	374	And this is your standard poll(2) backend. It's more complicated
324	than select, but handles sparse fds better and has no artificial	375	than select, but handles sparse fds better and has no artificial
325	limit on the number of fds you can use (except it will slow down	376	limit on the number of fds you can use (except it will slow down
326	considerably with a lot of inactive fds). It scales similarly to select,	377	considerably with a lot of inactive fds). It scales similarly to select,
327	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for	378	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
328	performance tips.	379	performance tips.
329		380
		381	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
		382	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
		383
330	=item C<EVBACKEND_EPOLL> (value 4, Linux)	384	=item C<EVBACKEND_EPOLL> (value 4, Linux)
331		385
332	For few fds, this backend is a bit little slower than poll and select,	386	For few fds, this backend is a bit little slower than poll and select,
333	but it scales phenomenally better. While poll and select usually scale	387	but it scales phenomenally better. While poll and select usually scale
334	like O(total_fds) where n is the total number of fds (or the highest fd),	388	like O(total_fds) where n is the total number of fds (or the highest fd),
335	epoll scales either O(1) or O(active_fds). The epoll design has a number	389	epoll scales either O(1) or O(active_fds).
336	of shortcomings, such as silently dropping events in some hard-to-detect	390
337	cases and rewiring a syscall per fd change, no fork support and bad	391	The epoll mechanism deserves honorable mention as the most misdesigned
338	support for dup.	392	of the more advanced event mechanisms: mere annoyances include silently
		393	dropping file descriptors, requiring a system call per change per file
		394	descriptor (and unnecessary guessing of parameters), problems with dup and
		395	so on. The biggest issue is fork races, however - if a program forks then
		396	I<both> parent and child process have to recreate the epoll set, which can
		397	take considerable time (one syscall per file descriptor) and is of course
		398	hard to detect.
		399
		400	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but
		401	of course I<doesn't>, and epoll just loves to report events for totally
		402	I<different> file descriptors (even already closed ones, so one cannot
		403	even remove them from the set) than registered in the set (especially
		404	on SMP systems). Libev tries to counter these spurious notifications by
		405	employing an additional generation counter and comparing that against the
		406	events to filter out spurious ones, recreating the set when required.
339		407
340	While stopping, setting and starting an I/O watcher in the same iteration	408	While stopping, setting and starting an I/O watcher in the same iteration
341	will result in some caching, there is still a syscall per such incident	409	will result in some caching, there is still a system call per such
342	(because the fd could point to a different file description now), so its	410	incident (because the same I<file descriptor> could point to a different
343	best to avoid that. Also, C<dup ()>'ed file descriptors might not work	411	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
344	very well if you register events for both fds.	412	file descriptors might not work very well if you register events for both
345		413	file descriptors.
346	Please note that epoll sometimes generates spurious notifications, so you
347	need to use non-blocking I/O or other means to avoid blocking when no data
348	(or space) is available.
349		414
350	Best performance from this backend is achieved by not unregistering all	415	Best performance from this backend is achieved by not unregistering all
351	watchers for a file descriptor until it has been closed, if possible, i.e.	416	watchers for a file descriptor until it has been closed, if possible,
352	keep at least one watcher active per fd at all times.	417	i.e. keep at least one watcher active per fd at all times. Stopping and
		418	starting a watcher (without re-setting it) also usually doesn't cause
		419	extra overhead. A fork can both result in spurious notifications as well
		420	as in libev having to destroy and recreate the epoll object, which can
		421	take considerable time and thus should be avoided.
353		422
354	While nominally embeddeble in other event loops, this feature is broken in	423	While nominally embeddable in other event loops, this feature is broken in
355	all kernel versions tested so far.	424	all kernel versions tested so far.
		425
		426	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		427	C<EVBACKEND_POLL>.
356		428
357	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	429	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
358		430
359	Kqueue deserves special mention, as at the time of this writing, it	431	Kqueue deserves special mention, as at the time of this writing, it
360	was broken on all BSDs except NetBSD (usually it doesn't work reliably	432	was broken on all BSDs except NetBSD (usually it doesn't work reliably
361	with anything but sockets and pipes, except on Darwin, where of course	433	with anything but sockets and pipes, except on Darwin, where of course
362	it's completely useless). For this reason it's not being "autodetected"	434	it's completely useless). Unlike epoll, however, whose brokenness
		435	is by design, these kqueue bugs can (and eventually will) be fixed
		436	without API changes to existing programs. For this reason it's not being
363	unless you explicitly specify it explicitly in the flags (i.e. using	437	"auto-detected" unless you explicitly specify it in the flags (i.e. using
364	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)	438	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
365	system like NetBSD.	439	system like NetBSD.
366		440
367	You still can embed kqueue into a normal poll or select backend and use it	441	You still can embed kqueue into a normal poll or select backend and use it
368	only for sockets (after having made sure that sockets work with kqueue on	442	only for sockets (after having made sure that sockets work with kqueue on
369	the target platform). See C<ev_embed> watchers for more info.	443	the target platform). See C<ev_embed> watchers for more info.
370		444
371	It scales in the same way as the epoll backend, but the interface to the	445	It scales in the same way as the epoll backend, but the interface to the
372	kernel is more efficient (which says nothing about its actual speed, of	446	kernel is more efficient (which says nothing about its actual speed, of
373	course). While stopping, setting and starting an I/O watcher does never	447	course). While stopping, setting and starting an I/O watcher does never
374	cause an extra syscall as with C<EVBACKEND_EPOLL>, it still adds up to	448	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
375	two event changes per incident, support for C<fork ()> is very bad and it	449	two event changes per incident. Support for C<fork ()> is very bad (but
376	drops fds silently in similarly hard-to-detect cases.	450	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		451	cases
377		452
378	This backend usually performs well under most conditions.	453	This backend usually performs well under most conditions.
379		454
380	While nominally embeddable in other event loops, this doesn't work	455	While nominally embeddable in other event loops, this doesn't work
381	everywhere, so you might need to test for this. And since it is broken	456	everywhere, so you might need to test for this. And since it is broken
382	almost everywhere, you should only use it when you have a lot of sockets	457	almost everywhere, you should only use it when you have a lot of sockets
383	(for which it usually works), by embedding it into another event loop	458	(for which it usually works), by embedding it into another event loop
384	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>) and using it only for	459	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>) and, did I mention it,
385	sockets.	460	using it only for sockets.
		461
		462	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		463	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		464	C<NOTE_EOF>.
386		465
387	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	466	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
388		467
389	This is not implemented yet (and might never be, unless you send me an	468	This is not implemented yet (and might never be, unless you send me an
390	implementation). According to reports, C</dev/poll> only supports sockets	469	implementation). According to reports, C</dev/poll> only supports sockets
…		…
394	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	473	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
395		474
396	This uses the Solaris 10 event port mechanism. As with everything on Solaris,	475	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
397	it's really slow, but it still scales very well (O(active_fds)).	476	it's really slow, but it still scales very well (O(active_fds)).
398		477
399	Please note that solaris event ports can deliver a lot of spurious	478	Please note that Solaris event ports can deliver a lot of spurious
400	notifications, so you need to use non-blocking I/O or other means to avoid	479	notifications, so you need to use non-blocking I/O or other means to avoid
401	blocking when no data (or space) is available.	480	blocking when no data (or space) is available.
402		481
403	While this backend scales well, it requires one system call per active	482	While this backend scales well, it requires one system call per active
404	file descriptor per loop iteration. For small and medium numbers of file	483	file descriptor per loop iteration. For small and medium numbers of file
405	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	484	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
406	might perform better.	485	might perform better.
407		486
		487	On the positive side, with the exception of the spurious readiness
		488	notifications, this backend actually performed fully to specification
		489	in all tests and is fully embeddable, which is a rare feat among the
		490	OS-specific backends (I vastly prefer correctness over speed hacks).
		491
		492	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		493	C<EVBACKEND_POLL>.
		494
408	=item C<EVBACKEND_ALL>	495	=item C<EVBACKEND_ALL>
409		496
410	Try all backends (even potentially broken ones that wouldn't be tried	497	Try all backends (even potentially broken ones that wouldn't be tried
411	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	498	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
412	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	499	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
413		500
414	It is definitely not recommended to use this flag.	501	It is definitely not recommended to use this flag.
415		502
416	=back	503	=back
417		504
418	If one or more of these are ored into the flags value, then only these	505	If one or more of these are or'ed into the flags value, then only these
419	backends will be tried (in the reverse order as given here). If none are	506	backends will be tried (in the reverse order as listed here). If none are
420	specified, most compiled-in backend will be tried, usually in reverse	507	specified, all backends in C<ev_recommended_backends ()> will be tried.
421	order of their flag values :)
422		508
423	The most typical usage is like this:	509	Example: This is the most typical usage.
424		510
425	if (!ev_default_loop (0))	511	if (!ev_default_loop (0))
426	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");	512	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
427		513
428	Restrict libev to the select and poll backends, and do not allow	514	Example: Restrict libev to the select and poll backends, and do not allow
429	environment settings to be taken into account:	515	environment settings to be taken into account:
430		516
431	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);	517	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
432		518
433	Use whatever libev has to offer, but make sure that kqueue is used if	519	Example: Use whatever libev has to offer, but make sure that kqueue is
434	available (warning, breaks stuff, best use only with your own private	520	used if available (warning, breaks stuff, best use only with your own
435	event loop and only if you know the OS supports your types of fds):	521	private event loop and only if you know the OS supports your types of
		522	fds):
436		523
437	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);	524	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
438		525
439	=item struct ev_loop *ev_loop_new (unsigned int flags)	526	=item struct ev_loop *ev_loop_new (unsigned int flags)
440		527
441	Similar to C<ev_default_loop>, but always creates a new event loop that is	528	Similar to C<ev_default_loop>, but always creates a new event loop that is
442	always distinct from the default loop. Unlike the default loop, it cannot	529	always distinct from the default loop. Unlike the default loop, it cannot
443	handle signal and child watchers, and attempts to do so will be greeted by	530	handle signal and child watchers, and attempts to do so will be greeted by
444	undefined behaviour (or a failed assertion if assertions are enabled).	531	undefined behaviour (or a failed assertion if assertions are enabled).
445		532
		533	Note that this function I<is> thread-safe, and the recommended way to use
		534	libev with threads is indeed to create one loop per thread, and using the
		535	default loop in the "main" or "initial" thread.
		536
446	Example: Try to create a event loop that uses epoll and nothing else.	537	Example: Try to create a event loop that uses epoll and nothing else.
447		538
448	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	539	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
449	if (!epoller)	540	if (!epoller)
450	fatal ("no epoll found here, maybe it hides under your chair");	541	fatal ("no epoll found here, maybe it hides under your chair");
451		542
452	=item ev_default_destroy ()	543	=item ev_default_destroy ()
453		544
454	Destroys the default loop again (frees all memory and kernel state	545	Destroys the default loop again (frees all memory and kernel state
455	etc.). None of the active event watchers will be stopped in the normal	546	etc.). None of the active event watchers will be stopped in the normal
456	sense, so e.g. C<ev_is_active> might still return true. It is your	547	sense, so e.g. C<ev_is_active> might still return true. It is your
457	responsibility to either stop all watchers cleanly yoursef I<before>	548	responsibility to either stop all watchers cleanly yourself I<before>
458	calling this function, or cope with the fact afterwards (which is usually	549	calling this function, or cope with the fact afterwards (which is usually
459	the easiest thing, you can just ignore the watchers and/or C<free ()> them	550	the easiest thing, you can just ignore the watchers and/or C<free ()> them
460	for example).	551	for example).
461		552
462	Note that certain global state, such as signal state, will not be freed by	553	Note that certain global state, such as signal state (and installed signal
463	this function, and related watchers (such as signal and child watchers)	554	handlers), will not be freed by this function, and related watchers (such
464	would need to be stopped manually.	555	as signal and child watchers) would need to be stopped manually.
465		556
466	In general it is not advisable to call this function except in the	557	In general it is not advisable to call this function except in the
467	rare occasion where you really need to free e.g. the signal handling	558	rare occasion where you really need to free e.g. the signal handling
468	pipe fds. If you need dynamically allocated loops it is better to use	559	pipe fds. If you need dynamically allocated loops it is better to use
469	C<ev_loop_new> and C<ev_loop_destroy>).	560	C<ev_loop_new> and C<ev_loop_destroy>).
…		…
473	Like C<ev_default_destroy>, but destroys an event loop created by an	564	Like C<ev_default_destroy>, but destroys an event loop created by an
474	earlier call to C<ev_loop_new>.	565	earlier call to C<ev_loop_new>.
475		566
476	=item ev_default_fork ()	567	=item ev_default_fork ()
477		568
		569	This function sets a flag that causes subsequent C<ev_loop> iterations
478	This function reinitialises the kernel state for backends that have	570	to reinitialise the kernel state for backends that have one. Despite the
479	one. Despite the name, you can call it anytime, but it makes most sense	571	name, you can call it anytime, but it makes most sense after forking, in
480	after forking, in either the parent or child process (or both, but that	572	the child process (or both child and parent, but that again makes little
481	again makes little sense).	573	sense). You I<must> call it in the child before using any of the libev
		574	functions, and it will only take effect at the next C<ev_loop> iteration.
482		575
483	You I<must> call this function in the child process after forking if and	576	On the other hand, you only need to call this function in the child
484	only if you want to use the event library in both processes. If you just	577	process if and only if you want to use the event library in the child. If
485	fork+exec, you don't have to call it.	578	you just fork+exec, you don't have to call it at all.
486		579
487	The function itself is quite fast and it's usually not a problem to call	580	The function itself is quite fast and it's usually not a problem to call
488	it just in case after a fork. To make this easy, the function will fit in	581	it just in case after a fork. To make this easy, the function will fit in
489	quite nicely into a call to C<pthread_atfork>:	582	quite nicely into a call to C<pthread_atfork>:
490		583
491	pthread_atfork (0, 0, ev_default_fork);	584	pthread_atfork (0, 0, ev_default_fork);
492		585
493	At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> are safe to use
494	without calling this function, so if you force one of those backends you
495	do not need to care.
496
497	=item ev_loop_fork (loop)	586	=item ev_loop_fork (loop)
498		587
499	Like C<ev_default_fork>, but acts on an event loop created by	588	Like C<ev_default_fork>, but acts on an event loop created by
500	C<ev_loop_new>. Yes, you have to call this on every allocated event loop	589	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
501	after fork, and how you do this is entirely your own problem.	590	after fork that you want to re-use in the child, and how you do this is
		591	entirely your own problem.
		592
		593	=item int ev_is_default_loop (loop)
		594
		595	Returns true when the given loop is, in fact, the default loop, and false
		596	otherwise.
502		597
503	=item unsigned int ev_loop_count (loop)	598	=item unsigned int ev_loop_count (loop)
504		599
505	Returns the count of loop iterations for the loop, which is identical to	600	Returns the count of loop iterations for the loop, which is identical to
506	the number of times libev did poll for new events. It starts at C<0> and	601	the number of times libev did poll for new events. It starts at C<0> and
…		…
521	received events and started processing them. This timestamp does not	616	received events and started processing them. This timestamp does not
522	change as long as callbacks are being processed, and this is also the base	617	change as long as callbacks are being processed, and this is also the base
523	time used for relative timers. You can treat it as the timestamp of the	618	time used for relative timers. You can treat it as the timestamp of the
524	event occurring (or more correctly, libev finding out about it).	619	event occurring (or more correctly, libev finding out about it).
525		620
		621	=item ev_now_update (loop)
		622
		623	Establishes the current time by querying the kernel, updating the time
		624	returned by C<ev_now ()> in the progress. This is a costly operation and
		625	is usually done automatically within C<ev_loop ()>.
		626
		627	This function is rarely useful, but when some event callback runs for a
		628	very long time without entering the event loop, updating libev's idea of
		629	the current time is a good idea.
		630
		631	See also "The special problem of time updates" in the C<ev_timer> section.
		632
526	=item ev_loop (loop, int flags)	633	=item ev_loop (loop, int flags)
527		634
528	Finally, this is it, the event handler. This function usually is called	635	Finally, this is it, the event handler. This function usually is called
529	after you initialised all your watchers and you want to start handling	636	after you initialised all your watchers and you want to start handling
530	events.	637	events.
…		…
532	If the flags argument is specified as C<0>, it will not return until	639	If the flags argument is specified as C<0>, it will not return until
533	either no event watchers are active anymore or C<ev_unloop> was called.	640	either no event watchers are active anymore or C<ev_unloop> was called.
534		641
535	Please note that an explicit C<ev_unloop> is usually better than	642	Please note that an explicit C<ev_unloop> is usually better than
536	relying on all watchers to be stopped when deciding when a program has	643	relying on all watchers to be stopped when deciding when a program has
537	finished (especially in interactive programs), but having a program that	644	finished (especially in interactive programs), but having a program
538	automatically loops as long as it has to and no longer by virtue of	645	that automatically loops as long as it has to and no longer by virtue
539	relying on its watchers stopping correctly is a thing of beauty.	646	of relying on its watchers stopping correctly, that is truly a thing of
		647	beauty.
540		648
541	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	649	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle
542	those events and any outstanding ones, but will not block your process in	650	those events and any already outstanding ones, but will not block your
543	case there are no events and will return after one iteration of the loop.	651	process in case there are no events and will return after one iteration of
		652	the loop.
544		653
545	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	654	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if
546	neccessary) and will handle those and any outstanding ones. It will block	655	necessary) and will handle those and any already outstanding ones. It
547	your process until at least one new event arrives, and will return after	656	will block your process until at least one new event arrives (which could
548	one iteration of the loop. This is useful if you are waiting for some	657	be an event internal to libev itself, so there is no guarantee that a
549	external event in conjunction with something not expressible using other	658	user-registered callback will be called), and will return after one
		659	iteration of the loop.
		660
		661	This is useful if you are waiting for some external event in conjunction
		662	with something not expressible using other libev watchers (i.e. "roll your
550	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is	663	own C<ev_loop>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
551	usually a better approach for this kind of thing.	664	usually a better approach for this kind of thing.
552		665
553	Here are the gory details of what C<ev_loop> does:	666	Here are the gory details of what C<ev_loop> does:
554		667
555	- Before the first iteration, call any pending watchers.	668	- Before the first iteration, call any pending watchers.
556	* If EVFLAG_FORKCHECK was used, check for a fork.	669	* If EVFLAG_FORKCHECK was used, check for a fork.
557	- If a fork was detected, queue and call all fork watchers.	670	- If a fork was detected (by any means), queue and call all fork watchers.
558	- Queue and call all prepare watchers.	671	- Queue and call all prepare watchers.
559	- If we have been forked, recreate the kernel state.	672	- If we have been forked, detach and recreate the kernel state
		673	as to not disturb the other process.
560	- Update the kernel state with all outstanding changes.	674	- Update the kernel state with all outstanding changes.
561	- Update the "event loop time".	675	- Update the "event loop time" (ev_now ()).
562	- Calculate for how long to sleep or block, if at all	676	- Calculate for how long to sleep or block, if at all
563	(active idle watchers, EVLOOP_NONBLOCK or not having	677	(active idle watchers, EVLOOP_NONBLOCK or not having
564	any active watchers at all will result in not sleeping).	678	any active watchers at all will result in not sleeping).
565	- Sleep if the I/O and timer collect interval say so.	679	- Sleep if the I/O and timer collect interval say so.
566	- Block the process, waiting for any events.	680	- Block the process, waiting for any events.
567	- Queue all outstanding I/O (fd) events.	681	- Queue all outstanding I/O (fd) events.
568	- Update the "event loop time" and do time jump handling.	682	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
569	- Queue all outstanding timers.	683	- Queue all expired timers.
570	- Queue all outstanding periodics.	684	- Queue all expired periodics.
571	- If no events are pending now, queue all idle watchers.	685	- Unless any events are pending now, queue all idle watchers.
572	- Queue all check watchers.	686	- Queue all check watchers.
573	- Call all queued watchers in reverse order (i.e. check watchers first).	687	- Call all queued watchers in reverse order (i.e. check watchers first).
574	Signals and child watchers are implemented as I/O watchers, and will	688	Signals and child watchers are implemented as I/O watchers, and will
575	be handled here by queueing them when their watcher gets executed.	689	be handled here by queueing them when their watcher gets executed.
576	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	690	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
…		…
581	anymore.	695	anymore.
582		696
583	... queue jobs here, make sure they register event watchers as long	697	... queue jobs here, make sure they register event watchers as long
584	... as they still have work to do (even an idle watcher will do..)	698	... as they still have work to do (even an idle watcher will do..)
585	ev_loop (my_loop, 0);	699	ev_loop (my_loop, 0);
586	... jobs done. yeah!	700	... jobs done or somebody called unloop. yeah!
587		701
588	=item ev_unloop (loop, how)	702	=item ev_unloop (loop, how)
589		703
590	Can be used to make a call to C<ev_loop> return early (but only after it	704	Can be used to make a call to C<ev_loop> return early (but only after it
591	has processed all outstanding events). The C<how> argument must be either	705	has processed all outstanding events). The C<how> argument must be either
592	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	706	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
593	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	707	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
594		708
595	This "unloop state" will be cleared when entering C<ev_loop> again.	709	This "unloop state" will be cleared when entering C<ev_loop> again.
596		710
		711	It is safe to call C<ev_unloop> from otuside any C<ev_loop> calls.
		712
597	=item ev_ref (loop)	713	=item ev_ref (loop)
598		714
599	=item ev_unref (loop)	715	=item ev_unref (loop)
600		716
601	Ref/unref can be used to add or remove a reference count on the event	717	Ref/unref can be used to add or remove a reference count on the event
602	loop: Every watcher keeps one reference, and as long as the reference	718	loop: Every watcher keeps one reference, and as long as the reference
603	count is nonzero, C<ev_loop> will not return on its own. If you have	719	count is nonzero, C<ev_loop> will not return on its own.
		720
604	a watcher you never unregister that should not keep C<ev_loop> from	721	If you have a watcher you never unregister that should not keep C<ev_loop>
605	returning, ev_unref() after starting, and ev_ref() before stopping it. For	722	from returning, call ev_unref() after starting, and ev_ref() before
		723	stopping it.
		724
606	example, libev itself uses this for its internal signal pipe: It is not	725	As an example, libev itself uses this for its internal signal pipe: It is
607	visible to the libev user and should not keep C<ev_loop> from exiting if	726	not visible to the libev user and should not keep C<ev_loop> from exiting
608	no event watchers registered by it are active. It is also an excellent	727	if no event watchers registered by it are active. It is also an excellent
609	way to do this for generic recurring timers or from within third-party	728	way to do this for generic recurring timers or from within third-party
610	libraries. Just remember to I<unref after start> and I<ref before stop>	729	libraries. Just remember to I<unref after start> and I<ref before stop>
611	(but only if the watcher wasn't active before, or was active before,	730	(but only if the watcher wasn't active before, or was active before,
612	respectively).	731	respectively).
613		732
614	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	733	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
615	running when nothing else is active.	734	running when nothing else is active.
616		735
617	struct ev_signal exitsig;	736	ev_signal exitsig;
618	ev_signal_init (&exitsig, sig_cb, SIGINT);	737	ev_signal_init (&exitsig, sig_cb, SIGINT);
619	ev_signal_start (loop, &exitsig);	738	ev_signal_start (loop, &exitsig);
620	evf_unref (loop);	739	evf_unref (loop);
621		740
622	Example: For some weird reason, unregister the above signal handler again.	741	Example: For some weird reason, unregister the above signal handler again.
623		742
624	ev_ref (loop);	743	ev_ref (loop);
625	ev_signal_stop (loop, &exitsig);	744	ev_signal_stop (loop, &exitsig);
626		745
627	=item ev_set_io_collect_interval (loop, ev_tstamp interval)	746	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
628		747
629	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)	748	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
630		749
631	These advanced functions influence the time that libev will spend waiting	750	These advanced functions influence the time that libev will spend waiting
632	for events. Both are by default C<0>, meaning that libev will try to	751	for events. Both time intervals are by default C<0>, meaning that libev
633	invoke timer/periodic callbacks and I/O callbacks with minimum latency.	752	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		753	latency.
634		754
635	Setting these to a higher value (the C<interval> I<must> be >= C<0>)	755	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
636	allows libev to delay invocation of I/O and timer/periodic callbacks to	756	allows libev to delay invocation of I/O and timer/periodic callbacks
637	increase efficiency of loop iterations.	757	to increase efficiency of loop iterations (or to increase power-saving
		758	opportunities).
638		759
639	The background is that sometimes your program runs just fast enough to	760	The idea is that sometimes your program runs just fast enough to handle
640	handle one (or very few) event(s) per loop iteration. While this makes	761	one (or very few) event(s) per loop iteration. While this makes the
641	the program responsive, it also wastes a lot of CPU time to poll for new	762	program responsive, it also wastes a lot of CPU time to poll for new
642	events, especially with backends like C<select ()> which have a high	763	events, especially with backends like C<select ()> which have a high
643	overhead for the actual polling but can deliver many events at once.	764	overhead for the actual polling but can deliver many events at once.
644		765
645	By setting a higher I<io collect interval> you allow libev to spend more	766	By setting a higher I<io collect interval> you allow libev to spend more
646	time collecting I/O events, so you can handle more events per iteration,	767	time collecting I/O events, so you can handle more events per iteration,
…		…
648	C<ev_timer>) will be not affected. Setting this to a non-null value will	769	C<ev_timer>) will be not affected. Setting this to a non-null value will
649	introduce an additional C<ev_sleep ()> call into most loop iterations.	770	introduce an additional C<ev_sleep ()> call into most loop iterations.
650		771
651	Likewise, by setting a higher I<timeout collect interval> you allow libev	772	Likewise, by setting a higher I<timeout collect interval> you allow libev
652	to spend more time collecting timeouts, at the expense of increased	773	to spend more time collecting timeouts, at the expense of increased
653	latency (the watcher callback will be called later). C<ev_io> watchers	774	latency/jitter/inexactness (the watcher callback will be called
654	will not be affected. Setting this to a non-null value will not introduce	775	later). C<ev_io> watchers will not be affected. Setting this to a non-null
655	any overhead in libev.	776	value will not introduce any overhead in libev.
656		777
657	Many (busy) programs can usually benefit by setting the io collect	778	Many (busy) programs can usually benefit by setting the I/O collect
658	interval to a value near C<0.1> or so, which is often enough for	779	interval to a value near C<0.1> or so, which is often enough for
659	interactive servers (of course not for games), likewise for timeouts. It	780	interactive servers (of course not for games), likewise for timeouts. It
660	usually doesn't make much sense to set it to a lower value than C<0.01>,	781	usually doesn't make much sense to set it to a lower value than C<0.01>,
661	as this approsaches the timing granularity of most systems.	782	as this approaches the timing granularity of most systems.
		783
		784	Setting the I<timeout collect interval> can improve the opportunity for
		785	saving power, as the program will "bundle" timer callback invocations that
		786	are "near" in time together, by delaying some, thus reducing the number of
		787	times the process sleeps and wakes up again. Another useful technique to
		788	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		789	they fire on, say, one-second boundaries only.
		790
		791	=item ev_loop_verify (loop)
		792
		793	This function only does something when C<EV_VERIFY> support has been
		794	compiled in, which is the default for non-minimal builds. It tries to go
		795	through all internal structures and checks them for validity. If anything
		796	is found to be inconsistent, it will print an error message to standard
		797	error and call C<abort ()>.
		798
		799	This can be used to catch bugs inside libev itself: under normal
		800	circumstances, this function will never abort as of course libev keeps its
		801	data structures consistent.
662		802
663	=back	803	=back
664		804
665		805
666	=head1 ANATOMY OF A WATCHER	806	=head1 ANATOMY OF A WATCHER
		807
		808	In the following description, uppercase C<TYPE> in names stands for the
		809	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		810	watchers and C<ev_io_start> for I/O watchers.
667		811
668	A watcher is a structure that you create and register to record your	812	A watcher is a structure that you create and register to record your
669	interest in some event. For instance, if you want to wait for STDIN to	813	interest in some event. For instance, if you want to wait for STDIN to
670	become readable, you would create an C<ev_io> watcher for that:	814	become readable, you would create an C<ev_io> watcher for that:
671		815
672	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	816	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
673	{	817	{
674	ev_io_stop (w);	818	ev_io_stop (w);
675	ev_unloop (loop, EVUNLOOP_ALL);	819	ev_unloop (loop, EVUNLOOP_ALL);
676	}	820	}
677		821
678	struct ev_loop *loop = ev_default_loop (0);	822	struct ev_loop *loop = ev_default_loop (0);
		823
679	struct ev_io stdin_watcher;	824	ev_io stdin_watcher;
		825
680	ev_init (&stdin_watcher, my_cb);	826	ev_init (&stdin_watcher, my_cb);
681	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	827	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
682	ev_io_start (loop, &stdin_watcher);	828	ev_io_start (loop, &stdin_watcher);
		829
683	ev_loop (loop, 0);	830	ev_loop (loop, 0);
684		831
685	As you can see, you are responsible for allocating the memory for your	832	As you can see, you are responsible for allocating the memory for your
686	watcher structures (and it is usually a bad idea to do this on the stack,	833	watcher structures (and it is I<usually> a bad idea to do this on the
687	although this can sometimes be quite valid).	834	stack).
		835
		836	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		837	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
688		838
689	Each watcher structure must be initialised by a call to C<ev_init	839	Each watcher structure must be initialised by a call to C<ev_init
690	(watcher *, callback)>, which expects a callback to be provided. This	840	(watcher *, callback)>, which expects a callback to be provided. This
691	callback gets invoked each time the event occurs (or, in the case of io	841	callback gets invoked each time the event occurs (or, in the case of I/O
692	watchers, each time the event loop detects that the file descriptor given	842	watchers, each time the event loop detects that the file descriptor given
693	is readable and/or writable).	843	is readable and/or writable).
694		844
695	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	845	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
696	with arguments specific to this watcher type. There is also a macro	846	macro to configure it, with arguments specific to the watcher type. There
697	to combine initialisation and setting in one call: C<< ev_<type>_init	847	is also a macro to combine initialisation and setting in one call: C<<
698	(watcher *, callback, ...) >>.	848	ev_TYPE_init (watcher *, callback, ...) >>.
699		849
700	To make the watcher actually watch out for events, you have to start it	850	To make the watcher actually watch out for events, you have to start it
701	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	851	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
702	*) >>), and you can stop watching for events at any time by calling the	852	*) >>), and you can stop watching for events at any time by calling the
703	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	853	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
704		854
705	As long as your watcher is active (has been started but not stopped) you	855	As long as your watcher is active (has been started but not stopped) you
706	must not touch the values stored in it. Most specifically you must never	856	must not touch the values stored in it. Most specifically you must never
707	reinitialise it or call its C<set> macro.	857	reinitialise it or call its C<ev_TYPE_set> macro.
708		858
709	Each and every callback receives the event loop pointer as first, the	859	Each and every callback receives the event loop pointer as first, the
710	registered watcher structure as second, and a bitset of received events as	860	registered watcher structure as second, and a bitset of received events as
711	third argument.	861	third argument.
712		862
…		…
766	=item C<EV_FORK>	916	=item C<EV_FORK>
767		917
768	The event loop has been resumed in the child process after fork (see	918	The event loop has been resumed in the child process after fork (see
769	C<ev_fork>).	919	C<ev_fork>).
770		920
		921	=item C<EV_ASYNC>
		922
		923	The given async watcher has been asynchronously notified (see C<ev_async>).
		924
771	=item C<EV_ERROR>	925	=item C<EV_ERROR>
772		926
773	An unspecified error has occured, the watcher has been stopped. This might	927	An unspecified error has occurred, the watcher has been stopped. This might
774	happen because the watcher could not be properly started because libev	928	happen because the watcher could not be properly started because libev
775	ran out of memory, a file descriptor was found to be closed or any other	929	ran out of memory, a file descriptor was found to be closed or any other
		930	problem. Libev considers these application bugs.
		931
776	problem. You best act on it by reporting the problem and somehow coping	932	You best act on it by reporting the problem and somehow coping with the
777	with the watcher being stopped.	933	watcher being stopped. Note that well-written programs should not receive
		934	an error ever, so when your watcher receives it, this usually indicates a
		935	bug in your program.
778		936
779	Libev will usually signal a few "dummy" events together with an error,	937	Libev will usually signal a few "dummy" events together with an error, for
780	for example it might indicate that a fd is readable or writable, and if	938	example it might indicate that a fd is readable or writable, and if your
781	your callbacks is well-written it can just attempt the operation and cope	939	callbacks is well-written it can just attempt the operation and cope with
782	with the error from read() or write(). This will not work in multithreaded	940	the error from read() or write(). This will not work in multi-threaded
783	programs, though, so beware.	941	programs, though, as the fd could already be closed and reused for another
		942	thing, so beware.
784		943
785	=back	944	=back
786		945
787	=head2 GENERIC WATCHER FUNCTIONS	946	=head2 GENERIC WATCHER FUNCTIONS
788
789	In the following description, C<TYPE> stands for the watcher type,
790	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
791		947
792	=over 4	948	=over 4
793		949
794	=item C<ev_init> (ev_TYPE *watcher, callback)	950	=item C<ev_init> (ev_TYPE *watcher, callback)
795		951
…		…
801	which rolls both calls into one.	957	which rolls both calls into one.
802		958
803	You can reinitialise a watcher at any time as long as it has been stopped	959	You can reinitialise a watcher at any time as long as it has been stopped
804	(or never started) and there are no pending events outstanding.	960	(or never started) and there are no pending events outstanding.
805		961
806	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	962	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
807	int revents)>.	963	int revents)>.
		964
		965	Example: Initialise an C<ev_io> watcher in two steps.
		966
		967	ev_io w;
		968	ev_init (&w, my_cb);
		969	ev_io_set (&w, STDIN_FILENO, EV_READ);
808		970
809	=item C<ev_TYPE_set> (ev_TYPE *, [args])	971	=item C<ev_TYPE_set> (ev_TYPE *, [args])
810		972
811	This macro initialises the type-specific parts of a watcher. You need to	973	This macro initialises the type-specific parts of a watcher. You need to
812	call C<ev_init> at least once before you call this macro, but you can	974	call C<ev_init> at least once before you call this macro, but you can
…		…
815	difference to the C<ev_init> macro).	977	difference to the C<ev_init> macro).
816		978
817	Although some watcher types do not have type-specific arguments	979	Although some watcher types do not have type-specific arguments
818	(e.g. C<ev_prepare>) you still need to call its C<set> macro.	980	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
819		981
		982	See C<ev_init>, above, for an example.
		983
820	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	984	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
821		985
822	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	986	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
823	calls into a single call. This is the most convinient method to initialise	987	calls into a single call. This is the most convenient method to initialise
824	a watcher. The same limitations apply, of course.	988	a watcher. The same limitations apply, of course.
		989
		990	Example: Initialise and set an C<ev_io> watcher in one step.
		991
		992	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
825		993
826	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	994	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)
827		995
828	Starts (activates) the given watcher. Only active watchers will receive	996	Starts (activates) the given watcher. Only active watchers will receive
829	events. If the watcher is already active nothing will happen.	997	events. If the watcher is already active nothing will happen.
830		998
		999	Example: Start the C<ev_io> watcher that is being abused as example in this
		1000	whole section.
		1001
		1002	ev_io_start (EV_DEFAULT_UC, &w);
		1003
831	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1004	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)
832		1005
833	Stops the given watcher again (if active) and clears the pending	1006	Stops the given watcher if active, and clears the pending status (whether
		1007	the watcher was active or not).
		1008
834	status. It is possible that stopped watchers are pending (for example,	1009	It is possible that stopped watchers are pending - for example,
835	non-repeating timers are being stopped when they become pending), but	1010	non-repeating timers are being stopped when they become pending - but
836	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If	1011	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
837	you want to free or reuse the memory used by the watcher it is therefore a	1012	pending. If you want to free or reuse the memory used by the watcher it is
838	good idea to always call its C<ev_TYPE_stop> function.	1013	therefore a good idea to always call its C<ev_TYPE_stop> function.
839		1014
840	=item bool ev_is_active (ev_TYPE *watcher)	1015	=item bool ev_is_active (ev_TYPE *watcher)
841		1016
842	Returns a true value iff the watcher is active (i.e. it has been started	1017	Returns a true value iff the watcher is active (i.e. it has been started
843	and not yet been stopped). As long as a watcher is active you must not modify	1018	and not yet been stopped). As long as a watcher is active you must not modify
…		…
885	The default priority used by watchers when no priority has been set is	1060	The default priority used by watchers when no priority has been set is
886	always C<0>, which is supposed to not be too high and not be too low :).	1061	always C<0>, which is supposed to not be too high and not be too low :).
887		1062
888	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1063	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
889	fine, as long as you do not mind that the priority value you query might	1064	fine, as long as you do not mind that the priority value you query might
890	or might not have been adjusted to be within valid range.	1065	or might not have been clamped to the valid range.
891		1066
892	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1067	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
893		1068
894	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1069	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
895	C<loop> nor C<revents> need to be valid as long as the watcher callback	1070	C<loop> nor C<revents> need to be valid as long as the watcher callback
896	can deal with that fact.	1071	can deal with that fact, as both are simply passed through to the
		1072	callback.
897		1073
898	=item int ev_clear_pending (loop, ev_TYPE *watcher)	1074	=item int ev_clear_pending (loop, ev_TYPE *watcher)
899		1075
900	If the watcher is pending, this function returns clears its pending status	1076	If the watcher is pending, this function clears its pending status and
901	and returns its C<revents> bitset (as if its callback was invoked). If the	1077	returns its C<revents> bitset (as if its callback was invoked). If the
902	watcher isn't pending it does nothing and returns C<0>.	1078	watcher isn't pending it does nothing and returns C<0>.
903		1079
		1080	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1081	callback to be invoked, which can be accomplished with this function.
		1082
904	=back	1083	=back
905		1084
906		1085
907	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1086	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
908		1087
909	Each watcher has, by default, a member C<void *data> that you can change	1088	Each watcher has, by default, a member C<void *data> that you can change
910	and read at any time, libev will completely ignore it. This can be used	1089	and read at any time: libev will completely ignore it. This can be used
911	to associate arbitrary data with your watcher. If you need more data and	1090	to associate arbitrary data with your watcher. If you need more data and
912	don't want to allocate memory and store a pointer to it in that data	1091	don't want to allocate memory and store a pointer to it in that data
913	member, you can also "subclass" the watcher type and provide your own	1092	member, you can also "subclass" the watcher type and provide your own
914	data:	1093	data:
915		1094
916	struct my_io	1095	struct my_io
917	{	1096	{
918	struct ev_io io;	1097	ev_io io;
919	int otherfd;	1098	int otherfd;
920	void *somedata;	1099	void *somedata;
921	struct whatever *mostinteresting;	1100	struct whatever *mostinteresting;
922	}	1101	};
		1102
		1103	...
		1104	struct my_io w;
		1105	ev_io_init (&w.io, my_cb, fd, EV_READ);
923		1106
924	And since your callback will be called with a pointer to the watcher, you	1107	And since your callback will be called with a pointer to the watcher, you
925	can cast it back to your own type:	1108	can cast it back to your own type:
926		1109
927	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1110	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
928	{	1111	{
929	struct my_io *w = (struct my_io *)w_;	1112	struct my_io *w = (struct my_io *)w_;
930	...	1113	...
931	}	1114	}
932		1115
933	More interesting and less C-conformant ways of casting your callback type	1116	More interesting and less C-conformant ways of casting your callback type
934	instead have been omitted.	1117	instead have been omitted.
935		1118
936	Another common scenario is having some data structure with multiple	1119	Another common scenario is to use some data structure with multiple
937	watchers:	1120	embedded watchers:
938		1121
939	struct my_biggy	1122	struct my_biggy
940	{	1123	{
941	int some_data;	1124	int some_data;
942	ev_timer t1;	1125	ev_timer t1;
943	ev_timer t2;	1126	ev_timer t2;
944	}	1127	}
945		1128
946	In this case getting the pointer to C<my_biggy> is a bit more complicated,	1129	In this case getting the pointer to C<my_biggy> is a bit more
947	you need to use C<offsetof>:	1130	complicated: Either you store the address of your C<my_biggy> struct
		1131	in the C<data> member of the watcher (for woozies), or you need to use
		1132	some pointer arithmetic using C<offsetof> inside your watchers (for real
		1133	programmers):
948		1134
949	#include <stddef.h>	1135	#include <stddef.h>
950		1136
951	static void	1137	static void
952	t1_cb (EV_P_ struct ev_timer *w, int revents)	1138	t1_cb (EV_P_ ev_timer *w, int revents)
953	{	1139	{
954	struct my_biggy big = (struct my_biggy *	1140	struct my_biggy big = (struct my_biggy *
955	(((char *)w) - offsetof (struct my_biggy, t1));	1141	(((char *)w) - offsetof (struct my_biggy, t1));
956	}	1142	}
957		1143
958	static void	1144	static void
959	t2_cb (EV_P_ struct ev_timer *w, int revents)	1145	t2_cb (EV_P_ ev_timer *w, int revents)
960	{	1146	{
961	struct my_biggy big = (struct my_biggy *	1147	struct my_biggy big = (struct my_biggy *
962	(((char *)w) - offsetof (struct my_biggy, t2));	1148	(((char *)w) - offsetof (struct my_biggy, t2));
963	}	1149	}
964		1150
965		1151
966	=head1 WATCHER TYPES	1152	=head1 WATCHER TYPES
967		1153
968	This section describes each watcher in detail, but will not repeat	1154	This section describes each watcher in detail, but will not repeat
…		…
992	In general you can register as many read and/or write event watchers per	1178	In general you can register as many read and/or write event watchers per
993	fd as you want (as long as you don't confuse yourself). Setting all file	1179	fd as you want (as long as you don't confuse yourself). Setting all file
994	descriptors to non-blocking mode is also usually a good idea (but not	1180	descriptors to non-blocking mode is also usually a good idea (but not
995	required if you know what you are doing).	1181	required if you know what you are doing).
996		1182
997	If you must do this, then force the use of a known-to-be-good backend	1183	If you cannot use non-blocking mode, then force the use of a
998	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and	1184	known-to-be-good backend (at the time of this writing, this includes only
999	C<EVBACKEND_POLL>).	1185	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>).
1000		1186
1001	Another thing you have to watch out for is that it is quite easy to	1187	Another thing you have to watch out for is that it is quite easy to
1002	receive "spurious" readyness notifications, that is your callback might	1188	receive "spurious" readiness notifications, that is your callback might
1003	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1189	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1004	because there is no data. Not only are some backends known to create a	1190	because there is no data. Not only are some backends known to create a
1005	lot of those (for example solaris ports), it is very easy to get into	1191	lot of those (for example Solaris ports), it is very easy to get into
1006	this situation even with a relatively standard program structure. Thus	1192	this situation even with a relatively standard program structure. Thus
1007	it is best to always use non-blocking I/O: An extra C<read>(2) returning	1193	it is best to always use non-blocking I/O: An extra C<read>(2) returning
1008	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1194	C<EAGAIN> is far preferable to a program hanging until some data arrives.
1009		1195
1010	If you cannot run the fd in non-blocking mode (for example you should not	1196	If you cannot run the fd in non-blocking mode (for example you should
1011	play around with an Xlib connection), then you have to seperately re-test	1197	not play around with an Xlib connection), then you have to separately
1012	whether a file descriptor is really ready with a known-to-be good interface	1198	re-test whether a file descriptor is really ready with a known-to-be good
1013	such as poll (fortunately in our Xlib example, Xlib already does this on	1199	interface such as poll (fortunately in our Xlib example, Xlib already
1014	its own, so its quite safe to use).	1200	does this on its own, so its quite safe to use). Some people additionally
		1201	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1202	indefinitely.
		1203
		1204	But really, best use non-blocking mode.
1015		1205
1016	=head3 The special problem of disappearing file descriptors	1206	=head3 The special problem of disappearing file descriptors
1017		1207
1018	Some backends (e.g. kqueue, epoll) need to be told about closing a file	1208	Some backends (e.g. kqueue, epoll) need to be told about closing a file
1019	descriptor (either by calling C<close> explicitly or by any other means,	1209	descriptor (either due to calling C<close> explicitly or any other means,
1020	such as C<dup>). The reason is that you register interest in some file	1210	such as C<dup2>). The reason is that you register interest in some file
1021	descriptor, but when it goes away, the operating system will silently drop	1211	descriptor, but when it goes away, the operating system will silently drop
1022	this interest. If another file descriptor with the same number then is	1212	this interest. If another file descriptor with the same number then is
1023	registered with libev, there is no efficient way to see that this is, in	1213	registered with libev, there is no efficient way to see that this is, in
1024	fact, a different file descriptor.	1214	fact, a different file descriptor.
1025		1215
…		…
1054	To support fork in your programs, you either have to call	1244	To support fork in your programs, you either have to call
1055	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,	1245	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
1056	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1246	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
1057	C<EVBACKEND_POLL>.	1247	C<EVBACKEND_POLL>.
1058		1248
		1249	=head3 The special problem of SIGPIPE
		1250
		1251	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1252	when writing to a pipe whose other end has been closed, your program gets
		1253	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1254	this is sensible behaviour, for daemons, this is usually undesirable.
		1255
		1256	So when you encounter spurious, unexplained daemon exits, make sure you
		1257	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1258	somewhere, as that would have given you a big clue).
		1259
1059		1260
1060	=head3 Watcher-Specific Functions	1261	=head3 Watcher-Specific Functions
1061		1262
1062	=over 4	1263	=over 4
1063		1264
1064	=item ev_io_init (ev_io *, callback, int fd, int events)	1265	=item ev_io_init (ev_io *, callback, int fd, int events)
1065		1266
1066	=item ev_io_set (ev_io *, int fd, int events)	1267	=item ev_io_set (ev_io *, int fd, int events)
1067		1268
1068	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1269	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
1069	rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or	1270	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
1070	C<EV_READ | EV_WRITE> to receive the given events.	1271	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
1071		1272
1072	=item int fd [read-only]	1273	=item int fd [read-only]
1073		1274
1074	The file descriptor being watched.	1275	The file descriptor being watched.
1075		1276
…		…
1083		1284
1084	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1285	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
1085	readable, but only once. Since it is likely line-buffered, you could	1286	readable, but only once. Since it is likely line-buffered, you could
1086	attempt to read a whole line in the callback.	1287	attempt to read a whole line in the callback.
1087		1288
1088	static void	1289	static void
1089	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1290	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
1090	{	1291	{
1091	ev_io_stop (loop, w);	1292	ev_io_stop (loop, w);
1092	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1293	.. read from stdin here (or from w->fd) and handle any I/O errors
1093	}	1294	}
1094		1295
1095	...	1296	...
1096	struct ev_loop *loop = ev_default_init (0);	1297	struct ev_loop *loop = ev_default_init (0);
1097	struct ev_io stdin_readable;	1298	ev_io stdin_readable;
1098	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1299	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1099	ev_io_start (loop, &stdin_readable);	1300	ev_io_start (loop, &stdin_readable);
1100	ev_loop (loop, 0);	1301	ev_loop (loop, 0);
1101		1302
1102		1303
1103	=head2 C<ev_timer> - relative and optionally repeating timeouts	1304	=head2 C<ev_timer> - relative and optionally repeating timeouts
1104		1305
1105	Timer watchers are simple relative timers that generate an event after a	1306	Timer watchers are simple relative timers that generate an event after a
1106	given time, and optionally repeating in regular intervals after that.	1307	given time, and optionally repeating in regular intervals after that.
1107		1308
1108	The timers are based on real time, that is, if you register an event that	1309	The timers are based on real time, that is, if you register an event that
1109	times out after an hour and you reset your system clock to last years	1310	times out after an hour and you reset your system clock to January last
1110	time, it will still time out after (roughly) and hour. "Roughly" because	1311	year, it will still time out after (roughly) one hour. "Roughly" because
1111	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1312	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1112	monotonic clock option helps a lot here).	1313	monotonic clock option helps a lot here).
		1314
		1315	The callback is guaranteed to be invoked only I<after> its timeout has
		1316	passed, but if multiple timers become ready during the same loop iteration
		1317	then order of execution is undefined.
		1318
		1319	=head3 Be smart about timeouts
		1320
		1321	Many real-world problems involve some kind of timeout, usually for error
		1322	recovery. A typical example is an HTTP request - if the other side hangs,
		1323	you want to raise some error after a while.
		1324
		1325	What follows are some ways to handle this problem, from obvious and
		1326	inefficient to smart and efficient.
		1327
		1328	In the following, a 60 second activity timeout is assumed - a timeout that
		1329	gets reset to 60 seconds each time there is activity (e.g. each time some
		1330	data or other life sign was received).
		1331
		1332	=over 4
		1333
		1334	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1335
		1336	This is the most obvious, but not the most simple way: In the beginning,
		1337	start the watcher:
		1338
		1339	ev_timer_init (timer, callback, 60., 0.);
		1340	ev_timer_start (loop, timer);
		1341
		1342	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1343	and start it again:
		1344
		1345	ev_timer_stop (loop, timer);
		1346	ev_timer_set (timer, 60., 0.);
		1347	ev_timer_start (loop, timer);
		1348
		1349	This is relatively simple to implement, but means that each time there is
		1350	some activity, libev will first have to remove the timer from its internal
		1351	data structure and then add it again. Libev tries to be fast, but it's
		1352	still not a constant-time operation.
		1353
		1354	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1355
		1356	This is the easiest way, and involves using C<ev_timer_again> instead of
		1357	C<ev_timer_start>.
		1358
		1359	To implement this, configure an C<ev_timer> with a C<repeat> value
		1360	of C<60> and then call C<ev_timer_again> at start and each time you
		1361	successfully read or write some data. If you go into an idle state where
		1362	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1363	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1364
		1365	That means you can ignore both the C<ev_timer_start> function and the
		1366	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1367	member and C<ev_timer_again>.
		1368
		1369	At start:
		1370
		1371	ev_timer_init (timer, callback);
		1372	timer->repeat = 60.;
		1373	ev_timer_again (loop, timer);
		1374
		1375	Each time there is some activity:
		1376
		1377	ev_timer_again (loop, timer);
		1378
		1379	It is even possible to change the time-out on the fly, regardless of
		1380	whether the watcher is active or not:
		1381
		1382	timer->repeat = 30.;
		1383	ev_timer_again (loop, timer);
		1384
		1385	This is slightly more efficient then stopping/starting the timer each time
		1386	you want to modify its timeout value, as libev does not have to completely
		1387	remove and re-insert the timer from/into its internal data structure.
		1388
		1389	It is, however, even simpler than the "obvious" way to do it.
		1390
		1391	=item 3. Let the timer time out, but then re-arm it as required.
		1392
		1393	This method is more tricky, but usually most efficient: Most timeouts are
		1394	relatively long compared to the intervals between other activity - in
		1395	our example, within 60 seconds, there are usually many I/O events with
		1396	associated activity resets.
		1397
		1398	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1399	but remember the time of last activity, and check for a real timeout only
		1400	within the callback:
		1401
		1402	ev_tstamp last_activity; // time of last activity
		1403
		1404	static void
		1405	callback (EV_P_ ev_timer *w, int revents)
		1406	{
		1407	ev_tstamp now = ev_now (EV_A);
		1408	ev_tstamp timeout = last_activity + 60.;
		1409
		1410	// if last_activity + 60. is older than now, we did time out
		1411	if (timeout < now)
		1412	{
		1413	// timeout occured, take action
		1414	}
		1415	else
		1416	{
		1417	// callback was invoked, but there was some activity, re-arm
		1418	// the watcher to fire in last_activity + 60, which is
		1419	// guaranteed to be in the future, so "again" is positive:
		1420	w->again = timeout - now;
		1421	ev_timer_again (EV_A_ w);
		1422	}
		1423	}
		1424
		1425	To summarise the callback: first calculate the real timeout (defined
		1426	as "60 seconds after the last activity"), then check if that time has
		1427	been reached, which means something I<did>, in fact, time out. Otherwise
		1428	the callback was invoked too early (C<timeout> is in the future), so
		1429	re-schedule the timer to fire at that future time, to see if maybe we have
		1430	a timeout then.
		1431
		1432	Note how C<ev_timer_again> is used, taking advantage of the
		1433	C<ev_timer_again> optimisation when the timer is already running.
		1434
		1435	This scheme causes more callback invocations (about one every 60 seconds
		1436	minus half the average time between activity), but virtually no calls to
		1437	libev to change the timeout.
		1438
		1439	To start the timer, simply initialise the watcher and set C<last_activity>
		1440	to the current time (meaning we just have some activity :), then call the
		1441	callback, which will "do the right thing" and start the timer:
		1442
		1443	ev_timer_init (timer, callback);
		1444	last_activity = ev_now (loop);
		1445	callback (loop, timer, EV_TIMEOUT);
		1446
		1447	And when there is some activity, simply store the current time in
		1448	C<last_activity>, no libev calls at all:
		1449
		1450	last_actiivty = ev_now (loop);
		1451
		1452	This technique is slightly more complex, but in most cases where the
		1453	time-out is unlikely to be triggered, much more efficient.
		1454
		1455	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1456	callback :) - just change the timeout and invoke the callback, which will
		1457	fix things for you.
		1458
		1459	=item 4. Wee, just use a double-linked list for your timeouts.
		1460
		1461	If there is not one request, but many thousands (millions...), all
		1462	employing some kind of timeout with the same timeout value, then one can
		1463	do even better:
		1464
		1465	When starting the timeout, calculate the timeout value and put the timeout
		1466	at the I<end> of the list.
		1467
		1468	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1469	the list is expected to fire (for example, using the technique #3).
		1470
		1471	When there is some activity, remove the timer from the list, recalculate
		1472	the timeout, append it to the end of the list again, and make sure to
		1473	update the C<ev_timer> if it was taken from the beginning of the list.
		1474
		1475	This way, one can manage an unlimited number of timeouts in O(1) time for
		1476	starting, stopping and updating the timers, at the expense of a major
		1477	complication, and having to use a constant timeout. The constant timeout
		1478	ensures that the list stays sorted.
		1479
		1480	=back
		1481
		1482	So which method the best?
		1483
		1484	Method #2 is a simple no-brain-required solution that is adequate in most
		1485	situations. Method #3 requires a bit more thinking, but handles many cases
		1486	better, and isn't very complicated either. In most case, choosing either
		1487	one is fine, with #3 being better in typical situations.
		1488
		1489	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1490	rather complicated, but extremely efficient, something that really pays
		1491	off after the first million or so of active timers, i.e. it's usually
		1492	overkill :)
		1493
		1494	=head3 The special problem of time updates
		1495
		1496	Establishing the current time is a costly operation (it usually takes at
		1497	least two system calls): EV therefore updates its idea of the current
		1498	time only before and after C<ev_loop> collects new events, which causes a
		1499	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		1500	lots of events in one iteration.
1113		1501
1114	The relative timeouts are calculated relative to the C<ev_now ()>	1502	The relative timeouts are calculated relative to the C<ev_now ()>
1115	time. This is usually the right thing as this timestamp refers to the time	1503	time. This is usually the right thing as this timestamp refers to the time
1116	of the event triggering whatever timeout you are modifying/starting. If	1504	of the event triggering whatever timeout you are modifying/starting. If
1117	you suspect event processing to be delayed and you I<need> to base the timeout	1505	you suspect event processing to be delayed and you I<need> to base the
1118	on the current time, use something like this to adjust for this:	1506	timeout on the current time, use something like this to adjust for this:
1119		1507
1120	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1508	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
1121		1509
1122	The callback is guarenteed to be invoked only when its timeout has passed,	1510	If the event loop is suspended for a long time, you can also force an
1123	but if multiple timers become ready during the same loop iteration then	1511	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1124	order of execution is undefined.	1512	()>.
1125		1513
1126	=head3 Watcher-Specific Functions and Data Members	1514	=head3 Watcher-Specific Functions and Data Members
1127		1515
1128	=over 4	1516	=over 4
1129		1517
1130	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1518	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
1131		1519
1132	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	1520	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
1133		1521
1134	Configure the timer to trigger after C<after> seconds. If C<repeat> is	1522	Configure the timer to trigger after C<after> seconds. If C<repeat>
1135	C<0.>, then it will automatically be stopped. If it is positive, then the	1523	is C<0.>, then it will automatically be stopped once the timeout is
1136	timer will automatically be configured to trigger again C<repeat> seconds	1524	reached. If it is positive, then the timer will automatically be
1137	later, again, and again, until stopped manually.	1525	configured to trigger again C<repeat> seconds later, again, and again,
		1526	until stopped manually.
1138		1527
1139	The timer itself will do a best-effort at avoiding drift, that is, if you	1528	The timer itself will do a best-effort at avoiding drift, that is, if
1140	configure a timer to trigger every 10 seconds, then it will trigger at	1529	you configure a timer to trigger every 10 seconds, then it will normally
1141	exactly 10 second intervals. If, however, your program cannot keep up with	1530	trigger at exactly 10 second intervals. If, however, your program cannot
1142	the timer (because it takes longer than those 10 seconds to do stuff) the	1531	keep up with the timer (because it takes longer than those 10 seconds to
1143	timer will not fire more than once per event loop iteration.	1532	do stuff) the timer will not fire more than once per event loop iteration.
1144		1533
1145	=item ev_timer_again (loop)	1534	=item ev_timer_again (loop, ev_timer *)
1146		1535
1147	This will act as if the timer timed out and restart it again if it is	1536	This will act as if the timer timed out and restart it again if it is
1148	repeating. The exact semantics are:	1537	repeating. The exact semantics are:
1149		1538
1150	If the timer is pending, its pending status is cleared.	1539	If the timer is pending, its pending status is cleared.
1151		1540
1152	If the timer is started but nonrepeating, stop it (as if it timed out).	1541	If the timer is started but non-repeating, stop it (as if it timed out).
1153		1542
1154	If the timer is repeating, either start it if necessary (with the	1543	If the timer is repeating, either start it if necessary (with the
1155	C<repeat> value), or reset the running timer to the C<repeat> value.	1544	C<repeat> value), or reset the running timer to the C<repeat> value.
1156		1545
1157	This sounds a bit complicated, but here is a useful and typical	1546	This sounds a bit complicated, see "Be smart about timeouts", above, for a
1158	example: Imagine you have a tcp connection and you want a so-called idle	1547	usage example.
1159	timeout, that is, you want to be called when there have been, say, 60
1160	seconds of inactivity on the socket. The easiest way to do this is to
1161	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
1162	C<ev_timer_again> each time you successfully read or write some data. If
1163	you go into an idle state where you do not expect data to travel on the
1164	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
1165	automatically restart it if need be.
1166
1167	That means you can ignore the C<after> value and C<ev_timer_start>
1168	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
1169
1170	ev_timer_init (timer, callback, 0., 5.);
1171	ev_timer_again (loop, timer);
1172	...
1173	timer->again = 17.;
1174	ev_timer_again (loop, timer);
1175	...
1176	timer->again = 10.;
1177	ev_timer_again (loop, timer);
1178
1179	This is more slightly efficient then stopping/starting the timer each time
1180	you want to modify its timeout value.
1181		1548
1182	=item ev_tstamp repeat [read-write]	1549	=item ev_tstamp repeat [read-write]
1183		1550
1184	The current C<repeat> value. Will be used each time the watcher times out	1551	The current C<repeat> value. Will be used each time the watcher times out
1185	or C<ev_timer_again> is called and determines the next timeout (if any),	1552	or C<ev_timer_again> is called, and determines the next timeout (if any),
1186	which is also when any modifications are taken into account.	1553	which is also when any modifications are taken into account.
1187		1554
1188	=back	1555	=back
1189		1556
1190	=head3 Examples	1557	=head3 Examples
1191		1558
1192	Example: Create a timer that fires after 60 seconds.	1559	Example: Create a timer that fires after 60 seconds.
1193		1560
1194	static void	1561	static void
1195	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1562	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1196	{	1563	{
1197	.. one minute over, w is actually stopped right here	1564	.. one minute over, w is actually stopped right here
1198	}	1565	}
1199		1566
1200	struct ev_timer mytimer;	1567	ev_timer mytimer;
1201	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	1568	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1202	ev_timer_start (loop, &mytimer);	1569	ev_timer_start (loop, &mytimer);
1203		1570
1204	Example: Create a timeout timer that times out after 10 seconds of	1571	Example: Create a timeout timer that times out after 10 seconds of
1205	inactivity.	1572	inactivity.
1206		1573
1207	static void	1574	static void
1208	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1575	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1209	{	1576	{
1210	.. ten seconds without any activity	1577	.. ten seconds without any activity
1211	}	1578	}
1212		1579
1213	struct ev_timer mytimer;	1580	ev_timer mytimer;
1214	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	1581	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1215	ev_timer_again (&mytimer); /* start timer */	1582	ev_timer_again (&mytimer); /* start timer */
1216	ev_loop (loop, 0);	1583	ev_loop (loop, 0);
1217		1584
1218	// and in some piece of code that gets executed on any "activity":	1585	// and in some piece of code that gets executed on any "activity":
1219	// reset the timeout to start ticking again at 10 seconds	1586	// reset the timeout to start ticking again at 10 seconds
1220	ev_timer_again (&mytimer);	1587	ev_timer_again (&mytimer);
1221		1588
1222		1589
1223	=head2 C<ev_periodic> - to cron or not to cron?	1590	=head2 C<ev_periodic> - to cron or not to cron?
1224		1591
1225	Periodic watchers are also timers of a kind, but they are very versatile	1592	Periodic watchers are also timers of a kind, but they are very versatile
1226	(and unfortunately a bit complex).	1593	(and unfortunately a bit complex).
1227		1594
1228	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1595	Unlike C<ev_timer>'s, they are not based on real time (or relative time)
1229	but on wallclock time (absolute time). You can tell a periodic watcher	1596	but on wall clock time (absolute time). You can tell a periodic watcher
1230	to trigger "at" some specific point in time. For example, if you tell a	1597	to trigger after some specific point in time. For example, if you tell a
1231	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()	1598	periodic watcher to trigger in 10 seconds (by specifying e.g. C<ev_now ()
1232	+ 10.>) and then reset your system clock to the last year, then it will	1599	+ 10.>, that is, an absolute time not a delay) and then reset your system
		1600	clock to January of the previous year, then it will take more than year
1233	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	1601	to trigger the event (unlike an C<ev_timer>, which would still trigger
1234	roughly 10 seconds later).	1602	roughly 10 seconds later as it uses a relative timeout).
1235		1603
1236	They can also be used to implement vastly more complex timers, such as	1604	C<ev_periodic>s can also be used to implement vastly more complex timers,
1237	triggering an event on each midnight, local time or other, complicated,	1605	such as triggering an event on each "midnight, local time", or other
1238	rules.	1606	complicated rules.
1239		1607
1240	As with timers, the callback is guarenteed to be invoked only when the	1608	As with timers, the callback is guaranteed to be invoked only when the
1241	time (C<at>) has been passed, but if multiple periodic timers become ready	1609	time (C<at>) has passed, but if multiple periodic timers become ready
1242	during the same loop iteration then order of execution is undefined.	1610	during the same loop iteration, then order of execution is undefined.
1243		1611
1244	=head3 Watcher-Specific Functions and Data Members	1612	=head3 Watcher-Specific Functions and Data Members
1245		1613
1246	=over 4	1614	=over 4
1247		1615
1248	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1616	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)
1249		1617
1250	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1618	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)
1251		1619
1252	Lots of arguments, lets sort it out... There are basically three modes of	1620	Lots of arguments, lets sort it out... There are basically three modes of
1253	operation, and we will explain them from simplest to complex:	1621	operation, and we will explain them from simplest to most complex:
1254		1622
1255	=over 4	1623	=over 4
1256		1624
1257	=item * absolute timer (at = time, interval = reschedule_cb = 0)	1625	=item * absolute timer (at = time, interval = reschedule_cb = 0)
1258		1626
1259	In this configuration the watcher triggers an event at the wallclock time	1627	In this configuration the watcher triggers an event after the wall clock
1260	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	1628	time C<at> has passed. It will not repeat and will not adjust when a time
1261	that is, if it is to be run at January 1st 2011 then it will run when the	1629	jump occurs, that is, if it is to be run at January 1st 2011 then it will
1262	system time reaches or surpasses this time.	1630	only run when the system clock reaches or surpasses this time.
1263		1631
1264	=item * non-repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	1632	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)
1265		1633
1266	In this mode the watcher will always be scheduled to time out at the next	1634	In this mode the watcher will always be scheduled to time out at the next
1267	C<at + N * interval> time (for some integer N, which can also be negative)	1635	C<at + N * interval> time (for some integer N, which can also be negative)
1268	and then repeat, regardless of any time jumps.	1636	and then repeat, regardless of any time jumps.
1269		1637
1270	This can be used to create timers that do not drift with respect to system	1638	This can be used to create timers that do not drift with respect to the
1271	time:	1639	system clock, for example, here is a C<ev_periodic> that triggers each
		1640	hour, on the hour:
1272		1641
1273	ev_periodic_set (&periodic, 0., 3600., 0);	1642	ev_periodic_set (&periodic, 0., 3600., 0);
1274		1643
1275	This doesn't mean there will always be 3600 seconds in between triggers,	1644	This doesn't mean there will always be 3600 seconds in between triggers,
1276	but only that the the callback will be called when the system time shows a	1645	but only that the callback will be called when the system time shows a
1277	full hour (UTC), or more correctly, when the system time is evenly divisible	1646	full hour (UTC), or more correctly, when the system time is evenly divisible
1278	by 3600.	1647	by 3600.
1279		1648
1280	Another way to think about it (for the mathematically inclined) is that	1649	Another way to think about it (for the mathematically inclined) is that
1281	C<ev_periodic> will try to run the callback in this mode at the next possible	1650	C<ev_periodic> will try to run the callback in this mode at the next possible
1282	time where C<time = at (mod interval)>, regardless of any time jumps.	1651	time where C<time = at (mod interval)>, regardless of any time jumps.
1283		1652
1284	For numerical stability it is preferable that the C<at> value is near	1653	For numerical stability it is preferable that the C<at> value is near
1285	C<ev_now ()> (the current time), but there is no range requirement for	1654	C<ev_now ()> (the current time), but there is no range requirement for
1286	this value.	1655	this value, and in fact is often specified as zero.
		1656
		1657	Note also that there is an upper limit to how often a timer can fire (CPU
		1658	speed for example), so if C<interval> is very small then timing stability
		1659	will of course deteriorate. Libev itself tries to be exact to be about one
		1660	millisecond (if the OS supports it and the machine is fast enough).
1287		1661
1288	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	1662	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)
1289		1663
1290	In this mode the values for C<interval> and C<at> are both being	1664	In this mode the values for C<interval> and C<at> are both being
1291	ignored. Instead, each time the periodic watcher gets scheduled, the	1665	ignored. Instead, each time the periodic watcher gets scheduled, the
1292	reschedule callback will be called with the watcher as first, and the	1666	reschedule callback will be called with the watcher as first, and the
1293	current time as second argument.	1667	current time as second argument.
1294		1668
1295	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	1669	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,
1296	ever, or make any event loop modifications>. If you need to stop it,	1670	ever, or make ANY event loop modifications whatsoever>.
1297	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by
1298	starting an C<ev_prepare> watcher, which is legal).
1299		1671
		1672	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		1673	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		1674	only event loop modification you are allowed to do).
		1675
1300	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	1676	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1301	ev_tstamp now)>, e.g.:	1677	*w, ev_tstamp now)>, e.g.:
1302		1678
		1679	static ev_tstamp
1303	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1680	my_rescheduler (ev_periodic *w, ev_tstamp now)
1304	{	1681	{
1305	return now + 60.;	1682	return now + 60.;
1306	}	1683	}
1307		1684
1308	It must return the next time to trigger, based on the passed time value	1685	It must return the next time to trigger, based on the passed time value
1309	(that is, the lowest time value larger than to the second argument). It	1686	(that is, the lowest time value larger than to the second argument). It
1310	will usually be called just before the callback will be triggered, but	1687	will usually be called just before the callback will be triggered, but
1311	might be called at other times, too.	1688	might be called at other times, too.
1312		1689
1313	NOTE: I<< This callback must always return a time that is later than the	1690	NOTE: I<< This callback must always return a time that is higher than or
1314	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	1691	equal to the passed C<now> value >>.
1315		1692
1316	This can be used to create very complex timers, such as a timer that	1693	This can be used to create very complex timers, such as a timer that
1317	triggers on each midnight, local time. To do this, you would calculate the	1694	triggers on "next midnight, local time". To do this, you would calculate the
1318	next midnight after C<now> and return the timestamp value for this. How	1695	next midnight after C<now> and return the timestamp value for this. How
1319	you do this is, again, up to you (but it is not trivial, which is the main	1696	you do this is, again, up to you (but it is not trivial, which is the main
1320	reason I omitted it as an example).	1697	reason I omitted it as an example).
1321		1698
1322	=back	1699	=back
…		…
1326	Simply stops and restarts the periodic watcher again. This is only useful	1703	Simply stops and restarts the periodic watcher again. This is only useful
1327	when you changed some parameters or the reschedule callback would return	1704	when you changed some parameters or the reschedule callback would return
1328	a different time than the last time it was called (e.g. in a crond like	1705	a different time than the last time it was called (e.g. in a crond like
1329	program when the crontabs have changed).	1706	program when the crontabs have changed).
1330		1707
		1708	=item ev_tstamp ev_periodic_at (ev_periodic *)
		1709
		1710	When active, returns the absolute time that the watcher is supposed to
		1711	trigger next.
		1712
1331	=item ev_tstamp offset [read-write]	1713	=item ev_tstamp offset [read-write]
1332		1714
1333	When repeating, this contains the offset value, otherwise this is the	1715	When repeating, this contains the offset value, otherwise this is the
1334	absolute point in time (the C<at> value passed to C<ev_periodic_set>).	1716	absolute point in time (the C<at> value passed to C<ev_periodic_set>).
1335		1717
…		…
1340		1722
1341	The current interval value. Can be modified any time, but changes only	1723	The current interval value. Can be modified any time, but changes only
1342	take effect when the periodic timer fires or C<ev_periodic_again> is being	1724	take effect when the periodic timer fires or C<ev_periodic_again> is being
1343	called.	1725	called.
1344		1726
1345	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	1727	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1346		1728
1347	The current reschedule callback, or C<0>, if this functionality is	1729	The current reschedule callback, or C<0>, if this functionality is
1348	switched off. Can be changed any time, but changes only take effect when	1730	switched off. Can be changed any time, but changes only take effect when
1349	the periodic timer fires or C<ev_periodic_again> is being called.	1731	the periodic timer fires or C<ev_periodic_again> is being called.
1350		1732
1351	=item ev_tstamp at [read-only]
1352
1353	When active, contains the absolute time that the watcher is supposed to
1354	trigger next.
1355
1356	=back	1733	=back
1357		1734
1358	=head3 Examples	1735	=head3 Examples
1359		1736
1360	Example: Call a callback every hour, or, more precisely, whenever the	1737	Example: Call a callback every hour, or, more precisely, whenever the
1361	system clock is divisible by 3600. The callback invocation times have	1738	system time is divisible by 3600. The callback invocation times have
1362	potentially a lot of jittering, but good long-term stability.	1739	potentially a lot of jitter, but good long-term stability.
1363		1740
1364	static void	1741	static void
1365	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1742	clock_cb (struct ev_loop *loop, ev_io *w, int revents)
1366	{	1743	{
1367	... its now a full hour (UTC, or TAI or whatever your clock follows)	1744	... its now a full hour (UTC, or TAI or whatever your clock follows)
1368	}	1745	}
1369		1746
1370	struct ev_periodic hourly_tick;	1747	ev_periodic hourly_tick;
1371	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	1748	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1372	ev_periodic_start (loop, &hourly_tick);	1749	ev_periodic_start (loop, &hourly_tick);
1373		1750
1374	Example: The same as above, but use a reschedule callback to do it:	1751	Example: The same as above, but use a reschedule callback to do it:
1375		1752
1376	#include <math.h>	1753	#include <math.h>
1377		1754
1378	static ev_tstamp	1755	static ev_tstamp
1379	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	1756	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1380	{	1757	{
1381	return fmod (now, 3600.) + 3600.;	1758	return now + (3600. - fmod (now, 3600.));
1382	}	1759	}
1383		1760
1384	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	1761	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1385		1762
1386	Example: Call a callback every hour, starting now:	1763	Example: Call a callback every hour, starting now:
1387		1764
1388	struct ev_periodic hourly_tick;	1765	ev_periodic hourly_tick;
1389	ev_periodic_init (&hourly_tick, clock_cb,	1766	ev_periodic_init (&hourly_tick, clock_cb,
1390	fmod (ev_now (loop), 3600.), 3600., 0);	1767	fmod (ev_now (loop), 3600.), 3600., 0);
1391	ev_periodic_start (loop, &hourly_tick);	1768	ev_periodic_start (loop, &hourly_tick);
1392		1769
1393		1770
1394	=head2 C<ev_signal> - signal me when a signal gets signalled!	1771	=head2 C<ev_signal> - signal me when a signal gets signalled!
1395		1772
1396	Signal watchers will trigger an event when the process receives a specific	1773	Signal watchers will trigger an event when the process receives a specific
1397	signal one or more times. Even though signals are very asynchronous, libev	1774	signal one or more times. Even though signals are very asynchronous, libev
1398	will try it's best to deliver signals synchronously, i.e. as part of the	1775	will try it's best to deliver signals synchronously, i.e. as part of the
1399	normal event processing, like any other event.	1776	normal event processing, like any other event.
1400		1777
		1778	If you want signals asynchronously, just use C<sigaction> as you would
		1779	do without libev and forget about sharing the signal. You can even use
		1780	C<ev_async> from a signal handler to synchronously wake up an event loop.
		1781
1401	You can configure as many watchers as you like per signal. Only when the	1782	You can configure as many watchers as you like per signal. Only when the
1402	first watcher gets started will libev actually register a signal watcher	1783	first watcher gets started will libev actually register a signal handler
1403	with the kernel (thus it coexists with your own signal handlers as long	1784	with the kernel (thus it coexists with your own signal handlers as long as
1404	as you don't register any with libev). Similarly, when the last signal	1785	you don't register any with libev for the same signal). Similarly, when
1405	watcher for a signal is stopped libev will reset the signal handler to	1786	the last signal watcher for a signal is stopped, libev will reset the
1406	SIG_DFL (regardless of what it was set to before).	1787	signal handler to SIG_DFL (regardless of what it was set to before).
		1788
		1789	If possible and supported, libev will install its handlers with
		1790	C<SA_RESTART> behaviour enabled, so system calls should not be unduly
		1791	interrupted. If you have a problem with system calls getting interrupted by
		1792	signals you can block all signals in an C<ev_check> watcher and unblock
		1793	them in an C<ev_prepare> watcher.
1407		1794
1408	=head3 Watcher-Specific Functions and Data Members	1795	=head3 Watcher-Specific Functions and Data Members
1409		1796
1410	=over 4	1797	=over 4
1411		1798
…		…
1420		1807
1421	The signal the watcher watches out for.	1808	The signal the watcher watches out for.
1422		1809
1423	=back	1810	=back
1424		1811
		1812	=head3 Examples
		1813
		1814	Example: Try to exit cleanly on SIGINT.
		1815
		1816	static void
		1817	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
		1818	{
		1819	ev_unloop (loop, EVUNLOOP_ALL);
		1820	}
		1821
		1822	ev_signal signal_watcher;
		1823	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		1824	ev_signal_start (loop, &signal_watcher);
		1825
1425		1826
1426	=head2 C<ev_child> - watch out for process status changes	1827	=head2 C<ev_child> - watch out for process status changes
1427		1828
1428	Child watchers trigger when your process receives a SIGCHLD in response to	1829	Child watchers trigger when your process receives a SIGCHLD in response to
1429	some child status changes (most typically when a child of yours dies).	1830	some child status changes (most typically when a child of yours dies or
		1831	exits). It is permissible to install a child watcher I<after> the child
		1832	has been forked (which implies it might have already exited), as long
		1833	as the event loop isn't entered (or is continued from a watcher), i.e.,
		1834	forking and then immediately registering a watcher for the child is fine,
		1835	but forking and registering a watcher a few event loop iterations later is
		1836	not.
		1837
		1838	Only the default event loop is capable of handling signals, and therefore
		1839	you can only register child watchers in the default event loop.
		1840
		1841	=head3 Process Interaction
		1842
		1843	Libev grabs C<SIGCHLD> as soon as the default event loop is
		1844	initialised. This is necessary to guarantee proper behaviour even if
		1845	the first child watcher is started after the child exits. The occurrence
		1846	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		1847	synchronously as part of the event loop processing. Libev always reaps all
		1848	children, even ones not watched.
		1849
		1850	=head3 Overriding the Built-In Processing
		1851
		1852	Libev offers no special support for overriding the built-in child
		1853	processing, but if your application collides with libev's default child
		1854	handler, you can override it easily by installing your own handler for
		1855	C<SIGCHLD> after initialising the default loop, and making sure the
		1856	default loop never gets destroyed. You are encouraged, however, to use an
		1857	event-based approach to child reaping and thus use libev's support for
		1858	that, so other libev users can use C<ev_child> watchers freely.
		1859
		1860	=head3 Stopping the Child Watcher
		1861
		1862	Currently, the child watcher never gets stopped, even when the
		1863	child terminates, so normally one needs to stop the watcher in the
		1864	callback. Future versions of libev might stop the watcher automatically
		1865	when a child exit is detected.
1430		1866
1431	=head3 Watcher-Specific Functions and Data Members	1867	=head3 Watcher-Specific Functions and Data Members
1432		1868
1433	=over 4	1869	=over 4
1434		1870
1435	=item ev_child_init (ev_child *, callback, int pid)	1871	=item ev_child_init (ev_child *, callback, int pid, int trace)
1436		1872
1437	=item ev_child_set (ev_child *, int pid)	1873	=item ev_child_set (ev_child *, int pid, int trace)
1438		1874
1439	Configures the watcher to wait for status changes of process C<pid> (or	1875	Configures the watcher to wait for status changes of process C<pid> (or
1440	I<any> process if C<pid> is specified as C<0>). The callback can look	1876	I<any> process if C<pid> is specified as C<0>). The callback can look
1441	at the C<rstatus> member of the C<ev_child> watcher structure to see	1877	at the C<rstatus> member of the C<ev_child> watcher structure to see
1442	the status word (use the macros from C<sys/wait.h> and see your systems	1878	the status word (use the macros from C<sys/wait.h> and see your systems
1443	C<waitpid> documentation). The C<rpid> member contains the pid of the	1879	C<waitpid> documentation). The C<rpid> member contains the pid of the
1444	process causing the status change.	1880	process causing the status change. C<trace> must be either C<0> (only
		1881	activate the watcher when the process terminates) or C<1> (additionally
		1882	activate the watcher when the process is stopped or continued).
1445		1883
1446	=item int pid [read-only]	1884	=item int pid [read-only]
1447		1885
1448	The process id this watcher watches out for, or C<0>, meaning any process id.	1886	The process id this watcher watches out for, or C<0>, meaning any process id.
1449		1887
…		…
1458		1896
1459	=back	1897	=back
1460		1898
1461	=head3 Examples	1899	=head3 Examples
1462		1900
1463	Example: Try to exit cleanly on SIGINT and SIGTERM.	1901	Example: C<fork()> a new process and install a child handler to wait for
		1902	its completion.
1464		1903
		1904	ev_child cw;
		1905
1465	static void	1906	static void
1466	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	1907	child_cb (EV_P_ ev_child *w, int revents)
1467	{	1908	{
1468	ev_unloop (loop, EVUNLOOP_ALL);	1909	ev_child_stop (EV_A_ w);
		1910	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1469	}	1911	}
1470		1912
1471	struct ev_signal signal_watcher;	1913	pid_t pid = fork ();
1472	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	1914
1473	ev_signal_start (loop, &sigint_cb);	1915	if (pid < 0)
		1916	// error
		1917	else if (pid == 0)
		1918	{
		1919	// the forked child executes here
		1920	exit (1);
		1921	}
		1922	else
		1923	{
		1924	ev_child_init (&cw, child_cb, pid, 0);
		1925	ev_child_start (EV_DEFAULT_ &cw);
		1926	}
1474		1927
1475		1928
1476	=head2 C<ev_stat> - did the file attributes just change?	1929	=head2 C<ev_stat> - did the file attributes just change?
1477		1930
1478	This watches a filesystem path for attribute changes. That is, it calls	1931	This watches a file system path for attribute changes. That is, it calls
1479	C<stat> regularly (or when the OS says it changed) and sees if it changed	1932	C<stat> on that path in regular intervals (or when the OS says it changed)
1480	compared to the last time, invoking the callback if it did.	1933	and sees if it changed compared to the last time, invoking the callback if
		1934	it did.
1481		1935
1482	The path does not need to exist: changing from "path exists" to "path does	1936	The path does not need to exist: changing from "path exists" to "path does
1483	not exist" is a status change like any other. The condition "path does	1937	not exist" is a status change like any other. The condition "path does not
1484	not exist" is signified by the C<st_nlink> field being zero (which is	1938	exist" (or more correctly "path cannot be stat'ed") is signified by the
1485	otherwise always forced to be at least one) and all the other fields of	1939	C<st_nlink> field being zero (which is otherwise always forced to be at
1486	the stat buffer having unspecified contents.	1940	least one) and all the other fields of the stat buffer having unspecified
		1941	contents.
1487		1942
1488	The path I<should> be absolute and I<must not> end in a slash. If it is	1943	The path I<must not> end in a slash or contain special components such as
		1944	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1489	relative and your working directory changes, the behaviour is undefined.	1945	your working directory changes, then the behaviour is undefined.
1490		1946
1491	Since there is no standard to do this, the portable implementation simply	1947	Since there is no portable change notification interface available, the
1492	calls C<stat (2)> regularly on the path to see if it changed somehow. You	1948	portable implementation simply calls C<stat(2)> regularly on the path
1493	can specify a recommended polling interval for this case. If you specify	1949	to see if it changed somehow. You can specify a recommended polling
1494	a polling interval of C<0> (highly recommended!) then a I<suitable,	1950	interval for this case. If you specify a polling interval of C<0> (highly
1495	unspecified default> value will be used (which you can expect to be around	1951	recommended!) then a I<suitable, unspecified default> value will be used
1496	five seconds, although this might change dynamically). Libev will also	1952	(which you can expect to be around five seconds, although this might
1497	impose a minimum interval which is currently around C<0.1>, but thats	1953	change dynamically). Libev will also impose a minimum interval which is
1498	usually overkill.	1954	currently around C<0.1>, but that's usually overkill.
1499		1955
1500	This watcher type is not meant for massive numbers of stat watchers,	1956	This watcher type is not meant for massive numbers of stat watchers,
1501	as even with OS-supported change notifications, this can be	1957	as even with OS-supported change notifications, this can be
1502	resource-intensive.	1958	resource-intensive.
1503		1959
1504	At the time of this writing, only the Linux inotify interface is	1960	At the time of this writing, the only OS-specific interface implemented
1505	implemented (implementing kqueue support is left as an exercise for the	1961	is the Linux inotify interface (implementing kqueue support is left as an
1506	reader). Inotify will be used to give hints only and should not change the	1962	exercise for the reader. Note, however, that the author sees no way of
1507	semantics of C<ev_stat> watchers, which means that libev sometimes needs	1963	implementing C<ev_stat> semantics with kqueue, except as a hint).
1508	to fall back to regular polling again even with inotify, but changes are
1509	usually detected immediately, and if the file exists there will be no
1510	polling.
1511		1964
1512	=head3 Inotify	1965	=head3 ABI Issues (Largefile Support)
1513		1966
		1967	Libev by default (unless the user overrides this) uses the default
		1968	compilation environment, which means that on systems with large file
		1969	support disabled by default, you get the 32 bit version of the stat
		1970	structure. When using the library from programs that change the ABI to
		1971	use 64 bit file offsets the programs will fail. In that case you have to
		1972	compile libev with the same flags to get binary compatibility. This is
		1973	obviously the case with any flags that change the ABI, but the problem is
		1974	most noticeably displayed with ev_stat and large file support.
		1975
		1976	The solution for this is to lobby your distribution maker to make large
		1977	file interfaces available by default (as e.g. FreeBSD does) and not
		1978	optional. Libev cannot simply switch on large file support because it has
		1979	to exchange stat structures with application programs compiled using the
		1980	default compilation environment.
		1981
		1982	=head3 Inotify and Kqueue
		1983
1514	When C<inotify (7)> support has been compiled into libev (generally only	1984	When C<inotify (7)> support has been compiled into libev and present at
1515	available on Linux) and present at runtime, it will be used to speed up	1985	runtime, it will be used to speed up change detection where possible. The
1516	change detection where possible. The inotify descriptor will be created lazily	1986	inotify descriptor will be created lazily when the first C<ev_stat>
1517	when the first C<ev_stat> watcher is being started.	1987	watcher is being started.
1518		1988
1519	Inotify presense does not change the semantics of C<ev_stat> watchers	1989	Inotify presence does not change the semantics of C<ev_stat> watchers
1520	except that changes might be detected earlier, and in some cases, to avoid	1990	except that changes might be detected earlier, and in some cases, to avoid
1521	making regular C<stat> calls. Even in the presense of inotify support	1991	making regular C<stat> calls. Even in the presence of inotify support
1522	there are many cases where libev has to resort to regular C<stat> polling.	1992	there are many cases where libev has to resort to regular C<stat> polling,
		1993	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		1994	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		1995	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		1996	xfs are fully working) libev usually gets away without polling.
1523		1997
1524	(There is no support for kqueue, as apparently it cannot be used to	1998	There is no support for kqueue, as apparently it cannot be used to
1525	implement this functionality, due to the requirement of having a file	1999	implement this functionality, due to the requirement of having a file
1526	descriptor open on the object at all times).	2000	descriptor open on the object at all times, and detecting renames, unlinks
		2001	etc. is difficult.
1527		2002
1528	=head3 The special problem of stat time resolution	2003	=head3 The special problem of stat time resolution
1529		2004
1530	The C<stat ()> syscall only supports full-second resolution portably, and	2005	The C<stat ()> system call only supports full-second resolution portably,
1531	even on systems where the resolution is higher, many filesystems still	2006	and even on systems where the resolution is higher, most file systems
1532	only support whole seconds.	2007	still only support whole seconds.
1533		2008
1534	That means that, if the time is the only thing that changes, you might	2009	That means that, if the time is the only thing that changes, you can
1535	miss updates: on the first update, C<ev_stat> detects a change and calls	2010	easily miss updates: on the first update, C<ev_stat> detects a change and
1536	your callback, which does something. When there is another update within	2011	calls your callback, which does something. When there is another update
1537	the same second, C<ev_stat> will be unable to detect it.	2012	within the same second, C<ev_stat> will be unable to detect unless the
		2013	stat data does change in other ways (e.g. file size).
1538		2014
1539	The solution to this is to delay acting on a change for a second (or till	2015	The solution to this is to delay acting on a change for slightly more
1540	the next second boundary), using a roughly one-second delay C<ev_timer>	2016	than a second (or till slightly after the next full second boundary), using
1541	(C<ev_timer_set (w, 0., 1.01); ev_timer_again (loop, w)>). The C<.01>	2017	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
1542	is added to work around small timing inconsistencies of some operating	2018	ev_timer_again (loop, w)>).
1543	systems.	2019
		2020	The C<.02> offset is added to work around small timing inconsistencies
		2021	of some operating systems (where the second counter of the current time
		2022	might be be delayed. One such system is the Linux kernel, where a call to
		2023	C<gettimeofday> might return a timestamp with a full second later than
		2024	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2025	update file times then there will be a small window where the kernel uses
		2026	the previous second to update file times but libev might already execute
		2027	the timer callback).
1544		2028
1545	=head3 Watcher-Specific Functions and Data Members	2029	=head3 Watcher-Specific Functions and Data Members
1546		2030
1547	=over 4	2031	=over 4
1548		2032
…		…
1554	C<path>. The C<interval> is a hint on how quickly a change is expected to	2038	C<path>. The C<interval> is a hint on how quickly a change is expected to
1555	be detected and should normally be specified as C<0> to let libev choose	2039	be detected and should normally be specified as C<0> to let libev choose
1556	a suitable value. The memory pointed to by C<path> must point to the same	2040	a suitable value. The memory pointed to by C<path> must point to the same
1557	path for as long as the watcher is active.	2041	path for as long as the watcher is active.
1558		2042
1559	The callback will be receive C<EV_STAT> when a change was detected,	2043	The callback will receive an C<EV_STAT> event when a change was detected,
1560	relative to the attributes at the time the watcher was started (or the	2044	relative to the attributes at the time the watcher was started (or the
1561	last change was detected).	2045	last change was detected).
1562		2046
1563	=item ev_stat_stat (ev_stat *)	2047	=item ev_stat_stat (loop, ev_stat *)
1564		2048
1565	Updates the stat buffer immediately with new values. If you change the	2049	Updates the stat buffer immediately with new values. If you change the
1566	watched path in your callback, you could call this fucntion to avoid	2050	watched path in your callback, you could call this function to avoid
1567	detecting this change (while introducing a race condition). Can also be	2051	detecting this change (while introducing a race condition if you are not
1568	useful simply to find out the new values.	2052	the only one changing the path). Can also be useful simply to find out the
		2053	new values.
1569		2054
1570	=item ev_statdata attr [read-only]	2055	=item ev_statdata attr [read-only]
1571		2056
1572	The most-recently detected attributes of the file. Although the type is of	2057	The most-recently detected attributes of the file. Although the type is
1573	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types	2058	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
1574	suitable for your system. If the C<st_nlink> member is C<0>, then there	2059	suitable for your system, but you can only rely on the POSIX-standardised
		2060	members to be present. If the C<st_nlink> member is C<0>, then there was
1575	was some error while C<stat>ing the file.	2061	some error while C<stat>ing the file.
1576		2062
1577	=item ev_statdata prev [read-only]	2063	=item ev_statdata prev [read-only]
1578		2064
1579	The previous attributes of the file. The callback gets invoked whenever	2065	The previous attributes of the file. The callback gets invoked whenever
1580	C<prev> != C<attr>.	2066	C<prev> != C<attr>, or, more precisely, one or more of these members
		2067	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2068	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
1581		2069
1582	=item ev_tstamp interval [read-only]	2070	=item ev_tstamp interval [read-only]
1583		2071
1584	The specified interval.	2072	The specified interval.
1585		2073
1586	=item const char *path [read-only]	2074	=item const char *path [read-only]
1587		2075
1588	The filesystem path that is being watched.	2076	The file system path that is being watched.
1589		2077
1590	=back	2078	=back
1591		2079
1592	=head3 Examples	2080	=head3 Examples
1593		2081
1594	Example: Watch C</etc/passwd> for attribute changes.	2082	Example: Watch C</etc/passwd> for attribute changes.
1595		2083
1596	static void	2084	static void
1597	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)	2085	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1598	{	2086	{
1599	/* /etc/passwd changed in some way */	2087	/* /etc/passwd changed in some way */
1600	if (w->attr.st_nlink)	2088	if (w->attr.st_nlink)
1601	{	2089	{
1602	printf ("passwd current size %ld\n", (long)w->attr.st_size);	2090	printf ("passwd current size %ld\n", (long)w->attr.st_size);
1603	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);	2091	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
1604	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);	2092	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
1605	}	2093	}
1606	else	2094	else
1607	/* you shalt not abuse printf for puts */	2095	/* you shalt not abuse printf for puts */
1608	puts ("wow, /etc/passwd is not there, expect problems. "	2096	puts ("wow, /etc/passwd is not there, expect problems. "
1609	"if this is windows, they already arrived\n");	2097	"if this is windows, they already arrived\n");
1610	}	2098	}
1611		2099
1612	...	2100	...
1613	ev_stat passwd;	2101	ev_stat passwd;
1614		2102
1615	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);	2103	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1616	ev_stat_start (loop, &passwd);	2104	ev_stat_start (loop, &passwd);
1617		2105
1618	Example: Like above, but additionally use a one-second delay so we do not	2106	Example: Like above, but additionally use a one-second delay so we do not
1619	miss updates (however, frequent updates will delay processing, too, so	2107	miss updates (however, frequent updates will delay processing, too, so
1620	one might do the work both on C<ev_stat> callback invocation I<and> on	2108	one might do the work both on C<ev_stat> callback invocation I<and> on
1621	C<ev_timer> callback invocation).	2109	C<ev_timer> callback invocation).
1622		2110
1623	static ev_stat passwd;	2111	static ev_stat passwd;
1624	static ev_timer timer;	2112	static ev_timer timer;
1625		2113
1626	static void	2114	static void
1627	timer_cb (EV_P_ ev_timer *w, int revents)	2115	timer_cb (EV_P_ ev_timer *w, int revents)
1628	{	2116	{
1629	ev_timer_stop (EV_A_ w);	2117	ev_timer_stop (EV_A_ w);
1630		2118
1631	/* now it's one second after the most recent passwd change */	2119	/* now it's one second after the most recent passwd change */
1632	}	2120	}
1633		2121
1634	static void	2122	static void
1635	stat_cb (EV_P_ ev_stat *w, int revents)	2123	stat_cb (EV_P_ ev_stat *w, int revents)
1636	{	2124	{
1637	/* reset the one-second timer */	2125	/* reset the one-second timer */
1638	ev_timer_again (EV_A_ &timer);	2126	ev_timer_again (EV_A_ &timer);
1639	}	2127	}
1640		2128
1641	...	2129	...
1642	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);	2130	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
1643	ev_stat_start (loop, &passwd);	2131	ev_stat_start (loop, &passwd);
1644	ev_timer_init (&timer, timer_cb, 0., 1.01);	2132	ev_timer_init (&timer, timer_cb, 0., 1.02);
1645		2133
1646		2134
1647	=head2 C<ev_idle> - when you've got nothing better to do...	2135	=head2 C<ev_idle> - when you've got nothing better to do...
1648		2136
1649	Idle watchers trigger events when no other events of the same or higher	2137	Idle watchers trigger events when no other events of the same or higher
1650	priority are pending (prepare, check and other idle watchers do not	2138	priority are pending (prepare, check and other idle watchers do not count
1651	count).	2139	as receiving "events").
1652		2140
1653	That is, as long as your process is busy handling sockets or timeouts	2141	That is, as long as your process is busy handling sockets or timeouts
1654	(or even signals, imagine) of the same or higher priority it will not be	2142	(or even signals, imagine) of the same or higher priority it will not be
1655	triggered. But when your process is idle (or only lower-priority watchers	2143	triggered. But when your process is idle (or only lower-priority watchers
1656	are pending), the idle watchers are being called once per event loop	2144	are pending), the idle watchers are being called once per event loop
…		…
1680	=head3 Examples	2168	=head3 Examples
1681		2169
1682	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2170	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1683	callback, free it. Also, use no error checking, as usual.	2171	callback, free it. Also, use no error checking, as usual.
1684		2172
1685	static void	2173	static void
1686	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2174	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1687	{	2175	{
1688	free (w);	2176	free (w);
1689	// now do something you wanted to do when the program has	2177	// now do something you wanted to do when the program has
1690	// no longer asnything immediate to do.	2178	// no longer anything immediate to do.
1691	}	2179	}
1692		2180
1693	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2181	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1694	ev_idle_init (idle_watcher, idle_cb);	2182	ev_idle_init (idle_watcher, idle_cb);
1695	ev_idle_start (loop, idle_cb);	2183	ev_idle_start (loop, idle_cb);
1696		2184
1697		2185
1698	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2186	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1699		2187
1700	Prepare and check watchers are usually (but not always) used in tandem:	2188	Prepare and check watchers are usually (but not always) used in pairs:
1701	prepare watchers get invoked before the process blocks and check watchers	2189	prepare watchers get invoked before the process blocks and check watchers
1702	afterwards.	2190	afterwards.
1703		2191
1704	You I<must not> call C<ev_loop> or similar functions that enter	2192	You I<must not> call C<ev_loop> or similar functions that enter
1705	the current event loop from either C<ev_prepare> or C<ev_check>	2193	the current event loop from either C<ev_prepare> or C<ev_check>
…		…
1708	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	2196	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
1709	C<ev_check> so if you have one watcher of each kind they will always be	2197	C<ev_check> so if you have one watcher of each kind they will always be
1710	called in pairs bracketing the blocking call.	2198	called in pairs bracketing the blocking call.
1711		2199
1712	Their main purpose is to integrate other event mechanisms into libev and	2200	Their main purpose is to integrate other event mechanisms into libev and
1713	their use is somewhat advanced. This could be used, for example, to track	2201	their use is somewhat advanced. They could be used, for example, to track
1714	variable changes, implement your own watchers, integrate net-snmp or a	2202	variable changes, implement your own watchers, integrate net-snmp or a
1715	coroutine library and lots more. They are also occasionally useful if	2203	coroutine library and lots more. They are also occasionally useful if
1716	you cache some data and want to flush it before blocking (for example,	2204	you cache some data and want to flush it before blocking (for example,
1717	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>	2205	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1718	watcher).	2206	watcher).
1719		2207
1720	This is done by examining in each prepare call which file descriptors need	2208	This is done by examining in each prepare call which file descriptors
1721	to be watched by the other library, registering C<ev_io> watchers for	2209	need to be watched by the other library, registering C<ev_io> watchers
1722	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2210	for them and starting an C<ev_timer> watcher for any timeouts (many
1723	provide just this functionality). Then, in the check watcher you check for	2211	libraries provide exactly this functionality). Then, in the check watcher,
1724	any events that occured (by checking the pending status of all watchers	2212	you check for any events that occurred (by checking the pending status
1725	and stopping them) and call back into the library. The I/O and timer	2213	of all watchers and stopping them) and call back into the library. The
1726	callbacks will never actually be called (but must be valid nevertheless,	2214	I/O and timer callbacks will never actually be called (but must be valid
1727	because you never know, you know?).	2215	nevertheless, because you never know, you know?).
1728		2216
1729	As another example, the Perl Coro module uses these hooks to integrate	2217	As another example, the Perl Coro module uses these hooks to integrate
1730	coroutines into libev programs, by yielding to other active coroutines	2218	coroutines into libev programs, by yielding to other active coroutines
1731	during each prepare and only letting the process block if no coroutines	2219	during each prepare and only letting the process block if no coroutines
1732	are ready to run (it's actually more complicated: it only runs coroutines	2220	are ready to run (it's actually more complicated: it only runs coroutines
…		…
1735	loop from blocking if lower-priority coroutines are active, thus mapping	2223	loop from blocking if lower-priority coroutines are active, thus mapping
1736	low-priority coroutines to idle/background tasks).	2224	low-priority coroutines to idle/background tasks).
1737		2225
1738	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	2226	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
1739	priority, to ensure that they are being run before any other watchers	2227	priority, to ensure that they are being run before any other watchers
		2228	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2229
1740	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,	2230	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
1741	too) should not activate ("feed") events into libev. While libev fully	2231	activate ("feed") events into libev. While libev fully supports this, they
1742	supports this, they will be called before other C<ev_check> watchers	2232	might get executed before other C<ev_check> watchers did their job. As
1743	did their job. As C<ev_check> watchers are often used to embed other	2233	C<ev_check> watchers are often used to embed other (non-libev) event
1744	(non-libev) event loops those other event loops might be in an unusable	2234	loops those other event loops might be in an unusable state until their
1745	state until their C<ev_check> watcher ran (always remind yourself to	2235	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
1746	coexist peacefully with others).	2236	others).
1747		2237
1748	=head3 Watcher-Specific Functions and Data Members	2238	=head3 Watcher-Specific Functions and Data Members
1749		2239
1750	=over 4	2240	=over 4
1751		2241
…		…
1753		2243
1754	=item ev_check_init (ev_check *, callback)	2244	=item ev_check_init (ev_check *, callback)
1755		2245
1756	Initialises and configures the prepare or check watcher - they have no	2246	Initialises and configures the prepare or check watcher - they have no
1757	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2247	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1758	macros, but using them is utterly, utterly and completely pointless.	2248	macros, but using them is utterly, utterly, utterly and completely
		2249	pointless.
1759		2250
1760	=back	2251	=back
1761		2252
1762	=head3 Examples	2253	=head3 Examples
1763		2254
1764	There are a number of principal ways to embed other event loops or modules	2255	There are a number of principal ways to embed other event loops or modules
1765	into libev. Here are some ideas on how to include libadns into libev	2256	into libev. Here are some ideas on how to include libadns into libev
1766	(there is a Perl module named C<EV::ADNS> that does this, which you could	2257	(there is a Perl module named C<EV::ADNS> that does this, which you could
1767	use for an actually working example. Another Perl module named C<EV::Glib>	2258	use as a working example. Another Perl module named C<EV::Glib> embeds a
1768	embeds a Glib main context into libev, and finally, C<Glib::EV> embeds EV	2259	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
1769	into the Glib event loop).	2260	Glib event loop).
1770		2261
1771	Method 1: Add IO watchers and a timeout watcher in a prepare handler,	2262	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
1772	and in a check watcher, destroy them and call into libadns. What follows	2263	and in a check watcher, destroy them and call into libadns. What follows
1773	is pseudo-code only of course. This requires you to either use a low	2264	is pseudo-code only of course. This requires you to either use a low
1774	priority for the check watcher or use C<ev_clear_pending> explicitly, as	2265	priority for the check watcher or use C<ev_clear_pending> explicitly, as
1775	the callbacks for the IO/timeout watchers might not have been called yet.	2266	the callbacks for the IO/timeout watchers might not have been called yet.
1776		2267
1777	static ev_io iow [nfd];	2268	static ev_io iow [nfd];
1778	static ev_timer tw;	2269	static ev_timer tw;
1779		2270
1780	static void	2271	static void
1781	io_cb (ev_loop *loop, ev_io *w, int revents)	2272	io_cb (struct ev_loop *loop, ev_io *w, int revents)
1782	{	2273	{
1783	}	2274	}
1784		2275
1785	// create io watchers for each fd and a timer before blocking	2276	// create io watchers for each fd and a timer before blocking
1786	static void	2277	static void
1787	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	2278	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1788	{	2279	{
1789	int timeout = 3600000;	2280	int timeout = 3600000;
1790	struct pollfd fds [nfd];	2281	struct pollfd fds [nfd];
1791	// actual code will need to loop here and realloc etc.	2282	// actual code will need to loop here and realloc etc.
1792	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2283	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1793		2284
1794	/* the callback is illegal, but won't be called as we stop during check */	2285	/* the callback is illegal, but won't be called as we stop during check */
1795	ev_timer_init (&tw, 0, timeout * 1e-3);	2286	ev_timer_init (&tw, 0, timeout * 1e-3);
1796	ev_timer_start (loop, &tw);	2287	ev_timer_start (loop, &tw);
1797		2288
1798	// create one ev_io per pollfd	2289	// create one ev_io per pollfd
1799	for (int i = 0; i < nfd; ++i)	2290	for (int i = 0; i < nfd; ++i)
1800	{	2291	{
1801	ev_io_init (iow + i, io_cb, fds [i].fd,	2292	ev_io_init (iow + i, io_cb, fds [i].fd,
1802	((fds [i].events & POLLIN ? EV_READ : 0)	2293	((fds [i].events & POLLIN ? EV_READ : 0)
1803	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));	2294	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1804		2295
1805	fds [i].revents = 0;	2296	fds [i].revents = 0;
1806	ev_io_start (loop, iow + i);	2297	ev_io_start (loop, iow + i);
1807	}	2298	}
1808	}	2299	}
1809		2300
1810	// stop all watchers after blocking	2301	// stop all watchers after blocking
1811	static void	2302	static void
1812	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	2303	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
1813	{	2304	{
1814	ev_timer_stop (loop, &tw);	2305	ev_timer_stop (loop, &tw);
1815		2306
1816	for (int i = 0; i < nfd; ++i)	2307	for (int i = 0; i < nfd; ++i)
1817	{	2308	{
1818	// set the relevant poll flags	2309	// set the relevant poll flags
1819	// could also call adns_processreadable etc. here	2310	// could also call adns_processreadable etc. here
1820	struct pollfd *fd = fds + i;	2311	struct pollfd *fd = fds + i;
1821	int revents = ev_clear_pending (iow + i);	2312	int revents = ev_clear_pending (iow + i);
1822	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;	2313	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1823	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;	2314	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1824		2315
1825	// now stop the watcher	2316	// now stop the watcher
1826	ev_io_stop (loop, iow + i);	2317	ev_io_stop (loop, iow + i);
1827	}	2318	}
1828		2319
1829	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));	2320	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1830	}	2321	}
1831		2322
1832	Method 2: This would be just like method 1, but you run C<adns_afterpoll>	2323	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
1833	in the prepare watcher and would dispose of the check watcher.	2324	in the prepare watcher and would dispose of the check watcher.
1834		2325
1835	Method 3: If the module to be embedded supports explicit event	2326	Method 3: If the module to be embedded supports explicit event
1836	notification (adns does), you can also make use of the actual watcher	2327	notification (libadns does), you can also make use of the actual watcher
1837	callbacks, and only destroy/create the watchers in the prepare watcher.	2328	callbacks, and only destroy/create the watchers in the prepare watcher.
1838		2329
1839	static void	2330	static void
1840	timer_cb (EV_P_ ev_timer *w, int revents)	2331	timer_cb (EV_P_ ev_timer *w, int revents)
1841	{	2332	{
1842	adns_state ads = (adns_state)w->data;	2333	adns_state ads = (adns_state)w->data;
1843	update_now (EV_A);	2334	update_now (EV_A);
1844		2335
1845	adns_processtimeouts (ads, &tv_now);	2336	adns_processtimeouts (ads, &tv_now);
1846	}	2337	}
1847		2338
1848	static void	2339	static void
1849	io_cb (EV_P_ ev_io *w, int revents)	2340	io_cb (EV_P_ ev_io *w, int revents)
1850	{	2341	{
1851	adns_state ads = (adns_state)w->data;	2342	adns_state ads = (adns_state)w->data;
1852	update_now (EV_A);	2343	update_now (EV_A);
1853		2344
1854	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);	2345	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
1855	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);	2346	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
1856	}	2347	}
1857		2348
1858	// do not ever call adns_afterpoll	2349	// do not ever call adns_afterpoll
1859		2350
1860	Method 4: Do not use a prepare or check watcher because the module you	2351	Method 4: Do not use a prepare or check watcher because the module you
1861	want to embed is too inflexible to support it. Instead, youc na override	2352	want to embed is not flexible enough to support it. Instead, you can
1862	their poll function. The drawback with this solution is that the main	2353	override their poll function. The drawback with this solution is that the
1863	loop is now no longer controllable by EV. The C<Glib::EV> module does	2354	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
1864	this.	2355	this approach, effectively embedding EV as a client into the horrible
		2356	libglib event loop.
1865		2357
1866	static gint	2358	static gint
1867	event_poll_func (GPollFD *fds, guint nfds, gint timeout)	2359	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
1868	{	2360	{
1869	int got_events = 0;	2361	int got_events = 0;
1870		2362
1871	for (n = 0; n < nfds; ++n)	2363	for (n = 0; n < nfds; ++n)
1872	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events	2364	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
1873		2365
1874	if (timeout >= 0)	2366	if (timeout >= 0)
1875	// create/start timer	2367	// create/start timer
1876		2368
1877	// poll	2369	// poll
1878	ev_loop (EV_A_ 0);	2370	ev_loop (EV_A_ 0);
1879		2371
1880	// stop timer again	2372	// stop timer again
1881	if (timeout >= 0)	2373	if (timeout >= 0)
1882	ev_timer_stop (EV_A_ &to);	2374	ev_timer_stop (EV_A_ &to);
1883		2375
1884	// stop io watchers again - their callbacks should have set	2376	// stop io watchers again - their callbacks should have set
1885	for (n = 0; n < nfds; ++n)	2377	for (n = 0; n < nfds; ++n)
1886	ev_io_stop (EV_A_ iow [n]);	2378	ev_io_stop (EV_A_ iow [n]);
1887		2379
1888	return got_events;	2380	return got_events;
1889	}	2381	}
1890		2382
1891		2383
1892	=head2 C<ev_embed> - when one backend isn't enough...	2384	=head2 C<ev_embed> - when one backend isn't enough...
1893		2385
1894	This is a rather advanced watcher type that lets you embed one event loop	2386	This is a rather advanced watcher type that lets you embed one event loop
…		…
1900	prioritise I/O.	2392	prioritise I/O.
1901		2393
1902	As an example for a bug workaround, the kqueue backend might only support	2394	As an example for a bug workaround, the kqueue backend might only support
1903	sockets on some platform, so it is unusable as generic backend, but you	2395	sockets on some platform, so it is unusable as generic backend, but you
1904	still want to make use of it because you have many sockets and it scales	2396	still want to make use of it because you have many sockets and it scales
1905	so nicely. In this case, you would create a kqueue-based loop and embed it	2397	so nicely. In this case, you would create a kqueue-based loop and embed
1906	into your default loop (which might use e.g. poll). Overall operation will	2398	it into your default loop (which might use e.g. poll). Overall operation
1907	be a bit slower because first libev has to poll and then call kevent, but	2399	will be a bit slower because first libev has to call C<poll> and then
1908	at least you can use both at what they are best.	2400	C<kevent>, but at least you can use both mechanisms for what they are
		2401	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
1909		2402
1910	As for prioritising I/O: rarely you have the case where some fds have	2403	As for prioritising I/O: under rare circumstances you have the case where
1911	to be watched and handled very quickly (with low latency), and even	2404	some fds have to be watched and handled very quickly (with low latency),
1912	priorities and idle watchers might have too much overhead. In this case	2405	and even priorities and idle watchers might have too much overhead. In
1913	you would put all the high priority stuff in one loop and all the rest in	2406	this case you would put all the high priority stuff in one loop and all
1914	a second one, and embed the second one in the first.	2407	the rest in a second one, and embed the second one in the first.
1915		2408
1916	As long as the watcher is active, the callback will be invoked every time	2409	As long as the watcher is active, the callback will be invoked every time
1917	there might be events pending in the embedded loop. The callback must then	2410	there might be events pending in the embedded loop. The callback must then
1918	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	2411	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke
1919	their callbacks (you could also start an idle watcher to give the embedded	2412	their callbacks (you could also start an idle watcher to give the embedded
…		…
1927	interested in that.	2420	interested in that.
1928		2421
1929	Also, there have not currently been made special provisions for forking:	2422	Also, there have not currently been made special provisions for forking:
1930	when you fork, you not only have to call C<ev_loop_fork> on both loops,	2423	when you fork, you not only have to call C<ev_loop_fork> on both loops,
1931	but you will also have to stop and restart any C<ev_embed> watchers	2424	but you will also have to stop and restart any C<ev_embed> watchers
1932	yourself.	2425	yourself - but you can use a fork watcher to handle this automatically,
		2426	and future versions of libev might do just that.
1933		2427
1934	Unfortunately, not all backends are embeddable, only the ones returned by	2428	Unfortunately, not all backends are embeddable: only the ones returned by
1935	C<ev_embeddable_backends> are, which, unfortunately, does not include any	2429	C<ev_embeddable_backends> are, which, unfortunately, does not include any
1936	portable one.	2430	portable one.
1937		2431
1938	So when you want to use this feature you will always have to be prepared	2432	So when you want to use this feature you will always have to be prepared
1939	that you cannot get an embeddable loop. The recommended way to get around	2433	that you cannot get an embeddable loop. The recommended way to get around
1940	this is to have a separate variables for your embeddable loop, try to	2434	this is to have a separate variables for your embeddable loop, try to
1941	create it, and if that fails, use the normal loop for everything.	2435	create it, and if that fails, use the normal loop for everything.
1942		2436
		2437	=head3 C<ev_embed> and fork
		2438
		2439	While the C<ev_embed> watcher is running, forks in the embedding loop will
		2440	automatically be applied to the embedded loop as well, so no special
		2441	fork handling is required in that case. When the watcher is not running,
		2442	however, it is still the task of the libev user to call C<ev_loop_fork ()>
		2443	as applicable.
		2444
1943	=head3 Watcher-Specific Functions and Data Members	2445	=head3 Watcher-Specific Functions and Data Members
1944		2446
1945	=over 4	2447	=over 4
1946		2448
1947	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	2449	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
…		…
1950		2452
1951	Configures the watcher to embed the given loop, which must be	2453	Configures the watcher to embed the given loop, which must be
1952	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	2454	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
1953	invoked automatically, otherwise it is the responsibility of the callback	2455	invoked automatically, otherwise it is the responsibility of the callback
1954	to invoke it (it will continue to be called until the sweep has been done,	2456	to invoke it (it will continue to be called until the sweep has been done,
1955	if you do not want thta, you need to temporarily stop the embed watcher).	2457	if you do not want that, you need to temporarily stop the embed watcher).
1956		2458
1957	=item ev_embed_sweep (loop, ev_embed *)	2459	=item ev_embed_sweep (loop, ev_embed *)
1958		2460
1959	Make a single, non-blocking sweep over the embedded loop. This works	2461	Make a single, non-blocking sweep over the embedded loop. This works
1960	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most	2462	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
1961	apropriate way for embedded loops.	2463	appropriate way for embedded loops.
1962		2464
1963	=item struct ev_loop *other [read-only]	2465	=item struct ev_loop *other [read-only]
1964		2466
1965	The embedded event loop.	2467	The embedded event loop.
1966		2468
…		…
1968		2470
1969	=head3 Examples	2471	=head3 Examples
1970		2472
1971	Example: Try to get an embeddable event loop and embed it into the default	2473	Example: Try to get an embeddable event loop and embed it into the default
1972	event loop. If that is not possible, use the default loop. The default	2474	event loop. If that is not possible, use the default loop. The default
1973	loop is stored in C<loop_hi>, while the mebeddable loop is stored in	2475	loop is stored in C<loop_hi>, while the embeddable loop is stored in
1974	C<loop_lo> (which is C<loop_hi> in the acse no embeddable loop can be	2476	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
1975	used).	2477	used).
1976		2478
1977	struct ev_loop *loop_hi = ev_default_init (0);	2479	struct ev_loop *loop_hi = ev_default_init (0);
1978	struct ev_loop *loop_lo = 0;	2480	struct ev_loop *loop_lo = 0;
1979	struct ev_embed embed;	2481	ev_embed embed;
1980		2482
1981	// see if there is a chance of getting one that works	2483	// see if there is a chance of getting one that works
1982	// (remember that a flags value of 0 means autodetection)	2484	// (remember that a flags value of 0 means autodetection)
1983	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()	2485	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
1984	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())	2486	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
1985	: 0;	2487	: 0;
1986		2488
1987	// if we got one, then embed it, otherwise default to loop_hi	2489	// if we got one, then embed it, otherwise default to loop_hi
1988	if (loop_lo)	2490	if (loop_lo)
1989	{	2491	{
1990	ev_embed_init (&embed, 0, loop_lo);	2492	ev_embed_init (&embed, 0, loop_lo);
1991	ev_embed_start (loop_hi, &embed);	2493	ev_embed_start (loop_hi, &embed);
1992	}	2494	}
1993	else	2495	else
1994	loop_lo = loop_hi;	2496	loop_lo = loop_hi;
1995		2497
1996	Example: Check if kqueue is available but not recommended and create	2498	Example: Check if kqueue is available but not recommended and create
1997	a kqueue backend for use with sockets (which usually work with any	2499	a kqueue backend for use with sockets (which usually work with any
1998	kqueue implementation). Store the kqueue/socket-only event loop in	2500	kqueue implementation). Store the kqueue/socket-only event loop in
1999	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).	2501	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
2000		2502
2001	struct ev_loop *loop = ev_default_init (0);	2503	struct ev_loop *loop = ev_default_init (0);
2002	struct ev_loop *loop_socket = 0;	2504	struct ev_loop *loop_socket = 0;
2003	struct ev_embed embed;	2505	ev_embed embed;
2004		2506
2005	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)	2507	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
2006	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))	2508	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
2007	{	2509	{
2008	ev_embed_init (&embed, 0, loop_socket);	2510	ev_embed_init (&embed, 0, loop_socket);
2009	ev_embed_start (loop, &embed);	2511	ev_embed_start (loop, &embed);
2010	}	2512	}
2011		2513
2012	if (!loop_socket)	2514	if (!loop_socket)
2013	loop_socket = loop;	2515	loop_socket = loop;
2014		2516
2015	// now use loop_socket for all sockets, and loop for everything else	2517	// now use loop_socket for all sockets, and loop for everything else
2016		2518
2017		2519
2018	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	2520	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
2019		2521
2020	Fork watchers are called when a C<fork ()> was detected (usually because	2522	Fork watchers are called when a C<fork ()> was detected (usually because
…		…
2036	believe me.	2538	believe me.
2037		2539
2038	=back	2540	=back
2039		2541
2040		2542
		2543	=head2 C<ev_async> - how to wake up another event loop
		2544
		2545	In general, you cannot use an C<ev_loop> from multiple threads or other
		2546	asynchronous sources such as signal handlers (as opposed to multiple event
		2547	loops - those are of course safe to use in different threads).
		2548
		2549	Sometimes, however, you need to wake up another event loop you do not
		2550	control, for example because it belongs to another thread. This is what
		2551	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you
		2552	can signal it by calling C<ev_async_send>, which is thread- and signal
		2553	safe.
		2554
		2555	This functionality is very similar to C<ev_signal> watchers, as signals,
		2556	too, are asynchronous in nature, and signals, too, will be compressed
		2557	(i.e. the number of callback invocations may be less than the number of
		2558	C<ev_async_sent> calls).
		2559
		2560	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		2561	just the default loop.
		2562
		2563	=head3 Queueing
		2564
		2565	C<ev_async> does not support queueing of data in any way. The reason
		2566	is that the author does not know of a simple (or any) algorithm for a
		2567	multiple-writer-single-reader queue that works in all cases and doesn't
		2568	need elaborate support such as pthreads.
		2569
		2570	That means that if you want to queue data, you have to provide your own
		2571	queue. But at least I can tell you how to implement locking around your
		2572	queue:
		2573
		2574	=over 4
		2575
		2576	=item queueing from a signal handler context
		2577
		2578	To implement race-free queueing, you simply add to the queue in the signal
		2579	handler but you block the signal handler in the watcher callback. Here is
		2580	an example that does that for some fictitious SIGUSR1 handler:
		2581
		2582	static ev_async mysig;
		2583
		2584	static void
		2585	sigusr1_handler (void)
		2586	{
		2587	sometype data;
		2588
		2589	// no locking etc.
		2590	queue_put (data);
		2591	ev_async_send (EV_DEFAULT_ &mysig);
		2592	}
		2593
		2594	static void
		2595	mysig_cb (EV_P_ ev_async *w, int revents)
		2596	{
		2597	sometype data;
		2598	sigset_t block, prev;
		2599
		2600	sigemptyset (&block);
		2601	sigaddset (&block, SIGUSR1);
		2602	sigprocmask (SIG_BLOCK, &block, &prev);
		2603
		2604	while (queue_get (&data))
		2605	process (data);
		2606
		2607	if (sigismember (&prev, SIGUSR1)
		2608	sigprocmask (SIG_UNBLOCK, &block, 0);
		2609	}
		2610
		2611	(Note: pthreads in theory requires you to use C<pthread_setmask>
		2612	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		2613	either...).
		2614
		2615	=item queueing from a thread context
		2616
		2617	The strategy for threads is different, as you cannot (easily) block
		2618	threads but you can easily preempt them, so to queue safely you need to
		2619	employ a traditional mutex lock, such as in this pthread example:
		2620
		2621	static ev_async mysig;
		2622	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		2623
		2624	static void
		2625	otherthread (void)
		2626	{
		2627	// only need to lock the actual queueing operation
		2628	pthread_mutex_lock (&mymutex);
		2629	queue_put (data);
		2630	pthread_mutex_unlock (&mymutex);
		2631
		2632	ev_async_send (EV_DEFAULT_ &mysig);
		2633	}
		2634
		2635	static void
		2636	mysig_cb (EV_P_ ev_async *w, int revents)
		2637	{
		2638	pthread_mutex_lock (&mymutex);
		2639
		2640	while (queue_get (&data))
		2641	process (data);
		2642
		2643	pthread_mutex_unlock (&mymutex);
		2644	}
		2645
		2646	=back
		2647
		2648
		2649	=head3 Watcher-Specific Functions and Data Members
		2650
		2651	=over 4
		2652
		2653	=item ev_async_init (ev_async *, callback)
		2654
		2655	Initialises and configures the async watcher - it has no parameters of any
		2656	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
		2657	trust me.
		2658
		2659	=item ev_async_send (loop, ev_async *)
		2660
		2661	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		2662	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		2663	C<ev_feed_event>, this call is safe to do from other threads, signal or
		2664	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
		2665	section below on what exactly this means).
		2666
		2667	This call incurs the overhead of a system call only once per loop iteration,
		2668	so while the overhead might be noticeable, it doesn't apply to repeated
		2669	calls to C<ev_async_send>.
		2670
		2671	=item bool = ev_async_pending (ev_async *)
		2672
		2673	Returns a non-zero value when C<ev_async_send> has been called on the
		2674	watcher but the event has not yet been processed (or even noted) by the
		2675	event loop.
		2676
		2677	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		2678	the loop iterates next and checks for the watcher to have become active,
		2679	it will reset the flag again. C<ev_async_pending> can be used to very
		2680	quickly check whether invoking the loop might be a good idea.
		2681
		2682	Not that this does I<not> check whether the watcher itself is pending, only
		2683	whether it has been requested to make this watcher pending.
		2684
		2685	=back
		2686
		2687
2041	=head1 OTHER FUNCTIONS	2688	=head1 OTHER FUNCTIONS
2042		2689
2043	There are some other functions of possible interest. Described. Here. Now.	2690	There are some other functions of possible interest. Described. Here. Now.
2044		2691
2045	=over 4	2692	=over 4
2046		2693
2047	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	2694	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
2048		2695
2049	This function combines a simple timer and an I/O watcher, calls your	2696	This function combines a simple timer and an I/O watcher, calls your
2050	callback on whichever event happens first and automatically stop both	2697	callback on whichever event happens first and automatically stops both
2051	watchers. This is useful if you want to wait for a single event on an fd	2698	watchers. This is useful if you want to wait for a single event on an fd
2052	or timeout without having to allocate/configure/start/stop/free one or	2699	or timeout without having to allocate/configure/start/stop/free one or
2053	more watchers yourself.	2700	more watchers yourself.
2054		2701
2055	If C<fd> is less than 0, then no I/O watcher will be started and events	2702	If C<fd> is less than 0, then no I/O watcher will be started and the
2056	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	2703	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
2057	C<events> set will be craeted and started.	2704	the given C<fd> and C<events> set will be created and started.
2058		2705
2059	If C<timeout> is less than 0, then no timeout watcher will be	2706	If C<timeout> is less than 0, then no timeout watcher will be
2060	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	2707	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
2061	repeat = 0) will be started. While C<0> is a valid timeout, it is of	2708	repeat = 0) will be started. C<0> is a valid timeout.
2062	dubious value.
2063		2709
2064	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	2710	The callback has the type C<void (*cb)(int revents, void *arg)> and gets
2065	passed an C<revents> set like normal event callbacks (a combination of	2711	passed an C<revents> set like normal event callbacks (a combination of
2066	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	2712	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
2067	value passed to C<ev_once>:	2713	value passed to C<ev_once>. Note that it is possible to receive I<both>
		2714	a timeout and an io event at the same time - you probably should give io
		2715	events precedence.
2068		2716
		2717	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		2718
2069	static void stdin_ready (int revents, void *arg)	2719	static void stdin_ready (int revents, void *arg)
2070	{	2720	{
2071	if (revents & EV_TIMEOUT)
2072	/* doh, nothing entered */;
2073	else if (revents & EV_READ)	2721	if (revents & EV_READ)
2074	/* stdin might have data for us, joy! */;	2722	/* stdin might have data for us, joy! */;
		2723	else if (revents & EV_TIMEOUT)
		2724	/* doh, nothing entered */;
2075	}	2725	}
2076		2726
2077	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	2727	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
2078		2728
2079	=item ev_feed_event (ev_loop *, watcher *, int revents)	2729	=item ev_feed_event (struct ev_loop *, watcher *, int revents)
2080		2730
2081	Feeds the given event set into the event loop, as if the specified event	2731	Feeds the given event set into the event loop, as if the specified event
2082	had happened for the specified watcher (which must be a pointer to an	2732	had happened for the specified watcher (which must be a pointer to an
2083	initialised but not necessarily started event watcher).	2733	initialised but not necessarily started event watcher).
2084		2734
2085	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	2735	=item ev_feed_fd_event (struct ev_loop *, int fd, int revents)
2086		2736
2087	Feed an event on the given fd, as if a file descriptor backend detected	2737	Feed an event on the given fd, as if a file descriptor backend detected
2088	the given events it.	2738	the given events it.
2089		2739
2090	=item ev_feed_signal_event (ev_loop *loop, int signum)	2740	=item ev_feed_signal_event (struct ev_loop *loop, int signum)
2091		2741
2092	Feed an event as if the given signal occured (C<loop> must be the default	2742	Feed an event as if the given signal occurred (C<loop> must be the default
2093	loop!).	2743	loop!).
2094		2744
2095	=back	2745	=back
2096		2746
2097		2747
…		…
2113		2763
2114	=item * Priorities are not currently supported. Initialising priorities	2764	=item * Priorities are not currently supported. Initialising priorities
2115	will fail and all watchers will have the same priority, even though there	2765	will fail and all watchers will have the same priority, even though there
2116	is an ev_pri field.	2766	is an ev_pri field.
2117		2767
		2768	=item * In libevent, the last base created gets the signals, in libev, the
		2769	first base created (== the default loop) gets the signals.
		2770
2118	=item * Other members are not supported.	2771	=item * Other members are not supported.
2119		2772
2120	=item * The libev emulation is I<not> ABI compatible to libevent, you need	2773	=item * The libev emulation is I<not> ABI compatible to libevent, you need
2121	to use the libev header file and library.	2774	to use the libev header file and library.
2122		2775
2123	=back	2776	=back
2124		2777
2125	=head1 C++ SUPPORT	2778	=head1 C++ SUPPORT
2126		2779
2127	Libev comes with some simplistic wrapper classes for C++ that mainly allow	2780	Libev comes with some simplistic wrapper classes for C++ that mainly allow
2128	you to use some convinience methods to start/stop watchers and also change	2781	you to use some convenience methods to start/stop watchers and also change
2129	the callback model to a model using method callbacks on objects.	2782	the callback model to a model using method callbacks on objects.
2130		2783
2131	To use it,	2784	To use it,
2132		2785
2133	#include <ev++.h>	2786	#include <ev++.h>
2134		2787
2135	This automatically includes F<ev.h> and puts all of its definitions (many	2788	This automatically includes F<ev.h> and puts all of its definitions (many
2136	of them macros) into the global namespace. All C++ specific things are	2789	of them macros) into the global namespace. All C++ specific things are
2137	put into the C<ev> namespace. It should support all the same embedding	2790	put into the C<ev> namespace. It should support all the same embedding
2138	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.	2791	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
…		…
2205	your compiler is good :), then the method will be fully inlined into the	2858	your compiler is good :), then the method will be fully inlined into the
2206	thunking function, making it as fast as a direct C callback.	2859	thunking function, making it as fast as a direct C callback.
2207		2860
2208	Example: simple class declaration and watcher initialisation	2861	Example: simple class declaration and watcher initialisation
2209		2862
2210	struct myclass	2863	struct myclass
2211	{	2864	{
2212	void io_cb (ev::io &w, int revents) { }	2865	void io_cb (ev::io &w, int revents) { }
2213	}	2866	}
2214		2867
2215	myclass obj;	2868	myclass obj;
2216	ev::io iow;	2869	ev::io iow;
2217	iow.set <myclass, &myclass::io_cb> (&obj);	2870	iow.set <myclass, &myclass::io_cb> (&obj);
2218		2871
2219	=item w->set<function> (void *data = 0)	2872	=item w->set<function> (void *data = 0)
2220		2873
2221	Also sets a callback, but uses a static method or plain function as	2874	Also sets a callback, but uses a static method or plain function as
2222	callback. The optional C<data> argument will be stored in the watcher's	2875	callback. The optional C<data> argument will be stored in the watcher's
…		…
2224		2877
2225	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.	2878	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
2226		2879
2227	See the method-C<set> above for more details.	2880	See the method-C<set> above for more details.
2228		2881
2229	Example:	2882	Example: Use a plain function as callback.
2230		2883
2231	static void io_cb (ev::io &w, int revents) { }	2884	static void io_cb (ev::io &w, int revents) { }
2232	iow.set <io_cb> ();	2885	iow.set <io_cb> ();
2233		2886
2234	=item w->set (struct ev_loop *)	2887	=item w->set (struct ev_loop *)
2235		2888
2236	Associates a different C<struct ev_loop> with this watcher. You can only	2889	Associates a different C<struct ev_loop> with this watcher. You can only
2237	do this when the watcher is inactive (and not pending either).	2890	do this when the watcher is inactive (and not pending either).
2238		2891
2239	=item w->set ([args])	2892	=item w->set ([arguments])
2240		2893
2241	Basically the same as C<ev_TYPE_set>, with the same args. Must be	2894	Basically the same as C<ev_TYPE_set>, with the same arguments. Must be
2242	called at least once. Unlike the C counterpart, an active watcher gets	2895	called at least once. Unlike the C counterpart, an active watcher gets
2243	automatically stopped and restarted when reconfiguring it with this	2896	automatically stopped and restarted when reconfiguring it with this
2244	method.	2897	method.
2245		2898
2246	=item w->start ()	2899	=item w->start ()
…		…
2270	=back	2923	=back
2271		2924
2272	Example: Define a class with an IO and idle watcher, start one of them in	2925	Example: Define a class with an IO and idle watcher, start one of them in
2273	the constructor.	2926	the constructor.
2274		2927
2275	class myclass	2928	class myclass
2276	{	2929	{
2277	ev_io io; void io_cb (ev::io &w, int revents);	2930	ev::io io ; void io_cb (ev::io &w, int revents);
2278	ev_idle idle void idle_cb (ev::idle &w, int revents);	2931	ev::idle idle; void idle_cb (ev::idle &w, int revents);
2279		2932
2280	myclass ();	2933	myclass (int fd)
2281	}	2934	{
2282
2283	myclass::myclass (int fd)
2284	{
2285	io .set <myclass, &myclass::io_cb > (this);	2935	io .set <myclass, &myclass::io_cb > (this);
2286	idle.set <myclass, &myclass::idle_cb> (this);	2936	idle.set <myclass, &myclass::idle_cb> (this);
2287		2937
2288	io.start (fd, ev::READ);	2938	io.start (fd, ev::READ);
		2939	}
2289	}	2940	};
		2941
		2942
		2943	=head1 OTHER LANGUAGE BINDINGS
		2944
		2945	Libev does not offer other language bindings itself, but bindings for a
		2946	number of languages exist in the form of third-party packages. If you know
		2947	any interesting language binding in addition to the ones listed here, drop
		2948	me a note.
		2949
		2950	=over 4
		2951
		2952	=item Perl
		2953
		2954	The EV module implements the full libev API and is actually used to test
		2955	libev. EV is developed together with libev. Apart from the EV core module,
		2956	there are additional modules that implement libev-compatible interfaces
		2957	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		2958	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		2959	and C<EV::Glib>).
		2960
		2961	It can be found and installed via CPAN, its homepage is at
		2962	L<http://software.schmorp.de/pkg/EV>.
		2963
		2964	=item Python
		2965
		2966	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		2967	seems to be quite complete and well-documented. Note, however, that the
		2968	patch they require for libev is outright dangerous as it breaks the ABI
		2969	for everybody else, and therefore, should never be applied in an installed
		2970	libev (if python requires an incompatible ABI then it needs to embed
		2971	libev).
		2972
		2973	=item Ruby
		2974
		2975	Tony Arcieri has written a ruby extension that offers access to a subset
		2976	of the libev API and adds file handle abstractions, asynchronous DNS and
		2977	more on top of it. It can be found via gem servers. Its homepage is at
		2978	L<http://rev.rubyforge.org/>.
		2979
		2980	=item D
		2981
		2982	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		2983	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		2984
		2985	=item Ocaml
		2986
		2987	Erkki Seppala has written Ocaml bindings for libev, to be found at
		2988	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		2989
		2990	=back
2290		2991
2291		2992
2292	=head1 MACRO MAGIC	2993	=head1 MACRO MAGIC
2293		2994
2294	Libev can be compiled with a variety of options, the most fundamantal	2995	Libev can be compiled with a variety of options, the most fundamental
2295	of which is C<EV_MULTIPLICITY>. This option determines whether (most)	2996	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
2296	functions and callbacks have an initial C<struct ev_loop *> argument.	2997	functions and callbacks have an initial C<struct ev_loop *> argument.
2297		2998
2298	To make it easier to write programs that cope with either variant, the	2999	To make it easier to write programs that cope with either variant, the
2299	following macros are defined:	3000	following macros are defined:
…		…
2304		3005
2305	This provides the loop I<argument> for functions, if one is required ("ev	3006	This provides the loop I<argument> for functions, if one is required ("ev
2306	loop argument"). The C<EV_A> form is used when this is the sole argument,	3007	loop argument"). The C<EV_A> form is used when this is the sole argument,
2307	C<EV_A_> is used when other arguments are following. Example:	3008	C<EV_A_> is used when other arguments are following. Example:
2308		3009
2309	ev_unref (EV_A);	3010	ev_unref (EV_A);
2310	ev_timer_add (EV_A_ watcher);	3011	ev_timer_add (EV_A_ watcher);
2311	ev_loop (EV_A_ 0);	3012	ev_loop (EV_A_ 0);
2312		3013
2313	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,	3014	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
2314	which is often provided by the following macro.	3015	which is often provided by the following macro.
2315		3016
2316	=item C<EV_P>, C<EV_P_>	3017	=item C<EV_P>, C<EV_P_>
2317		3018
2318	This provides the loop I<parameter> for functions, if one is required ("ev	3019	This provides the loop I<parameter> for functions, if one is required ("ev
2319	loop parameter"). The C<EV_P> form is used when this is the sole parameter,	3020	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
2320	C<EV_P_> is used when other parameters are following. Example:	3021	C<EV_P_> is used when other parameters are following. Example:
2321		3022
2322	// this is how ev_unref is being declared	3023	// this is how ev_unref is being declared
2323	static void ev_unref (EV_P);	3024	static void ev_unref (EV_P);
2324		3025
2325	// this is how you can declare your typical callback	3026	// this is how you can declare your typical callback
2326	static void cb (EV_P_ ev_timer *w, int revents)	3027	static void cb (EV_P_ ev_timer *w, int revents)
2327		3028
2328	It declares a parameter C<loop> of type C<struct ev_loop *>, quite	3029	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
2329	suitable for use with C<EV_A>.	3030	suitable for use with C<EV_A>.
2330		3031
2331	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	3032	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
2332		3033
2333	Similar to the other two macros, this gives you the value of the default	3034	Similar to the other two macros, this gives you the value of the default
2334	loop, if multiple loops are supported ("ev loop default").	3035	loop, if multiple loops are supported ("ev loop default").
		3036
		3037	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		3038
		3039	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		3040	default loop has been initialised (C<UC> == unchecked). Their behaviour
		3041	is undefined when the default loop has not been initialised by a previous
		3042	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		3043
		3044	It is often prudent to use C<EV_DEFAULT> when initialising the first
		3045	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
2335		3046
2336	=back	3047	=back
2337		3048
2338	Example: Declare and initialise a check watcher, utilising the above	3049	Example: Declare and initialise a check watcher, utilising the above
2339	macros so it will work regardless of whether multiple loops are supported	3050	macros so it will work regardless of whether multiple loops are supported
2340	or not.	3051	or not.
2341		3052
2342	static void	3053	static void
2343	check_cb (EV_P_ ev_timer *w, int revents)	3054	check_cb (EV_P_ ev_timer *w, int revents)
2344	{	3055	{
2345	ev_check_stop (EV_A_ w);	3056	ev_check_stop (EV_A_ w);
2346	}	3057	}
2347		3058
2348	ev_check check;	3059	ev_check check;
2349	ev_check_init (&check, check_cb);	3060	ev_check_init (&check, check_cb);
2350	ev_check_start (EV_DEFAULT_ &check);	3061	ev_check_start (EV_DEFAULT_ &check);
2351	ev_loop (EV_DEFAULT_ 0);	3062	ev_loop (EV_DEFAULT_ 0);
2352		3063
2353	=head1 EMBEDDING	3064	=head1 EMBEDDING
2354		3065
2355	Libev can (and often is) directly embedded into host	3066	Libev can (and often is) directly embedded into host
2356	applications. Examples of applications that embed it include the Deliantra	3067	applications. Examples of applications that embed it include the Deliantra
…		…
2363	libev somewhere in your source tree).	3074	libev somewhere in your source tree).
2364		3075
2365	=head2 FILESETS	3076	=head2 FILESETS
2366		3077
2367	Depending on what features you need you need to include one or more sets of files	3078	Depending on what features you need you need to include one or more sets of files
2368	in your app.	3079	in your application.
2369		3080
2370	=head3 CORE EVENT LOOP	3081	=head3 CORE EVENT LOOP
2371		3082
2372	To include only the libev core (all the C<ev_*> functions), with manual	3083	To include only the libev core (all the C<ev_*> functions), with manual
2373	configuration (no autoconf):	3084	configuration (no autoconf):
2374		3085
2375	#define EV_STANDALONE 1	3086	#define EV_STANDALONE 1
2376	#include "ev.c"	3087	#include "ev.c"
2377		3088
2378	This will automatically include F<ev.h>, too, and should be done in a	3089	This will automatically include F<ev.h>, too, and should be done in a
2379	single C source file only to provide the function implementations. To use	3090	single C source file only to provide the function implementations. To use
2380	it, do the same for F<ev.h> in all files wishing to use this API (best	3091	it, do the same for F<ev.h> in all files wishing to use this API (best
2381	done by writing a wrapper around F<ev.h> that you can include instead and	3092	done by writing a wrapper around F<ev.h> that you can include instead and
2382	where you can put other configuration options):	3093	where you can put other configuration options):
2383		3094
2384	#define EV_STANDALONE 1	3095	#define EV_STANDALONE 1
2385	#include "ev.h"	3096	#include "ev.h"
2386		3097
2387	Both header files and implementation files can be compiled with a C++	3098	Both header files and implementation files can be compiled with a C++
2388	compiler (at least, thats a stated goal, and breakage will be treated	3099	compiler (at least, that's a stated goal, and breakage will be treated
2389	as a bug).	3100	as a bug).
2390		3101
2391	You need the following files in your source tree, or in a directory	3102	You need the following files in your source tree, or in a directory
2392	in your include path (e.g. in libev/ when using -Ilibev):	3103	in your include path (e.g. in libev/ when using -Ilibev):
2393		3104
2394	ev.h	3105	ev.h
2395	ev.c	3106	ev.c
2396	ev_vars.h	3107	ev_vars.h
2397	ev_wrap.h	3108	ev_wrap.h
2398		3109
2399	ev_win32.c required on win32 platforms only	3110	ev_win32.c required on win32 platforms only
2400		3111
2401	ev_select.c only when select backend is enabled (which is enabled by default)	3112	ev_select.c only when select backend is enabled (which is enabled by default)
2402	ev_poll.c only when poll backend is enabled (disabled by default)	3113	ev_poll.c only when poll backend is enabled (disabled by default)
2403	ev_epoll.c only when the epoll backend is enabled (disabled by default)	3114	ev_epoll.c only when the epoll backend is enabled (disabled by default)
2404	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	3115	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
2405	ev_port.c only when the solaris port backend is enabled (disabled by default)	3116	ev_port.c only when the solaris port backend is enabled (disabled by default)
2406		3117
2407	F<ev.c> includes the backend files directly when enabled, so you only need	3118	F<ev.c> includes the backend files directly when enabled, so you only need
2408	to compile this single file.	3119	to compile this single file.
2409		3120
2410	=head3 LIBEVENT COMPATIBILITY API	3121	=head3 LIBEVENT COMPATIBILITY API
2411		3122
2412	To include the libevent compatibility API, also include:	3123	To include the libevent compatibility API, also include:
2413		3124
2414	#include "event.c"	3125	#include "event.c"
2415		3126
2416	in the file including F<ev.c>, and:	3127	in the file including F<ev.c>, and:
2417		3128
2418	#include "event.h"	3129	#include "event.h"
2419		3130
2420	in the files that want to use the libevent API. This also includes F<ev.h>.	3131	in the files that want to use the libevent API. This also includes F<ev.h>.
2421		3132
2422	You need the following additional files for this:	3133	You need the following additional files for this:
2423		3134
2424	event.h	3135	event.h
2425	event.c	3136	event.c
2426		3137
2427	=head3 AUTOCONF SUPPORT	3138	=head3 AUTOCONF SUPPORT
2428		3139
2429	Instead of using C<EV_STANDALONE=1> and providing your config in	3140	Instead of using C<EV_STANDALONE=1> and providing your configuration in
2430	whatever way you want, you can also C<m4_include([libev.m4])> in your	3141	whatever way you want, you can also C<m4_include([libev.m4])> in your
2431	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then	3142	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
2432	include F<config.h> and configure itself accordingly.	3143	include F<config.h> and configure itself accordingly.
2433		3144
2434	For this of course you need the m4 file:	3145	For this of course you need the m4 file:
2435		3146
2436	libev.m4	3147	libev.m4
2437		3148
2438	=head2 PREPROCESSOR SYMBOLS/MACROS	3149	=head2 PREPROCESSOR SYMBOLS/MACROS
2439		3150
2440	Libev can be configured via a variety of preprocessor symbols you have to define	3151	Libev can be configured via a variety of preprocessor symbols you have to
2441	before including any of its files. The default is not to build for multiplicity	3152	define before including any of its files. The default in the absence of
2442	and only include the select backend.	3153	autoconf is documented for every option.
2443		3154
2444	=over 4	3155	=over 4
2445		3156
2446	=item EV_STANDALONE	3157	=item EV_STANDALONE
2447		3158
…		…
2452	F<event.h> that are not directly supported by the libev core alone.	3163	F<event.h> that are not directly supported by the libev core alone.
2453		3164
2454	=item EV_USE_MONOTONIC	3165	=item EV_USE_MONOTONIC
2455		3166
2456	If defined to be C<1>, libev will try to detect the availability of the	3167	If defined to be C<1>, libev will try to detect the availability of the
2457	monotonic clock option at both compiletime and runtime. Otherwise no use	3168	monotonic clock option at both compile time and runtime. Otherwise no use
2458	of the monotonic clock option will be attempted. If you enable this, you	3169	of the monotonic clock option will be attempted. If you enable this, you
2459	usually have to link against librt or something similar. Enabling it when	3170	usually have to link against librt or something similar. Enabling it when
2460	the functionality isn't available is safe, though, although you have	3171	the functionality isn't available is safe, though, although you have
2461	to make sure you link against any libraries where the C<clock_gettime>	3172	to make sure you link against any libraries where the C<clock_gettime>
2462	function is hiding in (often F<-lrt>).	3173	function is hiding in (often F<-lrt>).
2463		3174
2464	=item EV_USE_REALTIME	3175	=item EV_USE_REALTIME
2465		3176
2466	If defined to be C<1>, libev will try to detect the availability of the	3177	If defined to be C<1>, libev will try to detect the availability of the
2467	realtime clock option at compiletime (and assume its availability at	3178	real-time clock option at compile time (and assume its availability at
2468	runtime if successful). Otherwise no use of the realtime clock option will	3179	runtime if successful). Otherwise no use of the real-time clock option will
2469	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	3180	be attempted. This effectively replaces C<gettimeofday> by C<clock_get
2470	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the	3181	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the
2471	note about libraries in the description of C<EV_USE_MONOTONIC>, though.	3182	note about libraries in the description of C<EV_USE_MONOTONIC>, though.
2472		3183
2473	=item EV_USE_NANOSLEEP	3184	=item EV_USE_NANOSLEEP
2474		3185
2475	If defined to be C<1>, libev will assume that C<nanosleep ()> is available	3186	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
2476	and will use it for delays. Otherwise it will use C<select ()>.	3187	and will use it for delays. Otherwise it will use C<select ()>.
2477		3188
		3189	=item EV_USE_EVENTFD
		3190
		3191	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		3192	available and will probe for kernel support at runtime. This will improve
		3193	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		3194	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		3195	2.7 or newer, otherwise disabled.
		3196
2478	=item EV_USE_SELECT	3197	=item EV_USE_SELECT
2479		3198
2480	If undefined or defined to be C<1>, libev will compile in support for the	3199	If undefined or defined to be C<1>, libev will compile in support for the
2481	C<select>(2) backend. No attempt at autodetection will be done: if no	3200	C<select>(2) backend. No attempt at auto-detection will be done: if no
2482	other method takes over, select will be it. Otherwise the select backend	3201	other method takes over, select will be it. Otherwise the select backend
2483	will not be compiled in.	3202	will not be compiled in.
2484		3203
2485	=item EV_SELECT_USE_FD_SET	3204	=item EV_SELECT_USE_FD_SET
2486		3205
2487	If defined to C<1>, then the select backend will use the system C<fd_set>	3206	If defined to C<1>, then the select backend will use the system C<fd_set>
2488	structure. This is useful if libev doesn't compile due to a missing	3207	structure. This is useful if libev doesn't compile due to a missing
2489	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on	3208	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout on
2490	exotic systems. This usually limits the range of file descriptors to some	3209	exotic systems. This usually limits the range of file descriptors to some
2491	low limit such as 1024 or might have other limitations (winsocket only	3210	low limit such as 1024 or might have other limitations (winsocket only
2492	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	3211	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might
2493	influence the size of the C<fd_set> used.	3212	influence the size of the C<fd_set> used.
2494		3213
…		…
2518		3237
2519	=item EV_USE_EPOLL	3238	=item EV_USE_EPOLL
2520		3239
2521	If defined to be C<1>, libev will compile in support for the Linux	3240	If defined to be C<1>, libev will compile in support for the Linux
2522	C<epoll>(7) backend. Its availability will be detected at runtime,	3241	C<epoll>(7) backend. Its availability will be detected at runtime,
2523	otherwise another method will be used as fallback. This is the	3242	otherwise another method will be used as fallback. This is the preferred
2524	preferred backend for GNU/Linux systems.	3243	backend for GNU/Linux systems. If undefined, it will be enabled if the
		3244	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2525		3245
2526	=item EV_USE_KQUEUE	3246	=item EV_USE_KQUEUE
2527		3247
2528	If defined to be C<1>, libev will compile in support for the BSD style	3248	If defined to be C<1>, libev will compile in support for the BSD style
2529	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	3249	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
2542	otherwise another method will be used as fallback. This is the preferred	3262	otherwise another method will be used as fallback. This is the preferred
2543	backend for Solaris 10 systems.	3263	backend for Solaris 10 systems.
2544		3264
2545	=item EV_USE_DEVPOLL	3265	=item EV_USE_DEVPOLL
2546		3266
2547	reserved for future expansion, works like the USE symbols above.	3267	Reserved for future expansion, works like the USE symbols above.
2548		3268
2549	=item EV_USE_INOTIFY	3269	=item EV_USE_INOTIFY
2550		3270
2551	If defined to be C<1>, libev will compile in support for the Linux inotify	3271	If defined to be C<1>, libev will compile in support for the Linux inotify
2552	interface to speed up C<ev_stat> watchers. Its actual availability will	3272	interface to speed up C<ev_stat> watchers. Its actual availability will
2553	be detected at runtime.	3273	be detected at runtime. If undefined, it will be enabled if the headers
		3274	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		3275
		3276	=item EV_ATOMIC_T
		3277
		3278	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		3279	access is atomic with respect to other threads or signal contexts. No such
		3280	type is easily found in the C language, so you can provide your own type
		3281	that you know is safe for your purposes. It is used both for signal handler "locking"
		3282	as well as for signal and thread safety in C<ev_async> watchers.
		3283
		3284	In the absence of this define, libev will use C<sig_atomic_t volatile>
		3285	(from F<signal.h>), which is usually good enough on most platforms.
2554		3286
2555	=item EV_H	3287	=item EV_H
2556		3288
2557	The name of the F<ev.h> header file used to include it. The default if	3289	The name of the F<ev.h> header file used to include it. The default if
2558	undefined is C<"ev.h"> in F<event.h> and F<ev.c>. This can be used to	3290	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
2559	virtually rename the F<ev.h> header file in case of conflicts.	3291	used to virtually rename the F<ev.h> header file in case of conflicts.
2560		3292
2561	=item EV_CONFIG_H	3293	=item EV_CONFIG_H
2562		3294
2563	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	3295	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
2564	F<ev.c>'s idea of where to find the F<config.h> file, similarly to	3296	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
2565	C<EV_H>, above.	3297	C<EV_H>, above.
2566		3298
2567	=item EV_EVENT_H	3299	=item EV_EVENT_H
2568		3300
2569	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	3301	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
2570	of how the F<event.h> header can be found, the dfeault is C<"event.h">.	3302	of how the F<event.h> header can be found, the default is C<"event.h">.
2571		3303
2572	=item EV_PROTOTYPES	3304	=item EV_PROTOTYPES
2573		3305
2574	If defined to be C<0>, then F<ev.h> will not define any function	3306	If defined to be C<0>, then F<ev.h> will not define any function
2575	prototypes, but still define all the structs and other symbols. This is	3307	prototypes, but still define all the structs and other symbols. This is
…		…
2596	When doing priority-based operations, libev usually has to linearly search	3328	When doing priority-based operations, libev usually has to linearly search
2597	all the priorities, so having many of them (hundreds) uses a lot of space	3329	all the priorities, so having many of them (hundreds) uses a lot of space
2598	and time, so using the defaults of five priorities (-2 .. +2) is usually	3330	and time, so using the defaults of five priorities (-2 .. +2) is usually
2599	fine.	3331	fine.
2600		3332
2601	If your embedding app does not need any priorities, defining these both to	3333	If your embedding application does not need any priorities, defining these
2602	C<0> will save some memory and cpu.	3334	both to C<0> will save some memory and CPU.
2603		3335
2604	=item EV_PERIODIC_ENABLE	3336	=item EV_PERIODIC_ENABLE
2605		3337
2606	If undefined or defined to be C<1>, then periodic timers are supported. If	3338	If undefined or defined to be C<1>, then periodic timers are supported. If
2607	defined to be C<0>, then they are not. Disabling them saves a few kB of	3339	defined to be C<0>, then they are not. Disabling them saves a few kB of
…		…
2614	code.	3346	code.
2615		3347
2616	=item EV_EMBED_ENABLE	3348	=item EV_EMBED_ENABLE
2617		3349
2618	If undefined or defined to be C<1>, then embed watchers are supported. If	3350	If undefined or defined to be C<1>, then embed watchers are supported. If
2619	defined to be C<0>, then they are not.	3351	defined to be C<0>, then they are not. Embed watchers rely on most other
		3352	watcher types, which therefore must not be disabled.
2620		3353
2621	=item EV_STAT_ENABLE	3354	=item EV_STAT_ENABLE
2622		3355
2623	If undefined or defined to be C<1>, then stat watchers are supported. If	3356	If undefined or defined to be C<1>, then stat watchers are supported. If
2624	defined to be C<0>, then they are not.	3357	defined to be C<0>, then they are not.
…		…
2626	=item EV_FORK_ENABLE	3359	=item EV_FORK_ENABLE
2627		3360
2628	If undefined or defined to be C<1>, then fork watchers are supported. If	3361	If undefined or defined to be C<1>, then fork watchers are supported. If
2629	defined to be C<0>, then they are not.	3362	defined to be C<0>, then they are not.
2630		3363
		3364	=item EV_ASYNC_ENABLE
		3365
		3366	If undefined or defined to be C<1>, then async watchers are supported. If
		3367	defined to be C<0>, then they are not.
		3368
2631	=item EV_MINIMAL	3369	=item EV_MINIMAL
2632		3370
2633	If you need to shave off some kilobytes of code at the expense of some	3371	If you need to shave off some kilobytes of code at the expense of some
2634	speed, define this symbol to C<1>. Currently only used for gcc to override	3372	speed, define this symbol to C<1>. Currently this is used to override some
2635	some inlining decisions, saves roughly 30% codesize of amd64.	3373	inlining decisions, saves roughly 30% code size on amd64. It also selects a
		3374	much smaller 2-heap for timer management over the default 4-heap.
2636		3375
2637	=item EV_PID_HASHSIZE	3376	=item EV_PID_HASHSIZE
2638		3377
2639	C<ev_child> watchers use a small hash table to distribute workload by	3378	C<ev_child> watchers use a small hash table to distribute workload by
2640	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	3379	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
…		…
2647	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),	3386	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
2648	usually more than enough. If you need to manage thousands of C<ev_stat>	3387	usually more than enough. If you need to manage thousands of C<ev_stat>
2649	watchers you might want to increase this value (I<must> be a power of	3388	watchers you might want to increase this value (I<must> be a power of
2650	two).	3389	two).
2651		3390
		3391	=item EV_USE_4HEAP
		3392
		3393	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3394	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		3395	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		3396	faster performance with many (thousands) of watchers.
		3397
		3398	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3399	(disabled).
		3400
		3401	=item EV_HEAP_CACHE_AT
		3402
		3403	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3404	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		3405	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		3406	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		3407	but avoids random read accesses on heap changes. This improves performance
		3408	noticeably with many (hundreds) of watchers.
		3409
		3410	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3411	(disabled).
		3412
		3413	=item EV_VERIFY
		3414
		3415	Controls how much internal verification (see C<ev_loop_verify ()>) will
		3416	be done: If set to C<0>, no internal verification code will be compiled
		3417	in. If set to C<1>, then verification code will be compiled in, but not
		3418	called. If set to C<2>, then the internal verification code will be
		3419	called once per loop, which can slow down libev. If set to C<3>, then the
		3420	verification code will be called very frequently, which will slow down
		3421	libev considerably.
		3422
		3423	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be
		3424	C<0>.
		3425
2652	=item EV_COMMON	3426	=item EV_COMMON
2653		3427
2654	By default, all watchers have a C<void *data> member. By redefining	3428	By default, all watchers have a C<void *data> member. By redefining
2655	this macro to a something else you can include more and other types of	3429	this macro to a something else you can include more and other types of
2656	members. You have to define it each time you include one of the files,	3430	members. You have to define it each time you include one of the files,
2657	though, and it must be identical each time.	3431	though, and it must be identical each time.
2658		3432
2659	For example, the perl EV module uses something like this:	3433	For example, the perl EV module uses something like this:
2660		3434
2661	#define EV_COMMON \	3435	#define EV_COMMON \
2662	SV *self; /* contains this struct */ \	3436	SV *self; /* contains this struct */ \
2663	SV *cb_sv, *fh /* note no trailing ";" */	3437	SV *cb_sv, *fh /* note no trailing ";" */
2664		3438
2665	=item EV_CB_DECLARE (type)	3439	=item EV_CB_DECLARE (type)
2666		3440
2667	=item EV_CB_INVOKE (watcher, revents)	3441	=item EV_CB_INVOKE (watcher, revents)
2668		3442
…		…
2673	definition and a statement, respectively. See the F<ev.h> header file for	3447	definition and a statement, respectively. See the F<ev.h> header file for
2674	their default definitions. One possible use for overriding these is to	3448	their default definitions. One possible use for overriding these is to
2675	avoid the C<struct ev_loop *> as first argument in all cases, or to use	3449	avoid the C<struct ev_loop *> as first argument in all cases, or to use
2676	method calls instead of plain function calls in C++.	3450	method calls instead of plain function calls in C++.
2677		3451
		3452	=back
		3453
2678	=head2 EXPORTED API SYMBOLS	3454	=head2 EXPORTED API SYMBOLS
2679		3455
2680	If you need to re-export the API (e.g. via a dll) and you need a list of	3456	If you need to re-export the API (e.g. via a DLL) and you need a list of
2681	exported symbols, you can use the provided F<Symbol.*> files which list	3457	exported symbols, you can use the provided F<Symbol.*> files which list
2682	all public symbols, one per line:	3458	all public symbols, one per line:
2683		3459
2684	Symbols.ev for libev proper	3460	Symbols.ev for libev proper
2685	Symbols.event for the libevent emulation	3461	Symbols.event for the libevent emulation
2686		3462
2687	This can also be used to rename all public symbols to avoid clashes with	3463	This can also be used to rename all public symbols to avoid clashes with
2688	multiple versions of libev linked together (which is obviously bad in	3464	multiple versions of libev linked together (which is obviously bad in
2689	itself, but sometimes it is inconvinient to avoid this).	3465	itself, but sometimes it is inconvenient to avoid this).
2690		3466
2691	A sed command like this will create wrapper C<#define>'s that you need to	3467	A sed command like this will create wrapper C<#define>'s that you need to
2692	include before including F<ev.h>:	3468	include before including F<ev.h>:
2693		3469
2694	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h	3470	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
…		…
2711	file.	3487	file.
2712		3488
2713	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	3489	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
2714	that everybody includes and which overrides some configure choices:	3490	that everybody includes and which overrides some configure choices:
2715		3491
2716	#define EV_MINIMAL 1	3492	#define EV_MINIMAL 1
2717	#define EV_USE_POLL 0	3493	#define EV_USE_POLL 0
2718	#define EV_MULTIPLICITY 0	3494	#define EV_MULTIPLICITY 0
2719	#define EV_PERIODIC_ENABLE 0	3495	#define EV_PERIODIC_ENABLE 0
2720	#define EV_STAT_ENABLE 0	3496	#define EV_STAT_ENABLE 0
2721	#define EV_FORK_ENABLE 0	3497	#define EV_FORK_ENABLE 0
2722	#define EV_CONFIG_H <config.h>	3498	#define EV_CONFIG_H <config.h>
2723	#define EV_MINPRI 0	3499	#define EV_MINPRI 0
2724	#define EV_MAXPRI 0	3500	#define EV_MAXPRI 0
2725		3501
2726	#include "ev++.h"	3502	#include "ev++.h"
2727		3503
2728	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	3504	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
2729		3505
2730	#include "ev_cpp.h"	3506	#include "ev_cpp.h"
2731	#include "ev.c"	3507	#include "ev.c"
2732		3508
		3509	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
2733		3510
2734	=head1 COMPLEXITIES	3511	=head2 THREADS AND COROUTINES
2735		3512
2736	In this section the complexities of (many of) the algorithms used inside	3513	=head3 THREADS
2737	libev will be explained. For complexity discussions about backends see the
2738	documentation for C<ev_default_init>.
2739		3514
2740	All of the following are about amortised time: If an array needs to be	3515	All libev functions are reentrant and thread-safe unless explicitly
2741	extended, libev needs to realloc and move the whole array, but this	3516	documented otherwise, but libev implements no locking itself. This means
2742	happens asymptotically never with higher number of elements, so O(1) might	3517	that you can use as many loops as you want in parallel, as long as there
2743	mean it might do a lengthy realloc operation in rare cases, but on average	3518	are no concurrent calls into any libev function with the same loop
2744	it is much faster and asymptotically approaches constant time.	3519	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		3520	of course): libev guarantees that different event loops share no data
		3521	structures that need any locking.
		3522
		3523	Or to put it differently: calls with different loop parameters can be done
		3524	concurrently from multiple threads, calls with the same loop parameter
		3525	must be done serially (but can be done from different threads, as long as
		3526	only one thread ever is inside a call at any point in time, e.g. by using
		3527	a mutex per loop).
		3528
		3529	Specifically to support threads (and signal handlers), libev implements
		3530	so-called C<ev_async> watchers, which allow some limited form of
		3531	concurrency on the same event loop, namely waking it up "from the
		3532	outside".
		3533
		3534	If you want to know which design (one loop, locking, or multiple loops
		3535	without or something else still) is best for your problem, then I cannot
		3536	help you, but here is some generic advice:
2745		3537
2746	=over 4	3538	=over 4
2747		3539
2748	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	3540	=item * most applications have a main thread: use the default libev loop
		3541	in that thread, or create a separate thread running only the default loop.
2749		3542
2750	This means that, when you have a watcher that triggers in one hour and	3543	This helps integrating other libraries or software modules that use libev
2751	there are 100 watchers that would trigger before that then inserting will	3544	themselves and don't care/know about threading.
2752	have to skip roughly seven (C<ld 100>) of these watchers.
2753		3545
2754	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)	3546	=item * one loop per thread is usually a good model.
2755		3547
2756	That means that changing a timer costs less than removing/adding them	3548	Doing this is almost never wrong, sometimes a better-performance model
2757	as only the relative motion in the event queue has to be paid for.	3549	exists, but it is always a good start.
2758		3550
2759	=item Starting io/check/prepare/idle/signal/child watchers: O(1)	3551	=item * other models exist, such as the leader/follower pattern, where one
		3552	loop is handed through multiple threads in a kind of round-robin fashion.
2760		3553
2761	These just add the watcher into an array or at the head of a list.	3554	Choosing a model is hard - look around, learn, know that usually you can do
		3555	better than you currently do :-)
2762		3556
2763	=item Stopping check/prepare/idle watchers: O(1)	3557	=item * often you need to talk to some other thread which blocks in the
		3558	event loop.
2764		3559
2765	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	3560	C<ev_async> watchers can be used to wake them up from other threads safely
		3561	(or from signal contexts...).
2766		3562
2767	These watchers are stored in lists then need to be walked to find the	3563	An example use would be to communicate signals or other events that only
2768	correct watcher to remove. The lists are usually short (you don't usually	3564	work in the default loop by registering the signal watcher with the
2769	have many watchers waiting for the same fd or signal).	3565	default loop and triggering an C<ev_async> watcher from the default loop
2770		3566	watcher callback into the event loop interested in the signal.
2771	=item Finding the next timer in each loop iteration: O(1)
2772
2773	By virtue of using a binary heap, the next timer is always found at the
2774	beginning of the storage array.
2775
2776	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
2777
2778	A change means an I/O watcher gets started or stopped, which requires
2779	libev to recalculate its status (and possibly tell the kernel, depending
2780	on backend and wether C<ev_io_set> was used).
2781
2782	=item Activating one watcher (putting it into the pending state): O(1)
2783
2784	=item Priority handling: O(number_of_priorities)
2785
2786	Priorities are implemented by allocating some space for each
2787	priority. When doing priority-based operations, libev usually has to
2788	linearly search all the priorities, but starting/stopping and activating
2789	watchers becomes O(1) w.r.t. prioritiy handling.
2790		3567
2791	=back	3568	=back
2792		3569
		3570	=head3 COROUTINES
2793		3571
2794	=head1 Win32 platform limitations and workarounds	3572	Libev is very accommodating to coroutines ("cooperative threads"):
		3573	libev fully supports nesting calls to its functions from different
		3574	coroutines (e.g. you can call C<ev_loop> on the same loop from two
		3575	different coroutines, and switch freely between both coroutines running the
		3576	loop, as long as you don't confuse yourself). The only exception is that
		3577	you must not do this from C<ev_periodic> reschedule callbacks.
		3578
		3579	Care has been taken to ensure that libev does not keep local state inside
		3580	C<ev_loop>, and other calls do not usually allow for coroutine switches as
		3581	they do not call any callbacks.
		3582
		3583	=head2 COMPILER WARNINGS
		3584
		3585	Depending on your compiler and compiler settings, you might get no or a
		3586	lot of warnings when compiling libev code. Some people are apparently
		3587	scared by this.
		3588
		3589	However, these are unavoidable for many reasons. For one, each compiler
		3590	has different warnings, and each user has different tastes regarding
		3591	warning options. "Warn-free" code therefore cannot be a goal except when
		3592	targeting a specific compiler and compiler-version.
		3593
		3594	Another reason is that some compiler warnings require elaborate
		3595	workarounds, or other changes to the code that make it less clear and less
		3596	maintainable.
		3597
		3598	And of course, some compiler warnings are just plain stupid, or simply
		3599	wrong (because they don't actually warn about the condition their message
		3600	seems to warn about). For example, certain older gcc versions had some
		3601	warnings that resulted an extreme number of false positives. These have
		3602	been fixed, but some people still insist on making code warn-free with
		3603	such buggy versions.
		3604
		3605	While libev is written to generate as few warnings as possible,
		3606	"warn-free" code is not a goal, and it is recommended not to build libev
		3607	with any compiler warnings enabled unless you are prepared to cope with
		3608	them (e.g. by ignoring them). Remember that warnings are just that:
		3609	warnings, not errors, or proof of bugs.
		3610
		3611
		3612	=head2 VALGRIND
		3613
		3614	Valgrind has a special section here because it is a popular tool that is
		3615	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		3616
		3617	If you think you found a bug (memory leak, uninitialised data access etc.)
		3618	in libev, then check twice: If valgrind reports something like:
		3619
		3620	==2274== definitely lost: 0 bytes in 0 blocks.
		3621	==2274== possibly lost: 0 bytes in 0 blocks.
		3622	==2274== still reachable: 256 bytes in 1 blocks.
		3623
		3624	Then there is no memory leak, just as memory accounted to global variables
		3625	is not a memleak - the memory is still being referenced, and didn't leak.
		3626
		3627	Similarly, under some circumstances, valgrind might report kernel bugs
		3628	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		3629	although an acceptable workaround has been found here), or it might be
		3630	confused.
		3631
		3632	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		3633	make it into some kind of religion.
		3634
		3635	If you are unsure about something, feel free to contact the mailing list
		3636	with the full valgrind report and an explanation on why you think this
		3637	is a bug in libev (best check the archives, too :). However, don't be
		3638	annoyed when you get a brisk "this is no bug" answer and take the chance
		3639	of learning how to interpret valgrind properly.
		3640
		3641	If you need, for some reason, empty reports from valgrind for your project
		3642	I suggest using suppression lists.
		3643
		3644
		3645	=head1 PORTABILITY NOTES
		3646
		3647	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
2795		3648
2796	Win32 doesn't support any of the standards (e.g. POSIX) that libev	3649	Win32 doesn't support any of the standards (e.g. POSIX) that libev
2797	requires, and its I/O model is fundamentally incompatible with the POSIX	3650	requires, and its I/O model is fundamentally incompatible with the POSIX
2798	model. Libev still offers limited functionality on this platform in	3651	model. Libev still offers limited functionality on this platform in
2799	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	3652	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
2800	descriptors. This only applies when using Win32 natively, not when using	3653	descriptors. This only applies when using Win32 natively, not when using
2801	e.g. cygwin.	3654	e.g. cygwin.
2802		3655
		3656	Lifting these limitations would basically require the full
		3657	re-implementation of the I/O system. If you are into these kinds of
		3658	things, then note that glib does exactly that for you in a very portable
		3659	way (note also that glib is the slowest event library known to man).
		3660
2803	There is no supported compilation method available on windows except	3661	There is no supported compilation method available on windows except
2804	embedding it into other applications.	3662	embedding it into other applications.
2805		3663
		3664	Not a libev limitation but worth mentioning: windows apparently doesn't
		3665	accept large writes: instead of resulting in a partial write, windows will
		3666	either accept everything or return C<ENOBUFS> if the buffer is too large,
		3667	so make sure you only write small amounts into your sockets (less than a
		3668	megabyte seems safe, but this apparently depends on the amount of memory
		3669	available).
		3670
2806	Due to the many, low, and arbitrary limits on the win32 platform and the	3671	Due to the many, low, and arbitrary limits on the win32 platform and
2807	abysmal performance of winsockets, using a large number of sockets is not	3672	the abysmal performance of winsockets, using a large number of sockets
2808	recommended (and not reasonable). If your program needs to use more than	3673	is not recommended (and not reasonable). If your program needs to use
2809	a hundred or so sockets, then likely it needs to use a totally different	3674	more than a hundred or so sockets, then likely it needs to use a totally
2810	implementation for windows, as libev offers the POSIX model, which cannot	3675	different implementation for windows, as libev offers the POSIX readiness
2811	be implemented efficiently on windows (microsoft monopoly games).	3676	notification model, which cannot be implemented efficiently on windows
		3677	(Microsoft monopoly games).
		3678
		3679	A typical way to use libev under windows is to embed it (see the embedding
		3680	section for details) and use the following F<evwrap.h> header file instead
		3681	of F<ev.h>:
		3682
		3683	#define EV_STANDALONE /* keeps ev from requiring config.h */
		3684	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		3685
		3686	#include "ev.h"
		3687
		3688	And compile the following F<evwrap.c> file into your project (make sure
		3689	you do I<not> compile the F<ev.c> or any other embedded source files!):
		3690
		3691	#include "evwrap.h"
		3692	#include "ev.c"
2812		3693
2813	=over 4	3694	=over 4
2814		3695
2815	=item The winsocket select function	3696	=item The winsocket select function
2816		3697
2817	The winsocket C<select> function doesn't follow POSIX in that it requires	3698	The winsocket C<select> function doesn't follow POSIX in that it
2818	socket I<handles> and not socket I<file descriptors>. This makes select	3699	requires socket I<handles> and not socket I<file descriptors> (it is
2819	very inefficient, and also requires a mapping from file descriptors	3700	also extremely buggy). This makes select very inefficient, and also
2820	to socket handles. See the discussion of the C<EV_SELECT_USE_FD_SET>,	3701	requires a mapping from file descriptors to socket handles (the Microsoft
2821	C<EV_SELECT_IS_WINSOCKET> and C<EV_FD_TO_WIN32_HANDLE> preprocessor	3702	C runtime provides the function C<_open_osfhandle> for this). See the
2822	symbols for more info.	3703	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		3704	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
2823		3705
2824	The configuration for a "naked" win32 using the microsoft runtime	3706	The configuration for a "naked" win32 using the Microsoft runtime
2825	libraries and raw winsocket select is:	3707	libraries and raw winsocket select is:
2826		3708
2827	#define EV_USE_SELECT 1	3709	#define EV_USE_SELECT 1
2828	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */	3710	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
2829		3711
2830	Note that winsockets handling of fd sets is O(n), so you can easily get a	3712	Note that winsockets handling of fd sets is O(n), so you can easily get a
2831	complexity in the O(n²) range when using win32.	3713	complexity in the O(n²) range when using win32.
2832		3714
2833	=item Limited number of file descriptors	3715	=item Limited number of file descriptors
2834		3716
2835	Windows has numerous arbitrary (and low) limits on things. Early versions	3717	Windows has numerous arbitrary (and low) limits on things.
2836	of winsocket's select only supported waiting for a max. of C<64> handles	3718
		3719	Early versions of winsocket's select only supported waiting for a maximum
2837	(probably owning to the fact that all windows kernels can only wait for	3720	of C<64> handles (probably owning to the fact that all windows kernels
2838	C<64> things at the same time internally; microsoft recommends spawning a	3721	can only wait for C<64> things at the same time internally; Microsoft
2839	chain of threads and wait for 63 handles and the previous thread in each).	3722	recommends spawning a chain of threads and wait for 63 handles and the
		3723	previous thread in each. Great).
2840		3724
2841	Newer versions support more handles, but you need to define C<FD_SETSIZE>	3725	Newer versions support more handles, but you need to define C<FD_SETSIZE>
2842	to some high number (e.g. C<2048>) before compiling the winsocket select	3726	to some high number (e.g. C<2048>) before compiling the winsocket select
2843	call (which might be in libev or elsewhere, for example, perl does its own	3727	call (which might be in libev or elsewhere, for example, perl does its own
2844	select emulation on windows).	3728	select emulation on windows).
2845		3729
2846	Another limit is the number of file descriptors in the microsoft runtime	3730	Another limit is the number of file descriptors in the Microsoft runtime
2847	libraries, which by default is C<64> (there must be a hidden I<64> fetish	3731	libraries, which by default is C<64> (there must be a hidden I<64> fetish
2848	or something like this inside microsoft). You can increase this by calling	3732	or something like this inside Microsoft). You can increase this by calling
2849	C<_setmaxstdio>, which can increase this limit to C<2048> (another	3733	C<_setmaxstdio>, which can increase this limit to C<2048> (another
2850	arbitrary limit), but is broken in many versions of the microsoft runtime	3734	arbitrary limit), but is broken in many versions of the Microsoft runtime
2851	libraries.	3735	libraries.
2852		3736
2853	This might get you to about C<512> or C<2048> sockets (depending on	3737	This might get you to about C<512> or C<2048> sockets (depending on
2854	windows version and/or the phase of the moon). To get more, you need to	3738	windows version and/or the phase of the moon). To get more, you need to
2855	wrap all I/O functions and provide your own fd management, but the cost of	3739	wrap all I/O functions and provide your own fd management, but the cost of
2856	calling select (O(n²)) will likely make this unworkable.	3740	calling select (O(n²)) will likely make this unworkable.
2857		3741
2858	=back	3742	=back
2859		3743
		3744	=head2 PORTABILITY REQUIREMENTS
		3745
		3746	In addition to a working ISO-C implementation and of course the
		3747	backend-specific APIs, libev relies on a few additional extensions:
		3748
		3749	=over 4
		3750
		3751	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		3752	calling conventions regardless of C<ev_watcher_type *>.
		3753
		3754	Libev assumes not only that all watcher pointers have the same internal
		3755	structure (guaranteed by POSIX but not by ISO C for example), but it also
		3756	assumes that the same (machine) code can be used to call any watcher
		3757	callback: The watcher callbacks have different type signatures, but libev
		3758	calls them using an C<ev_watcher *> internally.
		3759
		3760	=item C<sig_atomic_t volatile> must be thread-atomic as well
		3761
		3762	The type C<sig_atomic_t volatile> (or whatever is defined as
		3763	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		3764	threads. This is not part of the specification for C<sig_atomic_t>, but is
		3765	believed to be sufficiently portable.
		3766
		3767	=item C<sigprocmask> must work in a threaded environment
		3768
		3769	Libev uses C<sigprocmask> to temporarily block signals. This is not
		3770	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		3771	pthread implementations will either allow C<sigprocmask> in the "main
		3772	thread" or will block signals process-wide, both behaviours would
		3773	be compatible with libev. Interaction between C<sigprocmask> and
		3774	C<pthread_sigmask> could complicate things, however.
		3775
		3776	The most portable way to handle signals is to block signals in all threads
		3777	except the initial one, and run the default loop in the initial thread as
		3778	well.
		3779
		3780	=item C<long> must be large enough for common memory allocation sizes
		3781
		3782	To improve portability and simplify its API, libev uses C<long> internally
		3783	instead of C<size_t> when allocating its data structures. On non-POSIX
		3784	systems (Microsoft...) this might be unexpectedly low, but is still at
		3785	least 31 bits everywhere, which is enough for hundreds of millions of
		3786	watchers.
		3787
		3788	=item C<double> must hold a time value in seconds with enough accuracy
		3789
		3790	The type C<double> is used to represent timestamps. It is required to
		3791	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
		3792	enough for at least into the year 4000. This requirement is fulfilled by
		3793	implementations implementing IEEE 754 (basically all existing ones).
		3794
		3795	=back
		3796
		3797	If you know of other additional requirements drop me a note.
		3798
		3799
		3800	=head1 ALGORITHMIC COMPLEXITIES
		3801
		3802	In this section the complexities of (many of) the algorithms used inside
		3803	libev will be documented. For complexity discussions about backends see
		3804	the documentation for C<ev_default_init>.
		3805
		3806	All of the following are about amortised time: If an array needs to be
		3807	extended, libev needs to realloc and move the whole array, but this
		3808	happens asymptotically rarer with higher number of elements, so O(1) might
		3809	mean that libev does a lengthy realloc operation in rare cases, but on
		3810	average it is much faster and asymptotically approaches constant time.
		3811
		3812	=over 4
		3813
		3814	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
		3815
		3816	This means that, when you have a watcher that triggers in one hour and
		3817	there are 100 watchers that would trigger before that, then inserting will
		3818	have to skip roughly seven (C<ld 100>) of these watchers.
		3819
		3820	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
		3821
		3822	That means that changing a timer costs less than removing/adding them,
		3823	as only the relative motion in the event queue has to be paid for.
		3824
		3825	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
		3826
		3827	These just add the watcher into an array or at the head of a list.
		3828
		3829	=item Stopping check/prepare/idle/fork/async watchers: O(1)
		3830
		3831	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
		3832
		3833	These watchers are stored in lists, so they need to be walked to find the
		3834	correct watcher to remove. The lists are usually short (you don't usually
		3835	have many watchers waiting for the same fd or signal: one is typical, two
		3836	is rare).
		3837
		3838	=item Finding the next timer in each loop iteration: O(1)
		3839
		3840	By virtue of using a binary or 4-heap, the next timer is always found at a
		3841	fixed position in the storage array.
		3842
		3843	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		3844
		3845	A change means an I/O watcher gets started or stopped, which requires
		3846	libev to recalculate its status (and possibly tell the kernel, depending
		3847	on backend and whether C<ev_io_set> was used).
		3848
		3849	=item Activating one watcher (putting it into the pending state): O(1)
		3850
		3851	=item Priority handling: O(number_of_priorities)
		3852
		3853	Priorities are implemented by allocating some space for each
		3854	priority. When doing priority-based operations, libev usually has to
		3855	linearly search all the priorities, but starting/stopping and activating
		3856	watchers becomes O(1) with respect to priority handling.
		3857
		3858	=item Sending an ev_async: O(1)
		3859
		3860	=item Processing ev_async_send: O(number_of_async_watchers)
		3861
		3862	=item Processing signals: O(max_signal_number)
		3863
		3864	Sending involves a system call I<iff> there were no other C<ev_async_send>
		3865	calls in the current loop iteration. Checking for async and signal events
		3866	involves iterating over all running async watchers or all signal numbers.
		3867
		3868	=back
		3869
2860		3870
2861	=head1 AUTHOR	3871	=head1 AUTHOR
2862		3872
2863	Marc Lehmann <libev@schmorp.de>.	3873	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
2864		3874

Diff Legend

–	Removed lines
+	Added lines
<	Changed lines
>	Changed lines