[ViewVC] Diff of: cvs/libev/ev.pod

Comparing libev/ev.pod (file contents):
Revision 1.130 by root, Wed Feb 6 18:34:24 2008 UTC vs.
Revision 1.157 by root, Tue May 20 23:49:41 2008 UTC

…		…
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
		19	// all watcher callbacks have a similar signature
16	/* called when data readable on stdin */	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_ struct 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_ struct 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	struct 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<struct 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
…		…
181	See the description of C<ev_embed> watchers for more info.	196	See the description of C<ev_embed> watchers for more info.
182		197
183	=item ev_set_allocator (void (cb)(void *ptr, long size))	198	=item ev_set_allocator (void (cb)(void *ptr, long size))
184		199
185	Sets the allocation function to use (the prototype is similar - the	200	Sets the allocation function to use (the prototype is similar - the
186	semantics is identical - to the realloc C function). It is used to	201	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	202	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	203	when memory needs to be allocated (C<size != 0>), the library might abort
189	potentially destructive action. The default is your system realloc	204	or take some potentially destructive action.
190	function.	205
		206	Since some systems (at least OpenBSD and Darwin) fail to implement
		207	correct C<realloc> semantics, libev will use a wrapper around the system
		208	C<realloc> and C<free> functions by default.
191		209
192	You could override this function in high-availability programs to, say,	210	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,	211	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.	212	or even to sleep a while and retry until some memory is available.
195		213
196	Example: Replace the libev allocator with one that waits a bit and then	214	Example: Replace the libev allocator with one that waits a bit and then
197	retries).	215	retries (example requires a standards-compliant C<realloc>).
198		216
199	static void *	217	static void *
200	persistent_realloc (void *ptr, size_t size)	218	persistent_realloc (void *ptr, size_t size)
201	{	219	{
202	for (;;)	220	for (;;)
…		…
241		259
242	An event loop is described by a C<struct ev_loop *>. The library knows two	260	An event loop is described by a C<struct ev_loop *>. The library knows two
243	types of such loops, the I<default> loop, which supports signals and child	261	types of such loops, the I<default> loop, which supports signals and child
244	events, and dynamically created loops which do not.	262	events, and dynamically created loops which do not.
245		263
246	If you use threads, a common model is to run the default event loop
247	in your main thread (or in a separate thread) and for each thread you
248	create, you also create another event loop. Libev itself does no locking
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
253	=over 4	264	=over 4
254		265
255	=item struct ev_loop *ev_default_loop (unsigned int flags)	266	=item struct ev_loop *ev_default_loop (unsigned int flags)
256		267
257	This will initialise the default event loop if it hasn't been initialised	268	This will initialise the default event loop if it hasn't been initialised
…		…
259	false. If it already was initialised it simply returns it (and ignores the	270	false. If it already was initialised it simply returns it (and ignores the
260	flags. If that is troubling you, check C<ev_backend ()> afterwards).	271	flags. If that is troubling you, check C<ev_backend ()> afterwards).
261		272
262	If you don't know what event loop to use, use the one returned from this	273	If you don't know what event loop to use, use the one returned from this
263	function.	274	function.
		275
		276	Note that this function is I<not> thread-safe, so if you want to use it
		277	from multiple threads, you have to lock (note also that this is unlikely,
		278	as loops cannot bes hared easily between threads anyway).
264		279
265	The default loop is the only loop that can handle C<ev_signal> and	280	The default loop is the only loop that can handle C<ev_signal> and
266	C<ev_child> watchers, and to do this, it always registers a handler	281	C<ev_child> watchers, and to do this, it always registers a handler
267	for C<SIGCHLD>. If this is a problem for your app you can either	282	for C<SIGCHLD>. If this is a problem for your app you can either
268	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you	283	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you
…		…
297	enabling this flag.	312	enabling this flag.
298		313
299	This works by calling C<getpid ()> on every iteration of the loop,	314	This works by calling C<getpid ()> on every iteration of the loop,
300	and thus this might slow down your event loop if you do a lot of loop	315	and thus this might slow down your event loop if you do a lot of loop
301	iterations and little real work, but is usually not noticeable (on my	316	iterations and little real work, but is usually not noticeable (on my
302	Linux system for example, C<getpid> is actually a simple 5-insn sequence	317	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence
303	without a syscall and thus I<very> fast, but my Linux system also has	318	without a syscall and thus I<very> fast, but my GNU/Linux system also has
304	C<pthread_atfork> which is even faster).	319	C<pthread_atfork> which is even faster).
305		320
306	The big advantage of this flag is that you can forget about fork (and	321	The big advantage of this flag is that you can forget about fork (and
307	forget about forgetting to tell libev about forking) when you use this	322	forget about forgetting to tell libev about forking) when you use this
308	flag.	323	flag.
…		…
321	To get good performance out of this backend you need a high amount of	336	To get good performance out of this backend you need a high amount of
322	parallelity (most of the file descriptors should be busy). If you are	337	parallelity (most of the file descriptors should be busy). If you are
323	writing a server, you should C<accept ()> in a loop to accept as many	338	writing a server, you should C<accept ()> in a loop to accept as many
324	connections as possible during one iteration. You might also want to have	339	connections as possible during one iteration. You might also want to have
325	a look at C<ev_set_io_collect_interval ()> to increase the amount of	340	a look at C<ev_set_io_collect_interval ()> to increase the amount of
326	readyness notifications you get per iteration.	341	readiness notifications you get per iteration.
327		342
328	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)	343	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
329		344
330	And this is your standard poll(2) backend. It's more complicated	345	And this is your standard poll(2) backend. It's more complicated
331	than select, but handles sparse fds better and has no artificial	346	than select, but handles sparse fds better and has no artificial
…		…
339	For few fds, this backend is a bit little slower than poll and select,	354	For few fds, this backend is a bit little slower than poll and select,
340	but it scales phenomenally better. While poll and select usually scale	355	but it scales phenomenally better. While poll and select usually scale
341	like O(total_fds) where n is the total number of fds (or the highest fd),	356	like O(total_fds) where n is the total number of fds (or the highest fd),
342	epoll scales either O(1) or O(active_fds). The epoll design has a number	357	epoll scales either O(1) or O(active_fds). The epoll design has a number
343	of shortcomings, such as silently dropping events in some hard-to-detect	358	of shortcomings, such as silently dropping events in some hard-to-detect
344	cases and rewiring a syscall per fd change, no fork support and bad	359	cases and requiring a syscall per fd change, no fork support and bad
345	support for dup.	360	support for dup.
346		361
347	While stopping, setting and starting an I/O watcher in the same iteration	362	While stopping, setting and starting an I/O watcher in the same iteration
348	will result in some caching, there is still a syscall per such incident	363	will result in some caching, there is still a syscall per such incident
349	(because the fd could point to a different file description now), so its	364	(because the fd could point to a different file description now), so its
…		…
410	While this backend scales well, it requires one system call per active	425	While this backend scales well, it requires one system call per active
411	file descriptor per loop iteration. For small and medium numbers of file	426	file descriptor per loop iteration. For small and medium numbers of file
412	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	427	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
413	might perform better.	428	might perform better.
414		429
415	On the positive side, ignoring the spurious readyness notifications, this	430	On the positive side, ignoring the spurious readiness notifications, this
416	backend actually performed to specification in all tests and is fully	431	backend actually performed to specification in all tests and is fully
417	embeddable, which is a rare feat among the OS-specific backends.	432	embeddable, which is a rare feat among the OS-specific backends.
418		433
419	=item C<EVBACKEND_ALL>	434	=item C<EVBACKEND_ALL>
420		435
…		…
450		465
451	Similar to C<ev_default_loop>, but always creates a new event loop that is	466	Similar to C<ev_default_loop>, but always creates a new event loop that is
452	always distinct from the default loop. Unlike the default loop, it cannot	467	always distinct from the default loop. Unlike the default loop, it cannot
453	handle signal and child watchers, and attempts to do so will be greeted by	468	handle signal and child watchers, and attempts to do so will be greeted by
454	undefined behaviour (or a failed assertion if assertions are enabled).	469	undefined behaviour (or a failed assertion if assertions are enabled).
		470
		471	Note that this function I<is> thread-safe, and the recommended way to use
		472	libev with threads is indeed to create one loop per thread, and using the
		473	default loop in the "main" or "initial" thread.
455		474
456	Example: Try to create a event loop that uses epoll and nothing else.	475	Example: Try to create a event loop that uses epoll and nothing else.
457		476
458	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL \| EVFLAG_NOENV);	477	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL \| EVFLAG_NOENV);
459	if (!epoller)	478	if (!epoller)
…		…
505	=item ev_loop_fork (loop)	524	=item ev_loop_fork (loop)
506		525
507	Like C<ev_default_fork>, but acts on an event loop created by	526	Like C<ev_default_fork>, but acts on an event loop created by
508	C<ev_loop_new>. Yes, you have to call this on every allocated event loop	527	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
509	after fork, and how you do this is entirely your own problem.	528	after fork, and how you do this is entirely your own problem.
		529
		530	=item int ev_is_default_loop (loop)
		531
		532	Returns true when the given loop actually is the default loop, false otherwise.
510		533
511	=item unsigned int ev_loop_count (loop)	534	=item unsigned int ev_loop_count (loop)
512		535
513	Returns the count of loop iterations for the loop, which is identical to	536	Returns the count of loop iterations for the loop, which is identical to
514	the number of times libev did poll for new events. It starts at C<0> and	537	the number of times libev did poll for new events. It starts at C<0> and
…		…
1009	If you must do this, then force the use of a known-to-be-good backend	1032	If you must do this, then force the use of a known-to-be-good backend
1010	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and	1033	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
1011	C<EVBACKEND_POLL>).	1034	C<EVBACKEND_POLL>).
1012		1035
1013	Another thing you have to watch out for is that it is quite easy to	1036	Another thing you have to watch out for is that it is quite easy to
1014	receive "spurious" readyness notifications, that is your callback might	1037	receive "spurious" readiness notifications, that is your callback might
1015	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1038	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1016	because there is no data. Not only are some backends known to create a	1039	because there is no data. Not only are some backends known to create a
1017	lot of those (for example solaris ports), it is very easy to get into	1040	lot of those (for example solaris ports), it is very easy to get into
1018	this situation even with a relatively standard program structure. Thus	1041	this situation even with a relatively standard program structure. Thus
1019	it is best to always use non-blocking I/O: An extra C<read>(2) returning	1042	it is best to always use non-blocking I/O: An extra C<read>(2) returning
…		…
1066	To support fork in your programs, you either have to call	1089	To support fork in your programs, you either have to call
1067	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,	1090	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
1068	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1091	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
1069	C<EVBACKEND_POLL>.	1092	C<EVBACKEND_POLL>.
1070		1093
		1094	=head3 The special problem of SIGPIPE
		1095
		1096	While not really specific to libev, it is easy to forget about SIGPIPE:
		1097	when reading from a pipe whose other end has been closed, your program
		1098	gets send a SIGPIPE, which, by default, aborts your program. For most
		1099	programs this is sensible behaviour, for daemons, this is usually
		1100	undesirable.
		1101
		1102	So when you encounter spurious, unexplained daemon exits, make sure you
		1103	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1104	somewhere, as that would have given you a big clue).
		1105
1071		1106
1072	=head3 Watcher-Specific Functions	1107	=head3 Watcher-Specific Functions
1073		1108
1074	=over 4	1109	=over 4
1075		1110
…		…
1116		1151
1117	Timer watchers are simple relative timers that generate an event after a	1152	Timer watchers are simple relative timers that generate an event after a
1118	given time, and optionally repeating in regular intervals after that.	1153	given time, and optionally repeating in regular intervals after that.
1119		1154
1120	The timers are based on real time, that is, if you register an event that	1155	The timers are based on real time, that is, if you register an event that
1121	times out after an hour and you reset your system clock to last years	1156	times out after an hour and you reset your system clock to january last
1122	time, it will still time out after (roughly) and hour. "Roughly" because	1157	year, it will still time out after (roughly) and hour. "Roughly" because
1123	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1158	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1124	monotonic clock option helps a lot here).	1159	monotonic clock option helps a lot here).
1125		1160
1126	The relative timeouts are calculated relative to the C<ev_now ()>	1161	The relative timeouts are calculated relative to the C<ev_now ()>
1127	time. This is usually the right thing as this timestamp refers to the time	1162	time. This is usually the right thing as this timestamp refers to the time
…		…
1129	you suspect event processing to be delayed and you I<need> to base the timeout	1164	you suspect event processing to be delayed and you I<need> to base the timeout
1130	on the current time, use something like this to adjust for this:	1165	on the current time, use something like this to adjust for this:
1131		1166
1132	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1167	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
1133		1168
1134	The callback is guarenteed to be invoked only when its timeout has passed,	1169	The callback is guarenteed to be invoked only after its timeout has passed,
1135	but if multiple timers become ready during the same loop iteration then	1170	but if multiple timers become ready during the same loop iteration then
1136	order of execution is undefined.	1171	order of execution is undefined.
1137		1172
1138	=head3 Watcher-Specific Functions and Data Members	1173	=head3 Watcher-Specific Functions and Data Members
1139		1174
…		…
1141		1176
1142	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1177	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
1143		1178
1144	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	1179	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
1145		1180
1146	Configure the timer to trigger after C<after> seconds. If C<repeat> is	1181	Configure the timer to trigger after C<after> seconds. If C<repeat>
1147	C<0.>, then it will automatically be stopped. If it is positive, then the	1182	is C<0.>, then it will automatically be stopped once the timeout is
1148	timer will automatically be configured to trigger again C<repeat> seconds	1183	reached. If it is positive, then the timer will automatically be
1149	later, again, and again, until stopped manually.	1184	configured to trigger again C<repeat> seconds later, again, and again,
		1185	until stopped manually.
1150		1186
1151	The timer itself will do a best-effort at avoiding drift, that is, if you	1187	The timer itself will do a best-effort at avoiding drift, that is, if
1152	configure a timer to trigger every 10 seconds, then it will trigger at	1188	you configure a timer to trigger every 10 seconds, then it will normally
1153	exactly 10 second intervals. If, however, your program cannot keep up with	1189	trigger at exactly 10 second intervals. If, however, your program cannot
1154	the timer (because it takes longer than those 10 seconds to do stuff) the	1190	keep up with the timer (because it takes longer than those 10 seconds to
1155	timer will not fire more than once per event loop iteration.	1191	do stuff) the timer will not fire more than once per event loop iteration.
1156		1192
1157	=item ev_timer_again (loop)	1193	=item ev_timer_again (loop, ev_timer *)
1158		1194
1159	This will act as if the timer timed out and restart it again if it is	1195	This will act as if the timer timed out and restart it again if it is
1160	repeating. The exact semantics are:	1196	repeating. The exact semantics are:
1161		1197
1162	If the timer is pending, its pending status is cleared.	1198	If the timer is pending, its pending status is cleared.
…		…
1237	Periodic watchers are also timers of a kind, but they are very versatile	1273	Periodic watchers are also timers of a kind, but they are very versatile
1238	(and unfortunately a bit complex).	1274	(and unfortunately a bit complex).
1239		1275
1240	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1276	Unlike C<ev_timer>'s, they are not based on real time (or relative time)
1241	but on wallclock time (absolute time). You can tell a periodic watcher	1277	but on wallclock time (absolute time). You can tell a periodic watcher
1242	to trigger "at" some specific point in time. For example, if you tell a	1278	to trigger after some specific point in time. For example, if you tell a
1243	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()	1279	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()
1244	+ 10.>) and then reset your system clock to the last year, then it will	1280	+ 10.>, that is, an absolute time not a delay) and then reset your system
		1281	clock to january of the previous year, then it will take more than year
1245	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	1282	to trigger the event (unlike an C<ev_timer>, which would still trigger
1246	roughly 10 seconds later).	1283	roughly 10 seconds later as it uses a relative timeout).
1247		1284
1248	They can also be used to implement vastly more complex timers, such as	1285	C<ev_periodic>s can also be used to implement vastly more complex timers,
1249	triggering an event on each midnight, local time or other, complicated,	1286	such as triggering an event on each "midnight, local time", or other
1250	rules.	1287	complicated, rules.
1251		1288
1252	As with timers, the callback is guarenteed to be invoked only when the	1289	As with timers, the callback is guarenteed to be invoked only when the
1253	time (C<at>) has been passed, but if multiple periodic timers become ready	1290	time (C<at>) has passed, but if multiple periodic timers become ready
1254	during the same loop iteration then order of execution is undefined.	1291	during the same loop iteration then order of execution is undefined.
1255		1292
1256	=head3 Watcher-Specific Functions and Data Members	1293	=head3 Watcher-Specific Functions and Data Members
1257		1294
1258	=over 4	1295	=over 4
…		…
1266		1303
1267	=over 4	1304	=over 4
1268		1305
1269	=item * absolute timer (at = time, interval = reschedule_cb = 0)	1306	=item * absolute timer (at = time, interval = reschedule_cb = 0)
1270		1307
1271	In this configuration the watcher triggers an event at the wallclock time	1308	In this configuration the watcher triggers an event after the wallclock
1272	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	1309	time C<at> has passed and doesn't repeat. It will not adjust when a time
1273	that is, if it is to be run at January 1st 2011 then it will run when the	1310	jump occurs, that is, if it is to be run at January 1st 2011 then it will
1274	system time reaches or surpasses this time.	1311	run when the system time reaches or surpasses this time.
1275		1312
1276	=item * non-repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	1313	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)
1277		1314
1278	In this mode the watcher will always be scheduled to time out at the next	1315	In this mode the watcher will always be scheduled to time out at the next
1279	C<at + N * interval> time (for some integer N, which can also be negative)	1316	C<at + N * interval> time (for some integer N, which can also be negative)
1280	and then repeat, regardless of any time jumps.	1317	and then repeat, regardless of any time jumps.
1281		1318
1282	This can be used to create timers that do not drift with respect to system	1319	This can be used to create timers that do not drift with respect to system
1283	time:	1320	time, for example, here is a C<ev_periodic> that triggers each hour, on
		1321	the hour:
1284		1322
1285	ev_periodic_set (&periodic, 0., 3600., 0);	1323	ev_periodic_set (&periodic, 0., 3600., 0);
1286		1324
1287	This doesn't mean there will always be 3600 seconds in between triggers,	1325	This doesn't mean there will always be 3600 seconds in between triggers,
1288	but only that the the callback will be called when the system time shows a	1326	but only that the the callback will be called when the system time shows a
…		…
1293	C<ev_periodic> will try to run the callback in this mode at the next possible	1331	C<ev_periodic> will try to run the callback in this mode at the next possible
1294	time where C<time = at (mod interval)>, regardless of any time jumps.	1332	time where C<time = at (mod interval)>, regardless of any time jumps.
1295		1333
1296	For numerical stability it is preferable that the C<at> value is near	1334	For numerical stability it is preferable that the C<at> value is near
1297	C<ev_now ()> (the current time), but there is no range requirement for	1335	C<ev_now ()> (the current time), but there is no range requirement for
1298	this value.	1336	this value, and in fact is often specified as zero.
1299		1337
1300	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	1338	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)
1301		1339
1302	In this mode the values for C<interval> and C<at> are both being	1340	In this mode the values for C<interval> and C<at> are both being
1303	ignored. Instead, each time the periodic watcher gets scheduled, the	1341	ignored. Instead, each time the periodic watcher gets scheduled, the
1304	reschedule callback will be called with the watcher as first, and the	1342	reschedule callback will be called with the watcher as first, and the
1305	current time as second argument.	1343	current time as second argument.
1306		1344
1307	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	1345	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,
1308	ever, or make any event loop modifications>. If you need to stop it,	1346	ever, or make ANY event loop modifications whatsoever>.
1309	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by
1310	starting an C<ev_prepare> watcher, which is legal).
1311		1347
		1348	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		1349	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		1350	only event loop modification you are allowed to do).
		1351
1312	Its prototype is C<ev_tstamp (reschedule_cb)(struct ev_periodic w,	1352	The callback prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic
1313	ev_tstamp now)>, e.g.:	1353	*w, ev_tstamp now)>, e.g.:
1314		1354
1315	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1355	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)
1316	{	1356	{
1317	return now + 60.;	1357	return now + 60.;
1318	}	1358	}
…		…
1320	It must return the next time to trigger, based on the passed time value	1360	It must return the next time to trigger, based on the passed time value
1321	(that is, the lowest time value larger than to the second argument). It	1361	(that is, the lowest time value larger than to the second argument). It
1322	will usually be called just before the callback will be triggered, but	1362	will usually be called just before the callback will be triggered, but
1323	might be called at other times, too.	1363	might be called at other times, too.
1324		1364
1325	NOTE: I<< This callback must always return a time that is later than the	1365	NOTE: I<< This callback must always return a time that is higher than or
1326	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	1366	equal to the passed C<now> value >>.
1327		1367
1328	This can be used to create very complex timers, such as a timer that	1368	This can be used to create very complex timers, such as a timer that
1329	triggers on each midnight, local time. To do this, you would calculate the	1369	triggers on "next midnight, local time". To do this, you would calculate the
1330	next midnight after C<now> and return the timestamp value for this. How	1370	next midnight after C<now> and return the timestamp value for this. How
1331	you do this is, again, up to you (but it is not trivial, which is the main	1371	you do this is, again, up to you (but it is not trivial, which is the main
1332	reason I omitted it as an example).	1372	reason I omitted it as an example).
1333		1373
1334	=back	1374	=back
…		…
1338	Simply stops and restarts the periodic watcher again. This is only useful	1378	Simply stops and restarts the periodic watcher again. This is only useful
1339	when you changed some parameters or the reschedule callback would return	1379	when you changed some parameters or the reschedule callback would return
1340	a different time than the last time it was called (e.g. in a crond like	1380	a different time than the last time it was called (e.g. in a crond like
1341	program when the crontabs have changed).	1381	program when the crontabs have changed).
1342		1382
		1383	=item ev_tstamp ev_periodic_at (ev_periodic *)
		1384
		1385	When active, returns the absolute time that the watcher is supposed to
		1386	trigger next.
		1387
1343	=item ev_tstamp offset [read-write]	1388	=item ev_tstamp offset [read-write]
1344		1389
1345	When repeating, this contains the offset value, otherwise this is the	1390	When repeating, this contains the offset value, otherwise this is the
1346	absolute point in time (the C<at> value passed to C<ev_periodic_set>).	1391	absolute point in time (the C<at> value passed to C<ev_periodic_set>).
1347		1392
…		…
1357	=item ev_tstamp (reschedule_cb)(struct ev_periodic w, ev_tstamp now) [read-write]	1402	=item ev_tstamp (reschedule_cb)(struct ev_periodic w, ev_tstamp now) [read-write]
1358		1403
1359	The current reschedule callback, or C<0>, if this functionality is	1404	The current reschedule callback, or C<0>, if this functionality is
1360	switched off. Can be changed any time, but changes only take effect when	1405	switched off. Can be changed any time, but changes only take effect when
1361	the periodic timer fires or C<ev_periodic_again> is being called.	1406	the periodic timer fires or C<ev_periodic_again> is being called.
1362
1363	=item ev_tstamp at [read-only]
1364
1365	When active, contains the absolute time that the watcher is supposed to
1366	trigger next.
1367		1407
1368	=back	1408	=back
1369		1409
1370	=head3 Examples	1410	=head3 Examples
1371		1411
…		…
1415	with the kernel (thus it coexists with your own signal handlers as long	1455	with the kernel (thus it coexists with your own signal handlers as long
1416	as you don't register any with libev). Similarly, when the last signal	1456	as you don't register any with libev). Similarly, when the last signal
1417	watcher for a signal is stopped libev will reset the signal handler to	1457	watcher for a signal is stopped libev will reset the signal handler to
1418	SIG_DFL (regardless of what it was set to before).	1458	SIG_DFL (regardless of what it was set to before).
1419		1459
		1460	If possible and supported, libev will install its handlers with
		1461	C<SA_RESTART> behaviour enabled, so syscalls should not be unduly
		1462	interrupted. If you have a problem with syscalls getting interrupted by
		1463	signals you can block all signals in an C<ev_check> watcher and unblock
		1464	them in an C<ev_prepare> watcher.
		1465
1420	=head3 Watcher-Specific Functions and Data Members	1466	=head3 Watcher-Specific Functions and Data Members
1421		1467
1422	=over 4	1468	=over 4
1423		1469
1424	=item ev_signal_init (ev_signal *, callback, int signum)	1470	=item ev_signal_init (ev_signal *, callback, int signum)
…		…
1432		1478
1433	The signal the watcher watches out for.	1479	The signal the watcher watches out for.
1434		1480
1435	=back	1481	=back
1436		1482
		1483	=head3 Examples
		1484
		1485	Example: Try to exit cleanly on SIGINT and SIGTERM.
		1486
		1487	static void
		1488	sigint_cb (struct ev_loop loop, struct ev_signal w, int revents)
		1489	{
		1490	ev_unloop (loop, EVUNLOOP_ALL);
		1491	}
		1492
		1493	struct ev_signal signal_watcher;
		1494	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		1495	ev_signal_start (loop, &sigint_cb);
		1496
1437		1497
1438	=head2 C<ev_child> - watch out for process status changes	1498	=head2 C<ev_child> - watch out for process status changes
1439		1499
1440	Child watchers trigger when your process receives a SIGCHLD in response to	1500	Child watchers trigger when your process receives a SIGCHLD in response to
1441	some child status changes (most typically when a child of yours dies).	1501	some child status changes (most typically when a child of yours dies). It
		1502	is permissible to install a child watcher I<after> the child has been
		1503	forked (which implies it might have already exited), as long as the event
		1504	loop isn't entered (or is continued from a watcher).
		1505
		1506	Only the default event loop is capable of handling signals, and therefore
		1507	you can only rgeister child watchers in the default event loop.
		1508
		1509	=head3 Process Interaction
		1510
		1511	Libev grabs C<SIGCHLD> as soon as the default event loop is
		1512	initialised. This is necessary to guarantee proper behaviour even if
		1513	the first child watcher is started after the child exits. The occurance
		1514	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		1515	synchronously as part of the event loop processing. Libev always reaps all
		1516	children, even ones not watched.
		1517
		1518	=head3 Overriding the Built-In Processing
		1519
		1520	Libev offers no special support for overriding the built-in child
		1521	processing, but if your application collides with libev's default child
		1522	handler, you can override it easily by installing your own handler for
		1523	C<SIGCHLD> after initialising the default loop, and making sure the
		1524	default loop never gets destroyed. You are encouraged, however, to use an
		1525	event-based approach to child reaping and thus use libev's support for
		1526	that, so other libev users can use C<ev_child> watchers freely.
1442		1527
1443	=head3 Watcher-Specific Functions and Data Members	1528	=head3 Watcher-Specific Functions and Data Members
1444		1529
1445	=over 4	1530	=over 4
1446		1531
…		…
1472		1557
1473	=back	1558	=back
1474		1559
1475	=head3 Examples	1560	=head3 Examples
1476		1561
1477	Example: Try to exit cleanly on SIGINT and SIGTERM.	1562	Example: C<fork()> a new process and install a child handler to wait for
		1563	its completion.
		1564
		1565	ev_child cw;
1478		1566
1479	static void	1567	static void
1480	sigint_cb (struct ev_loop loop, struct ev_signal w, int revents)	1568	child_cb (EV_P_ struct ev_child *w, int revents)
1481	{	1569	{
1482	ev_unloop (loop, EVUNLOOP_ALL);	1570	ev_child_stop (EV_A_ w);
		1571	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1483	}	1572	}
1484		1573
1485	struct ev_signal signal_watcher;	1574	pid_t pid = fork ();
1486	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	1575
1487	ev_signal_start (loop, &sigint_cb);	1576	if (pid < 0)
		1577	// error
		1578	else if (pid == 0)
		1579	{
		1580	// the forked child executes here
		1581	exit (1);
		1582	}
		1583	else
		1584	{
		1585	ev_child_init (&cw, child_cb, pid, 0);
		1586	ev_child_start (EV_DEFAULT_ &cw);
		1587	}
1488		1588
1489		1589
1490	=head2 C<ev_stat> - did the file attributes just change?	1590	=head2 C<ev_stat> - did the file attributes just change?
1491		1591
1492	This watches a filesystem path for attribute changes. That is, it calls	1592	This watches a filesystem path for attribute changes. That is, it calls
…		…
1515	as even with OS-supported change notifications, this can be	1615	as even with OS-supported change notifications, this can be
1516	resource-intensive.	1616	resource-intensive.
1517		1617
1518	At the time of this writing, only the Linux inotify interface is	1618	At the time of this writing, only the Linux inotify interface is
1519	implemented (implementing kqueue support is left as an exercise for the	1619	implemented (implementing kqueue support is left as an exercise for the
		1620	reader, note, however, that the author sees no way of implementing ev_stat
1520	reader). Inotify will be used to give hints only and should not change the	1621	semantics with kqueue). Inotify will be used to give hints only and should
1521	semantics of C<ev_stat> watchers, which means that libev sometimes needs	1622	not change the semantics of C<ev_stat> watchers, which means that libev
1522	to fall back to regular polling again even with inotify, but changes are	1623	sometimes needs to fall back to regular polling again even with inotify,
1523	usually detected immediately, and if the file exists there will be no	1624	but changes are usually detected immediately, and if the file exists there
1524	polling.	1625	will be no polling.
		1626
		1627	=head3 ABI Issues (Largefile Support)
		1628
		1629	Libev by default (unless the user overrides this) uses the default
		1630	compilation environment, which means that on systems with optionally
		1631	disabled large file support, you get the 32 bit version of the stat
		1632	structure. When using the library from programs that change the ABI to
		1633	use 64 bit file offsets the programs will fail. In that case you have to
		1634	compile libev with the same flags to get binary compatibility. This is
		1635	obviously the case with any flags that change the ABI, but the problem is
		1636	most noticably with ev_stat and largefile support.
1525		1637
1526	=head3 Inotify	1638	=head3 Inotify
1527		1639
1528	When C<inotify (7)> support has been compiled into libev (generally only	1640	When C<inotify (7)> support has been compiled into libev (generally only
1529	available on Linux) and present at runtime, it will be used to speed up	1641	available on Linux) and present at runtime, it will be used to speed up
1530	change detection where possible. The inotify descriptor will be created lazily	1642	change detection where possible. The inotify descriptor will be created lazily
1531	when the first C<ev_stat> watcher is being started.	1643	when the first C<ev_stat> watcher is being started.
1532		1644
1533	Inotify presense does not change the semantics of C<ev_stat> watchers	1645	Inotify presence does not change the semantics of C<ev_stat> watchers
1534	except that changes might be detected earlier, and in some cases, to avoid	1646	except that changes might be detected earlier, and in some cases, to avoid
1535	making regular C<stat> calls. Even in the presense of inotify support	1647	making regular C<stat> calls. Even in the presence of inotify support
1536	there are many cases where libev has to resort to regular C<stat> polling.	1648	there are many cases where libev has to resort to regular C<stat> polling.
1537		1649
1538	(There is no support for kqueue, as apparently it cannot be used to	1650	(There is no support for kqueue, as apparently it cannot be used to
1539	implement this functionality, due to the requirement of having a file	1651	implement this functionality, due to the requirement of having a file
1540	descriptor open on the object at all times).	1652	descriptor open on the object at all times).
…		…
1543		1655
1544	The C<stat ()> syscall only supports full-second resolution portably, and	1656	The C<stat ()> syscall only supports full-second resolution portably, and
1545	even on systems where the resolution is higher, many filesystems still	1657	even on systems where the resolution is higher, many filesystems still
1546	only support whole seconds.	1658	only support whole seconds.
1547		1659
1548	That means that, if the time is the only thing that changes, you might	1660	That means that, if the time is the only thing that changes, you can
1549	miss updates: on the first update, C<ev_stat> detects a change and calls	1661	easily miss updates: on the first update, C<ev_stat> detects a change and
1550	your callback, which does something. When there is another update within	1662	calls your callback, which does something. When there is another update
1551	the same second, C<ev_stat> will be unable to detect it.	1663	within the same second, C<ev_stat> will be unable to detect it as the stat
		1664	data does not change.
1552		1665
1553	The solution to this is to delay acting on a change for a second (or till	1666	The solution to this is to delay acting on a change for slightly more
1554	the next second boundary), using a roughly one-second delay C<ev_timer>	1667	than a second (or till slightly after the next full second boundary), using
1555	(C<ev_timer_set (w, 0., 1.01); ev_timer_again (loop, w)>). The C<.01>	1668	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
1556	is added to work around small timing inconsistencies of some operating	1669	ev_timer_again (loop, w)>).
1557	systems.	1670
		1671	The C<.02> offset is added to work around small timing inconsistencies
		1672	of some operating systems (where the second counter of the current time
		1673	might be be delayed. One such system is the Linux kernel, where a call to
		1674	C<gettimeofday> might return a timestamp with a full second later than
		1675	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		1676	update file times then there will be a small window where the kernel uses
		1677	the previous second to update file times but libev might already execute
		1678	the timer callback).
1558		1679
1559	=head3 Watcher-Specific Functions and Data Members	1680	=head3 Watcher-Specific Functions and Data Members
1560		1681
1561	=over 4	1682	=over 4
1562		1683
…		…
1568	C<path>. The C<interval> is a hint on how quickly a change is expected to	1689	C<path>. The C<interval> is a hint on how quickly a change is expected to
1569	be detected and should normally be specified as C<0> to let libev choose	1690	be detected and should normally be specified as C<0> to let libev choose
1570	a suitable value. The memory pointed to by C<path> must point to the same	1691	a suitable value. The memory pointed to by C<path> must point to the same
1571	path for as long as the watcher is active.	1692	path for as long as the watcher is active.
1572		1693
1573	The callback will be receive C<EV_STAT> when a change was detected,	1694	The callback will receive C<EV_STAT> when a change was detected, relative
1574	relative to the attributes at the time the watcher was started (or the	1695	to the attributes at the time the watcher was started (or the last change
1575	last change was detected).	1696	was detected).
1576		1697
1577	=item ev_stat_stat (ev_stat *)	1698	=item ev_stat_stat (loop, ev_stat *)
1578		1699
1579	Updates the stat buffer immediately with new values. If you change the	1700	Updates the stat buffer immediately with new values. If you change the
1580	watched path in your callback, you could call this fucntion to avoid	1701	watched path in your callback, you could call this function to avoid
1581	detecting this change (while introducing a race condition). Can also be	1702	detecting this change (while introducing a race condition if you are not
1582	useful simply to find out the new values.	1703	the only one changing the path). Can also be useful simply to find out the
		1704	new values.
1583		1705
1584	=item ev_statdata attr [read-only]	1706	=item ev_statdata attr [read-only]
1585		1707
1586	The most-recently detected attributes of the file. Although the type is of	1708	The most-recently detected attributes of the file. Although the type is
1587	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types	1709	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
1588	suitable for your system. If the C<st_nlink> member is C<0>, then there	1710	suitable for your system, but you can only rely on the POSIX-standardised
		1711	members to be present. If the C<st_nlink> member is C<0>, then there was
1589	was some error while C<stat>ing the file.	1712	some error while C<stat>ing the file.
1590		1713
1591	=item ev_statdata prev [read-only]	1714	=item ev_statdata prev [read-only]
1592		1715
1593	The previous attributes of the file. The callback gets invoked whenever	1716	The previous attributes of the file. The callback gets invoked whenever
1594	C<prev> != C<attr>.	1717	C<prev> != C<attr>, or, more precisely, one or more of these members
		1718	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		1719	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
1595		1720
1596	=item ev_tstamp interval [read-only]	1721	=item ev_tstamp interval [read-only]
1597		1722
1598	The specified interval.	1723	The specified interval.
1599		1724
…		…
1653	}	1778	}
1654		1779
1655	...	1780	...
1656	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);	1781	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
1657	ev_stat_start (loop, &passwd);	1782	ev_stat_start (loop, &passwd);
1658	ev_timer_init (&timer, timer_cb, 0., 1.01);	1783	ev_timer_init (&timer, timer_cb, 0., 1.02);
1659		1784
1660		1785
1661	=head2 C<ev_idle> - when you've got nothing better to do...	1786	=head2 C<ev_idle> - when you've got nothing better to do...
1662		1787
1663	Idle watchers trigger events when no other events of the same or higher	1788	Idle watchers trigger events when no other events of the same or higher
…		…
1751		1876
1752	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	1877	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
1753	priority, to ensure that they are being run before any other watchers	1878	priority, to ensure that they are being run before any other watchers
1754	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,	1879	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,
1755	too) should not activate ("feed") events into libev. While libev fully	1880	too) should not activate ("feed") events into libev. While libev fully
1756	supports this, they will be called before other C<ev_check> watchers	1881	supports this, they might get executed before other C<ev_check> watchers
1757	did their job. As C<ev_check> watchers are often used to embed other	1882	did their job. As C<ev_check> watchers are often used to embed other
1758	(non-libev) event loops those other event loops might be in an unusable	1883	(non-libev) event loops those other event loops might be in an unusable
1759	state until their C<ev_check> watcher ran (always remind yourself to	1884	state until their C<ev_check> watcher ran (always remind yourself to
1760	coexist peacefully with others).	1885	coexist peacefully with others).
1761		1886
…		…
1776	=head3 Examples	1901	=head3 Examples
1777		1902
1778	There are a number of principal ways to embed other event loops or modules	1903	There are a number of principal ways to embed other event loops or modules
1779	into libev. Here are some ideas on how to include libadns into libev	1904	into libev. Here are some ideas on how to include libadns into libev
1780	(there is a Perl module named C<EV::ADNS> that does this, which you could	1905	(there is a Perl module named C<EV::ADNS> that does this, which you could
1781	use for an actually working example. Another Perl module named C<EV::Glib>	1906	use as a working example. Another Perl module named C<EV::Glib> embeds a
1782	embeds a Glib main context into libev, and finally, C<Glib::EV> embeds EV	1907	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
1783	into the Glib event loop).	1908	Glib event loop).
1784		1909
1785	Method 1: Add IO watchers and a timeout watcher in a prepare handler,	1910	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
1786	and in a check watcher, destroy them and call into libadns. What follows	1911	and in a check watcher, destroy them and call into libadns. What follows
1787	is pseudo-code only of course. This requires you to either use a low	1912	is pseudo-code only of course. This requires you to either use a low
1788	priority for the check watcher or use C<ev_clear_pending> explicitly, as	1913	priority for the check watcher or use C<ev_clear_pending> explicitly, as
…		…
2098	{	2223	{
2099	sometype data;	2224	sometype data;
2100		2225
2101	// no locking etc.	2226	// no locking etc.
2102	queue_put (data);	2227	queue_put (data);
2103	ev_async_send (DEFAULT_ &mysig);	2228	ev_async_send (EV_DEFAULT_ &mysig);
2104	}	2229	}
2105		2230
2106	static void	2231	static void
2107	mysig_cb (EV_P_ ev_async *w, int revents)	2232	mysig_cb (EV_P_ ev_async *w, int revents)
2108	{	2233	{
…		…
2139	// only need to lock the actual queueing operation	2264	// only need to lock the actual queueing operation
2140	pthread_mutex_lock (&mymutex);	2265	pthread_mutex_lock (&mymutex);
2141	queue_put (data);	2266	queue_put (data);
2142	pthread_mutex_unlock (&mymutex);	2267	pthread_mutex_unlock (&mymutex);
2143		2268
2144	ev_async_send (DEFAULT_ &mysig);	2269	ev_async_send (EV_DEFAULT_ &mysig);
2145	}	2270	}
2146		2271
2147	static void	2272	static void
2148	mysig_cb (EV_P_ ev_async *w, int revents)	2273	mysig_cb (EV_P_ ev_async *w, int revents)
2149	{	2274	{
…		…
2177	section below on what exactly this means).	2302	section below on what exactly this means).
2178		2303
2179	This call incurs the overhead of a syscall only once per loop iteration,	2304	This call incurs the overhead of a syscall only once per loop iteration,
2180	so while the overhead might be noticable, it doesn't apply to repeated	2305	so while the overhead might be noticable, it doesn't apply to repeated
2181	calls to C<ev_async_send>.	2306	calls to C<ev_async_send>.
		2307
		2308	=item bool = ev_async_pending (ev_async *)
		2309
		2310	Returns a non-zero value when C<ev_async_send> has been called on the
		2311	watcher but the event has not yet been processed (or even noted) by the
		2312	event loop.
		2313
		2314	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		2315	the loop iterates next and checks for the watcher to have become active,
		2316	it will reset the flag again. C<ev_async_pending> can be used to very
		2317	quickly check wether invoking the loop might be a good idea.
		2318
		2319	Not that this does I<not> check wether the watcher itself is pending, only
		2320	wether it has been requested to make this watcher pending.
2182		2321
2183	=back	2322	=back
2184		2323
2185		2324
2186	=head1 OTHER FUNCTIONS	2325	=head1 OTHER FUNCTIONS
…		…
2258		2397
2259	=item * Priorities are not currently supported. Initialising priorities	2398	=item * Priorities are not currently supported. Initialising priorities
2260	will fail and all watchers will have the same priority, even though there	2399	will fail and all watchers will have the same priority, even though there
2261	is an ev_pri field.	2400	is an ev_pri field.
2262		2401
		2402	=item * In libevent, the last base created gets the signals, in libev, the
		2403	first base created (== the default loop) gets the signals.
		2404
2263	=item * Other members are not supported.	2405	=item * Other members are not supported.
2264		2406
2265	=item * The libev emulation is I<not> ABI compatible to libevent, you need	2407	=item * The libev emulation is I<not> ABI compatible to libevent, you need
2266	to use the libev header file and library.	2408	to use the libev header file and library.
2267		2409
…		…
2430	io.start (fd, ev::READ);	2572	io.start (fd, ev::READ);
2431	}	2573	}
2432	};	2574	};
2433		2575
2434		2576
		2577	=head1 OTHER LANGUAGE BINDINGS
		2578
		2579	Libev does not offer other language bindings itself, but bindings for a
		2580	numbe rof languages exist in the form of third-party packages. If you know
		2581	any interesting language binding in addition to the ones listed here, drop
		2582	me a note.
		2583
		2584	=over 4
		2585
		2586	=item Perl
		2587
		2588	The EV module implements the full libev API and is actually used to test
		2589	libev. EV is developed together with libev. Apart from the EV core module,
		2590	there are additional modules that implement libev-compatible interfaces
		2591	to C<libadns> (C<EV::ADNS>), C<Net::SNMP> (C<Net::SNMP::EV>) and the
		2592	C<libglib> event core (C<Glib::EV> and C<EV::Glib>).
		2593
		2594	It can be found and installed via CPAN, its homepage is found at
		2595	L<http://software.schmorp.de/pkg/EV>.
		2596
		2597	=item Ruby
		2598
		2599	Tony Arcieri has written a ruby extension that offers access to a subset
		2600	of the libev API and adds filehandle abstractions, asynchronous DNS and
		2601	more on top of it. It can be found via gem servers. Its homepage is at
		2602	L<http://rev.rubyforge.org/>.
		2603
		2604	=item D
		2605
		2606	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		2607	be found at L<http://git.llucax.com.ar/?p=software/ev.d.git;a=summary>.
		2608
		2609	=back
		2610
		2611
2435	=head1 MACRO MAGIC	2612	=head1 MACRO MAGIC
2436		2613
2437	Libev can be compiled with a variety of options, the most fundamantal	2614	Libev can be compiled with a variety of options, the most fundamantal
2438	of which is C<EV_MULTIPLICITY>. This option determines whether (most)	2615	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
2439	functions and callbacks have an initial C<struct ev_loop *> argument.	2616	functions and callbacks have an initial C<struct ev_loop *> argument.
…		…
2473		2650
2474	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	2651	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
2475		2652
2476	Similar to the other two macros, this gives you the value of the default	2653	Similar to the other two macros, this gives you the value of the default
2477	loop, if multiple loops are supported ("ev loop default").	2654	loop, if multiple loops are supported ("ev loop default").
		2655
		2656	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		2657
		2658	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		2659	default loop has been initialised (C<UC> == unchecked). Their behaviour
		2660	is undefined when the default loop has not been initialised by a previous
		2661	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		2662
		2663	It is often prudent to use C<EV_DEFAULT> when initialising the first
		2664	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
2478		2665
2479	=back	2666	=back
2480		2667
2481	Example: Declare and initialise a check watcher, utilising the above	2668	Example: Declare and initialise a check watcher, utilising the above
2482	macros so it will work regardless of whether multiple loops are supported	2669	macros so it will work regardless of whether multiple loops are supported
…		…
2578		2765
2579	libev.m4	2766	libev.m4
2580		2767
2581	=head2 PREPROCESSOR SYMBOLS/MACROS	2768	=head2 PREPROCESSOR SYMBOLS/MACROS
2582		2769
2583	Libev can be configured via a variety of preprocessor symbols you have to define	2770	Libev can be configured via a variety of preprocessor symbols you have to
2584	before including any of its files. The default is not to build for multiplicity	2771	define before including any of its files. The default in the absense of
2585	and only include the select backend.	2772	autoconf is noted for every option.
2586		2773
2587	=over 4	2774	=over 4
2588		2775
2589	=item EV_STANDALONE	2776	=item EV_STANDALONE
2590		2777
…		…
2616	=item EV_USE_NANOSLEEP	2803	=item EV_USE_NANOSLEEP
2617		2804
2618	If defined to be C<1>, libev will assume that C<nanosleep ()> is available	2805	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
2619	and will use it for delays. Otherwise it will use C<select ()>.	2806	and will use it for delays. Otherwise it will use C<select ()>.
2620		2807
		2808	=item EV_USE_EVENTFD
		2809
		2810	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		2811	available and will probe for kernel support at runtime. This will improve
		2812	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		2813	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		2814	2.7 or newer, otherwise disabled.
		2815
2621	=item EV_USE_SELECT	2816	=item EV_USE_SELECT
2622		2817
2623	If undefined or defined to be C<1>, libev will compile in support for the	2818	If undefined or defined to be C<1>, libev will compile in support for the
2624	C<select>(2) backend. No attempt at autodetection will be done: if no	2819	C<select>(2) backend. No attempt at autodetection will be done: if no
2625	other method takes over, select will be it. Otherwise the select backend	2820	other method takes over, select will be it. Otherwise the select backend
…		…
2661		2856
2662	=item EV_USE_EPOLL	2857	=item EV_USE_EPOLL
2663		2858
2664	If defined to be C<1>, libev will compile in support for the Linux	2859	If defined to be C<1>, libev will compile in support for the Linux
2665	C<epoll>(7) backend. Its availability will be detected at runtime,	2860	C<epoll>(7) backend. Its availability will be detected at runtime,
2666	otherwise another method will be used as fallback. This is the	2861	otherwise another method will be used as fallback. This is the preferred
2667	preferred backend for GNU/Linux systems.	2862	backend for GNU/Linux systems. If undefined, it will be enabled if the
		2863	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2668		2864
2669	=item EV_USE_KQUEUE	2865	=item EV_USE_KQUEUE
2670		2866
2671	If defined to be C<1>, libev will compile in support for the BSD style	2867	If defined to be C<1>, libev will compile in support for the BSD style
2672	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	2868	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
2691		2887
2692	=item EV_USE_INOTIFY	2888	=item EV_USE_INOTIFY
2693		2889
2694	If defined to be C<1>, libev will compile in support for the Linux inotify	2890	If defined to be C<1>, libev will compile in support for the Linux inotify
2695	interface to speed up C<ev_stat> watchers. Its actual availability will	2891	interface to speed up C<ev_stat> watchers. Its actual availability will
2696	be detected at runtime.	2892	be detected at runtime. If undefined, it will be enabled if the headers
		2893	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2697		2894
2698	=item EV_ATOMIC_T	2895	=item EV_ATOMIC_T
2699		2896
2700	Libev requires an integer type (suitable for storing C<0> or C<1>) whose	2897	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
2701	access is atomic with respect to other threads or signal contexts. No such	2898	access is atomic with respect to other threads or signal contexts. No such
…		…
2788	defined to be C<0>, then they are not.	2985	defined to be C<0>, then they are not.
2789		2986
2790	=item EV_MINIMAL	2987	=item EV_MINIMAL
2791		2988
2792	If you need to shave off some kilobytes of code at the expense of some	2989	If you need to shave off some kilobytes of code at the expense of some
2793	speed, define this symbol to C<1>. Currently only used for gcc to override	2990	speed, define this symbol to C<1>. Currently this is used to override some
2794	some inlining decisions, saves roughly 30% codesize of amd64.	2991	inlining decisions, saves roughly 30% codesize of amd64. It also selects a
		2992	much smaller 2-heap for timer management over the default 4-heap.
2795		2993
2796	=item EV_PID_HASHSIZE	2994	=item EV_PID_HASHSIZE
2797		2995
2798	C<ev_child> watchers use a small hash table to distribute workload by	2996	C<ev_child> watchers use a small hash table to distribute workload by
2799	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	2997	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
…		…
2805	C<ev_stat> watchers use a small hash table to distribute workload by	3003	C<ev_stat> watchers use a small hash table to distribute workload by
2806	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),	3004	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
2807	usually more than enough. If you need to manage thousands of C<ev_stat>	3005	usually more than enough. If you need to manage thousands of C<ev_stat>
2808	watchers you might want to increase this value (I<must> be a power of	3006	watchers you might want to increase this value (I<must> be a power of
2809	two).	3007	two).
		3008
		3009	=item EV_USE_4HEAP
		3010
		3011	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3012	timer and periodics heap, libev uses a 4-heap when this symbol is defined
		3013	to C<1>. The 4-heap uses more complicated (longer) code but has
		3014	noticably faster performance with many (thousands) of watchers.
		3015
		3016	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3017	(disabled).
		3018
		3019	=item EV_HEAP_CACHE_AT
		3020
		3021	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3022	timer and periodics heap, libev can cache the timestamp (I<at>) within
		3023	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		3024	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		3025	but avoids random read accesses on heap changes. This improves performance
		3026	noticably with with many (hundreds) of watchers.
		3027
		3028	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3029	(disabled).
2810		3030
2811	=item EV_COMMON	3031	=item EV_COMMON
2812		3032
2813	By default, all watchers have a C<void *data> member. By redefining	3033	By default, all watchers have a C<void *data> member. By redefining
2814	this macro to a something else you can include more and other types of	3034	this macro to a something else you can include more and other types of
…		…
2888		3108
2889	#include "ev_cpp.h"	3109	#include "ev_cpp.h"
2890	#include "ev.c"	3110	#include "ev.c"
2891		3111
2892		3112
		3113	=head1 THREADS AND COROUTINES
		3114
		3115	=head2 THREADS
		3116
		3117	Libev itself is completely threadsafe, but it uses no locking. This
		3118	means that you can use as many loops as you want in parallel, as long as
		3119	only one thread ever calls into one libev function with the same loop
		3120	parameter.
		3121
		3122	Or put differently: calls with different loop parameters can be done in
		3123	parallel from multiple threads, calls with the same loop parameter must be
		3124	done serially (but can be done from different threads, as long as only one
		3125	thread ever is inside a call at any point in time, e.g. by using a mutex
		3126	per loop).
		3127
		3128	If you want to know which design is best for your problem, then I cannot
		3129	help you but by giving some generic advice:
		3130
		3131	=over 4
		3132
		3133	=item * most applications have a main thread: use the default libev loop
		3134	in that thread, or create a seperate thread running only the default loop.
		3135
		3136	This helps integrating other libraries or software modules that use libev
		3137	themselves and don't care/know about threading.
		3138
		3139	=item * one loop per thread is usually a good model.
		3140
		3141	Doing this is almost never wrong, sometimes a better-performance model
		3142	exists, but it is always a good start.
		3143
		3144	=item * other models exist, such as the leader/follower pattern, where one
		3145	loop is handed through multiple threads in a kind of round-robbin fashion.
		3146
		3147	Chosing a model is hard - look around, learn, know that usually you cna do
		3148	better than you currently do :-)
		3149
		3150	=item * often you need to talk to some other thread which blocks in the
		3151	event loop - C<ev_async> watchers can be used to wake them up from other
		3152	threads safely (or from signal contexts...).
		3153
		3154	=back
		3155
		3156	=head2 COROUTINES
		3157
		3158	Libev is much more accomodating to coroutines ("cooperative threads"):
		3159	libev fully supports nesting calls to it's functions from different
		3160	coroutines (e.g. you can call C<ev_loop> on the same loop from two
		3161	different coroutines and switch freely between both coroutines running the
		3162	loop, as long as you don't confuse yourself). The only exception is that
		3163	you must not do this from C<ev_periodic> reschedule callbacks.
		3164
		3165	Care has been invested into making sure that libev does not keep local
		3166	state inside C<ev_loop>, and other calls do not usually allow coroutine
		3167	switches.
		3168
		3169
2893	=head1 COMPLEXITIES	3170	=head1 COMPLEXITIES
2894		3171
2895	In this section the complexities of (many of) the algorithms used inside	3172	In this section the complexities of (many of) the algorithms used inside
2896	libev will be explained. For complexity discussions about backends see the	3173	libev will be explained. For complexity discussions about backends see the
2897	documentation for C<ev_default_init>.	3174	documentation for C<ev_default_init>.
…		…
2927	correct watcher to remove. The lists are usually short (you don't usually	3204	correct watcher to remove. The lists are usually short (you don't usually
2928	have many watchers waiting for the same fd or signal).	3205	have many watchers waiting for the same fd or signal).
2929		3206
2930	=item Finding the next timer in each loop iteration: O(1)	3207	=item Finding the next timer in each loop iteration: O(1)
2931		3208
2932	By virtue of using a binary heap, the next timer is always found at the	3209	By virtue of using a binary or 4-heap, the next timer is always found at a
2933	beginning of the storage array.	3210	fixed position in the storage array.
2934		3211
2935	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)	3212	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
2936		3213
2937	A change means an I/O watcher gets started or stopped, which requires	3214	A change means an I/O watcher gets started or stopped, which requires
2938	libev to recalculate its status (and possibly tell the kernel, depending	3215	libev to recalculate its status (and possibly tell the kernel, depending
…		…
2967	model. Libev still offers limited functionality on this platform in	3244	model. Libev still offers limited functionality on this platform in
2968	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	3245	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
2969	descriptors. This only applies when using Win32 natively, not when using	3246	descriptors. This only applies when using Win32 natively, not when using
2970	e.g. cygwin.	3247	e.g. cygwin.
2971		3248
		3249	Lifting these limitations would basically require the full
		3250	re-implementation of the I/O system. If you are into these kinds of
		3251	things, then note that glib does exactly that for you in a very portable
		3252	way (note also that glib is the slowest event library known to man).
		3253
2972	There is no supported compilation method available on windows except	3254	There is no supported compilation method available on windows except
2973	embedding it into other applications.	3255	embedding it into other applications.
2974		3256
2975	Due to the many, low, and arbitrary limits on the win32 platform and the	3257	Due to the many, low, and arbitrary limits on the win32 platform and
2976	abysmal performance of winsockets, using a large number of sockets is not	3258	the abysmal performance of winsockets, using a large number of sockets
2977	recommended (and not reasonable). If your program needs to use more than	3259	is not recommended (and not reasonable). If your program needs to use
2978	a hundred or so sockets, then likely it needs to use a totally different	3260	more than a hundred or so sockets, then likely it needs to use a totally
2979	implementation for windows, as libev offers the POSIX model, which cannot	3261	different implementation for windows, as libev offers the POSIX readiness
2980	be implemented efficiently on windows (microsoft monopoly games).	3262	notification model, which cannot be implemented efficiently on windows
		3263	(microsoft monopoly games).
2981		3264
2982	=over 4	3265	=over 4
2983		3266
2984	=item The winsocket select function	3267	=item The winsocket select function
2985		3268
…		…
2999	Note that winsockets handling of fd sets is O(n), so you can easily get a	3282	Note that winsockets handling of fd sets is O(n), so you can easily get a
3000	complexity in the O(n²) range when using win32.	3283	complexity in the O(n²) range when using win32.
3001		3284
3002	=item Limited number of file descriptors	3285	=item Limited number of file descriptors
3003		3286
3004	Windows has numerous arbitrary (and low) limits on things. Early versions	3287	Windows has numerous arbitrary (and low) limits on things.
3005	of winsocket's select only supported waiting for a max. of C<64> handles	3288
		3289	Early versions of winsocket's select only supported waiting for a maximum
3006	(probably owning to the fact that all windows kernels can only wait for	3290	of C<64> handles (probably owning to the fact that all windows kernels
3007	C<64> things at the same time internally; microsoft recommends spawning a	3291	can only wait for C<64> things at the same time internally; microsoft
3008	chain of threads and wait for 63 handles and the previous thread in each).	3292	recommends spawning a chain of threads and wait for 63 handles and the
		3293	previous thread in each. Great).
3009		3294
3010	Newer versions support more handles, but you need to define C<FD_SETSIZE>	3295	Newer versions support more handles, but you need to define C<FD_SETSIZE>
3011	to some high number (e.g. C<2048>) before compiling the winsocket select	3296	to some high number (e.g. C<2048>) before compiling the winsocket select
3012	call (which might be in libev or elsewhere, for example, perl does its own	3297	call (which might be in libev or elsewhere, for example, perl does its own
3013	select emulation on windows).	3298	select emulation on windows).
…		…
3025	calling select (O(n²)) will likely make this unworkable.	3310	calling select (O(n²)) will likely make this unworkable.
3026		3311
3027	=back	3312	=back
3028		3313
3029		3314
		3315	=head1 PORTABILITY REQUIREMENTS
		3316
		3317	In addition to a working ISO-C implementation, libev relies on a few
		3318	additional extensions:
		3319
		3320	=over 4
		3321
		3322	=item C<sig_atomic_t volatile> must be thread-atomic as well
		3323
		3324	The type C<sig_atomic_t volatile> (or whatever is defined as
		3325	C<EV_ATOMIC_T>) must be atomic w.r.t. accesses from different
		3326	threads. This is not part of the specification for C<sig_atomic_t>, but is
		3327	believed to be sufficiently portable.
		3328
		3329	=item C<sigprocmask> must work in a threaded environment
		3330
		3331	Libev uses C<sigprocmask> to temporarily block signals. This is not
		3332	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		3333	pthread implementations will either allow C<sigprocmask> in the "main
		3334	thread" or will block signals process-wide, both behaviours would
		3335	be compatible with libev. Interaction between C<sigprocmask> and
		3336	C<pthread_sigmask> could complicate things, however.
		3337
		3338	The most portable way to handle signals is to block signals in all threads
		3339	except the initial one, and run the default loop in the initial thread as
		3340	well.
		3341
		3342	=item C<long> must be large enough for common memory allocation sizes
		3343
		3344	To improve portability and simplify using libev, libev uses C<long>
		3345	internally instead of C<size_t> when allocating its data structures. On
		3346	non-POSIX systems (Microsoft...) this might be unexpectedly low, but
		3347	is still at least 31 bits everywhere, which is enough for hundreds of
		3348	millions of watchers.
		3349
		3350	=item C<double> must hold a time value in seconds with enough accuracy
		3351
		3352	The type C<double> is used to represent timestamps. It is required to
		3353	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
		3354	enough for at least into the year 4000. This requirement is fulfilled by
		3355	implementations implementing IEEE 754 (basically all existing ones).
		3356
		3357	=back
		3358
		3359	If you know of other additional requirements drop me a note.
		3360
		3361
		3362	=head1 VALGRIND
		3363
		3364	Valgrind has a special section here because it is a popular tool that is
		3365	highly useful, but valgrind reports are very hard to interpret.
		3366
		3367	If you think you found a bug (memory leak, uninitialised data access etc.)
		3368	in libev, then check twice: If valgrind reports something like:
		3369
		3370	==2274== definitely lost: 0 bytes in 0 blocks.
		3371	==2274== possibly lost: 0 bytes in 0 blocks.
		3372	==2274== still reachable: 256 bytes in 1 blocks.
		3373
		3374	then there is no memory leak. Similarly, under some circumstances,
		3375	valgrind might report kernel bugs as if it were a bug in libev, or it
		3376	might be confused (it is a very good tool, but only a tool).
		3377
		3378	If you are unsure about something, feel free to contact the mailing list
		3379	with the full valgrind report and an explanation on why you think this is
		3380	a bug in libev. However, don't be annoyed when you get a brisk "this is
		3381	no bug" answer and take the chance of learning how to interpret valgrind
		3382	properly.
		3383
		3384	If you need, for some reason, empty reports from valgrind for your project
		3385	I suggest using suppression lists.
		3386
		3387
3030	=head1 AUTHOR	3388	=head1 AUTHOR
3031		3389
3032	Marc Lehmann <libev@schmorp.de>.	3390	Marc Lehmann <libev@schmorp.de>.
3033		3391

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Comparing libev/ev.pod (file contents): Revision 1.130 by root, Wed Feb 6 18:34:24 2008 UTC vs. Revision 1.157 by root, Tue May 20 23:49:41 2008 UTC

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Comparing libev/ev.pod (file contents):
Revision 1.130 by root, Wed Feb 6 18:34:24 2008 UTC vs.
Revision 1.157 by root, Tue May 20 23:49:41 2008 UTC