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

Comparing libev/ev.pod (file contents):
Revision 1.196 by root, Tue Oct 21 20:04:14 2008 UTC vs.
Revision 1.205 by root, Mon Oct 27 12:20:32 2008 UTC

…		…
10		10
11	// a single header file is required	11	// a single header file is required
12	#include <ev.h>	12	#include <ev.h>
13		13
14	// every watcher type has its own typedef'd struct	14	// every watcher type has its own typedef'd struct
15	// with the name ev_<type>	15	// with the name ev_TYPE
16	ev_io stdin_watcher;	16	ev_io stdin_watcher;
17	ev_timer timeout_watcher;	17	ev_timer timeout_watcher;
18		18
19	// all watcher callbacks have a similar signature	19	// all watcher callbacks have a similar signature
20	// this callback is called when data is readable on stdin	20	// this callback is called when data is readable on stdin
21	static void	21	static void
22	stdin_cb (EV_P_ struct ev_io *w, int revents)	22	stdin_cb (EV_P_ ev_io *w, int revents)
23	{	23	{
24	puts ("stdin ready");	24	puts ("stdin ready");
25	// for one-shot events, one must manually stop the watcher	25	// for one-shot events, one must manually stop the watcher
26	// with its corresponding stop function.	26	// with its corresponding stop function.
27	ev_io_stop (EV_A_ w);	27	ev_io_stop (EV_A_ w);
…		…
30	ev_unloop (EV_A_ EVUNLOOP_ALL);	30	ev_unloop (EV_A_ EVUNLOOP_ALL);
31	}	31	}
32		32
33	// another callback, this time for a time-out	33	// another callback, this time for a time-out
34	static void	34	static void
35	timeout_cb (EV_P_ struct ev_timer *w, int revents)	35	timeout_cb (EV_P_ ev_timer *w, int revents)
36	{	36	{
37	puts ("timeout");	37	puts ("timeout");
38	// this causes the innermost ev_loop to stop iterating	38	// this causes the innermost ev_loop to stop iterating
39	ev_unloop (EV_A_ EVUNLOOP_ONE);	39	ev_unloop (EV_A_ EVUNLOOP_ONE);
40	}	40	}
41		41
42	int	42	int
43	main (void)	43	main (void)
44	{	44	{
45	// use the default event loop unless you have special needs	45	// use the default event loop unless you have special needs
46	struct ev_loop *loop = ev_default_loop (0);	46	ev_loop *loop = ev_default_loop (0);
47		47
48	// 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	49	// this one will watch for stdin to become readable
50	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);
51	ev_io_start (loop, &stdin_watcher);	51	ev_io_start (loop, &stdin_watcher);
…		…
103	Libev is very configurable. In this manual the default (and most common)	103	Libev is very configurable. In this manual the default (and most common)
104	configuration will be described, which supports multiple event loops. For	104	configuration will be described, which supports multiple event loops. For
105	more info about various configuration options please have a look at	105	more info about various configuration options please have a look at
106	B<EMBED> section in this manual. If libev was configured without support	106	B<EMBED> section in this manual. If libev was configured without support
107	for multiple event loops, then all functions taking an initial argument of	107	for multiple event loops, then all functions taking an initial argument of
108	name C<loop> (which is always of type C<struct ev_loop *>) will not have	108	name C<loop> (which is always of type C<ev_loop *>) will not have
109	this argument.	109	this argument.
110		110
111	=head2 TIME REPRESENTATION	111	=head2 TIME REPRESENTATION
112		112
113	Libev represents time as a single floating point number, representing the	113	Libev represents time as a single floating point number, representing the
…		…
276		276
277	=back	277	=back
278		278
279	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	279	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
280		280
281	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>
282	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>
283	events, and dynamically created loops which do not.	283	I<function>).
		284
		285	The library knows two types of such loops, the I<default> loop, which
		286	supports signals and child events, and dynamically created loops which do
		287	not.
284		288
285	=over 4	289	=over 4
286		290
287	=item struct ev_loop *ev_default_loop (unsigned int flags)	291	=item struct ev_loop *ev_default_loop (unsigned int flags)
288		292
…		…
380	=item C<EVBACKEND_EPOLL> (value 4, Linux)	384	=item C<EVBACKEND_EPOLL> (value 4, Linux)
381		385
382	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,
383	but it scales phenomenally better. While poll and select usually scale	387	but it scales phenomenally better. While poll and select usually scale
384	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),
385	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).
386	of shortcomings, such as silently dropping events in some hard-to-detect	390
387	cases and requiring a system call per fd change, no fork support and bad	391	The epoll syscalls are the most misdesigned of the more advanced
388	support for dup.	392	event mechanisms: probelsm include silently dropping events in some
		393	hard-to-detect cases, requiring a system call per fd change, no fork
		394	support, problems with dup and so on.
		395
		396	Epoll is also notoriously buggy - embedding epoll fds should work, but
		397	of course doesn't, and epoll just loves to report events for totally
		398	I<different> file descriptors (even already closed ones, so one cannot
		399	even remove them from the set) than registered in the set (especially
		400	on SMP systems). Libev tries to counter these spurious notifications by
		401	employing an additional generation counter and comparing that against the
		402	events to filter out spurious ones.
389		403
390	While stopping, setting and starting an I/O watcher in the same iteration	404	While stopping, setting and starting an I/O watcher in the same iteration
391	will result in some caching, there is still a system call per such incident	405	will result in some caching, there is still a system call per such incident
392	(because the fd could point to a different file description now), so its	406	(because the fd could point to a different file description now), so its
393	best to avoid that. Also, C<dup ()>'ed file descriptors might not work	407	best to avoid that. Also, C<dup ()>'ed file descriptors might not work
394	very well if you register events for both fds.	408	very well if you register events for both fds.
395
396	Please note that epoll sometimes generates spurious notifications, so you
397	need to use non-blocking I/O or other means to avoid blocking when no data
398	(or space) is available.
399		409
400	Best performance from this backend is achieved by not unregistering all	410	Best performance from this backend is achieved by not unregistering all
401	watchers for a file descriptor until it has been closed, if possible,	411	watchers for a file descriptor until it has been closed, if possible,
402	i.e. keep at least one watcher active per fd at all times. Stopping and	412	i.e. keep at least one watcher active per fd at all times. Stopping and
403	starting a watcher (without re-setting it) also usually doesn't cause	413	starting a watcher (without re-setting it) also usually doesn't cause
…		…
527	responsibility to either stop all watchers cleanly yourself I<before>	537	responsibility to either stop all watchers cleanly yourself I<before>
528	calling this function, or cope with the fact afterwards (which is usually	538	calling this function, or cope with the fact afterwards (which is usually
529	the easiest thing, you can just ignore the watchers and/or C<free ()> them	539	the easiest thing, you can just ignore the watchers and/or C<free ()> them
530	for example).	540	for example).
531		541
532	Note that certain global state, such as signal state, will not be freed by	542	Note that certain global state, such as signal state (and installed signal
533	this function, and related watchers (such as signal and child watchers)	543	handlers), will not be freed by this function, and related watchers (such
534	would need to be stopped manually.	544	as signal and child watchers) would need to be stopped manually.
535		545
536	In general it is not advisable to call this function except in the	546	In general it is not advisable to call this function except in the
537	rare occasion where you really need to free e.g. the signal handling	547	rare occasion where you really need to free e.g. the signal handling
538	pipe fds. If you need dynamically allocated loops it is better to use	548	pipe fds. If you need dynamically allocated loops it is better to use
539	C<ev_loop_new> and C<ev_loop_destroy>).	549	C<ev_loop_new> and C<ev_loop_destroy>).
…		…
710	respectively).	720	respectively).
711		721
712	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	722	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
713	running when nothing else is active.	723	running when nothing else is active.
714		724
715	struct ev_signal exitsig;	725	ev_signal exitsig;
716	ev_signal_init (&exitsig, sig_cb, SIGINT);	726	ev_signal_init (&exitsig, sig_cb, SIGINT);
717	ev_signal_start (loop, &exitsig);	727	ev_signal_start (loop, &exitsig);
718	evf_unref (loop);	728	evf_unref (loop);
719		729
720	Example: For some weird reason, unregister the above signal handler again.	730	Example: For some weird reason, unregister the above signal handler again.
…		…
768	they fire on, say, one-second boundaries only.	778	they fire on, say, one-second boundaries only.
769		779
770	=item ev_loop_verify (loop)	780	=item ev_loop_verify (loop)
771		781
772	This function only does something when C<EV_VERIFY> support has been	782	This function only does something when C<EV_VERIFY> support has been
773	compiled in. which is the default for non-minimal builds. It tries to go	783	compiled in, which is the default for non-minimal builds. It tries to go
774	through all internal structures and checks them for validity. If anything	784	through all internal structures and checks them for validity. If anything
775	is found to be inconsistent, it will print an error message to standard	785	is found to be inconsistent, it will print an error message to standard
776	error and call C<abort ()>.	786	error and call C<abort ()>.
777		787
778	This can be used to catch bugs inside libev itself: under normal	788	This can be used to catch bugs inside libev itself: under normal
…		…
782	=back	792	=back
783		793
784		794
785	=head1 ANATOMY OF A WATCHER	795	=head1 ANATOMY OF A WATCHER
786		796
		797	In the following description, uppercase C<TYPE> in names stands for the
		798	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		799	watchers and C<ev_io_start> for I/O watchers.
		800
787	A watcher is a structure that you create and register to record your	801	A watcher is a structure that you create and register to record your
788	interest in some event. For instance, if you want to wait for STDIN to	802	interest in some event. For instance, if you want to wait for STDIN to
789	become readable, you would create an C<ev_io> watcher for that:	803	become readable, you would create an C<ev_io> watcher for that:
790		804
791	static void my_cb (struct ev_loop loop, struct ev_io w, int revents)	805	static void my_cb (struct ev_loop loop, ev_io w, int revents)
792	{	806	{
793	ev_io_stop (w);	807	ev_io_stop (w);
794	ev_unloop (loop, EVUNLOOP_ALL);	808	ev_unloop (loop, EVUNLOOP_ALL);
795	}	809	}
796		810
797	struct ev_loop *loop = ev_default_loop (0);	811	struct ev_loop *loop = ev_default_loop (0);
		812
798	struct ev_io stdin_watcher;	813	ev_io stdin_watcher;
		814
799	ev_init (&stdin_watcher, my_cb);	815	ev_init (&stdin_watcher, my_cb);
800	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	816	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
801	ev_io_start (loop, &stdin_watcher);	817	ev_io_start (loop, &stdin_watcher);
		818
802	ev_loop (loop, 0);	819	ev_loop (loop, 0);
803		820
804	As you can see, you are responsible for allocating the memory for your	821	As you can see, you are responsible for allocating the memory for your
805	watcher structures (and it is usually a bad idea to do this on the stack,	822	watcher structures (and it is I<usually> a bad idea to do this on the
806	although this can sometimes be quite valid).	823	stack).
		824
		825	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		826	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
807		827
808	Each watcher structure must be initialised by a call to C<ev_init	828	Each watcher structure must be initialised by a call to C<ev_init
809	(watcher *, callback)>, which expects a callback to be provided. This	829	(watcher *, callback)>, which expects a callback to be provided. This
810	callback gets invoked each time the event occurs (or, in the case of I/O	830	callback gets invoked each time the event occurs (or, in the case of I/O
811	watchers, each time the event loop detects that the file descriptor given	831	watchers, each time the event loop detects that the file descriptor given
812	is readable and/or writable).	832	is readable and/or writable).
813		833
814	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	834	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
815	with arguments specific to this watcher type. There is also a macro	835	macro to configure it, with arguments specific to the watcher type. There
816	to combine initialisation and setting in one call: C<< ev_<type>_init	836	is also a macro to combine initialisation and setting in one call: C<<
817	(watcher *, callback, ...) >>.	837	ev_TYPE_init (watcher *, callback, ...) >>.
818		838
819	To make the watcher actually watch out for events, you have to start it	839	To make the watcher actually watch out for events, you have to start it
820	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	840	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
821	*) >>), and you can stop watching for events at any time by calling the	841	*) >>), and you can stop watching for events at any time by calling the
822	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	842	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
823		843
824	As long as your watcher is active (has been started but not stopped) you	844	As long as your watcher is active (has been started but not stopped) you
825	must not touch the values stored in it. Most specifically you must never	845	must not touch the values stored in it. Most specifically you must never
826	reinitialise it or call its C<set> macro.	846	reinitialise it or call its C<ev_TYPE_set> macro.
827		847
828	Each and every callback receives the event loop pointer as first, the	848	Each and every callback receives the event loop pointer as first, the
829	registered watcher structure as second, and a bitset of received events as	849	registered watcher structure as second, and a bitset of received events as
830	third argument.	850	third argument.
831		851
…		…
894	=item C<EV_ERROR>	914	=item C<EV_ERROR>
895		915
896	An unspecified error has occurred, the watcher has been stopped. This might	916	An unspecified error has occurred, the watcher has been stopped. This might
897	happen because the watcher could not be properly started because libev	917	happen because the watcher could not be properly started because libev
898	ran out of memory, a file descriptor was found to be closed or any other	918	ran out of memory, a file descriptor was found to be closed or any other
		919	problem. Libev considers these application bugs.
		920
899	problem. You best act on it by reporting the problem and somehow coping	921	You best act on it by reporting the problem and somehow coping with the
900	with the watcher being stopped.	922	watcher being stopped. Note that well-written programs should not receive
		923	an error ever, so when your watcher receives it, this usually indicates a
		924	bug in your program.
901		925
902	Libev will usually signal a few "dummy" events together with an error, for	926	Libev will usually signal a few "dummy" events together with an error, for
903	example it might indicate that a fd is readable or writable, and if your	927	example it might indicate that a fd is readable or writable, and if your
904	callbacks is well-written it can just attempt the operation and cope with	928	callbacks is well-written it can just attempt the operation and cope with
905	the error from read() or write(). This will not work in multi-threaded	929	the error from read() or write(). This will not work in multi-threaded
…		…
908		932
909	=back	933	=back
910		934
911	=head2 GENERIC WATCHER FUNCTIONS	935	=head2 GENERIC WATCHER FUNCTIONS
912		936
913	In the following description, C<TYPE> stands for the watcher type,
914	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
915
916	=over 4	937	=over 4
917		938
918	=item C<ev_init> (ev_TYPE *watcher, callback)	939	=item C<ev_init> (ev_TYPE *watcher, callback)
919		940
920	This macro initialises the generic portion of a watcher. The contents	941	This macro initialises the generic portion of a watcher. The contents
…		…
925	which rolls both calls into one.	946	which rolls both calls into one.
926		947
927	You can reinitialise a watcher at any time as long as it has been stopped	948	You can reinitialise a watcher at any time as long as it has been stopped
928	(or never started) and there are no pending events outstanding.	949	(or never started) and there are no pending events outstanding.
929		950
930	The callback is always of type C<void ()(ev_loop loop, ev_TYPE *watcher,	951	The callback is always of type C<void ()(struct ev_loop loop, ev_TYPE *watcher,
931	int revents)>.	952	int revents)>.
932		953
933	Example: Initialise an C<ev_io> watcher in two steps.	954	Example: Initialise an C<ev_io> watcher in two steps.
934		955
935	ev_io w;	956	ev_io w;
…		…
1028	The default priority used by watchers when no priority has been set is	1049	The default priority used by watchers when no priority has been set is
1029	always C<0>, which is supposed to not be too high and not be too low :).	1050	always C<0>, which is supposed to not be too high and not be too low :).
1030		1051
1031	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1052	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
1032	fine, as long as you do not mind that the priority value you query might	1053	fine, as long as you do not mind that the priority value you query might
1033	or might not have been adjusted to be within valid range.	1054	or might not have been clamped to the valid range.
1034		1055
1035	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1056	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
1036		1057
1037	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1058	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
1038	C<loop> nor C<revents> need to be valid as long as the watcher callback	1059	C<loop> nor C<revents> need to be valid as long as the watcher callback
…		…
1060	member, you can also "subclass" the watcher type and provide your own	1081	member, you can also "subclass" the watcher type and provide your own
1061	data:	1082	data:
1062		1083
1063	struct my_io	1084	struct my_io
1064	{	1085	{
1065	struct ev_io io;	1086	ev_io io;
1066	int otherfd;	1087	int otherfd;
1067	void *somedata;	1088	void *somedata;
1068	struct whatever *mostinteresting;	1089	struct whatever *mostinteresting;
1069	};	1090	};
1070		1091
…		…
1073	ev_io_init (&w.io, my_cb, fd, EV_READ);	1094	ev_io_init (&w.io, my_cb, fd, EV_READ);
1074		1095
1075	And since your callback will be called with a pointer to the watcher, you	1096	And since your callback will be called with a pointer to the watcher, you
1076	can cast it back to your own type:	1097	can cast it back to your own type:
1077		1098
1078	static void my_cb (struct ev_loop loop, struct ev_io w_, int revents)	1099	static void my_cb (struct ev_loop loop, ev_io w_, int revents)
1079	{	1100	{
1080	struct my_io w = (struct my_io )w_;	1101	struct my_io w = (struct my_io )w_;
1081	...	1102	...
1082	}	1103	}
1083		1104
…		…
1101	programmers):	1122	programmers):
1102		1123
1103	#include <stddef.h>	1124	#include <stddef.h>
1104		1125
1105	static void	1126	static void
1106	t1_cb (EV_P_ struct ev_timer *w, int revents)	1127	t1_cb (EV_P_ ev_timer *w, int revents)
1107	{	1128	{
1108	struct my_biggy big = (struct my_biggy *	1129	struct my_biggy big = (struct my_biggy *
1109	(((char *)w) - offsetof (struct my_biggy, t1));	1130	(((char *)w) - offsetof (struct my_biggy, t1));
1110	}	1131	}
1111		1132
1112	static void	1133	static void
1113	t2_cb (EV_P_ struct ev_timer *w, int revents)	1134	t2_cb (EV_P_ ev_timer *w, int revents)
1114	{	1135	{
1115	struct my_biggy big = (struct my_biggy *	1136	struct my_biggy big = (struct my_biggy *
1116	(((char *)w) - offsetof (struct my_biggy, t2));	1137	(((char *)w) - offsetof (struct my_biggy, t2));
1117	}	1138	}
1118		1139
…		…
1253	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1274	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
1254	readable, but only once. Since it is likely line-buffered, you could	1275	readable, but only once. Since it is likely line-buffered, you could
1255	attempt to read a whole line in the callback.	1276	attempt to read a whole line in the callback.
1256		1277
1257	static void	1278	static void
1258	stdin_readable_cb (struct ev_loop loop, struct ev_io w, int revents)	1279	stdin_readable_cb (struct ev_loop loop, ev_io w, int revents)
1259	{	1280	{
1260	ev_io_stop (loop, w);	1281	ev_io_stop (loop, w);
1261	.. read from stdin here (or from w->fd) and handle any I/O errors	1282	.. read from stdin here (or from w->fd) and handle any I/O errors
1262	}	1283	}
1263		1284
1264	...	1285	...
1265	struct ev_loop *loop = ev_default_init (0);	1286	struct ev_loop *loop = ev_default_init (0);
1266	struct ev_io stdin_readable;	1287	ev_io stdin_readable;
1267	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1288	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1268	ev_io_start (loop, &stdin_readable);	1289	ev_io_start (loop, &stdin_readable);
1269	ev_loop (loop, 0);	1290	ev_loop (loop, 0);
1270		1291
1271		1292
…		…
1282		1303
1283	The callback is guaranteed to be invoked only I<after> its timeout has	1304	The callback is guaranteed to be invoked only I<after> its timeout has
1284	passed, but if multiple timers become ready during the same loop iteration	1305	passed, but if multiple timers become ready during the same loop iteration
1285	then order of execution is undefined.	1306	then order of execution is undefined.
1286		1307
		1308	=head3 Be smart about timeouts
		1309
		1310	Many real-world problems involve some kind of timeout, usually for error
		1311	recovery. A typical example is an HTTP request - if the other side hangs,
		1312	you want to raise some error after a while.
		1313
		1314	What follows are some ways to handle this problem, from obvious and
		1315	inefficient to smart and efficient.
		1316
		1317	In the following, a 60 second activity timeout is assumed - a timeout that
		1318	gets reset to 60 seconds each time there is activity (e.g. each time some
		1319	data or other life sign was received).
		1320
		1321	=over 4
		1322
		1323	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1324
		1325	This is the most obvious, but not the most simple way: In the beginning,
		1326	start the watcher:
		1327
		1328	ev_timer_init (timer, callback, 60., 0.);
		1329	ev_timer_start (loop, timer);
		1330
		1331	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1332	and start it again:
		1333
		1334	ev_timer_stop (loop, timer);
		1335	ev_timer_set (timer, 60., 0.);
		1336	ev_timer_start (loop, timer);
		1337
		1338	This is relatively simple to implement, but means that each time there is
		1339	some activity, libev will first have to remove the timer from its internal
		1340	data structure and then add it again. Libev tries to be fast, but it's
		1341	still not a constant-time operation.
		1342
		1343	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1344
		1345	This is the easiest way, and involves using C<ev_timer_again> instead of
		1346	C<ev_timer_start>.
		1347
		1348	To implement this, configure an C<ev_timer> with a C<repeat> value
		1349	of C<60> and then call C<ev_timer_again> at start and each time you
		1350	successfully read or write some data. If you go into an idle state where
		1351	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1352	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1353
		1354	That means you can ignore both the C<ev_timer_start> function and the
		1355	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1356	member and C<ev_timer_again>.
		1357
		1358	At start:
		1359
		1360	ev_timer_init (timer, callback);
		1361	timer->repeat = 60.;
		1362	ev_timer_again (loop, timer);
		1363
		1364	Each time there is some activity:
		1365
		1366	ev_timer_again (loop, timer);
		1367
		1368	It is even possible to change the time-out on the fly, regardless of
		1369	whether the watcher is active or not:
		1370
		1371	timer->repeat = 30.;
		1372	ev_timer_again (loop, timer);
		1373
		1374	This is slightly more efficient then stopping/starting the timer each time
		1375	you want to modify its timeout value, as libev does not have to completely
		1376	remove and re-insert the timer from/into its internal data structure.
		1377
		1378	It is, however, even simpler than the "obvious" way to do it.
		1379
		1380	=item 3. Let the timer time out, but then re-arm it as required.
		1381
		1382	This method is more tricky, but usually most efficient: Most timeouts are
		1383	relatively long compared to the intervals between other activity - in
		1384	our example, within 60 seconds, there are usually many I/O events with
		1385	associated activity resets.
		1386
		1387	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1388	but remember the time of last activity, and check for a real timeout only
		1389	within the callback:
		1390
		1391	ev_tstamp last_activity; // time of last activity
		1392
		1393	static void
		1394	callback (EV_P_ ev_timer *w, int revents)
		1395	{
		1396	ev_tstamp now = ev_now (EV_A);
		1397	ev_tstamp timeout = last_activity + 60.;
		1398
		1399	// if last_activity + 60. is older than now, we did time out
		1400	if (timeout < now)
		1401	{
		1402	// timeout occured, take action
		1403	}
		1404	else
		1405	{
		1406	// callback was invoked, but there was some activity, re-arm
		1407	// the watcher to fire in last_activity + 60, which is
		1408	// guaranteed to be in the future, so "again" is positive:
		1409	w->again = timeout - now;
		1410	ev_timer_again (EV_A_ w);
		1411	}
		1412	}
		1413
		1414	To summarise the callback: first calculate the real timeout (defined
		1415	as "60 seconds after the last activity"), then check if that time has
		1416	been reached, which means something I<did>, in fact, time out. Otherwise
		1417	the callback was invoked too early (C<timeout> is in the future), so
		1418	re-schedule the timer to fire at that future time, to see if maybe we have
		1419	a timeout then.
		1420
		1421	Note how C<ev_timer_again> is used, taking advantage of the
		1422	C<ev_timer_again> optimisation when the timer is already running.
		1423
		1424	This scheme causes more callback invocations (about one every 60 seconds
		1425	minus half the average time between activity), but virtually no calls to
		1426	libev to change the timeout.
		1427
		1428	To start the timer, simply initialise the watcher and set C<last_activity>
		1429	to the current time (meaning we just have some activity :), then call the
		1430	callback, which will "do the right thing" and start the timer:
		1431
		1432	ev_timer_init (timer, callback);
		1433	last_activity = ev_now (loop);
		1434	callback (loop, timer, EV_TIMEOUT);
		1435
		1436	And when there is some activity, simply store the current time in
		1437	C<last_activity>, no libev calls at all:
		1438
		1439	last_actiivty = ev_now (loop);
		1440
		1441	This technique is slightly more complex, but in most cases where the
		1442	time-out is unlikely to be triggered, much more efficient.
		1443
		1444	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1445	callback :) - just change the timeout and invoke the callback, which will
		1446	fix things for you.
		1447
		1448	=item 4. Wee, just use a double-linked list for your timeouts.
		1449
		1450	If there is not one request, but many thousands (millions...), all
		1451	employing some kind of timeout with the same timeout value, then one can
		1452	do even better:
		1453
		1454	When starting the timeout, calculate the timeout value and put the timeout
		1455	at the I<end> of the list.
		1456
		1457	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1458	the list is expected to fire (for example, using the technique #3).
		1459
		1460	When there is some activity, remove the timer from the list, recalculate
		1461	the timeout, append it to the end of the list again, and make sure to
		1462	update the C<ev_timer> if it was taken from the beginning of the list.
		1463
		1464	This way, one can manage an unlimited number of timeouts in O(1) time for
		1465	starting, stopping and updating the timers, at the expense of a major
		1466	complication, and having to use a constant timeout. The constant timeout
		1467	ensures that the list stays sorted.
		1468
		1469	=back
		1470
		1471	So which method the best?
		1472
		1473	Method #2 is a simple no-brain-required solution that is adequate in most
		1474	situations. Method #3 requires a bit more thinking, but handles many cases
		1475	better, and isn't very complicated either. In most case, choosing either
		1476	one is fine, with #3 being better in typical situations.
		1477
		1478	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1479	rather complicated, but extremely efficient, something that really pays
		1480	off after the first million or so of active timers, i.e. it's usually
		1481	overkill :)
		1482
1287	=head3 The special problem of time updates	1483	=head3 The special problem of time updates
1288		1484
1289	Establishing the current time is a costly operation (it usually takes at	1485	Establishing the current time is a costly operation (it usually takes at
1290	least two system calls): EV therefore updates its idea of the current	1486	least two system calls): EV therefore updates its idea of the current
1291	time only before and after C<ev_loop> collects new events, which causes a	1487	time only before and after C<ev_loop> collects new events, which causes a
…		…
1334	If the timer is started but non-repeating, stop it (as if it timed out).	1530	If the timer is started but non-repeating, stop it (as if it timed out).
1335		1531
1336	If the timer is repeating, either start it if necessary (with the	1532	If the timer is repeating, either start it if necessary (with the
1337	C<repeat> value), or reset the running timer to the C<repeat> value.	1533	C<repeat> value), or reset the running timer to the C<repeat> value.
1338		1534
1339	This sounds a bit complicated, but here is a useful and typical	1535	This sounds a bit complicated, see "Be smart about timeouts", above, for a
1340	example: Imagine you have a TCP connection and you want a so-called idle	1536	usage example.
1341	timeout, that is, you want to be called when there have been, say, 60
1342	seconds of inactivity on the socket. The easiest way to do this is to
1343	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
1344	C<ev_timer_again> each time you successfully read or write some data. If
1345	you go into an idle state where you do not expect data to travel on the
1346	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
1347	automatically restart it if need be.
1348
1349	That means you can ignore the C<after> value and C<ev_timer_start>
1350	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
1351
1352	ev_timer_init (timer, callback, 0., 5.);
1353	ev_timer_again (loop, timer);
1354	...
1355	timer->again = 17.;
1356	ev_timer_again (loop, timer);
1357	...
1358	timer->again = 10.;
1359	ev_timer_again (loop, timer);
1360
1361	This is more slightly efficient then stopping/starting the timer each time
1362	you want to modify its timeout value.
1363
1364	Note, however, that it is often even more efficient to remember the
1365	time of the last activity and let the timer time-out naturally. In the
1366	callback, you then check whether the time-out is real, or, if there was
1367	some activity, you reschedule the watcher to time-out in "last_activity +
1368	timeout - ev_now ()" seconds.
1369		1537
1370	=item ev_tstamp repeat [read-write]	1538	=item ev_tstamp repeat [read-write]
1371		1539
1372	The current C<repeat> value. Will be used each time the watcher times out	1540	The current C<repeat> value. Will be used each time the watcher times out
1373	or C<ev_timer_again> is called, and determines the next timeout (if any),	1541	or C<ev_timer_again> is called, and determines the next timeout (if any),
…		…
1378	=head3 Examples	1546	=head3 Examples
1379		1547
1380	Example: Create a timer that fires after 60 seconds.	1548	Example: Create a timer that fires after 60 seconds.
1381		1549
1382	static void	1550	static void
1383	one_minute_cb (struct ev_loop loop, struct ev_timer w, int revents)	1551	one_minute_cb (struct ev_loop loop, ev_timer w, int revents)
1384	{	1552	{
1385	.. one minute over, w is actually stopped right here	1553	.. one minute over, w is actually stopped right here
1386	}	1554	}
1387		1555
1388	struct ev_timer mytimer;	1556	ev_timer mytimer;
1389	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	1557	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1390	ev_timer_start (loop, &mytimer);	1558	ev_timer_start (loop, &mytimer);
1391		1559
1392	Example: Create a timeout timer that times out after 10 seconds of	1560	Example: Create a timeout timer that times out after 10 seconds of
1393	inactivity.	1561	inactivity.
1394		1562
1395	static void	1563	static void
1396	timeout_cb (struct ev_loop loop, struct ev_timer w, int revents)	1564	timeout_cb (struct ev_loop loop, ev_timer w, int revents)
1397	{	1565	{
1398	.. ten seconds without any activity	1566	.. ten seconds without any activity
1399	}	1567	}
1400		1568
1401	struct ev_timer mytimer;	1569	ev_timer mytimer;
1402	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	1570	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1403	ev_timer_again (&mytimer); /* start timer */	1571	ev_timer_again (&mytimer); /* start timer */
1404	ev_loop (loop, 0);	1572	ev_loop (loop, 0);
1405		1573
1406	// and in some piece of code that gets executed on any "activity":	1574	// and in some piece of code that gets executed on any "activity":
…		…
1492		1660
1493	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop	1661	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
1494	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the	1662	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
1495	only event loop modification you are allowed to do).	1663	only event loop modification you are allowed to do).
1496		1664
1497	The callback prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic	1665	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1498	*w, ev_tstamp now)>, e.g.:	1666	*w, ev_tstamp now)>, e.g.:
1499		1667
		1668	static ev_tstamp
1500	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1669	my_rescheduler (ev_periodic *w, ev_tstamp now)
1501	{	1670	{
1502	return now + 60.;	1671	return now + 60.;
1503	}	1672	}
1504		1673
1505	It must return the next time to trigger, based on the passed time value	1674	It must return the next time to trigger, based on the passed time value
…		…
1542		1711
1543	The current interval value. Can be modified any time, but changes only	1712	The current interval value. Can be modified any time, but changes only
1544	take effect when the periodic timer fires or C<ev_periodic_again> is being	1713	take effect when the periodic timer fires or C<ev_periodic_again> is being
1545	called.	1714	called.
1546		1715
1547	=item ev_tstamp (reschedule_cb)(struct ev_periodic w, ev_tstamp now) [read-write]	1716	=item ev_tstamp (reschedule_cb)(ev_periodic w, ev_tstamp now) [read-write]
1548		1717
1549	The current reschedule callback, or C<0>, if this functionality is	1718	The current reschedule callback, or C<0>, if this functionality is
1550	switched off. Can be changed any time, but changes only take effect when	1719	switched off. Can be changed any time, but changes only take effect when
1551	the periodic timer fires or C<ev_periodic_again> is being called.	1720	the periodic timer fires or C<ev_periodic_again> is being called.
1552		1721
…		…
1557	Example: Call a callback every hour, or, more precisely, whenever the	1726	Example: Call a callback every hour, or, more precisely, whenever the
1558	system time is divisible by 3600. The callback invocation times have	1727	system time is divisible by 3600. The callback invocation times have
1559	potentially a lot of jitter, but good long-term stability.	1728	potentially a lot of jitter, but good long-term stability.
1560		1729
1561	static void	1730	static void
1562	clock_cb (struct ev_loop loop, struct ev_io w, int revents)	1731	clock_cb (struct ev_loop loop, ev_io w, int revents)
1563	{	1732	{
1564	... its now a full hour (UTC, or TAI or whatever your clock follows)	1733	... its now a full hour (UTC, or TAI or whatever your clock follows)
1565	}	1734	}
1566		1735
1567	struct ev_periodic hourly_tick;	1736	ev_periodic hourly_tick;
1568	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	1737	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1569	ev_periodic_start (loop, &hourly_tick);	1738	ev_periodic_start (loop, &hourly_tick);
1570		1739
1571	Example: The same as above, but use a reschedule callback to do it:	1740	Example: The same as above, but use a reschedule callback to do it:
1572		1741
1573	#include <math.h>	1742	#include <math.h>
1574		1743
1575	static ev_tstamp	1744	static ev_tstamp
1576	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	1745	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1577	{	1746	{
1578	return now + (3600. - fmod (now, 3600.));	1747	return now + (3600. - fmod (now, 3600.));
1579	}	1748	}
1580		1749
1581	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	1750	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1582		1751
1583	Example: Call a callback every hour, starting now:	1752	Example: Call a callback every hour, starting now:
1584		1753
1585	struct ev_periodic hourly_tick;	1754	ev_periodic hourly_tick;
1586	ev_periodic_init (&hourly_tick, clock_cb,	1755	ev_periodic_init (&hourly_tick, clock_cb,
1587	fmod (ev_now (loop), 3600.), 3600., 0);	1756	fmod (ev_now (loop), 3600.), 3600., 0);
1588	ev_periodic_start (loop, &hourly_tick);	1757	ev_periodic_start (loop, &hourly_tick);
1589		1758
1590		1759
…		…
1632	=head3 Examples	1801	=head3 Examples
1633		1802
1634	Example: Try to exit cleanly on SIGINT.	1803	Example: Try to exit cleanly on SIGINT.
1635		1804
1636	static void	1805	static void
1637	sigint_cb (struct ev_loop loop, struct ev_signal w, int revents)	1806	sigint_cb (struct ev_loop loop, ev_signal w, int revents)
1638	{	1807	{
1639	ev_unloop (loop, EVUNLOOP_ALL);	1808	ev_unloop (loop, EVUNLOOP_ALL);
1640	}	1809	}
1641		1810
1642	struct ev_signal signal_watcher;	1811	ev_signal signal_watcher;
1643	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	1812	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
1644	ev_signal_start (loop, &signal_watcher);	1813	ev_signal_start (loop, &signal_watcher);
1645		1814
1646		1815
1647	=head2 C<ev_child> - watch out for process status changes	1816	=head2 C<ev_child> - watch out for process status changes
…		…
1722	its completion.	1891	its completion.
1723		1892
1724	ev_child cw;	1893	ev_child cw;
1725		1894
1726	static void	1895	static void
1727	child_cb (EV_P_ struct ev_child *w, int revents)	1896	child_cb (EV_P_ ev_child *w, int revents)
1728	{	1897	{
1729	ev_child_stop (EV_A_ w);	1898	ev_child_stop (EV_A_ w);
1730	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);	1899	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1731	}	1900	}
1732		1901
…		…
1984		2153
1985	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2154	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1986	callback, free it. Also, use no error checking, as usual.	2155	callback, free it. Also, use no error checking, as usual.
1987		2156
1988	static void	2157	static void
1989	idle_cb (struct ev_loop loop, struct ev_idle w, int revents)	2158	idle_cb (struct ev_loop loop, ev_idle w, int revents)
1990	{	2159	{
1991	free (w);	2160	free (w);
1992	// now do something you wanted to do when the program has	2161	// now do something you wanted to do when the program has
1993	// no longer anything immediate to do.	2162	// no longer anything immediate to do.
1994	}	2163	}
1995		2164
1996	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2165	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1997	ev_idle_init (idle_watcher, idle_cb);	2166	ev_idle_init (idle_watcher, idle_cb);
1998	ev_idle_start (loop, idle_cb);	2167	ev_idle_start (loop, idle_cb);
1999		2168
2000		2169
2001	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2170	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
…		…
2082		2251
2083	static ev_io iow [nfd];	2252	static ev_io iow [nfd];
2084	static ev_timer tw;	2253	static ev_timer tw;
2085		2254
2086	static void	2255	static void
2087	io_cb (ev_loop loop, ev_io w, int revents)	2256	io_cb (struct ev_loop loop, ev_io w, int revents)
2088	{	2257	{
2089	}	2258	}
2090		2259
2091	// create io watchers for each fd and a timer before blocking	2260	// create io watchers for each fd and a timer before blocking
2092	static void	2261	static void
2093	adns_prepare_cb (ev_loop loop, ev_prepare w, int revents)	2262	adns_prepare_cb (struct ev_loop loop, ev_prepare w, int revents)
2094	{	2263	{
2095	int timeout = 3600000;	2264	int timeout = 3600000;
2096	struct pollfd fds [nfd];	2265	struct pollfd fds [nfd];
2097	// actual code will need to loop here and realloc etc.	2266	// actual code will need to loop here and realloc etc.
2098	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2267	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
…		…
2113	}	2282	}
2114	}	2283	}
2115		2284
2116	// stop all watchers after blocking	2285	// stop all watchers after blocking
2117	static void	2286	static void
2118	adns_check_cb (ev_loop loop, ev_check w, int revents)	2287	adns_check_cb (struct ev_loop loop, ev_check w, int revents)
2119	{	2288	{
2120	ev_timer_stop (loop, &tw);	2289	ev_timer_stop (loop, &tw);
2121		2290
2122	for (int i = 0; i < nfd; ++i)	2291	for (int i = 0; i < nfd; ++i)
2123	{	2292	{
…		…
2291	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be	2460	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
2292	used).	2461	used).
2293		2462
2294	struct ev_loop *loop_hi = ev_default_init (0);	2463	struct ev_loop *loop_hi = ev_default_init (0);
2295	struct ev_loop *loop_lo = 0;	2464	struct ev_loop *loop_lo = 0;
2296	struct ev_embed embed;	2465	ev_embed embed;
2297		2466
2298	// see if there is a chance of getting one that works	2467	// see if there is a chance of getting one that works
2299	// (remember that a flags value of 0 means autodetection)	2468	// (remember that a flags value of 0 means autodetection)
2300	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()	2469	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
2301	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())	2470	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
…		…
2315	kqueue implementation). Store the kqueue/socket-only event loop in	2484	kqueue implementation). Store the kqueue/socket-only event loop in
2316	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).	2485	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
2317		2486
2318	struct ev_loop *loop = ev_default_init (0);	2487	struct ev_loop *loop = ev_default_init (0);
2319	struct ev_loop *loop_socket = 0;	2488	struct ev_loop *loop_socket = 0;
2320	struct ev_embed embed;	2489	ev_embed embed;
2321		2490
2322	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)	2491	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
2323	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))	2492	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
2324	{	2493	{
2325	ev_embed_init (&embed, 0, loop_socket);	2494	ev_embed_init (&embed, 0, loop_socket);
…		…
2539	/* doh, nothing entered */;	2708	/* doh, nothing entered */;
2540	}	2709	}
2541		2710
2542	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	2711	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
2543		2712
2544	=item ev_feed_event (ev_loop , watcher , int revents)	2713	=item ev_feed_event (struct ev_loop , watcher , int revents)
2545		2714
2546	Feeds the given event set into the event loop, as if the specified event	2715	Feeds the given event set into the event loop, as if the specified event
2547	had happened for the specified watcher (which must be a pointer to an	2716	had happened for the specified watcher (which must be a pointer to an
2548	initialised but not necessarily started event watcher).	2717	initialised but not necessarily started event watcher).
2549		2718
2550	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	2719	=item ev_feed_fd_event (struct ev_loop *, int fd, int revents)
2551		2720
2552	Feed an event on the given fd, as if a file descriptor backend detected	2721	Feed an event on the given fd, as if a file descriptor backend detected
2553	the given events it.	2722	the given events it.
2554		2723
2555	=item ev_feed_signal_event (ev_loop *loop, int signum)	2724	=item ev_feed_signal_event (struct ev_loop *loop, int signum)
2556		2725
2557	Feed an event as if the given signal occurred (C<loop> must be the default	2726	Feed an event as if the given signal occurred (C<loop> must be the default
2558	loop!).	2727	loop!).
2559		2728
2560	=back	2729	=back
…		…
2794		2963
2795	=item D	2964	=item D
2796		2965
2797	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	2966	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
2798	be found at L<http://proj.llucax.com.ar/wiki/evd>.	2967	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		2968
		2969	=item Ocaml
		2970
		2971	Erkki Seppala has written Ocaml bindings for libev, to be found at
		2972	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
2799		2973
2800	=back	2974	=back
2801		2975
2802		2976
2803	=head1 MACRO MAGIC	2977	=head1 MACRO MAGIC

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Comparing libev/ev.pod (file contents): Revision 1.196 by root, Tue Oct 21 20:04:14 2008 UTC vs. Revision 1.205 by root, Mon Oct 27 12:20:32 2008 UTC

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Comparing libev/ev.pod (file contents):
Revision 1.196 by root, Tue Oct 21 20:04:14 2008 UTC vs.
Revision 1.205 by root, Mon Oct 27 12:20:32 2008 UTC