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

Comparing libev/ev.pod (file contents):
Revision 1.34 by root, Fri Nov 23 16:17:12 2007 UTC vs.
Revision 1.46 by root, Mon Nov 26 10:20:43 2007 UTC

…		…
106	returned by C<ev_supported_backends>, as for example kqueue is broken on	106	returned by C<ev_supported_backends>, as for example kqueue is broken on
107	most BSDs and will not be autodetected unless you explicitly request it	107	most BSDs and will not be autodetected unless you explicitly request it
108	(assuming you know what you are doing). This is the set of backends that	108	(assuming you know what you are doing). This is the set of backends that
109	libev will probe for if you specify no backends explicitly.	109	libev will probe for if you specify no backends explicitly.
110		110
		111	=item unsigned int ev_embeddable_backends ()
		112
		113	Returns the set of backends that are embeddable in other event loops. This
		114	is the theoretical, all-platform, value. To find which backends
		115	might be supported on the current system, you would need to look at
		116	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for
		117	recommended ones.
		118
		119	See the description of C<ev_embed> watchers for more info.
		120
111	=item ev_set_allocator (void (cb)(void *ptr, long size))	121	=item ev_set_allocator (void (cb)(void *ptr, long size))
112		122
113	Sets the allocation function to use (the prototype is similar to the	123	Sets the allocation function to use (the prototype is similar to the
114	realloc C function, the semantics are identical). It is used to allocate	124	realloc C function, the semantics are identical). It is used to allocate
115	and free memory (no surprises here). If it returns zero when memory	125	and free memory (no surprises here). If it returns zero when memory
…		…
313	fatal ("no epoll found here, maybe it hides under your chair");	323	fatal ("no epoll found here, maybe it hides under your chair");
314		324
315	=item ev_default_destroy ()	325	=item ev_default_destroy ()
316		326
317	Destroys the default loop again (frees all memory and kernel state	327	Destroys the default loop again (frees all memory and kernel state
318	etc.). This stops all registered event watchers (by not touching them in	328	etc.). None of the active event watchers will be stopped in the normal
319	any way whatsoever, although you cannot rely on this :).	329	sense, so e.g. C<ev_is_active> might still return true. It is your
		330	responsibility to either stop all watchers cleanly yoursef I<before>
		331	calling this function, or cope with the fact afterwards (which is usually
		332	the easiest thing, youc na just ignore the watchers and/or C<free ()> them
		333	for example).
320		334
321	=item ev_loop_destroy (loop)	335	=item ev_loop_destroy (loop)
322		336
323	Like C<ev_default_destroy>, but destroys an event loop created by an	337	Like C<ev_default_destroy>, but destroys an event loop created by an
324	earlier call to C<ev_loop_new>.	338	earlier call to C<ev_loop_new>.
…		…
454	ev_ref (myloop);	468	ev_ref (myloop);
455	ev_signal_stop (myloop, &exitsig);	469	ev_signal_stop (myloop, &exitsig);
456		470
457	=back	471	=back
458		472
		473
459	=head1 ANATOMY OF A WATCHER	474	=head1 ANATOMY OF A WATCHER
460		475
461	A watcher is a structure that you create and register to record your	476	A watcher is a structure that you create and register to record your
462	interest in some event. For instance, if you want to wait for STDIN to	477	interest in some event. For instance, if you want to wait for STDIN to
463	become readable, you would create an C<ev_io> watcher for that:	478	become readable, you would create an C<ev_io> watcher for that:
…		…
495	*) >>), and you can stop watching for events at any time by calling the	510	*) >>), and you can stop watching for events at any time by calling the
496	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	511	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.
497		512
498	As long as your watcher is active (has been started but not stopped) you	513	As long as your watcher is active (has been started but not stopped) you
499	must not touch the values stored in it. Most specifically you must never	514	must not touch the values stored in it. Most specifically you must never
500	reinitialise it or call its set macro.	515	reinitialise it or call its C<set> macro.
501
502	You can check whether an event is active by calling the C<ev_is_active
503	(watcher *)> macro. To see whether an event is outstanding (but the
504	callback for it has not been called yet) you can use the C<ev_is_pending
505	(watcher *)> macro.
506		516
507	Each and every callback receives the event loop pointer as first, the	517	Each and every callback receives the event loop pointer as first, the
508	registered watcher structure as second, and a bitset of received events as	518	registered watcher structure as second, and a bitset of received events as
509	third argument.	519	third argument.
510		520
…		…
567	with the error from read() or write(). This will not work in multithreaded	577	with the error from read() or write(). This will not work in multithreaded
568	programs, though, so beware.	578	programs, though, so beware.
569		579
570	=back	580	=back
571		581
		582	=head2 GENERIC WATCHER FUNCTIONS
		583
		584	In the following description, C<TYPE> stands for the watcher type,
		585	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
		586
		587	=over 4
		588
		589	=item C<ev_init> (ev_TYPE *watcher, callback)
		590
		591	This macro initialises the generic portion of a watcher. The contents
		592	of the watcher object can be arbitrary (so C<malloc> will do). Only
		593	the generic parts of the watcher are initialised, you I<need> to call
		594	the type-specific C<ev_TYPE_set> macro afterwards to initialise the
		595	type-specific parts. For each type there is also a C<ev_TYPE_init> macro
		596	which rolls both calls into one.
		597
		598	You can reinitialise a watcher at any time as long as it has been stopped
		599	(or never started) and there are no pending events outstanding.
		600
		601	The callback is always of type C<void ()(ev_loop loop, ev_TYPE *watcher,
		602	int revents)>.
		603
		604	=item C<ev_TYPE_set> (ev_TYPE *, [args])
		605
		606	This macro initialises the type-specific parts of a watcher. You need to
		607	call C<ev_init> at least once before you call this macro, but you can
		608	call C<ev_TYPE_set> any number of times. You must not, however, call this
		609	macro on a watcher that is active (it can be pending, however, which is a
		610	difference to the C<ev_init> macro).
		611
		612	Although some watcher types do not have type-specific arguments
		613	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
		614
		615	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
		616
		617	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
		618	calls into a single call. This is the most convinient method to initialise
		619	a watcher. The same limitations apply, of course.
		620
		621	=item C<ev_TYPE_start> (loop , ev_TYPE watcher)
		622
		623	Starts (activates) the given watcher. Only active watchers will receive
		624	events. If the watcher is already active nothing will happen.
		625
		626	=item C<ev_TYPE_stop> (loop , ev_TYPE watcher)
		627
		628	Stops the given watcher again (if active) and clears the pending
		629	status. It is possible that stopped watchers are pending (for example,
		630	non-repeating timers are being stopped when they become pending), but
		631	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If
		632	you want to free or reuse the memory used by the watcher it is therefore a
		633	good idea to always call its C<ev_TYPE_stop> function.
		634
		635	=item bool ev_is_active (ev_TYPE *watcher)
		636
		637	Returns a true value iff the watcher is active (i.e. it has been started
		638	and not yet been stopped). As long as a watcher is active you must not modify
		639	it.
		640
		641	=item bool ev_is_pending (ev_TYPE *watcher)
		642
		643	Returns a true value iff the watcher is pending, (i.e. it has outstanding
		644	events but its callback has not yet been invoked). As long as a watcher
		645	is pending (but not active) you must not call an init function on it (but
		646	C<ev_TYPE_set> is safe) and you must make sure the watcher is available to
		647	libev (e.g. you cnanot C<free ()> it).
		648
		649	=item callback = ev_cb (ev_TYPE *watcher)
		650
		651	Returns the callback currently set on the watcher.
		652
		653	=item ev_cb_set (ev_TYPE *watcher, callback)
		654
		655	Change the callback. You can change the callback at virtually any time
		656	(modulo threads).
		657
		658	=back
		659
		660
572	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	661	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
573		662
574	Each watcher has, by default, a member C<void *data> that you can change	663	Each watcher has, by default, a member C<void *data> that you can change
575	and read at any time, libev will completely ignore it. This can be used	664	and read at any time, libev will completely ignore it. This can be used
576	to associate arbitrary data with your watcher. If you need more data and	665	to associate arbitrary data with your watcher. If you need more data and
…		…
603		692
604	This section describes each watcher in detail, but will not repeat	693	This section describes each watcher in detail, but will not repeat
605	information given in the last section.	694	information given in the last section.
606		695
607		696
608	=head2 C<ev_io> - is this file descriptor readable or writable	697	=head2 C<ev_io> - is this file descriptor readable or writable?
609		698
610	I/O watchers check whether a file descriptor is readable or writable	699	I/O watchers check whether a file descriptor is readable or writable
611	in each iteration of the event loop (This behaviour is called	700	in each iteration of the event loop, or, more precisely, when reading
612	level-triggering because you keep receiving events as long as the	701	would not block the process and writing would at least be able to write
613	condition persists. Remember you can stop the watcher if you don't want to	702	some data. This behaviour is called level-triggering because you keep
614	act on the event and neither want to receive future events).	703	receiving events as long as the condition persists. Remember you can stop
		704	the watcher if you don't want to act on the event and neither want to
		705	receive future events.
615		706
616	In general you can register as many read and/or write event watchers per	707	In general you can register as many read and/or write event watchers per
617	fd as you want (as long as you don't confuse yourself). Setting all file	708	fd as you want (as long as you don't confuse yourself). Setting all file
618	descriptors to non-blocking mode is also usually a good idea (but not	709	descriptors to non-blocking mode is also usually a good idea (but not
619	required if you know what you are doing).	710	required if you know what you are doing).
620		711
621	You have to be careful with dup'ed file descriptors, though. Some backends	712	You have to be careful with dup'ed file descriptors, though. Some backends
622	(the linux epoll backend is a notable example) cannot handle dup'ed file	713	(the linux epoll backend is a notable example) cannot handle dup'ed file
623	descriptors correctly if you register interest in two or more fds pointing	714	descriptors correctly if you register interest in two or more fds pointing
624	to the same underlying file/socket etc. description (that is, they share	715	to the same underlying file/socket/etc. description (that is, they share
625	the same underlying "file open").	716	the same underlying "file open").
626		717
627	If you must do this, then force the use of a known-to-be-good backend	718	If you must do this, then force the use of a known-to-be-good backend
628	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and	719	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
629	C<EVBACKEND_POLL>).	720	C<EVBACKEND_POLL>).
630		721
		722	Another thing you have to watch out for is that it is quite easy to
		723	receive "spurious" readyness notifications, that is your callback might
		724	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
		725	because there is no data. Not only are some backends known to create a
		726	lot of those (for example solaris ports), it is very easy to get into
		727	this situation even with a relatively standard program structure. Thus
		728	it is best to always use non-blocking I/O: An extra C<read>(2) returning
		729	C<EAGAIN> is far preferable to a program hanging until some data arrives.
		730
		731	If you cannot run the fd in non-blocking mode (for example you should not
		732	play around with an Xlib connection), then you have to seperately re-test
		733	wether a file descriptor is really ready with a known-to-be good interface
		734	such as poll (fortunately in our Xlib example, Xlib already does this on
		735	its own, so its quite safe to use).
		736
631	=over 4	737	=over 4
632		738
633	=item ev_io_init (ev_io *, callback, int fd, int events)	739	=item ev_io_init (ev_io *, callback, int fd, int events)
634		740
635	=item ev_io_set (ev_io *, int fd, int events)	741	=item ev_io_set (ev_io *, int fd, int events)
636		742
637	Configures an C<ev_io> watcher. The fd is the file descriptor to rceeive	743	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
638	events for and events is either C<EV_READ>, C<EV_WRITE> or C<EV_READ \|	744	rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or
639	EV_WRITE> to receive the given events.	745	C<EV_READ \| EV_WRITE> to receive the given events.
640
641	Please note that most of the more scalable backend mechanisms (for example
642	epoll and solaris ports) can result in spurious readyness notifications
643	for file descriptors, so you practically need to use non-blocking I/O (and
644	treat callback invocation as hint only), or retest separately with a safe
645	interface before doing I/O (XLib can do this), or force the use of either
646	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>, which don't suffer from this
647	problem. Also note that it is quite easy to have your callback invoked
648	when the readyness condition is no longer valid even when employing
649	typical ways of handling events, so its a good idea to use non-blocking
650	I/O unconditionally.
651		746
652	=back	747	=back
653		748
654	Example: call C<stdin_readable_cb> when STDIN_FILENO has become, well	749	Example: call C<stdin_readable_cb> when STDIN_FILENO has become, well
655	readable, but only once. Since it is likely line-buffered, you could	750	readable, but only once. Since it is likely line-buffered, you could
…		…
668	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	763	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
669	ev_io_start (loop, &stdin_readable);	764	ev_io_start (loop, &stdin_readable);
670	ev_loop (loop, 0);	765	ev_loop (loop, 0);
671		766
672		767
673	=head2 C<ev_timer> - relative and optionally recurring timeouts	768	=head2 C<ev_timer> - relative and optionally repeating timeouts
674		769
675	Timer watchers are simple relative timers that generate an event after a	770	Timer watchers are simple relative timers that generate an event after a
676	given time, and optionally repeating in regular intervals after that.	771	given time, and optionally repeating in regular intervals after that.
677		772
678	The timers are based on real time, that is, if you register an event that	773	The timers are based on real time, that is, if you register an event that
…		…
760	// and in some piece of code that gets executed on any "activity":	855	// and in some piece of code that gets executed on any "activity":
761	// reset the timeout to start ticking again at 10 seconds	856	// reset the timeout to start ticking again at 10 seconds
762	ev_timer_again (&mytimer);	857	ev_timer_again (&mytimer);
763		858
764		859
765	=head2 C<ev_periodic> - to cron or not to cron	860	=head2 C<ev_periodic> - to cron or not to cron?
766		861
767	Periodic watchers are also timers of a kind, but they are very versatile	862	Periodic watchers are also timers of a kind, but they are very versatile
768	(and unfortunately a bit complex).	863	(and unfortunately a bit complex).
769		864
770	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	865	Unlike C<ev_timer>'s, they are not based on real time (or relative time)
771	but on wallclock time (absolute time). You can tell a periodic watcher	866	but on wallclock time (absolute time). You can tell a periodic watcher
772	to trigger "at" some specific point in time. For example, if you tell a	867	to trigger "at" some specific point in time. For example, if you tell a
773	periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now ()	868	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()
774	+ 10.>) and then reset your system clock to the last year, then it will	869	+ 10.>) and then reset your system clock to the last year, then it will
775	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	870	take a year to trigger the event (unlike an C<ev_timer>, which would trigger
776	roughly 10 seconds later and of course not if you reset your system time	871	roughly 10 seconds later and of course not if you reset your system time
777	again).	872	again).
778		873
…		…
898	ev_periodic_init (&hourly_tick, clock_cb,	993	ev_periodic_init (&hourly_tick, clock_cb,
899	fmod (ev_now (loop), 3600.), 3600., 0);	994	fmod (ev_now (loop), 3600.), 3600., 0);
900	ev_periodic_start (loop, &hourly_tick);	995	ev_periodic_start (loop, &hourly_tick);
901		996
902		997
903	=head2 C<ev_signal> - signal me when a signal gets signalled	998	=head2 C<ev_signal> - signal me when a signal gets signalled!
904		999
905	Signal watchers will trigger an event when the process receives a specific	1000	Signal watchers will trigger an event when the process receives a specific
906	signal one or more times. Even though signals are very asynchronous, libev	1001	signal one or more times. Even though signals are very asynchronous, libev
907	will try it's best to deliver signals synchronously, i.e. as part of the	1002	will try it's best to deliver signals synchronously, i.e. as part of the
908	normal event processing, like any other event.	1003	normal event processing, like any other event.
…		…
923	Configures the watcher to trigger on the given signal number (usually one	1018	Configures the watcher to trigger on the given signal number (usually one
924	of the C<SIGxxx> constants).	1019	of the C<SIGxxx> constants).
925		1020
926	=back	1021	=back
927		1022
		1023
928	=head2 C<ev_child> - wait for pid status changes	1024	=head2 C<ev_child> - watch out for process status changes
929		1025
930	Child watchers trigger when your process receives a SIGCHLD in response to	1026	Child watchers trigger when your process receives a SIGCHLD in response to
931	some child status changes (most typically when a child of yours dies).	1027	some child status changes (most typically when a child of yours dies).
932		1028
933	=over 4	1029	=over 4
…		…
956	struct ev_signal signal_watcher;	1052	struct ev_signal signal_watcher;
957	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	1053	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
958	ev_signal_start (loop, &sigint_cb);	1054	ev_signal_start (loop, &sigint_cb);
959		1055
960		1056
961	=head2 C<ev_idle> - when you've got nothing better to do	1057	=head2 C<ev_idle> - when you've got nothing better to do...
962		1058
963	Idle watchers trigger events when there are no other events are pending	1059	Idle watchers trigger events when there are no other events are pending
964	(prepare, check and other idle watchers do not count). That is, as long	1060	(prepare, check and other idle watchers do not count). That is, as long
965	as your process is busy handling sockets or timeouts (or even signals,	1061	as your process is busy handling sockets or timeouts (or even signals,
966	imagine) it will not be triggered. But when your process is idle all idle	1062	imagine) it will not be triggered. But when your process is idle all idle
…		…
1000	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	1096	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));
1001	ev_idle_init (idle_watcher, idle_cb);	1097	ev_idle_init (idle_watcher, idle_cb);
1002	ev_idle_start (loop, idle_cb);	1098	ev_idle_start (loop, idle_cb);
1003		1099
1004		1100
1005	=head2 C<ev_prepare> and C<ev_check> - customise your event loop	1101	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1006		1102
1007	Prepare and check watchers are usually (but not always) used in tandem:	1103	Prepare and check watchers are usually (but not always) used in tandem:
1008	prepare watchers get invoked before the process blocks and check watchers	1104	prepare watchers get invoked before the process blocks and check watchers
1009	afterwards.	1105	afterwards.
1010		1106
		1107	You I<must not> call C<ev_loop> or similar functions that enter
		1108	the current event loop from either C<ev_prepare> or C<ev_check>
		1109	watchers. Other loops than the current one are fine, however. The
		1110	rationale behind this is that you do not need to check for recursion in
		1111	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
		1112	C<ev_check> so if you have one watcher of each kind they will always be
		1113	called in pairs bracketing the blocking call.
		1114
1011	Their main purpose is to integrate other event mechanisms into libev. This	1115	Their main purpose is to integrate other event mechanisms into libev and
1012	could be used, for example, to track variable changes, implement your own	1116	their use is somewhat advanced. This could be used, for example, to track
1013	watchers, integrate net-snmp or a coroutine library and lots more.	1117	variable changes, implement your own watchers, integrate net-snmp or a
		1118	coroutine library and lots more. They are also occasionally useful if
		1119	you cache some data and want to flush it before blocking (for example,
		1120	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
		1121	watcher).
1014		1122
1015	This is done by examining in each prepare call which file descriptors need	1123	This is done by examining in each prepare call which file descriptors need
1016	to be watched by the other library, registering C<ev_io> watchers for	1124	to be watched by the other library, registering C<ev_io> watchers for
1017	them and starting an C<ev_timer> watcher for any timeouts (many libraries	1125	them and starting an C<ev_timer> watcher for any timeouts (many libraries
1018	provide just this functionality). Then, in the check watcher you check for	1126	provide just this functionality). Then, in the check watcher you check for
…		…
1040	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	1148	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1041	macros, but using them is utterly, utterly and completely pointless.	1149	macros, but using them is utterly, utterly and completely pointless.
1042		1150
1043	=back	1151	=back
1044		1152
1045	Example: TODO.	1153	Example: To include a library such as adns, you would add IO watchers
		1154	and a timeout watcher in a prepare handler, as required by libadns, and
		1155	in a check watcher, destroy them and call into libadns. What follows is
		1156	pseudo-code only of course:
		1157
		1158	static ev_io iow [nfd];
		1159	static ev_timer tw;
		1160
		1161	static void
		1162	io_cb (ev_loop loop, ev_io w, int revents)
		1163	{
		1164	// set the relevant poll flags
		1165	// could also call adns_processreadable etc. here
		1166	struct pollfd fd = (struct pollfd )w->data;
		1167	if (revents & EV_READ ) fd->revents \|= fd->events & POLLIN;
		1168	if (revents & EV_WRITE) fd->revents \|= fd->events & POLLOUT;
		1169	}
		1170
		1171	// create io watchers for each fd and a timer before blocking
		1172	static void
		1173	adns_prepare_cb (ev_loop loop, ev_prepare w, int revents)
		1174	{
		1175	int timeout = 3600000;truct pollfd fds [nfd];
		1176	// actual code will need to loop here and realloc etc.
		1177	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
		1178
		1179	/* the callback is illegal, but won't be called as we stop during check */
		1180	ev_timer_init (&tw, 0, timeout * 1e-3);
		1181	ev_timer_start (loop, &tw);
		1182
		1183	// create on ev_io per pollfd
		1184	for (int i = 0; i < nfd; ++i)
		1185	{
		1186	ev_io_init (iow + i, io_cb, fds [i].fd,
		1187	((fds [i].events & POLLIN ? EV_READ : 0)
		1188	\| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
		1189
		1190	fds [i].revents = 0;
		1191	iow [i].data = fds + i;
		1192	ev_io_start (loop, iow + i);
		1193	}
		1194	}
		1195
		1196	// stop all watchers after blocking
		1197	static void
		1198	adns_check_cb (ev_loop loop, ev_check w, int revents)
		1199	{
		1200	ev_timer_stop (loop, &tw);
		1201
		1202	for (int i = 0; i < nfd; ++i)
		1203	ev_io_stop (loop, iow + i);
		1204
		1205	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
		1206	}
		1207
		1208
		1209	=head2 C<ev_embed> - when one backend isn't enough...
		1210
		1211	This is a rather advanced watcher type that lets you embed one event loop
		1212	into another (currently only C<ev_io> events are supported in the embedded
		1213	loop, other types of watchers might be handled in a delayed or incorrect
		1214	fashion and must not be used).
		1215
		1216	There are primarily two reasons you would want that: work around bugs and
		1217	prioritise I/O.
		1218
		1219	As an example for a bug workaround, the kqueue backend might only support
		1220	sockets on some platform, so it is unusable as generic backend, but you
		1221	still want to make use of it because you have many sockets and it scales
		1222	so nicely. In this case, you would create a kqueue-based loop and embed it
		1223	into your default loop (which might use e.g. poll). Overall operation will
		1224	be a bit slower because first libev has to poll and then call kevent, but
		1225	at least you can use both at what they are best.
		1226
		1227	As for prioritising I/O: rarely you have the case where some fds have
		1228	to be watched and handled very quickly (with low latency), and even
		1229	priorities and idle watchers might have too much overhead. In this case
		1230	you would put all the high priority stuff in one loop and all the rest in
		1231	a second one, and embed the second one in the first.
		1232
		1233	As long as the watcher is active, the callback will be invoked every time
		1234	there might be events pending in the embedded loop. The callback must then
		1235	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke
		1236	their callbacks (you could also start an idle watcher to give the embedded
		1237	loop strictly lower priority for example). You can also set the callback
		1238	to C<0>, in which case the embed watcher will automatically execute the
		1239	embedded loop sweep.
		1240
		1241	As long as the watcher is started it will automatically handle events. The
		1242	callback will be invoked whenever some events have been handled. You can
		1243	set the callback to C<0> to avoid having to specify one if you are not
		1244	interested in that.
		1245
		1246	Also, there have not currently been made special provisions for forking:
		1247	when you fork, you not only have to call C<ev_loop_fork> on both loops,
		1248	but you will also have to stop and restart any C<ev_embed> watchers
		1249	yourself.
		1250
		1251	Unfortunately, not all backends are embeddable, only the ones returned by
		1252	C<ev_embeddable_backends> are, which, unfortunately, does not include any
		1253	portable one.
		1254
		1255	So when you want to use this feature you will always have to be prepared
		1256	that you cannot get an embeddable loop. The recommended way to get around
		1257	this is to have a separate variables for your embeddable loop, try to
		1258	create it, and if that fails, use the normal loop for everything:
		1259
		1260	struct ev_loop *loop_hi = ev_default_init (0);
		1261	struct ev_loop *loop_lo = 0;
		1262	struct ev_embed embed;
		1263
		1264	// see if there is a chance of getting one that works
		1265	// (remember that a flags value of 0 means autodetection)
		1266	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		1267	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		1268	: 0;
		1269
		1270	// if we got one, then embed it, otherwise default to loop_hi
		1271	if (loop_lo)
		1272	{
		1273	ev_embed_init (&embed, 0, loop_lo);
		1274	ev_embed_start (loop_hi, &embed);
		1275	}
		1276	else
		1277	loop_lo = loop_hi;
		1278
		1279	=over 4
		1280
		1281	=item ev_embed_init (ev_embed , callback, struct ev_loop embedded_loop)
		1282
		1283	=item ev_embed_set (ev_embed , callback, struct ev_loop embedded_loop)
		1284
		1285	Configures the watcher to embed the given loop, which must be
		1286	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
		1287	invoked automatically, otherwise it is the responsibility of the callback
		1288	to invoke it (it will continue to be called until the sweep has been done,
		1289	if you do not want thta, you need to temporarily stop the embed watcher).
		1290
		1291	=item ev_embed_sweep (loop, ev_embed *)
		1292
		1293	Make a single, non-blocking sweep over the embedded loop. This works
		1294	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
		1295	apropriate way for embedded loops.
		1296
		1297	=back
1046		1298
1047		1299
1048	=head1 OTHER FUNCTIONS	1300	=head1 OTHER FUNCTIONS
1049		1301
1050	There are some other functions of possible interest. Described. Here. Now.	1302	There are some other functions of possible interest. Described. Here. Now.
…		…
1081	/* stdin might have data for us, joy! */;	1333	/* stdin might have data for us, joy! */;
1082	}	1334	}
1083		1335
1084	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	1336	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
1085		1337
1086	=item ev_feed_event (loop, watcher, int events)	1338	=item ev_feed_event (ev_loop , watcher , int revents)
1087		1339
1088	Feeds the given event set into the event loop, as if the specified event	1340	Feeds the given event set into the event loop, as if the specified event
1089	had happened for the specified watcher (which must be a pointer to an	1341	had happened for the specified watcher (which must be a pointer to an
1090	initialised but not necessarily started event watcher).	1342	initialised but not necessarily started event watcher).
1091		1343
1092	=item ev_feed_fd_event (loop, int fd, int revents)	1344	=item ev_feed_fd_event (ev_loop *, int fd, int revents)
1093		1345
1094	Feed an event on the given fd, as if a file descriptor backend detected	1346	Feed an event on the given fd, as if a file descriptor backend detected
1095	the given events it.	1347	the given events it.
1096		1348
1097	=item ev_feed_signal_event (loop, int signum)	1349	=item ev_feed_signal_event (ev_loop *loop, int signum)
1098		1350
1099	Feed an event as if the given signal occured (loop must be the default loop!).	1351	Feed an event as if the given signal occured (C<loop> must be the default
		1352	loop!).
1100		1353
1101	=back	1354	=back
1102		1355
1103		1356
1104	=head1 LIBEVENT EMULATION	1357	=head1 LIBEVENT EMULATION
…		…
1128		1381
1129	=back	1382	=back
1130		1383
1131	=head1 C++ SUPPORT	1384	=head1 C++ SUPPORT
1132		1385
1133	TBD.	1386	Libev comes with some simplistic wrapper classes for C++ that mainly allow
		1387	you to use some convinience methods to start/stop watchers and also change
		1388	the callback model to a model using method callbacks on objects.
		1389
		1390	To use it,
		1391
		1392	#include <ev++.h>
		1393
		1394	(it is not installed by default). This automatically includes F<ev.h>
		1395	and puts all of its definitions (many of them macros) into the global
		1396	namespace. All C++ specific things are put into the C<ev> namespace.
		1397
		1398	It should support all the same embedding options as F<ev.h>, most notably
		1399	C<EV_MULTIPLICITY>.
		1400
		1401	Here is a list of things available in the C<ev> namespace:
		1402
		1403	=over 4
		1404
		1405	=item C<ev::READ>, C<ev::WRITE> etc.
		1406
		1407	These are just enum values with the same values as the C<EV_READ> etc.
		1408	macros from F<ev.h>.
		1409
		1410	=item C<ev::tstamp>, C<ev::now>
		1411
		1412	Aliases to the same types/functions as with the C<ev_> prefix.
		1413
		1414	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
		1415
		1416	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
		1417	the same name in the C<ev> namespace, with the exception of C<ev_signal>
		1418	which is called C<ev::sig> to avoid clashes with the C<signal> macro
		1419	defines by many implementations.
		1420
		1421	All of those classes have these methods:
		1422
		1423	=over 4
		1424
		1425	=item ev::TYPE::TYPE (object , object::method )
		1426
		1427	=item ev::TYPE::TYPE (object , object::method , struct ev_loop *)
		1428
		1429	=item ev::TYPE::~TYPE
		1430
		1431	The constructor takes a pointer to an object and a method pointer to
		1432	the event handler callback to call in this class. The constructor calls
		1433	C<ev_init> for you, which means you have to call the C<set> method
		1434	before starting it. If you do not specify a loop then the constructor
		1435	automatically associates the default loop with this watcher.
		1436
		1437	The destructor automatically stops the watcher if it is active.
		1438
		1439	=item w->set (struct ev_loop *)
		1440
		1441	Associates a different C<struct ev_loop> with this watcher. You can only
		1442	do this when the watcher is inactive (and not pending either).
		1443
		1444	=item w->set ([args])
		1445
		1446	Basically the same as C<ev_TYPE_set>, with the same args. Must be
		1447	called at least once. Unlike the C counterpart, an active watcher gets
		1448	automatically stopped and restarted.
		1449
		1450	=item w->start ()
		1451
		1452	Starts the watcher. Note that there is no C<loop> argument as the
		1453	constructor already takes the loop.
		1454
		1455	=item w->stop ()
		1456
		1457	Stops the watcher if it is active. Again, no C<loop> argument.
		1458
		1459	=item w->again () C<ev::timer>, C<ev::periodic> only
		1460
		1461	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
		1462	C<ev_TYPE_again> function.
		1463
		1464	=item w->sweep () C<ev::embed> only
		1465
		1466	Invokes C<ev_embed_sweep>.
		1467
		1468	=back
		1469
		1470	=back
		1471
		1472	Example: Define a class with an IO and idle watcher, start one of them in
		1473	the constructor.
		1474
		1475	class myclass
		1476	{
		1477	ev_io io; void io_cb (ev::io &w, int revents);
		1478	ev_idle idle void idle_cb (ev::idle &w, int revents);
		1479
		1480	myclass ();
		1481	}
		1482
		1483	myclass::myclass (int fd)
		1484	: io (this, &myclass::io_cb),
		1485	idle (this, &myclass::idle_cb)
		1486	{
		1487	io.start (fd, ev::READ);
		1488	}
		1489
		1490	=head1 EMBEDDING
		1491
		1492	Libev can (and often is) directly embedded into host
		1493	applications. Examples of applications that embed it include the Deliantra
		1494	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
		1495	and rxvt-unicode.
		1496
		1497	The goal is to enable you to just copy the neecssary files into your
		1498	source directory without having to change even a single line in them, so
		1499	you can easily upgrade by simply copying (or having a checked-out copy of
		1500	libev somewhere in your source tree).
		1501
		1502	=head2 FILESETS
		1503
		1504	Depending on what features you need you need to include one or more sets of files
		1505	in your app.
		1506
		1507	=head3 CORE EVENT LOOP
		1508
		1509	To include only the libev core (all the C<ev_*> functions), with manual
		1510	configuration (no autoconf):
		1511
		1512	#define EV_STANDALONE 1
		1513	#include "ev.c"
		1514
		1515	This will automatically include F<ev.h>, too, and should be done in a
		1516	single C source file only to provide the function implementations. To use
		1517	it, do the same for F<ev.h> in all files wishing to use this API (best
		1518	done by writing a wrapper around F<ev.h> that you can include instead and
		1519	where you can put other configuration options):
		1520
		1521	#define EV_STANDALONE 1
		1522	#include "ev.h"
		1523
		1524	Both header files and implementation files can be compiled with a C++
		1525	compiler (at least, thats a stated goal, and breakage will be treated
		1526	as a bug).
		1527
		1528	You need the following files in your source tree, or in a directory
		1529	in your include path (e.g. in libev/ when using -Ilibev):
		1530
		1531	ev.h
		1532	ev.c
		1533	ev_vars.h
		1534	ev_wrap.h
		1535
		1536	ev_win32.c required on win32 platforms only
		1537
		1538	ev_select.c only when select backend is enabled (which is by default)
		1539	ev_poll.c only when poll backend is enabled (disabled by default)
		1540	ev_epoll.c only when the epoll backend is enabled (disabled by default)
		1541	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
		1542	ev_port.c only when the solaris port backend is enabled (disabled by default)
		1543
		1544	F<ev.c> includes the backend files directly when enabled, so you only need
		1545	to compile this single file.
		1546
		1547	=head3 LIBEVENT COMPATIBILITY API
		1548
		1549	To include the libevent compatibility API, also include:
		1550
		1551	#include "event.c"
		1552
		1553	in the file including F<ev.c>, and:
		1554
		1555	#include "event.h"
		1556
		1557	in the files that want to use the libevent API. This also includes F<ev.h>.
		1558
		1559	You need the following additional files for this:
		1560
		1561	event.h
		1562	event.c
		1563
		1564	=head3 AUTOCONF SUPPORT
		1565
		1566	Instead of using C<EV_STANDALONE=1> and providing your config in
		1567	whatever way you want, you can also C<m4_include([libev.m4])> in your
		1568	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
		1569	include F<config.h> and configure itself accordingly.
		1570
		1571	For this of course you need the m4 file:
		1572
		1573	libev.m4
		1574
		1575	=head2 PREPROCESSOR SYMBOLS/MACROS
		1576
		1577	Libev can be configured via a variety of preprocessor symbols you have to define
		1578	before including any of its files. The default is not to build for multiplicity
		1579	and only include the select backend.
		1580
		1581	=over 4
		1582
		1583	=item EV_STANDALONE
		1584
		1585	Must always be C<1> if you do not use autoconf configuration, which
		1586	keeps libev from including F<config.h>, and it also defines dummy
		1587	implementations for some libevent functions (such as logging, which is not
		1588	supported). It will also not define any of the structs usually found in
		1589	F<event.h> that are not directly supported by the libev core alone.
		1590
		1591	=item EV_USE_MONOTONIC
		1592
		1593	If defined to be C<1>, libev will try to detect the availability of the
		1594	monotonic clock option at both compiletime and runtime. Otherwise no use
		1595	of the monotonic clock option will be attempted. If you enable this, you
		1596	usually have to link against librt or something similar. Enabling it when
		1597	the functionality isn't available is safe, though, althoguh you have
		1598	to make sure you link against any libraries where the C<clock_gettime>
		1599	function is hiding in (often F<-lrt>).
		1600
		1601	=item EV_USE_REALTIME
		1602
		1603	If defined to be C<1>, libev will try to detect the availability of the
		1604	realtime clock option at compiletime (and assume its availability at
		1605	runtime if successful). Otherwise no use of the realtime clock option will
		1606	be attempted. This effectively replaces C<gettimeofday> by C<clock_get
		1607	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See tzhe note about libraries
		1608	in the description of C<EV_USE_MONOTONIC>, though.
		1609
		1610	=item EV_USE_SELECT
		1611
		1612	If undefined or defined to be C<1>, libev will compile in support for the
		1613	C<select>(2) backend. No attempt at autodetection will be done: if no
		1614	other method takes over, select will be it. Otherwise the select backend
		1615	will not be compiled in.
		1616
		1617	=item EV_SELECT_USE_FD_SET
		1618
		1619	If defined to C<1>, then the select backend will use the system C<fd_set>
		1620	structure. This is useful if libev doesn't compile due to a missing
		1621	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on
		1622	exotic systems. This usually limits the range of file descriptors to some
		1623	low limit such as 1024 or might have other limitations (winsocket only
		1624	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might
		1625	influence the size of the C<fd_set> used.
		1626
		1627	=item EV_SELECT_IS_WINSOCKET
		1628
		1629	When defined to C<1>, the select backend will assume that
		1630	select/socket/connect etc. don't understand file descriptors but
		1631	wants osf handles on win32 (this is the case when the select to
		1632	be used is the winsock select). This means that it will call
		1633	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
		1634	it is assumed that all these functions actually work on fds, even
		1635	on win32. Should not be defined on non-win32 platforms.
		1636
		1637	=item EV_USE_POLL
		1638
		1639	If defined to be C<1>, libev will compile in support for the C<poll>(2)
		1640	backend. Otherwise it will be enabled on non-win32 platforms. It
		1641	takes precedence over select.
		1642
		1643	=item EV_USE_EPOLL
		1644
		1645	If defined to be C<1>, libev will compile in support for the Linux
		1646	C<epoll>(7) backend. Its availability will be detected at runtime,
		1647	otherwise another method will be used as fallback. This is the
		1648	preferred backend for GNU/Linux systems.
		1649
		1650	=item EV_USE_KQUEUE
		1651
		1652	If defined to be C<1>, libev will compile in support for the BSD style
		1653	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
		1654	otherwise another method will be used as fallback. This is the preferred
		1655	backend for BSD and BSD-like systems, although on most BSDs kqueue only
		1656	supports some types of fds correctly (the only platform we found that
		1657	supports ptys for example was NetBSD), so kqueue might be compiled in, but
		1658	not be used unless explicitly requested. The best way to use it is to find
		1659	out whether kqueue supports your type of fd properly and use an embedded
		1660	kqueue loop.
		1661
		1662	=item EV_USE_PORT
		1663
		1664	If defined to be C<1>, libev will compile in support for the Solaris
		1665	10 port style backend. Its availability will be detected at runtime,
		1666	otherwise another method will be used as fallback. This is the preferred
		1667	backend for Solaris 10 systems.
		1668
		1669	=item EV_USE_DEVPOLL
		1670
		1671	reserved for future expansion, works like the USE symbols above.
		1672
		1673	=item EV_H
		1674
		1675	The name of the F<ev.h> header file used to include it. The default if
		1676	undefined is C<< <ev.h> >> in F<event.h> and C<"ev.h"> in F<ev.c>. This
		1677	can be used to virtually rename the F<ev.h> header file in case of conflicts.
		1678
		1679	=item EV_CONFIG_H
		1680
		1681	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
		1682	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
		1683	C<EV_H>, above.
		1684
		1685	=item EV_EVENT_H
		1686
		1687	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
		1688	of how the F<event.h> header can be found.
		1689
		1690	=item EV_PROTOTYPES
		1691
		1692	If defined to be C<0>, then F<ev.h> will not define any function
		1693	prototypes, but still define all the structs and other symbols. This is
		1694	occasionally useful if you want to provide your own wrapper functions
		1695	around libev functions.
		1696
		1697	=item EV_MULTIPLICITY
		1698
		1699	If undefined or defined to C<1>, then all event-loop-specific functions
		1700	will have the C<struct ev_loop *> as first argument, and you can create
		1701	additional independent event loops. Otherwise there will be no support
		1702	for multiple event loops and there is no first event loop pointer
		1703	argument. Instead, all functions act on the single default loop.
		1704
		1705	=item EV_PERIODICS
		1706
		1707	If undefined or defined to be C<1>, then periodic timers are supported,
		1708	otherwise not. This saves a few kb of code.
		1709
		1710	=item EV_COMMON
		1711
		1712	By default, all watchers have a C<void *data> member. By redefining
		1713	this macro to a something else you can include more and other types of
		1714	members. You have to define it each time you include one of the files,
		1715	though, and it must be identical each time.
		1716
		1717	For example, the perl EV module uses something like this:
		1718
		1719	#define EV_COMMON \
		1720	SV self; / contains this struct */ \
		1721	SV cb_sv, fh /* note no trailing ";" */
		1722
		1723	=item EV_CB_DECLARE (type)
		1724
		1725	=item EV_CB_INVOKE (watcher, revents)
		1726
		1727	=item ev_set_cb (ev, cb)
		1728
		1729	Can be used to change the callback member declaration in each watcher,
		1730	and the way callbacks are invoked and set. Must expand to a struct member
		1731	definition and a statement, respectively. See the F<ev.v> header file for
		1732	their default definitions. One possible use for overriding these is to
		1733	avoid the C<struct ev_loop *> as first argument in all cases, or to use
		1734	method calls instead of plain function calls in C++.
		1735
		1736	=head2 EXAMPLES
		1737
		1738	For a real-world example of a program the includes libev
		1739	verbatim, you can have a look at the EV perl module
		1740	(L<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
		1741	the F<libev/> subdirectory and includes them in the F<EV/EVAPI.h> (public
		1742	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file
		1743	will be compiled. It is pretty complex because it provides its own header
		1744	file.
		1745
		1746	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
		1747	that everybody includes and which overrides some autoconf choices:
		1748
		1749	#define EV_USE_POLL 0
		1750	#define EV_MULTIPLICITY 0
		1751	#define EV_PERIODICS 0
		1752	#define EV_CONFIG_H <config.h>
		1753
		1754	#include "ev++.h"
		1755
		1756	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
		1757
		1758	#include "ev_cpp.h"
		1759	#include "ev.c"
		1760
		1761
		1762	=head1 COMPLEXITIES
		1763
		1764	In this section the complexities of (many of) the algorithms used inside
		1765	libev will be explained. For complexity discussions about backends see the
		1766	documentation for C<ev_default_init>.
		1767
		1768	=over 4
		1769
		1770	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
		1771
		1772	=item Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)
		1773
		1774	=item Starting io/check/prepare/idle/signal/child watchers: O(1)
		1775
		1776	=item Stopping check/prepare/idle watchers: O(1)
		1777
		1778	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % 16))
		1779
		1780	=item Finding the next timer per loop iteration: O(1)
		1781
		1782	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		1783
		1784	=item Activating one watcher: O(1)
		1785
		1786	=back
		1787
1134		1788
1135	=head1 AUTHOR	1789	=head1 AUTHOR
1136		1790
1137	Marc Lehmann <libev@schmorp.de>.	1791	Marc Lehmann <libev@schmorp.de>.
1138		1792

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Comparing libev/ev.pod (file contents): Revision 1.34 by root, Fri Nov 23 16:17:12 2007 UTC vs. Revision 1.46 by root, Mon Nov 26 10:20:43 2007 UTC

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Comparing libev/ev.pod (file contents):
Revision 1.34 by root, Fri Nov 23 16:17:12 2007 UTC vs.
Revision 1.46 by root, Mon Nov 26 10:20:43 2007 UTC