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

Comparing libev/ev.pod (file contents):
Revision 1.199 by root, Thu Oct 23 07:18:21 2008 UTC vs.
Revision 1.206 by root, Tue Oct 28 12:31:38 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
…		…
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<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 event
388	support for dup.	392	mechanisms: problems include silently dropping fds, requiring a system
		393	call per change per fd (and unnecessary guessing of parameters), problems
		394	with dup and so on. The biggest issue is fork races, however - if a
		395	program forks then I<both> parent and child process have to recreate the
		396	epoll set, which can take considerable time (one syscall per fd) and is of
		397	course hard to detect.
		398
		399	Epoll is also notoriously buggy - embedding epoll fds should work, but
		400	of course doesn't, and epoll just loves to report events for totally
		401	I<different> file descriptors (even already closed ones, so one cannot
		402	even remove them from the set) than registered in the set (especially
		403	on SMP systems). Libev tries to counter these spurious notifications by
		404	employing an additional generation counter and comparing that against the
		405	events to filter out spurious ones.
389		406
390	While stopping, setting and starting an I/O watcher in the same iteration	407	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	408	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	409	(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	410	best to avoid that. Also, C<dup ()>'ed file descriptors might not work
394	very well if you register events for both fds.	411	very well if you register events for both fds.
395		412
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
400	Best performance from this backend is achieved by not unregistering all	413	Best performance from this backend is achieved by not unregistering all
401	watchers for a file descriptor until it has been closed, if possible,	414	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	415	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	416	starting a watcher (without re-setting it) also usually doesn't cause
404	extra overhead.	417	extra overhead. A fork can both result in spurious notifications as well
		418	as in libev having to destroy and recreate the epoll object, which can
		419	take considerable time and thus should be avoided.
405		420
406	While nominally embeddable in other event loops, this feature is broken in	421	While nominally embeddable in other event loops, this feature is broken in
407	all kernel versions tested so far.	422	all kernel versions tested so far.
408		423
409	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	424	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
…		…
424		439
425	It scales in the same way as the epoll backend, but the interface to the	440	It scales in the same way as the epoll backend, but the interface to the
426	kernel is more efficient (which says nothing about its actual speed, of	441	kernel is more efficient (which says nothing about its actual speed, of
427	course). While stopping, setting and starting an I/O watcher does never	442	course). While stopping, setting and starting an I/O watcher does never
428	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to	443	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
429	two event changes per incident. Support for C<fork ()> is very bad and it	444	two event changes per incident. Support for C<fork ()> is very bad (but
430	drops fds silently in similarly hard-to-detect cases.	445	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		446	cases
431		447
432	This backend usually performs well under most conditions.	448	This backend usually performs well under most conditions.
433		449
434	While nominally embeddable in other event loops, this doesn't work	450	While nominally embeddable in other event loops, this doesn't work
435	everywhere, so you might need to test for this. And since it is broken	451	everywhere, so you might need to test for this. And since it is broken
…		…
464	might perform better.	480	might perform better.
465		481
466	On the positive side, with the exception of the spurious readiness	482	On the positive side, with the exception of the spurious readiness
467	notifications, this backend actually performed fully to specification	483	notifications, this backend actually performed fully to specification
468	in all tests and is fully embeddable, which is a rare feat among the	484	in all tests and is fully embeddable, which is a rare feat among the
469	OS-specific backends.	485	OS-specific backends (I vastly prefer correctness over speed hacks).
470		486
471	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	487	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
472	C<EVBACKEND_POLL>.	488	C<EVBACKEND_POLL>.
473		489
474	=item C<EVBACKEND_ALL>	490	=item C<EVBACKEND_ALL>
…		…
527	responsibility to either stop all watchers cleanly yourself I<before>	543	responsibility to either stop all watchers cleanly yourself I<before>
528	calling this function, or cope with the fact afterwards (which is usually	544	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	545	the easiest thing, you can just ignore the watchers and/or C<free ()> them
530	for example).	546	for example).
531		547
532	Note that certain global state, such as signal state, will not be freed by	548	Note that certain global state, such as signal state (and installed signal
533	this function, and related watchers (such as signal and child watchers)	549	handlers), will not be freed by this function, and related watchers (such
534	would need to be stopped manually.	550	as signal and child watchers) would need to be stopped manually.
535		551
536	In general it is not advisable to call this function except in the	552	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	553	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	554	pipe fds. If you need dynamically allocated loops it is better to use
539	C<ev_loop_new> and C<ev_loop_destroy>).	555	C<ev_loop_new> and C<ev_loop_destroy>).
…		…
768	they fire on, say, one-second boundaries only.	784	they fire on, say, one-second boundaries only.
769		785
770	=item ev_loop_verify (loop)	786	=item ev_loop_verify (loop)
771		787
772	This function only does something when C<EV_VERIFY> support has been	788	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	789	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	790	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	791	is found to be inconsistent, it will print an error message to standard
776	error and call C<abort ()>.	792	error and call C<abort ()>.
777		793
778	This can be used to catch bugs inside libev itself: under normal	794	This can be used to catch bugs inside libev itself: under normal
…		…
781		797
782	=back	798	=back
783		799
784		800
785	=head1 ANATOMY OF A WATCHER	801	=head1 ANATOMY OF A WATCHER
		802
		803	In the following description, uppercase C<TYPE> in names stands for the
		804	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		805	watchers and C<ev_io_start> for I/O watchers.
786		806
787	A watcher is a structure that you create and register to record your	807	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	808	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:	809	become readable, you would create an C<ev_io> watcher for that:
790		810
…		…
793	ev_io_stop (w);	813	ev_io_stop (w);
794	ev_unloop (loop, EVUNLOOP_ALL);	814	ev_unloop (loop, EVUNLOOP_ALL);
795	}	815	}
796		816
797	struct ev_loop *loop = ev_default_loop (0);	817	struct ev_loop *loop = ev_default_loop (0);
		818
798	ev_io stdin_watcher;	819	ev_io stdin_watcher;
		820
799	ev_init (&stdin_watcher, my_cb);	821	ev_init (&stdin_watcher, my_cb);
800	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	822	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
801	ev_io_start (loop, &stdin_watcher);	823	ev_io_start (loop, &stdin_watcher);
		824
802	ev_loop (loop, 0);	825	ev_loop (loop, 0);
803		826
804	As you can see, you are responsible for allocating the memory for your	827	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,	828	watcher structures (and it is I<usually> a bad idea to do this on the
806	although this can sometimes be quite valid).	829	stack).
		830
		831	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		832	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
807		833
808	Each watcher structure must be initialised by a call to C<ev_init	834	Each watcher structure must be initialised by a call to C<ev_init
809	(watcher *, callback)>, which expects a callback to be provided. This	835	(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	836	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	837	watchers, each time the event loop detects that the file descriptor given
812	is readable and/or writable).	838	is readable and/or writable).
813		839
814	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	840	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	841	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	842	is also a macro to combine initialisation and setting in one call: C<<
817	(watcher *, callback, ...) >>.	843	ev_TYPE_init (watcher *, callback, ...) >>.
818		844
819	To make the watcher actually watch out for events, you have to start it	845	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	846	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	847	*) >>), and you can stop watching for events at any time by calling the
822	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	848	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
823		849
824	As long as your watcher is active (has been started but not stopped) you	850	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	851	must not touch the values stored in it. Most specifically you must never
826	reinitialise it or call its C<set> macro.	852	reinitialise it or call its C<ev_TYPE_set> macro.
827		853
828	Each and every callback receives the event loop pointer as first, the	854	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	855	registered watcher structure as second, and a bitset of received events as
830	third argument.	856	third argument.
831		857
…		…
912		938
913	=back	939	=back
914		940
915	=head2 GENERIC WATCHER FUNCTIONS	941	=head2 GENERIC WATCHER FUNCTIONS
916		942
917	In the following description, C<TYPE> stands for the watcher type,
918	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
919
920	=over 4	943	=over 4
921		944
922	=item C<ev_init> (ev_TYPE *watcher, callback)	945	=item C<ev_init> (ev_TYPE *watcher, callback)
923		946
924	This macro initialises the generic portion of a watcher. The contents	947	This macro initialises the generic portion of a watcher. The contents
…		…
1032	The default priority used by watchers when no priority has been set is	1055	The default priority used by watchers when no priority has been set is
1033	always C<0>, which is supposed to not be too high and not be too low :).	1056	always C<0>, which is supposed to not be too high and not be too low :).
1034		1057
1035	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1058	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
1036	fine, as long as you do not mind that the priority value you query might	1059	fine, as long as you do not mind that the priority value you query might
1037	or might not have been adjusted to be within valid range.	1060	or might not have been clamped to the valid range.
1038		1061
1039	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1062	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
1040		1063
1041	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1064	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
1042	C<loop> nor C<revents> need to be valid as long as the watcher callback	1065	C<loop> nor C<revents> need to be valid as long as the watcher callback
…		…
1426		1449
1427	Changing the timeout is trivial as well (if it isn't hard-coded in the	1450	Changing the timeout is trivial as well (if it isn't hard-coded in the
1428	callback :) - just change the timeout and invoke the callback, which will	1451	callback :) - just change the timeout and invoke the callback, which will
1429	fix things for you.	1452	fix things for you.
1430		1453
1431	=item 4. Whee, use a double-linked list for your timeouts.	1454	=item 4. Wee, just use a double-linked list for your timeouts.
1432		1455
1433	If there is not one request, but many thousands, all employing some kind	1456	If there is not one request, but many thousands (millions...), all
1434	of timeout with the same timeout value, then one can do even better:	1457	employing some kind of timeout with the same timeout value, then one can
		1458	do even better:
1435		1459
1436	When starting the timeout, calculate the timeout value and put the timeout	1460	When starting the timeout, calculate the timeout value and put the timeout
1437	at the I<end> of the list.	1461	at the I<end> of the list.
1438		1462
1439	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of	1463	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
…		…
1448	complication, and having to use a constant timeout. The constant timeout	1472	complication, and having to use a constant timeout. The constant timeout
1449	ensures that the list stays sorted.	1473	ensures that the list stays sorted.
1450		1474
1451	=back	1475	=back
1452		1476
1453	So what method is the best?	1477	So which method the best?
1454		1478
1455	The method #2 is a simple no-brain-required solution that is adequate in	1479	Method #2 is a simple no-brain-required solution that is adequate in most
1456	most situations. Method #3 requires a bit more thinking, but handles many	1480	situations. Method #3 requires a bit more thinking, but handles many cases
1457	cases better, and isn't very complicated either. In most case, choosing	1481	better, and isn't very complicated either. In most case, choosing either
1458	either one is fine.	1482	one is fine, with #3 being better in typical situations.
1459		1483
1460	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is	1484	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
1461	rather complicated, but extremely efficient, something that really pays	1485	rather complicated, but extremely efficient, something that really pays
1462	off after the first or so million of active timers, i.e. it's usually	1486	off after the first million or so of active timers, i.e. it's usually
1463	overkill :)	1487	overkill :)
1464		1488
1465	=head3 The special problem of time updates	1489	=head3 The special problem of time updates
1466		1490
1467	Establishing the current time is a costly operation (it usually takes at	1491	Establishing the current time is a costly operation (it usually takes at
…		…
2946	=item D	2970	=item D
2947		2971
2948	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	2972	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
2949	be found at L<http://proj.llucax.com.ar/wiki/evd>.	2973	be found at L<http://proj.llucax.com.ar/wiki/evd>.
2950		2974
		2975	=item Ocaml
		2976
		2977	Erkki Seppala has written Ocaml bindings for libev, to be found at
		2978	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		2979
2951	=back	2980	=back
2952		2981
2953		2982
2954	=head1 MACRO MAGIC	2983	=head1 MACRO MAGIC
2955		2984

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Comparing libev/ev.pod (file contents): Revision 1.199 by root, Thu Oct 23 07:18:21 2008 UTC vs. Revision 1.206 by root, Tue Oct 28 12:31:38 2008 UTC

Diff Legend

Comparing libev/ev.pod (file contents):
Revision 1.199 by root, Thu Oct 23 07:18:21 2008 UTC vs.
Revision 1.206 by root, Tue Oct 28 12:31:38 2008 UTC