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

Comparing libev/ev.pod (file contents):
Revision 1.354 by root, Tue Jan 11 01:40:25 2011 UTC vs.
Revision 1.359 by root, Tue Jan 11 10:56:01 2011 UTC

…		…
1357	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related	1357	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
1358	functions that do not need a watcher.	1358	functions that do not need a watcher.
1359		1359
1360	=back	1360	=back
1361		1361
1362	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1362	See also the L<ASSOCIATING CUSTOM DATA WITH A WATCHER> and L<BUILDING YOUR
1363		1363	OWN COMPOSITE WATCHERS> idioms.
1364	Each watcher has, by default, a member C<void *data> that you can change
1365	and read at any time: libev will completely ignore it. This can be used
1366	to associate arbitrary data with your watcher. If you need more data and
1367	don't want to allocate memory and store a pointer to it in that data
1368	member, you can also "subclass" the watcher type and provide your own
1369	data:
1370
1371	struct my_io
1372	{
1373	ev_io io;
1374	int otherfd;
1375	void *somedata;
1376	struct whatever *mostinteresting;
1377	};
1378
1379	...
1380	struct my_io w;
1381	ev_io_init (&w.io, my_cb, fd, EV_READ);
1382
1383	And since your callback will be called with a pointer to the watcher, you
1384	can cast it back to your own type:
1385
1386	static void my_cb (struct ev_loop loop, ev_io w_, int revents)
1387	{
1388	struct my_io w = (struct my_io )w_;
1389	...
1390	}
1391
1392	More interesting and less C-conformant ways of casting your callback type
1393	instead have been omitted.
1394
1395	Another common scenario is to use some data structure with multiple
1396	embedded watchers:
1397
1398	struct my_biggy
1399	{
1400	int some_data;
1401	ev_timer t1;
1402	ev_timer t2;
1403	}
1404
1405	In this case getting the pointer to C<my_biggy> is a bit more
1406	complicated: Either you store the address of your C<my_biggy> struct
1407	in the C<data> member of the watcher (for woozies), or you need to use
1408	some pointer arithmetic using C<offsetof> inside your watchers (for real
1409	programmers):
1410
1411	#include <stddef.h>
1412
1413	static void
1414	t1_cb (EV_P_ ev_timer *w, int revents)
1415	{
1416	struct my_biggy big = (struct my_biggy *)
1417	(((char *)w) - offsetof (struct my_biggy, t1));
1418	}
1419
1420	static void
1421	t2_cb (EV_P_ ev_timer *w, int revents)
1422	{
1423	struct my_biggy big = (struct my_biggy *)
1424	(((char *)w) - offsetof (struct my_biggy, t2));
1425	}
1426		1364
1427	=head2 WATCHER STATES	1365	=head2 WATCHER STATES
1428		1366
1429	There are various watcher states mentioned throughout this manual -	1367	There are various watcher states mentioned throughout this manual -
1430	active, pending and so on. In this section these states and the rules to	1368	active, pending and so on. In this section these states and the rules to
…		…
1680	always get a readiness notification instantly, and your read (or possibly	1618	always get a readiness notification instantly, and your read (or possibly
1681	write) will still block on the disk I/O.	1619	write) will still block on the disk I/O.
1682		1620
1683	Another way to view it is that in the case of sockets, pipes, character	1621	Another way to view it is that in the case of sockets, pipes, character
1684	devices and so on, there is another party (the sender) that delivers data	1622	devices and so on, there is another party (the sender) that delivers data
1685	on it's own, but in the case of files, there is no such thing: the disk	1623	on its own, but in the case of files, there is no such thing: the disk
1686	will not send data on it's own, simply because it doesn't know what you	1624	will not send data on its own, simply because it doesn't know what you
1687	wish to read - you would first have to request some data.	1625	wish to read - you would first have to request some data.
1688		1626
1689	Since files are typically not-so-well supported by advanced notification	1627	Since files are typically not-so-well supported by advanced notification
1690	mechanism, libev tries hard to emulate POSIX behaviour with respect	1628	mechanism, libev tries hard to emulate POSIX behaviour with respect
1691	to files, even though you should not use it. The reason for this is	1629	to files, even though you should not use it. The reason for this is
…		…
3456		3394
3457	This section explains some common idioms that are not immediately	3395	This section explains some common idioms that are not immediately
3458	obvious. Note that examples are sprinkled over the whole manual, and this	3396	obvious. Note that examples are sprinkled over the whole manual, and this
3459	section only contains stuff that wouldn't fit anywhere else.	3397	section only contains stuff that wouldn't fit anywhere else.
3460		3398
3461	=over 4	3399	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
3462		3400
3463	=item Model/nested event loop invocations and exit conditions.	3401	Each watcher has, by default, a C<void *data> member that you can read
		3402	or modify at any time: libev will completely ignore it. This can be used
		3403	to associate arbitrary data with your watcher. If you need more data and
		3404	don't want to allocate memory separately and store a pointer to it in that
		3405	data member, you can also "subclass" the watcher type and provide your own
		3406	data:
		3407
		3408	struct my_io
		3409	{
		3410	ev_io io;
		3411	int otherfd;
		3412	void *somedata;
		3413	struct whatever *mostinteresting;
		3414	};
		3415
		3416	...
		3417	struct my_io w;
		3418	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3419
		3420	And since your callback will be called with a pointer to the watcher, you
		3421	can cast it back to your own type:
		3422
		3423	static void my_cb (struct ev_loop loop, ev_io w_, int revents)
		3424	{
		3425	struct my_io w = (struct my_io )w_;
		3426	...
		3427	}
		3428
		3429	More interesting and less C-conformant ways of casting your callback
		3430	function type instead have been omitted.
		3431
		3432	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3433
		3434	Another common scenario is to use some data structure with multiple
		3435	embedded watchers, in effect creating your own watcher that combines
		3436	multiple libev event sources into one "super-watcher":
		3437
		3438	struct my_biggy
		3439	{
		3440	int some_data;
		3441	ev_timer t1;
		3442	ev_timer t2;
		3443	}
		3444
		3445	In this case getting the pointer to C<my_biggy> is a bit more
		3446	complicated: Either you store the address of your C<my_biggy> struct in
		3447	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3448	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3449	real programmers):
		3450
		3451	#include <stddef.h>
		3452
		3453	static void
		3454	t1_cb (EV_P_ ev_timer *w, int revents)
		3455	{
		3456	struct my_biggy big = (struct my_biggy *)
		3457	(((char *)w) - offsetof (struct my_biggy, t1));
		3458	}
		3459
		3460	static void
		3461	t2_cb (EV_P_ ev_timer *w, int revents)
		3462	{
		3463	struct my_biggy big = (struct my_biggy *)
		3464	(((char *)w) - offsetof (struct my_biggy, t2));
		3465	}
		3466
		3467	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
3464		3468
3465	Often (especially in GUI toolkits) there are places where you have	3469	Often (especially in GUI toolkits) there are places where you have
3466	I<modal> interaction, which is most easily implemented by recursively	3470	I<modal> interaction, which is most easily implemented by recursively
3467	invoking C<ev_run>.	3471	invoking C<ev_run>.
3468		3472
…		…
3497	exit_main_loop = 1;	3501	exit_main_loop = 1;
3498		3502
3499	// exit both	3503	// exit both
3500	exit_main_loop = exit_nested_loop = 1;	3504	exit_main_loop = exit_nested_loop = 1;
3501		3505
3502	=item Thread locking example	3506	=head2 THREAD LOCKING EXAMPLE
3503		3507
3504	Here is a fictitious example of how to run an event loop in a different	3508	Here is a fictitious example of how to run an event loop in a different
3505	thread than where callbacks are being invoked and watchers are	3509	thread from where callbacks are being invoked and watchers are
3506	created/added/removed.	3510	created/added/removed.
3507		3511
3508	For a real-world example, see the C<EV::Loop::Async> perl module,	3512	For a real-world example, see the C<EV::Loop::Async> perl module,
3509	which uses exactly this technique (which is suited for many high-level	3513	which uses exactly this technique (which is suited for many high-level
3510	languages).	3514	languages).
…		…
3635	Note that sending the C<ev_async> watcher is required because otherwise	3639	Note that sending the C<ev_async> watcher is required because otherwise
3636	an event loop currently blocking in the kernel will have no knowledge	3640	an event loop currently blocking in the kernel will have no knowledge
3637	about the newly added timer. By waking up the loop it will pick up any new	3641	about the newly added timer. By waking up the loop it will pick up any new
3638	watchers in the next event loop iteration.	3642	watchers in the next event loop iteration.
3639		3643
3640	=back	3644	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3645
		3646	While the overhead of a callback that e.g. schedules a thread is small, it
		3647	is still an overhead. If you embed libev, and your main usage is with some
		3648	kind of threads or coroutines, you might want to customise libev so that
		3649	doesn't need callbacks anymore.
		3650
		3651	Imagine you have coroutines that you can switch to using a function
		3652	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3653	and that due to some magic, the currently active coroutine is stored in a
		3654	global called C<current_coro>. Then you can build your own "wait for libev
		3655	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3656	the differing C<;> conventions):
		3657
		3658	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3659	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3660
		3661	That means instead of having a C callback function, you store the
		3662	coroutine to switch to in each watcher, and instead of having libev call
		3663	your callback, you instead have it switch to that coroutine.
		3664
		3665	A coroutine might now wait for an event with a function called
		3666	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		3667	matter when, or whether the watcher is active or not when this function is
		3668	called):
		3669
		3670	void
		3671	wait_for_event (ev_watcher *w)
		3672	{
		3673	ev_cb_set (w) = current_coro;
		3674	switch_to (libev_coro);
		3675	}
		3676
		3677	That basically suspends the coroutine inside C<wait_for_event> and
		3678	continues the libev coroutine, which, when appropriate, switches back to
		3679	this or any other coroutine. I am sure if you sue this your own :)
		3680
		3681	You can do similar tricks if you have, say, threads with an event queue -
		3682	instead of storing a coroutine, you store the queue object and instead of
		3683	switching to a coroutine, you push the watcher onto the queue and notify
		3684	any waiters.
		3685
		3686	To embed libev, see L<EMBEDDING>, but in short, it's easiest to create two
		3687	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		3688
		3689	// my_ev.h
		3690	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3691	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb);
		3692	#include "../libev/ev.h"
		3693
		3694	// my_ev.c
		3695	#define EV_H "my_ev.h"
		3696	#include "../libev/ev.c"
		3697
		3698	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		3699	F<my_ev.c> into your project. When properly specifying include paths, you
		3700	can even use F<ev.h> as header file name directly.
3641		3701
3642		3702
3643	=head1 LIBEVENT EMULATION	3703	=head1 LIBEVENT EMULATION
3644		3704
3645	Libev offers a compatibility emulation layer for libevent. It cannot	3705	Libev offers a compatibility emulation layer for libevent. It cannot
…		…
4575	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	4635	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
4576		4636
4577	#include "ev_cpp.h"	4637	#include "ev_cpp.h"
4578	#include "ev.c"	4638	#include "ev.c"
4579		4639
4580	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES	4640	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
4581		4641
4582	=head2 THREADS AND COROUTINES	4642	=head2 THREADS AND COROUTINES
4583		4643
4584	=head3 THREADS	4644	=head3 THREADS
4585		4645
…		…
4636	default loop and triggering an C<ev_async> watcher from the default loop	4696	default loop and triggering an C<ev_async> watcher from the default loop
4637	watcher callback into the event loop interested in the signal.	4697	watcher callback into the event loop interested in the signal.
4638		4698
4639	=back	4699	=back
4640		4700
4641	See also L<Thread locking example>.	4701	See also L<THREAD LOCKING EXAMPLE>.
4642		4702
4643	=head3 COROUTINES	4703	=head3 COROUTINES
4644		4704
4645	Libev is very accommodating to coroutines ("cooperative threads"):	4705	Libev is very accommodating to coroutines ("cooperative threads"):
4646	libev fully supports nesting calls to its functions from different	4706	libev fully supports nesting calls to its functions from different

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Comparing libev/ev.pod (file contents): Revision 1.354 by root, Tue Jan 11 01:40:25 2011 UTC vs. Revision 1.359 by root, Tue Jan 11 10:56:01 2011 UTC

Diff Legend

Comparing libev/ev.pod (file contents):
Revision 1.354 by root, Tue Jan 11 01:40:25 2011 UTC vs.
Revision 1.359 by root, Tue Jan 11 10:56:01 2011 UTC