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

Comparing libev/ev.pod (file contents):
Revision 1.356 by root, Tue Jan 11 01:42:47 2011 UTC vs.
Revision 1.360 by root, Mon Jan 17 12:11:12 2011 UTC

…		…
441	when you want to receive them.	441	when you want to receive them.
442		442
443	This behaviour is useful when you want to do your own signal handling, or	443	This behaviour is useful when you want to do your own signal handling, or
444	want to handle signals only in specific threads and want to avoid libev	444	want to handle signals only in specific threads and want to avoid libev
445	unblocking the signals.	445	unblocking the signals.
		446
		447	It's also required by POSIX in a threaded program, as libev calls
		448	C<sigprocmask>, whose behaviour is officially unspecified.
446		449
447	This flag's behaviour will become the default in future versions of libev.	450	This flag's behaviour will become the default in future versions of libev.
448		451
449	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	452	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
450		453
…		…
1357	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related	1360	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
1358	functions that do not need a watcher.	1361	functions that do not need a watcher.
1359		1362
1360	=back	1363	=back
1361		1364
1362	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1365	See also the L<ASSOCIATING CUSTOM DATA WITH A WATCHER> and L<BUILDING YOUR
1363		1366	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		1367
1427	=head2 WATCHER STATES	1368	=head2 WATCHER STATES
1428		1369
1429	There are various watcher states mentioned throughout this manual -	1370	There are various watcher states mentioned throughout this manual -
1430	active, pending and so on. In this section these states and the rules to	1371	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	1621	always get a readiness notification instantly, and your read (or possibly
1681	write) will still block on the disk I/O.	1622	write) will still block on the disk I/O.
1682		1623
1683	Another way to view it is that in the case of sockets, pipes, character	1624	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	1625	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	1626	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	1627	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.	1628	wish to read - you would first have to request some data.
1688		1629
1689	Since files are typically not-so-well supported by advanced notification	1630	Since files are typically not-so-well supported by advanced notification
1690	mechanism, libev tries hard to emulate POSIX behaviour with respect	1631	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	1632	to files, even though you should not use it. The reason for this is
…		…
2362	=head3 The special problem of inheritance over fork/execve/pthread_create	2303	=head3 The special problem of inheritance over fork/execve/pthread_create
2363		2304
2364	Both the signal mask (C<sigprocmask>) and the signal disposition	2305	Both the signal mask (C<sigprocmask>) and the signal disposition
2365	(C<sigaction>) are unspecified after starting a signal watcher (and after	2306	(C<sigaction>) are unspecified after starting a signal watcher (and after
2366	stopping it again), that is, libev might or might not block the signal,	2307	stopping it again), that is, libev might or might not block the signal,
2367	and might or might not set or restore the installed signal handler.	2308	and might or might not set or restore the installed signal handler (but
		2309	see C<EVFLAG_NOSIGMASK>).
2368		2310
2369	While this does not matter for the signal disposition (libev never	2311	While this does not matter for the signal disposition (libev never
2370	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on	2312	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
2371	C<execve>), this matters for the signal mask: many programs do not expect	2313	C<execve>), this matters for the signal mask: many programs do not expect
2372	certain signals to be blocked.	2314	certain signals to be blocked.
…		…
3456		3398
3457	This section explains some common idioms that are not immediately	3399	This section explains some common idioms that are not immediately
3458	obvious. Note that examples are sprinkled over the whole manual, and this	3400	obvious. Note that examples are sprinkled over the whole manual, and this
3459	section only contains stuff that wouldn't fit anywhere else.	3401	section only contains stuff that wouldn't fit anywhere else.
3460		3402
		3403	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
		3404
		3405	Each watcher has, by default, a C<void *data> member that you can read
		3406	or modify at any time: libev will completely ignore it. This can be used
		3407	to associate arbitrary data with your watcher. If you need more data and
		3408	don't want to allocate memory separately and store a pointer to it in that
		3409	data member, you can also "subclass" the watcher type and provide your own
		3410	data:
		3411
		3412	struct my_io
		3413	{
		3414	ev_io io;
		3415	int otherfd;
		3416	void *somedata;
		3417	struct whatever *mostinteresting;
		3418	};
		3419
		3420	...
		3421	struct my_io w;
		3422	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3423
		3424	And since your callback will be called with a pointer to the watcher, you
		3425	can cast it back to your own type:
		3426
		3427	static void my_cb (struct ev_loop loop, ev_io w_, int revents)
		3428	{
		3429	struct my_io w = (struct my_io )w_;
		3430	...
		3431	}
		3432
		3433	More interesting and less C-conformant ways of casting your callback
		3434	function type instead have been omitted.
		3435
		3436	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3437
		3438	Another common scenario is to use some data structure with multiple
		3439	embedded watchers, in effect creating your own watcher that combines
		3440	multiple libev event sources into one "super-watcher":
		3441
		3442	struct my_biggy
		3443	{
		3444	int some_data;
		3445	ev_timer t1;
		3446	ev_timer t2;
		3447	}
		3448
		3449	In this case getting the pointer to C<my_biggy> is a bit more
		3450	complicated: Either you store the address of your C<my_biggy> struct in
		3451	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3452	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3453	real programmers):
		3454
		3455	#include <stddef.h>
		3456
		3457	static void
		3458	t1_cb (EV_P_ ev_timer *w, int revents)
		3459	{
		3460	struct my_biggy big = (struct my_biggy *)
		3461	(((char *)w) - offsetof (struct my_biggy, t1));
		3462	}
		3463
		3464	static void
		3465	t2_cb (EV_P_ ev_timer *w, int revents)
		3466	{
		3467	struct my_biggy big = (struct my_biggy *)
		3468	(((char *)w) - offsetof (struct my_biggy, t2));
		3469	}
		3470
3461	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS	3471	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
3462		3472
3463	Often (especially in GUI toolkits) there are places where you have	3473	Often (especially in GUI toolkits) there are places where you have
3464	I<modal> interaction, which is most easily implemented by recursively	3474	I<modal> interaction, which is most easily implemented by recursively
3465	invoking C<ev_run>.	3475	invoking C<ev_run>.
…		…
3498	exit_main_loop = exit_nested_loop = 1;	3508	exit_main_loop = exit_nested_loop = 1;
3499		3509
3500	=head2 THREAD LOCKING EXAMPLE	3510	=head2 THREAD LOCKING EXAMPLE
3501		3511
3502	Here is a fictitious example of how to run an event loop in a different	3512	Here is a fictitious example of how to run an event loop in a different
3503	thread than where callbacks are being invoked and watchers are	3513	thread from where callbacks are being invoked and watchers are
3504	created/added/removed.	3514	created/added/removed.
3505		3515
3506	For a real-world example, see the C<EV::Loop::Async> perl module,	3516	For a real-world example, see the C<EV::Loop::Async> perl module,
3507	which uses exactly this technique (which is suited for many high-level	3517	which uses exactly this technique (which is suited for many high-level
3508	languages).	3518	languages).
…		…
3632		3642
3633	Note that sending the C<ev_async> watcher is required because otherwise	3643	Note that sending the C<ev_async> watcher is required because otherwise
3634	an event loop currently blocking in the kernel will have no knowledge	3644	an event loop currently blocking in the kernel will have no knowledge
3635	about the newly added timer. By waking up the loop it will pick up any new	3645	about the newly added timer. By waking up the loop it will pick up any new
3636	watchers in the next event loop iteration.	3646	watchers in the next event loop iteration.
		3647
		3648	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3649
		3650	While the overhead of a callback that e.g. schedules a thread is small, it
		3651	is still an overhead. If you embed libev, and your main usage is with some
		3652	kind of threads or coroutines, you might want to customise libev so that
		3653	doesn't need callbacks anymore.
		3654
		3655	Imagine you have coroutines that you can switch to using a function
		3656	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3657	and that due to some magic, the currently active coroutine is stored in a
		3658	global called C<current_coro>. Then you can build your own "wait for libev
		3659	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3660	the differing C<;> conventions):
		3661
		3662	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3663	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3664
		3665	That means instead of having a C callback function, you store the
		3666	coroutine to switch to in each watcher, and instead of having libev call
		3667	your callback, you instead have it switch to that coroutine.
		3668
		3669	A coroutine might now wait for an event with a function called
		3670	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		3671	matter when, or whether the watcher is active or not when this function is
		3672	called):
		3673
		3674	void
		3675	wait_for_event (ev_watcher *w)
		3676	{
		3677	ev_cb_set (w) = current_coro;
		3678	switch_to (libev_coro);
		3679	}
		3680
		3681	That basically suspends the coroutine inside C<wait_for_event> and
		3682	continues the libev coroutine, which, when appropriate, switches back to
		3683	this or any other coroutine. I am sure if you sue this your own :)
		3684
		3685	You can do similar tricks if you have, say, threads with an event queue -
		3686	instead of storing a coroutine, you store the queue object and instead of
		3687	switching to a coroutine, you push the watcher onto the queue and notify
		3688	any waiters.
		3689
		3690	To embed libev, see L<EMBEDDING>, but in short, it's easiest to create two
		3691	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		3692
		3693	// my_ev.h
		3694	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3695	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb);
		3696	#include "../libev/ev.h"
		3697
		3698	// my_ev.c
		3699	#define EV_H "my_ev.h"
		3700	#include "../libev/ev.c"
		3701
		3702	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		3703	F<my_ev.c> into your project. When properly specifying include paths, you
		3704	can even use F<ev.h> as header file name directly.
3637		3705
3638		3706
3639	=head1 LIBEVENT EMULATION	3707	=head1 LIBEVENT EMULATION
3640		3708
3641	Libev offers a compatibility emulation layer for libevent. It cannot	3709	Libev offers a compatibility emulation layer for libevent. It cannot

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Comparing libev/ev.pod (file contents): Revision 1.356 by root, Tue Jan 11 01:42:47 2011 UTC vs. Revision 1.360 by root, Mon Jan 17 12:11:12 2011 UTC

Diff Legend

Comparing libev/ev.pod (file contents):
Revision 1.356 by root, Tue Jan 11 01:42:47 2011 UTC vs.
Revision 1.360 by root, Mon Jan 17 12:11:12 2011 UTC