[ViewVC] Diff of: cvs/libeio/eio.pod

Comparing libeio/eio.pod (file contents):
Revision 1.11 by root, Mon Jun 20 07:28:15 2011 UTC vs.
Revision 1.17 by root, Tue Jul 5 18:59:28 2011 UTC

…		…
45	Unlike the name component C<stamp> might indicate, it is also used for	45	Unlike the name component C<stamp> might indicate, it is also used for
46	time differences throughout libeio.	46	time differences throughout libeio.
47		47
48	=head2 FORK SUPPORT	48	=head2 FORK SUPPORT
49		49
50	Calling C<fork ()> is fully supported by this module. It is implemented in these steps:	50	Calling C<fork ()> is fully supported by this module - but you must not
		51	rely on this. It is currently implemented in these steps:
51		52
52	1. wait till all requests in "execute" state have been handled	53	1. wait till all requests in "execute" state have been handled
53	(basically requests that are already handed over to the kernel).	54	(basically requests that are already handed over to the kernel).
54	2. fork	55	2. fork
55	3. in the parent, continue business as usual, done	56	3. in the parent, continue business as usual, done
56	4. in the child, destroy all ready and pending requests and free the	57	4. in the child, destroy all ready and pending requests and free the
57	memory used by the worker threads. This gives you a fully empty	58	memory used by the worker threads. This gives you a fully empty
58	libeio queue.	59	libeio queue.
59		60
60	Note, however, since libeio does use threads, thr above guarantee doesn't	61	Note, however, since libeio does use threads, the above guarantee doesn't
61	cover your libc, for example, malloc and other libc functions are not	62	cover your libc, for example, malloc and other libc functions are not
62	fork-safe, so there is very little you can do after a fork, and in fatc,	63	fork-safe, so there is very little you can do after a fork, and in fact,
63	the above might crash, and thus change.	64	the above might crash, and thus change.
64		65
65	=head1 INITIALISATION/INTEGRATION	66	=head1 INITIALISATION/INTEGRATION
66		67
67	Before you can call any eio functions you first have to initialise the	68	Before you can call any eio functions you first have to initialise the
…		…
124	=back	125	=back
125		126
126	For libev, you would typically use an C<ev_async> watcher: the	127	For libev, you would typically use an C<ev_async> watcher: the
127	C<want_poll> callback would invoke C<ev_async_send> to wake up the event	128	C<want_poll> callback would invoke C<ev_async_send> to wake up the event
128	loop. Inside the callback set for the watcher, one would call C<eio_poll	129	loop. Inside the callback set for the watcher, one would call C<eio_poll
129	()> (followed by C<ev_async_send> again if C<eio_poll> indicates that not	130	()>.
130	all requests have been handled yet). The race is taken care of because	131
131	libev resets/rearms the async watcher before calling your callback,	132	If C<eio_poll ()> is configured to not handle all results in one go
132	and therefore, before calling C<eio_poll>. This might result in (some)	133	(i.e. it returns C<-1>) then you should start an idle watcher that calls
133	spurious wake-ups, but is generally harmless.	134	C<eio_poll> until it returns something C<!= -1>.
		135
		136	A full-featured conenctor between libeio and libev would look as follows
		137	(if C<eio_poll> is handling all requests, it can of course be simplified a
		138	lot by removing the idle watcher logic):
		139
		140	static struct ev_loop *loop;
		141	static ev_idle repeat_watcher;
		142	static ev_async ready_watcher;
		143
		144	/* idle watcher callback, only used when eio_poll */
		145	/* didn't handle all results in one call */
		146	static void
		147	repeat (EV_P_ ev_idle *w, int revents)
		148	{
		149	if (eio_poll () != -1)
		150	ev_idle_stop (EV_A_ w);
		151	}
		152
		153	/* eio has some results, process them */
		154	static void
		155	ready (EV_P_ ev_async *w, int revents)
		156	{
		157	if (eio_poll () == -1)
		158	ev_idle_start (EV_A_ &repeat_watcher);
		159	}
		160
		161	/* wake up the event loop */
		162	static void
		163	want_poll (void)
		164	{
		165	ev_async_send (loop, &ready_watcher)
		166	}
		167
		168	void
		169	my_init_eio ()
		170	{
		171	loop = EV_DEFAULT;
		172
		173	ev_idle_init (&repeat_watcher, repeat);
		174	ev_async_init (&ready_watcher, ready);
		175	ev_async_start (loop &watcher);
		176
		177	eio_init (want_poll, 0);
		178	}
134		179
135	For most other event loops, you would typically use a pipe - the event	180	For most other event loops, you would typically use a pipe - the event
136	loop should be told to wait for read readiness on the read end. In	181	loop should be told to wait for read readiness on the read end. In
137	C<want_poll> you would write a single byte, in C<done_poll> you would try	182	C<want_poll> you would write a single byte, in C<done_poll> you would try
138	to read that byte, and in the callback for the read end, you would call	183	to read that byte, and in the callback for the read end, you would call
139	C<eio_poll>. The race is avoided here because the event loop should invoke	184	C<eio_poll>.
140	your callback again and again until the byte has been read (as the pipe	185
141	read callback does not read it, only C<done_poll>).	186	You don't have to take special care in the case C<eio_poll> doesn't handle
		187	all requests, as the done callback will not be invoked, so the event loop
		188	will still signal readyness for the pipe until I<all> results have been
		189	processed.
142		190
143		191
144	=head1 HIGH LEVEL REQUEST API	192	=head1 HIGH LEVEL REQUEST API
145		193
146	Libeio has both a high-level API, which consists of calling a request	194	Libeio has both a high-level API, which consists of calling a request
…		…
153		201
154	You submit a request by calling the relevant C<eio_TYPE> function with the	202	You submit a request by calling the relevant C<eio_TYPE> function with the
155	required parameters, a callback of type C<int (eio_cb)(eio_req req)>	203	required parameters, a callback of type C<int (eio_cb)(eio_req req)>
156	(called C<eio_cb> below) and a freely usable C<void *data> argument.	204	(called C<eio_cb> below) and a freely usable C<void *data> argument.
157		205
158	The return value will either be 0	206	The return value will either be 0, in case something went really wrong
		207	(which can basically only happen on very fatal errors, such as C<malloc>
		208	returning 0, which is rather unlikely), or a pointer to the newly-created
		209	and submitted C<eio_req *>.
159		210
160	The callback will be called with an C<eio_req *> which contains the	211	The callback will be called with an C<eio_req *> which contains the
161	results of the request. The members you can access inside that structure	212	results of the request. The members you can access inside that structure
162	vary from request to request, except for:	213	vary from request to request, except for:
163		214
…		…
215	abort (); /* something ent wrong, we will all die!!! */	266	abort (); /* something ent wrong, we will all die!!! */
216		267
217	Note that you additionally need to call C<eio_poll> when the C<want_cb>	268	Note that you additionally need to call C<eio_poll> when the C<want_cb>
218	indicates that requests are ready to be processed.	269	indicates that requests are ready to be processed.
219		270
		271	=head2 CANCELLING REQUESTS
		272
		273	Sometimes the need for a request goes away before the request is
		274	finished. In that case, one can cancel the reqiest by a call to
		275	C<eio_cancel>:
		276
		277	=over 4
		278
		279	=item eio_cancel (eio_req *req)
		280
		281	Cancel the request. If the request is currently executing it might still
		282	continue to execute, and in other cases it might still take a while till
		283	the request is cancelled.
		284
		285	Even if cancelled, the finish callback will still be invoked - the
		286	callbacks of all cancellable requests need to check whether the request
		287	has been cancelled by calling C<EIO_CANCELLED (req)>:
		288
		289	static int
		290	my_eio_cb (eio_req *req)
		291	{
		292	if (EIO_CANCELLED (req))
		293	return 0;
		294	}
		295
		296	In addition, cancelled requests will either have C<< req->result >> set to
		297	C<-1> and C<errno> to C<ECANCELED>, or otherwise they were successfully
		298	executed despite being cancelled (e.g. when they have already been
		299	executed at the time they were cancelled).
		300
		301	=back
		302
220	=head2 AVAILABLE REQUESTS	303	=head2 AVAILABLE REQUESTS
221		304
222	The following request functions are available. I<All> of them return the	305	The following request functions are available. I<All> of them return the
223	C<eio_req *> on success and C<0> on failure, and I<all> of them have the	306	C<eio_req *> on success and C<0> on failure, and I<all> of them have the
224	same three trailing arguments: C<pri>, C<cb> and C<data>. The C<cb> is	307	same three trailing arguments: C<pri>, C<cb> and C<data>. The C<cb> is
…		…
317	char target = strndup ((char )req->ptr2, req->result);	400	char target = strndup ((char )req->ptr2, req->result);
318		401
319	free (target);	402	free (target);
320	}	403	}
321		404
		405	=item eio_realpath (const char path, int pri, eio_cb cb, void data)
		406
		407	Similar to the realpath libc function, but unlike that one, result is
		408	C<-1> on failure and the length of the returned path in C<ptr2> (which is
		409	not 0-terminated) - this is similar to readlink.
		410
322	=item eio_stat (const char path, int pri, eio_cb cb, void data)	411	=item eio_stat (const char path, int pri, eio_cb cb, void data)
323		412
324	=item eio_lstat (const char path, int pri, eio_cb cb, void data)	413	=item eio_lstat (const char path, int pri, eio_cb cb, void data)
325		414
326	=item eio_fstat (int fd, int pri, eio_cb cb, void *data)	415	=item eio_fstat (int fd, int pri, eio_cb cb, void *data)
327		416
328	Stats a file - if C<< req->result >> indicates success, then you can	417	Stats a file - if C<< req->result >> indicates success, then you can
329	access the C<struct stat>-like structure via C<< req->ptr2 >>:	418	access the C<struct stat>-like structure via C<< req->ptr2 >>:
330		419
331	EIO_STRUCT_STAT statdata = (EIO_STRUCT_STAT )req->ptr2;	420	EIO_STRUCT_STAT statdata = (EIO_STRUCT_STAT )req->ptr2;
332		421
333	=item eio_statvfs (const char path, int pri, eio_cb cb, void data)	422	=item eio_statvfs (const char path, int pri, eio_cb cb, void data)
334		423
335	=item eio_fstatvfs (int fd, int pri, eio_cb cb, void *data)	424	=item eio_fstatvfs (int fd, int pri, eio_cb cb, void *data)
336		425
337	Stats a filesystem - if C<< req->result >> indicates success, then you can	426	Stats a filesystem - if C<< req->result >> indicates success, then you can
338	access the C<struct statvfs>-like structure via C<< req->ptr2 >>:	427	access the C<struct statvfs>-like structure via C<< req->ptr2 >>:
339		428
340	EIO_STRUCT_STATVFS statdata = (EIO_STRUCT_STATVFS )req->ptr2;	429	EIO_STRUCT_STATVFS statdata = (EIO_STRUCT_STATVFS )req->ptr2;
341		430
342	=back	431	=back
343		432
344	=head3 READING DIRECTORIES	433	=head3 READING DIRECTORIES
345		434
…		…
385		474
386	If this flag is specified, then, in addition to the names in C<ptr2>,	475	If this flag is specified, then, in addition to the names in C<ptr2>,
387	also an array of C<struct eio_dirent> is returned, in C<ptr1>. A C<struct	476	also an array of C<struct eio_dirent> is returned, in C<ptr1>. A C<struct
388	eio_dirent> looks like this:	477	eio_dirent> looks like this:
389		478
390	struct eio_dirent	479	struct eio_dirent
391	{	480	{
392	int nameofs; /* offset of null-terminated name string in (char )req->ptr2 /	481	int nameofs; /* offset of null-terminated name string in (char )req->ptr2 /
393	unsigned short namelen; /* size of filename without trailing 0 */	482	unsigned short namelen; /* size of filename without trailing 0 */
394	unsigned char type; /* one of EIO_DT_* */	483	unsigned char type; /* one of EIO_DT_* */
395	signed char score; /* internal use */	484	signed char score; /* internal use */
396	ino_t inode; /* the inode number, if available, otherwise unspecified */	485	ino_t inode; /* the inode number, if available, otherwise unspecified */
397	};	486	};
398		487
399	The only members you normally would access are C<nameofs>, which is the	488	The only members you normally would access are C<nameofs>, which is the
400	byte-offset from C<ptr2> to the start of the name, C<namelen> and C<type>.	489	byte-offset from C<ptr2> to the start of the name, C<namelen> and C<type>.
401		490
402	C<type> can be one of:	491	C<type> can be one of:
…		…
568		657
569	=back	658	=back
570		659
571	=head3 GROUPING AND LIMITING REQUESTS	660	=head3 GROUPING AND LIMITING REQUESTS
572		661
		662	There is one more rather special request, C<eio_grp>. It is a very special
		663	aio request: Instead of doing something, it is a container for other eio
		664	requests.
		665
		666	There are two primary use cases for this: a) bundle many requests into a
		667	single, composite, request with a definite callback and the ability to
		668	cancel the whole request with its subrequests and b) limiting the number
		669	of "active" requests.
		670
		671	Further below you will find more dicussion of these topics - first follows
		672	the reference section detailing the request generator and other methods.
		673
		674	=over 4
		675
		676	=item eio_req grp = eio_grp (eio_cb cb, void data)
		677
		678	Creates, submits and returns a group request.
		679
		680	=item eio_grp_add (eio_req grp, eio_req req)
		681
		682	Adds a request to the request group.
		683
		684	=item eio_grp_cancel (eio_req *grp)
		685
		686	Cancels all requests I<in> the group, but I<not> the group request
		687	itself. You can cancel the group request via a normal C<eio_cancel> call.
		688
		689
		690
		691	=back
		692
		693
		694
573	#TODO	695	#TODO
574		696
575	/*****************************************************************************/	697	/*****************************************************************************/
576	/* groups */	698	/* groups */
577		699
578	eio_req eio_grp (eio_cb cb, void data);	700	eio_req eio_grp (eio_cb cb, void data);
579	void eio_grp_feed (eio_req grp, void (feed)(eio_req *req), int limit);	701	void eio_grp_feed (eio_req grp, void (feed)(eio_req *req), int limit);
580	void eio_grp_limit (eio_req *grp, int limit);	702	void eio_grp_limit (eio_req *grp, int limit);
581	void eio_grp_add (eio_req grp, eio_req req);
582	void eio_grp_cancel (eio_req grp); / cancels all sub requests but not the group */	703	void eio_grp_cancel (eio_req grp); / cancels all sub requests but not the group */
583		704
584		705
585	=back	706	=back
586		707
…		…
593	=head1 ANATOMY AND LIFETIME OF AN EIO REQUEST	714	=head1 ANATOMY AND LIFETIME OF AN EIO REQUEST
594		715
595	A request is represented by a structure of type C<eio_req>. To initialise	716	A request is represented by a structure of type C<eio_req>. To initialise
596	it, clear it to all zero bytes:	717	it, clear it to all zero bytes:
597		718
598	eio_req req;	719	eio_req req;
599		720
600	memset (&req, 0, sizeof (req));	721	memset (&req, 0, sizeof (req));
601		722
602	A more common way to initialise a new C<eio_req> is to use C<calloc>:	723	A more common way to initialise a new C<eio_req> is to use C<calloc>:
603		724
604	eio_req req = calloc (1, sizeof (req));	725	eio_req req = calloc (1, sizeof (req));
605		726
606	In either case, libeio neither allocates, initialises or frees the	727	In either case, libeio neither allocates, initialises or frees the
607	C<eio_req> structure for you - it merely uses it.	728	C<eio_req> structure for you - it merely uses it.
608		729
609	zero	730	zero

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Comparing libeio/eio.pod (file contents): Revision 1.11 by root, Mon Jun 20 07:28:15 2011 UTC vs. Revision 1.17 by root, Tue Jul 5 18:59:28 2011 UTC

Diff Legend

Comparing libeio/eio.pod (file contents):
Revision 1.11 by root, Mon Jun 20 07:28:15 2011 UTC vs.
Revision 1.17 by root, Tue Jul 5 18:59:28 2011 UTC