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

Comparing libeio/eio.pod (file contents):
Revision 1.15 by root, Tue Jul 5 16:57:41 2011 UTC vs.
Revision 1.20 by sf-exg, Thu Jul 7 17:35:52 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
…		…
130		131
131	If C<eio_poll ()> is configured to not handle all results in one go	132	If C<eio_poll ()> is configured to not handle all results in one go
132	(i.e. it returns C<-1>) then you should start an idle watcher that calls	133	(i.e. it returns C<-1>) then you should start an idle watcher that calls
133	C<eio_poll> until it returns something C<!= -1>.	134	C<eio_poll> until it returns something C<!= -1>.
134		135
135	A full-featured wrapper would look as follows (if C<eio_poll> is handling	136	A full-featured connector between libeio and libev would look as follows
136	all requests, it can of course be simplified a lot by removing the idle	137	(if C<eio_poll> is handling all requests, it can of course be simplified a
137	watcher logic):	138	lot by removing the idle watcher logic):
138		139
139	static struct ev_loop *loop;	140	static struct ev_loop *loop;
140	static ev_idle repeat_watcher;	141	static ev_idle repeat_watcher;
141	static ev_async ready_watcher;	142	static ev_async ready_watcher;
142		143
143	/* idle watcher callback, only used when eio_poll */	144	/* idle watcher callback, only used when eio_poll */
144	/* didn't handle all results in one call */	145	/* didn't handle all results in one call */
145	static void	146	static void
146	repeat (EV_P_ ev_idle *w, int revents)	147	repeat (EV_P_ ev_idle *w, int revents)
147	{	148	{
148	if (eio_poll () != -1)	149	if (eio_poll () != -1)
149	ev_idle_stop (EV_A_ w);	150	ev_idle_stop (EV_A_ w);
150	}	151	}
151		152
152	/* eio has some results, process them */	153	/* eio has some results, process them */
153	static void	154	static void
154	ready (EV_P_ ev_async *w, int revents)	155	ready (EV_P_ ev_async *w, int revents)
155	{	156	{
156	if (eio_poll () == -1)	157	if (eio_poll () == -1)
157	ev_idle_start (EV_A_ &repeat_watcher);	158	ev_idle_start (EV_A_ &repeat_watcher);
158	}	159	}
159		160
160	/* wake up the event loop */	161	/* wake up the event loop */
161	static void	162	static void
162	want_poll (void)	163	want_poll (void)
163	{	164	{
164	ev_async_send (loop, &ready_watcher)	165	ev_async_send (loop, &ready_watcher)
165	}	166	}
166		167
167	void	168	void
168	my_init_eio ()	169	my_init_eio ()
169	{	170	{
170	loop = EV_DEFAULT;	171	loop = EV_DEFAULT;
171		172
172	ev_idle_init (&repeat_watcher, repeat);	173	ev_idle_init (&repeat_watcher, repeat);
173	ev_async_init (&ready_watcher, ready);	174	ev_async_init (&ready_watcher, ready);
174	ev_async_start (loop &watcher);	175	ev_async_start (loop &watcher);
175		176
176	eio_init (want_poll, 0);	177	eio_init (want_poll, 0);
177	}	178	}
178		179
179	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
180	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
181	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
182	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
183	C<eio_poll>. The race is avoided here because the event loop should invoke	184	C<eio_poll>.
184	your callback again and again until the byte has been read (as the pipe	185
185	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 readiness for the pipe until I<all> results have been
		189	processed.
186		190
187		191
188	=head1 HIGH LEVEL REQUEST API	192	=head1 HIGH LEVEL REQUEST API
189		193
190	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
…		…
257	}	261	}
258		262
259	/* the first three arguments are passed to open(2) */	263	/* the first three arguments are passed to open(2) */
260	/* the remaining are priority, callback and data */	264	/* the remaining are priority, callback and data */
261	if (!eio_open ("/etc/passwd", O_RDONLY, 0, 0, file_open_done, 0))	265	if (!eio_open ("/etc/passwd", O_RDONLY, 0, 0, file_open_done, 0))
262	abort (); /* something ent wrong, we will all die!!! */	266	abort (); /* something went wrong, we will all die!!! */
263		267
264	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>
265	indicates that requests are ready to be processed.	269	indicates that requests are ready to be processed.
		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 request 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 (and all its subrequests). If the request is currently
		282	executing it might still continue to execute, and in other cases it might
		283	still take a while till 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 I<either> have C<< req->result >>
		297	set to C<-1> and C<errno> to C<ECANCELED>, or I<otherwise> they were
		298	successfully executed, despite being cancelled (e.g. when they have
		299	already been executed at the time they were cancelled).
		300
		301	C<EIO_CANCELLED> is still true for requests that have successfully
		302	executed, as long as C<eio_cancel> was called on them at some point.
		303
		304	=back
266		305
267	=head2 AVAILABLE REQUESTS	306	=head2 AVAILABLE REQUESTS
268		307
269	The following request functions are available. I<All> of them return the	308	The following request functions are available. I<All> of them return the
270	C<eio_req *> on success and C<0> on failure, and I<all> of them have the	309	C<eio_req *> on success and C<0> on failure, and I<all> of them have the
…		…
379	=item eio_fstat (int fd, int pri, eio_cb cb, void *data)	418	=item eio_fstat (int fd, int pri, eio_cb cb, void *data)
380		419
381	Stats a file - if C<< req->result >> indicates success, then you can	420	Stats a file - if C<< req->result >> indicates success, then you can
382	access the C<struct stat>-like structure via C<< req->ptr2 >>:	421	access the C<struct stat>-like structure via C<< req->ptr2 >>:
383		422
384	EIO_STRUCT_STAT statdata = (EIO_STRUCT_STAT )req->ptr2;	423	EIO_STRUCT_STAT statdata = (EIO_STRUCT_STAT )req->ptr2;
385		424
386	=item eio_statvfs (const char path, int pri, eio_cb cb, void data)	425	=item eio_statvfs (const char path, int pri, eio_cb cb, void data)
387		426
388	=item eio_fstatvfs (int fd, int pri, eio_cb cb, void *data)	427	=item eio_fstatvfs (int fd, int pri, eio_cb cb, void *data)
389		428
390	Stats a filesystem - if C<< req->result >> indicates success, then you can	429	Stats a filesystem - if C<< req->result >> indicates success, then you can
391	access the C<struct statvfs>-like structure via C<< req->ptr2 >>:	430	access the C<struct statvfs>-like structure via C<< req->ptr2 >>:
392		431
393	EIO_STRUCT_STATVFS statdata = (EIO_STRUCT_STATVFS )req->ptr2;	432	EIO_STRUCT_STATVFS statdata = (EIO_STRUCT_STATVFS )req->ptr2;
394		433
395	=back	434	=back
396		435
397	=head3 READING DIRECTORIES	436	=head3 READING DIRECTORIES
398		437
399	Reading directories sounds simple, but can be rather demanding, especially	438	Reading directories sounds simple, but can be rather demanding, especially
400	if you want to do stuff such as traversing a diretcory hierarchy or	439	if you want to do stuff such as traversing a directory hierarchy or
401	processing all files in a directory. Libeio can assist thess complex tasks	440	processing all files in a directory. Libeio can assist these complex tasks
402	with it's C<eio_readdir> call.	441	with it's C<eio_readdir> call.
403		442
404	=over 4	443	=over 4
405		444
406	=item eio_readdir (const char path, int flags, int pri, eio_cb cb, void data)	445	=item eio_readdir (const char path, int flags, int pri, eio_cb cb, void data)
…		…
438		477
439	If this flag is specified, then, in addition to the names in C<ptr2>,	478	If this flag is specified, then, in addition to the names in C<ptr2>,
440	also an array of C<struct eio_dirent> is returned, in C<ptr1>. A C<struct	479	also an array of C<struct eio_dirent> is returned, in C<ptr1>. A C<struct
441	eio_dirent> looks like this:	480	eio_dirent> looks like this:
442		481
443	struct eio_dirent	482	struct eio_dirent
444	{	483	{
445	int nameofs; /* offset of null-terminated name string in (char )req->ptr2 /	484	int nameofs; /* offset of null-terminated name string in (char )req->ptr2 /
446	unsigned short namelen; /* size of filename without trailing 0 */	485	unsigned short namelen; /* size of filename without trailing 0 */
447	unsigned char type; /* one of EIO_DT_* */	486	unsigned char type; /* one of EIO_DT_* */
448	signed char score; /* internal use */	487	signed char score; /* internal use */
449	ino_t inode; /* the inode number, if available, otherwise unspecified */	488	ino_t inode; /* the inode number, if available, otherwise unspecified */
450	};	489	};
451		490
452	The only members you normally would access are C<nameofs>, which is the	491	The only members you normally would access are C<nameofs>, which is the
453	byte-offset from C<ptr2> to the start of the name, C<namelen> and C<type>.	492	byte-offset from C<ptr2> to the start of the name, C<namelen> and C<type>.
454		493
455	C<type> can be one of:	494	C<type> can be one of:
…		…
498	When this flag is specified, then the names will be returned in an order	537	When this flag is specified, then the names will be returned in an order
499	suitable for stat()'ing each one. That is, when you plan to stat()	538	suitable for stat()'ing each one. That is, when you plan to stat()
500	all files in the given directory, then the returned order will likely	539	all files in the given directory, then the returned order will likely
501	be fastest.	540	be fastest.
502		541
503	If both this flag and C<EIO_READDIR_DIRS_FIRST> are specified, then	542	If both this flag and C<EIO_READDIR_DIRS_FIRST> are specified, then the
504	the likely dirs come first, resulting in a less optimal stat order.	543	likely directories come first, resulting in a less optimal stat order.
505		544
506	=item EIO_READDIR_FOUND_UNKNOWN	545	=item EIO_READDIR_FOUND_UNKNOWN
507		546
508	This flag should not be specified when calling C<eio_readdir>. Instead,	547	This flag should not be specified when calling C<eio_readdir>. Instead,
509	it is being set by C<eio_readdir> (you can access the C<flags> via C<<	548	it is being set by C<eio_readdir> (you can access the C<flags> via C<<
510	req->int1 >>, when any of the C<type>'s found were C<EIO_DT_UNKNOWN>. The	549	req->int1 >>, when any of the C<type>'s found were C<EIO_DT_UNKNOWN>. The
511	absense of this flag therefore indicates that all C<type>'s are known,	550	absence of this flag therefore indicates that all C<type>'s are known,
512	which can be used to speed up some algorithms.	551	which can be used to speed up some algorithms.
513		552
514	A typical use case would be to identify all subdirectories within a	553	A typical use case would be to identify all subdirectories within a
515	directory - you would ask C<eio_readdir> for C<EIO_READDIR_DIRS_FIRST>. If	554	directory - you would ask C<eio_readdir> for C<EIO_READDIR_DIRS_FIRST>. If
516	then this flag is I<NOT> set, then all the entries at the beginning of the	555	then this flag is I<NOT> set, then all the entries at the beginning of the
…		…
604		643
605	eio_custom (my_open, 0, my_open_done, "/etc/passwd");	644	eio_custom (my_open, 0, my_open_done, "/etc/passwd");
606		645
607	=item eio_busy (eio_tstamp delay, int pri, eio_cb cb, void *data)	646	=item eio_busy (eio_tstamp delay, int pri, eio_cb cb, void *data)
608		647
609	This is a a request that takes C<delay> seconds to execute, but otherwise	648	This is a request that takes C<delay> seconds to execute, but otherwise
610	does nothing - it simply puts one of the worker threads to sleep for this	649	does nothing - it simply puts one of the worker threads to sleep for this
611	long.	650	long.
612		651
613	This request can be used to artificially increase load, e.g. for debugging	652	This request can be used to artificially increase load, e.g. for debugging
614	or benchmarking reasons.	653	or benchmarking reasons.
…		…
630	There are two primary use cases for this: a) bundle many requests into a	669	There are two primary use cases for this: a) bundle many requests into a
631	single, composite, request with a definite callback and the ability to	670	single, composite, request with a definite callback and the ability to
632	cancel the whole request with its subrequests and b) limiting the number	671	cancel the whole request with its subrequests and b) limiting the number
633	of "active" requests.	672	of "active" requests.
634		673
635	Further below you will find more dicussion of these topics - first follows	674	Further below you will find more discussion of these topics - first
636	the reference section detailing the request generator and other methods.	675	follows the reference section detailing the request generator and other
		676	methods.
637		677
638	=over 4	678	=over 4
639		679
640	=item eio_grp (eio_cb cb, void *data)	680	=item eio_req grp = eio_grp (eio_cb cb, void data)
641		681
642	Creates and submits a group request.	682	Creates, submits and returns a group request.
		683
		684	=item eio_grp_add (eio_req grp, eio_req req)
		685
		686	Adds a request to the request group.
		687
		688	=item eio_grp_cancel (eio_req *grp)
		689
		690	Cancels all requests I<in> the group, but I<not> the group request
		691	itself. You can cancel the group request via a normal C<eio_cancel> call.
		692
		693
643		694
644	=back	695	=back
645		696
646		697
647		698
…		…
651	/* groups */	702	/* groups */
652		703
653	eio_req eio_grp (eio_cb cb, void data);	704	eio_req eio_grp (eio_cb cb, void data);
654	void eio_grp_feed (eio_req grp, void (feed)(eio_req *req), int limit);	705	void eio_grp_feed (eio_req grp, void (feed)(eio_req *req), int limit);
655	void eio_grp_limit (eio_req *grp, int limit);	706	void eio_grp_limit (eio_req *grp, int limit);
656	void eio_grp_add (eio_req grp, eio_req req);
657	void eio_grp_cancel (eio_req grp); / cancels all sub requests but not the group */	707	void eio_grp_cancel (eio_req grp); / cancels all sub requests but not the group */
658		708
659		709
660	=back	710	=back
661		711
…		…
668	=head1 ANATOMY AND LIFETIME OF AN EIO REQUEST	718	=head1 ANATOMY AND LIFETIME OF AN EIO REQUEST
669		719
670	A request is represented by a structure of type C<eio_req>. To initialise	720	A request is represented by a structure of type C<eio_req>. To initialise
671	it, clear it to all zero bytes:	721	it, clear it to all zero bytes:
672		722
673	eio_req req;	723	eio_req req;
674		724
675	memset (&req, 0, sizeof (req));	725	memset (&req, 0, sizeof (req));
676		726
677	A more common way to initialise a new C<eio_req> is to use C<calloc>:	727	A more common way to initialise a new C<eio_req> is to use C<calloc>:
678		728
679	eio_req req = calloc (1, sizeof (req));	729	eio_req req = calloc (1, sizeof (req));
680		730
681	In either case, libeio neither allocates, initialises or frees the	731	In either case, libeio neither allocates, initialises or frees the
682	C<eio_req> structure for you - it merely uses it.	732	C<eio_req> structure for you - it merely uses it.
683		733
684	zero	734	zero
…		…
702	for example, in interactive programs, you might want to limit this time to	752	for example, in interactive programs, you might want to limit this time to
703	C<0.01> seconds or so.	753	C<0.01> seconds or so.
704		754
705	Note that:	755	Note that:
706		756
		757	=over 4
		758
707	a) libeio doesn't know how long your request callbacks take, so the time	759	=item a) libeio doesn't know how long your request callbacks take, so the
708	spent in C<eio_poll> is up to one callback invocation longer then this	760	time spent in C<eio_poll> is up to one callback invocation longer then
709	interval.	761	this interval.
710		762
711	b) this is implemented by calling C<gettimeofday> after each request,	763	=item b) this is implemented by calling C<gettimeofday> after each
712	which can be costly.	764	request, which can be costly.
713		765
714	c) at least one request will be handled.	766	=item c) at least one request will be handled.
		767
		768	=back
715		769
716	=item eio_set_max_poll_reqs (unsigned int nreqs)	770	=item eio_set_max_poll_reqs (unsigned int nreqs)
717		771
718	When C<nreqs> is non-zero, then C<eio_poll> will not handle more than	772	When C<nreqs> is non-zero, then C<eio_poll> will not handle more than
719	C<nreqs> requests per invocation. This is a less costly way to limit the	773	C<nreqs> requests per invocation. This is a less costly way to limit the

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Comparing libeio/eio.pod (file contents): Revision 1.15 by root, Tue Jul 5 16:57:41 2011 UTC vs. Revision 1.20 by sf-exg, Thu Jul 7 17:35:52 2011 UTC

Diff Legend

Comparing libeio/eio.pod (file contents):
Revision 1.15 by root, Tue Jul 5 16:57:41 2011 UTC vs.
Revision 1.20 by sf-exg, Thu Jul 7 17:35:52 2011 UTC