[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 1.24 by sf-exg, Thu Jul 14 08:51:29 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
…		…
366	free (target);	405	free (target);
367	}	406	}
368		407
369	=item eio_realpath (const char path, int pri, eio_cb cb, void data)	408	=item eio_realpath (const char path, int pri, eio_cb cb, void data)
370		409
371	Similar to the realpath libc function, but unlike that one, result is	410	Similar to the realpath libc function, but unlike that one, C<<
372	C<-1> on failure and the length of the returned path in C<ptr2> (which is	411	req->result >> is C<-1> on failure. On success, the result is the length
373	not 0-terminated) - this is similar to readlink.	412	of the returned path in C<ptr2> (which is I<NOT> 0-terminated) - this is
		413	similar to readlink.
374		414
375	=item eio_stat (const char path, int pri, eio_cb cb, void data)	415	=item eio_stat (const char path, int pri, eio_cb cb, void data)
376		416
377	=item eio_lstat (const char path, int pri, eio_cb cb, void data)	417	=item eio_lstat (const char path, int pri, eio_cb cb, void data)
378		418
379	=item eio_fstat (int fd, int pri, eio_cb cb, void *data)	419	=item eio_fstat (int fd, int pri, eio_cb cb, void *data)
380		420
381	Stats a file - if C<< req->result >> indicates success, then you can	421	Stats a file - if C<< req->result >> indicates success, then you can
382	access the C<struct stat>-like structure via C<< req->ptr2 >>:	422	access the C<struct stat>-like structure via C<< req->ptr2 >>:
383		423
384	EIO_STRUCT_STAT statdata = (EIO_STRUCT_STAT )req->ptr2;	424	EIO_STRUCT_STAT statdata = (EIO_STRUCT_STAT )req->ptr2;
385		425
386	=item eio_statvfs (const char path, int pri, eio_cb cb, void data)	426	=item eio_statvfs (const char path, int pri, eio_cb cb, void data)
387		427
388	=item eio_fstatvfs (int fd, int pri, eio_cb cb, void *data)	428	=item eio_fstatvfs (int fd, int pri, eio_cb cb, void *data)
389		429
390	Stats a filesystem - if C<< req->result >> indicates success, then you can	430	Stats a filesystem - if C<< req->result >> indicates success, then you can
391	access the C<struct statvfs>-like structure via C<< req->ptr2 >>:	431	access the C<struct statvfs>-like structure via C<< req->ptr2 >>:
392		432
393	EIO_STRUCT_STATVFS statdata = (EIO_STRUCT_STATVFS )req->ptr2;	433	EIO_STRUCT_STATVFS statdata = (EIO_STRUCT_STATVFS )req->ptr2;
394		434
395	=back	435	=back
396		436
397	=head3 READING DIRECTORIES	437	=head3 READING DIRECTORIES
398		438
399	Reading directories sounds simple, but can be rather demanding, especially	439	Reading directories sounds simple, but can be rather demanding, especially
400	if you want to do stuff such as traversing a diretcory hierarchy or	440	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	441	processing all files in a directory. Libeio can assist these complex tasks
402	with it's C<eio_readdir> call.	442	with it's C<eio_readdir> call.
403		443
404	=over 4	444	=over 4
405		445
406	=item eio_readdir (const char path, int flags, int pri, eio_cb cb, void data)	446	=item eio_readdir (const char path, int flags, int pri, eio_cb cb, void data)
…		…
438		478
439	If this flag is specified, then, in addition to the names in C<ptr2>,	479	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	480	also an array of C<struct eio_dirent> is returned, in C<ptr1>. A C<struct
441	eio_dirent> looks like this:	481	eio_dirent> looks like this:
442		482
443	struct eio_dirent	483	struct eio_dirent
444	{	484	{
445	int nameofs; /* offset of null-terminated name string in (char )req->ptr2 /	485	int nameofs; /* offset of null-terminated name string in (char )req->ptr2 /
446	unsigned short namelen; /* size of filename without trailing 0 */	486	unsigned short namelen; /* size of filename without trailing 0 */
447	unsigned char type; /* one of EIO_DT_* */	487	unsigned char type; /* one of EIO_DT_* */
448	signed char score; /* internal use */	488	signed char score; /* internal use */
449	ino_t inode; /* the inode number, if available, otherwise unspecified */	489	ino_t inode; /* the inode number, if available, otherwise unspecified */
450	};	490	};
451		491
452	The only members you normally would access are C<nameofs>, which is the	492	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>.	493	byte-offset from C<ptr2> to the start of the name, C<namelen> and C<type>.
454		494
455	C<type> can be one of:	495	C<type> can be one of:
…		…
498	When this flag is specified, then the names will be returned in an order	538	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()	539	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	540	all files in the given directory, then the returned order will likely
501	be fastest.	541	be fastest.
502		542
503	If both this flag and C<EIO_READDIR_DIRS_FIRST> are specified, then	543	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.	544	likely directories come first, resulting in a less optimal stat order.
505		545
506	=item EIO_READDIR_FOUND_UNKNOWN	546	=item EIO_READDIR_FOUND_UNKNOWN
507		547
508	This flag should not be specified when calling C<eio_readdir>. Instead,	548	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<<	549	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	550	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,	551	absence of this flag therefore indicates that all C<type>'s are known,
512	which can be used to speed up some algorithms.	552	which can be used to speed up some algorithms.
513		553
514	A typical use case would be to identify all subdirectories within a	554	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	555	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	556	then this flag is I<NOT> set, then all the entries at the beginning of the
…		…
554	as calling C<fdatasync>.	594	as calling C<fdatasync>.
555		595
556	Flags can be any combination of C<EIO_SYNC_FILE_RANGE_WAIT_BEFORE>,	596	Flags can be any combination of C<EIO_SYNC_FILE_RANGE_WAIT_BEFORE>,
557	C<EIO_SYNC_FILE_RANGE_WRITE> and C<EIO_SYNC_FILE_RANGE_WAIT_AFTER>.	597	C<EIO_SYNC_FILE_RANGE_WRITE> and C<EIO_SYNC_FILE_RANGE_WAIT_AFTER>.
558		598
		599	=item eio_fallocate (int fd, int mode, off_t offset, off_t len, int pri, eio_cb cb, void *data)
		600
		601	Calls C<fallocate> (note: I<NOT> C<posix_fallocate>!). If the syscall is
		602	missing, then it returns failure and sets C<errno> to C<ENOSYS>.
		603
		604	The C<mode> argument can be C<0> (for behaviour similar to
		605	C<posix_fallocate>), or C<EIO_FALLOC_FL_KEEP_SIZE>, which keeps the size
		606	of the file unchanged (but still preallocates space beyond end of file).
		607
559	=back	608	=back
560		609
561	=head3 LIBEIO-SPECIFIC REQUESTS	610	=head3 LIBEIO-SPECIFIC REQUESTS
562		611
563	These requests are specific to libeio and do not correspond to any OS call.	612	These requests are specific to libeio and do not correspond to any OS call.
…		…
604		653
605	eio_custom (my_open, 0, my_open_done, "/etc/passwd");	654	eio_custom (my_open, 0, my_open_done, "/etc/passwd");
606		655
607	=item eio_busy (eio_tstamp delay, int pri, eio_cb cb, void *data)	656	=item eio_busy (eio_tstamp delay, int pri, eio_cb cb, void *data)
608		657
609	This is a a request that takes C<delay> seconds to execute, but otherwise	658	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	659	does nothing - it simply puts one of the worker threads to sleep for this
611	long.	660	long.
612		661
613	This request can be used to artificially increase load, e.g. for debugging	662	This request can be used to artificially increase load, e.g. for debugging
614	or benchmarking reasons.	663	or benchmarking reasons.
…		…
630	There are two primary use cases for this: a) bundle many requests into a	679	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	680	single, composite, request with a definite callback and the ability to
632	cancel the whole request with its subrequests and b) limiting the number	681	cancel the whole request with its subrequests and b) limiting the number
633	of "active" requests.	682	of "active" requests.
634		683
635	Further below you will find more dicussion of these topics - first follows	684	Further below you will find more discussion of these topics - first
636	the reference section detailing the request generator and other methods.	685	follows the reference section detailing the request generator and other
		686	methods.
637		687
638	=over 4	688	=over 4
639		689
640	=item eio_grp (eio_cb cb, void *data)	690	=item eio_req grp = eio_grp (eio_cb cb, void data)
641		691
642	Creates and submits a group request.	692	Creates, submits and returns a group request. Note that it doesn't have a
		693	priority, unlike all other requests.
643		694
644	=back	695	=item eio_grp_add (eio_req grp, eio_req req)
645		696
		697	Adds a request to the request group.
		698
		699	=item eio_grp_cancel (eio_req *grp)
		700
		701	Cancels all requests I<in> the group, but I<not> the group request
		702	itself. You can cancel the group request I<and> all subrequests via a
		703	normal C<eio_cancel> call.
		704
		705	=back
		706
		707	=head4 GROUP REQUEST LIFETIME
		708
		709	Left alone, a group request will instantly move to the pending state and
		710	will be finished at the next call of C<eio_poll>.
		711
		712	The usefulness stems from the fact that, if a subrequest is added to a
		713	group I<before> a call to C<eio_poll>, via C<eio_grp_add>, then the group
		714	will not finish until all the subrequests have finished.
		715
		716	So the usage cycle of a group request is like this: after it is created,
		717	you normally instantly add a subrequest. If none is added, the group
		718	request will finish on it's own. As long as subrequests are added before
		719	the group request is finished it will be kept from finishing, that is the
		720	callbacks of any subrequests can, in turn, add more requests to the group,
		721	and as long as any requests are active, the group request itself will not
		722	finish.
		723
		724	=head4 CREATING COMPOSITE REQUESTS
		725
		726	Imagine you wanted to create an C<eio_load> request that opens a file,
		727	reads it and closes it. This means it has to execute at least three eio
		728	requests, but for various reasons it might be nice if that request looked
		729	like any other eio request.
		730
		731	This can be done with groups:
		732
		733	=over 4
		734
		735	=item 1) create the request object
		736
		737	Create a group that contains all further requests. This is the request you
		738	can return as "the load request".
		739
		740	=item 2) open the file, maybe
		741
		742	Next, open the file with C<eio_open> and add the request to the group
		743	request and you are finished setting up the request.
		744
		745	If, for some reason, you cannot C<eio_open> (path is a null ptr?) you
		746	can set C<< grp->result >> to C<-1> to signal an error and let the group
		747	request finish on its own.
		748
		749	=item 3) open callback adds more requests
		750
		751	In the open callback, if the open was not successful, copy C<<
		752	req->errorno >> to C<< grp->errorno >> and set C<< grp->errorno >> to
		753	C<-1> to signal an error.
		754
		755	Otherwise, malloc some memory or so and issue a read request, adding the
		756	read request to the group.
		757
		758	=item 4) continue issuing requests till finished
		759
		760	In the real callback, check for errors and possibly continue with
		761	C<eio_close> or any other eio request in the same way.
		762
		763	As soon as no new requests are added the group request will finish. Make
		764	sure you I<always> set C<< grp->result >> to some sensible value.
		765
		766	=back
		767
		768	=head4 REQUEST LIMITING
646		769
647		770
648	#TODO	771	#TODO
649		772
650	/*****************************************************************************/
651	/* groups */
652
653	eio_req eio_grp (eio_cb cb, void data);
654	void eio_grp_feed (eio_req grp, void (feed)(eio_req *req), int limit);
655	void eio_grp_limit (eio_req *grp, int limit);	773	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 */
658		774
659		775
660	=back	776	=back
661		777
662		778
…		…
668	=head1 ANATOMY AND LIFETIME OF AN EIO REQUEST	784	=head1 ANATOMY AND LIFETIME OF AN EIO REQUEST
669		785
670	A request is represented by a structure of type C<eio_req>. To initialise	786	A request is represented by a structure of type C<eio_req>. To initialise
671	it, clear it to all zero bytes:	787	it, clear it to all zero bytes:
672		788
673	eio_req req;	789	eio_req req;
674		790
675	memset (&req, 0, sizeof (req));	791	memset (&req, 0, sizeof (req));
676		792
677	A more common way to initialise a new C<eio_req> is to use C<calloc>:	793	A more common way to initialise a new C<eio_req> is to use C<calloc>:
678		794
679	eio_req req = calloc (1, sizeof (req));	795	eio_req req = calloc (1, sizeof (req));
680		796
681	In either case, libeio neither allocates, initialises or frees the	797	In either case, libeio neither allocates, initialises or frees the
682	C<eio_req> structure for you - it merely uses it.	798	C<eio_req> structure for you - it merely uses it.
683		799
684	zero	800	zero
…		…
702	for example, in interactive programs, you might want to limit this time to	818	for example, in interactive programs, you might want to limit this time to
703	C<0.01> seconds or so.	819	C<0.01> seconds or so.
704		820
705	Note that:	821	Note that:
706		822
		823	=over 4
		824
707	a) libeio doesn't know how long your request callbacks take, so the time	825	=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	826	time spent in C<eio_poll> is up to one callback invocation longer then
709	interval.	827	this interval.
710		828
711	b) this is implemented by calling C<gettimeofday> after each request,	829	=item b) this is implemented by calling C<gettimeofday> after each
712	which can be costly.	830	request, which can be costly.
713		831
714	c) at least one request will be handled.	832	=item c) at least one request will be handled.
		833
		834	=back
715		835
716	=item eio_set_max_poll_reqs (unsigned int nreqs)	836	=item eio_set_max_poll_reqs (unsigned int nreqs)
717		837
718	When C<nreqs> is non-zero, then C<eio_poll> will not handle more than	838	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	839	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 1.24 by sf-exg, Thu Jul 14 08:51:29 2011 UTC

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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 1.24 by sf-exg, Thu Jul 14 08:51:29 2011 UTC