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

Comparing libeio/eio.pod (file contents):
Revision 1.12 by root, Wed Jun 29 10:32:55 2011 UTC vs.
Revision 1.21 by root, Thu Jul 7 22:36:18 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 connector 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 readiness 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
…		…
213	}	261	}
214		262
215	/* the first three arguments are passed to open(2) */	263	/* the first three arguments are passed to open(2) */
216	/* the remaining are priority, callback and data */	264	/* the remaining are priority, callback and data */
217	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))
218	abort (); /* something ent wrong, we will all die!!! */	266	abort (); /* something went wrong, we will all die!!! */
219		267
220	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>
221	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
222		305
223	=head2 AVAILABLE REQUESTS	306	=head2 AVAILABLE REQUESTS
224		307
225	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
226	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
…		…
320	char target = strndup ((char )req->ptr2, req->result);	403	char target = strndup ((char )req->ptr2, req->result);
321		404
322	free (target);	405	free (target);
323	}	406	}
324		407
		408	=item eio_realpath (const char path, int pri, eio_cb cb, void data)
		409
		410	Similar to the realpath libc function, but unlike that one, result is
		411	C<-1> on failure and the length of the returned path in C<ptr2> (which is
		412	not 0-terminated) - this is similar to readlink.
		413
325	=item eio_stat (const char path, int pri, eio_cb cb, void data)	414	=item eio_stat (const char path, int pri, eio_cb cb, void data)
326		415
327	=item eio_lstat (const char path, int pri, eio_cb cb, void data)	416	=item eio_lstat (const char path, int pri, eio_cb cb, void data)
328		417
329	=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)
330		419
331	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
332	access the C<struct stat>-like structure via C<< req->ptr2 >>:	421	access the C<struct stat>-like structure via C<< req->ptr2 >>:
333		422
334	EIO_STRUCT_STAT statdata = (EIO_STRUCT_STAT )req->ptr2;	423	EIO_STRUCT_STAT statdata = (EIO_STRUCT_STAT )req->ptr2;
335		424
336	=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)
337		426
338	=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)
339		428
340	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
341	access the C<struct statvfs>-like structure via C<< req->ptr2 >>:	430	access the C<struct statvfs>-like structure via C<< req->ptr2 >>:
342		431
343	EIO_STRUCT_STATVFS statdata = (EIO_STRUCT_STATVFS )req->ptr2;	432	EIO_STRUCT_STATVFS statdata = (EIO_STRUCT_STATVFS )req->ptr2;
344		433
345	=back	434	=back
346		435
347	=head3 READING DIRECTORIES	436	=head3 READING DIRECTORIES
348		437
349	Reading directories sounds simple, but can be rather demanding, especially	438	Reading directories sounds simple, but can be rather demanding, especially
350	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
351	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
352	with it's C<eio_readdir> call.	441	with it's C<eio_readdir> call.
353		442
354	=over 4	443	=over 4
355		444
356	=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)
…		…
388		477
389	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>,
390	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
391	eio_dirent> looks like this:	480	eio_dirent> looks like this:
392		481
393	struct eio_dirent	482	struct eio_dirent
394	{	483	{
395	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 /
396	unsigned short namelen; /* size of filename without trailing 0 */	485	unsigned short namelen; /* size of filename without trailing 0 */
397	unsigned char type; /* one of EIO_DT_* */	486	unsigned char type; /* one of EIO_DT_* */
398	signed char score; /* internal use */	487	signed char score; /* internal use */
399	ino_t inode; /* the inode number, if available, otherwise unspecified */	488	ino_t inode; /* the inode number, if available, otherwise unspecified */
400	};	489	};
401		490
402	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
403	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>.
404		493
405	C<type> can be one of:	494	C<type> can be one of:
…		…
448	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
449	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()
450	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
451	be fastest.	540	be fastest.
452		541
453	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
454	the likely dirs come first, resulting in a less optimal stat order.	543	likely directories come first, resulting in a less optimal stat order.
455		544
456	=item EIO_READDIR_FOUND_UNKNOWN	545	=item EIO_READDIR_FOUND_UNKNOWN
457		546
458	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,
459	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<<
460	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
461	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,
462	which can be used to speed up some algorithms.	551	which can be used to speed up some algorithms.
463		552
464	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
465	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
466	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
…		…
504	as calling C<fdatasync>.	593	as calling C<fdatasync>.
505		594
506	Flags can be any combination of C<EIO_SYNC_FILE_RANGE_WAIT_BEFORE>,	595	Flags can be any combination of C<EIO_SYNC_FILE_RANGE_WAIT_BEFORE>,
507	C<EIO_SYNC_FILE_RANGE_WRITE> and C<EIO_SYNC_FILE_RANGE_WAIT_AFTER>.	596	C<EIO_SYNC_FILE_RANGE_WRITE> and C<EIO_SYNC_FILE_RANGE_WAIT_AFTER>.
508		597
		598	=item eio_fallocate (int fd, int mode, off_t offset, off_t len, int pri, eio_cb cb, void *data)
		599
		600	Calls C<fallocate> (note: I<NOT> C<posix_fallocate>!). If the syscall is
		601	missing, then it returns failure and sets C<errno> to C<ENOSYS>.
		602
		603	The C<mode> argument can be C<0> (for behaviour similar to
		604	C<posix_fallocate>), or C<EIO_FALLOC_FL_KEEP_SIZE>, which keeps the size
		605	of the file unchanged (but still preallocates space beyond end of file).
		606
509	=back	607	=back
510		608
511	=head3 LIBEIO-SPECIFIC REQUESTS	609	=head3 LIBEIO-SPECIFIC REQUESTS
512		610
513	These requests are specific to libeio and do not correspond to any OS call.	611	These requests are specific to libeio and do not correspond to any OS call.
…		…
554		652
555	eio_custom (my_open, 0, my_open_done, "/etc/passwd");	653	eio_custom (my_open, 0, my_open_done, "/etc/passwd");
556		654
557	=item eio_busy (eio_tstamp delay, int pri, eio_cb cb, void *data)	655	=item eio_busy (eio_tstamp delay, int pri, eio_cb cb, void *data)
558		656
559	This is a a request that takes C<delay> seconds to execute, but otherwise	657	This is a request that takes C<delay> seconds to execute, but otherwise
560	does nothing - it simply puts one of the worker threads to sleep for this	658	does nothing - it simply puts one of the worker threads to sleep for this
561	long.	659	long.
562		660
563	This request can be used to artificially increase load, e.g. for debugging	661	This request can be used to artificially increase load, e.g. for debugging
564	or benchmarking reasons.	662	or benchmarking reasons.
…		…
580	There are two primary use cases for this: a) bundle many requests into a	678	There are two primary use cases for this: a) bundle many requests into a
581	single, composite, request with a definite callback and the ability to	679	single, composite, request with a definite callback and the ability to
582	cancel the whole request with its subrequests and b) limiting the number	680	cancel the whole request with its subrequests and b) limiting the number
583	of "active" requests.	681	of "active" requests.
584		682
585	Further below you will find more dicussion of these topics - first follows	683	Further below you will find more discussion of these topics - first
586	the reference section detailing the request generator and other methods.	684	follows the reference section detailing the request generator and other
		685	methods.
587		686
588	=over 4	687	=over 4
589		688
590	=item eio_grp (eio_cb cb, void *data)	689	=item eio_req grp = eio_grp (eio_cb cb, void data)
591		690
592	Creates and submits a group request.	691	Creates, submits and returns a group request.
		692
		693	=item eio_grp_add (eio_req grp, eio_req req)
		694
		695	Adds a request to the request group.
		696
		697	=item eio_grp_cancel (eio_req *grp)
		698
		699	Cancels all requests I<in> the group, but I<not> the group request
		700	itself. You can cancel the group request via a normal C<eio_cancel> call.
		701
		702
593		703
594	=back	704	=back
595		705
596		706
597		707
…		…
601	/* groups */	711	/* groups */
602		712
603	eio_req eio_grp (eio_cb cb, void data);	713	eio_req eio_grp (eio_cb cb, void data);
604	void eio_grp_feed (eio_req grp, void (feed)(eio_req *req), int limit);	714	void eio_grp_feed (eio_req grp, void (feed)(eio_req *req), int limit);
605	void eio_grp_limit (eio_req *grp, int limit);	715	void eio_grp_limit (eio_req *grp, int limit);
606	void eio_grp_add (eio_req grp, eio_req req);
607	void eio_grp_cancel (eio_req grp); / cancels all sub requests but not the group */	716	void eio_grp_cancel (eio_req grp); / cancels all sub requests but not the group */
608		717
609		718
610	=back	719	=back
611		720
…		…
618	=head1 ANATOMY AND LIFETIME OF AN EIO REQUEST	727	=head1 ANATOMY AND LIFETIME OF AN EIO REQUEST
619		728
620	A request is represented by a structure of type C<eio_req>. To initialise	729	A request is represented by a structure of type C<eio_req>. To initialise
621	it, clear it to all zero bytes:	730	it, clear it to all zero bytes:
622		731
623	eio_req req;	732	eio_req req;
624		733
625	memset (&req, 0, sizeof (req));	734	memset (&req, 0, sizeof (req));
626		735
627	A more common way to initialise a new C<eio_req> is to use C<calloc>:	736	A more common way to initialise a new C<eio_req> is to use C<calloc>:
628		737
629	eio_req req = calloc (1, sizeof (req));	738	eio_req req = calloc (1, sizeof (req));
630		739
631	In either case, libeio neither allocates, initialises or frees the	740	In either case, libeio neither allocates, initialises or frees the
632	C<eio_req> structure for you - it merely uses it.	741	C<eio_req> structure for you - it merely uses it.
633		742
634	zero	743	zero
…		…
652	for example, in interactive programs, you might want to limit this time to	761	for example, in interactive programs, you might want to limit this time to
653	C<0.01> seconds or so.	762	C<0.01> seconds or so.
654		763
655	Note that:	764	Note that:
656		765
		766	=over 4
		767
657	a) libeio doesn't know how long your request callbacks take, so the time	768	=item a) libeio doesn't know how long your request callbacks take, so the
658	spent in C<eio_poll> is up to one callback invocation longer then this	769	time spent in C<eio_poll> is up to one callback invocation longer then
659	interval.	770	this interval.
660		771
661	b) this is implemented by calling C<gettimeofday> after each request,	772	=item b) this is implemented by calling C<gettimeofday> after each
662	which can be costly.	773	request, which can be costly.
663		774
664	c) at least one request will be handled.	775	=item c) at least one request will be handled.
		776
		777	=back
665		778
666	=item eio_set_max_poll_reqs (unsigned int nreqs)	779	=item eio_set_max_poll_reqs (unsigned int nreqs)
667		780
668	When C<nreqs> is non-zero, then C<eio_poll> will not handle more than	781	When C<nreqs> is non-zero, then C<eio_poll> will not handle more than
669	C<nreqs> requests per invocation. This is a less costly way to limit the	782	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 1.12 by root, Wed Jun 29 10:32:55 2011 UTC vs. Revision 1.21 by root, Thu Jul 7 22:36:18 2011 UTC

Diff Legend

Comparing libeio/eio.pod (file contents):
Revision 1.12 by root, Wed Jun 29 10:32:55 2011 UTC vs.
Revision 1.21 by root, Thu Jul 7 22:36:18 2011 UTC