[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 1.32 by root, Sat Jan 19 00:02:34 2013 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	Usage of pthreads in a program changes the semantics of fork
		51	considerably. Specifically, only async-safe functions can be called after
		52	fork. Libeio uses pthreads, so this applies, and makes using fork hard for
		53	anything but relatively fork + exec uses.
51		54
52	1. wait till all requests in "execute" state have been handled	55	This library only works in the process that initialised it: Forking is
53	(basically requests that are already handed over to the kernel).	56	fully supported, but using libeio in any other process than the one that
54	2. fork	57	called C<eio_init> is not.
55	3. in the parent, continue business as usual, done
56	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	libeio queue.
59		58
60	Note, however, since libeio does use threads, thr above guarantee doesn't	59	You might get around by not I<using> libeio before (or after) forking in
61	cover your libc, for example, malloc and other libc functions are not	60	the parent, and using it in the child afterwards. You could also try to
62	fork-safe, so there is very little you can do after a fork, and in fatc,	61	call the L<eio_init> function again in the child, which will brutally
63	the above might crash, and thus change.	62	reinitialise all data structures, which isn't POSIX conformant, but
		63	typically works.
		64
		65	Otherwise, the only recommendation you should follow is: treat fork code
		66	the same way you treat signal handlers, and only ever call C<eio_init> in
		67	the process that uses it, and only once ever.
64		68
65	=head1 INITIALISATION/INTEGRATION	69	=head1 INITIALISATION/INTEGRATION
66		70
67	Before you can call any eio functions you first have to initialise the	71	Before you can call any eio functions you first have to initialise the
68	library. The library integrates into any event loop, but can also be used	72	library. The library integrates into any event loop, but can also be used
…		…
77	This function initialises the library. On success it returns C<0>, on	81	This function initialises the library. On success it returns C<0>, on
78	failure it returns C<-1> and sets C<errno> appropriately.	82	failure it returns C<-1> and sets C<errno> appropriately.
79		83
80	It accepts two function pointers specifying callbacks as argument, both of	84	It accepts two function pointers specifying callbacks as argument, both of
81	which can be C<0>, in which case the callback isn't called.	85	which can be C<0>, in which case the callback isn't called.
		86
		87	There is currently no way to change these callbacks later, or to
		88	"uninitialise" the library again.
82		89
83	=item want_poll callback	90	=item want_poll callback
84		91
85	The C<want_poll> callback is invoked whenever libeio wants attention (i.e.	92	The C<want_poll> callback is invoked whenever libeio wants attention (i.e.
86	it wants to be polled by calling C<eio_poll>). It is "edge-triggered",	93	it wants to be polled by calling C<eio_poll>). It is "edge-triggered",
…		…
130		137
131	If C<eio_poll ()> is configured to not handle all results in one go	138	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	139	(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>.	140	C<eio_poll> until it returns something C<!= -1>.
134		141
135	A full-featured wrapper would look as follows (if C<eio_poll> is handling	142	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	143	(if C<eio_poll> is handling all requests, it can of course be simplified a
137	watcher logic):	144	lot by removing the idle watcher logic):
138		145
139	static struct ev_loop *loop;	146	static struct ev_loop *loop;
140	static ev_idle repeat_watcher;	147	static ev_idle repeat_watcher;
141	static ev_async ready_watcher;	148	static ev_async ready_watcher;
142		149
143	/* idle watcher callback, only used when eio_poll */	150	/* idle watcher callback, only used when eio_poll */
144	/* didn't handle all results in one call */	151	/* didn't handle all results in one call */
145	static void	152	static void
146	repeat (EV_P_ ev_idle *w, int revents)	153	repeat (EV_P_ ev_idle *w, int revents)
147	{	154	{
148	if (eio_poll () != -1)	155	if (eio_poll () != -1)
149	ev_idle_stop (EV_A_ w);	156	ev_idle_stop (EV_A_ w);
150	}	157	}
151		158
152	/* eio has some results, process them */	159	/* eio has some results, process them */
153	static void	160	static void
154	ready (EV_P_ ev_async *w, int revents)	161	ready (EV_P_ ev_async *w, int revents)
155	{	162	{
156	if (eio_poll () == -1)	163	if (eio_poll () == -1)
157	ev_idle_start (EV_A_ &repeat_watcher);	164	ev_idle_start (EV_A_ &repeat_watcher);
158	}	165	}
159		166
160	/* wake up the event loop */	167	/* wake up the event loop */
161	static void	168	static void
162	want_poll (void)	169	want_poll (void)
163	{	170	{
164	ev_async_send (loop, &ready_watcher)	171	ev_async_send (loop, &ready_watcher)
165	}	172	}
166		173
167	void	174	void
168	my_init_eio ()	175	my_init_eio ()
169	{	176	{
170	loop = EV_DEFAULT;	177	loop = EV_DEFAULT;
171		178
172	ev_idle_init (&repeat_watcher, repeat);	179	ev_idle_init (&repeat_watcher, repeat);
173	ev_async_init (&ready_watcher, ready);	180	ev_async_init (&ready_watcher, ready);
174	ev_async_start (loop &watcher);	181	ev_async_start (loop &watcher);
175		182
176	eio_init (want_poll, 0);	183	eio_init (want_poll, 0);
177	}	184	}
178		185
179	For most other event loops, you would typically use a pipe - the event	186	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	187	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	188	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	189	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	190	C<eio_poll>.
184	your callback again and again until the byte has been read (as the pipe	191
185	read callback does not read it, only C<done_poll>).	192	You don't have to take special care in the case C<eio_poll> doesn't handle
		193	all requests, as the done callback will not be invoked, so the event loop
		194	will still signal readiness for the pipe until I<all> results have been
		195	processed.
186		196
187		197
188	=head1 HIGH LEVEL REQUEST API	198	=head1 HIGH LEVEL REQUEST API
189		199
190	Libeio has both a high-level API, which consists of calling a request	200	Libeio has both a high-level API, which consists of calling a request
…		…
223		233
224	The C<void *data> member simply stores the value of the C<data> argument.	234	The C<void *data> member simply stores the value of the C<data> argument.
225		235
226	=back	236	=back
227		237
		238	Members not explicitly described as accessible must not be
		239	accessed. Specifically, there is no guarantee that any members will still
		240	have the value they had when the request was submitted.
		241
228	The return value of the callback is normally C<0>, which tells libeio to	242	The return value of the callback is normally C<0>, which tells libeio to
229	continue normally. If a callback returns a nonzero value, libeio will	243	continue normally. If a callback returns a nonzero value, libeio will
230	stop processing results (in C<eio_poll>) and will return the value to its	244	stop processing results (in C<eio_poll>) and will return the value to its
231	caller.	245	caller.
232		246
233	Memory areas passed to libeio must stay valid as long as a request	247	Memory areas passed to libeio wrappers must stay valid as long as a
234	executes, with the exception of paths, which are being copied	248	request executes, with the exception of paths, which are being copied
235	internally. Any memory libeio itself allocates will be freed after the	249	internally. Any memory libeio itself allocates will be freed after the
236	finish callback has been called. If you want to manage all memory passed	250	finish callback has been called. If you want to manage all memory passed
237	to libeio yourself you can use the low-level API.	251	to libeio yourself you can use the low-level API.
238		252
239	For example, to open a file, you could do this:	253	For example, to open a file, you could do this:
…		…
257	}	271	}
258		272
259	/* the first three arguments are passed to open(2) */	273	/* the first three arguments are passed to open(2) */
260	/* the remaining are priority, callback and data */	274	/* the remaining are priority, callback and data */
261	if (!eio_open ("/etc/passwd", O_RDONLY, 0, 0, file_open_done, 0))	275	if (!eio_open ("/etc/passwd", O_RDONLY, 0, 0, file_open_done, 0))
262	abort (); /* something ent wrong, we will all die!!! */	276	abort (); /* something went wrong, we will all die!!! */
263		277
264	Note that you additionally need to call C<eio_poll> when the C<want_cb>	278	Note that you additionally need to call C<eio_poll> when the C<want_cb>
265	indicates that requests are ready to be processed.	279	indicates that requests are ready to be processed.
		280
		281	=head2 CANCELLING REQUESTS
		282
		283	Sometimes the need for a request goes away before the request is
		284	finished. In that case, one can cancel the request by a call to
		285	C<eio_cancel>:
		286
		287	=over 4
		288
		289	=item eio_cancel (eio_req *req)
		290
		291	Cancel the request (and all its subrequests). If the request is currently
		292	executing it might still continue to execute, and in other cases it might
		293	still take a while till the request is cancelled.
		294
		295	Even if cancelled, the finish callback will still be invoked - the
		296	callbacks of all cancellable requests need to check whether the request
		297	has been cancelled by calling C<EIO_CANCELLED (req)>:
		298
		299	static int
		300	my_eio_cb (eio_req *req)
		301	{
		302	if (EIO_CANCELLED (req))
		303	return 0;
		304	}
		305
		306	In addition, cancelled requests will I<either> have C<< req->result >>
		307	set to C<-1> and C<errno> to C<ECANCELED>, or I<otherwise> they were
		308	successfully executed, despite being cancelled (e.g. when they have
		309	already been executed at the time they were cancelled).
		310
		311	C<EIO_CANCELLED> is still true for requests that have successfully
		312	executed, as long as C<eio_cancel> was called on them at some point.
		313
		314	=back
266		315
267	=head2 AVAILABLE REQUESTS	316	=head2 AVAILABLE REQUESTS
268		317
269	The following request functions are available. I<All> of them return the	318	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	319	C<eio_req *> on success and C<0> on failure, and I<all> of them have the
…		…
366	free (target);	415	free (target);
367	}	416	}
368		417
369	=item eio_realpath (const char path, int pri, eio_cb cb, void data)	418	=item eio_realpath (const char path, int pri, eio_cb cb, void data)
370		419
371	Similar to the realpath libc function, but unlike that one, result is	420	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	421	req->result >> is C<-1> on failure. On success, the result is the length
373	not 0-terminated) - this is similar to readlink.	422	of the returned path in C<ptr2> (which is I<NOT> 0-terminated) - this is
		423	similar to readlink.
374		424
375	=item eio_stat (const char path, int pri, eio_cb cb, void data)	425	=item eio_stat (const char path, int pri, eio_cb cb, void data)
376		426
377	=item eio_lstat (const char path, int pri, eio_cb cb, void data)	427	=item eio_lstat (const char path, int pri, eio_cb cb, void data)
378		428
379	=item eio_fstat (int fd, int pri, eio_cb cb, void *data)	429	=item eio_fstat (int fd, int pri, eio_cb cb, void *data)
380		430
381	Stats a file - if C<< req->result >> indicates success, then you can	431	Stats a file - if C<< req->result >> indicates success, then you can
382	access the C<struct stat>-like structure via C<< req->ptr2 >>:	432	access the C<struct stat>-like structure via C<< req->ptr2 >>:
383		433
384	EIO_STRUCT_STAT statdata = (EIO_STRUCT_STAT )req->ptr2;	434	EIO_STRUCT_STAT statdata = (EIO_STRUCT_STAT )req->ptr2;
385		435
386	=item eio_statvfs (const char path, int pri, eio_cb cb, void data)	436	=item eio_statvfs (const char path, int pri, eio_cb cb, void data)
387		437
388	=item eio_fstatvfs (int fd, int pri, eio_cb cb, void *data)	438	=item eio_fstatvfs (int fd, int pri, eio_cb cb, void *data)
389		439
390	Stats a filesystem - if C<< req->result >> indicates success, then you can	440	Stats a filesystem - if C<< req->result >> indicates success, then you can
391	access the C<struct statvfs>-like structure via C<< req->ptr2 >>:	441	access the C<struct statvfs>-like structure via C<< req->ptr2 >>:
392		442
393	EIO_STRUCT_STATVFS statdata = (EIO_STRUCT_STATVFS )req->ptr2;	443	EIO_STRUCT_STATVFS statdata = (EIO_STRUCT_STATVFS )req->ptr2;
394		444
395	=back	445	=back
396		446
397	=head3 READING DIRECTORIES	447	=head3 READING DIRECTORIES
398		448
399	Reading directories sounds simple, but can be rather demanding, especially	449	Reading directories sounds simple, but can be rather demanding, especially
400	if you want to do stuff such as traversing a diretcory hierarchy or	450	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	451	processing all files in a directory. Libeio can assist these complex tasks
402	with it's C<eio_readdir> call.	452	with it's C<eio_readdir> call.
403		453
404	=over 4	454	=over 4
405		455
406	=item eio_readdir (const char path, int flags, int pri, eio_cb cb, void data)	456	=item eio_readdir (const char path, int flags, int pri, eio_cb cb, void data)
…		…
438		488
439	If this flag is specified, then, in addition to the names in C<ptr2>,	489	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	490	also an array of C<struct eio_dirent> is returned, in C<ptr1>. A C<struct
441	eio_dirent> looks like this:	491	eio_dirent> looks like this:
442		492
443	struct eio_dirent	493	struct eio_dirent
444	{	494	{
445	int nameofs; /* offset of null-terminated name string in (char )req->ptr2 /	495	int nameofs; /* offset of null-terminated name string in (char )req->ptr2 /
446	unsigned short namelen; /* size of filename without trailing 0 */	496	unsigned short namelen; /* size of filename without trailing 0 */
447	unsigned char type; /* one of EIO_DT_* */	497	unsigned char type; /* one of EIO_DT_* */
448	signed char score; /* internal use */	498	signed char score; /* internal use */
449	ino_t inode; /* the inode number, if available, otherwise unspecified */	499	ino_t inode; /* the inode number, if available, otherwise unspecified */
450	};	500	};
451		501
452	The only members you normally would access are C<nameofs>, which is the	502	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>.	503	byte-offset from C<ptr2> to the start of the name, C<namelen> and C<type>.
454		504
455	C<type> can be one of:	505	C<type> can be one of:
…		…
498	When this flag is specified, then the names will be returned in an order	548	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()	549	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	550	all files in the given directory, then the returned order will likely
501	be fastest.	551	be fastest.
502		552
503	If both this flag and C<EIO_READDIR_DIRS_FIRST> are specified, then	553	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.	554	likely directories come first, resulting in a less optimal stat order.
505		555
506	=item EIO_READDIR_FOUND_UNKNOWN	556	=item EIO_READDIR_FOUND_UNKNOWN
507		557
508	This flag should not be specified when calling C<eio_readdir>. Instead,	558	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<<	559	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	560	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,	561	absence of this flag therefore indicates that all C<type>'s are known,
512	which can be used to speed up some algorithms.	562	which can be used to speed up some algorithms.
513		563
514	A typical use case would be to identify all subdirectories within a	564	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	565	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	566	then this flag is I<NOT> set, then all the entries at the beginning of the
…		…
546	=item eio_readahead (int fd, off_t offset, size_t length, int pri, eio_cb cb, void *data)	596	=item eio_readahead (int fd, off_t offset, size_t length, int pri, eio_cb cb, void *data)
547		597
548	Calls C<readahead(2)>. If the syscall is missing, then the call is	598	Calls C<readahead(2)>. If the syscall is missing, then the call is
549	emulated by simply reading the data (currently in 64kiB chunks).	599	emulated by simply reading the data (currently in 64kiB chunks).
550		600
		601	=item eio_syncfs (int fd, int pri, eio_cb cb, void *data)
		602
		603	Calls Linux' C<syncfs> syscall, if available. Returns C<-1> and sets
		604	C<errno> to C<ENOSYS> if the call is missing I<but still calls sync()>,
		605	if the C<fd> is C<< >= 0 >>, so you can probe for the availability of the
		606	syscall with a negative C<fd> argument and checking for C<-1/ENOSYS>.
		607
551	=item eio_sync_file_range (int fd, off_t offset, size_t nbytes, unsigned int flags, int pri, eio_cb cb, void *data)	608	=item eio_sync_file_range (int fd, off_t offset, size_t nbytes, unsigned int flags, int pri, eio_cb cb, void *data)
552		609
553	Calls C<sync_file_range>. If the syscall is missing, then this is the same	610	Calls C<sync_file_range>. If the syscall is missing, then this is the same
554	as calling C<fdatasync>.	611	as calling C<fdatasync>.
555		612
556	Flags can be any combination of C<EIO_SYNC_FILE_RANGE_WAIT_BEFORE>,	613	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>.	614	C<EIO_SYNC_FILE_RANGE_WRITE> and C<EIO_SYNC_FILE_RANGE_WAIT_AFTER>.
558		615
		616	=item eio_fallocate (int fd, int mode, off_t offset, off_t len, int pri, eio_cb cb, void *data)
		617
		618	Calls C<fallocate> (note: I<NOT> C<posix_fallocate>!). If the syscall is
		619	missing, then it returns failure and sets C<errno> to C<ENOSYS>.
		620
		621	The C<mode> argument can be C<0> (for behaviour similar to
		622	C<posix_fallocate>), or C<EIO_FALLOC_FL_KEEP_SIZE>, which keeps the size
		623	of the file unchanged (but still preallocates space beyond end of file).
		624
559	=back	625	=back
560		626
561	=head3 LIBEIO-SPECIFIC REQUESTS	627	=head3 LIBEIO-SPECIFIC REQUESTS
562		628
563	These requests are specific to libeio and do not correspond to any OS call.	629	These requests are specific to libeio and do not correspond to any OS call.
564		630
565	=over 4	631	=over 4
566		632
567	=item eio_mtouch (void addr, size_t length, int flags, int pri, eio_cb cb, void data)	633	=item eio_mtouch (void addr, size_t length, int flags, int pri, eio_cb cb, void data)
568		634
569	Reads (C<flags == 0>) or modifies (C<flags == EIO_MT_MODIFY) the given	635	Reads (C<flags == 0>) or modifies (C<flags == EIO_MT_MODIFY>) the given
570	memory area, page-wise, that is, it reads (or reads and writes back) the	636	memory area, page-wise, that is, it reads (or reads and writes back) the
571	first octet of every page that spans the memory area.	637	first octet of every page that spans the memory area.
572		638
573	This can be used to page in some mmapped file, or dirty some pages. Note	639	This can be used to page in some mmapped file, or dirty some pages. Note
574	that dirtying is an unlocked read-write access, so races can ensue when	640	that dirtying is an unlocked read-write access, so races can ensue when
…		…
604		670
605	eio_custom (my_open, 0, my_open_done, "/etc/passwd");	671	eio_custom (my_open, 0, my_open_done, "/etc/passwd");
606		672
607	=item eio_busy (eio_tstamp delay, int pri, eio_cb cb, void *data)	673	=item eio_busy (eio_tstamp delay, int pri, eio_cb cb, void *data)
608		674
609	This is a a request that takes C<delay> seconds to execute, but otherwise	675	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	676	does nothing - it simply puts one of the worker threads to sleep for this
611	long.	677	long.
612		678
613	This request can be used to artificially increase load, e.g. for debugging	679	This request can be used to artificially increase load, e.g. for debugging
614	or benchmarking reasons.	680	or benchmarking reasons.
…		…
630	There are two primary use cases for this: a) bundle many requests into a	696	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	697	single, composite, request with a definite callback and the ability to
632	cancel the whole request with its subrequests and b) limiting the number	698	cancel the whole request with its subrequests and b) limiting the number
633	of "active" requests.	699	of "active" requests.
634		700
635	Further below you will find more dicussion of these topics - first follows	701	Further below you will find more discussion of these topics - first
636	the reference section detailing the request generator and other methods.	702	follows the reference section detailing the request generator and other
		703	methods.
637		704
638	=over 4	705	=over 4
639		706
640	=item eio_grp (eio_cb cb, void *data)	707	=item eio_req grp = eio_grp (eio_cb cb, void data)
641		708
642	Creates and submits a group request.	709	Creates, submits and returns a group request. Note that it doesn't have a
		710	priority, unlike all other requests.
643		711
644	=back	712	=item eio_grp_add (eio_req grp, eio_req req)
645		713
		714	Adds a request to the request group.
		715
		716	=item eio_grp_cancel (eio_req *grp)
		717
		718	Cancels all requests I<in> the group, but I<not> the group request
		719	itself. You can cancel the group request I<and> all subrequests via a
		720	normal C<eio_cancel> call.
		721
		722	=back
		723
		724	=head4 GROUP REQUEST LIFETIME
		725
		726	Left alone, a group request will instantly move to the pending state and
		727	will be finished at the next call of C<eio_poll>.
		728
		729	The usefulness stems from the fact that, if a subrequest is added to a
		730	group I<before> a call to C<eio_poll>, via C<eio_grp_add>, then the group
		731	will not finish until all the subrequests have finished.
		732
		733	So the usage cycle of a group request is like this: after it is created,
		734	you normally instantly add a subrequest. If none is added, the group
		735	request will finish on it's own. As long as subrequests are added before
		736	the group request is finished it will be kept from finishing, that is the
		737	callbacks of any subrequests can, in turn, add more requests to the group,
		738	and as long as any requests are active, the group request itself will not
		739	finish.
		740
		741	=head4 CREATING COMPOSITE REQUESTS
		742
		743	Imagine you wanted to create an C<eio_load> request that opens a file,
		744	reads it and closes it. This means it has to execute at least three eio
		745	requests, but for various reasons it might be nice if that request looked
		746	like any other eio request.
		747
		748	This can be done with groups:
		749
		750	=over 4
		751
		752	=item 1) create the request object
		753
		754	Create a group that contains all further requests. This is the request you
		755	can return as "the load request".
		756
		757	=item 2) open the file, maybe
		758
		759	Next, open the file with C<eio_open> and add the request to the group
		760	request and you are finished setting up the request.
		761
		762	If, for some reason, you cannot C<eio_open> (path is a null ptr?) you
		763	can set C<< grp->result >> to C<-1> to signal an error and let the group
		764	request finish on its own.
		765
		766	=item 3) open callback adds more requests
		767
		768	In the open callback, if the open was not successful, copy C<<
		769	req->errorno >> to C<< grp->errorno >> and set C<< grp->result >> to
		770	C<-1> to signal an error.
		771
		772	Otherwise, malloc some memory or so and issue a read request, adding the
		773	read request to the group.
		774
		775	=item 4) continue issuing requests till finished
		776
		777	In the read callback, check for errors and possibly continue with
		778	C<eio_close> or any other eio request in the same way.
		779
		780	As soon as no new requests are added, the group request will finish. Make
		781	sure you I<always> set C<< grp->result >> to some sensible value.
		782
		783	=back
		784
		785	=head4 REQUEST LIMITING
646		786
647		787
648	#TODO	788	#TODO
649		789
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);	790	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		791
659		792
660	=back	793	=back
661		794
662		795
…		…
668	=head1 ANATOMY AND LIFETIME OF AN EIO REQUEST	801	=head1 ANATOMY AND LIFETIME OF AN EIO REQUEST
669		802
670	A request is represented by a structure of type C<eio_req>. To initialise	803	A request is represented by a structure of type C<eio_req>. To initialise
671	it, clear it to all zero bytes:	804	it, clear it to all zero bytes:
672		805
673	eio_req req;	806	eio_req req;
674		807
675	memset (&req, 0, sizeof (req));	808	memset (&req, 0, sizeof (req));
676		809
677	A more common way to initialise a new C<eio_req> is to use C<calloc>:	810	A more common way to initialise a new C<eio_req> is to use C<calloc>:
678		811
679	eio_req req = calloc (1, sizeof (req));	812	eio_req req = calloc (1, sizeof (req));
680		813
681	In either case, libeio neither allocates, initialises or frees the	814	In either case, libeio neither allocates, initialises or frees the
682	C<eio_req> structure for you - it merely uses it.	815	C<eio_req> structure for you - it merely uses it.
683		816
684	zero	817	zero
…		…
702	for example, in interactive programs, you might want to limit this time to	835	for example, in interactive programs, you might want to limit this time to
703	C<0.01> seconds or so.	836	C<0.01> seconds or so.
704		837
705	Note that:	838	Note that:
706		839
		840	=over 4
		841
707	a) libeio doesn't know how long your request callbacks take, so the time	842	=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	843	time spent in C<eio_poll> is up to one callback invocation longer then
709	interval.	844	this interval.
710		845
711	b) this is implemented by calling C<gettimeofday> after each request,	846	=item b) this is implemented by calling C<gettimeofday> after each
712	which can be costly.	847	request, which can be costly.
713		848
714	c) at least one request will be handled.	849	=item c) at least one request will be handled.
		850
		851	=back
715		852
716	=item eio_set_max_poll_reqs (unsigned int nreqs)	853	=item eio_set_max_poll_reqs (unsigned int nreqs)
717		854
718	When C<nreqs> is non-zero, then C<eio_poll> will not handle more than	855	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	856	C<nreqs> requests per invocation. This is a less costly way to limit the
…		…
789	This symbol governs the stack size for each eio thread. Libeio itself	926	This symbol governs the stack size for each eio thread. Libeio itself
790	was written to use very little stackspace, but when using C<EIO_CUSTOM>	927	was written to use very little stackspace, but when using C<EIO_CUSTOM>
791	requests, you might want to increase this.	928	requests, you might want to increase this.
792		929
793	If this symbol is undefined (the default) then libeio will use its default	930	If this symbol is undefined (the default) then libeio will use its default
794	stack size (C<sizeof (long) * 4096> currently). If it is defined, but	931	stack size (C<sizeof (void ) 4096> currently). In all other cases, the
795	C<0>, then the default operating system stack size will be used. In all
796	other cases, the value must be an expression that evaluates to the desired	932	value must be an expression that evaluates to the desired stack size.
797	stack size.
798		933
799	=back	934	=back
800		935
801		936
802	=head1 PORTABILITY REQUIREMENTS	937	=head1 PORTABILITY REQUIREMENTS

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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 1.32 by root, Sat Jan 19 00:02:34 2013 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 1.32 by root, Sat Jan 19 00:02:34 2013 UTC