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

Comparing libeio/eio.pod (file contents):
Revision 1.10 by root, Sun Jun 5 23:22:04 2011 UTC vs.
Revision 1.29 by sf-exg, Mon Sep 26 17:10:10 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	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",
…		…
124	=back	131	=back
125		132
126	For libev, you would typically use an C<ev_async> watcher: the	133	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	134	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	135	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	136	()>.
130	all requests have been handled yet). The race is taken care of because	137
131	libev resets/rearms the async watcher before calling your callback,	138	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)	139	(i.e. it returns C<-1>) then you should start an idle watcher that calls
133	spurious wake-ups, but is generally harmless.	140	C<eio_poll> until it returns something C<!= -1>.
		141
		142	A full-featured connector between libeio and libev would look as follows
		143	(if C<eio_poll> is handling all requests, it can of course be simplified a
		144	lot by removing the idle watcher logic):
		145
		146	static struct ev_loop *loop;
		147	static ev_idle repeat_watcher;
		148	static ev_async ready_watcher;
		149
		150	/* idle watcher callback, only used when eio_poll */
		151	/* didn't handle all results in one call */
		152	static void
		153	repeat (EV_P_ ev_idle *w, int revents)
		154	{
		155	if (eio_poll () != -1)
		156	ev_idle_stop (EV_A_ w);
		157	}
		158
		159	/* eio has some results, process them */
		160	static void
		161	ready (EV_P_ ev_async *w, int revents)
		162	{
		163	if (eio_poll () == -1)
		164	ev_idle_start (EV_A_ &repeat_watcher);
		165	}
		166
		167	/* wake up the event loop */
		168	static void
		169	want_poll (void)
		170	{
		171	ev_async_send (loop, &ready_watcher)
		172	}
		173
		174	void
		175	my_init_eio ()
		176	{
		177	loop = EV_DEFAULT;
		178
		179	ev_idle_init (&repeat_watcher, repeat);
		180	ev_async_init (&ready_watcher, ready);
		181	ev_async_start (loop &watcher);
		182
		183	eio_init (want_poll, 0);
		184	}
134		185
135	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
136	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
137	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
138	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
139	C<eio_poll>. The race is avoided here because the event loop should invoke	190	C<eio_poll>.
140	your callback again and again until the byte has been read (as the pipe	191
141	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.
142		196
143		197
144	=head1 HIGH LEVEL REQUEST API	198	=head1 HIGH LEVEL REQUEST API
145		199
146	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
…		…
153		207
154	You submit a request by calling the relevant C<eio_TYPE> function with the	208	You submit a request by calling the relevant C<eio_TYPE> function with the
155	required parameters, a callback of type C<int (eio_cb)(eio_req req)>	209	required parameters, a callback of type C<int (eio_cb)(eio_req req)>
156	(called C<eio_cb> below) and a freely usable C<void *data> argument.	210	(called C<eio_cb> below) and a freely usable C<void *data> argument.
157		211
158	The return value will either be 0	212	The return value will either be 0, in case something went really wrong
		213	(which can basically only happen on very fatal errors, such as C<malloc>
		214	returning 0, which is rather unlikely), or a pointer to the newly-created
		215	and submitted C<eio_req *>.
159		216
160	The callback will be called with an C<eio_req *> which contains the	217	The callback will be called with an C<eio_req *> which contains the
161	results of the request. The members you can access inside that structure	218	results of the request. The members you can access inside that structure
162	vary from request to request, except for:	219	vary from request to request, except for:
163		220
…		…
175	=item C<void *data>	232	=item C<void *data>
176		233
177	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.
178		235
179	=back	236	=back
		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.
180		241
181	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
182	continue normally. If a callback returns a nonzero value, libeio will	243	continue normally. If a callback returns a nonzero value, libeio will
183	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
184	caller.	245	caller.
185		246
186	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
187	executes, with the exception of paths, which are being copied	248	request executes, with the exception of paths, which are being copied
188	internally. Any memory libeio itself allocates will be freed after the	249	internally. Any memory libeio itself allocates will be freed after the
189	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
190	to libeio yourself you can use the low-level API.	251	to libeio yourself you can use the low-level API.
191		252
192	For example, to open a file, you could do this:	253	For example, to open a file, you could do this:
…		…
210	}	271	}
211		272
212	/* the first three arguments are passed to open(2) */	273	/* the first three arguments are passed to open(2) */
213	/* the remaining are priority, callback and data */	274	/* the remaining are priority, callback and data */
214	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))
215	abort (); /* something ent wrong, we will all die!!! */	276	abort (); /* something went wrong, we will all die!!! */
216		277
217	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>
218	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
219		315
220	=head2 AVAILABLE REQUESTS	316	=head2 AVAILABLE REQUESTS
221		317
222	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
223	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
…		…
226	custom data value as C<data>.	322	custom data value as C<data>.
227		323
228	=head3 POSIX API WRAPPERS	324	=head3 POSIX API WRAPPERS
229		325
230	These requests simply wrap the POSIX call of the same name, with the same	326	These requests simply wrap the POSIX call of the same name, with the same
231	arguments. If a function is not implemented by the OS and cnanot be emulated	327	arguments. If a function is not implemented by the OS and cannot be emulated
232	in some way, then all of these return C<-1> and set C<errorno> to C<ENOSYS>.	328	in some way, then all of these return C<-1> and set C<errorno> to C<ENOSYS>.
233		329
234	=over 4	330	=over 4
235		331
236	=item eio_open (const char path, int flags, mode_t mode, int pri, eio_cb cb, void data)	332	=item eio_open (const char path, int flags, mode_t mode, int pri, eio_cb cb, void data)
…		…
317	char target = strndup ((char )req->ptr2, req->result);	413	char target = strndup ((char )req->ptr2, req->result);
318		414
319	free (target);	415	free (target);
320	}	416	}
321		417
		418	=item eio_realpath (const char path, int pri, eio_cb cb, void data)
		419
		420	Similar to the realpath libc function, but unlike that one, C<<
		421	req->result >> is C<-1> on failure. On success, the result is the length
		422	of the returned path in C<ptr2> (which is I<NOT> 0-terminated) - this is
		423	similar to readlink.
		424
322	=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)
323		426
324	=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)
325		428
326	=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)
327		430
328	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
329	access the C<struct stat>-like structure via C<< req->ptr2 >>:	432	access the C<struct stat>-like structure via C<< req->ptr2 >>:
330		433
331	EIO_STRUCT_STAT statdata = (EIO_STRUCT_STAT )req->ptr2;	434	EIO_STRUCT_STAT statdata = (EIO_STRUCT_STAT )req->ptr2;
332		435
333	=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)
334		437
335	=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)
336		439
337	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
338	access the C<struct statvfs>-like structure via C<< req->ptr2 >>:	441	access the C<struct statvfs>-like structure via C<< req->ptr2 >>:
339		442
340	EIO_STRUCT_STATVFS statdata = (EIO_STRUCT_STATVFS )req->ptr2;	443	EIO_STRUCT_STATVFS statdata = (EIO_STRUCT_STATVFS )req->ptr2;
341		444
342	=back	445	=back
343		446
344	=head3 READING DIRECTORIES	447	=head3 READING DIRECTORIES
345		448
346	Reading directories sounds simple, but can be rather demanding, especially	449	Reading directories sounds simple, but can be rather demanding, especially
347	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
348	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
349	with it's C<eio_readdir> call.	452	with it's C<eio_readdir> call.
350		453
351	=over 4	454	=over 4
352		455
353	=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)
…		…
385		488
386	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>,
387	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
388	eio_dirent> looks like this:	491	eio_dirent> looks like this:
389		492
390	struct eio_dirent	493	struct eio_dirent
391	{	494	{
392	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 /
393	unsigned short namelen; /* size of filename without trailing 0 */	496	unsigned short namelen; /* size of filename without trailing 0 */
394	unsigned char type; /* one of EIO_DT_* */	497	unsigned char type; /* one of EIO_DT_* */
395	signed char score; /* internal use */	498	signed char score; /* internal use */
396	ino_t inode; /* the inode number, if available, otherwise unspecified */	499	ino_t inode; /* the inode number, if available, otherwise unspecified */
397	};	500	};
398		501
399	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
400	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>.
401		504
402	C<type> can be one of:	505	C<type> can be one of:
…		…
445	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
446	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()
447	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
448	be fastest.	551	be fastest.
449		552
450	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
451	the likely dirs come first, resulting in a less optimal stat order.	554	likely directories come first, resulting in a less optimal stat order.
452		555
453	=item EIO_READDIR_FOUND_UNKNOWN	556	=item EIO_READDIR_FOUND_UNKNOWN
454		557
455	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,
456	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<<
457	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
458	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,
459	which can be used to speed up some algorithms.	562	which can be used to speed up some algorithms.
460		563
461	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
462	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
463	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
…		…
493	=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)
494		597
495	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
496	emulated by simply reading the data (currently in 64kiB chunks).	599	emulated by simply reading the data (currently in 64kiB chunks).
497		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
498	=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)
499		609
500	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
501	as calling C<fdatasync>.	611	as calling C<fdatasync>.
502		612
503	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>,
504	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>.
		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).
505		624
506	=back	625	=back
507		626
508	=head3 LIBEIO-SPECIFIC REQUESTS	627	=head3 LIBEIO-SPECIFIC REQUESTS
509		628
…		…
551		670
552	eio_custom (my_open, 0, my_open_done, "/etc/passwd");	671	eio_custom (my_open, 0, my_open_done, "/etc/passwd");
553		672
554	=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)
555		674
556	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
557	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
558	long.	677	long.
559		678
560	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
561	or benchmarking reasons.	680	or benchmarking reasons.
…		…
568		687
569	=back	688	=back
570		689
571	=head3 GROUPING AND LIMITING REQUESTS	690	=head3 GROUPING AND LIMITING REQUESTS
572		691
		692	There is one more rather special request, C<eio_grp>. It is a very special
		693	aio request: Instead of doing something, it is a container for other eio
		694	requests.
		695
		696	There are two primary use cases for this: a) bundle many requests into a
		697	single, composite, request with a definite callback and the ability to
		698	cancel the whole request with its subrequests and b) limiting the number
		699	of "active" requests.
		700
		701	Further below you will find more discussion of these topics - first
		702	follows the reference section detailing the request generator and other
		703	methods.
		704
		705	=over 4
		706
		707	=item eio_req grp = eio_grp (eio_cb cb, void data)
		708
		709	Creates, submits and returns a group request. Note that it doesn't have a
		710	priority, unlike all other requests.
		711
		712	=item eio_grp_add (eio_req grp, eio_req req)
		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->errorno >> 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 real 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
		786
		787
573	#TODO	788	#TODO
574		789
575	/*****************************************************************************/
576	/* groups */
577
578	eio_req eio_grp (eio_cb cb, void data);
579	void eio_grp_feed (eio_req grp, void (feed)(eio_req *req), int limit);
580	void eio_grp_limit (eio_req *grp, int limit);	790	void eio_grp_limit (eio_req *grp, int limit);
581	void eio_grp_add (eio_req grp, eio_req req);
582	void eio_grp_cancel (eio_req grp); / cancels all sub requests but not the group */
583		791
584		792
585	=back	793	=back
586		794
587		795
…		…
593	=head1 ANATOMY AND LIFETIME OF AN EIO REQUEST	801	=head1 ANATOMY AND LIFETIME OF AN EIO REQUEST
594		802
595	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
596	it, clear it to all zero bytes:	804	it, clear it to all zero bytes:
597		805
598	eio_req req;	806	eio_req req;
599		807
600	memset (&req, 0, sizeof (req));	808	memset (&req, 0, sizeof (req));
601		809
602	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>:
603		811
604	eio_req req = calloc (1, sizeof (req));	812	eio_req req = calloc (1, sizeof (req));
605		813
606	In either case, libeio neither allocates, initialises or frees the	814	In either case, libeio neither allocates, initialises or frees the
607	C<eio_req> structure for you - it merely uses it.	815	C<eio_req> structure for you - it merely uses it.
608		816
609	zero	817	zero
…		…
627	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
628	C<0.01> seconds or so.	836	C<0.01> seconds or so.
629		837
630	Note that:	838	Note that:
631		839
		840	=over 4
		841
632	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
633	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
634	interval.	844	this interval.
635		845
636	b) this is implemented by calling C<gettimeofday> after each request,	846	=item b) this is implemented by calling C<gettimeofday> after each
637	which can be costly.	847	request, which can be costly.
638		848
639	c) at least one request will be handled.	849	=item c) at least one request will be handled.
		850
		851	=back
640		852
641	=item eio_set_max_poll_reqs (unsigned int nreqs)	853	=item eio_set_max_poll_reqs (unsigned int nreqs)
642		854
643	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
644	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
…		…
714	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
715	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>
716	requests, you might want to increase this.	928	requests, you might want to increase this.
717		929
718	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
719	stack size (C<sizeof (long) * 4096> currently). If it is defined, but	931	stack size (C<sizeof (void ) 4096> currently). If it is defined, but
720	C<0>, then the default operating system stack size will be used. In all	932	C<0>, then the default operating system stack size will be used. In all
721	other cases, the value must be an expression that evaluates to the desired	933	other cases, the value must be an expression that evaluates to the desired
722	stack size.	934	stack size.
723		935
724	=back	936	=back

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Comparing libeio/eio.pod (file contents): Revision 1.10 by root, Sun Jun 5 23:22:04 2011 UTC vs. Revision 1.29 by sf-exg, Mon Sep 26 17:10:10 2011 UTC

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Comparing libeio/eio.pod (file contents):
Revision 1.10 by root, Sun Jun 5 23:22:04 2011 UTC vs.
Revision 1.29 by sf-exg, Mon Sep 26 17:10:10 2011 UTC