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

Comparing libeio/eio.pod (file contents):
Revision 1.8 by root, Sun Jun 5 22:45:49 2011 UTC vs.
Revision 1.27 by root, Sun Jul 24 03:32:54 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
…		…
210	}	267	}
211		268
212	/* the first three arguments are passed to open(2) */	269	/* the first three arguments are passed to open(2) */
213	/* the remaining are priority, callback and data */	270	/* the remaining are priority, callback and data */
214	if (!eio_open ("/etc/passwd", O_RDONLY, 0, 0, file_open_done, 0))	271	if (!eio_open ("/etc/passwd", O_RDONLY, 0, 0, file_open_done, 0))
215	abort (); /* something ent wrong, we will all die!!! */	272	abort (); /* something went wrong, we will all die!!! */
216		273
217	Note that you additionally need to call C<eio_poll> when the C<want_cb>	274	Note that you additionally need to call C<eio_poll> when the C<want_cb>
218	indicates that requests are ready to be processed.	275	indicates that requests are ready to be processed.
		276
		277	=head2 CANCELLING REQUESTS
		278
		279	Sometimes the need for a request goes away before the request is
		280	finished. In that case, one can cancel the request by a call to
		281	C<eio_cancel>:
		282
		283	=over 4
		284
		285	=item eio_cancel (eio_req *req)
		286
		287	Cancel the request (and all its subrequests). If the request is currently
		288	executing it might still continue to execute, and in other cases it might
		289	still take a while till the request is cancelled.
		290
		291	Even if cancelled, the finish callback will still be invoked - the
		292	callbacks of all cancellable requests need to check whether the request
		293	has been cancelled by calling C<EIO_CANCELLED (req)>:
		294
		295	static int
		296	my_eio_cb (eio_req *req)
		297	{
		298	if (EIO_CANCELLED (req))
		299	return 0;
		300	}
		301
		302	In addition, cancelled requests will I<either> have C<< req->result >>
		303	set to C<-1> and C<errno> to C<ECANCELED>, or I<otherwise> they were
		304	successfully executed, despite being cancelled (e.g. when they have
		305	already been executed at the time they were cancelled).
		306
		307	C<EIO_CANCELLED> is still true for requests that have successfully
		308	executed, as long as C<eio_cancel> was called on them at some point.
		309
		310	=back
219		311
220	=head2 AVAILABLE REQUESTS	312	=head2 AVAILABLE REQUESTS
221		313
222	The following request functions are available. I<All> of them return the	314	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	315	C<eio_req *> on success and C<0> on failure, and I<all> of them have the
…		…
226	custom data value as C<data>.	318	custom data value as C<data>.
227		319
228	=head3 POSIX API WRAPPERS	320	=head3 POSIX API WRAPPERS
229		321
230	These requests simply wrap the POSIX call of the same name, with the same	322	These requests simply wrap the POSIX call of the same name, with the same
231	arguments:	323	arguments. If a function is not implemented by the OS and cannot be emulated
		324	in some way, then all of these return C<-1> and set C<errorno> to C<ENOSYS>.
232		325
233	=over 4	326	=over 4
234		327
235	=item eio_open (const char path, int flags, mode_t mode, int pri, eio_cb cb, void data)	328	=item eio_open (const char path, int flags, mode_t mode, int pri, eio_cb cb, void data)
236		329
		330	=item eio_truncate (const char path, off_t offset, int pri, eio_cb cb, void data)
		331
		332	=item eio_chown (const char path, uid_t uid, gid_t gid, int pri, eio_cb cb, void data)
		333
		334	=item eio_chmod (const char path, mode_t mode, int pri, eio_cb cb, void data)
		335
		336	=item eio_mkdir (const char path, mode_t mode, int pri, eio_cb cb, void data)
		337
		338	=item eio_rmdir (const char path, int pri, eio_cb cb, void data)
		339
		340	=item eio_unlink (const char path, int pri, eio_cb cb, void data)
		341
237	=item eio_utime (const char path, eio_tstamp atime, eio_tstamp mtime, int pri, eio_cb cb, void data)	342	=item eio_utime (const char path, eio_tstamp atime, eio_tstamp mtime, int pri, eio_cb cb, void data)
238		343
239	=item eio_truncate (const char path, off_t offset, int pri, eio_cb cb, void data)
240
241	=item eio_chown (const char path, uid_t uid, gid_t gid, int pri, eio_cb cb, void data)
242
243	=item eio_chmod (const char path, mode_t mode, int pri, eio_cb cb, void data)
244
245	=item eio_mkdir (const char path, mode_t mode, int pri, eio_cb cb, void data)
246
247	=item eio_rmdir (const char path, int pri, eio_cb cb, void data)
248
249	=item eio_unlink (const char path, int pri, eio_cb cb, void data)
250
251	=item eio_readlink (const char path, int pri, eio_cb cb, void data) /* result=ptr2 allocated dynamically */
252
253	=item eio_stat (const char path, int pri, eio_cb cb, void data) /* stat buffer=ptr2 allocated dynamically */
254
255	=item eio_lstat (const char path, int pri, eio_cb cb, void data) /* stat buffer=ptr2 allocated dynamically */
256
257	=item eio_statvfs (const char path, int pri, eio_cb cb, void data) /* stat buffer=ptr2 allocated dynamically */
258
259	=item eio_mknod (const char path, mode_t mode, dev_t dev, int pri, eio_cb cb, void data)	344	=item eio_mknod (const char path, mode_t mode, dev_t dev, int pri, eio_cb cb, void data)
260		345
261	=item eio_link (const char path, const char new_path, int pri, eio_cb cb, void *data)	346	=item eio_link (const char path, const char new_path, int pri, eio_cb cb, void *data)
262		347
263	=item eio_symlink (const char path, const char new_path, int pri, eio_cb cb, void *data)	348	=item eio_symlink (const char path, const char new_path, int pri, eio_cb cb, void *data)
264		349
265	=item eio_rename (const char path, const char new_path, int pri, eio_cb cb, void *data)	350	=item eio_rename (const char path, const char new_path, int pri, eio_cb cb, void *data)
266		351
267	=item eio_msync (void addr, size_t length, int flags, int pri, eio_cb cb, void data)
268
269	=item eio_mlock (void addr, size_t length, int pri, eio_cb cb, void data)	352	=item eio_mlock (void addr, size_t length, int pri, eio_cb cb, void data)
270
271	=item eio_mlockall (int flags, int pri, eio_cb cb, void *data)
272		353
273	=item eio_close (int fd, int pri, eio_cb cb, void *data)	354	=item eio_close (int fd, int pri, eio_cb cb, void *data)
274		355
275	=item eio_sync (int pri, eio_cb cb, void *data)	356	=item eio_sync (int pri, eio_cb cb, void *data)
276		357
…		…
305		386
306	Not surprisingly, pread and pwrite are not thread-safe on Darwin (OS/X),	387	Not surprisingly, pread and pwrite are not thread-safe on Darwin (OS/X),
307	so it is advised not to submit multiple requests on the same fd on this	388	so it is advised not to submit multiple requests on the same fd on this
308	horrible pile of garbage.	389	horrible pile of garbage.
309		390
		391	=item eio_mlockall (int flags, int pri, eio_cb cb, void *data)
		392
		393	Like C<mlockall>, but the flag value constants are called
		394	C<EIO_MCL_CURRENT> and C<EIO_MCL_FUTURE>.
		395
		396	=item eio_msync (void addr, size_t length, int flags, int pri, eio_cb cb, void data)
		397
		398	Just like msync, except that the flag values are called C<EIO_MS_ASYNC>,
		399	C<EIO_MS_INVALIDATE> and C<EIO_MS_SYNC>.
		400
		401	=item eio_readlink (const char path, int pri, eio_cb cb, void data)
		402
		403	If successful, the path read by C<readlink(2)> can be accessed via C<<
		404	req->ptr2 >> and is I<NOT> null-terminated, with the length specified as
		405	C<< req->result >>.
		406
		407	if (req->result >= 0)
		408	{
		409	char target = strndup ((char )req->ptr2, req->result);
		410
		411	free (target);
		412	}
		413
		414	=item eio_realpath (const char path, int pri, eio_cb cb, void data)
		415
		416	Similar to the realpath libc function, but unlike that one, C<<
		417	req->result >> is C<-1> on failure. On success, the result is the length
		418	of the returned path in C<ptr2> (which is I<NOT> 0-terminated) - this is
		419	similar to readlink.
		420
		421	=item eio_stat (const char path, int pri, eio_cb cb, void data)
		422
		423	=item eio_lstat (const char path, int pri, eio_cb cb, void data)
		424
310	=item eio_fstat (int fd, int pri, eio_cb cb, void *data)	425	=item eio_fstat (int fd, int pri, eio_cb cb, void *data)
311		426
312	Stats a file - if C<< req->result >> indicates success, then you can	427	Stats a file - if C<< req->result >> indicates success, then you can
313	access the C<struct stat>-like structure via C<< req->ptr2 >>:	428	access the C<struct stat>-like structure via C<< req->ptr2 >>:
314		429
315	EIO_STRUCT_STAT statdata = (EIO_STRUCT_STAT )req->ptr2;	430	EIO_STRUCT_STAT statdata = (EIO_STRUCT_STAT )req->ptr2;
316		431
317	=item eio_fstatvfs (int fd, int pri, eio_cb cb, void data) / stat buffer=ptr2 allocated dynamically */	432	=item eio_statvfs (const char path, int pri, eio_cb cb, void data)
		433
		434	=item eio_fstatvfs (int fd, int pri, eio_cb cb, void *data)
318		435
319	Stats a filesystem - if C<< req->result >> indicates success, then you can	436	Stats a filesystem - if C<< req->result >> indicates success, then you can
320	access the C<struct statvfs>-like structure via C<< req->ptr2 >>:	437	access the C<struct statvfs>-like structure via C<< req->ptr2 >>:
321		438
322	EIO_STRUCT_STATVFS statdata = (EIO_STRUCT_STATVFS )req->ptr2;	439	EIO_STRUCT_STATVFS statdata = (EIO_STRUCT_STATVFS )req->ptr2;
323		440
324	=back	441	=back
325		442
326	=head3 READING DIRECTORIES	443	=head3 READING DIRECTORIES
327		444
328	Reading directories sounds simple, but can be rather demanding, especially	445	Reading directories sounds simple, but can be rather demanding, especially
329	if you want to do stuff such as traversing a diretcory hierarchy or	446	if you want to do stuff such as traversing a directory hierarchy or
330	processing all files in a directory. Libeio can assist thess complex tasks	447	processing all files in a directory. Libeio can assist these complex tasks
331	with it's C<eio_readdir> call.	448	with it's C<eio_readdir> call.
332		449
333	=over 4	450	=over 4
334		451
335	=item eio_readdir (const char path, int flags, int pri, eio_cb cb, void data)	452	=item eio_readdir (const char path, int flags, int pri, eio_cb cb, void data)
…		…
338	(via the C<opendir>, C<readdir> and C<closedir> calls) and returns either	455	(via the C<opendir>, C<readdir> and C<closedir> calls) and returns either
339	the names or an array of C<struct eio_dirent>, depending on the C<flags>	456	the names or an array of C<struct eio_dirent>, depending on the C<flags>
340	argument.	457	argument.
341		458
342	The C<< req->result >> indicates either the number of files found, or	459	The C<< req->result >> indicates either the number of files found, or
343	C<-1> on error. On success, zero-terminated names can be found as C<< req->ptr2 >>,	460	C<-1> on error. On success, null-terminated names can be found as C<< req->ptr2 >>,
344	and C<struct eio_dirents>, if requested by C<flags>, can be found via C<<	461	and C<struct eio_dirents>, if requested by C<flags>, can be found via C<<
345	req->ptr1 >>.	462	req->ptr1 >>.
346		463
347	Here is an example that prints all the names:	464	Here is an example that prints all the names:
348		465
…		…
367		484
368	If this flag is specified, then, in addition to the names in C<ptr2>,	485	If this flag is specified, then, in addition to the names in C<ptr2>,
369	also an array of C<struct eio_dirent> is returned, in C<ptr1>. A C<struct	486	also an array of C<struct eio_dirent> is returned, in C<ptr1>. A C<struct
370	eio_dirent> looks like this:	487	eio_dirent> looks like this:
371		488
372	struct eio_dirent	489	struct eio_dirent
373	{	490	{
374	int nameofs; /* offset of null-terminated name string in (char )req->ptr2 /	491	int nameofs; /* offset of null-terminated name string in (char )req->ptr2 /
375	unsigned short namelen; /* size of filename without trailing 0 */	492	unsigned short namelen; /* size of filename without trailing 0 */
376	unsigned char type; /* one of EIO_DT_* */	493	unsigned char type; /* one of EIO_DT_* */
377	signed char score; /* internal use */	494	signed char score; /* internal use */
378	ino_t inode; /* the inode number, if available, otherwise unspecified */	495	ino_t inode; /* the inode number, if available, otherwise unspecified */
379	};	496	};
380		497
381	The only members you normally would access are C<nameofs>, which is the	498	The only members you normally would access are C<nameofs>, which is the
382	byte-offset from C<ptr2> to the start of the name, C<namelen> and C<type>.	499	byte-offset from C<ptr2> to the start of the name, C<namelen> and C<type>.
383		500
384	C<type> can be one of:	501	C<type> can be one of:
…		…
427	When this flag is specified, then the names will be returned in an order	544	When this flag is specified, then the names will be returned in an order
428	suitable for stat()'ing each one. That is, when you plan to stat()	545	suitable for stat()'ing each one. That is, when you plan to stat()
429	all files in the given directory, then the returned order will likely	546	all files in the given directory, then the returned order will likely
430	be fastest.	547	be fastest.
431		548
432	If both this flag and C<EIO_READDIR_DIRS_FIRST> are specified, then	549	If both this flag and C<EIO_READDIR_DIRS_FIRST> are specified, then the
433	the likely dirs come first, resulting in a less optimal stat order.	550	likely directories come first, resulting in a less optimal stat order.
434		551
435	=item EIO_READDIR_FOUND_UNKNOWN	552	=item EIO_READDIR_FOUND_UNKNOWN
436		553
437	This flag should not be specified when calling C<eio_readdir>. Instead,	554	This flag should not be specified when calling C<eio_readdir>. Instead,
438	it is being set by C<eio_readdir> (you can access the C<flags> via C<<	555	it is being set by C<eio_readdir> (you can access the C<flags> via C<<
439	req->int1 >>, when any of the C<type>'s found were C<EIO_DT_UNKNOWN>. The	556	req->int1 >>, when any of the C<type>'s found were C<EIO_DT_UNKNOWN>. The
440	absense of this flag therefore indicates that all C<type>'s are known,	557	absence of this flag therefore indicates that all C<type>'s are known,
441	which can be used to speed up some algorithms.	558	which can be used to speed up some algorithms.
442		559
443	A typical use case would be to identify all subdirectories within a	560	A typical use case would be to identify all subdirectories within a
444	directory - you would ask C<eio_readdir> for C<EIO_READDIR_DIRS_FIRST>. If	561	directory - you would ask C<eio_readdir> for C<EIO_READDIR_DIRS_FIRST>. If
445	then this flag is I<NOT> set, then all the entries at the beginning of the	562	then this flag is I<NOT> set, then all the entries at the beginning of the
…		…
475	=item eio_readahead (int fd, off_t offset, size_t length, int pri, eio_cb cb, void *data)	592	=item eio_readahead (int fd, off_t offset, size_t length, int pri, eio_cb cb, void *data)
476		593
477	Calls C<readahead(2)>. If the syscall is missing, then the call is	594	Calls C<readahead(2)>. If the syscall is missing, then the call is
478	emulated by simply reading the data (currently in 64kiB chunks).	595	emulated by simply reading the data (currently in 64kiB chunks).
479		596
		597	=item eio_syncfs (int fd, int pri, eio_cb cb, void *data)
		598
		599	Calls Linux' C<syncfs> syscall, if available. Returns C<-1> and sets
		600	C<errno> to C<ENOSYS> if the call is missing I<but still calls sync()>,
		601	if the C<fd> is C<< >= 0 >>, so you can probe for the availability of the
		602	syscall with a negative C<fd> argument and checking for C<-1/ENOSYS>.
		603
480	=item eio_sync_file_range (int fd, off_t offset, size_t nbytes, unsigned int flags, int pri, eio_cb cb, void *data)	604	=item eio_sync_file_range (int fd, off_t offset, size_t nbytes, unsigned int flags, int pri, eio_cb cb, void *data)
481		605
482	Calls C<sync_file_range>. If the syscall is missing, then this is the same	606	Calls C<sync_file_range>. If the syscall is missing, then this is the same
483	as calling C<fdatasync>.	607	as calling C<fdatasync>.
484		608
		609	Flags can be any combination of C<EIO_SYNC_FILE_RANGE_WAIT_BEFORE>,
		610	C<EIO_SYNC_FILE_RANGE_WRITE> and C<EIO_SYNC_FILE_RANGE_WAIT_AFTER>.
		611
		612	=item eio_fallocate (int fd, int mode, off_t offset, off_t len, int pri, eio_cb cb, void *data)
		613
		614	Calls C<fallocate> (note: I<NOT> C<posix_fallocate>!). If the syscall is
		615	missing, then it returns failure and sets C<errno> to C<ENOSYS>.
		616
		617	The C<mode> argument can be C<0> (for behaviour similar to
		618	C<posix_fallocate>), or C<EIO_FALLOC_FL_KEEP_SIZE>, which keeps the size
		619	of the file unchanged (but still preallocates space beyond end of file).
		620
485	=back	621	=back
486		622
487	=head3 LIBEIO-SPECIFIC REQUESTS	623	=head3 LIBEIO-SPECIFIC REQUESTS
488		624
489	These requests are specific to libeio and do not correspond to any OS call.	625	These requests are specific to libeio and do not correspond to any OS call.
490		626
491	=over 4	627	=over 4
492		628
493	=item eio_mtouch (void addr, size_t length, int flags, int pri, eio_cb cb, void data)	629	=item eio_mtouch (void addr, size_t length, int flags, int pri, eio_cb cb, void data)
494		630
		631	Reads (C<flags == 0>) or modifies (C<flags == EIO_MT_MODIFY) the given
		632	memory area, page-wise, that is, it reads (or reads and writes back) the
		633	first octet of every page that spans the memory area.
		634
		635	This can be used to page in some mmapped file, or dirty some pages. Note
		636	that dirtying is an unlocked read-write access, so races can ensue when
		637	the some other thread modifies the data stored in that memory area.
		638
495	=item eio_custom (void ()(eio_req ) execute, int pri, eio_cb cb, void *data)	639	=item eio_custom (void ()(eio_req ) execute, int pri, eio_cb cb, void *data)
496		640
497	Executes a custom request, i.e., a user-specified callback.	641	Executes a custom request, i.e., a user-specified callback.
498		642
499	The callback gets the C<eio_req *> as parameter and is expected to read	643	The callback gets the C<eio_req *> as parameter and is expected to read
500	and modify any request-specific members. Specifically, it should set C<<	644	and modify any request-specific members. Specifically, it should set C<<
…		…
520	req->result = open (req->data, O_RDONLY);	664	req->result = open (req->data, O_RDONLY);
521	}	665	}
522		666
523	eio_custom (my_open, 0, my_open_done, "/etc/passwd");	667	eio_custom (my_open, 0, my_open_done, "/etc/passwd");
524		668
525	=item eio_busy (eio_tstamp delay, int pri, eio_cb cb, void *data)	669	=item eio_busy (eio_tstamp delay, int pri, eio_cb cb, void *data)
526		670
527	This is a a request that takes C<delay> seconds to execute, but otherwise	671	This is a request that takes C<delay> seconds to execute, but otherwise
528	does nothing - it simply puts one of the worker threads to sleep for this	672	does nothing - it simply puts one of the worker threads to sleep for this
529	long.	673	long.
530		674
531	This request can be used to artificially increase load, e.g. for debugging	675	This request can be used to artificially increase load, e.g. for debugging
532	or benchmarking reasons.	676	or benchmarking reasons.
533		677
534	=item eio_nop (int pri, eio_cb cb, void *data)	678	=item eio_nop (int pri, eio_cb cb, void *data)
535		679
536	This request does nothing, except go through the whole request cycle. This	680	This request does nothing, except go through the whole request cycle. This
537	can be used to measure latency or in some cases to simplify code, but is	681	can be used to measure latency or in some cases to simplify code, but is
538	not really of much use.	682	not really of much use.
539		683
540	=back	684	=back
541		685
542	=head3 GROUPING AND LIMITING REQUESTS	686	=head3 GROUPING AND LIMITING REQUESTS
543		687
		688	There is one more rather special request, C<eio_grp>. It is a very special
		689	aio request: Instead of doing something, it is a container for other eio
		690	requests.
		691
		692	There are two primary use cases for this: a) bundle many requests into a
		693	single, composite, request with a definite callback and the ability to
		694	cancel the whole request with its subrequests and b) limiting the number
		695	of "active" requests.
		696
		697	Further below you will find more discussion of these topics - first
		698	follows the reference section detailing the request generator and other
		699	methods.
		700
		701	=over 4
		702
		703	=item eio_req grp = eio_grp (eio_cb cb, void data)
		704
		705	Creates, submits and returns a group request. Note that it doesn't have a
		706	priority, unlike all other requests.
		707
		708	=item eio_grp_add (eio_req grp, eio_req req)
		709
		710	Adds a request to the request group.
		711
		712	=item eio_grp_cancel (eio_req *grp)
		713
		714	Cancels all requests I<in> the group, but I<not> the group request
		715	itself. You can cancel the group request I<and> all subrequests via a
		716	normal C<eio_cancel> call.
		717
		718	=back
		719
		720	=head4 GROUP REQUEST LIFETIME
		721
		722	Left alone, a group request will instantly move to the pending state and
		723	will be finished at the next call of C<eio_poll>.
		724
		725	The usefulness stems from the fact that, if a subrequest is added to a
		726	group I<before> a call to C<eio_poll>, via C<eio_grp_add>, then the group
		727	will not finish until all the subrequests have finished.
		728
		729	So the usage cycle of a group request is like this: after it is created,
		730	you normally instantly add a subrequest. If none is added, the group
		731	request will finish on it's own. As long as subrequests are added before
		732	the group request is finished it will be kept from finishing, that is the
		733	callbacks of any subrequests can, in turn, add more requests to the group,
		734	and as long as any requests are active, the group request itself will not
		735	finish.
		736
		737	=head4 CREATING COMPOSITE REQUESTS
		738
		739	Imagine you wanted to create an C<eio_load> request that opens a file,
		740	reads it and closes it. This means it has to execute at least three eio
		741	requests, but for various reasons it might be nice if that request looked
		742	like any other eio request.
		743
		744	This can be done with groups:
		745
		746	=over 4
		747
		748	=item 1) create the request object
		749
		750	Create a group that contains all further requests. This is the request you
		751	can return as "the load request".
		752
		753	=item 2) open the file, maybe
		754
		755	Next, open the file with C<eio_open> and add the request to the group
		756	request and you are finished setting up the request.
		757
		758	If, for some reason, you cannot C<eio_open> (path is a null ptr?) you
		759	can set C<< grp->result >> to C<-1> to signal an error and let the group
		760	request finish on its own.
		761
		762	=item 3) open callback adds more requests
		763
		764	In the open callback, if the open was not successful, copy C<<
		765	req->errorno >> to C<< grp->errorno >> and set C<< grp->errorno >> to
		766	C<-1> to signal an error.
		767
		768	Otherwise, malloc some memory or so and issue a read request, adding the
		769	read request to the group.
		770
		771	=item 4) continue issuing requests till finished
		772
		773	In the real callback, check for errors and possibly continue with
		774	C<eio_close> or any other eio request in the same way.
		775
		776	As soon as no new requests are added the group request will finish. Make
		777	sure you I<always> set C<< grp->result >> to some sensible value.
		778
		779	=back
		780
		781	=head4 REQUEST LIMITING
		782
		783
544	#TODO	784	#TODO
545		785
546	/*****************************************************************************/
547	/* groups */
548
549	eio_req eio_grp (eio_cb cb, void data);
550	void eio_grp_feed (eio_req grp, void (feed)(eio_req *req), int limit);
551	void eio_grp_limit (eio_req *grp, int limit);	786	void eio_grp_limit (eio_req *grp, int limit);
552	void eio_grp_add (eio_req grp, eio_req req);
553	void eio_grp_cancel (eio_req grp); / cancels all sub requests but not the group */
554		787
555		788
556	=back	789	=back
557		790
558		791
…		…
564	=head1 ANATOMY AND LIFETIME OF AN EIO REQUEST	797	=head1 ANATOMY AND LIFETIME OF AN EIO REQUEST
565		798
566	A request is represented by a structure of type C<eio_req>. To initialise	799	A request is represented by a structure of type C<eio_req>. To initialise
567	it, clear it to all zero bytes:	800	it, clear it to all zero bytes:
568		801
569	eio_req req;	802	eio_req req;
570		803
571	memset (&req, 0, sizeof (req));	804	memset (&req, 0, sizeof (req));
572		805
573	A more common way to initialise a new C<eio_req> is to use C<calloc>:	806	A more common way to initialise a new C<eio_req> is to use C<calloc>:
574		807
575	eio_req req = calloc (1, sizeof (req));	808	eio_req req = calloc (1, sizeof (req));
576		809
577	In either case, libeio neither allocates, initialises or frees the	810	In either case, libeio neither allocates, initialises or frees the
578	C<eio_req> structure for you - it merely uses it.	811	C<eio_req> structure for you - it merely uses it.
579		812
580	zero	813	zero
…		…
598	for example, in interactive programs, you might want to limit this time to	831	for example, in interactive programs, you might want to limit this time to
599	C<0.01> seconds or so.	832	C<0.01> seconds or so.
600		833
601	Note that:	834	Note that:
602		835
		836	=over 4
		837
603	a) libeio doesn't know how long your request callbacks take, so the time	838	=item a) libeio doesn't know how long your request callbacks take, so the
604	spent in C<eio_poll> is up to one callback invocation longer then this	839	time spent in C<eio_poll> is up to one callback invocation longer then
605	interval.	840	this interval.
606		841
607	b) this is implemented by calling C<gettimeofday> after each request,	842	=item b) this is implemented by calling C<gettimeofday> after each
608	which can be costly.	843	request, which can be costly.
609		844
610	c) at least one request will be handled.	845	=item c) at least one request will be handled.
		846
		847	=back
611		848
612	=item eio_set_max_poll_reqs (unsigned int nreqs)	849	=item eio_set_max_poll_reqs (unsigned int nreqs)
613		850
614	When C<nreqs> is non-zero, then C<eio_poll> will not handle more than	851	When C<nreqs> is non-zero, then C<eio_poll> will not handle more than
615	C<nreqs> requests per invocation. This is a less costly way to limit the	852	C<nreqs> requests per invocation. This is a less costly way to limit the
…		…
685	This symbol governs the stack size for each eio thread. Libeio itself	922	This symbol governs the stack size for each eio thread. Libeio itself
686	was written to use very little stackspace, but when using C<EIO_CUSTOM>	923	was written to use very little stackspace, but when using C<EIO_CUSTOM>
687	requests, you might want to increase this.	924	requests, you might want to increase this.
688		925
689	If this symbol is undefined (the default) then libeio will use its default	926	If this symbol is undefined (the default) then libeio will use its default
690	stack size (C<sizeof (long) * 4096> currently). If it is defined, but	927	stack size (C<sizeof (void ) 4096> currently). If it is defined, but
691	C<0>, then the default operating system stack size will be used. In all	928	C<0>, then the default operating system stack size will be used. In all
692	other cases, the value must be an expression that evaluates to the desired	929	other cases, the value must be an expression that evaluates to the desired
693	stack size.	930	stack size.
694		931
695	=back	932	=back

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Comparing libeio/eio.pod (file contents): Revision 1.8 by root, Sun Jun 5 22:45:49 2011 UTC vs. Revision 1.27 by root, Sun Jul 24 03:32:54 2011 UTC

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Comparing libeio/eio.pod (file contents):
Revision 1.8 by root, Sun Jun 5 22:45:49 2011 UTC vs.
Revision 1.27 by root, Sun Jul 24 03:32:54 2011 UTC