[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 1.18 by root, Tue Jul 5 20:34:42 2011 UTC

…		…
45	Unlike the name component C<stamp> might indicate, it is also used for	45	Unlike the name component C<stamp> might indicate, it is also used for
46	time differences throughout libeio.	46	time differences throughout libeio.
47		47
48	=head2 FORK SUPPORT	48	=head2 FORK SUPPORT
49		49
50	Calling C<fork ()> is fully supported by this module. It is implemented in these steps:	50	Calling C<fork ()> is fully supported by this module - but you must not
		51	rely on this. It is currently implemented in these steps:
51		52
52	1. wait till all requests in "execute" state have been handled	53	1. wait till all requests in "execute" state have been handled
53	(basically requests that are already handed over to the kernel).	54	(basically requests that are already handed over to the kernel).
54	2. fork	55	2. fork
55	3. in the parent, continue business as usual, done	56	3. in the parent, continue business as usual, done
56	4. in the child, destroy all ready and pending requests and free the	57	4. in the child, destroy all ready and pending requests and free the
57	memory used by the worker threads. This gives you a fully empty	58	memory used by the worker threads. This gives you a fully empty
58	libeio queue.	59	libeio queue.
59		60
60	Note, however, since libeio does use threads, thr above guarantee doesn't	61	Note, however, since libeio does use threads, the above guarantee doesn't
61	cover your libc, for example, malloc and other libc functions are not	62	cover your libc, for example, malloc and other libc functions are not
62	fork-safe, so there is very little you can do after a fork, and in fatc,	63	fork-safe, so there is very little you can do after a fork, and in fact,
63	the above might crash, and thus change.	64	the above might crash, and thus change.
64		65
65	=head1 INITIALISATION/INTEGRATION	66	=head1 INITIALISATION/INTEGRATION
66		67
67	Before you can call any eio functions you first have to initialise the	68	Before you can call any eio functions you first have to initialise the
…		…
124	=back	125	=back
125		126
126	For libev, you would typically use an C<ev_async> watcher: the	127	For libev, you would typically use an C<ev_async> watcher: the
127	C<want_poll> callback would invoke C<ev_async_send> to wake up the event	128	C<want_poll> callback would invoke C<ev_async_send> to wake up the event
128	loop. Inside the callback set for the watcher, one would call C<eio_poll	129	loop. Inside the callback set for the watcher, one would call C<eio_poll
129	()> (followed by C<ev_async_send> again if C<eio_poll> indicates that not	130	()>.
130	all requests have been handled yet). The race is taken care of because	131
131	libev resets/rearms the async watcher before calling your callback,	132	If C<eio_poll ()> is configured to not handle all results in one go
132	and therefore, before calling C<eio_poll>. This might result in (some)	133	(i.e. it returns C<-1>) then you should start an idle watcher that calls
133	spurious wake-ups, but is generally harmless.	134	C<eio_poll> until it returns something C<!= -1>.
		135
		136	A full-featured conenctor between libeio and libev would look as follows
		137	(if C<eio_poll> is handling all requests, it can of course be simplified a
		138	lot by removing the idle watcher logic):
		139
		140	static struct ev_loop *loop;
		141	static ev_idle repeat_watcher;
		142	static ev_async ready_watcher;
		143
		144	/* idle watcher callback, only used when eio_poll */
		145	/* didn't handle all results in one call */
		146	static void
		147	repeat (EV_P_ ev_idle *w, int revents)
		148	{
		149	if (eio_poll () != -1)
		150	ev_idle_stop (EV_A_ w);
		151	}
		152
		153	/* eio has some results, process them */
		154	static void
		155	ready (EV_P_ ev_async *w, int revents)
		156	{
		157	if (eio_poll () == -1)
		158	ev_idle_start (EV_A_ &repeat_watcher);
		159	}
		160
		161	/* wake up the event loop */
		162	static void
		163	want_poll (void)
		164	{
		165	ev_async_send (loop, &ready_watcher)
		166	}
		167
		168	void
		169	my_init_eio ()
		170	{
		171	loop = EV_DEFAULT;
		172
		173	ev_idle_init (&repeat_watcher, repeat);
		174	ev_async_init (&ready_watcher, ready);
		175	ev_async_start (loop &watcher);
		176
		177	eio_init (want_poll, 0);
		178	}
134		179
135	For most other event loops, you would typically use a pipe - the event	180	For most other event loops, you would typically use a pipe - the event
136	loop should be told to wait for read readiness on the read end. In	181	loop should be told to wait for read readiness on the read end. In
137	C<want_poll> you would write a single byte, in C<done_poll> you would try	182	C<want_poll> you would write a single byte, in C<done_poll> you would try
138	to read that byte, and in the callback for the read end, you would call	183	to read that byte, and in the callback for the read end, you would call
139	C<eio_poll>. The race is avoided here because the event loop should invoke	184	C<eio_poll>.
140	your callback again and again until the byte has been read (as the pipe	185
141	read callback does not read it, only C<done_poll>).	186	You don't have to take special care in the case C<eio_poll> doesn't handle
		187	all requests, as the done callback will not be invoked, so the event loop
		188	will still signal readiness for the pipe until I<all> results have been
		189	processed.
142		190
143		191
144	=head1 HIGH LEVEL REQUEST API	192	=head1 HIGH LEVEL REQUEST API
145		193
146	Libeio has both a high-level API, which consists of calling a request	194	Libeio has both a high-level API, which consists of calling a request
…		…
153		201
154	You submit a request by calling the relevant C<eio_TYPE> function with the	202	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)>	203	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.	204	(called C<eio_cb> below) and a freely usable C<void *data> argument.
157		205
158	The return value will either be 0	206	The return value will either be 0, in case something went really wrong
		207	(which can basically only happen on very fatal errors, such as C<malloc>
		208	returning 0, which is rather unlikely), or a pointer to the newly-created
		209	and submitted C<eio_req *>.
159		210
160	The callback will be called with an C<eio_req *> which contains the	211	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	212	results of the request. The members you can access inside that structure
162	vary from request to request, except for:	213	vary from request to request, except for:
163		214
…		…
210	}	261	}
211		262
212	/* the first three arguments are passed to open(2) */	263	/* the first three arguments are passed to open(2) */
213	/* the remaining are priority, callback and data */	264	/* the remaining are priority, callback and data */
214	if (!eio_open ("/etc/passwd", O_RDONLY, 0, 0, file_open_done, 0))	265	if (!eio_open ("/etc/passwd", O_RDONLY, 0, 0, file_open_done, 0))
215	abort (); /* something ent wrong, we will all die!!! */	266	abort (); /* something went wrong, we will all die!!! */
216		267
217	Note that you additionally need to call C<eio_poll> when the C<want_cb>	268	Note that you additionally need to call C<eio_poll> when the C<want_cb>
218	indicates that requests are ready to be processed.	269	indicates that requests are ready to be processed.
		270
		271	=head2 CANCELLING REQUESTS
		272
		273	Sometimes the need for a request goes away before the request is
		274	finished. In that case, one can cancel the request by a call to
		275	C<eio_cancel>:
		276
		277	=over 4
		278
		279	=item eio_cancel (eio_req *req)
		280
		281	Cancel the request (and all it's subrequests). If the request is currently
		282	executing it might still continue to execute, and in other cases it might
		283	still take a while till the request is cancelled.
		284
		285	Even if cancelled, the finish callback will still be invoked - the
		286	callbacks of all cancellable requests need to check whether the request
		287	has been cancelled by calling C<EIO_CANCELLED (req)>:
		288
		289	static int
		290	my_eio_cb (eio_req *req)
		291	{
		292	if (EIO_CANCELLED (req))
		293	return 0;
		294	}
		295
		296	In addition, cancelled requests will I<either> have C<< req->result >>
		297	set to C<-1> and C<errno> to C<ECANCELED>, or I<otherwise> they were
		298	successfully executed, despite being cancelled (e.g. when they have
		299	already been executed at the time they were cancelled).
		300
		301	C<EIO_CANCELLED> is still true for requests that have successfully
		302	executed, as long as C<eio_cancel> was called on them at some point.
		303
		304	=back
219		305
220	=head2 AVAILABLE REQUESTS	306	=head2 AVAILABLE REQUESTS
221		307
222	The following request functions are available. I<All> of them return the	308	The following request functions are available. I<All> of them return the
223	C<eio_req *> on success and C<0> on failure, and I<all> of them have the	309	C<eio_req *> on success and C<0> on failure, and I<all> of them have the
…		…
226	custom data value as C<data>.	312	custom data value as C<data>.
227		313
228	=head3 POSIX API WRAPPERS	314	=head3 POSIX API WRAPPERS
229		315
230	These requests simply wrap the POSIX call of the same name, with the same	316	These requests simply wrap the POSIX call of the same name, with the same
231	arguments:	317	arguments. If a function is not implemented by the OS and cannot be emulated
		318	in some way, then all of these return C<-1> and set C<errorno> to C<ENOSYS>.
232		319
233	=over 4	320	=over 4
234		321
235	=item eio_open (const char path, int flags, mode_t mode, int pri, eio_cb cb, void data)	322	=item eio_open (const char path, int flags, mode_t mode, int pri, eio_cb cb, void data)
236		323
		324	=item eio_truncate (const char path, off_t offset, int pri, eio_cb cb, void data)
		325
		326	=item eio_chown (const char path, uid_t uid, gid_t gid, int pri, eio_cb cb, void data)
		327
		328	=item eio_chmod (const char path, mode_t mode, int pri, eio_cb cb, void data)
		329
		330	=item eio_mkdir (const char path, mode_t mode, int pri, eio_cb cb, void data)
		331
		332	=item eio_rmdir (const char path, int pri, eio_cb cb, void data)
		333
		334	=item eio_unlink (const char path, int pri, eio_cb cb, void data)
		335
237	=item eio_utime (const char path, eio_tstamp atime, eio_tstamp mtime, int pri, eio_cb cb, void data)	336	=item eio_utime (const char path, eio_tstamp atime, eio_tstamp mtime, int pri, eio_cb cb, void data)
238		337
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)	338	=item eio_mknod (const char path, mode_t mode, dev_t dev, int pri, eio_cb cb, void data)
260		339
261	=item eio_link (const char path, const char new_path, int pri, eio_cb cb, void *data)	340	=item eio_link (const char path, const char new_path, int pri, eio_cb cb, void *data)
262		341
263	=item eio_symlink (const char path, const char new_path, int pri, eio_cb cb, void *data)	342	=item eio_symlink (const char path, const char new_path, int pri, eio_cb cb, void *data)
264		343
265	=item eio_rename (const char path, const char new_path, int pri, eio_cb cb, void *data)	344	=item eio_rename (const char path, const char new_path, int pri, eio_cb cb, void *data)
266		345
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)	346	=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		347
273	=item eio_close (int fd, int pri, eio_cb cb, void *data)	348	=item eio_close (int fd, int pri, eio_cb cb, void *data)
274		349
275	=item eio_sync (int pri, eio_cb cb, void *data)	350	=item eio_sync (int pri, eio_cb cb, void *data)
276		351
…		…
305		380
306	Not surprisingly, pread and pwrite are not thread-safe on Darwin (OS/X),	381	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	382	so it is advised not to submit multiple requests on the same fd on this
308	horrible pile of garbage.	383	horrible pile of garbage.
309		384
		385	=item eio_mlockall (int flags, int pri, eio_cb cb, void *data)
		386
		387	Like C<mlockall>, but the flag value constants are called
		388	C<EIO_MCL_CURRENT> and C<EIO_MCL_FUTURE>.
		389
		390	=item eio_msync (void addr, size_t length, int flags, int pri, eio_cb cb, void data)
		391
		392	Just like msync, except that the flag values are called C<EIO_MS_ASYNC>,
		393	C<EIO_MS_INVALIDATE> and C<EIO_MS_SYNC>.
		394
		395	=item eio_readlink (const char path, int pri, eio_cb cb, void data)
		396
		397	If successful, the path read by C<readlink(2)> can be accessed via C<<
		398	req->ptr2 >> and is I<NOT> null-terminated, with the length specified as
		399	C<< req->result >>.
		400
		401	if (req->result >= 0)
		402	{
		403	char target = strndup ((char )req->ptr2, req->result);
		404
		405	free (target);
		406	}
		407
		408	=item eio_realpath (const char path, int pri, eio_cb cb, void data)
		409
		410	Similar to the realpath libc function, but unlike that one, result is
		411	C<-1> on failure and the length of the returned path in C<ptr2> (which is
		412	not 0-terminated) - this is similar to readlink.
		413
		414	=item eio_stat (const char path, int pri, eio_cb cb, void data)
		415
		416	=item eio_lstat (const char path, int pri, eio_cb cb, void data)
		417
310	=item eio_fstat (int fd, int pri, eio_cb cb, void *data)	418	=item eio_fstat (int fd, int pri, eio_cb cb, void *data)
311		419
312	Stats a file - if C<< req->result >> indicates success, then you can	420	Stats a file - if C<< req->result >> indicates success, then you can
313	access the C<struct stat>-like structure via C<< req->ptr2 >>:	421	access the C<struct stat>-like structure via C<< req->ptr2 >>:
314		422
315	EIO_STRUCT_STAT statdata = (EIO_STRUCT_STAT )req->ptr2;	423	EIO_STRUCT_STAT statdata = (EIO_STRUCT_STAT )req->ptr2;
316		424
317	=item eio_fstatvfs (int fd, int pri, eio_cb cb, void data) / stat buffer=ptr2 allocated dynamically */	425	=item eio_statvfs (const char path, int pri, eio_cb cb, void data)
		426
		427	=item eio_fstatvfs (int fd, int pri, eio_cb cb, void *data)
318		428
319	Stats a filesystem - if C<< req->result >> indicates success, then you can	429	Stats a filesystem - if C<< req->result >> indicates success, then you can
320	access the C<struct statvfs>-like structure via C<< req->ptr2 >>:	430	access the C<struct statvfs>-like structure via C<< req->ptr2 >>:
321		431
322	EIO_STRUCT_STATVFS statdata = (EIO_STRUCT_STATVFS )req->ptr2;	432	EIO_STRUCT_STATVFS statdata = (EIO_STRUCT_STATVFS )req->ptr2;
323		433
324	=back	434	=back
325		435
326	=head3 READING DIRECTORIES	436	=head3 READING DIRECTORIES
327		437
328	Reading directories sounds simple, but can be rather demanding, especially	438	Reading directories sounds simple, but can be rather demanding, especially
329	if you want to do stuff such as traversing a diretcory hierarchy or	439	if you want to do stuff such as traversing a directory hierarchy or
330	processing all files in a directory. Libeio can assist thess complex tasks	440	processing all files in a directory. Libeio can assist these complex tasks
331	with it's C<eio_readdir> call.	441	with it's C<eio_readdir> call.
332		442
333	=over 4	443	=over 4
334		444
335	=item eio_readdir (const char path, int flags, int pri, eio_cb cb, void data)	445	=item eio_readdir (const char path, int flags, int pri, eio_cb cb, void data)
…		…
338	(via the C<opendir>, C<readdir> and C<closedir> calls) and returns either	448	(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>	449	the names or an array of C<struct eio_dirent>, depending on the C<flags>
340	argument.	450	argument.
341		451
342	The C<< req->result >> indicates either the number of files found, or	452	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 >>,	453	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<<	454	and C<struct eio_dirents>, if requested by C<flags>, can be found via C<<
345	req->ptr1 >>.	455	req->ptr1 >>.
346		456
347	Here is an example that prints all the names:	457	Here is an example that prints all the names:
348		458
…		…
367		477
368	If this flag is specified, then, in addition to the names in C<ptr2>,	478	If this flag is specified, then, in addition to the names in C<ptr2>,
369	also an array of C<struct eio_dirent> is returned, in C<ptr1>. A C<struct	479	also an array of C<struct eio_dirent> is returned, in C<ptr1>. A C<struct
370	eio_dirent> looks like this:	480	eio_dirent> looks like this:
371		481
372	struct eio_dirent	482	struct eio_dirent
373	{	483	{
374	int nameofs; /* offset of null-terminated name string in (char )req->ptr2 /	484	int nameofs; /* offset of null-terminated name string in (char )req->ptr2 /
375	unsigned short namelen; /* size of filename without trailing 0 */	485	unsigned short namelen; /* size of filename without trailing 0 */
376	unsigned char type; /* one of EIO_DT_* */	486	unsigned char type; /* one of EIO_DT_* */
377	signed char score; /* internal use */	487	signed char score; /* internal use */
378	ino_t inode; /* the inode number, if available, otherwise unspecified */	488	ino_t inode; /* the inode number, if available, otherwise unspecified */
379	};	489	};
380		490
381	The only members you normally would access are C<nameofs>, which is the	491	The only members you normally would access are C<nameofs>, which is the
382	byte-offset from C<ptr2> to the start of the name, C<namelen> and C<type>.	492	byte-offset from C<ptr2> to the start of the name, C<namelen> and C<type>.
383		493
384	C<type> can be one of:	494	C<type> can be one of:
…		…
427	When this flag is specified, then the names will be returned in an order	537	When this flag is specified, then the names will be returned in an order
428	suitable for stat()'ing each one. That is, when you plan to stat()	538	suitable for stat()'ing each one. That is, when you plan to stat()
429	all files in the given directory, then the returned order will likely	539	all files in the given directory, then the returned order will likely
430	be fastest.	540	be fastest.
431		541
432	If both this flag and C<EIO_READDIR_DIRS_FIRST> are specified, then	542	If both this flag and C<EIO_READDIR_DIRS_FIRST> are specified, then the
433	the likely dirs come first, resulting in a less optimal stat order.	543	likely directories come first, resulting in a less optimal stat order.
434		544
435	=item EIO_READDIR_FOUND_UNKNOWN	545	=item EIO_READDIR_FOUND_UNKNOWN
436		546
437	This flag should not be specified when calling C<eio_readdir>. Instead,	547	This flag should not be specified when calling C<eio_readdir>. Instead,
438	it is being set by C<eio_readdir> (you can access the C<flags> via C<<	548	it is being set by C<eio_readdir> (you can access the C<flags> via C<<
439	req->int1 >>, when any of the C<type>'s found were C<EIO_DT_UNKNOWN>. The	549	req->int1 >>, when any of the C<type>'s found were C<EIO_DT_UNKNOWN>. The
440	absense of this flag therefore indicates that all C<type>'s are known,	550	absence of this flag therefore indicates that all C<type>'s are known,
441	which can be used to speed up some algorithms.	551	which can be used to speed up some algorithms.
442		552
443	A typical use case would be to identify all subdirectories within a	553	A typical use case would be to identify all subdirectories within a
444	directory - you would ask C<eio_readdir> for C<EIO_READDIR_DIRS_FIRST>. If	554	directory - you would ask C<eio_readdir> for C<EIO_READDIR_DIRS_FIRST>. If
445	then this flag is I<NOT> set, then all the entries at the beginning of the	555	then this flag is I<NOT> set, then all the entries at the beginning of the
…		…
480	=item eio_sync_file_range (int fd, off_t offset, size_t nbytes, unsigned int flags, int pri, eio_cb cb, void *data)	590	=item eio_sync_file_range (int fd, off_t offset, size_t nbytes, unsigned int flags, int pri, eio_cb cb, void *data)
481		591
482	Calls C<sync_file_range>. If the syscall is missing, then this is the same	592	Calls C<sync_file_range>. If the syscall is missing, then this is the same
483	as calling C<fdatasync>.	593	as calling C<fdatasync>.
484		594
		595	Flags can be any combination of C<EIO_SYNC_FILE_RANGE_WAIT_BEFORE>,
		596	C<EIO_SYNC_FILE_RANGE_WRITE> and C<EIO_SYNC_FILE_RANGE_WAIT_AFTER>.
		597
485	=back	598	=back
486		599
487	=head3 LIBEIO-SPECIFIC REQUESTS	600	=head3 LIBEIO-SPECIFIC REQUESTS
488		601
489	These requests are specific to libeio and do not correspond to any OS call.	602	These requests are specific to libeio and do not correspond to any OS call.
490		603
491	=over 4	604	=over 4
492		605
493	=item eio_mtouch (void addr, size_t length, int flags, int pri, eio_cb cb, void data)	606	=item eio_mtouch (void addr, size_t length, int flags, int pri, eio_cb cb, void data)
494		607
		608	Reads (C<flags == 0>) or modifies (C<flags == EIO_MT_MODIFY) the given
		609	memory area, page-wise, that is, it reads (or reads and writes back) the
		610	first octet of every page that spans the memory area.
		611
		612	This can be used to page in some mmapped file, or dirty some pages. Note
		613	that dirtying is an unlocked read-write access, so races can ensue when
		614	the some other thread modifies the data stored in that memory area.
		615
495	=item eio_custom (void ()(eio_req ) execute, int pri, eio_cb cb, void *data)	616	=item eio_custom (void ()(eio_req ) execute, int pri, eio_cb cb, void *data)
496		617
497	Executes a custom request, i.e., a user-specified callback.	618	Executes a custom request, i.e., a user-specified callback.
498		619
499	The callback gets the C<eio_req *> as parameter and is expected to read	620	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<<	621	and modify any request-specific members. Specifically, it should set C<<
…		…
520	req->result = open (req->data, O_RDONLY);	641	req->result = open (req->data, O_RDONLY);
521	}	642	}
522		643
523	eio_custom (my_open, 0, my_open_done, "/etc/passwd");	644	eio_custom (my_open, 0, my_open_done, "/etc/passwd");
524		645
525	=item eio_busy (eio_tstamp delay, int pri, eio_cb cb, void *data)	646	=item eio_busy (eio_tstamp delay, int pri, eio_cb cb, void *data)
526		647
527	This is a a request that takes C<delay> seconds to execute, but otherwise	648	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	649	does nothing - it simply puts one of the worker threads to sleep for this
529	long.	650	long.
530		651
531	This request can be used to artificially increase load, e.g. for debugging	652	This request can be used to artificially increase load, e.g. for debugging
532	or benchmarking reasons.	653	or benchmarking reasons.
533		654
534	=item eio_nop (int pri, eio_cb cb, void *data)	655	=item eio_nop (int pri, eio_cb cb, void *data)
535		656
536	This request does nothing, except go through the whole request cycle. This	657	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	658	can be used to measure latency or in some cases to simplify code, but is
538	not really of much use.	659	not really of much use.
539		660
540	=back	661	=back
541		662
542	=head3 GROUPING AND LIMITING REQUESTS	663	=head3 GROUPING AND LIMITING REQUESTS
543		664
		665	There is one more rather special request, C<eio_grp>. It is a very special
		666	aio request: Instead of doing something, it is a container for other eio
		667	requests.
		668
		669	There are two primary use cases for this: a) bundle many requests into a
		670	single, composite, request with a definite callback and the ability to
		671	cancel the whole request with its subrequests and b) limiting the number
		672	of "active" requests.
		673
		674	Further below you will find more discussion of these topics - first
		675	follows the reference section detailing the request generator and other
		676	methods.
		677
		678	=over 4
		679
		680	=item eio_req grp = eio_grp (eio_cb cb, void data)
		681
		682	Creates, submits and returns a group request.
		683
		684	=item eio_grp_add (eio_req grp, eio_req req)
		685
		686	Adds a request to the request group.
		687
		688	=item eio_grp_cancel (eio_req *grp)
		689
		690	Cancels all requests I<in> the group, but I<not> the group request
		691	itself. You can cancel the group request via a normal C<eio_cancel> call.
		692
		693
		694
		695	=back
		696
		697
		698
544	#TODO	699	#TODO
545		700
546	/*****************************************************************************/	701	/*****************************************************************************/
547	/* groups */	702	/* groups */
548		703
549	eio_req eio_grp (eio_cb cb, void data);	704	eio_req eio_grp (eio_cb cb, void data);
550	void eio_grp_feed (eio_req grp, void (feed)(eio_req *req), int limit);	705	void eio_grp_feed (eio_req grp, void (feed)(eio_req *req), int limit);
551	void eio_grp_limit (eio_req *grp, int limit);	706	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 */	707	void eio_grp_cancel (eio_req grp); / cancels all sub requests but not the group */
554		708
555		709
556	=back	710	=back
557		711
…		…
564	=head1 ANATOMY AND LIFETIME OF AN EIO REQUEST	718	=head1 ANATOMY AND LIFETIME OF AN EIO REQUEST
565		719
566	A request is represented by a structure of type C<eio_req>. To initialise	720	A request is represented by a structure of type C<eio_req>. To initialise
567	it, clear it to all zero bytes:	721	it, clear it to all zero bytes:
568		722
569	eio_req req;	723	eio_req req;
570		724
571	memset (&req, 0, sizeof (req));	725	memset (&req, 0, sizeof (req));
572		726
573	A more common way to initialise a new C<eio_req> is to use C<calloc>:	727	A more common way to initialise a new C<eio_req> is to use C<calloc>:
574		728
575	eio_req req = calloc (1, sizeof (req));	729	eio_req req = calloc (1, sizeof (req));
576		730
577	In either case, libeio neither allocates, initialises or frees the	731	In either case, libeio neither allocates, initialises or frees the
578	C<eio_req> structure for you - it merely uses it.	732	C<eio_req> structure for you - it merely uses it.
579		733
580	zero	734	zero
…		…
598	for example, in interactive programs, you might want to limit this time to	752	for example, in interactive programs, you might want to limit this time to
599	C<0.01> seconds or so.	753	C<0.01> seconds or so.
600		754
601	Note that:	755	Note that:
602		756
		757	=over 4
		758
603	a) libeio doesn't know how long your request callbacks take, so the time	759	=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	760	time spent in C<eio_poll> is up to one callback invocation longer then
605	interval.	761	this interval.
606		762
607	b) this is implemented by calling C<gettimeofday> after each request,	763	=item b) this is implemented by calling C<gettimeofday> after each
608	which can be costly.	764	request, which can be costly.
609		765
610	c) at least one request will be handled.	766	=item c) at least one request will be handled.
		767
		768	=back
611		769
612	=item eio_set_max_poll_reqs (unsigned int nreqs)	770	=item eio_set_max_poll_reqs (unsigned int nreqs)
613		771
614	When C<nreqs> is non-zero, then C<eio_poll> will not handle more than	772	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	773	C<nreqs> requests per invocation. This is a less costly way to limit the

Diff Legend

-–
+Removed lines
-+
+Added lines
-<
+Changed lines
->
+Changed lines

Comparing libeio/eio.pod (file contents): Revision 1.8 by root, Sun Jun 5 22:45:49 2011 UTC vs. Revision 1.18 by root, Tue Jul 5 20:34:42 2011 UTC

Diff Legend

Comparing libeio/eio.pod (file contents):
Revision 1.8 by root, Sun Jun 5 22:45:49 2011 UTC vs.
Revision 1.18 by root, Tue Jul 5 20:34:42 2011 UTC