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

Comparing libeio/eio.pod (file contents):
Revision 1.7 by root, Sun Jun 5 22:44:30 2011 UTC vs.
Revision 1.23 by root, Wed Jul 13 21:31:40 2011 UTC

…		…
45	Unlike the name component C<stamp> might indicate, it is also used for	45	Unlike the name component C<stamp> might indicate, it is also used for
46	time differences throughout libeio.	46	time differences throughout libeio.
47		47
48	=head2 FORK SUPPORT	48	=head2 FORK SUPPORT
49		49
50	Calling C<fork ()> is fully supported by this module. It is implemented in these steps:	50	Calling C<fork ()> is fully supported by this module - but you must not
		51	rely on this. It is currently implemented in these steps:
51		52
52	1. wait till all requests in "execute" state have been handled	53	1. wait till all requests in "execute" state have been handled
53	(basically requests that are already handed over to the kernel).	54	(basically requests that are already handed over to the kernel).
54	2. fork	55	2. fork
55	3. in the parent, continue business as usual, done	56	3. in the parent, continue business as usual, done
56	4. in the child, destroy all ready and pending requests and free the	57	4. in the child, destroy all ready and pending requests and free the
57	memory used by the worker threads. This gives you a fully empty	58	memory used by the worker threads. This gives you a fully empty
58	libeio queue.	59	libeio queue.
59		60
60	Note, however, since libeio does use threads, thr above guarantee doesn't	61	Note, however, since libeio does use threads, the above guarantee doesn't
61	cover your libc, for example, malloc and other libc functions are not	62	cover your libc, for example, malloc and other libc functions are not
62	fork-safe, so there is very little you can do after a fork, and in fatc,	63	fork-safe, so there is very little you can do after a fork, and in fact,
63	the above might crash, and thus change.	64	the above might crash, and thus change.
64		65
65	=head1 INITIALISATION/INTEGRATION	66	=head1 INITIALISATION/INTEGRATION
66		67
67	Before you can call any eio functions you first have to initialise the	68	Before you can call any eio functions you first have to initialise the
…		…
124	=back	125	=back
125		126
126	For libev, you would typically use an C<ev_async> watcher: the	127	For libev, you would typically use an C<ev_async> watcher: the
127	C<want_poll> callback would invoke C<ev_async_send> to wake up the event	128	C<want_poll> callback would invoke C<ev_async_send> to wake up the event
128	loop. Inside the callback set for the watcher, one would call C<eio_poll	129	loop. Inside the callback set for the watcher, one would call C<eio_poll
129	()> (followed by C<ev_async_send> again if C<eio_poll> indicates that not	130	()>.
130	all requests have been handled yet). The race is taken care of because	131
131	libev resets/rearms the async watcher before calling your callback,	132	If C<eio_poll ()> is configured to not handle all results in one go
132	and therefore, before calling C<eio_poll>. This might result in (some)	133	(i.e. it returns C<-1>) then you should start an idle watcher that calls
133	spurious wake-ups, but is generally harmless.	134	C<eio_poll> until it returns something C<!= -1>.
		135
		136	A full-featured connector between libeio and libev would look as follows
		137	(if C<eio_poll> is handling all requests, it can of course be simplified a
		138	lot by removing the idle watcher logic):
		139
		140	static struct ev_loop *loop;
		141	static ev_idle repeat_watcher;
		142	static ev_async ready_watcher;
		143
		144	/* idle watcher callback, only used when eio_poll */
		145	/* didn't handle all results in one call */
		146	static void
		147	repeat (EV_P_ ev_idle *w, int revents)
		148	{
		149	if (eio_poll () != -1)
		150	ev_idle_stop (EV_A_ w);
		151	}
		152
		153	/* eio has some results, process them */
		154	static void
		155	ready (EV_P_ ev_async *w, int revents)
		156	{
		157	if (eio_poll () == -1)
		158	ev_idle_start (EV_A_ &repeat_watcher);
		159	}
		160
		161	/* wake up the event loop */
		162	static void
		163	want_poll (void)
		164	{
		165	ev_async_send (loop, &ready_watcher)
		166	}
		167
		168	void
		169	my_init_eio ()
		170	{
		171	loop = EV_DEFAULT;
		172
		173	ev_idle_init (&repeat_watcher, repeat);
		174	ev_async_init (&ready_watcher, ready);
		175	ev_async_start (loop &watcher);
		176
		177	eio_init (want_poll, 0);
		178	}
134		179
135	For most other event loops, you would typically use a pipe - the event	180	For most other event loops, you would typically use a pipe - the event
136	loop should be told to wait for read readiness on the read end. In	181	loop should be told to wait for read readiness on the read end. In
137	C<want_poll> you would write a single byte, in C<done_poll> you would try	182	C<want_poll> you would write a single byte, in C<done_poll> you would try
138	to read that byte, and in the callback for the read end, you would call	183	to read that byte, and in the callback for the read end, you would call
139	C<eio_poll>. The race is avoided here because the event loop should invoke
140	your callback again and again until the byte has been read (as the pipe
141	read callback does not read it, only C<done_poll>).
142
143	=head2 CONFIGURATION
144
145	The functions in this section can sometimes be useful, but the default
146	configuration will do in most case, so you should skip this section on
147	first reading.
148
149	=over 4
150
151	=item eio_set_max_poll_time (eio_tstamp nseconds)
152
153	This causes C<eio_poll ()> to return after it has detected that it was
154	running for C<nsecond> seconds or longer (this number can be fractional).
155
156	This can be used to limit the amount of time spent handling eio requests,
157	for example, in interactive programs, you might want to limit this time to
158	C<0.01> seconds or so.
159
160	Note that:
161
162	a) libeio doesn't know how long your request callbacks take, so the time
163	spent in C<eio_poll> is up to one callback invocation longer then this
164	interval.
165
166	b) this is implemented by calling C<gettimeofday> after each request,
167	which can be costly.
168
169	c) at least one request will be handled.
170
171	=item eio_set_max_poll_reqs (unsigned int nreqs)
172
173	When C<nreqs> is non-zero, then C<eio_poll> will not handle more than
174	C<nreqs> requests per invocation. This is a less costly way to limit the
175	amount of work done by C<eio_poll> then setting a time limit.
176
177	If you know your callbacks are generally fast, you could use this to
178	encourage interactiveness in your programs by setting it to C<10>, C<100>
179	or even C<1000>.
180
181	=item eio_set_min_parallel (unsigned int nthreads)
182
183	Make sure libeio can handle at least this many requests in parallel. It
184	might be able handle more.
185
186	=item eio_set_max_parallel (unsigned int nthreads)
187
188	Set the maximum number of threads that libeio will spawn.
189
190	=item eio_set_max_idle (unsigned int nthreads)
191
192	Libeio uses threads internally to handle most requests, and will start and stop threads on demand.
193
194	This call can be used to limit the number of idle threads (threads without
195	work to do): libeio will keep some threads idle in preparation for more
196	requests, but never longer than C<nthreads> threads.
197
198	In addition to this, libeio will also stop threads when they are idle for
199	a few seconds, regardless of this setting.
200
201	=item unsigned int eio_nthreads ()
202
203	Return the number of worker threads currently running.
204
205	=item unsigned int eio_nreqs ()
206
207	Return the number of requests currently handled by libeio. This is the
208	total number of requests that have been submitted to libeio, but not yet
209	destroyed.
210
211	=item unsigned int eio_nready ()
212
213	Returns the number of ready requests, i.e. requests that have been
214	submitted but have not yet entered the execution phase.
215
216	=item unsigned int eio_npending ()
217
218	Returns the number of pending requests, i.e. requests that have been
219	executed and have results, but have not been finished yet by a call to
220	C<eio_poll>).	184	C<eio_poll>.
221		185
222	=back	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.
223		190
224		191
225	=head1 HIGH LEVEL REQUEST API	192	=head1 HIGH LEVEL REQUEST API
226		193
227	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
…		…
234		201
235	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
236	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)>
237	(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.
238		205
239	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 *>.
240		210
241	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
242	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
243	vary from request to request, except for:	213	vary from request to request, except for:
244		214
…		…
291	}	261	}
292		262
293	/* the first three arguments are passed to open(2) */	263	/* the first three arguments are passed to open(2) */
294	/* the remaining are priority, callback and data */	264	/* the remaining are priority, callback and data */
295	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))
296	abort (); /* something ent wrong, we will all die!!! */	266	abort (); /* something went wrong, we will all die!!! */
297		267
298	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>
299	indicates that requests are ready to be processed.	269	indicates that requests are ready to be processed.
		270
		271	=head2 CANCELLING REQUESTS
		272
		273	Sometimes the need for a request goes away before the request is
		274	finished. In that case, one can cancel the request by a call to
		275	C<eio_cancel>:
		276
		277	=over 4
		278
		279	=item eio_cancel (eio_req *req)
		280
		281	Cancel the request (and all its subrequests). If the request is currently
		282	executing it might still continue to execute, and in other cases it might
		283	still take a while till the request is cancelled.
		284
		285	Even if cancelled, the finish callback will still be invoked - the
		286	callbacks of all cancellable requests need to check whether the request
		287	has been cancelled by calling C<EIO_CANCELLED (req)>:
		288
		289	static int
		290	my_eio_cb (eio_req *req)
		291	{
		292	if (EIO_CANCELLED (req))
		293	return 0;
		294	}
		295
		296	In addition, cancelled requests will I<either> have C<< req->result >>
		297	set to C<-1> and C<errno> to C<ECANCELED>, or I<otherwise> they were
		298	successfully executed, despite being cancelled (e.g. when they have
		299	already been executed at the time they were cancelled).
		300
		301	C<EIO_CANCELLED> is still true for requests that have successfully
		302	executed, as long as C<eio_cancel> was called on them at some point.
		303
		304	=back
300		305
301	=head2 AVAILABLE REQUESTS	306	=head2 AVAILABLE REQUESTS
302		307
303	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
304	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
…		…
307	custom data value as C<data>.	312	custom data value as C<data>.
308		313
309	=head3 POSIX API WRAPPERS	314	=head3 POSIX API WRAPPERS
310		315
311	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
312	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>.
313		319
314	=over 4	320	=over 4
315		321
316	=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)
317		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
318	=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)
319		337
320	=item eio_truncate (const char path, off_t offset, int pri, eio_cb cb, void data)
321
322	=item eio_chown (const char path, uid_t uid, gid_t gid, int pri, eio_cb cb, void data)
323
324	=item eio_chmod (const char path, mode_t mode, int pri, eio_cb cb, void data)
325
326	=item eio_mkdir (const char path, mode_t mode, int pri, eio_cb cb, void data)
327
328	=item eio_rmdir (const char path, int pri, eio_cb cb, void data)
329
330	=item eio_unlink (const char path, int pri, eio_cb cb, void data)
331
332	=item eio_readlink (const char path, int pri, eio_cb cb, void data) /* result=ptr2 allocated dynamically */
333
334	=item eio_stat (const char path, int pri, eio_cb cb, void data) /* stat buffer=ptr2 allocated dynamically */
335
336	=item eio_lstat (const char path, int pri, eio_cb cb, void data) /* stat buffer=ptr2 allocated dynamically */
337
338	=item eio_statvfs (const char path, int pri, eio_cb cb, void data) /* stat buffer=ptr2 allocated dynamically */
339
340	=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)
341		339
342	=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)
343		341
344	=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)
345		343
346	=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)
347		345
348	=item eio_msync (void addr, size_t length, int flags, int pri, eio_cb cb, void data)
349
350	=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)
351
352	=item eio_mlockall (int flags, int pri, eio_cb cb, void *data)
353		347
354	=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)
355		349
356	=item eio_sync (int pri, eio_cb cb, void *data)	350	=item eio_sync (int pri, eio_cb cb, void *data)
357		351
…		…
386		380
387	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),
388	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
389	horrible pile of garbage.	383	horrible pile of garbage.
390		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, C<<
		411	req->result >> is C<-1> on failure. On success, the result is the length
		412	of the returned path in C<ptr2> (which is I<NOT> 0-terminated) - this is
		413	similar to readlink.
		414
		415	=item eio_stat (const char path, int pri, eio_cb cb, void data)
		416
		417	=item eio_lstat (const char path, int pri, eio_cb cb, void data)
		418
391	=item eio_fstat (int fd, int pri, eio_cb cb, void *data)	419	=item eio_fstat (int fd, int pri, eio_cb cb, void *data)
392		420
393	Stats a file - if C<< req->result >> indicates success, then you can	421	Stats a file - if C<< req->result >> indicates success, then you can
394	access the C<struct stat>-like structure via C<< req->ptr2 >>:	422	access the C<struct stat>-like structure via C<< req->ptr2 >>:
395		423
396	EIO_STRUCT_STAT statdata = (EIO_STRUCT_STAT )req->ptr2;	424	EIO_STRUCT_STAT statdata = (EIO_STRUCT_STAT )req->ptr2;
397		425
398	=item eio_fstatvfs (int fd, int pri, eio_cb cb, void data) / stat buffer=ptr2 allocated dynamically */	426	=item eio_statvfs (const char path, int pri, eio_cb cb, void data)
		427
		428	=item eio_fstatvfs (int fd, int pri, eio_cb cb, void *data)
399		429
400	Stats a filesystem - if C<< req->result >> indicates success, then you can	430	Stats a filesystem - if C<< req->result >> indicates success, then you can
401	access the C<struct statvfs>-like structure via C<< req->ptr2 >>:	431	access the C<struct statvfs>-like structure via C<< req->ptr2 >>:
402		432
403	EIO_STRUCT_STATVFS statdata = (EIO_STRUCT_STATVFS )req->ptr2;	433	EIO_STRUCT_STATVFS statdata = (EIO_STRUCT_STATVFS )req->ptr2;
404		434
405	=back	435	=back
406		436
407	=head3 READING DIRECTORIES	437	=head3 READING DIRECTORIES
408		438
409	Reading directories sounds simple, but can be rather demanding, especially	439	Reading directories sounds simple, but can be rather demanding, especially
410	if you want to do stuff such as traversing a diretcory hierarchy or	440	if you want to do stuff such as traversing a directory hierarchy or
411	processing all files in a directory. Libeio can assist thess complex tasks	441	processing all files in a directory. Libeio can assist these complex tasks
412	with it's C<eio_readdir> call.	442	with it's C<eio_readdir> call.
413		443
414	=over 4	444	=over 4
415		445
416	=item eio_readdir (const char path, int flags, int pri, eio_cb cb, void data)	446	=item eio_readdir (const char path, int flags, int pri, eio_cb cb, void data)
…		…
419	(via the C<opendir>, C<readdir> and C<closedir> calls) and returns either	449	(via the C<opendir>, C<readdir> and C<closedir> calls) and returns either
420	the names or an array of C<struct eio_dirent>, depending on the C<flags>	450	the names or an array of C<struct eio_dirent>, depending on the C<flags>
421	argument.	451	argument.
422		452
423	The C<< req->result >> indicates either the number of files found, or	453	The C<< req->result >> indicates either the number of files found, or
424	C<-1> on error. On success, zero-terminated names can be found as C<< req->ptr2 >>,	454	C<-1> on error. On success, null-terminated names can be found as C<< req->ptr2 >>,
425	and C<struct eio_dirents>, if requested by C<flags>, can be found via C<<	455	and C<struct eio_dirents>, if requested by C<flags>, can be found via C<<
426	req->ptr1 >>.	456	req->ptr1 >>.
427		457
428	Here is an example that prints all the names:	458	Here is an example that prints all the names:
429		459
…		…
448		478
449	If this flag is specified, then, in addition to the names in C<ptr2>,	479	If this flag is specified, then, in addition to the names in C<ptr2>,
450	also an array of C<struct eio_dirent> is returned, in C<ptr1>. A C<struct	480	also an array of C<struct eio_dirent> is returned, in C<ptr1>. A C<struct
451	eio_dirent> looks like this:	481	eio_dirent> looks like this:
452		482
453	struct eio_dirent	483	struct eio_dirent
454	{	484	{
455	int nameofs; /* offset of null-terminated name string in (char )req->ptr2 /	485	int nameofs; /* offset of null-terminated name string in (char )req->ptr2 /
456	unsigned short namelen; /* size of filename without trailing 0 */	486	unsigned short namelen; /* size of filename without trailing 0 */
457	unsigned char type; /* one of EIO_DT_* */	487	unsigned char type; /* one of EIO_DT_* */
458	signed char score; /* internal use */	488	signed char score; /* internal use */
459	ino_t inode; /* the inode number, if available, otherwise unspecified */	489	ino_t inode; /* the inode number, if available, otherwise unspecified */
460	};	490	};
461		491
462	The only members you normally would access are C<nameofs>, which is the	492	The only members you normally would access are C<nameofs>, which is the
463	byte-offset from C<ptr2> to the start of the name, C<namelen> and C<type>.	493	byte-offset from C<ptr2> to the start of the name, C<namelen> and C<type>.
464		494
465	C<type> can be one of:	495	C<type> can be one of:
…		…
508	When this flag is specified, then the names will be returned in an order	538	When this flag is specified, then the names will be returned in an order
509	suitable for stat()'ing each one. That is, when you plan to stat()	539	suitable for stat()'ing each one. That is, when you plan to stat()
510	all files in the given directory, then the returned order will likely	540	all files in the given directory, then the returned order will likely
511	be fastest.	541	be fastest.
512		542
513	If both this flag and C<EIO_READDIR_DIRS_FIRST> are specified, then	543	If both this flag and C<EIO_READDIR_DIRS_FIRST> are specified, then the
514	the likely dirs come first, resulting in a less optimal stat order.	544	likely directories come first, resulting in a less optimal stat order.
515		545
516	=item EIO_READDIR_FOUND_UNKNOWN	546	=item EIO_READDIR_FOUND_UNKNOWN
517		547
518	This flag should not be specified when calling C<eio_readdir>. Instead,	548	This flag should not be specified when calling C<eio_readdir>. Instead,
519	it is being set by C<eio_readdir> (you can access the C<flags> via C<<	549	it is being set by C<eio_readdir> (you can access the C<flags> via C<<
520	req->int1 >>, when any of the C<type>'s found were C<EIO_DT_UNKNOWN>. The	550	req->int1 >>, when any of the C<type>'s found were C<EIO_DT_UNKNOWN>. The
521	absense of this flag therefore indicates that all C<type>'s are known,	551	absence of this flag therefore indicates that all C<type>'s are known,
522	which can be used to speed up some algorithms.	552	which can be used to speed up some algorithms.
523		553
524	A typical use case would be to identify all subdirectories within a	554	A typical use case would be to identify all subdirectories within a
525	directory - you would ask C<eio_readdir> for C<EIO_READDIR_DIRS_FIRST>. If	555	directory - you would ask C<eio_readdir> for C<EIO_READDIR_DIRS_FIRST>. If
526	then this flag is I<NOT> set, then all the entries at the beginning of the	556	then this flag is I<NOT> set, then all the entries at the beginning of the
…		…
561	=item eio_sync_file_range (int fd, off_t offset, size_t nbytes, unsigned int flags, int pri, eio_cb cb, void *data)	591	=item eio_sync_file_range (int fd, off_t offset, size_t nbytes, unsigned int flags, int pri, eio_cb cb, void *data)
562		592
563	Calls C<sync_file_range>. If the syscall is missing, then this is the same	593	Calls C<sync_file_range>. If the syscall is missing, then this is the same
564	as calling C<fdatasync>.	594	as calling C<fdatasync>.
565		595
		596	Flags can be any combination of C<EIO_SYNC_FILE_RANGE_WAIT_BEFORE>,
		597	C<EIO_SYNC_FILE_RANGE_WRITE> and C<EIO_SYNC_FILE_RANGE_WAIT_AFTER>.
		598
		599	=item eio_fallocate (int fd, int mode, off_t offset, off_t len, int pri, eio_cb cb, void *data)
		600
		601	Calls C<fallocate> (note: I<NOT> C<posix_fallocate>!). If the syscall is
		602	missing, then it returns failure and sets C<errno> to C<ENOSYS>.
		603
		604	The C<mode> argument can be C<0> (for behaviour similar to
		605	C<posix_fallocate>), or C<EIO_FALLOC_FL_KEEP_SIZE>, which keeps the size
		606	of the file unchanged (but still preallocates space beyond end of file).
		607
566	=back	608	=back
567		609
568	=head3 LIBEIO-SPECIFIC REQUESTS	610	=head3 LIBEIO-SPECIFIC REQUESTS
569		611
570	These requests are specific to libeio and do not correspond to any OS call.	612	These requests are specific to libeio and do not correspond to any OS call.
571		613
572	=over 4	614	=over 4
573		615
574	=item eio_mtouch (void addr, size_t length, int flags, int pri, eio_cb cb, void data)	616	=item eio_mtouch (void addr, size_t length, int flags, int pri, eio_cb cb, void data)
575		617
		618	Reads (C<flags == 0>) or modifies (C<flags == EIO_MT_MODIFY) the given
		619	memory area, page-wise, that is, it reads (or reads and writes back) the
		620	first octet of every page that spans the memory area.
		621
		622	This can be used to page in some mmapped file, or dirty some pages. Note
		623	that dirtying is an unlocked read-write access, so races can ensue when
		624	the some other thread modifies the data stored in that memory area.
		625
576	=item eio_custom (void ()(eio_req ) execute, int pri, eio_cb cb, void *data)	626	=item eio_custom (void ()(eio_req ) execute, int pri, eio_cb cb, void *data)
577		627
578	Executes a custom request, i.e., a user-specified callback.	628	Executes a custom request, i.e., a user-specified callback.
579		629
580	The callback gets the C<eio_req *> as parameter and is expected to read	630	The callback gets the C<eio_req *> as parameter and is expected to read
581	and modify any request-specific members. Specifically, it should set C<<	631	and modify any request-specific members. Specifically, it should set C<<
…		…
601	req->result = open (req->data, O_RDONLY);	651	req->result = open (req->data, O_RDONLY);
602	}	652	}
603		653
604	eio_custom (my_open, 0, my_open_done, "/etc/passwd");	654	eio_custom (my_open, 0, my_open_done, "/etc/passwd");
605		655
606	=item eio_busy (eio_tstamp delay, int pri, eio_cb cb, void *data)	656	=item eio_busy (eio_tstamp delay, int pri, eio_cb cb, void *data)
607		657
608	This is a a request that takes C<delay> seconds to execute, but otherwise	658	This is a request that takes C<delay> seconds to execute, but otherwise
609	does nothing - it simply puts one of the worker threads to sleep for this	659	does nothing - it simply puts one of the worker threads to sleep for this
610	long.	660	long.
611		661
612	This request can be used to artificially increase load, e.g. for debugging	662	This request can be used to artificially increase load, e.g. for debugging
613	or benchmarking reasons.	663	or benchmarking reasons.
614		664
615	=item eio_nop (int pri, eio_cb cb, void *data)	665	=item eio_nop (int pri, eio_cb cb, void *data)
616		666
617	This request does nothing, except go through the whole request cycle. This	667	This request does nothing, except go through the whole request cycle. This
618	can be used to measure latency or in some cases to simplify code, but is	668	can be used to measure latency or in some cases to simplify code, but is
619	not really of much use.	669	not really of much use.
620		670
621	=back	671	=back
622		672
623	=head3 GROUPING AND LIMITING REQUESTS	673	=head3 GROUPING AND LIMITING REQUESTS
624		674
		675	There is one more rather special request, C<eio_grp>. It is a very special
		676	aio request: Instead of doing something, it is a container for other eio
		677	requests.
		678
		679	There are two primary use cases for this: a) bundle many requests into a
		680	single, composite, request with a definite callback and the ability to
		681	cancel the whole request with its subrequests and b) limiting the number
		682	of "active" requests.
		683
		684	Further below you will find more discussion of these topics - first
		685	follows the reference section detailing the request generator and other
		686	methods.
		687
		688	=over 4
		689
		690	=item eio_req grp = eio_grp (eio_cb cb, void data)
		691
		692	Creates, submits and returns a group request. Note that it doesn't have a
		693	priority, unlike all other requests.
		694
		695	=item eio_grp_add (eio_req grp, eio_req req)
		696
		697	Adds a request to the request group.
		698
		699	=item eio_grp_cancel (eio_req *grp)
		700
		701	Cancels all requests I<in> the group, but I<not> the group request
		702	itself. You can cancel the group request I<and> all subrequests via a
		703	normal C<eio_cancel> call.
		704
		705	=back
		706
		707	=head4 GROUP REQUEST LIFETIME
		708
		709	Left alone, a group request will instantly move to the pending state and
		710	will be finished at the next call of C<eio_poll>.
		711
		712	There usefulness stems from the fact that, if a subrequest is added to a
		713	group I<before> a call to C<eio_poll>, via C<eio_grp_add>, then the group
		714	will not finish until all the subrequests have finished.
		715
		716	So the usage cycle of a group request is like this: after it is created,
		717	you normally instantly add a subrequest. If none is added, the group
		718	request will finish on it's own. As long as subrequests are added before
		719	the group request is finished it will be kept from finishing, that is the
		720	callbacks of any subrequests can, in turn, add more requests to the group,
		721	and as long as any requests are active, the group request itself will not
		722	finish.
		723
		724	=head4 CREATING COMPOSITE REQUESTS
		725
		726	Imagine you wanted to create an C<eio_load> request that opens a file,
		727	reads it and closes it. This means it has to execute at least three eio
		728	requests, but for various reasons it might be nice if that request looked
		729	like any other eio request.
		730
		731	This can be done with groups:
		732
		733	=over 4
		734
		735	=item 1) create the request object
		736
		737	Create a group that contains all further requests. This is the request you
		738	can return as "the load request".
		739
		740	=item 2) open the file, maybe
		741
		742	Next, open the file with C<eio_open> and add the request to the group
		743	request and you are finished steting up the request.
		744
		745	If, for some reason, you cannot C<eio_open> (path is a null ptr?) you
		746	cna set C<< grp->result >> to C<-1> to signal an error and let the gorup
		747	request finish on its own.
		748
		749	=item 3) open callback adds more requests
		750
		751	In the open callback, if the open was not successful, copy C<<
		752	req->errorno >> to C<< grp->errorno >> and set C<< grp->errorno >> to
		753	C<-1> to signal an error.
		754
		755	Otherwise, malloc some memory or so and issue a read request, adding the
		756	read request to the group.
		757
		758	=item 4) continue issuign requests till finished
		759
		760	In the real callback, check for errors and possibly continue with
		761	C<eio_close> or any other eio request in the same way.
		762
		763	As soon as no new requests are added the group request will finish. Make
		764	sure you I<always> set C<< grp->result >> to some sensible value.
		765
		766	=back
		767
		768	=head4 REQUEST LIMITING
		769
		770
625	#TODO	771	#TODO
626		772
627	/*****************************************************************************/
628	/* groups */
629
630	eio_req eio_grp (eio_cb cb, void data);
631	void eio_grp_feed (eio_req grp, void (feed)(eio_req *req), int limit);
632	void eio_grp_limit (eio_req *grp, int limit);	773	void eio_grp_limit (eio_req *grp, int limit);
633	void eio_grp_add (eio_req grp, eio_req req);
634	void eio_grp_cancel (eio_req grp); / cancels all sub requests but not the group */
635		774
636		775
637	=back	776	=back
638		777
639		778
…		…
645	=head1 ANATOMY AND LIFETIME OF AN EIO REQUEST	784	=head1 ANATOMY AND LIFETIME OF AN EIO REQUEST
646		785
647	A request is represented by a structure of type C<eio_req>. To initialise	786	A request is represented by a structure of type C<eio_req>. To initialise
648	it, clear it to all zero bytes:	787	it, clear it to all zero bytes:
649		788
650	eio_req req;	789	eio_req req;
651		790
652	memset (&req, 0, sizeof (req));	791	memset (&req, 0, sizeof (req));
653		792
654	A more common way to initialise a new C<eio_req> is to use C<calloc>:	793	A more common way to initialise a new C<eio_req> is to use C<calloc>:
655		794
656	eio_req req = calloc (1, sizeof (req));	795	eio_req req = calloc (1, sizeof (req));
657		796
658	In either case, libeio neither allocates, initialises or frees the	797	In either case, libeio neither allocates, initialises or frees the
659	C<eio_req> structure for you - it merely uses it.	798	C<eio_req> structure for you - it merely uses it.
660		799
661	zero	800	zero
662		801
663	#TODO	802	#TODO
		803
		804	=head2 CONFIGURATION
		805
		806	The functions in this section can sometimes be useful, but the default
		807	configuration will do in most case, so you should skip this section on
		808	first reading.
		809
		810	=over 4
		811
		812	=item eio_set_max_poll_time (eio_tstamp nseconds)
		813
		814	This causes C<eio_poll ()> to return after it has detected that it was
		815	running for C<nsecond> seconds or longer (this number can be fractional).
		816
		817	This can be used to limit the amount of time spent handling eio requests,
		818	for example, in interactive programs, you might want to limit this time to
		819	C<0.01> seconds or so.
		820
		821	Note that:
		822
		823	=over 4
		824
		825	=item a) libeio doesn't know how long your request callbacks take, so the
		826	time spent in C<eio_poll> is up to one callback invocation longer then
		827	this interval.
		828
		829	=item b) this is implemented by calling C<gettimeofday> after each
		830	request, which can be costly.
		831
		832	=item c) at least one request will be handled.
		833
		834	=back
		835
		836	=item eio_set_max_poll_reqs (unsigned int nreqs)
		837
		838	When C<nreqs> is non-zero, then C<eio_poll> will not handle more than
		839	C<nreqs> requests per invocation. This is a less costly way to limit the
		840	amount of work done by C<eio_poll> then setting a time limit.
		841
		842	If you know your callbacks are generally fast, you could use this to
		843	encourage interactiveness in your programs by setting it to C<10>, C<100>
		844	or even C<1000>.
		845
		846	=item eio_set_min_parallel (unsigned int nthreads)
		847
		848	Make sure libeio can handle at least this many requests in parallel. It
		849	might be able handle more.
		850
		851	=item eio_set_max_parallel (unsigned int nthreads)
		852
		853	Set the maximum number of threads that libeio will spawn.
		854
		855	=item eio_set_max_idle (unsigned int nthreads)
		856
		857	Libeio uses threads internally to handle most requests, and will start and stop threads on demand.
		858
		859	This call can be used to limit the number of idle threads (threads without
		860	work to do): libeio will keep some threads idle in preparation for more
		861	requests, but never longer than C<nthreads> threads.
		862
		863	In addition to this, libeio will also stop threads when they are idle for
		864	a few seconds, regardless of this setting.
		865
		866	=item unsigned int eio_nthreads ()
		867
		868	Return the number of worker threads currently running.
		869
		870	=item unsigned int eio_nreqs ()
		871
		872	Return the number of requests currently handled by libeio. This is the
		873	total number of requests that have been submitted to libeio, but not yet
		874	destroyed.
		875
		876	=item unsigned int eio_nready ()
		877
		878	Returns the number of ready requests, i.e. requests that have been
		879	submitted but have not yet entered the execution phase.
		880
		881	=item unsigned int eio_npending ()
		882
		883	Returns the number of pending requests, i.e. requests that have been
		884	executed and have results, but have not been finished yet by a call to
		885	C<eio_poll>).
		886
		887	=back
664		888
665	=head1 EMBEDDING	889	=head1 EMBEDDING
666		890
667	Libeio can be embedded directly into programs. This functionality is not	891	Libeio can be embedded directly into programs. This functionality is not
668	documented and not (yet) officially supported.	892	documented and not (yet) officially supported.

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Comparing libeio/eio.pod (file contents):
Revision 1.7 by root, Sun Jun 5 22:44:30 2011 UTC vs.
Revision 1.23 by root, Wed Jul 13 21:31:40 2011 UTC