[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 1.26 by root, Mon Jul 18 02:59:58 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
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>).	190	C<eio_poll>.
221		191
222	=back	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.
223		196
224		197
225	=head1 HIGH LEVEL REQUEST API	198	=head1 HIGH LEVEL REQUEST API
226		199
227	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
…		…
234		207
235	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
236	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)>
237	(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.
238		211
239	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 *>.
240		216
241	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
242	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
243	vary from request to request, except for:	219	vary from request to request, except for:
244		220
…		…
291	}	267	}
292		268
293	/* the first three arguments are passed to open(2) */	269	/* the first three arguments are passed to open(2) */
294	/* the remaining are priority, callback and data */	270	/* the remaining are priority, callback and data */
295	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))
296	abort (); /* something ent wrong, we will all die!!! */	272	abort (); /* something went wrong, we will all die!!! */
297		273
298	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>
299	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
300		311
301	=head2 AVAILABLE REQUESTS	312	=head2 AVAILABLE REQUESTS
302		313
303	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
304	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
…		…
307	custom data value as C<data>.	318	custom data value as C<data>.
308		319
309	=head3 POSIX API WRAPPERS	320	=head3 POSIX API WRAPPERS
310		321
311	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
312	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>.
313		325
314	=over 4	326	=over 4
315		327
316	=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)
317		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
318	=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)
319		343
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)	344	=item eio_mknod (const char path, mode_t mode, dev_t dev, int pri, eio_cb cb, void data)
341		345
342	=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)
343		347
344	=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)
345		349
346	=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)
347		351
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)	352	=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		353
354	=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)
355		355
356	=item eio_sync (int pri, eio_cb cb, void *data)	356	=item eio_sync (int pri, eio_cb cb, void *data)
357		357
…		…
386		386
387	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),
388	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
389	horrible pile of garbage.	389	horrible pile of garbage.
390		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
391	=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)
392		426
393	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
394	access the C<struct stat>-like structure via C<< req->ptr2 >>:	428	access the C<struct stat>-like structure via C<< req->ptr2 >>:
395		429
396	EIO_STRUCT_STAT statdata = (EIO_STRUCT_STAT )req->ptr2;	430	EIO_STRUCT_STAT statdata = (EIO_STRUCT_STAT )req->ptr2;
397		431
398	=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)
399		435
400	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
401	access the C<struct statvfs>-like structure via C<< req->ptr2 >>:	437	access the C<struct statvfs>-like structure via C<< req->ptr2 >>:
402		438
403	EIO_STRUCT_STATVFS statdata = (EIO_STRUCT_STATVFS )req->ptr2;	439	EIO_STRUCT_STATVFS statdata = (EIO_STRUCT_STATVFS )req->ptr2;
404		440
405	=back	441	=back
406		442
407	=head3 READING DIRECTORIES	443	=head3 READING DIRECTORIES
408		444
409	Reading directories sounds simple, but can be rather demanding, especially	445	Reading directories sounds simple, but can be rather demanding, especially
410	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
411	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
412	with it's C<eio_readdir> call.	448	with it's C<eio_readdir> call.
413		449
414	=over 4	450	=over 4
415		451
416	=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)
…		…
419	(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
420	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>
421	argument.	457	argument.
422		458
423	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
424	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 >>,
425	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<<
426	req->ptr1 >>.	462	req->ptr1 >>.
427		463
428	Here is an example that prints all the names:	464	Here is an example that prints all the names:
429		465
…		…
448		484
449	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>,
450	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
451	eio_dirent> looks like this:	487	eio_dirent> looks like this:
452		488
453	struct eio_dirent	489	struct eio_dirent
454	{	490	{
455	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 /
456	unsigned short namelen; /* size of filename without trailing 0 */	492	unsigned short namelen; /* size of filename without trailing 0 */
457	unsigned char type; /* one of EIO_DT_* */	493	unsigned char type; /* one of EIO_DT_* */
458	signed char score; /* internal use */	494	signed char score; /* internal use */
459	ino_t inode; /* the inode number, if available, otherwise unspecified */	495	ino_t inode; /* the inode number, if available, otherwise unspecified */
460	};	496	};
461		497
462	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
463	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>.
464		500
465	C<type> can be one of:	501	C<type> can be one of:
…		…
508	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
509	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()
510	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
511	be fastest.	547	be fastest.
512		548
513	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
514	the likely dirs come first, resulting in a less optimal stat order.	550	likely directories come first, resulting in a less optimal stat order.
515		551
516	=item EIO_READDIR_FOUND_UNKNOWN	552	=item EIO_READDIR_FOUND_UNKNOWN
517		553
518	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,
519	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<<
520	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
521	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,
522	which can be used to speed up some algorithms.	558	which can be used to speed up some algorithms.
523		559
524	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
525	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
526	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
…		…
561	=item eio_sync_file_range (int fd, off_t offset, size_t nbytes, unsigned int flags, int pri, eio_cb cb, void *data)	597	=item eio_sync_file_range (int fd, off_t offset, size_t nbytes, unsigned int flags, int pri, eio_cb cb, void *data)
562		598
563	Calls C<sync_file_range>. If the syscall is missing, then this is the same	599	Calls C<sync_file_range>. If the syscall is missing, then this is the same
564	as calling C<fdatasync>.	600	as calling C<fdatasync>.
565		601
		602	Flags can be any combination of C<EIO_SYNC_FILE_RANGE_WAIT_BEFORE>,
		603	C<EIO_SYNC_FILE_RANGE_WRITE> and C<EIO_SYNC_FILE_RANGE_WAIT_AFTER>.
		604
		605	=item eio_fallocate (int fd, int mode, off_t offset, off_t len, int pri, eio_cb cb, void *data)
		606
		607	Calls C<fallocate> (note: I<NOT> C<posix_fallocate>!). If the syscall is
		608	missing, then it returns failure and sets C<errno> to C<ENOSYS>.
		609
		610	The C<mode> argument can be C<0> (for behaviour similar to
		611	C<posix_fallocate>), or C<EIO_FALLOC_FL_KEEP_SIZE>, which keeps the size
		612	of the file unchanged (but still preallocates space beyond end of file).
		613
566	=back	614	=back
567		615
568	=head3 LIBEIO-SPECIFIC REQUESTS	616	=head3 LIBEIO-SPECIFIC REQUESTS
569		617
570	These requests are specific to libeio and do not correspond to any OS call.	618	These requests are specific to libeio and do not correspond to any OS call.
571		619
572	=over 4	620	=over 4
573		621
574	=item eio_mtouch (void addr, size_t length, int flags, int pri, eio_cb cb, void data)	622	=item eio_mtouch (void addr, size_t length, int flags, int pri, eio_cb cb, void data)
575		623
		624	Reads (C<flags == 0>) or modifies (C<flags == EIO_MT_MODIFY) the given
		625	memory area, page-wise, that is, it reads (or reads and writes back) the
		626	first octet of every page that spans the memory area.
		627
		628	This can be used to page in some mmapped file, or dirty some pages. Note
		629	that dirtying is an unlocked read-write access, so races can ensue when
		630	the some other thread modifies the data stored in that memory area.
		631
576	=item eio_custom (void ()(eio_req ) execute, int pri, eio_cb cb, void *data)	632	=item eio_custom (void ()(eio_req ) execute, int pri, eio_cb cb, void *data)
577		633
578	Executes a custom request, i.e., a user-specified callback.	634	Executes a custom request, i.e., a user-specified callback.
579		635
580	The callback gets the C<eio_req *> as parameter and is expected to read	636	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<<	637	and modify any request-specific members. Specifically, it should set C<<
…		…
601	req->result = open (req->data, O_RDONLY);	657	req->result = open (req->data, O_RDONLY);
602	}	658	}
603		659
604	eio_custom (my_open, 0, my_open_done, "/etc/passwd");	660	eio_custom (my_open, 0, my_open_done, "/etc/passwd");
605		661
606	=item eio_busy (eio_tstamp delay, int pri, eio_cb cb, void *data)	662	=item eio_busy (eio_tstamp delay, int pri, eio_cb cb, void *data)
607		663
608	This is a a request that takes C<delay> seconds to execute, but otherwise	664	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	665	does nothing - it simply puts one of the worker threads to sleep for this
610	long.	666	long.
611		667
612	This request can be used to artificially increase load, e.g. for debugging	668	This request can be used to artificially increase load, e.g. for debugging
613	or benchmarking reasons.	669	or benchmarking reasons.
614		670
615	=item eio_nop (int pri, eio_cb cb, void *data)	671	=item eio_nop (int pri, eio_cb cb, void *data)
616		672
617	This request does nothing, except go through the whole request cycle. This	673	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	674	can be used to measure latency or in some cases to simplify code, but is
619	not really of much use.	675	not really of much use.
620		676
621	=back	677	=back
622		678
623	=head3 GROUPING AND LIMITING REQUESTS	679	=head3 GROUPING AND LIMITING REQUESTS
624		680
		681	There is one more rather special request, C<eio_grp>. It is a very special
		682	aio request: Instead of doing something, it is a container for other eio
		683	requests.
		684
		685	There are two primary use cases for this: a) bundle many requests into a
		686	single, composite, request with a definite callback and the ability to
		687	cancel the whole request with its subrequests and b) limiting the number
		688	of "active" requests.
		689
		690	Further below you will find more discussion of these topics - first
		691	follows the reference section detailing the request generator and other
		692	methods.
		693
		694	=over 4
		695
		696	=item eio_req grp = eio_grp (eio_cb cb, void data)
		697
		698	Creates, submits and returns a group request. Note that it doesn't have a
		699	priority, unlike all other requests.
		700
		701	=item eio_grp_add (eio_req grp, eio_req req)
		702
		703	Adds a request to the request group.
		704
		705	=item eio_grp_cancel (eio_req *grp)
		706
		707	Cancels all requests I<in> the group, but I<not> the group request
		708	itself. You can cancel the group request I<and> all subrequests via a
		709	normal C<eio_cancel> call.
		710
		711	=back
		712
		713	=head4 GROUP REQUEST LIFETIME
		714
		715	Left alone, a group request will instantly move to the pending state and
		716	will be finished at the next call of C<eio_poll>.
		717
		718	The usefulness stems from the fact that, if a subrequest is added to a
		719	group I<before> a call to C<eio_poll>, via C<eio_grp_add>, then the group
		720	will not finish until all the subrequests have finished.
		721
		722	So the usage cycle of a group request is like this: after it is created,
		723	you normally instantly add a subrequest. If none is added, the group
		724	request will finish on it's own. As long as subrequests are added before
		725	the group request is finished it will be kept from finishing, that is the
		726	callbacks of any subrequests can, in turn, add more requests to the group,
		727	and as long as any requests are active, the group request itself will not
		728	finish.
		729
		730	=head4 CREATING COMPOSITE REQUESTS
		731
		732	Imagine you wanted to create an C<eio_load> request that opens a file,
		733	reads it and closes it. This means it has to execute at least three eio
		734	requests, but for various reasons it might be nice if that request looked
		735	like any other eio request.
		736
		737	This can be done with groups:
		738
		739	=over 4
		740
		741	=item 1) create the request object
		742
		743	Create a group that contains all further requests. This is the request you
		744	can return as "the load request".
		745
		746	=item 2) open the file, maybe
		747
		748	Next, open the file with C<eio_open> and add the request to the group
		749	request and you are finished setting up the request.
		750
		751	If, for some reason, you cannot C<eio_open> (path is a null ptr?) you
		752	can set C<< grp->result >> to C<-1> to signal an error and let the group
		753	request finish on its own.
		754
		755	=item 3) open callback adds more requests
		756
		757	In the open callback, if the open was not successful, copy C<<
		758	req->errorno >> to C<< grp->errorno >> and set C<< grp->errorno >> to
		759	C<-1> to signal an error.
		760
		761	Otherwise, malloc some memory or so and issue a read request, adding the
		762	read request to the group.
		763
		764	=item 4) continue issuing requests till finished
		765
		766	In the real callback, check for errors and possibly continue with
		767	C<eio_close> or any other eio request in the same way.
		768
		769	As soon as no new requests are added the group request will finish. Make
		770	sure you I<always> set C<< grp->result >> to some sensible value.
		771
		772	=back
		773
		774	=head4 REQUEST LIMITING
		775
		776
625	#TODO	777	#TODO
626		778
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);	779	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		780
636		781
637	=back	782	=back
638		783
639		784
…		…
645	=head1 ANATOMY AND LIFETIME OF AN EIO REQUEST	790	=head1 ANATOMY AND LIFETIME OF AN EIO REQUEST
646		791
647	A request is represented by a structure of type C<eio_req>. To initialise	792	A request is represented by a structure of type C<eio_req>. To initialise
648	it, clear it to all zero bytes:	793	it, clear it to all zero bytes:
649		794
650	eio_req req;	795	eio_req req;
651		796
652	memset (&req, 0, sizeof (req));	797	memset (&req, 0, sizeof (req));
653		798
654	A more common way to initialise a new C<eio_req> is to use C<calloc>:	799	A more common way to initialise a new C<eio_req> is to use C<calloc>:
655		800
656	eio_req req = calloc (1, sizeof (req));	801	eio_req req = calloc (1, sizeof (req));
657		802
658	In either case, libeio neither allocates, initialises or frees the	803	In either case, libeio neither allocates, initialises or frees the
659	C<eio_req> structure for you - it merely uses it.	804	C<eio_req> structure for you - it merely uses it.
660		805
661	zero	806	zero
662		807
663	#TODO	808	#TODO
		809
		810	=head2 CONFIGURATION
		811
		812	The functions in this section can sometimes be useful, but the default
		813	configuration will do in most case, so you should skip this section on
		814	first reading.
		815
		816	=over 4
		817
		818	=item eio_set_max_poll_time (eio_tstamp nseconds)
		819
		820	This causes C<eio_poll ()> to return after it has detected that it was
		821	running for C<nsecond> seconds or longer (this number can be fractional).
		822
		823	This can be used to limit the amount of time spent handling eio requests,
		824	for example, in interactive programs, you might want to limit this time to
		825	C<0.01> seconds or so.
		826
		827	Note that:
		828
		829	=over 4
		830
		831	=item a) libeio doesn't know how long your request callbacks take, so the
		832	time spent in C<eio_poll> is up to one callback invocation longer then
		833	this interval.
		834
		835	=item b) this is implemented by calling C<gettimeofday> after each
		836	request, which can be costly.
		837
		838	=item c) at least one request will be handled.
		839
		840	=back
		841
		842	=item eio_set_max_poll_reqs (unsigned int nreqs)
		843
		844	When C<nreqs> is non-zero, then C<eio_poll> will not handle more than
		845	C<nreqs> requests per invocation. This is a less costly way to limit the
		846	amount of work done by C<eio_poll> then setting a time limit.
		847
		848	If you know your callbacks are generally fast, you could use this to
		849	encourage interactiveness in your programs by setting it to C<10>, C<100>
		850	or even C<1000>.
		851
		852	=item eio_set_min_parallel (unsigned int nthreads)
		853
		854	Make sure libeio can handle at least this many requests in parallel. It
		855	might be able handle more.
		856
		857	=item eio_set_max_parallel (unsigned int nthreads)
		858
		859	Set the maximum number of threads that libeio will spawn.
		860
		861	=item eio_set_max_idle (unsigned int nthreads)
		862
		863	Libeio uses threads internally to handle most requests, and will start and stop threads on demand.
		864
		865	This call can be used to limit the number of idle threads (threads without
		866	work to do): libeio will keep some threads idle in preparation for more
		867	requests, but never longer than C<nthreads> threads.
		868
		869	In addition to this, libeio will also stop threads when they are idle for
		870	a few seconds, regardless of this setting.
		871
		872	=item unsigned int eio_nthreads ()
		873
		874	Return the number of worker threads currently running.
		875
		876	=item unsigned int eio_nreqs ()
		877
		878	Return the number of requests currently handled by libeio. This is the
		879	total number of requests that have been submitted to libeio, but not yet
		880	destroyed.
		881
		882	=item unsigned int eio_nready ()
		883
		884	Returns the number of ready requests, i.e. requests that have been
		885	submitted but have not yet entered the execution phase.
		886
		887	=item unsigned int eio_npending ()
		888
		889	Returns the number of pending requests, i.e. requests that have been
		890	executed and have results, but have not been finished yet by a call to
		891	C<eio_poll>).
		892
		893	=back
664		894
665	=head1 EMBEDDING	895	=head1 EMBEDDING
666		896
667	Libeio can be embedded directly into programs. This functionality is not	897	Libeio can be embedded directly into programs. This functionality is not
668	documented and not (yet) officially supported.	898	documented and not (yet) officially supported.
…		…
685	This symbol governs the stack size for each eio thread. Libeio itself	915	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>	916	was written to use very little stackspace, but when using C<EIO_CUSTOM>
687	requests, you might want to increase this.	917	requests, you might want to increase this.
688		918
689	If this symbol is undefined (the default) then libeio will use its default	919	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	920	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	921	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	922	other cases, the value must be an expression that evaluates to the desired
693	stack size.	923	stack size.
694		924
695	=back	925	=back

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Revision 1.26 by root, Mon Jul 18 02:59:58 2011 UTC