[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 1.17 by root, Tue Jul 5 18:59:28 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
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 readyness 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
…		…
296	abort (); /* something ent wrong, we will all die!!! */	266	abort (); /* something ent 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.
300		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 reqiest 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. If the request is currently executing it might still
		282	continue to execute, and in other cases it might still take a while till
		283	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 either have C<< req->result >> set to
		297	C<-1> and C<errno> to C<ECANCELED>, or otherwise they were successfully
		298	executed despite being cancelled (e.g. when they have already been
		299	executed at the time they were cancelled).
		300
		301	=back
		302
301	=head2 AVAILABLE REQUESTS	303	=head2 AVAILABLE REQUESTS
302		304
303	The following request functions are available. I<All> of them return the	305	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	306	C<eio_req *> on success and C<0> on failure, and I<all> of them have the
305	same three trailing arguments: C<pri>, C<cb> and C<data>. The C<cb> is	307	same three trailing arguments: C<pri>, C<cb> and C<data>. The C<cb> is
…		…
307	custom data value as C<data>.	309	custom data value as C<data>.
308		310
309	=head3 POSIX API WRAPPERS	311	=head3 POSIX API WRAPPERS
310		312
311	These requests simply wrap the POSIX call of the same name, with the same	313	These requests simply wrap the POSIX call of the same name, with the same
312	arguments:	314	arguments. If a function is not implemented by the OS and cannot be emulated
		315	in some way, then all of these return C<-1> and set C<errorno> to C<ENOSYS>.
313		316
314	=over 4	317	=over 4
315		318
316	=item eio_open (const char path, int flags, mode_t mode, int pri, eio_cb cb, void data)	319	=item eio_open (const char path, int flags, mode_t mode, int pri, eio_cb cb, void data)
317		320
		321	=item eio_truncate (const char path, off_t offset, int pri, eio_cb cb, void data)
		322
		323	=item eio_chown (const char path, uid_t uid, gid_t gid, int pri, eio_cb cb, void data)
		324
		325	=item eio_chmod (const char path, mode_t mode, int pri, eio_cb cb, void data)
		326
		327	=item eio_mkdir (const char path, mode_t mode, int pri, eio_cb cb, void data)
		328
		329	=item eio_rmdir (const char path, int pri, eio_cb cb, void data)
		330
		331	=item eio_unlink (const char path, int pri, eio_cb cb, void data)
		332
318	=item eio_utime (const char path, eio_tstamp atime, eio_tstamp mtime, int pri, eio_cb cb, void data)	333	=item eio_utime (const char path, eio_tstamp atime, eio_tstamp mtime, int pri, eio_cb cb, void data)
319		334
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)	335	=item eio_mknod (const char path, mode_t mode, dev_t dev, int pri, eio_cb cb, void data)
341		336
342	=item eio_link (const char path, const char new_path, int pri, eio_cb cb, void *data)	337	=item eio_link (const char path, const char new_path, int pri, eio_cb cb, void *data)
343		338
344	=item eio_symlink (const char path, const char new_path, int pri, eio_cb cb, void *data)	339	=item eio_symlink (const char path, const char new_path, int pri, eio_cb cb, void *data)
345		340
346	=item eio_rename (const char path, const char new_path, int pri, eio_cb cb, void *data)	341	=item eio_rename (const char path, const char new_path, int pri, eio_cb cb, void *data)
347		342
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)	343	=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		344
354	=item eio_close (int fd, int pri, eio_cb cb, void *data)	345	=item eio_close (int fd, int pri, eio_cb cb, void *data)
355		346
356	=item eio_sync (int pri, eio_cb cb, void *data)	347	=item eio_sync (int pri, eio_cb cb, void *data)
357		348
…		…
386		377
387	Not surprisingly, pread and pwrite are not thread-safe on Darwin (OS/X),	378	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	379	so it is advised not to submit multiple requests on the same fd on this
389	horrible pile of garbage.	380	horrible pile of garbage.
390		381
		382	=item eio_mlockall (int flags, int pri, eio_cb cb, void *data)
		383
		384	Like C<mlockall>, but the flag value constants are called
		385	C<EIO_MCL_CURRENT> and C<EIO_MCL_FUTURE>.
		386
		387	=item eio_msync (void addr, size_t length, int flags, int pri, eio_cb cb, void data)
		388
		389	Just like msync, except that the flag values are called C<EIO_MS_ASYNC>,
		390	C<EIO_MS_INVALIDATE> and C<EIO_MS_SYNC>.
		391
		392	=item eio_readlink (const char path, int pri, eio_cb cb, void data)
		393
		394	If successful, the path read by C<readlink(2)> can be accessed via C<<
		395	req->ptr2 >> and is I<NOT> null-terminated, with the length specified as
		396	C<< req->result >>.
		397
		398	if (req->result >= 0)
		399	{
		400	char target = strndup ((char )req->ptr2, req->result);
		401
		402	free (target);
		403	}
		404
		405	=item eio_realpath (const char path, int pri, eio_cb cb, void data)
		406
		407	Similar to the realpath libc function, but unlike that one, result is
		408	C<-1> on failure and the length of the returned path in C<ptr2> (which is
		409	not 0-terminated) - this is similar to readlink.
		410
		411	=item eio_stat (const char path, int pri, eio_cb cb, void data)
		412
		413	=item eio_lstat (const char path, int pri, eio_cb cb, void data)
		414
391	=item eio_fstat (int fd, int pri, eio_cb cb, void *data)	415	=item eio_fstat (int fd, int pri, eio_cb cb, void *data)
392		416
393	Stats a file - if C<< req->result >> indicates success, then you can	417	Stats a file - if C<< req->result >> indicates success, then you can
394	access the C<struct stat>-like structure via C<< req->ptr2 >>:	418	access the C<struct stat>-like structure via C<< req->ptr2 >>:
395		419
396	EIO_STRUCT_STAT statdata = (EIO_STRUCT_STAT )req->ptr2;	420	EIO_STRUCT_STAT statdata = (EIO_STRUCT_STAT )req->ptr2;
397		421
398	=item eio_fstatvfs (int fd, int pri, eio_cb cb, void data) / stat buffer=ptr2 allocated dynamically */	422	=item eio_statvfs (const char path, int pri, eio_cb cb, void data)
		423
		424	=item eio_fstatvfs (int fd, int pri, eio_cb cb, void *data)
399		425
400	Stats a filesystem - if C<< req->result >> indicates success, then you can	426	Stats a filesystem - if C<< req->result >> indicates success, then you can
401	access the C<struct statvfs>-like structure via C<< req->ptr2 >>:	427	access the C<struct statvfs>-like structure via C<< req->ptr2 >>:
402		428
403	EIO_STRUCT_STATVFS statdata = (EIO_STRUCT_STATVFS )req->ptr2;	429	EIO_STRUCT_STATVFS statdata = (EIO_STRUCT_STATVFS )req->ptr2;
404		430
405	=back	431	=back
406		432
407	=head3 READING DIRECTORIES	433	=head3 READING DIRECTORIES
408		434
…		…
419	(via the C<opendir>, C<readdir> and C<closedir> calls) and returns either	445	(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>	446	the names or an array of C<struct eio_dirent>, depending on the C<flags>
421	argument.	447	argument.
422		448
423	The C<< req->result >> indicates either the number of files found, or	449	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 >>,	450	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<<	451	and C<struct eio_dirents>, if requested by C<flags>, can be found via C<<
426	req->ptr1 >>.	452	req->ptr1 >>.
427		453
428	Here is an example that prints all the names:	454	Here is an example that prints all the names:
429		455
…		…
448		474
449	If this flag is specified, then, in addition to the names in C<ptr2>,	475	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	476	also an array of C<struct eio_dirent> is returned, in C<ptr1>. A C<struct
451	eio_dirent> looks like this:	477	eio_dirent> looks like this:
452		478
453	struct eio_dirent	479	struct eio_dirent
454	{	480	{
455	int nameofs; /* offset of null-terminated name string in (char )req->ptr2 /	481	int nameofs; /* offset of null-terminated name string in (char )req->ptr2 /
456	unsigned short namelen; /* size of filename without trailing 0 */	482	unsigned short namelen; /* size of filename without trailing 0 */
457	unsigned char type; /* one of EIO_DT_* */	483	unsigned char type; /* one of EIO_DT_* */
458	signed char score; /* internal use */	484	signed char score; /* internal use */
459	ino_t inode; /* the inode number, if available, otherwise unspecified */	485	ino_t inode; /* the inode number, if available, otherwise unspecified */
460	};	486	};
461		487
462	The only members you normally would access are C<nameofs>, which is the	488	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>.	489	byte-offset from C<ptr2> to the start of the name, C<namelen> and C<type>.
464		490
465	C<type> can be one of:	491	C<type> can be one of:
…		…
561	=item eio_sync_file_range (int fd, off_t offset, size_t nbytes, unsigned int flags, int pri, eio_cb cb, void *data)	587	=item eio_sync_file_range (int fd, off_t offset, size_t nbytes, unsigned int flags, int pri, eio_cb cb, void *data)
562		588
563	Calls C<sync_file_range>. If the syscall is missing, then this is the same	589	Calls C<sync_file_range>. If the syscall is missing, then this is the same
564	as calling C<fdatasync>.	590	as calling C<fdatasync>.
565		591
		592	Flags can be any combination of C<EIO_SYNC_FILE_RANGE_WAIT_BEFORE>,
		593	C<EIO_SYNC_FILE_RANGE_WRITE> and C<EIO_SYNC_FILE_RANGE_WAIT_AFTER>.
		594
566	=back	595	=back
567		596
568	=head3 LIBEIO-SPECIFIC REQUESTS	597	=head3 LIBEIO-SPECIFIC REQUESTS
569		598
570	These requests are specific to libeio and do not correspond to any OS call.	599	These requests are specific to libeio and do not correspond to any OS call.
571		600
572	=over 4	601	=over 4
573		602
574	=item eio_mtouch (void addr, size_t length, int flags, int pri, eio_cb cb, void data)	603	=item eio_mtouch (void addr, size_t length, int flags, int pri, eio_cb cb, void data)
575		604
		605	Reads (C<flags == 0>) or modifies (C<flags == EIO_MT_MODIFY) the given
		606	memory area, page-wise, that is, it reads (or reads and writes back) the
		607	first octet of every page that spans the memory area.
		608
		609	This can be used to page in some mmapped file, or dirty some pages. Note
		610	that dirtying is an unlocked read-write access, so races can ensue when
		611	the some other thread modifies the data stored in that memory area.
		612
576	=item eio_custom (void ()(eio_req ) execute, int pri, eio_cb cb, void *data)	613	=item eio_custom (void ()(eio_req ) execute, int pri, eio_cb cb, void *data)
577		614
578	Executes a custom request, i.e., a user-specified callback.	615	Executes a custom request, i.e., a user-specified callback.
579		616
580	The callback gets the C<eio_req *> as parameter and is expected to read	617	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<<	618	and modify any request-specific members. Specifically, it should set C<<
…		…
601	req->result = open (req->data, O_RDONLY);	638	req->result = open (req->data, O_RDONLY);
602	}	639	}
603		640
604	eio_custom (my_open, 0, my_open_done, "/etc/passwd");	641	eio_custom (my_open, 0, my_open_done, "/etc/passwd");
605		642
606	=item eio_busy (eio_tstamp delay, int pri, eio_cb cb, void *data)	643	=item eio_busy (eio_tstamp delay, int pri, eio_cb cb, void *data)
607		644
608	This is a a request that takes C<delay> seconds to execute, but otherwise	645	This is a 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	646	does nothing - it simply puts one of the worker threads to sleep for this
610	long.	647	long.
611		648
612	This request can be used to artificially increase load, e.g. for debugging	649	This request can be used to artificially increase load, e.g. for debugging
613	or benchmarking reasons.	650	or benchmarking reasons.
614		651
615	=item eio_nop (int pri, eio_cb cb, void *data)	652	=item eio_nop (int pri, eio_cb cb, void *data)
616		653
617	This request does nothing, except go through the whole request cycle. This	654	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	655	can be used to measure latency or in some cases to simplify code, but is
619	not really of much use.	656	not really of much use.
620		657
621	=back	658	=back
622		659
623	=head3 GROUPING AND LIMITING REQUESTS	660	=head3 GROUPING AND LIMITING REQUESTS
624		661
		662	There is one more rather special request, C<eio_grp>. It is a very special
		663	aio request: Instead of doing something, it is a container for other eio
		664	requests.
		665
		666	There are two primary use cases for this: a) bundle many requests into a
		667	single, composite, request with a definite callback and the ability to
		668	cancel the whole request with its subrequests and b) limiting the number
		669	of "active" requests.
		670
		671	Further below you will find more dicussion of these topics - first follows
		672	the reference section detailing the request generator and other methods.
		673
		674	=over 4
		675
		676	=item eio_req grp = eio_grp (eio_cb cb, void data)
		677
		678	Creates, submits and returns a group request.
		679
		680	=item eio_grp_add (eio_req grp, eio_req req)
		681
		682	Adds a request to the request group.
		683
		684	=item eio_grp_cancel (eio_req *grp)
		685
		686	Cancels all requests I<in> the group, but I<not> the group request
		687	itself. You can cancel the group request via a normal C<eio_cancel> call.
		688
		689
		690
		691	=back
		692
		693
		694
625	#TODO	695	#TODO
626		696
627	/*****************************************************************************/	697	/*****************************************************************************/
628	/* groups */	698	/* groups */
629		699
630	eio_req eio_grp (eio_cb cb, void data);	700	eio_req eio_grp (eio_cb cb, void data);
631	void eio_grp_feed (eio_req grp, void (feed)(eio_req *req), int limit);	701	void eio_grp_feed (eio_req grp, void (feed)(eio_req *req), int limit);
632	void eio_grp_limit (eio_req *grp, int limit);	702	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 */	703	void eio_grp_cancel (eio_req grp); / cancels all sub requests but not the group */
635		704
636		705
637	=back	706	=back
638		707
…		…
645	=head1 ANATOMY AND LIFETIME OF AN EIO REQUEST	714	=head1 ANATOMY AND LIFETIME OF AN EIO REQUEST
646		715
647	A request is represented by a structure of type C<eio_req>. To initialise	716	A request is represented by a structure of type C<eio_req>. To initialise
648	it, clear it to all zero bytes:	717	it, clear it to all zero bytes:
649		718
650	eio_req req;	719	eio_req req;
651		720
652	memset (&req, 0, sizeof (req));	721	memset (&req, 0, sizeof (req));
653		722
654	A more common way to initialise a new C<eio_req> is to use C<calloc>:	723	A more common way to initialise a new C<eio_req> is to use C<calloc>:
655		724
656	eio_req req = calloc (1, sizeof (req));	725	eio_req req = calloc (1, sizeof (req));
657		726
658	In either case, libeio neither allocates, initialises or frees the	727	In either case, libeio neither allocates, initialises or frees the
659	C<eio_req> structure for you - it merely uses it.	728	C<eio_req> structure for you - it merely uses it.
660		729
661	zero	730	zero
662		731
663	#TODO	732	#TODO
		733
		734	=head2 CONFIGURATION
		735
		736	The functions in this section can sometimes be useful, but the default
		737	configuration will do in most case, so you should skip this section on
		738	first reading.
		739
		740	=over 4
		741
		742	=item eio_set_max_poll_time (eio_tstamp nseconds)
		743
		744	This causes C<eio_poll ()> to return after it has detected that it was
		745	running for C<nsecond> seconds or longer (this number can be fractional).
		746
		747	This can be used to limit the amount of time spent handling eio requests,
		748	for example, in interactive programs, you might want to limit this time to
		749	C<0.01> seconds or so.
		750
		751	Note that:
		752
		753	a) libeio doesn't know how long your request callbacks take, so the time
		754	spent in C<eio_poll> is up to one callback invocation longer then this
		755	interval.
		756
		757	b) this is implemented by calling C<gettimeofday> after each request,
		758	which can be costly.
		759
		760	c) at least one request will be handled.
		761
		762	=item eio_set_max_poll_reqs (unsigned int nreqs)
		763
		764	When C<nreqs> is non-zero, then C<eio_poll> will not handle more than
		765	C<nreqs> requests per invocation. This is a less costly way to limit the
		766	amount of work done by C<eio_poll> then setting a time limit.
		767
		768	If you know your callbacks are generally fast, you could use this to
		769	encourage interactiveness in your programs by setting it to C<10>, C<100>
		770	or even C<1000>.
		771
		772	=item eio_set_min_parallel (unsigned int nthreads)
		773
		774	Make sure libeio can handle at least this many requests in parallel. It
		775	might be able handle more.
		776
		777	=item eio_set_max_parallel (unsigned int nthreads)
		778
		779	Set the maximum number of threads that libeio will spawn.
		780
		781	=item eio_set_max_idle (unsigned int nthreads)
		782
		783	Libeio uses threads internally to handle most requests, and will start and stop threads on demand.
		784
		785	This call can be used to limit the number of idle threads (threads without
		786	work to do): libeio will keep some threads idle in preparation for more
		787	requests, but never longer than C<nthreads> threads.
		788
		789	In addition to this, libeio will also stop threads when they are idle for
		790	a few seconds, regardless of this setting.
		791
		792	=item unsigned int eio_nthreads ()
		793
		794	Return the number of worker threads currently running.
		795
		796	=item unsigned int eio_nreqs ()
		797
		798	Return the number of requests currently handled by libeio. This is the
		799	total number of requests that have been submitted to libeio, but not yet
		800	destroyed.
		801
		802	=item unsigned int eio_nready ()
		803
		804	Returns the number of ready requests, i.e. requests that have been
		805	submitted but have not yet entered the execution phase.
		806
		807	=item unsigned int eio_npending ()
		808
		809	Returns the number of pending requests, i.e. requests that have been
		810	executed and have results, but have not been finished yet by a call to
		811	C<eio_poll>).
		812
		813	=back
664		814
665	=head1 EMBEDDING	815	=head1 EMBEDDING
666		816
667	Libeio can be embedded directly into programs. This functionality is not	817	Libeio can be embedded directly into programs. This functionality is not
668	documented and not (yet) officially supported.	818	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 1.17 by root, Tue Jul 5 18:59:28 2011 UTC

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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 1.17 by root, Tue Jul 5 18:59:28 2011 UTC