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

Comparing libeio/eio.pod (file contents):
Revision 1.14 by root, Tue Jul 5 14:02:15 2011 UTC vs.
Revision 1.32 by root, Sat Jan 19 00:02:34 2013 UTC

…		…
45	Unlike the name component C<stamp> might indicate, it is also used for	45	Unlike the name component C<stamp> might indicate, it is also used for
46	time differences throughout libeio.	46	time differences throughout libeio.
47		47
48	=head2 FORK SUPPORT	48	=head2 FORK SUPPORT
49		49
50	Calling C<fork ()> is fully supported by this module. It is implemented in these steps:	50	Usage of pthreads in a program changes the semantics of fork
		51	considerably. Specifically, only async-safe functions can be called after
		52	fork. Libeio uses pthreads, so this applies, and makes using fork hard for
		53	anything but relatively fork + exec uses.
51		54
52	1. wait till all requests in "execute" state have been handled	55	This library only works in the process that initialised it: Forking is
53	(basically requests that are already handed over to the kernel).	56	fully supported, but using libeio in any other process than the one that
54	2. fork	57	called C<eio_init> is not.
55	3. in the parent, continue business as usual, done
56	4. in the child, destroy all ready and pending requests and free the
57	memory used by the worker threads. This gives you a fully empty
58	libeio queue.
59		58
60	Note, however, since libeio does use threads, thr above guarantee doesn't	59	You might get around by not I<using> libeio before (or after) forking in
61	cover your libc, for example, malloc and other libc functions are not	60	the parent, and using it in the child afterwards. You could also try to
62	fork-safe, so there is very little you can do after a fork, and in fatc,	61	call the L<eio_init> function again in the child, which will brutally
63	the above might crash, and thus change.	62	reinitialise all data structures, which isn't POSIX conformant, but
		63	typically works.
		64
		65	Otherwise, the only recommendation you should follow is: treat fork code
		66	the same way you treat signal handlers, and only ever call C<eio_init> in
		67	the process that uses it, and only once ever.
64		68
65	=head1 INITIALISATION/INTEGRATION	69	=head1 INITIALISATION/INTEGRATION
66		70
67	Before you can call any eio functions you first have to initialise the	71	Before you can call any eio functions you first have to initialise the
68	library. The library integrates into any event loop, but can also be used	72	library. The library integrates into any event loop, but can also be used
…		…
77	This function initialises the library. On success it returns C<0>, on	81	This function initialises the library. On success it returns C<0>, on
78	failure it returns C<-1> and sets C<errno> appropriately.	82	failure it returns C<-1> and sets C<errno> appropriately.
79		83
80	It accepts two function pointers specifying callbacks as argument, both of	84	It accepts two function pointers specifying callbacks as argument, both of
81	which can be C<0>, in which case the callback isn't called.	85	which can be C<0>, in which case the callback isn't called.
		86
		87	There is currently no way to change these callbacks later, or to
		88	"uninitialise" the library again.
82		89
83	=item want_poll callback	90	=item want_poll callback
84		91
85	The C<want_poll> callback is invoked whenever libeio wants attention (i.e.	92	The C<want_poll> callback is invoked whenever libeio wants attention (i.e.
86	it wants to be polled by calling C<eio_poll>). It is "edge-triggered",	93	it wants to be polled by calling C<eio_poll>). It is "edge-triggered",
…		…
124	=back	131	=back
125		132
126	For libev, you would typically use an C<ev_async> watcher: the	133	For libev, you would typically use an C<ev_async> watcher: the
127	C<want_poll> callback would invoke C<ev_async_send> to wake up the event	134	C<want_poll> callback would invoke C<ev_async_send> to wake up the event
128	loop. Inside the callback set for the watcher, one would call C<eio_poll	135	loop. Inside the callback set for the watcher, one would call C<eio_poll
129	()> (followed by C<ev_async_send> again if C<eio_poll> indicates that not	136	()>.
130	all requests have been handled yet). The race is taken care of because	137
131	libev resets/rearms the async watcher before calling your callback,	138	If C<eio_poll ()> is configured to not handle all results in one go
132	and therefore, before calling C<eio_poll>. This might result in (some)	139	(i.e. it returns C<-1>) then you should start an idle watcher that calls
133	spurious wake-ups, but is generally harmless.	140	C<eio_poll> until it returns something C<!= -1>.
		141
		142	A full-featured connector between libeio and libev would look as follows
		143	(if C<eio_poll> is handling all requests, it can of course be simplified a
		144	lot by removing the idle watcher logic):
		145
		146	static struct ev_loop *loop;
		147	static ev_idle repeat_watcher;
		148	static ev_async ready_watcher;
		149
		150	/* idle watcher callback, only used when eio_poll */
		151	/* didn't handle all results in one call */
		152	static void
		153	repeat (EV_P_ ev_idle *w, int revents)
		154	{
		155	if (eio_poll () != -1)
		156	ev_idle_stop (EV_A_ w);
		157	}
		158
		159	/* eio has some results, process them */
		160	static void
		161	ready (EV_P_ ev_async *w, int revents)
		162	{
		163	if (eio_poll () == -1)
		164	ev_idle_start (EV_A_ &repeat_watcher);
		165	}
		166
		167	/* wake up the event loop */
		168	static void
		169	want_poll (void)
		170	{
		171	ev_async_send (loop, &ready_watcher)
		172	}
		173
		174	void
		175	my_init_eio ()
		176	{
		177	loop = EV_DEFAULT;
		178
		179	ev_idle_init (&repeat_watcher, repeat);
		180	ev_async_init (&ready_watcher, ready);
		181	ev_async_start (loop &watcher);
		182
		183	eio_init (want_poll, 0);
		184	}
134		185
135	For most other event loops, you would typically use a pipe - the event	186	For most other event loops, you would typically use a pipe - the event
136	loop should be told to wait for read readiness on the read end. In	187	loop should be told to wait for read readiness on the read end. In
137	C<want_poll> you would write a single byte, in C<done_poll> you would try	188	C<want_poll> you would write a single byte, in C<done_poll> you would try
138	to read that byte, and in the callback for the read end, you would call	189	to read that byte, and in the callback for the read end, you would call
139	C<eio_poll>. The race is avoided here because the event loop should invoke	190	C<eio_poll>.
140	your callback again and again until the byte has been read (as the pipe	191
141	read callback does not read it, only C<done_poll>).	192	You don't have to take special care in the case C<eio_poll> doesn't handle
		193	all requests, as the done callback will not be invoked, so the event loop
		194	will still signal readiness for the pipe until I<all> results have been
		195	processed.
142		196
143		197
144	=head1 HIGH LEVEL REQUEST API	198	=head1 HIGH LEVEL REQUEST API
145		199
146	Libeio has both a high-level API, which consists of calling a request	200	Libeio has both a high-level API, which consists of calling a request
…		…
179		233
180	The C<void *data> member simply stores the value of the C<data> argument.	234	The C<void *data> member simply stores the value of the C<data> argument.
181		235
182	=back	236	=back
183		237
		238	Members not explicitly described as accessible must not be
		239	accessed. Specifically, there is no guarantee that any members will still
		240	have the value they had when the request was submitted.
		241
184	The return value of the callback is normally C<0>, which tells libeio to	242	The return value of the callback is normally C<0>, which tells libeio to
185	continue normally. If a callback returns a nonzero value, libeio will	243	continue normally. If a callback returns a nonzero value, libeio will
186	stop processing results (in C<eio_poll>) and will return the value to its	244	stop processing results (in C<eio_poll>) and will return the value to its
187	caller.	245	caller.
188		246
189	Memory areas passed to libeio must stay valid as long as a request	247	Memory areas passed to libeio wrappers must stay valid as long as a
190	executes, with the exception of paths, which are being copied	248	request executes, with the exception of paths, which are being copied
191	internally. Any memory libeio itself allocates will be freed after the	249	internally. Any memory libeio itself allocates will be freed after the
192	finish callback has been called. If you want to manage all memory passed	250	finish callback has been called. If you want to manage all memory passed
193	to libeio yourself you can use the low-level API.	251	to libeio yourself you can use the low-level API.
194		252
195	For example, to open a file, you could do this:	253	For example, to open a file, you could do this:
…		…
213	}	271	}
214		272
215	/* the first three arguments are passed to open(2) */	273	/* the first three arguments are passed to open(2) */
216	/* the remaining are priority, callback and data */	274	/* the remaining are priority, callback and data */
217	if (!eio_open ("/etc/passwd", O_RDONLY, 0, 0, file_open_done, 0))	275	if (!eio_open ("/etc/passwd", O_RDONLY, 0, 0, file_open_done, 0))
218	abort (); /* something ent wrong, we will all die!!! */	276	abort (); /* something went wrong, we will all die!!! */
219		277
220	Note that you additionally need to call C<eio_poll> when the C<want_cb>	278	Note that you additionally need to call C<eio_poll> when the C<want_cb>
221	indicates that requests are ready to be processed.	279	indicates that requests are ready to be processed.
		280
		281	=head2 CANCELLING REQUESTS
		282
		283	Sometimes the need for a request goes away before the request is
		284	finished. In that case, one can cancel the request by a call to
		285	C<eio_cancel>:
		286
		287	=over 4
		288
		289	=item eio_cancel (eio_req *req)
		290
		291	Cancel the request (and all its subrequests). If the request is currently
		292	executing it might still continue to execute, and in other cases it might
		293	still take a while till the request is cancelled.
		294
		295	Even if cancelled, the finish callback will still be invoked - the
		296	callbacks of all cancellable requests need to check whether the request
		297	has been cancelled by calling C<EIO_CANCELLED (req)>:
		298
		299	static int
		300	my_eio_cb (eio_req *req)
		301	{
		302	if (EIO_CANCELLED (req))
		303	return 0;
		304	}
		305
		306	In addition, cancelled requests will I<either> have C<< req->result >>
		307	set to C<-1> and C<errno> to C<ECANCELED>, or I<otherwise> they were
		308	successfully executed, despite being cancelled (e.g. when they have
		309	already been executed at the time they were cancelled).
		310
		311	C<EIO_CANCELLED> is still true for requests that have successfully
		312	executed, as long as C<eio_cancel> was called on them at some point.
		313
		314	=back
222		315
223	=head2 AVAILABLE REQUESTS	316	=head2 AVAILABLE REQUESTS
224		317
225	The following request functions are available. I<All> of them return the	318	The following request functions are available. I<All> of them return the
226	C<eio_req *> on success and C<0> on failure, and I<all> of them have the	319	C<eio_req *> on success and C<0> on failure, and I<all> of them have the
…		…
322	free (target);	415	free (target);
323	}	416	}
324		417
325	=item eio_realpath (const char path, int pri, eio_cb cb, void data)	418	=item eio_realpath (const char path, int pri, eio_cb cb, void data)
326		419
327	Similar to the realpath libc function, but unlike that one, result is	420	Similar to the realpath libc function, but unlike that one, C<<
328	C<-1> on failure and the length of the returned path in C<ptr2> (which is	421	req->result >> is C<-1> on failure. On success, the result is the length
329	not 0-terminated) - this is similar to readlink.	422	of the returned path in C<ptr2> (which is I<NOT> 0-terminated) - this is
		423	similar to readlink.
330		424
331	=item eio_stat (const char path, int pri, eio_cb cb, void data)	425	=item eio_stat (const char path, int pri, eio_cb cb, void data)
332		426
333	=item eio_lstat (const char path, int pri, eio_cb cb, void data)	427	=item eio_lstat (const char path, int pri, eio_cb cb, void data)
334		428
335	=item eio_fstat (int fd, int pri, eio_cb cb, void *data)	429	=item eio_fstat (int fd, int pri, eio_cb cb, void *data)
336		430
337	Stats a file - if C<< req->result >> indicates success, then you can	431	Stats a file - if C<< req->result >> indicates success, then you can
338	access the C<struct stat>-like structure via C<< req->ptr2 >>:	432	access the C<struct stat>-like structure via C<< req->ptr2 >>:
339		433
340	EIO_STRUCT_STAT statdata = (EIO_STRUCT_STAT )req->ptr2;	434	EIO_STRUCT_STAT statdata = (EIO_STRUCT_STAT )req->ptr2;
341		435
342	=item eio_statvfs (const char path, int pri, eio_cb cb, void data)	436	=item eio_statvfs (const char path, int pri, eio_cb cb, void data)
343		437
344	=item eio_fstatvfs (int fd, int pri, eio_cb cb, void *data)	438	=item eio_fstatvfs (int fd, int pri, eio_cb cb, void *data)
345		439
346	Stats a filesystem - if C<< req->result >> indicates success, then you can	440	Stats a filesystem - if C<< req->result >> indicates success, then you can
347	access the C<struct statvfs>-like structure via C<< req->ptr2 >>:	441	access the C<struct statvfs>-like structure via C<< req->ptr2 >>:
348		442
349	EIO_STRUCT_STATVFS statdata = (EIO_STRUCT_STATVFS )req->ptr2;	443	EIO_STRUCT_STATVFS statdata = (EIO_STRUCT_STATVFS )req->ptr2;
350		444
351	=back	445	=back
352		446
353	=head3 READING DIRECTORIES	447	=head3 READING DIRECTORIES
354		448
355	Reading directories sounds simple, but can be rather demanding, especially	449	Reading directories sounds simple, but can be rather demanding, especially
356	if you want to do stuff such as traversing a diretcory hierarchy or	450	if you want to do stuff such as traversing a directory hierarchy or
357	processing all files in a directory. Libeio can assist thess complex tasks	451	processing all files in a directory. Libeio can assist these complex tasks
358	with it's C<eio_readdir> call.	452	with it's C<eio_readdir> call.
359		453
360	=over 4	454	=over 4
361		455
362	=item eio_readdir (const char path, int flags, int pri, eio_cb cb, void data)	456	=item eio_readdir (const char path, int flags, int pri, eio_cb cb, void data)
…		…
394		488
395	If this flag is specified, then, in addition to the names in C<ptr2>,	489	If this flag is specified, then, in addition to the names in C<ptr2>,
396	also an array of C<struct eio_dirent> is returned, in C<ptr1>. A C<struct	490	also an array of C<struct eio_dirent> is returned, in C<ptr1>. A C<struct
397	eio_dirent> looks like this:	491	eio_dirent> looks like this:
398		492
399	struct eio_dirent	493	struct eio_dirent
400	{	494	{
401	int nameofs; /* offset of null-terminated name string in (char )req->ptr2 /	495	int nameofs; /* offset of null-terminated name string in (char )req->ptr2 /
402	unsigned short namelen; /* size of filename without trailing 0 */	496	unsigned short namelen; /* size of filename without trailing 0 */
403	unsigned char type; /* one of EIO_DT_* */	497	unsigned char type; /* one of EIO_DT_* */
404	signed char score; /* internal use */	498	signed char score; /* internal use */
405	ino_t inode; /* the inode number, if available, otherwise unspecified */	499	ino_t inode; /* the inode number, if available, otherwise unspecified */
406	};	500	};
407		501
408	The only members you normally would access are C<nameofs>, which is the	502	The only members you normally would access are C<nameofs>, which is the
409	byte-offset from C<ptr2> to the start of the name, C<namelen> and C<type>.	503	byte-offset from C<ptr2> to the start of the name, C<namelen> and C<type>.
410		504
411	C<type> can be one of:	505	C<type> can be one of:
…		…
454	When this flag is specified, then the names will be returned in an order	548	When this flag is specified, then the names will be returned in an order
455	suitable for stat()'ing each one. That is, when you plan to stat()	549	suitable for stat()'ing each one. That is, when you plan to stat()
456	all files in the given directory, then the returned order will likely	550	all files in the given directory, then the returned order will likely
457	be fastest.	551	be fastest.
458		552
459	If both this flag and C<EIO_READDIR_DIRS_FIRST> are specified, then	553	If both this flag and C<EIO_READDIR_DIRS_FIRST> are specified, then the
460	the likely dirs come first, resulting in a less optimal stat order.	554	likely directories come first, resulting in a less optimal stat order.
461		555
462	=item EIO_READDIR_FOUND_UNKNOWN	556	=item EIO_READDIR_FOUND_UNKNOWN
463		557
464	This flag should not be specified when calling C<eio_readdir>. Instead,	558	This flag should not be specified when calling C<eio_readdir>. Instead,
465	it is being set by C<eio_readdir> (you can access the C<flags> via C<<	559	it is being set by C<eio_readdir> (you can access the C<flags> via C<<
466	req->int1 >>, when any of the C<type>'s found were C<EIO_DT_UNKNOWN>. The	560	req->int1 >>, when any of the C<type>'s found were C<EIO_DT_UNKNOWN>. The
467	absense of this flag therefore indicates that all C<type>'s are known,	561	absence of this flag therefore indicates that all C<type>'s are known,
468	which can be used to speed up some algorithms.	562	which can be used to speed up some algorithms.
469		563
470	A typical use case would be to identify all subdirectories within a	564	A typical use case would be to identify all subdirectories within a
471	directory - you would ask C<eio_readdir> for C<EIO_READDIR_DIRS_FIRST>. If	565	directory - you would ask C<eio_readdir> for C<EIO_READDIR_DIRS_FIRST>. If
472	then this flag is I<NOT> set, then all the entries at the beginning of the	566	then this flag is I<NOT> set, then all the entries at the beginning of the
…		…
502	=item eio_readahead (int fd, off_t offset, size_t length, int pri, eio_cb cb, void *data)	596	=item eio_readahead (int fd, off_t offset, size_t length, int pri, eio_cb cb, void *data)
503		597
504	Calls C<readahead(2)>. If the syscall is missing, then the call is	598	Calls C<readahead(2)>. If the syscall is missing, then the call is
505	emulated by simply reading the data (currently in 64kiB chunks).	599	emulated by simply reading the data (currently in 64kiB chunks).
506		600
		601	=item eio_syncfs (int fd, int pri, eio_cb cb, void *data)
		602
		603	Calls Linux' C<syncfs> syscall, if available. Returns C<-1> and sets
		604	C<errno> to C<ENOSYS> if the call is missing I<but still calls sync()>,
		605	if the C<fd> is C<< >= 0 >>, so you can probe for the availability of the
		606	syscall with a negative C<fd> argument and checking for C<-1/ENOSYS>.
		607
507	=item eio_sync_file_range (int fd, off_t offset, size_t nbytes, unsigned int flags, int pri, eio_cb cb, void *data)	608	=item eio_sync_file_range (int fd, off_t offset, size_t nbytes, unsigned int flags, int pri, eio_cb cb, void *data)
508		609
509	Calls C<sync_file_range>. If the syscall is missing, then this is the same	610	Calls C<sync_file_range>. If the syscall is missing, then this is the same
510	as calling C<fdatasync>.	611	as calling C<fdatasync>.
511		612
512	Flags can be any combination of C<EIO_SYNC_FILE_RANGE_WAIT_BEFORE>,	613	Flags can be any combination of C<EIO_SYNC_FILE_RANGE_WAIT_BEFORE>,
513	C<EIO_SYNC_FILE_RANGE_WRITE> and C<EIO_SYNC_FILE_RANGE_WAIT_AFTER>.	614	C<EIO_SYNC_FILE_RANGE_WRITE> and C<EIO_SYNC_FILE_RANGE_WAIT_AFTER>.
514		615
		616	=item eio_fallocate (int fd, int mode, off_t offset, off_t len, int pri, eio_cb cb, void *data)
		617
		618	Calls C<fallocate> (note: I<NOT> C<posix_fallocate>!). If the syscall is
		619	missing, then it returns failure and sets C<errno> to C<ENOSYS>.
		620
		621	The C<mode> argument can be C<0> (for behaviour similar to
		622	C<posix_fallocate>), or C<EIO_FALLOC_FL_KEEP_SIZE>, which keeps the size
		623	of the file unchanged (but still preallocates space beyond end of file).
		624
515	=back	625	=back
516		626
517	=head3 LIBEIO-SPECIFIC REQUESTS	627	=head3 LIBEIO-SPECIFIC REQUESTS
518		628
519	These requests are specific to libeio and do not correspond to any OS call.	629	These requests are specific to libeio and do not correspond to any OS call.
520		630
521	=over 4	631	=over 4
522		632
523	=item eio_mtouch (void addr, size_t length, int flags, int pri, eio_cb cb, void data)	633	=item eio_mtouch (void addr, size_t length, int flags, int pri, eio_cb cb, void data)
524		634
525	Reads (C<flags == 0>) or modifies (C<flags == EIO_MT_MODIFY) the given	635	Reads (C<flags == 0>) or modifies (C<flags == EIO_MT_MODIFY>) the given
526	memory area, page-wise, that is, it reads (or reads and writes back) the	636	memory area, page-wise, that is, it reads (or reads and writes back) the
527	first octet of every page that spans the memory area.	637	first octet of every page that spans the memory area.
528		638
529	This can be used to page in some mmapped file, or dirty some pages. Note	639	This can be used to page in some mmapped file, or dirty some pages. Note
530	that dirtying is an unlocked read-write access, so races can ensue when	640	that dirtying is an unlocked read-write access, so races can ensue when
…		…
560		670
561	eio_custom (my_open, 0, my_open_done, "/etc/passwd");	671	eio_custom (my_open, 0, my_open_done, "/etc/passwd");
562		672
563	=item eio_busy (eio_tstamp delay, int pri, eio_cb cb, void *data)	673	=item eio_busy (eio_tstamp delay, int pri, eio_cb cb, void *data)
564		674
565	This is a a request that takes C<delay> seconds to execute, but otherwise	675	This is a request that takes C<delay> seconds to execute, but otherwise
566	does nothing - it simply puts one of the worker threads to sleep for this	676	does nothing - it simply puts one of the worker threads to sleep for this
567	long.	677	long.
568		678
569	This request can be used to artificially increase load, e.g. for debugging	679	This request can be used to artificially increase load, e.g. for debugging
570	or benchmarking reasons.	680	or benchmarking reasons.
…		…
586	There are two primary use cases for this: a) bundle many requests into a	696	There are two primary use cases for this: a) bundle many requests into a
587	single, composite, request with a definite callback and the ability to	697	single, composite, request with a definite callback and the ability to
588	cancel the whole request with its subrequests and b) limiting the number	698	cancel the whole request with its subrequests and b) limiting the number
589	of "active" requests.	699	of "active" requests.
590		700
591	Further below you will find more dicussion of these topics - first follows	701	Further below you will find more discussion of these topics - first
592	the reference section detailing the request generator and other methods.	702	follows the reference section detailing the request generator and other
		703	methods.
593		704
594	=over 4	705	=over 4
595		706
596	=item eio_grp (eio_cb cb, void *data)	707	=item eio_req grp = eio_grp (eio_cb cb, void data)
597		708
598	Creates and submits a group request.	709	Creates, submits and returns a group request. Note that it doesn't have a
		710	priority, unlike all other requests.
599		711
600	=back	712	=item eio_grp_add (eio_req grp, eio_req req)
601		713
		714	Adds a request to the request group.
		715
		716	=item eio_grp_cancel (eio_req *grp)
		717
		718	Cancels all requests I<in> the group, but I<not> the group request
		719	itself. You can cancel the group request I<and> all subrequests via a
		720	normal C<eio_cancel> call.
		721
		722	=back
		723
		724	=head4 GROUP REQUEST LIFETIME
		725
		726	Left alone, a group request will instantly move to the pending state and
		727	will be finished at the next call of C<eio_poll>.
		728
		729	The usefulness stems from the fact that, if a subrequest is added to a
		730	group I<before> a call to C<eio_poll>, via C<eio_grp_add>, then the group
		731	will not finish until all the subrequests have finished.
		732
		733	So the usage cycle of a group request is like this: after it is created,
		734	you normally instantly add a subrequest. If none is added, the group
		735	request will finish on it's own. As long as subrequests are added before
		736	the group request is finished it will be kept from finishing, that is the
		737	callbacks of any subrequests can, in turn, add more requests to the group,
		738	and as long as any requests are active, the group request itself will not
		739	finish.
		740
		741	=head4 CREATING COMPOSITE REQUESTS
		742
		743	Imagine you wanted to create an C<eio_load> request that opens a file,
		744	reads it and closes it. This means it has to execute at least three eio
		745	requests, but for various reasons it might be nice if that request looked
		746	like any other eio request.
		747
		748	This can be done with groups:
		749
		750	=over 4
		751
		752	=item 1) create the request object
		753
		754	Create a group that contains all further requests. This is the request you
		755	can return as "the load request".
		756
		757	=item 2) open the file, maybe
		758
		759	Next, open the file with C<eio_open> and add the request to the group
		760	request and you are finished setting up the request.
		761
		762	If, for some reason, you cannot C<eio_open> (path is a null ptr?) you
		763	can set C<< grp->result >> to C<-1> to signal an error and let the group
		764	request finish on its own.
		765
		766	=item 3) open callback adds more requests
		767
		768	In the open callback, if the open was not successful, copy C<<
		769	req->errorno >> to C<< grp->errorno >> and set C<< grp->result >> to
		770	C<-1> to signal an error.
		771
		772	Otherwise, malloc some memory or so and issue a read request, adding the
		773	read request to the group.
		774
		775	=item 4) continue issuing requests till finished
		776
		777	In the read callback, check for errors and possibly continue with
		778	C<eio_close> or any other eio request in the same way.
		779
		780	As soon as no new requests are added, the group request will finish. Make
		781	sure you I<always> set C<< grp->result >> to some sensible value.
		782
		783	=back
		784
		785	=head4 REQUEST LIMITING
602		786
603		787
604	#TODO	788	#TODO
605		789
606	/*****************************************************************************/
607	/* groups */
608
609	eio_req eio_grp (eio_cb cb, void data);
610	void eio_grp_feed (eio_req grp, void (feed)(eio_req *req), int limit);
611	void eio_grp_limit (eio_req *grp, int limit);	790	void eio_grp_limit (eio_req *grp, int limit);
612	void eio_grp_add (eio_req grp, eio_req req);
613	void eio_grp_cancel (eio_req grp); / cancels all sub requests but not the group */
614		791
615		792
616	=back	793	=back
617		794
618		795
…		…
624	=head1 ANATOMY AND LIFETIME OF AN EIO REQUEST	801	=head1 ANATOMY AND LIFETIME OF AN EIO REQUEST
625		802
626	A request is represented by a structure of type C<eio_req>. To initialise	803	A request is represented by a structure of type C<eio_req>. To initialise
627	it, clear it to all zero bytes:	804	it, clear it to all zero bytes:
628		805
629	eio_req req;	806	eio_req req;
630		807
631	memset (&req, 0, sizeof (req));	808	memset (&req, 0, sizeof (req));
632		809
633	A more common way to initialise a new C<eio_req> is to use C<calloc>:	810	A more common way to initialise a new C<eio_req> is to use C<calloc>:
634		811
635	eio_req req = calloc (1, sizeof (req));	812	eio_req req = calloc (1, sizeof (req));
636		813
637	In either case, libeio neither allocates, initialises or frees the	814	In either case, libeio neither allocates, initialises or frees the
638	C<eio_req> structure for you - it merely uses it.	815	C<eio_req> structure for you - it merely uses it.
639		816
640	zero	817	zero
…		…
658	for example, in interactive programs, you might want to limit this time to	835	for example, in interactive programs, you might want to limit this time to
659	C<0.01> seconds or so.	836	C<0.01> seconds or so.
660		837
661	Note that:	838	Note that:
662		839
		840	=over 4
		841
663	a) libeio doesn't know how long your request callbacks take, so the time	842	=item a) libeio doesn't know how long your request callbacks take, so the
664	spent in C<eio_poll> is up to one callback invocation longer then this	843	time spent in C<eio_poll> is up to one callback invocation longer then
665	interval.	844	this interval.
666		845
667	b) this is implemented by calling C<gettimeofday> after each request,	846	=item b) this is implemented by calling C<gettimeofday> after each
668	which can be costly.	847	request, which can be costly.
669		848
670	c) at least one request will be handled.	849	=item c) at least one request will be handled.
		850
		851	=back
671		852
672	=item eio_set_max_poll_reqs (unsigned int nreqs)	853	=item eio_set_max_poll_reqs (unsigned int nreqs)
673		854
674	When C<nreqs> is non-zero, then C<eio_poll> will not handle more than	855	When C<nreqs> is non-zero, then C<eio_poll> will not handle more than
675	C<nreqs> requests per invocation. This is a less costly way to limit the	856	C<nreqs> requests per invocation. This is a less costly way to limit the
…		…
745	This symbol governs the stack size for each eio thread. Libeio itself	926	This symbol governs the stack size for each eio thread. Libeio itself
746	was written to use very little stackspace, but when using C<EIO_CUSTOM>	927	was written to use very little stackspace, but when using C<EIO_CUSTOM>
747	requests, you might want to increase this.	928	requests, you might want to increase this.
748		929
749	If this symbol is undefined (the default) then libeio will use its default	930	If this symbol is undefined (the default) then libeio will use its default
750	stack size (C<sizeof (long) * 4096> currently). If it is defined, but	931	stack size (C<sizeof (void ) 4096> currently). In all other cases, the
751	C<0>, then the default operating system stack size will be used. In all
752	other cases, the value must be an expression that evaluates to the desired	932	value must be an expression that evaluates to the desired stack size.
753	stack size.
754		933
755	=back	934	=back
756		935
757		936
758	=head1 PORTABILITY REQUIREMENTS	937	=head1 PORTABILITY REQUIREMENTS

Diff Legend

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

Comparing libeio/eio.pod (file contents): Revision 1.14 by root, Tue Jul 5 14:02:15 2011 UTC vs. Revision 1.32 by root, Sat Jan 19 00:02:34 2013 UTC

Diff Legend

Comparing libeio/eio.pod (file contents):
Revision 1.14 by root, Tue Jul 5 14:02:15 2011 UTC vs.
Revision 1.32 by root, Sat Jan 19 00:02:34 2013 UTC