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

Comparing libeio/eio.pod (file contents):
Revision 1.15 by root, Tue Jul 5 16:57:41 2011 UTC vs.
Revision 1.35 by root, Mon Aug 18 08:11:54 2014 UTC

…		…
25	similar functions, as well as less rarely ones such as C<mknod>, C<futime>	25	similar functions, as well as less rarely ones such as C<mknod>, C<futime>
26	or C<readlink>.	26	or C<readlink>.
27		27
28	It also offers wrappers around C<sendfile> (Solaris, Linux, HP-UX and	28	It also offers wrappers around C<sendfile> (Solaris, Linux, HP-UX and
29	FreeBSD, with emulation on other platforms) and C<readahead> (Linux, with	29	FreeBSD, with emulation on other platforms) and C<readahead> (Linux, with
30	emulation elsewhere>).	30	emulation elsewhere).
31		31
32	The goal is to enable you to write fully non-blocking programs. For	32	The goal is to enable you to write fully non-blocking programs. For
33	example, in a game server, you would not want to freeze for a few seconds	33	example, in a game server, you would not want to freeze for a few seconds
34	just because the server is running a backup and you happen to call	34	just because the server is running a backup and you happen to call
35	C<readdir>.	35	C<readdir>.
…		…
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",
…		…
130		137
131	If C<eio_poll ()> is configured to not handle all results in one go	138	If C<eio_poll ()> is configured to not handle all results in one go
132	(i.e. it returns C<-1>) then you should start an idle watcher that calls	139	(i.e. it returns C<-1>) then you should start an idle watcher that calls
133	C<eio_poll> until it returns something C<!= -1>.	140	C<eio_poll> until it returns something C<!= -1>.
134		141
135	A full-featured wrapper would look as follows (if C<eio_poll> is handling	142	A full-featured connector between libeio and libev would look as follows
136	all requests, it can of course be simplified a lot by removing the idle	143	(if C<eio_poll> is handling all requests, it can of course be simplified a
137	watcher logic):	144	lot by removing the idle watcher logic):
138		145
139	static struct ev_loop *loop;	146	static struct ev_loop *loop;
140	static ev_idle repeat_watcher;	147	static ev_idle repeat_watcher;
141	static ev_async ready_watcher;	148	static ev_async ready_watcher;
142		149
143	/* idle watcher callback, only used when eio_poll */	150	/* idle watcher callback, only used when eio_poll */
144	/* didn't handle all results in one call */	151	/* didn't handle all results in one call */
145	static void	152	static void
146	repeat (EV_P_ ev_idle *w, int revents)	153	repeat (EV_P_ ev_idle *w, int revents)
147	{	154	{
148	if (eio_poll () != -1)	155	if (eio_poll () != -1)
149	ev_idle_stop (EV_A_ w);	156	ev_idle_stop (EV_A_ w);
150	}	157	}
151		158
152	/* eio has some results, process them */	159	/* eio has some results, process them */
153	static void	160	static void
154	ready (EV_P_ ev_async *w, int revents)	161	ready (EV_P_ ev_async *w, int revents)
155	{	162	{
156	if (eio_poll () == -1)	163	if (eio_poll () == -1)
157	ev_idle_start (EV_A_ &repeat_watcher);	164	ev_idle_start (EV_A_ &repeat_watcher);
158	}	165	}
159		166
160	/* wake up the event loop */	167	/* wake up the event loop */
161	static void	168	static void
162	want_poll (void)	169	want_poll (void)
163	{	170	{
164	ev_async_send (loop, &ready_watcher)	171	ev_async_send (loop, &ready_watcher)
165	}	172	}
166		173
167	void	174	void
168	my_init_eio ()	175	my_init_eio ()
169	{	176	{
170	loop = EV_DEFAULT;	177	loop = EV_DEFAULT;
171		178
172	ev_idle_init (&repeat_watcher, repeat);	179	ev_idle_init (&repeat_watcher, repeat);
173	ev_async_init (&ready_watcher, ready);	180	ev_async_init (&ready_watcher, ready);
174	ev_async_start (loop &watcher);	181	ev_async_start (loop, &watcher);
175		182
176	eio_init (want_poll, 0);	183	eio_init (want_poll, 0);
177	}	184	}
178		185
179	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
180	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
181	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
182	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
183	C<eio_poll>. The race is avoided here because the event loop should invoke	190	C<eio_poll>.
184	your callback again and again until the byte has been read (as the pipe	191
185	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.
186		196
187		197
188	=head1 HIGH LEVEL REQUEST API	198	=head1 HIGH LEVEL REQUEST API
189		199
190	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
…		…
223		233
224	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.
225		235
226	=back	236	=back
227		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
228	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
229	continue normally. If a callback returns a nonzero value, libeio will	243	continue normally. If a callback returns a nonzero value, libeio will
230	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
231	caller.	245	caller.
232		246
233	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
234	executes, with the exception of paths, which are being copied	248	request executes, with the exception of paths, which are being copied
235	internally. Any memory libeio itself allocates will be freed after the	249	internally. Any memory libeio itself allocates will be freed after the
236	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
237	to libeio yourself you can use the low-level API.	251	to libeio yourself you can use the low-level API.
238		252
239	For example, to open a file, you could do this:	253	For example, to open a file, you could do this:
…		…
257	}	271	}
258		272
259	/* the first three arguments are passed to open(2) */	273	/* the first three arguments are passed to open(2) */
260	/* the remaining are priority, callback and data */	274	/* the remaining are priority, callback and data */
261	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))
262	abort (); /* something ent wrong, we will all die!!! */	276	abort (); /* something went wrong, we will all die!!! */
263		277
264	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>
265	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	When cancelled, the finish callback will not be invoked.
		296
		297	C<EIO_CANCELLED> is still true for requests that have successfully
		298	executed, as long as C<eio_cancel> was called on them at some point.
		299
		300	=back
266		301
267	=head2 AVAILABLE REQUESTS	302	=head2 AVAILABLE REQUESTS
268		303
269	The following request functions are available. I<All> of them return the	304	The following request functions are available. I<All> of them return the
270	C<eio_req *> on success and C<0> on failure, and I<all> of them have the	305	C<eio_req *> on success and C<0> on failure, and I<all> of them have the
…		…
366	free (target);	401	free (target);
367	}	402	}
368		403
369	=item eio_realpath (const char path, int pri, eio_cb cb, void data)	404	=item eio_realpath (const char path, int pri, eio_cb cb, void data)
370		405
371	Similar to the realpath libc function, but unlike that one, result is	406	Similar to the realpath libc function, but unlike that one, C<<
372	C<-1> on failure and the length of the returned path in C<ptr2> (which is	407	req->result >> is C<-1> on failure. On success, the result is the length
373	not 0-terminated) - this is similar to readlink.	408	of the returned path in C<ptr2> (which is I<NOT> 0-terminated) - this is
		409	similar to readlink.
374		410
375	=item eio_stat (const char path, int pri, eio_cb cb, void data)	411	=item eio_stat (const char path, int pri, eio_cb cb, void data)
376		412
377	=item eio_lstat (const char path, int pri, eio_cb cb, void data)	413	=item eio_lstat (const char path, int pri, eio_cb cb, void data)
378		414
379	=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)
380		416
381	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
382	access the C<struct stat>-like structure via C<< req->ptr2 >>:	418	access the C<struct stat>-like structure via C<< req->ptr2 >>:
383		419
384	EIO_STRUCT_STAT statdata = (EIO_STRUCT_STAT )req->ptr2;	420	EIO_STRUCT_STAT statdata = (EIO_STRUCT_STAT )req->ptr2;
385		421
386	=item eio_statvfs (const char path, int pri, eio_cb cb, void data)	422	=item eio_statvfs (const char path, int pri, eio_cb cb, void data)
387		423
388	=item eio_fstatvfs (int fd, int pri, eio_cb cb, void *data)	424	=item eio_fstatvfs (int fd, int pri, eio_cb cb, void *data)
389		425
390	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
391	access the C<struct statvfs>-like structure via C<< req->ptr2 >>:	427	access the C<struct statvfs>-like structure via C<< req->ptr2 >>:
392		428
393	EIO_STRUCT_STATVFS statdata = (EIO_STRUCT_STATVFS )req->ptr2;	429	EIO_STRUCT_STATVFS statdata = (EIO_STRUCT_STATVFS )req->ptr2;
394		430
395	=back	431	=back
396		432
397	=head3 READING DIRECTORIES	433	=head3 READING DIRECTORIES
398		434
399	Reading directories sounds simple, but can be rather demanding, especially	435	Reading directories sounds simple, but can be rather demanding, especially
400	if you want to do stuff such as traversing a diretcory hierarchy or	436	if you want to do stuff such as traversing a directory hierarchy or
401	processing all files in a directory. Libeio can assist thess complex tasks	437	processing all files in a directory. Libeio can assist these complex tasks
402	with it's C<eio_readdir> call.	438	with it's C<eio_readdir> call.
403		439
404	=over 4	440	=over 4
405		441
406	=item eio_readdir (const char path, int flags, int pri, eio_cb cb, void data)	442	=item eio_readdir (const char path, int flags, int pri, eio_cb cb, void data)
…		…
438		474
439	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>,
440	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
441	eio_dirent> looks like this:	477	eio_dirent> looks like this:
442		478
443	struct eio_dirent	479	struct eio_dirent
444	{	480	{
445	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 /
446	unsigned short namelen; /* size of filename without trailing 0 */	482	unsigned short namelen; /* size of filename without trailing 0 */
447	unsigned char type; /* one of EIO_DT_* */	483	unsigned char type; /* one of EIO_DT_* */
448	signed char score; /* internal use */	484	signed char score; /* internal use */
449	ino_t inode; /* the inode number, if available, otherwise unspecified */	485	ino_t inode; /* the inode number, if available, otherwise unspecified */
450	};	486	};
451		487
452	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
453	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>.
454		490
455	C<type> can be one of:	491	C<type> can be one of:
…		…
498	When this flag is specified, then the names will be returned in an order	534	When this flag is specified, then the names will be returned in an order
499	suitable for stat()'ing each one. That is, when you plan to stat()	535	suitable for stat()'ing each one. That is, when you plan to stat()
500	all files in the given directory, then the returned order will likely	536	all files in the given directory, then the returned order will likely
501	be fastest.	537	be fastest.
502		538
503	If both this flag and C<EIO_READDIR_DIRS_FIRST> are specified, then	539	If both this flag and C<EIO_READDIR_DIRS_FIRST> are specified, then the
504	the likely dirs come first, resulting in a less optimal stat order.	540	likely directories come first, resulting in a less optimal stat order.
505		541
506	=item EIO_READDIR_FOUND_UNKNOWN	542	=item EIO_READDIR_FOUND_UNKNOWN
507		543
508	This flag should not be specified when calling C<eio_readdir>. Instead,	544	This flag should not be specified when calling C<eio_readdir>. Instead,
509	it is being set by C<eio_readdir> (you can access the C<flags> via C<<	545	it is being set by C<eio_readdir> (you can access the C<flags> via C<<
510	req->int1 >>, when any of the C<type>'s found were C<EIO_DT_UNKNOWN>. The	546	req->int1 >>, when any of the C<type>'s found were C<EIO_DT_UNKNOWN>. The
511	absense of this flag therefore indicates that all C<type>'s are known,	547	absence of this flag therefore indicates that all C<type>'s are known,
512	which can be used to speed up some algorithms.	548	which can be used to speed up some algorithms.
513		549
514	A typical use case would be to identify all subdirectories within a	550	A typical use case would be to identify all subdirectories within a
515	directory - you would ask C<eio_readdir> for C<EIO_READDIR_DIRS_FIRST>. If	551	directory - you would ask C<eio_readdir> for C<EIO_READDIR_DIRS_FIRST>. If
516	then this flag is I<NOT> set, then all the entries at the beginning of the	552	then this flag is I<NOT> set, then all the entries at the beginning of the
…		…
546	=item eio_readahead (int fd, off_t offset, size_t length, int pri, eio_cb cb, void *data)	582	=item eio_readahead (int fd, off_t offset, size_t length, int pri, eio_cb cb, void *data)
547		583
548	Calls C<readahead(2)>. If the syscall is missing, then the call is	584	Calls C<readahead(2)>. If the syscall is missing, then the call is
549	emulated by simply reading the data (currently in 64kiB chunks).	585	emulated by simply reading the data (currently in 64kiB chunks).
550		586
		587	=item eio_syncfs (int fd, int pri, eio_cb cb, void *data)
		588
		589	Calls Linux' C<syncfs> syscall, if available. Returns C<-1> and sets
		590	C<errno> to C<ENOSYS> if the call is missing I<but still calls sync()>,
		591	if the C<fd> is C<< >= 0 >>, so you can probe for the availability of the
		592	syscall with a negative C<fd> argument and checking for C<-1/ENOSYS>.
		593
551	=item eio_sync_file_range (int fd, off_t offset, size_t nbytes, unsigned int flags, int pri, eio_cb cb, void *data)	594	=item eio_sync_file_range (int fd, off_t offset, size_t nbytes, unsigned int flags, int pri, eio_cb cb, void *data)
552		595
553	Calls C<sync_file_range>. If the syscall is missing, then this is the same	596	Calls C<sync_file_range>. If the syscall is missing, then this is the same
554	as calling C<fdatasync>.	597	as calling C<fdatasync>.
555		598
556	Flags can be any combination of C<EIO_SYNC_FILE_RANGE_WAIT_BEFORE>,	599	Flags can be any combination of C<EIO_SYNC_FILE_RANGE_WAIT_BEFORE>,
557	C<EIO_SYNC_FILE_RANGE_WRITE> and C<EIO_SYNC_FILE_RANGE_WAIT_AFTER>.	600	C<EIO_SYNC_FILE_RANGE_WRITE> and C<EIO_SYNC_FILE_RANGE_WAIT_AFTER>.
558		601
		602	=item eio_fallocate (int fd, int mode, off_t offset, off_t len, int pri, eio_cb cb, void *data)
		603
		604	Calls C<fallocate> (note: I<NOT> C<posix_fallocate>!). If the syscall is
		605	missing, then it returns failure and sets C<errno> to C<ENOSYS>.
		606
		607	The C<mode> argument can be C<0> (for behaviour similar to
		608	C<posix_fallocate>), or C<EIO_FALLOC_FL_KEEP_SIZE>, which keeps the size
		609	of the file unchanged (but still preallocates space beyond end of file).
		610
559	=back	611	=back
560		612
561	=head3 LIBEIO-SPECIFIC REQUESTS	613	=head3 LIBEIO-SPECIFIC REQUESTS
562		614
563	These requests are specific to libeio and do not correspond to any OS call.	615	These requests are specific to libeio and do not correspond to any OS call.
564		616
565	=over 4	617	=over 4
566		618
567	=item eio_mtouch (void addr, size_t length, int flags, int pri, eio_cb cb, void data)	619	=item eio_mtouch (void addr, size_t length, int flags, int pri, eio_cb cb, void data)
568		620
569	Reads (C<flags == 0>) or modifies (C<flags == EIO_MT_MODIFY) the given	621	Reads (C<flags == 0>) or modifies (C<flags == EIO_MT_MODIFY>) the given
570	memory area, page-wise, that is, it reads (or reads and writes back) the	622	memory area, page-wise, that is, it reads (or reads and writes back) the
571	first octet of every page that spans the memory area.	623	first octet of every page that spans the memory area.
572		624
573	This can be used to page in some mmapped file, or dirty some pages. Note	625	This can be used to page in some mmapped file, or dirty some pages. Note
574	that dirtying is an unlocked read-write access, so races can ensue when	626	that dirtying is an unlocked read-write access, so races can ensue when
…		…
604		656
605	eio_custom (my_open, 0, my_open_done, "/etc/passwd");	657	eio_custom (my_open, 0, my_open_done, "/etc/passwd");
606		658
607	=item eio_busy (eio_tstamp delay, int pri, eio_cb cb, void *data)	659	=item eio_busy (eio_tstamp delay, int pri, eio_cb cb, void *data)
608		660
609	This is a a request that takes C<delay> seconds to execute, but otherwise	661	This is a request that takes C<delay> seconds to execute, but otherwise
610	does nothing - it simply puts one of the worker threads to sleep for this	662	does nothing - it simply puts one of the worker threads to sleep for this
611	long.	663	long.
612		664
613	This request can be used to artificially increase load, e.g. for debugging	665	This request can be used to artificially increase load, e.g. for debugging
614	or benchmarking reasons.	666	or benchmarking reasons.
…		…
630	There are two primary use cases for this: a) bundle many requests into a	682	There are two primary use cases for this: a) bundle many requests into a
631	single, composite, request with a definite callback and the ability to	683	single, composite, request with a definite callback and the ability to
632	cancel the whole request with its subrequests and b) limiting the number	684	cancel the whole request with its subrequests and b) limiting the number
633	of "active" requests.	685	of "active" requests.
634		686
635	Further below you will find more dicussion of these topics - first follows	687	Further below you will find more discussion of these topics - first
636	the reference section detailing the request generator and other methods.	688	follows the reference section detailing the request generator and other
		689	methods.
637		690
638	=over 4	691	=over 4
639		692
640	=item eio_grp (eio_cb cb, void *data)	693	=item eio_req grp = eio_grp (eio_cb cb, void data)
641		694
642	Creates and submits a group request.	695	Creates, submits and returns a group request. Note that it doesn't have a
		696	priority, unlike all other requests.
643		697
644	=back	698	=item eio_grp_add (eio_req grp, eio_req req)
645		699
		700	Adds a request to the request group.
		701
		702	=item eio_grp_cancel (eio_req *grp)
		703
		704	Cancels all requests I<in> the group, but I<not> the group request
		705	itself. You can cancel the group request I<and> all subrequests via a
		706	normal C<eio_cancel> call.
		707
		708	=back
		709
		710	=head4 GROUP REQUEST LIFETIME
		711
		712	Left alone, a group request will instantly move to the pending state and
		713	will be finished at the next call of C<eio_poll>.
		714
		715	The usefulness stems from the fact that, if a subrequest is added to a
		716	group I<before> a call to C<eio_poll>, via C<eio_grp_add>, then the group
		717	will not finish until all the subrequests have finished.
		718
		719	So the usage cycle of a group request is like this: after it is created,
		720	you normally instantly add a subrequest. If none is added, the group
		721	request will finish on it's own. As long as subrequests are added before
		722	the group request is finished it will be kept from finishing, that is the
		723	callbacks of any subrequests can, in turn, add more requests to the group,
		724	and as long as any requests are active, the group request itself will not
		725	finish.
		726
		727	=head4 CREATING COMPOSITE REQUESTS
		728
		729	Imagine you wanted to create an C<eio_load> request that opens a file,
		730	reads it and closes it. This means it has to execute at least three eio
		731	requests, but for various reasons it might be nice if that request looked
		732	like any other eio request.
		733
		734	This can be done with groups:
		735
		736	=over 4
		737
		738	=item 1) create the request object
		739
		740	Create a group that contains all further requests. This is the request you
		741	can return as "the load request".
		742
		743	=item 2) open the file, maybe
		744
		745	Next, open the file with C<eio_open> and add the request to the group
		746	request and you are finished setting up the request.
		747
		748	If, for some reason, you cannot C<eio_open> (path is a null ptr?) you
		749	can set C<< grp->result >> to C<-1> to signal an error and let the group
		750	request finish on its own.
		751
		752	=item 3) open callback adds more requests
		753
		754	In the open callback, if the open was not successful, copy C<<
		755	req->errorno >> to C<< grp->errorno >> and set C<< grp->result >> to
		756	C<-1> to signal an error.
		757
		758	Otherwise, malloc some memory or so and issue a read request, adding the
		759	read request to the group.
		760
		761	=item 4) continue issuing requests till finished
		762
		763	In the read callback, check for errors and possibly continue with
		764	C<eio_close> or any other eio request in the same way.
		765
		766	As soon as no new requests are added, the group request will finish. Make
		767	sure you I<always> set C<< grp->result >> to some sensible value.
		768
		769	=back
		770
		771	=head4 REQUEST LIMITING
646		772
647		773
648	#TODO	774	#TODO
649		775
650	/*****************************************************************************/
651	/* groups */
652
653	eio_req eio_grp (eio_cb cb, void data);
654	void eio_grp_feed (eio_req grp, void (feed)(eio_req *req), int limit);
655	void eio_grp_limit (eio_req *grp, int limit);	776	void eio_grp_limit (eio_req *grp, int limit);
656	void eio_grp_add (eio_req grp, eio_req req);
657	void eio_grp_cancel (eio_req grp); / cancels all sub requests but not the group */
658		777
659
660	=back
661		778
662		779
663	=head1 LOW LEVEL REQUEST API	780	=head1 LOW LEVEL REQUEST API
664		781
665	#TODO	782	#TODO
…		…
668	=head1 ANATOMY AND LIFETIME OF AN EIO REQUEST	785	=head1 ANATOMY AND LIFETIME OF AN EIO REQUEST
669		786
670	A request is represented by a structure of type C<eio_req>. To initialise	787	A request is represented by a structure of type C<eio_req>. To initialise
671	it, clear it to all zero bytes:	788	it, clear it to all zero bytes:
672		789
673	eio_req req;	790	eio_req req;
674		791
675	memset (&req, 0, sizeof (req));	792	memset (&req, 0, sizeof (req));
676		793
677	A more common way to initialise a new C<eio_req> is to use C<calloc>:	794	A more common way to initialise a new C<eio_req> is to use C<calloc>:
678		795
679	eio_req req = calloc (1, sizeof (req));	796	eio_req req = calloc (1, sizeof (req));
680		797
681	In either case, libeio neither allocates, initialises or frees the	798	In either case, libeio neither allocates, initialises or frees the
682	C<eio_req> structure for you - it merely uses it.	799	C<eio_req> structure for you - it merely uses it.
683		800
684	zero	801	zero
…		…
702	for example, in interactive programs, you might want to limit this time to	819	for example, in interactive programs, you might want to limit this time to
703	C<0.01> seconds or so.	820	C<0.01> seconds or so.
704		821
705	Note that:	822	Note that:
706		823
		824	=over 4
		825
707	a) libeio doesn't know how long your request callbacks take, so the time	826	=item a) libeio doesn't know how long your request callbacks take, so the
708	spent in C<eio_poll> is up to one callback invocation longer then this	827	time spent in C<eio_poll> is up to one callback invocation longer then
709	interval.	828	this interval.
710		829
711	b) this is implemented by calling C<gettimeofday> after each request,	830	=item b) this is implemented by calling C<gettimeofday> after each
712	which can be costly.	831	request, which can be costly.
713		832
714	c) at least one request will be handled.	833	=item c) at least one request will be handled.
		834
		835	=back
715		836
716	=item eio_set_max_poll_reqs (unsigned int nreqs)	837	=item eio_set_max_poll_reqs (unsigned int nreqs)
717		838
718	When C<nreqs> is non-zero, then C<eio_poll> will not handle more than	839	When C<nreqs> is non-zero, then C<eio_poll> will not handle more than
719	C<nreqs> requests per invocation. This is a less costly way to limit the	840	C<nreqs> requests per invocation. This is a less costly way to limit the
…		…
789	This symbol governs the stack size for each eio thread. Libeio itself	910	This symbol governs the stack size for each eio thread. Libeio itself
790	was written to use very little stackspace, but when using C<EIO_CUSTOM>	911	was written to use very little stackspace, but when using C<EIO_CUSTOM>
791	requests, you might want to increase this.	912	requests, you might want to increase this.
792		913
793	If this symbol is undefined (the default) then libeio will use its default	914	If this symbol is undefined (the default) then libeio will use its default
794	stack size (C<sizeof (long) * 4096> currently). If it is defined, but	915	stack size (C<sizeof (void ) 4096> currently). In all other cases, the
795	C<0>, then the default operating system stack size will be used. In all
796	other cases, the value must be an expression that evaluates to the desired	916	value must be an expression that evaluates to the desired stack size.
797	stack size.
798		917
799	=back	918	=back
800		919
801		920
802	=head1 PORTABILITY REQUIREMENTS	921	=head1 PORTABILITY REQUIREMENTS

Diff Legend

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

Comparing libeio/eio.pod (file contents): Revision 1.15 by root, Tue Jul 5 16:57:41 2011 UTC vs. Revision 1.35 by root, Mon Aug 18 08:11:54 2014 UTC

Diff Legend

Comparing libeio/eio.pod (file contents):
Revision 1.15 by root, Tue Jul 5 16:57:41 2011 UTC vs.
Revision 1.35 by root, Mon Aug 18 08:11:54 2014 UTC