[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 1.36 by root, Sun Jan 24 16:36:20 2016 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",
…		…
97	This callback is invoked when libeio detects that all pending requests	104	This callback is invoked when libeio detects that all pending requests
98	have been handled. It is "edge-triggered", that is, it will only be	105	have been handled. It is "edge-triggered", that is, it will only be
99	called once after C<want_poll>. To put it differently, C<want_poll> and	106	called once after C<want_poll>. To put it differently, C<want_poll> and
100	C<done_poll> are invoked in pairs: after C<want_poll> you have to call	107	C<done_poll> are invoked in pairs: after C<want_poll> you have to call
101	C<eio_poll ()> until either C<eio_poll> indicates that everything has been	108	C<eio_poll ()> until either C<eio_poll> indicates that everything has been
102	handled or C<done_poll> has been called, which signals the same.	109	handled or C<done_poll> has been called, which signals the same - only one
		110	method is needed.
103		111
104	Note that C<eio_poll> might return after C<done_poll> and C<want_poll>	112	Note that C<eio_poll> might return after C<done_poll> and C<want_poll>
105	have been called again, so watch out for races in your code.	113	have been called again, so watch out for races in your code.
106		114
		115	It is quite common to have an empty C<done_call> callback and only use
		116	the return value from C<eio_poll>, or, when C<eio_poll> is configured to
		117	handle all outstanding replies, it's enough to call C<eio_poll> once.
		118
107	As with C<want_poll>, this callback is called while locks are being held,	119	As with C<want_poll>, this callback is called while locks are being held,
108	so you I<must not call any libeio functions form within this callback>.	120	so you I<must not call any libeio functions from within this callback>.
109		121
110	=item int eio_poll ()	122	=item int eio_poll ()
111		123
112	This function has to be called whenever there are pending requests that	124	This function has to be called whenever there are pending requests that
113	need finishing. You usually call this after C<want_poll> has indicated	125	need finishing. You usually call this after C<want_poll> has indicated
…		…
130		142
131	If C<eio_poll ()> is configured to not handle all results in one go	143	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	144	(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>.	145	C<eio_poll> until it returns something C<!= -1>.
134		146
135	A full-featured wrapper would look as follows (if C<eio_poll> is handling	147	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	148	(if C<eio_poll> is handling all requests, it can of course be simplified a
137	watcher logic):	149	lot by removing the idle watcher logic):
138		150
139	static struct ev_loop *loop;	151	static struct ev_loop *loop;
140	static ev_idle repeat_watcher;	152	static ev_idle repeat_watcher;
141	static ev_async ready_watcher;	153	static ev_async ready_watcher;
142		154
143	/* idle watcher callback, only used when eio_poll */	155	/* idle watcher callback, only used when eio_poll */
144	/* didn't handle all results in one call */	156	/* didn't handle all results in one call */
145	static void	157	static void
146	repeat (EV_P_ ev_idle *w, int revents)	158	repeat (EV_P_ ev_idle *w, int revents)
147	{	159	{
148	if (eio_poll () != -1)	160	if (eio_poll () != -1)
149	ev_idle_stop (EV_A_ w);	161	ev_idle_stop (EV_A_ w);
150	}	162	}
151		163
152	/* eio has some results, process them */	164	/* eio has some results, process them */
153	static void	165	static void
154	ready (EV_P_ ev_async *w, int revents)	166	ready (EV_P_ ev_async *w, int revents)
155	{	167	{
156	if (eio_poll () == -1)	168	if (eio_poll () == -1)
157	ev_idle_start (EV_A_ &repeat_watcher);	169	ev_idle_start (EV_A_ &repeat_watcher);
158	}	170	}
159		171
160	/* wake up the event loop */	172	/* wake up the event loop */
161	static void	173	static void
162	want_poll (void)	174	want_poll (void)
163	{	175	{
164	ev_async_send (loop, &ready_watcher)	176	ev_async_send (loop, &ready_watcher)
165	}	177	}
166		178
167	void	179	void
168	my_init_eio ()	180	my_init_eio ()
169	{	181	{
170	loop = EV_DEFAULT;	182	loop = EV_DEFAULT;
171		183
172	ev_idle_init (&repeat_watcher, repeat);	184	ev_idle_init (&repeat_watcher, repeat);
173	ev_async_init (&ready_watcher, ready);	185	ev_async_init (&ready_watcher, ready);
174	ev_async_start (loop &watcher);	186	ev_async_start (loop, &watcher);
175		187
176	eio_init (want_poll, 0);	188	eio_init (want_poll, 0);
177	}	189	}
178		190
179	For most other event loops, you would typically use a pipe - the event	191	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	192	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	193	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	194	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	195	C<eio_poll>.
184	your callback again and again until the byte has been read (as the pipe	196
185	read callback does not read it, only C<done_poll>).	197	You don't have to take special care in the case C<eio_poll> doesn't handle
		198	all requests, as the done callback will not be invoked, so the event loop
		199	will still signal readiness for the pipe until I<all> results have been
		200	processed.
186		201
187		202
188	=head1 HIGH LEVEL REQUEST API	203	=head1 HIGH LEVEL REQUEST API
189		204
190	Libeio has both a high-level API, which consists of calling a request	205	Libeio has both a high-level API, which consists of calling a request
…		…
223		238
224	The C<void *data> member simply stores the value of the C<data> argument.	239	The C<void *data> member simply stores the value of the C<data> argument.
225		240
226	=back	241	=back
227		242
		243	Members not explicitly described as accessible must not be
		244	accessed. Specifically, there is no guarantee that any members will still
		245	have the value they had when the request was submitted.
		246
228	The return value of the callback is normally C<0>, which tells libeio to	247	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	248	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	249	stop processing results (in C<eio_poll>) and will return the value to its
231	caller.	250	caller.
232		251
233	Memory areas passed to libeio must stay valid as long as a request	252	Memory areas passed to libeio wrappers must stay valid as long as a
234	executes, with the exception of paths, which are being copied	253	request executes, with the exception of paths, which are being copied
235	internally. Any memory libeio itself allocates will be freed after the	254	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	255	finish callback has been called. If you want to manage all memory passed
237	to libeio yourself you can use the low-level API.	256	to libeio yourself you can use the low-level API.
238		257
239	For example, to open a file, you could do this:	258	For example, to open a file, you could do this:
…		…
257	}	276	}
258		277
259	/* the first three arguments are passed to open(2) */	278	/* the first three arguments are passed to open(2) */
260	/* the remaining are priority, callback and data */	279	/* the remaining are priority, callback and data */
261	if (!eio_open ("/etc/passwd", O_RDONLY, 0, 0, file_open_done, 0))	280	if (!eio_open ("/etc/passwd", O_RDONLY, 0, 0, file_open_done, 0))
262	abort (); /* something ent wrong, we will all die!!! */	281	abort (); /* something went wrong, we will all die!!! */
263		282
264	Note that you additionally need to call C<eio_poll> when the C<want_cb>	283	Note that you additionally need to call C<eio_poll> when the C<want_cb>
265	indicates that requests are ready to be processed.	284	indicates that requests are ready to be processed.
		285
		286	=head2 CANCELLING REQUESTS
		287
		288	Sometimes the need for a request goes away before the request is
		289	finished. In that case, one can cancel the request by a call to
		290	C<eio_cancel>:
		291
		292	=over 4
		293
		294	=item eio_cancel (eio_req *req)
		295
		296	Cancel the request (and all its subrequests). If the request is currently
		297	executing it might still continue to execute, and in other cases it might
		298	still take a while till the request is cancelled.
		299
		300	When cancelled, the finish callback will not be invoked.
		301
		302	C<EIO_CANCELLED> is still true for requests that have successfully
		303	executed, as long as C<eio_cancel> was called on them at some point.
		304
		305	=back
266		306
267	=head2 AVAILABLE REQUESTS	307	=head2 AVAILABLE REQUESTS
268		308
269	The following request functions are available. I<All> of them return the	309	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	310	C<eio_req *> on success and C<0> on failure, and I<all> of them have the
…		…
366	free (target);	406	free (target);
367	}	407	}
368		408
369	=item eio_realpath (const char path, int pri, eio_cb cb, void data)	409	=item eio_realpath (const char path, int pri, eio_cb cb, void data)
370		410
371	Similar to the realpath libc function, but unlike that one, result is	411	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	412	req->result >> is C<-1> on failure. On success, the result is the length
373	not 0-terminated) - this is similar to readlink.	413	of the returned path in C<ptr2> (which is I<NOT> 0-terminated) - this is
		414	similar to readlink.
374		415
375	=item eio_stat (const char path, int pri, eio_cb cb, void data)	416	=item eio_stat (const char path, int pri, eio_cb cb, void data)
376		417
377	=item eio_lstat (const char path, int pri, eio_cb cb, void data)	418	=item eio_lstat (const char path, int pri, eio_cb cb, void data)
378		419
379	=item eio_fstat (int fd, int pri, eio_cb cb, void *data)	420	=item eio_fstat (int fd, int pri, eio_cb cb, void *data)
380		421
381	Stats a file - if C<< req->result >> indicates success, then you can	422	Stats a file - if C<< req->result >> indicates success, then you can
382	access the C<struct stat>-like structure via C<< req->ptr2 >>:	423	access the C<struct stat>-like structure via C<< req->ptr2 >>:
383		424
384	EIO_STRUCT_STAT statdata = (EIO_STRUCT_STAT )req->ptr2;	425	EIO_STRUCT_STAT statdata = (EIO_STRUCT_STAT )req->ptr2;
385		426
386	=item eio_statvfs (const char path, int pri, eio_cb cb, void data)	427	=item eio_statvfs (const char path, int pri, eio_cb cb, void data)
387		428
388	=item eio_fstatvfs (int fd, int pri, eio_cb cb, void *data)	429	=item eio_fstatvfs (int fd, int pri, eio_cb cb, void *data)
389		430
390	Stats a filesystem - if C<< req->result >> indicates success, then you can	431	Stats a filesystem - if C<< req->result >> indicates success, then you can
391	access the C<struct statvfs>-like structure via C<< req->ptr2 >>:	432	access the C<struct statvfs>-like structure via C<< req->ptr2 >>:
392		433
393	EIO_STRUCT_STATVFS statdata = (EIO_STRUCT_STATVFS )req->ptr2;	434	EIO_STRUCT_STATVFS statdata = (EIO_STRUCT_STATVFS )req->ptr2;
394		435
395	=back	436	=back
396		437
397	=head3 READING DIRECTORIES	438	=head3 READING DIRECTORIES
398		439
399	Reading directories sounds simple, but can be rather demanding, especially	440	Reading directories sounds simple, but can be rather demanding, especially
400	if you want to do stuff such as traversing a diretcory hierarchy or	441	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	442	processing all files in a directory. Libeio can assist these complex tasks
402	with it's C<eio_readdir> call.	443	with it's C<eio_readdir> call.
403		444
404	=over 4	445	=over 4
405		446
406	=item eio_readdir (const char path, int flags, int pri, eio_cb cb, void data)	447	=item eio_readdir (const char path, int flags, int pri, eio_cb cb, void data)
…		…
438		479
439	If this flag is specified, then, in addition to the names in C<ptr2>,	480	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	481	also an array of C<struct eio_dirent> is returned, in C<ptr1>. A C<struct
441	eio_dirent> looks like this:	482	eio_dirent> looks like this:
442		483
443	struct eio_dirent	484	struct eio_dirent
444	{	485	{
445	int nameofs; /* offset of null-terminated name string in (char )req->ptr2 /	486	int nameofs; /* offset of null-terminated name string in (char )req->ptr2 /
446	unsigned short namelen; /* size of filename without trailing 0 */	487	unsigned short namelen; /* size of filename without trailing 0 */
447	unsigned char type; /* one of EIO_DT_* */	488	unsigned char type; /* one of EIO_DT_* */
448	signed char score; /* internal use */	489	signed char score; /* internal use */
449	ino_t inode; /* the inode number, if available, otherwise unspecified */	490	ino_t inode; /* the inode number, if available, otherwise unspecified */
450	};	491	};
451		492
452	The only members you normally would access are C<nameofs>, which is the	493	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>.	494	byte-offset from C<ptr2> to the start of the name, C<namelen> and C<type>.
454		495
455	C<type> can be one of:	496	C<type> can be one of:
…		…
498	When this flag is specified, then the names will be returned in an order	539	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()	540	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	541	all files in the given directory, then the returned order will likely
501	be fastest.	542	be fastest.
502		543
503	If both this flag and C<EIO_READDIR_DIRS_FIRST> are specified, then	544	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.	545	likely directories come first, resulting in a less optimal stat order.
505		546
506	=item EIO_READDIR_FOUND_UNKNOWN	547	=item EIO_READDIR_FOUND_UNKNOWN
507		548
508	This flag should not be specified when calling C<eio_readdir>. Instead,	549	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<<	550	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	551	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,	552	absence of this flag therefore indicates that all C<type>'s are known,
512	which can be used to speed up some algorithms.	553	which can be used to speed up some algorithms.
513		554
514	A typical use case would be to identify all subdirectories within a	555	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	556	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	557	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)	587	=item eio_readahead (int fd, off_t offset, size_t length, int pri, eio_cb cb, void *data)
547		588
548	Calls C<readahead(2)>. If the syscall is missing, then the call is	589	Calls C<readahead(2)>. If the syscall is missing, then the call is
549	emulated by simply reading the data (currently in 64kiB chunks).	590	emulated by simply reading the data (currently in 64kiB chunks).
550		591
		592	=item eio_syncfs (int fd, int pri, eio_cb cb, void *data)
		593
		594	Calls Linux' C<syncfs> syscall, if available. Returns C<-1> and sets
		595	C<errno> to C<ENOSYS> if the call is missing I<but still calls sync()>,
		596	if the C<fd> is C<< >= 0 >>, so you can probe for the availability of the
		597	syscall with a negative C<fd> argument and checking for C<-1/ENOSYS>.
		598
551	=item eio_sync_file_range (int fd, off_t offset, size_t nbytes, unsigned int flags, int pri, eio_cb cb, void *data)	599	=item eio_sync_file_range (int fd, off_t offset, size_t nbytes, unsigned int flags, int pri, eio_cb cb, void *data)
552		600
553	Calls C<sync_file_range>. If the syscall is missing, then this is the same	601	Calls C<sync_file_range>. If the syscall is missing, then this is the same
554	as calling C<fdatasync>.	602	as calling C<fdatasync>.
555		603
556	Flags can be any combination of C<EIO_SYNC_FILE_RANGE_WAIT_BEFORE>,	604	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>.	605	C<EIO_SYNC_FILE_RANGE_WRITE> and C<EIO_SYNC_FILE_RANGE_WAIT_AFTER>.
558		606
		607	=item eio_fallocate (int fd, int mode, off_t offset, off_t len, int pri, eio_cb cb, void *data)
		608
		609	Calls C<fallocate> (note: I<NOT> C<posix_fallocate>!). If the syscall is
		610	missing, then it returns failure and sets C<errno> to C<ENOSYS>.
		611
		612	The C<mode> argument can be C<0> (for behaviour similar to
		613	C<posix_fallocate>), or C<EIO_FALLOC_FL_KEEP_SIZE>, which keeps the size
		614	of the file unchanged (but still preallocates space beyond end of file).
		615
559	=back	616	=back
560		617
561	=head3 LIBEIO-SPECIFIC REQUESTS	618	=head3 LIBEIO-SPECIFIC REQUESTS
562		619
563	These requests are specific to libeio and do not correspond to any OS call.	620	These requests are specific to libeio and do not correspond to any OS call.
564		621
565	=over 4	622	=over 4
566		623
567	=item eio_mtouch (void addr, size_t length, int flags, int pri, eio_cb cb, void data)	624	=item eio_mtouch (void addr, size_t length, int flags, int pri, eio_cb cb, void data)
568		625
569	Reads (C<flags == 0>) or modifies (C<flags == EIO_MT_MODIFY) the given	626	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	627	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.	628	first octet of every page that spans the memory area.
572		629
573	This can be used to page in some mmapped file, or dirty some pages. Note	630	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	631	that dirtying is an unlocked read-write access, so races can ensue when
…		…
604		661
605	eio_custom (my_open, 0, my_open_done, "/etc/passwd");	662	eio_custom (my_open, 0, my_open_done, "/etc/passwd");
606		663
607	=item eio_busy (eio_tstamp delay, int pri, eio_cb cb, void *data)	664	=item eio_busy (eio_tstamp delay, int pri, eio_cb cb, void *data)
608		665
609	This is a a request that takes C<delay> seconds to execute, but otherwise	666	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	667	does nothing - it simply puts one of the worker threads to sleep for this
611	long.	668	long.
612		669
613	This request can be used to artificially increase load, e.g. for debugging	670	This request can be used to artificially increase load, e.g. for debugging
614	or benchmarking reasons.	671	or benchmarking reasons.
…		…
630	There are two primary use cases for this: a) bundle many requests into a	687	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	688	single, composite, request with a definite callback and the ability to
632	cancel the whole request with its subrequests and b) limiting the number	689	cancel the whole request with its subrequests and b) limiting the number
633	of "active" requests.	690	of "active" requests.
634		691
635	Further below you will find more dicussion of these topics - first follows	692	Further below you will find more discussion of these topics - first
636	the reference section detailing the request generator and other methods.	693	follows the reference section detailing the request generator and other
		694	methods.
637		695
638	=over 4	696	=over 4
639		697
640	=item eio_grp (eio_cb cb, void *data)	698	=item eio_req grp = eio_grp (eio_cb cb, void data)
641		699
642	Creates and submits a group request.	700	Creates, submits and returns a group request. Note that it doesn't have a
		701	priority, unlike all other requests.
643		702
644	=back	703	=item eio_grp_add (eio_req grp, eio_req req)
645		704
		705	Adds a request to the request group.
		706
		707	=item eio_grp_cancel (eio_req *grp)
		708
		709	Cancels all requests I<in> the group, but I<not> the group request
		710	itself. You can cancel the group request I<and> all subrequests via a
		711	normal C<eio_cancel> call.
		712
		713	=back
		714
		715	=head4 GROUP REQUEST LIFETIME
		716
		717	Left alone, a group request will instantly move to the pending state and
		718	will be finished at the next call of C<eio_poll>.
		719
		720	The usefulness stems from the fact that, if a subrequest is added to a
		721	group I<before> a call to C<eio_poll>, via C<eio_grp_add>, then the group
		722	will not finish until all the subrequests have finished.
		723
		724	So the usage cycle of a group request is like this: after it is created,
		725	you normally instantly add a subrequest. If none is added, the group
		726	request will finish on it's own. As long as subrequests are added before
		727	the group request is finished it will be kept from finishing, that is the
		728	callbacks of any subrequests can, in turn, add more requests to the group,
		729	and as long as any requests are active, the group request itself will not
		730	finish.
		731
		732	=head4 CREATING COMPOSITE REQUESTS
		733
		734	Imagine you wanted to create an C<eio_load> request that opens a file,
		735	reads it and closes it. This means it has to execute at least three eio
		736	requests, but for various reasons it might be nice if that request looked
		737	like any other eio request.
		738
		739	This can be done with groups:
		740
		741	=over 4
		742
		743	=item 1) create the request object
		744
		745	Create a group that contains all further requests. This is the request you
		746	can return as "the load request".
		747
		748	=item 2) open the file, maybe
		749
		750	Next, open the file with C<eio_open> and add the request to the group
		751	request and you are finished setting up the request.
		752
		753	If, for some reason, you cannot C<eio_open> (path is a null ptr?) you
		754	can set C<< grp->result >> to C<-1> to signal an error and let the group
		755	request finish on its own.
		756
		757	=item 3) open callback adds more requests
		758
		759	In the open callback, if the open was not successful, copy C<<
		760	req->errorno >> to C<< grp->errorno >> and set C<< grp->result >> to
		761	C<-1> to signal an error.
		762
		763	Otherwise, malloc some memory or so and issue a read request, adding the
		764	read request to the group.
		765
		766	=item 4) continue issuing requests till finished
		767
		768	In the read callback, check for errors and possibly continue with
		769	C<eio_close> or any other eio request in the same way.
		770
		771	As soon as no new requests are added, the group request will finish. Make
		772	sure you I<always> set C<< grp->result >> to some sensible value.
		773
		774	=back
		775
		776	=head4 REQUEST LIMITING
646		777
647		778
648	#TODO	779	#TODO
649		780
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);	781	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		782
659
660	=back
661		783
662		784
663	=head1 LOW LEVEL REQUEST API	785	=head1 LOW LEVEL REQUEST API
664		786
665	#TODO	787	#TODO
…		…
668	=head1 ANATOMY AND LIFETIME OF AN EIO REQUEST	790	=head1 ANATOMY AND LIFETIME OF AN EIO REQUEST
669		791
670	A request is represented by a structure of type C<eio_req>. To initialise	792	A request is represented by a structure of type C<eio_req>. To initialise
671	it, clear it to all zero bytes:	793	it, clear it to all zero bytes:
672		794
673	eio_req req;	795	eio_req req;
674		796
675	memset (&req, 0, sizeof (req));	797	memset (&req, 0, sizeof (req));
676		798
677	A more common way to initialise a new C<eio_req> is to use C<calloc>:	799	A more common way to initialise a new C<eio_req> is to use C<calloc>:
678		800
679	eio_req req = calloc (1, sizeof (req));	801	eio_req req = calloc (1, sizeof (req));
680		802
681	In either case, libeio neither allocates, initialises or frees the	803	In either case, libeio neither allocates, initialises or frees the
682	C<eio_req> structure for you - it merely uses it.	804	C<eio_req> structure for you - it merely uses it.
683		805
684	zero	806	zero
…		…
702	for example, in interactive programs, you might want to limit this time to	824	for example, in interactive programs, you might want to limit this time to
703	C<0.01> seconds or so.	825	C<0.01> seconds or so.
704		826
705	Note that:	827	Note that:
706		828
		829	=over 4
		830
707	a) libeio doesn't know how long your request callbacks take, so the time	831	=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	832	time spent in C<eio_poll> is up to one callback invocation longer then
709	interval.	833	this interval.
710		834
711	b) this is implemented by calling C<gettimeofday> after each request,	835	=item b) this is implemented by calling C<gettimeofday> after each
712	which can be costly.	836	request, which can be costly.
713		837
714	c) at least one request will be handled.	838	=item c) at least one request will be handled.
		839
		840	=back
715		841
716	=item eio_set_max_poll_reqs (unsigned int nreqs)	842	=item eio_set_max_poll_reqs (unsigned int nreqs)
717		843
718	When C<nreqs> is non-zero, then C<eio_poll> will not handle more than	844	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	845	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	915	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>	916	was written to use very little stackspace, but when using C<EIO_CUSTOM>
791	requests, you might want to increase this.	917	requests, you might want to increase this.
792		918
793	If this symbol is undefined (the default) then libeio will use its default	919	If this symbol is undefined (the default) then libeio will use its default
794	stack size (C<sizeof (long) * 4096> currently). If it is defined, but	920	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	921	value must be an expression that evaluates to the desired stack size.
797	stack size.
798		922
799	=back	923	=back
800		924
801		925
802	=head1 PORTABILITY REQUIREMENTS	926	=head1 PORTABILITY REQUIREMENTS

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Comparing libeio/eio.pod (file contents): Revision 1.15 by root, Tue Jul 5 16:57:41 2011 UTC vs. Revision 1.36 by root, Sun Jan 24 16:36:20 2016 UTC

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Comparing libeio/eio.pod (file contents):
Revision 1.15 by root, Tue Jul 5 16:57:41 2011 UTC vs.
Revision 1.36 by root, Sun Jan 24 16:36:20 2016 UTC