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

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Revision 1.2 by root, Fri Jul 11 10:54:50 2008 UTC vs.
Revision 1.34 by root, Mon Mar 11 07:59:41 2013 UTC

…		…
11	The newest version of this document is also available as an html-formatted	11	The newest version of this document is also available as an html-formatted
12	web page you might find easier to navigate when reading it for the first	12	web page you might find easier to navigate when reading it for the first
13	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libeio/eio.pod>.	13	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libeio/eio.pod>.
14		14
15	Note that this library is a by-product of the C<IO::AIO> perl	15	Note that this library is a by-product of the C<IO::AIO> perl
16	module, and many of the subtler points regarding requets lifetime	16	module, and many of the subtler points regarding requests lifetime
17	and so on are only documented in its documentation at the	17	and so on are only documented in its documentation at the
18	moment: L<http://pod.tst.eu/http://cvs.schmorp.de/IO-AIO/AIO.pm>.	18	moment: L<http://pod.tst.eu/http://cvs.schmorp.de/IO-AIO/AIO.pm>.
19		19
20	=head2 FEATURES	20	=head2 FEATURES
21		21
22	This library provides fully asynchronous versions of most POSIX functions	22	This library provides fully asynchronous versions of most POSIX functions
23	dealign with I/O. Unlike most asynchronous libraries, this not only	23	dealing with I/O. Unlike most asynchronous libraries, this not only
24	includes C<read> and C<write>, but also C<open>, C<stat>, C<unlink> and	24	includes C<read> and C<write>, but also C<open>, C<stat>, C<unlink> and
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 enbale 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>.
36		36
37	=head2 TIME REPRESENTATION	37	=head2 TIME REPRESENTATION
38		38
39	Libeio represents time as a single floating point number, representing the	39	Libeio represents time as a single floating point number, representing the
40	(fractional) number of seconds since the (POSIX) epoch (somewhere near	40	(fractional) number of seconds since the (POSIX) epoch (somewhere near
41	the beginning of 1970, details are complicated, don't ask). This type is	41	the beginning of 1970, details are complicated, don't ask). This type is
42	called C<eio_tstamp>, but it is guarenteed to be of type C<double> (or	42	called C<eio_tstamp>, but it is guaranteed to be of type C<double> (or
43	better), so you can freely use C<double> yourself.	43	better), so you can freely use C<double> yourself.
44		44
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	58
56	4. in the child, destroy all ready and pending requests and free the	59	You might get around by not I<using> libeio before (or after) forking in
57	memory used by the worker threads. This gives you a fully empty	60	the parent, and using it in the child afterwards. You could also try to
58	libeio queue.	61	call the L<eio_init> function again in the child, which will brutally
		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.
59		68
60	=head1 INITIALISATION/INTEGRATION	69	=head1 INITIALISATION/INTEGRATION
61		70
62	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
63	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
…		…
72	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
73	failure it returns C<-1> and sets C<errno> appropriately.	82	failure it returns C<-1> and sets C<errno> appropriately.
74		83
75	It accepts two function pointers specifying callbacks as argument, both of	84	It accepts two function pointers specifying callbacks as argument, both of
76	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.
77		89
78	=item want_poll callback	90	=item want_poll callback
79		91
80	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.
81	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	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.
98		110
99	Note that C<eio_poll> might return after C<done_poll> and C<want_poll>	111	Note that C<eio_poll> might return after C<done_poll> and C<want_poll>
100	have been called again, so watch out for races in your code.	112	have been called again, so watch out for races in your code.
101		113
102	As with C<want_poll>, this callback is called while lcoks are being held,	114	As with C<want_poll>, this callback is called while locks are being held,
103	so you I<must not call any libeio functions form within this callback>.	115	so you I<must not call any libeio functions form within this callback>.
104		116
105	=item int eio_poll ()	117	=item int eio_poll ()
106		118
107	This function has to be called whenever there are pending requests that	119	This function has to be called whenever there are pending requests that
…		…
119	=back	131	=back
120		132
121	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
122	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
123	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
124	()> (followed by C<ev_async_send> again if C<eio_poll> indicates that not	136	()>.
125	all requests have been handled yet). The race is taken care of because	137
126	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
127	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
128	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	}
129		185
130	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
131	loop should be told to wait for read readyness on the read end. In	187	loop should be told to wait for read readiness on the read end. In
132	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
133	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
134	C<eio_poll>. The race is avoided here because the event loop should invoke	190	C<eio_poll>.
135	your callback again and again until the byte has been read (as the pipe	191
136	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.
		196
		197
		198	=head1 HIGH LEVEL REQUEST API
		199
		200	Libeio has both a high-level API, which consists of calling a request
		201	function with a callback to be called on completion, and a low-level API
		202	where you fill out request structures and submit them.
		203
		204	This section describes the high-level API.
		205
		206	=head2 REQUEST SUBMISSION AND RESULT PROCESSING
		207
		208	You submit a request by calling the relevant C<eio_TYPE> function with the
		209	required parameters, a callback of type C<int (eio_cb)(eio_req req)>
		210	(called C<eio_cb> below) and a freely usable C<void *data> argument.
		211
		212	The return value will either be 0, in case something went really wrong
		213	(which can basically only happen on very fatal errors, such as C<malloc>
		214	returning 0, which is rather unlikely), or a pointer to the newly-created
		215	and submitted C<eio_req *>.
		216
		217	The callback will be called with an C<eio_req *> which contains the
		218	results of the request. The members you can access inside that structure
		219	vary from request to request, except for:
		220
		221	=over 4
		222
		223	=item C<ssize_t result>
		224
		225	This contains the result value from the call (usually the same as the
		226	syscall of the same name).
		227
		228	=item C<int errorno>
		229
		230	This contains the value of C<errno> after the call.
		231
		232	=item C<void *data>
		233
		234	The C<void *data> member simply stores the value of the C<data> argument.
		235
		236	=back
		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
		242	The return value of the callback is normally C<0>, which tells libeio to
		243	continue normally. If a callback returns a nonzero value, libeio will
		244	stop processing results (in C<eio_poll>) and will return the value to its
		245	caller.
		246
		247	Memory areas passed to libeio wrappers must stay valid as long as a
		248	request executes, with the exception of paths, which are being copied
		249	internally. Any memory libeio itself allocates will be freed after the
		250	finish callback has been called. If you want to manage all memory passed
		251	to libeio yourself you can use the low-level API.
		252
		253	For example, to open a file, you could do this:
		254
		255	static int
		256	file_open_done (eio_req *req)
		257	{
		258	if (req->result < 0)
		259	{
		260	/* open() returned -1 */
		261	errno = req->errorno;
		262	perror ("open");
		263	}
		264	else
		265	{
		266	int fd = req->result;
		267	/* now we have the new fd in fd */
		268	}
		269
		270	return 0;
		271	}
		272
		273	/* the first three arguments are passed to open(2) */
		274	/* the remaining are priority, callback and data */
		275	if (!eio_open ("/etc/passwd", O_RDONLY, 0, 0, file_open_done, 0))
		276	abort (); /* something went wrong, we will all die!!! */
		277
		278	Note that you additionally need to call C<eio_poll> when the C<want_cb>
		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
		315
		316	=head2 AVAILABLE REQUESTS
		317
		318	The following request functions are available. I<All> of them return the
		319	C<eio_req *> on success and C<0> on failure, and I<all> of them have the
		320	same three trailing arguments: C<pri>, C<cb> and C<data>. The C<cb> is
		321	mandatory, but in most cases, you pass in C<0> as C<pri> and C<0> or some
		322	custom data value as C<data>.
		323
		324	=head3 POSIX API WRAPPERS
		325
		326	These requests simply wrap the POSIX call of the same name, with the same
		327	arguments. If a function is not implemented by the OS and cannot be emulated
		328	in some way, then all of these return C<-1> and set C<errorno> to C<ENOSYS>.
		329
		330	=over 4
		331
		332	=item eio_open (const char path, int flags, mode_t mode, int pri, eio_cb cb, void data)
		333
		334	=item eio_truncate (const char path, off_t offset, int pri, eio_cb cb, void data)
		335
		336	=item eio_chown (const char path, uid_t uid, gid_t gid, int pri, eio_cb cb, void data)
		337
		338	=item eio_chmod (const char path, mode_t mode, int pri, eio_cb cb, void data)
		339
		340	=item eio_mkdir (const char path, mode_t mode, int pri, eio_cb cb, void data)
		341
		342	=item eio_rmdir (const char path, int pri, eio_cb cb, void data)
		343
		344	=item eio_unlink (const char path, int pri, eio_cb cb, void data)
		345
		346	=item eio_utime (const char path, eio_tstamp atime, eio_tstamp mtime, int pri, eio_cb cb, void data)
		347
		348	=item eio_mknod (const char path, mode_t mode, dev_t dev, int pri, eio_cb cb, void data)
		349
		350	=item eio_link (const char path, const char new_path, int pri, eio_cb cb, void *data)
		351
		352	=item eio_symlink (const char path, const char new_path, int pri, eio_cb cb, void *data)
		353
		354	=item eio_rename (const char path, const char new_path, int pri, eio_cb cb, void *data)
		355
		356	=item eio_mlock (void addr, size_t length, int pri, eio_cb cb, void data)
		357
		358	=item eio_close (int fd, int pri, eio_cb cb, void *data)
		359
		360	=item eio_sync (int pri, eio_cb cb, void *data)
		361
		362	=item eio_fsync (int fd, int pri, eio_cb cb, void *data)
		363
		364	=item eio_fdatasync (int fd, int pri, eio_cb cb, void *data)
		365
		366	=item eio_futime (int fd, eio_tstamp atime, eio_tstamp mtime, int pri, eio_cb cb, void *data)
		367
		368	=item eio_ftruncate (int fd, off_t offset, int pri, eio_cb cb, void *data)
		369
		370	=item eio_fchmod (int fd, mode_t mode, int pri, eio_cb cb, void *data)
		371
		372	=item eio_fchown (int fd, uid_t uid, gid_t gid, int pri, eio_cb cb, void *data)
		373
		374	=item eio_dup2 (int fd, int fd2, int pri, eio_cb cb, void *data)
		375
		376	These have the same semantics as the syscall of the same name, their
		377	return value is available as C<< req->result >> later.
		378
		379	=item eio_read (int fd, void buf, size_t length, off_t offset, int pri, eio_cb cb, void data)
		380
		381	=item eio_write (int fd, void buf, size_t length, off_t offset, int pri, eio_cb cb, void data)
		382
		383	These two requests are called C<read> and C<write>, but actually wrap
		384	C<pread> and C<pwrite>. On systems that lack these calls (such as cygwin),
		385	libeio uses lseek/read_or_write/lseek and a mutex to serialise the
		386	requests, so all these requests run serially and do not disturb each
		387	other. However, they still disturb the file offset while they run, so it's
		388	not safe to call these functions concurrently with non-libeio functions on
		389	the same fd on these systems.
		390
		391	Not surprisingly, pread and pwrite are not thread-safe on Darwin (OS/X),
		392	so it is advised not to submit multiple requests on the same fd on this
		393	horrible pile of garbage.
		394
		395	=item eio_mlockall (int flags, int pri, eio_cb cb, void *data)
		396
		397	Like C<mlockall>, but the flag value constants are called
		398	C<EIO_MCL_CURRENT> and C<EIO_MCL_FUTURE>.
		399
		400	=item eio_msync (void addr, size_t length, int flags, int pri, eio_cb cb, void data)
		401
		402	Just like msync, except that the flag values are called C<EIO_MS_ASYNC>,
		403	C<EIO_MS_INVALIDATE> and C<EIO_MS_SYNC>.
		404
		405	=item eio_readlink (const char path, int pri, eio_cb cb, void data)
		406
		407	If successful, the path read by C<readlink(2)> can be accessed via C<<
		408	req->ptr2 >> and is I<NOT> null-terminated, with the length specified as
		409	C<< req->result >>.
		410
		411	if (req->result >= 0)
		412	{
		413	char target = strndup ((char )req->ptr2, req->result);
		414
		415	free (target);
		416	}
		417
		418	=item eio_realpath (const char path, int pri, eio_cb cb, void data)
		419
		420	Similar to the realpath libc function, but unlike that one, C<<
		421	req->result >> is C<-1> on failure. On success, the result is the length
		422	of the returned path in C<ptr2> (which is I<NOT> 0-terminated) - this is
		423	similar to readlink.
		424
		425	=item eio_stat (const char path, int pri, eio_cb cb, void data)
		426
		427	=item eio_lstat (const char path, int pri, eio_cb cb, void data)
		428
		429	=item eio_fstat (int fd, int pri, eio_cb cb, void *data)
		430
		431	Stats a file - if C<< req->result >> indicates success, then you can
		432	access the C<struct stat>-like structure via C<< req->ptr2 >>:
		433
		434	EIO_STRUCT_STAT statdata = (EIO_STRUCT_STAT )req->ptr2;
		435
		436	=item eio_statvfs (const char path, int pri, eio_cb cb, void data)
		437
		438	=item eio_fstatvfs (int fd, int pri, eio_cb cb, void *data)
		439
		440	Stats a filesystem - if C<< req->result >> indicates success, then you can
		441	access the C<struct statvfs>-like structure via C<< req->ptr2 >>:
		442
		443	EIO_STRUCT_STATVFS statdata = (EIO_STRUCT_STATVFS )req->ptr2;
		444
		445	=back
		446
		447	=head3 READING DIRECTORIES
		448
		449	Reading directories sounds simple, but can be rather demanding, especially
		450	if you want to do stuff such as traversing a directory hierarchy or
		451	processing all files in a directory. Libeio can assist these complex tasks
		452	with it's C<eio_readdir> call.
		453
		454	=over 4
		455
		456	=item eio_readdir (const char path, int flags, int pri, eio_cb cb, void data)
		457
		458	This is a very complex call. It basically reads through a whole directory
		459	(via the C<opendir>, C<readdir> and C<closedir> calls) and returns either
		460	the names or an array of C<struct eio_dirent>, depending on the C<flags>
		461	argument.
		462
		463	The C<< req->result >> indicates either the number of files found, or
		464	C<-1> on error. On success, null-terminated names can be found as C<< req->ptr2 >>,
		465	and C<struct eio_dirents>, if requested by C<flags>, can be found via C<<
		466	req->ptr1 >>.
		467
		468	Here is an example that prints all the names:
		469
		470	int i;
		471	char names = (char )req->ptr2;
		472
		473	for (i = 0; i < req->result; ++i)
		474	{
		475	printf ("name #%d: %s\n", i, names);
		476
		477	/* move to next name */
		478	names += strlen (names) + 1;
		479	}
		480
		481	Pseudo-entries such as F<.> and F<..> are never returned by C<eio_readdir>.
		482
		483	C<flags> can be any combination of:
		484
		485	=over 4
		486
		487	=item EIO_READDIR_DENTS
		488
		489	If this flag is specified, then, in addition to the names in C<ptr2>,
		490	also an array of C<struct eio_dirent> is returned, in C<ptr1>. A C<struct
		491	eio_dirent> looks like this:
		492
		493	struct eio_dirent
		494	{
		495	int nameofs; /* offset of null-terminated name string in (char )req->ptr2 /
		496	unsigned short namelen; /* size of filename without trailing 0 */
		497	unsigned char type; /* one of EIO_DT_* */
		498	signed char score; /* internal use */
		499	ino_t inode; /* the inode number, if available, otherwise unspecified */
		500	};
		501
		502	The only members you normally would access are C<nameofs>, which is the
		503	byte-offset from C<ptr2> to the start of the name, C<namelen> and C<type>.
		504
		505	C<type> can be one of:
		506
		507	C<EIO_DT_UNKNOWN> - if the type is not known (very common) and you have to C<stat>
		508	the name yourself if you need to know,
		509	one of the "standard" POSIX file types (C<EIO_DT_REG>, C<EIO_DT_DIR>, C<EIO_DT_LNK>,
		510	C<EIO_DT_FIFO>, C<EIO_DT_SOCK>, C<EIO_DT_CHR>, C<EIO_DT_BLK>)
		511	or some OS-specific type (currently
		512	C<EIO_DT_MPC> - multiplexed char device (v7+coherent),
		513	C<EIO_DT_NAM> - xenix special named file,
		514	C<EIO_DT_MPB> - multiplexed block device (v7+coherent),
		515	C<EIO_DT_NWK> - HP-UX network special,
		516	C<EIO_DT_CMP> - VxFS compressed,
		517	C<EIO_DT_DOOR> - solaris door, or
		518	C<EIO_DT_WHT>).
		519
		520	This example prints all names and their type:
		521
		522	int i;
		523	struct eio_dirent ents = (struct eio_dirent )req->ptr1;
		524	char names = (char )req->ptr2;
		525
		526	for (i = 0; i < req->result; ++i)
		527	{
		528	struct eio_dirent *ent = ents + i;
		529	char *name = names + ent->nameofs;
		530
		531	printf ("name #%d: %s (type %d)\n", i, name, ent->type);
		532	}
		533
		534	=item EIO_READDIR_DIRS_FIRST
		535
		536	When this flag is specified, then the names will be returned in an order
		537	where likely directories come first, in optimal C<stat> order. This is
		538	useful when you need to quickly find directories, or you want to find all
		539	directories while avoiding to stat() each entry.
		540
		541	If the system returns type information in readdir, then this is used
		542	to find directories directly. Otherwise, likely directories are names
		543	beginning with ".", or otherwise names with no dots, of which names with
		544	short names are tried first.
		545
		546	=item EIO_READDIR_STAT_ORDER
		547
		548	When this flag is specified, then the names will be returned in an order
		549	suitable for stat()'ing each one. That is, when you plan to stat()
		550	all files in the given directory, then the returned order will likely
		551	be fastest.
		552
		553	If both this flag and C<EIO_READDIR_DIRS_FIRST> are specified, then the
		554	likely directories come first, resulting in a less optimal stat order.
		555
		556	=item EIO_READDIR_FOUND_UNKNOWN
		557
		558	This flag should not be specified when calling C<eio_readdir>. Instead,
		559	it is being set by C<eio_readdir> (you can access the C<flags> via C<<
		560	req->int1 >>, when any of the C<type>'s found were C<EIO_DT_UNKNOWN>. The
		561	absence of this flag therefore indicates that all C<type>'s are known,
		562	which can be used to speed up some algorithms.
		563
		564	A typical use case would be to identify all subdirectories within a
		565	directory - you would ask C<eio_readdir> for C<EIO_READDIR_DIRS_FIRST>. If
		566	then this flag is I<NOT> set, then all the entries at the beginning of the
		567	returned array of type C<EIO_DT_DIR> are the directories. Otherwise, you
		568	should start C<stat()>'ing the entries starting at the beginning of the
		569	array, stopping as soon as you found all directories (the count can be
		570	deduced by the link count of the directory).
		571
		572	=back
		573
		574	=back
		575
		576	=head3 OS-SPECIFIC CALL WRAPPERS
		577
		578	These wrap OS-specific calls (usually Linux ones), and might or might not
		579	be emulated on other operating systems. Calls that are not emulated will
		580	return C<-1> and set C<errno> to C<ENOSYS>.
		581
		582	=over 4
		583
		584	=item eio_sendfile (int out_fd, int in_fd, off_t in_offset, size_t length, int pri, eio_cb cb, void *data)
		585
		586	Wraps the C<sendfile> syscall. The arguments follow the Linux version, but
		587	libeio supports and will use similar calls on FreeBSD, HP/UX, Solaris and
		588	Darwin.
		589
		590	If the OS doesn't support some sendfile-like call, or the call fails,
		591	indicating support for the given file descriptor type (for example,
		592	Linux's sendfile might not support file to file copies), then libeio will
		593	emulate the call in userspace, so there are almost no limitations on its
		594	use.
		595
		596	=item eio_readahead (int fd, off_t offset, size_t length, int pri, eio_cb cb, void *data)
		597
		598	Calls C<readahead(2)>. If the syscall is missing, then the call is
		599	emulated by simply reading the data (currently in 64kiB chunks).
		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
		608	=item eio_sync_file_range (int fd, off_t offset, size_t nbytes, unsigned int flags, int pri, eio_cb cb, void *data)
		609
		610	Calls C<sync_file_range>. If the syscall is missing, then this is the same
		611	as calling C<fdatasync>.
		612
		613	Flags can be any combination of C<EIO_SYNC_FILE_RANGE_WAIT_BEFORE>,
		614	C<EIO_SYNC_FILE_RANGE_WRITE> and C<EIO_SYNC_FILE_RANGE_WAIT_AFTER>.
		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
		625	=back
		626
		627	=head3 LIBEIO-SPECIFIC REQUESTS
		628
		629	These requests are specific to libeio and do not correspond to any OS call.
		630
		631	=over 4
		632
		633	=item eio_mtouch (void addr, size_t length, int flags, int pri, eio_cb cb, void data)
		634
		635	Reads (C<flags == 0>) or modifies (C<flags == EIO_MT_MODIFY>) the given
		636	memory area, page-wise, that is, it reads (or reads and writes back) the
		637	first octet of every page that spans the memory area.
		638
		639	This can be used to page in some mmapped file, or dirty some pages. Note
		640	that dirtying is an unlocked read-write access, so races can ensue when
		641	the some other thread modifies the data stored in that memory area.
		642
		643	=item eio_custom (void ()(eio_req ) execute, int pri, eio_cb cb, void *data)
		644
		645	Executes a custom request, i.e., a user-specified callback.
		646
		647	The callback gets the C<eio_req *> as parameter and is expected to read
		648	and modify any request-specific members. Specifically, it should set C<<
		649	req->result >> to the result value, just like other requests.
		650
		651	Here is an example that simply calls C<open>, like C<eio_open>, but it
		652	uses the C<data> member as filename and uses a hardcoded C<O_RDONLY>. If
		653	you want to pass more/other parameters, you either need to pass some
		654	struct or so via C<data> or provide your own wrapper using the low-level
		655	API.
		656
		657	static int
		658	my_open_done (eio_req *req)
		659	{
		660	int fd = req->result;
		661
		662	return 0;
		663	}
		664
		665	static void
		666	my_open (eio_req *req)
		667	{
		668	req->result = open (req->data, O_RDONLY);
		669	}
		670
		671	eio_custom (my_open, 0, my_open_done, "/etc/passwd");
		672
		673	=item eio_busy (eio_tstamp delay, int pri, eio_cb cb, void *data)
		674
		675	This is a request that takes C<delay> seconds to execute, but otherwise
		676	does nothing - it simply puts one of the worker threads to sleep for this
		677	long.
		678
		679	This request can be used to artificially increase load, e.g. for debugging
		680	or benchmarking reasons.
		681
		682	=item eio_nop (int pri, eio_cb cb, void *data)
		683
		684	This request does nothing, except go through the whole request cycle. This
		685	can be used to measure latency or in some cases to simplify code, but is
		686	not really of much use.
		687
		688	=back
		689
		690	=head3 GROUPING AND LIMITING REQUESTS
		691
		692	There is one more rather special request, C<eio_grp>. It is a very special
		693	aio request: Instead of doing something, it is a container for other eio
		694	requests.
		695
		696	There are two primary use cases for this: a) bundle many requests into a
		697	single, composite, request with a definite callback and the ability to
		698	cancel the whole request with its subrequests and b) limiting the number
		699	of "active" requests.
		700
		701	Further below you will find more discussion of these topics - first
		702	follows the reference section detailing the request generator and other
		703	methods.
		704
		705	=over 4
		706
		707	=item eio_req grp = eio_grp (eio_cb cb, void data)
		708
		709	Creates, submits and returns a group request. Note that it doesn't have a
		710	priority, unlike all other requests.
		711
		712	=item eio_grp_add (eio_req grp, eio_req req)
		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
		786
		787
		788	#TODO
		789
		790	void eio_grp_limit (eio_req *grp, int limit);
		791
		792
		793
		794	=head1 LOW LEVEL REQUEST API
		795
		796	#TODO
		797
		798
		799	=head1 ANATOMY AND LIFETIME OF AN EIO REQUEST
		800
		801	A request is represented by a structure of type C<eio_req>. To initialise
		802	it, clear it to all zero bytes:
		803
		804	eio_req req;
		805
		806	memset (&req, 0, sizeof (req));
		807
		808	A more common way to initialise a new C<eio_req> is to use C<calloc>:
		809
		810	eio_req req = calloc (1, sizeof (req));
		811
		812	In either case, libeio neither allocates, initialises or frees the
		813	C<eio_req> structure for you - it merely uses it.
		814
		815	zero
		816
		817	#TODO
137		818
138	=head2 CONFIGURATION	819	=head2 CONFIGURATION
139		820
140	The functions in this section can sometimes be useful, but the default	821	The functions in this section can sometimes be useful, but the default
141	configuration will do in most case, so you should skip this section on	822	configuration will do in most case, so you should skip this section on
…		…
152	for example, in interactive programs, you might want to limit this time to	833	for example, in interactive programs, you might want to limit this time to
153	C<0.01> seconds or so.	834	C<0.01> seconds or so.
154		835
155	Note that:	836	Note that:
156		837
		838	=over 4
		839
157	a) libeio doesn't know how long your request callbacks take, so the time	840	=item a) libeio doesn't know how long your request callbacks take, so the
158	spent in C<eio_poll> is up to one callback invocation longer then this	841	time spent in C<eio_poll> is up to one callback invocation longer then
159	interval.	842	this interval.
160		843
161	b) this is implemented by calling C<gettimeofday> after each request,	844	=item b) this is implemented by calling C<gettimeofday> after each
162	which can be costly.	845	request, which can be costly.
163		846
164	c) at least one request will be handled.	847	=item c) at least one request will be handled.
		848
		849	=back
165		850
166	=item eio_set_max_poll_reqs (unsigned int nreqs)	851	=item eio_set_max_poll_reqs (unsigned int nreqs)
167		852
168	When C<nreqs> is non-zero, then C<eio_poll> will not handle more than	853	When C<nreqs> is non-zero, then C<eio_poll> will not handle more than
169	C<nreqs> requests per invocation. This is a less costly way to limit the	854	C<nreqs> requests per invocation. This is a less costly way to limit the
…		…
185	=item eio_set_max_idle (unsigned int nthreads)	870	=item eio_set_max_idle (unsigned int nthreads)
186		871
187	Libeio uses threads internally to handle most requests, and will start and stop threads on demand.	872	Libeio uses threads internally to handle most requests, and will start and stop threads on demand.
188		873
189	This call can be used to limit the number of idle threads (threads without	874	This call can be used to limit the number of idle threads (threads without
190	work to do): libeio will keep some threads idle in preperation for more	875	work to do): libeio will keep some threads idle in preparation for more
191	requests, but never longer than C<nthreads> threads.	876	requests, but never longer than C<nthreads> threads.
192		877
193	In addition to this, libeio will also stop threads when they are idle for	878	In addition to this, libeio will also stop threads when they are idle for
194	a few seconds, regardless of this setting.	879	a few seconds, regardless of this setting.
195		880
…		…
214	executed and have results, but have not been finished yet by a call to	899	executed and have results, but have not been finished yet by a call to
215	C<eio_poll>).	900	C<eio_poll>).
216		901
217	=back	902	=back
218		903
219
220	=head1 ANATOMY OF AN EIO REQUEST
221
222	#TODO
223
224
225	=head1 HIGH LEVEL REQUEST API
226
227	#TODO
228
229	=back
230
231
232	=head1 LOW LEVEL REQUEST API
233
234	#TODO
235
236	=head1 EMBEDDING	904	=head1 EMBEDDING
237		905
238	Libeio can be embedded directly into programs. This functionality is not	906	Libeio can be embedded directly into programs. This functionality is not
239	documented and not (yet) officially supported.	907	documented and not (yet) officially supported.
240		908
		909	Note that, when including C<libeio.m4>, you are responsible for defining
		910	the compilation environment (C<_LARGEFILE_SOURCE>, C<_GNU_SOURCE> etc.).
		911
241	If you need to know how, check the C<IO::AIO> perl module, which does	912	If you need to know how, check the C<IO::AIO> perl module, which does
242	exactly that.	913	exactly that.
		914
		915
		916	=head1 COMPILETIME CONFIGURATION
		917
		918	These symbols, if used, must be defined when compiling F<eio.c>.
		919
		920	=over 4
		921
		922	=item EIO_STACKSIZE
		923
		924	This symbol governs the stack size for each eio thread. Libeio itself
		925	was written to use very little stackspace, but when using C<EIO_CUSTOM>
		926	requests, you might want to increase this.
		927
		928	If this symbol is undefined (the default) then libeio will use its default
		929	stack size (C<sizeof (void ) 4096> currently). In all other cases, the
		930	value must be an expression that evaluates to the desired stack size.
		931
		932	=back
243		933
244		934
245	=head1 PORTABILITY REQUIREMENTS	935	=head1 PORTABILITY REQUIREMENTS
246		936
247	In addition to a working ISO-C implementation, libeio relies on a few	937	In addition to a working ISO-C implementation, libeio relies on a few

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Comparing libeio/eio.pod (file contents): Revision 1.2 by root, Fri Jul 11 10:54:50 2008 UTC vs. Revision 1.34 by root, Mon Mar 11 07:59:41 2013 UTC

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Comparing libeio/eio.pod (file contents):
Revision 1.2 by root, Fri Jul 11 10:54:50 2008 UTC vs.
Revision 1.34 by root, Mon Mar 11 07:59:41 2013 UTC