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Revision 1.3 by root, Wed Oct 22 18:15:36 2008 UTC vs.
Revision 1.35 by root, Mon Aug 18 08:11:54 2014 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	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
		301
		302	=head2 AVAILABLE REQUESTS
		303
		304	The following request functions are available. I<All> of them return the
		305	C<eio_req *> on success and C<0> on failure, and I<all> of them have the
		306	same three trailing arguments: C<pri>, C<cb> and C<data>. The C<cb> is
		307	mandatory, but in most cases, you pass in C<0> as C<pri> and C<0> or some
		308	custom data value as C<data>.
		309
		310	=head3 POSIX API WRAPPERS
		311
		312	These requests simply wrap the POSIX call of the same name, with the same
		313	arguments. If a function is not implemented by the OS and cannot be emulated
		314	in some way, then all of these return C<-1> and set C<errorno> to C<ENOSYS>.
		315
		316	=over 4
		317
		318	=item eio_open (const char path, int flags, mode_t mode, int pri, eio_cb cb, void data)
		319
		320	=item eio_truncate (const char path, off_t offset, int pri, eio_cb cb, void data)
		321
		322	=item eio_chown (const char path, uid_t uid, gid_t gid, int pri, eio_cb cb, void data)
		323
		324	=item eio_chmod (const char path, mode_t mode, int pri, eio_cb cb, void data)
		325
		326	=item eio_mkdir (const char path, mode_t mode, int pri, eio_cb cb, void data)
		327
		328	=item eio_rmdir (const char path, int pri, eio_cb cb, void data)
		329
		330	=item eio_unlink (const char path, int pri, eio_cb cb, void data)
		331
		332	=item eio_utime (const char path, eio_tstamp atime, eio_tstamp mtime, int pri, eio_cb cb, void data)
		333
		334	=item eio_mknod (const char path, mode_t mode, dev_t dev, int pri, eio_cb cb, void data)
		335
		336	=item eio_link (const char path, const char new_path, int pri, eio_cb cb, void *data)
		337
		338	=item eio_symlink (const char path, const char new_path, int pri, eio_cb cb, void *data)
		339
		340	=item eio_rename (const char path, const char new_path, int pri, eio_cb cb, void *data)
		341
		342	=item eio_mlock (void addr, size_t length, int pri, eio_cb cb, void data)
		343
		344	=item eio_close (int fd, int pri, eio_cb cb, void *data)
		345
		346	=item eio_sync (int pri, eio_cb cb, void *data)
		347
		348	=item eio_fsync (int fd, int pri, eio_cb cb, void *data)
		349
		350	=item eio_fdatasync (int fd, int pri, eio_cb cb, void *data)
		351
		352	=item eio_futime (int fd, eio_tstamp atime, eio_tstamp mtime, int pri, eio_cb cb, void *data)
		353
		354	=item eio_ftruncate (int fd, off_t offset, int pri, eio_cb cb, void *data)
		355
		356	=item eio_fchmod (int fd, mode_t mode, int pri, eio_cb cb, void *data)
		357
		358	=item eio_fchown (int fd, uid_t uid, gid_t gid, int pri, eio_cb cb, void *data)
		359
		360	=item eio_dup2 (int fd, int fd2, int pri, eio_cb cb, void *data)
		361
		362	These have the same semantics as the syscall of the same name, their
		363	return value is available as C<< req->result >> later.
		364
		365	=item eio_read (int fd, void buf, size_t length, off_t offset, int pri, eio_cb cb, void data)
		366
		367	=item eio_write (int fd, void buf, size_t length, off_t offset, int pri, eio_cb cb, void data)
		368
		369	These two requests are called C<read> and C<write>, but actually wrap
		370	C<pread> and C<pwrite>. On systems that lack these calls (such as cygwin),
		371	libeio uses lseek/read_or_write/lseek and a mutex to serialise the
		372	requests, so all these requests run serially and do not disturb each
		373	other. However, they still disturb the file offset while they run, so it's
		374	not safe to call these functions concurrently with non-libeio functions on
		375	the same fd on these systems.
		376
		377	Not surprisingly, pread and pwrite are not thread-safe on Darwin (OS/X),
		378	so it is advised not to submit multiple requests on the same fd on this
		379	horrible pile of garbage.
		380
		381	=item eio_mlockall (int flags, int pri, eio_cb cb, void *data)
		382
		383	Like C<mlockall>, but the flag value constants are called
		384	C<EIO_MCL_CURRENT> and C<EIO_MCL_FUTURE>.
		385
		386	=item eio_msync (void addr, size_t length, int flags, int pri, eio_cb cb, void data)
		387
		388	Just like msync, except that the flag values are called C<EIO_MS_ASYNC>,
		389	C<EIO_MS_INVALIDATE> and C<EIO_MS_SYNC>.
		390
		391	=item eio_readlink (const char path, int pri, eio_cb cb, void data)
		392
		393	If successful, the path read by C<readlink(2)> can be accessed via C<<
		394	req->ptr2 >> and is I<NOT> null-terminated, with the length specified as
		395	C<< req->result >>.
		396
		397	if (req->result >= 0)
		398	{
		399	char target = strndup ((char )req->ptr2, req->result);
		400
		401	free (target);
		402	}
		403
		404	=item eio_realpath (const char path, int pri, eio_cb cb, void data)
		405
		406	Similar to the realpath libc function, but unlike that one, C<<
		407	req->result >> is C<-1> on failure. On success, the result is the length
		408	of the returned path in C<ptr2> (which is I<NOT> 0-terminated) - this is
		409	similar to readlink.
		410
		411	=item eio_stat (const char path, int pri, eio_cb cb, void data)
		412
		413	=item eio_lstat (const char path, int pri, eio_cb cb, void data)
		414
		415	=item eio_fstat (int fd, int pri, eio_cb cb, void *data)
		416
		417	Stats a file - if C<< req->result >> indicates success, then you can
		418	access the C<struct stat>-like structure via C<< req->ptr2 >>:
		419
		420	EIO_STRUCT_STAT statdata = (EIO_STRUCT_STAT )req->ptr2;
		421
		422	=item eio_statvfs (const char path, int pri, eio_cb cb, void data)
		423
		424	=item eio_fstatvfs (int fd, int pri, eio_cb cb, void *data)
		425
		426	Stats a filesystem - if C<< req->result >> indicates success, then you can
		427	access the C<struct statvfs>-like structure via C<< req->ptr2 >>:
		428
		429	EIO_STRUCT_STATVFS statdata = (EIO_STRUCT_STATVFS )req->ptr2;
		430
		431	=back
		432
		433	=head3 READING DIRECTORIES
		434
		435	Reading directories sounds simple, but can be rather demanding, especially
		436	if you want to do stuff such as traversing a directory hierarchy or
		437	processing all files in a directory. Libeio can assist these complex tasks
		438	with it's C<eio_readdir> call.
		439
		440	=over 4
		441
		442	=item eio_readdir (const char path, int flags, int pri, eio_cb cb, void data)
		443
		444	This is a very complex call. It basically reads through a whole directory
		445	(via the C<opendir>, C<readdir> and C<closedir> calls) and returns either
		446	the names or an array of C<struct eio_dirent>, depending on the C<flags>
		447	argument.
		448
		449	The C<< req->result >> indicates either the number of files found, or
		450	C<-1> on error. On success, null-terminated names can be found as C<< req->ptr2 >>,
		451	and C<struct eio_dirents>, if requested by C<flags>, can be found via C<<
		452	req->ptr1 >>.
		453
		454	Here is an example that prints all the names:
		455
		456	int i;
		457	char names = (char )req->ptr2;
		458
		459	for (i = 0; i < req->result; ++i)
		460	{
		461	printf ("name #%d: %s\n", i, names);
		462
		463	/* move to next name */
		464	names += strlen (names) + 1;
		465	}
		466
		467	Pseudo-entries such as F<.> and F<..> are never returned by C<eio_readdir>.
		468
		469	C<flags> can be any combination of:
		470
		471	=over 4
		472
		473	=item EIO_READDIR_DENTS
		474
		475	If this flag is specified, then, in addition to the names in C<ptr2>,
		476	also an array of C<struct eio_dirent> is returned, in C<ptr1>. A C<struct
		477	eio_dirent> looks like this:
		478
		479	struct eio_dirent
		480	{
		481	int nameofs; /* offset of null-terminated name string in (char )req->ptr2 /
		482	unsigned short namelen; /* size of filename without trailing 0 */
		483	unsigned char type; /* one of EIO_DT_* */
		484	signed char score; /* internal use */
		485	ino_t inode; /* the inode number, if available, otherwise unspecified */
		486	};
		487
		488	The only members you normally would access are C<nameofs>, which is the
		489	byte-offset from C<ptr2> to the start of the name, C<namelen> and C<type>.
		490
		491	C<type> can be one of:
		492
		493	C<EIO_DT_UNKNOWN> - if the type is not known (very common) and you have to C<stat>
		494	the name yourself if you need to know,
		495	one of the "standard" POSIX file types (C<EIO_DT_REG>, C<EIO_DT_DIR>, C<EIO_DT_LNK>,
		496	C<EIO_DT_FIFO>, C<EIO_DT_SOCK>, C<EIO_DT_CHR>, C<EIO_DT_BLK>)
		497	or some OS-specific type (currently
		498	C<EIO_DT_MPC> - multiplexed char device (v7+coherent),
		499	C<EIO_DT_NAM> - xenix special named file,
		500	C<EIO_DT_MPB> - multiplexed block device (v7+coherent),
		501	C<EIO_DT_NWK> - HP-UX network special,
		502	C<EIO_DT_CMP> - VxFS compressed,
		503	C<EIO_DT_DOOR> - solaris door, or
		504	C<EIO_DT_WHT>).
		505
		506	This example prints all names and their type:
		507
		508	int i;
		509	struct eio_dirent ents = (struct eio_dirent )req->ptr1;
		510	char names = (char )req->ptr2;
		511
		512	for (i = 0; i < req->result; ++i)
		513	{
		514	struct eio_dirent *ent = ents + i;
		515	char *name = names + ent->nameofs;
		516
		517	printf ("name #%d: %s (type %d)\n", i, name, ent->type);
		518	}
		519
		520	=item EIO_READDIR_DIRS_FIRST
		521
		522	When this flag is specified, then the names will be returned in an order
		523	where likely directories come first, in optimal C<stat> order. This is
		524	useful when you need to quickly find directories, or you want to find all
		525	directories while avoiding to stat() each entry.
		526
		527	If the system returns type information in readdir, then this is used
		528	to find directories directly. Otherwise, likely directories are names
		529	beginning with ".", or otherwise names with no dots, of which names with
		530	short names are tried first.
		531
		532	=item EIO_READDIR_STAT_ORDER
		533
		534	When this flag is specified, then the names will be returned in an order
		535	suitable for stat()'ing each one. That is, when you plan to stat()
		536	all files in the given directory, then the returned order will likely
		537	be fastest.
		538
		539	If both this flag and C<EIO_READDIR_DIRS_FIRST> are specified, then the
		540	likely directories come first, resulting in a less optimal stat order.
		541
		542	=item EIO_READDIR_FOUND_UNKNOWN
		543
		544	This flag should not be specified when calling C<eio_readdir>. Instead,
		545	it is being set by C<eio_readdir> (you can access the C<flags> via C<<
		546	req->int1 >>, when any of the C<type>'s found were C<EIO_DT_UNKNOWN>. The
		547	absence of this flag therefore indicates that all C<type>'s are known,
		548	which can be used to speed up some algorithms.
		549
		550	A typical use case would be to identify all subdirectories within a
		551	directory - you would ask C<eio_readdir> for C<EIO_READDIR_DIRS_FIRST>. If
		552	then this flag is I<NOT> set, then all the entries at the beginning of the
		553	returned array of type C<EIO_DT_DIR> are the directories. Otherwise, you
		554	should start C<stat()>'ing the entries starting at the beginning of the
		555	array, stopping as soon as you found all directories (the count can be
		556	deduced by the link count of the directory).
		557
		558	=back
		559
		560	=back
		561
		562	=head3 OS-SPECIFIC CALL WRAPPERS
		563
		564	These wrap OS-specific calls (usually Linux ones), and might or might not
		565	be emulated on other operating systems. Calls that are not emulated will
		566	return C<-1> and set C<errno> to C<ENOSYS>.
		567
		568	=over 4
		569
		570	=item eio_sendfile (int out_fd, int in_fd, off_t in_offset, size_t length, int pri, eio_cb cb, void *data)
		571
		572	Wraps the C<sendfile> syscall. The arguments follow the Linux version, but
		573	libeio supports and will use similar calls on FreeBSD, HP/UX, Solaris and
		574	Darwin.
		575
		576	If the OS doesn't support some sendfile-like call, or the call fails,
		577	indicating support for the given file descriptor type (for example,
		578	Linux's sendfile might not support file to file copies), then libeio will
		579	emulate the call in userspace, so there are almost no limitations on its
		580	use.
		581
		582	=item eio_readahead (int fd, off_t offset, size_t length, int pri, eio_cb cb, void *data)
		583
		584	Calls C<readahead(2)>. If the syscall is missing, then the call is
		585	emulated by simply reading the data (currently in 64kiB chunks).
		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
		594	=item eio_sync_file_range (int fd, off_t offset, size_t nbytes, unsigned int flags, int pri, eio_cb cb, void *data)
		595
		596	Calls C<sync_file_range>. If the syscall is missing, then this is the same
		597	as calling C<fdatasync>.
		598
		599	Flags can be any combination of C<EIO_SYNC_FILE_RANGE_WAIT_BEFORE>,
		600	C<EIO_SYNC_FILE_RANGE_WRITE> and C<EIO_SYNC_FILE_RANGE_WAIT_AFTER>.
		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
		611	=back
		612
		613	=head3 LIBEIO-SPECIFIC REQUESTS
		614
		615	These requests are specific to libeio and do not correspond to any OS call.
		616
		617	=over 4
		618
		619	=item eio_mtouch (void addr, size_t length, int flags, int pri, eio_cb cb, void data)
		620
		621	Reads (C<flags == 0>) or modifies (C<flags == EIO_MT_MODIFY>) the given
		622	memory area, page-wise, that is, it reads (or reads and writes back) the
		623	first octet of every page that spans the memory area.
		624
		625	This can be used to page in some mmapped file, or dirty some pages. Note
		626	that dirtying is an unlocked read-write access, so races can ensue when
		627	the some other thread modifies the data stored in that memory area.
		628
		629	=item eio_custom (void ()(eio_req ) execute, int pri, eio_cb cb, void *data)
		630
		631	Executes a custom request, i.e., a user-specified callback.
		632
		633	The callback gets the C<eio_req *> as parameter and is expected to read
		634	and modify any request-specific members. Specifically, it should set C<<
		635	req->result >> to the result value, just like other requests.
		636
		637	Here is an example that simply calls C<open>, like C<eio_open>, but it
		638	uses the C<data> member as filename and uses a hardcoded C<O_RDONLY>. If
		639	you want to pass more/other parameters, you either need to pass some
		640	struct or so via C<data> or provide your own wrapper using the low-level
		641	API.
		642
		643	static int
		644	my_open_done (eio_req *req)
		645	{
		646	int fd = req->result;
		647
		648	return 0;
		649	}
		650
		651	static void
		652	my_open (eio_req *req)
		653	{
		654	req->result = open (req->data, O_RDONLY);
		655	}
		656
		657	eio_custom (my_open, 0, my_open_done, "/etc/passwd");
		658
		659	=item eio_busy (eio_tstamp delay, int pri, eio_cb cb, void *data)
		660
		661	This is a request that takes C<delay> seconds to execute, but otherwise
		662	does nothing - it simply puts one of the worker threads to sleep for this
		663	long.
		664
		665	This request can be used to artificially increase load, e.g. for debugging
		666	or benchmarking reasons.
		667
		668	=item eio_nop (int pri, eio_cb cb, void *data)
		669
		670	This request does nothing, except go through the whole request cycle. This
		671	can be used to measure latency or in some cases to simplify code, but is
		672	not really of much use.
		673
		674	=back
		675
		676	=head3 GROUPING AND LIMITING REQUESTS
		677
		678	There is one more rather special request, C<eio_grp>. It is a very special
		679	aio request: Instead of doing something, it is a container for other eio
		680	requests.
		681
		682	There are two primary use cases for this: a) bundle many requests into a
		683	single, composite, request with a definite callback and the ability to
		684	cancel the whole request with its subrequests and b) limiting the number
		685	of "active" requests.
		686
		687	Further below you will find more discussion of these topics - first
		688	follows the reference section detailing the request generator and other
		689	methods.
		690
		691	=over 4
		692
		693	=item eio_req grp = eio_grp (eio_cb cb, void data)
		694
		695	Creates, submits and returns a group request. Note that it doesn't have a
		696	priority, unlike all other requests.
		697
		698	=item eio_grp_add (eio_req grp, eio_req req)
		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
		772
		773
		774	#TODO
		775
		776	void eio_grp_limit (eio_req *grp, int limit);
		777
		778
		779
		780	=head1 LOW LEVEL REQUEST API
		781
		782	#TODO
		783
		784
		785	=head1 ANATOMY AND LIFETIME OF AN EIO REQUEST
		786
		787	A request is represented by a structure of type C<eio_req>. To initialise
		788	it, clear it to all zero bytes:
		789
		790	eio_req req;
		791
		792	memset (&req, 0, sizeof (req));
		793
		794	A more common way to initialise a new C<eio_req> is to use C<calloc>:
		795
		796	eio_req req = calloc (1, sizeof (req));
		797
		798	In either case, libeio neither allocates, initialises or frees the
		799	C<eio_req> structure for you - it merely uses it.
		800
		801	zero
		802
		803	#TODO
137		804
138	=head2 CONFIGURATION	805	=head2 CONFIGURATION
139		806
140	The functions in this section can sometimes be useful, but the default	807	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	808	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	819	for example, in interactive programs, you might want to limit this time to
153	C<0.01> seconds or so.	820	C<0.01> seconds or so.
154		821
155	Note that:	822	Note that:
156		823
		824	=over 4
		825
157	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
158	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
159	interval.	828	this interval.
160		829
161	b) this is implemented by calling C<gettimeofday> after each request,	830	=item b) this is implemented by calling C<gettimeofday> after each
162	which can be costly.	831	request, which can be costly.
163		832
164	c) at least one request will be handled.	833	=item c) at least one request will be handled.
		834
		835	=back
165		836
166	=item eio_set_max_poll_reqs (unsigned int nreqs)	837	=item eio_set_max_poll_reqs (unsigned int nreqs)
167		838
168	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
169	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
…		…
185	=item eio_set_max_idle (unsigned int nthreads)	856	=item eio_set_max_idle (unsigned int nthreads)
186		857
187	Libeio uses threads internally to handle most requests, and will start and stop threads on demand.	858	Libeio uses threads internally to handle most requests, and will start and stop threads on demand.
188		859
189	This call can be used to limit the number of idle threads (threads without	860	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	861	work to do): libeio will keep some threads idle in preparation for more
191	requests, but never longer than C<nthreads> threads.	862	requests, but never longer than C<nthreads> threads.
192		863
193	In addition to this, libeio will also stop threads when they are idle for	864	In addition to this, libeio will also stop threads when they are idle for
194	a few seconds, regardless of this setting.	865	a few seconds, regardless of this setting.
195		866
…		…
214	executed and have results, but have not been finished yet by a call to	885	executed and have results, but have not been finished yet by a call to
215	C<eio_poll>).	886	C<eio_poll>).
216		887
217	=back	888	=back
218		889
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	890	=head1 EMBEDDING
237		891
238	Libeio can be embedded directly into programs. This functionality is not	892	Libeio can be embedded directly into programs. This functionality is not
239	documented and not (yet) officially supported.	893	documented and not (yet) officially supported.
240		894
241	Note that, when including C<libeio.m4>, you are responsible for defining	895	Note that, when including C<libeio.m4>, you are responsible for defining
242	the compilation environment (C<_LARGEFILE_SOURCE>, C<_GNU_SOURCE> etc.).	896	the compilation environment (C<_LARGEFILE_SOURCE>, C<_GNU_SOURCE> etc.).
243		897
244	If you need to know how, check the C<IO::AIO> perl module, which does	898	If you need to know how, check the C<IO::AIO> perl module, which does
245	exactly that.	899	exactly that.
		900
		901
		902	=head1 COMPILETIME CONFIGURATION
		903
		904	These symbols, if used, must be defined when compiling F<eio.c>.
		905
		906	=over 4
		907
		908	=item EIO_STACKSIZE
		909
		910	This symbol governs the stack size for each eio thread. Libeio itself
		911	was written to use very little stackspace, but when using C<EIO_CUSTOM>
		912	requests, you might want to increase this.
		913
		914	If this symbol is undefined (the default) then libeio will use its default
		915	stack size (C<sizeof (void ) 4096> currently). In all other cases, the
		916	value must be an expression that evaluates to the desired stack size.
		917
		918	=back
246		919
247		920
248	=head1 PORTABILITY REQUIREMENTS	921	=head1 PORTABILITY REQUIREMENTS
249		922
250	In addition to a working ISO-C implementation, libeio relies on a few	923	In addition to a working ISO-C implementation, libeio relies on a few

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Comparing libeio/eio.pod (file contents): Revision 1.3 by root, Wed Oct 22 18:15:36 2008 UTC vs. Revision 1.35 by root, Mon Aug 18 08:11:54 2014 UTC

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Comparing libeio/eio.pod (file contents):
Revision 1.3 by root, Wed Oct 22 18:15:36 2008 UTC vs.
Revision 1.35 by root, Mon Aug 18 08:11:54 2014 UTC