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

Comparing libeio/eio.pod (file contents):
Revision 1.5 by root, Sun Nov 29 15:53:48 2009 UTC vs.
Revision 1.19 by root, Tue Jul 5 20:38:47 2011 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
…		…
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	Calling C<fork ()> is fully supported by this module - but you must not
		51	rely on this. It is currently implemented in these steps:
51		52
52	1. wait till all requests in "execute" state have been handled	53	1. wait till all requests in "execute" state have been handled
53	(basically requests that are already handed over to the kernel).	54	(basically requests that are already handed over to the kernel).
54	2. fork	55	2. fork
55	3. in the parent, continue business as usual, done	56	3. in the parent, continue business as usual, done
56	4. in the child, destroy all ready and pending requests and free the	57	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	memory used by the worker threads. This gives you a fully empty
58	libeio queue.	59	libeio queue.
		60
		61	Note, however, since libeio does use threads, the above guarantee doesn't
		62	cover your libc, for example, malloc and other libc functions are not
		63	fork-safe, so there is very little you can do after a fork, and in fact,
		64	the above might crash, and thus change.
59		65
60	=head1 INITIALISATION/INTEGRATION	66	=head1 INITIALISATION/INTEGRATION
61		67
62	Before you can call any eio functions you first have to initialise the	68	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	69	library. The library integrates into any event loop, but can also be used
…		…
97	handled or C<done_poll> has been called, which signals the same.	103	handled or C<done_poll> has been called, which signals the same.
98		104
99	Note that C<eio_poll> might return after C<done_poll> and C<want_poll>	105	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.	106	have been called again, so watch out for races in your code.
101		107
102	As with C<want_poll>, this callback is called while lcoks are being held,	108	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>.	109	so you I<must not call any libeio functions form within this callback>.
104		110
105	=item int eio_poll ()	111	=item int eio_poll ()
106		112
107	This function has to be called whenever there are pending requests that	113	This function has to be called whenever there are pending requests that
…		…
119	=back	125	=back
120		126
121	For libev, you would typically use an C<ev_async> watcher: the	127	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	128	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	129	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	130	()>.
125	all requests have been handled yet). The race is taken care of because	131
126	libev resets/rearms the async watcher before calling your callback,	132	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)	133	(i.e. it returns C<-1>) then you should start an idle watcher that calls
128	spurious wake-ups, but is generally harmless.	134	C<eio_poll> until it returns something C<!= -1>.
		135
		136	A full-featured conenctor between libeio and libev would look as follows
		137	(if C<eio_poll> is handling all requests, it can of course be simplified a
		138	lot by removing the idle watcher logic):
		139
		140	static struct ev_loop *loop;
		141	static ev_idle repeat_watcher;
		142	static ev_async ready_watcher;
		143
		144	/* idle watcher callback, only used when eio_poll */
		145	/* didn't handle all results in one call */
		146	static void
		147	repeat (EV_P_ ev_idle *w, int revents)
		148	{
		149	if (eio_poll () != -1)
		150	ev_idle_stop (EV_A_ w);
		151	}
		152
		153	/* eio has some results, process them */
		154	static void
		155	ready (EV_P_ ev_async *w, int revents)
		156	{
		157	if (eio_poll () == -1)
		158	ev_idle_start (EV_A_ &repeat_watcher);
		159	}
		160
		161	/* wake up the event loop */
		162	static void
		163	want_poll (void)
		164	{
		165	ev_async_send (loop, &ready_watcher)
		166	}
		167
		168	void
		169	my_init_eio ()
		170	{
		171	loop = EV_DEFAULT;
		172
		173	ev_idle_init (&repeat_watcher, repeat);
		174	ev_async_init (&ready_watcher, ready);
		175	ev_async_start (loop &watcher);
		176
		177	eio_init (want_poll, 0);
		178	}
129		179
130	For most other event loops, you would typically use a pipe - the event	180	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	181	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	182	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	183	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	184	C<eio_poll>.
135	your callback again and again until the byte has been read (as the pipe	185
136	read callback does not read it, only C<done_poll>).	186	You don't have to take special care in the case C<eio_poll> doesn't handle
		187	all requests, as the done callback will not be invoked, so the event loop
		188	will still signal readiness for the pipe until I<all> results have been
		189	processed.
		190
		191
		192	=head1 HIGH LEVEL REQUEST API
		193
		194	Libeio has both a high-level API, which consists of calling a request
		195	function with a callback to be called on completion, and a low-level API
		196	where you fill out request structures and submit them.
		197
		198	This section describes the high-level API.
		199
		200	=head2 REQUEST SUBMISSION AND RESULT PROCESSING
		201
		202	You submit a request by calling the relevant C<eio_TYPE> function with the
		203	required parameters, a callback of type C<int (eio_cb)(eio_req req)>
		204	(called C<eio_cb> below) and a freely usable C<void *data> argument.
		205
		206	The return value will either be 0, in case something went really wrong
		207	(which can basically only happen on very fatal errors, such as C<malloc>
		208	returning 0, which is rather unlikely), or a pointer to the newly-created
		209	and submitted C<eio_req *>.
		210
		211	The callback will be called with an C<eio_req *> which contains the
		212	results of the request. The members you can access inside that structure
		213	vary from request to request, except for:
		214
		215	=over 4
		216
		217	=item C<ssize_t result>
		218
		219	This contains the result value from the call (usually the same as the
		220	syscall of the same name).
		221
		222	=item C<int errorno>
		223
		224	This contains the value of C<errno> after the call.
		225
		226	=item C<void *data>
		227
		228	The C<void *data> member simply stores the value of the C<data> argument.
		229
		230	=back
		231
		232	The return value of the callback is normally C<0>, which tells libeio to
		233	continue normally. If a callback returns a nonzero value, libeio will
		234	stop processing results (in C<eio_poll>) and will return the value to its
		235	caller.
		236
		237	Memory areas passed to libeio must stay valid as long as a request
		238	executes, with the exception of paths, which are being copied
		239	internally. Any memory libeio itself allocates will be freed after the
		240	finish callback has been called. If you want to manage all memory passed
		241	to libeio yourself you can use the low-level API.
		242
		243	For example, to open a file, you could do this:
		244
		245	static int
		246	file_open_done (eio_req *req)
		247	{
		248	if (req->result < 0)
		249	{
		250	/* open() returned -1 */
		251	errno = req->errorno;
		252	perror ("open");
		253	}
		254	else
		255	{
		256	int fd = req->result;
		257	/* now we have the new fd in fd */
		258	}
		259
		260	return 0;
		261	}
		262
		263	/* the first three arguments are passed to open(2) */
		264	/* the remaining are priority, callback and data */
		265	if (!eio_open ("/etc/passwd", O_RDONLY, 0, 0, file_open_done, 0))
		266	abort (); /* something went wrong, we will all die!!! */
		267
		268	Note that you additionally need to call C<eio_poll> when the C<want_cb>
		269	indicates that requests are ready to be processed.
		270
		271	=head2 CANCELLING REQUESTS
		272
		273	Sometimes the need for a request goes away before the request is
		274	finished. In that case, one can cancel the request by a call to
		275	C<eio_cancel>:
		276
		277	=over 4
		278
		279	=item eio_cancel (eio_req *req)
		280
		281	Cancel the request (and all its subrequests). If the request is currently
		282	executing it might still continue to execute, and in other cases it might
		283	still take a while till the request is cancelled.
		284
		285	Even if cancelled, the finish callback will still be invoked - the
		286	callbacks of all cancellable requests need to check whether the request
		287	has been cancelled by calling C<EIO_CANCELLED (req)>:
		288
		289	static int
		290	my_eio_cb (eio_req *req)
		291	{
		292	if (EIO_CANCELLED (req))
		293	return 0;
		294	}
		295
		296	In addition, cancelled requests will I<either> have C<< req->result >>
		297	set to C<-1> and C<errno> to C<ECANCELED>, or I<otherwise> they were
		298	successfully executed, despite being cancelled (e.g. when they have
		299	already been executed at the time they were cancelled).
		300
		301	C<EIO_CANCELLED> is still true for requests that have successfully
		302	executed, as long as C<eio_cancel> was called on them at some point.
		303
		304	=back
		305
		306	=head2 AVAILABLE REQUESTS
		307
		308	The following request functions are available. I<All> of them return the
		309	C<eio_req *> on success and C<0> on failure, and I<all> of them have the
		310	same three trailing arguments: C<pri>, C<cb> and C<data>. The C<cb> is
		311	mandatory, but in most cases, you pass in C<0> as C<pri> and C<0> or some
		312	custom data value as C<data>.
		313
		314	=head3 POSIX API WRAPPERS
		315
		316	These requests simply wrap the POSIX call of the same name, with the same
		317	arguments. If a function is not implemented by the OS and cannot be emulated
		318	in some way, then all of these return C<-1> and set C<errorno> to C<ENOSYS>.
		319
		320	=over 4
		321
		322	=item eio_open (const char path, int flags, mode_t mode, int pri, eio_cb cb, void data)
		323
		324	=item eio_truncate (const char path, off_t offset, int pri, eio_cb cb, void data)
		325
		326	=item eio_chown (const char path, uid_t uid, gid_t gid, int pri, eio_cb cb, void data)
		327
		328	=item eio_chmod (const char path, mode_t mode, int pri, eio_cb cb, void data)
		329
		330	=item eio_mkdir (const char path, mode_t mode, int pri, eio_cb cb, void data)
		331
		332	=item eio_rmdir (const char path, int pri, eio_cb cb, void data)
		333
		334	=item eio_unlink (const char path, int pri, eio_cb cb, void data)
		335
		336	=item eio_utime (const char path, eio_tstamp atime, eio_tstamp mtime, int pri, eio_cb cb, void data)
		337
		338	=item eio_mknod (const char path, mode_t mode, dev_t dev, int pri, eio_cb cb, void data)
		339
		340	=item eio_link (const char path, const char new_path, int pri, eio_cb cb, void *data)
		341
		342	=item eio_symlink (const char path, const char new_path, int pri, eio_cb cb, void *data)
		343
		344	=item eio_rename (const char path, const char new_path, int pri, eio_cb cb, void *data)
		345
		346	=item eio_mlock (void addr, size_t length, int pri, eio_cb cb, void data)
		347
		348	=item eio_close (int fd, int pri, eio_cb cb, void *data)
		349
		350	=item eio_sync (int pri, eio_cb cb, void *data)
		351
		352	=item eio_fsync (int fd, int pri, eio_cb cb, void *data)
		353
		354	=item eio_fdatasync (int fd, int pri, eio_cb cb, void *data)
		355
		356	=item eio_futime (int fd, eio_tstamp atime, eio_tstamp mtime, int pri, eio_cb cb, void *data)
		357
		358	=item eio_ftruncate (int fd, off_t offset, int pri, eio_cb cb, void *data)
		359
		360	=item eio_fchmod (int fd, mode_t mode, int pri, eio_cb cb, void *data)
		361
		362	=item eio_fchown (int fd, uid_t uid, gid_t gid, int pri, eio_cb cb, void *data)
		363
		364	=item eio_dup2 (int fd, int fd2, int pri, eio_cb cb, void *data)
		365
		366	These have the same semantics as the syscall of the same name, their
		367	return value is available as C<< req->result >> later.
		368
		369	=item eio_read (int fd, void buf, size_t length, off_t offset, int pri, eio_cb cb, void data)
		370
		371	=item eio_write (int fd, void buf, size_t length, off_t offset, int pri, eio_cb cb, void data)
		372
		373	These two requests are called C<read> and C<write>, but actually wrap
		374	C<pread> and C<pwrite>. On systems that lack these calls (such as cygwin),
		375	libeio uses lseek/read_or_write/lseek and a mutex to serialise the
		376	requests, so all these requests run serially and do not disturb each
		377	other. However, they still disturb the file offset while they run, so it's
		378	not safe to call these functions concurrently with non-libeio functions on
		379	the same fd on these systems.
		380
		381	Not surprisingly, pread and pwrite are not thread-safe on Darwin (OS/X),
		382	so it is advised not to submit multiple requests on the same fd on this
		383	horrible pile of garbage.
		384
		385	=item eio_mlockall (int flags, int pri, eio_cb cb, void *data)
		386
		387	Like C<mlockall>, but the flag value constants are called
		388	C<EIO_MCL_CURRENT> and C<EIO_MCL_FUTURE>.
		389
		390	=item eio_msync (void addr, size_t length, int flags, int pri, eio_cb cb, void data)
		391
		392	Just like msync, except that the flag values are called C<EIO_MS_ASYNC>,
		393	C<EIO_MS_INVALIDATE> and C<EIO_MS_SYNC>.
		394
		395	=item eio_readlink (const char path, int pri, eio_cb cb, void data)
		396
		397	If successful, the path read by C<readlink(2)> can be accessed via C<<
		398	req->ptr2 >> and is I<NOT> null-terminated, with the length specified as
		399	C<< req->result >>.
		400
		401	if (req->result >= 0)
		402	{
		403	char target = strndup ((char )req->ptr2, req->result);
		404
		405	free (target);
		406	}
		407
		408	=item eio_realpath (const char path, int pri, eio_cb cb, void data)
		409
		410	Similar to the realpath libc function, but unlike that one, result is
		411	C<-1> on failure and the length of the returned path in C<ptr2> (which is
		412	not 0-terminated) - this is similar to readlink.
		413
		414	=item eio_stat (const char path, int pri, eio_cb cb, void data)
		415
		416	=item eio_lstat (const char path, int pri, eio_cb cb, void data)
		417
		418	=item eio_fstat (int fd, int pri, eio_cb cb, void *data)
		419
		420	Stats a file - if C<< req->result >> indicates success, then you can
		421	access the C<struct stat>-like structure via C<< req->ptr2 >>:
		422
		423	EIO_STRUCT_STAT statdata = (EIO_STRUCT_STAT )req->ptr2;
		424
		425	=item eio_statvfs (const char path, int pri, eio_cb cb, void data)
		426
		427	=item eio_fstatvfs (int fd, int pri, eio_cb cb, void *data)
		428
		429	Stats a filesystem - if C<< req->result >> indicates success, then you can
		430	access the C<struct statvfs>-like structure via C<< req->ptr2 >>:
		431
		432	EIO_STRUCT_STATVFS statdata = (EIO_STRUCT_STATVFS )req->ptr2;
		433
		434	=back
		435
		436	=head3 READING DIRECTORIES
		437
		438	Reading directories sounds simple, but can be rather demanding, especially
		439	if you want to do stuff such as traversing a directory hierarchy or
		440	processing all files in a directory. Libeio can assist these complex tasks
		441	with it's C<eio_readdir> call.
		442
		443	=over 4
		444
		445	=item eio_readdir (const char path, int flags, int pri, eio_cb cb, void data)
		446
		447	This is a very complex call. It basically reads through a whole directory
		448	(via the C<opendir>, C<readdir> and C<closedir> calls) and returns either
		449	the names or an array of C<struct eio_dirent>, depending on the C<flags>
		450	argument.
		451
		452	The C<< req->result >> indicates either the number of files found, or
		453	C<-1> on error. On success, null-terminated names can be found as C<< req->ptr2 >>,
		454	and C<struct eio_dirents>, if requested by C<flags>, can be found via C<<
		455	req->ptr1 >>.
		456
		457	Here is an example that prints all the names:
		458
		459	int i;
		460	char names = (char )req->ptr2;
		461
		462	for (i = 0; i < req->result; ++i)
		463	{
		464	printf ("name #%d: %s\n", i, names);
		465
		466	/* move to next name */
		467	names += strlen (names) + 1;
		468	}
		469
		470	Pseudo-entries such as F<.> and F<..> are never returned by C<eio_readdir>.
		471
		472	C<flags> can be any combination of:
		473
		474	=over 4
		475
		476	=item EIO_READDIR_DENTS
		477
		478	If this flag is specified, then, in addition to the names in C<ptr2>,
		479	also an array of C<struct eio_dirent> is returned, in C<ptr1>. A C<struct
		480	eio_dirent> looks like this:
		481
		482	struct eio_dirent
		483	{
		484	int nameofs; /* offset of null-terminated name string in (char )req->ptr2 /
		485	unsigned short namelen; /* size of filename without trailing 0 */
		486	unsigned char type; /* one of EIO_DT_* */
		487	signed char score; /* internal use */
		488	ino_t inode; /* the inode number, if available, otherwise unspecified */
		489	};
		490
		491	The only members you normally would access are C<nameofs>, which is the
		492	byte-offset from C<ptr2> to the start of the name, C<namelen> and C<type>.
		493
		494	C<type> can be one of:
		495
		496	C<EIO_DT_UNKNOWN> - if the type is not known (very common) and you have to C<stat>
		497	the name yourself if you need to know,
		498	one of the "standard" POSIX file types (C<EIO_DT_REG>, C<EIO_DT_DIR>, C<EIO_DT_LNK>,
		499	C<EIO_DT_FIFO>, C<EIO_DT_SOCK>, C<EIO_DT_CHR>, C<EIO_DT_BLK>)
		500	or some OS-specific type (currently
		501	C<EIO_DT_MPC> - multiplexed char device (v7+coherent),
		502	C<EIO_DT_NAM> - xenix special named file,
		503	C<EIO_DT_MPB> - multiplexed block device (v7+coherent),
		504	C<EIO_DT_NWK> - HP-UX network special,
		505	C<EIO_DT_CMP> - VxFS compressed,
		506	C<EIO_DT_DOOR> - solaris door, or
		507	C<EIO_DT_WHT>).
		508
		509	This example prints all names and their type:
		510
		511	int i;
		512	struct eio_dirent ents = (struct eio_dirent )req->ptr1;
		513	char names = (char )req->ptr2;
		514
		515	for (i = 0; i < req->result; ++i)
		516	{
		517	struct eio_dirent *ent = ents + i;
		518	char *name = names + ent->nameofs;
		519
		520	printf ("name #%d: %s (type %d)\n", i, name, ent->type);
		521	}
		522
		523	=item EIO_READDIR_DIRS_FIRST
		524
		525	When this flag is specified, then the names will be returned in an order
		526	where likely directories come first, in optimal C<stat> order. This is
		527	useful when you need to quickly find directories, or you want to find all
		528	directories while avoiding to stat() each entry.
		529
		530	If the system returns type information in readdir, then this is used
		531	to find directories directly. Otherwise, likely directories are names
		532	beginning with ".", or otherwise names with no dots, of which names with
		533	short names are tried first.
		534
		535	=item EIO_READDIR_STAT_ORDER
		536
		537	When this flag is specified, then the names will be returned in an order
		538	suitable for stat()'ing each one. That is, when you plan to stat()
		539	all files in the given directory, then the returned order will likely
		540	be fastest.
		541
		542	If both this flag and C<EIO_READDIR_DIRS_FIRST> are specified, then the
		543	likely directories come first, resulting in a less optimal stat order.
		544
		545	=item EIO_READDIR_FOUND_UNKNOWN
		546
		547	This flag should not be specified when calling C<eio_readdir>. Instead,
		548	it is being set by C<eio_readdir> (you can access the C<flags> via C<<
		549	req->int1 >>, when any of the C<type>'s found were C<EIO_DT_UNKNOWN>. The
		550	absence of this flag therefore indicates that all C<type>'s are known,
		551	which can be used to speed up some algorithms.
		552
		553	A typical use case would be to identify all subdirectories within a
		554	directory - you would ask C<eio_readdir> for C<EIO_READDIR_DIRS_FIRST>. If
		555	then this flag is I<NOT> set, then all the entries at the beginning of the
		556	returned array of type C<EIO_DT_DIR> are the directories. Otherwise, you
		557	should start C<stat()>'ing the entries starting at the beginning of the
		558	array, stopping as soon as you found all directories (the count can be
		559	deduced by the link count of the directory).
		560
		561	=back
		562
		563	=back
		564
		565	=head3 OS-SPECIFIC CALL WRAPPERS
		566
		567	These wrap OS-specific calls (usually Linux ones), and might or might not
		568	be emulated on other operating systems. Calls that are not emulated will
		569	return C<-1> and set C<errno> to C<ENOSYS>.
		570
		571	=over 4
		572
		573	=item eio_sendfile (int out_fd, int in_fd, off_t in_offset, size_t length, int pri, eio_cb cb, void *data)
		574
		575	Wraps the C<sendfile> syscall. The arguments follow the Linux version, but
		576	libeio supports and will use similar calls on FreeBSD, HP/UX, Solaris and
		577	Darwin.
		578
		579	If the OS doesn't support some sendfile-like call, or the call fails,
		580	indicating support for the given file descriptor type (for example,
		581	Linux's sendfile might not support file to file copies), then libeio will
		582	emulate the call in userspace, so there are almost no limitations on its
		583	use.
		584
		585	=item eio_readahead (int fd, off_t offset, size_t length, int pri, eio_cb cb, void *data)
		586
		587	Calls C<readahead(2)>. If the syscall is missing, then the call is
		588	emulated by simply reading the data (currently in 64kiB chunks).
		589
		590	=item eio_sync_file_range (int fd, off_t offset, size_t nbytes, unsigned int flags, int pri, eio_cb cb, void *data)
		591
		592	Calls C<sync_file_range>. If the syscall is missing, then this is the same
		593	as calling C<fdatasync>.
		594
		595	Flags can be any combination of C<EIO_SYNC_FILE_RANGE_WAIT_BEFORE>,
		596	C<EIO_SYNC_FILE_RANGE_WRITE> and C<EIO_SYNC_FILE_RANGE_WAIT_AFTER>.
		597
		598	=back
		599
		600	=head3 LIBEIO-SPECIFIC REQUESTS
		601
		602	These requests are specific to libeio and do not correspond to any OS call.
		603
		604	=over 4
		605
		606	=item eio_mtouch (void addr, size_t length, int flags, int pri, eio_cb cb, void data)
		607
		608	Reads (C<flags == 0>) or modifies (C<flags == EIO_MT_MODIFY) the given
		609	memory area, page-wise, that is, it reads (or reads and writes back) the
		610	first octet of every page that spans the memory area.
		611
		612	This can be used to page in some mmapped file, or dirty some pages. Note
		613	that dirtying is an unlocked read-write access, so races can ensue when
		614	the some other thread modifies the data stored in that memory area.
		615
		616	=item eio_custom (void ()(eio_req ) execute, int pri, eio_cb cb, void *data)
		617
		618	Executes a custom request, i.e., a user-specified callback.
		619
		620	The callback gets the C<eio_req *> as parameter and is expected to read
		621	and modify any request-specific members. Specifically, it should set C<<
		622	req->result >> to the result value, just like other requests.
		623
		624	Here is an example that simply calls C<open>, like C<eio_open>, but it
		625	uses the C<data> member as filename and uses a hardcoded C<O_RDONLY>. If
		626	you want to pass more/other parameters, you either need to pass some
		627	struct or so via C<data> or provide your own wrapper using the low-level
		628	API.
		629
		630	static int
		631	my_open_done (eio_req *req)
		632	{
		633	int fd = req->result;
		634
		635	return 0;
		636	}
		637
		638	static void
		639	my_open (eio_req *req)
		640	{
		641	req->result = open (req->data, O_RDONLY);
		642	}
		643
		644	eio_custom (my_open, 0, my_open_done, "/etc/passwd");
		645
		646	=item eio_busy (eio_tstamp delay, int pri, eio_cb cb, void *data)
		647
		648	This is a request that takes C<delay> seconds to execute, but otherwise
		649	does nothing - it simply puts one of the worker threads to sleep for this
		650	long.
		651
		652	This request can be used to artificially increase load, e.g. for debugging
		653	or benchmarking reasons.
		654
		655	=item eio_nop (int pri, eio_cb cb, void *data)
		656
		657	This request does nothing, except go through the whole request cycle. This
		658	can be used to measure latency or in some cases to simplify code, but is
		659	not really of much use.
		660
		661	=back
		662
		663	=head3 GROUPING AND LIMITING REQUESTS
		664
		665	There is one more rather special request, C<eio_grp>. It is a very special
		666	aio request: Instead of doing something, it is a container for other eio
		667	requests.
		668
		669	There are two primary use cases for this: a) bundle many requests into a
		670	single, composite, request with a definite callback and the ability to
		671	cancel the whole request with its subrequests and b) limiting the number
		672	of "active" requests.
		673
		674	Further below you will find more discussion of these topics - first
		675	follows the reference section detailing the request generator and other
		676	methods.
		677
		678	=over 4
		679
		680	=item eio_req grp = eio_grp (eio_cb cb, void data)
		681
		682	Creates, submits and returns a group request.
		683
		684	=item eio_grp_add (eio_req grp, eio_req req)
		685
		686	Adds a request to the request group.
		687
		688	=item eio_grp_cancel (eio_req *grp)
		689
		690	Cancels all requests I<in> the group, but I<not> the group request
		691	itself. You can cancel the group request via a normal C<eio_cancel> call.
		692
		693
		694
		695	=back
		696
		697
		698
		699	#TODO
		700
		701	/*****************************************************************************/
		702	/* groups */
		703
		704	eio_req eio_grp (eio_cb cb, void data);
		705	void eio_grp_feed (eio_req grp, void (feed)(eio_req *req), int limit);
		706	void eio_grp_limit (eio_req *grp, int limit);
		707	void eio_grp_cancel (eio_req grp); / cancels all sub requests but not the group */
		708
		709
		710	=back
		711
		712
		713	=head1 LOW LEVEL REQUEST API
		714
		715	#TODO
		716
		717
		718	=head1 ANATOMY AND LIFETIME OF AN EIO REQUEST
		719
		720	A request is represented by a structure of type C<eio_req>. To initialise
		721	it, clear it to all zero bytes:
		722
		723	eio_req req;
		724
		725	memset (&req, 0, sizeof (req));
		726
		727	A more common way to initialise a new C<eio_req> is to use C<calloc>:
		728
		729	eio_req req = calloc (1, sizeof (req));
		730
		731	In either case, libeio neither allocates, initialises or frees the
		732	C<eio_req> structure for you - it merely uses it.
		733
		734	zero
		735
		736	#TODO
137		737
138	=head2 CONFIGURATION	738	=head2 CONFIGURATION
139		739
140	The functions in this section can sometimes be useful, but the default	740	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	741	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	752	for example, in interactive programs, you might want to limit this time to
153	C<0.01> seconds or so.	753	C<0.01> seconds or so.
154		754
155	Note that:	755	Note that:
156		756
		757	=over 4
		758
157	a) libeio doesn't know how long your request callbacks take, so the time	759	=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	760	time spent in C<eio_poll> is up to one callback invocation longer then
159	interval.	761	this interval.
160		762
161	b) this is implemented by calling C<gettimeofday> after each request,	763	=item b) this is implemented by calling C<gettimeofday> after each
162	which can be costly.	764	request, which can be costly.
163		765
164	c) at least one request will be handled.	766	=item c) at least one request will be handled.
		767
		768	=back
165		769
166	=item eio_set_max_poll_reqs (unsigned int nreqs)	770	=item eio_set_max_poll_reqs (unsigned int nreqs)
167		771
168	When C<nreqs> is non-zero, then C<eio_poll> will not handle more than	772	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	773	C<nreqs> requests per invocation. This is a less costly way to limit the
…		…
185	=item eio_set_max_idle (unsigned int nthreads)	789	=item eio_set_max_idle (unsigned int nthreads)
186		790
187	Libeio uses threads internally to handle most requests, and will start and stop threads on demand.	791	Libeio uses threads internally to handle most requests, and will start and stop threads on demand.
188		792
189	This call can be used to limit the number of idle threads (threads without	793	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	794	work to do): libeio will keep some threads idle in preparation for more
191	requests, but never longer than C<nthreads> threads.	795	requests, but never longer than C<nthreads> threads.
192		796
193	In addition to this, libeio will also stop threads when they are idle for	797	In addition to this, libeio will also stop threads when they are idle for
194	a few seconds, regardless of this setting.	798	a few seconds, regardless of this setting.
195		799
…		…
213	Returns the number of pending requests, i.e. requests that have been	817	Returns the number of pending requests, i.e. requests that have been
214	executed and have results, but have not been finished yet by a call to	818	executed and have results, but have not been finished yet by a call to
215	C<eio_poll>).	819	C<eio_poll>).
216		820
217	=back	821	=back
218
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		822
236	=head1 EMBEDDING	823	=head1 EMBEDDING
237		824
238	Libeio can be embedded directly into programs. This functionality is not	825	Libeio can be embedded directly into programs. This functionality is not
239	documented and not (yet) officially supported.	826	documented and not (yet) officially supported.

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Comparing libeio/eio.pod (file contents): Revision 1.5 by root, Sun Nov 29 15:53:48 2009 UTC vs. Revision 1.19 by root, Tue Jul 5 20:38:47 2011 UTC

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Comparing libeio/eio.pod (file contents):
Revision 1.5 by root, Sun Nov 29 15:53:48 2009 UTC vs.
Revision 1.19 by root, Tue Jul 5 20:38:47 2011 UTC