[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 1.23 by root, Wed Jul 13 21:31:40 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
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	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 connector 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, C<<
		411	req->result >> is C<-1> on failure. On success, the result is the length
		412	of the returned path in C<ptr2> (which is I<NOT> 0-terminated) - this is
		413	similar to readlink.
		414
		415	=item eio_stat (const char path, int pri, eio_cb cb, void data)
		416
		417	=item eio_lstat (const char path, int pri, eio_cb cb, void data)
		418
		419	=item eio_fstat (int fd, int pri, eio_cb cb, void *data)
		420
		421	Stats a file - if C<< req->result >> indicates success, then you can
		422	access the C<struct stat>-like structure via C<< req->ptr2 >>:
		423
		424	EIO_STRUCT_STAT statdata = (EIO_STRUCT_STAT )req->ptr2;
		425
		426	=item eio_statvfs (const char path, int pri, eio_cb cb, void data)
		427
		428	=item eio_fstatvfs (int fd, int pri, eio_cb cb, void *data)
		429
		430	Stats a filesystem - if C<< req->result >> indicates success, then you can
		431	access the C<struct statvfs>-like structure via C<< req->ptr2 >>:
		432
		433	EIO_STRUCT_STATVFS statdata = (EIO_STRUCT_STATVFS )req->ptr2;
		434
		435	=back
		436
		437	=head3 READING DIRECTORIES
		438
		439	Reading directories sounds simple, but can be rather demanding, especially
		440	if you want to do stuff such as traversing a directory hierarchy or
		441	processing all files in a directory. Libeio can assist these complex tasks
		442	with it's C<eio_readdir> call.
		443
		444	=over 4
		445
		446	=item eio_readdir (const char path, int flags, int pri, eio_cb cb, void data)
		447
		448	This is a very complex call. It basically reads through a whole directory
		449	(via the C<opendir>, C<readdir> and C<closedir> calls) and returns either
		450	the names or an array of C<struct eio_dirent>, depending on the C<flags>
		451	argument.
		452
		453	The C<< req->result >> indicates either the number of files found, or
		454	C<-1> on error. On success, null-terminated names can be found as C<< req->ptr2 >>,
		455	and C<struct eio_dirents>, if requested by C<flags>, can be found via C<<
		456	req->ptr1 >>.
		457
		458	Here is an example that prints all the names:
		459
		460	int i;
		461	char names = (char )req->ptr2;
		462
		463	for (i = 0; i < req->result; ++i)
		464	{
		465	printf ("name #%d: %s\n", i, names);
		466
		467	/* move to next name */
		468	names += strlen (names) + 1;
		469	}
		470
		471	Pseudo-entries such as F<.> and F<..> are never returned by C<eio_readdir>.
		472
		473	C<flags> can be any combination of:
		474
		475	=over 4
		476
		477	=item EIO_READDIR_DENTS
		478
		479	If this flag is specified, then, in addition to the names in C<ptr2>,
		480	also an array of C<struct eio_dirent> is returned, in C<ptr1>. A C<struct
		481	eio_dirent> looks like this:
		482
		483	struct eio_dirent
		484	{
		485	int nameofs; /* offset of null-terminated name string in (char )req->ptr2 /
		486	unsigned short namelen; /* size of filename without trailing 0 */
		487	unsigned char type; /* one of EIO_DT_* */
		488	signed char score; /* internal use */
		489	ino_t inode; /* the inode number, if available, otherwise unspecified */
		490	};
		491
		492	The only members you normally would access are C<nameofs>, which is the
		493	byte-offset from C<ptr2> to the start of the name, C<namelen> and C<type>.
		494
		495	C<type> can be one of:
		496
		497	C<EIO_DT_UNKNOWN> - if the type is not known (very common) and you have to C<stat>
		498	the name yourself if you need to know,
		499	one of the "standard" POSIX file types (C<EIO_DT_REG>, C<EIO_DT_DIR>, C<EIO_DT_LNK>,
		500	C<EIO_DT_FIFO>, C<EIO_DT_SOCK>, C<EIO_DT_CHR>, C<EIO_DT_BLK>)
		501	or some OS-specific type (currently
		502	C<EIO_DT_MPC> - multiplexed char device (v7+coherent),
		503	C<EIO_DT_NAM> - xenix special named file,
		504	C<EIO_DT_MPB> - multiplexed block device (v7+coherent),
		505	C<EIO_DT_NWK> - HP-UX network special,
		506	C<EIO_DT_CMP> - VxFS compressed,
		507	C<EIO_DT_DOOR> - solaris door, or
		508	C<EIO_DT_WHT>).
		509
		510	This example prints all names and their type:
		511
		512	int i;
		513	struct eio_dirent ents = (struct eio_dirent )req->ptr1;
		514	char names = (char )req->ptr2;
		515
		516	for (i = 0; i < req->result; ++i)
		517	{
		518	struct eio_dirent *ent = ents + i;
		519	char *name = names + ent->nameofs;
		520
		521	printf ("name #%d: %s (type %d)\n", i, name, ent->type);
		522	}
		523
		524	=item EIO_READDIR_DIRS_FIRST
		525
		526	When this flag is specified, then the names will be returned in an order
		527	where likely directories come first, in optimal C<stat> order. This is
		528	useful when you need to quickly find directories, or you want to find all
		529	directories while avoiding to stat() each entry.
		530
		531	If the system returns type information in readdir, then this is used
		532	to find directories directly. Otherwise, likely directories are names
		533	beginning with ".", or otherwise names with no dots, of which names with
		534	short names are tried first.
		535
		536	=item EIO_READDIR_STAT_ORDER
		537
		538	When this flag is specified, then the names will be returned in an order
		539	suitable for stat()'ing each one. That is, when you plan to stat()
		540	all files in the given directory, then the returned order will likely
		541	be fastest.
		542
		543	If both this flag and C<EIO_READDIR_DIRS_FIRST> are specified, then the
		544	likely directories come first, resulting in a less optimal stat order.
		545
		546	=item EIO_READDIR_FOUND_UNKNOWN
		547
		548	This flag should not be specified when calling C<eio_readdir>. Instead,
		549	it is being set by C<eio_readdir> (you can access the C<flags> via C<<
		550	req->int1 >>, when any of the C<type>'s found were C<EIO_DT_UNKNOWN>. The
		551	absence of this flag therefore indicates that all C<type>'s are known,
		552	which can be used to speed up some algorithms.
		553
		554	A typical use case would be to identify all subdirectories within a
		555	directory - you would ask C<eio_readdir> for C<EIO_READDIR_DIRS_FIRST>. If
		556	then this flag is I<NOT> set, then all the entries at the beginning of the
		557	returned array of type C<EIO_DT_DIR> are the directories. Otherwise, you
		558	should start C<stat()>'ing the entries starting at the beginning of the
		559	array, stopping as soon as you found all directories (the count can be
		560	deduced by the link count of the directory).
		561
		562	=back
		563
		564	=back
		565
		566	=head3 OS-SPECIFIC CALL WRAPPERS
		567
		568	These wrap OS-specific calls (usually Linux ones), and might or might not
		569	be emulated on other operating systems. Calls that are not emulated will
		570	return C<-1> and set C<errno> to C<ENOSYS>.
		571
		572	=over 4
		573
		574	=item eio_sendfile (int out_fd, int in_fd, off_t in_offset, size_t length, int pri, eio_cb cb, void *data)
		575
		576	Wraps the C<sendfile> syscall. The arguments follow the Linux version, but
		577	libeio supports and will use similar calls on FreeBSD, HP/UX, Solaris and
		578	Darwin.
		579
		580	If the OS doesn't support some sendfile-like call, or the call fails,
		581	indicating support for the given file descriptor type (for example,
		582	Linux's sendfile might not support file to file copies), then libeio will
		583	emulate the call in userspace, so there are almost no limitations on its
		584	use.
		585
		586	=item eio_readahead (int fd, off_t offset, size_t length, int pri, eio_cb cb, void *data)
		587
		588	Calls C<readahead(2)>. If the syscall is missing, then the call is
		589	emulated by simply reading the data (currently in 64kiB chunks).
		590
		591	=item eio_sync_file_range (int fd, off_t offset, size_t nbytes, unsigned int flags, int pri, eio_cb cb, void *data)
		592
		593	Calls C<sync_file_range>. If the syscall is missing, then this is the same
		594	as calling C<fdatasync>.
		595
		596	Flags can be any combination of C<EIO_SYNC_FILE_RANGE_WAIT_BEFORE>,
		597	C<EIO_SYNC_FILE_RANGE_WRITE> and C<EIO_SYNC_FILE_RANGE_WAIT_AFTER>.
		598
		599	=item eio_fallocate (int fd, int mode, off_t offset, off_t len, int pri, eio_cb cb, void *data)
		600
		601	Calls C<fallocate> (note: I<NOT> C<posix_fallocate>!). If the syscall is
		602	missing, then it returns failure and sets C<errno> to C<ENOSYS>.
		603
		604	The C<mode> argument can be C<0> (for behaviour similar to
		605	C<posix_fallocate>), or C<EIO_FALLOC_FL_KEEP_SIZE>, which keeps the size
		606	of the file unchanged (but still preallocates space beyond end of file).
		607
		608	=back
		609
		610	=head3 LIBEIO-SPECIFIC REQUESTS
		611
		612	These requests are specific to libeio and do not correspond to any OS call.
		613
		614	=over 4
		615
		616	=item eio_mtouch (void addr, size_t length, int flags, int pri, eio_cb cb, void data)
		617
		618	Reads (C<flags == 0>) or modifies (C<flags == EIO_MT_MODIFY) the given
		619	memory area, page-wise, that is, it reads (or reads and writes back) the
		620	first octet of every page that spans the memory area.
		621
		622	This can be used to page in some mmapped file, or dirty some pages. Note
		623	that dirtying is an unlocked read-write access, so races can ensue when
		624	the some other thread modifies the data stored in that memory area.
		625
		626	=item eio_custom (void ()(eio_req ) execute, int pri, eio_cb cb, void *data)
		627
		628	Executes a custom request, i.e., a user-specified callback.
		629
		630	The callback gets the C<eio_req *> as parameter and is expected to read
		631	and modify any request-specific members. Specifically, it should set C<<
		632	req->result >> to the result value, just like other requests.
		633
		634	Here is an example that simply calls C<open>, like C<eio_open>, but it
		635	uses the C<data> member as filename and uses a hardcoded C<O_RDONLY>. If
		636	you want to pass more/other parameters, you either need to pass some
		637	struct or so via C<data> or provide your own wrapper using the low-level
		638	API.
		639
		640	static int
		641	my_open_done (eio_req *req)
		642	{
		643	int fd = req->result;
		644
		645	return 0;
		646	}
		647
		648	static void
		649	my_open (eio_req *req)
		650	{
		651	req->result = open (req->data, O_RDONLY);
		652	}
		653
		654	eio_custom (my_open, 0, my_open_done, "/etc/passwd");
		655
		656	=item eio_busy (eio_tstamp delay, int pri, eio_cb cb, void *data)
		657
		658	This is a request that takes C<delay> seconds to execute, but otherwise
		659	does nothing - it simply puts one of the worker threads to sleep for this
		660	long.
		661
		662	This request can be used to artificially increase load, e.g. for debugging
		663	or benchmarking reasons.
		664
		665	=item eio_nop (int pri, eio_cb cb, void *data)
		666
		667	This request does nothing, except go through the whole request cycle. This
		668	can be used to measure latency or in some cases to simplify code, but is
		669	not really of much use.
		670
		671	=back
		672
		673	=head3 GROUPING AND LIMITING REQUESTS
		674
		675	There is one more rather special request, C<eio_grp>. It is a very special
		676	aio request: Instead of doing something, it is a container for other eio
		677	requests.
		678
		679	There are two primary use cases for this: a) bundle many requests into a
		680	single, composite, request with a definite callback and the ability to
		681	cancel the whole request with its subrequests and b) limiting the number
		682	of "active" requests.
		683
		684	Further below you will find more discussion of these topics - first
		685	follows the reference section detailing the request generator and other
		686	methods.
		687
		688	=over 4
		689
		690	=item eio_req grp = eio_grp (eio_cb cb, void data)
		691
		692	Creates, submits and returns a group request. Note that it doesn't have a
		693	priority, unlike all other requests.
		694
		695	=item eio_grp_add (eio_req grp, eio_req req)
		696
		697	Adds a request to the request group.
		698
		699	=item eio_grp_cancel (eio_req *grp)
		700
		701	Cancels all requests I<in> the group, but I<not> the group request
		702	itself. You can cancel the group request I<and> all subrequests via a
		703	normal C<eio_cancel> call.
		704
		705	=back
		706
		707	=head4 GROUP REQUEST LIFETIME
		708
		709	Left alone, a group request will instantly move to the pending state and
		710	will be finished at the next call of C<eio_poll>.
		711
		712	There usefulness stems from the fact that, if a subrequest is added to a
		713	group I<before> a call to C<eio_poll>, via C<eio_grp_add>, then the group
		714	will not finish until all the subrequests have finished.
		715
		716	So the usage cycle of a group request is like this: after it is created,
		717	you normally instantly add a subrequest. If none is added, the group
		718	request will finish on it's own. As long as subrequests are added before
		719	the group request is finished it will be kept from finishing, that is the
		720	callbacks of any subrequests can, in turn, add more requests to the group,
		721	and as long as any requests are active, the group request itself will not
		722	finish.
		723
		724	=head4 CREATING COMPOSITE REQUESTS
		725
		726	Imagine you wanted to create an C<eio_load> request that opens a file,
		727	reads it and closes it. This means it has to execute at least three eio
		728	requests, but for various reasons it might be nice if that request looked
		729	like any other eio request.
		730
		731	This can be done with groups:
		732
		733	=over 4
		734
		735	=item 1) create the request object
		736
		737	Create a group that contains all further requests. This is the request you
		738	can return as "the load request".
		739
		740	=item 2) open the file, maybe
		741
		742	Next, open the file with C<eio_open> and add the request to the group
		743	request and you are finished steting up the request.
		744
		745	If, for some reason, you cannot C<eio_open> (path is a null ptr?) you
		746	cna set C<< grp->result >> to C<-1> to signal an error and let the gorup
		747	request finish on its own.
		748
		749	=item 3) open callback adds more requests
		750
		751	In the open callback, if the open was not successful, copy C<<
		752	req->errorno >> to C<< grp->errorno >> and set C<< grp->errorno >> to
		753	C<-1> to signal an error.
		754
		755	Otherwise, malloc some memory or so and issue a read request, adding the
		756	read request to the group.
		757
		758	=item 4) continue issuign requests till finished
		759
		760	In the real callback, check for errors and possibly continue with
		761	C<eio_close> or any other eio request in the same way.
		762
		763	As soon as no new requests are added the group request will finish. Make
		764	sure you I<always> set C<< grp->result >> to some sensible value.
		765
		766	=back
		767
		768	=head4 REQUEST LIMITING
		769
		770
		771	#TODO
		772
		773	void eio_grp_limit (eio_req *grp, int limit);
		774
		775
		776	=back
		777
		778
		779	=head1 LOW LEVEL REQUEST API
		780
		781	#TODO
		782
		783
		784	=head1 ANATOMY AND LIFETIME OF AN EIO REQUEST
		785
		786	A request is represented by a structure of type C<eio_req>. To initialise
		787	it, clear it to all zero bytes:
		788
		789	eio_req req;
		790
		791	memset (&req, 0, sizeof (req));
		792
		793	A more common way to initialise a new C<eio_req> is to use C<calloc>:
		794
		795	eio_req req = calloc (1, sizeof (req));
		796
		797	In either case, libeio neither allocates, initialises or frees the
		798	C<eio_req> structure for you - it merely uses it.
		799
		800	zero
		801
		802	#TODO
137		803
138	=head2 CONFIGURATION	804	=head2 CONFIGURATION
139		805
140	The functions in this section can sometimes be useful, but the default	806	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	807	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	818	for example, in interactive programs, you might want to limit this time to
153	C<0.01> seconds or so.	819	C<0.01> seconds or so.
154		820
155	Note that:	821	Note that:
156		822
		823	=over 4
		824
157	a) libeio doesn't know how long your request callbacks take, so the time	825	=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	826	time spent in C<eio_poll> is up to one callback invocation longer then
159	interval.	827	this interval.
160		828
161	b) this is implemented by calling C<gettimeofday> after each request,	829	=item b) this is implemented by calling C<gettimeofday> after each
162	which can be costly.	830	request, which can be costly.
163		831
164	c) at least one request will be handled.	832	=item c) at least one request will be handled.
		833
		834	=back
165		835
166	=item eio_set_max_poll_reqs (unsigned int nreqs)	836	=item eio_set_max_poll_reqs (unsigned int nreqs)
167		837
168	When C<nreqs> is non-zero, then C<eio_poll> will not handle more than	838	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	839	C<nreqs> requests per invocation. This is a less costly way to limit the
…		…
185	=item eio_set_max_idle (unsigned int nthreads)	855	=item eio_set_max_idle (unsigned int nthreads)
186		856
187	Libeio uses threads internally to handle most requests, and will start and stop threads on demand.	857	Libeio uses threads internally to handle most requests, and will start and stop threads on demand.
188		858
189	This call can be used to limit the number of idle threads (threads without	859	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	860	work to do): libeio will keep some threads idle in preparation for more
191	requests, but never longer than C<nthreads> threads.	861	requests, but never longer than C<nthreads> threads.
192		862
193	In addition to this, libeio will also stop threads when they are idle for	863	In addition to this, libeio will also stop threads when they are idle for
194	a few seconds, regardless of this setting.	864	a few seconds, regardless of this setting.
195		865
…		…
214	executed and have results, but have not been finished yet by a call to	884	executed and have results, but have not been finished yet by a call to
215	C<eio_poll>).	885	C<eio_poll>).
216		886
217	=back	887	=back
218		888
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	889	=head1 EMBEDDING
237		890
238	Libeio can be embedded directly into programs. This functionality is not	891	Libeio can be embedded directly into programs. This functionality is not
239	documented and not (yet) officially supported.	892	documented and not (yet) officially supported.
240		893
		894	Note that, when including C<libeio.m4>, you are responsible for defining
		895	the compilation environment (C<_LARGEFILE_SOURCE>, C<_GNU_SOURCE> etc.).
		896
241	If you need to know how, check the C<IO::AIO> perl module, which does	897	If you need to know how, check the C<IO::AIO> perl module, which does
242	exactly that.	898	exactly that.
		899
		900
		901	=head1 COMPILETIME CONFIGURATION
		902
		903	These symbols, if used, must be defined when compiling F<eio.c>.
		904
		905	=over 4
		906
		907	=item EIO_STACKSIZE
		908
		909	This symbol governs the stack size for each eio thread. Libeio itself
		910	was written to use very little stackspace, but when using C<EIO_CUSTOM>
		911	requests, you might want to increase this.
		912
		913	If this symbol is undefined (the default) then libeio will use its default
		914	stack size (C<sizeof (long) * 4096> currently). If it is defined, but
		915	C<0>, then the default operating system stack size will be used. In all
		916	other cases, the value must be an expression that evaluates to the desired
		917	stack size.
		918
		919	=back
243		920
244		921
245	=head1 PORTABILITY REQUIREMENTS	922	=head1 PORTABILITY REQUIREMENTS
246		923
247	In addition to a working ISO-C implementation, libeio relies on a few	924	In addition to a working ISO-C implementation, libeio relies on a few

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Revision 1.2 by root, Fri Jul 11 10:54:50 2008 UTC vs.
Revision 1.23 by root, Wed Jul 13 21:31:40 2011 UTC