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

Comparing libeio/eio.pod (file contents):
Revision 1.3 by root, Wed Oct 22 18:15:36 2008 UTC vs.
Revision 1.17 by root, Tue Jul 5 18:59:28 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 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 readyness 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 ent 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 reqiest 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. If the request is currently executing it might still
		282	continue to execute, and in other cases it might still take a while till
		283	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 either have C<< req->result >> set to
		297	C<-1> and C<errno> to C<ECANCELED>, or otherwise they were successfully
		298	executed despite being cancelled (e.g. when they have already been
		299	executed at the time they were cancelled).
		300
		301	=back
		302
		303	=head2 AVAILABLE REQUESTS
		304
		305	The following request functions are available. I<All> of them return the
		306	C<eio_req *> on success and C<0> on failure, and I<all> of them have the
		307	same three trailing arguments: C<pri>, C<cb> and C<data>. The C<cb> is
		308	mandatory, but in most cases, you pass in C<0> as C<pri> and C<0> or some
		309	custom data value as C<data>.
		310
		311	=head3 POSIX API WRAPPERS
		312
		313	These requests simply wrap the POSIX call of the same name, with the same
		314	arguments. If a function is not implemented by the OS and cannot be emulated
		315	in some way, then all of these return C<-1> and set C<errorno> to C<ENOSYS>.
		316
		317	=over 4
		318
		319	=item eio_open (const char path, int flags, mode_t mode, int pri, eio_cb cb, void data)
		320
		321	=item eio_truncate (const char path, off_t offset, int pri, eio_cb cb, void data)
		322
		323	=item eio_chown (const char path, uid_t uid, gid_t gid, int pri, eio_cb cb, void data)
		324
		325	=item eio_chmod (const char path, mode_t mode, int pri, eio_cb cb, void data)
		326
		327	=item eio_mkdir (const char path, mode_t mode, int pri, eio_cb cb, void data)
		328
		329	=item eio_rmdir (const char path, int pri, eio_cb cb, void data)
		330
		331	=item eio_unlink (const char path, int pri, eio_cb cb, void data)
		332
		333	=item eio_utime (const char path, eio_tstamp atime, eio_tstamp mtime, int pri, eio_cb cb, void data)
		334
		335	=item eio_mknod (const char path, mode_t mode, dev_t dev, int pri, eio_cb cb, void data)
		336
		337	=item eio_link (const char path, const char new_path, int pri, eio_cb cb, void *data)
		338
		339	=item eio_symlink (const char path, const char new_path, int pri, eio_cb cb, void *data)
		340
		341	=item eio_rename (const char path, const char new_path, int pri, eio_cb cb, void *data)
		342
		343	=item eio_mlock (void addr, size_t length, int pri, eio_cb cb, void data)
		344
		345	=item eio_close (int fd, int pri, eio_cb cb, void *data)
		346
		347	=item eio_sync (int pri, eio_cb cb, void *data)
		348
		349	=item eio_fsync (int fd, int pri, eio_cb cb, void *data)
		350
		351	=item eio_fdatasync (int fd, int pri, eio_cb cb, void *data)
		352
		353	=item eio_futime (int fd, eio_tstamp atime, eio_tstamp mtime, int pri, eio_cb cb, void *data)
		354
		355	=item eio_ftruncate (int fd, off_t offset, int pri, eio_cb cb, void *data)
		356
		357	=item eio_fchmod (int fd, mode_t mode, int pri, eio_cb cb, void *data)
		358
		359	=item eio_fchown (int fd, uid_t uid, gid_t gid, int pri, eio_cb cb, void *data)
		360
		361	=item eio_dup2 (int fd, int fd2, int pri, eio_cb cb, void *data)
		362
		363	These have the same semantics as the syscall of the same name, their
		364	return value is available as C<< req->result >> later.
		365
		366	=item eio_read (int fd, void buf, size_t length, off_t offset, int pri, eio_cb cb, void data)
		367
		368	=item eio_write (int fd, void buf, size_t length, off_t offset, int pri, eio_cb cb, void data)
		369
		370	These two requests are called C<read> and C<write>, but actually wrap
		371	C<pread> and C<pwrite>. On systems that lack these calls (such as cygwin),
		372	libeio uses lseek/read_or_write/lseek and a mutex to serialise the
		373	requests, so all these requests run serially and do not disturb each
		374	other. However, they still disturb the file offset while they run, so it's
		375	not safe to call these functions concurrently with non-libeio functions on
		376	the same fd on these systems.
		377
		378	Not surprisingly, pread and pwrite are not thread-safe on Darwin (OS/X),
		379	so it is advised not to submit multiple requests on the same fd on this
		380	horrible pile of garbage.
		381
		382	=item eio_mlockall (int flags, int pri, eio_cb cb, void *data)
		383
		384	Like C<mlockall>, but the flag value constants are called
		385	C<EIO_MCL_CURRENT> and C<EIO_MCL_FUTURE>.
		386
		387	=item eio_msync (void addr, size_t length, int flags, int pri, eio_cb cb, void data)
		388
		389	Just like msync, except that the flag values are called C<EIO_MS_ASYNC>,
		390	C<EIO_MS_INVALIDATE> and C<EIO_MS_SYNC>.
		391
		392	=item eio_readlink (const char path, int pri, eio_cb cb, void data)
		393
		394	If successful, the path read by C<readlink(2)> can be accessed via C<<
		395	req->ptr2 >> and is I<NOT> null-terminated, with the length specified as
		396	C<< req->result >>.
		397
		398	if (req->result >= 0)
		399	{
		400	char target = strndup ((char )req->ptr2, req->result);
		401
		402	free (target);
		403	}
		404
		405	=item eio_realpath (const char path, int pri, eio_cb cb, void data)
		406
		407	Similar to the realpath libc function, but unlike that one, result is
		408	C<-1> on failure and the length of the returned path in C<ptr2> (which is
		409	not 0-terminated) - this is 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 diretcory hierarchy or
		437	processing all files in a directory. Libeio can assist thess 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
		540	the likely dirs 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	absense 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_sync_file_range (int fd, off_t offset, size_t nbytes, unsigned int flags, int pri, eio_cb cb, void *data)
		588
		589	Calls C<sync_file_range>. If the syscall is missing, then this is the same
		590	as calling C<fdatasync>.
		591
		592	Flags can be any combination of C<EIO_SYNC_FILE_RANGE_WAIT_BEFORE>,
		593	C<EIO_SYNC_FILE_RANGE_WRITE> and C<EIO_SYNC_FILE_RANGE_WAIT_AFTER>.
		594
		595	=back
		596
		597	=head3 LIBEIO-SPECIFIC REQUESTS
		598
		599	These requests are specific to libeio and do not correspond to any OS call.
		600
		601	=over 4
		602
		603	=item eio_mtouch (void addr, size_t length, int flags, int pri, eio_cb cb, void data)
		604
		605	Reads (C<flags == 0>) or modifies (C<flags == EIO_MT_MODIFY) the given
		606	memory area, page-wise, that is, it reads (or reads and writes back) the
		607	first octet of every page that spans the memory area.
		608
		609	This can be used to page in some mmapped file, or dirty some pages. Note
		610	that dirtying is an unlocked read-write access, so races can ensue when
		611	the some other thread modifies the data stored in that memory area.
		612
		613	=item eio_custom (void ()(eio_req ) execute, int pri, eio_cb cb, void *data)
		614
		615	Executes a custom request, i.e., a user-specified callback.
		616
		617	The callback gets the C<eio_req *> as parameter and is expected to read
		618	and modify any request-specific members. Specifically, it should set C<<
		619	req->result >> to the result value, just like other requests.
		620
		621	Here is an example that simply calls C<open>, like C<eio_open>, but it
		622	uses the C<data> member as filename and uses a hardcoded C<O_RDONLY>. If
		623	you want to pass more/other parameters, you either need to pass some
		624	struct or so via C<data> or provide your own wrapper using the low-level
		625	API.
		626
		627	static int
		628	my_open_done (eio_req *req)
		629	{
		630	int fd = req->result;
		631
		632	return 0;
		633	}
		634
		635	static void
		636	my_open (eio_req *req)
		637	{
		638	req->result = open (req->data, O_RDONLY);
		639	}
		640
		641	eio_custom (my_open, 0, my_open_done, "/etc/passwd");
		642
		643	=item eio_busy (eio_tstamp delay, int pri, eio_cb cb, void *data)
		644
		645	This is a a request that takes C<delay> seconds to execute, but otherwise
		646	does nothing - it simply puts one of the worker threads to sleep for this
		647	long.
		648
		649	This request can be used to artificially increase load, e.g. for debugging
		650	or benchmarking reasons.
		651
		652	=item eio_nop (int pri, eio_cb cb, void *data)
		653
		654	This request does nothing, except go through the whole request cycle. This
		655	can be used to measure latency or in some cases to simplify code, but is
		656	not really of much use.
		657
		658	=back
		659
		660	=head3 GROUPING AND LIMITING REQUESTS
		661
		662	There is one more rather special request, C<eio_grp>. It is a very special
		663	aio request: Instead of doing something, it is a container for other eio
		664	requests.
		665
		666	There are two primary use cases for this: a) bundle many requests into a
		667	single, composite, request with a definite callback and the ability to
		668	cancel the whole request with its subrequests and b) limiting the number
		669	of "active" requests.
		670
		671	Further below you will find more dicussion of these topics - first follows
		672	the reference section detailing the request generator and other methods.
		673
		674	=over 4
		675
		676	=item eio_req grp = eio_grp (eio_cb cb, void data)
		677
		678	Creates, submits and returns a group request.
		679
		680	=item eio_grp_add (eio_req grp, eio_req req)
		681
		682	Adds a request to the request group.
		683
		684	=item eio_grp_cancel (eio_req *grp)
		685
		686	Cancels all requests I<in> the group, but I<not> the group request
		687	itself. You can cancel the group request via a normal C<eio_cancel> call.
		688
		689
		690
		691	=back
		692
		693
		694
		695	#TODO
		696
		697	/*****************************************************************************/
		698	/* groups */
		699
		700	eio_req eio_grp (eio_cb cb, void data);
		701	void eio_grp_feed (eio_req grp, void (feed)(eio_req *req), int limit);
		702	void eio_grp_limit (eio_req *grp, int limit);
		703	void eio_grp_cancel (eio_req grp); / cancels all sub requests but not the group */
		704
		705
		706	=back
		707
		708
		709	=head1 LOW LEVEL REQUEST API
		710
		711	#TODO
		712
		713
		714	=head1 ANATOMY AND LIFETIME OF AN EIO REQUEST
		715
		716	A request is represented by a structure of type C<eio_req>. To initialise
		717	it, clear it to all zero bytes:
		718
		719	eio_req req;
		720
		721	memset (&req, 0, sizeof (req));
		722
		723	A more common way to initialise a new C<eio_req> is to use C<calloc>:
		724
		725	eio_req req = calloc (1, sizeof (req));
		726
		727	In either case, libeio neither allocates, initialises or frees the
		728	C<eio_req> structure for you - it merely uses it.
		729
		730	zero
		731
		732	#TODO
137		733
138	=head2 CONFIGURATION	734	=head2 CONFIGURATION
139		735
140	The functions in this section can sometimes be useful, but the default	736	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	737	configuration will do in most case, so you should skip this section on
…		…
185	=item eio_set_max_idle (unsigned int nthreads)	781	=item eio_set_max_idle (unsigned int nthreads)
186		782
187	Libeio uses threads internally to handle most requests, and will start and stop threads on demand.	783	Libeio uses threads internally to handle most requests, and will start and stop threads on demand.
188		784
189	This call can be used to limit the number of idle threads (threads without	785	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	786	work to do): libeio will keep some threads idle in preparation for more
191	requests, but never longer than C<nthreads> threads.	787	requests, but never longer than C<nthreads> threads.
192		788
193	In addition to this, libeio will also stop threads when they are idle for	789	In addition to this, libeio will also stop threads when they are idle for
194	a few seconds, regardless of this setting.	790	a few seconds, regardless of this setting.
195		791
…		…
214	executed and have results, but have not been finished yet by a call to	810	executed and have results, but have not been finished yet by a call to
215	C<eio_poll>).	811	C<eio_poll>).
216		812
217	=back	813	=back
218		814
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	815	=head1 EMBEDDING
237		816
238	Libeio can be embedded directly into programs. This functionality is not	817	Libeio can be embedded directly into programs. This functionality is not
239	documented and not (yet) officially supported.	818	documented and not (yet) officially supported.
240		819
241	Note that, when including C<libeio.m4>, you are responsible for defining	820	Note that, when including C<libeio.m4>, you are responsible for defining
242	the compilation environment (C<_LARGEFILE_SOURCE>, C<_GNU_SOURCE> etc.).	821	the compilation environment (C<_LARGEFILE_SOURCE>, C<_GNU_SOURCE> etc.).
243		822
244	If you need to know how, check the C<IO::AIO> perl module, which does	823	If you need to know how, check the C<IO::AIO> perl module, which does
245	exactly that.	824	exactly that.
		825
		826
		827	=head1 COMPILETIME CONFIGURATION
		828
		829	These symbols, if used, must be defined when compiling F<eio.c>.
		830
		831	=over 4
		832
		833	=item EIO_STACKSIZE
		834
		835	This symbol governs the stack size for each eio thread. Libeio itself
		836	was written to use very little stackspace, but when using C<EIO_CUSTOM>
		837	requests, you might want to increase this.
		838
		839	If this symbol is undefined (the default) then libeio will use its default
		840	stack size (C<sizeof (long) * 4096> currently). If it is defined, but
		841	C<0>, then the default operating system stack size will be used. In all
		842	other cases, the value must be an expression that evaluates to the desired
		843	stack size.
		844
		845	=back
246		846
247		847
248	=head1 PORTABILITY REQUIREMENTS	848	=head1 PORTABILITY REQUIREMENTS
249		849
250	In addition to a working ISO-C implementation, libeio relies on a few	850	In addition to a working ISO-C implementation, libeio relies on a few

Diff Legend

-–
+Removed lines
-+
+Added lines
-<
+Changed lines
->
+Changed lines

Comparing libeio/eio.pod (file contents): Revision 1.3 by root, Wed Oct 22 18:15:36 2008 UTC vs. Revision 1.17 by root, Tue Jul 5 18:59:28 2011 UTC

Diff Legend

Comparing libeio/eio.pod (file contents):
Revision 1.3 by root, Wed Oct 22 18:15:36 2008 UTC vs.
Revision 1.17 by root, Tue Jul 5 18:59:28 2011 UTC