[ViewVC] Diff of: cvs/IO-AIO/README

Comparing IO-AIO/README (file contents):
Revision 1.8 by root, Sun Jul 31 17:24:05 2005 UTC vs.
Revision 1.23 by root, Mon Jan 22 15:59:52 2007 UTC

…		…
3		3
4	SYNOPSIS	4	SYNOPSIS
5	use IO::AIO;	5	use IO::AIO;
6		6
7	aio_open "/etc/passwd", O_RDONLY, 0, sub {	7	aio_open "/etc/passwd", O_RDONLY, 0, sub {
8	my ($fh) = @_;	8	my $fh = shift
		9	or die "/etc/passwd: $!";
9	...	10	...
10	};	11	};
11		12
12	aio_unlink "/tmp/file", sub { };	13	aio_unlink "/tmp/file", sub { };
13		14
14	aio_read $fh, 30000, 1024, $buffer, 0, sub {	15	aio_read $fh, 30000, 1024, $buffer, 0, sub {
15	$_[0] > 0 or die "read error: $!";	16	$_[0] > 0 or die "read error: $!";
16	};	17	};
17		18
18	# Event	19	# version 2+ has request and group objects
		20	use IO::AIO 2;
		21
		22	aioreq_pri 4; # give next request a very high priority
		23	my $req = aio_unlink "/tmp/file", sub { };
		24	$req->cancel; # cancel request if still in queue
		25
		26	my $grp = aio_group sub { print "all stats done\n" };
		27	add $grp aio_stat "..." for ...;
		28
		29	# AnyEvent integration
		30	open my $fh, "<&=" . IO::AIO::poll_fileno or die "$!";
		31	my $w = AnyEvent->io (fh => $fh, poll => 'r', cb => sub { IO::AIO::poll_cb });
		32
		33	# Event integration
19	Event->io (fd => IO::AIO::poll_fileno,	34	Event->io (fd => IO::AIO::poll_fileno,
20	poll => 'r',	35	poll => 'r',
21	cb => \&IO::AIO::poll_cb);	36	cb => \&IO::AIO::poll_cb);
22		37
23	# Glib/Gtk2	38	# Glib/Gtk2 integration
24	add_watch Glib::IO IO::AIO::poll_fileno,	39	add_watch Glib::IO IO::AIO::poll_fileno,
25	in => sub { IO::AIO::poll_cb; 1 };	40	in => sub { IO::AIO::poll_cb; 1 };
26		41
27	# Tk	42	# Tk integration
28	Tk::Event::IO->fileevent (IO::AIO::poll_fileno, "",	43	Tk::Event::IO->fileevent (IO::AIO::poll_fileno, "",
29	readable => \&IO::AIO::poll_cb);	44	readable => \&IO::AIO::poll_cb);
30		45
31	# Danga::Socket	46	# Danga::Socket integration
32	Danga::Socket->AddOtherFds (IO::AIO::poll_fileno =>	47	Danga::Socket->AddOtherFds (IO::AIO::poll_fileno =>
33	\&IO::AIO::poll_cb);	48	\&IO::AIO::poll_cb);
34		49
35	DESCRIPTION	50	DESCRIPTION
36	This module implements asynchronous I/O using whatever means your	51	This module implements asynchronous I/O using whatever means your
37	operating system supports.	52	operating system supports.
38		53
		54	Asynchronous means that operations that can normally block your program
		55	(e.g. reading from disk) will be done asynchronously: the operation will
		56	still block, but you can do something else in the meantime. This is
		57	extremely useful for programs that need to stay interactive even when
		58	doing heavy I/O (GUI programs, high performance network servers etc.),
		59	but can also be used to easily do operations in parallel that are
		60	normally done sequentially, e.g. stat'ing many files, which is much
		61	faster on a RAID volume or over NFS when you do a number of stat
		62	operations concurrently.
		63
		64	While most of this works on all types of file descriptors (for example
		65	sockets), using these functions on file descriptors that support
		66	nonblocking operation (again, sockets, pipes etc.) is very inefficient
		67	or might not work (aio_read fails on sockets/pipes/fifos). Use an event
		68	loop for that (such as the Event module): IO::AIO will naturally fit
		69	into such an event loop itself.
		70
39	Currently, a number of threads are started that execute your read/writes	71	In this version, a number of threads are started that execute your
40	and signal their completion. You don't need thread support in your libc	72	requests and signal their completion. You don't need thread support in
41	or perl, and the threads created by this module will not be visible to	73	perl, and the threads created by this module will not be visible to
42	the pthreads library. In the future, this module might make use of the	74	perl. In the future, this module might make use of the native aio
43	native aio functions available on many operating systems. However, they	75	functions available on many operating systems. However, they are often
44	are often not well-supported (Linux doesn't allow them on normal files	76	not well-supported or restricted (GNU/Linux doesn't allow them on normal
45	currently, for example), and they would only support aio_read and	77	files currently, for example), and they would only support aio_read and
46	aio_write, so the remaining functionality would have to be implemented	78	aio_write, so the remaining functionality would have to be implemented
47	using threads anyway.	79	using threads anyway.
48		80
49	Although the module will work with in the presence of other threads, it	81	Although the module will work with in the presence of other (Perl-)
50	is currently not reentrant, so use appropriate locking yourself, always	82	threads, it is currently not reentrant in any way, so use appropriate
51	call "poll_cb" from within the same thread, or never call "poll_cb" (or	83	locking yourself, always call "poll_cb" from within the same thread, or
52	other "aio_" functions) recursively.	84	never call "poll_cb" (or other "aio_" functions) recursively.
		85
		86	EXAMPLE
		87	This is a simple example that uses the Event module and loads
		88	/etc/passwd asynchronously:
		89
		90	use Fcntl;
		91	use Event;
		92	use IO::AIO;
		93
		94	# register the IO::AIO callback with Event
		95	Event->io (fd => IO::AIO::poll_fileno,
		96	poll => 'r',
		97	cb => \&IO::AIO::poll_cb);
		98
		99	# queue the request to open /etc/passwd
		100	aio_open "/etc/passwd", O_RDONLY, 0, sub {
		101	my $fh = shift
		102	or die "error while opening: $!";
		103
		104	# stat'ing filehandles is generally non-blocking
		105	my $size = -s $fh;
		106
		107	# queue a request to read the file
		108	my $contents;
		109	aio_read $fh, 0, $size, $contents, 0, sub {
		110	$_[0] == $size
		111	or die "short read: $!";
		112
		113	close $fh;
		114
		115	# file contents now in $contents
		116	print $contents;
		117
		118	# exit event loop and program
		119	Event::unloop;
		120	};
		121	};
		122
		123	# possibly queue up other requests, or open GUI windows,
		124	# check for sockets etc. etc.
		125
		126	# process events as long as there are some:
		127	Event::loop;
		128
		129	REQUEST ANATOMY AND LIFETIME
		130	Every "aio_*" function creates a request. which is a C data structure
		131	not directly visible to Perl.
		132
		133	If called in non-void context, every request function returns a Perl
		134	object representing the request. In void context, nothing is returned,
		135	which saves a bit of memory.
		136
		137	The perl object is a fairly standard ref-to-hash object. The hash
		138	contents are not used by IO::AIO so you are free to store anything you
		139	like in it.
		140
		141	During their existance, aio requests travel through the following
		142	states, in order:
		143
		144	ready
		145	Immediately after a request is created it is put into the ready
		146	state, waiting for a thread to execute it.
		147
		148	execute
		149	A thread has accepted the request for processing and is currently
		150	executing it (e.g. blocking in read).
		151
		152	pending
		153	The request has been executed and is waiting for result processing.
		154
		155	While request submission and execution is fully asynchronous, result
		156	processing is not and relies on the perl interpreter calling
		157	"poll_cb" (or another function with the same effect).
		158
		159	result
		160	The request results are processed synchronously by "poll_cb".
		161
		162	The "poll_cb" function will process all outstanding aio requests by
		163	calling their callbacks, freeing memory associated with them and
		164	managing any groups they are contained in.
		165
		166	done
		167	Request has reached the end of its lifetime and holds no resources
		168	anymore (except possibly for the Perl object, but its connection to
		169	the actual aio request is severed and calling its methods will
		170	either do nothing or result in a runtime error).
53		171
54	FUNCTIONS	172	FUNCTIONS
55	AIO FUNCTIONS	173	AIO REQUEST FUNCTIONS
56	All the "aio_*" calls are more or less thin wrappers around the syscall	174	All the "aio_*" calls are more or less thin wrappers around the syscall
57	with the same name (sans "aio_"). The arguments are similar or	175	with the same name (sans "aio_"). The arguments are similar or
58	identical, and they all accept an additional (and optional) $callback	176	identical, and they all accept an additional (and optional) $callback
59	argument which must be a code reference. This code reference will get	177	argument which must be a code reference. This code reference will get
60	called with the syscall return code (e.g. most syscalls return -1 on	178	called with the syscall return code (e.g. most syscalls return -1 on
…		…
62	argument when the given syscall has been executed asynchronously.	180	argument when the given syscall has been executed asynchronously.
63		181
64	All functions expecting a filehandle keep a copy of the filehandle	182	All functions expecting a filehandle keep a copy of the filehandle
65	internally until the request has finished.	183	internally until the request has finished.
66		184
		185	All functions return request objects of type IO::AIO::REQ that allow
		186	further manipulation of those requests while they are in-flight.
		187
67	The filenames you pass to these routines must be absolute. The reason	188	The pathnames you pass to these routines must be absolute and encoded
68	for this is that at the time the request is being executed, the current	189	as octets. The reason for the former is that at the time the request is
69	working directory could have changed. Alternatively, you can make sure	190	being executed, the current working directory could have changed.
70	that you never change the current working directory.	191	Alternatively, you can make sure that you never change the current
		192	working directory anywhere in the program and then use relative paths.
71		193
		194	To encode pathnames as octets, either make sure you either: a) always
		195	pass in filenames you got from outside (command line, readdir etc.)
		196	without tinkering, b) are ASCII or ISO 8859-1, c) use the Encode module
		197	and encode your pathnames to the locale (or other) encoding in effect in
		198	the user environment, d) use Glib::filename_from_unicode on unicode
		199	filenames or e) use something else to ensure your scalar has the correct
		200	contents.
		201
		202	This works, btw. independent of the internal UTF-8 bit, which IO::AIO
		203	handles correctly wether it is set or not.
		204
		205	$prev_pri = aioreq_pri [$pri]
		206	Returns the priority value that would be used for the next request
		207	and, if $pri is given, sets the priority for the next aio request.
		208
		209	The default priority is 0, the minimum and maximum priorities are -4
		210	and 4, respectively. Requests with higher priority will be serviced
		211	first.
		212
		213	The priority will be reset to 0 after each call to one of the
		214	"aio_*" functions.
		215
		216	Example: open a file with low priority, then read something from it
		217	with higher priority so the read request is serviced before other
		218	low priority open requests (potentially spamming the cache):
		219
		220	aioreq_pri -3;
		221	aio_open ..., sub {
		222	return unless $_[0];
		223
		224	aioreq_pri -2;
		225	aio_read $_[0], ..., sub {
		226	...
		227	};
		228	};
		229
		230	aioreq_nice $pri_adjust
		231	Similar to "aioreq_pri", but subtracts the given value from the
		232	current priority, so the effect is cumulative.
		233
72	aio_open $pathname, $flags, $mode, $callback	234	aio_open $pathname, $flags, $mode, $callback->($fh)
73	Asynchronously open or create a file and call the callback with a	235	Asynchronously open or create a file and call the callback with a
74	newly created filehandle for the file.	236	newly created filehandle for the file.
75		237
76	The pathname passed to "aio_open" must be absolute. See API NOTES,	238	The pathname passed to "aio_open" must be absolute. See API NOTES,
77	above, for an explanation.	239	above, for an explanation.
…		…
80	They are the same as used by "sysopen".	242	They are the same as used by "sysopen".
81		243
82	Likewise, $mode specifies the mode of the newly created file, if it	244	Likewise, $mode specifies the mode of the newly created file, if it
83	didn't exist and "O_CREAT" has been given, just like perl's	245	didn't exist and "O_CREAT" has been given, just like perl's
84	"sysopen", except that it is mandatory (i.e. use 0 if you don't	246	"sysopen", except that it is mandatory (i.e. use 0 if you don't
85	create new files, and 0666 or 0777 if you do).	247	create new files, and 0666 or 0777 if you do). Note that the $mode
		248	will be modified by the umask in effect then the request is being
		249	executed, so better never change the umask.
86		250
87	Example:	251	Example:
88		252
89	aio_open "/etc/passwd", O_RDONLY, 0, sub {	253	aio_open "/etc/passwd", O_RDONLY, 0, sub {
90	if ($_[0]) {	254	if ($_[0]) {
…		…
93	} else {	257	} else {
94	die "open failed: $!\n";	258	die "open failed: $!\n";
95	}	259	}
96	};	260	};
97		261
98	aio_close $fh, $callback	262	aio_close $fh, $callback->($status)
99	Asynchronously close a file and call the callback with the result	263	Asynchronously close a file and call the callback with the result
100	code. WARNING: although accepted, you should not pass in a perl	264	code. WARNING: although accepted, you should not pass in a perl
101	filehandle here, as perl will likely close the file descriptor	265	filehandle here, as perl will likely close the file descriptor
102	another time when the filehandle is destroyed. Normally, you can	266	another time when the filehandle is destroyed. Normally, you can
103	safely call perls "close" or just let filehandles go out of scope.	267	safely call perls "close" or just let filehandles go out of scope.
104		268
105	This is supposed to be a bug in the API, so that might change. It's	269	This is supposed to be a bug in the API, so that might change. It's
106	therefore best to avoid this function.	270	therefore best to avoid this function.
107		271
108	aio_read $fh,$offset,$length, $data,$dataoffset,$callback	272	aio_read $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
109	aio_write $fh,$offset,$length, $data,$dataoffset,$callback	273	aio_write $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
110	Reads or writes "length" bytes from the specified "fh" and "offset"	274	Reads or writes "length" bytes from the specified "fh" and "offset"
111	into the scalar given by "data" and offset "dataoffset" and calls	275	into the scalar given by "data" and offset "dataoffset" and calls
112	the callback without the actual number of bytes read (or -1 on	276	the callback without the actual number of bytes read (or -1 on
113	error, just like the syscall).	277	error, just like the syscall).
114		278
		279	The $data scalar MUST NOT be modified in any way while the request
		280	is outstanding. Modifying it can result in segfaults or WW3 (if the
		281	necessary/optional hardware is installed).
		282
115	Example: Read 15 bytes at offset 7 into scalar $buffer, starting at	283	Example: Read 15 bytes at offset 7 into scalar $buffer, starting at
116	offset 0 within the scalar:	284	offset 0 within the scalar:
117		285
118	aio_read $fh, 7, 15, $buffer, 0, sub {	286	aio_read $fh, 7, 15, $buffer, 0, sub {
119	$_[0] > 0 or die "read error: $!";	287	$_[0] > 0 or die "read error: $!";
120	print "read $_[0] bytes: <$buffer>\n";	288	print "read $_[0] bytes: <$buffer>\n";
121	};	289	};
122		290
		291	aio_sendfile $out_fh, $in_fh, $in_offset, $length, $callback->($retval)
		292	Tries to copy $length bytes from $in_fh to $out_fh. It starts
		293	reading at byte offset $in_offset, and starts writing at the current
		294	file offset of $out_fh. Because of that, it is not safe to issue
		295	more than one "aio_sendfile" per $out_fh, as they will interfere
		296	with each other.
		297
		298	This call tries to make use of a native "sendfile" syscall to
		299	provide zero-copy operation. For this to work, $out_fh should refer
		300	to a socket, and $in_fh should refer to mmap'able file.
		301
		302	If the native sendfile call fails or is not implemented, it will be
		303	emulated, so you can call "aio_sendfile" on any type of filehandle
		304	regardless of the limitations of the operating system.
		305
		306	Please note, however, that "aio_sendfile" can read more bytes from
		307	$in_fh than are written, and there is no way to find out how many
		308	bytes have been read from "aio_sendfile" alone, as "aio_sendfile"
		309	only provides the number of bytes written to $out_fh. Only if the
		310	result value equals $length one can assume that $length bytes have
		311	been read.
		312
123	aio_readahead $fh,$offset,$length, $callback	313	aio_readahead $fh,$offset,$length, $callback->($retval)
124	Asynchronously reads the specified byte range into the page cache,
125	using the "readahead" syscall. If that syscall doesn't exist (likely
126	if your OS isn't Linux) the status will be -1 and $! is set to
127	"ENOSYS".
128
129	"aio_readahead" populates the page cache with data from a file so	314	"aio_readahead" populates the page cache with data from a file so
130	that subsequent reads from that file will not block on disk I/O. The	315	that subsequent reads from that file will not block on disk I/O. The
131	$offset argument specifies the starting point from which data is to	316	$offset argument specifies the starting point from which data is to
132	be read and $length specifies the number of bytes to be read. I/O is	317	be read and $length specifies the number of bytes to be read. I/O is
133	performed in whole pages, so that offset is effectively rounded down	318	performed in whole pages, so that offset is effectively rounded down
134	to a page boundary and bytes are read up to the next page boundary	319	to a page boundary and bytes are read up to the next page boundary
135	greater than or equal to (off-set+length). "aio_readahead" does not	320	greater than or equal to (off-set+length). "aio_readahead" does not
136	read beyond the end of the file. The current file offset of the file	321	read beyond the end of the file. The current file offset of the file
137	is left unchanged.	322	is left unchanged.
138		323
		324	If that syscall doesn't exist (likely if your OS isn't Linux) it
		325	will be emulated by simply reading the data, which would have a
		326	similar effect.
		327
139	aio_stat $fh_or_path, $callback	328	aio_stat $fh_or_path, $callback->($status)
140	aio_lstat $fh, $callback	329	aio_lstat $fh, $callback->($status)
141	Works like perl's "stat" or "lstat" in void context. The callback	330	Works like perl's "stat" or "lstat" in void context. The callback
142	will be called after the stat and the results will be available	331	will be called after the stat and the results will be available
143	using "stat _" or "-s _" etc...	332	using "stat _" or "-s _" etc...
144		333
145	The pathname passed to "aio_stat" must be absolute. See API NOTES,	334	The pathname passed to "aio_stat" must be absolute. See API NOTES,
…		…
155	aio_stat "/etc/passwd", sub {	344	aio_stat "/etc/passwd", sub {
156	$_[0] and die "stat failed: $!";	345	$_[0] and die "stat failed: $!";
157	print "size is ", -s _, "\n";	346	print "size is ", -s _, "\n";
158	};	347	};
159		348
160	aio_unlink $pathname, $callback	349	aio_unlink $pathname, $callback->($status)
161	Asynchronously unlink (delete) a file and call the callback with the	350	Asynchronously unlink (delete) a file and call the callback with the
162	result code.	351	result code.
163		352
		353	aio_mknod $path, $mode, $dev, $callback->($status)
		354	[EXPERIMENTAL]
		355
		356	Asynchronously create a device node (or fifo). See mknod(2).
		357
		358	The only (POSIX-) portable way of calling this function is:
		359
		360	aio_mknod $path, IO::AIO::S_IFIFO \| $mode, 0, sub { ...
		361
		362	aio_link $srcpath, $dstpath, $callback->($status)
		363	Asynchronously create a new link to the existing object at $srcpath
		364	at the path $dstpath and call the callback with the result code.
		365
		366	aio_symlink $srcpath, $dstpath, $callback->($status)
		367	Asynchronously create a new symbolic link to the existing object at
		368	$srcpath at the path $dstpath and call the callback with the result
		369	code.
		370
		371	aio_readlink $path, $callback->($link)
		372	Asynchronously read the symlink specified by $path and pass it to
		373	the callback. If an error occurs, nothing or undef gets passed to
		374	the callback.
		375
		376	aio_rename $srcpath, $dstpath, $callback->($status)
		377	Asynchronously rename the object at $srcpath to $dstpath, just as
		378	rename(2) and call the callback with the result code.
		379
		380	aio_mkdir $pathname, $mode, $callback->($status)
		381	Asynchronously mkdir (create) a directory and call the callback with
		382	the result code. $mode will be modified by the umask at the time the
		383	request is executed, so do not change your umask.
		384
		385	aio_rmdir $pathname, $callback->($status)
		386	Asynchronously rmdir (delete) a directory and call the callback with
		387	the result code.
		388
		389	aio_readdir $pathname, $callback->($entries)
		390	Unlike the POSIX call of the same name, "aio_readdir" reads an
		391	entire directory (i.e. opendir + readdir + closedir). The entries
		392	will not be sorted, and will NOT include the "." and ".." entries.
		393
		394	The callback a single argument which is either "undef" or an
		395	array-ref with the filenames.
		396
		397	aio_load $path, $data, $callback->($status)
		398	This is a composite request that tries to fully load the given file
		399	into memory. Status is the same as with aio_read.
		400
		401	aio_copy $srcpath, $dstpath, $callback->($status)
		402	Try to copy the file (directories not supported as either source
		403	or destination) from $srcpath to $dstpath and call the callback with
		404	the 0 (error) or -1 ok.
		405
		406	This is a composite request that it creates the destination file
		407	with mode 0200 and copies the contents of the source file into it
		408	using "aio_sendfile", followed by restoring atime, mtime, access
		409	mode and uid/gid, in that order.
		410
		411	If an error occurs, the partial destination file will be unlinked,
		412	if possible, except when setting atime, mtime, access mode and
		413	uid/gid, where errors are being ignored.
		414
		415	aio_move $srcpath, $dstpath, $callback->($status)
		416	Try to move the file (directories not supported as either source
		417	or destination) from $srcpath to $dstpath and call the callback with
		418	the 0 (error) or -1 ok.
		419
		420	This is a composite request that tries to rename(2) the file first.
		421	If rename files with "EXDEV", it copies the file with "aio_copy"
		422	and, if that is successful, unlinking the $srcpath.
		423
		424	aio_scandir $path, $maxreq, $callback->($dirs, $nondirs)
		425	Scans a directory (similar to "aio_readdir") but additionally tries
		426	to efficiently separate the entries of directory $path into two sets
		427	of names, directories you can recurse into (directories), and ones
		428	you cannot recurse into (everything else, including symlinks to
		429	directories).
		430
		431	"aio_scandir" is a composite request that creates of many sub
		432	requests_ $maxreq specifies the maximum number of outstanding aio
		433	requests that this function generates. If it is "<= 0", then a
		434	suitable default will be chosen (currently 4).
		435
		436	On error, the callback is called without arguments, otherwise it
		437	receives two array-refs with path-relative entry names.
		438
		439	Example:
		440
		441	aio_scandir $dir, 0, sub {
		442	my ($dirs, $nondirs) = @_;
		443	print "real directories: @$dirs\n";
		444	print "everything else: @$nondirs\n";
		445	};
		446
		447	Implementation notes.
		448
		449	The "aio_readdir" cannot be avoided, but "stat()"'ing every entry
		450	can.
		451
		452	After reading the directory, the modification time, size etc. of the
		453	directory before and after the readdir is checked, and if they match
		454	(and isn't the current time), the link count will be used to decide
		455	how many entries are directories (if >= 2). Otherwise, no knowledge
		456	of the number of subdirectories will be assumed.
		457
		458	Then entries will be sorted into likely directories (everything
		459	without a non-initial dot currently) and likely non-directories
		460	(everything else). Then every entry plus an appended "/." will be
		461	"stat"'ed, likely directories first. If that succeeds, it assumes
		462	that the entry is a directory or a symlink to directory (which will
		463	be checked seperately). This is often faster than stat'ing the entry
		464	itself because filesystems might detect the type of the entry
		465	without reading the inode data (e.g. ext2fs filetype feature).
		466
		467	If the known number of directories (link count - 2) has been
		468	reached, the rest of the entries is assumed to be non-directories.
		469
		470	This only works with certainty on POSIX (= UNIX) filesystems, which
		471	fortunately are the vast majority of filesystems around.
		472
		473	It will also likely work on non-POSIX filesystems with reduced
		474	efficiency as those tend to return 0 or 1 as link counts, which
		475	disables the directory counting heuristic.
		476
		477	aio_rmtree $path, $callback->($status)
		478	Delete a directory tree starting (and including) $path, return the
		479	status of the final "rmdir" only. This is a composite request that
		480	uses "aio_scandir" to recurse into and rmdir directories, and unlink
		481	everything else.
		482
164	aio_fsync $fh, $callback	483	aio_fsync $fh, $callback->($status)
165	Asynchronously call fsync on the given filehandle and call the	484	Asynchronously call fsync on the given filehandle and call the
166	callback with the fsync result code.	485	callback with the fsync result code.
167		486
168	aio_fdatasync $fh, $callback	487	aio_fdatasync $fh, $callback->($status)
169	Asynchronously call fdatasync on the given filehandle and call the	488	Asynchronously call fdatasync on the given filehandle and call the
170	callback with the fdatasync result code. Might set $! to "ENOSYS" if	489	callback with the fdatasync result code.
171	"fdatasync" is not available.	490
		491	If this call isn't available because your OS lacks it or it couldn't
		492	be detected, it will be emulated by calling "fsync" instead.
		493
		494	aio_group $callback->(...)
		495	This is a very special aio request: Instead of doing something, it
		496	is a container for other aio requests, which is useful if you want
		497	to bundle many requests into a single, composite, request with a
		498	definite callback and the ability to cancel the whole request with
		499	its subrequests.
		500
		501	Returns an object of class IO::AIO::GRP. See its documentation below
		502	for more info.
		503
		504	Example:
		505
		506	my $grp = aio_group sub {
		507	print "all stats done\n";
		508	};
		509
		510	add $grp
		511	(aio_stat ...),
		512	(aio_stat ...),
		513	...;
		514
		515	aio_nop $callback->()
		516	This is a special request - it does nothing in itself and is only
		517	used for side effects, such as when you want to add a dummy request
		518	to a group so that finishing the requests in the group depends on
		519	executing the given code.
		520
		521	While this request does nothing, it still goes through the execution
		522	phase and still requires a worker thread. Thus, the callback will
		523	not be executed immediately but only after other requests in the
		524	queue have entered their execution phase. This can be used to
		525	measure request latency.
		526
		527	IO::AIO::aio_busy $fractional_seconds, $callback->() NOT EXPORTED
		528	Mainly used for debugging and benchmarking, this aio request puts
		529	one of the request workers to sleep for the given time.
		530
		531	While it is theoretically handy to have simple I/O scheduling
		532	requests like sleep and file handle readable/writable, the overhead
		533	this creates is immense (it blocks a thread for a long time) so do
		534	not use this function except to put your application under
		535	artificial I/O pressure.
		536
		537	IO::AIO::REQ CLASS
		538	All non-aggregate "aio_*" functions return an object of this class when
		539	called in non-void context.
		540
		541	cancel $req
		542	Cancels the request, if possible. Has the effect of skipping
		543	execution when entering the execute state and skipping calling the
		544	callback when entering the the result state, but will leave the
		545	request otherwise untouched. That means that requests that currently
		546	execute will not be stopped and resources held by the request will
		547	not be freed prematurely.
		548
		549	cb $req $callback->(...)
		550	Replace (or simply set) the callback registered to the request.
		551
		552	IO::AIO::GRP CLASS
		553	This class is a subclass of IO::AIO::REQ, so all its methods apply to
		554	objects of this class, too.
		555
		556	A IO::AIO::GRP object is a special request that can contain multiple
		557	other aio requests.
		558
		559	You create one by calling the "aio_group" constructing function with a
		560	callback that will be called when all contained requests have entered
		561	the "done" state:
		562
		563	my $grp = aio_group sub {
		564	print "all requests are done\n";
		565	};
		566
		567	You add requests by calling the "add" method with one or more
		568	"IO::AIO::REQ" objects:
		569
		570	$grp->add (aio_unlink "...");
		571
		572	add $grp aio_stat "...", sub {
		573	$_[0] or return $grp->result ("error");
		574
		575	# add another request dynamically, if first succeeded
		576	add $grp aio_open "...", sub {
		577	$grp->result ("ok");
		578	};
		579	};
		580
		581	This makes it very easy to create composite requests (see the source of
		582	"aio_move" for an application) that work and feel like simple requests.
		583
		584	* The IO::AIO::GRP objects will be cleaned up during calls to
		585	"IO::AIO::poll_cb", just like any other request.
		586	* They can be canceled like any other request. Canceling will cancel not
		587	only the request itself, but also all requests it contains.
		588	* They can also can also be added to other IO::AIO::GRP objects.
		589	* You must not add requests to a group from within the group callback
		590	(or any later time).
		591
		592	Their lifetime, simplified, looks like this: when they are empty, they
		593	will finish very quickly. If they contain only requests that are in the
		594	"done" state, they will also finish. Otherwise they will continue to
		595	exist.
		596
		597	That means after creating a group you have some time to add requests.
		598	And in the callbacks of those requests, you can add further requests to
		599	the group. And only when all those requests have finished will the the
		600	group itself finish.
		601
		602	add $grp ...
		603	$grp->add (...)
		604	Add one or more requests to the group. Any type of IO::AIO::REQ can
		605	be added, including other groups, as long as you do not create
		606	circular dependencies.
		607
		608	Returns all its arguments.
		609
		610	$grp->cancel_subs
		611	Cancel all subrequests and clears any feeder, but not the group
		612	request itself. Useful when you queued a lot of events but got a
		613	result early.
		614
		615	$grp->result (...)
		616	Set the result value(s) that will be passed to the group callback
		617	when all subrequests have finished and set thre groups errno to the
		618	current value of errno (just like calling "errno" without an error
		619	number). By default, no argument will be passed and errno is zero.
		620
		621	$grp->errno ([$errno])
		622	Sets the group errno value to $errno, or the current value of errno
		623	when the argument is missing.
		624
		625	Every aio request has an associated errno value that is restored
		626	when the callback is invoked. This method lets you change this value
		627	from its default (0).
		628
		629	Calling "result" will also set errno, so make sure you either set $!
		630	before the call to "result", or call c<errno> after it.
		631
		632	feed $grp $callback->($grp)
		633	Sets a feeder/generator on this group: every group can have an
		634	attached generator that generates requests if idle. The idea behind
		635	this is that, although you could just queue as many requests as you
		636	want in a group, this might starve other requests for a potentially
		637	long time. For example, "aio_scandir" might generate hundreds of
		638	thousands "aio_stat" requests, delaying any later requests for a
		639	long time.
		640
		641	To avoid this, and allow incremental generation of requests, you can
		642	instead a group and set a feeder on it that generates those
		643	requests. The feed callback will be called whenever there are few
		644	enough (see "limit", below) requests active in the group itself and
		645	is expected to queue more requests.
		646
		647	The feed callback can queue as many requests as it likes (i.e. "add"
		648	does not impose any limits).
		649
		650	If the feed does not queue more requests when called, it will be
		651	automatically removed from the group.
		652
		653	If the feed limit is 0, it will be set to 2 automatically.
		654
		655	Example:
		656
		657	# stat all files in @files, but only ever use four aio requests concurrently:
		658
		659	my $grp = aio_group sub { print "finished\n" };
		660	limit $grp 4;
		661	feed $grp sub {
		662	my $file = pop @files
		663	or return;
		664
		665	add $grp aio_stat $file, sub { ... };
		666	};
		667
		668	limit $grp $num
		669	Sets the feeder limit for the group: The feeder will be called
		670	whenever the group contains less than this many requests.
		671
		672	Setting the limit to 0 will pause the feeding process.
172		673
173	SUPPORT FUNCTIONS	674	SUPPORT FUNCTIONS
		675	EVENT PROCESSING AND EVENT LOOP INTEGRATION
174	$fileno = IO::AIO::poll_fileno	676	$fileno = IO::AIO::poll_fileno
175	Return the request result pipe file descriptor. This filehandle	677	Return the request result pipe file descriptor. This filehandle
176	must be polled for reading by some mechanism outside this module	678	must be polled for reading by some mechanism outside this module
177	(e.g. Event or select, see below or the SYNOPSIS). If the pipe	679	(e.g. Event or select, see below or the SYNOPSIS). If the pipe
178	becomes readable you have to call "poll_cb" to check the results.	680	becomes readable you have to call "poll_cb" to check the results.
179		681
180	See "poll_cb" for an example.	682	See "poll_cb" for an example.
181		683
182	IO::AIO::poll_cb	684	IO::AIO::poll_cb
183	Process all outstanding events on the result pipe. You have to call	685	Process some outstanding events on the result pipe. You have to call
184	this regularly. Returns the number of events processed. Returns	686	this regularly. Returns the number of events processed. Returns
185	immediately when no events are outstanding.	687	immediately when no events are outstanding. The amount of events
		688	processed depends on the settings of "IO::AIO::max_poll_req" and
		689	"IO::AIO::max_poll_time".
		690
		691	If not all requests were processed for whatever reason, the
		692	filehandle will still be ready when "poll_cb" returns.
186		693
187	Example: Install an Event watcher that automatically calls	694	Example: Install an Event watcher that automatically calls
188	IO::AIO::poll_cb with high priority:	695	IO::AIO::poll_cb with high priority:
189		696
190	Event->io (fd => IO::AIO::poll_fileno,	697	Event->io (fd => IO::AIO::poll_fileno,
191	poll => 'r', async => 1,	698	poll => 'r', async => 1,
192	cb => \&IO::AIO::poll_cb);	699	cb => \&IO::AIO::poll_cb);
193		700
		701	IO::AIO::max_poll_reqs $nreqs
		702	IO::AIO::max_poll_time $seconds
		703	These set the maximum number of requests (default 0, meaning
		704	infinity) that are being processed by "IO::AIO::poll_cb" in one
		705	call, respectively the maximum amount of time (default 0, meaning
		706	infinity) spent in "IO::AIO::poll_cb" to process requests (more
		707	correctly the mininum amount of time "poll_cb" is allowed to use).
		708
		709	Setting "max_poll_time" to a non-zero value creates an overhead of
		710	one syscall per request processed, which is not normally a problem
		711	unless your callbacks are really really fast or your OS is really
		712	really slow (I am not mentioning Solaris here). Using
		713	"max_poll_reqs" incurs no overhead.
		714
		715	Setting these is useful if you want to ensure some level of
		716	interactiveness when perl is not fast enough to process all requests
		717	in time.
		718
		719	For interactive programs, values such as 0.01 to 0.1 should be fine.
		720
		721	Example: Install an Event watcher that automatically calls
		722	IO::AIO::poll_cb with low priority, to ensure that other parts of
		723	the program get the CPU sometimes even under high AIO load.
		724
		725	# try not to spend much more than 0.1s in poll_cb
		726	IO::AIO::max_poll_time 0.1;
		727
		728	# use a low priority so other tasks have priority
		729	Event->io (fd => IO::AIO::poll_fileno,
		730	poll => 'r', nice => 1,
		731	cb => &IO::AIO::poll_cb);
		732
194	IO::AIO::poll_wait	733	IO::AIO::poll_wait
		734	If there are any outstanding requests and none of them in the result
195	Wait till the result filehandle becomes ready for reading (simply	735	phase, wait till the result filehandle becomes ready for reading
196	does a "select" on the filehandle. This is useful if you want to	736	(simply does a "select" on the filehandle. This is useful if you
197	synchronously wait for some requests to finish).	737	want to synchronously wait for some requests to finish).
198		738
199	See "nreqs" for an example.	739	See "nreqs" for an example.
200		740
		741	IO::AIO::poll
		742	Waits until some requests have been handled.
		743
		744	Returns the number of requests processed, but is otherwise strictly
		745	equivalent to:
		746
		747	IO::AIO::poll_wait, IO::AIO::poll_cb
		748
201	IO::AIO::nreqs	749	IO::AIO::flush
202	Returns the number of requests currently outstanding (i.e. for which	750	Wait till all outstanding AIO requests have been handled.
203	their callback has not been invoked yet).
204		751
205	Example: wait till there are no outstanding requests anymore:	752	Strictly equivalent to:
206		753
207	IO::AIO::poll_wait, IO::AIO::poll_cb	754	IO::AIO::poll_wait, IO::AIO::poll_cb
208	while IO::AIO::nreqs;	755	while IO::AIO::nreqs;
209		756
210	IO::AIO::flush	757	CONTROLLING THE NUMBER OF THREADS
211	Wait till all outstanding AIO requests have been handled.
212
213	Strictly equivalent to:
214
215	IO::AIO::poll_wait, IO::AIO::poll_cb
216	while IO::AIO::nreqs;
217
218	IO::AIO::poll
219	Waits until some requests have been handled.
220
221	Strictly equivalent to:
222
223	IO::AIO::poll_wait, IO::AIO::poll_cb
224	if IO::AIO::nreqs;
225
226	IO::AIO::min_parallel $nthreads	758	IO::AIO::min_parallel $nthreads
227	Set the minimum number of AIO threads to $nthreads. The default is	759	Set the minimum number of AIO threads to $nthreads. The current
228	1, which means a single asynchronous operation can be done at one	760	default is 8, which means eight asynchronous operations can execute
229	time (the number of outstanding operations, however, is unlimited).	761	concurrently at any one time (the number of outstanding requests,
		762	however, is unlimited).
230		763
		764	IO::AIO starts threads only on demand, when an AIO request is queued
		765	and no free thread exists. Please note that queueing up a hundred
		766	requests can create demand for a hundred threads, even if it turns
		767	out that everything is in the cache and could have been processed
		768	faster by a single thread.
		769
231	It is recommended to keep the number of threads low, as some Linux	770	It is recommended to keep the number of threads relatively low, as
232	kernel versions will scale negatively with the number of threads	771	some Linux kernel versions will scale negatively with the number of
233	(higher parallelity => MUCH higher latency). With current Linux 2.6	772	threads (higher parallelity => MUCH higher latency). With current
234	versions, 4-32 threads should be fine.	773	Linux 2.6 versions, 4-32 threads should be fine.
235		774
236	Under normal circumstances you don't need to call this function, as	775	Under most circumstances you don't need to call this function, as
237	this module automatically starts some threads (the exact number	776	the module selects a default that is suitable for low to moderate
238	might change, and is currently 4).	777	load.
239		778
240	IO::AIO::max_parallel $nthreads	779	IO::AIO::max_parallel $nthreads
241	Sets the maximum number of AIO threads to $nthreads. If more than	780	Sets the maximum number of AIO threads to $nthreads. If more than
242	the specified number of threads are currently running, kill them.	781	the specified number of threads are currently running, this function
243	This function blocks until the limit is reached.	782	kills them. This function blocks until the limit is reached.
		783
		784	While $nthreads are zero, aio requests get queued but not executed
		785	until the number of threads has been increased again.
244		786
245	This module automatically runs "max_parallel 0" at program end, to	787	This module automatically runs "max_parallel 0" at program end, to
246	ensure that all threads are killed and that there are no outstanding	788	ensure that all threads are killed and that there are no outstanding
247	requests.	789	requests.
248		790
249	Under normal circumstances you don't need to call this function.	791	Under normal circumstances you don't need to call this function.
250		792
		793	IO::AIO::max_idle $nthreads
		794	Limit the number of threads (default: 4) that are allowed to idle
		795	(i.e., threads that did not get a request to process within 10
		796	seconds). That means if a thread becomes idle while $nthreads other
		797	threads are also idle, it will free its resources and exit.
		798
		799	This is useful when you allow a large number of threads (e.g. 100 or
		800	1000) to allow for extremely high load situations, but want to free
		801	resources under normal circumstances (1000 threads can easily
		802	consume 30MB of RAM).
		803
		804	The default is probably ok in most situations, especially if thread
		805	creation is fast. If thread creation is very slow on your system you
		806	might want to use larger values.
		807
251	$oldnreqs = IO::AIO::max_outstanding $nreqs	808	$oldmaxreqs = IO::AIO::max_outstanding $maxreqs
		809	This is a very bad function to use in interactive programs because
		810	it blocks, and a bad way to reduce concurrency because it is
		811	inexact: Better use an "aio_group" together with a feed callback.
		812
252	Sets the maximum number of outstanding requests to $nreqs. If you	813	Sets the maximum number of outstanding requests to $nreqs. If you to
253	try to queue up more than this number of requests, the caller will	814	queue up more than this number of requests, the next call to the
254	block until some requests have been handled.	815	"poll_cb" (and "poll_some" and other functions calling "poll_cb")
		816	function will block until the limit is no longer exceeded.
255		817
256	The default is very large, so normally there is no practical limit.	818	The default value is very large, so there is no practical limit on
257	If you queue up many requests in a loop it it often improves speed	819	the number of outstanding requests.
258	if you set this to a relatively low number, such as 100.
259		820
260	Under normal circumstances you don't need to call this function.	821	You can still queue as many requests as you want. Therefore,
		822	"max_oustsanding" is mainly useful in simple scripts (with low
		823	values) or as a stop gap to shield against fatal memory overflow
		824	(with large values).
		825
		826	STATISTICAL INFORMATION
		827	IO::AIO::nreqs
		828	Returns the number of requests currently in the ready, execute or
		829	pending states (i.e. for which their callback has not been invoked
		830	yet).
		831
		832	Example: wait till there are no outstanding requests anymore:
		833
		834	IO::AIO::poll_wait, IO::AIO::poll_cb
		835	while IO::AIO::nreqs;
		836
		837	IO::AIO::nready
		838	Returns the number of requests currently in the ready state (not yet
		839	executed).
		840
		841	IO::AIO::npending
		842	Returns the number of requests currently in the pending state
		843	(executed, but not yet processed by poll_cb).
		844
		845	FORK BEHAVIOUR
		846	This module should do "the right thing" when the process using it forks:
		847
		848	Before the fork, IO::AIO enters a quiescent state where no requests can
		849	be added in other threads and no results will be processed. After the
		850	fork the parent simply leaves the quiescent state and continues
		851	request/result processing, while the child frees the request/result
		852	queue (so that the requests started before the fork will only be handled
		853	in the parent). Threads will be started on demand until the limit set in
		854	the parent process has been reached again.
		855
		856	In short: the parent will, after a short pause, continue as if fork had
		857	not been called, while the child will act as if IO::AIO has not been
		858	used yet.
		859
		860	MEMORY USAGE
		861	Per-request usage:
		862
		863	Each aio request uses - depending on your architecture - around 100-200
		864	bytes of memory. In addition, stat requests need a stat buffer (possibly
		865	a few hundred bytes), readdir requires a result buffer and so on. Perl
		866	scalars and other data passed into aio requests will also be locked and
		867	will consume memory till the request has entered the done state.
		868
		869	This is now awfully much, so queuing lots of requests is not usually a
		870	problem.
		871
		872	Per-thread usage:
		873
		874	In the execution phase, some aio requests require more memory for
		875	temporary buffers, and each thread requires a stack and other data
		876	structures (usually around 16k-128k, depending on the OS).
		877
		878	KNOWN BUGS
		879	Known bugs will be fixed in the next release.
261		880
262	SEE ALSO	881	SEE ALSO
263	Coro, Linux::AIO.	882	Coro::AIO.
264		883
265	AUTHOR	884	AUTHOR
266	Marc Lehmann <schmorp@schmorp.de>	885	Marc Lehmann <schmorp@schmorp.de>
267	http://home.schmorp.de/	886	http://home.schmorp.de/
268		887

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Revision 1.23 by root, Mon Jan 22 15:59:52 2007 UTC