[ViewVC] Diff of: cvs/IO-AIO/AIO.pm

Comparing IO-AIO/AIO.pm (file contents):
Revision 1.1 by root, Sun Jul 10 17:07:44 2005 UTC vs.
Revision 1.46 by root, Mon Dec 26 20:17:13 2005 UTC

…		…
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	use IO::AIO;	7	use IO::AIO;
8		8
		9	aio_open "/etc/passwd", O_RDONLY, 0, sub {
		10	my ($fh) = @_;
		11	...
		12	};
		13
		14	aio_unlink "/tmp/file", sub { };
		15
		16	aio_read $fh, 30000, 1024, $buffer, 0, sub {
		17	$_[0] > 0 or die "read error: $!";
		18	};
		19
		20	# AnyEvent
		21	open my $fh, "<&=" . IO::AIO::poll_fileno or die "$!";
		22	my $w = AnyEvent->io (fh => $fh, poll => 'r', cb => sub { IO::AIO::poll_cb });
		23
		24	# Event
		25	Event->io (fd => IO::AIO::poll_fileno,
		26	poll => 'r',
		27	cb => \&IO::AIO::poll_cb);
		28
		29	# Glib/Gtk2
		30	add_watch Glib::IO IO::AIO::poll_fileno,
		31	in => sub { IO::AIO::poll_cb; 1 };
		32
		33	# Tk
		34	Tk::Event::IO->fileevent (IO::AIO::poll_fileno, "",
		35	readable => \&IO::AIO::poll_cb);
		36
		37	# Danga::Socket
		38	Danga::Socket->AddOtherFds (IO::AIO::poll_fileno =>
		39	\&IO::AIO::poll_cb);
		40
		41
9	=head1 DESCRIPTION	42	=head1 DESCRIPTION
10		43
11	This module implements asynchronous I/O using whatever means your	44	This module implements asynchronous I/O using whatever means your
12	operating system supports. Currently, it falls back to Linux::AIO if that	45	operating system supports.
13	module is available, or uses pthreads to emulato aio functionality.
14		46
15	Currently, in this module a number of threads are started that execute	47	Currently, a number of threads are started that execute your read/writes
16	your read/writes and signal their completion. You don't need thread	48	and signal their completion. You don't need thread support in your libc or
17	support in your libc or perl, and the threads created by this module will	49	perl, and the threads created by this module will not be visible to the
18	not be visible to the pthreads library.	50	pthreads library. In the future, this module might make use of the native
		51	aio functions available on many operating systems. However, they are often
		52	not well-supported (Linux doesn't allow them on normal files currently,
		53	for example), and they would only support aio_read and aio_write, so the
		54	remaining functionality would have to be implemented using threads anyway.
19		55
20	Although the module will work with in the presence of other threads, it is	56	Although the module will work with in the presence of other threads, it is
21	not reentrant, so use appropriate locking yourself.	57	currently not reentrant, so use appropriate locking yourself, always call
22		58	C<poll_cb> from within the same thread, or never call C<poll_cb> (or other
23	=head2 API NOTES	59	C<aio_> functions) recursively.
24
25	All the C<aio_*> calls are more or less thin wrappers around the syscall
26	with the same name (sans C<aio_>). The arguments are similar or identical,
27	and they all accept an additional C<$callback> argument which must be
28	a code reference. This code reference will get called with the syscall
29	return code (e.g. most syscalls return C<-1> on error, unlike perl, which
30	usually delivers "false") as it's sole argument when the given syscall has
31	been executed asynchronously.
32
33	All functions that expect a filehandle will also accept a file descriptor.
34
35	The filenames you pass to these routines I<must> be absolute. The reason
36	is that at the time the request is being executed, the current working
37	directory could have changed. Alternatively, you can make sure that you
38	never change the current working directory.
39
40	=over 4
41		60
42	=cut	61	=cut
43		62
44	package IO::AIO;	63	package IO::AIO;
45		64
		65	no warnings;
		66
46	use base 'Exporter';	67	use base 'Exporter';
47		68
		69	use Fcntl ();
		70
48	BEGIN {	71	BEGIN {
49	$VERSION = 0.1;	72	$VERSION = '1.71';
50		73
51	@EXPORT = qw(aio_read aio_write aio_open aio_close aio_stat aio_lstat aio_unlink	74	@EXPORT = qw(aio_sendfile aio_read aio_write aio_open aio_close aio_stat
		75	aio_lstat aio_unlink aio_rmdir aio_readdir aio_scandir aio_symlink
52	aio_fsync aio_fdatasync aio_readahead);	76	aio_fsync aio_fdatasync aio_readahead);
53	@EXPORT_OK = qw(poll_fileno poll_cb min_parallel max_parallel nreqs);	77	@EXPORT_OK = qw(poll_fileno poll_cb min_parallel max_parallel
		78	max_outstanding nreqs);
54		79
55	require XSLoader;	80	require XSLoader;
56	XSLoader::load IO::AIO, $VERSION;	81	XSLoader::load IO::AIO, $VERSION;
57	}	82	}
58		83
59	=item IO::AIO::min_parallel $nthreads	84	=head1 FUNCTIONS
60		85
61	Set the minimum number of AIO threads to C<$nthreads>. The default is	86	=head2 AIO FUNCTIONS
62	C<1>, which means a single asynchronous operation can be done at one time
63	(the number of outstanding operations, however, is unlimited).
64		87
65	It is recommended to keep the number of threads low, as some linux	88	All the C<aio_*> calls are more or less thin wrappers around the syscall
66	kernel versions will scale negatively with the number of threads (higher	89	with the same name (sans C<aio_>). The arguments are similar or identical,
67	parallelity => MUCH higher latency).	90	and they all accept an additional (and optional) C<$callback> argument
		91	which must be a code reference. This code reference will get called with
		92	the syscall return code (e.g. most syscalls return C<-1> on error, unlike
		93	perl, which usually delivers "false") as it's sole argument when the given
		94	syscall has been executed asynchronously.
68		95
69	Under normal circumstances you don't need to call this function, as this	96	All functions expecting a filehandle keep a copy of the filehandle
70	module automatically starts a single async thread.	97	internally until the request has finished.
71		98
72	=item IO::AIO::max_parallel $nthreads	99	The pathnames you pass to these routines I<must> be absolute and
		100	encoded in byte form. The reason for the former is that at the time the
		101	request is being executed, the current working directory could have
		102	changed. Alternatively, you can make sure that you never change the
		103	current working directory.
73		104
74	Sets the maximum number of AIO threads to C<$nthreads>. If more than	105	To encode pathnames to byte form, either make sure you either: a)
75	the specified number of threads are currently running, kill them. This	106	always pass in filenames you got from outside (command line, readdir
76	function blocks until the limit is reached.	107	etc.), b) are ASCII or ISO 8859-1, c) use the Encode module and encode
		108	your pathnames to the locale (or other) encoding in effect in the user
		109	environment, d) use Glib::filename_from_unicode on unicode filenames or e)
		110	use something else.
77		111
78	This module automatically runs C<max_parallel 0> at program end, to ensure	112	=over 4
79	that all threads are killed and that there are no outstanding requests.
80		113
81	Under normal circumstances you don't need to call this function.
82
83	=item $fileno = IO::AIO::poll_fileno
84
85	Return the I<request result pipe filehandle>. This filehandle must be
86	polled for reading by some mechanism outside this module (e.g. Event
87	or select, see below). If the pipe becomes readable you have to call
88	C<poll_cb> to check the results.
89
90	See C<poll_cb> for an example.
91
92	=item IO::AIO::poll_cb
93
94	Process all outstanding events on the result pipe. You have to call this
95	regularly. Returns the number of events processed. Returns immediately
96	when no events are outstanding.
97
98	You can use Event to multiplex, e.g.:
99
100	Event->io (fd => IO::AIO::poll_fileno,
101	poll => 'r', async => 1,
102	cb => \&IO::AIO::poll_cb);
103
104	=item IO::AIO::poll_wait
105
106	Wait till the result filehandle becomes ready for reading (simply does a
107	select on the filehandle. This is useful if you want to synchronously wait
108	for some requests to finish).
109
110	See C<nreqs> for an example.
111
112	=item IO::AIO::nreqs
113
114	Returns the number of requests currently outstanding.
115
116	Example: wait till there are no outstanding requests anymore:
117
118	IO::AIO::poll_wait, IO::AIO::poll_cb
119	while IO::AIO::nreqs;
120
121	=item aio_open $pathname, $flags, $mode, $callback	114	=item aio_open $pathname, $flags, $mode, $callback->($fh)
122		115
123	Asynchronously open or create a file and call the callback with the	116	Asynchronously open or create a file and call the callback with a newly
124	filedescriptor (NOT a perl filehandle, sorry for that, but watch out, this	117	created filehandle for the file.
125	might change in the future).
126		118
127	The pathname passed to C<aio_open> must be absolute. See API NOTES, above,	119	The pathname passed to C<aio_open> must be absolute. See API NOTES, above,
128	for an explanation.	120	for an explanation.
129		121
130	The C<$mode> argument is a bitmask. See the C<Fcntl> module for a	122	The C<$flags> argument is a bitmask. See the C<Fcntl> module for a
131	list. They are the same as used in C<sysopen>.	123	list. They are the same as used by C<sysopen>.
		124
		125	Likewise, C<$mode> specifies the mode of the newly created file, if it
		126	didn't exist and C<O_CREAT> has been given, just like perl's C<sysopen>,
		127	except that it is mandatory (i.e. use C<0> if you don't create new files,
		128	and C<0666> or C<0777> if you do).
132		129
133	Example:	130	Example:
134		131
135	aio_open "/etc/passwd", O_RDONLY, 0, sub {	132	aio_open "/etc/passwd", O_RDONLY, 0, sub {
136	if ($_[0] >= 0) {	133	if ($_[0]) {
137	open my $fh, "<&$_[0]"; # create a copy for perl
138	aio_close $_[0], sub { }; # close the aio handle
139	print "open successful, fh is $fh\n";	134	print "open successful, fh is $_[0]\n";
140	...	135	...
141	} else {	136	} else {
142	die "open failed: $!\n";	137	die "open failed: $!\n";
143	}	138	}
144	};	139	};
145		140
146	=item aio_close $fh, $callback	141	=item aio_close $fh, $callback->($status)
147		142
148	Asynchronously close a file and call the callback with the result code.	143	Asynchronously close a file and call the callback with the result
		144	code. I<WARNING:> although accepted, you should not pass in a perl
		145	filehandle here, as perl will likely close the file descriptor another
		146	time when the filehandle is destroyed. Normally, you can safely call perls
		147	C<close> or just let filehandles go out of scope.
149		148
		149	This is supposed to be a bug in the API, so that might change. It's
		150	therefore best to avoid this function.
		151
150	=item aio_read $fh,$offset,$length, $data,$dataoffset,$callback	152	=item aio_read $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
151		153
152	=item aio_write $fh,$offset,$length, $data,$dataoffset,$callback	154	=item aio_write $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
153		155
154	Reads or writes C<length> bytes from the specified C<fh> and C<offset>	156	Reads or writes C<length> bytes from the specified C<fh> and C<offset>
155	into the scalar given by C<data> and offset C<dataoffset> and calls the	157	into the scalar given by C<data> and offset C<dataoffset> and calls the
156	callback without the actual number of bytes read (or -1 on error, just	158	callback without the actual number of bytes read (or -1 on error, just
157	like the syscall).	159	like the syscall).
158		160
		161	The C<$data> scalar I<MUST NOT> be modified in any way while the request
		162	is outstanding. Modifying it can result in segfaults or WW3 (if the
		163	necessary/optional hardware is installed).
		164
159	Example: Read 15 bytes at offset 7 into scalar C<$buffer>, strating at	165	Example: Read 15 bytes at offset 7 into scalar C<$buffer>, starting at
160	offset C<0> within the scalar:	166	offset C<0> within the scalar:
161		167
162	aio_read $fh, 7, 15, $buffer, 0, sub {	168	aio_read $fh, 7, 15, $buffer, 0, sub {
163	$_[0] >= 0 or die "read error: $!";	169	$_[0] > 0 or die "read error: $!";
164	print "read <$buffer>\n";	170	print "read $_[0] bytes: <$buffer>\n";
165	};	171	};
166		172
		173	=item aio_sendfile $out_fh, $in_fh, $in_offset, $length, $callback->($retval)
		174
		175	Tries to copy C<$length> bytes from C<$in_fh> to C<$out_fh>. It starts
		176	reading at byte offset C<$in_offset>, and starts writing at the current
		177	file offset of C<$out_fh>. Because of that, it is not safe to issue more
		178	than one C<aio_sendfile> per C<$out_fh>, as they will interfere with each
		179	other.
		180
		181	This call tries to make use of a native C<sendfile> syscall to provide
		182	zero-copy operation. For this to work, C<$out_fh> should refer to a
		183	socket, and C<$in_fh> should refer to mmap'able file.
		184
		185	If the native sendfile call fails or is not implemented, it will be
		186	emulated, so you can call C<aio_sendfile> on any type of filehandle
		187	regardless of the limitations of the operating system.
		188
		189	Please note, however, that C<aio_sendfile> can read more bytes from
		190	C<$in_fh> than are written, and there is no way to find out how many
		191	bytes have been read from C<aio_sendfile> alone, as C<aio_sendfile> only
		192	provides the number of bytes written to C<$out_fh>. Only if the result
		193	value equals C<$length> one can assume that C<$length> bytes have been
		194	read.
		195
167	=item aio_readahead $fh,$offset,$length, $callback	196	=item aio_readahead $fh,$offset,$length, $callback->($retval)
168		197
169	Asynchronously reads the specified byte range into the page cache, using
170	the C<readahead> syscall. If that syscall doesn't exist the status will be
171	C<-1> and C<$!> is set to ENOSYS.
172
173	readahead() populates the page cache with data from a file so that	198	C<aio_readahead> populates the page cache with data from a file so that
174	subsequent reads from that file will not block on disk I/O. The C<$offset>	199	subsequent reads from that file will not block on disk I/O. The C<$offset>
175	argument specifies the starting point from which data is to be read and	200	argument specifies the starting point from which data is to be read and
176	C<$length> specifies the number of bytes to be read. I/O is performed in	201	C<$length> specifies the number of bytes to be read. I/O is performed in
177	whole pages, so that offset is effectively rounded down to a page boundary	202	whole pages, so that offset is effectively rounded down to a page boundary
178	and bytes are read up to the next page boundary greater than or equal to	203	and bytes are read up to the next page boundary greater than or equal to
179	(off-set+length). aio_readahead() does not read beyond the end of the	204	(off-set+length). C<aio_readahead> does not read beyond the end of the
180	file. The current file offset of the file is left unchanged.	205	file. The current file offset of the file is left unchanged.
181		206
		207	If that syscall doesn't exist (likely if your OS isn't Linux) it will be
		208	emulated by simply reading the data, which would have a similar effect.
		209
182	=item aio_stat $fh_or_path, $callback	210	=item aio_stat $fh_or_path, $callback->($status)
183		211
184	=item aio_lstat $fh, $callback	212	=item aio_lstat $fh, $callback->($status)
185		213
186	Works like perl's C<stat> or C<lstat> in void context. The callback will	214	Works like perl's C<stat> or C<lstat> in void context. The callback will
187	be called after the stat and the results will be available using C<stat _>	215	be called after the stat and the results will be available using C<stat _>
188	or C<-s _> etc...	216	or C<-s _> etc...
189		217
…		…
199	aio_stat "/etc/passwd", sub {	227	aio_stat "/etc/passwd", sub {
200	$_[0] and die "stat failed: $!";	228	$_[0] and die "stat failed: $!";
201	print "size is ", -s _, "\n";	229	print "size is ", -s _, "\n";
202	};	230	};
203		231
204	=item aio_unlink $pathname, $callback	232	=item aio_unlink $pathname, $callback->($status)
205		233
206	Asynchronously unlink (delete) a file and call the callback with the	234	Asynchronously unlink (delete) a file and call the callback with the
207	result code.	235	result code.
208		236
		237	=item aio_rmdir $pathname, $callback->($status)
		238
		239	Asynchronously rmdir (delete) a directory and call the callback with the
		240	result code.
		241
		242	=item aio_readdir $pathname, $callback->($entries)
		243
		244	Unlike the POSIX call of the same name, C<aio_readdir> reads an entire
		245	directory (i.e. opendir + readdir + closedir). The entries will not be
		246	sorted, and will B<NOT> include the C<.> and C<..> entries.
		247
		248	The callback a single argument which is either C<undef> or an array-ref
		249	with the filenames.
		250
		251	=item aio_scandir $path, $maxreq, $callback->($dirs, $nondirs)
		252
		253	Scans a directory (similar to C<aio_readdir>) and tries to separate the
		254	entries of directory C<$path> into two sets of names, ones you can recurse
		255	into (directories), and ones you cannot recurse into (everything else).
		256
		257	C<aio_scandir> is a composite request that consists of many
		258	aio-primitives. C<$maxreq> specifies the maximum number of outstanding
		259	aio requests that this function generates. If it is C<< <= 0 >>, then a
		260	suitable default will be chosen (currently 8).
		261
		262	On error, the callback is called without arguments, otherwise it receives
		263	two array-refs with path-relative entry names.
		264
		265	Example:
		266
		267	aio_scandir $dir, 0, sub {
		268	my ($dirs, $nondirs) = @_;
		269	print "real directories: @$dirs\n";
		270	print "everything else: @$nondirs\n";
		271	};
		272
		273	Implementation notes.
		274
		275	The C<aio_readdir> cannot be avoided, but C<stat()>'ing every entry can.
		276
		277	After reading the directory, the modification time, size etc. of the
		278	directory before and after the readdir is checked, and if they match, the
		279	link count will be used to decide how many entries are directories (if
		280	>= 2). Otherwise, no knowledge of the number of subdirectories will be
		281	assumed.
		282
		283	Then entires will be sorted into likely directories (everything without a
		284	non-initial dot) and likely non-directories (everything else). Then every
		285	entry + C</.> will be C<stat>'ed, likely directories first. This is often
		286	faster because filesystems might detect the type of the entry without
		287	reading the inode data (e.g. ext2s filetype feature). If that succeeds,
		288	it assumes that the entry is a directory or a symlink to directory (which
		289	will be checked seperately).
		290
		291	If the known number of directories has been reached, the rest of the
		292	entries is assumed to be non-directories.
		293
		294	=cut
		295
		296	sub aio_scandir($$$) {
		297	my ($path, $maxreq, $cb) = @_;
		298
		299	$maxreq = 8 if $maxreq <= 0;
		300
		301	# stat once
		302	aio_stat $path, sub {
		303	$cb->() if $_[0];
		304	my $hash1 = join ":", (stat _)[0,1,3,7,9];
		305
		306	# read the directory entries
		307	aio_readdir $path, sub {
		308	my $entries = shift
		309	or return $cb->();
		310
		311	# stat the dir another time
		312	aio_stat $path, sub {
		313	my $hash2 = join ":", (stat _)[0,1,3,7,9];
		314
		315	my $ndirs;
		316
		317	# take the slow route if anything looks fishy
		318	if ($hash1 ne $hash2) {
		319	$ndirs = -1;
		320	} else {
		321	# if nlink == 2, we are finished
		322	# on non-posix-fs's, we rely on nlink < 2
		323	$ndirs = (stat _)[3] - 2
		324	or return $cb->([], $entries);
		325	}
		326
		327	# sort into likely dirs and likely nondirs
		328	# dirs == files without ".", short entries first
		329	$entries = [map $_->[0],
		330	sort { $b->[1] cmp $a->[1] }
		331	map [$_, sprintf "%s%04d", (/.\./ ? "1" : "0"), length],
		332	@$entries];
		333
		334	my (@dirs, @nondirs);
		335
		336	my ($statcb, $schedcb);
		337	my $nreq = 0;
		338
		339	$schedcb = sub {
		340	if (@$entries) {
		341	if ($nreq < $maxreq) {
		342	my $ent = pop @$entries;
		343	$nreq++;
		344	aio_stat "$path/$ent/.", sub { $statcb->($_[0], $ent) };
		345	}
		346	} elsif (!$nreq) {
		347	# finished
		348	undef $statcb;
		349	undef $schedcb;
		350	$cb->(\@dirs, \@nondirs) if $cb;
		351	undef $cb;
		352	}
		353	};
		354	$statcb = sub {
		355	my ($status, $entry) = @_;
		356
		357	if ($status < 0) {
		358	$nreq--;
		359	push @nondirs, $entry;
		360	&$schedcb;
		361	} else {
		362	# need to check for real directory
		363	aio_lstat "$path/$entry", sub {
		364	$nreq--;
		365
		366	if (-d _) {
		367	push @dirs, $entry;
		368
		369	if (!--$ndirs) {
		370	push @nondirs, @$entries;
		371	$entries = [];
		372	}
		373	} else {
		374	push @nondirs, $entry;
		375	}
		376
		377	&$schedcb;
		378	}
		379	}
		380	};
		381
		382	&$schedcb while @$entries && $nreq < $maxreq;
		383	};
		384	};
		385	};
		386	}
		387
209	=item aio_fsync $fh, $callback	388	=item aio_fsync $fh, $callback->($status)
210		389
211	Asynchronously call fsync on the given filehandle and call the callback	390	Asynchronously call fsync on the given filehandle and call the callback
212	with the fsync result code.	391	with the fsync result code.
213		392
214	=item aio_fdatasync $fh, $callback	393	=item aio_fdatasync $fh, $callback->($status)
215		394
216	Asynchronously call fdatasync on the given filehandle and call the	395	Asynchronously call fdatasync on the given filehandle and call the
217	callback with the fdatasync result code.	396	callback with the fdatasync result code.
218		397
		398	If this call isn't available because your OS lacks it or it couldn't be
		399	detected, it will be emulated by calling C<fsync> instead.
		400
		401	=back
		402
		403	=head2 SUPPORT FUNCTIONS
		404
		405	=over 4
		406
		407	=item $fileno = IO::AIO::poll_fileno
		408
		409	Return the I<request result pipe file descriptor>. This filehandle must be
		410	polled for reading by some mechanism outside this module (e.g. Event or
		411	select, see below or the SYNOPSIS). If the pipe becomes readable you have
		412	to call C<poll_cb> to check the results.
		413
		414	See C<poll_cb> for an example.
		415
		416	=item IO::AIO::poll_cb
		417
		418	Process all outstanding events on the result pipe. You have to call this
		419	regularly. Returns the number of events processed. Returns immediately
		420	when no events are outstanding.
		421
		422	Example: Install an Event watcher that automatically calls
		423	IO::AIO::poll_cb with high priority:
		424
		425	Event->io (fd => IO::AIO::poll_fileno,
		426	poll => 'r', async => 1,
		427	cb => \&IO::AIO::poll_cb);
		428
		429	=item IO::AIO::poll_wait
		430
		431	Wait till the result filehandle becomes ready for reading (simply does a
		432	C<select> on the filehandle. This is useful if you want to synchronously wait
		433	for some requests to finish).
		434
		435	See C<nreqs> for an example.
		436
		437	=item IO::AIO::nreqs
		438
		439	Returns the number of requests currently outstanding (i.e. for which their
		440	callback has not been invoked yet).
		441
		442	Example: wait till there are no outstanding requests anymore:
		443
		444	IO::AIO::poll_wait, IO::AIO::poll_cb
		445	while IO::AIO::nreqs;
		446
		447	=item IO::AIO::flush
		448
		449	Wait till all outstanding AIO requests have been handled.
		450
		451	Strictly equivalent to:
		452
		453	IO::AIO::poll_wait, IO::AIO::poll_cb
		454	while IO::AIO::nreqs;
		455
		456	=item IO::AIO::poll
		457
		458	Waits until some requests have been handled.
		459
		460	Strictly equivalent to:
		461
		462	IO::AIO::poll_wait, IO::AIO::poll_cb
		463	if IO::AIO::nreqs;
		464
		465	=item IO::AIO::min_parallel $nthreads
		466
		467	Set the minimum number of AIO threads to C<$nthreads>. The current default
		468	is C<4>, which means four asynchronous operations can be done at one time
		469	(the number of outstanding operations, however, is unlimited).
		470
		471	IO::AIO starts threads only on demand, when an AIO request is queued and
		472	no free thread exists.
		473
		474	It is recommended to keep the number of threads low, as some Linux
		475	kernel versions will scale negatively with the number of threads (higher
		476	parallelity => MUCH higher latency). With current Linux 2.6 versions, 4-32
		477	threads should be fine.
		478
		479	Under most circumstances you don't need to call this function, as the
		480	module selects a default that is suitable for low to moderate load.
		481
		482	=item IO::AIO::max_parallel $nthreads
		483
		484	Sets the maximum number of AIO threads to C<$nthreads>. If more than the
		485	specified number of threads are currently running, this function kills
		486	them. This function blocks until the limit is reached.
		487
		488	While C<$nthreads> are zero, aio requests get queued but not executed
		489	until the number of threads has been increased again.
		490
		491	This module automatically runs C<max_parallel 0> at program end, to ensure
		492	that all threads are killed and that there are no outstanding requests.
		493
		494	Under normal circumstances you don't need to call this function.
		495
		496	=item $oldnreqs = IO::AIO::max_outstanding $nreqs
		497
		498	Sets the maximum number of outstanding requests to C<$nreqs>. If you
		499	try to queue up more than this number of requests, the caller will block until
		500	some requests have been handled.
		501
		502	The default is very large, so normally there is no practical limit. If you
		503	queue up many requests in a loop it often improves speed if you set
		504	this to a relatively low number, such as C<100>.
		505
		506	Under normal circumstances you don't need to call this function.
		507
		508	=back
		509
219	=cut	510	=cut
		511
		512	# support function to convert a fd into a perl filehandle
		513	sub _fd2fh {
		514	return undef if $_[0] < 0;
		515
		516	# try to generate nice filehandles
		517	my $sym = "IO::AIO::fd#$_[0]";
		518	local *$sym;
		519
		520	open *$sym, "+<&=$_[0]" # usually works under any unix
		521	or open *$sym, "<&=$_[0]" # cygwin needs this
		522	or open *$sym, ">&=$_[0]" # or this
		523	or return undef;
		524
		525	*$sym
		526	}
220		527
221	min_parallel 4;	528	min_parallel 4;
222		529
223	END {	530	END {
224	max_parallel 0;	531	max_parallel 0;
225	}	532	}
226		533
227	1;	534	1;
228		535
229	=back	536	=head2 FORK BEHAVIOUR
230		537
231	=head1 BUGS	538	Before the fork, IO::AIO enters a quiescent state where no requests
232		539	can be added in other threads and no results will be processed. After
233	- aio_open gives a fd, but all other functions expect a perl filehandle.	540	the fork the parent simply leaves the quiescent state and continues
		541	request/result processing, while the child clears the request/result
		542	queue (so the requests started before the fork will only be handled in
		543	the parent). Threats will be started on demand until the limit ste in the
		544	parent process has been reached again.
234		545
235	=head1 SEE ALSO	546	=head1 SEE ALSO
236		547
237	L<Coro>, L<Linux::AIO>.	548	L<Coro>, L<Linux::AIO>.
238		549

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Comparing IO-AIO/AIO.pm (file contents):
Revision 1.1 by root, Sun Jul 10 17:07:44 2005 UTC vs.
Revision 1.46 by root, Mon Dec 26 20:17:13 2005 UTC