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

Comparing IO-AIO/AIO.pm (file contents):
Revision 1.3 by root, Sun Jul 10 20:07:11 2005 UTC vs.
Revision 1.41 by root, Wed Sep 7 17:41:17 2005 UTC

…		…
3	IO::AIO - Asynchronous Input/Output	3	IO::AIO - Asynchronous Input/Output
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	use IO::AIO;	7	use IO::AIO;
		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: $!";
		18	};
		19
		20	# Event
		21	Event->io (fd => IO::AIO::poll_fileno,
		22	poll => 'r',
		23	cb => \&IO::AIO::poll_cb);
		24
		25	# Glib/Gtk2
		26	add_watch Glib::IO IO::AIO::poll_fileno,
		27	in => sub { IO::AIO::poll_cb; 1 };
		28
		29	# Tk
		30	Tk::Event::IO->fileevent (IO::AIO::poll_fileno, "",
		31	readable => \&IO::AIO::poll_cb);
		32
		33	# Danga::Socket
		34	Danga::Socket->AddOtherFds (IO::AIO::poll_fileno =>
		35	\&IO::AIO::poll_cb);
		36
8		37
9	=head1 DESCRIPTION	38	=head1 DESCRIPTION
10		39
11	This module implements asynchronous I/O using whatever means your	40	This module implements asynchronous I/O using whatever means your
12	operating system supports.	41	operating system supports.
…		…
19	not well-supported (Linux doesn't allow them on normal files currently,	48	not well-supported (Linux doesn't allow them on normal files currently,
20	for example), and they would only support aio_read and aio_write, so the	49	for example), and they would only support aio_read and aio_write, so the
21	remaining functionality would have to be implemented using threads anyway.	50	remaining functionality would have to be implemented using threads anyway.
22		51
23	Although the module will work with in the presence of other threads, it is	52	Although the module will work with in the presence of other threads, it is
24	currently not reentrant, so use appropriate locking yourself.	53	currently not reentrant, so use appropriate locking yourself, always call
25		54	C<poll_cb> from within the same thread, or never call C<poll_cb> (or other
26	=head2 API NOTES	55	C<aio_> functions) recursively.
27
28	All the C<aio_*> calls are more or less thin wrappers around the syscall
29	with the same name (sans C<aio_>). The arguments are similar or identical,
30	and they all accept an additional C<$callback> argument which must be
31	a code reference. This code reference will get called with the syscall
32	return code (e.g. most syscalls return C<-1> on error, unlike perl, which
33	usually delivers "false") as it's sole argument when the given syscall has
34	been executed asynchronously.
35
36	All functions that expect a filehandle will also accept a file descriptor.
37
38	The filenames you pass to these routines I<must> be absolute. The reason
39	is that at the time the request is being executed, the current working
40	directory could have changed. Alternatively, you can make sure that you
41	never change the current working directory.
42
43	=over 4
44		56
45	=cut	57	=cut
46		58
47	package IO::AIO;	59	package IO::AIO;
48		60
		61	no warnings;
		62
49	use base 'Exporter';	63	use base 'Exporter';
50		64
51	use Fcntl ();	65	use Fcntl ();
52		66
53	BEGIN {	67	BEGIN {
54	$VERSION = 0.2;	68	$VERSION = '1.61';
55		69
56	@EXPORT = qw(aio_read aio_write aio_open aio_close aio_stat aio_lstat aio_unlink	70	@EXPORT = qw(aio_sendfile aio_read aio_write aio_open aio_close aio_stat
		71	aio_lstat aio_unlink aio_rmdir aio_readdir aio_scandir aio_symlink
57	aio_fsync aio_fdatasync aio_readahead);	72	aio_fsync aio_fdatasync aio_readahead);
58	@EXPORT_OK = qw(poll_fileno poll_cb min_parallel max_parallel nreqs);	73	@EXPORT_OK = qw(poll_fileno poll_cb min_parallel max_parallel
		74	max_outstanding nreqs);
59		75
60	require XSLoader;	76	require XSLoader;
61	XSLoader::load IO::AIO, $VERSION;	77	XSLoader::load IO::AIO, $VERSION;
62	}	78	}
63		79
64	=item IO::AIO::min_parallel $nthreads	80	=head1 FUNCTIONS
65		81
66	Set the minimum number of AIO threads to C<$nthreads>. The default is	82	=head2 AIO FUNCTIONS
67	C<1>, which means a single asynchronous operation can be done at one time
68	(the number of outstanding operations, however, is unlimited).
69		83
70	It is recommended to keep the number of threads low, as some linux	84	All the C<aio_*> calls are more or less thin wrappers around the syscall
71	kernel versions will scale negatively with the number of threads (higher	85	with the same name (sans C<aio_>). The arguments are similar or identical,
72	parallelity => MUCH higher latency).	86	and they all accept an additional (and optional) C<$callback> argument
		87	which must be a code reference. This code reference will get called with
		88	the syscall return code (e.g. most syscalls return C<-1> on error, unlike
		89	perl, which usually delivers "false") as it's sole argument when the given
		90	syscall has been executed asynchronously.
73		91
74	Under normal circumstances you don't need to call this function, as this	92	All functions expecting a filehandle keep a copy of the filehandle
75	module automatically starts a single async thread.	93	internally until the request has finished.
76		94
77	=item IO::AIO::max_parallel $nthreads	95	The pathnames you pass to these routines I<must> be absolute and
		96	encoded in byte form. The reason for the former is that at the time the
		97	request is being executed, the current working directory could have
		98	changed. Alternatively, you can make sure that you never change the
		99	current working directory.
78		100
79	Sets the maximum number of AIO threads to C<$nthreads>. If more than	101	To encode pathnames to byte form, either make sure you either: a)
80	the specified number of threads are currently running, kill them. This	102	always pass in filenames you got from outside (command line, readdir
81	function blocks until the limit is reached.	103	etc.), b) are ASCII or ISO 8859-1, c) use the Encode module and encode
		104	your pathnames to the locale (or other) encoding in effect in the user
		105	environment, d) use Glib::filename_from_unicode on unicode filenames or e)
		106	use something else.
82		107
83	This module automatically runs C<max_parallel 0> at program end, to ensure	108	=over 4
84	that all threads are killed and that there are no outstanding requests.
85		109
86	Under normal circumstances you don't need to call this function.
87
88	=item $fileno = IO::AIO::poll_fileno
89
90	Return the I<request result pipe filehandle>. This filehandle must be
91	polled for reading by some mechanism outside this module (e.g. Event
92	or select, see below). If the pipe becomes readable you have to call
93	C<poll_cb> to check the results.
94
95	See C<poll_cb> for an example.
96
97	=item IO::AIO::poll_cb
98
99	Process all outstanding events on the result pipe. You have to call this
100	regularly. Returns the number of events processed. Returns immediately
101	when no events are outstanding.
102
103	You can use Event to multiplex, e.g.:
104
105	Event->io (fd => IO::AIO::poll_fileno,
106	poll => 'r', async => 1,
107	cb => \&IO::AIO::poll_cb);
108
109	=item IO::AIO::poll_wait
110
111	Wait till the result filehandle becomes ready for reading (simply does a
112	select on the filehandle. This is useful if you want to synchronously wait
113	for some requests to finish).
114
115	See C<nreqs> for an example.
116
117	=item IO::AIO::nreqs
118
119	Returns the number of requests currently outstanding.
120
121	Example: wait till there are no outstanding requests anymore:
122
123	IO::AIO::poll_wait, IO::AIO::poll_cb
124	while IO::AIO::nreqs;
125
126	=item aio_open $pathname, $flags, $mode, $callback	110	=item aio_open $pathname, $flags, $mode, $callback->($fh)
127		111
128	Asynchronously open or create a file and call the callback with a newly	112	Asynchronously open or create a file and call the callback with a newly
129	created filehandle for the file.	113	created filehandle for the file.
130		114
131	The pathname passed to C<aio_open> must be absolute. See API NOTES, above,	115	The pathname passed to C<aio_open> must be absolute. See API NOTES, above,
132	for an explanation.	116	for an explanation.
133		117
134	The C<$mode> argument is a bitmask. See the C<Fcntl> module for a	118	The C<$flags> argument is a bitmask. See the C<Fcntl> module for a
135	list. They are the same as used in C<sysopen>.	119	list. They are the same as used by C<sysopen>.
		120
		121	Likewise, C<$mode> specifies the mode of the newly created file, if it
		122	didn't exist and C<O_CREAT> has been given, just like perl's C<sysopen>,
		123	except that it is mandatory (i.e. use C<0> if you don't create new files,
		124	and C<0666> or C<0777> if you do).
136		125
137	Example:	126	Example:
138		127
139	aio_open "/etc/passwd", O_RDONLY, 0, sub {	128	aio_open "/etc/passwd", O_RDONLY, 0, sub {
140	if ($_[0]) {	129	if ($_[0]) {
…		…
143	} else {	132	} else {
144	die "open failed: $!\n";	133	die "open failed: $!\n";
145	}	134	}
146	};	135	};
147		136
148	=item aio_close $fh, $callback	137	=item aio_close $fh, $callback->($status)
149		138
150	Asynchronously close a file and call the callback with the result	139	Asynchronously close a file and call the callback with the result
151	code. I<WARNING:> although accepted, you should not pass in a perl	140	code. I<WARNING:> although accepted, you should not pass in a perl
152	filehandle here, as perl will likely close the file descriptor itself when	141	filehandle here, as perl will likely close the file descriptor another
153	the filehandle is destroyed. Normally, you can safely call perls C<close>	142	time when the filehandle is destroyed. Normally, you can safely call perls
154	or just let filehandles go out of scope.	143	C<close> or just let filehandles go out of scope.
155		144
		145	This is supposed to be a bug in the API, so that might change. It's
		146	therefore best to avoid this function.
		147
156	=item aio_read $fh,$offset,$length, $data,$dataoffset,$callback	148	=item aio_read $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
157		149
158	=item aio_write $fh,$offset,$length, $data,$dataoffset,$callback	150	=item aio_write $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
159		151
160	Reads or writes C<length> bytes from the specified C<fh> and C<offset>	152	Reads or writes C<length> bytes from the specified C<fh> and C<offset>
161	into the scalar given by C<data> and offset C<dataoffset> and calls the	153	into the scalar given by C<data> and offset C<dataoffset> and calls the
162	callback without the actual number of bytes read (or -1 on error, just	154	callback without the actual number of bytes read (or -1 on error, just
163	like the syscall).	155	like the syscall).
164		156
		157	The C<$data> scalar I<MUST NOT> be modified in any way while the request
		158	is outstanding. Modifying it can result in segfaults or WW3 (if the
		159	necessary/optional hardware is installed).
		160
165	Example: Read 15 bytes at offset 7 into scalar C<$buffer>, strating at	161	Example: Read 15 bytes at offset 7 into scalar C<$buffer>, starting at
166	offset C<0> within the scalar:	162	offset C<0> within the scalar:
167		163
168	aio_read $fh, 7, 15, $buffer, 0, sub {	164	aio_read $fh, 7, 15, $buffer, 0, sub {
169	$_[0] >= 0 or die "read error: $!";	165	$_[0] > 0 or die "read error: $!";
170	print "read <$buffer>\n";	166	print "read $_[0] bytes: <$buffer>\n";
171	};	167	};
172		168
		169	=item aio_sendfile $out_fh, $in_fh, $in_offset, $length, $callback->($retval)
		170
		171	Tries to copy C<$length> bytes from C<$in_fh> to C<$out_fh>. It starts
		172	reading at byte offset C<$in_offset>, and starts writing at the current
		173	file offset of C<$out_fh>. Because of that, it is not safe to issue more
		174	than one C<aio_sendfile> per C<$out_fh>, as they will interfere with each
		175	other.
		176
		177	This call tries to make use of a native C<sendfile> syscall to provide
		178	zero-copy operation. For this to work, C<$out_fh> should refer to a
		179	socket, and C<$in_fh> should refer to mmap'able file.
		180
		181	If the native sendfile call fails or is not implemented, it will be
		182	emulated, so you can call C<aio_sendfile> on any type of filehandle
		183	regardless of the limitations of the operating system.
		184
		185	Please note, however, that C<aio_sendfile> can read more bytes from
		186	C<$in_fh> than are written, and there is no way to find out how many
		187	bytes have been read from C<aio_sendfile> alone, as C<aio_sendfile> only
		188	provides the number of bytes written to C<$out_fh>. Only if the result
		189	value equals C<$length> one can assume that C<$length> bytes have been
		190	read.
		191
173	=item aio_readahead $fh,$offset,$length, $callback	192	=item aio_readahead $fh,$offset,$length, $callback->($retval)
174		193
175	Asynchronously reads the specified byte range into the page cache, using
176	the C<readahead> syscall. If that syscall doesn't exist the status will be
177	C<-1> and C<$!> is set to ENOSYS.
178
179	readahead() populates the page cache with data from a file so that	194	C<aio_readahead> populates the page cache with data from a file so that
180	subsequent reads from that file will not block on disk I/O. The C<$offset>	195	subsequent reads from that file will not block on disk I/O. The C<$offset>
181	argument specifies the starting point from which data is to be read and	196	argument specifies the starting point from which data is to be read and
182	C<$length> specifies the number of bytes to be read. I/O is performed in	197	C<$length> specifies the number of bytes to be read. I/O is performed in
183	whole pages, so that offset is effectively rounded down to a page boundary	198	whole pages, so that offset is effectively rounded down to a page boundary
184	and bytes are read up to the next page boundary greater than or equal to	199	and bytes are read up to the next page boundary greater than or equal to
185	(off-set+length). aio_readahead() does not read beyond the end of the	200	(off-set+length). C<aio_readahead> does not read beyond the end of the
186	file. The current file offset of the file is left unchanged.	201	file. The current file offset of the file is left unchanged.
187		202
		203	If that syscall doesn't exist (likely if your OS isn't Linux) it will be
		204	emulated by simply reading the data, which would have a similar effect.
		205
188	=item aio_stat $fh_or_path, $callback	206	=item aio_stat $fh_or_path, $callback->($status)
189		207
190	=item aio_lstat $fh, $callback	208	=item aio_lstat $fh, $callback->($status)
191		209
192	Works like perl's C<stat> or C<lstat> in void context. The callback will	210	Works like perl's C<stat> or C<lstat> in void context. The callback will
193	be called after the stat and the results will be available using C<stat _>	211	be called after the stat and the results will be available using C<stat _>
194	or C<-s _> etc...	212	or C<-s _> etc...
195		213
…		…
205	aio_stat "/etc/passwd", sub {	223	aio_stat "/etc/passwd", sub {
206	$_[0] and die "stat failed: $!";	224	$_[0] and die "stat failed: $!";
207	print "size is ", -s _, "\n";	225	print "size is ", -s _, "\n";
208	};	226	};
209		227
210	=item aio_unlink $pathname, $callback	228	=item aio_unlink $pathname, $callback->($status)
211		229
212	Asynchronously unlink (delete) a file and call the callback with the	230	Asynchronously unlink (delete) a file and call the callback with the
213	result code.	231	result code.
214		232
		233	=item aio_rmdir $pathname, $callback->($status)
		234
		235	Asynchronously rmdir (delete) a directory and call the callback with the
		236	result code.
		237
		238	=item aio_readdir $pathname $callback->($entries)
		239
		240	Unlike the POSIX call of the same name, C<aio_readdir> reads an entire
		241	directory (i.e. opendir + readdir + closedir). The entries will not be
		242	sorted, and will B<NOT> include the C<.> and C<..> entries.
		243
		244	The callback a single argument which is either C<undef> or an array-ref
		245	with the filenames.
		246
		247	=item aio_scandir $path, $maxreq, $callback->($dirs, $nondirs)
		248
		249	Scans a directory (similar to C<aio_readdir>) and tries to separate the
		250	entries of directory C<$path> into two sets of names, ones you can recurse
		251	into (directories), and ones you cannot recurse into (everything else).
		252
		253	C<aio_scandir> is a composite request that consists of many
		254	aio-primitives. C<$maxreq> specifies the maximum number of outstanding
		255	aio requests that this function generates. If it is C<< <= 0 >>, then a
		256	suitable default will be chosen (currently 8).
		257
		258	On error, the callback is called without arguments, otherwise it receives
		259	two array-refs with path-relative entry names.
		260
		261	Example:
		262
		263	aio_scandir $dir, 0, sub {
		264	my ($dirs, $nondirs) = @_;
		265	print "real directories: @$dirs\n";
		266	print "everything else: @$nondirs\n";
		267	};
		268
		269	Implementation notes.
		270
		271	The C<aio_readdir> cannot be avoided, but C<stat()>'ing every entry can.
		272
		273	After reading the directory, the modification time, size etc. of the
		274	directory before and after the readdir is checked, and if they match, the
		275	link count will be used to decide how many entries are directories (if
		276	>= 2). Otherwise, no knowledge of the number of subdirectories will be
		277	assumed.
		278
		279	Then entires will be sorted into likely directories (everything without a
		280	non-initial dot) and likely non-directories (everything else). Then every
		281	entry + C</.> will be C<stat>'ed, likely directories first. This is often
		282	faster because filesystems might detect the type of the entry without
		283	reading the inode data (e.g. ext2s filetype feature). If that succeeds,
		284	it assumes that the entry is a directory or a symlink to directory (which
		285	will be checked seperately).
		286
		287	If the known number of directories has been reached, the rest of the
		288	entries is assumed to be non-directories.
		289
		290	=cut
		291
		292	sub aio_scandir($$$) {
		293	my ($path, $maxreq, $cb) = @_;
		294
		295	$maxreq = 8 if $maxreq <= 0;
		296
		297	# stat once
		298	aio_stat $path, sub {
		299	$cb->() if $_[0];
		300	my $hash1 = join ":", (stat _)[0,1,3,7,9];
		301
		302	# read the directory entries
		303	aio_readdir $path, sub {
		304	my $entries = shift
		305	or return $cb->();
		306
		307	# stat the dir another time
		308	aio_stat $path, sub {
		309	my $hash2 = join ":", (stat _)[0,1,3,7,9];
		310
		311	my $ndirs;
		312
		313	# take the slow route if anything looks fishy
		314	if ($hash1 ne $hash2) {
		315	$ndirs = -1;
		316	} else {
		317	# if nlink == 2, we are finished
		318	# on non-posix-fs's, we rely on nlink < 2
		319	$ndirs = (stat _)[3] - 2
		320	or $cb->([], $entries);
		321	}
		322
		323	# sort into likely dirs and likely nondirs
		324	# dirs == files without ".", short entries first
		325	$entries = [map $_->[0],
		326	sort { $b->[1] cmp $a->[1] }
		327	map [$_, sprintf "%s%04d", (/.\./ ? "1" : "0"), length],
		328	@$entries];
		329
		330	my (@dirs, @nondirs);
		331
		332	my ($statcb, $schedcb);
		333	my $nreq = 0;
		334
		335	$schedcb = sub {
		336	if (@$entries) {
		337	if ($nreq < $maxreq) {
		338	my $ent = pop @$entries;
		339	$nreq++;
		340	aio_stat "$path/$ent/.", sub { $statcb->($_[0], $ent) };
		341	}
		342	} elsif (!$nreq) {
		343	# finished
		344	undef $statcb;
		345	undef $schedcb;
		346	$cb->(\@dirs, \@nondirs);
		347	undef $cb;
		348	}
		349	};
		350	$statcb = sub {
		351	my ($status, $entry) = @_;
		352
		353	if ($status < 0) {
		354	$nreq--;
		355	push @nondirs, $entry;
		356	&$schedcb;
		357	} else {
		358	# need to check for real directory
		359	aio_lstat "$path/$entry", sub {
		360	$nreq--;
		361
		362	if (-d _) {
		363	push @dirs, $entry;
		364
		365	if (!--$ndirs) {
		366	push @nondirs, @$entries;
		367	$entries = [];
		368	}
		369	} else {
		370	push @nondirs, $entry;
		371	}
		372
		373	&$schedcb;
		374	}
		375	}
		376	};
		377
		378	&$schedcb while @$entries && $nreq < $maxreq;
		379	};
		380	};
		381	};
		382	}
		383
215	=item aio_fsync $fh, $callback	384	=item aio_fsync $fh, $callback->($status)
216		385
217	Asynchronously call fsync on the given filehandle and call the callback	386	Asynchronously call fsync on the given filehandle and call the callback
218	with the fsync result code.	387	with the fsync result code.
219		388
220	=item aio_fdatasync $fh, $callback	389	=item aio_fdatasync $fh, $callback->($status)
221		390
222	Asynchronously call fdatasync on the given filehandle and call the	391	Asynchronously call fdatasync on the given filehandle and call the
223	callback with the fdatasync result code.	392	callback with the fdatasync result code.
		393
		394	If this call isn't available because your OS lacks it or it couldn't be
		395	detected, it will be emulated by calling C<fsync> instead.
		396
		397	=back
		398
		399	=head2 SUPPORT FUNCTIONS
		400
		401	=over 4
		402
		403	=item $fileno = IO::AIO::poll_fileno
		404
		405	Return the I<request result pipe file descriptor>. This filehandle must be
		406	polled for reading by some mechanism outside this module (e.g. Event or
		407	select, see below or the SYNOPSIS). If the pipe becomes readable you have
		408	to call C<poll_cb> to check the results.
		409
		410	See C<poll_cb> for an example.
		411
		412	=item IO::AIO::poll_cb
		413
		414	Process all outstanding events on the result pipe. You have to call this
		415	regularly. Returns the number of events processed. Returns immediately
		416	when no events are outstanding.
		417
		418	Example: Install an Event watcher that automatically calls
		419	IO::AIO::poll_cb with high priority:
		420
		421	Event->io (fd => IO::AIO::poll_fileno,
		422	poll => 'r', async => 1,
		423	cb => \&IO::AIO::poll_cb);
		424
		425	=item IO::AIO::poll_wait
		426
		427	Wait till the result filehandle becomes ready for reading (simply does a
		428	C<select> on the filehandle. This is useful if you want to synchronously wait
		429	for some requests to finish).
		430
		431	See C<nreqs> for an example.
		432
		433	=item IO::AIO::nreqs
		434
		435	Returns the number of requests currently outstanding (i.e. for which their
		436	callback has not been invoked yet).
		437
		438	Example: wait till there are no outstanding requests anymore:
		439
		440	IO::AIO::poll_wait, IO::AIO::poll_cb
		441	while IO::AIO::nreqs;
		442
		443	=item IO::AIO::flush
		444
		445	Wait till all outstanding AIO requests have been handled.
		446
		447	Strictly equivalent to:
		448
		449	IO::AIO::poll_wait, IO::AIO::poll_cb
		450	while IO::AIO::nreqs;
		451
		452	=item IO::AIO::poll
		453
		454	Waits until some requests have been handled.
		455
		456	Strictly equivalent to:
		457
		458	IO::AIO::poll_wait, IO::AIO::poll_cb
		459	if IO::AIO::nreqs;
		460
		461	=item IO::AIO::min_parallel $nthreads
		462
		463	Set the minimum number of AIO threads to C<$nthreads>. The current default
		464	is C<4>, which means four asynchronous operations can be done at one time
		465	(the number of outstanding operations, however, is unlimited).
		466
		467	IO::AIO starts threads only on demand, when an AIO request is queued and
		468	no free thread exists.
		469
		470	It is recommended to keep the number of threads low, as some Linux
		471	kernel versions will scale negatively with the number of threads (higher
		472	parallelity => MUCH higher latency). With current Linux 2.6 versions, 4-32
		473	threads should be fine.
		474
		475	Under most circumstances you don't need to call this function, as the
		476	module selects a default that is suitable for low to moderate load.
		477
		478	=item IO::AIO::max_parallel $nthreads
		479
		480	Sets the maximum number of AIO threads to C<$nthreads>. If more than the
		481	specified number of threads are currently running, this function kills
		482	them. This function blocks until the limit is reached.
		483
		484	While C<$nthreads> are zero, aio requests get queued but not executed
		485	until the number of threads has been increased again.
		486
		487	This module automatically runs C<max_parallel 0> at program end, to ensure
		488	that all threads are killed and that there are no outstanding requests.
		489
		490	Under normal circumstances you don't need to call this function.
		491
		492	=item $oldnreqs = IO::AIO::max_outstanding $nreqs
		493
		494	Sets the maximum number of outstanding requests to C<$nreqs>. If you
		495	try to queue up more than this number of requests, the caller will block until
		496	some requests have been handled.
		497
		498	The default is very large, so normally there is no practical limit. If you
		499	queue up many requests in a loop it often improves speed if you set
		500	this to a relatively low number, such as C<100>.
		501
		502	Under normal circumstances you don't need to call this function.
		503
		504	=back
224		505
225	=cut	506	=cut
226		507
227	# support function to convert a fd into a perl filehandle	508	# support function to convert a fd into a perl filehandle
228	sub _fd2fh {	509	sub _fd2fh {
229	return undef if $_[0] < 0;	510	return undef if $_[0] < 0;
230		511
231	# try to be perl5.6-compatible	512	# try to generate nice filehandles
232	local *AIO_FH;	513	my $sym = "IO::AIO::fd#$_[0]";
233	open AIO_FH, "+<&=$_[0]"	514	local *$sym;
		515
		516	open *$sym, "+<&=$_[0]" # usually works under any unix
		517	or open *$sym, "<&=$_[0]" # cygwin needs this
		518	or open *$sym, ">&=$_[0]" # or this
234	or return undef;	519	or return undef;
235		520
236	*AIO_FH	521	*$sym
237	}	522	}
238		523
239	min_parallel 4;	524	min_parallel 4;
240		525
241	END {	526	END {
242	max_parallel 0;	527	max_parallel 0;
243	}	528	}
244		529
245	1;	530	1;
246		531
247	=back	532	=head2 FORK BEHAVIOUR
248		533
249	=head1 BUGS	534	Before the fork, IO::AIO enters a quiescent state where no requests
250		535	can be added in other threads and no results will be processed. After
251	- could be optimized to use more semaphores instead of filehandles.	536	the fork the parent simply leaves the quiescent state and continues
		537	request/result processing, while the child clears the request/result
		538	queue (so the requests started before the fork will only be handled in
		539	the parent). Threats will be started on demand until the limit ste in the
		540	parent process has been reached again.
252		541
253	=head1 SEE ALSO	542	=head1 SEE ALSO
254		543
255	L<Coro>, L<Linux::AIO>.	544	L<Coro>, L<Linux::AIO>.
256		545

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Comparing IO-AIO/AIO.pm (file contents):
Revision 1.3 by root, Sun Jul 10 20:07:11 2005 UTC vs.
Revision 1.41 by root, Wed Sep 7 17:41:17 2005 UTC