[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 1.50 by root, Sat Jun 24 16:27:02 2006 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 = '1.8';
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 aio_rename aio_link aio_move);
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_move $srcpath, $dstpath, $callback->($status)
		174
		175	[EXPERIMENTAL]
		176
		177	Try to move the I<file> (directories not supported as either source or destination)
		178	from C<$srcpath> to C<$dstpath> and call the callback with the C<0> (error) or C<-1> ok.
		179
		180	This is a composite request that tries to rename(2) the file first. If
		181	rename files with C<EXDEV>, it creates the destination file with mode 0200
		182	and copies the contents of the source file into it using C<aio_sendfile>,
		183	followed by restoring atime, mtime, access mode and uid/gid, in that
		184	order, and unlinking the C<$srcpath>.
		185
		186	If an error occurs, the partial destination file will be unlinked, if
		187	possible, except when setting atime, mtime, access mode and uid/gid, where
		188	errors are being ignored.
		189
		190	=cut
		191
		192	sub aio_move($$$) {
		193	my ($src, $dst, $cb) = @_;
		194
		195	aio_rename $src, $dst, sub {
		196	if ($_[0] && $! == Errno::EXDEV) {
		197	aio_open $src, O_RDONLY, 0, sub {
		198	if (my $src_fh = $_[0]) {
		199	my @stat = stat $src_fh;
		200
		201	aio_open $dst, O_WRONLY, 0200, sub {
		202	if (my $dst_fh = $_[0]) {
		203	aio_sendfile $dst_fh, $src_fh, 0, $stat[7], sub {
		204	close $src_fh;
		205
		206	if ($_[0] == $stat[7]) {
		207	utime $stat[8], $stat[9], $dst;
		208	chmod $stat[2] & 07777, $dst_fh;
		209	chown $stat[4], $stat[5], $dst_fh;
		210	close $dst_fh;
		211
		212	aio_unlink $src, sub {
		213	$cb->($_[0]);
		214	};
		215	} else {
		216	my $errno = $!;
		217	aio_unlink $dst, sub {
		218	$! = $errno;
		219	$cb->(-1);
		220	};
		221	}
		222	};
		223	} else {
		224	$cb->(-1);
		225	}
		226	},
		227
		228	} else {
		229	$cb->(-1);
		230	}
		231	};
		232	} else {
		233	$cb->($_[0]);
		234	}
		235	};
		236	}
		237
		238	=item aio_sendfile $out_fh, $in_fh, $in_offset, $length, $callback->($retval)
		239
		240	Tries to copy C<$length> bytes from C<$in_fh> to C<$out_fh>. It starts
		241	reading at byte offset C<$in_offset>, and starts writing at the current
		242	file offset of C<$out_fh>. Because of that, it is not safe to issue more
		243	than one C<aio_sendfile> per C<$out_fh>, as they will interfere with each
		244	other.
		245
		246	This call tries to make use of a native C<sendfile> syscall to provide
		247	zero-copy operation. For this to work, C<$out_fh> should refer to a
		248	socket, and C<$in_fh> should refer to mmap'able file.
		249
		250	If the native sendfile call fails or is not implemented, it will be
		251	emulated, so you can call C<aio_sendfile> on any type of filehandle
		252	regardless of the limitations of the operating system.
		253
		254	Please note, however, that C<aio_sendfile> can read more bytes from
		255	C<$in_fh> than are written, and there is no way to find out how many
		256	bytes have been read from C<aio_sendfile> alone, as C<aio_sendfile> only
		257	provides the number of bytes written to C<$out_fh>. Only if the result
		258	value equals C<$length> one can assume that C<$length> bytes have been
		259	read.
		260
167	=item aio_readahead $fh,$offset,$length, $callback	261	=item aio_readahead $fh,$offset,$length, $callback->($retval)
168		262
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	263	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>	264	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	265	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	266	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	267	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	268	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	269	(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.	270	file. The current file offset of the file is left unchanged.
181		271
		272	If that syscall doesn't exist (likely if your OS isn't Linux) it will be
		273	emulated by simply reading the data, which would have a similar effect.
		274
182	=item aio_stat $fh_or_path, $callback	275	=item aio_stat $fh_or_path, $callback->($status)
183		276
184	=item aio_lstat $fh, $callback	277	=item aio_lstat $fh, $callback->($status)
185		278
186	Works like perl's C<stat> or C<lstat> in void context. The callback will	279	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 _>	280	be called after the stat and the results will be available using C<stat _>
188	or C<-s _> etc...	281	or C<-s _> etc...
189		282
…		…
199	aio_stat "/etc/passwd", sub {	292	aio_stat "/etc/passwd", sub {
200	$_[0] and die "stat failed: $!";	293	$_[0] and die "stat failed: $!";
201	print "size is ", -s _, "\n";	294	print "size is ", -s _, "\n";
202	};	295	};
203		296
204	=item aio_unlink $pathname, $callback	297	=item aio_unlink $pathname, $callback->($status)
205		298
206	Asynchronously unlink (delete) a file and call the callback with the	299	Asynchronously unlink (delete) a file and call the callback with the
207	result code.	300	result code.
208		301
		302	=item aio_link $srcpath, $dstpath, $callback->($status)
		303
		304	Asynchronously create a new link to the existing object at C<$srcpath> at
		305	the path C<$dstpath> and call the callback with the result code.
		306
		307	=item aio_symlink $srcpath, $dstpath, $callback->($status)
		308
		309	Asynchronously create a new symbolic link to the existing object at C<$srcpath> at
		310	the path C<$dstpath> and call the callback with the result code.
		311
		312	=item aio_rename $srcpath, $dstpath, $callback->($status)
		313
		314	Asynchronously rename the object at C<$srcpath> to C<$dstpath>, just as
		315	rename(2) and call the callback with the result code.
		316
		317	=item aio_rmdir $pathname, $callback->($status)
		318
		319	Asynchronously rmdir (delete) a directory and call the callback with the
		320	result code.
		321
		322	=item aio_readdir $pathname, $callback->($entries)
		323
		324	Unlike the POSIX call of the same name, C<aio_readdir> reads an entire
		325	directory (i.e. opendir + readdir + closedir). The entries will not be
		326	sorted, and will B<NOT> include the C<.> and C<..> entries.
		327
		328	The callback a single argument which is either C<undef> or an array-ref
		329	with the filenames.
		330
		331	=item aio_scandir $path, $maxreq, $callback->($dirs, $nondirs)
		332
		333	Scans a directory (similar to C<aio_readdir>) and tries to separate the
		334	entries of directory C<$path> into two sets of names, ones you can recurse
		335	into (directories), and ones you cannot recurse into (everything else).
		336
		337	C<aio_scandir> is a composite request that consists of many
		338	aio-primitives. C<$maxreq> specifies the maximum number of outstanding
		339	aio requests that this function generates. If it is C<< <= 0 >>, then a
		340	suitable default will be chosen (currently 8).
		341
		342	On error, the callback is called without arguments, otherwise it receives
		343	two array-refs with path-relative entry names.
		344
		345	Example:
		346
		347	aio_scandir $dir, 0, sub {
		348	my ($dirs, $nondirs) = @_;
		349	print "real directories: @$dirs\n";
		350	print "everything else: @$nondirs\n";
		351	};
		352
		353	Implementation notes.
		354
		355	The C<aio_readdir> cannot be avoided, but C<stat()>'ing every entry can.
		356
		357	After reading the directory, the modification time, size etc. of the
		358	directory before and after the readdir is checked, and if they match, the
		359	link count will be used to decide how many entries are directories (if
		360	>= 2). Otherwise, no knowledge of the number of subdirectories will be
		361	assumed.
		362
		363	Then entires will be sorted into likely directories (everything without a
		364	non-initial dot) and likely non-directories (everything else). Then every
		365	entry + C</.> will be C<stat>'ed, likely directories first. This is often
		366	faster because filesystems might detect the type of the entry without
		367	reading the inode data (e.g. ext2fs filetype feature). If that succeeds,
		368	it assumes that the entry is a directory or a symlink to directory (which
		369	will be checked seperately).
		370
		371	If the known number of directories has been reached, the rest of the
		372	entries is assumed to be non-directories.
		373
		374	=cut
		375
		376	sub aio_scandir($$$) {
		377	my ($path, $maxreq, $cb) = @_;
		378
		379	$maxreq = 8 if $maxreq <= 0;
		380
		381	# stat once
		382	aio_stat $path, sub {
		383	return $cb->() if $_[0];
		384	my $hash1 = join ":", (stat _)[0,1,3,7,9];
		385
		386	# read the directory entries
		387	aio_readdir $path, sub {
		388	my $entries = shift
		389	or return $cb->();
		390
		391	# stat the dir another time
		392	aio_stat $path, sub {
		393	my $hash2 = join ":", (stat _)[0,1,3,7,9];
		394
		395	my $ndirs;
		396
		397	# take the slow route if anything looks fishy
		398	if ($hash1 ne $hash2) {
		399	$ndirs = -1;
		400	} else {
		401	# if nlink == 2, we are finished
		402	# on non-posix-fs's, we rely on nlink < 2
		403	$ndirs = (stat _)[3] - 2
		404	or return $cb->([], $entries);
		405	}
		406
		407	# sort into likely dirs and likely nondirs
		408	# dirs == files without ".", short entries first
		409	$entries = [map $_->[0],
		410	sort { $b->[1] cmp $a->[1] }
		411	map [$_, sprintf "%s%04d", (/.\./ ? "1" : "0"), length],
		412	@$entries];
		413
		414	my (@dirs, @nondirs);
		415
		416	my ($statcb, $schedcb);
		417	my $nreq = 0;
		418
		419	$schedcb = sub {
		420	if (@$entries) {
		421	if ($nreq < $maxreq) {
		422	my $ent = pop @$entries;
		423	$nreq++;
		424	aio_stat "$path/$ent/.", sub { $statcb->($_[0], $ent) };
		425	}
		426	} elsif (!$nreq) {
		427	# finished
		428	undef $statcb;
		429	undef $schedcb;
		430	$cb->(\@dirs, \@nondirs) if $cb;
		431	undef $cb;
		432	}
		433	};
		434	$statcb = sub {
		435	my ($status, $entry) = @_;
		436
		437	if ($status < 0) {
		438	$nreq--;
		439	push @nondirs, $entry;
		440	&$schedcb;
		441	} else {
		442	# need to check for real directory
		443	aio_lstat "$path/$entry", sub {
		444	$nreq--;
		445
		446	if (-d _) {
		447	push @dirs, $entry;
		448
		449	if (!--$ndirs) {
		450	push @nondirs, @$entries;
		451	$entries = [];
		452	}
		453	} else {
		454	push @nondirs, $entry;
		455	}
		456
		457	&$schedcb;
		458	}
		459	}
		460	};
		461
		462	&$schedcb while @$entries && $nreq < $maxreq;
		463	};
		464	};
		465	};
		466	}
		467
209	=item aio_fsync $fh, $callback	468	=item aio_fsync $fh, $callback->($status)
210		469
211	Asynchronously call fsync on the given filehandle and call the callback	470	Asynchronously call fsync on the given filehandle and call the callback
212	with the fsync result code.	471	with the fsync result code.
213		472
214	=item aio_fdatasync $fh, $callback	473	=item aio_fdatasync $fh, $callback->($status)
215		474
216	Asynchronously call fdatasync on the given filehandle and call the	475	Asynchronously call fdatasync on the given filehandle and call the
217	callback with the fdatasync result code.	476	callback with the fdatasync result code.
218		477
		478	If this call isn't available because your OS lacks it or it couldn't be
		479	detected, it will be emulated by calling C<fsync> instead.
		480
		481	=back
		482
		483	=head2 SUPPORT FUNCTIONS
		484
		485	=over 4
		486
		487	=item $fileno = IO::AIO::poll_fileno
		488
		489	Return the I<request result pipe file descriptor>. This filehandle must be
		490	polled for reading by some mechanism outside this module (e.g. Event or
		491	select, see below or the SYNOPSIS). If the pipe becomes readable you have
		492	to call C<poll_cb> to check the results.
		493
		494	See C<poll_cb> for an example.
		495
		496	=item IO::AIO::poll_cb
		497
		498	Process all outstanding events on the result pipe. You have to call this
		499	regularly. Returns the number of events processed. Returns immediately
		500	when no events are outstanding.
		501
		502	Example: Install an Event watcher that automatically calls
		503	IO::AIO::poll_cb with high priority:
		504
		505	Event->io (fd => IO::AIO::poll_fileno,
		506	poll => 'r', async => 1,
		507	cb => \&IO::AIO::poll_cb);
		508
		509	=item IO::AIO::poll_wait
		510
		511	Wait till the result filehandle becomes ready for reading (simply does a
		512	C<select> on the filehandle. This is useful if you want to synchronously wait
		513	for some requests to finish).
		514
		515	See C<nreqs> for an example.
		516
		517	=item IO::AIO::nreqs
		518
		519	Returns the number of requests currently outstanding (i.e. for which their
		520	callback has not been invoked yet).
		521
		522	Example: wait till there are no outstanding requests anymore:
		523
		524	IO::AIO::poll_wait, IO::AIO::poll_cb
		525	while IO::AIO::nreqs;
		526
		527	=item IO::AIO::flush
		528
		529	Wait till all outstanding AIO requests have been handled.
		530
		531	Strictly equivalent to:
		532
		533	IO::AIO::poll_wait, IO::AIO::poll_cb
		534	while IO::AIO::nreqs;
		535
		536	=item IO::AIO::poll
		537
		538	Waits until some requests have been handled.
		539
		540	Strictly equivalent to:
		541
		542	IO::AIO::poll_wait, IO::AIO::poll_cb
		543	if IO::AIO::nreqs;
		544
		545	=item IO::AIO::min_parallel $nthreads
		546
		547	Set the minimum number of AIO threads to C<$nthreads>. The current default
		548	is C<4>, which means four asynchronous operations can be done at one time
		549	(the number of outstanding operations, however, is unlimited).
		550
		551	IO::AIO starts threads only on demand, when an AIO request is queued and
		552	no free thread exists.
		553
		554	It is recommended to keep the number of threads low, as some Linux
		555	kernel versions will scale negatively with the number of threads (higher
		556	parallelity => MUCH higher latency). With current Linux 2.6 versions, 4-32
		557	threads should be fine.
		558
		559	Under most circumstances you don't need to call this function, as the
		560	module selects a default that is suitable for low to moderate load.
		561
		562	=item IO::AIO::max_parallel $nthreads
		563
		564	Sets the maximum number of AIO threads to C<$nthreads>. If more than the
		565	specified number of threads are currently running, this function kills
		566	them. This function blocks until the limit is reached.
		567
		568	While C<$nthreads> are zero, aio requests get queued but not executed
		569	until the number of threads has been increased again.
		570
		571	This module automatically runs C<max_parallel 0> at program end, to ensure
		572	that all threads are killed and that there are no outstanding requests.
		573
		574	Under normal circumstances you don't need to call this function.
		575
		576	=item $oldnreqs = IO::AIO::max_outstanding $nreqs
		577
		578	Sets the maximum number of outstanding requests to C<$nreqs>. If you
		579	try to queue up more than this number of requests, the caller will block until
		580	some requests have been handled.
		581
		582	The default is very large, so normally there is no practical limit. If you
		583	queue up many requests in a loop it often improves speed if you set
		584	this to a relatively low number, such as C<100>.
		585
		586	Under normal circumstances you don't need to call this function.
		587
		588	=back
		589
219	=cut	590	=cut
		591
		592	# support function to convert a fd into a perl filehandle
		593	sub _fd2fh {
		594	return undef if $_[0] < 0;
		595
		596	# try to generate nice filehandles
		597	my $sym = "IO::AIO::fd#$_[0]";
		598	local *$sym;
		599
		600	open *$sym, "+<&=$_[0]" # usually works under any unix
		601	or open *$sym, "<&=$_[0]" # cygwin needs this
		602	or open *$sym, ">&=$_[0]" # or this
		603	or return undef;
		604
		605	*$sym
		606	}
220		607
221	min_parallel 4;	608	min_parallel 4;
222		609
223	END {	610	END {
224	max_parallel 0;	611	max_parallel 0;
225	}	612	}
226		613
227	1;	614	1;
228		615
229	=back	616	=head2 FORK BEHAVIOUR
230		617
231	=head1 BUGS	618	Before the fork, IO::AIO enters a quiescent state where no requests
232		619	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.	620	the fork the parent simply leaves the quiescent state and continues
		621	request/result processing, while the child clears the request/result
		622	queue (so the requests started before the fork will only be handled in
		623	the parent). Threats will be started on demand until the limit ste in the
		624	parent process has been reached again.
234		625
235	=head1 SEE ALSO	626	=head1 SEE ALSO
236		627
237	L<Coro>, L<Linux::AIO>.	628	L<Coro>, L<Linux::AIO>.
238		629

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Revision 1.1 by root, Sun Jul 10 17:07:44 2005 UTC vs.
Revision 1.50 by root, Sat Jun 24 16:27:02 2006 UTC