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

Comparing IO-AIO/AIO.pm (file contents):
Revision 1.29 by root, Wed Aug 17 04:47:02 2005 UTC vs.
Revision 1.70 by root, Tue Oct 24 03:40:38 2006 UTC

…		…
15		15
16	aio_read $fh, 30000, 1024, $buffer, 0, sub {	16	aio_read $fh, 30000, 1024, $buffer, 0, sub {
17	$_[0] > 0 or die "read error: $!";	17	$_[0] > 0 or die "read error: $!";
18	};	18	};
19		19
20	# Event	20	# version 2+ has request and group objects
		21	use IO::AIO 2;
		22
		23	aioreq_pri 4; # give next request a very high priority
		24	my $req = aio_unlink "/tmp/file", sub { };
		25	$req->cancel; # cancel request if still in queue
		26
		27	my $grp = aio_group sub { print "all stats done\n" };
		28	add $grp aio_stat "..." for ...;
		29
		30	# AnyEvent integration
		31	open my $fh, "<&=" . IO::AIO::poll_fileno or die "$!";
		32	my $w = AnyEvent->io (fh => $fh, poll => 'r', cb => sub { IO::AIO::poll_cb });
		33
		34	# Event integration
21	Event->io (fd => IO::AIO::poll_fileno,	35	Event->io (fd => IO::AIO::poll_fileno,
22	poll => 'r',	36	poll => 'r',
23	cb => \&IO::AIO::poll_cb);	37	cb => \&IO::AIO::poll_cb);
24		38
25	# Glib/Gtk2	39	# Glib/Gtk2 integration
26	add_watch Glib::IO IO::AIO::poll_fileno,	40	add_watch Glib::IO IO::AIO::poll_fileno,
27	in => sub { IO::AIO::poll_cb; 1 };	41	in => sub { IO::AIO::poll_cb; 1 };
28		42
29	# Tk	43	# Tk integration
30	Tk::Event::IO->fileevent (IO::AIO::poll_fileno, "",	44	Tk::Event::IO->fileevent (IO::AIO::poll_fileno, "",
31	readable => \&IO::AIO::poll_cb);	45	readable => \&IO::AIO::poll_cb);
32		46
33	# Danga::Socket	47	# Danga::Socket integration
34	Danga::Socket->AddOtherFds (IO::AIO::poll_fileno =>	48	Danga::Socket->AddOtherFds (IO::AIO::poll_fileno =>
35	\&IO::AIO::poll_cb);	49	\&IO::AIO::poll_cb);
36		50
37
38	=head1 DESCRIPTION	51	=head1 DESCRIPTION
39		52
40	This module implements asynchronous I/O using whatever means your	53	This module implements asynchronous I/O using whatever means your
41	operating system supports.	54	operating system supports.
42		55
43	Currently, a number of threads are started that execute your read/writes	56	Currently, a number of threads are started that execute your read/writes
44	and signal their completion. You don't need thread support in your libc or	57	and signal their completion. You don't need thread support in perl, and
45	perl, and the threads created by this module will not be visible to the	58	the threads created by this module will not be visible to perl. In the
46	pthreads library. In the future, this module might make use of the native	59	future, this module might make use of the native aio functions available
47	aio functions available on many operating systems. However, they are often	60	on many operating systems. However, they are often not well-supported
48	not well-supported (Linux doesn't allow them on normal files currently,	61	(Linux doesn't allow them on normal files currently, for example),
49	for example), and they would only support aio_read and aio_write, so the	62	and they would only support aio_read and aio_write, so the remaining
50	remaining functionality would have to be implemented using threads anyway.	63	functionality would have to be implemented using threads anyway.
51		64
52	Although the module will work with in the presence of other threads, it is	65	Although the module will work with in the presence of other threads,
53	currently not reentrant, so use appropriate locking yourself, always call	66	it is currently not reentrant in any way, so use appropriate locking
54	C<poll_cb> from within the same thread, or never call C<poll_cb> (or other	67	yourself, always call C<poll_cb> from within the same thread, or never
55	C<aio_> functions) recursively.	68	call C<poll_cb> (or other C<aio_> functions) recursively.
56		69
57	=cut	70	=cut
58		71
59	package IO::AIO;	72	package IO::AIO;
60		73
61	no warnings;	74	no warnings;
		75	use strict 'vars';
62		76
63	use base 'Exporter';	77	use base 'Exporter';
64		78
65	use Fcntl ();
66
67	BEGIN {	79	BEGIN {
68	$VERSION = 1.2;	80	our $VERSION = '2.0';
69		81
70	@EXPORT = qw(aio_read aio_write aio_open aio_close aio_stat aio_lstat aio_unlink	82	our @AIO_REQ = qw(aio_sendfile aio_read aio_write aio_open aio_close aio_stat
71	aio_rmdir aio_symlink aio_fsync aio_fdatasync aio_readahead);	83	aio_lstat aio_unlink aio_rmdir aio_readdir aio_scandir aio_symlink
72	@EXPORT_OK = qw(poll_fileno poll_cb min_parallel max_parallel max_outstanding nreqs);	84	aio_fsync aio_fdatasync aio_readahead aio_rename aio_link aio_move
		85	aio_group aio_nop);
		86	our @EXPORT = (@AIO_REQ, qw(aioreq_pri aioreq_nice));
		87	our @EXPORT_OK = qw(poll_fileno poll_cb poll_wait flush
		88	min_parallel max_parallel max_outstanding nreqs);
		89
		90	@IO::AIO::GRP::ISA = 'IO::AIO::REQ';
73		91
74	require XSLoader;	92	require XSLoader;
75	XSLoader::load IO::AIO, $VERSION;	93	XSLoader::load ("IO::AIO", $VERSION);
76	}	94	}
77		95
78	=head1 FUNCTIONS	96	=head1 FUNCTIONS
79		97
80	=head2 AIO FUNCTIONS	98	=head2 AIO FUNCTIONS
…		…
88	syscall has been executed asynchronously.	106	syscall has been executed asynchronously.
89		107
90	All functions expecting a filehandle keep a copy of the filehandle	108	All functions expecting a filehandle keep a copy of the filehandle
91	internally until the request has finished.	109	internally until the request has finished.
92		110
		111	All requests return objects of type L<IO::AIO::REQ> that allow further
		112	manipulation of those requests while they are in-flight.
		113
93	The pathnames you pass to these routines I<must> be absolute and	114	The pathnames you pass to these routines I<must> be absolute and
94	encoded in byte form. The reason for the former is that at the time the	115	encoded in byte form. The reason for the former is that at the time the
95	request is being executed, the current working directory could have	116	request is being executed, the current working directory could have
96	changed. Alternatively, you can make sure that you never change the	117	changed. Alternatively, you can make sure that you never change the
97	current working directory.	118	current working directory.
…		…
103	environment, d) use Glib::filename_from_unicode on unicode filenames or e)	124	environment, d) use Glib::filename_from_unicode on unicode filenames or e)
104	use something else.	125	use something else.
105		126
106	=over 4	127	=over 4
107		128
		129	=item aioreq_pri $pri
		130
		131	Sets the priority for the next aio request. The default priority
		132	is C<0>, the minimum and maximum priorities are C<-4> and C<4>,
		133	respectively. Requests with higher priority will be serviced first.
		134
		135	The priority will be reset to C<0> after each call to one of the C<aio_>
		136	functions.
		137
		138	Example: open a file with low priority, then read something from it with
		139	higher priority so the read request is serviced before other low priority
		140	open requests (potentially spamming the cache):
		141
		142	aioreq_pri -3;
		143	aio_open ..., sub {
		144	return unless $_[0];
		145
		146	aioreq_pri -2;
		147	aio_read $_[0], ..., sub {
		148	...
		149	};
		150	};
		151
		152	=item aioreq_nice $pri_adjust
		153
		154	Similar to C<aioreq_pri>, but subtracts the given value from the current
		155	priority, so effects are cumulative.
		156
108	=item aio_open $pathname, $flags, $mode, $callback	157	=item aio_open $pathname, $flags, $mode, $callback->($fh)
109		158
110	Asynchronously open or create a file and call the callback with a newly	159	Asynchronously open or create a file and call the callback with a newly
111	created filehandle for the file.	160	created filehandle for the file.
112		161
113	The pathname passed to C<aio_open> must be absolute. See API NOTES, above,	162	The pathname passed to C<aio_open> must be absolute. See API NOTES, above,
…		…
130	} else {	179	} else {
131	die "open failed: $!\n";	180	die "open failed: $!\n";
132	}	181	}
133	};	182	};
134		183
135	=item aio_close $fh, $callback	184	=item aio_close $fh, $callback->($status)
136		185
137	Asynchronously close a file and call the callback with the result	186	Asynchronously close a file and call the callback with the result
138	code. I<WARNING:> although accepted, you should not pass in a perl	187	code. I<WARNING:> although accepted, you should not pass in a perl
139	filehandle here, as perl will likely close the file descriptor another	188	filehandle here, as perl will likely close the file descriptor another
140	time when the filehandle is destroyed. Normally, you can safely call perls	189	time when the filehandle is destroyed. Normally, you can safely call perls
141	C<close> or just let filehandles go out of scope.	190	C<close> or just let filehandles go out of scope.
142		191
143	This is supposed to be a bug in the API, so that might change. It's	192	This is supposed to be a bug in the API, so that might change. It's
144	therefore best to avoid this function.	193	therefore best to avoid this function.
145		194
146	=item aio_read $fh,$offset,$length, $data,$dataoffset,$callback	195	=item aio_read $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
147		196
148	=item aio_write $fh,$offset,$length, $data,$dataoffset,$callback	197	=item aio_write $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
149		198
150	Reads or writes C<length> bytes from the specified C<fh> and C<offset>	199	Reads or writes C<length> bytes from the specified C<fh> and C<offset>
151	into the scalar given by C<data> and offset C<dataoffset> and calls the	200	into the scalar given by C<data> and offset C<dataoffset> and calls the
152	callback without the actual number of bytes read (or -1 on error, just	201	callback without the actual number of bytes read (or -1 on error, just
153	like the syscall).	202	like the syscall).
154		203
		204	The C<$data> scalar I<MUST NOT> be modified in any way while the request
		205	is outstanding. Modifying it can result in segfaults or WW3 (if the
		206	necessary/optional hardware is installed).
		207
155	Example: Read 15 bytes at offset 7 into scalar C<$buffer>, starting at	208	Example: Read 15 bytes at offset 7 into scalar C<$buffer>, starting at
156	offset C<0> within the scalar:	209	offset C<0> within the scalar:
157		210
158	aio_read $fh, 7, 15, $buffer, 0, sub {	211	aio_read $fh, 7, 15, $buffer, 0, sub {
159	$_[0] > 0 or die "read error: $!";	212	$_[0] > 0 or die "read error: $!";
160	print "read $_[0] bytes: <$buffer>\n";	213	print "read $_[0] bytes: <$buffer>\n";
161	};	214	};
162		215
		216	=item aio_move $srcpath, $dstpath, $callback->($status)
		217
		218	[EXPERIMENTAL due to internal aio_group use]
		219
		220	Try to move the I<file> (directories not supported as either source or
		221	destination) from C<$srcpath> to C<$dstpath> and call the callback with
		222	the C<0> (error) or C<-1> ok.
		223
		224	This is a composite request that tries to rename(2) the file first. If
		225	rename files with C<EXDEV>, it creates the destination file with mode 0200
		226	and copies the contents of the source file into it using C<aio_sendfile>,
		227	followed by restoring atime, mtime, access mode and uid/gid, in that
		228	order, and unlinking the C<$srcpath>.
		229
		230	If an error occurs, the partial destination file will be unlinked, if
		231	possible, except when setting atime, mtime, access mode and uid/gid, where
		232	errors are being ignored.
		233
		234	=cut
		235
		236	sub aio_move($$$) {
		237	my ($src, $dst, $cb) = @_;
		238
		239	my $grp = aio_group $cb;
		240
		241	add $grp aio_rename $src, $dst, sub {
		242	if ($_[0] && $! == EXDEV) {
		243	add $grp aio_open $src, O_RDONLY, 0, sub {
		244	if (my $src_fh = $_[0]) {
		245	my @stat = stat $src_fh;
		246
		247	add $grp aio_open $dst, O_WRONLY, 0200, sub {
		248	if (my $dst_fh = $_[0]) {
		249	add $grp aio_sendfile $dst_fh, $src_fh, 0, $stat[7], sub {
		250	close $src_fh;
		251
		252	if ($_[0] == $stat[7]) {
		253	utime $stat[8], $stat[9], $dst;
		254	chmod $stat[2] & 07777, $dst_fh;
		255	chown $stat[4], $stat[5], $dst_fh;
		256	close $dst_fh;
		257
		258	add $grp aio_unlink $src, sub {
		259	$grp->result ($_[0]);
		260	};
		261	} else {
		262	my $errno = $!;
		263	add $grp aio_unlink $dst, sub {
		264	$! = $errno;
		265	$grp->result (-1);
		266	};
		267	}
		268	};
		269	} else {
		270	$grp->result (-1);
		271	}
		272	},
		273
		274	} else {
		275	$grp->result (-1);
		276	}
		277	};
		278	} else {
		279	$grp->result ($_[0]);
		280	}
		281	};
		282
		283	$grp
		284	}
		285
		286	=item aio_sendfile $out_fh, $in_fh, $in_offset, $length, $callback->($retval)
		287
		288	Tries to copy C<$length> bytes from C<$in_fh> to C<$out_fh>. It starts
		289	reading at byte offset C<$in_offset>, and starts writing at the current
		290	file offset of C<$out_fh>. Because of that, it is not safe to issue more
		291	than one C<aio_sendfile> per C<$out_fh>, as they will interfere with each
		292	other.
		293
		294	This call tries to make use of a native C<sendfile> syscall to provide
		295	zero-copy operation. For this to work, C<$out_fh> should refer to a
		296	socket, and C<$in_fh> should refer to mmap'able file.
		297
		298	If the native sendfile call fails or is not implemented, it will be
		299	emulated, so you can call C<aio_sendfile> on any type of filehandle
		300	regardless of the limitations of the operating system.
		301
		302	Please note, however, that C<aio_sendfile> can read more bytes from
		303	C<$in_fh> than are written, and there is no way to find out how many
		304	bytes have been read from C<aio_sendfile> alone, as C<aio_sendfile> only
		305	provides the number of bytes written to C<$out_fh>. Only if the result
		306	value equals C<$length> one can assume that C<$length> bytes have been
		307	read.
		308
163	=item aio_readahead $fh,$offset,$length, $callback	309	=item aio_readahead $fh,$offset,$length, $callback->($retval)
164		310
165	C<aio_readahead> populates the page cache with data from a file so that	311	C<aio_readahead> populates the page cache with data from a file so that
166	subsequent reads from that file will not block on disk I/O. The C<$offset>	312	subsequent reads from that file will not block on disk I/O. The C<$offset>
167	argument specifies the starting point from which data is to be read and	313	argument specifies the starting point from which data is to be read and
168	C<$length> specifies the number of bytes to be read. I/O is performed in	314	C<$length> specifies the number of bytes to be read. I/O is performed in
…		…
172	file. The current file offset of the file is left unchanged.	318	file. The current file offset of the file is left unchanged.
173		319
174	If that syscall doesn't exist (likely if your OS isn't Linux) it will be	320	If that syscall doesn't exist (likely if your OS isn't Linux) it will be
175	emulated by simply reading the data, which would have a similar effect.	321	emulated by simply reading the data, which would have a similar effect.
176		322
177	=item aio_stat $fh_or_path, $callback	323	=item aio_stat $fh_or_path, $callback->($status)
178		324
179	=item aio_lstat $fh, $callback	325	=item aio_lstat $fh, $callback->($status)
180		326
181	Works like perl's C<stat> or C<lstat> in void context. The callback will	327	Works like perl's C<stat> or C<lstat> in void context. The callback will
182	be called after the stat and the results will be available using C<stat _>	328	be called after the stat and the results will be available using C<stat _>
183	or C<-s _> etc...	329	or C<-s _> etc...
184		330
…		…
194	aio_stat "/etc/passwd", sub {	340	aio_stat "/etc/passwd", sub {
195	$_[0] and die "stat failed: $!";	341	$_[0] and die "stat failed: $!";
196	print "size is ", -s _, "\n";	342	print "size is ", -s _, "\n";
197	};	343	};
198		344
199	=item aio_unlink $pathname, $callback	345	=item aio_unlink $pathname, $callback->($status)
200		346
201	Asynchronously unlink (delete) a file and call the callback with the	347	Asynchronously unlink (delete) a file and call the callback with the
202	result code.	348	result code.
203		349
		350	=item aio_link $srcpath, $dstpath, $callback->($status)
		351
		352	Asynchronously create a new link to the existing object at C<$srcpath> at
		353	the path C<$dstpath> and call the callback with the result code.
		354
		355	=item aio_symlink $srcpath, $dstpath, $callback->($status)
		356
		357	Asynchronously create a new symbolic link to the existing object at C<$srcpath> at
		358	the path C<$dstpath> and call the callback with the result code.
		359
		360	=item aio_rename $srcpath, $dstpath, $callback->($status)
		361
		362	Asynchronously rename the object at C<$srcpath> to C<$dstpath>, just as
		363	rename(2) and call the callback with the result code.
		364
204	=item aio_rmdir $pathname, $callback	365	=item aio_rmdir $pathname, $callback->($status)
205		366
206	Asynchronously rmdir (delete) a directory and call the callback with the	367	Asynchronously rmdir (delete) a directory and call the callback with the
207	result code.	368	result code.
208		369
		370	=item aio_readdir $pathname, $callback->($entries)
		371
		372	Unlike the POSIX call of the same name, C<aio_readdir> reads an entire
		373	directory (i.e. opendir + readdir + closedir). The entries will not be
		374	sorted, and will B<NOT> include the C<.> and C<..> entries.
		375
		376	The callback a single argument which is either C<undef> or an array-ref
		377	with the filenames.
		378
		379	=item aio_scandir $path, $maxreq, $callback->($dirs, $nondirs)
		380
		381	[EXPERIMENTAL due to internal aio_group use]
		382
		383	Scans a directory (similar to C<aio_readdir>) but additionally tries to
		384	separate the entries of directory C<$path> into two sets of names, ones
		385	you can recurse into (directories or links to them), and ones you cannot
		386	recurse into (everything else).
		387
		388	C<aio_scandir> is a composite request that creates of many sub requests_
		389	C<$maxreq> specifies the maximum number of outstanding aio requests that
		390	this function generates. If it is C<< <= 0 >>, then a suitable default
		391	will be chosen (currently 6).
		392
		393	On error, the callback is called without arguments, otherwise it receives
		394	two array-refs with path-relative entry names.
		395
		396	Example:
		397
		398	aio_scandir $dir, 0, sub {
		399	my ($dirs, $nondirs) = @_;
		400	print "real directories: @$dirs\n";
		401	print "everything else: @$nondirs\n";
		402	};
		403
		404	Implementation notes.
		405
		406	The C<aio_readdir> cannot be avoided, but C<stat()>'ing every entry can.
		407
		408	After reading the directory, the modification time, size etc. of the
		409	directory before and after the readdir is checked, and if they match (and
		410	isn't the current time), the link count will be used to decide how many
		411	entries are directories (if >= 2). Otherwise, no knowledge of the number
		412	of subdirectories will be assumed.
		413
		414	Then entries will be sorted into likely directories (everything without
		415	a non-initial dot currently) and likely non-directories (everything
		416	else). Then every entry plus an appended C</.> will be C<stat>'ed,
		417	likely directories first. If that succeeds, it assumes that the entry
		418	is a directory or a symlink to directory (which will be checked
		419	seperately). This is often faster than stat'ing the entry itself because
		420	filesystems might detect the type of the entry without reading the inode
		421	data (e.g. ext2fs filetype feature).
		422
		423	If the known number of directories (link count - 2) has been reached, the
		424	rest of the entries is assumed to be non-directories.
		425
		426	This only works with certainty on POSIX (= UNIX) filesystems, which
		427	fortunately are the vast majority of filesystems around.
		428
		429	It will also likely work on non-POSIX filesystems with reduced efficiency
		430	as those tend to return 0 or 1 as link counts, which disables the
		431	directory counting heuristic.
		432
		433	=cut
		434
		435	sub aio_scandir($$$) {
		436	my ($path, $maxreq, $cb) = @_;
		437
		438	my $grp = aio_group $cb;
		439
		440	$maxreq = 6 if $maxreq <= 0;
		441
		442	# stat once
		443	add $grp aio_stat $path, sub {
		444	return $grp->result () if $_[0];
		445	my $now = time;
		446	my $hash1 = join ":", (stat _)[0,1,3,7,9];
		447
		448	# read the directory entries
		449	add $grp aio_readdir $path, sub {
		450	my $entries = shift
		451	or return $grp->result ();
		452
		453	# stat the dir another time
		454	add $grp aio_stat $path, sub {
		455	my $hash2 = join ":", (stat _)[0,1,3,7,9];
		456
		457	my $ndirs;
		458
		459	# take the slow route if anything looks fishy
		460	if ($hash1 ne $hash2 or (stat _)[9] == $now) {
		461	$ndirs = -1;
		462	} else {
		463	# if nlink == 2, we are finished
		464	# on non-posix-fs's, we rely on nlink < 2
		465	$ndirs = (stat _)[3] - 2
		466	or return $grp->result ([], $entries);
		467	}
		468
		469	# sort into likely dirs and likely nondirs
		470	# dirs == files without ".", short entries first
		471	$entries = [map $_->[0],
		472	sort { $b->[1] cmp $a->[1] }
		473	map [$_, sprintf "%s%04d", (/.\./ ? "1" : "0"), length],
		474	@$entries];
		475
		476	my (@dirs, @nondirs);
		477
		478	my ($statcb, $schedcb);
		479	my $nreq = 0;
		480
		481	my $statgrp = add $grp aio_group;
		482
		483	$schedcb = sub {
		484	if (@$entries) {
		485	if ($nreq < $maxreq) {
		486	my $ent = pop @$entries;
		487	$nreq++;
		488	add $statgrp aio_stat "$path/$ent/.", sub { $statcb->($_[0], $ent) };
		489	}
		490	} elsif (!$nreq) {
		491	# finished
		492	$statgrp->cancel;
		493	undef $statcb;
		494	undef $schedcb;
		495	$grp->result (\@dirs, \@nondirs);
		496	}
		497	};
		498	$statcb = sub {
		499	my ($status, $entry) = @_;
		500
		501	if ($status < 0) {
		502	$nreq--;
		503	push @nondirs, $entry;
		504	&$schedcb;
		505	} else {
		506	# need to check for real directory
		507	add $grp aio_lstat "$path/$entry", sub {
		508	$nreq--;
		509
		510	if (-d _) {
		511	push @dirs, $entry;
		512
		513	if (!--$ndirs) {
		514	push @nondirs, @$entries;
		515	$entries = [];
		516	}
		517	} else {
		518	push @nondirs, $entry;
		519	}
		520
		521	&$schedcb;
		522	}
		523	}
		524	};
		525
		526	&$schedcb while @$entries && $nreq < $maxreq;
		527	};
		528	};
		529	};
		530
		531	$grp
		532	}
		533
209	=item aio_fsync $fh, $callback	534	=item aio_fsync $fh, $callback->($status)
210		535
211	Asynchronously call fsync on the given filehandle and call the callback	536	Asynchronously call fsync on the given filehandle and call the callback
212	with the fsync result code.	537	with the fsync result code.
213		538
214	=item aio_fdatasync $fh, $callback	539	=item aio_fdatasync $fh, $callback->($status)
215		540
216	Asynchronously call fdatasync on the given filehandle and call the	541	Asynchronously call fdatasync on the given filehandle and call the
217	callback with the fdatasync result code.	542	callback with the fdatasync result code.
218		543
219	If this call isn't available because your OS lacks it or it couldn't be	544	If this call isn't available because your OS lacks it or it couldn't be
220	detected, it will be emulated by calling C<fsync> instead.	545	detected, it will be emulated by calling C<fsync> instead.
		546
		547	=item aio_group $callback->(...)
		548
		549	[EXPERIMENTAL]
		550
		551	This is a very special aio request: Instead of doing something, it is a
		552	container for other aio requests, which is useful if you want to bundle
		553	many requests into a single, composite, request.
		554
		555	Returns an object of class L<IO::AIO::GRP>. See its documentation below
		556	for more info.
		557
		558	Example:
		559
		560	my $grp = aio_group sub {
		561	print "all stats done\n";
		562	};
		563
		564	add $grp
		565	(aio_stat ...),
		566	(aio_stat ...),
		567	...;
		568
		569	=item aio_nop $callback->()
		570
		571	This is a special request - it does nothing in itself and is only used for
		572	side effects, such as when you want to add a dummy request to a group so
		573	that finishing the requests in the group depends on executing the given
		574	code.
		575
		576	While this request does nothing, it still goes through the execution
		577	phase and still requires a worker thread. Thus, the callback will not
		578	be executed immediately but only after other requests in the queue have
		579	entered their execution phase. This can be used to measure request
		580	latency.
		581
		582	=item IO::AIO::aio_sleep $fractional_seconds, $callback->() NOT EXPORTED
		583
		584	Mainly used for debugging and benchmarking, this aio request puts one of
		585	the request workers to sleep for the given time.
		586
		587	While it is theoretically handy to have simple I/O scheduling requests
		588	like sleep and file handle readable/writable, the overhead this creates
		589	is immense, so do not use this function except to put your application
		590	under artificial I/O pressure.
		591
		592	=back
		593
		594	=head2 IO::AIO::REQ CLASS
		595
		596	All non-aggregate C<aio_*> functions return an object of this class when
		597	called in non-void context.
		598
		599	A request always moves through the following five states in its lifetime,
		600	in order: B<ready> (request has been created, but has not been executed
		601	yet), B<execute> (request is currently being executed), B<pending>
		602	(request has been executed but callback has not been called yet),
		603	B<result> (results are being processed synchronously, includes calling the
		604	callback) and B<done> (request has reached the end of its lifetime and
		605	holds no resources anymore).
		606
		607	=over 4
		608
		609	=item cancel $req
		610
		611	Cancels the request, if possible. Has the effect of skipping execution
		612	when entering the B<execute> state and skipping calling the callback when
		613	entering the the B<result> state, but will leave the request otherwise
		614	untouched. That means that requests that currently execute will not be
		615	stopped and resources held by the request will not be freed prematurely.
		616
		617	=item cb $req $callback->(...)
		618
		619	Replace (or simply set) the callback registered to the request.
		620
		621	=back
		622
		623	=head2 IO::AIO::GRP CLASS
		624
		625	This class is a subclass of L<IO::AIO::REQ>, so all its methods apply to
		626	objects of this class, too.
		627
		628	A IO::AIO::GRP object is a special request that can contain multiple other
		629	aio requests.
		630
		631	You create one by calling the C<aio_group> constructing function with a
		632	callback that will be called when all contained requests have entered the
		633	C<done> state:
		634
		635	my $grp = aio_group sub {
		636	print "all requests are done\n";
		637	};
		638
		639	You add requests by calling the C<add> method with one or more
		640	C<IO::AIO::REQ> objects:
		641
		642	$grp->add (aio_unlink "...");
		643
		644	add $grp aio_stat "...", sub {
		645	$_[0] or return $grp->result ("error");
		646
		647	# add another request dynamically, if first succeeded
		648	add $grp aio_open "...", sub {
		649	$grp->result ("ok");
		650	};
		651	};
		652
		653	This makes it very easy to create composite requests (see the source of
		654	C<aio_move> for an application) that work and feel like simple requests.
		655
		656	=over 4
		657
		658	=item * The IO::AIO::GRP objects will be cleaned up during calls to
		659	C<IO::AIO::poll_cb>, just like any other request.
		660
		661	=item * They can be canceled like any other request. Canceling will cancel not
		662	only the request itself, but also all requests it contains.
		663
		664	=item * They can also can also be added to other IO::AIO::GRP objects.
		665
		666	=item * You must not add requests to a group from within the group callback (or
		667	any later time).
		668
		669	=item * This does not harmonise well with C<max_outstanding>, so best do
		670	not combine C<aio_group> with it. Groups and feeders are recommended for
		671	this kind of concurrency-limiting.
		672
		673	=back
		674
		675	Their lifetime, simplified, looks like this: when they are empty, they
		676	will finish very quickly. If they contain only requests that are in the
		677	C<done> state, they will also finish. Otherwise they will continue to
		678	exist.
		679
		680	That means after creating a group you have some time to add requests. And
		681	in the callbacks of those requests, you can add further requests to the
		682	group. And only when all those requests have finished will the the group
		683	itself finish.
		684
		685	=over 4
		686
		687	=item add $grp ...
		688
		689	=item $grp->add (...)
		690
		691	Add one or more requests to the group. Any type of L<IO::AIO::REQ> can
		692	be added, including other groups, as long as you do not create circular
		693	dependencies.
		694
		695	Returns all its arguments.
		696
		697	=item $grp->result (...)
		698
		699	Set the result value(s) that will be passed to the group callback when all
		700	subrequests have finished. By default, no argument will be passed.
		701
		702	=item feed $grp $callback->($grp)
		703
		704	[VERY EXPERIMENTAL]
		705
		706	Sets a feeder/generator on this group: every group can have an attached
		707	generator that generates requests if idle. The idea behind this is that,
		708	although you could just queue as many requests as you want in a group,
		709	this might starve other requests for a potentially long time. For
		710	example, C<aio_scandir> might generate hundreds of thousands C<aio_stat>
		711	requests, delaying any later requests for a long time.
		712
		713	To avoid this, and allow incremental generation of requests, you can
		714	instead a group and set a feeder on it that generates those requests. The
		715	feed callback will be called whenever there are few enough (see C<limit>,
		716	below) requests active in the group itself and is expected to queue more
		717	requests.
		718
		719	The feed callback can queue as many requests as it likes (i.e. C<add> does
		720	not impose any limits).
		721
		722	If the feed does not queue more requests when called, it will be
		723	automatically removed from the group.
		724
		725	If the feed limit is C<0>, it will be set to C<2> automatically.
		726
		727	Example:
		728
		729	# stat all files in @files, but only ever use four aio requests concurrently:
		730
		731	my $grp = aio_group sub { print "finished\n" };
		732	limit $grp 4;
		733	feed $grp sub {
		734	my $file = pop @files
		735	or return;
		736
		737	add $grp aio_stat $file, sub { ... };
		738	};
		739
		740	=item limit $grp $num
		741
		742	Sets the feeder limit for the group: The feeder will be called whenever
		743	the group contains less than this many requests.
		744
		745	Setting the limit to C<0> will pause the feeding process.
221		746
222	=back	747	=back
223		748
224	=head2 SUPPORT FUNCTIONS	749	=head2 SUPPORT FUNCTIONS
225		750
…		…
283	IO::AIO::poll_wait, IO::AIO::poll_cb	808	IO::AIO::poll_wait, IO::AIO::poll_cb
284	if IO::AIO::nreqs;	809	if IO::AIO::nreqs;
285		810
286	=item IO::AIO::min_parallel $nthreads	811	=item IO::AIO::min_parallel $nthreads
287		812
288	Set the minimum number of AIO threads to C<$nthreads>. The default is	813	Set the minimum number of AIO threads to C<$nthreads>. The current
289	C<1>, which means a single asynchronous operation can be done at one time	814	default is C<8>, which means eight asynchronous operations can execute
290	(the number of outstanding operations, however, is unlimited).	815	concurrently at any one time (the number of outstanding requests,
		816	however, is unlimited).
291		817
		818	IO::AIO starts threads only on demand, when an AIO request is queued and
		819	no free thread exists.
		820
292	It is recommended to keep the number of threads low, as some Linux	821	It is recommended to keep the number of threads relatively low, as some
293	kernel versions will scale negatively with the number of threads (higher	822	Linux kernel versions will scale negatively with the number of threads
294	parallelity => MUCH higher latency). With current Linux 2.6 versions, 4-32	823	(higher parallelity => MUCH higher latency). With current Linux 2.6
295	threads should be fine.	824	versions, 4-32 threads should be fine.
296		825
297	Under normal circumstances you don't need to call this function, as this	826	Under most circumstances you don't need to call this function, as the
298	module automatically starts some threads (the exact number might change,	827	module selects a default that is suitable for low to moderate load.
299	and is currently 4).
300		828
301	=item IO::AIO::max_parallel $nthreads	829	=item IO::AIO::max_parallel $nthreads
302		830
303	Sets the maximum number of AIO threads to C<$nthreads>. If more than	831	Sets the maximum number of AIO threads to C<$nthreads>. If more than the
304	the specified number of threads are currently running, kill them. This	832	specified number of threads are currently running, this function kills
305	function blocks until the limit is reached.	833	them. This function blocks until the limit is reached.
		834
		835	While C<$nthreads> are zero, aio requests get queued but not executed
		836	until the number of threads has been increased again.
306		837
307	This module automatically runs C<max_parallel 0> at program end, to ensure	838	This module automatically runs C<max_parallel 0> at program end, to ensure
308	that all threads are killed and that there are no outstanding requests.	839	that all threads are killed and that there are no outstanding requests.
309		840
310	Under normal circumstances you don't need to call this function.	841	Under normal circumstances you don't need to call this function.
311		842
312	=item $oldnreqs = IO::AIO::max_outstanding $nreqs	843	=item $oldnreqs = IO::AIO::max_outstanding $nreqs
		844
		845	[DEPRECATED]
313		846
314	Sets the maximum number of outstanding requests to C<$nreqs>. If you	847	Sets the maximum number of outstanding requests to C<$nreqs>. If you
315	try to queue up more than this number of requests, the caller will block until	848	try to queue up more than this number of requests, the caller will block until
316	some requests have been handled.	849	some requests have been handled.
317		850
318	The default is very large, so normally there is no practical limit. If you	851	The default is very large, so normally there is no practical limit. If you
319	queue up many requests in a loop it it often improves speed if you set	852	queue up many requests in a loop it often improves speed if you set
320	this to a relatively low number, such as C<100>.	853	this to a relatively low number, such as C<100>.
		854
		855	This function does not work well together with C<aio_group>'s, and their
		856	feeder interface is better suited to limiting concurrency, so do not use
		857	this function.
321		858
322	Under normal circumstances you don't need to call this function.	859	Under normal circumstances you don't need to call this function.
323		860
324	=back	861	=back
325		862
…		…
339	or return undef;	876	or return undef;
340		877
341	*$sym	878	*$sym
342	}	879	}
343		880
344	min_parallel 4;	881	min_parallel 8;
345		882
346	END {	883	END {
347	max_parallel 0;	884	max_parallel 0;
348	}	885	}
349		886
350	1;	887	1;
351		888
352	=head2 FORK BEHAVIOUR	889	=head2 FORK BEHAVIOUR
353		890
354	Before the fork IO::AIO first handles all outstanding requests - if other	891	This module should do "the right thing" when the process using it forks:
355	threads add requests during this period, this time is prolonged. It then	892
356	enters a quiescent state where no requests can be added in other threads	893	Before the fork, IO::AIO enters a quiescent state where no requests
357	and no results will be processed. After the fork the parent simply leaves	894	can be added in other threads and no results will be processed. After
358	the quiescent state and continues request processing, while the child will	895	the fork the parent simply leaves the quiescent state and continues
359	free the request and result queue and start the same number of threads as	896	request/result processing, while the child clears the request/result
360	were in use by the parent.	897	queue (so the requests started before the fork will only be handled in
		898	the parent). Threads will be started on demand until the limit ste in the
		899	parent process has been reached again.
		900
		901	In short: the parent will, after a short pause, continue as if fork had
		902	not been called, while the child will act as if IO::AIO has not been used
		903	yet.
		904
		905	=head2 MEMORY USAGE
		906
		907	Each aio request uses - depending on your architecture - around 128 bytes
		908	of memory. In addition, stat requests need a stat buffer (possibly a few
		909	hundred bytes). Perl scalars and other data passed into aio requests will
		910	also be locked.
		911
		912	This is now awfully much, so queuing lots of requests is not usually a
		913	problem.
		914
		915	Each thread needs a stack area which is usually around 16k, sometimes much
		916	larger, depending on the OS.
361		917
362	=head1 SEE ALSO	918	=head1 SEE ALSO
363		919
364	L<Coro>, L<Linux::AIO>.	920	L<Coro::AIO>.
365		921
366	=head1 AUTHOR	922	=head1 AUTHOR
367		923
368	Marc Lehmann <schmorp@schmorp.de>	924	Marc Lehmann <schmorp@schmorp.de>
369	http://home.schmorp.de/	925	http://home.schmorp.de/

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Revision 1.29 by root, Wed Aug 17 04:47:02 2005 UTC vs.
Revision 1.70 by root, Tue Oct 24 03:40:38 2006 UTC