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

Comparing IO-AIO/AIO.pm (file contents):
Revision 1.50 by root, Sat Jun 24 16:27:02 2006 UTC vs.
Revision 1.64 by root, Mon Oct 23 00:50:10 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	# AnyEvent	20	# version 2+ has request and group objects
		21	use IO::AIO 2;
		22
		23	my $req = aio_unlink "/tmp/file", sub { };
		24	$req->cancel; # cancel request if still in queue
		25
		26	my $grp = aio_group sub { print "all stats done\n" };
		27	add $grp aio_stat "..." for ...;
		28
		29	# AnyEvent integration
21	open my $fh, "<&=" . IO::AIO::poll_fileno or die "$!";	30	open my $fh, "<&=" . IO::AIO::poll_fileno or die "$!";
22	my $w = AnyEvent->io (fh => $fh, poll => 'r', cb => sub { IO::AIO::poll_cb });	31	my $w = AnyEvent->io (fh => $fh, poll => 'r', cb => sub { IO::AIO::poll_cb });
23		32
24	# Event	33	# Event integration
25	Event->io (fd => IO::AIO::poll_fileno,	34	Event->io (fd => IO::AIO::poll_fileno,
26	poll => 'r',	35	poll => 'r',
27	cb => \&IO::AIO::poll_cb);	36	cb => \&IO::AIO::poll_cb);
28		37
29	# Glib/Gtk2	38	# Glib/Gtk2 integration
30	add_watch Glib::IO IO::AIO::poll_fileno,	39	add_watch Glib::IO IO::AIO::poll_fileno,
31	in => sub { IO::AIO::poll_cb; 1 };	40	in => sub { IO::AIO::poll_cb; 1 };
32		41
33	# Tk	42	# Tk integration
34	Tk::Event::IO->fileevent (IO::AIO::poll_fileno, "",	43	Tk::Event::IO->fileevent (IO::AIO::poll_fileno, "",
35	readable => \&IO::AIO::poll_cb);	44	readable => \&IO::AIO::poll_cb);
36		45
37	# Danga::Socket	46	# Danga::Socket integration
38	Danga::Socket->AddOtherFds (IO::AIO::poll_fileno =>	47	Danga::Socket->AddOtherFds (IO::AIO::poll_fileno =>
39	\&IO::AIO::poll_cb);	48	\&IO::AIO::poll_cb);
40
41		49
42	=head1 DESCRIPTION	50	=head1 DESCRIPTION
43		51
44	This module implements asynchronous I/O using whatever means your	52	This module implements asynchronous I/O using whatever means your
45	operating system supports.	53	operating system supports.
…		…
61	=cut	69	=cut
62		70
63	package IO::AIO;	71	package IO::AIO;
64		72
65	no warnings;	73	no warnings;
		74	use strict 'vars';
66		75
67	use base 'Exporter';	76	use base 'Exporter';
68		77
69	use Fcntl ();
70
71	BEGIN {	78	BEGIN {
72	$VERSION = '1.8';	79	our $VERSION = '2.0';
73		80
74	@EXPORT = qw(aio_sendfile aio_read aio_write aio_open aio_close aio_stat	81	our @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	82	aio_lstat aio_unlink aio_rmdir aio_readdir aio_scandir aio_symlink
76	aio_fsync aio_fdatasync aio_readahead aio_rename aio_link aio_move);	83	aio_fsync aio_fdatasync aio_readahead aio_rename aio_link aio_move
		84	aio_group aio_nop);
77	@EXPORT_OK = qw(poll_fileno poll_cb min_parallel max_parallel	85	our @EXPORT_OK = qw(poll_fileno poll_cb min_parallel max_parallel max_outstanding nreqs);
78	max_outstanding nreqs);	86
		87	@IO::AIO::GRP::ISA = 'IO::AIO::REQ';
79		88
80	require XSLoader;	89	require XSLoader;
81	XSLoader::load IO::AIO, $VERSION;	90	XSLoader::load ("IO::AIO", $VERSION);
82	}	91	}
83		92
84	=head1 FUNCTIONS	93	=head1 FUNCTIONS
85		94
86	=head2 AIO FUNCTIONS	95	=head2 AIO FUNCTIONS
…		…
93	perl, which usually delivers "false") as it's sole argument when the given	102	perl, which usually delivers "false") as it's sole argument when the given
94	syscall has been executed asynchronously.	103	syscall has been executed asynchronously.
95		104
96	All functions expecting a filehandle keep a copy of the filehandle	105	All functions expecting a filehandle keep a copy of the filehandle
97	internally until the request has finished.	106	internally until the request has finished.
		107
		108	All requests return objects of type L<IO::AIO::REQ> that allow further
		109	manipulation of those requests while they are in-flight.
98		110
99	The pathnames you pass to these routines I<must> be absolute and	111	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	112	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	113	request is being executed, the current working directory could have
102	changed. Alternatively, you can make sure that you never change the	114	changed. Alternatively, you can make sure that you never change the
…		…
170	print "read $_[0] bytes: <$buffer>\n";	182	print "read $_[0] bytes: <$buffer>\n";
171	};	183	};
172		184
173	=item aio_move $srcpath, $dstpath, $callback->($status)	185	=item aio_move $srcpath, $dstpath, $callback->($status)
174		186
175	[EXPERIMENTAL]	187	[EXPERIMENTAL due to internal aio_group use]
176		188
177	Try to move the I<file> (directories not supported as either source or destination)	189	Try to move the I<file> (directories not supported as either source or
178	from C<$srcpath> to C<$dstpath> and call the callback with the C<0> (error) or C<-1> ok.	190	destination) from C<$srcpath> to C<$dstpath> and call the callback with
		191	the C<0> (error) or C<-1> ok.
179		192
180	This is a composite request that tries to rename(2) the file first. If	193	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	194	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>,	195	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	196	followed by restoring atime, mtime, access mode and uid/gid, in that
…		…
190	=cut	203	=cut
191		204
192	sub aio_move($$$) {	205	sub aio_move($$$) {
193	my ($src, $dst, $cb) = @_;	206	my ($src, $dst, $cb) = @_;
194		207
		208	my $grp = aio_group $cb;
		209
195	aio_rename $src, $dst, sub {	210	add $grp aio_rename $src, $dst, sub {
196	if ($_[0] && $! == Errno::EXDEV) {	211	if ($_[0] && $! == EXDEV) {
197	aio_open $src, O_RDONLY, 0, sub {	212	add $grp aio_open $src, O_RDONLY, 0, sub {
198	if (my $src_fh = $_[0]) {	213	if (my $src_fh = $_[0]) {
199	my @stat = stat $src_fh;	214	my @stat = stat $src_fh;
200		215
201	aio_open $dst, O_WRONLY, 0200, sub {	216	add $grp aio_open $dst, O_WRONLY, 0200, sub {
202	if (my $dst_fh = $_[0]) {	217	if (my $dst_fh = $_[0]) {
203	aio_sendfile $dst_fh, $src_fh, 0, $stat[7], sub {	218	add $grp aio_sendfile $dst_fh, $src_fh, 0, $stat[7], sub {
204	close $src_fh;	219	close $src_fh;
205		220
206	if ($_[0] == $stat[7]) {	221	if ($_[0] == $stat[7]) {
207	utime $stat[8], $stat[9], $dst;	222	utime $stat[8], $stat[9], $dst;
208	chmod $stat[2] & 07777, $dst_fh;	223	chmod $stat[2] & 07777, $dst_fh;
209	chown $stat[4], $stat[5], $dst_fh;	224	chown $stat[4], $stat[5], $dst_fh;
210	close $dst_fh;	225	close $dst_fh;
211		226
212	aio_unlink $src, sub {	227	add $grp aio_unlink $src, sub {
213	$cb->($_[0]);	228	$grp->result ($_[0]);
214	};	229	};
215	} else {	230	} else {
216	my $errno = $!;	231	my $errno = $!;
217	aio_unlink $dst, sub {	232	add $grp aio_unlink $dst, sub {
218	$! = $errno;	233	$! = $errno;
219	$cb->(-1);	234	$grp->result (-1);
220	};	235	};
221	}	236	}
222	};	237	};
223	} else {	238	} else {
224	$cb->(-1);	239	$grp->result (-1);
225	}	240	}
226	},	241	},
227		242
228	} else {	243	} else {
229	$cb->(-1);	244	$grp->result (-1);
230	}	245	}
231	};	246	};
232	} else {	247	} else {
233	$cb->($_[0]);	248	$grp->result ($_[0]);
234	}	249	}
235	};	250	};
		251
		252	$grp
236	}	253	}
237		254
238	=item aio_sendfile $out_fh, $in_fh, $in_offset, $length, $callback->($retval)	255	=item aio_sendfile $out_fh, $in_fh, $in_offset, $length, $callback->($retval)
239		256
240	Tries to copy C<$length> bytes from C<$in_fh> to C<$out_fh>. It starts	257	Tries to copy C<$length> bytes from C<$in_fh> to C<$out_fh>. It starts
…		…
328	The callback a single argument which is either C<undef> or an array-ref	345	The callback a single argument which is either C<undef> or an array-ref
329	with the filenames.	346	with the filenames.
330		347
331	=item aio_scandir $path, $maxreq, $callback->($dirs, $nondirs)	348	=item aio_scandir $path, $maxreq, $callback->($dirs, $nondirs)
332		349
		350	[EXPERIMENTAL due to internal aio_group use]
		351
333	Scans a directory (similar to C<aio_readdir>) and tries to separate the	352	Scans a directory (similar to C<aio_readdir>) but additionally tries to
334	entries of directory C<$path> into two sets of names, ones you can recurse	353	separate the entries of directory C<$path> into two sets of names, ones
335	into (directories), and ones you cannot recurse into (everything else).	354	you can recurse into (directories or links to them), and ones you cannot
		355	recurse into (everything else).
336		356
337	C<aio_scandir> is a composite request that consists of many	357	C<aio_scandir> is a composite request that creates of many sub requests_
338	aio-primitives. C<$maxreq> specifies the maximum number of outstanding	358	C<$maxreq> specifies the maximum number of outstanding aio requests that
339	aio requests that this function generates. If it is C<< <= 0 >>, then a	359	this function generates. If it is C<< <= 0 >>, then a suitable default
340	suitable default will be chosen (currently 8).	360	will be chosen (currently 6).
341		361
342	On error, the callback is called without arguments, otherwise it receives	362	On error, the callback is called without arguments, otherwise it receives
343	two array-refs with path-relative entry names.	363	two array-refs with path-relative entry names.
344		364
345	Example:	365	Example:
…		…
353	Implementation notes.	373	Implementation notes.
354		374
355	The C<aio_readdir> cannot be avoided, but C<stat()>'ing every entry can.	375	The C<aio_readdir> cannot be avoided, but C<stat()>'ing every entry can.
356		376
357	After reading the directory, the modification time, size etc. of the	377	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	378	directory before and after the readdir is checked, and if they match (and
359	link count will be used to decide how many entries are directories (if	379	isn't the current time), the link count will be used to decide how many
360	>= 2). Otherwise, no knowledge of the number of subdirectories will be	380	entries are directories (if >= 2). Otherwise, no knowledge of the number
361	assumed.	381	of subdirectories will be assumed.
362		382
363	Then entires will be sorted into likely directories (everything without a	383	Then entries will be sorted into likely directories (everything without
364	non-initial dot) and likely non-directories (everything else). Then every	384	a non-initial dot currently) and likely non-directories (everything
365	entry + C</.> will be C<stat>'ed, likely directories first. This is often	385	else). Then every entry plus an appended C</.> will be C<stat>'ed,
		386	likely directories first. If that succeeds, it assumes that the entry
		387	is a directory or a symlink to directory (which will be checked
		388	seperately). This is often faster than stat'ing the entry itself because
366	faster because filesystems might detect the type of the entry without	389	filesystems might detect the type of the entry without reading the inode
367	reading the inode data (e.g. ext2fs filetype feature). If that succeeds,	390	data (e.g. ext2fs filetype feature).
368	it assumes that the entry is a directory or a symlink to directory (which
369	will be checked seperately).
370		391
371	If the known number of directories has been reached, the rest of the	392	If the known number of directories (link count - 2) has been reached, the
372	entries is assumed to be non-directories.	393	rest of the entries is assumed to be non-directories.
		394
		395	This only works with certainty on POSIX (= UNIX) filesystems, which
		396	fortunately are the vast majority of filesystems around.
		397
		398	It will also likely work on non-POSIX filesystems with reduced efficiency
		399	as those tend to return 0 or 1 as link counts, which disables the
		400	directory counting heuristic.
373		401
374	=cut	402	=cut
375		403
376	sub aio_scandir($$$) {	404	sub aio_scandir($$$) {
377	my ($path, $maxreq, $cb) = @_;	405	my ($path, $maxreq, $cb) = @_;
378		406
		407	my $grp = aio_group $cb;
		408
379	$maxreq = 8 if $maxreq <= 0;	409	$maxreq = 6 if $maxreq <= 0;
380		410
381	# stat once	411	# stat once
382	aio_stat $path, sub {	412	add $grp aio_stat $path, sub {
383	return $cb->() if $_[0];	413	return $grp->result () if $_[0];
		414	my $now = time;
384	my $hash1 = join ":", (stat _)[0,1,3,7,9];	415	my $hash1 = join ":", (stat _)[0,1,3,7,9];
385		416
386	# read the directory entries	417	# read the directory entries
387	aio_readdir $path, sub {	418	add $grp aio_readdir $path, sub {
388	my $entries = shift	419	my $entries = shift
389	or return $cb->();	420	or return $grp->result ();
390		421
391	# stat the dir another time	422	# stat the dir another time
392	aio_stat $path, sub {	423	add $grp aio_stat $path, sub {
393	my $hash2 = join ":", (stat _)[0,1,3,7,9];	424	my $hash2 = join ":", (stat _)[0,1,3,7,9];
394		425
395	my $ndirs;	426	my $ndirs;
396		427
397	# take the slow route if anything looks fishy	428	# take the slow route if anything looks fishy
398	if ($hash1 ne $hash2) {	429	if ($hash1 ne $hash2 or (stat _)[9] == $now) {
399	$ndirs = -1;	430	$ndirs = -1;
400	} else {	431	} else {
401	# if nlink == 2, we are finished	432	# if nlink == 2, we are finished
402	# on non-posix-fs's, we rely on nlink < 2	433	# on non-posix-fs's, we rely on nlink < 2
403	$ndirs = (stat _)[3] - 2	434	$ndirs = (stat _)[3] - 2
404	or return $cb->([], $entries);	435	or return $grp->result ([], $entries);
405	}	436	}
406		437
407	# sort into likely dirs and likely nondirs	438	# sort into likely dirs and likely nondirs
408	# dirs == files without ".", short entries first	439	# dirs == files without ".", short entries first
409	$entries = [map $_->[0],	440	$entries = [map $_->[0],
…		…
414	my (@dirs, @nondirs);	445	my (@dirs, @nondirs);
415		446
416	my ($statcb, $schedcb);	447	my ($statcb, $schedcb);
417	my $nreq = 0;	448	my $nreq = 0;
418		449
		450	my $statgrp = add $grp aio_group;
		451
419	$schedcb = sub {	452	$schedcb = sub {
420	if (@$entries) {	453	if (@$entries) {
421	if ($nreq < $maxreq) {	454	if ($nreq < $maxreq) {
422	my $ent = pop @$entries;	455	my $ent = pop @$entries;
423	$nreq++;	456	$nreq++;
424	aio_stat "$path/$ent/.", sub { $statcb->($_[0], $ent) };	457	add $statgrp aio_stat "$path/$ent/.", sub { $statcb->($_[0], $ent) };
425	}	458	}
426	} elsif (!$nreq) {	459	} elsif (!$nreq) {
427	# finished	460	# finished
		461	$statgrp->cancel;
428	undef $statcb;	462	undef $statcb;
429	undef $schedcb;	463	undef $schedcb;
430	$cb->(\@dirs, \@nondirs) if $cb;	464	$grp->result (\@dirs, \@nondirs);
431	undef $cb;
432	}	465	}
433	};	466	};
434	$statcb = sub {	467	$statcb = sub {
435	my ($status, $entry) = @_;	468	my ($status, $entry) = @_;
436		469
…		…
438	$nreq--;	471	$nreq--;
439	push @nondirs, $entry;	472	push @nondirs, $entry;
440	&$schedcb;	473	&$schedcb;
441	} else {	474	} else {
442	# need to check for real directory	475	# need to check for real directory
443	aio_lstat "$path/$entry", sub {	476	add $grp aio_lstat "$path/$entry", sub {
444	$nreq--;	477	$nreq--;
445		478
446	if (-d _) {	479	if (-d _) {
447	push @dirs, $entry;	480	push @dirs, $entry;
448		481
…		…
461		494
462	&$schedcb while @$entries && $nreq < $maxreq;	495	&$schedcb while @$entries && $nreq < $maxreq;
463	};	496	};
464	};	497	};
465	};	498	};
		499
		500	$grp
466	}	501	}
467		502
468	=item aio_fsync $fh, $callback->($status)	503	=item aio_fsync $fh, $callback->($status)
469		504
470	Asynchronously call fsync on the given filehandle and call the callback	505	Asynchronously call fsync on the given filehandle and call the callback
…		…
475	Asynchronously call fdatasync on the given filehandle and call the	510	Asynchronously call fdatasync on the given filehandle and call the
476	callback with the fdatasync result code.	511	callback with the fdatasync result code.
477		512
478	If this call isn't available because your OS lacks it or it couldn't be	513	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.	514	detected, it will be emulated by calling C<fsync> instead.
		515
		516	=item aio_group $callback->(...)
		517
		518	[EXPERIMENTAL]
		519
		520	This is a very special aio request: Instead of doing something, it is a
		521	container for other aio requests, which is useful if you want to bundle
		522	many requests into a single, composite, request.
		523
		524	Returns an object of class L<IO::AIO::GRP>. See its documentation below
		525	for more info.
		526
		527	Example:
		528
		529	my $grp = aio_group sub {
		530	print "all stats done\n";
		531	};
		532
		533	add $grp
		534	(aio_stat ...),
		535	(aio_stat ...),
		536	...;
		537
		538	=item aio_nop $callback->()
		539
		540	This is a special request - it does nothing in itself and is only used for
		541	side effects, such as when you want to add a dummy request to a group so
		542	that finishing the requests in the group depends on executing the given
		543	code.
		544
		545	While this request does nothing, it still goes through the execution
		546	phase and still requires a worker thread. Thus, the callback will not
		547	be executed immediately but only after other requests in the queue have
		548	entered their execution phase. This can be used to measure request
		549	latency.
		550
		551	=item IO::AIO::aio_sleep $fractional_seconds, $callback->() NOT EXPORTED
		552
		553	Mainly used for debugging and benchmarking, this aio request puts one of
		554	the request workers to sleep for the given time.
		555
		556	While it is theoretically handy to have simple I/O scheduling requests
		557	like sleep and file handle readable/writable, the overhead this creates
		558	is immense, so do not use this function except to put your application
		559	under artificial I/O pressure.
		560
		561	=back
		562
		563	=head2 IO::AIO::REQ CLASS
		564
		565	All non-aggregate C<aio_*> functions return an object of this class when
		566	called in non-void context.
		567
		568	A request always moves through the following five states in its lifetime,
		569	in order: B<ready> (request has been created, but has not been executed
		570	yet), B<execute> (request is currently being executed), B<pending>
		571	(request has been executed but callback has not been called yet),
		572	B<result> (results are being processed synchronously, includes calling the
		573	callback) and B<done> (request has reached the end of its lifetime and
		574	holds no resources anymore).
		575
		576	=over 4
		577
		578	=item $req->cancel
		579
		580	Cancels the request, if possible. Has the effect of skipping execution
		581	when entering the B<execute> state and skipping calling the callback when
		582	entering the the B<result> state, but will leave the request otherwise
		583	untouched. That means that requests that currently execute will not be
		584	stopped and resources held by the request will not be freed prematurely.
		585
		586	=back
		587
		588	=head2 IO::AIO::GRP CLASS
		589
		590	This class is a subclass of L<IO::AIO::REQ>, so all its methods apply to
		591	objects of this class, too.
		592
		593	A IO::AIO::GRP object is a special request that can contain multiple other
		594	aio requests.
		595
		596	You create one by calling the C<aio_group> constructing function with a
		597	callback that will be called when all contained requests have entered the
		598	C<done> state:
		599
		600	my $grp = aio_group sub {
		601	print "all requests are done\n";
		602	};
		603
		604	You add requests by calling the C<add> method with one or more
		605	C<IO::AIO::REQ> objects:
		606
		607	$grp->add (aio_unlink "...");
		608
		609	add $grp aio_stat "...", sub {
		610	$_[0] or return $grp->result ("error");
		611
		612	# add another request dynamically, if first succeeded
		613	add $grp aio_open "...", sub {
		614	$grp->result ("ok");
		615	};
		616	};
		617
		618	This makes it very easy to create composite requests (see the source of
		619	C<aio_move> for an application) that work and feel like simple requests.
		620
		621	=over 4
		622
		623	=item * The IO::AIO::GRP objects will be cleaned up during calls to
		624	C<IO::AIO::poll_cb>, just like any other request.
		625
		626	=item * They can be canceled like any other request. Canceling will cancel not
		627	only the request itself, but also all requests it contains.
		628
		629	=item * They can also can also be added to other IO::AIO::GRP objects.
		630
		631	=item * You must not add requests to a group from within the group callback (or
		632	any later time).
		633
		634	=item * This does not harmonise well with C<max_outstanding>, so best do
		635	not combine C<aio_group> with it. Groups and feeders are recommended for
		636	this kind of concurrency-limiting.
		637
		638	=back
		639
		640	Their lifetime, simplified, looks like this: when they are empty, they
		641	will finish very quickly. If they contain only requests that are in the
		642	C<done> state, they will also finish. Otherwise they will continue to
		643	exist.
		644
		645	That means after creating a group you have some time to add requests. And
		646	in the callbacks of those requests, you can add further requests to the
		647	group. And only when all those requests have finished will the the group
		648	itself finish.
		649
		650	=over 4
		651
		652	=item $grp->add (...)
		653
		654	=item add $grp ...
		655
		656	Add one or more requests to the group. Any type of L<IO::AIO::REQ> can
		657	be added, including other groups, as long as you do not create circular
		658	dependencies.
		659
		660	Returns all its arguments.
		661
		662	=item $grp->result (...)
		663
		664	Set the result value(s) that will be passed to the group callback when all
		665	subrequests have finished. By default, no argument will be passed.
		666
		667	=item $grp->set_feeder ($callback->($grp))
		668
		669	[VERY EXPERIMENTAL]
		670
		671	Sets a feeder/generator on this group: every group can have an attached
		672	generator that generates requests if idle. The idea behind this is that,
		673	although you could just queue as many requests as you want in a group,
		674	this might starve other requests for a potentially long time. For
		675	example, C<aio_scandir> might generate hundreds of thousands C<aio_stat>
		676	requests, delaying any later requests for a long time.
		677
		678	To avoid this, and allow incremental generation of requests, you can
		679	instead a group and set a feeder on it that generates those requests. The
		680	feeder will be called whenever there are few enough (see C<feeder_limit>,
		681	below) requests active in the group itself and is expected to queue more
		682	requests.
		683
		684	The feeder can queue as many requests as it likes (i.e. C<add> does not
		685	impose any limits).
		686
		687	If the feeder does not queue more requests when called, it will be
		688	automatically removed from the group.
		689
		690	If the feeder limit is C<0>, it will be set to C<2> automatically.
		691
		692	Example:
		693
		694	# stat all files in @files, but only ever use four aio requests concurrently:
		695
		696	my $grp = aio_group sub { print "finished\n" };
		697	$grp->feeder_limit (4);
		698	$grp->set_feeder (sub {
		699	my $file = pop @files
		700	or return;
		701
		702	add $grp aio_stat $file, sub { ... };
		703	});
		704
		705	=item $grp->feeder_limit ($num)
		706
		707	Sets the feeder limit for the group: The feeder will be called whenever
		708	the group contains less than this many requests.
		709
		710	Setting the limit to C<0> will pause the feeding process.
480		711
481	=back	712	=back
482		713
483	=head2 SUPPORT FUNCTIONS	714	=head2 SUPPORT FUNCTIONS
484		715
…		…
542	IO::AIO::poll_wait, IO::AIO::poll_cb	773	IO::AIO::poll_wait, IO::AIO::poll_cb
543	if IO::AIO::nreqs;	774	if IO::AIO::nreqs;
544		775
545	=item IO::AIO::min_parallel $nthreads	776	=item IO::AIO::min_parallel $nthreads
546		777
547	Set the minimum number of AIO threads to C<$nthreads>. The current default	778	Set the minimum number of AIO threads to C<$nthreads>. The current
548	is C<4>, which means four asynchronous operations can be done at one time	779	default is C<8>, which means eight asynchronous operations can execute
549	(the number of outstanding operations, however, is unlimited).	780	concurrently at any one time (the number of outstanding requests,
		781	however, is unlimited).
550		782
551	IO::AIO starts threads only on demand, when an AIO request is queued and	783	IO::AIO starts threads only on demand, when an AIO request is queued and
552	no free thread exists.	784	no free thread exists.
553		785
554	It is recommended to keep the number of threads low, as some Linux	786	It is recommended to keep the number of threads relatively low, as some
555	kernel versions will scale negatively with the number of threads (higher	787	Linux kernel versions will scale negatively with the number of threads
556	parallelity => MUCH higher latency). With current Linux 2.6 versions, 4-32	788	(higher parallelity => MUCH higher latency). With current Linux 2.6
557	threads should be fine.	789	versions, 4-32 threads should be fine.
558		790
559	Under most circumstances you don't need to call this function, as the	791	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.	792	module selects a default that is suitable for low to moderate load.
561		793
562	=item IO::AIO::max_parallel $nthreads	794	=item IO::AIO::max_parallel $nthreads
…		…
573		805
574	Under normal circumstances you don't need to call this function.	806	Under normal circumstances you don't need to call this function.
575		807
576	=item $oldnreqs = IO::AIO::max_outstanding $nreqs	808	=item $oldnreqs = IO::AIO::max_outstanding $nreqs
577		809
		810	[DEPRECATED]
		811
578	Sets the maximum number of outstanding requests to C<$nreqs>. If you	812	Sets the maximum number of outstanding requests to C<$nreqs>. If you
579	try to queue up more than this number of requests, the caller will block until	813	try to queue up more than this number of requests, the caller will block until
580	some requests have been handled.	814	some requests have been handled.
581		815
582	The default is very large, so normally there is no practical limit. If you	816	The default is very large, so normally there is no practical limit. If you
583	queue up many requests in a loop it often improves speed if you set	817	queue up many requests in a loop it often improves speed if you set
584	this to a relatively low number, such as C<100>.	818	this to a relatively low number, such as C<100>.
		819
		820	This function does not work well together with C<aio_group>'s, and their
		821	feeder interface is better suited to limiting concurrency, so do not use
		822	this function.
585		823
586	Under normal circumstances you don't need to call this function.	824	Under normal circumstances you don't need to call this function.
587		825
588	=back	826	=back
589		827
…		…
603	or return undef;	841	or return undef;
604		842
605	*$sym	843	*$sym
606	}	844	}
607		845
608	min_parallel 4;	846	min_parallel 8;
609		847
610	END {	848	END {
611	max_parallel 0;	849	max_parallel 0;
612	}	850	}
613		851
614	1;	852	1;
615		853
616	=head2 FORK BEHAVIOUR	854	=head2 FORK BEHAVIOUR
		855
		856	This module should do "the right thing" when the process using it forks:
617		857
618	Before the fork, IO::AIO enters a quiescent state where no requests	858	Before the fork, IO::AIO enters a quiescent state where no requests
619	can be added in other threads and no results will be processed. After	859	can be added in other threads and no results will be processed. After
620	the fork the parent simply leaves the quiescent state and continues	860	the fork the parent simply leaves the quiescent state and continues
621	request/result processing, while the child clears the request/result	861	request/result processing, while the child clears the request/result
622	queue (so the requests started before the fork will only be handled in	862	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	863	the parent). Threads will be started on demand until the limit ste in the
624	parent process has been reached again.	864	parent process has been reached again.
625		865
		866	In short: the parent will, after a short pause, continue as if fork had
		867	not been called, while the child will act as if IO::AIO has not been used
		868	yet.
		869
		870	=head2 MEMORY USAGE
		871
		872	Each aio request uses - depending on your architecture - around 128 bytes
		873	of memory. In addition, stat requests need a stat buffer (possibly a few
		874	hundred bytes). Perl scalars and other data passed into aio requests will
		875	also be locked.
		876
		877	This is now awfully much, so queuing lots of requests is not usually a
		878	problem.
		879
		880	Each thread needs a stack area which is usually around 16k, sometimes much
		881	larger, depending on the OS.
		882
626	=head1 SEE ALSO	883	=head1 SEE ALSO
627		884
628	L<Coro>, L<Linux::AIO>.	885	L<Coro>, L<Linux::AIO> (obsolete).
629		886
630	=head1 AUTHOR	887	=head1 AUTHOR
631		888
632	Marc Lehmann <schmorp@schmorp.de>	889	Marc Lehmann <schmorp@schmorp.de>
633	http://home.schmorp.de/	890	http://home.schmorp.de/

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Revision 1.50 by root, Sat Jun 24 16:27:02 2006 UTC vs.
Revision 1.64 by root, Mon Oct 23 00:50:10 2006 UTC