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

Comparing IO-AIO/AIO.pm (file contents):
Revision 1.2 by root, Sun Jul 10 18:16:49 2005 UTC vs.
Revision 1.72 by root, Tue Oct 24 14:25:53 2006 UTC

…		…
3	IO::AIO - Asynchronous Input/Output	3	IO::AIO - Asynchronous Input/Output
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	use IO::AIO;	7	use IO::AIO;
		8
		9	aio_open "/etc/passwd", O_RDONLY, 0, sub {
		10	my ($fh) = @_;
		11	...
		12	};
		13
		14	aio_unlink "/tmp/file", sub { };
		15
		16	aio_read $fh, 30000, 1024, $buffer, 0, sub {
		17	$_[0] > 0 or die "read error: $!";
		18	};
		19
		20	# 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
		35	Event->io (fd => IO::AIO::poll_fileno,
		36	poll => 'r',
		37	cb => \&IO::AIO::poll_cb);
		38
		39	# Glib/Gtk2 integration
		40	add_watch Glib::IO IO::AIO::poll_fileno,
		41	in => sub { IO::AIO::poll_cb; 1 };
		42
		43	# Tk integration
		44	Tk::Event::IO->fileevent (IO::AIO::poll_fileno, "",
		45	readable => \&IO::AIO::poll_cb);
		46
		47	# Danga::Socket integration
		48	Danga::Socket->AddOtherFds (IO::AIO::poll_fileno =>
		49	\&IO::AIO::poll_cb);
8		50
9	=head1 DESCRIPTION	51	=head1 DESCRIPTION
10		52
11	This module implements asynchronous I/O using whatever means your	53	This module implements asynchronous I/O using whatever means your
12	operating system supports.	54	operating system supports.
13		55
14	Currently, a number of threads are started that execute your read/writes	56	In this version, a number of threads are started that execute your
15	and signal their completion. You don't need thread support in your libc or	57	requests and signal their completion. You don't need thread support
16	perl, and the threads created by this module will not be visible to the	58	in perl, and the threads created by this module will not be visible
17	pthreads library. In the future, this module might make use of the native	59	to perl. In the future, this module might make use of the native aio
18	aio functions available on many operating systems. However, they are often	60	functions available on many operating systems. However, they are often
19	not well-supported (Linux doesn't allow them on normal files currently,	61	not well-supported or restricted (Linux doesn't allow them on normal
20	for example), and they would only support aio_read and aio_write, so the	62	files currently, for example), and they would only support aio_read and
21	remaining functionality would have to be implemented using threads anyway.	63	aio_write, so the remaining functionality would have to be implemented
		64	using threads anyway.
22		65
23	Although the module will work with in the presence of other threads, it is	66	Although the module will work with in the presence of other (Perl-)
24	currently not reentrant, so use appropriate locking yourself.	67	threads, it is currently not reentrant in any way, so use appropriate
		68	locking yourself, always call C<poll_cb> from within the same thread, or
		69	never call C<poll_cb> (or other C<aio_> functions) recursively.
25		70
26	=head2 API NOTES	71	=head1 REQUEST ANATOMY AND LIFETIME
		72
		73	Every C<aio_*> function creates a request. which is a C data structure not
		74	directly visible to Perl.
		75
		76	If called in non-void context, every request function returns a Perl
		77	object representing the request. In void context, nothing is returned,
		78	which saves a bit of memory.
		79
		80	The perl object is a fairly standard ref-to-hash object. The hash contents
		81	are not used by IO::AIO so you are free to store anything you like in it.
		82
		83	During their existance, aio requests travel through the following states,
		84	in order:
		85
		86	=over 4
		87
		88	=item ready
		89
		90	Immediately after a request is created it is put into the ready state,
		91	waiting for a thread to execute it.
		92
		93	=item execute
		94
		95	A thread has accepted the request for processing and is currently
		96	executing it (e.g. blocking in read).
		97
		98	=item pending
		99
		100	The request has been executed and is waiting for result processing.
		101
		102	While request submission and execution is fully asynchronous, result
		103	processing is not and relies on the perl interpreter calling C<poll_cb>
		104	(or another function with the same effect).
		105
		106	=item result
		107
		108	The request results are processed synchronously by C<poll_cb>.
		109
		110	The C<poll_cb> function will process all outstanding aio requests by
		111	calling their callbacks, freeing memory associated with them and managing
		112	any groups they are contained in.
		113
		114	=item done
		115
		116	Request has reached the end of its lifetime and holds no resources anymore
		117	(except possibly for the Perl object, but its connection to the actual
		118	aio request is severed and calling its methods will either do nothing or
		119	result in a runtime error).
		120
		121	=cut
		122
		123	package IO::AIO;
		124
		125	no warnings;
		126	use strict 'vars';
		127
		128	use base 'Exporter';
		129
		130	BEGIN {
		131	our $VERSION = '2.0';
		132
		133	our @AIO_REQ = qw(aio_sendfile aio_read aio_write aio_open aio_close aio_stat
		134	aio_lstat aio_unlink aio_rmdir aio_readdir aio_scandir aio_symlink
		135	aio_fsync aio_fdatasync aio_readahead aio_rename aio_link aio_move
		136	aio_group aio_nop);
		137	our @EXPORT = (@AIO_REQ, qw(aioreq_pri aioreq_nice));
		138	our @EXPORT_OK = qw(poll_fileno poll_cb poll_wait flush
		139	min_parallel max_parallel max_outstanding nreqs);
		140
		141	@IO::AIO::GRP::ISA = 'IO::AIO::REQ';
		142
		143	require XSLoader;
		144	XSLoader::load ("IO::AIO", $VERSION);
		145	}
		146
		147	=head1 FUNCTIONS
		148
		149	=head2 AIO FUNCTIONS
27		150
28	All the C<aio_*> calls are more or less thin wrappers around the syscall	151	All the C<aio_*> calls are more or less thin wrappers around the syscall
29	with the same name (sans C<aio_>). The arguments are similar or identical,	152	with the same name (sans C<aio_>). The arguments are similar or identical,
30	and they all accept an additional C<$callback> argument which must be	153	and they all accept an additional (and optional) C<$callback> argument
31	a code reference. This code reference will get called with the syscall	154	which must be a code reference. This code reference will get called with
32	return code (e.g. most syscalls return C<-1> on error, unlike perl, which	155	the syscall return code (e.g. most syscalls return C<-1> on error, unlike
33	usually delivers "false") as it's sole argument when the given syscall has	156	perl, which usually delivers "false") as it's sole argument when the given
34	been executed asynchronously.	157	syscall has been executed asynchronously.
35		158
36	All functions that expect a filehandle will also accept a file descriptor.	159	All functions expecting a filehandle keep a copy of the filehandle
		160	internally until the request has finished.
37		161
		162	All requests return objects of type L<IO::AIO::REQ> that allow further
		163	manipulation of those requests while they are in-flight.
		164
38	The filenames you pass to these routines I<must> be absolute. The reason	165	The pathnames you pass to these routines I<must> be absolute and
39	is that at the time the request is being executed, the current working	166	encoded in byte form. The reason for the former is that at the time the
40	directory could have changed. Alternatively, you can make sure that you	167	request is being executed, the current working directory could have
		168	changed. Alternatively, you can make sure that you never change the
41	never change the current working directory.	169	current working directory.
		170
		171	To encode pathnames to byte form, either make sure you either: a)
		172	always pass in filenames you got from outside (command line, readdir
		173	etc.), b) are ASCII or ISO 8859-1, c) use the Encode module and encode
		174	your pathnames to the locale (or other) encoding in effect in the user
		175	environment, d) use Glib::filename_from_unicode on unicode filenames or e)
		176	use something else.
42		177
43	=over 4	178	=over 4
44		179
45	=cut	180	=item aioreq_pri $pri
46		181
47	package IO::AIO;	182	Sets the priority for the next aio request. The default priority
		183	is C<0>, the minimum and maximum priorities are C<-4> and C<4>,
		184	respectively. Requests with higher priority will be serviced first.
48		185
49	use base 'Exporter';	186	The priority will be reset to C<0> after each call to one of the C<aio_>
		187	functions.
50		188
51	use Fcntl ();	189	Example: open a file with low priority, then read something from it with
		190	higher priority so the read request is serviced before other low priority
		191	open requests (potentially spamming the cache):
52		192
53	BEGIN {	193	aioreq_pri -3;
54	$VERSION = 0.1;	194	aio_open ..., sub {
		195	return unless $_[0];
55		196
56	@EXPORT = qw(aio_read aio_write aio_open aio_close aio_stat aio_lstat aio_unlink	197	aioreq_pri -2;
57	aio_fsync aio_fdatasync aio_readahead);	198	aio_read $_[0], ..., sub {
58	@EXPORT_OK = qw(poll_fileno poll_cb min_parallel max_parallel nreqs);	199	...
		200	};
		201	};
59		202
60	require XSLoader;	203	=item aioreq_nice $pri_adjust
61	XSLoader::load IO::AIO, $VERSION;
62	}
63		204
64	=item IO::AIO::min_parallel $nthreads	205	Similar to C<aioreq_pri>, but subtracts the given value from the current
		206	priority, so effects are cumulative.
65		207
66	Set the minimum number of AIO threads to C<$nthreads>. The default is
67	C<1>, which means a single asynchronous operation can be done at one time
68	(the number of outstanding operations, however, is unlimited).
69
70	It is recommended to keep the number of threads low, as some linux
71	kernel versions will scale negatively with the number of threads (higher
72	parallelity => MUCH higher latency).
73
74	Under normal circumstances you don't need to call this function, as this
75	module automatically starts a single async thread.
76
77	=item IO::AIO::max_parallel $nthreads
78
79	Sets the maximum number of AIO threads to C<$nthreads>. If more than
80	the specified number of threads are currently running, kill them. This
81	function blocks until the limit is reached.
82
83	This module automatically runs C<max_parallel 0> at program end, to ensure
84	that all threads are killed and that there are no outstanding requests.
85
86	Under normal circumstances you don't need to call this function.
87
88	=item $fileno = IO::AIO::poll_fileno
89
90	Return the I<request result pipe filehandle>. This filehandle must be
91	polled for reading by some mechanism outside this module (e.g. Event
92	or select, see below). If the pipe becomes readable you have to call
93	C<poll_cb> to check the results.
94
95	See C<poll_cb> for an example.
96
97	=item IO::AIO::poll_cb
98
99	Process all outstanding events on the result pipe. You have to call this
100	regularly. Returns the number of events processed. Returns immediately
101	when no events are outstanding.
102
103	You can use Event to multiplex, e.g.:
104
105	Event->io (fd => IO::AIO::poll_fileno,
106	poll => 'r', async => 1,
107	cb => \&IO::AIO::poll_cb);
108
109	=item IO::AIO::poll_wait
110
111	Wait till the result filehandle becomes ready for reading (simply does a
112	select on the filehandle. This is useful if you want to synchronously wait
113	for some requests to finish).
114
115	See C<nreqs> for an example.
116
117	=item IO::AIO::nreqs
118
119	Returns the number of requests currently outstanding.
120
121	Example: wait till there are no outstanding requests anymore:
122
123	IO::AIO::poll_wait, IO::AIO::poll_cb
124	while IO::AIO::nreqs;
125
126	=item aio_open $pathname, $flags, $mode, $callback	208	=item aio_open $pathname, $flags, $mode, $callback->($fh)
127		209
128	Asynchronously open or create a file and call the callback with a newly	210	Asynchronously open or create a file and call the callback with a newly
129	created filehandle for the file.	211	created filehandle for the file.
130		212
131	The pathname passed to C<aio_open> must be absolute. See API NOTES, above,	213	The pathname passed to C<aio_open> must be absolute. See API NOTES, above,
132	for an explanation.	214	for an explanation.
133		215
134	The C<$mode> argument is a bitmask. See the C<Fcntl> module for a	216	The C<$flags> argument is a bitmask. See the C<Fcntl> module for a
135	list. They are the same as used in C<sysopen>.	217	list. They are the same as used by C<sysopen>.
		218
		219	Likewise, C<$mode> specifies the mode of the newly created file, if it
		220	didn't exist and C<O_CREAT> has been given, just like perl's C<sysopen>,
		221	except that it is mandatory (i.e. use C<0> if you don't create new files,
		222	and C<0666> or C<0777> if you do).
136		223
137	Example:	224	Example:
138		225
139	aio_open "/etc/passwd", O_RDONLY, 0, sub {	226	aio_open "/etc/passwd", O_RDONLY, 0, sub {
140	if ($_[0]) {	227	if ($_[0]) {
…		…
143	} else {	230	} else {
144	die "open failed: $!\n";	231	die "open failed: $!\n";
145	}	232	}
146	};	233	};
147		234
148	=item aio_close $fh, $callback	235	=item aio_close $fh, $callback->($status)
149		236
150	Asynchronously close a file and call the callback with the result	237	Asynchronously close a file and call the callback with the result
151	code. I<WARNING:> although accepted, you should not pass in a perl	238	code. I<WARNING:> although accepted, you should not pass in a perl
152	filehandle here, as perl will likely close the file descriptor itself when	239	filehandle here, as perl will likely close the file descriptor another
153	the filehandle is destroyed. Normally, you can safely call perls C<close>	240	time when the filehandle is destroyed. Normally, you can safely call perls
154	or just let filehandles go out of scope.	241	C<close> or just let filehandles go out of scope.
155		242
		243	This is supposed to be a bug in the API, so that might change. It's
		244	therefore best to avoid this function.
		245
156	=item aio_read $fh,$offset,$length, $data,$dataoffset,$callback	246	=item aio_read $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
157		247
158	=item aio_write $fh,$offset,$length, $data,$dataoffset,$callback	248	=item aio_write $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
159		249
160	Reads or writes C<length> bytes from the specified C<fh> and C<offset>	250	Reads or writes C<length> bytes from the specified C<fh> and C<offset>
161	into the scalar given by C<data> and offset C<dataoffset> and calls the	251	into the scalar given by C<data> and offset C<dataoffset> and calls the
162	callback without the actual number of bytes read (or -1 on error, just	252	callback without the actual number of bytes read (or -1 on error, just
163	like the syscall).	253	like the syscall).
164		254
		255	The C<$data> scalar I<MUST NOT> be modified in any way while the request
		256	is outstanding. Modifying it can result in segfaults or WW3 (if the
		257	necessary/optional hardware is installed).
		258
165	Example: Read 15 bytes at offset 7 into scalar C<$buffer>, strating at	259	Example: Read 15 bytes at offset 7 into scalar C<$buffer>, starting at
166	offset C<0> within the scalar:	260	offset C<0> within the scalar:
167		261
168	aio_read $fh, 7, 15, $buffer, 0, sub {	262	aio_read $fh, 7, 15, $buffer, 0, sub {
169	$_[0] >= 0 or die "read error: $!";	263	$_[0] > 0 or die "read error: $!";
170	print "read <$buffer>\n";	264	print "read $_[0] bytes: <$buffer>\n";
171	};	265	};
172		266
		267	=item aio_move $srcpath, $dstpath, $callback->($status)
		268
		269	Try to move the I<file> (directories not supported as either source or
		270	destination) from C<$srcpath> to C<$dstpath> and call the callback with
		271	the C<0> (error) or C<-1> ok.
		272
		273	This is a composite request that tries to rename(2) the file first. If
		274	rename files with C<EXDEV>, it creates the destination file with mode 0200
		275	and copies the contents of the source file into it using C<aio_sendfile>,
		276	followed by restoring atime, mtime, access mode and uid/gid, in that
		277	order, and unlinking the C<$srcpath>.
		278
		279	If an error occurs, the partial destination file will be unlinked, if
		280	possible, except when setting atime, mtime, access mode and uid/gid, where
		281	errors are being ignored.
		282
		283	=cut
		284
		285	sub aio_move($$$) {
		286	my ($src, $dst, $cb) = @_;
		287
		288	my $grp = aio_group $cb;
		289
		290	add $grp aio_rename $src, $dst, sub {
		291	if ($_[0] && $! == EXDEV) {
		292	add $grp aio_open $src, O_RDONLY, 0, sub {
		293	if (my $src_fh = $_[0]) {
		294	my @stat = stat $src_fh;
		295
		296	add $grp aio_open $dst, O_WRONLY, 0200, sub {
		297	if (my $dst_fh = $_[0]) {
		298	add $grp aio_sendfile $dst_fh, $src_fh, 0, $stat[7], sub {
		299	close $src_fh;
		300
		301	if ($_[0] == $stat[7]) {
		302	utime $stat[8], $stat[9], $dst;
		303	chmod $stat[2] & 07777, $dst_fh;
		304	chown $stat[4], $stat[5], $dst_fh;
		305	close $dst_fh;
		306
		307	add $grp aio_unlink $src, sub {
		308	$grp->result ($_[0]);
		309	};
		310	} else {
		311	my $errno = $!;
		312	add $grp aio_unlink $dst, sub {
		313	$! = $errno;
		314	$grp->result (-1);
		315	};
		316	}
		317	};
		318	} else {
		319	$grp->result (-1);
		320	}
		321	},
		322
		323	} else {
		324	$grp->result (-1);
		325	}
		326	};
		327	} else {
		328	$grp->result ($_[0]);
		329	}
		330	};
		331
		332	$grp
		333	}
		334
		335	=item aio_sendfile $out_fh, $in_fh, $in_offset, $length, $callback->($retval)
		336
		337	Tries to copy C<$length> bytes from C<$in_fh> to C<$out_fh>. It starts
		338	reading at byte offset C<$in_offset>, and starts writing at the current
		339	file offset of C<$out_fh>. Because of that, it is not safe to issue more
		340	than one C<aio_sendfile> per C<$out_fh>, as they will interfere with each
		341	other.
		342
		343	This call tries to make use of a native C<sendfile> syscall to provide
		344	zero-copy operation. For this to work, C<$out_fh> should refer to a
		345	socket, and C<$in_fh> should refer to mmap'able file.
		346
		347	If the native sendfile call fails or is not implemented, it will be
		348	emulated, so you can call C<aio_sendfile> on any type of filehandle
		349	regardless of the limitations of the operating system.
		350
		351	Please note, however, that C<aio_sendfile> can read more bytes from
		352	C<$in_fh> than are written, and there is no way to find out how many
		353	bytes have been read from C<aio_sendfile> alone, as C<aio_sendfile> only
		354	provides the number of bytes written to C<$out_fh>. Only if the result
		355	value equals C<$length> one can assume that C<$length> bytes have been
		356	read.
		357
173	=item aio_readahead $fh,$offset,$length, $callback	358	=item aio_readahead $fh,$offset,$length, $callback->($retval)
174		359
175	Asynchronously reads the specified byte range into the page cache, using
176	the C<readahead> syscall. If that syscall doesn't exist the status will be
177	C<-1> and C<$!> is set to ENOSYS.
178
179	readahead() populates the page cache with data from a file so that	360	C<aio_readahead> populates the page cache with data from a file so that
180	subsequent reads from that file will not block on disk I/O. The C<$offset>	361	subsequent reads from that file will not block on disk I/O. The C<$offset>
181	argument specifies the starting point from which data is to be read and	362	argument specifies the starting point from which data is to be read and
182	C<$length> specifies the number of bytes to be read. I/O is performed in	363	C<$length> specifies the number of bytes to be read. I/O is performed in
183	whole pages, so that offset is effectively rounded down to a page boundary	364	whole pages, so that offset is effectively rounded down to a page boundary
184	and bytes are read up to the next page boundary greater than or equal to	365	and bytes are read up to the next page boundary greater than or equal to
185	(off-set+length). aio_readahead() does not read beyond the end of the	366	(off-set+length). C<aio_readahead> does not read beyond the end of the
186	file. The current file offset of the file is left unchanged.	367	file. The current file offset of the file is left unchanged.
187		368
		369	If that syscall doesn't exist (likely if your OS isn't Linux) it will be
		370	emulated by simply reading the data, which would have a similar effect.
		371
188	=item aio_stat $fh_or_path, $callback	372	=item aio_stat $fh_or_path, $callback->($status)
189		373
190	=item aio_lstat $fh, $callback	374	=item aio_lstat $fh, $callback->($status)
191		375
192	Works like perl's C<stat> or C<lstat> in void context. The callback will	376	Works like perl's C<stat> or C<lstat> in void context. The callback will
193	be called after the stat and the results will be available using C<stat _>	377	be called after the stat and the results will be available using C<stat _>
194	or C<-s _> etc...	378	or C<-s _> etc...
195		379
…		…
205	aio_stat "/etc/passwd", sub {	389	aio_stat "/etc/passwd", sub {
206	$_[0] and die "stat failed: $!";	390	$_[0] and die "stat failed: $!";
207	print "size is ", -s _, "\n";	391	print "size is ", -s _, "\n";
208	};	392	};
209		393
210	=item aio_unlink $pathname, $callback	394	=item aio_unlink $pathname, $callback->($status)
211		395
212	Asynchronously unlink (delete) a file and call the callback with the	396	Asynchronously unlink (delete) a file and call the callback with the
213	result code.	397	result code.
214		398
		399	=item aio_link $srcpath, $dstpath, $callback->($status)
		400
		401	Asynchronously create a new link to the existing object at C<$srcpath> at
		402	the path C<$dstpath> and call the callback with the result code.
		403
		404	=item aio_symlink $srcpath, $dstpath, $callback->($status)
		405
		406	Asynchronously create a new symbolic link to the existing object at C<$srcpath> at
		407	the path C<$dstpath> and call the callback with the result code.
		408
		409	=item aio_rename $srcpath, $dstpath, $callback->($status)
		410
		411	Asynchronously rename the object at C<$srcpath> to C<$dstpath>, just as
		412	rename(2) and call the callback with the result code.
		413
		414	=item aio_rmdir $pathname, $callback->($status)
		415
		416	Asynchronously rmdir (delete) a directory and call the callback with the
		417	result code.
		418
		419	=item aio_readdir $pathname, $callback->($entries)
		420
		421	Unlike the POSIX call of the same name, C<aio_readdir> reads an entire
		422	directory (i.e. opendir + readdir + closedir). The entries will not be
		423	sorted, and will B<NOT> include the C<.> and C<..> entries.
		424
		425	The callback a single argument which is either C<undef> or an array-ref
		426	with the filenames.
		427
		428	=item aio_scandir $path, $maxreq, $callback->($dirs, $nondirs)
		429
		430	Scans a directory (similar to C<aio_readdir>) but additionally tries to
		431	separate the entries of directory C<$path> into two sets of names, ones
		432	you can recurse into (directories or links to them), and ones you cannot
		433	recurse into (everything else).
		434
		435	C<aio_scandir> is a composite request that creates of many sub requests_
		436	C<$maxreq> specifies the maximum number of outstanding aio requests that
		437	this function generates. If it is C<< <= 0 >>, then a suitable default
		438	will be chosen (currently 6).
		439
		440	On error, the callback is called without arguments, otherwise it receives
		441	two array-refs with path-relative entry names.
		442
		443	Example:
		444
		445	aio_scandir $dir, 0, sub {
		446	my ($dirs, $nondirs) = @_;
		447	print "real directories: @$dirs\n";
		448	print "everything else: @$nondirs\n";
		449	};
		450
		451	Implementation notes.
		452
		453	The C<aio_readdir> cannot be avoided, but C<stat()>'ing every entry can.
		454
		455	After reading the directory, the modification time, size etc. of the
		456	directory before and after the readdir is checked, and if they match (and
		457	isn't the current time), the link count will be used to decide how many
		458	entries are directories (if >= 2). Otherwise, no knowledge of the number
		459	of subdirectories will be assumed.
		460
		461	Then entries will be sorted into likely directories (everything without
		462	a non-initial dot currently) and likely non-directories (everything
		463	else). Then every entry plus an appended C</.> will be C<stat>'ed,
		464	likely directories first. If that succeeds, it assumes that the entry
		465	is a directory or a symlink to directory (which will be checked
		466	seperately). This is often faster than stat'ing the entry itself because
		467	filesystems might detect the type of the entry without reading the inode
		468	data (e.g. ext2fs filetype feature).
		469
		470	If the known number of directories (link count - 2) has been reached, the
		471	rest of the entries is assumed to be non-directories.
		472
		473	This only works with certainty on POSIX (= UNIX) filesystems, which
		474	fortunately are the vast majority of filesystems around.
		475
		476	It will also likely work on non-POSIX filesystems with reduced efficiency
		477	as those tend to return 0 or 1 as link counts, which disables the
		478	directory counting heuristic.
		479
		480	=cut
		481
		482	sub aio_scandir($$$) {
		483	my ($path, $maxreq, $cb) = @_;
		484
		485	my $grp = aio_group $cb;
		486
		487	$maxreq = 6 if $maxreq <= 0;
		488
		489	# stat once
		490	add $grp aio_stat $path, sub {
		491	return $grp->result () if $_[0];
		492	my $now = time;
		493	my $hash1 = join ":", (stat _)[0,1,3,7,9];
		494
		495	# read the directory entries
		496	add $grp aio_readdir $path, sub {
		497	my $entries = shift
		498	or return $grp->result ();
		499
		500	# stat the dir another time
		501	add $grp aio_stat $path, sub {
		502	my $hash2 = join ":", (stat _)[0,1,3,7,9];
		503
		504	my $ndirs;
		505
		506	# take the slow route if anything looks fishy
		507	if ($hash1 ne $hash2 or (stat _)[9] == $now) {
		508	$ndirs = -1;
		509	} else {
		510	# if nlink == 2, we are finished
		511	# on non-posix-fs's, we rely on nlink < 2
		512	$ndirs = (stat _)[3] - 2
		513	or return $grp->result ([], $entries);
		514	}
		515
		516	# sort into likely dirs and likely nondirs
		517	# dirs == files without ".", short entries first
		518	$entries = [map $_->[0],
		519	sort { $b->[1] cmp $a->[1] }
		520	map [$_, sprintf "%s%04d", (/.\./ ? "1" : "0"), length],
		521	@$entries];
		522
		523	my (@dirs, @nondirs);
		524
		525	my ($statcb, $schedcb);
		526	my $nreq = 0;
		527
		528	my $statgrp = add $grp aio_group;
		529
		530	$schedcb = sub {
		531	if (@$entries) {
		532	if ($nreq < $maxreq) {
		533	my $ent = pop @$entries;
		534	$nreq++;
		535	add $statgrp aio_stat "$path/$ent/.", sub { $statcb->($_[0], $ent) };
		536	}
		537	} elsif (!$nreq) {
		538	# finished
		539	$statgrp->cancel;
		540	undef $statcb;
		541	undef $schedcb;
		542	$grp->result (\@dirs, \@nondirs);
		543	}
		544	};
		545	$statcb = sub {
		546	my ($status, $entry) = @_;
		547
		548	if ($status < 0) {
		549	$nreq--;
		550	push @nondirs, $entry;
		551	&$schedcb;
		552	} else {
		553	# need to check for real directory
		554	add $grp aio_lstat "$path/$entry", sub {
		555	$nreq--;
		556
		557	if (-d _) {
		558	push @dirs, $entry;
		559
		560	if (!--$ndirs) {
		561	push @nondirs, @$entries;
		562	$entries = [];
		563	}
		564	} else {
		565	push @nondirs, $entry;
		566	}
		567
		568	&$schedcb;
		569	}
		570	}
		571	};
		572
		573	&$schedcb while @$entries && $nreq < $maxreq;
		574	};
		575	};
		576	};
		577
		578	$grp
		579	}
		580
215	=item aio_fsync $fh, $callback	581	=item aio_fsync $fh, $callback->($status)
216		582
217	Asynchronously call fsync on the given filehandle and call the callback	583	Asynchronously call fsync on the given filehandle and call the callback
218	with the fsync result code.	584	with the fsync result code.
219		585
220	=item aio_fdatasync $fh, $callback	586	=item aio_fdatasync $fh, $callback->($status)
221		587
222	Asynchronously call fdatasync on the given filehandle and call the	588	Asynchronously call fdatasync on the given filehandle and call the
223	callback with the fdatasync result code.	589	callback with the fdatasync result code.
		590
		591	If this call isn't available because your OS lacks it or it couldn't be
		592	detected, it will be emulated by calling C<fsync> instead.
		593
		594	=item aio_group $callback->(...)
		595
		596	[EXPERIMENTAL]
		597
		598	This is a very special aio request: Instead of doing something, it is a
		599	container for other aio requests, which is useful if you want to bundle
		600	many requests into a single, composite, request with a definite callback
		601	and the ability to cancel the whole request with its subrequests.
		602
		603	Returns an object of class L<IO::AIO::GRP>. See its documentation below
		604	for more info.
		605
		606	Example:
		607
		608	my $grp = aio_group sub {
		609	print "all stats done\n";
		610	};
		611
		612	add $grp
		613	(aio_stat ...),
		614	(aio_stat ...),
		615	...;
		616
		617	=item aio_nop $callback->()
		618
		619	This is a special request - it does nothing in itself and is only used for
		620	side effects, such as when you want to add a dummy request to a group so
		621	that finishing the requests in the group depends on executing the given
		622	code.
		623
		624	While this request does nothing, it still goes through the execution
		625	phase and still requires a worker thread. Thus, the callback will not
		626	be executed immediately but only after other requests in the queue have
		627	entered their execution phase. This can be used to measure request
		628	latency.
		629
		630	=item IO::AIO::aio_busy $fractional_seconds, $callback->() NOT EXPORTED
		631
		632	Mainly used for debugging and benchmarking, this aio request puts one of
		633	the request workers to sleep for the given time.
		634
		635	While it is theoretically handy to have simple I/O scheduling requests
		636	like sleep and file handle readable/writable, the overhead this creates is
		637	immense (it blocks a thread for a long time) so do not use this function
		638	except to put your application under artificial I/O pressure.
		639
		640	=back
		641
		642	=head2 IO::AIO::REQ CLASS
		643
		644	All non-aggregate C<aio_*> functions return an object of this class when
		645	called in non-void context.
		646
		647	=over 4
		648
		649	=item cancel $req
		650
		651	Cancels the request, if possible. Has the effect of skipping execution
		652	when entering the B<execute> state and skipping calling the callback when
		653	entering the the B<result> state, but will leave the request otherwise
		654	untouched. That means that requests that currently execute will not be
		655	stopped and resources held by the request will not be freed prematurely.
		656
		657	=item cb $req $callback->(...)
		658
		659	Replace (or simply set) the callback registered to the request.
		660
		661	=back
		662
		663	=head2 IO::AIO::GRP CLASS
		664
		665	This class is a subclass of L<IO::AIO::REQ>, so all its methods apply to
		666	objects of this class, too.
		667
		668	A IO::AIO::GRP object is a special request that can contain multiple other
		669	aio requests.
		670
		671	You create one by calling the C<aio_group> constructing function with a
		672	callback that will be called when all contained requests have entered the
		673	C<done> state:
		674
		675	my $grp = aio_group sub {
		676	print "all requests are done\n";
		677	};
		678
		679	You add requests by calling the C<add> method with one or more
		680	C<IO::AIO::REQ> objects:
		681
		682	$grp->add (aio_unlink "...");
		683
		684	add $grp aio_stat "...", sub {
		685	$_[0] or return $grp->result ("error");
		686
		687	# add another request dynamically, if first succeeded
		688	add $grp aio_open "...", sub {
		689	$grp->result ("ok");
		690	};
		691	};
		692
		693	This makes it very easy to create composite requests (see the source of
		694	C<aio_move> for an application) that work and feel like simple requests.
		695
		696	=over 4
		697
		698	=item * The IO::AIO::GRP objects will be cleaned up during calls to
		699	C<IO::AIO::poll_cb>, just like any other request.
		700
		701	=item * They can be canceled like any other request. Canceling will cancel not
		702	only the request itself, but also all requests it contains.
		703
		704	=item * They can also can also be added to other IO::AIO::GRP objects.
		705
		706	=item * You must not add requests to a group from within the group callback (or
		707	any later time).
		708
		709	=item * This does not harmonise well with C<max_outstanding>, so best do
		710	not combine C<aio_group> with it. Groups and feeders are recommended for
		711	this kind of concurrency-limiting.
		712
		713	=back
		714
		715	Their lifetime, simplified, looks like this: when they are empty, they
		716	will finish very quickly. If they contain only requests that are in the
		717	C<done> state, they will also finish. Otherwise they will continue to
		718	exist.
		719
		720	That means after creating a group you have some time to add requests. And
		721	in the callbacks of those requests, you can add further requests to the
		722	group. And only when all those requests have finished will the the group
		723	itself finish.
		724
		725	=over 4
		726
		727	=item add $grp ...
		728
		729	=item $grp->add (...)
		730
		731	Add one or more requests to the group. Any type of L<IO::AIO::REQ> can
		732	be added, including other groups, as long as you do not create circular
		733	dependencies.
		734
		735	Returns all its arguments.
		736
		737	=item $grp->result (...)
		738
		739	Set the result value(s) that will be passed to the group callback when all
		740	subrequests have finished. By default, no argument will be passed.
		741
		742	=item feed $grp $callback->($grp)
		743
		744	[VERY EXPERIMENTAL]
		745
		746	Sets a feeder/generator on this group: every group can have an attached
		747	generator that generates requests if idle. The idea behind this is that,
		748	although you could just queue as many requests as you want in a group,
		749	this might starve other requests for a potentially long time. For
		750	example, C<aio_scandir> might generate hundreds of thousands C<aio_stat>
		751	requests, delaying any later requests for a long time.
		752
		753	To avoid this, and allow incremental generation of requests, you can
		754	instead a group and set a feeder on it that generates those requests. The
		755	feed callback will be called whenever there are few enough (see C<limit>,
		756	below) requests active in the group itself and is expected to queue more
		757	requests.
		758
		759	The feed callback can queue as many requests as it likes (i.e. C<add> does
		760	not impose any limits).
		761
		762	If the feed does not queue more requests when called, it will be
		763	automatically removed from the group.
		764
		765	If the feed limit is C<0>, it will be set to C<2> automatically.
		766
		767	Example:
		768
		769	# stat all files in @files, but only ever use four aio requests concurrently:
		770
		771	my $grp = aio_group sub { print "finished\n" };
		772	limit $grp 4;
		773	feed $grp sub {
		774	my $file = pop @files
		775	or return;
		776
		777	add $grp aio_stat $file, sub { ... };
		778	};
		779
		780	=item limit $grp $num
		781
		782	Sets the feeder limit for the group: The feeder will be called whenever
		783	the group contains less than this many requests.
		784
		785	Setting the limit to C<0> will pause the feeding process.
		786
		787	=back
		788
		789	=head2 SUPPORT FUNCTIONS
		790
		791	=over 4
		792
		793	=item $fileno = IO::AIO::poll_fileno
		794
		795	Return the I<request result pipe file descriptor>. This filehandle must be
		796	polled for reading by some mechanism outside this module (e.g. Event or
		797	select, see below or the SYNOPSIS). If the pipe becomes readable you have
		798	to call C<poll_cb> to check the results.
		799
		800	See C<poll_cb> for an example.
		801
		802	=item IO::AIO::poll_cb
		803
		804	Process all outstanding events on the result pipe. You have to call this
		805	regularly. Returns the number of events processed. Returns immediately
		806	when no events are outstanding.
		807
		808	Example: Install an Event watcher that automatically calls
		809	IO::AIO::poll_cb with high priority:
		810
		811	Event->io (fd => IO::AIO::poll_fileno,
		812	poll => 'r', async => 1,
		813	cb => \&IO::AIO::poll_cb);
		814
		815	=item IO::AIO::poll_wait
		816
		817	Wait till the result filehandle becomes ready for reading (simply does a
		818	C<select> on the filehandle. This is useful if you want to synchronously wait
		819	for some requests to finish).
		820
		821	See C<nreqs> for an example.
		822
		823	=item IO::AIO::nreqs
		824
		825	Returns the number of requests currently outstanding (i.e. for which their
		826	callback has not been invoked yet).
		827
		828	Example: wait till there are no outstanding requests anymore:
		829
		830	IO::AIO::poll_wait, IO::AIO::poll_cb
		831	while IO::AIO::nreqs;
		832
		833	=item IO::AIO::flush
		834
		835	Wait till all outstanding AIO requests have been handled.
		836
		837	Strictly equivalent to:
		838
		839	IO::AIO::poll_wait, IO::AIO::poll_cb
		840	while IO::AIO::nreqs;
		841
		842	=item IO::AIO::poll
		843
		844	Waits until some requests have been handled.
		845
		846	Strictly equivalent to:
		847
		848	IO::AIO::poll_wait, IO::AIO::poll_cb
		849	if IO::AIO::nreqs;
		850
		851	=item IO::AIO::min_parallel $nthreads
		852
		853	Set the minimum number of AIO threads to C<$nthreads>. The current
		854	default is C<8>, which means eight asynchronous operations can execute
		855	concurrently at any one time (the number of outstanding requests,
		856	however, is unlimited).
		857
		858	IO::AIO starts threads only on demand, when an AIO request is queued and
		859	no free thread exists.
		860
		861	It is recommended to keep the number of threads relatively low, as some
		862	Linux kernel versions will scale negatively with the number of threads
		863	(higher parallelity => MUCH higher latency). With current Linux 2.6
		864	versions, 4-32 threads should be fine.
		865
		866	Under most circumstances you don't need to call this function, as the
		867	module selects a default that is suitable for low to moderate load.
		868
		869	=item IO::AIO::max_parallel $nthreads
		870
		871	Sets the maximum number of AIO threads to C<$nthreads>. If more than the
		872	specified number of threads are currently running, this function kills
		873	them. This function blocks until the limit is reached.
		874
		875	While C<$nthreads> are zero, aio requests get queued but not executed
		876	until the number of threads has been increased again.
		877
		878	This module automatically runs C<max_parallel 0> at program end, to ensure
		879	that all threads are killed and that there are no outstanding requests.
		880
		881	Under normal circumstances you don't need to call this function.
		882
		883	=item $oldnreqs = IO::AIO::max_outstanding $nreqs
		884
		885	[DEPRECATED]
		886
		887	Sets the maximum number of outstanding requests to C<$nreqs>. If you
		888	try to queue up more than this number of requests, the caller will block until
		889	some requests have been handled.
		890
		891	The default is very large, so normally there is no practical limit. If you
		892	queue up many requests in a loop it often improves speed if you set
		893	this to a relatively low number, such as C<100>.
		894
		895	This function does not work well together with C<aio_group>'s, and their
		896	feeder interface is better suited to limiting concurrency, so do not use
		897	this function.
		898
		899	Under normal circumstances you don't need to call this function.
		900
		901	=back
224		902
225	=cut	903	=cut
226		904
227	# support function to convert a fd into a perl filehandle	905	# support function to convert a fd into a perl filehandle
228	sub _fd2fh {	906	sub _fd2fh {
229	return undef if $_[0] < 0;	907	return undef if $_[0] < 0;
230		908
231	# try to be perl5.6-compatible	909	# try to generate nice filehandles
232	local *AIO_FH;	910	my $sym = "IO::AIO::fd#$_[0]";
233	open AIO_FH, "+<&=$_[0]"	911	local *$sym;
		912
		913	open *$sym, "+<&=$_[0]" # usually works under any unix
		914	or open *$sym, "<&=$_[0]" # cygwin needs this
		915	or open *$sym, ">&=$_[0]" # or this
234	or return undef;	916	or return undef;
235		917
236	*AIO_FH	918	*$sym
237	}	919	}
238		920
239	min_parallel 4;	921	min_parallel 8;
240		922
241	END {	923	END {
242	max_parallel 0;	924	max_parallel 0;
243	}	925	}
244		926
245	1;	927	1;
246		928
247	=back	929	=head2 FORK BEHAVIOUR
248		930
		931	This module should do "the right thing" when the process using it forks:
		932
		933	Before the fork, IO::AIO enters a quiescent state where no requests
		934	can be added in other threads and no results will be processed. After
		935	the fork the parent simply leaves the quiescent state and continues
		936	request/result processing, while the child frees the request/result queue
		937	(so that the requests started before the fork will only be handled in the
		938	parent). Threads will be started on demand until the limit set in the
		939	parent process has been reached again.
		940
		941	Temporary memory that was allocated for request processing is not
		942	reclaimed in the child, however. While this is possible in some cases, it
		943	is almost impossible in others (threads are evil you know), so you will
		944	have to live with it. This is around 64k buffer (for sendfile, readahead
		945	emulation) + the size of the directory being scanned (readdir).
		946
		947	In short: the parent will, after a short pause, continue as if fork had
		948	not been called, while the child will act as if IO::AIO has not been used
		949	yet.
		950
		951	=head2 MEMORY USAGE
		952
		953	Per-request usage:
		954
		955	Each aio request uses - depending on your architecture - around 100-200
		956	bytes of memory. In addition, stat requests need a stat buffer (possibly
		957	a few hundred bytes), readdir requires a result buffer and so on. Perl
		958	scalars and other data passed into aio requests will also be locked and
		959	will consume memory till the request has entered the done state.
		960
		961	This is now awfully much, so queuing lots of requests is not usually a
		962	problem.
		963
		964	Per-thread usage:
		965
		966	In the execution phase, some aio requests require more memory for
		967	temporary buffers, and each thread requires a stack and other data
		968	structures (usually around 16k-128k, depending on the OS).
		969
249	=head1 BUGS	970	=head1 KNOWN BUGS
250		971
251	- could be optimized to use more semaphores instead of filehandles.	972	See FORK BEHAVIOUR, above.
252		973
253	=head1 SEE ALSO	974	=head1 SEE ALSO
254		975
255	L<Coro>, L<Linux::AIO>.	976	L<Coro::AIO>.
256		977
257	=head1 AUTHOR	978	=head1 AUTHOR
258		979
259	Marc Lehmann <schmorp@schmorp.de>	980	Marc Lehmann <schmorp@schmorp.de>
260	http://home.schmorp.de/	981	http://home.schmorp.de/

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Comparing IO-AIO/AIO.pm (file contents):
Revision 1.2 by root, Sun Jul 10 18:16:49 2005 UTC vs.
Revision 1.72 by root, Tue Oct 24 14:25:53 2006 UTC