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

Comparing IO-AIO/AIO.pm (file contents):
Revision 1.3 by root, Sun Jul 10 20:07:11 2005 UTC vs.
Revision 1.81 by root, Fri Oct 27 19:17:23 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 nreqs nready npending);
		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 $prev_pri = aioreq_pri [$pri]
46		181
47	package IO::AIO;	182	Returns the priority value that would be used for the next request and, if
		183	C<$pri> is given, sets the priority for the next aio request.
48		184
49	use base 'Exporter';	185	The default priority is C<0>, the minimum and maximum priorities are C<-4>
		186	and C<4>, respectively. Requests with higher priority will be serviced
		187	first.
50		188
51	use Fcntl ();	189	The priority will be reset to C<0> after each call to one of the C<aio_*>
		190	functions.
52		191
53	BEGIN {	192	Example: open a file with low priority, then read something from it with
54	$VERSION = 0.2;	193	higher priority so the read request is serviced before other low priority
		194	open requests (potentially spamming the cache):
55		195
56	@EXPORT = qw(aio_read aio_write aio_open aio_close aio_stat aio_lstat aio_unlink	196	aioreq_pri -3;
57	aio_fsync aio_fdatasync aio_readahead);	197	aio_open ..., sub {
58	@EXPORT_OK = qw(poll_fileno poll_cb min_parallel max_parallel nreqs);	198	return unless $_[0];
59		199
60	require XSLoader;	200	aioreq_pri -2;
61	XSLoader::load IO::AIO, $VERSION;	201	aio_read $_[0], ..., sub {
62	}	202	...
		203	};
		204	};
63		205
64	=item IO::AIO::min_parallel $nthreads	206	=item aioreq_nice $pri_adjust
65		207
66	Set the minimum number of AIO threads to C<$nthreads>. The default is	208	Similar to C<aioreq_pri>, but subtracts the given value from the current
67	C<1>, which means a single asynchronous operation can be done at one time	209	priority, so effects are cumulative.
68	(the number of outstanding operations, however, is unlimited).
69		210
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	211	=item aio_open $pathname, $flags, $mode, $callback->($fh)
127		212
128	Asynchronously open or create a file and call the callback with a newly	213	Asynchronously open or create a file and call the callback with a newly
129	created filehandle for the file.	214	created filehandle for the file.
130		215
131	The pathname passed to C<aio_open> must be absolute. See API NOTES, above,	216	The pathname passed to C<aio_open> must be absolute. See API NOTES, above,
132	for an explanation.	217	for an explanation.
133		218
134	The C<$mode> argument is a bitmask. See the C<Fcntl> module for a	219	The C<$flags> argument is a bitmask. See the C<Fcntl> module for a
135	list. They are the same as used in C<sysopen>.	220	list. They are the same as used by C<sysopen>.
		221
		222	Likewise, C<$mode> specifies the mode of the newly created file, if it
		223	didn't exist and C<O_CREAT> has been given, just like perl's C<sysopen>,
		224	except that it is mandatory (i.e. use C<0> if you don't create new files,
		225	and C<0666> or C<0777> if you do).
136		226
137	Example:	227	Example:
138		228
139	aio_open "/etc/passwd", O_RDONLY, 0, sub {	229	aio_open "/etc/passwd", O_RDONLY, 0, sub {
140	if ($_[0]) {	230	if ($_[0]) {
…		…
143	} else {	233	} else {
144	die "open failed: $!\n";	234	die "open failed: $!\n";
145	}	235	}
146	};	236	};
147		237
148	=item aio_close $fh, $callback	238	=item aio_close $fh, $callback->($status)
149		239
150	Asynchronously close a file and call the callback with the result	240	Asynchronously close a file and call the callback with the result
151	code. I<WARNING:> although accepted, you should not pass in a perl	241	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	242	filehandle here, as perl will likely close the file descriptor another
153	the filehandle is destroyed. Normally, you can safely call perls C<close>	243	time when the filehandle is destroyed. Normally, you can safely call perls
154	or just let filehandles go out of scope.	244	C<close> or just let filehandles go out of scope.
155		245
		246	This is supposed to be a bug in the API, so that might change. It's
		247	therefore best to avoid this function.
		248
156	=item aio_read $fh,$offset,$length, $data,$dataoffset,$callback	249	=item aio_read $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
157		250
158	=item aio_write $fh,$offset,$length, $data,$dataoffset,$callback	251	=item aio_write $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
159		252
160	Reads or writes C<length> bytes from the specified C<fh> and C<offset>	253	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	254	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	255	callback without the actual number of bytes read (or -1 on error, just
163	like the syscall).	256	like the syscall).
164		257
		258	The C<$data> scalar I<MUST NOT> be modified in any way while the request
		259	is outstanding. Modifying it can result in segfaults or WW3 (if the
		260	necessary/optional hardware is installed).
		261
165	Example: Read 15 bytes at offset 7 into scalar C<$buffer>, strating at	262	Example: Read 15 bytes at offset 7 into scalar C<$buffer>, starting at
166	offset C<0> within the scalar:	263	offset C<0> within the scalar:
167		264
168	aio_read $fh, 7, 15, $buffer, 0, sub {	265	aio_read $fh, 7, 15, $buffer, 0, sub {
169	$_[0] >= 0 or die "read error: $!";	266	$_[0] > 0 or die "read error: $!";
170	print "read <$buffer>\n";	267	print "read $_[0] bytes: <$buffer>\n";
171	};	268	};
172		269
		270	=item aio_move $srcpath, $dstpath, $callback->($status)
		271
		272	Try to move the I<file> (directories not supported as either source or
		273	destination) from C<$srcpath> to C<$dstpath> and call the callback with
		274	the C<0> (error) or C<-1> ok.
		275
		276	This is a composite request that tries to rename(2) the file first. If
		277	rename files with C<EXDEV>, it creates the destination file with mode 0200
		278	and copies the contents of the source file into it using C<aio_sendfile>,
		279	followed by restoring atime, mtime, access mode and uid/gid, in that
		280	order, and unlinking the C<$srcpath>.
		281
		282	If an error occurs, the partial destination file will be unlinked, if
		283	possible, except when setting atime, mtime, access mode and uid/gid, where
		284	errors are being ignored.
		285
		286	=cut
		287
		288	sub aio_move($$$) {
		289	my ($src, $dst, $cb) = @_;
		290
		291	my $pri = aioreq_pri;
		292	my $grp = aio_group $cb;
		293
		294	aioreq_pri $pri;
		295	add $grp aio_rename $src, $dst, sub {
		296	if ($_[0] && $! == EXDEV) {
		297	aioreq_pri $pri;
		298	add $grp aio_open $src, O_RDONLY, 0, sub {
		299	if (my $src_fh = $_[0]) {
		300	my @stat = stat $src_fh;
		301
		302	aioreq_pri $pri;
		303	add $grp aio_open $dst, O_WRONLY, 0200, sub {
		304	if (my $dst_fh = $_[0]) {
		305	aioreq_pri $pri;
		306	add $grp aio_sendfile $dst_fh, $src_fh, 0, $stat[7], sub {
		307	close $src_fh;
		308
		309	if ($_[0] == $stat[7]) {
		310	utime $stat[8], $stat[9], $dst;
		311	chmod $stat[2] & 07777, $dst_fh;
		312	chown $stat[4], $stat[5], $dst_fh;
		313	close $dst_fh;
		314
		315	aioreq_pri $pri;
		316	add $grp aio_unlink $src, sub {
		317	$grp->result ($_[0]);
		318	};
		319	} else {
		320	my $errno = $!;
		321	aioreq_pri $pri;
		322	add $grp aio_unlink $dst, sub {
		323	$! = $errno;
		324	$grp->result (-1);
		325	};
		326	}
		327	};
		328	} else {
		329	$grp->result (-1);
		330	}
		331	},
		332
		333	} else {
		334	$grp->result (-1);
		335	}
		336	};
		337	} else {
		338	$grp->result ($_[0]);
		339	}
		340	};
		341
		342	$grp
		343	}
		344
		345	=item aio_sendfile $out_fh, $in_fh, $in_offset, $length, $callback->($retval)
		346
		347	Tries to copy C<$length> bytes from C<$in_fh> to C<$out_fh>. It starts
		348	reading at byte offset C<$in_offset>, and starts writing at the current
		349	file offset of C<$out_fh>. Because of that, it is not safe to issue more
		350	than one C<aio_sendfile> per C<$out_fh>, as they will interfere with each
		351	other.
		352
		353	This call tries to make use of a native C<sendfile> syscall to provide
		354	zero-copy operation. For this to work, C<$out_fh> should refer to a
		355	socket, and C<$in_fh> should refer to mmap'able file.
		356
		357	If the native sendfile call fails or is not implemented, it will be
		358	emulated, so you can call C<aio_sendfile> on any type of filehandle
		359	regardless of the limitations of the operating system.
		360
		361	Please note, however, that C<aio_sendfile> can read more bytes from
		362	C<$in_fh> than are written, and there is no way to find out how many
		363	bytes have been read from C<aio_sendfile> alone, as C<aio_sendfile> only
		364	provides the number of bytes written to C<$out_fh>. Only if the result
		365	value equals C<$length> one can assume that C<$length> bytes have been
		366	read.
		367
173	=item aio_readahead $fh,$offset,$length, $callback	368	=item aio_readahead $fh,$offset,$length, $callback->($retval)
174		369
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	370	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>	371	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	372	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	373	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	374	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	375	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	376	(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.	377	file. The current file offset of the file is left unchanged.
187		378
		379	If that syscall doesn't exist (likely if your OS isn't Linux) it will be
		380	emulated by simply reading the data, which would have a similar effect.
		381
188	=item aio_stat $fh_or_path, $callback	382	=item aio_stat $fh_or_path, $callback->($status)
189		383
190	=item aio_lstat $fh, $callback	384	=item aio_lstat $fh, $callback->($status)
191		385
192	Works like perl's C<stat> or C<lstat> in void context. The callback will	386	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 _>	387	be called after the stat and the results will be available using C<stat _>
194	or C<-s _> etc...	388	or C<-s _> etc...
195		389
…		…
205	aio_stat "/etc/passwd", sub {	399	aio_stat "/etc/passwd", sub {
206	$_[0] and die "stat failed: $!";	400	$_[0] and die "stat failed: $!";
207	print "size is ", -s _, "\n";	401	print "size is ", -s _, "\n";
208	};	402	};
209		403
210	=item aio_unlink $pathname, $callback	404	=item aio_unlink $pathname, $callback->($status)
211		405
212	Asynchronously unlink (delete) a file and call the callback with the	406	Asynchronously unlink (delete) a file and call the callback with the
213	result code.	407	result code.
214		408
		409	=item aio_link $srcpath, $dstpath, $callback->($status)
		410
		411	Asynchronously create a new link to the existing object at C<$srcpath> at
		412	the path C<$dstpath> and call the callback with the result code.
		413
		414	=item aio_symlink $srcpath, $dstpath, $callback->($status)
		415
		416	Asynchronously create a new symbolic link to the existing object at C<$srcpath> at
		417	the path C<$dstpath> and call the callback with the result code.
		418
		419	=item aio_rename $srcpath, $dstpath, $callback->($status)
		420
		421	Asynchronously rename the object at C<$srcpath> to C<$dstpath>, just as
		422	rename(2) and call the callback with the result code.
		423
		424	=item aio_rmdir $pathname, $callback->($status)
		425
		426	Asynchronously rmdir (delete) a directory and call the callback with the
		427	result code.
		428
		429	=item aio_readdir $pathname, $callback->($entries)
		430
		431	Unlike the POSIX call of the same name, C<aio_readdir> reads an entire
		432	directory (i.e. opendir + readdir + closedir). The entries will not be
		433	sorted, and will B<NOT> include the C<.> and C<..> entries.
		434
		435	The callback a single argument which is either C<undef> or an array-ref
		436	with the filenames.
		437
		438	=item aio_scandir $path, $maxreq, $callback->($dirs, $nondirs)
		439
		440	Scans a directory (similar to C<aio_readdir>) but additionally tries to
		441	efficiently separate the entries of directory C<$path> into two sets of
		442	names, directories you can recurse into (directories), and ones you cannot
		443	recurse into (everything else, including symlinks to directories).
		444
		445	C<aio_scandir> is a composite request that creates of many sub requests_
		446	C<$maxreq> specifies the maximum number of outstanding aio requests that
		447	this function generates. If it is C<< <= 0 >>, then a suitable default
		448	will be chosen (currently 4).
		449
		450	On error, the callback is called without arguments, otherwise it receives
		451	two array-refs with path-relative entry names.
		452
		453	Example:
		454
		455	aio_scandir $dir, 0, sub {
		456	my ($dirs, $nondirs) = @_;
		457	print "real directories: @$dirs\n";
		458	print "everything else: @$nondirs\n";
		459	};
		460
		461	Implementation notes.
		462
		463	The C<aio_readdir> cannot be avoided, but C<stat()>'ing every entry can.
		464
		465	After reading the directory, the modification time, size etc. of the
		466	directory before and after the readdir is checked, and if they match (and
		467	isn't the current time), the link count will be used to decide how many
		468	entries are directories (if >= 2). Otherwise, no knowledge of the number
		469	of subdirectories will be assumed.
		470
		471	Then entries will be sorted into likely directories (everything without
		472	a non-initial dot currently) and likely non-directories (everything
		473	else). Then every entry plus an appended C</.> will be C<stat>'ed,
		474	likely directories first. If that succeeds, it assumes that the entry
		475	is a directory or a symlink to directory (which will be checked
		476	seperately). This is often faster than stat'ing the entry itself because
		477	filesystems might detect the type of the entry without reading the inode
		478	data (e.g. ext2fs filetype feature).
		479
		480	If the known number of directories (link count - 2) has been reached, the
		481	rest of the entries is assumed to be non-directories.
		482
		483	This only works with certainty on POSIX (= UNIX) filesystems, which
		484	fortunately are the vast majority of filesystems around.
		485
		486	It will also likely work on non-POSIX filesystems with reduced efficiency
		487	as those tend to return 0 or 1 as link counts, which disables the
		488	directory counting heuristic.
		489
		490	=cut
		491
		492	sub aio_scandir($$$) {
		493	my ($path, $maxreq, $cb) = @_;
		494
		495	my $pri = aioreq_pri;
		496
		497	my $grp = aio_group $cb;
		498
		499	$maxreq = 4 if $maxreq <= 0;
		500
		501	# stat once
		502	aioreq_pri $pri;
		503	add $grp aio_stat $path, sub {
		504	return $grp->result () if $_[0];
		505	my $now = time;
		506	my $hash1 = join ":", (stat _)[0,1,3,7,9];
		507
		508	# read the directory entries
		509	aioreq_pri $pri;
		510	add $grp aio_readdir $path, sub {
		511	my $entries = shift
		512	or return $grp->result ();
		513
		514	# stat the dir another time
		515	aioreq_pri $pri;
		516	add $grp aio_stat $path, sub {
		517	my $hash2 = join ":", (stat _)[0,1,3,7,9];
		518
		519	my $ndirs;
		520
		521	# take the slow route if anything looks fishy
		522	if ($hash1 ne $hash2 or (stat _)[9] == $now) {
		523	$ndirs = -1;
		524	} else {
		525	# if nlink == 2, we are finished
		526	# on non-posix-fs's, we rely on nlink < 2
		527	$ndirs = (stat _)[3] - 2
		528	or return $grp->result ([], $entries);
		529	}
		530
		531	# sort into likely dirs and likely nondirs
		532	# dirs == files without ".", short entries first
		533	$entries = [map $_->[0],
		534	sort { $b->[1] cmp $a->[1] }
		535	map [$_, sprintf "%s%04d", (/.\./ ? "1" : "0"), length],
		536	@$entries];
		537
		538	my (@dirs, @nondirs);
		539
		540	my $statgrp = add $grp aio_group sub {
		541	$grp->result (\@dirs, \@nondirs);
		542	};
		543
		544	limit $statgrp $maxreq;
		545	feed $statgrp sub {
		546	return unless @$entries;
		547	my $entry = pop @$entries;
		548
		549	aioreq_pri $pri;
		550	add $statgrp aio_stat "$path/$entry/.", sub {
		551	if ($_[0] < 0) {
		552	push @nondirs, $entry;
		553	} else {
		554	# need to check for real directory
		555	aioreq_pri $pri;
		556	add $statgrp aio_lstat "$path/$entry", sub {
		557	if (-d _) {
		558	push @dirs, $entry;
		559
		560	unless (--$ndirs) {
		561	push @nondirs, @$entries;
		562	feed $statgrp;
		563	}
		564	} else {
		565	push @nondirs, $entry;
		566	}
		567	}
		568	}
		569	};
		570	};
		571	};
		572	};
		573	};
		574
		575	$grp
		576	}
		577
215	=item aio_fsync $fh, $callback	578	=item aio_fsync $fh, $callback->($status)
216		579
217	Asynchronously call fsync on the given filehandle and call the callback	580	Asynchronously call fsync on the given filehandle and call the callback
218	with the fsync result code.	581	with the fsync result code.
219		582
220	=item aio_fdatasync $fh, $callback	583	=item aio_fdatasync $fh, $callback->($status)
221		584
222	Asynchronously call fdatasync on the given filehandle and call the	585	Asynchronously call fdatasync on the given filehandle and call the
223	callback with the fdatasync result code.	586	callback with the fdatasync result code.
		587
		588	If this call isn't available because your OS lacks it or it couldn't be
		589	detected, it will be emulated by calling C<fsync> instead.
		590
		591	=item aio_group $callback->(...)
		592
		593	This is a very special aio request: Instead of doing something, it is a
		594	container for other aio requests, which is useful if you want to bundle
		595	many requests into a single, composite, request with a definite callback
		596	and the ability to cancel the whole request with its subrequests.
		597
		598	Returns an object of class L<IO::AIO::GRP>. See its documentation below
		599	for more info.
		600
		601	Example:
		602
		603	my $grp = aio_group sub {
		604	print "all stats done\n";
		605	};
		606
		607	add $grp
		608	(aio_stat ...),
		609	(aio_stat ...),
		610	...;
		611
		612	=item aio_nop $callback->()
		613
		614	This is a special request - it does nothing in itself and is only used for
		615	side effects, such as when you want to add a dummy request to a group so
		616	that finishing the requests in the group depends on executing the given
		617	code.
		618
		619	While this request does nothing, it still goes through the execution
		620	phase and still requires a worker thread. Thus, the callback will not
		621	be executed immediately but only after other requests in the queue have
		622	entered their execution phase. This can be used to measure request
		623	latency.
		624
		625	=item IO::AIO::aio_busy $fractional_seconds, $callback->() NOT EXPORTED
		626
		627	Mainly used for debugging and benchmarking, this aio request puts one of
		628	the request workers to sleep for the given time.
		629
		630	While it is theoretically handy to have simple I/O scheduling requests
		631	like sleep and file handle readable/writable, the overhead this creates is
		632	immense (it blocks a thread for a long time) so do not use this function
		633	except to put your application under artificial I/O pressure.
		634
		635	=back
		636
		637	=head2 IO::AIO::REQ CLASS
		638
		639	All non-aggregate C<aio_*> functions return an object of this class when
		640	called in non-void context.
		641
		642	=over 4
		643
		644	=item cancel $req
		645
		646	Cancels the request, if possible. Has the effect of skipping execution
		647	when entering the B<execute> state and skipping calling the callback when
		648	entering the the B<result> state, but will leave the request otherwise
		649	untouched. That means that requests that currently execute will not be
		650	stopped and resources held by the request will not be freed prematurely.
		651
		652	=item cb $req $callback->(...)
		653
		654	Replace (or simply set) the callback registered to the request.
		655
		656	=back
		657
		658	=head2 IO::AIO::GRP CLASS
		659
		660	This class is a subclass of L<IO::AIO::REQ>, so all its methods apply to
		661	objects of this class, too.
		662
		663	A IO::AIO::GRP object is a special request that can contain multiple other
		664	aio requests.
		665
		666	You create one by calling the C<aio_group> constructing function with a
		667	callback that will be called when all contained requests have entered the
		668	C<done> state:
		669
		670	my $grp = aio_group sub {
		671	print "all requests are done\n";
		672	};
		673
		674	You add requests by calling the C<add> method with one or more
		675	C<IO::AIO::REQ> objects:
		676
		677	$grp->add (aio_unlink "...");
		678
		679	add $grp aio_stat "...", sub {
		680	$_[0] or return $grp->result ("error");
		681
		682	# add another request dynamically, if first succeeded
		683	add $grp aio_open "...", sub {
		684	$grp->result ("ok");
		685	};
		686	};
		687
		688	This makes it very easy to create composite requests (see the source of
		689	C<aio_move> for an application) that work and feel like simple requests.
		690
		691	=over 4
		692
		693	=item * The IO::AIO::GRP objects will be cleaned up during calls to
		694	C<IO::AIO::poll_cb>, just like any other request.
		695
		696	=item * They can be canceled like any other request. Canceling will cancel not
		697	only the request itself, but also all requests it contains.
		698
		699	=item * They can also can also be added to other IO::AIO::GRP objects.
		700
		701	=item * You must not add requests to a group from within the group callback (or
		702	any later time).
		703
		704	=back
		705
		706	Their lifetime, simplified, looks like this: when they are empty, they
		707	will finish very quickly. If they contain only requests that are in the
		708	C<done> state, they will also finish. Otherwise they will continue to
		709	exist.
		710
		711	That means after creating a group you have some time to add requests. And
		712	in the callbacks of those requests, you can add further requests to the
		713	group. And only when all those requests have finished will the the group
		714	itself finish.
		715
		716	=over 4
		717
		718	=item add $grp ...
		719
		720	=item $grp->add (...)
		721
		722	Add one or more requests to the group. Any type of L<IO::AIO::REQ> can
		723	be added, including other groups, as long as you do not create circular
		724	dependencies.
		725
		726	Returns all its arguments.
		727
		728	=item $grp->cancel_subs
		729
		730	Cancel all subrequests and clears any feeder, but not the group request
		731	itself. Useful when you queued a lot of events but got a result early.
		732
		733	=item $grp->result (...)
		734
		735	Set the result value(s) that will be passed to the group callback when all
		736	subrequests have finished and set thre groups errno to the current value
		737	of errno (just like calling C<errno> without an error number). By default,
		738	no argument will be passed and errno is zero.
		739
		740	=item $grp->errno ([$errno])
		741
		742	Sets the group errno value to C<$errno>, or the current value of errno
		743	when the argument is missing.
		744
		745	Every aio request has an associated errno value that is restored when
		746	the callback is invoked. This method lets you change this value from its
		747	default (0).
		748
		749	Calling C<result> will also set errno, so make sure you either set C<$!>
		750	before the call to C<result>, or call c<errno> after it.
		751
		752	=item feed $grp $callback->($grp)
		753
		754	Sets a feeder/generator on this group: every group can have an attached
		755	generator that generates requests if idle. The idea behind this is that,
		756	although you could just queue as many requests as you want in a group,
		757	this might starve other requests for a potentially long time. For
		758	example, C<aio_scandir> might generate hundreds of thousands C<aio_stat>
		759	requests, delaying any later requests for a long time.
		760
		761	To avoid this, and allow incremental generation of requests, you can
		762	instead a group and set a feeder on it that generates those requests. The
		763	feed callback will be called whenever there are few enough (see C<limit>,
		764	below) requests active in the group itself and is expected to queue more
		765	requests.
		766
		767	The feed callback can queue as many requests as it likes (i.e. C<add> does
		768	not impose any limits).
		769
		770	If the feed does not queue more requests when called, it will be
		771	automatically removed from the group.
		772
		773	If the feed limit is C<0>, it will be set to C<2> automatically.
		774
		775	Example:
		776
		777	# stat all files in @files, but only ever use four aio requests concurrently:
		778
		779	my $grp = aio_group sub { print "finished\n" };
		780	limit $grp 4;
		781	feed $grp sub {
		782	my $file = pop @files
		783	or return;
		784
		785	add $grp aio_stat $file, sub { ... };
		786	};
		787
		788	=item limit $grp $num
		789
		790	Sets the feeder limit for the group: The feeder will be called whenever
		791	the group contains less than this many requests.
		792
		793	Setting the limit to C<0> will pause the feeding process.
		794
		795	=back
		796
		797	=head2 SUPPORT FUNCTIONS
		798
		799	=over 4
		800
		801	=item $fileno = IO::AIO::poll_fileno
		802
		803	Return the I<request result pipe file descriptor>. This filehandle must be
		804	polled for reading by some mechanism outside this module (e.g. Event or
		805	select, see below or the SYNOPSIS). If the pipe becomes readable you have
		806	to call C<poll_cb> to check the results.
		807
		808	See C<poll_cb> for an example.
		809
		810	=item IO::AIO::poll_cb
		811
		812	Process all outstanding events on the result pipe. You have to call this
		813	regularly. Returns the number of events processed. Returns immediately
		814	when no events are outstanding.
		815
		816	If not all requests were processed for whatever reason, the filehandle
		817	will still be ready when C<poll_cb> returns.
		818
		819	Example: Install an Event watcher that automatically calls
		820	IO::AIO::poll_cb with high priority:
		821
		822	Event->io (fd => IO::AIO::poll_fileno,
		823	poll => 'r', async => 1,
		824	cb => \&IO::AIO::poll_cb);
		825
		826	=item IO::AIO::poll_some $max_requests
		827
		828	Similar to C<poll_cb>, but only processes up to C<$max_requests> requests
		829	at a time.
		830
		831	Useful if you want to ensure some level of interactiveness when perl is
		832	not fast enough to process all requests in time.
		833
		834	Example: Install an Event watcher that automatically calls
		835	IO::AIO::poll_some with low priority, to ensure that other parts of the
		836	program get the CPU sometimes even under high AIO load.
		837
		838	Event->io (fd => IO::AIO::poll_fileno,
		839	poll => 'r', nice => 1,
		840	cb => sub { IO::AIO::poll_some 256 });
		841
		842	=item IO::AIO::poll_wait
		843
		844	Wait till the result filehandle becomes ready for reading (simply does a
		845	C<select> on the filehandle. This is useful if you want to synchronously wait
		846	for some requests to finish).
		847
		848	See C<nreqs> for an example.
		849
		850	=item IO::AIO::nreqs
		851
		852	Returns the number of requests currently in the ready, execute or pending
		853	states (i.e. for which their callback has not been invoked yet).
		854
		855	Example: wait till there are no outstanding requests anymore:
		856
		857	IO::AIO::poll_wait, IO::AIO::poll_cb
		858	while IO::AIO::nreqs;
		859
		860	=item IO::AIO::nready
		861
		862	Returns the number of requests currently in the ready state (not yet
		863	executed).
		864
		865	=item IO::AIO::npending
		866
		867	Returns the number of requests currently in the pending state (executed,
		868	but not yet processed by poll_cb).
		869
		870	=item IO::AIO::flush
		871
		872	Wait till all outstanding AIO requests have been handled.
		873
		874	Strictly equivalent to:
		875
		876	IO::AIO::poll_wait, IO::AIO::poll_cb
		877	while IO::AIO::nreqs;
		878
		879	=item IO::AIO::poll
		880
		881	Waits until some requests have been handled.
		882
		883	Strictly equivalent to:
		884
		885	IO::AIO::poll_wait, IO::AIO::poll_cb
		886	if IO::AIO::nreqs;
		887
		888	=item IO::AIO::min_parallel $nthreads
		889
		890	Set the minimum number of AIO threads to C<$nthreads>. The current
		891	default is C<8>, which means eight asynchronous operations can execute
		892	concurrently at any one time (the number of outstanding requests,
		893	however, is unlimited).
		894
		895	IO::AIO starts threads only on demand, when an AIO request is queued and
		896	no free thread exists.
		897
		898	It is recommended to keep the number of threads relatively low, as some
		899	Linux kernel versions will scale negatively with the number of threads
		900	(higher parallelity => MUCH higher latency). With current Linux 2.6
		901	versions, 4-32 threads should be fine.
		902
		903	Under most circumstances you don't need to call this function, as the
		904	module selects a default that is suitable for low to moderate load.
		905
		906	=item IO::AIO::max_parallel $nthreads
		907
		908	Sets the maximum number of AIO threads to C<$nthreads>. If more than the
		909	specified number of threads are currently running, this function kills
		910	them. This function blocks until the limit is reached.
		911
		912	While C<$nthreads> are zero, aio requests get queued but not executed
		913	until the number of threads has been increased again.
		914
		915	This module automatically runs C<max_parallel 0> at program end, to ensure
		916	that all threads are killed and that there are no outstanding requests.
		917
		918	Under normal circumstances you don't need to call this function.
		919
		920	=item $oldmaxreqs = IO::AIO::max_outstanding $maxreqs
		921
		922	This is a very bad function to use in interactive programs because it
		923	blocks, and a bad way to reduce concurrency because it is inexact: Better
		924	use an C<aio_group> together with a feed callback.
		925
		926	Sets the maximum number of outstanding requests to C<$nreqs>. If you
		927	to queue up more than this number of requests, the next call to the
		928	C<poll_cb> (and C<poll_some> and other functions calling C<poll_cb>)
		929	function will block until the limit is no longer exceeded.
		930
		931	The default value is very large, so there is no practical limit on the
		932	number of outstanding requests.
		933
		934	You can still queue as many requests as you want. Therefore,
		935	C<max_oustsanding> is mainly useful in simple scripts (with low values) or
		936	as a stop gap to shield against fatal memory overflow (with large values).
		937
		938	=back
224		939
225	=cut	940	=cut
226		941
227	# support function to convert a fd into a perl filehandle	942	# support function to convert a fd into a perl filehandle
228	sub _fd2fh {	943	sub _fd2fh {
229	return undef if $_[0] < 0;	944	return undef if $_[0] < 0;
230		945
231	# try to be perl5.6-compatible	946	# try to generate nice filehandles
232	local *AIO_FH;	947	my $sym = "IO::AIO::fd#$_[0]";
233	open AIO_FH, "+<&=$_[0]"	948	local *$sym;
		949
		950	open *$sym, "+<&=$_[0]" # usually works under any unix
		951	or open *$sym, "<&=$_[0]" # cygwin needs this
		952	or open *$sym, ">&=$_[0]" # or this
234	or return undef;	953	or return undef;
235		954
236	*AIO_FH	955	*$sym
237	}	956	}
238		957
239	min_parallel 4;	958	min_parallel 8;
240
241	END {
242	max_parallel 0;
243	}
244		959
245	1;	960	1;
246		961
247	=back	962	=head2 FORK BEHAVIOUR
248		963
		964	This module should do "the right thing" when the process using it forks:
		965
		966	Before the fork, IO::AIO enters a quiescent state where no requests
		967	can be added in other threads and no results will be processed. After
		968	the fork the parent simply leaves the quiescent state and continues
		969	request/result processing, while the child frees the request/result queue
		970	(so that the requests started before the fork will only be handled in the
		971	parent). Threads will be started on demand until the limit set in the
		972	parent process has been reached again.
		973
		974	In short: the parent will, after a short pause, continue as if fork had
		975	not been called, while the child will act as if IO::AIO has not been used
		976	yet.
		977
		978	=head2 MEMORY USAGE
		979
		980	Per-request usage:
		981
		982	Each aio request uses - depending on your architecture - around 100-200
		983	bytes of memory. In addition, stat requests need a stat buffer (possibly
		984	a few hundred bytes), readdir requires a result buffer and so on. Perl
		985	scalars and other data passed into aio requests will also be locked and
		986	will consume memory till the request has entered the done state.
		987
		988	This is now awfully much, so queuing lots of requests is not usually a
		989	problem.
		990
		991	Per-thread usage:
		992
		993	In the execution phase, some aio requests require more memory for
		994	temporary buffers, and each thread requires a stack and other data
		995	structures (usually around 16k-128k, depending on the OS).
		996
249	=head1 BUGS	997	=head1 KNOWN BUGS
250		998
251	- could be optimized to use more semaphores instead of filehandles.	999	Known bugs will be fixed in the next release.
252		1000
253	=head1 SEE ALSO	1001	=head1 SEE ALSO
254		1002
255	L<Coro>, L<Linux::AIO>.	1003	L<Coro::AIO>.
256		1004
257	=head1 AUTHOR	1005	=head1 AUTHOR
258		1006
259	Marc Lehmann <schmorp@schmorp.de>	1007	Marc Lehmann <schmorp@schmorp.de>
260	http://home.schmorp.de/	1008	http://home.schmorp.de/

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Comparing IO-AIO/AIO.pm (file contents): Revision 1.3 by root, Sun Jul 10 20:07:11 2005 UTC vs. Revision 1.81 by root, Fri Oct 27 19:17:23 2006 UTC

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Comparing IO-AIO/AIO.pm (file contents):
Revision 1.3 by root, Sun Jul 10 20:07:11 2005 UTC vs.
Revision 1.81 by root, Fri Oct 27 19:17:23 2006 UTC