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

Comparing IO-AIO/AIO.pm (file contents):
Revision 1.9 by root, Sun Jul 10 22:20:55 2005 UTC vs.
Revision 1.99 by root, Sun Jan 7 21:32:20 2007 UTC

…		…
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	use IO::AIO;	7	use IO::AIO;
8		8
9	aio_open "/etc/passwd", O_RDONLY, 0, sub {	9	aio_open "/etc/passwd", O_RDONLY, 0, sub {
10	my ($fh) = @_;	10	my $fh = shift
		11	or die "/etc/passwd: $!";
11	...	12	...
12	};	13	};
13		14
14	aio_unlink "/tmp/file", sub { };	15	aio_unlink "/tmp/file", sub { };
15		16
16	aio_read $fh, 30000, 1024, $buffer, 0, sub {	17	aio_read $fh, 30000, 1024, $buffer, 0, sub {
17	$_[0] > 0 or die "read error: $!";	18	$_[0] > 0 or die "read error: $!";
18	};	19	};
19		20
20	# Event	21	# version 2+ has request and group objects
		22	use IO::AIO 2;
		23
		24	aioreq_pri 4; # give next request a very high priority
		25	my $req = aio_unlink "/tmp/file", sub { };
		26	$req->cancel; # cancel request if still in queue
		27
		28	my $grp = aio_group sub { print "all stats done\n" };
		29	add $grp aio_stat "..." for ...;
		30
		31	# AnyEvent integration
		32	open my $fh, "<&=" . IO::AIO::poll_fileno or die "$!";
		33	my $w = AnyEvent->io (fh => $fh, poll => 'r', cb => sub { IO::AIO::poll_cb });
		34
		35	# Event integration
21	Event->io (fd => IO::AIO::poll_fileno,	36	Event->io (fd => IO::AIO::poll_fileno,
22	poll => 'r',	37	poll => 'r',
23	cb => \&IO::AIO::poll_cb);	38	cb => \&IO::AIO::poll_cb);
24		39
25	# Glib/Gtk2	40	# Glib/Gtk2 integration
26	add_watch Glib::IO IO::AIO::poll_fileno,	41	add_watch Glib::IO IO::AIO::poll_fileno,
27	\&IO::AIO::poll_cb;	42	in => sub { IO::AIO::poll_cb; 1 };
28		43
29	# Tk	44	# Tk integration
30	Tk::Event::IO->fileevent (IO::AIO::poll_fileno, "",	45	Tk::Event::IO->fileevent (IO::AIO::poll_fileno, "",
31	readable => \&IO::AIO::poll_cb);	46	readable => \&IO::AIO::poll_cb);
32		47
		48	# Danga::Socket integration
		49	Danga::Socket->AddOtherFds (IO::AIO::poll_fileno =>
		50	\&IO::AIO::poll_cb);
		51
33	=head1 DESCRIPTION	52	=head1 DESCRIPTION
34		53
35	This module implements asynchronous I/O using whatever means your	54	This module implements asynchronous I/O using whatever means your
36	operating system supports.	55	operating system supports.
37		56
		57	Asynchronous means that operations that can normally block your program
		58	(e.g. reading from disk) will be done asynchronously: the operation
		59	will still block, but you can do something else in the meantime. This
		60	is extremely useful for programs that need to stay interactive even
		61	when doing heavy I/O (GUI programs, high performance network servers
		62	etc.), but can also be used to easily do operations in parallel that are
		63	normally done sequentially, e.g. stat'ing many files, which is much faster
		64	on a RAID volume or over NFS when you do a number of stat operations
		65	concurrently.
		66
		67	While most of this works on all types of file descriptors (for example
		68	sockets), using these functions on file descriptors that support
		69	nonblocking operation (again, sockets, pipes etc.) is very inefficient or
		70	might not work (aio_read fails on sockets/pipes/fifos). Use an event loop
		71	for that (such as the L<Event\|Event> module): IO::AIO will naturally fit
		72	into such an event loop itself.
		73
38	Currently, a number of threads are started that execute your read/writes	74	In this version, a number of threads are started that execute your
39	and signal their completion. You don't need thread support in your libc or	75	requests and signal their completion. You don't need thread support
40	perl, and the threads created by this module will not be visible to the	76	in perl, and the threads created by this module will not be visible
41	pthreads library. In the future, this module might make use of the native	77	to perl. In the future, this module might make use of the native aio
42	aio functions available on many operating systems. However, they are often	78	functions available on many operating systems. However, they are often
43	not well-supported (Linux doesn't allow them on normal files currently,	79	not well-supported or restricted (GNU/Linux doesn't allow them on normal
44	for example), and they would only support aio_read and aio_write, so the	80	files currently, for example), and they would only support aio_read and
45	remaining functionality would have to be implemented using threads anyway.	81	aio_write, so the remaining functionality would have to be implemented
		82	using threads anyway.
46		83
47	Although the module will work with in the presence of other threads, it is	84	Although the module will work with in the presence of other (Perl-)
48	currently not reentrant, so use appropriate locking yourself.	85	threads, it is currently not reentrant in any way, so use appropriate
		86	locking yourself, always call C<poll_cb> from within the same thread, or
		87	never call C<poll_cb> (or other C<aio_> functions) recursively.
		88
		89	=head2 EXAMPLE
		90
		91	This is a simple example that uses the Event module and loads
		92	F</etc/passwd> asynchronously:
		93
		94	use Fcntl;
		95	use Event;
		96	use IO::AIO;
		97
		98	# register the IO::AIO callback with Event
		99	Event->io (fd => IO::AIO::poll_fileno,
		100	poll => 'r',
		101	cb => \&IO::AIO::poll_cb);
		102
		103	# queue the request to open /etc/passwd
		104	aio_open "/etc/passwd", O_RDONLY, 0, sub {
		105	my $fh = shift
		106	or die "error while opening: $!";
		107
		108	# stat'ing filehandles is generally non-blocking
		109	my $size = -s $fh;
		110
		111	# queue a request to read the file
		112	my $contents;
		113	aio_read $fh, 0, $size, $contents, 0, sub {
		114	$_[0] == $size
		115	or die "short read: $!";
		116
		117	close $fh;
		118
		119	# file contents now in $contents
		120	print $contents;
		121
		122	# exit event loop and program
		123	Event::unloop;
		124	};
		125	};
		126
		127	# possibly queue up other requests, or open GUI windows,
		128	# check for sockets etc. etc.
		129
		130	# process events as long as there are some:
		131	Event::loop;
		132
		133	=head1 REQUEST ANATOMY AND LIFETIME
		134
		135	Every C<aio_*> function creates a request. which is a C data structure not
		136	directly visible to Perl.
		137
		138	If called in non-void context, every request function returns a Perl
		139	object representing the request. In void context, nothing is returned,
		140	which saves a bit of memory.
		141
		142	The perl object is a fairly standard ref-to-hash object. The hash contents
		143	are not used by IO::AIO so you are free to store anything you like in it.
		144
		145	During their existance, aio requests travel through the following states,
		146	in order:
		147
		148	=over 4
		149
		150	=item ready
		151
		152	Immediately after a request is created it is put into the ready state,
		153	waiting for a thread to execute it.
		154
		155	=item execute
		156
		157	A thread has accepted the request for processing and is currently
		158	executing it (e.g. blocking in read).
		159
		160	=item pending
		161
		162	The request has been executed and is waiting for result processing.
		163
		164	While request submission and execution is fully asynchronous, result
		165	processing is not and relies on the perl interpreter calling C<poll_cb>
		166	(or another function with the same effect).
		167
		168	=item result
		169
		170	The request results are processed synchronously by C<poll_cb>.
		171
		172	The C<poll_cb> function will process all outstanding aio requests by
		173	calling their callbacks, freeing memory associated with them and managing
		174	any groups they are contained in.
		175
		176	=item done
		177
		178	Request has reached the end of its lifetime and holds no resources anymore
		179	(except possibly for the Perl object, but its connection to the actual
		180	aio request is severed and calling its methods will either do nothing or
		181	result in a runtime error).
		182
		183	=back
49		184
50	=cut	185	=cut
51		186
52	package IO::AIO;	187	package IO::AIO;
53		188
		189	no warnings;
		190	use strict 'vars';
		191
54	use base 'Exporter';	192	use base 'Exporter';
55		193
56	use Fcntl ();
57
58	BEGIN {	194	BEGIN {
59	$VERSION = 0.2;	195	our $VERSION = '2.32';
60		196
61	@EXPORT = qw(aio_read aio_write aio_open aio_close aio_stat aio_lstat aio_unlink	197	our @AIO_REQ = qw(aio_sendfile aio_read aio_write aio_open aio_close aio_stat
62	aio_fsync aio_fdatasync aio_readahead);	198	aio_lstat aio_unlink aio_rmdir aio_readdir aio_scandir aio_symlink
63	@EXPORT_OK = qw(poll_fileno poll_cb min_parallel max_parallel max_outstanding nreqs);	199	aio_readlink aio_fsync aio_fdatasync aio_readahead aio_rename aio_link
		200	aio_move aio_copy aio_group aio_nop aio_mknod aio_load aio_rmtree);
		201	our @EXPORT = (@AIO_REQ, qw(aioreq_pri aioreq_nice aio_block));
		202	our @EXPORT_OK = qw(poll_fileno poll_cb poll_wait flush
		203	min_parallel max_parallel max_idle
		204	nreqs nready npending nthreads
		205	max_poll_time max_poll_reqs);
		206
		207	@IO::AIO::GRP::ISA = 'IO::AIO::REQ';
64		208
65	require XSLoader;	209	require XSLoader;
66	XSLoader::load IO::AIO, $VERSION;	210	XSLoader::load ("IO::AIO", $VERSION);
67	}	211	}
68		212
69	=head1 FUNCTIONS	213	=head1 FUNCTIONS
70		214
71	=head2 AIO FUNCTIONS	215	=head2 AIO REQUEST FUNCTIONS
72		216
73	All the C<aio_*> calls are more or less thin wrappers around the syscall	217	All the C<aio_*> calls are more or less thin wrappers around the syscall
74	with the same name (sans C<aio_>). The arguments are similar or identical,	218	with the same name (sans C<aio_>). The arguments are similar or identical,
75	and they all accept an additional C<$callback> argument which must be	219	and they all accept an additional (and optional) C<$callback> argument
76	a code reference. This code reference will get called with the syscall	220	which must be a code reference. This code reference will get called with
77	return code (e.g. most syscalls return C<-1> on error, unlike perl, which	221	the syscall return code (e.g. most syscalls return C<-1> on error, unlike
78	usually delivers "false") as it's sole argument when the given syscall has	222	perl, which usually delivers "false") as it's sole argument when the given
79	been executed asynchronously.	223	syscall has been executed asynchronously.
80		224
81	All functions that expect a filehandle will also accept a file descriptor.	225	All functions expecting a filehandle keep a copy of the filehandle
		226	internally until the request has finished.
82		227
		228	All functions return request objects of type L<IO::AIO::REQ> that allow
		229	further manipulation of those requests while they are in-flight.
		230
83	The filenames you pass to these routines I<must> be absolute. The reason	231	The pathnames you pass to these routines I<must> be absolute and
84	is that at the time the request is being executed, the current working	232	encoded as octets. The reason for the former is that at the time the
85	directory could have changed. Alternatively, you can make sure that you	233	request is being executed, the current working directory could have
86	never change the current working directory.	234	changed. Alternatively, you can make sure that you never change the
		235	current working directory anywhere in the program and then use relative
		236	paths.
		237
		238	To encode pathnames as octets, either make sure you either: a) always pass
		239	in filenames you got from outside (command line, readdir etc.) without
		240	tinkering, b) are ASCII or ISO 8859-1, c) use the Encode module and encode
		241	your pathnames to the locale (or other) encoding in effect in the user
		242	environment, d) use Glib::filename_from_unicode on unicode filenames or e)
		243	use something else to ensure your scalar has the correct contents.
		244
		245	This works, btw. independent of the internal UTF-8 bit, which IO::AIO
		246	handles correctly wether it is set or not.
87		247
88	=over 4	248	=over 4
89		249
		250	=item $prev_pri = aioreq_pri [$pri]
		251
		252	Returns the priority value that would be used for the next request and, if
		253	C<$pri> is given, sets the priority for the next aio request.
		254
		255	The default priority is C<0>, the minimum and maximum priorities are C<-4>
		256	and C<4>, respectively. Requests with higher priority will be serviced
		257	first.
		258
		259	The priority will be reset to C<0> after each call to one of the C<aio_*>
		260	functions.
		261
		262	Example: open a file with low priority, then read something from it with
		263	higher priority so the read request is serviced before other low priority
		264	open requests (potentially spamming the cache):
		265
		266	aioreq_pri -3;
		267	aio_open ..., sub {
		268	return unless $_[0];
		269
		270	aioreq_pri -2;
		271	aio_read $_[0], ..., sub {
		272	...
		273	};
		274	};
		275
		276	=item aioreq_nice $pri_adjust
		277
		278	Similar to C<aioreq_pri>, but subtracts the given value from the current
		279	priority, so the effect is cumulative.
		280
90	=item aio_open $pathname, $flags, $mode, $callback	281	=item aio_open $pathname, $flags, $mode, $callback->($fh)
91		282
92	Asynchronously open or create a file and call the callback with a newly	283	Asynchronously open or create a file and call the callback with a newly
93	created filehandle for the file.	284	created filehandle for the file.
94		285
95	The pathname passed to C<aio_open> must be absolute. See API NOTES, above,	286	The pathname passed to C<aio_open> must be absolute. See API NOTES, above,
96	for an explanation.	287	for an explanation.
97		288
98	The C<$mode> argument is a bitmask. See the C<Fcntl> module for a	289	The C<$flags> argument is a bitmask. See the C<Fcntl> module for a
99	list. They are the same as used in C<sysopen>.	290	list. They are the same as used by C<sysopen>.
		291
		292	Likewise, C<$mode> specifies the mode of the newly created file, if it
		293	didn't exist and C<O_CREAT> has been given, just like perl's C<sysopen>,
		294	except that it is mandatory (i.e. use C<0> if you don't create new files,
		295	and C<0666> or C<0777> if you do).
100		296
101	Example:	297	Example:
102		298
103	aio_open "/etc/passwd", O_RDONLY, 0, sub {	299	aio_open "/etc/passwd", O_RDONLY, 0, sub {
104	if ($_[0]) {	300	if ($_[0]) {
…		…
107	} else {	303	} else {
108	die "open failed: $!\n";	304	die "open failed: $!\n";
109	}	305	}
110	};	306	};
111		307
112	=item aio_close $fh, $callback	308	=item aio_close $fh, $callback->($status)
113		309
114	Asynchronously close a file and call the callback with the result	310	Asynchronously close a file and call the callback with the result
115	code. I<WARNING:> although accepted, you should not pass in a perl	311	code. I<WARNING:> although accepted, you should not pass in a perl
116	filehandle here, as perl will likely close the file descriptor itself when	312	filehandle here, as perl will likely close the file descriptor another
117	the filehandle is destroyed. Normally, you can safely call perls C<close>	313	time when the filehandle is destroyed. Normally, you can safely call perls
118	or just let filehandles go out of scope.	314	C<close> or just let filehandles go out of scope.
119		315
		316	This is supposed to be a bug in the API, so that might change. It's
		317	therefore best to avoid this function.
		318
120	=item aio_read $fh,$offset,$length, $data,$dataoffset,$callback	319	=item aio_read $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
121		320
122	=item aio_write $fh,$offset,$length, $data,$dataoffset,$callback	321	=item aio_write $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
123		322
124	Reads or writes C<length> bytes from the specified C<fh> and C<offset>	323	Reads or writes C<length> bytes from the specified C<fh> and C<offset>
125	into the scalar given by C<data> and offset C<dataoffset> and calls the	324	into the scalar given by C<data> and offset C<dataoffset> and calls the
126	callback without the actual number of bytes read (or -1 on error, just	325	callback without the actual number of bytes read (or -1 on error, just
127	like the syscall).	326	like the syscall).
128		327
		328	The C<$data> scalar I<MUST NOT> be modified in any way while the request
		329	is outstanding. Modifying it can result in segfaults or WW3 (if the
		330	necessary/optional hardware is installed).
		331
129	Example: Read 15 bytes at offset 7 into scalar C<$buffer>, strating at	332	Example: Read 15 bytes at offset 7 into scalar C<$buffer>, starting at
130	offset C<0> within the scalar:	333	offset C<0> within the scalar:
131		334
132	aio_read $fh, 7, 15, $buffer, 0, sub {	335	aio_read $fh, 7, 15, $buffer, 0, sub {
133	$_[0] > 0 or die "read error: $!";	336	$_[0] > 0 or die "read error: $!";
134	print "read $_[0] bytes: <$buffer>\n";	337	print "read $_[0] bytes: <$buffer>\n";
135	};	338	};
136		339
		340	=item aio_sendfile $out_fh, $in_fh, $in_offset, $length, $callback->($retval)
		341
		342	Tries to copy C<$length> bytes from C<$in_fh> to C<$out_fh>. It starts
		343	reading at byte offset C<$in_offset>, and starts writing at the current
		344	file offset of C<$out_fh>. Because of that, it is not safe to issue more
		345	than one C<aio_sendfile> per C<$out_fh>, as they will interfere with each
		346	other.
		347
		348	This call tries to make use of a native C<sendfile> syscall to provide
		349	zero-copy operation. For this to work, C<$out_fh> should refer to a
		350	socket, and C<$in_fh> should refer to mmap'able file.
		351
		352	If the native sendfile call fails or is not implemented, it will be
		353	emulated, so you can call C<aio_sendfile> on any type of filehandle
		354	regardless of the limitations of the operating system.
		355
		356	Please note, however, that C<aio_sendfile> can read more bytes from
		357	C<$in_fh> than are written, and there is no way to find out how many
		358	bytes have been read from C<aio_sendfile> alone, as C<aio_sendfile> only
		359	provides the number of bytes written to C<$out_fh>. Only if the result
		360	value equals C<$length> one can assume that C<$length> bytes have been
		361	read.
		362
137	=item aio_readahead $fh,$offset,$length, $callback	363	=item aio_readahead $fh,$offset,$length, $callback->($retval)
138		364
139	Asynchronously reads the specified byte range into the page cache, using
140	the C<readahead> syscall. If that syscall doesn't exist the status will be
141	C<-1> and C<$!> is set to ENOSYS.
142
143	readahead() populates the page cache with data from a file so that	365	C<aio_readahead> populates the page cache with data from a file so that
144	subsequent reads from that file will not block on disk I/O. The C<$offset>	366	subsequent reads from that file will not block on disk I/O. The C<$offset>
145	argument specifies the starting point from which data is to be read and	367	argument specifies the starting point from which data is to be read and
146	C<$length> specifies the number of bytes to be read. I/O is performed in	368	C<$length> specifies the number of bytes to be read. I/O is performed in
147	whole pages, so that offset is effectively rounded down to a page boundary	369	whole pages, so that offset is effectively rounded down to a page boundary
148	and bytes are read up to the next page boundary greater than or equal to	370	and bytes are read up to the next page boundary greater than or equal to
149	(off-set+length). aio_readahead() does not read beyond the end of the	371	(off-set+length). C<aio_readahead> does not read beyond the end of the
150	file. The current file offset of the file is left unchanged.	372	file. The current file offset of the file is left unchanged.
151		373
		374	If that syscall doesn't exist (likely if your OS isn't Linux) it will be
		375	emulated by simply reading the data, which would have a similar effect.
		376
152	=item aio_stat $fh_or_path, $callback	377	=item aio_stat $fh_or_path, $callback->($status)
153		378
154	=item aio_lstat $fh, $callback	379	=item aio_lstat $fh, $callback->($status)
155		380
156	Works like perl's C<stat> or C<lstat> in void context. The callback will	381	Works like perl's C<stat> or C<lstat> in void context. The callback will
157	be called after the stat and the results will be available using C<stat _>	382	be called after the stat and the results will be available using C<stat _>
158	or C<-s _> etc...	383	or C<-s _> etc...
159		384
…		…
169	aio_stat "/etc/passwd", sub {	394	aio_stat "/etc/passwd", sub {
170	$_[0] and die "stat failed: $!";	395	$_[0] and die "stat failed: $!";
171	print "size is ", -s _, "\n";	396	print "size is ", -s _, "\n";
172	};	397	};
173		398
174	=item aio_unlink $pathname, $callback	399	=item aio_unlink $pathname, $callback->($status)
175		400
176	Asynchronously unlink (delete) a file and call the callback with the	401	Asynchronously unlink (delete) a file and call the callback with the
177	result code.	402	result code.
178		403
		404	=item aio_mknod $path, $mode, $dev, $callback->($status)
		405
		406	[EXPERIMENTAL]
		407
		408	Asynchronously create a device node (or fifo). See mknod(2).
		409
		410	The only (POSIX-) portable way of calling this function is:
		411
		412	aio_mknod $path, IO::AIO::S_IFIFO \| $mode, 0, sub { ...
		413
		414	=item aio_link $srcpath, $dstpath, $callback->($status)
		415
		416	Asynchronously create a new 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_symlink $srcpath, $dstpath, $callback->($status)
		420
		421	Asynchronously create a new symbolic link to the existing object at C<$srcpath> at
		422	the path C<$dstpath> and call the callback with the result code.
		423
		424	=item aio_readlink $path, $callback->($link)
		425
		426	Asynchronously read the symlink specified by C<$path> and pass it to
		427	the callback. If an error occurs, nothing or undef gets passed to the
		428	callback.
		429
		430	=item aio_rename $srcpath, $dstpath, $callback->($status)
		431
		432	Asynchronously rename the object at C<$srcpath> to C<$dstpath>, just as
		433	rename(2) and call the callback with the result code.
		434
		435	=item aio_rmdir $pathname, $callback->($status)
		436
		437	Asynchronously rmdir (delete) a directory and call the callback with the
		438	result code.
		439
		440	=item aio_readdir $pathname, $callback->($entries)
		441
		442	Unlike the POSIX call of the same name, C<aio_readdir> reads an entire
		443	directory (i.e. opendir + readdir + closedir). The entries will not be
		444	sorted, and will B<NOT> include the C<.> and C<..> entries.
		445
		446	The callback a single argument which is either C<undef> or an array-ref
		447	with the filenames.
		448
		449	=item aio_load $path, $data, $callback->($status)
		450
		451	This is a composite request that tries to fully load the given file into
		452	memory. Status is the same as with aio_read.
		453
		454	=cut
		455
		456	sub aio_load($$;$) {
		457	aio_block {
		458	my ($path, undef, $cb) = @_;
		459	my $data = \$_[1];
		460
		461	my $pri = aioreq_pri;
		462	my $grp = aio_group $cb;
		463
		464	aioreq_pri $pri;
		465	add $grp aio_open $path, O_RDONLY, 0, sub {
		466	my ($fh) = @_
		467	or return $grp->result (-1);
		468
		469	aioreq_pri $pri;
		470	add $grp aio_read $fh, 0, (-s $fh), $$data, 0, sub {
		471	$grp->result ($_[0]);
		472	};
		473	};
		474
		475	$grp
		476	}
		477	}
		478
		479	=item aio_copy $srcpath, $dstpath, $callback->($status)
		480
		481	Try to copy the I<file> (directories not supported as either source or
		482	destination) from C<$srcpath> to C<$dstpath> and call the callback with
		483	the C<0> (error) or C<-1> ok.
		484
		485	This is a composite request that it creates the destination file with
		486	mode 0200 and copies the contents of the source file into it using
		487	C<aio_sendfile>, followed by restoring atime, mtime, access mode and
		488	uid/gid, in that order.
		489
		490	If an error occurs, the partial destination file will be unlinked, if
		491	possible, except when setting atime, mtime, access mode and uid/gid, where
		492	errors are being ignored.
		493
		494	=cut
		495
		496	sub aio_copy($$;$) {
		497	aio_block {
		498	my ($src, $dst, $cb) = @_;
		499
		500	my $pri = aioreq_pri;
		501	my $grp = aio_group $cb;
		502
		503	aioreq_pri $pri;
		504	add $grp aio_open $src, O_RDONLY, 0, sub {
		505	if (my $src_fh = $_[0]) {
		506	my @stat = stat $src_fh;
		507
		508	aioreq_pri $pri;
		509	add $grp aio_open $dst, O_CREAT \| O_WRONLY \| O_TRUNC, 0200, sub {
		510	if (my $dst_fh = $_[0]) {
		511	aioreq_pri $pri;
		512	add $grp aio_sendfile $dst_fh, $src_fh, 0, $stat[7], sub {
		513	if ($_[0] == $stat[7]) {
		514	$grp->result (0);
		515	close $src_fh;
		516
		517	# those should not normally block. should. should.
		518	utime $stat[8], $stat[9], $dst;
		519	chmod $stat[2] & 07777, $dst_fh;
		520	chown $stat[4], $stat[5], $dst_fh;
		521	close $dst_fh;
		522	} else {
		523	$grp->result (-1);
		524	close $src_fh;
		525	close $dst_fh;
		526
		527	aioreq $pri;
		528	add $grp aio_unlink $dst;
		529	}
		530	};
		531	} else {
		532	$grp->result (-1);
		533	}
		534	},
		535
		536	} else {
		537	$grp->result (-1);
		538	}
		539	};
		540
		541	$grp
		542	}
		543	}
		544
		545	=item aio_move $srcpath, $dstpath, $callback->($status)
		546
		547	Try to move the I<file> (directories not supported as either source or
		548	destination) from C<$srcpath> to C<$dstpath> and call the callback with
		549	the C<0> (error) or C<-1> ok.
		550
		551	This is a composite request that tries to rename(2) the file first. If
		552	rename files with C<EXDEV>, it copies the file with C<aio_copy> and, if
		553	that is successful, unlinking the C<$srcpath>.
		554
		555	=cut
		556
		557	sub aio_move($$;$) {
		558	aio_block {
		559	my ($src, $dst, $cb) = @_;
		560
		561	my $pri = aioreq_pri;
		562	my $grp = aio_group $cb;
		563
		564	aioreq_pri $pri;
		565	add $grp aio_rename $src, $dst, sub {
		566	if ($_[0] && $! == EXDEV) {
		567	aioreq_pri $pri;
		568	add $grp aio_copy $src, $dst, sub {
		569	$grp->result ($_[0]);
		570
		571	if (!$_[0]) {
		572	aioreq_pri $pri;
		573	add $grp aio_unlink $src;
		574	}
		575	};
		576	} else {
		577	$grp->result ($_[0]);
		578	}
		579	};
		580
		581	$grp
		582	}
		583	}
		584
		585	=item aio_scandir $path, $maxreq, $callback->($dirs, $nondirs)
		586
		587	Scans a directory (similar to C<aio_readdir>) but additionally tries to
		588	efficiently separate the entries of directory C<$path> into two sets of
		589	names, directories you can recurse into (directories), and ones you cannot
		590	recurse into (everything else, including symlinks to directories).
		591
		592	C<aio_scandir> is a composite request that creates of many sub requests_
		593	C<$maxreq> specifies the maximum number of outstanding aio requests that
		594	this function generates. If it is C<< <= 0 >>, then a suitable default
		595	will be chosen (currently 4).
		596
		597	On error, the callback is called without arguments, otherwise it receives
		598	two array-refs with path-relative entry names.
		599
		600	Example:
		601
		602	aio_scandir $dir, 0, sub {
		603	my ($dirs, $nondirs) = @_;
		604	print "real directories: @$dirs\n";
		605	print "everything else: @$nondirs\n";
		606	};
		607
		608	Implementation notes.
		609
		610	The C<aio_readdir> cannot be avoided, but C<stat()>'ing every entry can.
		611
		612	After reading the directory, the modification time, size etc. of the
		613	directory before and after the readdir is checked, and if they match (and
		614	isn't the current time), the link count will be used to decide how many
		615	entries are directories (if >= 2). Otherwise, no knowledge of the number
		616	of subdirectories will be assumed.
		617
		618	Then entries will be sorted into likely directories (everything without
		619	a non-initial dot currently) and likely non-directories (everything
		620	else). Then every entry plus an appended C</.> will be C<stat>'ed,
		621	likely directories first. If that succeeds, it assumes that the entry
		622	is a directory or a symlink to directory (which will be checked
		623	seperately). This is often faster than stat'ing the entry itself because
		624	filesystems might detect the type of the entry without reading the inode
		625	data (e.g. ext2fs filetype feature).
		626
		627	If the known number of directories (link count - 2) has been reached, the
		628	rest of the entries is assumed to be non-directories.
		629
		630	This only works with certainty on POSIX (= UNIX) filesystems, which
		631	fortunately are the vast majority of filesystems around.
		632
		633	It will also likely work on non-POSIX filesystems with reduced efficiency
		634	as those tend to return 0 or 1 as link counts, which disables the
		635	directory counting heuristic.
		636
		637	=cut
		638
		639	sub aio_scandir($$$) {
		640	aio_block {
		641	my ($path, $maxreq, $cb) = @_;
		642
		643	my $pri = aioreq_pri;
		644
		645	my $grp = aio_group $cb;
		646
		647	$maxreq = 4 if $maxreq <= 0;
		648
		649	# stat once
		650	aioreq_pri $pri;
		651	add $grp aio_stat $path, sub {
		652	return $grp->result () if $_[0];
		653	my $now = time;
		654	my $hash1 = join ":", (stat _)[0,1,3,7,9];
		655
		656	# read the directory entries
		657	aioreq_pri $pri;
		658	add $grp aio_readdir $path, sub {
		659	my $entries = shift
		660	or return $grp->result ();
		661
		662	# stat the dir another time
		663	aioreq_pri $pri;
		664	add $grp aio_stat $path, sub {
		665	my $hash2 = join ":", (stat _)[0,1,3,7,9];
		666
		667	my $ndirs;
		668
		669	# take the slow route if anything looks fishy
		670	if ($hash1 ne $hash2 or (stat _)[9] == $now) {
		671	$ndirs = -1;
		672	} else {
		673	# if nlink == 2, we are finished
		674	# on non-posix-fs's, we rely on nlink < 2
		675	$ndirs = (stat _)[3] - 2
		676	or return $grp->result ([], $entries);
		677	}
		678
		679	# sort into likely dirs and likely nondirs
		680	# dirs == files without ".", short entries first
		681	$entries = [map $_->[0],
		682	sort { $b->[1] cmp $a->[1] }
		683	map [$_, sprintf "%s%04d", (/.\./ ? "1" : "0"), length],
		684	@$entries];
		685
		686	my (@dirs, @nondirs);
		687
		688	my $statgrp = add $grp aio_group sub {
		689	$grp->result (\@dirs, \@nondirs);
		690	};
		691
		692	limit $statgrp $maxreq;
		693	feed $statgrp sub {
		694	return unless @$entries;
		695	my $entry = pop @$entries;
		696
		697	aioreq_pri $pri;
		698	add $statgrp aio_stat "$path/$entry/.", sub {
		699	if ($_[0] < 0) {
		700	push @nondirs, $entry;
		701	} else {
		702	# need to check for real directory
		703	aioreq_pri $pri;
		704	add $statgrp aio_lstat "$path/$entry", sub {
		705	if (-d _) {
		706	push @dirs, $entry;
		707
		708	unless (--$ndirs) {
		709	push @nondirs, @$entries;
		710	feed $statgrp;
		711	}
		712	} else {
		713	push @nondirs, $entry;
		714	}
		715	}
		716	}
		717	};
		718	};
		719	};
		720	};
		721	};
		722
		723	$grp
		724	}
		725	}
		726
		727	=item aio_rmtree $path, $callback->($status)
		728
		729	Delete a directory tree starting (and including) C<$path>, return the status of the final C<rmdir> only.
		730	This is a composite request that uses C<aio_scandir> to recurse into and rmdir directories, and
		731	unlink everything else.
		732
		733	=cut
		734
		735	sub aio_rmtree;
		736	sub aio_rmtree {
		737	aio_block {
		738	my ($path, $cb) = @_;
		739
		740	my $pri = aioreq_pri;
		741	my $grp = aio_group $cb;
		742
		743	aioreq_pri $pri;
		744	add $grp aio_scandir $path, 0, sub {
		745	my ($dirs, $nondirs) = @_;
		746
		747	my $dirgrp = aio_group sub {
		748	add $grp aio_rmdir $path, sub {
		749	$grp->result ($_[0]);
		750	};
		751	};
		752
		753	(aioreq_pri $pri), add $dirgrp aio_rmtree "$path/$_" for @$dirs;
		754	(aioreq_pri $pri), add $dirgrp aio_unlink "$path/$_" for @$nondirs;
		755
		756	add $grp $dirgrp;
		757	};
		758
		759	$grp
		760	}
		761	}
		762
179	=item aio_fsync $fh, $callback	763	=item aio_fsync $fh, $callback->($status)
180		764
181	Asynchronously call fsync on the given filehandle and call the callback	765	Asynchronously call fsync on the given filehandle and call the callback
182	with the fsync result code.	766	with the fsync result code.
183		767
184	=item aio_fdatasync $fh, $callback	768	=item aio_fdatasync $fh, $callback->($status)
185		769
186	Asynchronously call fdatasync on the given filehandle and call the	770	Asynchronously call fdatasync on the given filehandle and call the
187	callback with the fdatasync result code.	771	callback with the fdatasync result code.
188		772
		773	If this call isn't available because your OS lacks it or it couldn't be
		774	detected, it will be emulated by calling C<fsync> instead.
		775
		776	=item aio_group $callback->(...)
		777
		778	This is a very special aio request: Instead of doing something, it is a
		779	container for other aio requests, which is useful if you want to bundle
		780	many requests into a single, composite, request with a definite callback
		781	and the ability to cancel the whole request with its subrequests.
		782
		783	Returns an object of class L<IO::AIO::GRP>. See its documentation below
		784	for more info.
		785
		786	Example:
		787
		788	my $grp = aio_group sub {
		789	print "all stats done\n";
		790	};
		791
		792	add $grp
		793	(aio_stat ...),
		794	(aio_stat ...),
		795	...;
		796
		797	=item aio_nop $callback->()
		798
		799	This is a special request - it does nothing in itself and is only used for
		800	side effects, such as when you want to add a dummy request to a group so
		801	that finishing the requests in the group depends on executing the given
		802	code.
		803
		804	While this request does nothing, it still goes through the execution
		805	phase and still requires a worker thread. Thus, the callback will not
		806	be executed immediately but only after other requests in the queue have
		807	entered their execution phase. This can be used to measure request
		808	latency.
		809
		810	=item IO::AIO::aio_busy $fractional_seconds, $callback->() NOT EXPORTED
		811
		812	Mainly used for debugging and benchmarking, this aio request puts one of
		813	the request workers to sleep for the given time.
		814
		815	While it is theoretically handy to have simple I/O scheduling requests
		816	like sleep and file handle readable/writable, the overhead this creates is
		817	immense (it blocks a thread for a long time) so do not use this function
		818	except to put your application under artificial I/O pressure.
		819
189	=back	820	=back
190		821
		822	=head2 IO::AIO::REQ CLASS
		823
		824	All non-aggregate C<aio_*> functions return an object of this class when
		825	called in non-void context.
		826
		827	=over 4
		828
		829	=item cancel $req
		830
		831	Cancels the request, if possible. Has the effect of skipping execution
		832	when entering the B<execute> state and skipping calling the callback when
		833	entering the the B<result> state, but will leave the request otherwise
		834	untouched. That means that requests that currently execute will not be
		835	stopped and resources held by the request will not be freed prematurely.
		836
		837	=item cb $req $callback->(...)
		838
		839	Replace (or simply set) the callback registered to the request.
		840
		841	=back
		842
		843	=head2 IO::AIO::GRP CLASS
		844
		845	This class is a subclass of L<IO::AIO::REQ>, so all its methods apply to
		846	objects of this class, too.
		847
		848	A IO::AIO::GRP object is a special request that can contain multiple other
		849	aio requests.
		850
		851	You create one by calling the C<aio_group> constructing function with a
		852	callback that will be called when all contained requests have entered the
		853	C<done> state:
		854
		855	my $grp = aio_group sub {
		856	print "all requests are done\n";
		857	};
		858
		859	You add requests by calling the C<add> method with one or more
		860	C<IO::AIO::REQ> objects:
		861
		862	$grp->add (aio_unlink "...");
		863
		864	add $grp aio_stat "...", sub {
		865	$_[0] or return $grp->result ("error");
		866
		867	# add another request dynamically, if first succeeded
		868	add $grp aio_open "...", sub {
		869	$grp->result ("ok");
		870	};
		871	};
		872
		873	This makes it very easy to create composite requests (see the source of
		874	C<aio_move> for an application) that work and feel like simple requests.
		875
		876	=over 4
		877
		878	=item * The IO::AIO::GRP objects will be cleaned up during calls to
		879	C<IO::AIO::poll_cb>, just like any other request.
		880
		881	=item * They can be canceled like any other request. Canceling will cancel not
		882	only the request itself, but also all requests it contains.
		883
		884	=item * They can also can also be added to other IO::AIO::GRP objects.
		885
		886	=item * You must not add requests to a group from within the group callback (or
		887	any later time).
		888
		889	=back
		890
		891	Their lifetime, simplified, looks like this: when they are empty, they
		892	will finish very quickly. If they contain only requests that are in the
		893	C<done> state, they will also finish. Otherwise they will continue to
		894	exist.
		895
		896	That means after creating a group you have some time to add requests. And
		897	in the callbacks of those requests, you can add further requests to the
		898	group. And only when all those requests have finished will the the group
		899	itself finish.
		900
		901	=over 4
		902
		903	=item add $grp ...
		904
		905	=item $grp->add (...)
		906
		907	Add one or more requests to the group. Any type of L<IO::AIO::REQ> can
		908	be added, including other groups, as long as you do not create circular
		909	dependencies.
		910
		911	Returns all its arguments.
		912
		913	=item $grp->cancel_subs
		914
		915	Cancel all subrequests and clears any feeder, but not the group request
		916	itself. Useful when you queued a lot of events but got a result early.
		917
		918	=item $grp->result (...)
		919
		920	Set the result value(s) that will be passed to the group callback when all
		921	subrequests have finished and set thre groups errno to the current value
		922	of errno (just like calling C<errno> without an error number). By default,
		923	no argument will be passed and errno is zero.
		924
		925	=item $grp->errno ([$errno])
		926
		927	Sets the group errno value to C<$errno>, or the current value of errno
		928	when the argument is missing.
		929
		930	Every aio request has an associated errno value that is restored when
		931	the callback is invoked. This method lets you change this value from its
		932	default (0).
		933
		934	Calling C<result> will also set errno, so make sure you either set C<$!>
		935	before the call to C<result>, or call c<errno> after it.
		936
		937	=item feed $grp $callback->($grp)
		938
		939	Sets a feeder/generator on this group: every group can have an attached
		940	generator that generates requests if idle. The idea behind this is that,
		941	although you could just queue as many requests as you want in a group,
		942	this might starve other requests for a potentially long time. For
		943	example, C<aio_scandir> might generate hundreds of thousands C<aio_stat>
		944	requests, delaying any later requests for a long time.
		945
		946	To avoid this, and allow incremental generation of requests, you can
		947	instead a group and set a feeder on it that generates those requests. The
		948	feed callback will be called whenever there are few enough (see C<limit>,
		949	below) requests active in the group itself and is expected to queue more
		950	requests.
		951
		952	The feed callback can queue as many requests as it likes (i.e. C<add> does
		953	not impose any limits).
		954
		955	If the feed does not queue more requests when called, it will be
		956	automatically removed from the group.
		957
		958	If the feed limit is C<0>, it will be set to C<2> automatically.
		959
		960	Example:
		961
		962	# stat all files in @files, but only ever use four aio requests concurrently:
		963
		964	my $grp = aio_group sub { print "finished\n" };
		965	limit $grp 4;
		966	feed $grp sub {
		967	my $file = pop @files
		968	or return;
		969
		970	add $grp aio_stat $file, sub { ... };
		971	};
		972
		973	=item limit $grp $num
		974
		975	Sets the feeder limit for the group: The feeder will be called whenever
		976	the group contains less than this many requests.
		977
		978	Setting the limit to C<0> will pause the feeding process.
		979
		980	=back
		981
191	=head2 SUPPORT FUNCTIONS	982	=head2 SUPPORT FUNCTIONS
192		983
		984	=head3 EVENT PROCESSING AND EVENT LOOP INTEGRATION
		985
193	=over 4	986	=over 4
194		987
195	=item $fileno = IO::AIO::poll_fileno	988	=item $fileno = IO::AIO::poll_fileno
196		989
197	Return the I<request result pipe filehandle>. This filehandle must be	990	Return the I<request result pipe file descriptor>. This filehandle must be
198	polled for reading by some mechanism outside this module (e.g. Event	991	polled for reading by some mechanism outside this module (e.g. Event or
199	or select, see below). If the pipe becomes readable you have to call	992	select, see below or the SYNOPSIS). If the pipe becomes readable you have
200	C<poll_cb> to check the results.	993	to call C<poll_cb> to check the results.
201		994
202	See C<poll_cb> for an example.	995	See C<poll_cb> for an example.
203		996
204	=item IO::AIO::poll_cb	997	=item IO::AIO::poll_cb
205		998
206	Process all outstanding events on the result pipe. You have to call this	999	Process some outstanding events on the result pipe. You have to call this
207	regularly. Returns the number of events processed. Returns immediately	1000	regularly. Returns the number of events processed. Returns immediately
208	when no events are outstanding.	1001	when no events are outstanding. The amount of events processed depends on
		1002	the settings of C<IO::AIO::max_poll_req> and C<IO::AIO::max_poll_time>.
209		1003
210	You can use Event to multiplex, e.g.:	1004	If not all requests were processed for whatever reason, the filehandle
		1005	will still be ready when C<poll_cb> returns.
		1006
		1007	Example: Install an Event watcher that automatically calls
		1008	IO::AIO::poll_cb with high priority:
211		1009
212	Event->io (fd => IO::AIO::poll_fileno,	1010	Event->io (fd => IO::AIO::poll_fileno,
213	poll => 'r', async => 1,	1011	poll => 'r', async => 1,
214	cb => \&IO::AIO::poll_cb);	1012	cb => \&IO::AIO::poll_cb);
215		1013
		1014	=item IO::AIO::max_poll_reqs $nreqs
		1015
		1016	=item IO::AIO::max_poll_time $seconds
		1017
		1018	These set the maximum number of requests (default C<0>, meaning infinity)
		1019	that are being processed by C<IO::AIO::poll_cb> in one call, respectively
		1020	the maximum amount of time (default C<0>, meaning infinity) spent in
		1021	C<IO::AIO::poll_cb> to process requests (more correctly the mininum amount
		1022	of time C<poll_cb> is allowed to use).
		1023
		1024	Setting C<max_poll_time> to a non-zero value creates an overhead of one
		1025	syscall per request processed, which is not normally a problem unless your
		1026	callbacks are really really fast or your OS is really really slow (I am
		1027	not mentioning Solaris here). Using C<max_poll_reqs> incurs no overhead.
		1028
		1029	Setting these is useful if you want to ensure some level of
		1030	interactiveness when perl is not fast enough to process all requests in
		1031	time.
		1032
		1033	For interactive programs, values such as C<0.01> to C<0.1> should be fine.
		1034
		1035	Example: Install an Event watcher that automatically calls
		1036	IO::AIO::poll_cb with low priority, to ensure that other parts of the
		1037	program get the CPU sometimes even under high AIO load.
		1038
		1039	# try not to spend much more than 0.1s in poll_cb
		1040	IO::AIO::max_poll_time 0.1;
		1041
		1042	# use a low priority so other tasks have priority
		1043	Event->io (fd => IO::AIO::poll_fileno,
		1044	poll => 'r', nice => 1,
		1045	cb => &IO::AIO::poll_cb);
		1046
216	=item IO::AIO::poll_wait	1047	=item IO::AIO::poll_wait
217		1048
		1049	If there are any outstanding requests and none of them in the result
218	Wait till the result filehandle becomes ready for reading (simply does a	1050	phase, wait till the result filehandle becomes ready for reading (simply
219	select on the filehandle. This is useful if you want to synchronously wait	1051	does a C<select> on the filehandle. This is useful if you want to
220	for some requests to finish).	1052	synchronously wait for some requests to finish).
221		1053
222	See C<nreqs> for an example.	1054	See C<nreqs> for an example.
223		1055
		1056	=item IO::AIO::poll
		1057
		1058	Waits until some requests have been handled.
		1059
		1060	Returns the number of requests processed, but is otherwise strictly
		1061	equivalent to:
		1062
		1063	IO::AIO::poll_wait, IO::AIO::poll_cb
		1064
224	=item IO::AIO::nreqs	1065	=item IO::AIO::flush
225		1066
226	Returns the number of requests currently outstanding.	1067	Wait till all outstanding AIO requests have been handled.
227		1068
228	Example: wait till there are no outstanding requests anymore:	1069	Strictly equivalent to:
229		1070
230	IO::AIO::poll_wait, IO::AIO::poll_cb	1071	IO::AIO::poll_wait, IO::AIO::poll_cb
231	while IO::AIO::nreqs;	1072	while IO::AIO::nreqs;
232		1073
		1074	=head3 CONTROLLING THE NUMBER OF THREADS
		1075
233	=item IO::AIO::min_parallel $nthreads	1076	=item IO::AIO::min_parallel $nthreads
234		1077
235	Set the minimum number of AIO threads to C<$nthreads>. The default is	1078	Set the minimum number of AIO threads to C<$nthreads>. The current
236	C<1>, which means a single asynchronous operation can be done at one time	1079	default is C<8>, which means eight asynchronous operations can execute
237	(the number of outstanding operations, however, is unlimited).	1080	concurrently at any one time (the number of outstanding requests,
		1081	however, is unlimited).
238		1082
		1083	IO::AIO starts threads only on demand, when an AIO request is queued and
		1084	no free thread exists. Please note that queueing up a hundred requests can
		1085	create demand for a hundred threads, even if it turns out that everything
		1086	is in the cache and could have been processed faster by a single thread.
		1087
239	It is recommended to keep the number of threads low, as some Linux	1088	It is recommended to keep the number of threads relatively low, as some
240	kernel versions will scale negatively with the number of threads (higher	1089	Linux kernel versions will scale negatively with the number of threads
241	parallelity => MUCH higher latency). With current Linux 2.6 versions, 4-32	1090	(higher parallelity => MUCH higher latency). With current Linux 2.6
242	threads should be fine.	1091	versions, 4-32 threads should be fine.
243		1092
244	Under normal circumstances you don't need to call this function, as this	1093	Under most circumstances you don't need to call this function, as the
245	module automatically starts some threads (the exact number might change,	1094	module selects a default that is suitable for low to moderate load.
246	and is currently 4).
247		1095
248	=item IO::AIO::max_parallel $nthreads	1096	=item IO::AIO::max_parallel $nthreads
249		1097
250	Sets the maximum number of AIO threads to C<$nthreads>. If more than	1098	Sets the maximum number of AIO threads to C<$nthreads>. If more than the
251	the specified number of threads are currently running, kill them. This	1099	specified number of threads are currently running, this function kills
252	function blocks until the limit is reached.	1100	them. This function blocks until the limit is reached.
		1101
		1102	While C<$nthreads> are zero, aio requests get queued but not executed
		1103	until the number of threads has been increased again.
253		1104
254	This module automatically runs C<max_parallel 0> at program end, to ensure	1105	This module automatically runs C<max_parallel 0> at program end, to ensure
255	that all threads are killed and that there are no outstanding requests.	1106	that all threads are killed and that there are no outstanding requests.
256		1107
257	Under normal circumstances you don't need to call this function.	1108	Under normal circumstances you don't need to call this function.
258		1109
		1110	=item IO::AIO::max_idle $nthreads
		1111
		1112	Limit the number of threads (default: 4) that are allowed to idle (i.e.,
		1113	threads that did not get a request to process within 10 seconds). That
		1114	means if a thread becomes idle while C<$nthreads> other threads are also
		1115	idle, it will free its resources and exit.
		1116
		1117	This is useful when you allow a large number of threads (e.g. 100 or 1000)
		1118	to allow for extremely high load situations, but want to free resources
		1119	under normal circumstances (1000 threads can easily consume 30MB of RAM).
		1120
		1121	The default is probably ok in most situations, especially if thread
		1122	creation is fast. If thread creation is very slow on your system you might
		1123	want to use larger values.
		1124
259	=item $oldnreqs = IO::AIO::max_outstanding $nreqs	1125	=item $oldmaxreqs = IO::AIO::max_outstanding $maxreqs
		1126
		1127	This is a very bad function to use in interactive programs because it
		1128	blocks, and a bad way to reduce concurrency because it is inexact: Better
		1129	use an C<aio_group> together with a feed callback.
260		1130
261	Sets the maximum number of outstanding requests to C<$nreqs>. If you	1131	Sets the maximum number of outstanding requests to C<$nreqs>. If you
262	try to queue up more than this number of requests, the caller will block until	1132	to queue up more than this number of requests, the next call to the
263	some requests have been handled.	1133	C<poll_cb> (and C<poll_some> and other functions calling C<poll_cb>)
		1134	function will block until the limit is no longer exceeded.
264		1135
265	The default is very large, so normally there is no practical limit. If you	1136	The default value is very large, so there is no practical limit on the
266	queue up many requests in a loop it it often improves speed if you set	1137	number of outstanding requests.
267	this to a relatively low number, such as C<100>.
268		1138
269	Under normal circumstances you don't need to call this function.	1139	You can still queue as many requests as you want. Therefore,
		1140	C<max_oustsanding> is mainly useful in simple scripts (with low values) or
		1141	as a stop gap to shield against fatal memory overflow (with large values).
		1142
		1143	=head3 STATISTICAL INFORMATION
		1144
		1145	=item IO::AIO::nreqs
		1146
		1147	Returns the number of requests currently in the ready, execute or pending
		1148	states (i.e. for which their callback has not been invoked yet).
		1149
		1150	Example: wait till there are no outstanding requests anymore:
		1151
		1152	IO::AIO::poll_wait, IO::AIO::poll_cb
		1153	while IO::AIO::nreqs;
		1154
		1155	=item IO::AIO::nready
		1156
		1157	Returns the number of requests currently in the ready state (not yet
		1158	executed).
		1159
		1160	=item IO::AIO::npending
		1161
		1162	Returns the number of requests currently in the pending state (executed,
		1163	but not yet processed by poll_cb).
270		1164
271	=back	1165	=back
272		1166
273	=cut	1167	=cut
274		1168
275	# support function to convert a fd into a perl filehandle	1169	# support function to convert a fd into a perl filehandle
276	sub _fd2fh {	1170	sub _fd2fh {
277	return undef if $_[0] < 0;	1171	return undef if $_[0] < 0;
278		1172
279	# try to be perl5.6-compatible	1173	# try to generate nice filehandles
280	local *AIO_FH;	1174	my $sym = "IO::AIO::fd#$_[0]";
281	open AIO_FH, "+<&=$_[0]"	1175	local *$sym;
		1176
		1177	open *$sym, "+<&=$_[0]" # usually works under any unix
		1178	or open *$sym, "<&=$_[0]" # cygwin needs this
		1179	or open *$sym, ">&=$_[0]" # or this
282	or return undef;	1180	or return undef;
283		1181
284	*AIO_FH	1182	*$sym
285	}	1183	}
286		1184
287	min_parallel 4;	1185	min_parallel 8;
288		1186
289	END {	1187	END { flush }
290	max_parallel 0;
291	}
292		1188
293	1;	1189	1;
294		1190
		1191	=head2 FORK BEHAVIOUR
		1192
		1193	This module should do "the right thing" when the process using it forks:
		1194
		1195	Before the fork, IO::AIO enters a quiescent state where no requests
		1196	can be added in other threads and no results will be processed. After
		1197	the fork the parent simply leaves the quiescent state and continues
		1198	request/result processing, while the child frees the request/result queue
		1199	(so that the requests started before the fork will only be handled in the
		1200	parent). Threads will be started on demand until the limit set in the
		1201	parent process has been reached again.
		1202
		1203	In short: the parent will, after a short pause, continue as if fork had
		1204	not been called, while the child will act as if IO::AIO has not been used
		1205	yet.
		1206
		1207	=head2 MEMORY USAGE
		1208
		1209	Per-request usage:
		1210
		1211	Each aio request uses - depending on your architecture - around 100-200
		1212	bytes of memory. In addition, stat requests need a stat buffer (possibly
		1213	a few hundred bytes), readdir requires a result buffer and so on. Perl
		1214	scalars and other data passed into aio requests will also be locked and
		1215	will consume memory till the request has entered the done state.
		1216
		1217	This is now awfully much, so queuing lots of requests is not usually a
		1218	problem.
		1219
		1220	Per-thread usage:
		1221
		1222	In the execution phase, some aio requests require more memory for
		1223	temporary buffers, and each thread requires a stack and other data
		1224	structures (usually around 16k-128k, depending on the OS).
		1225
		1226	=head1 KNOWN BUGS
		1227
		1228	Known bugs will be fixed in the next release.
		1229
295	=head1 SEE ALSO	1230	=head1 SEE ALSO
296		1231
297	L<Coro>, L<Linux::AIO>.	1232	L<Coro::AIO>.
298		1233
299	=head1 AUTHOR	1234	=head1 AUTHOR
300		1235
301	Marc Lehmann <schmorp@schmorp.de>	1236	Marc Lehmann <schmorp@schmorp.de>
302	http://home.schmorp.de/	1237	http://home.schmorp.de/

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Revision 1.99 by root, Sun Jan 7 21:32:20 2007 UTC