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Revision 1.6 by root, Sun Jul 10 22:19:48 2005 UTC vs.
Revision 1.185 by root, Sat Dec 11 19:06:07 2010 UTC

…		…
4		4
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", IO::AIO::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
21	Event->io (fd => IO::AIO::poll_fileno,	22	use IO::AIO 2;
22	poll => 'r', async => 1,
23	cb => \&IO::AIO::poll_cb);
24		23
25	# Glib/Gtk2	24	aioreq_pri 4; # give next request a very high priority
26	add_watch Glib::IO IO::AIO::poll_fileno,	25	my $req = aio_unlink "/tmp/file", sub { };
27	\&IO::AIO::poll_cb;	26	$req->cancel; # cancel request if still in queue
28		27
29	# Tk	28	my $grp = aio_group sub { print "all stats done\n" };
30	Tk::Event::IO->fileevent (IO::AIO::poll_fileno, "",	29	add $grp aio_stat "..." for ...;
31	readable => \&IO::AIO::poll_cb);
32		30
33	=head1 DESCRIPTION	31	=head1 DESCRIPTION
34		32
35	This module implements asynchronous I/O using whatever means your	33	This module implements asynchronous I/O using whatever means your
36	operating system supports.	34	operating system supports. It is implemented as an interface to C<libeio>
		35	(L<http://software.schmorp.de/pkg/libeio.html>).
37		36
		37	Asynchronous means that operations that can normally block your program
		38	(e.g. reading from disk) will be done asynchronously: the operation
		39	will still block, but you can do something else in the meantime. This
		40	is extremely useful for programs that need to stay interactive even
		41	when doing heavy I/O (GUI programs, high performance network servers
		42	etc.), but can also be used to easily do operations in parallel that are
		43	normally done sequentially, e.g. stat'ing many files, which is much faster
		44	on a RAID volume or over NFS when you do a number of stat operations
		45	concurrently.
		46
		47	While most of this works on all types of file descriptors (for
		48	example sockets), using these functions on file descriptors that
		49	support nonblocking operation (again, sockets, pipes etc.) is
		50	very inefficient. Use an event loop for that (such as the L<EV>
		51	module): IO::AIO will naturally fit into such an event loop itself.
		52
38	Currently, a number of threads are started that execute your read/writes	53	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	54	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	55	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	56	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	57	functions available on many operating systems. However, they are often
43	not well-supported (Linux doesn't allow them on normal files currently,	58	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	59	files currently, for example), and they would only support aio_read and
45	remaining functionality would have to be implemented using threads anyway.	60	aio_write, so the remaining functionality would have to be implemented
		61	using threads anyway.
46		62
47	Although the module will work with in the presence of other threads, it is	63	Although the module will work in the presence of other (Perl-) threads,
48	currently not reentrant, so use appropriate locking yourself.	64	it is currently not reentrant in any way, so use appropriate locking
		65	yourself, always call C<poll_cb> from within the same thread, or never
		66	call C<poll_cb> (or other C<aio_> functions) recursively.
		67
		68	=head2 EXAMPLE
		69
		70	This is a simple example that uses the EV module and loads
		71	F</etc/passwd> asynchronously:
		72
		73	use Fcntl;
		74	use EV;
		75	use IO::AIO;
		76
		77	# register the IO::AIO callback with EV
		78	my $aio_w = EV::io IO::AIO::poll_fileno, EV::READ, \&IO::AIO::poll_cb;
		79
		80	# queue the request to open /etc/passwd
		81	aio_open "/etc/passwd", IO::AIO::O_RDONLY, 0, sub {
		82	my $fh = shift
		83	or die "error while opening: $!";
		84
		85	# stat'ing filehandles is generally non-blocking
		86	my $size = -s $fh;
		87
		88	# queue a request to read the file
		89	my $contents;
		90	aio_read $fh, 0, $size, $contents, 0, sub {
		91	$_[0] == $size
		92	or die "short read: $!";
		93
		94	close $fh;
		95
		96	# file contents now in $contents
		97	print $contents;
		98
		99	# exit event loop and program
		100	EV::unloop;
		101	};
		102	};
		103
		104	# possibly queue up other requests, or open GUI windows,
		105	# check for sockets etc. etc.
		106
		107	# process events as long as there are some:
		108	EV::loop;
		109
		110	=head1 REQUEST ANATOMY AND LIFETIME
		111
		112	Every C<aio_*> function creates a request. which is a C data structure not
		113	directly visible to Perl.
		114
		115	If called in non-void context, every request function returns a Perl
		116	object representing the request. In void context, nothing is returned,
		117	which saves a bit of memory.
		118
		119	The perl object is a fairly standard ref-to-hash object. The hash contents
		120	are not used by IO::AIO so you are free to store anything you like in it.
		121
		122	During their existance, aio requests travel through the following states,
		123	in order:
		124
		125	=over 4
		126
		127	=item ready
		128
		129	Immediately after a request is created it is put into the ready state,
		130	waiting for a thread to execute it.
		131
		132	=item execute
		133
		134	A thread has accepted the request for processing and is currently
		135	executing it (e.g. blocking in read).
		136
		137	=item pending
		138
		139	The request has been executed and is waiting for result processing.
		140
		141	While request submission and execution is fully asynchronous, result
		142	processing is not and relies on the perl interpreter calling C<poll_cb>
		143	(or another function with the same effect).
		144
		145	=item result
		146
		147	The request results are processed synchronously by C<poll_cb>.
		148
		149	The C<poll_cb> function will process all outstanding aio requests by
		150	calling their callbacks, freeing memory associated with them and managing
		151	any groups they are contained in.
		152
		153	=item done
		154
		155	Request has reached the end of its lifetime and holds no resources anymore
		156	(except possibly for the Perl object, but its connection to the actual
		157	aio request is severed and calling its methods will either do nothing or
		158	result in a runtime error).
		159
		160	=back
49		161
50	=cut	162	=cut
51		163
52	package IO::AIO;	164	package IO::AIO;
53		165
		166	use Carp ();
		167
		168	use common::sense;
		169
54	use base 'Exporter';	170	use base 'Exporter';
55		171
56	use Fcntl ();
57
58	BEGIN {	172	BEGIN {
59	$VERSION = 0.2;	173	our $VERSION = '3.7';
60		174
61	@EXPORT = qw(aio_read aio_write aio_open aio_close aio_stat aio_lstat aio_unlink	175	our @AIO_REQ = qw(aio_sendfile aio_read aio_write aio_open aio_close
62	aio_fsync aio_fdatasync aio_readahead);	176	aio_stat aio_lstat aio_unlink aio_rmdir aio_readdir aio_readdirx
63	@EXPORT_OK = qw(poll_fileno poll_cb min_parallel max_parallel max_outstanding nreqs);	177	aio_scandir aio_symlink aio_readlink aio_sync aio_fsync
		178	aio_fdatasync aio_sync_file_range aio_pathsync aio_readahead
		179	aio_rename aio_link aio_move aio_copy aio_group
		180	aio_nop aio_mknod aio_load aio_rmtree aio_mkdir aio_chown
		181	aio_chmod aio_utime aio_truncate
		182	aio_msync aio_mtouch aio_mlock aio_mlockall
		183	aio_statvfs);
		184
		185	our @EXPORT = (@AIO_REQ, qw(aioreq_pri aioreq_nice));
		186	our @EXPORT_OK = qw(poll_fileno poll_cb poll_wait flush
		187	min_parallel max_parallel max_idle
		188	nreqs nready npending nthreads
		189	max_poll_time max_poll_reqs
		190	sendfile fadvise madvise
		191	mmap munmap munlock munlockall);
		192
		193	push @AIO_REQ, qw(aio_busy); # not exported
		194
		195	@IO::AIO::GRP::ISA = 'IO::AIO::REQ';
64		196
65	require XSLoader;	197	require XSLoader;
66	XSLoader::load IO::AIO, $VERSION;	198	XSLoader::load ("IO::AIO", $VERSION);
67	}	199	}
68		200
69	=head1 FUNCTIONS	201	=head1 FUNCTIONS
70		202
		203	=head2 QUICK OVERVIEW
		204
		205	This section simply lists the prototypes of the most important functions
		206	for quick reference. See the following sections for function-by-function
		207	documentation.
		208
		209	aio_open $pathname, $flags, $mode, $callback->($fh)
		210	aio_close $fh, $callback->($status)
		211	aio_read $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
		212	aio_write $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
		213	aio_sendfile $out_fh, $in_fh, $in_offset, $length, $callback->($retval)
		214	aio_readahead $fh,$offset,$length, $callback->($retval)
		215	aio_stat $fh_or_path, $callback->($status)
		216	aio_lstat $fh, $callback->($status)
		217	aio_statvfs $fh_or_path, $callback->($statvfs)
		218	aio_utime $fh_or_path, $atime, $mtime, $callback->($status)
		219	aio_chown $fh_or_path, $uid, $gid, $callback->($status)
		220	aio_truncate $fh_or_path, $offset, $callback->($status)
		221	aio_chmod $fh_or_path, $mode, $callback->($status)
		222	aio_unlink $pathname, $callback->($status)
		223	aio_mknod $path, $mode, $dev, $callback->($status)
		224	aio_link $srcpath, $dstpath, $callback->($status)
		225	aio_symlink $srcpath, $dstpath, $callback->($status)
		226	aio_readlink $path, $callback->($link)
		227	aio_rename $srcpath, $dstpath, $callback->($status)
		228	aio_mkdir $pathname, $mode, $callback->($status)
		229	aio_rmdir $pathname, $callback->($status)
		230	aio_readdir $pathname, $callback->($entries)
		231	aio_readdirx $pathname, $flags, $callback->($entries, $flags)
		232	IO::AIO::READDIR_DENTS IO::AIO::READDIR_DIRS_FIRST
		233	IO::AIO::READDIR_STAT_ORDER IO::AIO::READDIR_FOUND_UNKNOWN
		234	aio_load $path, $data, $callback->($status)
		235	aio_copy $srcpath, $dstpath, $callback->($status)
		236	aio_move $srcpath, $dstpath, $callback->($status)
		237	aio_scandir $path, $maxreq, $callback->($dirs, $nondirs)
		238	aio_rmtree $path, $callback->($status)
		239	aio_sync $callback->($status)
		240	aio_fsync $fh, $callback->($status)
		241	aio_fdatasync $fh, $callback->($status)
		242	aio_sync_file_range $fh, $offset, $nbytes, $flags, $callback->($status)
		243	aio_pathsync $path, $callback->($status)
		244	aio_msync $scalar, $offset = 0, $length = undef, flags = 0, $callback->($status)
		245	aio_mtouch $scalar, $offset = 0, $length = undef, flags = 0, $callback->($status)
		246	aio_mlock $scalar, $offset = 0, $length = undef, $callback->($status)
		247	aio_mlockall $flags, $callback->($status)
		248	aio_group $callback->(...)
		249	aio_nop $callback->()
		250
		251	$prev_pri = aioreq_pri [$pri]
		252	aioreq_nice $pri_adjust
		253
		254	IO::AIO::poll_wait
		255	IO::AIO::poll_cb
		256	IO::AIO::poll
		257	IO::AIO::flush
		258	IO::AIO::max_poll_reqs $nreqs
		259	IO::AIO::max_poll_time $seconds
		260	IO::AIO::min_parallel $nthreads
		261	IO::AIO::max_parallel $nthreads
		262	IO::AIO::max_idle $nthreads
		263	IO::AIO::max_outstanding $maxreqs
		264	IO::AIO::nreqs
		265	IO::AIO::nready
		266	IO::AIO::npending
		267
		268	IO::AIO::sendfile $ofh, $ifh, $offset, $count
		269	IO::AIO::fadvise $fh, $offset, $len, $advice
		270	IO::AIO::madvise $scalar, $offset, $length, $advice
		271	IO::AIO::mprotect $scalar, $offset, $length, $protect
		272	IO::AIO::munlock $scalar, $offset = 0, $length = undef
		273	IO::AIO::munlockall
		274
71	=head2 AIO FUNCTIONS	275	=head2 AIO REQUEST FUNCTIONS
72		276
73	All the C<aio_*> calls are more or less thin wrappers around the syscall	277	All the C<aio_*> calls are more or less thin wrappers around the syscall
74	with the same name (sans C<aio_>). The arguments are similar or identical,	278	with the same name (sans C<aio_>). The arguments are similar or identical,
75	and they all accept an additional C<$callback> argument which must be	279	and they all accept an additional (and optional) C<$callback> argument
76	a code reference. This code reference will get called with the syscall	280	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	281	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	282	perl, which usually delivers "false") as its sole argument after the given
79	been executed asynchronously.	283	syscall has been executed asynchronously.
80		284
81	All functions that expect a filehandle will also accept a file descriptor.	285	All functions expecting a filehandle keep a copy of the filehandle
		286	internally until the request has finished.
82		287
		288	All functions return request objects of type L<IO::AIO::REQ> that allow
		289	further manipulation of those requests while they are in-flight.
		290
83	The filenames you pass to these routines I<must> be absolute. The reason	291	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	292	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	293	request is being executed, the current working directory could have
86	never change the current working directory.	294	changed. Alternatively, you can make sure that you never change the
		295	current working directory anywhere in the program and then use relative
		296	paths.
		297
		298	To encode pathnames as octets, either make sure you either: a) always pass
		299	in filenames you got from outside (command line, readdir etc.) without
		300	tinkering, b) are ASCII or ISO 8859-1, c) use the Encode module and encode
		301	your pathnames to the locale (or other) encoding in effect in the user
		302	environment, d) use Glib::filename_from_unicode on unicode filenames or e)
		303	use something else to ensure your scalar has the correct contents.
		304
		305	This works, btw. independent of the internal UTF-8 bit, which IO::AIO
		306	handles correctly whether it is set or not.
87		307
88	=over 4	308	=over 4
89		309
		310	=item $prev_pri = aioreq_pri [$pri]
		311
		312	Returns the priority value that would be used for the next request and, if
		313	C<$pri> is given, sets the priority for the next aio request.
		314
		315	The default priority is C<0>, the minimum and maximum priorities are C<-4>
		316	and C<4>, respectively. Requests with higher priority will be serviced
		317	first.
		318
		319	The priority will be reset to C<0> after each call to one of the C<aio_*>
		320	functions.
		321
		322	Example: open a file with low priority, then read something from it with
		323	higher priority so the read request is serviced before other low priority
		324	open requests (potentially spamming the cache):
		325
		326	aioreq_pri -3;
		327	aio_open ..., sub {
		328	return unless $_[0];
		329
		330	aioreq_pri -2;
		331	aio_read $_[0], ..., sub {
		332	...
		333	};
		334	};
		335
		336
		337	=item aioreq_nice $pri_adjust
		338
		339	Similar to C<aioreq_pri>, but subtracts the given value from the current
		340	priority, so the effect is cumulative.
		341
		342
90	=item aio_open $pathname, $flags, $mode, $callback	343	=item aio_open $pathname, $flags, $mode, $callback->($fh)
91		344
92	Asynchronously open or create a file and call the callback with a newly	345	Asynchronously open or create a file and call the callback with a newly
93	created filehandle for the file.	346	created filehandle for the file.
94		347
95	The pathname passed to C<aio_open> must be absolute. See API NOTES, above,	348	The pathname passed to C<aio_open> must be absolute. See API NOTES, above,
96	for an explanation.	349	for an explanation.
97		350
98	The C<$mode> argument is a bitmask. See the C<Fcntl> module for a	351	The C<$flags> argument is a bitmask. See the C<Fcntl> module for a
99	list. They are the same as used in C<sysopen>.	352	list. They are the same as used by C<sysopen>.
		353
		354	Likewise, C<$mode> specifies the mode of the newly created file, if it
		355	didn't exist and C<O_CREAT> has been given, just like perl's C<sysopen>,
		356	except that it is mandatory (i.e. use C<0> if you don't create new files,
		357	and C<0666> or C<0777> if you do). Note that the C<$mode> will be modified
		358	by the umask in effect then the request is being executed, so better never
		359	change the umask.
100		360
101	Example:	361	Example:
102		362
103	aio_open "/etc/passwd", O_RDONLY, 0, sub {	363	aio_open "/etc/passwd", IO::AIO::O_RDONLY, 0, sub {
104	if ($_[0]) {	364	if ($_[0]) {
105	print "open successful, fh is $_[0]\n";	365	print "open successful, fh is $_[0]\n";
106	...	366	...
107	} else {	367	} else {
108	die "open failed: $!\n";	368	die "open failed: $!\n";
109	}	369	}
110	};	370	};
111		371
		372
112	=item aio_close $fh, $callback	373	=item aio_close $fh, $callback->($status)
113		374
114	Asynchronously close a file and call the callback with the result	375	Asynchronously close a file and call the callback with the result
115	code. I<WARNING:> although accepted, you should not pass in a perl	376	code.
116	filehandle here, as perl will likely close the file descriptor itself when
117	the filehandle is destroyed. Normally, you can safely call perls C<close>
118	or just let filehandles go out of scope.
119		377
		378	Unfortunately, you can't do this to perl. Perl I<insists> very strongly on
		379	closing the file descriptor associated with the filehandle itself.
		380
		381	Therefore, C<aio_close> will not close the filehandle - instead it will
		382	use dup2 to overwrite the file descriptor with the write-end of a pipe
		383	(the pipe fd will be created on demand and will be cached).
		384
		385	Or in other words: the file descriptor will be closed, but it will not be
		386	free for reuse until the perl filehandle is closed.
		387
		388	=cut
		389
120	=item aio_read $fh,$offset,$length, $data,$dataoffset,$callback	390	=item aio_read $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
121		391
122	=item aio_write $fh,$offset,$length, $data,$dataoffset,$callback	392	=item aio_write $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
123		393
124	Reads or writes C<length> bytes from the specified C<fh> and C<offset>	394	Reads or writes C<$length> bytes from or to the specified C<$fh> and
125	into the scalar given by C<data> and offset C<dataoffset> and calls the	395	C<$offset> into the scalar given by C<$data> and offset C<$dataoffset>
126	callback without the actual number of bytes read (or -1 on error, just	396	and calls the callback without the actual number of bytes read (or -1 on
127	like the syscall).	397	error, just like the syscall).
128		398
		399	C<aio_read> will, like C<sysread>, shrink or grow the C<$data> scalar to
		400	offset plus the actual number of bytes read.
		401
		402	If C<$offset> is undefined, then the current file descriptor offset will
		403	be used (and updated), otherwise the file descriptor offset will not be
		404	changed by these calls.
		405
		406	If C<$length> is undefined in C<aio_write>, use the remaining length of
		407	C<$data>.
		408
		409	If C<$dataoffset> is less than zero, it will be counted from the end of
		410	C<$data>.
		411
		412	The C<$data> scalar I<MUST NOT> be modified in any way while the request
		413	is outstanding. Modifying it can result in segfaults or World War III (if
		414	the necessary/optional hardware is installed).
		415
129	Example: Read 15 bytes at offset 7 into scalar C<$buffer>, strating at	416	Example: Read 15 bytes at offset 7 into scalar C<$buffer>, starting at
130	offset C<0> within the scalar:	417	offset C<0> within the scalar:
131		418
132	aio_read $fh, 7, 15, $buffer, 0, sub {	419	aio_read $fh, 7, 15, $buffer, 0, sub {
133	$_[0] >= 0 or die "read error: $!";	420	$_[0] > 0 or die "read error: $!";
134	print "read <$buffer>\n";	421	print "read $_[0] bytes: <$buffer>\n";
135	};	422	};
136		423
		424
		425	=item aio_sendfile $out_fh, $in_fh, $in_offset, $length, $callback->($retval)
		426
		427	Tries to copy C<$length> bytes from C<$in_fh> to C<$out_fh>. It starts
		428	reading at byte offset C<$in_offset>, and starts writing at the current
		429	file offset of C<$out_fh>. Because of that, it is not safe to issue more
		430	than one C<aio_sendfile> per C<$out_fh>, as they will interfere with each
		431	other.
		432
		433	Please note that C<aio_sendfile> can read more bytes from C<$in_fh> than
		434	are written, and there is no way to find out how many bytes have been read
		435	from C<aio_sendfile> alone, as C<aio_sendfile> only provides the number of
		436	bytes written to C<$out_fh>. Only if the result value equals C<$length>
		437	one can assume that C<$length> bytes have been read.
		438
		439	Unlike with other C<aio_> functions, it makes a lot of sense to use
		440	C<aio_sendfile> on non-blocking sockets, as long as one end (typically
		441	the C<$in_fh>) is a file - the file I/O will then be asynchronous, while
		442	the socket I/O will be non-blocking. Note, however, that you can run into
		443	a trap where C<aio_sendfile> reads some data with readahead, then fails
		444	to write all data, and when the socket is ready the next time, the data
		445	in the cache is already lost, forcing C<aio_sendfile> to again hit the
		446	disk. Explicit C<aio_read> + C<aio_write> let's you control resource usage
		447	much better.
		448
		449	This call tries to make use of a native C<sendfile> syscall to provide
		450	zero-copy operation. For this to work, C<$out_fh> should refer to a
		451	socket, and C<$in_fh> should refer to an mmap'able file.
		452
		453	If a native sendfile cannot be found or it fails with C<ENOSYS>,
		454	C<ENOTSUP>, C<EOPNOTSUPP>, C<EAFNOSUPPORT>, C<EPROTOTYPE> or C<ENOTSOCK>,
		455	it will be emulated, so you can call C<aio_sendfile> on any type of
		456	filehandle regardless of the limitations of the operating system.
		457
		458
137	=item aio_readahead $fh,$offset,$length, $callback	459	=item aio_readahead $fh,$offset,$length, $callback->($retval)
138		460
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<$!> is set to ENOSYS.
142
143	readahead() populates the page cache with data from a file so that	461	C<aio_readahead> populates the page cache with data from a file so that
144	subsequent reads from that file will not block on disk I/O. The C<$offset>	462	subsequent reads from that file will not block on disk I/O. The C<$offset>
145	argument specifies the starting point from which data is to be read and	463	argument specifies the starting point from which data is to be read and
146	C<$length> specifies the number of bytes to be read. I/O is performed in	464	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	465	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	466	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	467	(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.	468	file. The current file offset of the file is left unchanged.
151		469
		470	If that syscall doesn't exist (likely if your OS isn't Linux) it will be
		471	emulated by simply reading the data, which would have a similar effect.
		472
		473
152	=item aio_stat $fh_or_path, $callback	474	=item aio_stat $fh_or_path, $callback->($status)
153		475
154	=item aio_lstat $fh, $callback	476	=item aio_lstat $fh, $callback->($status)
155		477
156	Works like perl's C<stat> or C<lstat> in void context. The callback will	478	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 _>	479	be called after the stat and the results will be available using C<stat _>
158	or C<-s _> etc...	480	or C<-s _> etc...
159		481
…		…
169	aio_stat "/etc/passwd", sub {	491	aio_stat "/etc/passwd", sub {
170	$_[0] and die "stat failed: $!";	492	$_[0] and die "stat failed: $!";
171	print "size is ", -s _, "\n";	493	print "size is ", -s _, "\n";
172	};	494	};
173		495
		496
		497	=item aio_statvfs $fh_or_path, $callback->($statvfs)
		498
		499	Works like the POSIX C<statvfs> or C<fstatvfs> syscalls, depending on
		500	whether a file handle or path was passed.
		501
		502	On success, the callback is passed a hash reference with the following
		503	members: C<bsize>, C<frsize>, C<blocks>, C<bfree>, C<bavail>, C<files>,
		504	C<ffree>, C<favail>, C<fsid>, C<flag> and C<namemax>. On failure, C<undef>
		505	is passed.
		506
		507	The following POSIX IO::AIO::ST_* constants are defined: C<ST_RDONLY> and
		508	C<ST_NOSUID>.
		509
		510	The following non-POSIX IO::AIO::ST_* flag masks are defined to
		511	their correct value when available, or to C<0> on systems that do
		512	not support them: C<ST_NODEV>, C<ST_NOEXEC>, C<ST_SYNCHRONOUS>,
		513	C<ST_MANDLOCK>, C<ST_WRITE>, C<ST_APPEND>, C<ST_IMMUTABLE>, C<ST_NOATIME>,
		514	C<ST_NODIRATIME> and C<ST_RELATIME>.
		515
		516	Example: stat C</wd> and dump out the data if successful.
		517
		518	aio_statvfs "/wd", sub {
		519	my $f = $_[0]
		520	or die "statvfs: $!";
		521
		522	use Data::Dumper;
		523	say Dumper $f;
		524	};
		525
		526	# result:
		527	{
		528	bsize => 1024,
		529	bfree => 4333064312,
		530	blocks => 10253828096,
		531	files => 2050765568,
		532	flag => 4096,
		533	favail => 2042092649,
		534	bavail => 4333064312,
		535	ffree => 2042092649,
		536	namemax => 255,
		537	frsize => 1024,
		538	fsid => 1810
		539	}
		540
		541
		542	=item aio_utime $fh_or_path, $atime, $mtime, $callback->($status)
		543
		544	Works like perl's C<utime> function (including the special case of $atime
		545	and $mtime being undef). Fractional times are supported if the underlying
		546	syscalls support them.
		547
		548	When called with a pathname, uses utimes(2) if available, otherwise
		549	utime(2). If called on a file descriptor, uses futimes(2) if available,
		550	otherwise returns ENOSYS, so this is not portable.
		551
		552	Examples:
		553
		554	# set atime and mtime to current time (basically touch(1)):
		555	aio_utime "path", undef, undef;
		556	# set atime to current time and mtime to beginning of the epoch:
		557	aio_utime "path", time, undef; # undef==0
		558
		559
		560	=item aio_chown $fh_or_path, $uid, $gid, $callback->($status)
		561
		562	Works like perl's C<chown> function, except that C<undef> for either $uid
		563	or $gid is being interpreted as "do not change" (but -1 can also be used).
		564
		565	Examples:
		566
		567	# same as "chown root path" in the shell:
		568	aio_chown "path", 0, -1;
		569	# same as above:
		570	aio_chown "path", 0, undef;
		571
		572
		573	=item aio_truncate $fh_or_path, $offset, $callback->($status)
		574
		575	Works like truncate(2) or ftruncate(2).
		576
		577
		578	=item aio_chmod $fh_or_path, $mode, $callback->($status)
		579
		580	Works like perl's C<chmod> function.
		581
		582
174	=item aio_unlink $pathname, $callback	583	=item aio_unlink $pathname, $callback->($status)
175		584
176	Asynchronously unlink (delete) a file and call the callback with the	585	Asynchronously unlink (delete) a file and call the callback with the
177	result code.	586	result code.
178		587
		588
		589	=item aio_mknod $path, $mode, $dev, $callback->($status)
		590
		591	[EXPERIMENTAL]
		592
		593	Asynchronously create a device node (or fifo). See mknod(2).
		594
		595	The only (POSIX-) portable way of calling this function is:
		596
		597	aio_mknod $path, IO::AIO::S_IFIFO | $mode, 0, sub { ...
		598
		599
		600	=item aio_link $srcpath, $dstpath, $callback->($status)
		601
		602	Asynchronously create a new link to the existing object at C<$srcpath> at
		603	the path C<$dstpath> and call the callback with the result code.
		604
		605
		606	=item aio_symlink $srcpath, $dstpath, $callback->($status)
		607
		608	Asynchronously create a new symbolic link to the existing object at C<$srcpath> at
		609	the path C<$dstpath> and call the callback with the result code.
		610
		611
		612	=item aio_readlink $path, $callback->($link)
		613
		614	Asynchronously read the symlink specified by C<$path> and pass it to
		615	the callback. If an error occurs, nothing or undef gets passed to the
		616	callback.
		617
		618
		619	=item aio_rename $srcpath, $dstpath, $callback->($status)
		620
		621	Asynchronously rename the object at C<$srcpath> to C<$dstpath>, just as
		622	rename(2) and call the callback with the result code.
		623
		624
		625	=item aio_mkdir $pathname, $mode, $callback->($status)
		626
		627	Asynchronously mkdir (create) a directory and call the callback with
		628	the result code. C<$mode> will be modified by the umask at the time the
		629	request is executed, so do not change your umask.
		630
		631
		632	=item aio_rmdir $pathname, $callback->($status)
		633
		634	Asynchronously rmdir (delete) a directory and call the callback with the
		635	result code.
		636
		637
		638	=item aio_readdir $pathname, $callback->($entries)
		639
		640	Unlike the POSIX call of the same name, C<aio_readdir> reads an entire
		641	directory (i.e. opendir + readdir + closedir). The entries will not be
		642	sorted, and will B<NOT> include the C<.> and C<..> entries.
		643
		644	The callback is passed a single argument which is either C<undef> or an
		645	array-ref with the filenames.
		646
		647
		648	=item aio_readdirx $pathname, $flags, $callback->($entries, $flags)
		649
		650	Quite similar to C<aio_readdir>, but the C<$flags> argument allows to tune
		651	behaviour and output format. In case of an error, C<$entries> will be
		652	C<undef>.
		653
		654	The flags are a combination of the following constants, ORed together (the
		655	flags will also be passed to the callback, possibly modified):
		656
		657	=over 4
		658
		659	=item IO::AIO::READDIR_DENTS
		660
		661	When this flag is off, then the callback gets an arrayref with of names
		662	only (as with C<aio_readdir>), otherwise it gets an arrayref with
		663	C<[$name, $type, $inode]> arrayrefs, each describing a single directory
		664	entry in more detail.
		665
		666	C<$name> is the name of the entry.
		667
		668	C<$type> is one of the C<IO::AIO::DT_xxx> constants:
		669
		670	C<IO::AIO::DT_UNKNOWN>, C<IO::AIO::DT_FIFO>, C<IO::AIO::DT_CHR>, C<IO::AIO::DT_DIR>,
		671	C<IO::AIO::DT_BLK>, C<IO::AIO::DT_REG>, C<IO::AIO::DT_LNK>, C<IO::AIO::DT_SOCK>,
		672	C<IO::AIO::DT_WHT>.
		673
		674	C<IO::AIO::DT_UNKNOWN> means just that: readdir does not know. If you need to
		675	know, you have to run stat yourself. Also, for speed reasons, the C<$type>
		676	scalars are read-only: you can not modify them.
		677
		678	C<$inode> is the inode number (which might not be exact on systems with 64
		679	bit inode numbers and 32 bit perls). This field has unspecified content on
		680	systems that do not deliver the inode information.
		681
		682	=item IO::AIO::READDIR_DIRS_FIRST
		683
		684	When this flag is set, then the names will be returned in an order where
		685	likely directories come first. This is useful when you need to quickly
		686	find directories, or you want to find all directories while avoiding to
		687	stat() each entry.
		688
		689	If the system returns type information in readdir, then this is used
		690	to find directories directly. Otherwise, likely directories are files
		691	beginning with ".", or otherwise files with no dots, of which files with
		692	short names are tried first.
		693
		694	=item IO::AIO::READDIR_STAT_ORDER
		695
		696	When this flag is set, then the names will be returned in an order
		697	suitable for stat()'ing each one. That is, when you plan to stat()
		698	all files in the given directory, then the returned order will likely
		699	be fastest.
		700
		701	If both this flag and C<IO::AIO::READDIR_DIRS_FIRST> are specified, then
		702	the likely dirs come first, resulting in a less optimal stat order.
		703
		704	=item IO::AIO::READDIR_FOUND_UNKNOWN
		705
		706	This flag should not be set when calling C<aio_readdirx>. Instead, it
		707	is being set by C<aio_readdirx>, when any of the C<$type>'s found were
		708	C<IO::AIO::DT_UNKNOWN>. The absense of this flag therefore indicates that all
		709	C<$type>'s are known, which can be used to speed up some algorithms.
		710
		711	=back
		712
		713
		714	=item aio_load $path, $data, $callback->($status)
		715
		716	This is a composite request that tries to fully load the given file into
		717	memory. Status is the same as with aio_read.
		718
		719	=cut
		720
		721	sub aio_load($$;$) {
		722	my ($path, undef, $cb) = @_;
		723	my $data = \$_[1];
		724
		725	my $pri = aioreq_pri;
		726	my $grp = aio_group $cb;
		727
		728	aioreq_pri $pri;
		729	add $grp aio_open $path, O_RDONLY, 0, sub {
		730	my $fh = shift
		731	or return $grp->result (-1);
		732
		733	aioreq_pri $pri;
		734	add $grp aio_read $fh, 0, (-s $fh), $$data, 0, sub {
		735	$grp->result ($_[0]);
		736	};
		737	};
		738
		739	$grp
		740	}
		741
		742	=item aio_copy $srcpath, $dstpath, $callback->($status)
		743
		744	Try to copy the I<file> (directories not supported as either source or
		745	destination) from C<$srcpath> to C<$dstpath> and call the callback with
		746	a status of C<0> (ok) or C<-1> (error, see C<$!>).
		747
		748	This is a composite request that creates the destination file with
		749	mode 0200 and copies the contents of the source file into it using
		750	C<aio_sendfile>, followed by restoring atime, mtime, access mode and
		751	uid/gid, in that order.
		752
		753	If an error occurs, the partial destination file will be unlinked, if
		754	possible, except when setting atime, mtime, access mode and uid/gid, where
		755	errors are being ignored.
		756
		757	=cut
		758
		759	sub aio_copy($$;$) {
		760	my ($src, $dst, $cb) = @_;
		761
		762	my $pri = aioreq_pri;
		763	my $grp = aio_group $cb;
		764
		765	aioreq_pri $pri;
		766	add $grp aio_open $src, O_RDONLY, 0, sub {
		767	if (my $src_fh = $_[0]) {
		768	my @stat = stat $src_fh; # hmm, might block over nfs?
		769
		770	aioreq_pri $pri;
		771	add $grp aio_open $dst, O_CREAT | O_WRONLY | O_TRUNC, 0200, sub {
		772	if (my $dst_fh = $_[0]) {
		773	aioreq_pri $pri;
		774	add $grp aio_sendfile $dst_fh, $src_fh, 0, $stat[7], sub {
		775	if ($_[0] == $stat[7]) {
		776	$grp->result (0);
		777	close $src_fh;
		778
		779	my $ch = sub {
		780	aioreq_pri $pri;
		781	add $grp aio_chmod $dst_fh, $stat[2] & 07777, sub {
		782	aioreq_pri $pri;
		783	add $grp aio_chown $dst_fh, $stat[4], $stat[5], sub {
		784	aioreq_pri $pri;
		785	add $grp aio_close $dst_fh;
		786	}
		787	};
		788	};
		789
		790	aioreq_pri $pri;
		791	add $grp aio_utime $dst_fh, $stat[8], $stat[9], sub {
		792	if ($_[0] < 0 && $! == ENOSYS) {
		793	aioreq_pri $pri;
		794	add $grp aio_utime $dst, $stat[8], $stat[9], $ch;
		795	} else {
		796	$ch->();
		797	}
		798	};
		799	} else {
		800	$grp->result (-1);
		801	close $src_fh;
		802	close $dst_fh;
		803
		804	aioreq $pri;
		805	add $grp aio_unlink $dst;
		806	}
		807	};
		808	} else {
		809	$grp->result (-1);
		810	}
		811	},
		812
		813	} else {
		814	$grp->result (-1);
		815	}
		816	};
		817
		818	$grp
		819	}
		820
		821	=item aio_move $srcpath, $dstpath, $callback->($status)
		822
		823	Try to move the I<file> (directories not supported as either source or
		824	destination) from C<$srcpath> to C<$dstpath> and call the callback with
		825	a status of C<0> (ok) or C<-1> (error, see C<$!>).
		826
		827	This is a composite request that tries to rename(2) the file first; if
		828	rename fails with C<EXDEV>, it copies the file with C<aio_copy> and, if
		829	that is successful, unlinks the C<$srcpath>.
		830
		831	=cut
		832
		833	sub aio_move($$;$) {
		834	my ($src, $dst, $cb) = @_;
		835
		836	my $pri = aioreq_pri;
		837	my $grp = aio_group $cb;
		838
		839	aioreq_pri $pri;
		840	add $grp aio_rename $src, $dst, sub {
		841	if ($_[0] && $! == EXDEV) {
		842	aioreq_pri $pri;
		843	add $grp aio_copy $src, $dst, sub {
		844	$grp->result ($_[0]);
		845
		846	if (!$_[0]) {
		847	aioreq_pri $pri;
		848	add $grp aio_unlink $src;
		849	}
		850	};
		851	} else {
		852	$grp->result ($_[0]);
		853	}
		854	};
		855
		856	$grp
		857	}
		858
		859	=item aio_scandir $path, $maxreq, $callback->($dirs, $nondirs)
		860
		861	Scans a directory (similar to C<aio_readdir>) but additionally tries to
		862	efficiently separate the entries of directory C<$path> into two sets of
		863	names, directories you can recurse into (directories), and ones you cannot
		864	recurse into (everything else, including symlinks to directories).
		865
		866	C<aio_scandir> is a composite request that creates of many sub requests_
		867	C<$maxreq> specifies the maximum number of outstanding aio requests that
		868	this function generates. If it is C<< <= 0 >>, then a suitable default
		869	will be chosen (currently 4).
		870
		871	On error, the callback is called without arguments, otherwise it receives
		872	two array-refs with path-relative entry names.
		873
		874	Example:
		875
		876	aio_scandir $dir, 0, sub {
		877	my ($dirs, $nondirs) = @_;
		878	print "real directories: @$dirs\n";
		879	print "everything else: @$nondirs\n";
		880	};
		881
		882	Implementation notes.
		883
		884	The C<aio_readdir> cannot be avoided, but C<stat()>'ing every entry can.
		885
		886	If readdir returns file type information, then this is used directly to
		887	find directories.
		888
		889	Otherwise, after reading the directory, the modification time, size etc.
		890	of the directory before and after the readdir is checked, and if they
		891	match (and isn't the current time), the link count will be used to decide
		892	how many entries are directories (if >= 2). Otherwise, no knowledge of the
		893	number of subdirectories will be assumed.
		894
		895	Then entries will be sorted into likely directories a non-initial dot
		896	currently) and likely non-directories (see C<aio_readdirx>). Then every
		897	entry plus an appended C</.> will be C<stat>'ed, likely directories first,
		898	in order of their inode numbers. If that succeeds, it assumes that the
		899	entry is a directory or a symlink to directory (which will be checked
		900	seperately). This is often faster than stat'ing the entry itself because
		901	filesystems might detect the type of the entry without reading the inode
		902	data (e.g. ext2fs filetype feature), even on systems that cannot return
		903	the filetype information on readdir.
		904
		905	If the known number of directories (link count - 2) has been reached, the
		906	rest of the entries is assumed to be non-directories.
		907
		908	This only works with certainty on POSIX (= UNIX) filesystems, which
		909	fortunately are the vast majority of filesystems around.
		910
		911	It will also likely work on non-POSIX filesystems with reduced efficiency
		912	as those tend to return 0 or 1 as link counts, which disables the
		913	directory counting heuristic.
		914
		915	=cut
		916
		917	sub aio_scandir($$;$) {
		918	my ($path, $maxreq, $cb) = @_;
		919
		920	my $pri = aioreq_pri;
		921
		922	my $grp = aio_group $cb;
		923
		924	$maxreq = 4 if $maxreq <= 0;
		925
		926	# stat once
		927	aioreq_pri $pri;
		928	add $grp aio_stat $path, sub {
		929	return $grp->result () if $_[0];
		930	my $now = time;
		931	my $hash1 = join ":", (stat _)[0,1,3,7,9];
		932
		933	# read the directory entries
		934	aioreq_pri $pri;
		935	add $grp aio_readdirx $path, READDIR_DIRS_FIRST, sub {
		936	my $entries = shift
		937	or return $grp->result ();
		938
		939	# stat the dir another time
		940	aioreq_pri $pri;
		941	add $grp aio_stat $path, sub {
		942	my $hash2 = join ":", (stat _)[0,1,3,7,9];
		943
		944	my $ndirs;
		945
		946	# take the slow route if anything looks fishy
		947	if ($hash1 ne $hash2 or (stat _)[9] == $now) {
		948	$ndirs = -1;
		949	} else {
		950	# if nlink == 2, we are finished
		951	# for non-posix-fs's, we rely on nlink < 2
		952	$ndirs = (stat _)[3] - 2
		953	or return $grp->result ([], $entries);
		954	}
		955
		956	my (@dirs, @nondirs);
		957
		958	my $statgrp = add $grp aio_group sub {
		959	$grp->result (\@dirs, \@nondirs);
		960	};
		961
		962	limit $statgrp $maxreq;
		963	feed $statgrp sub {
		964	return unless @$entries;
		965	my $entry = shift @$entries;
		966
		967	aioreq_pri $pri;
		968	add $statgrp aio_stat "$path/$entry/.", sub {
		969	if ($_[0] < 0) {
		970	push @nondirs, $entry;
		971	} else {
		972	# need to check for real directory
		973	aioreq_pri $pri;
		974	add $statgrp aio_lstat "$path/$entry", sub {
		975	if (-d _) {
		976	push @dirs, $entry;
		977
		978	unless (--$ndirs) {
		979	push @nondirs, @$entries;
		980	feed $statgrp;
		981	}
		982	} else {
		983	push @nondirs, $entry;
		984	}
		985	}
		986	}
		987	};
		988	};
		989	};
		990	};
		991	};
		992
		993	$grp
		994	}
		995
		996	=item aio_rmtree $path, $callback->($status)
		997
		998	Delete a directory tree starting (and including) C<$path>, return the
		999	status of the final C<rmdir> only. This is a composite request that
		1000	uses C<aio_scandir> to recurse into and rmdir directories, and unlink
		1001	everything else.
		1002
		1003	=cut
		1004
		1005	sub aio_rmtree;
		1006	sub aio_rmtree($;$) {
		1007	my ($path, $cb) = @_;
		1008
		1009	my $pri = aioreq_pri;
		1010	my $grp = aio_group $cb;
		1011
		1012	aioreq_pri $pri;
		1013	add $grp aio_scandir $path, 0, sub {
		1014	my ($dirs, $nondirs) = @_;
		1015
		1016	my $dirgrp = aio_group sub {
		1017	add $grp aio_rmdir $path, sub {
		1018	$grp->result ($_[0]);
		1019	};
		1020	};
		1021
		1022	(aioreq_pri $pri), add $dirgrp aio_rmtree "$path/$_" for @$dirs;
		1023	(aioreq_pri $pri), add $dirgrp aio_unlink "$path/$_" for @$nondirs;
		1024
		1025	add $grp $dirgrp;
		1026	};
		1027
		1028	$grp
		1029	}
		1030
		1031	=item aio_sync $callback->($status)
		1032
		1033	Asynchronously call sync and call the callback when finished.
		1034
179	=item aio_fsync $fh, $callback	1035	=item aio_fsync $fh, $callback->($status)
180		1036
181	Asynchronously call fsync on the given filehandle and call the callback	1037	Asynchronously call fsync on the given filehandle and call the callback
182	with the fsync result code.	1038	with the fsync result code.
183		1039
184	=item aio_fdatasync $fh, $callback	1040	=item aio_fdatasync $fh, $callback->($status)
185		1041
186	Asynchronously call fdatasync on the given filehandle and call the	1042	Asynchronously call fdatasync on the given filehandle and call the
187	callback with the fdatasync result code.	1043	callback with the fdatasync result code.
188		1044
		1045	If this call isn't available because your OS lacks it or it couldn't be
		1046	detected, it will be emulated by calling C<fsync> instead.
		1047
		1048	=item aio_sync_file_range $fh, $offset, $nbytes, $flags, $callback->($status)
		1049
		1050	Sync the data portion of the file specified by C<$offset> and C<$length>
		1051	to disk (but NOT the metadata), by calling the Linux-specific
		1052	sync_file_range call. If sync_file_range is not available or it returns
		1053	ENOSYS, then fdatasync or fsync is being substituted.
		1054
		1055	C<$flags> can be a combination of C<IO::AIO::SYNC_FILE_RANGE_WAIT_BEFORE>,
		1056	C<IO::AIO::SYNC_FILE_RANGE_WRITE> and
		1057	C<IO::AIO::SYNC_FILE_RANGE_WAIT_AFTER>: refer to the sync_file_range
		1058	manpage for details.
		1059
		1060	=item aio_pathsync $path, $callback->($status)
		1061
		1062	This request tries to open, fsync and close the given path. This is a
		1063	composite request intended to sync directories after directory operations
		1064	(E.g. rename). This might not work on all operating systems or have any
		1065	specific effect, but usually it makes sure that directory changes get
		1066	written to disc. It works for anything that can be opened for read-only,
		1067	not just directories.
		1068
		1069	Future versions of this function might fall back to other methods when
		1070	C<fsync> on the directory fails (such as calling C<sync>).
		1071
		1072	Passes C<0> when everything went ok, and C<-1> on error.
		1073
		1074	=cut
		1075
		1076	sub aio_pathsync($;$) {
		1077	my ($path, $cb) = @_;
		1078
		1079	my $pri = aioreq_pri;
		1080	my $grp = aio_group $cb;
		1081
		1082	aioreq_pri $pri;
		1083	add $grp aio_open $path, O_RDONLY, 0, sub {
		1084	my ($fh) = @_;
		1085	if ($fh) {
		1086	aioreq_pri $pri;
		1087	add $grp aio_fsync $fh, sub {
		1088	$grp->result ($_[0]);
		1089
		1090	aioreq_pri $pri;
		1091	add $grp aio_close $fh;
		1092	};
		1093	} else {
		1094	$grp->result (-1);
		1095	}
		1096	};
		1097
		1098	$grp
		1099	}
		1100
		1101	=item aio_msync $scalar, $offset = 0, $length = undef, flags = 0, $callback->($status)
		1102
		1103	This is a rather advanced IO::AIO call, which only works on mmap(2)ed
		1104	scalars (see the C<IO::AIO::mmap> function, although it also works on data
		1105	scalars managed by the L<Sys::Mmap> or L<Mmap> modules, note that the
		1106	scalar must only be modified in-place while an aio operation is pending on
		1107	it).
		1108
		1109	It calls the C<msync> function of your OS, if available, with the memory
		1110	area starting at C<$offset> in the string and ending C<$length> bytes
		1111	later. If C<$length> is negative, counts from the end, and if C<$length>
		1112	is C<undef>, then it goes till the end of the string. The flags can be
		1113	a combination of C<IO::AIO::MS_ASYNC>, C<IO::AIO::MS_INVALIDATE> and
		1114	C<IO::AIO::MS_SYNC>.
		1115
		1116	=item aio_mtouch $scalar, $offset = 0, $length = undef, flags = 0, $callback->($status)
		1117
		1118	This is a rather advanced IO::AIO call, which works best on mmap(2)ed
		1119	scalars.
		1120
		1121	It touches (reads or writes) all memory pages in the specified
		1122	range inside the scalar. All caveats and parameters are the same
		1123	as for C<aio_msync>, above, except for flags, which must be either
		1124	C<0> (which reads all pages and ensures they are instantiated) or
		1125	C<IO::AIO::MT_MODIFY>, which modifies the memory page s(by reading and
		1126	writing an octet from it, which dirties the page).
		1127
		1128	=item aio_mlock $scalar, $offset = 0, $length = undef, $callback->($status)
		1129
		1130	This is a rather advanced IO::AIO call, which works best on mmap(2)ed
		1131	scalars.
		1132
		1133	It reads in all the pages of the underlying storage into memory (if any)
		1134	and locks them, so they are not getting swapped/paged out or removed.
		1135
		1136	If C<$length> is undefined, then the scalar will be locked till the end.
		1137
		1138	On systems that do not implement C<mlock>, this function returns C<-1>
		1139	and sets errno to C<ENOSYS>.
		1140
		1141	Note that the corresponding C<munlock> is synchronous and is
		1142	documented under L<MISCELLANEOUS FUNCTIONS>.
		1143
		1144	Example: open a file, mmap and mlock it - both will be undone when
		1145	C<$data> gets destroyed.
		1146
		1147	open my $fh, "<", $path or die "$path: $!";
		1148	my $data;
		1149	IO::AIO::mmap $data, -s $fh, IO::AIO::PROT_READ, IO::AIO::MAP_SHARED, $fh;
		1150	aio_mlock $data; # mlock in background
		1151
		1152	=item aio_mlockall $flags, $callback->($status)
		1153
		1154	Calls the C<mlockall> function with the given C<$flags> (a combination of
		1155	C<IO::AIO::MCL_CURRENT> and C<IO::AIO::MCL_FUTURE>).
		1156
		1157	On systems that do not implement C<mlockall>, this function returns C<-1>
		1158	and sets errno to C<ENOSYS>.
		1159
		1160	Note that the corresponding C<munlockall> is synchronous and is
		1161	documented under L<MISCELLANEOUS FUNCTIONS>.
		1162
		1163	Example: asynchronously lock all current and future pages into memory.
		1164
		1165	aio_mlockall IO::AIO::MCL_FUTURE;
		1166
		1167	=item aio_group $callback->(...)
		1168
		1169	This is a very special aio request: Instead of doing something, it is a
		1170	container for other aio requests, which is useful if you want to bundle
		1171	many requests into a single, composite, request with a definite callback
		1172	and the ability to cancel the whole request with its subrequests.
		1173
		1174	Returns an object of class L<IO::AIO::GRP>. See its documentation below
		1175	for more info.
		1176
		1177	Example:
		1178
		1179	my $grp = aio_group sub {
		1180	print "all stats done\n";
		1181	};
		1182
		1183	add $grp
		1184	(aio_stat ...),
		1185	(aio_stat ...),
		1186	...;
		1187
		1188	=item aio_nop $callback->()
		1189
		1190	This is a special request - it does nothing in itself and is only used for
		1191	side effects, such as when you want to add a dummy request to a group so
		1192	that finishing the requests in the group depends on executing the given
		1193	code.
		1194
		1195	While this request does nothing, it still goes through the execution
		1196	phase and still requires a worker thread. Thus, the callback will not
		1197	be executed immediately but only after other requests in the queue have
		1198	entered their execution phase. This can be used to measure request
		1199	latency.
		1200
		1201	=item IO::AIO::aio_busy $fractional_seconds, $callback->() *NOT EXPORTED*
		1202
		1203	Mainly used for debugging and benchmarking, this aio request puts one of
		1204	the request workers to sleep for the given time.
		1205
		1206	While it is theoretically handy to have simple I/O scheduling requests
		1207	like sleep and file handle readable/writable, the overhead this creates is
		1208	immense (it blocks a thread for a long time) so do not use this function
		1209	except to put your application under artificial I/O pressure.
		1210
189	=back	1211	=back
190		1212
		1213	=head2 IO::AIO::REQ CLASS
		1214
		1215	All non-aggregate C<aio_*> functions return an object of this class when
		1216	called in non-void context.
		1217
		1218	=over 4
		1219
		1220	=item cancel $req
		1221
		1222	Cancels the request, if possible. Has the effect of skipping execution
		1223	when entering the B<execute> state and skipping calling the callback when
		1224	entering the the B<result> state, but will leave the request otherwise
		1225	untouched (with the exception of readdir). That means that requests that
		1226	currently execute will not be stopped and resources held by the request
		1227	will not be freed prematurely.
		1228
		1229	=item cb $req $callback->(...)
		1230
		1231	Replace (or simply set) the callback registered to the request.
		1232
		1233	=back
		1234
		1235	=head2 IO::AIO::GRP CLASS
		1236
		1237	This class is a subclass of L<IO::AIO::REQ>, so all its methods apply to
		1238	objects of this class, too.
		1239
		1240	A IO::AIO::GRP object is a special request that can contain multiple other
		1241	aio requests.
		1242
		1243	You create one by calling the C<aio_group> constructing function with a
		1244	callback that will be called when all contained requests have entered the
		1245	C<done> state:
		1246
		1247	my $grp = aio_group sub {
		1248	print "all requests are done\n";
		1249	};
		1250
		1251	You add requests by calling the C<add> method with one or more
		1252	C<IO::AIO::REQ> objects:
		1253
		1254	$grp->add (aio_unlink "...");
		1255
		1256	add $grp aio_stat "...", sub {
		1257	$_[0] or return $grp->result ("error");
		1258
		1259	# add another request dynamically, if first succeeded
		1260	add $grp aio_open "...", sub {
		1261	$grp->result ("ok");
		1262	};
		1263	};
		1264
		1265	This makes it very easy to create composite requests (see the source of
		1266	C<aio_move> for an application) that work and feel like simple requests.
		1267
		1268	=over 4
		1269
		1270	=item * The IO::AIO::GRP objects will be cleaned up during calls to
		1271	C<IO::AIO::poll_cb>, just like any other request.
		1272
		1273	=item * They can be canceled like any other request. Canceling will cancel not
		1274	only the request itself, but also all requests it contains.
		1275
		1276	=item * They can also can also be added to other IO::AIO::GRP objects.
		1277
		1278	=item * You must not add requests to a group from within the group callback (or
		1279	any later time).
		1280
		1281	=back
		1282
		1283	Their lifetime, simplified, looks like this: when they are empty, they
		1284	will finish very quickly. If they contain only requests that are in the
		1285	C<done> state, they will also finish. Otherwise they will continue to
		1286	exist.
		1287
		1288	That means after creating a group you have some time to add requests
		1289	(precisely before the callback has been invoked, which is only done within
		1290	the C<poll_cb>). And in the callbacks of those requests, you can add
		1291	further requests to the group. And only when all those requests have
		1292	finished will the the group itself finish.
		1293
		1294	=over 4
		1295
		1296	=item add $grp ...
		1297
		1298	=item $grp->add (...)
		1299
		1300	Add one or more requests to the group. Any type of L<IO::AIO::REQ> can
		1301	be added, including other groups, as long as you do not create circular
		1302	dependencies.
		1303
		1304	Returns all its arguments.
		1305
		1306	=item $grp->cancel_subs
		1307
		1308	Cancel all subrequests and clears any feeder, but not the group request
		1309	itself. Useful when you queued a lot of events but got a result early.
		1310
		1311	The group request will finish normally (you cannot add requests to the
		1312	group).
		1313
		1314	=item $grp->result (...)
		1315
		1316	Set the result value(s) that will be passed to the group callback when all
		1317	subrequests have finished and set the groups errno to the current value
		1318	of errno (just like calling C<errno> without an error number). By default,
		1319	no argument will be passed and errno is zero.
		1320
		1321	=item $grp->errno ([$errno])
		1322
		1323	Sets the group errno value to C<$errno>, or the current value of errno
		1324	when the argument is missing.
		1325
		1326	Every aio request has an associated errno value that is restored when
		1327	the callback is invoked. This method lets you change this value from its
		1328	default (0).
		1329
		1330	Calling C<result> will also set errno, so make sure you either set C<$!>
		1331	before the call to C<result>, or call c<errno> after it.
		1332
		1333	=item feed $grp $callback->($grp)
		1334
		1335	Sets a feeder/generator on this group: every group can have an attached
		1336	generator that generates requests if idle. The idea behind this is that,
		1337	although you could just queue as many requests as you want in a group,
		1338	this might starve other requests for a potentially long time. For example,
		1339	C<aio_scandir> might generate hundreds of thousands C<aio_stat> requests,
		1340	delaying any later requests for a long time.
		1341
		1342	To avoid this, and allow incremental generation of requests, you can
		1343	instead a group and set a feeder on it that generates those requests. The
		1344	feed callback will be called whenever there are few enough (see C<limit>,
		1345	below) requests active in the group itself and is expected to queue more
		1346	requests.
		1347
		1348	The feed callback can queue as many requests as it likes (i.e. C<add> does
		1349	not impose any limits).
		1350
		1351	If the feed does not queue more requests when called, it will be
		1352	automatically removed from the group.
		1353
		1354	If the feed limit is C<0> when this method is called, it will be set to
		1355	C<2> automatically.
		1356
		1357	Example:
		1358
		1359	# stat all files in @files, but only ever use four aio requests concurrently:
		1360
		1361	my $grp = aio_group sub { print "finished\n" };
		1362	limit $grp 4;
		1363	feed $grp sub {
		1364	my $file = pop @files
		1365	or return;
		1366
		1367	add $grp aio_stat $file, sub { ... };
		1368	};
		1369
		1370	=item limit $grp $num
		1371
		1372	Sets the feeder limit for the group: The feeder will be called whenever
		1373	the group contains less than this many requests.
		1374
		1375	Setting the limit to C<0> will pause the feeding process.
		1376
		1377	The default value for the limit is C<0>, but note that setting a feeder
		1378	automatically bumps it up to C<2>.
		1379
		1380	=back
		1381
191	=head2 SUPPORT FUNCTIONS	1382	=head2 SUPPORT FUNCTIONS
192		1383
		1384	=head3 EVENT PROCESSING AND EVENT LOOP INTEGRATION
		1385
193	=over 4	1386	=over 4
194		1387
195	=item $fileno = IO::AIO::poll_fileno	1388	=item $fileno = IO::AIO::poll_fileno
196		1389
197	Return the I<request result pipe filehandle>. This filehandle must be	1390	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	1391	polled for reading by some mechanism outside this module (e.g. EV, Glib,
199	or select, see below). If the pipe becomes readable you have to call	1392	select and so on, see below or the SYNOPSIS). If the pipe becomes readable
200	C<poll_cb> to check the results.	1393	you have to call C<poll_cb> to check the results.
201		1394
202	See C<poll_cb> for an example.	1395	See C<poll_cb> for an example.
203		1396
204	=item IO::AIO::poll_cb	1397	=item IO::AIO::poll_cb
205		1398
206	Process all outstanding events on the result pipe. You have to call this	1399	Process some outstanding events on the result pipe. You have to call this
207	regularly. Returns the number of events processed. Returns immediately	1400	regularly. Returns C<0> if all events could be processed, or C<-1> if it
208	when no events are outstanding.	1401	returned earlier for whatever reason. Returns immediately when no events
		1402	are outstanding. The amount of events processed depends on the settings of
		1403	C<IO::AIO::max_poll_req> and C<IO::AIO::max_poll_time>.
209		1404
210	You can use Event to multiplex, e.g.:	1405	If not all requests were processed for whatever reason, the filehandle
		1406	will still be ready when C<poll_cb> returns, so normally you don't have to
		1407	do anything special to have it called later.
		1408
		1409	Example: Install an Event watcher that automatically calls
		1410	IO::AIO::poll_cb with high priority (more examples can be found in the
		1411	SYNOPSIS section, at the top of this document):
211		1412
212	Event->io (fd => IO::AIO::poll_fileno,	1413	Event->io (fd => IO::AIO::poll_fileno,
213	poll => 'r', async => 1,	1414	poll => 'r', async => 1,
214	cb => \&IO::AIO::poll_cb);	1415	cb => \&IO::AIO::poll_cb);
215		1416
216	=item IO::AIO::poll_wait	1417	=item IO::AIO::poll_wait
217		1418
		1419	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	1420	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	1421	does a C<select> on the filehandle. This is useful if you want to
220	for some requests to finish).	1422	synchronously wait for some requests to finish).
221		1423
222	See C<nreqs> for an example.	1424	See C<nreqs> for an example.
223		1425
		1426	=item IO::AIO::poll
		1427
		1428	Waits until some requests have been handled.
		1429
		1430	Returns the number of requests processed, but is otherwise strictly
		1431	equivalent to:
		1432
		1433	IO::AIO::poll_wait, IO::AIO::poll_cb
		1434
224	=item IO::AIO::nreqs	1435	=item IO::AIO::flush
225		1436
226	Returns the number of requests currently outstanding.	1437	Wait till all outstanding AIO requests have been handled.
227		1438
228	Example: wait till there are no outstanding requests anymore:	1439	Strictly equivalent to:
229		1440
230	IO::AIO::poll_wait, IO::AIO::poll_cb	1441	IO::AIO::poll_wait, IO::AIO::poll_cb
231	while IO::AIO::nreqs;	1442	while IO::AIO::nreqs;
232		1443
		1444	=item IO::AIO::max_poll_reqs $nreqs
		1445
		1446	=item IO::AIO::max_poll_time $seconds
		1447
		1448	These set the maximum number of requests (default C<0>, meaning infinity)
		1449	that are being processed by C<IO::AIO::poll_cb> in one call, respectively
		1450	the maximum amount of time (default C<0>, meaning infinity) spent in
		1451	C<IO::AIO::poll_cb> to process requests (more correctly the mininum amount
		1452	of time C<poll_cb> is allowed to use).
		1453
		1454	Setting C<max_poll_time> to a non-zero value creates an overhead of one
		1455	syscall per request processed, which is not normally a problem unless your
		1456	callbacks are really really fast or your OS is really really slow (I am
		1457	not mentioning Solaris here). Using C<max_poll_reqs> incurs no overhead.
		1458
		1459	Setting these is useful if you want to ensure some level of
		1460	interactiveness when perl is not fast enough to process all requests in
		1461	time.
		1462
		1463	For interactive programs, values such as C<0.01> to C<0.1> should be fine.
		1464
		1465	Example: Install an Event watcher that automatically calls
		1466	IO::AIO::poll_cb with low priority, to ensure that other parts of the
		1467	program get the CPU sometimes even under high AIO load.
		1468
		1469	# try not to spend much more than 0.1s in poll_cb
		1470	IO::AIO::max_poll_time 0.1;
		1471
		1472	# use a low priority so other tasks have priority
		1473	Event->io (fd => IO::AIO::poll_fileno,
		1474	poll => 'r', nice => 1,
		1475	cb => &IO::AIO::poll_cb);
		1476
		1477	=back
		1478
		1479	=head3 CONTROLLING THE NUMBER OF THREADS
		1480
		1481	=over
		1482
233	=item IO::AIO::min_parallel $nthreads	1483	=item IO::AIO::min_parallel $nthreads
234		1484
235	Set the minimum number of AIO threads to C<$nthreads>. The default is	1485	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	1486	default is C<8>, which means eight asynchronous operations can execute
237	(the number of outstanding operations, however, is unlimited).	1487	concurrently at any one time (the number of outstanding requests,
		1488	however, is unlimited).
238		1489
		1490	IO::AIO starts threads only on demand, when an AIO request is queued and
		1491	no free thread exists. Please note that queueing up a hundred requests can
		1492	create demand for a hundred threads, even if it turns out that everything
		1493	is in the cache and could have been processed faster by a single thread.
		1494
239	It is recommended to keep the number of threads low, as some Linux	1495	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	1496	Linux kernel versions will scale negatively with the number of threads
241	parallelity => MUCH higher latency). With current Linux 2.6 versions, 4-32	1497	(higher parallelity => MUCH higher latency). With current Linux 2.6
242	threads should be fine.	1498	versions, 4-32 threads should be fine.
243		1499
244	Under normal circumstances you don't need to call this function, as this	1500	Under most circumstances you don't need to call this function, as the
245	module automatically starts some threads (the exact number might change,	1501	module selects a default that is suitable for low to moderate load.
246	and is currently 4).
247		1502
248	=item IO::AIO::max_parallel $nthreads	1503	=item IO::AIO::max_parallel $nthreads
249		1504
250	Sets the maximum number of AIO threads to C<$nthreads>. If more than	1505	Sets the maximum number of AIO threads to C<$nthreads>. If more than the
251	the specified number of threads are currently running, kill them. This	1506	specified number of threads are currently running, this function kills
252	function blocks until the limit is reached.	1507	them. This function blocks until the limit is reached.
		1508
		1509	While C<$nthreads> are zero, aio requests get queued but not executed
		1510	until the number of threads has been increased again.
253		1511
254	This module automatically runs C<max_parallel 0> at program end, to ensure	1512	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.	1513	that all threads are killed and that there are no outstanding requests.
256		1514
257	Under normal circumstances you don't need to call this function.	1515	Under normal circumstances you don't need to call this function.
258		1516
		1517	=item IO::AIO::max_idle $nthreads
		1518
		1519	Limit the number of threads (default: 4) that are allowed to idle (i.e.,
		1520	threads that did not get a request to process within 10 seconds). That
		1521	means if a thread becomes idle while C<$nthreads> other threads are also
		1522	idle, it will free its resources and exit.
		1523
		1524	This is useful when you allow a large number of threads (e.g. 100 or 1000)
		1525	to allow for extremely high load situations, but want to free resources
		1526	under normal circumstances (1000 threads can easily consume 30MB of RAM).
		1527
		1528	The default is probably ok in most situations, especially if thread
		1529	creation is fast. If thread creation is very slow on your system you might
		1530	want to use larger values.
		1531
259	=item $oldnreqs = IO::AIO::max_outstanding $nreqs	1532	=item IO::AIO::max_outstanding $maxreqs
		1533
		1534	This is a very bad function to use in interactive programs because it
		1535	blocks, and a bad way to reduce concurrency because it is inexact: Better
		1536	use an C<aio_group> together with a feed callback.
260		1537
261	Sets the maximum number of outstanding requests to C<$nreqs>. If you	1538	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	1539	do queue up more than this number of requests, the next call to the
263	some requests have been handled.	1540	C<poll_cb> (and C<poll_some> and other functions calling C<poll_cb>)
		1541	function will block until the limit is no longer exceeded.
264		1542
265	The default is very large, so normally there is no practical limit. If you	1543	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	1544	number of outstanding requests.
267	this to a relatively low number, such as C<100>.
268		1545
269	Under normal circumstances you don't need to call this function.	1546	You can still queue as many requests as you want. Therefore,
		1547	C<max_outstanding> is mainly useful in simple scripts (with low values) or
		1548	as a stop gap to shield against fatal memory overflow (with large values).
270		1549
271	=back	1550	=back
272		1551
		1552	=head3 STATISTICAL INFORMATION
		1553
		1554	=over
		1555
		1556	=item IO::AIO::nreqs
		1557
		1558	Returns the number of requests currently in the ready, execute or pending
		1559	states (i.e. for which their callback has not been invoked yet).
		1560
		1561	Example: wait till there are no outstanding requests anymore:
		1562
		1563	IO::AIO::poll_wait, IO::AIO::poll_cb
		1564	while IO::AIO::nreqs;
		1565
		1566	=item IO::AIO::nready
		1567
		1568	Returns the number of requests currently in the ready state (not yet
		1569	executed).
		1570
		1571	=item IO::AIO::npending
		1572
		1573	Returns the number of requests currently in the pending state (executed,
		1574	but not yet processed by poll_cb).
		1575
		1576	=back
		1577
		1578	=head3 MISCELLANEOUS FUNCTIONS
		1579
		1580	IO::AIO implements some functions that might be useful, but are not
		1581	asynchronous.
		1582
		1583	=over 4
		1584
		1585	=item IO::AIO::sendfile $ofh, $ifh, $offset, $count
		1586
		1587	Calls the C<eio_sendfile_sync> function, which is like C<aio_sendfile>,
		1588	but is blocking (this makes most sense if you know the input data is
		1589	likely cached already and the output filehandle is set to non-blocking
		1590	operations).
		1591
		1592	Returns the number of bytes copied, or C<-1> on error.
		1593
		1594	=item IO::AIO::fadvise $fh, $offset, $len, $advice
		1595
		1596	Simply calls the C<posix_fadvise> function (see its
		1597	manpage for details). The following advice constants are
		1598	avaiable: C<IO::AIO::FADV_NORMAL>, C<IO::AIO::FADV_SEQUENTIAL>,
		1599	C<IO::AIO::FADV_RANDOM>, C<IO::AIO::FADV_NOREUSE>,
		1600	C<IO::AIO::FADV_WILLNEED>, C<IO::AIO::FADV_DONTNEED>.
		1601
		1602	On systems that do not implement C<posix_fadvise>, this function returns
		1603	ENOSYS, otherwise the return value of C<posix_fadvise>.
		1604
		1605	=item IO::AIO::madvise $scalar, $offset, $len, $advice
		1606
		1607	Simply calls the C<posix_madvise> function (see its
		1608	manpage for details). The following advice constants are
		1609	avaiable: C<IO::AIO::MADV_NORMAL>, C<IO::AIO::MADV_SEQUENTIAL>,
		1610	C<IO::AIO::MADV_RANDOM>, C<IO::AIO::MADV_WILLNEED>, C<IO::AIO::MADV_DONTNEED>.
		1611
		1612	On systems that do not implement C<posix_madvise>, this function returns
		1613	ENOSYS, otherwise the return value of C<posix_madvise>.
		1614
		1615	=item IO::AIO::mprotect $scalar, $offset, $len, $protect
		1616
		1617	Simply calls the C<mprotect> function on the preferably AIO::mmap'ed
		1618	$scalar (see its manpage for details). The following protect
		1619	constants are avaiable: C<IO::AIO::PROT_NONE>, C<IO::AIO::PROT_READ>,
		1620	C<IO::AIO::PROT_WRITE>, C<IO::AIO::PROT_EXEC>.
		1621
		1622	On systems that do not implement C<mprotect>, this function returns
		1623	ENOSYS, otherwise the return value of C<mprotect>.
		1624
		1625	=item IO::AIO::mmap $scalar, $length, $prot, $flags, $fh[, $offset]
		1626
		1627	Memory-maps a file (or anonymous memory range) and attaches it to the
		1628	given C<$scalar>, which will act like a string scalar.
		1629
		1630	The only operations allowed on the scalar are C<substr>/C<vec> that don't
		1631	change the string length, and most read-only operations such as copying it
		1632	or searching it with regexes and so on.
		1633
		1634	Anything else is unsafe and will, at best, result in memory leaks.
		1635
		1636	The memory map associated with the C<$scalar> is automatically removed
		1637	when the C<$scalar> is destroyed, or when the C<IO::AIO::mmap> or
		1638	C<IO::AIO::munmap> functions are called.
		1639
		1640	This calls the C<mmap>(2) function internally. See your system's manual
		1641	page for details on the C<$length>, C<$prot> and C<$flags> parameters.
		1642
		1643	The C<$length> must be larger than zero and smaller than the actual
		1644	filesize.
		1645
		1646	C<$prot> is a combination of C<IO::AIO::PROT_NONE>, C<IO::AIO::PROT_EXEC>,
		1647	C<IO::AIO::PROT_READ> and/or C<IO::AIO::PROT_WRITE>,
		1648
		1649	C<$flags> can be a combination of C<IO::AIO::MAP_SHARED> or
		1650	C<IO::AIO::MAP_PRIVATE>, or a number of system-specific flags (when
		1651	not available, the are defined as 0): C<IO::AIO::MAP_ANONYMOUS>
		1652	(which is set to C<MAP_ANON> if your system only provides this
		1653	constant), C<IO::AIO::MAP_HUGETLB>, C<IO::AIO::MAP_LOCKED>,
		1654	C<IO::AIO::MAP_NORESERVE>, C<IO::AIO::MAP_POPULATE> or
		1655	C<IO::AIO::MAP_NONBLOCK>
		1656
		1657	If C<$fh> is C<undef>, then a file descriptor of C<-1> is passed.
		1658
		1659	C<$offset> is the offset from the start of the file - it generally must be
		1660	a multiple of C<IO::AIO::PAGESIZE> and defaults to C<0>.
		1661
		1662	Example:
		1663
		1664	use Digest::MD5;
		1665	use IO::AIO;
		1666
		1667	open my $fh, "<verybigfile"
		1668	or die "$!";
		1669
		1670	IO::AIO::mmap my $data, -s $fh, IO::AIO::PROT_READ, IO::AIO::MAP_SHARED, $fh
		1671	or die "verybigfile: $!";
		1672
		1673	my $fast_md5 = md5 $data;
		1674
		1675	=item IO::AIO::munmap $scalar
		1676
		1677	Removes a previous mmap and undefines the C<$scalar>.
		1678
		1679	=item IO::AIO::munlock $scalar, $offset = 0, $length = undef
		1680
		1681	Calls the C<munlock> function, undoing the effects of a previous
		1682	C<aio_mlock> call (see its description for details).
		1683
		1684	=item IO::AIO::munlockall
		1685
		1686	Calls the C<munlockall> function.
		1687
		1688	On systems that do not implement C<munlockall>, this function returns
		1689	ENOSYS, otherwise the return value of C<munlockall>.
		1690
		1691	=back
		1692
273	=cut	1693	=cut
274		1694
275	# support function to convert a fd into a perl filehandle
276	sub _fd2fh {
277	return undef if $_[0] < 0;
278
279	# try to be perl5.6-compatible
280	local *AIO_FH;
281	open AIO_FH, "+<&=$_[0]"
282	or return undef;
283
284	*AIO_FH
285	}
286
287	min_parallel 4;	1695	min_parallel 8;
288		1696
289	END {	1697	END { flush }
290	max_parallel 0;
291	}
292		1698
293	1;	1699	1;
294		1700
		1701	=head1 EVENT LOOP INTEGRATION
		1702
		1703	It is recommended to use L<AnyEvent::AIO> to integrate IO::AIO
		1704	automatically into many event loops:
		1705
		1706	# AnyEvent integration (EV, Event, Glib, Tk, POE, urxvt, pureperl...)
		1707	use AnyEvent::AIO;
		1708
		1709	You can also integrate IO::AIO manually into many event loops, here are
		1710	some examples of how to do this:
		1711
		1712	# EV integration
		1713	my $aio_w = EV::io IO::AIO::poll_fileno, EV::READ, \&IO::AIO::poll_cb;
		1714
		1715	# Event integration
		1716	Event->io (fd => IO::AIO::poll_fileno,
		1717	poll => 'r',
		1718	cb => \&IO::AIO::poll_cb);
		1719
		1720	# Glib/Gtk2 integration
		1721	add_watch Glib::IO IO::AIO::poll_fileno,
		1722	in => sub { IO::AIO::poll_cb; 1 };
		1723
		1724	# Tk integration
		1725	Tk::Event::IO->fileevent (IO::AIO::poll_fileno, "",
		1726	readable => \&IO::AIO::poll_cb);
		1727
		1728	# Danga::Socket integration
		1729	Danga::Socket->AddOtherFds (IO::AIO::poll_fileno =>
		1730	\&IO::AIO::poll_cb);
		1731
		1732	=head2 FORK BEHAVIOUR
		1733
		1734	This module should do "the right thing" when the process using it forks:
		1735
		1736	Before the fork, IO::AIO enters a quiescent state where no requests
		1737	can be added in other threads and no results will be processed. After
		1738	the fork the parent simply leaves the quiescent state and continues
		1739	request/result processing, while the child frees the request/result queue
		1740	(so that the requests started before the fork will only be handled in the
		1741	parent). Threads will be started on demand until the limit set in the
		1742	parent process has been reached again.
		1743
		1744	In short: the parent will, after a short pause, continue as if fork had
		1745	not been called, while the child will act as if IO::AIO has not been used
		1746	yet.
		1747
		1748	=head2 MEMORY USAGE
		1749
		1750	Per-request usage:
		1751
		1752	Each aio request uses - depending on your architecture - around 100-200
		1753	bytes of memory. In addition, stat requests need a stat buffer (possibly
		1754	a few hundred bytes), readdir requires a result buffer and so on. Perl
		1755	scalars and other data passed into aio requests will also be locked and
		1756	will consume memory till the request has entered the done state.
		1757
		1758	This is not awfully much, so queuing lots of requests is not usually a
		1759	problem.
		1760
		1761	Per-thread usage:
		1762
		1763	In the execution phase, some aio requests require more memory for
		1764	temporary buffers, and each thread requires a stack and other data
		1765	structures (usually around 16k-128k, depending on the OS).
		1766
		1767	=head1 KNOWN BUGS
		1768
		1769	Known bugs will be fixed in the next release.
		1770
295	=head1 SEE ALSO	1771	=head1 SEE ALSO
296		1772
297	L<Coro>, L<Linux::AIO>.	1773	L<AnyEvent::AIO> for easy integration into event loops, L<Coro::AIO> for a
		1774	more natural syntax.
298		1775
299	=head1 AUTHOR	1776	=head1 AUTHOR
300		1777
301	Marc Lehmann <schmorp@schmorp.de>	1778	Marc Lehmann <schmorp@schmorp.de>
302	http://home.schmorp.de/	1779	http://home.schmorp.de/

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