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Revision 1.6 by root, Sun Jul 10 22:19:48 2005 UTC vs.
Revision 1.208 by root, Mon Sep 26 20:19:08 2011 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 = '4.0';
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_realpath aio_sync
		178	aio_fsync aio_syncfs aio_fdatasync aio_sync_file_range aio_fallocate
		179	aio_pathsync aio_readahead
		180	aio_rename aio_link aio_move aio_copy aio_group
		181	aio_nop aio_mknod aio_load aio_rmtree aio_mkdir aio_chown
		182	aio_chmod aio_utime aio_truncate
		183	aio_msync aio_mtouch aio_mlock aio_mlockall
		184	aio_statvfs
		185	aio_wd);
		186
		187	our @EXPORT = (@AIO_REQ, qw(aioreq_pri aioreq_nice));
		188	our @EXPORT_OK = qw(poll_fileno poll_cb poll_wait flush
		189	min_parallel max_parallel max_idle idle_timeout
		190	nreqs nready npending nthreads
		191	max_poll_time max_poll_reqs
		192	sendfile fadvise madvise
		193	mmap munmap munlock munlockall);
		194
		195	push @AIO_REQ, qw(aio_busy); # not exported
		196
		197	@IO::AIO::GRP::ISA = 'IO::AIO::REQ';
64		198
65	require XSLoader;	199	require XSLoader;
66	XSLoader::load IO::AIO, $VERSION;	200	XSLoader::load ("IO::AIO", $VERSION);
67	}	201	}
68		202
69	=head1 FUNCTIONS	203	=head1 FUNCTIONS
70		204
		205	=head2 QUICK OVERVIEW
		206
		207	This section simply lists the prototypes of the most important functions
		208	for quick reference. See the following sections for function-by-function
		209	documentation.
		210
		211	aio_wd $pathname, $callback->($wd)
		212	aio_open $pathname, $flags, $mode, $callback->($fh)
		213	aio_close $fh, $callback->($status)
		214	aio_read $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
		215	aio_write $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
		216	aio_sendfile $out_fh, $in_fh, $in_offset, $length, $callback->($retval)
		217	aio_readahead $fh,$offset,$length, $callback->($retval)
		218	aio_stat $fh_or_path, $callback->($status)
		219	aio_lstat $fh, $callback->($status)
		220	aio_statvfs $fh_or_path, $callback->($statvfs)
		221	aio_utime $fh_or_path, $atime, $mtime, $callback->($status)
		222	aio_chown $fh_or_path, $uid, $gid, $callback->($status)
		223	aio_truncate $fh_or_path, $offset, $callback->($status)
		224	aio_chmod $fh_or_path, $mode, $callback->($status)
		225	aio_unlink $pathname, $callback->($status)
		226	aio_mknod $path, $mode, $dev, $callback->($status)
		227	aio_link $srcpath, $dstpath, $callback->($status)
		228	aio_symlink $srcpath, $dstpath, $callback->($status)
		229	aio_readlink $path, $callback->($link)
		230	aio_realpath $path, $callback->($link)
		231	aio_rename $srcpath, $dstpath, $callback->($status)
		232	aio_mkdir $pathname, $mode, $callback->($status)
		233	aio_rmdir $pathname, $callback->($status)
		234	aio_readdir $pathname, $callback->($entries)
		235	aio_readdirx $pathname, $flags, $callback->($entries, $flags)
		236	IO::AIO::READDIR_DENTS IO::AIO::READDIR_DIRS_FIRST
		237	IO::AIO::READDIR_STAT_ORDER IO::AIO::READDIR_FOUND_UNKNOWN
		238	aio_load $path, $data, $callback->($status)
		239	aio_copy $srcpath, $dstpath, $callback->($status)
		240	aio_move $srcpath, $dstpath, $callback->($status)
		241	aio_scandir $path, $maxreq, $callback->($dirs, $nondirs)
		242	aio_rmtree $path, $callback->($status)
		243	aio_sync $callback->($status)
		244	aio_syncfs $fh, $callback->($status)
		245	aio_fsync $fh, $callback->($status)
		246	aio_fdatasync $fh, $callback->($status)
		247	aio_sync_file_range $fh, $offset, $nbytes, $flags, $callback->($status)
		248	aio_pathsync $path, $callback->($status)
		249	aio_msync $scalar, $offset = 0, $length = undef, flags = 0, $callback->($status)
		250	aio_mtouch $scalar, $offset = 0, $length = undef, flags = 0, $callback->($status)
		251	aio_mlock $scalar, $offset = 0, $length = undef, $callback->($status)
		252	aio_mlockall $flags, $callback->($status)
		253	aio_group $callback->(...)
		254	aio_nop $callback->()
		255
		256	$prev_pri = aioreq_pri [$pri]
		257	aioreq_nice $pri_adjust
		258
		259	IO::AIO::poll_wait
		260	IO::AIO::poll_cb
		261	IO::AIO::poll
		262	IO::AIO::flush
		263	IO::AIO::max_poll_reqs $nreqs
		264	IO::AIO::max_poll_time $seconds
		265	IO::AIO::min_parallel $nthreads
		266	IO::AIO::max_parallel $nthreads
		267	IO::AIO::max_idle $nthreads
		268	IO::AIO::idle_timeout $seconds
		269	IO::AIO::max_outstanding $maxreqs
		270	IO::AIO::nreqs
		271	IO::AIO::nready
		272	IO::AIO::npending
		273
		274	IO::AIO::sendfile $ofh, $ifh, $offset, $count
		275	IO::AIO::fadvise $fh, $offset, $len, $advice
		276	IO::AIO::madvise $scalar, $offset, $length, $advice
		277	IO::AIO::mprotect $scalar, $offset, $length, $protect
		278	IO::AIO::munlock $scalar, $offset = 0, $length = undef
		279	IO::AIO::munlockall
		280
71	=head2 AIO FUNCTIONS	281	=head2 AIO REQUEST FUNCTIONS
72		282
73	All the C<aio_*> calls are more or less thin wrappers around the syscall	283	All the C<aio_*> calls are more or less thin wrappers around the syscall
74	with the same name (sans C<aio_>). The arguments are similar or identical,	284	with the same name (sans C<aio_>). The arguments are similar or identical,
75	and they all accept an additional C<$callback> argument which must be	285	and they all accept an additional (and optional) C<$callback> argument
76	a code reference. This code reference will get called with the syscall	286	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	287	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	288	perl, which usually delivers "false") as its sole argument after the given
79	been executed asynchronously.	289	syscall has been executed asynchronously.
80		290
81	All functions that expect a filehandle will also accept a file descriptor.	291	All functions expecting a filehandle keep a copy of the filehandle
		292	internally until the request has finished.
82		293
		294	All functions return request objects of type L<IO::AIO::REQ> that allow
		295	further manipulation of those requests while they are in-flight.
		296
83	The filenames you pass to these routines I<must> be absolute. The reason	297	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	298	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	299	request is being executed, the current working directory could have
86	never change the current working directory.	300	changed. Alternatively, you can make sure that you never change the
		301	current working directory anywhere in the program and then use relative
		302	paths.
		303
		304	To encode pathnames as octets, either make sure you either: a) always pass
		305	in filenames you got from outside (command line, readdir etc.) without
		306	tinkering, b) are ASCII or ISO 8859-1, c) use the Encode module and encode
		307	your pathnames to the locale (or other) encoding in effect in the user
		308	environment, d) use Glib::filename_from_unicode on unicode filenames or e)
		309	use something else to ensure your scalar has the correct contents.
		310
		311	This works, btw. independent of the internal UTF-8 bit, which IO::AIO
		312	handles correctly whether it is set or not.
87		313
88	=over 4	314	=over 4
89		315
		316	=item $prev_pri = aioreq_pri [$pri]
		317
		318	Returns the priority value that would be used for the next request and, if
		319	C<$pri> is given, sets the priority for the next aio request.
		320
		321	The default priority is C<0>, the minimum and maximum priorities are C<-4>
		322	and C<4>, respectively. Requests with higher priority will be serviced
		323	first.
		324
		325	The priority will be reset to C<0> after each call to one of the C<aio_*>
		326	functions.
		327
		328	Example: open a file with low priority, then read something from it with
		329	higher priority so the read request is serviced before other low priority
		330	open requests (potentially spamming the cache):
		331
		332	aioreq_pri -3;
		333	aio_open ..., sub {
		334	return unless $_[0];
		335
		336	aioreq_pri -2;
		337	aio_read $_[0], ..., sub {
		338	...
		339	};
		340	};
		341
		342
		343	=item aioreq_nice $pri_adjust
		344
		345	Similar to C<aioreq_pri>, but subtracts the given value from the current
		346	priority, so the effect is cumulative.
		347
		348
90	=item aio_open $pathname, $flags, $mode, $callback	349	=item aio_open $pathname, $flags, $mode, $callback->($fh)
91		350
92	Asynchronously open or create a file and call the callback with a newly	351	Asynchronously open or create a file and call the callback with a newly
93	created filehandle for the file.	352	created filehandle for the file.
94		353
95	The pathname passed to C<aio_open> must be absolute. See API NOTES, above,	354	The pathname passed to C<aio_open> must be absolute. See API NOTES, above,
96	for an explanation.	355	for an explanation.
97		356
98	The C<$mode> argument is a bitmask. See the C<Fcntl> module for a	357	The C<$flags> argument is a bitmask. See the C<Fcntl> module for a
99	list. They are the same as used in C<sysopen>.	358	list. They are the same as used by C<sysopen>.
		359
		360	Likewise, C<$mode> specifies the mode of the newly created file, if it
		361	didn't exist and C<O_CREAT> has been given, just like perl's C<sysopen>,
		362	except that it is mandatory (i.e. use C<0> if you don't create new files,
		363	and C<0666> or C<0777> if you do). Note that the C<$mode> will be modified
		364	by the umask in effect then the request is being executed, so better never
		365	change the umask.
100		366
101	Example:	367	Example:
102		368
103	aio_open "/etc/passwd", O_RDONLY, 0, sub {	369	aio_open "/etc/passwd", IO::AIO::O_RDONLY, 0, sub {
104	if ($_[0]) {	370	if ($_[0]) {
105	print "open successful, fh is $_[0]\n";	371	print "open successful, fh is $_[0]\n";
106	...	372	...
107	} else {	373	} else {
108	die "open failed: $!\n";	374	die "open failed: $!\n";
109	}	375	}
110	};	376	};
111		377
		378	In addition to all the common open modes/flags (C<O_RDONLY>, C<O_WRONLY>,
		379	C<O_RDWR>, C<O_CREAT>, C<O_TRUNC>, C<O_EXCL> and C<O_APPEND>), the
		380	following POSIX and non-POSIX constants are available (missing ones on
		381	your system are, as usual, C<0>):
		382
		383	C<O_ASYNC>, C<O_DIRECT>, C<O_NOATIME>, C<O_CLOEXEC>, C<O_NOCTTY>, C<O_NOFOLLOW>,
		384	C<O_NONBLOCK>, C<O_EXEC>, C<O_SEARCH>, C<O_DIRECTORY>, C<O_DSYNC>,
		385	C<O_RSYNC>, C<O_SYNC> and C<O_TTY_INIT>.
		386
		387
112	=item aio_close $fh, $callback	388	=item aio_close $fh, $callback->($status)
113		389
114	Asynchronously close a file and call the callback with the result	390	Asynchronously close a file and call the callback with the result
115	code. I<WARNING:> although accepted, you should not pass in a perl	391	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		392
		393	Unfortunately, you can't do this to perl. Perl I<insists> very strongly on
		394	closing the file descriptor associated with the filehandle itself.
		395
		396	Therefore, C<aio_close> will not close the filehandle - instead it will
		397	use dup2 to overwrite the file descriptor with the write-end of a pipe
		398	(the pipe fd will be created on demand and will be cached).
		399
		400	Or in other words: the file descriptor will be closed, but it will not be
		401	free for reuse until the perl filehandle is closed.
		402
		403	=cut
		404
120	=item aio_read $fh,$offset,$length, $data,$dataoffset,$callback	405	=item aio_read $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
121		406
122	=item aio_write $fh,$offset,$length, $data,$dataoffset,$callback	407	=item aio_write $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
123		408
124	Reads or writes C<length> bytes from the specified C<fh> and C<offset>	409	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	410	C<$offset> into the scalar given by C<$data> and offset C<$dataoffset>
126	callback without the actual number of bytes read (or -1 on error, just	411	and calls the callback without the actual number of bytes read (or -1 on
127	like the syscall).	412	error, just like the syscall).
128		413
		414	C<aio_read> will, like C<sysread>, shrink or grow the C<$data> scalar to
		415	offset plus the actual number of bytes read.
		416
		417	If C<$offset> is undefined, then the current file descriptor offset will
		418	be used (and updated), otherwise the file descriptor offset will not be
		419	changed by these calls.
		420
		421	If C<$length> is undefined in C<aio_write>, use the remaining length of
		422	C<$data>.
		423
		424	If C<$dataoffset> is less than zero, it will be counted from the end of
		425	C<$data>.
		426
		427	The C<$data> scalar I<MUST NOT> be modified in any way while the request
		428	is outstanding. Modifying it can result in segfaults or World War III (if
		429	the necessary/optional hardware is installed).
		430
129	Example: Read 15 bytes at offset 7 into scalar C<$buffer>, strating at	431	Example: Read 15 bytes at offset 7 into scalar C<$buffer>, starting at
130	offset C<0> within the scalar:	432	offset C<0> within the scalar:
131		433
132	aio_read $fh, 7, 15, $buffer, 0, sub {	434	aio_read $fh, 7, 15, $buffer, 0, sub {
133	$_[0] >= 0 or die "read error: $!";	435	$_[0] > 0 or die "read error: $!";
134	print "read <$buffer>\n";	436	print "read $_[0] bytes: <$buffer>\n";
135	};	437	};
136		438
		439
		440	=item aio_sendfile $out_fh, $in_fh, $in_offset, $length, $callback->($retval)
		441
		442	Tries to copy C<$length> bytes from C<$in_fh> to C<$out_fh>. It starts
		443	reading at byte offset C<$in_offset>, and starts writing at the current
		444	file offset of C<$out_fh>. Because of that, it is not safe to issue more
		445	than one C<aio_sendfile> per C<$out_fh>, as they will interfere with each
		446	other. The same C<$in_fh> works fine though, as this function does not
		447	move or use the file offset of C<$in_fh>.
		448
		449	Please note that C<aio_sendfile> can read more bytes from C<$in_fh> than
		450	are written, and there is no way to find out how many more bytes have been
		451	read from C<aio_sendfile> alone, as C<aio_sendfile> only provides the
		452	number of bytes written to C<$out_fh>. Only if the result value equals
		453	C<$length> one can assume that C<$length> bytes have been read.
		454
		455	Unlike with other C<aio_> functions, it makes a lot of sense to use
		456	C<aio_sendfile> on non-blocking sockets, as long as one end (typically
		457	the C<$in_fh>) is a file - the file I/O will then be asynchronous, while
		458	the socket I/O will be non-blocking. Note, however, that you can run
		459	into a trap where C<aio_sendfile> reads some data with readahead, then
		460	fails to write all data, and when the socket is ready the next time, the
		461	data in the cache is already lost, forcing C<aio_sendfile> to again hit
		462	the disk. Explicit C<aio_read> + C<aio_write> let's you better control
		463	resource usage.
		464
		465	This call tries to make use of a native C<sendfile>-like syscall to
		466	provide zero-copy operation. For this to work, C<$out_fh> should refer to
		467	a socket, and C<$in_fh> should refer to an mmap'able file.
		468
		469	If a native sendfile cannot be found or it fails with C<ENOSYS>,
		470	C<EINVAL>, C<ENOTSUP>, C<EOPNOTSUPP>, C<EAFNOSUPPORT>, C<EPROTOTYPE> or
		471	C<ENOTSOCK>, it will be emulated, so you can call C<aio_sendfile> on any
		472	type of filehandle regardless of the limitations of the operating system.
		473
		474	As native sendfile syscalls (as practically any non-POSIX interface hacked
		475	together in a hurry to improve benchmark numbers) tend to be rather buggy
		476	on many systems, this implementation tries to work around some known bugs
		477	in Linux and FreeBSD kernels (probably others, too), but that might fail,
		478	so you really really should check the return value of C<aio_sendfile> -
		479	fewre bytes than expected might have been transferred.
		480
		481
137	=item aio_readahead $fh,$offset,$length, $callback	482	=item aio_readahead $fh,$offset,$length, $callback->($retval)
138		483
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<$!> is set to ENOSYS.
142
143	readahead() populates the page cache with data from a file so that	484	C<aio_readahead> populates the page cache with data from a file so that
144	subsequent reads from that file will not block on disk I/O. The C<$offset>	485	subsequent reads from that file will not block on disk I/O. The C<$offset>
145	argument specifies the starting point from which data is to be read and	486	argument specifies the starting point from which data is to be read and
146	C<$length> specifies the number of bytes to be read. I/O is performed in	487	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	488	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	489	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	490	(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.	491	file. The current file offset of the file is left unchanged.
151		492
		493	If that syscall doesn't exist (likely if your OS isn't Linux) it will be
		494	emulated by simply reading the data, which would have a similar effect.
		495
		496
152	=item aio_stat $fh_or_path, $callback	497	=item aio_stat $fh_or_path, $callback->($status)
153		498
154	=item aio_lstat $fh, $callback	499	=item aio_lstat $fh, $callback->($status)
155		500
156	Works like perl's C<stat> or C<lstat> in void context. The callback will	501	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 _>	502	be called after the stat and the results will be available using C<stat _>
158	or C<-s _> etc...	503	or C<-s _> etc...
159		504
…		…
161	for an explanation.	506	for an explanation.
162		507
163	Currently, the stats are always 64-bit-stats, i.e. instead of returning an	508	Currently, the stats are always 64-bit-stats, i.e. instead of returning an
164	error when stat'ing a large file, the results will be silently truncated	509	error when stat'ing a large file, the results will be silently truncated
165	unless perl itself is compiled with large file support.	510	unless perl itself is compiled with large file support.
		511
		512	To help interpret the mode and dev/rdev stat values, IO::AIO offers the
		513	following constants and functions (if not implemented, the constants will
		514	be C<0> and the functions will either C<croak> or fall back on traditional
		515	behaviour).
		516
		517	C<S_IFMT>, C<S_IFIFO>, C<S_IFCHR>, C<S_IFBLK>, C<S_IFLNK>, C<S_IFREG>,
		518	C<S_IFDIR>, C<S_IFWHT>, C<S_IFSOCK>, C<IO::AIO::major $dev_t>,
		519	C<IO::AIO::minor $dev_t>, C<IO::AIO::makedev $major, $minor>.
166		520
167	Example: Print the length of F</etc/passwd>:	521	Example: Print the length of F</etc/passwd>:
168		522
169	aio_stat "/etc/passwd", sub {	523	aio_stat "/etc/passwd", sub {
170	$_[0] and die "stat failed: $!";	524	$_[0] and die "stat failed: $!";
171	print "size is ", -s _, "\n";	525	print "size is ", -s _, "\n";
172	};	526	};
173		527
		528
		529	=item aio_statvfs $fh_or_path, $callback->($statvfs)
		530
		531	Works like the POSIX C<statvfs> or C<fstatvfs> syscalls, depending on
		532	whether a file handle or path was passed.
		533
		534	On success, the callback is passed a hash reference with the following
		535	members: C<bsize>, C<frsize>, C<blocks>, C<bfree>, C<bavail>, C<files>,
		536	C<ffree>, C<favail>, C<fsid>, C<flag> and C<namemax>. On failure, C<undef>
		537	is passed.
		538
		539	The following POSIX IO::AIO::ST_* constants are defined: C<ST_RDONLY> and
		540	C<ST_NOSUID>.
		541
		542	The following non-POSIX IO::AIO::ST_* flag masks are defined to
		543	their correct value when available, or to C<0> on systems that do
		544	not support them: C<ST_NODEV>, C<ST_NOEXEC>, C<ST_SYNCHRONOUS>,
		545	C<ST_MANDLOCK>, C<ST_WRITE>, C<ST_APPEND>, C<ST_IMMUTABLE>, C<ST_NOATIME>,
		546	C<ST_NODIRATIME> and C<ST_RELATIME>.
		547
		548	Example: stat C</wd> and dump out the data if successful.
		549
		550	aio_statvfs "/wd", sub {
		551	my $f = $_[0]
		552	or die "statvfs: $!";
		553
		554	use Data::Dumper;
		555	say Dumper $f;
		556	};
		557
		558	# result:
		559	{
		560	bsize => 1024,
		561	bfree => 4333064312,
		562	blocks => 10253828096,
		563	files => 2050765568,
		564	flag => 4096,
		565	favail => 2042092649,
		566	bavail => 4333064312,
		567	ffree => 2042092649,
		568	namemax => 255,
		569	frsize => 1024,
		570	fsid => 1810
		571	}
		572
		573
		574	=item aio_utime $fh_or_path, $atime, $mtime, $callback->($status)
		575
		576	Works like perl's C<utime> function (including the special case of $atime
		577	and $mtime being undef). Fractional times are supported if the underlying
		578	syscalls support them.
		579
		580	When called with a pathname, uses utimes(2) if available, otherwise
		581	utime(2). If called on a file descriptor, uses futimes(2) if available,
		582	otherwise returns ENOSYS, so this is not portable.
		583
		584	Examples:
		585
		586	# set atime and mtime to current time (basically touch(1)):
		587	aio_utime "path", undef, undef;
		588	# set atime to current time and mtime to beginning of the epoch:
		589	aio_utime "path", time, undef; # undef==0
		590
		591
		592	=item aio_chown $fh_or_path, $uid, $gid, $callback->($status)
		593
		594	Works like perl's C<chown> function, except that C<undef> for either $uid
		595	or $gid is being interpreted as "do not change" (but -1 can also be used).
		596
		597	Examples:
		598
		599	# same as "chown root path" in the shell:
		600	aio_chown "path", 0, -1;
		601	# same as above:
		602	aio_chown "path", 0, undef;
		603
		604
		605	=item aio_truncate $fh_or_path, $offset, $callback->($status)
		606
		607	Works like truncate(2) or ftruncate(2).
		608
		609
		610	=item aio_chmod $fh_or_path, $mode, $callback->($status)
		611
		612	Works like perl's C<chmod> function.
		613
		614
174	=item aio_unlink $pathname, $callback	615	=item aio_unlink $pathname, $callback->($status)
175		616
176	Asynchronously unlink (delete) a file and call the callback with the	617	Asynchronously unlink (delete) a file and call the callback with the
177	result code.	618	result code.
178		619
		620
		621	=item aio_mknod $path, $mode, $dev, $callback->($status)
		622
		623	[EXPERIMENTAL]
		624
		625	Asynchronously create a device node (or fifo). See mknod(2).
		626
		627	The only (POSIX-) portable way of calling this function is:
		628
		629	aio_mknod $path, IO::AIO::S_IFIFO | $mode, 0, sub { ...
		630
		631	See C<aio_stat> for info about some potentially helpful extra constants
		632	and functions.
		633
		634	=item aio_link $srcpath, $dstpath, $callback->($status)
		635
		636	Asynchronously create a new link to the existing object at C<$srcpath> at
		637	the path C<$dstpath> and call the callback with the result code.
		638
		639
		640	=item aio_symlink $srcpath, $dstpath, $callback->($status)
		641
		642	Asynchronously create a new symbolic link to the existing object at C<$srcpath> at
		643	the path C<$dstpath> and call the callback with the result code.
		644
		645
		646	=item aio_readlink $path, $callback->($link)
		647
		648	Asynchronously read the symlink specified by C<$path> and pass it to
		649	the callback. If an error occurs, nothing or undef gets passed to the
		650	callback.
		651
		652
		653	=item aio_realpath $path, $callback->($path)
		654
		655	Asynchronously make the path absolute and resolve any symlinks in
		656	C<$path>. The resulting path only consists of directories (Same as
		657	L<Cwd::realpath>).
		658
		659	This request can be used to get the absolute path of the current working
		660	directory by passing it a path of F<.> (a single dot).
		661
		662
		663	=item aio_rename $srcpath, $dstpath, $callback->($status)
		664
		665	Asynchronously rename the object at C<$srcpath> to C<$dstpath>, just as
		666	rename(2) and call the callback with the result code.
		667
		668
		669	=item aio_mkdir $pathname, $mode, $callback->($status)
		670
		671	Asynchronously mkdir (create) a directory and call the callback with
		672	the result code. C<$mode> will be modified by the umask at the time the
		673	request is executed, so do not change your umask.
		674
		675
		676	=item aio_rmdir $pathname, $callback->($status)
		677
		678	Asynchronously rmdir (delete) a directory and call the callback with the
		679	result code.
		680
		681
		682	=item aio_readdir $pathname, $callback->($entries)
		683
		684	Unlike the POSIX call of the same name, C<aio_readdir> reads an entire
		685	directory (i.e. opendir + readdir + closedir). The entries will not be
		686	sorted, and will B<NOT> include the C<.> and C<..> entries.
		687
		688	The callback is passed a single argument which is either C<undef> or an
		689	array-ref with the filenames.
		690
		691
		692	=item aio_readdirx $pathname, $flags, $callback->($entries, $flags)
		693
		694	Quite similar to C<aio_readdir>, but the C<$flags> argument allows one to
		695	tune behaviour and output format. In case of an error, C<$entries> will be
		696	C<undef>.
		697
		698	The flags are a combination of the following constants, ORed together (the
		699	flags will also be passed to the callback, possibly modified):
		700
		701	=over 4
		702
		703	=item IO::AIO::READDIR_DENTS
		704
		705	When this flag is off, then the callback gets an arrayref consisting of
		706	names only (as with C<aio_readdir>), otherwise it gets an arrayref with
		707	C<[$name, $type, $inode]> arrayrefs, each describing a single directory
		708	entry in more detail.
		709
		710	C<$name> is the name of the entry.
		711
		712	C<$type> is one of the C<IO::AIO::DT_xxx> constants:
		713
		714	C<IO::AIO::DT_UNKNOWN>, C<IO::AIO::DT_FIFO>, C<IO::AIO::DT_CHR>, C<IO::AIO::DT_DIR>,
		715	C<IO::AIO::DT_BLK>, C<IO::AIO::DT_REG>, C<IO::AIO::DT_LNK>, C<IO::AIO::DT_SOCK>,
		716	C<IO::AIO::DT_WHT>.
		717
		718	C<IO::AIO::DT_UNKNOWN> means just that: readdir does not know. If you need to
		719	know, you have to run stat yourself. Also, for speed reasons, the C<$type>
		720	scalars are read-only: you can not modify them.
		721
		722	C<$inode> is the inode number (which might not be exact on systems with 64
		723	bit inode numbers and 32 bit perls). This field has unspecified content on
		724	systems that do not deliver the inode information.
		725
		726	=item IO::AIO::READDIR_DIRS_FIRST
		727
		728	When this flag is set, then the names will be returned in an order where
		729	likely directories come first, in optimal stat order. This is useful when
		730	you need to quickly find directories, or you want to find all directories
		731	while avoiding to stat() each entry.
		732
		733	If the system returns type information in readdir, then this is used
		734	to find directories directly. Otherwise, likely directories are names
		735	beginning with ".", or otherwise names with no dots, of which names with
		736	short names are tried first.
		737
		738	=item IO::AIO::READDIR_STAT_ORDER
		739
		740	When this flag is set, then the names will be returned in an order
		741	suitable for stat()'ing each one. That is, when you plan to stat()
		742	all files in the given directory, then the returned order will likely
		743	be fastest.
		744
		745	If both this flag and C<IO::AIO::READDIR_DIRS_FIRST> are specified, then
		746	the likely dirs come first, resulting in a less optimal stat order.
		747
		748	=item IO::AIO::READDIR_FOUND_UNKNOWN
		749
		750	This flag should not be set when calling C<aio_readdirx>. Instead, it
		751	is being set by C<aio_readdirx>, when any of the C<$type>'s found were
		752	C<IO::AIO::DT_UNKNOWN>. The absence of this flag therefore indicates that all
		753	C<$type>'s are known, which can be used to speed up some algorithms.
		754
		755	=back
		756
		757
		758	=item aio_load $path, $data, $callback->($status)
		759
		760	This is a composite request that tries to fully load the given file into
		761	memory. Status is the same as with aio_read.
		762
		763	=cut
		764
		765	sub aio_load($$;$) {
		766	my ($path, undef, $cb) = @_;
		767	my $data = \$_[1];
		768
		769	my $pri = aioreq_pri;
		770	my $grp = aio_group $cb;
		771
		772	aioreq_pri $pri;
		773	add $grp aio_open $path, O_RDONLY, 0, sub {
		774	my $fh = shift
		775	or return $grp->result (-1);
		776
		777	aioreq_pri $pri;
		778	add $grp aio_read $fh, 0, (-s $fh), $$data, 0, sub {
		779	$grp->result ($_[0]);
		780	};
		781	};
		782
		783	$grp
		784	}
		785
		786	=item aio_copy $srcpath, $dstpath, $callback->($status)
		787
		788	Try to copy the I<file> (directories not supported as either source or
		789	destination) from C<$srcpath> to C<$dstpath> and call the callback with
		790	a status of C<0> (ok) or C<-1> (error, see C<$!>).
		791
		792	This is a composite request that creates the destination file with
		793	mode 0200 and copies the contents of the source file into it using
		794	C<aio_sendfile>, followed by restoring atime, mtime, access mode and
		795	uid/gid, in that order.
		796
		797	If an error occurs, the partial destination file will be unlinked, if
		798	possible, except when setting atime, mtime, access mode and uid/gid, where
		799	errors are being ignored.
		800
		801	=cut
		802
		803	sub aio_copy($$;$) {
		804	my ($src, $dst, $cb) = @_;
		805
		806	my $pri = aioreq_pri;
		807	my $grp = aio_group $cb;
		808
		809	aioreq_pri $pri;
		810	add $grp aio_open $src, O_RDONLY, 0, sub {
		811	if (my $src_fh = $_[0]) {
		812	my @stat = stat $src_fh; # hmm, might block over nfs?
		813
		814	aioreq_pri $pri;
		815	add $grp aio_open $dst, O_CREAT | O_WRONLY | O_TRUNC, 0200, sub {
		816	if (my $dst_fh = $_[0]) {
		817	aioreq_pri $pri;
		818	add $grp aio_sendfile $dst_fh, $src_fh, 0, $stat[7], sub {
		819	if ($_[0] == $stat[7]) {
		820	$grp->result (0);
		821	close $src_fh;
		822
		823	my $ch = sub {
		824	aioreq_pri $pri;
		825	add $grp aio_chmod $dst_fh, $stat[2] & 07777, sub {
		826	aioreq_pri $pri;
		827	add $grp aio_chown $dst_fh, $stat[4], $stat[5], sub {
		828	aioreq_pri $pri;
		829	add $grp aio_close $dst_fh;
		830	}
		831	};
		832	};
		833
		834	aioreq_pri $pri;
		835	add $grp aio_utime $dst_fh, $stat[8], $stat[9], sub {
		836	if ($_[0] < 0 && $! == ENOSYS) {
		837	aioreq_pri $pri;
		838	add $grp aio_utime $dst, $stat[8], $stat[9], $ch;
		839	} else {
		840	$ch->();
		841	}
		842	};
		843	} else {
		844	$grp->result (-1);
		845	close $src_fh;
		846	close $dst_fh;
		847
		848	aioreq $pri;
		849	add $grp aio_unlink $dst;
		850	}
		851	};
		852	} else {
		853	$grp->result (-1);
		854	}
		855	},
		856
		857	} else {
		858	$grp->result (-1);
		859	}
		860	};
		861
		862	$grp
		863	}
		864
		865	=item aio_move $srcpath, $dstpath, $callback->($status)
		866
		867	Try to move the I<file> (directories not supported as either source or
		868	destination) from C<$srcpath> to C<$dstpath> and call the callback with
		869	a status of C<0> (ok) or C<-1> (error, see C<$!>).
		870
		871	This is a composite request that tries to rename(2) the file first; if
		872	rename fails with C<EXDEV>, it copies the file with C<aio_copy> and, if
		873	that is successful, unlinks the C<$srcpath>.
		874
		875	=cut
		876
		877	sub aio_move($$;$) {
		878	my ($src, $dst, $cb) = @_;
		879
		880	my $pri = aioreq_pri;
		881	my $grp = aio_group $cb;
		882
		883	aioreq_pri $pri;
		884	add $grp aio_rename $src, $dst, sub {
		885	if ($_[0] && $! == EXDEV) {
		886	aioreq_pri $pri;
		887	add $grp aio_copy $src, $dst, sub {
		888	$grp->result ($_[0]);
		889
		890	unless ($_[0]) {
		891	aioreq_pri $pri;
		892	add $grp aio_unlink $src;
		893	}
		894	};
		895	} else {
		896	$grp->result ($_[0]);
		897	}
		898	};
		899
		900	$grp
		901	}
		902
		903	=item aio_scandir $path, $maxreq, $callback->($dirs, $nondirs)
		904
		905	Scans a directory (similar to C<aio_readdir>) but additionally tries to
		906	efficiently separate the entries of directory C<$path> into two sets of
		907	names, directories you can recurse into (directories), and ones you cannot
		908	recurse into (everything else, including symlinks to directories).
		909
		910	C<aio_scandir> is a composite request that creates of many sub requests_
		911	C<$maxreq> specifies the maximum number of outstanding aio requests that
		912	this function generates. If it is C<< <= 0 >>, then a suitable default
		913	will be chosen (currently 4).
		914
		915	On error, the callback is called without arguments, otherwise it receives
		916	two array-refs with path-relative entry names.
		917
		918	Example:
		919
		920	aio_scandir $dir, 0, sub {
		921	my ($dirs, $nondirs) = @_;
		922	print "real directories: @$dirs\n";
		923	print "everything else: @$nondirs\n";
		924	};
		925
		926	Implementation notes.
		927
		928	The C<aio_readdir> cannot be avoided, but C<stat()>'ing every entry can.
		929
		930	If readdir returns file type information, then this is used directly to
		931	find directories.
		932
		933	Otherwise, after reading the directory, the modification time, size etc.
		934	of the directory before and after the readdir is checked, and if they
		935	match (and isn't the current time), the link count will be used to decide
		936	how many entries are directories (if >= 2). Otherwise, no knowledge of the
		937	number of subdirectories will be assumed.
		938
		939	Then entries will be sorted into likely directories a non-initial dot
		940	currently) and likely non-directories (see C<aio_readdirx>). Then every
		941	entry plus an appended C</.> will be C<stat>'ed, likely directories first,
		942	in order of their inode numbers. If that succeeds, it assumes that the
		943	entry is a directory or a symlink to directory (which will be checked
		944	separately). This is often faster than stat'ing the entry itself because
		945	filesystems might detect the type of the entry without reading the inode
		946	data (e.g. ext2fs filetype feature), even on systems that cannot return
		947	the filetype information on readdir.
		948
		949	If the known number of directories (link count - 2) has been reached, the
		950	rest of the entries is assumed to be non-directories.
		951
		952	This only works with certainty on POSIX (= UNIX) filesystems, which
		953	fortunately are the vast majority of filesystems around.
		954
		955	It will also likely work on non-POSIX filesystems with reduced efficiency
		956	as those tend to return 0 or 1 as link counts, which disables the
		957	directory counting heuristic.
		958
		959	=cut
		960
		961	sub aio_scandir($$;$) {
		962	my ($path, $maxreq, $cb) = @_;
		963
		964	my $pri = aioreq_pri;
		965
		966	my $grp = aio_group $cb;
		967
		968	$maxreq = 4 if $maxreq <= 0;
		969
		970	# stat once
		971	aioreq_pri $pri;
		972	add $grp aio_stat $path, sub {
		973	return $grp->result () if $_[0];
		974	my $now = time;
		975	my $hash1 = join ":", (stat _)[0,1,3,7,9];
		976
		977	# read the directory entries
		978	aioreq_pri $pri;
		979	add $grp aio_readdirx $path, READDIR_DIRS_FIRST, sub {
		980	my $entries = shift
		981	or return $grp->result ();
		982
		983	# stat the dir another time
		984	aioreq_pri $pri;
		985	add $grp aio_stat $path, sub {
		986	my $hash2 = join ":", (stat _)[0,1,3,7,9];
		987
		988	my $ndirs;
		989
		990	# take the slow route if anything looks fishy
		991	if ($hash1 ne $hash2 or (stat _)[9] == $now) {
		992	$ndirs = -1;
		993	} else {
		994	# if nlink == 2, we are finished
		995	# for non-posix-fs's, we rely on nlink < 2
		996	$ndirs = (stat _)[3] - 2
		997	or return $grp->result ([], $entries);
		998	}
		999
		1000	my (@dirs, @nondirs);
		1001
		1002	my $statgrp = add $grp aio_group sub {
		1003	$grp->result (\@dirs, \@nondirs);
		1004	};
		1005
		1006	limit $statgrp $maxreq;
		1007	feed $statgrp sub {
		1008	return unless @$entries;
		1009	my $entry = shift @$entries;
		1010
		1011	aioreq_pri $pri;
		1012	add $statgrp aio_stat "$path/$entry/.", sub {
		1013	if ($_[0] < 0) {
		1014	push @nondirs, $entry;
		1015	} else {
		1016	# need to check for real directory
		1017	aioreq_pri $pri;
		1018	add $statgrp aio_lstat "$path/$entry", sub {
		1019	if (-d _) {
		1020	push @dirs, $entry;
		1021
		1022	unless (--$ndirs) {
		1023	push @nondirs, @$entries;
		1024	feed $statgrp;
		1025	}
		1026	} else {
		1027	push @nondirs, $entry;
		1028	}
		1029	}
		1030	}
		1031	};
		1032	};
		1033	};
		1034	};
		1035	};
		1036
		1037	$grp
		1038	}
		1039
		1040	=item aio_rmtree $path, $callback->($status)
		1041
		1042	Delete a directory tree starting (and including) C<$path>, return the
		1043	status of the final C<rmdir> only. This is a composite request that
		1044	uses C<aio_scandir> to recurse into and rmdir directories, and unlink
		1045	everything else.
		1046
		1047	=cut
		1048
		1049	sub aio_rmtree;
		1050	sub aio_rmtree($;$) {
		1051	my ($path, $cb) = @_;
		1052
		1053	my $pri = aioreq_pri;
		1054	my $grp = aio_group $cb;
		1055
		1056	aioreq_pri $pri;
		1057	add $grp aio_scandir $path, 0, sub {
		1058	my ($dirs, $nondirs) = @_;
		1059
		1060	my $dirgrp = aio_group sub {
		1061	add $grp aio_rmdir $path, sub {
		1062	$grp->result ($_[0]);
		1063	};
		1064	};
		1065
		1066	(aioreq_pri $pri), add $dirgrp aio_rmtree "$path/$_" for @$dirs;
		1067	(aioreq_pri $pri), add $dirgrp aio_unlink "$path/$_" for @$nondirs;
		1068
		1069	add $grp $dirgrp;
		1070	};
		1071
		1072	$grp
		1073	}
		1074
		1075	=item aio_sync $callback->($status)
		1076
		1077	Asynchronously call sync and call the callback when finished.
		1078
179	=item aio_fsync $fh, $callback	1079	=item aio_fsync $fh, $callback->($status)
180		1080
181	Asynchronously call fsync on the given filehandle and call the callback	1081	Asynchronously call fsync on the given filehandle and call the callback
182	with the fsync result code.	1082	with the fsync result code.
183		1083
184	=item aio_fdatasync $fh, $callback	1084	=item aio_fdatasync $fh, $callback->($status)
185		1085
186	Asynchronously call fdatasync on the given filehandle and call the	1086	Asynchronously call fdatasync on the given filehandle and call the
187	callback with the fdatasync result code.	1087	callback with the fdatasync result code.
188		1088
		1089	If this call isn't available because your OS lacks it or it couldn't be
		1090	detected, it will be emulated by calling C<fsync> instead.
		1091
		1092	=item aio_syncfs $fh, $callback->($status)
		1093
		1094	Asynchronously call the syncfs syscall to sync the filesystem associated
		1095	to the given filehandle and call the callback with the syncfs result
		1096	code. If syncfs is not available, calls sync(), but returns C<-1> and sets
		1097	errno to C<ENOSYS> nevertheless.
		1098
		1099	=item aio_sync_file_range $fh, $offset, $nbytes, $flags, $callback->($status)
		1100
		1101	Sync the data portion of the file specified by C<$offset> and C<$length>
		1102	to disk (but NOT the metadata), by calling the Linux-specific
		1103	sync_file_range call. If sync_file_range is not available or it returns
		1104	ENOSYS, then fdatasync or fsync is being substituted.
		1105
		1106	C<$flags> can be a combination of C<IO::AIO::SYNC_FILE_RANGE_WAIT_BEFORE>,
		1107	C<IO::AIO::SYNC_FILE_RANGE_WRITE> and
		1108	C<IO::AIO::SYNC_FILE_RANGE_WAIT_AFTER>: refer to the sync_file_range
		1109	manpage for details.
		1110
		1111	=item aio_pathsync $path, $callback->($status)
		1112
		1113	This request tries to open, fsync and close the given path. This is a
		1114	composite request intended to sync directories after directory operations
		1115	(E.g. rename). This might not work on all operating systems or have any
		1116	specific effect, but usually it makes sure that directory changes get
		1117	written to disc. It works for anything that can be opened for read-only,
		1118	not just directories.
		1119
		1120	Future versions of this function might fall back to other methods when
		1121	C<fsync> on the directory fails (such as calling C<sync>).
		1122
		1123	Passes C<0> when everything went ok, and C<-1> on error.
		1124
		1125	=cut
		1126
		1127	sub aio_pathsync($;$) {
		1128	my ($path, $cb) = @_;
		1129
		1130	my $pri = aioreq_pri;
		1131	my $grp = aio_group $cb;
		1132
		1133	aioreq_pri $pri;
		1134	add $grp aio_open $path, O_RDONLY, 0, sub {
		1135	my ($fh) = @_;
		1136	if ($fh) {
		1137	aioreq_pri $pri;
		1138	add $grp aio_fsync $fh, sub {
		1139	$grp->result ($_[0]);
		1140
		1141	aioreq_pri $pri;
		1142	add $grp aio_close $fh;
		1143	};
		1144	} else {
		1145	$grp->result (-1);
		1146	}
		1147	};
		1148
		1149	$grp
		1150	}
		1151
		1152	=item aio_msync $scalar, $offset = 0, $length = undef, flags = 0, $callback->($status)
		1153
		1154	This is a rather advanced IO::AIO call, which only works on mmap(2)ed
		1155	scalars (see the C<IO::AIO::mmap> function, although it also works on data
		1156	scalars managed by the L<Sys::Mmap> or L<Mmap> modules, note that the
		1157	scalar must only be modified in-place while an aio operation is pending on
		1158	it).
		1159
		1160	It calls the C<msync> function of your OS, if available, with the memory
		1161	area starting at C<$offset> in the string and ending C<$length> bytes
		1162	later. If C<$length> is negative, counts from the end, and if C<$length>
		1163	is C<undef>, then it goes till the end of the string. The flags can be
		1164	a combination of C<IO::AIO::MS_ASYNC>, C<IO::AIO::MS_INVALIDATE> and
		1165	C<IO::AIO::MS_SYNC>.
		1166
		1167	=item aio_mtouch $scalar, $offset = 0, $length = undef, flags = 0, $callback->($status)
		1168
		1169	This is a rather advanced IO::AIO call, which works best on mmap(2)ed
		1170	scalars.
		1171
		1172	It touches (reads or writes) all memory pages in the specified
		1173	range inside the scalar. All caveats and parameters are the same
		1174	as for C<aio_msync>, above, except for flags, which must be either
		1175	C<0> (which reads all pages and ensures they are instantiated) or
		1176	C<IO::AIO::MT_MODIFY>, which modifies the memory page s(by reading and
		1177	writing an octet from it, which dirties the page).
		1178
		1179	=item aio_mlock $scalar, $offset = 0, $length = undef, $callback->($status)
		1180
		1181	This is a rather advanced IO::AIO call, which works best on mmap(2)ed
		1182	scalars.
		1183
		1184	It reads in all the pages of the underlying storage into memory (if any)
		1185	and locks them, so they are not getting swapped/paged out or removed.
		1186
		1187	If C<$length> is undefined, then the scalar will be locked till the end.
		1188
		1189	On systems that do not implement C<mlock>, this function returns C<-1>
		1190	and sets errno to C<ENOSYS>.
		1191
		1192	Note that the corresponding C<munlock> is synchronous and is
		1193	documented under L<MISCELLANEOUS FUNCTIONS>.
		1194
		1195	Example: open a file, mmap and mlock it - both will be undone when
		1196	C<$data> gets destroyed.
		1197
		1198	open my $fh, "<", $path or die "$path: $!";
		1199	my $data;
		1200	IO::AIO::mmap $data, -s $fh, IO::AIO::PROT_READ, IO::AIO::MAP_SHARED, $fh;
		1201	aio_mlock $data; # mlock in background
		1202
		1203	=item aio_mlockall $flags, $callback->($status)
		1204
		1205	Calls the C<mlockall> function with the given C<$flags> (a combination of
		1206	C<IO::AIO::MCL_CURRENT> and C<IO::AIO::MCL_FUTURE>).
		1207
		1208	On systems that do not implement C<mlockall>, this function returns C<-1>
		1209	and sets errno to C<ENOSYS>.
		1210
		1211	Note that the corresponding C<munlockall> is synchronous and is
		1212	documented under L<MISCELLANEOUS FUNCTIONS>.
		1213
		1214	Example: asynchronously lock all current and future pages into memory.
		1215
		1216	aio_mlockall IO::AIO::MCL_FUTURE;
		1217
		1218	=item aio_group $callback->(...)
		1219
		1220	This is a very special aio request: Instead of doing something, it is a
		1221	container for other aio requests, which is useful if you want to bundle
		1222	many requests into a single, composite, request with a definite callback
		1223	and the ability to cancel the whole request with its subrequests.
		1224
		1225	Returns an object of class L<IO::AIO::GRP>. See its documentation below
		1226	for more info.
		1227
		1228	Example:
		1229
		1230	my $grp = aio_group sub {
		1231	print "all stats done\n";
		1232	};
		1233
		1234	add $grp
		1235	(aio_stat ...),
		1236	(aio_stat ...),
		1237	...;
		1238
		1239	=item aio_nop $callback->()
		1240
		1241	This is a special request - it does nothing in itself and is only used for
		1242	side effects, such as when you want to add a dummy request to a group so
		1243	that finishing the requests in the group depends on executing the given
		1244	code.
		1245
		1246	While this request does nothing, it still goes through the execution
		1247	phase and still requires a worker thread. Thus, the callback will not
		1248	be executed immediately but only after other requests in the queue have
		1249	entered their execution phase. This can be used to measure request
		1250	latency.
		1251
		1252	=item IO::AIO::aio_busy $fractional_seconds, $callback->() *NOT EXPORTED*
		1253
		1254	Mainly used for debugging and benchmarking, this aio request puts one of
		1255	the request workers to sleep for the given time.
		1256
		1257	While it is theoretically handy to have simple I/O scheduling requests
		1258	like sleep and file handle readable/writable, the overhead this creates is
		1259	immense (it blocks a thread for a long time) so do not use this function
		1260	except to put your application under artificial I/O pressure.
		1261
189	=back	1262	=back
190		1263
		1264	=head2 IO::AIO::REQ CLASS
		1265
		1266	All non-aggregate C<aio_*> functions return an object of this class when
		1267	called in non-void context.
		1268
		1269	=over 4
		1270
		1271	=item cancel $req
		1272
		1273	Cancels the request, if possible. Has the effect of skipping execution
		1274	when entering the B<execute> state and skipping calling the callback when
		1275	entering the the B<result> state, but will leave the request otherwise
		1276	untouched (with the exception of readdir). That means that requests that
		1277	currently execute will not be stopped and resources held by the request
		1278	will not be freed prematurely.
		1279
		1280	=item cb $req $callback->(...)
		1281
		1282	Replace (or simply set) the callback registered to the request.
		1283
		1284	=back
		1285
		1286	=head2 IO::AIO::GRP CLASS
		1287
		1288	This class is a subclass of L<IO::AIO::REQ>, so all its methods apply to
		1289	objects of this class, too.
		1290
		1291	A IO::AIO::GRP object is a special request that can contain multiple other
		1292	aio requests.
		1293
		1294	You create one by calling the C<aio_group> constructing function with a
		1295	callback that will be called when all contained requests have entered the
		1296	C<done> state:
		1297
		1298	my $grp = aio_group sub {
		1299	print "all requests are done\n";
		1300	};
		1301
		1302	You add requests by calling the C<add> method with one or more
		1303	C<IO::AIO::REQ> objects:
		1304
		1305	$grp->add (aio_unlink "...");
		1306
		1307	add $grp aio_stat "...", sub {
		1308	$_[0] or return $grp->result ("error");
		1309
		1310	# add another request dynamically, if first succeeded
		1311	add $grp aio_open "...", sub {
		1312	$grp->result ("ok");
		1313	};
		1314	};
		1315
		1316	This makes it very easy to create composite requests (see the source of
		1317	C<aio_move> for an application) that work and feel like simple requests.
		1318
		1319	=over 4
		1320
		1321	=item * The IO::AIO::GRP objects will be cleaned up during calls to
		1322	C<IO::AIO::poll_cb>, just like any other request.
		1323
		1324	=item * They can be canceled like any other request. Canceling will cancel not
		1325	only the request itself, but also all requests it contains.
		1326
		1327	=item * They can also can also be added to other IO::AIO::GRP objects.
		1328
		1329	=item * You must not add requests to a group from within the group callback (or
		1330	any later time).
		1331
		1332	=back
		1333
		1334	Their lifetime, simplified, looks like this: when they are empty, they
		1335	will finish very quickly. If they contain only requests that are in the
		1336	C<done> state, they will also finish. Otherwise they will continue to
		1337	exist.
		1338
		1339	That means after creating a group you have some time to add requests
		1340	(precisely before the callback has been invoked, which is only done within
		1341	the C<poll_cb>). And in the callbacks of those requests, you can add
		1342	further requests to the group. And only when all those requests have
		1343	finished will the the group itself finish.
		1344
		1345	=over 4
		1346
		1347	=item add $grp ...
		1348
		1349	=item $grp->add (...)
		1350
		1351	Add one or more requests to the group. Any type of L<IO::AIO::REQ> can
		1352	be added, including other groups, as long as you do not create circular
		1353	dependencies.
		1354
		1355	Returns all its arguments.
		1356
		1357	=item $grp->cancel_subs
		1358
		1359	Cancel all subrequests and clears any feeder, but not the group request
		1360	itself. Useful when you queued a lot of events but got a result early.
		1361
		1362	The group request will finish normally (you cannot add requests to the
		1363	group).
		1364
		1365	=item $grp->result (...)
		1366
		1367	Set the result value(s) that will be passed to the group callback when all
		1368	subrequests have finished and set the groups errno to the current value
		1369	of errno (just like calling C<errno> without an error number). By default,
		1370	no argument will be passed and errno is zero.
		1371
		1372	=item $grp->errno ([$errno])
		1373
		1374	Sets the group errno value to C<$errno>, or the current value of errno
		1375	when the argument is missing.
		1376
		1377	Every aio request has an associated errno value that is restored when
		1378	the callback is invoked. This method lets you change this value from its
		1379	default (0).
		1380
		1381	Calling C<result> will also set errno, so make sure you either set C<$!>
		1382	before the call to C<result>, or call c<errno> after it.
		1383
		1384	=item feed $grp $callback->($grp)
		1385
		1386	Sets a feeder/generator on this group: every group can have an attached
		1387	generator that generates requests if idle. The idea behind this is that,
		1388	although you could just queue as many requests as you want in a group,
		1389	this might starve other requests for a potentially long time. For example,
		1390	C<aio_scandir> might generate hundreds of thousands C<aio_stat> requests,
		1391	delaying any later requests for a long time.
		1392
		1393	To avoid this, and allow incremental generation of requests, you can
		1394	instead a group and set a feeder on it that generates those requests. The
		1395	feed callback will be called whenever there are few enough (see C<limit>,
		1396	below) requests active in the group itself and is expected to queue more
		1397	requests.
		1398
		1399	The feed callback can queue as many requests as it likes (i.e. C<add> does
		1400	not impose any limits).
		1401
		1402	If the feed does not queue more requests when called, it will be
		1403	automatically removed from the group.
		1404
		1405	If the feed limit is C<0> when this method is called, it will be set to
		1406	C<2> automatically.
		1407
		1408	Example:
		1409
		1410	# stat all files in @files, but only ever use four aio requests concurrently:
		1411
		1412	my $grp = aio_group sub { print "finished\n" };
		1413	limit $grp 4;
		1414	feed $grp sub {
		1415	my $file = pop @files
		1416	or return;
		1417
		1418	add $grp aio_stat $file, sub { ... };
		1419	};
		1420
		1421	=item limit $grp $num
		1422
		1423	Sets the feeder limit for the group: The feeder will be called whenever
		1424	the group contains less than this many requests.
		1425
		1426	Setting the limit to C<0> will pause the feeding process.
		1427
		1428	The default value for the limit is C<0>, but note that setting a feeder
		1429	automatically bumps it up to C<2>.
		1430
		1431	=back
		1432
191	=head2 SUPPORT FUNCTIONS	1433	=head2 SUPPORT FUNCTIONS
192		1434
		1435	=head3 EVENT PROCESSING AND EVENT LOOP INTEGRATION
		1436
193	=over 4	1437	=over 4
194		1438
195	=item $fileno = IO::AIO::poll_fileno	1439	=item $fileno = IO::AIO::poll_fileno
196		1440
197	Return the I<request result pipe filehandle>. This filehandle must be	1441	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	1442	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	1443	select and so on, see below or the SYNOPSIS). If the pipe becomes readable
200	C<poll_cb> to check the results.	1444	you have to call C<poll_cb> to check the results.
201		1445
202	See C<poll_cb> for an example.	1446	See C<poll_cb> for an example.
203		1447
204	=item IO::AIO::poll_cb	1448	=item IO::AIO::poll_cb
205		1449
206	Process all outstanding events on the result pipe. You have to call this	1450	Process some outstanding events on the result pipe. You have to call
207	regularly. Returns the number of events processed. Returns immediately	1451	this regularly. Returns C<0> if all events could be processed (or there
208	when no events are outstanding.	1452	were no events to process), or C<-1> if it returned earlier for whatever
		1453	reason. Returns immediately when no events are outstanding. The amount of
		1454	events processed depends on the settings of C<IO::AIO::max_poll_req> and
		1455	C<IO::AIO::max_poll_time>.
209		1456
210	You can use Event to multiplex, e.g.:	1457	If not all requests were processed for whatever reason, the filehandle
		1458	will still be ready when C<poll_cb> returns, so normally you don't have to
		1459	do anything special to have it called later.
		1460
		1461	Apart from calling C<IO::AIO::poll_cb> when the event filehandle becomes
		1462	ready, it can be beneficial to call this function from loops which submit
		1463	a lot of requests, to make sure the results get processed when they become
		1464	available and not just when the loop is finished and the event loop takes
		1465	over again. This function returns very fast when there are no outstanding
		1466	requests.
		1467
		1468	Example: Install an Event watcher that automatically calls
		1469	IO::AIO::poll_cb with high priority (more examples can be found in the
		1470	SYNOPSIS section, at the top of this document):
211		1471
212	Event->io (fd => IO::AIO::poll_fileno,	1472	Event->io (fd => IO::AIO::poll_fileno,
213	poll => 'r', async => 1,	1473	poll => 'r', async => 1,
214	cb => \&IO::AIO::poll_cb);	1474	cb => \&IO::AIO::poll_cb);
215		1475
216	=item IO::AIO::poll_wait	1476	=item IO::AIO::poll_wait
217		1477
		1478	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	1479	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	1480	does a C<select> on the filehandle. This is useful if you want to
220	for some requests to finish).	1481	synchronously wait for some requests to finish).
221		1482
222	See C<nreqs> for an example.	1483	See C<nreqs> for an example.
223		1484
		1485	=item IO::AIO::poll
		1486
		1487	Waits until some requests have been handled.
		1488
		1489	Returns the number of requests processed, but is otherwise strictly
		1490	equivalent to:
		1491
		1492	IO::AIO::poll_wait, IO::AIO::poll_cb
		1493
224	=item IO::AIO::nreqs	1494	=item IO::AIO::flush
225		1495
226	Returns the number of requests currently outstanding.	1496	Wait till all outstanding AIO requests have been handled.
227		1497
228	Example: wait till there are no outstanding requests anymore:	1498	Strictly equivalent to:
229		1499
230	IO::AIO::poll_wait, IO::AIO::poll_cb	1500	IO::AIO::poll_wait, IO::AIO::poll_cb
231	while IO::AIO::nreqs;	1501	while IO::AIO::nreqs;
232		1502
		1503	=item IO::AIO::max_poll_reqs $nreqs
		1504
		1505	=item IO::AIO::max_poll_time $seconds
		1506
		1507	These set the maximum number of requests (default C<0>, meaning infinity)
		1508	that are being processed by C<IO::AIO::poll_cb> in one call, respectively
		1509	the maximum amount of time (default C<0>, meaning infinity) spent in
		1510	C<IO::AIO::poll_cb> to process requests (more correctly the mininum amount
		1511	of time C<poll_cb> is allowed to use).
		1512
		1513	Setting C<max_poll_time> to a non-zero value creates an overhead of one
		1514	syscall per request processed, which is not normally a problem unless your
		1515	callbacks are really really fast or your OS is really really slow (I am
		1516	not mentioning Solaris here). Using C<max_poll_reqs> incurs no overhead.
		1517
		1518	Setting these is useful if you want to ensure some level of
		1519	interactiveness when perl is not fast enough to process all requests in
		1520	time.
		1521
		1522	For interactive programs, values such as C<0.01> to C<0.1> should be fine.
		1523
		1524	Example: Install an Event watcher that automatically calls
		1525	IO::AIO::poll_cb with low priority, to ensure that other parts of the
		1526	program get the CPU sometimes even under high AIO load.
		1527
		1528	# try not to spend much more than 0.1s in poll_cb
		1529	IO::AIO::max_poll_time 0.1;
		1530
		1531	# use a low priority so other tasks have priority
		1532	Event->io (fd => IO::AIO::poll_fileno,
		1533	poll => 'r', nice => 1,
		1534	cb => &IO::AIO::poll_cb);
		1535
		1536	=back
		1537
		1538	=head3 CONTROLLING THE NUMBER OF THREADS
		1539
		1540	=over
		1541
233	=item IO::AIO::min_parallel $nthreads	1542	=item IO::AIO::min_parallel $nthreads
234		1543
235	Set the minimum number of AIO threads to C<$nthreads>. The default is	1544	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	1545	default is C<8>, which means eight asynchronous operations can execute
237	(the number of outstanding operations, however, is unlimited).	1546	concurrently at any one time (the number of outstanding requests,
		1547	however, is unlimited).
238		1548
		1549	IO::AIO starts threads only on demand, when an AIO request is queued and
		1550	no free thread exists. Please note that queueing up a hundred requests can
		1551	create demand for a hundred threads, even if it turns out that everything
		1552	is in the cache and could have been processed faster by a single thread.
		1553
239	It is recommended to keep the number of threads low, as some Linux	1554	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	1555	Linux kernel versions will scale negatively with the number of threads
241	parallelity => MUCH higher latency). With current Linux 2.6 versions, 4-32	1556	(higher parallelity => MUCH higher latency). With current Linux 2.6
242	threads should be fine.	1557	versions, 4-32 threads should be fine.
243		1558
244	Under normal circumstances you don't need to call this function, as this	1559	Under most circumstances you don't need to call this function, as the
245	module automatically starts some threads (the exact number might change,	1560	module selects a default that is suitable for low to moderate load.
246	and is currently 4).
247		1561
248	=item IO::AIO::max_parallel $nthreads	1562	=item IO::AIO::max_parallel $nthreads
249		1563
250	Sets the maximum number of AIO threads to C<$nthreads>. If more than	1564	Sets the maximum number of AIO threads to C<$nthreads>. If more than the
251	the specified number of threads are currently running, kill them. This	1565	specified number of threads are currently running, this function kills
252	function blocks until the limit is reached.	1566	them. This function blocks until the limit is reached.
		1567
		1568	While C<$nthreads> are zero, aio requests get queued but not executed
		1569	until the number of threads has been increased again.
253		1570
254	This module automatically runs C<max_parallel 0> at program end, to ensure	1571	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.	1572	that all threads are killed and that there are no outstanding requests.
256		1573
257	Under normal circumstances you don't need to call this function.	1574	Under normal circumstances you don't need to call this function.
258		1575
		1576	=item IO::AIO::max_idle $nthreads
		1577
		1578	Limit the number of threads (default: 4) that are allowed to idle
		1579	(i.e., threads that did not get a request to process within the idle
		1580	timeout (default: 10 seconds). That means if a thread becomes idle while
		1581	C<$nthreads> other threads are also idle, it will free its resources and
		1582	exit.
		1583
		1584	This is useful when you allow a large number of threads (e.g. 100 or 1000)
		1585	to allow for extremely high load situations, but want to free resources
		1586	under normal circumstances (1000 threads can easily consume 30MB of RAM).
		1587
		1588	The default is probably ok in most situations, especially if thread
		1589	creation is fast. If thread creation is very slow on your system you might
		1590	want to use larger values.
		1591
		1592	=item IO::AIO::idle_timeout $seconds
		1593
		1594	Sets the minimum idle timeout (default 10) after which worker threads are
		1595	allowed to exit. SEe C<IO::AIO::max_idle>.
		1596
259	=item $oldnreqs = IO::AIO::max_outstanding $nreqs	1597	=item IO::AIO::max_outstanding $maxreqs
260		1598
261	Sets the maximum number of outstanding requests to C<$nreqs>. If you	1599	Sets the maximum number of outstanding requests to C<$nreqs>. If
262	try to queue up more than this number of requests, the caller will block until	1600	you do queue up more than this number of requests, the next call to
263	some requests have been handled.	1601	C<IO::AIO::poll_cb> (and other functions calling C<poll_cb>, such as
		1602	C<IO::AIO::flush> or C<IO::AIO::poll>) will block until the limit is no
		1603	longer exceeded.
264		1604
265	The default is very large, so normally there is no practical limit. If you	1605	In other words, this setting does not enforce a queue limit, but can be
266	queue up many requests in a loop it it often improves speed if you set	1606	used to make poll functions block if the limit is exceeded.
267	this to a relatively low number, such as C<100>.
268		1607
269	Under normal circumstances you don't need to call this function.	1608	This is a very bad function to use in interactive programs because it
		1609	blocks, and a bad way to reduce concurrency because it is inexact: Better
		1610	use an C<aio_group> together with a feed callback.
		1611
		1612	It's main use is in scripts without an event loop - when you want to stat
		1613	a lot of files, you can write somehting like this:
		1614
		1615	IO::AIO::max_outstanding 32;
		1616
		1617	for my $path (...) {
		1618	aio_stat $path , ...;
		1619	IO::AIO::poll_cb;
		1620	}
		1621
		1622	IO::AIO::flush;
		1623
		1624	The call to C<poll_cb> inside the loop will normally return instantly, but
		1625	as soon as more thna C<32> reqeusts are in-flight, it will block until
		1626	some requests have been handled. This keeps the loop from pushing a large
		1627	number of C<aio_stat> requests onto the queue.
		1628
		1629	The default value for C<max_outstanding> is very large, so there is no
		1630	practical limit on the number of outstanding requests.
270		1631
271	=back	1632	=back
272		1633
		1634	=head3 STATISTICAL INFORMATION
		1635
		1636	=over
		1637
		1638	=item IO::AIO::nreqs
		1639
		1640	Returns the number of requests currently in the ready, execute or pending
		1641	states (i.e. for which their callback has not been invoked yet).
		1642
		1643	Example: wait till there are no outstanding requests anymore:
		1644
		1645	IO::AIO::poll_wait, IO::AIO::poll_cb
		1646	while IO::AIO::nreqs;
		1647
		1648	=item IO::AIO::nready
		1649
		1650	Returns the number of requests currently in the ready state (not yet
		1651	executed).
		1652
		1653	=item IO::AIO::npending
		1654
		1655	Returns the number of requests currently in the pending state (executed,
		1656	but not yet processed by poll_cb).
		1657
		1658	=back
		1659
		1660	=head3 MISCELLANEOUS FUNCTIONS
		1661
		1662	IO::AIO implements some functions that might be useful, but are not
		1663	asynchronous.
		1664
		1665	=over 4
		1666
		1667	=item IO::AIO::sendfile $ofh, $ifh, $offset, $count
		1668
		1669	Calls the C<eio_sendfile_sync> function, which is like C<aio_sendfile>,
		1670	but is blocking (this makes most sense if you know the input data is
		1671	likely cached already and the output filehandle is set to non-blocking
		1672	operations).
		1673
		1674	Returns the number of bytes copied, or C<-1> on error.
		1675
		1676	=item IO::AIO::fadvise $fh, $offset, $len, $advice
		1677
		1678	Simply calls the C<posix_fadvise> function (see its
		1679	manpage for details). The following advice constants are
		1680	available: C<IO::AIO::FADV_NORMAL>, C<IO::AIO::FADV_SEQUENTIAL>,
		1681	C<IO::AIO::FADV_RANDOM>, C<IO::AIO::FADV_NOREUSE>,
		1682	C<IO::AIO::FADV_WILLNEED>, C<IO::AIO::FADV_DONTNEED>.
		1683
		1684	On systems that do not implement C<posix_fadvise>, this function returns
		1685	ENOSYS, otherwise the return value of C<posix_fadvise>.
		1686
		1687	=item IO::AIO::madvise $scalar, $offset, $len, $advice
		1688
		1689	Simply calls the C<posix_madvise> function (see its
		1690	manpage for details). The following advice constants are
		1691	available: C<IO::AIO::MADV_NORMAL>, C<IO::AIO::MADV_SEQUENTIAL>,
		1692	C<IO::AIO::MADV_RANDOM>, C<IO::AIO::MADV_WILLNEED>, C<IO::AIO::MADV_DONTNEED>.
		1693
		1694	On systems that do not implement C<posix_madvise>, this function returns
		1695	ENOSYS, otherwise the return value of C<posix_madvise>.
		1696
		1697	=item IO::AIO::mprotect $scalar, $offset, $len, $protect
		1698
		1699	Simply calls the C<mprotect> function on the preferably AIO::mmap'ed
		1700	$scalar (see its manpage for details). The following protect
		1701	constants are available: C<IO::AIO::PROT_NONE>, C<IO::AIO::PROT_READ>,
		1702	C<IO::AIO::PROT_WRITE>, C<IO::AIO::PROT_EXEC>.
		1703
		1704	On systems that do not implement C<mprotect>, this function returns
		1705	ENOSYS, otherwise the return value of C<mprotect>.
		1706
		1707	=item IO::AIO::mmap $scalar, $length, $prot, $flags, $fh[, $offset]
		1708
		1709	Memory-maps a file (or anonymous memory range) and attaches it to the
		1710	given C<$scalar>, which will act like a string scalar.
		1711
		1712	The only operations allowed on the scalar are C<substr>/C<vec> that don't
		1713	change the string length, and most read-only operations such as copying it
		1714	or searching it with regexes and so on.
		1715
		1716	Anything else is unsafe and will, at best, result in memory leaks.
		1717
		1718	The memory map associated with the C<$scalar> is automatically removed
		1719	when the C<$scalar> is destroyed, or when the C<IO::AIO::mmap> or
		1720	C<IO::AIO::munmap> functions are called.
		1721
		1722	This calls the C<mmap>(2) function internally. See your system's manual
		1723	page for details on the C<$length>, C<$prot> and C<$flags> parameters.
		1724
		1725	The C<$length> must be larger than zero and smaller than the actual
		1726	filesize.
		1727
		1728	C<$prot> is a combination of C<IO::AIO::PROT_NONE>, C<IO::AIO::PROT_EXEC>,
		1729	C<IO::AIO::PROT_READ> and/or C<IO::AIO::PROT_WRITE>,
		1730
		1731	C<$flags> can be a combination of C<IO::AIO::MAP_SHARED> or
		1732	C<IO::AIO::MAP_PRIVATE>, or a number of system-specific flags (when
		1733	not available, the are defined as 0): C<IO::AIO::MAP_ANONYMOUS>
		1734	(which is set to C<MAP_ANON> if your system only provides this
		1735	constant), C<IO::AIO::MAP_HUGETLB>, C<IO::AIO::MAP_LOCKED>,
		1736	C<IO::AIO::MAP_NORESERVE>, C<IO::AIO::MAP_POPULATE> or
		1737	C<IO::AIO::MAP_NONBLOCK>
		1738
		1739	If C<$fh> is C<undef>, then a file descriptor of C<-1> is passed.
		1740
		1741	C<$offset> is the offset from the start of the file - it generally must be
		1742	a multiple of C<IO::AIO::PAGESIZE> and defaults to C<0>.
		1743
		1744	Example:
		1745
		1746	use Digest::MD5;
		1747	use IO::AIO;
		1748
		1749	open my $fh, "<verybigfile"
		1750	or die "$!";
		1751
		1752	IO::AIO::mmap my $data, -s $fh, IO::AIO::PROT_READ, IO::AIO::MAP_SHARED, $fh
		1753	or die "verybigfile: $!";
		1754
		1755	my $fast_md5 = md5 $data;
		1756
		1757	=item IO::AIO::munmap $scalar
		1758
		1759	Removes a previous mmap and undefines the C<$scalar>.
		1760
		1761	=item IO::AIO::munlock $scalar, $offset = 0, $length = undef
		1762
		1763	Calls the C<munlock> function, undoing the effects of a previous
		1764	C<aio_mlock> call (see its description for details).
		1765
		1766	=item IO::AIO::munlockall
		1767
		1768	Calls the C<munlockall> function.
		1769
		1770	On systems that do not implement C<munlockall>, this function returns
		1771	ENOSYS, otherwise the return value of C<munlockall>.
		1772
		1773	=back
		1774
273	=cut	1775	=cut
274		1776
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;	1777	min_parallel 8;
288		1778
289	END {	1779	END { flush }
290	max_parallel 0;
291	}
292		1780
293	1;	1781	1;
294		1782
		1783	=head1 EVENT LOOP INTEGRATION
		1784
		1785	It is recommended to use L<AnyEvent::AIO> to integrate IO::AIO
		1786	automatically into many event loops:
		1787
		1788	# AnyEvent integration (EV, Event, Glib, Tk, POE, urxvt, pureperl...)
		1789	use AnyEvent::AIO;
		1790
		1791	You can also integrate IO::AIO manually into many event loops, here are
		1792	some examples of how to do this:
		1793
		1794	# EV integration
		1795	my $aio_w = EV::io IO::AIO::poll_fileno, EV::READ, \&IO::AIO::poll_cb;
		1796
		1797	# Event integration
		1798	Event->io (fd => IO::AIO::poll_fileno,
		1799	poll => 'r',
		1800	cb => \&IO::AIO::poll_cb);
		1801
		1802	# Glib/Gtk2 integration
		1803	add_watch Glib::IO IO::AIO::poll_fileno,
		1804	in => sub { IO::AIO::poll_cb; 1 };
		1805
		1806	# Tk integration
		1807	Tk::Event::IO->fileevent (IO::AIO::poll_fileno, "",
		1808	readable => \&IO::AIO::poll_cb);
		1809
		1810	# Danga::Socket integration
		1811	Danga::Socket->AddOtherFds (IO::AIO::poll_fileno =>
		1812	\&IO::AIO::poll_cb);
		1813
		1814	=head2 FORK BEHAVIOUR
		1815
		1816	Usage of pthreads in a program changes the semantics of fork
		1817	considerably. Specifically, only async-safe functions can be called after
		1818	fork. Perl doesn't know about this, so in general, you cannot call fork
		1819	with defined behaviour in perl if pthreads are involved. IO::AIO uses
		1820	pthreads, so this applies, but many other extensions and (for inexplicable
		1821	reasons) perl itself often is linked against pthreads, so this limitation
		1822	applies to quite a lot of perls.
		1823
		1824	This module no longer tries to fight your OS, or POSIX. That means IO::AIO
		1825	only works in the process that loaded it. Forking is fully supported, but
		1826	using IO::AIO in the child is not.
		1827
		1828	You might get around by not I<using> IO::AIO before (or after)
		1829	forking. You could also try to call the L<IO::AIO::reinit> function in the
		1830	child:
		1831
		1832	=over 4
		1833
		1834	=item IO::AIO::reinit
		1835
		1836	Abandons all current requests and I/O threads and simply reinitialises all
		1837	data structures. This is not an operation supported by any standards, but
		1838	happens to work on GNU/Linux and some newer BSD systems.
		1839
		1840	The only reasonable use for this function is to call it after forking, if
		1841	C<IO::AIO> was used in the parent. Calling it while IO::AIO is active in
		1842	the process will result in undefined behaviour. Calling it at any time
		1843	will also result in any undefined (by POSIX) behaviour.
		1844
		1845	=back
		1846
		1847	=head2 MEMORY USAGE
		1848
		1849	Per-request usage:
		1850
		1851	Each aio request uses - depending on your architecture - around 100-200
		1852	bytes of memory. In addition, stat requests need a stat buffer (possibly
		1853	a few hundred bytes), readdir requires a result buffer and so on. Perl
		1854	scalars and other data passed into aio requests will also be locked and
		1855	will consume memory till the request has entered the done state.
		1856
		1857	This is not awfully much, so queuing lots of requests is not usually a
		1858	problem.
		1859
		1860	Per-thread usage:
		1861
		1862	In the execution phase, some aio requests require more memory for
		1863	temporary buffers, and each thread requires a stack and other data
		1864	structures (usually around 16k-128k, depending on the OS).
		1865
		1866	=head1 KNOWN BUGS
		1867
		1868	Known bugs will be fixed in the next release.
		1869
295	=head1 SEE ALSO	1870	=head1 SEE ALSO
296		1871
297	L<Coro>, L<Linux::AIO>.	1872	L<AnyEvent::AIO> for easy integration into event loops, L<Coro::AIO> for a
		1873	more natural syntax.
298		1874
299	=head1 AUTHOR	1875	=head1 AUTHOR
300		1876
301	Marc Lehmann <schmorp@schmorp.de>	1877	Marc Lehmann <schmorp@schmorp.de>
302	http://home.schmorp.de/	1878	http://home.schmorp.de/

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