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Revision 1.39 by root, Sun Aug 28 11:05:50 2005 UTC vs.
Revision 1.302 by root, Wed Apr 3 03:03:53 2019 UTC

1	=head1 NAME	1	=head1 NAME
2		2
3	IO::AIO - Asynchronous Input/Output	3	IO::AIO - Asynchronous/Advanced Input/Output
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',
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	in => sub { IO::AIO::poll_cb; 1 };	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
33	# Danga::Socket
34	Danga::Socket->AddOtherFds (IO::AIO::poll_fileno =>
35	\&IO::AIO::poll_cb);
36
37		30
38	=head1 DESCRIPTION	31	=head1 DESCRIPTION
39		32
40	This module implements asynchronous I/O using whatever means your	33	This module implements asynchronous I/O using whatever means your
41	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>).
42		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
43	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
44	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
45	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
46	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
47	aio functions available on many operating systems. However, they are often	57	functions available on many operating systems. However, they are often
48	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
49	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
50	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.
51		62
		63	In addition to asynchronous I/O, this module also exports some rather
		64	arcane interfaces, such as C<madvise> or linux's C<splice> system call,
		65	which is why the C<A> in C<AIO> can also mean I<advanced>.
		66
52	Although the module will work with in the presence of other threads, it is	67	Although the module will work in the presence of other (Perl-) threads,
53	currently not reentrant, so use appropriate locking yourself, always call	68	it is currently not reentrant in any way, so use appropriate locking
54	C<poll_cb> from within the same thread, or never call C<poll_cb> (or other	69	yourself, always call C<poll_cb> from within the same thread, or never
55	C<aio_> functions) recursively.	70	call C<poll_cb> (or other C<aio_> functions) recursively.
		71
		72	=head2 EXAMPLE
		73
		74	This is a simple example that uses the EV module and loads
		75	F</etc/passwd> asynchronously:
		76
		77	use EV;
		78	use IO::AIO;
		79
		80	# register the IO::AIO callback with EV
		81	my $aio_w = EV::io IO::AIO::poll_fileno, EV::READ, \&IO::AIO::poll_cb;
		82
		83	# queue the request to open /etc/passwd
		84	aio_open "/etc/passwd", IO::AIO::O_RDONLY, 0, sub {
		85	my $fh = shift
		86	or die "error while opening: $!";
		87
		88	# stat'ing filehandles is generally non-blocking
		89	my $size = -s $fh;
		90
		91	# queue a request to read the file
		92	my $contents;
		93	aio_read $fh, 0, $size, $contents, 0, sub {
		94	$_[0] == $size
		95	or die "short read: $!";
		96
		97	close $fh;
		98
		99	# file contents now in $contents
		100	print $contents;
		101
		102	# exit event loop and program
		103	EV::break;
		104	};
		105	};
		106
		107	# possibly queue up other requests, or open GUI windows,
		108	# check for sockets etc. etc.
		109
		110	# process events as long as there are some:
		111	EV::run;
		112
		113	=head1 REQUEST ANATOMY AND LIFETIME
		114
		115	Every C<aio_*> function creates a request. which is a C data structure not
		116	directly visible to Perl.
		117
		118	If called in non-void context, every request function returns a Perl
		119	object representing the request. In void context, nothing is returned,
		120	which saves a bit of memory.
		121
		122	The perl object is a fairly standard ref-to-hash object. The hash contents
		123	are not used by IO::AIO so you are free to store anything you like in it.
		124
		125	During their existance, aio requests travel through the following states,
		126	in order:
		127
		128	=over 4
		129
		130	=item ready
		131
		132	Immediately after a request is created it is put into the ready state,
		133	waiting for a thread to execute it.
		134
		135	=item execute
		136
		137	A thread has accepted the request for processing and is currently
		138	executing it (e.g. blocking in read).
		139
		140	=item pending
		141
		142	The request has been executed and is waiting for result processing.
		143
		144	While request submission and execution is fully asynchronous, result
		145	processing is not and relies on the perl interpreter calling C<poll_cb>
		146	(or another function with the same effect).
		147
		148	=item result
		149
		150	The request results are processed synchronously by C<poll_cb>.
		151
		152	The C<poll_cb> function will process all outstanding aio requests by
		153	calling their callbacks, freeing memory associated with them and managing
		154	any groups they are contained in.
		155
		156	=item done
		157
		158	Request has reached the end of its lifetime and holds no resources anymore
		159	(except possibly for the Perl object, but its connection to the actual
		160	aio request is severed and calling its methods will either do nothing or
		161	result in a runtime error).
		162
		163	=back
56		164
57	=cut	165	=cut
58		166
59	package IO::AIO;	167	package IO::AIO;
60		168
61	no warnings;	169	use Carp ();
		170
		171	use common::sense;
62		172
63	use base 'Exporter';	173	use base 'Exporter';
64		174
65	use Fcntl ();
66
67	BEGIN {	175	BEGIN {
68	$VERSION = 1.6;	176	our $VERSION = 4.72;
69		177
70	@EXPORT = qw(aio_sendfile aio_read aio_write aio_open aio_close aio_stat	178	our @AIO_REQ = qw(aio_sendfile aio_seek aio_read aio_write aio_open aio_close
71	aio_lstat aio_unlink aio_rmdir aio_readdir aio_symlink	179	aio_stat aio_lstat aio_unlink aio_rmdir aio_readdir aio_readdirx
72	aio_fsync aio_fdatasync aio_readahead);	180	aio_scandir aio_symlink aio_readlink aio_realpath aio_fcntl aio_ioctl
73	@EXPORT_OK = qw(poll_fileno poll_cb min_parallel max_parallel	181	aio_sync aio_fsync aio_syncfs aio_fdatasync aio_sync_file_range
74	max_outstanding nreqs);	182	aio_pathsync aio_readahead aio_fiemap aio_allocate
		183	aio_rename aio_rename2 aio_link aio_move aio_copy aio_group
		184	aio_nop aio_mknod aio_load aio_rmtree aio_mkdir aio_chown
		185	aio_chmod aio_utime aio_truncate
		186	aio_msync aio_mtouch aio_mlock aio_mlockall
		187	aio_statvfs
		188	aio_slurp
		189	aio_wd);
		190
		191	our @EXPORT = (@AIO_REQ, qw(aioreq_pri aioreq_nice));
		192	our @EXPORT_OK = qw(poll_fileno poll_cb poll_wait flush
		193	min_parallel max_parallel max_idle idle_timeout
		194	nreqs nready npending nthreads
		195	max_poll_time max_poll_reqs
		196	sendfile fadvise madvise
		197	mmap munmap mremap munlock munlockall);
		198
		199	push @AIO_REQ, qw(aio_busy); # not exported
		200
		201	@IO::AIO::GRP::ISA = 'IO::AIO::REQ';
75		202
76	require XSLoader;	203	require XSLoader;
77	XSLoader::load IO::AIO, $VERSION;	204	XSLoader::load ("IO::AIO", $VERSION);
78	}	205	}
79		206
80	=head1 FUNCTIONS	207	=head1 FUNCTIONS
81		208
82	=head2 AIO FUNCTIONS	209	=head2 QUICK OVERVIEW
		210
		211	This section simply lists the prototypes most of the functions for
		212	quick reference. See the following sections for function-by-function
		213	documentation.
		214
		215	aio_wd $pathname, $callback->($wd)
		216	aio_open $pathname, $flags, $mode, $callback->($fh)
		217	aio_close $fh, $callback->($status)
		218	aio_seek $fh,$offset,$whence, $callback->($offs)
		219	aio_read $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
		220	aio_write $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
		221	aio_sendfile $out_fh, $in_fh, $in_offset, $length, $callback->($retval)
		222	aio_readahead $fh,$offset,$length, $callback->($retval)
		223	aio_stat $fh_or_path, $callback->($status)
		224	aio_lstat $fh, $callback->($status)
		225	aio_statvfs $fh_or_path, $callback->($statvfs)
		226	aio_utime $fh_or_path, $atime, $mtime, $callback->($status)
		227	aio_chown $fh_or_path, $uid, $gid, $callback->($status)
		228	aio_chmod $fh_or_path, $mode, $callback->($status)
		229	aio_truncate $fh_or_path, $offset, $callback->($status)
		230	aio_allocate $fh, $mode, $offset, $len, $callback->($status)
		231	aio_fiemap $fh, $start, $length, $flags, $count, $cb->(\@extents)
		232	aio_unlink $pathname, $callback->($status)
		233	aio_mknod $pathname, $mode, $dev, $callback->($status)
		234	aio_link $srcpath, $dstpath, $callback->($status)
		235	aio_symlink $srcpath, $dstpath, $callback->($status)
		236	aio_readlink $pathname, $callback->($link)
		237	aio_realpath $pathname, $callback->($path)
		238	aio_rename $srcpath, $dstpath, $callback->($status)
		239	aio_rename2 $srcpath, $dstpath, $flags, $callback->($status)
		240	aio_mkdir $pathname, $mode, $callback->($status)
		241	aio_rmdir $pathname, $callback->($status)
		242	aio_readdir $pathname, $callback->($entries)
		243	aio_readdirx $pathname, $flags, $callback->($entries, $flags)
		244	IO::AIO::READDIR_DENTS IO::AIO::READDIR_DIRS_FIRST
		245	IO::AIO::READDIR_STAT_ORDER IO::AIO::READDIR_FOUND_UNKNOWN
		246	aio_scandir $pathname, $maxreq, $callback->($dirs, $nondirs)
		247	aio_load $pathname, $data, $callback->($status)
		248	aio_copy $srcpath, $dstpath, $callback->($status)
		249	aio_move $srcpath, $dstpath, $callback->($status)
		250	aio_rmtree $pathname, $callback->($status)
		251	aio_fcntl $fh, $cmd, $arg, $callback->($status)
		252	aio_ioctl $fh, $request, $buf, $callback->($status)
		253	aio_sync $callback->($status)
		254	aio_syncfs $fh, $callback->($status)
		255	aio_fsync $fh, $callback->($status)
		256	aio_fdatasync $fh, $callback->($status)
		257	aio_sync_file_range $fh, $offset, $nbytes, $flags, $callback->($status)
		258	aio_pathsync $pathname, $callback->($status)
		259	aio_msync $scalar, $offset = 0, $length = undef, flags = MS_SYNC, $callback->($status)
		260	aio_mtouch $scalar, $offset = 0, $length = undef, flags = 0, $callback->($status)
		261	aio_mlock $scalar, $offset = 0, $length = undef, $callback->($status)
		262	aio_mlockall $flags, $callback->($status)
		263	aio_group $callback->(...)
		264	aio_nop $callback->()
		265
		266	$prev_pri = aioreq_pri [$pri]
		267	aioreq_nice $pri_adjust
		268
		269	IO::AIO::poll_wait
		270	IO::AIO::poll_cb
		271	IO::AIO::poll
		272	IO::AIO::flush
		273	IO::AIO::max_poll_reqs $nreqs
		274	IO::AIO::max_poll_time $seconds
		275	IO::AIO::min_parallel $nthreads
		276	IO::AIO::max_parallel $nthreads
		277	IO::AIO::max_idle $nthreads
		278	IO::AIO::idle_timeout $seconds
		279	IO::AIO::max_outstanding $maxreqs
		280	IO::AIO::nreqs
		281	IO::AIO::nready
		282	IO::AIO::npending
		283	IO::AIO::reinit
		284
		285	$nfd = IO::AIO::get_fdlimit [EXPERIMENTAL]
		286	IO::AIO::min_fdlimit $nfd [EXPERIMENTAL]
		287
		288	IO::AIO::sendfile $ofh, $ifh, $offset, $count
		289	IO::AIO::fadvise $fh, $offset, $len, $advice
		290
		291	IO::AIO::mmap $scalar, $length, $prot, $flags[, $fh[, $offset]]
		292	IO::AIO::munmap $scalar
		293	IO::AIO::mremap $scalar, $new_length, $flags[, $new_address]
		294	IO::AIO::madvise $scalar, $offset, $length, $advice
		295	IO::AIO::mprotect $scalar, $offset, $length, $protect
		296	IO::AIO::munlock $scalar, $offset = 0, $length = undef
		297	IO::AIO::munlockall
		298
		299	# stat extensions
		300	$counter = IO::AIO::st_gen
		301	$seconds = IO::AIO::st_atime, IO::AIO::st_mtime, IO::AIO::st_ctime, IO::AIO::st_btime
		302	($atime, $mtime, $ctime, $btime, ...) = IO::AIO::st_xtime
		303	$nanoseconds = IO::AIO::st_atimensec, IO::AIO::st_mtimensec, IO::AIO::st_ctimensec, IO::AIO::st_btimensec
		304	$seconds = IO::AIO::st_btimesec
		305	($atime, $mtime, $ctime, $btime, ...) = IO::AIO::st_xtimensec
		306
		307	# very much unportable syscalls
		308	IO::AIO::splice $r_fh, $r_off, $w_fh, $w_off, $length, $flags
		309	IO::AIO::tee $r_fh, $w_fh, $length, $flags
		310	$actual_size = IO::AIO::pipesize $r_fh[, $new_size]
		311	($rfh, $wfh) = IO::AIO::pipe2 [$flags]
		312	$fh = IO::AIO::memfd_create $pathname[, $flags]
		313	$fh = IO::AIO::eventfd [$initval, [$flags]]
		314	$fh = IO::AIO::timerfd_create $clockid[, $flags]
		315	($cur_interval, $cur_value) = IO::AIO::timerfd_settime $fh, $flags, $new_interval, $nbw_value
		316	($cur_interval, $cur_value) = IO::AIO::timerfd_gettime $fh
		317
		318	=head2 API NOTES
83		319
84	All the C<aio_*> calls are more or less thin wrappers around the syscall	320	All the C<aio_*> calls are more or less thin wrappers around the syscall
85	with the same name (sans C<aio_>). The arguments are similar or identical,	321	with the same name (sans C<aio_>). The arguments are similar or identical,
86	and they all accept an additional (and optional) C<$callback> argument	322	and they all accept an additional (and optional) C<$callback> argument
87	which must be a code reference. This code reference will get called with	323	which must be a code reference. This code reference will be called after
88	the syscall return code (e.g. most syscalls return C<-1> on error, unlike	324	the syscall has been executed in an asynchronous fashion. The results
89	perl, which usually delivers "false") as it's sole argument when the given	325	of the request will be passed as arguments to the callback (and, if an
90	syscall has been executed asynchronously.	326	error occured, in C<$!>) - for most requests the syscall return code (e.g.
		327	most syscalls return C<-1> on error, unlike perl, which usually delivers
		328	"false").
		329
		330	Some requests (such as C<aio_readdir>) pass the actual results and
		331	communicate failures by passing C<undef>.
91		332
92	All functions expecting a filehandle keep a copy of the filehandle	333	All functions expecting a filehandle keep a copy of the filehandle
93	internally until the request has finished.	334	internally until the request has finished.
94		335
		336	All functions return request objects of type L<IO::AIO::REQ> that allow
		337	further manipulation of those requests while they are in-flight.
		338
95	The pathnames you pass to these routines I<must> be absolute and	339	The pathnames you pass to these routines I<should> be absolute. The
96	encoded in byte form. The reason for the former is that at the time the	340	reason for this is that at the time the request is being executed, the
97	request is being executed, the current working directory could have	341	current working directory could have changed. Alternatively, you can
98	changed. Alternatively, you can make sure that you never change the	342	make sure that you never change the current working directory anywhere
99	current working directory.	343	in the program and then use relative paths. You can also take advantage
		344	of IO::AIOs working directory abstraction, that lets you specify paths
		345	relative to some previously-opened "working directory object" - see the
		346	description of the C<IO::AIO::WD> class later in this document.
100		347
101	To encode pathnames to byte form, either make sure you either: a)	348	To encode pathnames as octets, either make sure you either: a) always pass
102	always pass in filenames you got from outside (command line, readdir	349	in filenames you got from outside (command line, readdir etc.) without
103	etc.), b) are ASCII or ISO 8859-1, c) use the Encode module and encode	350	tinkering, b) are in your native filesystem encoding, c) use the Encode
104	your pathnames to the locale (or other) encoding in effect in the user	351	module and encode your pathnames to the locale (or other) encoding in
105	environment, d) use Glib::filename_from_unicode on unicode filenames or e)	352	effect in the user environment, d) use Glib::filename_from_unicode on
106	use something else.	353	unicode filenames or e) use something else to ensure your scalar has the
		354	correct contents.
		355
		356	This works, btw. independent of the internal UTF-8 bit, which IO::AIO
		357	handles correctly whether it is set or not.
		358
		359	=head2 AIO REQUEST FUNCTIONS
107		360
108	=over 4	361	=over 4
109		362
		363	=item $prev_pri = aioreq_pri [$pri]
		364
		365	Returns the priority value that would be used for the next request and, if
		366	C<$pri> is given, sets the priority for the next aio request.
		367
		368	The default priority is C<0>, the minimum and maximum priorities are C<-4>
		369	and C<4>, respectively. Requests with higher priority will be serviced
		370	first.
		371
		372	The priority will be reset to C<0> after each call to one of the C<aio_*>
		373	functions.
		374
		375	Example: open a file with low priority, then read something from it with
		376	higher priority so the read request is serviced before other low priority
		377	open requests (potentially spamming the cache):
		378
		379	aioreq_pri -3;
		380	aio_open ..., sub {
		381	return unless $_[0];
		382
		383	aioreq_pri -2;
		384	aio_read $_[0], ..., sub {
		385	...
		386	};
		387	};
		388
		389
		390	=item aioreq_nice $pri_adjust
		391
		392	Similar to C<aioreq_pri>, but subtracts the given value from the current
		393	priority, so the effect is cumulative.
		394
		395
110	=item aio_open $pathname, $flags, $mode, $callback	396	=item aio_open $pathname, $flags, $mode, $callback->($fh)
111		397
112	Asynchronously open or create a file and call the callback with a newly	398	Asynchronously open or create a file and call the callback with a newly
113	created filehandle for the file.	399	created filehandle for the file (or C<undef> in case of an error).
114		400
115	The pathname passed to C<aio_open> must be absolute. See API NOTES, above,	401	The pathname passed to C<aio_open> must be absolute. See API NOTES, above,
116	for an explanation.	402	for an explanation.
117		403
118	The C<$flags> argument is a bitmask. See the C<Fcntl> module for a	404	The C<$flags> argument is a bitmask. See the C<Fcntl> module for a
119	list. They are the same as used by C<sysopen>.	405	list. They are the same as used by C<sysopen>.
120		406
121	Likewise, C<$mode> specifies the mode of the newly created file, if it	407	Likewise, C<$mode> specifies the mode of the newly created file, if it
122	didn't exist and C<O_CREAT> has been given, just like perl's C<sysopen>,	408	didn't exist and C<O_CREAT> has been given, just like perl's C<sysopen>,
123	except that it is mandatory (i.e. use C<0> if you don't create new files,	409	except that it is mandatory (i.e. use C<0> if you don't create new files,
124	and C<0666> or C<0777> if you do).	410	and C<0666> or C<0777> if you do). Note that the C<$mode> will be modified
		411	by the umask in effect then the request is being executed, so better never
		412	change the umask.
125		413
126	Example:	414	Example:
127		415
128	aio_open "/etc/passwd", O_RDONLY, 0, sub {	416	aio_open "/etc/passwd", IO::AIO::O_RDONLY, 0, sub {
129	if ($_[0]) {	417	if ($_[0]) {
130	print "open successful, fh is $_[0]\n";	418	print "open successful, fh is $_[0]\n";
131	...	419	...
132	} else {	420	} else {
133	die "open failed: $!\n";	421	die "open failed: $!\n";
134	}	422	}
135	};	423	};
136		424
		425	In addition to all the common open modes/flags (C<O_RDONLY>, C<O_WRONLY>,
		426	C<O_RDWR>, C<O_CREAT>, C<O_TRUNC>, C<O_EXCL> and C<O_APPEND>), the
		427	following POSIX and non-POSIX constants are available (missing ones on
		428	your system are, as usual, C<0>):
		429
		430	C<O_ASYNC>, C<O_DIRECT>, C<O_NOATIME>, C<O_CLOEXEC>, C<O_NOCTTY>, C<O_NOFOLLOW>,
		431	C<O_NONBLOCK>, C<O_EXEC>, C<O_SEARCH>, C<O_DIRECTORY>, C<O_DSYNC>,
		432	C<O_RSYNC>, C<O_SYNC>, C<O_PATH>, C<O_TMPFILE>, C<O_TTY_INIT> and C<O_ACCMODE>.
		433
		434
137	=item aio_close $fh, $callback	435	=item aio_close $fh, $callback->($status)
138		436
139	Asynchronously close a file and call the callback with the result	437	Asynchronously close a file and call the callback with the result
140	code. I<WARNING:> although accepted, you should not pass in a perl	438	code.
141	filehandle here, as perl will likely close the file descriptor another
142	time when the filehandle is destroyed. Normally, you can safely call perls
143	C<close> or just let filehandles go out of scope.
144		439
145	This is supposed to be a bug in the API, so that might change. It's	440	Unfortunately, you can't do this to perl. Perl I<insists> very strongly on
146	therefore best to avoid this function.	441	closing the file descriptor associated with the filehandle itself.
147		442
		443	Therefore, C<aio_close> will not close the filehandle - instead it will
		444	use dup2 to overwrite the file descriptor with the write-end of a pipe
		445	(the pipe fd will be created on demand and will be cached).
		446
		447	Or in other words: the file descriptor will be closed, but it will not be
		448	free for reuse until the perl filehandle is closed.
		449
		450	=cut
		451
		452	=item aio_seek $fh, $offset, $whence, $callback->($offs)
		453
		454	Seeks the filehandle to the new C<$offset>, similarly to perl's
		455	C<sysseek>. The C<$whence> can use the traditional values (C<0> for
		456	C<IO::AIO::SEEK_SET>, C<1> for C<IO::AIO::SEEK_CUR> or C<2> for
		457	C<IO::AIO::SEEK_END>).
		458
		459	The resulting absolute offset will be passed to the callback, or C<-1> in
		460	case of an error.
		461
		462	In theory, the C<$whence> constants could be different than the
		463	corresponding values from L<Fcntl>, but perl guarantees they are the same,
		464	so don't panic.
		465
		466	As a GNU/Linux (and maybe Solaris) extension, also the constants
		467	C<IO::AIO::SEEK_DATA> and C<IO::AIO::SEEK_HOLE> are available, if they
		468	could be found. No guarantees about suitability for use in C<aio_seek> or
		469	Perl's C<sysseek> can be made though, although I would naively assume they
		470	"just work".
		471
148	=item aio_read $fh,$offset,$length, $data,$dataoffset,$callback	472	=item aio_read $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
149		473
150	=item aio_write $fh,$offset,$length, $data,$dataoffset,$callback	474	=item aio_write $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
151		475
152	Reads or writes C<length> bytes from the specified C<fh> and C<offset>	476	Reads or writes C<$length> bytes from or to the specified C<$fh> and
153	into the scalar given by C<data> and offset C<dataoffset> and calls the	477	C<$offset> into the scalar given by C<$data> and offset C<$dataoffset> and
154	callback without the actual number of bytes read (or -1 on error, just	478	calls the callback with the actual number of bytes transferred (or -1 on
155	like the syscall).	479	error, just like the syscall).
		480
		481	C<aio_read> will, like C<sysread>, shrink or grow the C<$data> scalar to
		482	offset plus the actual number of bytes read.
		483
		484	If C<$offset> is undefined, then the current file descriptor offset will
		485	be used (and updated), otherwise the file descriptor offset will not be
		486	changed by these calls.
		487
		488	If C<$length> is undefined in C<aio_write>, use the remaining length of
		489	C<$data>.
		490
		491	If C<$dataoffset> is less than zero, it will be counted from the end of
		492	C<$data>.
156		493
157	The C<$data> scalar I<MUST NOT> be modified in any way while the request	494	The C<$data> scalar I<MUST NOT> be modified in any way while the request
158	is outstanding. Modifying it can result in segfaults or WW3 (if the	495	is outstanding. Modifying it can result in segfaults or World War III (if
159	necessary/optional hardware is installed).	496	the necessary/optional hardware is installed).
160		497
161	Example: Read 15 bytes at offset 7 into scalar C<$buffer>, starting at	498	Example: Read 15 bytes at offset 7 into scalar C<$buffer>, starting at
162	offset C<0> within the scalar:	499	offset C<0> within the scalar:
163		500
164	aio_read $fh, 7, 15, $buffer, 0, sub {	501	aio_read $fh, 7, 15, $buffer, 0, sub {
165	$_[0] > 0 or die "read error: $!";	502	$_[0] > 0 or die "read error: $!";
166	print "read $_[0] bytes: <$buffer>\n";	503	print "read $_[0] bytes: <$buffer>\n";
167	};	504	};
168		505
		506
169	=item aio_sendfile $out_fh, $in_fh, $in_offset, $length, $callback	507	=item aio_sendfile $out_fh, $in_fh, $in_offset, $length, $callback->($retval)
170		508
171	Tries to copy C<$length> bytes from C<$in_fh> to C<$out_fh>. It starts	509	Tries to copy C<$length> bytes from C<$in_fh> to C<$out_fh>. It starts
172	reading at byte offset C<$in_offset>, and starts writing at the current	510	reading at byte offset C<$in_offset>, and starts writing at the current
173	file offset of C<$out_fh>. Because of that, it is not safe to issue more	511	file offset of C<$out_fh>. Because of that, it is not safe to issue more
174	than one C<aio_sendfile> per C<$out_fh>, as they will interfere with each	512	than one C<aio_sendfile> per C<$out_fh>, as they will interfere with each
175	other.	513	other. The same C<$in_fh> works fine though, as this function does not
		514	move or use the file offset of C<$in_fh>.
176		515
		516	Please note that C<aio_sendfile> can read more bytes from C<$in_fh> than
		517	are written, and there is no way to find out how many more bytes have been
		518	read from C<aio_sendfile> alone, as C<aio_sendfile> only provides the
		519	number of bytes written to C<$out_fh>. Only if the result value equals
		520	C<$length> one can assume that C<$length> bytes have been read.
		521
		522	Unlike with other C<aio_> functions, it makes a lot of sense to use
		523	C<aio_sendfile> on non-blocking sockets, as long as one end (typically
		524	the C<$in_fh>) is a file - the file I/O will then be asynchronous, while
		525	the socket I/O will be non-blocking. Note, however, that you can run
		526	into a trap where C<aio_sendfile> reads some data with readahead, then
		527	fails to write all data, and when the socket is ready the next time, the
		528	data in the cache is already lost, forcing C<aio_sendfile> to again hit
		529	the disk. Explicit C<aio_read> + C<aio_write> let's you better control
		530	resource usage.
		531
177	This call tries to make use of a native C<sendfile> syscall to provide	532	This call tries to make use of a native C<sendfile>-like syscall to
178	zero-copy operation. For this to work, C<$out_fh> should refer to a	533	provide zero-copy operation. For this to work, C<$out_fh> should refer to
179	socket, and C<$in_fh> should refer to mmap'able file.	534	a socket, and C<$in_fh> should refer to an mmap'able file.
180		535
181	If the native sendfile call fails or is not implemented, it will be	536	If a native sendfile cannot be found or it fails with C<ENOSYS>,
182	emulated, so you can call C<aio_sendfile> on any type of filehandle	537	C<EINVAL>, C<ENOTSUP>, C<EOPNOTSUPP>, C<EAFNOSUPPORT>, C<EPROTOTYPE> or
		538	C<ENOTSOCK>, it will be emulated, so you can call C<aio_sendfile> on any
183	regardless of the limitations of the operating system.	539	type of filehandle regardless of the limitations of the operating system.
184		540
185	Please note, however, that C<aio_sendfile> can read more bytes from	541	As native sendfile syscalls (as practically any non-POSIX interface hacked
186	C<$in_fh> than are written, and there is no way to find out how many	542	together in a hurry to improve benchmark numbers) tend to be rather buggy
187	bytes have been read from C<aio_sendfile> alone, as C<aio_sendfile> only	543	on many systems, this implementation tries to work around some known bugs
188	provides the number of bytes written to C<$out_fh>. Only if the result	544	in Linux and FreeBSD kernels (probably others, too), but that might fail,
189	value equals C<$length> one can assume that C<$length> bytes have been	545	so you really really should check the return value of C<aio_sendfile> -
190	read.	546	fewer bytes than expected might have been transferred.
191		547
		548
192	=item aio_readahead $fh,$offset,$length, $callback	549	=item aio_readahead $fh,$offset,$length, $callback->($retval)
193		550
194	C<aio_readahead> populates the page cache with data from a file so that	551	C<aio_readahead> populates the page cache with data from a file so that
195	subsequent reads from that file will not block on disk I/O. The C<$offset>	552	subsequent reads from that file will not block on disk I/O. The C<$offset>
196	argument specifies the starting point from which data is to be read and	553	argument specifies the starting point from which data is to be read and
197	C<$length> specifies the number of bytes to be read. I/O is performed in	554	C<$length> specifies the number of bytes to be read. I/O is performed in
198	whole pages, so that offset is effectively rounded down to a page boundary	555	whole pages, so that offset is effectively rounded down to a page boundary
199	and bytes are read up to the next page boundary greater than or equal to	556	and bytes are read up to the next page boundary greater than or equal to
200	(off-set+length). C<aio_readahead> does not read beyond the end of the	557	(off-set+length). C<aio_readahead> does not read beyond the end of the
201	file. The current file offset of the file is left unchanged.	558	file. The current file offset of the file is left unchanged.
202		559
203	If that syscall doesn't exist (likely if your OS isn't Linux) it will be	560	If that syscall doesn't exist (likely if your kernel isn't Linux) it will
204	emulated by simply reading the data, which would have a similar effect.	561	be emulated by simply reading the data, which would have a similar effect.
205		562
		563
206	=item aio_stat $fh_or_path, $callback	564	=item aio_stat $fh_or_path, $callback->($status)
207		565
208	=item aio_lstat $fh, $callback	566	=item aio_lstat $fh, $callback->($status)
209		567
210	Works like perl's C<stat> or C<lstat> in void context. The callback will	568	Works almost exactly like perl's C<stat> or C<lstat> in void context. The
211	be called after the stat and the results will be available using C<stat _>	569	callback will be called after the stat and the results will be available
212	or C<-s _> etc...	570	using C<stat _> or C<-s _> and other tests (with the exception of C<-B>
		571	and C<-T>).
213		572
214	The pathname passed to C<aio_stat> must be absolute. See API NOTES, above,	573	The pathname passed to C<aio_stat> must be absolute. See API NOTES, above,
215	for an explanation.	574	for an explanation.
216		575
217	Currently, the stats are always 64-bit-stats, i.e. instead of returning an	576	Currently, the stats are always 64-bit-stats, i.e. instead of returning an
218	error when stat'ing a large file, the results will be silently truncated	577	error when stat'ing a large file, the results will be silently truncated
219	unless perl itself is compiled with large file support.	578	unless perl itself is compiled with large file support.
		579
		580	To help interpret the mode and dev/rdev stat values, IO::AIO offers the
		581	following constants and functions (if not implemented, the constants will
		582	be C<0> and the functions will either C<croak> or fall back on traditional
		583	behaviour).
		584
		585	C<S_IFMT>, C<S_IFIFO>, C<S_IFCHR>, C<S_IFBLK>, C<S_IFLNK>, C<S_IFREG>,
		586	C<S_IFDIR>, C<S_IFWHT>, C<S_IFSOCK>, C<IO::AIO::major $dev_t>,
		587	C<IO::AIO::minor $dev_t>, C<IO::AIO::makedev $major, $minor>.
		588
		589	To access higher resolution stat timestamps, see L<SUBSECOND STAT TIME
		590	ACCESS>.
220		591
221	Example: Print the length of F</etc/passwd>:	592	Example: Print the length of F</etc/passwd>:
222		593
223	aio_stat "/etc/passwd", sub {	594	aio_stat "/etc/passwd", sub {
224	$_[0] and die "stat failed: $!";	595	$_[0] and die "stat failed: $!";
225	print "size is ", -s _, "\n";	596	print "size is ", -s _, "\n";
226	};	597	};
227		598
		599
		600	=item aio_statvfs $fh_or_path, $callback->($statvfs)
		601
		602	Works like the POSIX C<statvfs> or C<fstatvfs> syscalls, depending on
		603	whether a file handle or path was passed.
		604
		605	On success, the callback is passed a hash reference with the following
		606	members: C<bsize>, C<frsize>, C<blocks>, C<bfree>, C<bavail>, C<files>,
		607	C<ffree>, C<favail>, C<fsid>, C<flag> and C<namemax>. On failure, C<undef>
		608	is passed.
		609
		610	The following POSIX IO::AIO::ST_* constants are defined: C<ST_RDONLY> and
		611	C<ST_NOSUID>.
		612
		613	The following non-POSIX IO::AIO::ST_* flag masks are defined to
		614	their correct value when available, or to C<0> on systems that do
		615	not support them: C<ST_NODEV>, C<ST_NOEXEC>, C<ST_SYNCHRONOUS>,
		616	C<ST_MANDLOCK>, C<ST_WRITE>, C<ST_APPEND>, C<ST_IMMUTABLE>, C<ST_NOATIME>,
		617	C<ST_NODIRATIME> and C<ST_RELATIME>.
		618
		619	Example: stat C</wd> and dump out the data if successful.
		620
		621	aio_statvfs "/wd", sub {
		622	my $f = $_[0]
		623	or die "statvfs: $!";
		624
		625	use Data::Dumper;
		626	say Dumper $f;
		627	};
		628
		629	# result:
		630	{
		631	bsize => 1024,
		632	bfree => 4333064312,
		633	blocks => 10253828096,
		634	files => 2050765568,
		635	flag => 4096,
		636	favail => 2042092649,
		637	bavail => 4333064312,
		638	ffree => 2042092649,
		639	namemax => 255,
		640	frsize => 1024,
		641	fsid => 1810
		642	}
		643
		644	=item aio_utime $fh_or_path, $atime, $mtime, $callback->($status)
		645
		646	Works like perl's C<utime> function (including the special case of $atime
		647	and $mtime being undef). Fractional times are supported if the underlying
		648	syscalls support them.
		649
		650	When called with a pathname, uses utimensat(2) or utimes(2) if available,
		651	otherwise utime(2). If called on a file descriptor, uses futimens(2)
		652	or futimes(2) if available, otherwise returns ENOSYS, so this is not
		653	portable.
		654
		655	Examples:
		656
		657	# set atime and mtime to current time (basically touch(1)):
		658	aio_utime "path", undef, undef;
		659	# set atime to current time and mtime to beginning of the epoch:
		660	aio_utime "path", time, undef; # undef==0
		661
		662
		663	=item aio_chown $fh_or_path, $uid, $gid, $callback->($status)
		664
		665	Works like perl's C<chown> function, except that C<undef> for either $uid
		666	or $gid is being interpreted as "do not change" (but -1 can also be used).
		667
		668	Examples:
		669
		670	# same as "chown root path" in the shell:
		671	aio_chown "path", 0, -1;
		672	# same as above:
		673	aio_chown "path", 0, undef;
		674
		675
		676	=item aio_truncate $fh_or_path, $offset, $callback->($status)
		677
		678	Works like truncate(2) or ftruncate(2).
		679
		680
		681	=item aio_allocate $fh, $mode, $offset, $len, $callback->($status)
		682
		683	Allocates or frees disk space according to the C<$mode> argument. See the
		684	linux C<fallocate> documentation for details.
		685
		686	C<$mode> is usually C<0> or C<IO::AIO::FALLOC_FL_KEEP_SIZE> to allocate
		687	space, or C<IO::AIO::FALLOC_FL_PUNCH_HOLE | IO::AIO::FALLOC_FL_KEEP_SIZE>,
		688	to deallocate a file range.
		689
		690	IO::AIO also supports C<FALLOC_FL_COLLAPSE_RANGE>, to remove a range
		691	(without leaving a hole), C<FALLOC_FL_ZERO_RANGE>, to zero a range,
		692	C<FALLOC_FL_INSERT_RANGE> to insert a range and C<FALLOC_FL_UNSHARE_RANGE>
		693	to unshare shared blocks (see your L<fallocate(2)> manpage).
		694
		695	The file system block size used by C<fallocate> is presumably the
		696	C<f_bsize> returned by C<statvfs>, but different filesystems and filetypes
		697	can dictate other limitations.
		698
		699	If C<fallocate> isn't available or cannot be emulated (currently no
		700	emulation will be attempted), passes C<-1> and sets C<$!> to C<ENOSYS>.
		701
		702
		703	=item aio_chmod $fh_or_path, $mode, $callback->($status)
		704
		705	Works like perl's C<chmod> function.
		706
		707
228	=item aio_unlink $pathname, $callback	708	=item aio_unlink $pathname, $callback->($status)
229		709
230	Asynchronously unlink (delete) a file and call the callback with the	710	Asynchronously unlink (delete) a file and call the callback with the
231	result code.	711	result code.
232		712
		713
		714	=item aio_mknod $pathname, $mode, $dev, $callback->($status)
		715
		716	[EXPERIMENTAL]
		717
		718	Asynchronously create a device node (or fifo). See mknod(2).
		719
		720	The only (POSIX-) portable way of calling this function is:
		721
		722	aio_mknod $pathname, IO::AIO::S_IFIFO | $mode, 0, sub { ...
		723
		724	See C<aio_stat> for info about some potentially helpful extra constants
		725	and functions.
		726
		727	=item aio_link $srcpath, $dstpath, $callback->($status)
		728
		729	Asynchronously create a new link to the existing object at C<$srcpath> at
		730	the path C<$dstpath> and call the callback with the result code.
		731
		732
		733	=item aio_symlink $srcpath, $dstpath, $callback->($status)
		734
		735	Asynchronously create a new symbolic link to the existing object at C<$srcpath> at
		736	the path C<$dstpath> and call the callback with the result code.
		737
		738
		739	=item aio_readlink $pathname, $callback->($link)
		740
		741	Asynchronously read the symlink specified by C<$path> and pass it to
		742	the callback. If an error occurs, nothing or undef gets passed to the
		743	callback.
		744
		745
		746	=item aio_realpath $pathname, $callback->($path)
		747
		748	Asynchronously make the path absolute and resolve any symlinks in
		749	C<$path>. The resulting path only consists of directories (same as
		750	L<Cwd::realpath>).
		751
		752	This request can be used to get the absolute path of the current working
		753	directory by passing it a path of F<.> (a single dot).
		754
		755
		756	=item aio_rename $srcpath, $dstpath, $callback->($status)
		757
		758	Asynchronously rename the object at C<$srcpath> to C<$dstpath>, just as
		759	rename(2) and call the callback with the result code.
		760
		761	On systems that support the AIO::WD working directory abstraction
		762	natively, the case C<[$wd, "."]> as C<$srcpath> is specialcased - instead
		763	of failing, C<rename> is called on the absolute path of C<$wd>.
		764
		765
		766	=item aio_rename2 $srcpath, $dstpath, $flags, $callback->($status)
		767
		768	Basically a version of C<aio_rename> with an additional C<$flags>
		769	argument. Calling this with C<$flags=0> is the same as calling
		770	C<aio_rename>.
		771
		772	Non-zero flags are currently only supported on GNU/Linux systems that
		773	support renameat2. Other systems fail with C<ENOSYS> in this case.
		774
		775	The following constants are available (missing ones are, as usual C<0>),
		776	see renameat2(2) for details:
		777
		778	C<IO::AIO::RENAME_NOREPLACE>, C<IO::AIO::RENAME_EXCHANGE>
		779	and C<IO::AIO::RENAME_WHITEOUT>.
		780
		781
		782	=item aio_mkdir $pathname, $mode, $callback->($status)
		783
		784	Asynchronously mkdir (create) a directory and call the callback with
		785	the result code. C<$mode> will be modified by the umask at the time the
		786	request is executed, so do not change your umask.
		787
		788
233	=item aio_rmdir $pathname, $callback	789	=item aio_rmdir $pathname, $callback->($status)
234		790
235	Asynchronously rmdir (delete) a directory and call the callback with the	791	Asynchronously rmdir (delete) a directory and call the callback with the
236	result code.	792	result code.
237		793
		794	On systems that support the AIO::WD working directory abstraction
		795	natively, the case C<[$wd, "."]> is specialcased - instead of failing,
		796	C<rmdir> is called on the absolute path of C<$wd>.
		797
		798
238	=item aio_readdir $pathname $callback	799	=item aio_readdir $pathname, $callback->($entries)
239		800
240	Unlike the POSIX call of the same name, C<aio_readdir> reads an entire	801	Unlike the POSIX call of the same name, C<aio_readdir> reads an entire
241	directory (i.e. opendir + readdir + closedir). The entries will not be	802	directory (i.e. opendir + readdir + closedir). The entries will not be
242	sorted, and will B<NOT> include the C<.> and C<..> entries.	803	sorted, and will B<NOT> include the C<.> and C<..> entries.
243		804
244	The callback a single argument which is either C<undef> or an array-ref	805	The callback is passed a single argument which is either C<undef> or an
245	with the filenames.	806	array-ref with the filenames.
246		807
		808
		809	=item aio_readdirx $pathname, $flags, $callback->($entries, $flags)
		810
		811	Quite similar to C<aio_readdir>, but the C<$flags> argument allows one to
		812	tune behaviour and output format. In case of an error, C<$entries> will be
		813	C<undef>.
		814
		815	The flags are a combination of the following constants, ORed together (the
		816	flags will also be passed to the callback, possibly modified):
		817
		818	=over 4
		819
		820	=item IO::AIO::READDIR_DENTS
		821
		822	Normally the callback gets an arrayref consisting of names only (as
		823	with C<aio_readdir>). If this flag is set, then the callback gets an
		824	arrayref with C<[$name, $type, $inode]> arrayrefs, each describing a
		825	single directory entry in more detail:
		826
		827	C<$name> is the name of the entry.
		828
		829	C<$type> is one of the C<IO::AIO::DT_xxx> constants:
		830
		831	C<IO::AIO::DT_UNKNOWN>, C<IO::AIO::DT_FIFO>, C<IO::AIO::DT_CHR>, C<IO::AIO::DT_DIR>,
		832	C<IO::AIO::DT_BLK>, C<IO::AIO::DT_REG>, C<IO::AIO::DT_LNK>, C<IO::AIO::DT_SOCK>,
		833	C<IO::AIO::DT_WHT>.
		834
		835	C<IO::AIO::DT_UNKNOWN> means just that: readdir does not know. If you need
		836	to know, you have to run stat yourself. Also, for speed/memory reasons,
		837	the C<$type> scalars are read-only: you must not modify them.
		838
		839	C<$inode> is the inode number (which might not be exact on systems with 64
		840	bit inode numbers and 32 bit perls). This field has unspecified content on
		841	systems that do not deliver the inode information.
		842
		843	=item IO::AIO::READDIR_DIRS_FIRST
		844
		845	When this flag is set, then the names will be returned in an order where
		846	likely directories come first, in optimal stat order. This is useful when
		847	you need to quickly find directories, or you want to find all directories
		848	while avoiding to stat() each entry.
		849
		850	If the system returns type information in readdir, then this is used
		851	to find directories directly. Otherwise, likely directories are names
		852	beginning with ".", or otherwise names with no dots, of which names with
		853	short names are tried first.
		854
		855	=item IO::AIO::READDIR_STAT_ORDER
		856
		857	When this flag is set, then the names will be returned in an order
		858	suitable for stat()'ing each one. That is, when you plan to stat() most or
		859	all files in the given directory, then the returned order will likely be
		860	faster.
		861
		862	If both this flag and C<IO::AIO::READDIR_DIRS_FIRST> are specified,
		863	then the likely dirs come first, resulting in a less optimal stat order
		864	for stat'ing all entries, but likely a more optimal order for finding
		865	subdirectories.
		866
		867	=item IO::AIO::READDIR_FOUND_UNKNOWN
		868
		869	This flag should not be set when calling C<aio_readdirx>. Instead, it
		870	is being set by C<aio_readdirx>, when any of the C<$type>'s found were
		871	C<IO::AIO::DT_UNKNOWN>. The absence of this flag therefore indicates that all
		872	C<$type>'s are known, which can be used to speed up some algorithms.
		873
		874	=back
		875
		876
		877	=item aio_slurp $pathname, $offset, $length, $data, $callback->($status)
		878
		879	Opens, reads and closes the given file. The data is put into C<$data>,
		880	which is resized as required.
		881
		882	If C<$offset> is negative, then it is counted from the end of the file.
		883
		884	If C<$length> is zero, then the remaining length of the file is
		885	used. Also, in this case, the same limitations to modifying C<$data> apply
		886	as when IO::AIO::mmap is used, i.e. it must only be modified in-place
		887	with C<substr>. If the size of the file is known, specifying a non-zero
		888	C<$length> results in a performance advantage.
		889
		890	This request is similar to the older C<aio_load> request, but since it is
		891	a single request, it might be more efficient to use.
		892
		893	Example: load F</etc/passwd> into C<$passwd>.
		894
		895	my $passwd;
		896	aio_slurp "/etc/passwd", 0, 0, $passwd, sub {
		897	$_[0] >= 0
		898	or die "/etc/passwd: $!\n";
		899
		900	printf "/etc/passwd is %d bytes long, and contains:\n", length $passwd;
		901	print $passwd;
		902	};
		903	IO::AIO::flush;
		904
		905
		906	=item aio_load $pathname, $data, $callback->($status)
		907
		908	This is a composite request that tries to fully load the given file into
		909	memory. Status is the same as with aio_read.
		910
		911	Using C<aio_slurp> might be more efficient, as it is a single request.
		912
		913	=cut
		914
		915	sub aio_load($$;$) {
		916	my ($path, undef, $cb) = @_;
		917	my $data = \$_[1];
		918
		919	my $pri = aioreq_pri;
		920	my $grp = aio_group $cb;
		921
		922	aioreq_pri $pri;
		923	add $grp aio_open $path, O_RDONLY, 0, sub {
		924	my $fh = shift
		925	or return $grp->result (-1);
		926
		927	aioreq_pri $pri;
		928	add $grp aio_read $fh, 0, (-s $fh), $$data, 0, sub {
		929	$grp->result ($_[0]);
		930	};
		931	};
		932
		933	$grp
		934	}
		935
		936	=item aio_copy $srcpath, $dstpath, $callback->($status)
		937
		938	Try to copy the I<file> (directories not supported as either source or
		939	destination) from C<$srcpath> to C<$dstpath> and call the callback with
		940	a status of C<0> (ok) or C<-1> (error, see C<$!>).
		941
		942	Existing destination files will be truncated.
		943
		944	This is a composite request that creates the destination file with
		945	mode 0200 and copies the contents of the source file into it using
		946	C<aio_sendfile>, followed by restoring atime, mtime, access mode and
		947	uid/gid, in that order.
		948
		949	If an error occurs, the partial destination file will be unlinked, if
		950	possible, except when setting atime, mtime, access mode and uid/gid, where
		951	errors are being ignored.
		952
		953	=cut
		954
		955	sub aio_copy($$;$) {
		956	my ($src, $dst, $cb) = @_;
		957
		958	my $pri = aioreq_pri;
		959	my $grp = aio_group $cb;
		960
		961	aioreq_pri $pri;
		962	add $grp aio_open $src, O_RDONLY, 0, sub {
		963	if (my $src_fh = $_[0]) {
		964	my @stat = stat $src_fh; # hmm, might block over nfs?
		965
		966	aioreq_pri $pri;
		967	add $grp aio_open $dst, O_CREAT | O_WRONLY | O_TRUNC, 0200, sub {
		968	if (my $dst_fh = $_[0]) {
		969	aioreq_pri $pri;
		970	add $grp aio_sendfile $dst_fh, $src_fh, 0, $stat[7], sub {
		971	if ($_[0] == $stat[7]) {
		972	$grp->result (0);
		973	close $src_fh;
		974
		975	my $ch = sub {
		976	aioreq_pri $pri;
		977	add $grp aio_chmod $dst_fh, $stat[2] & 07777, sub {
		978	aioreq_pri $pri;
		979	add $grp aio_chown $dst_fh, $stat[4], $stat[5], sub {
		980	aioreq_pri $pri;
		981	add $grp aio_close $dst_fh;
		982	}
		983	};
		984	};
		985
		986	aioreq_pri $pri;
		987	add $grp aio_utime $dst_fh, $stat[8], $stat[9], sub {
		988	if ($_[0] < 0 && $! == ENOSYS) {
		989	aioreq_pri $pri;
		990	add $grp aio_utime $dst, $stat[8], $stat[9], $ch;
		991	} else {
		992	$ch->();
		993	}
		994	};
		995	} else {
		996	$grp->result (-1);
		997	close $src_fh;
		998	close $dst_fh;
		999
		1000	aioreq $pri;
		1001	add $grp aio_unlink $dst;
		1002	}
		1003	};
		1004	} else {
		1005	$grp->result (-1);
		1006	}
		1007	},
		1008
		1009	} else {
		1010	$grp->result (-1);
		1011	}
		1012	};
		1013
		1014	$grp
		1015	}
		1016
		1017	=item aio_move $srcpath, $dstpath, $callback->($status)
		1018
		1019	Try to move the I<file> (directories not supported as either source or
		1020	destination) from C<$srcpath> to C<$dstpath> and call the callback with
		1021	a status of C<0> (ok) or C<-1> (error, see C<$!>).
		1022
		1023	This is a composite request that tries to rename(2) the file first; if
		1024	rename fails with C<EXDEV>, it copies the file with C<aio_copy> and, if
		1025	that is successful, unlinks the C<$srcpath>.
		1026
		1027	=cut
		1028
		1029	sub aio_move($$;$) {
		1030	my ($src, $dst, $cb) = @_;
		1031
		1032	my $pri = aioreq_pri;
		1033	my $grp = aio_group $cb;
		1034
		1035	aioreq_pri $pri;
		1036	add $grp aio_rename $src, $dst, sub {
		1037	if ($_[0] && $! == EXDEV) {
		1038	aioreq_pri $pri;
		1039	add $grp aio_copy $src, $dst, sub {
		1040	$grp->result ($_[0]);
		1041
		1042	unless ($_[0]) {
		1043	aioreq_pri $pri;
		1044	add $grp aio_unlink $src;
		1045	}
		1046	};
		1047	} else {
		1048	$grp->result ($_[0]);
		1049	}
		1050	};
		1051
		1052	$grp
		1053	}
		1054
		1055	=item aio_scandir $pathname, $maxreq, $callback->($dirs, $nondirs)
		1056
		1057	Scans a directory (similar to C<aio_readdir>) but additionally tries to
		1058	efficiently separate the entries of directory C<$path> into two sets of
		1059	names, directories you can recurse into (directories), and ones you cannot
		1060	recurse into (everything else, including symlinks to directories).
		1061
		1062	C<aio_scandir> is a composite request that generates many sub requests.
		1063	C<$maxreq> specifies the maximum number of outstanding aio requests that
		1064	this function generates. If it is C<< <= 0 >>, then a suitable default
		1065	will be chosen (currently 4).
		1066
		1067	On error, the callback is called without arguments, otherwise it receives
		1068	two array-refs with path-relative entry names.
		1069
		1070	Example:
		1071
		1072	aio_scandir $dir, 0, sub {
		1073	my ($dirs, $nondirs) = @_;
		1074	print "real directories: @$dirs\n";
		1075	print "everything else: @$nondirs\n";
		1076	};
		1077
		1078	Implementation notes.
		1079
		1080	The C<aio_readdir> cannot be avoided, but C<stat()>'ing every entry can.
		1081
		1082	If readdir returns file type information, then this is used directly to
		1083	find directories.
		1084
		1085	Otherwise, after reading the directory, the modification time, size etc.
		1086	of the directory before and after the readdir is checked, and if they
		1087	match (and isn't the current time), the link count will be used to decide
		1088	how many entries are directories (if >= 2). Otherwise, no knowledge of the
		1089	number of subdirectories will be assumed.
		1090
		1091	Then entries will be sorted into likely directories a non-initial dot
		1092	currently) and likely non-directories (see C<aio_readdirx>). Then every
		1093	entry plus an appended C</.> will be C<stat>'ed, likely directories first,
		1094	in order of their inode numbers. If that succeeds, it assumes that the
		1095	entry is a directory or a symlink to directory (which will be checked
		1096	separately). This is often faster than stat'ing the entry itself because
		1097	filesystems might detect the type of the entry without reading the inode
		1098	data (e.g. ext2fs filetype feature), even on systems that cannot return
		1099	the filetype information on readdir.
		1100
		1101	If the known number of directories (link count - 2) has been reached, the
		1102	rest of the entries is assumed to be non-directories.
		1103
		1104	This only works with certainty on POSIX (= UNIX) filesystems, which
		1105	fortunately are the vast majority of filesystems around.
		1106
		1107	It will also likely work on non-POSIX filesystems with reduced efficiency
		1108	as those tend to return 0 or 1 as link counts, which disables the
		1109	directory counting heuristic.
		1110
		1111	=cut
		1112
		1113	sub aio_scandir($$;$) {
		1114	my ($path, $maxreq, $cb) = @_;
		1115
		1116	my $pri = aioreq_pri;
		1117
		1118	my $grp = aio_group $cb;
		1119
		1120	$maxreq = 4 if $maxreq <= 0;
		1121
		1122	# get a wd object
		1123	aioreq_pri $pri;
		1124	add $grp aio_wd $path, sub {
		1125	$_[0]
		1126	or return $grp->result ();
		1127
		1128	my $wd = [shift, "."];
		1129
		1130	# stat once
		1131	aioreq_pri $pri;
		1132	add $grp aio_stat $wd, sub {
		1133	return $grp->result () if $_[0];
		1134	my $now = time;
		1135	my $hash1 = join ":", (stat _)[0,1,3,7,9];
		1136	my $rdxflags = READDIR_DIRS_FIRST;
		1137
		1138	if ((stat _)[3] < 2) {
		1139	# at least one non-POSIX filesystem exists
		1140	# that returns useful DT_type values: btrfs,
		1141	# so optimise for this here by requesting dents
		1142	$rdxflags |= READDIR_DENTS;
		1143	}
		1144
		1145	# read the directory entries
		1146	aioreq_pri $pri;
		1147	add $grp aio_readdirx $wd, $rdxflags, sub {
		1148	my ($entries, $flags) = @_
		1149	or return $grp->result ();
		1150
		1151	if ($rdxflags & READDIR_DENTS) {
		1152	# if we requested type values, see if we can use them directly.
		1153
		1154	# if there were any DT_UNKNOWN entries then we assume we
		1155	# don't know. alternatively, we could assume that if we get
		1156	# one DT_DIR, then all directories are indeed marked with
		1157	# DT_DIR, but this seems not required for btrfs, and this
		1158	# is basically the "btrfs can't get it's act together" code
		1159	# branch.
		1160	unless ($flags & READDIR_FOUND_UNKNOWN) {
		1161	# now we have valid DT_ information for all entries,
		1162	# so use it as an optimisation without further stat's.
		1163	# they must also all be at the beginning of @$entries
		1164	# by now.
		1165
		1166	my $dirs;
		1167
		1168	if (@$entries) {
		1169	for (0 .. $#$entries) {
		1170	if ($entries->[$_][1] != DT_DIR) {
		1171	# splice out directories
		1172	$dirs = [splice @$entries, 0, $_];
		1173	last;
		1174	}
		1175	}
		1176
		1177	# if we didn't find any non-dir, then all entries are dirs
		1178	unless ($dirs) {
		1179	($dirs, $entries) = ($entries, []);
		1180	}
		1181	} else {
		1182	# directory is empty, so there are no sbdirs
		1183	$dirs = [];
		1184	}
		1185
		1186	# either splice'd the directories out or the dir was empty.
		1187	# convert dents to filenames
		1188	$_ = $_->[0] for @$dirs;
		1189	$_ = $_->[0] for @$entries;
		1190
		1191	return $grp->result ($dirs, $entries);
		1192	}
		1193
		1194	# cannot use, so return to our old ways
		1195	# by pretending we only scanned for names.
		1196	$_ = $_->[0] for @$entries;
		1197	}
		1198
		1199	# stat the dir another time
		1200	aioreq_pri $pri;
		1201	add $grp aio_stat $wd, sub {
		1202	my $hash2 = join ":", (stat _)[0,1,3,7,9];
		1203
		1204	my $ndirs;
		1205
		1206	# take the slow route if anything looks fishy
		1207	if ($hash1 ne $hash2 or (stat _)[9] == $now) {
		1208	$ndirs = -1;
		1209	} else {
		1210	# if nlink == 2, we are finished
		1211	# for non-posix-fs's, we rely on nlink < 2
		1212	$ndirs = (stat _)[3] - 2
		1213	or return $grp->result ([], $entries);
		1214	}
		1215
		1216	my (@dirs, @nondirs);
		1217
		1218	my $statgrp = add $grp aio_group sub {
		1219	$grp->result (\@dirs, \@nondirs);
		1220	};
		1221
		1222	limit $statgrp $maxreq;
		1223	feed $statgrp sub {
		1224	return unless @$entries;
		1225	my $entry = shift @$entries;
		1226
		1227	aioreq_pri $pri;
		1228	$wd->[1] = "$entry/.";
		1229	add $statgrp aio_stat $wd, sub {
		1230	if ($_[0] < 0) {
		1231	push @nondirs, $entry;
		1232	} else {
		1233	# need to check for real directory
		1234	aioreq_pri $pri;
		1235	$wd->[1] = $entry;
		1236	add $statgrp aio_lstat $wd, sub {
		1237	if (-d _) {
		1238	push @dirs, $entry;
		1239
		1240	unless (--$ndirs) {
		1241	push @nondirs, @$entries;
		1242	feed $statgrp;
		1243	}
		1244	} else {
		1245	push @nondirs, $entry;
		1246	}
		1247	}
		1248	}
		1249	};
		1250	};
		1251	};
		1252	};
		1253	};
		1254	};
		1255
		1256	$grp
		1257	}
		1258
		1259	=item aio_rmtree $pathname, $callback->($status)
		1260
		1261	Delete a directory tree starting (and including) C<$path>, return the
		1262	status of the final C<rmdir> only. This is a composite request that
		1263	uses C<aio_scandir> to recurse into and rmdir directories, and unlink
		1264	everything else.
		1265
		1266	=cut
		1267
		1268	sub aio_rmtree;
		1269	sub aio_rmtree($;$) {
		1270	my ($path, $cb) = @_;
		1271
		1272	my $pri = aioreq_pri;
		1273	my $grp = aio_group $cb;
		1274
		1275	aioreq_pri $pri;
		1276	add $grp aio_scandir $path, 0, sub {
		1277	my ($dirs, $nondirs) = @_;
		1278
		1279	my $dirgrp = aio_group sub {
		1280	add $grp aio_rmdir $path, sub {
		1281	$grp->result ($_[0]);
		1282	};
		1283	};
		1284
		1285	(aioreq_pri $pri), add $dirgrp aio_rmtree "$path/$_" for @$dirs;
		1286	(aioreq_pri $pri), add $dirgrp aio_unlink "$path/$_" for @$nondirs;
		1287
		1288	add $grp $dirgrp;
		1289	};
		1290
		1291	$grp
		1292	}
		1293
		1294	=item aio_fcntl $fh, $cmd, $arg, $callback->($status)
		1295
		1296	=item aio_ioctl $fh, $request, $buf, $callback->($status)
		1297
		1298	These work just like the C<fcntl> and C<ioctl> built-in functions, except
		1299	they execute asynchronously and pass the return value to the callback.
		1300
		1301	Both calls can be used for a lot of things, some of which make more sense
		1302	to run asynchronously in their own thread, while some others make less
		1303	sense. For example, calls that block waiting for external events, such
		1304	as locking, will also lock down an I/O thread while it is waiting, which
		1305	can deadlock the whole I/O system. At the same time, there might be no
		1306	alternative to using a thread to wait.
		1307
		1308	So in general, you should only use these calls for things that do
		1309	(filesystem) I/O, not for things that wait for other events (network,
		1310	other processes), although if you are careful and know what you are doing,
		1311	you still can.
		1312
		1313	The following constants are available (missing ones are, as usual C<0>):
		1314
		1315	C<F_DUPFD_CLOEXEC>,
		1316
		1317	C<F_OFD_GETLK>, C<F_OFD_SETLK>, C<F_OFD_GETLKW>,
		1318
		1319	C<FIFREEZE>, C<FITHAW>, C<FITRIM>, C<FICLONE>, C<FICLONERANGE>, C<FIDEDUPERANGE>.
		1320
		1321	C<FS_IOC_GETFLAGS>, C<FS_IOC_SETFLAGS>, C<FS_IOC_GETVERSION>, C<FS_IOC_SETVERSION>,
		1322	C<FS_IOC_FIEMAP>.
		1323
		1324	C<FS_IOC_FSGETXATTR>, C<FS_IOC_FSSETXATTR>, C<FS_IOC_SET_ENCRYPTION_POLICY>,
		1325	C<FS_IOC_GET_ENCRYPTION_PWSALT>, C<FS_IOC_GET_ENCRYPTION_POLICY>, C<FS_KEY_DESCRIPTOR_SIZE>.
		1326
		1327	C<FS_SECRM_FL>, C<FS_UNRM_FL>, C<FS_COMPR_FL>, C<FS_SYNC_FL>, C<FS_IMMUTABLE_FL>,
		1328	C<FS_APPEND_FL>, C<FS_NODUMP_FL>, C<FS_NOATIME_FL>, C<FS_DIRTY_FL>,
		1329	C<FS_COMPRBLK_FL>, C<FS_NOCOMP_FL>, C<FS_ENCRYPT_FL>, C<FS_BTREE_FL>,
		1330	C<FS_INDEX_FL>, C<FS_JOURNAL_DATA_FL>, C<FS_NOTAIL_FL>, C<FS_DIRSYNC_FL>, C<FS_TOPDIR_FL>,
		1331	C<FS_FL_USER_MODIFIABLE>.
		1332
		1333	C<FS_XFLAG_REALTIME>, C<FS_XFLAG_PREALLOC>, C<FS_XFLAG_IMMUTABLE>, C<FS_XFLAG_APPEND>,
		1334	C<FS_XFLAG_SYNC>, C<FS_XFLAG_NOATIME>, C<FS_XFLAG_NODUMP>, C<FS_XFLAG_RTINHERIT>,
		1335	C<FS_XFLAG_PROJINHERIT>, C<FS_XFLAG_NOSYMLINKS>, C<FS_XFLAG_EXTSIZE>, C<FS_XFLAG_EXTSZINHERIT>,
		1336	C<FS_XFLAG_NODEFRAG>, C<FS_XFLAG_FILESTREAM>, C<FS_XFLAG_DAX>, C<FS_XFLAG_HASATTR>,
		1337
		1338	=item aio_sync $callback->($status)
		1339
		1340	Asynchronously call sync and call the callback when finished.
		1341
247	=item aio_fsync $fh, $callback	1342	=item aio_fsync $fh, $callback->($status)
248		1343
249	Asynchronously call fsync on the given filehandle and call the callback	1344	Asynchronously call fsync on the given filehandle and call the callback
250	with the fsync result code.	1345	with the fsync result code.
251		1346
252	=item aio_fdatasync $fh, $callback	1347	=item aio_fdatasync $fh, $callback->($status)
253		1348
254	Asynchronously call fdatasync on the given filehandle and call the	1349	Asynchronously call fdatasync on the given filehandle and call the
255	callback with the fdatasync result code.	1350	callback with the fdatasync result code.
256		1351
257	If this call isn't available because your OS lacks it or it couldn't be	1352	If this call isn't available because your OS lacks it or it couldn't be
258	detected, it will be emulated by calling C<fsync> instead.	1353	detected, it will be emulated by calling C<fsync> instead.
259		1354
		1355	=item aio_syncfs $fh, $callback->($status)
		1356
		1357	Asynchronously call the syncfs syscall to sync the filesystem associated
		1358	to the given filehandle and call the callback with the syncfs result
		1359	code. If syncfs is not available, calls sync(), but returns C<-1> and sets
		1360	errno to C<ENOSYS> nevertheless.
		1361
		1362	=item aio_sync_file_range $fh, $offset, $nbytes, $flags, $callback->($status)
		1363
		1364	Sync the data portion of the file specified by C<$offset> and C<$length>
		1365	to disk (but NOT the metadata), by calling the Linux-specific
		1366	sync_file_range call. If sync_file_range is not available or it returns
		1367	ENOSYS, then fdatasync or fsync is being substituted.
		1368
		1369	C<$flags> can be a combination of C<IO::AIO::SYNC_FILE_RANGE_WAIT_BEFORE>,
		1370	C<IO::AIO::SYNC_FILE_RANGE_WRITE> and
		1371	C<IO::AIO::SYNC_FILE_RANGE_WAIT_AFTER>: refer to the sync_file_range
		1372	manpage for details.
		1373
		1374	=item aio_pathsync $pathname, $callback->($status)
		1375
		1376	This request tries to open, fsync and close the given path. This is a
		1377	composite request intended to sync directories after directory operations
		1378	(E.g. rename). This might not work on all operating systems or have any
		1379	specific effect, but usually it makes sure that directory changes get
		1380	written to disc. It works for anything that can be opened for read-only,
		1381	not just directories.
		1382
		1383	Future versions of this function might fall back to other methods when
		1384	C<fsync> on the directory fails (such as calling C<sync>).
		1385
		1386	Passes C<0> when everything went ok, and C<-1> on error.
		1387
		1388	=cut
		1389
		1390	sub aio_pathsync($;$) {
		1391	my ($path, $cb) = @_;
		1392
		1393	my $pri = aioreq_pri;
		1394	my $grp = aio_group $cb;
		1395
		1396	aioreq_pri $pri;
		1397	add $grp aio_open $path, O_RDONLY, 0, sub {
		1398	my ($fh) = @_;
		1399	if ($fh) {
		1400	aioreq_pri $pri;
		1401	add $grp aio_fsync $fh, sub {
		1402	$grp->result ($_[0]);
		1403
		1404	aioreq_pri $pri;
		1405	add $grp aio_close $fh;
		1406	};
		1407	} else {
		1408	$grp->result (-1);
		1409	}
		1410	};
		1411
		1412	$grp
		1413	}
		1414
		1415	=item aio_msync $scalar, $offset = 0, $length = undef, flags = MS_SYNC, $callback->($status)
		1416
		1417	This is a rather advanced IO::AIO call, which only works on mmap(2)ed
		1418	scalars (see the C<IO::AIO::mmap> function, although it also works on data
		1419	scalars managed by the L<Sys::Mmap> or L<Mmap> modules, note that the
		1420	scalar must only be modified in-place while an aio operation is pending on
		1421	it).
		1422
		1423	It calls the C<msync> function of your OS, if available, with the memory
		1424	area starting at C<$offset> in the string and ending C<$length> bytes
		1425	later. If C<$length> is negative, counts from the end, and if C<$length>
		1426	is C<undef>, then it goes till the end of the string. The flags can be
		1427	either C<IO::AIO::MS_ASYNC> or C<IO::AIO::MS_SYNC>, plus an optional
		1428	C<IO::AIO::MS_INVALIDATE>.
		1429
		1430	=item aio_mtouch $scalar, $offset = 0, $length = undef, flags = 0, $callback->($status)
		1431
		1432	This is a rather advanced IO::AIO call, which works best on mmap(2)ed
		1433	scalars.
		1434
		1435	It touches (reads or writes) all memory pages in the specified
		1436	range inside the scalar. All caveats and parameters are the same
		1437	as for C<aio_msync>, above, except for flags, which must be either
		1438	C<0> (which reads all pages and ensures they are instantiated) or
		1439	C<IO::AIO::MT_MODIFY>, which modifies the memory pages (by reading and
		1440	writing an octet from it, which dirties the page).
		1441
		1442	=item aio_mlock $scalar, $offset = 0, $length = undef, $callback->($status)
		1443
		1444	This is a rather advanced IO::AIO call, which works best on mmap(2)ed
		1445	scalars.
		1446
		1447	It reads in all the pages of the underlying storage into memory (if any)
		1448	and locks them, so they are not getting swapped/paged out or removed.
		1449
		1450	If C<$length> is undefined, then the scalar will be locked till the end.
		1451
		1452	On systems that do not implement C<mlock>, this function returns C<-1>
		1453	and sets errno to C<ENOSYS>.
		1454
		1455	Note that the corresponding C<munlock> is synchronous and is
		1456	documented under L<MISCELLANEOUS FUNCTIONS>.
		1457
		1458	Example: open a file, mmap and mlock it - both will be undone when
		1459	C<$data> gets destroyed.
		1460
		1461	open my $fh, "<", $path or die "$path: $!";
		1462	my $data;
		1463	IO::AIO::mmap $data, -s $fh, IO::AIO::PROT_READ, IO::AIO::MAP_SHARED, $fh;
		1464	aio_mlock $data; # mlock in background
		1465
		1466	=item aio_mlockall $flags, $callback->($status)
		1467
		1468	Calls the C<mlockall> function with the given C<$flags> (a
		1469	combination of C<IO::AIO::MCL_CURRENT>, C<IO::AIO::MCL_FUTURE> and
		1470	C<IO::AIO::MCL_ONFAULT>).
		1471
		1472	On systems that do not implement C<mlockall>, this function returns C<-1>
		1473	and sets errno to C<ENOSYS>. Similarly, flag combinations not supported
		1474	by the system result in a return value of C<-1> with errno being set to
		1475	C<EINVAL>.
		1476
		1477	Note that the corresponding C<munlockall> is synchronous and is
		1478	documented under L<MISCELLANEOUS FUNCTIONS>.
		1479
		1480	Example: asynchronously lock all current and future pages into memory.
		1481
		1482	aio_mlockall IO::AIO::MCL_FUTURE;
		1483
		1484	=item aio_fiemap $fh, $start, $length, $flags, $count, $cb->(\@extents)
		1485
		1486	Queries the extents of the given file (by calling the Linux C<FIEMAP>
		1487	ioctl, see L<http://cvs.schmorp.de/IO-AIO/doc/fiemap.txt> for details). If
		1488	the ioctl is not available on your OS, then this request will fail with
		1489	C<ENOSYS>.
		1490
		1491	C<$start> is the starting offset to query extents for, C<$length> is the
		1492	size of the range to query - if it is C<undef>, then the whole file will
		1493	be queried.
		1494
		1495	C<$flags> is a combination of flags (C<IO::AIO::FIEMAP_FLAG_SYNC> or
		1496	C<IO::AIO::FIEMAP_FLAG_XATTR> - C<IO::AIO::FIEMAP_FLAGS_COMPAT> is also
		1497	exported), and is normally C<0> or C<IO::AIO::FIEMAP_FLAG_SYNC> to query
		1498	the data portion.
		1499
		1500	C<$count> is the maximum number of extent records to return. If it is
		1501	C<undef>, then IO::AIO queries all extents of the range. As a very special
		1502	case, if it is C<0>, then the callback receives the number of extents
		1503	instead of the extents themselves (which is unreliable, see below).
		1504
		1505	If an error occurs, the callback receives no arguments. The special
		1506	C<errno> value C<IO::AIO::EBADR> is available to test for flag errors.
		1507
		1508	Otherwise, the callback receives an array reference with extent
		1509	structures. Each extent structure is an array reference itself, with the
		1510	following members:
		1511
		1512	[$logical, $physical, $length, $flags]
		1513
		1514	Flags is any combination of the following flag values (typically either C<0>
		1515	or C<IO::AIO::FIEMAP_EXTENT_LAST> (1)):
		1516
		1517	C<IO::AIO::FIEMAP_EXTENT_LAST>, C<IO::AIO::FIEMAP_EXTENT_UNKNOWN>,
		1518	C<IO::AIO::FIEMAP_EXTENT_DELALLOC>, C<IO::AIO::FIEMAP_EXTENT_ENCODED>,
		1519	C<IO::AIO::FIEMAP_EXTENT_DATA_ENCRYPTED>, C<IO::AIO::FIEMAP_EXTENT_NOT_ALIGNED>,
		1520	C<IO::AIO::FIEMAP_EXTENT_DATA_INLINE>, C<IO::AIO::FIEMAP_EXTENT_DATA_TAIL>,
		1521	C<IO::AIO::FIEMAP_EXTENT_UNWRITTEN>, C<IO::AIO::FIEMAP_EXTENT_MERGED> or
		1522	C<IO::AIO::FIEMAP_EXTENT_SHARED>.
		1523
		1524	At the time of this writing (Linux 3.2), this request is unreliable unless
		1525	C<$count> is C<undef>, as the kernel has all sorts of bugs preventing
		1526	it to return all extents of a range for files with a large number of
		1527	extents. The code (only) works around all these issues if C<$count> is
		1528	C<undef>.
		1529
		1530	=item aio_group $callback->(...)
		1531
		1532	This is a very special aio request: Instead of doing something, it is a
		1533	container for other aio requests, which is useful if you want to bundle
		1534	many requests into a single, composite, request with a definite callback
		1535	and the ability to cancel the whole request with its subrequests.
		1536
		1537	Returns an object of class L<IO::AIO::GRP>. See its documentation below
		1538	for more info.
		1539
		1540	Example:
		1541
		1542	my $grp = aio_group sub {
		1543	print "all stats done\n";
		1544	};
		1545
		1546	add $grp
		1547	(aio_stat ...),
		1548	(aio_stat ...),
		1549	...;
		1550
		1551	=item aio_nop $callback->()
		1552
		1553	This is a special request - it does nothing in itself and is only used for
		1554	side effects, such as when you want to add a dummy request to a group so
		1555	that finishing the requests in the group depends on executing the given
		1556	code.
		1557
		1558	While this request does nothing, it still goes through the execution
		1559	phase and still requires a worker thread. Thus, the callback will not
		1560	be executed immediately but only after other requests in the queue have
		1561	entered their execution phase. This can be used to measure request
		1562	latency.
		1563
		1564	=item IO::AIO::aio_busy $fractional_seconds, $callback->() *NOT EXPORTED*
		1565
		1566	Mainly used for debugging and benchmarking, this aio request puts one of
		1567	the request workers to sleep for the given time.
		1568
		1569	While it is theoretically handy to have simple I/O scheduling requests
		1570	like sleep and file handle readable/writable, the overhead this creates is
		1571	immense (it blocks a thread for a long time) so do not use this function
		1572	except to put your application under artificial I/O pressure.
		1573
260	=back	1574	=back
261		1575
		1576
		1577	=head2 IO::AIO::WD - multiple working directories
		1578
		1579	Your process only has one current working directory, which is used by all
		1580	threads. This makes it hard to use relative paths (some other component
		1581	could call C<chdir> at any time, and it is hard to control when the path
		1582	will be used by IO::AIO).
		1583
		1584	One solution for this is to always use absolute paths. This usually works,
		1585	but can be quite slow (the kernel has to walk the whole path on every
		1586	access), and can also be a hassle to implement.
		1587
		1588	Newer POSIX systems have a number of functions (openat, fdopendir,
		1589	futimensat and so on) that make it possible to specify working directories
		1590	per operation.
		1591
		1592	For portability, and because the clowns who "designed", or shall I write,
		1593	perpetrated this new interface were obviously half-drunk, this abstraction
		1594	cannot be perfect, though.
		1595
		1596	IO::AIO allows you to convert directory paths into a so-called IO::AIO::WD
		1597	object. This object stores the canonicalised, absolute version of the
		1598	path, and on systems that allow it, also a directory file descriptor.
		1599
		1600	Everywhere where a pathname is accepted by IO::AIO (e.g. in C<aio_stat>
		1601	or C<aio_unlink>), one can specify an array reference with an IO::AIO::WD
		1602	object and a pathname instead (or the IO::AIO::WD object alone, which
		1603	gets interpreted as C<[$wd, "."]>). If the pathname is absolute, the
		1604	IO::AIO::WD object is ignored, otherwise the pathname is resolved relative
		1605	to that IO::AIO::WD object.
		1606
		1607	For example, to get a wd object for F</etc> and then stat F<passwd>
		1608	inside, you would write:
		1609
		1610	aio_wd "/etc", sub {
		1611	my $etcdir = shift;
		1612
		1613	# although $etcdir can be undef on error, there is generally no reason
		1614	# to check for errors here, as aio_stat will fail with ENOENT
		1615	# when $etcdir is undef.
		1616
		1617	aio_stat [$etcdir, "passwd"], sub {
		1618	# yay
		1619	};
		1620	};
		1621
		1622	The fact that C<aio_wd> is a request and not a normal function shows that
		1623	creating an IO::AIO::WD object is itself a potentially blocking operation,
		1624	which is why it is done asynchronously.
		1625
		1626	To stat the directory obtained with C<aio_wd> above, one could write
		1627	either of the following three request calls:
		1628
		1629	aio_lstat "/etc" , sub { ... # pathname as normal string
		1630	aio_lstat [$wd, "."], sub { ... # "." relative to $wd (i.e. $wd itself)
		1631	aio_lstat $wd , sub { ... # shorthand for the previous
		1632
		1633	As with normal pathnames, IO::AIO keeps a copy of the working directory
		1634	object and the pathname string, so you could write the following without
		1635	causing any issues due to C<$path> getting reused:
		1636
		1637	my $path = [$wd, undef];
		1638
		1639	for my $name (qw(abc def ghi)) {
		1640	$path->[1] = $name;
		1641	aio_stat $path, sub {
		1642	# ...
		1643	};
		1644	}
		1645
		1646	There are some caveats: when directories get renamed (or deleted), the
		1647	pathname string doesn't change, so will point to the new directory (or
		1648	nowhere at all), while the directory fd, if available on the system,
		1649	will still point to the original directory. Most functions accepting a
		1650	pathname will use the directory fd on newer systems, and the string on
		1651	older systems. Some functions (such as C<aio_realpath>) will always rely on
		1652	the string form of the pathname.
		1653
		1654	So this functionality is mainly useful to get some protection against
		1655	C<chdir>, to easily get an absolute path out of a relative path for future
		1656	reference, and to speed up doing many operations in the same directory
		1657	(e.g. when stat'ing all files in a directory).
		1658
		1659	The following functions implement this working directory abstraction:
		1660
		1661	=over 4
		1662
		1663	=item aio_wd $pathname, $callback->($wd)
		1664
		1665	Asynchonously canonicalise the given pathname and convert it to an
		1666	IO::AIO::WD object representing it. If possible and supported on the
		1667	system, also open a directory fd to speed up pathname resolution relative
		1668	to this working directory.
		1669
		1670	If something goes wrong, then C<undef> is passwd to the callback instead
		1671	of a working directory object and C<$!> is set appropriately. Since
		1672	passing C<undef> as working directory component of a pathname fails the
		1673	request with C<ENOENT>, there is often no need for error checking in the
		1674	C<aio_wd> callback, as future requests using the value will fail in the
		1675	expected way.
		1676
		1677	=item IO::AIO::CWD
		1678
		1679	This is a compiletime constant (object) that represents the process
		1680	current working directory.
		1681
		1682	Specifying this object as working directory object for a pathname is as if
		1683	the pathname would be specified directly, without a directory object. For
		1684	example, these calls are functionally identical:
		1685
		1686	aio_stat "somefile", sub { ... };
		1687	aio_stat [IO::AIO::CWD, "somefile"], sub { ... };
		1688
		1689	=back
		1690
		1691	To recover the path associated with an IO::AIO::WD object, you can use
		1692	C<aio_realpath>:
		1693
		1694	aio_realpath $wd, sub {
		1695	warn "path is $_[0]\n";
		1696	};
		1697
		1698	Currently, C<aio_statvfs> always, and C<aio_rename> and C<aio_rmdir>
		1699	sometimes, fall back to using an absolue path.
		1700
		1701	=head2 IO::AIO::REQ CLASS
		1702
		1703	All non-aggregate C<aio_*> functions return an object of this class when
		1704	called in non-void context.
		1705
		1706	=over 4
		1707
		1708	=item cancel $req
		1709
		1710	Cancels the request, if possible. Has the effect of skipping execution
		1711	when entering the B<execute> state and skipping calling the callback when
		1712	entering the the B<result> state, but will leave the request otherwise
		1713	untouched (with the exception of readdir). That means that requests that
		1714	currently execute will not be stopped and resources held by the request
		1715	will not be freed prematurely.
		1716
		1717	=item cb $req $callback->(...)
		1718
		1719	Replace (or simply set) the callback registered to the request.
		1720
		1721	=back
		1722
		1723	=head2 IO::AIO::GRP CLASS
		1724
		1725	This class is a subclass of L<IO::AIO::REQ>, so all its methods apply to
		1726	objects of this class, too.
		1727
		1728	A IO::AIO::GRP object is a special request that can contain multiple other
		1729	aio requests.
		1730
		1731	You create one by calling the C<aio_group> constructing function with a
		1732	callback that will be called when all contained requests have entered the
		1733	C<done> state:
		1734
		1735	my $grp = aio_group sub {
		1736	print "all requests are done\n";
		1737	};
		1738
		1739	You add requests by calling the C<add> method with one or more
		1740	C<IO::AIO::REQ> objects:
		1741
		1742	$grp->add (aio_unlink "...");
		1743
		1744	add $grp aio_stat "...", sub {
		1745	$_[0] or return $grp->result ("error");
		1746
		1747	# add another request dynamically, if first succeeded
		1748	add $grp aio_open "...", sub {
		1749	$grp->result ("ok");
		1750	};
		1751	};
		1752
		1753	This makes it very easy to create composite requests (see the source of
		1754	C<aio_move> for an application) that work and feel like simple requests.
		1755
		1756	=over 4
		1757
		1758	=item * The IO::AIO::GRP objects will be cleaned up during calls to
		1759	C<IO::AIO::poll_cb>, just like any other request.
		1760
		1761	=item * They can be canceled like any other request. Canceling will cancel not
		1762	only the request itself, but also all requests it contains.
		1763
		1764	=item * They can also can also be added to other IO::AIO::GRP objects.
		1765
		1766	=item * You must not add requests to a group from within the group callback (or
		1767	any later time).
		1768
		1769	=back
		1770
		1771	Their lifetime, simplified, looks like this: when they are empty, they
		1772	will finish very quickly. If they contain only requests that are in the
		1773	C<done> state, they will also finish. Otherwise they will continue to
		1774	exist.
		1775
		1776	That means after creating a group you have some time to add requests
		1777	(precisely before the callback has been invoked, which is only done within
		1778	the C<poll_cb>). And in the callbacks of those requests, you can add
		1779	further requests to the group. And only when all those requests have
		1780	finished will the the group itself finish.
		1781
		1782	=over 4
		1783
		1784	=item add $grp ...
		1785
		1786	=item $grp->add (...)
		1787
		1788	Add one or more requests to the group. Any type of L<IO::AIO::REQ> can
		1789	be added, including other groups, as long as you do not create circular
		1790	dependencies.
		1791
		1792	Returns all its arguments.
		1793
		1794	=item $grp->cancel_subs
		1795
		1796	Cancel all subrequests and clears any feeder, but not the group request
		1797	itself. Useful when you queued a lot of events but got a result early.
		1798
		1799	The group request will finish normally (you cannot add requests to the
		1800	group).
		1801
		1802	=item $grp->result (...)
		1803
		1804	Set the result value(s) that will be passed to the group callback when all
		1805	subrequests have finished and set the groups errno to the current value
		1806	of errno (just like calling C<errno> without an error number). By default,
		1807	no argument will be passed and errno is zero.
		1808
		1809	=item $grp->errno ([$errno])
		1810
		1811	Sets the group errno value to C<$errno>, or the current value of errno
		1812	when the argument is missing.
		1813
		1814	Every aio request has an associated errno value that is restored when
		1815	the callback is invoked. This method lets you change this value from its
		1816	default (0).
		1817
		1818	Calling C<result> will also set errno, so make sure you either set C<$!>
		1819	before the call to C<result>, or call c<errno> after it.
		1820
		1821	=item feed $grp $callback->($grp)
		1822
		1823	Sets a feeder/generator on this group: every group can have an attached
		1824	generator that generates requests if idle. The idea behind this is that,
		1825	although you could just queue as many requests as you want in a group,
		1826	this might starve other requests for a potentially long time. For example,
		1827	C<aio_scandir> might generate hundreds of thousands of C<aio_stat>
		1828	requests, delaying any later requests for a long time.
		1829
		1830	To avoid this, and allow incremental generation of requests, you can
		1831	instead a group and set a feeder on it that generates those requests. The
		1832	feed callback will be called whenever there are few enough (see C<limit>,
		1833	below) requests active in the group itself and is expected to queue more
		1834	requests.
		1835
		1836	The feed callback can queue as many requests as it likes (i.e. C<add> does
		1837	not impose any limits).
		1838
		1839	If the feed does not queue more requests when called, it will be
		1840	automatically removed from the group.
		1841
		1842	If the feed limit is C<0> when this method is called, it will be set to
		1843	C<2> automatically.
		1844
		1845	Example:
		1846
		1847	# stat all files in @files, but only ever use four aio requests concurrently:
		1848
		1849	my $grp = aio_group sub { print "finished\n" };
		1850	limit $grp 4;
		1851	feed $grp sub {
		1852	my $file = pop @files
		1853	or return;
		1854
		1855	add $grp aio_stat $file, sub { ... };
		1856	};
		1857
		1858	=item limit $grp $num
		1859
		1860	Sets the feeder limit for the group: The feeder will be called whenever
		1861	the group contains less than this many requests.
		1862
		1863	Setting the limit to C<0> will pause the feeding process.
		1864
		1865	The default value for the limit is C<0>, but note that setting a feeder
		1866	automatically bumps it up to C<2>.
		1867
		1868	=back
		1869
		1870
262	=head2 SUPPORT FUNCTIONS	1871	=head2 SUPPORT FUNCTIONS
263		1872
		1873	=head3 EVENT PROCESSING AND EVENT LOOP INTEGRATION
		1874
264	=over 4	1875	=over 4
265		1876
266	=item $fileno = IO::AIO::poll_fileno	1877	=item $fileno = IO::AIO::poll_fileno
267		1878
268	Return the I<request result pipe file descriptor>. This filehandle must be	1879	Return the I<request result pipe file descriptor>. This filehandle must be
269	polled for reading by some mechanism outside this module (e.g. Event or	1880	polled for reading by some mechanism outside this module (e.g. EV, Glib,
270	select, see below or the SYNOPSIS). If the pipe becomes readable you have	1881	select and so on, see below or the SYNOPSIS). If the pipe becomes readable
271	to call C<poll_cb> to check the results.	1882	you have to call C<poll_cb> to check the results.
272		1883
273	See C<poll_cb> for an example.	1884	See C<poll_cb> for an example.
274		1885
275	=item IO::AIO::poll_cb	1886	=item IO::AIO::poll_cb
276		1887
277	Process all outstanding events on the result pipe. You have to call this	1888	Process some requests that have reached the result phase (i.e. they have
278	regularly. Returns the number of events processed. Returns immediately	1889	been executed but the results are not yet reported). You have to call
279	when no events are outstanding.	1890	this "regularly" to finish outstanding requests.
		1891
		1892	Returns C<0> if all events could be processed (or there were no
		1893	events to process), or C<-1> if it returned earlier for whatever
		1894	reason. Returns immediately when no events are outstanding. The amount
		1895	of events processed depends on the settings of C<IO::AIO::max_poll_req>,
		1896	C<IO::AIO::max_poll_time> and C<IO::AIO::max_outstanding>.
		1897
		1898	If not all requests were processed for whatever reason, the poll file
		1899	descriptor will still be ready when C<poll_cb> returns, so normally you
		1900	don't have to do anything special to have it called later.
		1901
		1902	Apart from calling C<IO::AIO::poll_cb> when the event filehandle becomes
		1903	ready, it can be beneficial to call this function from loops which submit
		1904	a lot of requests, to make sure the results get processed when they become
		1905	available and not just when the loop is finished and the event loop takes
		1906	over again. This function returns very fast when there are no outstanding
		1907	requests.
280		1908
281	Example: Install an Event watcher that automatically calls	1909	Example: Install an Event watcher that automatically calls
282	IO::AIO::poll_cb with high priority:	1910	IO::AIO::poll_cb with high priority (more examples can be found in the
		1911	SYNOPSIS section, at the top of this document):
283		1912
284	Event->io (fd => IO::AIO::poll_fileno,	1913	Event->io (fd => IO::AIO::poll_fileno,
285	poll => 'r', async => 1,	1914	poll => 'r', async => 1,
286	cb => \&IO::AIO::poll_cb);	1915	cb => \&IO::AIO::poll_cb);
287		1916
288	=item IO::AIO::poll_wait	1917	=item IO::AIO::poll_wait
289		1918
290	Wait till the result filehandle becomes ready for reading (simply does a	1919	Wait until either at least one request is in the result phase or no
291	C<select> on the filehandle. This is useful if you want to synchronously wait	1920	requests are outstanding anymore.
292	for some requests to finish).	1921
		1922	This is useful if you want to synchronously wait for some requests to
		1923	become ready, without actually handling them.
293		1924
294	See C<nreqs> for an example.	1925	See C<nreqs> for an example.
295		1926
		1927	=item IO::AIO::poll
		1928
		1929	Waits until some requests have been handled.
		1930
		1931	Returns the number of requests processed, but is otherwise strictly
		1932	equivalent to:
		1933
		1934	IO::AIO::poll_wait, IO::AIO::poll_cb
		1935
296	=item IO::AIO::nreqs	1936	=item IO::AIO::flush
297		1937
298	Returns the number of requests currently outstanding (i.e. for which their	1938	Wait till all outstanding AIO requests have been handled.
299	callback has not been invoked yet).
300		1939
301	Example: wait till there are no outstanding requests anymore:	1940	Strictly equivalent to:
302		1941
303	IO::AIO::poll_wait, IO::AIO::poll_cb	1942	IO::AIO::poll_wait, IO::AIO::poll_cb
304	while IO::AIO::nreqs;	1943	while IO::AIO::nreqs;
305		1944
		1945	This function can be useful at program aborts, to make sure outstanding
		1946	I/O has been done (C<IO::AIO> uses an C<END> block which already calls
		1947	this function on normal exits), or when you are merely using C<IO::AIO>
		1948	for its more advanced functions, rather than for async I/O, e.g.:
		1949
		1950	my ($dirs, $nondirs);
		1951	IO::AIO::aio_scandir "/tmp", 0, sub { ($dirs, $nondirs) = @_ };
306	=item IO::AIO::flush	1952	IO::AIO::flush;
		1953	# $dirs, $nondirs are now set
307		1954
308	Wait till all outstanding AIO requests have been handled.	1955	=item IO::AIO::max_poll_reqs $nreqs
309		1956
310	Strictly equivalent to:	1957	=item IO::AIO::max_poll_time $seconds
311		1958
312	IO::AIO::poll_wait, IO::AIO::poll_cb	1959	These set the maximum number of requests (default C<0>, meaning infinity)
313	while IO::AIO::nreqs;	1960	that are being processed by C<IO::AIO::poll_cb> in one call, respectively
		1961	the maximum amount of time (default C<0>, meaning infinity) spent in
		1962	C<IO::AIO::poll_cb> to process requests (more correctly the mininum amount
		1963	of time C<poll_cb> is allowed to use).
314		1964
315	=item IO::AIO::poll	1965	Setting C<max_poll_time> to a non-zero value creates an overhead of one
		1966	syscall per request processed, which is not normally a problem unless your
		1967	callbacks are really really fast or your OS is really really slow (I am
		1968	not mentioning Solaris here). Using C<max_poll_reqs> incurs no overhead.
316		1969
317	Waits until some requests have been handled.	1970	Setting these is useful if you want to ensure some level of
		1971	interactiveness when perl is not fast enough to process all requests in
		1972	time.
318		1973
319	Strictly equivalent to:	1974	For interactive programs, values such as C<0.01> to C<0.1> should be fine.
320		1975
321	IO::AIO::poll_wait, IO::AIO::poll_cb	1976	Example: Install an Event watcher that automatically calls
322	if IO::AIO::nreqs;	1977	IO::AIO::poll_cb with low priority, to ensure that other parts of the
		1978	program get the CPU sometimes even under high AIO load.
		1979
		1980	# try not to spend much more than 0.1s in poll_cb
		1981	IO::AIO::max_poll_time 0.1;
		1982
		1983	# use a low priority so other tasks have priority
		1984	Event->io (fd => IO::AIO::poll_fileno,
		1985	poll => 'r', nice => 1,
		1986	cb => &IO::AIO::poll_cb);
		1987
		1988	=back
		1989
		1990
		1991	=head3 CONTROLLING THE NUMBER OF THREADS
		1992
		1993	=over
323		1994
324	=item IO::AIO::min_parallel $nthreads	1995	=item IO::AIO::min_parallel $nthreads
325		1996
326	Set the minimum number of AIO threads to C<$nthreads>. The current default	1997	Set the minimum number of AIO threads to C<$nthreads>. The current
327	is C<4>, which means four asynchronous operations can be done at one time	1998	default is C<8>, which means eight asynchronous operations can execute
328	(the number of outstanding operations, however, is unlimited).	1999	concurrently at any one time (the number of outstanding requests,
		2000	however, is unlimited).
329		2001
330	IO::AIO starts threads only on demand, when an AIO request is queued and	2002	IO::AIO starts threads only on demand, when an AIO request is queued and
331	no free thread exists.	2003	no free thread exists. Please note that queueing up a hundred requests can
		2004	create demand for a hundred threads, even if it turns out that everything
		2005	is in the cache and could have been processed faster by a single thread.
332		2006
333	It is recommended to keep the number of threads low, as some Linux	2007	It is recommended to keep the number of threads relatively low, as some
334	kernel versions will scale negatively with the number of threads (higher	2008	Linux kernel versions will scale negatively with the number of threads
335	parallelity => MUCH higher latency). With current Linux 2.6 versions, 4-32	2009	(higher parallelity => MUCH higher latency). With current Linux 2.6
336	threads should be fine.	2010	versions, 4-32 threads should be fine.
337		2011
338	Under most circumstances you don't need to call this function, as the	2012	Under most circumstances you don't need to call this function, as the
339	module selects a default that is suitable for low to moderate load.	2013	module selects a default that is suitable for low to moderate load.
340		2014
341	=item IO::AIO::max_parallel $nthreads	2015	=item IO::AIO::max_parallel $nthreads
…		…
350	This module automatically runs C<max_parallel 0> at program end, to ensure	2024	This module automatically runs C<max_parallel 0> at program end, to ensure
351	that all threads are killed and that there are no outstanding requests.	2025	that all threads are killed and that there are no outstanding requests.
352		2026
353	Under normal circumstances you don't need to call this function.	2027	Under normal circumstances you don't need to call this function.
354		2028
		2029	=item IO::AIO::max_idle $nthreads
		2030
		2031	Limit the number of threads (default: 4) that are allowed to idle
		2032	(i.e., threads that did not get a request to process within the idle
		2033	timeout (default: 10 seconds). That means if a thread becomes idle while
		2034	C<$nthreads> other threads are also idle, it will free its resources and
		2035	exit.
		2036
		2037	This is useful when you allow a large number of threads (e.g. 100 or 1000)
		2038	to allow for extremely high load situations, but want to free resources
		2039	under normal circumstances (1000 threads can easily consume 30MB of RAM).
		2040
		2041	The default is probably ok in most situations, especially if thread
		2042	creation is fast. If thread creation is very slow on your system you might
		2043	want to use larger values.
		2044
		2045	=item IO::AIO::idle_timeout $seconds
		2046
		2047	Sets the minimum idle timeout (default 10) after which worker threads are
		2048	allowed to exit. SEe C<IO::AIO::max_idle>.
		2049
355	=item $oldnreqs = IO::AIO::max_outstanding $nreqs	2050	=item IO::AIO::max_outstanding $maxreqs
356		2051
357	Sets the maximum number of outstanding requests to C<$nreqs>. If you	2052	Sets the maximum number of outstanding requests to C<$nreqs>. If
358	try to queue up more than this number of requests, the caller will block until	2053	you do queue up more than this number of requests, the next call to
359	some requests have been handled.	2054	C<IO::AIO::poll_cb> (and other functions calling C<poll_cb>, such as
		2055	C<IO::AIO::flush> or C<IO::AIO::poll>) will block until the limit is no
		2056	longer exceeded.
360		2057
361	The default is very large, so normally there is no practical limit. If you	2058	In other words, this setting does not enforce a queue limit, but can be
362	queue up many requests in a loop it often improves speed if you set	2059	used to make poll functions block if the limit is exceeded.
363	this to a relatively low number, such as C<100>.
364		2060
365	Under normal circumstances you don't need to call this function.	2061	This is a very bad function to use in interactive programs because it
		2062	blocks, and a bad way to reduce concurrency because it is inexact: Better
		2063	use an C<aio_group> together with a feed callback.
		2064
		2065	Its main use is in scripts without an event loop - when you want to stat
		2066	a lot of files, you can write something like this:
		2067
		2068	IO::AIO::max_outstanding 32;
		2069
		2070	for my $path (...) {
		2071	aio_stat $path , ...;
		2072	IO::AIO::poll_cb;
		2073	}
		2074
		2075	IO::AIO::flush;
		2076
		2077	The call to C<poll_cb> inside the loop will normally return instantly, but
		2078	as soon as more thna C<32> reqeusts are in-flight, it will block until
		2079	some requests have been handled. This keeps the loop from pushing a large
		2080	number of C<aio_stat> requests onto the queue.
		2081
		2082	The default value for C<max_outstanding> is very large, so there is no
		2083	practical limit on the number of outstanding requests.
366		2084
367	=back	2085	=back
368		2086
		2087
		2088	=head3 STATISTICAL INFORMATION
		2089
		2090	=over
		2091
		2092	=item IO::AIO::nreqs
		2093
		2094	Returns the number of requests currently in the ready, execute or pending
		2095	states (i.e. for which their callback has not been invoked yet).
		2096
		2097	Example: wait till there are no outstanding requests anymore:
		2098
		2099	IO::AIO::poll_wait, IO::AIO::poll_cb
		2100	while IO::AIO::nreqs;
		2101
		2102	=item IO::AIO::nready
		2103
		2104	Returns the number of requests currently in the ready state (not yet
		2105	executed).
		2106
		2107	=item IO::AIO::npending
		2108
		2109	Returns the number of requests currently in the pending state (executed,
		2110	but not yet processed by poll_cb).
		2111
		2112	=back
		2113
		2114
		2115	=head3 SUBSECOND STAT TIME ACCESS
		2116
		2117	Both C<aio_stat>/C<aio_lstat> and perl's C<stat>/C<lstat> functions can
		2118	generally find access/modification and change times with subsecond time
		2119	accuracy of the system supports it, but perl's built-in functions only
		2120	return the integer part.
		2121
		2122	The following functions return the timestamps of the most recent
		2123	stat with subsecond precision on most systems and work both after
		2124	C<aio_stat>/C<aio_lstat> and perl's C<stat>/C<lstat> calls. Their return
		2125	value is only meaningful after a successful C<stat>/C<lstat> call, or
		2126	during/after a successful C<aio_stat>/C<aio_lstat> callback.
		2127
		2128	This is similar to the L<Time::HiRes> C<stat> functions, but can return
		2129	full resolution without rounding and work with standard perl C<stat>,
		2130	alleviating the need to call the special C<Time::HiRes> functions, which
		2131	do not act like their perl counterparts.
		2132
		2133	On operating systems or file systems where subsecond time resolution is
		2134	not supported or could not be detected, a fractional part of C<0> is
		2135	returned, so it is always safe to call these functions.
		2136
		2137	=over 4
		2138
		2139	=item $seconds = IO::AIO::st_atime, IO::AIO::st_mtime, IO::AIO::st_ctime, IO::AIO::st_btime
		2140
		2141	Return the access, modication, change or birth time, respectively,
		2142	including fractional part. Due to the limited precision of floating point,
		2143	the accuracy on most platforms is only a bit better than milliseconds
		2144	for times around now - see the I<nsec> function family, below, for full
		2145	accuracy.
		2146
		2147	File birth time is only available when the OS and perl support it (on
		2148	FreeBSD and NetBSD at the time of this writing, although support is
		2149	adaptive, so if your OS/perl gains support, IO::AIO can take advantage of
		2150	it). On systems where it isn't available, C<0> is currently returned, but
		2151	this might change to C<undef> in a future version.
		2152
		2153	=item ($atime, $mtime, $ctime, $btime, ...) = IO::AIO::st_xtime
		2154
		2155	Returns access, modification, change and birth time all in one go, and
		2156	maybe more times in the future version.
		2157
		2158	=item $nanoseconds = IO::AIO::st_atimensec, IO::AIO::st_mtimensec, IO::AIO::st_ctimensec, IO::AIO::st_btimensec
		2159
		2160	Return the fractional access, modifcation, change or birth time, in nanoseconds,
		2161	as an integer in the range C<0> to C<999999999>.
		2162
		2163	Note that no accessors are provided for access, modification and
		2164	change times - you need to get those from C<stat _> if required (C<int
		2165	IO::AIO::st_atime> and so on will I<not> generally give you the correct
		2166	value).
		2167
		2168	=item $seconds = IO::AIO::st_btimesec
		2169
		2170	The (integral) seconds part of the file birth time, if available.
		2171
		2172	=item ($atime, $mtime, $ctime, $btime, ...) = IO::AIO::st_xtimensec
		2173
		2174	Like the functions above, but returns all four times in one go (and maybe
		2175	more in future versions).
		2176
		2177	=item $counter = IO::AIO::st_gen
		2178
		2179	Returns the generation counter (in practice this is just a random number)
		2180	of the file. This is only available on platforms which have this member in
		2181	their C<struct stat> (most BSDs at the time of this writing) and generally
		2182	only to the root usert. If unsupported, C<0> is returned, but this might
		2183	change to C<undef> in a future version.
		2184
		2185	=back
		2186
		2187	Example: print the high resolution modification time of F</etc>, using
		2188	C<stat>, and C<IO::AIO::aio_stat>.
		2189
		2190	if (stat "/etc") {
		2191	printf "stat(/etc) mtime: %f\n", IO::AIO::st_mtime;
		2192	}
		2193
		2194	IO::AIO::aio_stat "/etc", sub {
		2195	$_[0]
		2196	and return;
		2197
		2198	printf "aio_stat(/etc) mtime: %d.%09d\n", (stat _)[9], IO::AIO::st_mtimensec;
		2199	};
		2200
		2201	IO::AIO::flush;
		2202
		2203	Output of the awbove on my system, showing reduced and full accuracy:
		2204
		2205	stat(/etc) mtime: 1534043702.020808
		2206	aio_stat(/etc) mtime: 1534043702.020807792
		2207
		2208
		2209	=head3 MISCELLANEOUS FUNCTIONS
		2210
		2211	IO::AIO implements some functions that are useful when you want to use
		2212	some "Advanced I/O" function not available to in Perl, without going the
		2213	"Asynchronous I/O" route. Many of these have an asynchronous C<aio_*>
		2214	counterpart.
		2215
		2216	=over 4
		2217
		2218	=item $numfd = IO::AIO::get_fdlimit
		2219
		2220	This function is I<EXPERIMENTAL> and subject to change.
		2221
		2222	Tries to find the current file descriptor limit and returns it, or
		2223	C<undef> and sets C<$!> in case of an error. The limit is one larger than
		2224	the highest valid file descriptor number.
		2225
		2226	=item IO::AIO::min_fdlimit [$numfd]
		2227
		2228	This function is I<EXPERIMENTAL> and subject to change.
		2229
		2230	Try to increase the current file descriptor limit(s) to at least C<$numfd>
		2231	by changing the soft or hard file descriptor resource limit. If C<$numfd>
		2232	is missing, it will try to set a very high limit, although this is not
		2233	recommended when you know the actual minimum that you require.
		2234
		2235	If the limit cannot be raised enough, the function makes a best-effort
		2236	attempt to increase the limit as much as possible, using various
		2237	tricks, while still failing. You can query the resulting limit using
		2238	C<IO::AIO::get_fdlimit>.
		2239
		2240	If an error occurs, returns C<undef> and sets C<$!>, otherwise returns
		2241	true.
		2242
		2243	=item IO::AIO::sendfile $ofh, $ifh, $offset, $count
		2244
		2245	Calls the C<eio_sendfile_sync> function, which is like C<aio_sendfile>,
		2246	but is blocking (this makes most sense if you know the input data is
		2247	likely cached already and the output filehandle is set to non-blocking
		2248	operations).
		2249
		2250	Returns the number of bytes copied, or C<-1> on error.
		2251
		2252	=item IO::AIO::fadvise $fh, $offset, $len, $advice
		2253
		2254	Simply calls the C<posix_fadvise> function (see its
		2255	manpage for details). The following advice constants are
		2256	available: C<IO::AIO::FADV_NORMAL>, C<IO::AIO::FADV_SEQUENTIAL>,
		2257	C<IO::AIO::FADV_RANDOM>, C<IO::AIO::FADV_NOREUSE>,
		2258	C<IO::AIO::FADV_WILLNEED>, C<IO::AIO::FADV_DONTNEED>.
		2259
		2260	On systems that do not implement C<posix_fadvise>, this function returns
		2261	ENOSYS, otherwise the return value of C<posix_fadvise>.
		2262
		2263	=item IO::AIO::madvise $scalar, $offset, $len, $advice
		2264
		2265	Simply calls the C<posix_madvise> function (see its
		2266	manpage for details). The following advice constants are
		2267	available: C<IO::AIO::MADV_NORMAL>, C<IO::AIO::MADV_SEQUENTIAL>,
		2268	C<IO::AIO::MADV_RANDOM>, C<IO::AIO::MADV_WILLNEED>,
		2269	C<IO::AIO::MADV_DONTNEED>.
		2270
		2271	If C<$offset> is negative, counts from the end. If C<$length> is negative,
		2272	the remaining length of the C<$scalar> is used. If possible, C<$length>
		2273	will be reduced to fit into the C<$scalar>.
		2274
		2275	On systems that do not implement C<posix_madvise>, this function returns
		2276	ENOSYS, otherwise the return value of C<posix_madvise>.
		2277
		2278	=item IO::AIO::mprotect $scalar, $offset, $len, $protect
		2279
		2280	Simply calls the C<mprotect> function on the preferably AIO::mmap'ed
		2281	$scalar (see its manpage for details). The following protect
		2282	constants are available: C<IO::AIO::PROT_NONE>, C<IO::AIO::PROT_READ>,
		2283	C<IO::AIO::PROT_WRITE>, C<IO::AIO::PROT_EXEC>.
		2284
		2285	If C<$offset> is negative, counts from the end. If C<$length> is negative,
		2286	the remaining length of the C<$scalar> is used. If possible, C<$length>
		2287	will be reduced to fit into the C<$scalar>.
		2288
		2289	On systems that do not implement C<mprotect>, this function returns
		2290	ENOSYS, otherwise the return value of C<mprotect>.
		2291
		2292	=item IO::AIO::mmap $scalar, $length, $prot, $flags, $fh[, $offset]
		2293
		2294	Memory-maps a file (or anonymous memory range) and attaches it to the
		2295	given C<$scalar>, which will act like a string scalar. Returns true on
		2296	success, and false otherwise.
		2297
		2298	The scalar must exist, but its contents do not matter - this means you
		2299	cannot use a nonexistant array or hash element. When in doubt, C<undef>
		2300	the scalar first.
		2301
		2302	The only operations allowed on the mmapped scalar are C<substr>/C<vec>,
		2303	which don't change the string length, and most read-only operations such
		2304	as copying it or searching it with regexes and so on.
		2305
		2306	Anything else is unsafe and will, at best, result in memory leaks.
		2307
		2308	The memory map associated with the C<$scalar> is automatically removed
		2309	when the C<$scalar> is undef'd or destroyed, or when the C<IO::AIO::mmap>
		2310	or C<IO::AIO::munmap> functions are called on it.
		2311
		2312	This calls the C<mmap>(2) function internally. See your system's manual
		2313	page for details on the C<$length>, C<$prot> and C<$flags> parameters.
		2314
		2315	The C<$length> must be larger than zero and smaller than the actual
		2316	filesize.
		2317
		2318	C<$prot> is a combination of C<IO::AIO::PROT_NONE>, C<IO::AIO::PROT_EXEC>,
		2319	C<IO::AIO::PROT_READ> and/or C<IO::AIO::PROT_WRITE>,
		2320
		2321	C<$flags> can be a combination of
		2322	C<IO::AIO::MAP_SHARED> or
		2323	C<IO::AIO::MAP_PRIVATE>,
		2324	or a number of system-specific flags (when not available, the are C<0>):
		2325	C<IO::AIO::MAP_ANONYMOUS> (which is set to C<MAP_ANON> if your system only provides this constant),
		2326	C<IO::AIO::MAP_LOCKED>,
		2327	C<IO::AIO::MAP_NORESERVE>,
		2328	C<IO::AIO::MAP_POPULATE>,
		2329	C<IO::AIO::MAP_NONBLOCK>,
		2330	C<IO::AIO::MAP_FIXED>,
		2331	C<IO::AIO::MAP_GROWSDOWN>,
		2332	C<IO::AIO::MAP_32BIT>,
		2333	C<IO::AIO::MAP_HUGETLB> or
		2334	C<IO::AIO::MAP_STACK>.
		2335
		2336	If C<$fh> is C<undef>, then a file descriptor of C<-1> is passed.
		2337
		2338	C<$offset> is the offset from the start of the file - it generally must be
		2339	a multiple of C<IO::AIO::PAGESIZE> and defaults to C<0>.
		2340
		2341	Example:
		2342
		2343	use Digest::MD5;
		2344	use IO::AIO;
		2345
		2346	open my $fh, "<verybigfile"
		2347	or die "$!";
		2348
		2349	IO::AIO::mmap my $data, -s $fh, IO::AIO::PROT_READ, IO::AIO::MAP_SHARED, $fh
		2350	or die "verybigfile: $!";
		2351
		2352	my $fast_md5 = md5 $data;
		2353
		2354	=item IO::AIO::munmap $scalar
		2355
		2356	Removes a previous mmap and undefines the C<$scalar>.
		2357
		2358	=item IO::AIO::mremap $scalar, $new_length, $flags = MREMAP_MAYMOVE[, $new_address = 0]
		2359
		2360	Calls the Linux-specific mremap(2) system call. The C<$scalar> must have
		2361	been mapped by C<IO::AIO::mmap>, and C<$flags> must currently either be
		2362	C<0> or C<IO::AIO::MREMAP_MAYMOVE>.
		2363
		2364	Returns true if successful, and false otherwise. If the underlying mmapped
		2365	region has changed address, then the true value has the numerical value
		2366	C<1>, otherwise it has the numerical value C<0>:
		2367
		2368	my $success = IO::AIO::mremap $mmapped, 8192, IO::AIO::MREMAP_MAYMOVE
		2369	or die "mremap: $!";
		2370
		2371	if ($success*1) {
		2372	warn "scalar has chanegd address in memory\n";
		2373	}
		2374
		2375	C<IO::AIO::MREMAP_FIXED> and the C<$new_address> argument are currently
		2376	implemented, but not supported and might go away in a future version.
		2377
		2378	On systems where this call is not supported or is not emulated, this call
		2379	returns falls and sets C<$!> to C<ENOSYS>.
		2380
		2381	=item IO::AIO::mlockall $flags
		2382
		2383	Calls the C<eio_mlockall_sync> function, which is like C<aio_mlockall>,
		2384	but is blocking.
		2385
		2386	=item IO::AIO::munlock $scalar, $offset = 0, $length = undef
		2387
		2388	Calls the C<munlock> function, undoing the effects of a previous
		2389	C<aio_mlock> call (see its description for details).
		2390
		2391	=item IO::AIO::munlockall
		2392
		2393	Calls the C<munlockall> function.
		2394
		2395	On systems that do not implement C<munlockall>, this function returns
		2396	ENOSYS, otherwise the return value of C<munlockall>.
		2397
		2398	=item IO::AIO::splice $r_fh, $r_off, $w_fh, $w_off, $length, $flags
		2399
		2400	Calls the GNU/Linux C<splice(2)> syscall, if available. If C<$r_off> or
		2401	C<$w_off> are C<undef>, then C<NULL> is passed for these, otherwise they
		2402	should be the file offset.
		2403
		2404	C<$r_fh> and C<$w_fh> should not refer to the same file, as splice might
		2405	silently corrupt the data in this case.
		2406
		2407	The following symbol flag values are available: C<IO::AIO::SPLICE_F_MOVE>,
		2408	C<IO::AIO::SPLICE_F_NONBLOCK>, C<IO::AIO::SPLICE_F_MORE> and
		2409	C<IO::AIO::SPLICE_F_GIFT>.
		2410
		2411	See the C<splice(2)> manpage for details.
		2412
		2413	=item IO::AIO::tee $r_fh, $w_fh, $length, $flags
		2414
		2415	Calls the GNU/Linux C<tee(2)> syscall, see its manpage and the
		2416	description for C<IO::AIO::splice> above for details.
		2417
		2418	=item $actual_size = IO::AIO::pipesize $r_fh[, $new_size]
		2419
		2420	Attempts to query or change the pipe buffer size. Obviously works only
		2421	on pipes, and currently works only on GNU/Linux systems, and fails with
		2422	C<-1>/C<ENOSYS> everywhere else. If anybody knows how to influence pipe buffer
		2423	size on other systems, drop me a note.
		2424
		2425	=item ($rfh, $wfh) = IO::AIO::pipe2 [$flags]
		2426
		2427	This is a direct interface to the Linux L<pipe2(2)> system call. If
		2428	C<$flags> is missing or C<0>, then this should be the same as a call to
		2429	perl's built-in C<pipe> function and create a new pipe, and works on
		2430	systems that lack the pipe2 syscall. On win32, this case invokes C<_pipe
		2431	(..., 4096, O_BINARY)>.
		2432
		2433	If C<$flags> is non-zero, it tries to invoke the pipe2 system call with
		2434	the given flags (Linux 2.6.27, glibc 2.9).
		2435
		2436	On success, the read and write file handles are returned.
		2437
		2438	On error, nothing will be returned. If the pipe2 syscall is missing and
		2439	C<$flags> is non-zero, fails with C<ENOSYS>.
		2440
		2441	Please refer to L<pipe2(2)> for more info on the C<$flags>, but at the
		2442	time of this writing, C<IO::AIO::O_CLOEXEC>, C<IO::AIO::O_NONBLOCK> and
		2443	C<IO::AIO::O_DIRECT> (Linux 3.4, for packet-based pipes) were supported.
		2444
		2445	Example: create a pipe race-free w.r.t. threads and fork:
		2446
		2447	my ($rfh, $wfh) = IO::AIO::pipe2 IO::AIO::O_CLOEXEC
		2448	or die "pipe2: $!\n";
		2449
		2450	=item $fh = IO::AIO::memfd_create $pathname[, $flags]
		2451
		2452	This is a direct interface to the Linux L<memfd_create(2)> system
		2453	call. The (unhelpful) default for C<$flags> is C<0>, but your default
		2454	should be C<IO::AIO::MFD_CLOEXEC>.
		2455
		2456	On success, the new memfd filehandle is returned, otherwise returns
		2457	C<undef>. If the memfd_create syscall is missing, fails with C<ENOSYS>.
		2458
		2459	Please refer to L<memfd_create(2)> for more info on this call.
		2460
		2461	The following C<$flags> values are available: C<IO::AIO::MFD_CLOEXEC>,
		2462	C<IO::AIO::MFD_ALLOW_SEALING> and C<IO::AIO::MFD_HUGETLB>.
		2463
		2464	Example: create a new memfd.
		2465
		2466	my $fh = IO::AIO::memfd_create "somenameforprocfd", IO::AIO::MFD_CLOEXEC
		2467	or die "m,emfd_create: $!\n";
		2468	=item $fh = IO::AIO::eventfd [$initval, [$flags]]
		2469
		2470	This is a direct interface to the Linux L<eventfd(2)> system call. The
		2471	(unhelpful) defaults for C<$initval> and C<$flags> are C<0> for both.
		2472
		2473	On success, the new eventfd filehandle is returned, otherwise returns
		2474	C<undef>. If the eventfd syscall is missing, fails with C<ENOSYS>.
		2475
		2476	Please refer to L<eventfd(2)> for more info on this call.
		2477
		2478	The following symbol flag values are available: C<IO::AIO::EFD_CLOEXEC>,
		2479	C<IO::AIO::EFD_NONBLOCK> and C<IO::AIO::EFD_SEMAPHORE> (Linux 2.6.30).
		2480
		2481	Example: create a new eventfd filehandle:
		2482
		2483	$fh = IO::AIO::eventfd 0, IO::AIO::EFD_CLOEXEC
		2484	or die "eventfd: $!\n";
		2485
		2486	=item $fh = IO::AIO::timerfd_create $clockid[, $flags]
		2487
		2488	This is a direct interface to the Linux L<timerfd_create(2)> system
		2489	call. The (unhelpful) default for C<$flags> is C<0>, but your default
		2490	should be C<IO::AIO::TFD_CLOEXEC>.
		2491
		2492	On success, the new timerfd filehandle is returned, otherwise returns
		2493	C<undef>. If the timerfd_create syscall is missing, fails with C<ENOSYS>.
		2494
		2495	Please refer to L<timerfd_create(2)> for more info on this call.
		2496
		2497	The following C<$clockid> values are
		2498	available: C<IO::AIO::CLOCK_REALTIME>, C<IO::AIO::CLOCK_MONOTONIC>
		2499	C<IO::AIO::CLOCK_CLOCK_BOOTTIME> (Linux 3.15)
		2500	C<IO::AIO::CLOCK_CLOCK_REALTIME_ALARM> (Linux 3.11) and
		2501	C<IO::AIO::CLOCK_CLOCK_BOOTTIME_ALARM> (Linux 3.11).
		2502
		2503	The following C<$flags> values are available (Linux
		2504	2.6.27): C<IO::AIO::TFD_NONBLOCK> and C<IO::AIO::TFD_CLOEXEC>.
		2505
		2506	Example: create a new timerfd and set it to one-second repeated alarms,
		2507	then wait for two alarms:
		2508
		2509	my $fh = IO::AIO::timerfd_create IO::AIO::CLOCK_BOOTTIME, IO::AIO::TFD_CLOEXEC
		2510	or die "timerfd_create: $!\n";
		2511
		2512	defined IO::AIO::timerfd_settime $fh, 0, 1, 1
		2513	or die "timerfd_settime: $!\n";
		2514
		2515	for (1..2) {
		2516	8 == sysread $fh, my $buf, 8
		2517	or die "timerfd read failure\n";
		2518
		2519	printf "number of expirations (likely 1): %d\n",
		2520	unpack "Q", $buf;
		2521	}
		2522
		2523	=item ($cur_interval, $cur_value) = IO::AIO::timerfd_settime $fh, $flags, $new_interval, $nbw_value
		2524
		2525	This is a direct interface to the Linux L<timerfd_settime(2)> system
		2526	call. Please refer to its manpage for more info on this call.
		2527
		2528	The new itimerspec is specified using two (possibly fractional) second
		2529	values, C<$new_interval> and C<$new_value>).
		2530
		2531	On success, the current interval and value are returned (as per
		2532	C<timerfd_gettime>). On failure, the empty list is returned.
		2533
		2534	The following C<$flags> values are
		2535	available: C<IO::AIO::TFD_TIMER_ABSTIME> and
		2536	C<IO::AIO::TFD_TIMER_CANCEL_ON_SET>.
		2537
		2538	See C<IO::AIO::timerfd_create> for a full example.
		2539
		2540	=item ($cur_interval, $cur_value) = IO::AIO::timerfd_gettime $fh
		2541
		2542	This is a direct interface to the Linux L<timerfd_gettime(2)> system
		2543	call. Please refer to its manpage for more info on this call.
		2544
		2545	On success, returns the current values of interval and value for the given
		2546	timerfd (as potentially fractional second values). On failure, the empty
		2547	list is returned.
		2548
		2549	=back
		2550
369	=cut	2551	=cut
370		2552
371	# support function to convert a fd into a perl filehandle
372	sub _fd2fh {
373	return undef if $_[0] < 0;
374
375	# try to generate nice filehandles
376	my $sym = "IO::AIO::fd#$_[0]";
377	local *$sym;
378
379	open *$sym, "+<&=$_[0]" # usually works under any unix
380	or open *$sym, "<&=$_[0]" # cygwin needs this
381	or open *$sym, ">&=$_[0]" # or this
382	or return undef;
383
384	*$sym
385	}
386
387	min_parallel 4;	2553	min_parallel 8;
388		2554
389	END {	2555	END { flush }
390	max_parallel 0;
391	}
392		2556
393	1;	2557	1;
394		2558
		2559	=head1 EVENT LOOP INTEGRATION
		2560
		2561	It is recommended to use L<AnyEvent::AIO> to integrate IO::AIO
		2562	automatically into many event loops:
		2563
		2564	# AnyEvent integration (EV, Event, Glib, Tk, POE, urxvt, pureperl...)
		2565	use AnyEvent::AIO;
		2566
		2567	You can also integrate IO::AIO manually into many event loops, here are
		2568	some examples of how to do this:
		2569
		2570	# EV integration
		2571	my $aio_w = EV::io IO::AIO::poll_fileno, EV::READ, \&IO::AIO::poll_cb;
		2572
		2573	# Event integration
		2574	Event->io (fd => IO::AIO::poll_fileno,
		2575	poll => 'r',
		2576	cb => \&IO::AIO::poll_cb);
		2577
		2578	# Glib/Gtk2 integration
		2579	add_watch Glib::IO IO::AIO::poll_fileno,
		2580	in => sub { IO::AIO::poll_cb; 1 };
		2581
		2582	# Tk integration
		2583	Tk::Event::IO->fileevent (IO::AIO::poll_fileno, "",
		2584	readable => \&IO::AIO::poll_cb);
		2585
		2586	# Danga::Socket integration
		2587	Danga::Socket->AddOtherFds (IO::AIO::poll_fileno =>
		2588	\&IO::AIO::poll_cb);
		2589
395	=head2 FORK BEHAVIOUR	2590	=head2 FORK BEHAVIOUR
396		2591
397	Before the fork, IO::AIO enters a quiescent state where no requests	2592	Usage of pthreads in a program changes the semantics of fork
398	can be added in other threads and no results will be processed. After	2593	considerably. Specifically, only async-safe functions can be called after
399	the fork the parent simply leaves the quiescent state and continues	2594	fork. Perl doesn't know about this, so in general, you cannot call fork
400	request/result processing, while the child clears the request/result	2595	with defined behaviour in perl if pthreads are involved. IO::AIO uses
401	queue (so the requests started before the fork will only be handled in	2596	pthreads, so this applies, but many other extensions and (for inexplicable
402	the parent). Threats will be started on demand until the limit ste in the	2597	reasons) perl itself often is linked against pthreads, so this limitation
403	parent process has been reached again.	2598	applies to quite a lot of perls.
		2599
		2600	This module no longer tries to fight your OS, or POSIX. That means IO::AIO
		2601	only works in the process that loaded it. Forking is fully supported, but
		2602	using IO::AIO in the child is not.
		2603
		2604	You might get around by not I<using> IO::AIO before (or after)
		2605	forking. You could also try to call the L<IO::AIO::reinit> function in the
		2606	child:
		2607
		2608	=over 4
		2609
		2610	=item IO::AIO::reinit
		2611
		2612	Abandons all current requests and I/O threads and simply reinitialises all
		2613	data structures. This is not an operation supported by any standards, but
		2614	happens to work on GNU/Linux and some newer BSD systems.
		2615
		2616	The only reasonable use for this function is to call it after forking, if
		2617	C<IO::AIO> was used in the parent. Calling it while IO::AIO is active in
		2618	the process will result in undefined behaviour. Calling it at any time
		2619	will also result in any undefined (by POSIX) behaviour.
		2620
		2621	=back
		2622
		2623	=head2 LINUX-SPECIFIC CALLS
		2624
		2625	When a call is documented as "linux-specific" then this means it
		2626	originated on GNU/Linux. C<IO::AIO> will usually try to autodetect the
		2627	availability and compatibility of such calls regardless of the platform
		2628	it is compiled on, so platforms such as FreeBSD which often implement
		2629	these calls will work. When in doubt, call them and see if they fail wth
		2630	C<ENOSYS>.
		2631
		2632	=head2 MEMORY USAGE
		2633
		2634	Per-request usage:
		2635
		2636	Each aio request uses - depending on your architecture - around 100-200
		2637	bytes of memory. In addition, stat requests need a stat buffer (possibly
		2638	a few hundred bytes), readdir requires a result buffer and so on. Perl
		2639	scalars and other data passed into aio requests will also be locked and
		2640	will consume memory till the request has entered the done state.
		2641
		2642	This is not awfully much, so queuing lots of requests is not usually a
		2643	problem.
		2644
		2645	Per-thread usage:
		2646
		2647	In the execution phase, some aio requests require more memory for
		2648	temporary buffers, and each thread requires a stack and other data
		2649	structures (usually around 16k-128k, depending on the OS).
		2650
		2651	=head1 KNOWN BUGS
		2652
		2653	Known bugs will be fixed in the next release :)
		2654
		2655	=head1 KNOWN ISSUES
		2656
		2657	Calls that try to "import" foreign memory areas (such as C<IO::AIO::mmap>
		2658	or C<IO::AIO::aio_slurp>) do not work with generic lvalues, such as
		2659	non-created hash slots or other scalars I didn't think of. It's best to
		2660	avoid such and either use scalar variables or making sure that the scalar
		2661	exists (e.g. by storing C<undef>) and isn't "funny" (e.g. tied).
		2662
		2663	I am not sure anything can be done about this, so this is considered a
		2664	known issue, rather than a bug.
404		2665
405	=head1 SEE ALSO	2666	=head1 SEE ALSO
406		2667
407	L<Coro>, L<Linux::AIO>.	2668	L<AnyEvent::AIO> for easy integration into event loops, L<Coro::AIO> for a
		2669	more natural syntax.
408		2670
409	=head1 AUTHOR	2671	=head1 AUTHOR
410		2672
411	Marc Lehmann <schmorp@schmorp.de>	2673	Marc Lehmann <schmorp@schmorp.de>
412	http://home.schmorp.de/	2674	http://home.schmorp.de/

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