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Revision 1.24 by root, Sun Jul 31 18:45:48 2005 UTC vs.
Revision 1.298 by root, Thu Nov 29 21:48:44 2018 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 = 1.1;	176	our $VERSION = 4.6;
69		177
70	@EXPORT = qw(aio_read aio_write aio_open aio_close aio_stat aio_lstat aio_unlink	178	our @AIO_REQ = qw(aio_sendfile aio_seek aio_read aio_write aio_open aio_close
71	aio_fsync aio_fdatasync aio_readahead);	179	aio_stat aio_lstat aio_unlink aio_rmdir aio_readdir aio_readdirx
72	@EXPORT_OK = qw(poll_fileno poll_cb min_parallel max_parallel max_outstanding nreqs);	180	aio_scandir aio_symlink aio_readlink aio_realpath aio_fcntl aio_ioctl
		181	aio_sync aio_fsync aio_syncfs aio_fdatasync aio_sync_file_range
		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';
73		202
74	require XSLoader;	203	require XSLoader;
75	XSLoader::load IO::AIO, $VERSION;	204	XSLoader::load ("IO::AIO", $VERSION);
76	}	205	}
77		206
78	=head1 FUNCTIONS	207	=head1 FUNCTIONS
79		208
80	=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	$nfd = IO::AIO::get_fdlimit [EXPERIMENTAL]
		284	IO::AIO::min_fdlimit $nfd [EXPERIMENTAL]
		285
		286	IO::AIO::sendfile $ofh, $ifh, $offset, $count
		287	IO::AIO::fadvise $fh, $offset, $len, $advice
		288	IO::AIO::mmap $scalar, $length, $prot, $flags[, $fh[, $offset]]
		289	IO::AIO::munmap $scalar
		290	IO::AIO::mremap $scalar, $new_length, $flags[, $new_address]
		291	IO::AIO::madvise $scalar, $offset, $length, $advice
		292	IO::AIO::mprotect $scalar, $offset, $length, $protect
		293	IO::AIO::munlock $scalar, $offset = 0, $length = undef
		294	IO::AIO::munlockall
		295
		296	=head2 API NOTES
81		297
82	All the C<aio_*> calls are more or less thin wrappers around the syscall	298	All the C<aio_*> calls are more or less thin wrappers around the syscall
83	with the same name (sans C<aio_>). The arguments are similar or identical,	299	with the same name (sans C<aio_>). The arguments are similar or identical,
84	and they all accept an additional (and optional) C<$callback> argument	300	and they all accept an additional (and optional) C<$callback> argument
85	which must be a code reference. This code reference will get called with	301	which must be a code reference. This code reference will be called after
86	the syscall return code (e.g. most syscalls return C<-1> on error, unlike	302	the syscall has been executed in an asynchronous fashion. The results
87	perl, which usually delivers "false") as it's sole argument when the given	303	of the request will be passed as arguments to the callback (and, if an
88	syscall has been executed asynchronously.	304	error occured, in C<$!>) - for most requests the syscall return code (e.g.
		305	most syscalls return C<-1> on error, unlike perl, which usually delivers
		306	"false").
		307
		308	Some requests (such as C<aio_readdir>) pass the actual results and
		309	communicate failures by passing C<undef>.
89		310
90	All functions expecting a filehandle keep a copy of the filehandle	311	All functions expecting a filehandle keep a copy of the filehandle
91	internally until the request has finished.	312	internally until the request has finished.
92		313
		314	All functions return request objects of type L<IO::AIO::REQ> that allow
		315	further manipulation of those requests while they are in-flight.
		316
93	The filenames you pass to these routines I<must> be absolute. The reason	317	The pathnames you pass to these routines I<should> be absolute. The
94	for this is that at the time the request is being executed, the current	318	reason for this is that at the time the request is being executed, the
95	working directory could have changed. Alternatively, you can make sure	319	current working directory could have changed. Alternatively, you can
96	that you never change the current working directory.	320	make sure that you never change the current working directory anywhere
		321	in the program and then use relative paths. You can also take advantage
		322	of IO::AIOs working directory abstraction, that lets you specify paths
		323	relative to some previously-opened "working directory object" - see the
		324	description of the C<IO::AIO::WD> class later in this document.
		325
		326	To encode pathnames as octets, either make sure you either: a) always pass
		327	in filenames you got from outside (command line, readdir etc.) without
		328	tinkering, b) are in your native filesystem encoding, c) use the Encode
		329	module and encode your pathnames to the locale (or other) encoding in
		330	effect in the user environment, d) use Glib::filename_from_unicode on
		331	unicode filenames or e) use something else to ensure your scalar has the
		332	correct contents.
		333
		334	This works, btw. independent of the internal UTF-8 bit, which IO::AIO
		335	handles correctly whether it is set or not.
		336
		337	=head2 AIO REQUEST FUNCTIONS
97		338
98	=over 4	339	=over 4
99		340
		341	=item $prev_pri = aioreq_pri [$pri]
		342
		343	Returns the priority value that would be used for the next request and, if
		344	C<$pri> is given, sets the priority for the next aio request.
		345
		346	The default priority is C<0>, the minimum and maximum priorities are C<-4>
		347	and C<4>, respectively. Requests with higher priority will be serviced
		348	first.
		349
		350	The priority will be reset to C<0> after each call to one of the C<aio_*>
		351	functions.
		352
		353	Example: open a file with low priority, then read something from it with
		354	higher priority so the read request is serviced before other low priority
		355	open requests (potentially spamming the cache):
		356
		357	aioreq_pri -3;
		358	aio_open ..., sub {
		359	return unless $_[0];
		360
		361	aioreq_pri -2;
		362	aio_read $_[0], ..., sub {
		363	...
		364	};
		365	};
		366
		367
		368	=item aioreq_nice $pri_adjust
		369
		370	Similar to C<aioreq_pri>, but subtracts the given value from the current
		371	priority, so the effect is cumulative.
		372
		373
100	=item aio_open $pathname, $flags, $mode, $callback	374	=item aio_open $pathname, $flags, $mode, $callback->($fh)
101		375
102	Asynchronously open or create a file and call the callback with a newly	376	Asynchronously open or create a file and call the callback with a newly
103	created filehandle for the file.	377	created filehandle for the file (or C<undef> in case of an error).
104		378
105	The pathname passed to C<aio_open> must be absolute. See API NOTES, above,	379	The pathname passed to C<aio_open> must be absolute. See API NOTES, above,
106	for an explanation.	380	for an explanation.
107		381
108	The C<$flags> argument is a bitmask. See the C<Fcntl> module for a	382	The C<$flags> argument is a bitmask. See the C<Fcntl> module for a
109	list. They are the same as used by C<sysopen>.	383	list. They are the same as used by C<sysopen>.
110		384
111	Likewise, C<$mode> specifies the mode of the newly created file, if it	385	Likewise, C<$mode> specifies the mode of the newly created file, if it
112	didn't exist and C<O_CREAT> has been given, just like perl's C<sysopen>,	386	didn't exist and C<O_CREAT> has been given, just like perl's C<sysopen>,
113	except that it is mandatory (i.e. use C<0> if you don't create new files,	387	except that it is mandatory (i.e. use C<0> if you don't create new files,
114	and C<0666> or C<0777> if you do).	388	and C<0666> or C<0777> if you do). Note that the C<$mode> will be modified
		389	by the umask in effect then the request is being executed, so better never
		390	change the umask.
115		391
116	Example:	392	Example:
117		393
118	aio_open "/etc/passwd", O_RDONLY, 0, sub {	394	aio_open "/etc/passwd", IO::AIO::O_RDONLY, 0, sub {
119	if ($_[0]) {	395	if ($_[0]) {
120	print "open successful, fh is $_[0]\n";	396	print "open successful, fh is $_[0]\n";
121	...	397	...
122	} else {	398	} else {
123	die "open failed: $!\n";	399	die "open failed: $!\n";
124	}	400	}
125	};	401	};
126		402
		403	In addition to all the common open modes/flags (C<O_RDONLY>, C<O_WRONLY>,
		404	C<O_RDWR>, C<O_CREAT>, C<O_TRUNC>, C<O_EXCL> and C<O_APPEND>), the
		405	following POSIX and non-POSIX constants are available (missing ones on
		406	your system are, as usual, C<0>):
		407
		408	C<O_ASYNC>, C<O_DIRECT>, C<O_NOATIME>, C<O_CLOEXEC>, C<O_NOCTTY>, C<O_NOFOLLOW>,
		409	C<O_NONBLOCK>, C<O_EXEC>, C<O_SEARCH>, C<O_DIRECTORY>, C<O_DSYNC>,
		410	C<O_RSYNC>, C<O_SYNC>, C<O_PATH>, C<O_TMPFILE>, C<O_TTY_INIT> and C<O_ACCMODE>.
		411
		412
127	=item aio_close $fh, $callback	413	=item aio_close $fh, $callback->($status)
128		414
129	Asynchronously close a file and call the callback with the result	415	Asynchronously close a file and call the callback with the result
130	code. I<WARNING:> although accepted, you should not pass in a perl	416	code.
131	filehandle here, as perl will likely close the file descriptor another
132	time when the filehandle is destroyed. Normally, you can safely call perls
133	C<close> or just let filehandles go out of scope.
134		417
135	This is supposed to be a bug in the API, so that might change. It's	418	Unfortunately, you can't do this to perl. Perl I<insists> very strongly on
136	therefore best to avoid this function.	419	closing the file descriptor associated with the filehandle itself.
137		420
		421	Therefore, C<aio_close> will not close the filehandle - instead it will
		422	use dup2 to overwrite the file descriptor with the write-end of a pipe
		423	(the pipe fd will be created on demand and will be cached).
		424
		425	Or in other words: the file descriptor will be closed, but it will not be
		426	free for reuse until the perl filehandle is closed.
		427
		428	=cut
		429
		430	=item aio_seek $fh, $offset, $whence, $callback->($offs)
		431
		432	Seeks the filehandle to the new C<$offset>, similarly to perl's
		433	C<sysseek>. The C<$whence> can use the traditional values (C<0> for
		434	C<IO::AIO::SEEK_SET>, C<1> for C<IO::AIO::SEEK_CUR> or C<2> for
		435	C<IO::AIO::SEEK_END>).
		436
		437	The resulting absolute offset will be passed to the callback, or C<-1> in
		438	case of an error.
		439
		440	In theory, the C<$whence> constants could be different than the
		441	corresponding values from L<Fcntl>, but perl guarantees they are the same,
		442	so don't panic.
		443
		444	As a GNU/Linux (and maybe Solaris) extension, also the constants
		445	C<IO::AIO::SEEK_DATA> and C<IO::AIO::SEEK_HOLE> are available, if they
		446	could be found. No guarantees about suitability for use in C<aio_seek> or
		447	Perl's C<sysseek> can be made though, although I would naively assume they
		448	"just work".
		449
138	=item aio_read $fh,$offset,$length, $data,$dataoffset,$callback	450	=item aio_read $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
139		451
140	=item aio_write $fh,$offset,$length, $data,$dataoffset,$callback	452	=item aio_write $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
141		453
142	Reads or writes C<length> bytes from the specified C<fh> and C<offset>	454	Reads or writes C<$length> bytes from or to the specified C<$fh> and
143	into the scalar given by C<data> and offset C<dataoffset> and calls the	455	C<$offset> into the scalar given by C<$data> and offset C<$dataoffset> and
144	callback without the actual number of bytes read (or -1 on error, just	456	calls the callback with the actual number of bytes transferred (or -1 on
145	like the syscall).	457	error, just like the syscall).
		458
		459	C<aio_read> will, like C<sysread>, shrink or grow the C<$data> scalar to
		460	offset plus the actual number of bytes read.
		461
		462	If C<$offset> is undefined, then the current file descriptor offset will
		463	be used (and updated), otherwise the file descriptor offset will not be
		464	changed by these calls.
		465
		466	If C<$length> is undefined in C<aio_write>, use the remaining length of
		467	C<$data>.
		468
		469	If C<$dataoffset> is less than zero, it will be counted from the end of
		470	C<$data>.
		471
		472	The C<$data> scalar I<MUST NOT> be modified in any way while the request
		473	is outstanding. Modifying it can result in segfaults or World War III (if
		474	the necessary/optional hardware is installed).
146		475
147	Example: Read 15 bytes at offset 7 into scalar C<$buffer>, starting at	476	Example: Read 15 bytes at offset 7 into scalar C<$buffer>, starting at
148	offset C<0> within the scalar:	477	offset C<0> within the scalar:
149		478
150	aio_read $fh, 7, 15, $buffer, 0, sub {	479	aio_read $fh, 7, 15, $buffer, 0, sub {
151	$_[0] > 0 or die "read error: $!";	480	$_[0] > 0 or die "read error: $!";
152	print "read $_[0] bytes: <$buffer>\n";	481	print "read $_[0] bytes: <$buffer>\n";
153	};	482	};
154		483
		484
		485	=item aio_sendfile $out_fh, $in_fh, $in_offset, $length, $callback->($retval)
		486
		487	Tries to copy C<$length> bytes from C<$in_fh> to C<$out_fh>. It starts
		488	reading at byte offset C<$in_offset>, and starts writing at the current
		489	file offset of C<$out_fh>. Because of that, it is not safe to issue more
		490	than one C<aio_sendfile> per C<$out_fh>, as they will interfere with each
		491	other. The same C<$in_fh> works fine though, as this function does not
		492	move or use the file offset of C<$in_fh>.
		493
		494	Please note that C<aio_sendfile> can read more bytes from C<$in_fh> than
		495	are written, and there is no way to find out how many more bytes have been
		496	read from C<aio_sendfile> alone, as C<aio_sendfile> only provides the
		497	number of bytes written to C<$out_fh>. Only if the result value equals
		498	C<$length> one can assume that C<$length> bytes have been read.
		499
		500	Unlike with other C<aio_> functions, it makes a lot of sense to use
		501	C<aio_sendfile> on non-blocking sockets, as long as one end (typically
		502	the C<$in_fh>) is a file - the file I/O will then be asynchronous, while
		503	the socket I/O will be non-blocking. Note, however, that you can run
		504	into a trap where C<aio_sendfile> reads some data with readahead, then
		505	fails to write all data, and when the socket is ready the next time, the
		506	data in the cache is already lost, forcing C<aio_sendfile> to again hit
		507	the disk. Explicit C<aio_read> + C<aio_write> let's you better control
		508	resource usage.
		509
		510	This call tries to make use of a native C<sendfile>-like syscall to
		511	provide zero-copy operation. For this to work, C<$out_fh> should refer to
		512	a socket, and C<$in_fh> should refer to an mmap'able file.
		513
		514	If a native sendfile cannot be found or it fails with C<ENOSYS>,
		515	C<EINVAL>, C<ENOTSUP>, C<EOPNOTSUPP>, C<EAFNOSUPPORT>, C<EPROTOTYPE> or
		516	C<ENOTSOCK>, it will be emulated, so you can call C<aio_sendfile> on any
		517	type of filehandle regardless of the limitations of the operating system.
		518
		519	As native sendfile syscalls (as practically any non-POSIX interface hacked
		520	together in a hurry to improve benchmark numbers) tend to be rather buggy
		521	on many systems, this implementation tries to work around some known bugs
		522	in Linux and FreeBSD kernels (probably others, too), but that might fail,
		523	so you really really should check the return value of C<aio_sendfile> -
		524	fewer bytes than expected might have been transferred.
		525
		526
155	=item aio_readahead $fh,$offset,$length, $callback	527	=item aio_readahead $fh,$offset,$length, $callback->($retval)
156
157	Asynchronously reads the specified byte range into the page cache, using
158	the C<readahead> syscall. If that syscall doesn't exist (likely if your OS
159	isn't Linux) the status will be C<-1> and C<$!> is set to C<ENOSYS>.
160		528
161	C<aio_readahead> populates the page cache with data from a file so that	529	C<aio_readahead> populates the page cache with data from a file so that
162	subsequent reads from that file will not block on disk I/O. The C<$offset>	530	subsequent reads from that file will not block on disk I/O. The C<$offset>
163	argument specifies the starting point from which data is to be read and	531	argument specifies the starting point from which data is to be read and
164	C<$length> specifies the number of bytes to be read. I/O is performed in	532	C<$length> specifies the number of bytes to be read. I/O is performed in
165	whole pages, so that offset is effectively rounded down to a page boundary	533	whole pages, so that offset is effectively rounded down to a page boundary
166	and bytes are read up to the next page boundary greater than or equal to	534	and bytes are read up to the next page boundary greater than or equal to
167	(off-set+length). C<aio_readahead> does not read beyond the end of the	535	(off-set+length). C<aio_readahead> does not read beyond the end of the
168	file. The current file offset of the file is left unchanged.	536	file. The current file offset of the file is left unchanged.
169		537
		538	If that syscall doesn't exist (likely if your kernel isn't Linux) it will
		539	be emulated by simply reading the data, which would have a similar effect.
		540
		541
170	=item aio_stat $fh_or_path, $callback	542	=item aio_stat $fh_or_path, $callback->($status)
171		543
172	=item aio_lstat $fh, $callback	544	=item aio_lstat $fh, $callback->($status)
173		545
174	Works like perl's C<stat> or C<lstat> in void context. The callback will	546	Works almost exactly like perl's C<stat> or C<lstat> in void context. The
175	be called after the stat and the results will be available using C<stat _>	547	callback will be called after the stat and the results will be available
176	or C<-s _> etc...	548	using C<stat _> or C<-s _> and other tests (with the exception of C<-B>
		549	and C<-T>).
177		550
178	The pathname passed to C<aio_stat> must be absolute. See API NOTES, above,	551	The pathname passed to C<aio_stat> must be absolute. See API NOTES, above,
179	for an explanation.	552	for an explanation.
180		553
181	Currently, the stats are always 64-bit-stats, i.e. instead of returning an	554	Currently, the stats are always 64-bit-stats, i.e. instead of returning an
182	error when stat'ing a large file, the results will be silently truncated	555	error when stat'ing a large file, the results will be silently truncated
183	unless perl itself is compiled with large file support.	556	unless perl itself is compiled with large file support.
		557
		558	To help interpret the mode and dev/rdev stat values, IO::AIO offers the
		559	following constants and functions (if not implemented, the constants will
		560	be C<0> and the functions will either C<croak> or fall back on traditional
		561	behaviour).
		562
		563	C<S_IFMT>, C<S_IFIFO>, C<S_IFCHR>, C<S_IFBLK>, C<S_IFLNK>, C<S_IFREG>,
		564	C<S_IFDIR>, C<S_IFWHT>, C<S_IFSOCK>, C<IO::AIO::major $dev_t>,
		565	C<IO::AIO::minor $dev_t>, C<IO::AIO::makedev $major, $minor>.
		566
		567	To access higher resolution stat timestamps, see L<SUBSECOND STAT TIME
		568	ACCESS>.
184		569
185	Example: Print the length of F</etc/passwd>:	570	Example: Print the length of F</etc/passwd>:
186		571
187	aio_stat "/etc/passwd", sub {	572	aio_stat "/etc/passwd", sub {
188	$_[0] and die "stat failed: $!";	573	$_[0] and die "stat failed: $!";
189	print "size is ", -s _, "\n";	574	print "size is ", -s _, "\n";
190	};	575	};
191		576
		577
		578	=item aio_statvfs $fh_or_path, $callback->($statvfs)
		579
		580	Works like the POSIX C<statvfs> or C<fstatvfs> syscalls, depending on
		581	whether a file handle or path was passed.
		582
		583	On success, the callback is passed a hash reference with the following
		584	members: C<bsize>, C<frsize>, C<blocks>, C<bfree>, C<bavail>, C<files>,
		585	C<ffree>, C<favail>, C<fsid>, C<flag> and C<namemax>. On failure, C<undef>
		586	is passed.
		587
		588	The following POSIX IO::AIO::ST_* constants are defined: C<ST_RDONLY> and
		589	C<ST_NOSUID>.
		590
		591	The following non-POSIX IO::AIO::ST_* flag masks are defined to
		592	their correct value when available, or to C<0> on systems that do
		593	not support them: C<ST_NODEV>, C<ST_NOEXEC>, C<ST_SYNCHRONOUS>,
		594	C<ST_MANDLOCK>, C<ST_WRITE>, C<ST_APPEND>, C<ST_IMMUTABLE>, C<ST_NOATIME>,
		595	C<ST_NODIRATIME> and C<ST_RELATIME>.
		596
		597	Example: stat C</wd> and dump out the data if successful.
		598
		599	aio_statvfs "/wd", sub {
		600	my $f = $_[0]
		601	or die "statvfs: $!";
		602
		603	use Data::Dumper;
		604	say Dumper $f;
		605	};
		606
		607	# result:
		608	{
		609	bsize => 1024,
		610	bfree => 4333064312,
		611	blocks => 10253828096,
		612	files => 2050765568,
		613	flag => 4096,
		614	favail => 2042092649,
		615	bavail => 4333064312,
		616	ffree => 2042092649,
		617	namemax => 255,
		618	frsize => 1024,
		619	fsid => 1810
		620	}
		621
		622	=item aio_utime $fh_or_path, $atime, $mtime, $callback->($status)
		623
		624	Works like perl's C<utime> function (including the special case of $atime
		625	and $mtime being undef). Fractional times are supported if the underlying
		626	syscalls support them.
		627
		628	When called with a pathname, uses utimensat(2) or utimes(2) if available,
		629	otherwise utime(2). If called on a file descriptor, uses futimens(2)
		630	or futimes(2) if available, otherwise returns ENOSYS, so this is not
		631	portable.
		632
		633	Examples:
		634
		635	# set atime and mtime to current time (basically touch(1)):
		636	aio_utime "path", undef, undef;
		637	# set atime to current time and mtime to beginning of the epoch:
		638	aio_utime "path", time, undef; # undef==0
		639
		640
		641	=item aio_chown $fh_or_path, $uid, $gid, $callback->($status)
		642
		643	Works like perl's C<chown> function, except that C<undef> for either $uid
		644	or $gid is being interpreted as "do not change" (but -1 can also be used).
		645
		646	Examples:
		647
		648	# same as "chown root path" in the shell:
		649	aio_chown "path", 0, -1;
		650	# same as above:
		651	aio_chown "path", 0, undef;
		652
		653
		654	=item aio_truncate $fh_or_path, $offset, $callback->($status)
		655
		656	Works like truncate(2) or ftruncate(2).
		657
		658
		659	=item aio_allocate $fh, $mode, $offset, $len, $callback->($status)
		660
		661	Allocates or frees disk space according to the C<$mode> argument. See the
		662	linux C<fallocate> documentation for details.
		663
		664	C<$mode> is usually C<0> or C<IO::AIO::FALLOC_FL_KEEP_SIZE> to allocate
		665	space, or C<IO::AIO::FALLOC_FL_PUNCH_HOLE | IO::AIO::FALLOC_FL_KEEP_SIZE>,
		666	to deallocate a file range.
		667
		668	IO::AIO also supports C<FALLOC_FL_COLLAPSE_RANGE>, to remove a range
		669	(without leaving a hole), C<FALLOC_FL_ZERO_RANGE>, to zero a range,
		670	C<FALLOC_FL_INSERT_RANGE> to insert a range and C<FALLOC_FL_UNSHARE_RANGE>
		671	to unshare shared blocks (see your L<fallocate(2)> manpage).
		672
		673	The file system block size used by C<fallocate> is presumably the
		674	C<f_bsize> returned by C<statvfs>, but different filesystems and filetypes
		675	can dictate other limitations.
		676
		677	If C<fallocate> isn't available or cannot be emulated (currently no
		678	emulation will be attempted), passes C<-1> and sets C<$!> to C<ENOSYS>.
		679
		680
		681	=item aio_chmod $fh_or_path, $mode, $callback->($status)
		682
		683	Works like perl's C<chmod> function.
		684
		685
192	=item aio_unlink $pathname, $callback	686	=item aio_unlink $pathname, $callback->($status)
193		687
194	Asynchronously unlink (delete) a file and call the callback with the	688	Asynchronously unlink (delete) a file and call the callback with the
195	result code.	689	result code.
196		690
		691
		692	=item aio_mknod $pathname, $mode, $dev, $callback->($status)
		693
		694	[EXPERIMENTAL]
		695
		696	Asynchronously create a device node (or fifo). See mknod(2).
		697
		698	The only (POSIX-) portable way of calling this function is:
		699
		700	aio_mknod $pathname, IO::AIO::S_IFIFO | $mode, 0, sub { ...
		701
		702	See C<aio_stat> for info about some potentially helpful extra constants
		703	and functions.
		704
		705	=item aio_link $srcpath, $dstpath, $callback->($status)
		706
		707	Asynchronously create a new link to the existing object at C<$srcpath> at
		708	the path C<$dstpath> and call the callback with the result code.
		709
		710
		711	=item aio_symlink $srcpath, $dstpath, $callback->($status)
		712
		713	Asynchronously create a new symbolic link to the existing object at C<$srcpath> at
		714	the path C<$dstpath> and call the callback with the result code.
		715
		716
		717	=item aio_readlink $pathname, $callback->($link)
		718
		719	Asynchronously read the symlink specified by C<$path> and pass it to
		720	the callback. If an error occurs, nothing or undef gets passed to the
		721	callback.
		722
		723
		724	=item aio_realpath $pathname, $callback->($path)
		725
		726	Asynchronously make the path absolute and resolve any symlinks in
		727	C<$path>. The resulting path only consists of directories (same as
		728	L<Cwd::realpath>).
		729
		730	This request can be used to get the absolute path of the current working
		731	directory by passing it a path of F<.> (a single dot).
		732
		733
		734	=item aio_rename $srcpath, $dstpath, $callback->($status)
		735
		736	Asynchronously rename the object at C<$srcpath> to C<$dstpath>, just as
		737	rename(2) and call the callback with the result code.
		738
		739	On systems that support the AIO::WD working directory abstraction
		740	natively, the case C<[$wd, "."]> as C<$srcpath> is specialcased - instead
		741	of failing, C<rename> is called on the absolute path of C<$wd>.
		742
		743
		744	=item aio_rename2 $srcpath, $dstpath, $flags, $callback->($status)
		745
		746	Basically a version of C<aio_rename> with an additional C<$flags>
		747	argument. Calling this with C<$flags=0> is the same as calling
		748	C<aio_rename>.
		749
		750	Non-zero flags are currently only supported on GNU/Linux systems that
		751	support renameat2. Other systems fail with C<ENOSYS> in this case.
		752
		753	The following constants are available (missing ones are, as usual C<0>),
		754	see renameat2(2) for details:
		755
		756	C<IO::AIO::RENAME_NOREPLACE>, C<IO::AIO::RENAME_EXCHANGE>
		757	and C<IO::AIO::RENAME_WHITEOUT>.
		758
		759
		760	=item aio_mkdir $pathname, $mode, $callback->($status)
		761
		762	Asynchronously mkdir (create) a directory and call the callback with
		763	the result code. C<$mode> will be modified by the umask at the time the
		764	request is executed, so do not change your umask.
		765
		766
		767	=item aio_rmdir $pathname, $callback->($status)
		768
		769	Asynchronously rmdir (delete) a directory and call the callback with the
		770	result code.
		771
		772	On systems that support the AIO::WD working directory abstraction
		773	natively, the case C<[$wd, "."]> is specialcased - instead of failing,
		774	C<rmdir> is called on the absolute path of C<$wd>.
		775
		776
		777	=item aio_readdir $pathname, $callback->($entries)
		778
		779	Unlike the POSIX call of the same name, C<aio_readdir> reads an entire
		780	directory (i.e. opendir + readdir + closedir). The entries will not be
		781	sorted, and will B<NOT> include the C<.> and C<..> entries.
		782
		783	The callback is passed a single argument which is either C<undef> or an
		784	array-ref with the filenames.
		785
		786
		787	=item aio_readdirx $pathname, $flags, $callback->($entries, $flags)
		788
		789	Quite similar to C<aio_readdir>, but the C<$flags> argument allows one to
		790	tune behaviour and output format. In case of an error, C<$entries> will be
		791	C<undef>.
		792
		793	The flags are a combination of the following constants, ORed together (the
		794	flags will also be passed to the callback, possibly modified):
		795
		796	=over 4
		797
		798	=item IO::AIO::READDIR_DENTS
		799
		800	Normally the callback gets an arrayref consisting of names only (as
		801	with C<aio_readdir>). If this flag is set, then the callback gets an
		802	arrayref with C<[$name, $type, $inode]> arrayrefs, each describing a
		803	single directory entry in more detail:
		804
		805	C<$name> is the name of the entry.
		806
		807	C<$type> is one of the C<IO::AIO::DT_xxx> constants:
		808
		809	C<IO::AIO::DT_UNKNOWN>, C<IO::AIO::DT_FIFO>, C<IO::AIO::DT_CHR>, C<IO::AIO::DT_DIR>,
		810	C<IO::AIO::DT_BLK>, C<IO::AIO::DT_REG>, C<IO::AIO::DT_LNK>, C<IO::AIO::DT_SOCK>,
		811	C<IO::AIO::DT_WHT>.
		812
		813	C<IO::AIO::DT_UNKNOWN> means just that: readdir does not know. If you need
		814	to know, you have to run stat yourself. Also, for speed/memory reasons,
		815	the C<$type> scalars are read-only: you must not modify them.
		816
		817	C<$inode> is the inode number (which might not be exact on systems with 64
		818	bit inode numbers and 32 bit perls). This field has unspecified content on
		819	systems that do not deliver the inode information.
		820
		821	=item IO::AIO::READDIR_DIRS_FIRST
		822
		823	When this flag is set, then the names will be returned in an order where
		824	likely directories come first, in optimal stat order. This is useful when
		825	you need to quickly find directories, or you want to find all directories
		826	while avoiding to stat() each entry.
		827
		828	If the system returns type information in readdir, then this is used
		829	to find directories directly. Otherwise, likely directories are names
		830	beginning with ".", or otherwise names with no dots, of which names with
		831	short names are tried first.
		832
		833	=item IO::AIO::READDIR_STAT_ORDER
		834
		835	When this flag is set, then the names will be returned in an order
		836	suitable for stat()'ing each one. That is, when you plan to stat() most or
		837	all files in the given directory, then the returned order will likely be
		838	faster.
		839
		840	If both this flag and C<IO::AIO::READDIR_DIRS_FIRST> are specified,
		841	then the likely dirs come first, resulting in a less optimal stat order
		842	for stat'ing all entries, but likely a more optimal order for finding
		843	subdirectories.
		844
		845	=item IO::AIO::READDIR_FOUND_UNKNOWN
		846
		847	This flag should not be set when calling C<aio_readdirx>. Instead, it
		848	is being set by C<aio_readdirx>, when any of the C<$type>'s found were
		849	C<IO::AIO::DT_UNKNOWN>. The absence of this flag therefore indicates that all
		850	C<$type>'s are known, which can be used to speed up some algorithms.
		851
		852	=back
		853
		854
		855	=item aio_slurp $pathname, $offset, $length, $data, $callback->($status)
		856
		857	Opens, reads and closes the given file. The data is put into C<$data>,
		858	which is resized as required.
		859
		860	If C<$offset> is negative, then it is counted from the end of the file.
		861
		862	If C<$length> is zero, then the remaining length of the file is
		863	used. Also, in this case, the same limitations to modifying C<$data> apply
		864	as when IO::AIO::mmap is used, i.e. it must only be modified in-place
		865	with C<substr>. If the size of the file is known, specifying a non-zero
		866	C<$length> results in a performance advantage.
		867
		868	This request is similar to the older C<aio_load> request, but since it is
		869	a single request, it might be more efficient to use.
		870
		871	Example: load F</etc/passwd> into C<$passwd>.
		872
		873	my $passwd;
		874	aio_slurp "/etc/passwd", 0, 0, $passwd, sub {
		875	$_[0] >= 0
		876	or die "/etc/passwd: $!\n";
		877
		878	printf "/etc/passwd is %d bytes long, and contains:\n", length $passwd;
		879	print $passwd;
		880	};
		881	IO::AIO::flush;
		882
		883
		884	=item aio_load $pathname, $data, $callback->($status)
		885
		886	This is a composite request that tries to fully load the given file into
		887	memory. Status is the same as with aio_read.
		888
		889	Using C<aio_slurp> might be more efficient, as it is a single request.
		890
		891	=cut
		892
		893	sub aio_load($$;$) {
		894	my ($path, undef, $cb) = @_;
		895	my $data = \$_[1];
		896
		897	my $pri = aioreq_pri;
		898	my $grp = aio_group $cb;
		899
		900	aioreq_pri $pri;
		901	add $grp aio_open $path, O_RDONLY, 0, sub {
		902	my $fh = shift
		903	or return $grp->result (-1);
		904
		905	aioreq_pri $pri;
		906	add $grp aio_read $fh, 0, (-s $fh), $$data, 0, sub {
		907	$grp->result ($_[0]);
		908	};
		909	};
		910
		911	$grp
		912	}
		913
		914	=item aio_copy $srcpath, $dstpath, $callback->($status)
		915
		916	Try to copy the I<file> (directories not supported as either source or
		917	destination) from C<$srcpath> to C<$dstpath> and call the callback with
		918	a status of C<0> (ok) or C<-1> (error, see C<$!>).
		919
		920	Existing destination files will be truncated.
		921
		922	This is a composite request that creates the destination file with
		923	mode 0200 and copies the contents of the source file into it using
		924	C<aio_sendfile>, followed by restoring atime, mtime, access mode and
		925	uid/gid, in that order.
		926
		927	If an error occurs, the partial destination file will be unlinked, if
		928	possible, except when setting atime, mtime, access mode and uid/gid, where
		929	errors are being ignored.
		930
		931	=cut
		932
		933	sub aio_copy($$;$) {
		934	my ($src, $dst, $cb) = @_;
		935
		936	my $pri = aioreq_pri;
		937	my $grp = aio_group $cb;
		938
		939	aioreq_pri $pri;
		940	add $grp aio_open $src, O_RDONLY, 0, sub {
		941	if (my $src_fh = $_[0]) {
		942	my @stat = stat $src_fh; # hmm, might block over nfs?
		943
		944	aioreq_pri $pri;
		945	add $grp aio_open $dst, O_CREAT | O_WRONLY | O_TRUNC, 0200, sub {
		946	if (my $dst_fh = $_[0]) {
		947	aioreq_pri $pri;
		948	add $grp aio_sendfile $dst_fh, $src_fh, 0, $stat[7], sub {
		949	if ($_[0] == $stat[7]) {
		950	$grp->result (0);
		951	close $src_fh;
		952
		953	my $ch = sub {
		954	aioreq_pri $pri;
		955	add $grp aio_chmod $dst_fh, $stat[2] & 07777, sub {
		956	aioreq_pri $pri;
		957	add $grp aio_chown $dst_fh, $stat[4], $stat[5], sub {
		958	aioreq_pri $pri;
		959	add $grp aio_close $dst_fh;
		960	}
		961	};
		962	};
		963
		964	aioreq_pri $pri;
		965	add $grp aio_utime $dst_fh, $stat[8], $stat[9], sub {
		966	if ($_[0] < 0 && $! == ENOSYS) {
		967	aioreq_pri $pri;
		968	add $grp aio_utime $dst, $stat[8], $stat[9], $ch;
		969	} else {
		970	$ch->();
		971	}
		972	};
		973	} else {
		974	$grp->result (-1);
		975	close $src_fh;
		976	close $dst_fh;
		977
		978	aioreq $pri;
		979	add $grp aio_unlink $dst;
		980	}
		981	};
		982	} else {
		983	$grp->result (-1);
		984	}
		985	},
		986
		987	} else {
		988	$grp->result (-1);
		989	}
		990	};
		991
		992	$grp
		993	}
		994
		995	=item aio_move $srcpath, $dstpath, $callback->($status)
		996
		997	Try to move the I<file> (directories not supported as either source or
		998	destination) from C<$srcpath> to C<$dstpath> and call the callback with
		999	a status of C<0> (ok) or C<-1> (error, see C<$!>).
		1000
		1001	This is a composite request that tries to rename(2) the file first; if
		1002	rename fails with C<EXDEV>, it copies the file with C<aio_copy> and, if
		1003	that is successful, unlinks the C<$srcpath>.
		1004
		1005	=cut
		1006
		1007	sub aio_move($$;$) {
		1008	my ($src, $dst, $cb) = @_;
		1009
		1010	my $pri = aioreq_pri;
		1011	my $grp = aio_group $cb;
		1012
		1013	aioreq_pri $pri;
		1014	add $grp aio_rename $src, $dst, sub {
		1015	if ($_[0] && $! == EXDEV) {
		1016	aioreq_pri $pri;
		1017	add $grp aio_copy $src, $dst, sub {
		1018	$grp->result ($_[0]);
		1019
		1020	unless ($_[0]) {
		1021	aioreq_pri $pri;
		1022	add $grp aio_unlink $src;
		1023	}
		1024	};
		1025	} else {
		1026	$grp->result ($_[0]);
		1027	}
		1028	};
		1029
		1030	$grp
		1031	}
		1032
		1033	=item aio_scandir $pathname, $maxreq, $callback->($dirs, $nondirs)
		1034
		1035	Scans a directory (similar to C<aio_readdir>) but additionally tries to
		1036	efficiently separate the entries of directory C<$path> into two sets of
		1037	names, directories you can recurse into (directories), and ones you cannot
		1038	recurse into (everything else, including symlinks to directories).
		1039
		1040	C<aio_scandir> is a composite request that generates many sub requests.
		1041	C<$maxreq> specifies the maximum number of outstanding aio requests that
		1042	this function generates. If it is C<< <= 0 >>, then a suitable default
		1043	will be chosen (currently 4).
		1044
		1045	On error, the callback is called without arguments, otherwise it receives
		1046	two array-refs with path-relative entry names.
		1047
		1048	Example:
		1049
		1050	aio_scandir $dir, 0, sub {
		1051	my ($dirs, $nondirs) = @_;
		1052	print "real directories: @$dirs\n";
		1053	print "everything else: @$nondirs\n";
		1054	};
		1055
		1056	Implementation notes.
		1057
		1058	The C<aio_readdir> cannot be avoided, but C<stat()>'ing every entry can.
		1059
		1060	If readdir returns file type information, then this is used directly to
		1061	find directories.
		1062
		1063	Otherwise, after reading the directory, the modification time, size etc.
		1064	of the directory before and after the readdir is checked, and if they
		1065	match (and isn't the current time), the link count will be used to decide
		1066	how many entries are directories (if >= 2). Otherwise, no knowledge of the
		1067	number of subdirectories will be assumed.
		1068
		1069	Then entries will be sorted into likely directories a non-initial dot
		1070	currently) and likely non-directories (see C<aio_readdirx>). Then every
		1071	entry plus an appended C</.> will be C<stat>'ed, likely directories first,
		1072	in order of their inode numbers. If that succeeds, it assumes that the
		1073	entry is a directory or a symlink to directory (which will be checked
		1074	separately). This is often faster than stat'ing the entry itself because
		1075	filesystems might detect the type of the entry without reading the inode
		1076	data (e.g. ext2fs filetype feature), even on systems that cannot return
		1077	the filetype information on readdir.
		1078
		1079	If the known number of directories (link count - 2) has been reached, the
		1080	rest of the entries is assumed to be non-directories.
		1081
		1082	This only works with certainty on POSIX (= UNIX) filesystems, which
		1083	fortunately are the vast majority of filesystems around.
		1084
		1085	It will also likely work on non-POSIX filesystems with reduced efficiency
		1086	as those tend to return 0 or 1 as link counts, which disables the
		1087	directory counting heuristic.
		1088
		1089	=cut
		1090
		1091	sub aio_scandir($$;$) {
		1092	my ($path, $maxreq, $cb) = @_;
		1093
		1094	my $pri = aioreq_pri;
		1095
		1096	my $grp = aio_group $cb;
		1097
		1098	$maxreq = 4 if $maxreq <= 0;
		1099
		1100	# get a wd object
		1101	aioreq_pri $pri;
		1102	add $grp aio_wd $path, sub {
		1103	$_[0]
		1104	or return $grp->result ();
		1105
		1106	my $wd = [shift, "."];
		1107
		1108	# stat once
		1109	aioreq_pri $pri;
		1110	add $grp aio_stat $wd, sub {
		1111	return $grp->result () if $_[0];
		1112	my $now = time;
		1113	my $hash1 = join ":", (stat _)[0,1,3,7,9];
		1114
		1115	# read the directory entries
		1116	aioreq_pri $pri;
		1117	add $grp aio_readdirx $wd, READDIR_DIRS_FIRST, sub {
		1118	my $entries = shift
		1119	or return $grp->result ();
		1120
		1121	# stat the dir another time
		1122	aioreq_pri $pri;
		1123	add $grp aio_stat $wd, sub {
		1124	my $hash2 = join ":", (stat _)[0,1,3,7,9];
		1125
		1126	my $ndirs;
		1127
		1128	# take the slow route if anything looks fishy
		1129	if ($hash1 ne $hash2 or (stat _)[9] == $now) {
		1130	$ndirs = -1;
		1131	} else {
		1132	# if nlink == 2, we are finished
		1133	# for non-posix-fs's, we rely on nlink < 2
		1134	$ndirs = (stat _)[3] - 2
		1135	or return $grp->result ([], $entries);
		1136	}
		1137
		1138	my (@dirs, @nondirs);
		1139
		1140	my $statgrp = add $grp aio_group sub {
		1141	$grp->result (\@dirs, \@nondirs);
		1142	};
		1143
		1144	limit $statgrp $maxreq;
		1145	feed $statgrp sub {
		1146	return unless @$entries;
		1147	my $entry = shift @$entries;
		1148
		1149	aioreq_pri $pri;
		1150	$wd->[1] = "$entry/.";
		1151	add $statgrp aio_stat $wd, sub {
		1152	if ($_[0] < 0) {
		1153	push @nondirs, $entry;
		1154	} else {
		1155	# need to check for real directory
		1156	aioreq_pri $pri;
		1157	$wd->[1] = $entry;
		1158	add $statgrp aio_lstat $wd, sub {
		1159	if (-d _) {
		1160	push @dirs, $entry;
		1161
		1162	unless (--$ndirs) {
		1163	push @nondirs, @$entries;
		1164	feed $statgrp;
		1165	}
		1166	} else {
		1167	push @nondirs, $entry;
		1168	}
		1169	}
		1170	}
		1171	};
		1172	};
		1173	};
		1174	};
		1175	};
		1176	};
		1177
		1178	$grp
		1179	}
		1180
		1181	=item aio_rmtree $pathname, $callback->($status)
		1182
		1183	Delete a directory tree starting (and including) C<$path>, return the
		1184	status of the final C<rmdir> only. This is a composite request that
		1185	uses C<aio_scandir> to recurse into and rmdir directories, and unlink
		1186	everything else.
		1187
		1188	=cut
		1189
		1190	sub aio_rmtree;
		1191	sub aio_rmtree($;$) {
		1192	my ($path, $cb) = @_;
		1193
		1194	my $pri = aioreq_pri;
		1195	my $grp = aio_group $cb;
		1196
		1197	aioreq_pri $pri;
		1198	add $grp aio_scandir $path, 0, sub {
		1199	my ($dirs, $nondirs) = @_;
		1200
		1201	my $dirgrp = aio_group sub {
		1202	add $grp aio_rmdir $path, sub {
		1203	$grp->result ($_[0]);
		1204	};
		1205	};
		1206
		1207	(aioreq_pri $pri), add $dirgrp aio_rmtree "$path/$_" for @$dirs;
		1208	(aioreq_pri $pri), add $dirgrp aio_unlink "$path/$_" for @$nondirs;
		1209
		1210	add $grp $dirgrp;
		1211	};
		1212
		1213	$grp
		1214	}
		1215
		1216	=item aio_fcntl $fh, $cmd, $arg, $callback->($status)
		1217
		1218	=item aio_ioctl $fh, $request, $buf, $callback->($status)
		1219
		1220	These work just like the C<fcntl> and C<ioctl> built-in functions, except
		1221	they execute asynchronously and pass the return value to the callback.
		1222
		1223	Both calls can be used for a lot of things, some of which make more sense
		1224	to run asynchronously in their own thread, while some others make less
		1225	sense. For example, calls that block waiting for external events, such
		1226	as locking, will also lock down an I/O thread while it is waiting, which
		1227	can deadlock the whole I/O system. At the same time, there might be no
		1228	alternative to using a thread to wait.
		1229
		1230	So in general, you should only use these calls for things that do
		1231	(filesystem) I/O, not for things that wait for other events (network,
		1232	other processes), although if you are careful and know what you are doing,
		1233	you still can.
		1234
		1235	The following constants are available (missing ones are, as usual C<0>):
		1236
		1237	C<F_DUPFD_CLOEXEC>,
		1238
		1239	C<F_OFD_GETLK>, C<F_OFD_SETLK>, C<F_OFD_GETLKW>,
		1240
		1241	C<FIFREEZE>, C<FITHAW>, C<FITRIM>, C<FICLONE>, C<FICLONERANGE>, C<FIDEDUPERANGE>.
		1242
		1243	C<FS_IOC_GETFLAGS>, C<FS_IOC_SETFLAGS>, C<FS_IOC_GETVERSION>, C<FS_IOC_SETVERSION>,
		1244	C<FS_IOC_FIEMAP>.
		1245
		1246	C<FS_IOC_FSGETXATTR>, C<FS_IOC_FSSETXATTR>, C<FS_IOC_SET_ENCRYPTION_POLICY>,
		1247	C<FS_IOC_GET_ENCRYPTION_PWSALT>, C<FS_IOC_GET_ENCRYPTION_POLICY>, C<FS_KEY_DESCRIPTOR_SIZE>.
		1248
		1249	C<FS_SECRM_FL>, C<FS_UNRM_FL>, C<FS_COMPR_FL>, C<FS_SYNC_FL>, C<FS_IMMUTABLE_FL>,
		1250	C<FS_APPEND_FL>, C<FS_NODUMP_FL>, C<FS_NOATIME_FL>, C<FS_DIRTY_FL>,
		1251	C<FS_COMPRBLK_FL>, C<FS_NOCOMP_FL>, C<FS_ENCRYPT_FL>, C<FS_BTREE_FL>,
		1252	C<FS_INDEX_FL>, C<FS_JOURNAL_DATA_FL>, C<FS_NOTAIL_FL>, C<FS_DIRSYNC_FL>, C<FS_TOPDIR_FL>,
		1253	C<FS_FL_USER_MODIFIABLE>.
		1254
		1255	C<FS_XFLAG_REALTIME>, C<FS_XFLAG_PREALLOC>, C<FS_XFLAG_IMMUTABLE>, C<FS_XFLAG_APPEND>,
		1256	C<FS_XFLAG_SYNC>, C<FS_XFLAG_NOATIME>, C<FS_XFLAG_NODUMP>, C<FS_XFLAG_RTINHERIT>,
		1257	C<FS_XFLAG_PROJINHERIT>, C<FS_XFLAG_NOSYMLINKS>, C<FS_XFLAG_EXTSIZE>, C<FS_XFLAG_EXTSZINHERIT>,
		1258	C<FS_XFLAG_NODEFRAG>, C<FS_XFLAG_FILESTREAM>, C<FS_XFLAG_DAX>, C<FS_XFLAG_HASATTR>,
		1259
		1260	=item aio_sync $callback->($status)
		1261
		1262	Asynchronously call sync and call the callback when finished.
		1263
197	=item aio_fsync $fh, $callback	1264	=item aio_fsync $fh, $callback->($status)
198		1265
199	Asynchronously call fsync on the given filehandle and call the callback	1266	Asynchronously call fsync on the given filehandle and call the callback
200	with the fsync result code.	1267	with the fsync result code.
201		1268
202	=item aio_fdatasync $fh, $callback	1269	=item aio_fdatasync $fh, $callback->($status)
203		1270
204	Asynchronously call fdatasync on the given filehandle and call the	1271	Asynchronously call fdatasync on the given filehandle and call the
205	callback with the fdatasync result code. Might set C<$!> to C<ENOSYS> if	1272	callback with the fdatasync result code.
206	C<fdatasync> is not available.	1273
		1274	If this call isn't available because your OS lacks it or it couldn't be
		1275	detected, it will be emulated by calling C<fsync> instead.
		1276
		1277	=item aio_syncfs $fh, $callback->($status)
		1278
		1279	Asynchronously call the syncfs syscall to sync the filesystem associated
		1280	to the given filehandle and call the callback with the syncfs result
		1281	code. If syncfs is not available, calls sync(), but returns C<-1> and sets
		1282	errno to C<ENOSYS> nevertheless.
		1283
		1284	=item aio_sync_file_range $fh, $offset, $nbytes, $flags, $callback->($status)
		1285
		1286	Sync the data portion of the file specified by C<$offset> and C<$length>
		1287	to disk (but NOT the metadata), by calling the Linux-specific
		1288	sync_file_range call. If sync_file_range is not available or it returns
		1289	ENOSYS, then fdatasync or fsync is being substituted.
		1290
		1291	C<$flags> can be a combination of C<IO::AIO::SYNC_FILE_RANGE_WAIT_BEFORE>,
		1292	C<IO::AIO::SYNC_FILE_RANGE_WRITE> and
		1293	C<IO::AIO::SYNC_FILE_RANGE_WAIT_AFTER>: refer to the sync_file_range
		1294	manpage for details.
		1295
		1296	=item aio_pathsync $pathname, $callback->($status)
		1297
		1298	This request tries to open, fsync and close the given path. This is a
		1299	composite request intended to sync directories after directory operations
		1300	(E.g. rename). This might not work on all operating systems or have any
		1301	specific effect, but usually it makes sure that directory changes get
		1302	written to disc. It works for anything that can be opened for read-only,
		1303	not just directories.
		1304
		1305	Future versions of this function might fall back to other methods when
		1306	C<fsync> on the directory fails (such as calling C<sync>).
		1307
		1308	Passes C<0> when everything went ok, and C<-1> on error.
		1309
		1310	=cut
		1311
		1312	sub aio_pathsync($;$) {
		1313	my ($path, $cb) = @_;
		1314
		1315	my $pri = aioreq_pri;
		1316	my $grp = aio_group $cb;
		1317
		1318	aioreq_pri $pri;
		1319	add $grp aio_open $path, O_RDONLY, 0, sub {
		1320	my ($fh) = @_;
		1321	if ($fh) {
		1322	aioreq_pri $pri;
		1323	add $grp aio_fsync $fh, sub {
		1324	$grp->result ($_[0]);
		1325
		1326	aioreq_pri $pri;
		1327	add $grp aio_close $fh;
		1328	};
		1329	} else {
		1330	$grp->result (-1);
		1331	}
		1332	};
		1333
		1334	$grp
		1335	}
		1336
		1337	=item aio_msync $scalar, $offset = 0, $length = undef, flags = MS_SYNC, $callback->($status)
		1338
		1339	This is a rather advanced IO::AIO call, which only works on mmap(2)ed
		1340	scalars (see the C<IO::AIO::mmap> function, although it also works on data
		1341	scalars managed by the L<Sys::Mmap> or L<Mmap> modules, note that the
		1342	scalar must only be modified in-place while an aio operation is pending on
		1343	it).
		1344
		1345	It calls the C<msync> function of your OS, if available, with the memory
		1346	area starting at C<$offset> in the string and ending C<$length> bytes
		1347	later. If C<$length> is negative, counts from the end, and if C<$length>
		1348	is C<undef>, then it goes till the end of the string. The flags can be
		1349	either C<IO::AIO::MS_ASYNC> or C<IO::AIO::MS_SYNC>, plus an optional
		1350	C<IO::AIO::MS_INVALIDATE>.
		1351
		1352	=item aio_mtouch $scalar, $offset = 0, $length = undef, flags = 0, $callback->($status)
		1353
		1354	This is a rather advanced IO::AIO call, which works best on mmap(2)ed
		1355	scalars.
		1356
		1357	It touches (reads or writes) all memory pages in the specified
		1358	range inside the scalar. All caveats and parameters are the same
		1359	as for C<aio_msync>, above, except for flags, which must be either
		1360	C<0> (which reads all pages and ensures they are instantiated) or
		1361	C<IO::AIO::MT_MODIFY>, which modifies the memory pages (by reading and
		1362	writing an octet from it, which dirties the page).
		1363
		1364	=item aio_mlock $scalar, $offset = 0, $length = undef, $callback->($status)
		1365
		1366	This is a rather advanced IO::AIO call, which works best on mmap(2)ed
		1367	scalars.
		1368
		1369	It reads in all the pages of the underlying storage into memory (if any)
		1370	and locks them, so they are not getting swapped/paged out or removed.
		1371
		1372	If C<$length> is undefined, then the scalar will be locked till the end.
		1373
		1374	On systems that do not implement C<mlock>, this function returns C<-1>
		1375	and sets errno to C<ENOSYS>.
		1376
		1377	Note that the corresponding C<munlock> is synchronous and is
		1378	documented under L<MISCELLANEOUS FUNCTIONS>.
		1379
		1380	Example: open a file, mmap and mlock it - both will be undone when
		1381	C<$data> gets destroyed.
		1382
		1383	open my $fh, "<", $path or die "$path: $!";
		1384	my $data;
		1385	IO::AIO::mmap $data, -s $fh, IO::AIO::PROT_READ, IO::AIO::MAP_SHARED, $fh;
		1386	aio_mlock $data; # mlock in background
		1387
		1388	=item aio_mlockall $flags, $callback->($status)
		1389
		1390	Calls the C<mlockall> function with the given C<$flags> (a
		1391	combination of C<IO::AIO::MCL_CURRENT>, C<IO::AIO::MCL_FUTURE> and
		1392	C<IO::AIO::MCL_ONFAULT>).
		1393
		1394	On systems that do not implement C<mlockall>, this function returns C<-1>
		1395	and sets errno to C<ENOSYS>. Similarly, flag combinations not supported
		1396	by the system result in a return value of C<-1> with errno being set to
		1397	C<EINVAL>.
		1398
		1399	Note that the corresponding C<munlockall> is synchronous and is
		1400	documented under L<MISCELLANEOUS FUNCTIONS>.
		1401
		1402	Example: asynchronously lock all current and future pages into memory.
		1403
		1404	aio_mlockall IO::AIO::MCL_FUTURE;
		1405
		1406	=item aio_fiemap $fh, $start, $length, $flags, $count, $cb->(\@extents)
		1407
		1408	Queries the extents of the given file (by calling the Linux C<FIEMAP>
		1409	ioctl, see L<http://cvs.schmorp.de/IO-AIO/doc/fiemap.txt> for details). If
		1410	the ioctl is not available on your OS, then this request will fail with
		1411	C<ENOSYS>.
		1412
		1413	C<$start> is the starting offset to query extents for, C<$length> is the
		1414	size of the range to query - if it is C<undef>, then the whole file will
		1415	be queried.
		1416
		1417	C<$flags> is a combination of flags (C<IO::AIO::FIEMAP_FLAG_SYNC> or
		1418	C<IO::AIO::FIEMAP_FLAG_XATTR> - C<IO::AIO::FIEMAP_FLAGS_COMPAT> is also
		1419	exported), and is normally C<0> or C<IO::AIO::FIEMAP_FLAG_SYNC> to query
		1420	the data portion.
		1421
		1422	C<$count> is the maximum number of extent records to return. If it is
		1423	C<undef>, then IO::AIO queries all extents of the range. As a very special
		1424	case, if it is C<0>, then the callback receives the number of extents
		1425	instead of the extents themselves (which is unreliable, see below).
		1426
		1427	If an error occurs, the callback receives no arguments. The special
		1428	C<errno> value C<IO::AIO::EBADR> is available to test for flag errors.
		1429
		1430	Otherwise, the callback receives an array reference with extent
		1431	structures. Each extent structure is an array reference itself, with the
		1432	following members:
		1433
		1434	[$logical, $physical, $length, $flags]
		1435
		1436	Flags is any combination of the following flag values (typically either C<0>
		1437	or C<IO::AIO::FIEMAP_EXTENT_LAST> (1)):
		1438
		1439	C<IO::AIO::FIEMAP_EXTENT_LAST>, C<IO::AIO::FIEMAP_EXTENT_UNKNOWN>,
		1440	C<IO::AIO::FIEMAP_EXTENT_DELALLOC>, C<IO::AIO::FIEMAP_EXTENT_ENCODED>,
		1441	C<IO::AIO::FIEMAP_EXTENT_DATA_ENCRYPTED>, C<IO::AIO::FIEMAP_EXTENT_NOT_ALIGNED>,
		1442	C<IO::AIO::FIEMAP_EXTENT_DATA_INLINE>, C<IO::AIO::FIEMAP_EXTENT_DATA_TAIL>,
		1443	C<IO::AIO::FIEMAP_EXTENT_UNWRITTEN>, C<IO::AIO::FIEMAP_EXTENT_MERGED> or
		1444	C<IO::AIO::FIEMAP_EXTENT_SHARED>.
		1445
		1446	At the time of this writing (Linux 3.2), this request is unreliable unless
		1447	C<$count> is C<undef>, as the kernel has all sorts of bugs preventing
		1448	it to return all extents of a range for files with a large number of
		1449	extents. The code (only) works around all these issues if C<$count> is
		1450	C<undef>.
		1451
		1452	=item aio_group $callback->(...)
		1453
		1454	This is a very special aio request: Instead of doing something, it is a
		1455	container for other aio requests, which is useful if you want to bundle
		1456	many requests into a single, composite, request with a definite callback
		1457	and the ability to cancel the whole request with its subrequests.
		1458
		1459	Returns an object of class L<IO::AIO::GRP>. See its documentation below
		1460	for more info.
		1461
		1462	Example:
		1463
		1464	my $grp = aio_group sub {
		1465	print "all stats done\n";
		1466	};
		1467
		1468	add $grp
		1469	(aio_stat ...),
		1470	(aio_stat ...),
		1471	...;
		1472
		1473	=item aio_nop $callback->()
		1474
		1475	This is a special request - it does nothing in itself and is only used for
		1476	side effects, such as when you want to add a dummy request to a group so
		1477	that finishing the requests in the group depends on executing the given
		1478	code.
		1479
		1480	While this request does nothing, it still goes through the execution
		1481	phase and still requires a worker thread. Thus, the callback will not
		1482	be executed immediately but only after other requests in the queue have
		1483	entered their execution phase. This can be used to measure request
		1484	latency.
		1485
		1486	=item IO::AIO::aio_busy $fractional_seconds, $callback->() *NOT EXPORTED*
		1487
		1488	Mainly used for debugging and benchmarking, this aio request puts one of
		1489	the request workers to sleep for the given time.
		1490
		1491	While it is theoretically handy to have simple I/O scheduling requests
		1492	like sleep and file handle readable/writable, the overhead this creates is
		1493	immense (it blocks a thread for a long time) so do not use this function
		1494	except to put your application under artificial I/O pressure.
207		1495
208	=back	1496	=back
209		1497
		1498
		1499	=head2 IO::AIO::WD - multiple working directories
		1500
		1501	Your process only has one current working directory, which is used by all
		1502	threads. This makes it hard to use relative paths (some other component
		1503	could call C<chdir> at any time, and it is hard to control when the path
		1504	will be used by IO::AIO).
		1505
		1506	One solution for this is to always use absolute paths. This usually works,
		1507	but can be quite slow (the kernel has to walk the whole path on every
		1508	access), and can also be a hassle to implement.
		1509
		1510	Newer POSIX systems have a number of functions (openat, fdopendir,
		1511	futimensat and so on) that make it possible to specify working directories
		1512	per operation.
		1513
		1514	For portability, and because the clowns who "designed", or shall I write,
		1515	perpetrated this new interface were obviously half-drunk, this abstraction
		1516	cannot be perfect, though.
		1517
		1518	IO::AIO allows you to convert directory paths into a so-called IO::AIO::WD
		1519	object. This object stores the canonicalised, absolute version of the
		1520	path, and on systems that allow it, also a directory file descriptor.
		1521
		1522	Everywhere where a pathname is accepted by IO::AIO (e.g. in C<aio_stat>
		1523	or C<aio_unlink>), one can specify an array reference with an IO::AIO::WD
		1524	object and a pathname instead (or the IO::AIO::WD object alone, which
		1525	gets interpreted as C<[$wd, "."]>). If the pathname is absolute, the
		1526	IO::AIO::WD object is ignored, otherwise the pathname is resolved relative
		1527	to that IO::AIO::WD object.
		1528
		1529	For example, to get a wd object for F</etc> and then stat F<passwd>
		1530	inside, you would write:
		1531
		1532	aio_wd "/etc", sub {
		1533	my $etcdir = shift;
		1534
		1535	# although $etcdir can be undef on error, there is generally no reason
		1536	# to check for errors here, as aio_stat will fail with ENOENT
		1537	# when $etcdir is undef.
		1538
		1539	aio_stat [$etcdir, "passwd"], sub {
		1540	# yay
		1541	};
		1542	};
		1543
		1544	The fact that C<aio_wd> is a request and not a normal function shows that
		1545	creating an IO::AIO::WD object is itself a potentially blocking operation,
		1546	which is why it is done asynchronously.
		1547
		1548	To stat the directory obtained with C<aio_wd> above, one could write
		1549	either of the following three request calls:
		1550
		1551	aio_lstat "/etc" , sub { ... # pathname as normal string
		1552	aio_lstat [$wd, "."], sub { ... # "." relative to $wd (i.e. $wd itself)
		1553	aio_lstat $wd , sub { ... # shorthand for the previous
		1554
		1555	As with normal pathnames, IO::AIO keeps a copy of the working directory
		1556	object and the pathname string, so you could write the following without
		1557	causing any issues due to C<$path> getting reused:
		1558
		1559	my $path = [$wd, undef];
		1560
		1561	for my $name (qw(abc def ghi)) {
		1562	$path->[1] = $name;
		1563	aio_stat $path, sub {
		1564	# ...
		1565	};
		1566	}
		1567
		1568	There are some caveats: when directories get renamed (or deleted), the
		1569	pathname string doesn't change, so will point to the new directory (or
		1570	nowhere at all), while the directory fd, if available on the system,
		1571	will still point to the original directory. Most functions accepting a
		1572	pathname will use the directory fd on newer systems, and the string on
		1573	older systems. Some functions (such as C<aio_realpath>) will always rely on
		1574	the string form of the pathname.
		1575
		1576	So this functionality is mainly useful to get some protection against
		1577	C<chdir>, to easily get an absolute path out of a relative path for future
		1578	reference, and to speed up doing many operations in the same directory
		1579	(e.g. when stat'ing all files in a directory).
		1580
		1581	The following functions implement this working directory abstraction:
		1582
		1583	=over 4
		1584
		1585	=item aio_wd $pathname, $callback->($wd)
		1586
		1587	Asynchonously canonicalise the given pathname and convert it to an
		1588	IO::AIO::WD object representing it. If possible and supported on the
		1589	system, also open a directory fd to speed up pathname resolution relative
		1590	to this working directory.
		1591
		1592	If something goes wrong, then C<undef> is passwd to the callback instead
		1593	of a working directory object and C<$!> is set appropriately. Since
		1594	passing C<undef> as working directory component of a pathname fails the
		1595	request with C<ENOENT>, there is often no need for error checking in the
		1596	C<aio_wd> callback, as future requests using the value will fail in the
		1597	expected way.
		1598
		1599	=item IO::AIO::CWD
		1600
		1601	This is a compiletime constant (object) that represents the process
		1602	current working directory.
		1603
		1604	Specifying this object as working directory object for a pathname is as if
		1605	the pathname would be specified directly, without a directory object. For
		1606	example, these calls are functionally identical:
		1607
		1608	aio_stat "somefile", sub { ... };
		1609	aio_stat [IO::AIO::CWD, "somefile"], sub { ... };
		1610
		1611	=back
		1612
		1613	To recover the path associated with an IO::AIO::WD object, you can use
		1614	C<aio_realpath>:
		1615
		1616	aio_realpath $wd, sub {
		1617	warn "path is $_[0]\n";
		1618	};
		1619
		1620	Currently, C<aio_statvfs> always, and C<aio_rename> and C<aio_rmdir>
		1621	sometimes, fall back to using an absolue path.
		1622
		1623	=head2 IO::AIO::REQ CLASS
		1624
		1625	All non-aggregate C<aio_*> functions return an object of this class when
		1626	called in non-void context.
		1627
		1628	=over 4
		1629
		1630	=item cancel $req
		1631
		1632	Cancels the request, if possible. Has the effect of skipping execution
		1633	when entering the B<execute> state and skipping calling the callback when
		1634	entering the the B<result> state, but will leave the request otherwise
		1635	untouched (with the exception of readdir). That means that requests that
		1636	currently execute will not be stopped and resources held by the request
		1637	will not be freed prematurely.
		1638
		1639	=item cb $req $callback->(...)
		1640
		1641	Replace (or simply set) the callback registered to the request.
		1642
		1643	=back
		1644
		1645	=head2 IO::AIO::GRP CLASS
		1646
		1647	This class is a subclass of L<IO::AIO::REQ>, so all its methods apply to
		1648	objects of this class, too.
		1649
		1650	A IO::AIO::GRP object is a special request that can contain multiple other
		1651	aio requests.
		1652
		1653	You create one by calling the C<aio_group> constructing function with a
		1654	callback that will be called when all contained requests have entered the
		1655	C<done> state:
		1656
		1657	my $grp = aio_group sub {
		1658	print "all requests are done\n";
		1659	};
		1660
		1661	You add requests by calling the C<add> method with one or more
		1662	C<IO::AIO::REQ> objects:
		1663
		1664	$grp->add (aio_unlink "...");
		1665
		1666	add $grp aio_stat "...", sub {
		1667	$_[0] or return $grp->result ("error");
		1668
		1669	# add another request dynamically, if first succeeded
		1670	add $grp aio_open "...", sub {
		1671	$grp->result ("ok");
		1672	};
		1673	};
		1674
		1675	This makes it very easy to create composite requests (see the source of
		1676	C<aio_move> for an application) that work and feel like simple requests.
		1677
		1678	=over 4
		1679
		1680	=item * The IO::AIO::GRP objects will be cleaned up during calls to
		1681	C<IO::AIO::poll_cb>, just like any other request.
		1682
		1683	=item * They can be canceled like any other request. Canceling will cancel not
		1684	only the request itself, but also all requests it contains.
		1685
		1686	=item * They can also can also be added to other IO::AIO::GRP objects.
		1687
		1688	=item * You must not add requests to a group from within the group callback (or
		1689	any later time).
		1690
		1691	=back
		1692
		1693	Their lifetime, simplified, looks like this: when they are empty, they
		1694	will finish very quickly. If they contain only requests that are in the
		1695	C<done> state, they will also finish. Otherwise they will continue to
		1696	exist.
		1697
		1698	That means after creating a group you have some time to add requests
		1699	(precisely before the callback has been invoked, which is only done within
		1700	the C<poll_cb>). And in the callbacks of those requests, you can add
		1701	further requests to the group. And only when all those requests have
		1702	finished will the the group itself finish.
		1703
		1704	=over 4
		1705
		1706	=item add $grp ...
		1707
		1708	=item $grp->add (...)
		1709
		1710	Add one or more requests to the group. Any type of L<IO::AIO::REQ> can
		1711	be added, including other groups, as long as you do not create circular
		1712	dependencies.
		1713
		1714	Returns all its arguments.
		1715
		1716	=item $grp->cancel_subs
		1717
		1718	Cancel all subrequests and clears any feeder, but not the group request
		1719	itself. Useful when you queued a lot of events but got a result early.
		1720
		1721	The group request will finish normally (you cannot add requests to the
		1722	group).
		1723
		1724	=item $grp->result (...)
		1725
		1726	Set the result value(s) that will be passed to the group callback when all
		1727	subrequests have finished and set the groups errno to the current value
		1728	of errno (just like calling C<errno> without an error number). By default,
		1729	no argument will be passed and errno is zero.
		1730
		1731	=item $grp->errno ([$errno])
		1732
		1733	Sets the group errno value to C<$errno>, or the current value of errno
		1734	when the argument is missing.
		1735
		1736	Every aio request has an associated errno value that is restored when
		1737	the callback is invoked. This method lets you change this value from its
		1738	default (0).
		1739
		1740	Calling C<result> will also set errno, so make sure you either set C<$!>
		1741	before the call to C<result>, or call c<errno> after it.
		1742
		1743	=item feed $grp $callback->($grp)
		1744
		1745	Sets a feeder/generator on this group: every group can have an attached
		1746	generator that generates requests if idle. The idea behind this is that,
		1747	although you could just queue as many requests as you want in a group,
		1748	this might starve other requests for a potentially long time. For example,
		1749	C<aio_scandir> might generate hundreds of thousands of C<aio_stat>
		1750	requests, delaying any later requests for a long time.
		1751
		1752	To avoid this, and allow incremental generation of requests, you can
		1753	instead a group and set a feeder on it that generates those requests. The
		1754	feed callback will be called whenever there are few enough (see C<limit>,
		1755	below) requests active in the group itself and is expected to queue more
		1756	requests.
		1757
		1758	The feed callback can queue as many requests as it likes (i.e. C<add> does
		1759	not impose any limits).
		1760
		1761	If the feed does not queue more requests when called, it will be
		1762	automatically removed from the group.
		1763
		1764	If the feed limit is C<0> when this method is called, it will be set to
		1765	C<2> automatically.
		1766
		1767	Example:
		1768
		1769	# stat all files in @files, but only ever use four aio requests concurrently:
		1770
		1771	my $grp = aio_group sub { print "finished\n" };
		1772	limit $grp 4;
		1773	feed $grp sub {
		1774	my $file = pop @files
		1775	or return;
		1776
		1777	add $grp aio_stat $file, sub { ... };
		1778	};
		1779
		1780	=item limit $grp $num
		1781
		1782	Sets the feeder limit for the group: The feeder will be called whenever
		1783	the group contains less than this many requests.
		1784
		1785	Setting the limit to C<0> will pause the feeding process.
		1786
		1787	The default value for the limit is C<0>, but note that setting a feeder
		1788	automatically bumps it up to C<2>.
		1789
		1790	=back
		1791
		1792
210	=head2 SUPPORT FUNCTIONS	1793	=head2 SUPPORT FUNCTIONS
211		1794
		1795	=head3 EVENT PROCESSING AND EVENT LOOP INTEGRATION
		1796
212	=over 4	1797	=over 4
213		1798
214	=item $fileno = IO::AIO::poll_fileno	1799	=item $fileno = IO::AIO::poll_fileno
215		1800
216	Return the I<request result pipe file descriptor>. This filehandle must be	1801	Return the I<request result pipe file descriptor>. This filehandle must be
217	polled for reading by some mechanism outside this module (e.g. Event or	1802	polled for reading by some mechanism outside this module (e.g. EV, Glib,
218	select, see below or the SYNOPSIS). If the pipe becomes readable you have	1803	select and so on, see below or the SYNOPSIS). If the pipe becomes readable
219	to call C<poll_cb> to check the results.	1804	you have to call C<poll_cb> to check the results.
220		1805
221	See C<poll_cb> for an example.	1806	See C<poll_cb> for an example.
222		1807
223	=item IO::AIO::poll_cb	1808	=item IO::AIO::poll_cb
224		1809
225	Process all outstanding events on the result pipe. You have to call this	1810	Process some requests that have reached the result phase (i.e. they have
226	regularly. Returns the number of events processed. Returns immediately	1811	been executed but the results are not yet reported). You have to call
227	when no events are outstanding.	1812	this "regularly" to finish outstanding requests.
		1813
		1814	Returns C<0> if all events could be processed (or there were no
		1815	events to process), or C<-1> if it returned earlier for whatever
		1816	reason. Returns immediately when no events are outstanding. The amount
		1817	of events processed depends on the settings of C<IO::AIO::max_poll_req>,
		1818	C<IO::AIO::max_poll_time> and C<IO::AIO::max_outstanding>.
		1819
		1820	If not all requests were processed for whatever reason, the poll file
		1821	descriptor will still be ready when C<poll_cb> returns, so normally you
		1822	don't have to do anything special to have it called later.
		1823
		1824	Apart from calling C<IO::AIO::poll_cb> when the event filehandle becomes
		1825	ready, it can be beneficial to call this function from loops which submit
		1826	a lot of requests, to make sure the results get processed when they become
		1827	available and not just when the loop is finished and the event loop takes
		1828	over again. This function returns very fast when there are no outstanding
		1829	requests.
228		1830
229	Example: Install an Event watcher that automatically calls	1831	Example: Install an Event watcher that automatically calls
230	IO::AIO::poll_cb with high priority:	1832	IO::AIO::poll_cb with high priority (more examples can be found in the
		1833	SYNOPSIS section, at the top of this document):
231		1834
232	Event->io (fd => IO::AIO::poll_fileno,	1835	Event->io (fd => IO::AIO::poll_fileno,
233	poll => 'r', async => 1,	1836	poll => 'r', async => 1,
234	cb => \&IO::AIO::poll_cb);	1837	cb => \&IO::AIO::poll_cb);
235		1838
236	=item IO::AIO::poll_wait	1839	=item IO::AIO::poll_wait
237		1840
238	Wait till the result filehandle becomes ready for reading (simply does a	1841	Wait until either at least one request is in the result phase or no
239	C<select> on the filehandle. This is useful if you want to synchronously wait	1842	requests are outstanding anymore.
240	for some requests to finish).	1843
		1844	This is useful if you want to synchronously wait for some requests to
		1845	become ready, without actually handling them.
241		1846
242	See C<nreqs> for an example.	1847	See C<nreqs> for an example.
243		1848
		1849	=item IO::AIO::poll
		1850
		1851	Waits until some requests have been handled.
		1852
		1853	Returns the number of requests processed, but is otherwise strictly
		1854	equivalent to:
		1855
		1856	IO::AIO::poll_wait, IO::AIO::poll_cb
		1857
244	=item IO::AIO::nreqs	1858	=item IO::AIO::flush
245		1859
246	Returns the number of requests currently outstanding (i.e. for which their	1860	Wait till all outstanding AIO requests have been handled.
247	callback has not been invoked yet).
248		1861
249	Example: wait till there are no outstanding requests anymore:	1862	Strictly equivalent to:
250		1863
251	IO::AIO::poll_wait, IO::AIO::poll_cb	1864	IO::AIO::poll_wait, IO::AIO::poll_cb
252	while IO::AIO::nreqs;	1865	while IO::AIO::nreqs;
253		1866
		1867	This function can be useful at program aborts, to make sure outstanding
		1868	I/O has been done (C<IO::AIO> uses an C<END> block which already calls
		1869	this function on normal exits), or when you are merely using C<IO::AIO>
		1870	for its more advanced functions, rather than for async I/O, e.g.:
		1871
		1872	my ($dirs, $nondirs);
		1873	IO::AIO::aio_scandir "/tmp", 0, sub { ($dirs, $nondirs) = @_ };
		1874	IO::AIO::flush;
		1875	# $dirs, $nondirs are now set
		1876
		1877	=item IO::AIO::max_poll_reqs $nreqs
		1878
		1879	=item IO::AIO::max_poll_time $seconds
		1880
		1881	These set the maximum number of requests (default C<0>, meaning infinity)
		1882	that are being processed by C<IO::AIO::poll_cb> in one call, respectively
		1883	the maximum amount of time (default C<0>, meaning infinity) spent in
		1884	C<IO::AIO::poll_cb> to process requests (more correctly the mininum amount
		1885	of time C<poll_cb> is allowed to use).
		1886
		1887	Setting C<max_poll_time> to a non-zero value creates an overhead of one
		1888	syscall per request processed, which is not normally a problem unless your
		1889	callbacks are really really fast or your OS is really really slow (I am
		1890	not mentioning Solaris here). Using C<max_poll_reqs> incurs no overhead.
		1891
		1892	Setting these is useful if you want to ensure some level of
		1893	interactiveness when perl is not fast enough to process all requests in
		1894	time.
		1895
		1896	For interactive programs, values such as C<0.01> to C<0.1> should be fine.
		1897
		1898	Example: Install an Event watcher that automatically calls
		1899	IO::AIO::poll_cb with low priority, to ensure that other parts of the
		1900	program get the CPU sometimes even under high AIO load.
		1901
		1902	# try not to spend much more than 0.1s in poll_cb
		1903	IO::AIO::max_poll_time 0.1;
		1904
		1905	# use a low priority so other tasks have priority
		1906	Event->io (fd => IO::AIO::poll_fileno,
		1907	poll => 'r', nice => 1,
		1908	cb => &IO::AIO::poll_cb);
		1909
		1910	=back
		1911
		1912
		1913	=head3 CONTROLLING THE NUMBER OF THREADS
		1914
		1915	=over
		1916
		1917	=item IO::AIO::min_parallel $nthreads
		1918
		1919	Set the minimum number of AIO threads to C<$nthreads>. The current
		1920	default is C<8>, which means eight asynchronous operations can execute
		1921	concurrently at any one time (the number of outstanding requests,
		1922	however, is unlimited).
		1923
		1924	IO::AIO starts threads only on demand, when an AIO request is queued and
		1925	no free thread exists. Please note that queueing up a hundred requests can
		1926	create demand for a hundred threads, even if it turns out that everything
		1927	is in the cache and could have been processed faster by a single thread.
		1928
		1929	It is recommended to keep the number of threads relatively low, as some
		1930	Linux kernel versions will scale negatively with the number of threads
		1931	(higher parallelity => MUCH higher latency). With current Linux 2.6
		1932	versions, 4-32 threads should be fine.
		1933
		1934	Under most circumstances you don't need to call this function, as the
		1935	module selects a default that is suitable for low to moderate load.
		1936
		1937	=item IO::AIO::max_parallel $nthreads
		1938
		1939	Sets the maximum number of AIO threads to C<$nthreads>. If more than the
		1940	specified number of threads are currently running, this function kills
		1941	them. This function blocks until the limit is reached.
		1942
		1943	While C<$nthreads> are zero, aio requests get queued but not executed
		1944	until the number of threads has been increased again.
		1945
		1946	This module automatically runs C<max_parallel 0> at program end, to ensure
		1947	that all threads are killed and that there are no outstanding requests.
		1948
		1949	Under normal circumstances you don't need to call this function.
		1950
		1951	=item IO::AIO::max_idle $nthreads
		1952
		1953	Limit the number of threads (default: 4) that are allowed to idle
		1954	(i.e., threads that did not get a request to process within the idle
		1955	timeout (default: 10 seconds). That means if a thread becomes idle while
		1956	C<$nthreads> other threads are also idle, it will free its resources and
		1957	exit.
		1958
		1959	This is useful when you allow a large number of threads (e.g. 100 or 1000)
		1960	to allow for extremely high load situations, but want to free resources
		1961	under normal circumstances (1000 threads can easily consume 30MB of RAM).
		1962
		1963	The default is probably ok in most situations, especially if thread
		1964	creation is fast. If thread creation is very slow on your system you might
		1965	want to use larger values.
		1966
		1967	=item IO::AIO::idle_timeout $seconds
		1968
		1969	Sets the minimum idle timeout (default 10) after which worker threads are
		1970	allowed to exit. SEe C<IO::AIO::max_idle>.
		1971
		1972	=item IO::AIO::max_outstanding $maxreqs
		1973
		1974	Sets the maximum number of outstanding requests to C<$nreqs>. If
		1975	you do queue up more than this number of requests, the next call to
		1976	C<IO::AIO::poll_cb> (and other functions calling C<poll_cb>, such as
		1977	C<IO::AIO::flush> or C<IO::AIO::poll>) will block until the limit is no
		1978	longer exceeded.
		1979
		1980	In other words, this setting does not enforce a queue limit, but can be
		1981	used to make poll functions block if the limit is exceeded.
		1982
		1983	This is a very bad function to use in interactive programs because it
		1984	blocks, and a bad way to reduce concurrency because it is inexact: Better
		1985	use an C<aio_group> together with a feed callback.
		1986
		1987	Its main use is in scripts without an event loop - when you want to stat
		1988	a lot of files, you can write something like this:
		1989
		1990	IO::AIO::max_outstanding 32;
		1991
		1992	for my $path (...) {
		1993	aio_stat $path , ...;
		1994	IO::AIO::poll_cb;
		1995	}
		1996
		1997	IO::AIO::flush;
		1998
		1999	The call to C<poll_cb> inside the loop will normally return instantly, but
		2000	as soon as more thna C<32> reqeusts are in-flight, it will block until
		2001	some requests have been handled. This keeps the loop from pushing a large
		2002	number of C<aio_stat> requests onto the queue.
		2003
		2004	The default value for C<max_outstanding> is very large, so there is no
		2005	practical limit on the number of outstanding requests.
		2006
		2007	=back
		2008
		2009
		2010	=head3 STATISTICAL INFORMATION
		2011
		2012	=over
		2013
254	=item IO::AIO::flush	2014	=item IO::AIO::nreqs
255		2015
256	Wait till all outstanding AIO requests have been handled.	2016	Returns the number of requests currently in the ready, execute or pending
		2017	states (i.e. for which their callback has not been invoked yet).
257		2018
258	Strictly equivalent to:	2019	Example: wait till there are no outstanding requests anymore:
259		2020
260	IO::AIO::poll_wait, IO::AIO::poll_cb	2021	IO::AIO::poll_wait, IO::AIO::poll_cb
261	while IO::AIO::nreqs;	2022	while IO::AIO::nreqs;
262		2023
		2024	=item IO::AIO::nready
		2025
		2026	Returns the number of requests currently in the ready state (not yet
		2027	executed).
		2028
263	=item IO::AIO::poll	2029	=item IO::AIO::npending
264		2030
265	Waits until some requests have been handled.	2031	Returns the number of requests currently in the pending state (executed,
266		2032	but not yet processed by poll_cb).
267	Strictly equivalent to:
268
269	IO::AIO::poll_wait, IO::AIO::poll_cb
270	if IO::AIO::nreqs;
271
272	=item IO::AIO::min_parallel $nthreads
273
274	Set the minimum number of AIO threads to C<$nthreads>. The default is
275	C<1>, which means a single asynchronous operation can be done at one time
276	(the number of outstanding operations, however, is unlimited).
277
278	It is recommended to keep the number of threads low, as some Linux
279	kernel versions will scale negatively with the number of threads (higher
280	parallelity => MUCH higher latency). With current Linux 2.6 versions, 4-32
281	threads should be fine.
282
283	Under normal circumstances you don't need to call this function, as this
284	module automatically starts some threads (the exact number might change,
285	and is currently 4).
286
287	=item IO::AIO::max_parallel $nthreads
288
289	Sets the maximum number of AIO threads to C<$nthreads>. If more than
290	the specified number of threads are currently running, kill them. This
291	function blocks until the limit is reached.
292
293	This module automatically runs C<max_parallel 0> at program end, to ensure
294	that all threads are killed and that there are no outstanding requests.
295
296	Under normal circumstances you don't need to call this function.
297
298	=item $oldnreqs = IO::AIO::max_outstanding $nreqs
299
300	Sets the maximum number of outstanding requests to C<$nreqs>. If you
301	try to queue up more than this number of requests, the caller will block until
302	some requests have been handled.
303
304	The default is very large, so normally there is no practical limit. If you
305	queue up many requests in a loop it it often improves speed if you set
306	this to a relatively low number, such as C<100>.
307
308	Under normal circumstances you don't need to call this function.
309		2033
310	=back	2034	=back
311		2035
		2036
		2037	=head3 SUBSECOND STAT TIME ACCESS
		2038
		2039	Both C<aio_stat>/C<aio_lstat> and perl's C<stat>/C<lstat> functions can
		2040	generally find access/modification and change times with subsecond time
		2041	accuracy of the system supports it, but perl's built-in functions only
		2042	return the integer part.
		2043
		2044	The following functions return the timestamps of the most recent
		2045	stat with subsecond precision on most systems and work both after
		2046	C<aio_stat>/C<aio_lstat> and perl's C<stat>/C<lstat> calls. Their return
		2047	value is only meaningful after a successful C<stat>/C<lstat> call, or
		2048	during/after a successful C<aio_stat>/C<aio_lstat> callback.
		2049
		2050	This is similar to the L<Time::HiRes> C<stat> functions, but can return
		2051	full resolution without rounding and work with standard perl C<stat>,
		2052	alleviating the need to call the special C<Time::HiRes> functions, which
		2053	do not act like their perl counterparts.
		2054
		2055	On operating systems or file systems where subsecond time resolution is
		2056	not supported or could not be detected, a fractional part of C<0> is
		2057	returned, so it is always safe to call these functions.
		2058
		2059	=over 4
		2060
		2061	=item $seconds = IO::AIO::st_atime, IO::AIO::st_mtime, IO::AIO::st_ctime, IO::AIO::st_btime
		2062
		2063	Return the access, modication, change or birth time, respectively,
		2064	including fractional part. Due to the limited precision of floating point,
		2065	the accuracy on most platforms is only a bit better than milliseconds
		2066	for times around now - see the I<nsec> function family, below, for full
		2067	accuracy.
		2068
		2069	File birth time is only available when the OS and perl support it (on
		2070	FreeBSD and NetBSD at the time of this writing, although support is
		2071	adaptive, so if your OS/perl gains support, IO::AIO can take avdantage of
		2072	it). On systems where it isn't available, C<0> is currently returned, but
		2073	this might change to C<undef> in a future version.
		2074
		2075	=item ($atime, $mtime, $ctime, $btime, ...) = IO::AIO::st_xtime
		2076
		2077	Returns access, modification, change and birth time all in one go, and
		2078	maybe more times in the future version.
		2079
		2080	=item $nanoseconds = IO::AIO::st_atimensec, IO::AIO::st_mtimensec, IO::AIO::st_ctimensec, IO::AIO::st_btimensec
		2081
		2082	Return the fractional access, modifcation, change or birth time, in nanoseconds,
		2083	as an integer in the range C<0> to C<999999999>.
		2084
		2085	Note that no accessors are provided for access, modification and
		2086	change times - you need to get those from C<stat _> if required (C<int
		2087	IO::AIO::st_atime> and so on will I<not> generally give you the correct
		2088	value).
		2089
		2090	=item $seconds = IO::AIO::st_btimesec
		2091
		2092	The (integral) seconds part of the file birth time, if available.
		2093
		2094	=item ($atime, $mtime, $ctime, $btime, ...) = IO::AIO::st_xtimensec
		2095
		2096	Like the functions above, but returns all four times in one go (and maybe
		2097	more in future versions).
		2098
		2099	=item $counter = IO::AIO::st_gen
		2100
		2101	Returns the generation counter (in practice this is just a random number)
		2102	of the file. This is only available on platforms which have this member in
		2103	their C<struct stat> (most BSDs at the time of this writing) and generally
		2104	only to the root usert. If unsupported, C<0> is returned, but this might
		2105	change to C<undef> in a future version.
		2106
		2107	=back
		2108
		2109	Example: print the high resolution modification time of F</etc>, using
		2110	C<stat>, and C<IO::AIO::aio_stat>.
		2111
		2112	if (stat "/etc") {
		2113	printf "stat(/etc) mtime: %f\n", IO::AIO::st_mtime;
		2114	}
		2115
		2116	IO::AIO::aio_stat "/etc", sub {
		2117	$_[0]
		2118	and return;
		2119
		2120	printf "aio_stat(/etc) mtime: %d.%09d\n", (stat _)[9], IO::AIO::st_mtimensec;
		2121	};
		2122
		2123	IO::AIO::flush;
		2124
		2125	Output of the awbove on my system, showing reduced and full accuracy:
		2126
		2127	stat(/etc) mtime: 1534043702.020808
		2128	aio_stat(/etc) mtime: 1534043702.020807792
		2129
		2130
		2131	=head3 MISCELLANEOUS FUNCTIONS
		2132
		2133	IO::AIO implements some functions that are useful when you want to use
		2134	some "Advanced I/O" function not available to in Perl, without going the
		2135	"Asynchronous I/O" route. Many of these have an asynchronous C<aio_*>
		2136	counterpart.
		2137
		2138	=over 4
		2139
		2140	=item $numfd = IO::AIO::get_fdlimit
		2141
		2142	This function is I<EXPERIMENTAL> and subject to change.
		2143
		2144	Tries to find the current file descriptor limit and returns it, or
		2145	C<undef> and sets C<$!> in case of an error. The limit is one larger than
		2146	the highest valid file descriptor number.
		2147
		2148	=item IO::AIO::min_fdlimit [$numfd]
		2149
		2150	This function is I<EXPERIMENTAL> and subject to change.
		2151
		2152	Try to increase the current file descriptor limit(s) to at least C<$numfd>
		2153	by changing the soft or hard file descriptor resource limit. If C<$numfd>
		2154	is missing, it will try to set a very high limit, although this is not
		2155	recommended when you know the actual minimum that you require.
		2156
		2157	If the limit cannot be raised enough, the function makes a best-effort
		2158	attempt to increase the limit as much as possible, using various
		2159	tricks, while still failing. You can query the resulting limit using
		2160	C<IO::AIO::get_fdlimit>.
		2161
		2162	If an error occurs, returns C<undef> and sets C<$!>, otherwise returns
		2163	true.
		2164
		2165	=item IO::AIO::sendfile $ofh, $ifh, $offset, $count
		2166
		2167	Calls the C<eio_sendfile_sync> function, which is like C<aio_sendfile>,
		2168	but is blocking (this makes most sense if you know the input data is
		2169	likely cached already and the output filehandle is set to non-blocking
		2170	operations).
		2171
		2172	Returns the number of bytes copied, or C<-1> on error.
		2173
		2174	=item IO::AIO::fadvise $fh, $offset, $len, $advice
		2175
		2176	Simply calls the C<posix_fadvise> function (see its
		2177	manpage for details). The following advice constants are
		2178	available: C<IO::AIO::FADV_NORMAL>, C<IO::AIO::FADV_SEQUENTIAL>,
		2179	C<IO::AIO::FADV_RANDOM>, C<IO::AIO::FADV_NOREUSE>,
		2180	C<IO::AIO::FADV_WILLNEED>, C<IO::AIO::FADV_DONTNEED>.
		2181
		2182	On systems that do not implement C<posix_fadvise>, this function returns
		2183	ENOSYS, otherwise the return value of C<posix_fadvise>.
		2184
		2185	=item IO::AIO::madvise $scalar, $offset, $len, $advice
		2186
		2187	Simply calls the C<posix_madvise> function (see its
		2188	manpage for details). The following advice constants are
		2189	available: C<IO::AIO::MADV_NORMAL>, C<IO::AIO::MADV_SEQUENTIAL>,
		2190	C<IO::AIO::MADV_RANDOM>, C<IO::AIO::MADV_WILLNEED>,
		2191	C<IO::AIO::MADV_DONTNEED>.
		2192
		2193	If C<$offset> is negative, counts from the end. If C<$length> is negative,
		2194	the remaining length of the C<$scalar> is used. If possible, C<$length>
		2195	will be reduced to fit into the C<$scalar>.
		2196
		2197	On systems that do not implement C<posix_madvise>, this function returns
		2198	ENOSYS, otherwise the return value of C<posix_madvise>.
		2199
		2200	=item IO::AIO::mprotect $scalar, $offset, $len, $protect
		2201
		2202	Simply calls the C<mprotect> function on the preferably AIO::mmap'ed
		2203	$scalar (see its manpage for details). The following protect
		2204	constants are available: C<IO::AIO::PROT_NONE>, C<IO::AIO::PROT_READ>,
		2205	C<IO::AIO::PROT_WRITE>, C<IO::AIO::PROT_EXEC>.
		2206
		2207	If C<$offset> is negative, counts from the end. If C<$length> is negative,
		2208	the remaining length of the C<$scalar> is used. If possible, C<$length>
		2209	will be reduced to fit into the C<$scalar>.
		2210
		2211	On systems that do not implement C<mprotect>, this function returns
		2212	ENOSYS, otherwise the return value of C<mprotect>.
		2213
		2214	=item IO::AIO::mmap $scalar, $length, $prot, $flags, $fh[, $offset]
		2215
		2216	Memory-maps a file (or anonymous memory range) and attaches it to the
		2217	given C<$scalar>, which will act like a string scalar. Returns true on
		2218	success, and false otherwise.
		2219
		2220	The scalar must exist, but its contents do not matter - this means you
		2221	cannot use a nonexistant array or hash element. When in doubt, C<undef>
		2222	the scalar first.
		2223
		2224	The only operations allowed on the mmapped scalar are C<substr>/C<vec>,
		2225	which don't change the string length, and most read-only operations such
		2226	as copying it or searching it with regexes and so on.
		2227
		2228	Anything else is unsafe and will, at best, result in memory leaks.
		2229
		2230	The memory map associated with the C<$scalar> is automatically removed
		2231	when the C<$scalar> is undef'd or destroyed, or when the C<IO::AIO::mmap>
		2232	or C<IO::AIO::munmap> functions are called on it.
		2233
		2234	This calls the C<mmap>(2) function internally. See your system's manual
		2235	page for details on the C<$length>, C<$prot> and C<$flags> parameters.
		2236
		2237	The C<$length> must be larger than zero and smaller than the actual
		2238	filesize.
		2239
		2240	C<$prot> is a combination of C<IO::AIO::PROT_NONE>, C<IO::AIO::PROT_EXEC>,
		2241	C<IO::AIO::PROT_READ> and/or C<IO::AIO::PROT_WRITE>,
		2242
		2243	C<$flags> can be a combination of
		2244	C<IO::AIO::MAP_SHARED> or
		2245	C<IO::AIO::MAP_PRIVATE>,
		2246	or a number of system-specific flags (when not available, the are C<0>):
		2247	C<IO::AIO::MAP_ANONYMOUS> (which is set to C<MAP_ANON> if your system only provides this constant),
		2248	C<IO::AIO::MAP_LOCKED>,
		2249	C<IO::AIO::MAP_NORESERVE>,
		2250	C<IO::AIO::MAP_POPULATE>,
		2251	C<IO::AIO::MAP_NONBLOCK>,
		2252	C<IO::AIO::MAP_FIXED>,
		2253	C<IO::AIO::MAP_GROWSDOWN>,
		2254	C<IO::AIO::MAP_32BIT>,
		2255	C<IO::AIO::MAP_HUGETLB> or
		2256	C<IO::AIO::MAP_STACK>.
		2257
		2258	If C<$fh> is C<undef>, then a file descriptor of C<-1> is passed.
		2259
		2260	C<$offset> is the offset from the start of the file - it generally must be
		2261	a multiple of C<IO::AIO::PAGESIZE> and defaults to C<0>.
		2262
		2263	Example:
		2264
		2265	use Digest::MD5;
		2266	use IO::AIO;
		2267
		2268	open my $fh, "<verybigfile"
		2269	or die "$!";
		2270
		2271	IO::AIO::mmap my $data, -s $fh, IO::AIO::PROT_READ, IO::AIO::MAP_SHARED, $fh
		2272	or die "verybigfile: $!";
		2273
		2274	my $fast_md5 = md5 $data;
		2275
		2276	=item IO::AIO::munmap $scalar
		2277
		2278	Removes a previous mmap and undefines the C<$scalar>.
		2279
		2280	=item IO::AIO::mremap $scalar, $new_length, $flags = MREMAP_MAYMOVE[, $new_address = 0]
		2281
		2282	Calls the Linux-specific mremap(2) system call. The C<$scalar> must have
		2283	been mapped by C<IO::AIO::mmap>, and C<$flags> must currently either be
		2284	C<0> or C<IO::AIO::MREMAP_MAYMOVE>.
		2285
		2286	Returns true if successful, and false otherwise. If the underlying mmapped
		2287	region has changed address, then the true value has the numerical value
		2288	C<1>, otherwise it has the numerical value C<0>:
		2289
		2290	my $success = IO::AIO::mremap $mmapped, 8192, IO::AIO::MREMAP_MAYMOVE
		2291	or die "mremap: $!";
		2292
		2293	if ($success*1) {
		2294	warn "scalar has chanegd address in memory\n";
		2295	}
		2296
		2297	C<IO::AIO::MREMAP_FIXED> and the C<$new_address> argument are currently
		2298	implemented, but not supported and might go away in a future version.
		2299
		2300	On systems where this call is not supported or is not emulated, this call
		2301	returns falls and sets C<$!> to C<ENOSYS>.
		2302
		2303	=item IO::AIO::mlockall $flags
		2304
		2305	Calls the C<eio_mlockall_sync> function, which is like C<aio_mlockall>,
		2306	but is blocking.
		2307
		2308	=item IO::AIO::munlock $scalar, $offset = 0, $length = undef
		2309
		2310	Calls the C<munlock> function, undoing the effects of a previous
		2311	C<aio_mlock> call (see its description for details).
		2312
		2313	=item IO::AIO::munlockall
		2314
		2315	Calls the C<munlockall> function.
		2316
		2317	On systems that do not implement C<munlockall>, this function returns
		2318	ENOSYS, otherwise the return value of C<munlockall>.
		2319
		2320	=item IO::AIO::splice $r_fh, $r_off, $w_fh, $w_off, $length, $flags
		2321
		2322	Calls the GNU/Linux C<splice(2)> syscall, if available. If C<$r_off> or
		2323	C<$w_off> are C<undef>, then C<NULL> is passed for these, otherwise they
		2324	should be the file offset.
		2325
		2326	C<$r_fh> and C<$w_fh> should not refer to the same file, as splice might
		2327	silently corrupt the data in this case.
		2328
		2329	The following symbol flag values are available: C<IO::AIO::SPLICE_F_MOVE>,
		2330	C<IO::AIO::SPLICE_F_NONBLOCK>, C<IO::AIO::SPLICE_F_MORE> and
		2331	C<IO::AIO::SPLICE_F_GIFT>.
		2332
		2333	See the C<splice(2)> manpage for details.
		2334
		2335	=item IO::AIO::tee $r_fh, $w_fh, $length, $flags
		2336
		2337	Calls the GNU/Linux C<tee(2)> syscall, see its manpage and the
		2338	description for C<IO::AIO::splice> above for details.
		2339
		2340	=item $actual_size = IO::AIO::pipesize $r_fh[, $new_size]
		2341
		2342	Attempts to query or change the pipe buffer size. Obviously works only
		2343	on pipes, and currently works only on GNU/Linux systems, and fails with
		2344	C<-1>/C<ENOSYS> everywhere else. If anybody knows how to influence pipe buffer
		2345	size on other systems, drop me a note.
		2346
		2347	=item ($rfh, $wfh) = IO::AIO::pipe2 [$flags]
		2348
		2349	This is a direct interface to the Linux L<pipe2(2)> system call. If
		2350	C<$flags> is missing or C<0>, then this should be the same as a call to
		2351	perl's built-in C<pipe> function and create a new pipe, and works on
		2352	systems that lack the pipe2 syscall. On win32, this case invokes C<_pipe
		2353	(..., 4096, O_BINARY)>.
		2354
		2355	If C<$flags> is non-zero, it tries to invoke the pipe2 system call with
		2356	the given flags (Linux 2.6.27, glibc 2.9).
		2357
		2358	On success, the read and write file handles are returned.
		2359
		2360	On error, nothing will be returned. If the pipe2 syscall is missing and
		2361	C<$flags> is non-zero, fails with C<ENOSYS>.
		2362
		2363	Please refer to L<pipe2(2)> for more info on the C<$flags>, but at the
		2364	time of this writing, C<IO::AIO::O_CLOEXEC>, C<IO::AIO::O_NONBLOCK> and
		2365	C<IO::AIO::O_DIRECT> (Linux 3.4, for packet-based pipes) were supported.
		2366
		2367	Example: create a pipe race-free w.r.t. threads and fork:
		2368
		2369	my ($rfh, $wfh) = IO::AIO::pipe2 IO::AIO::O_CLOEXEC
		2370	or die "pipe2: $!\n";
		2371
		2372	=item $fh = IO::AIO::eventfd [$initval, [$flags]]
		2373
		2374	This is a direct interface to the Linux L<eventfd(2)> system call. The
		2375	(unhelpful) defaults for C<$initval> and C<$flags> are C<0> for both.
		2376
		2377	On success, the new eventfd filehandle is returned, otherwise returns
		2378	C<undef>. If the eventfd syscall is missing, fails with C<ENOSYS>.
		2379
		2380	Please refer to L<eventfd(2)> for more info on this call.
		2381
		2382	The following symbol flag values are available: C<IO::AIO::EFD_CLOEXEC>,
		2383	C<IO::AIO::EFD_NONBLOCK> and C<IO::AIO::EFD_SEMAPHORE> (Linux 2.6.30).
		2384
		2385	Example: create a new eventfd filehandle:
		2386
		2387	$fh = IO::AIO::eventfd 0, IO::AIO::O_CLOEXEC
		2388	or die "eventfd: $!\n";
		2389
		2390	=item $fh = IO::AIO::timerfd_create $clockid[, $flags]
		2391
		2392	This is a direct interface to the Linux L<timerfd_create(2)> system call. The
		2393	(unhelpful) default for C<$flags> is C<0>.
		2394
		2395	On success, the new timerfd filehandle is returned, otherwise returns
		2396	C<undef>. If the eventfd syscall is missing, fails with C<ENOSYS>.
		2397
		2398	Please refer to L<timerfd_create(2)> for more info on this call.
		2399
		2400	The following C<$clockid> values are
		2401	available: C<IO::AIO::CLOCK_REALTIME>, C<IO::AIO::CLOCK_MONOTONIC>
		2402	C<IO::AIO::CLOCK_CLOCK_BOOTTIME> (Linux 3.15)
		2403	C<IO::AIO::CLOCK_CLOCK_REALTIME_ALARM> (Linux 3.11) and
		2404	C<IO::AIO::CLOCK_CLOCK_BOOTTIME_ALARM> (Linux 3.11).
		2405
		2406	The following C<$flags> values are available (Linux
		2407	2.6.27): C<IO::AIO::TFD_NONBLOCK> and C<IO::AIO::TFD_CLOEXEC>.
		2408
		2409	Example: create a new timerfd and set it to one-second repeated alarms,
		2410	then wait for two alarms:
		2411
		2412	my $fh = IO::AIO::timerfd_create IO::AIO::CLOCK_BOOTTIME, IO::AIO::TFD_CLOEXEC
		2413	or die "timerfd_create: $!\n";
		2414
		2415	defined IO::AIO::timerfd_settime $fh, 0, 1, 1
		2416	or die "timerfd_settime: $!\n";
		2417
		2418	for (1..2) {
		2419	8 == sysread $fh, my $buf, 8
		2420	or die "timerfd read failure\n";
		2421
		2422	printf "number of expirations (likely 1): %d\n",
		2423	unpack "Q", $buf;
		2424	}
		2425
		2426	=item ($cur_interval, $cur_value) = IO::AIO::timerfd_settime $fh, $flags, $new_interval, $nbw_value
		2427
		2428	This is a direct interface to the Linux L<timerfd_settime(2)> system
		2429	call. Please refer to its manpage for more info on this call.
		2430
		2431	The new itimerspec is specified using two (possibly fractional) second
		2432	values, C<$new_interval> and C<$new_value>).
		2433
		2434	On success, the current interval and value are returned (as per
		2435	C<timerfd_gettime>). On failure, the empty list is returned.
		2436
		2437	The following C<$flags> values are
		2438	available: C<IO::AIO::TFD_TIMER_ABSTIME> and
		2439	C<IO::AIO::TFD_TIMER_CANCEL_ON_SET>.
		2440
		2441	See C<IO::AIO::timerfd_create> for a full example.
		2442
		2443	=item ($cur_interval, $cur_value) = IO::AIO::timerfd_gettime $fh
		2444
		2445	This is a direct interface to the Linux L<timerfd_gettime(2)> system
		2446	call. Please refer to its manpage for more info on this call.
		2447
		2448	On success, returns the current values of interval and value for the given
		2449	timerfd (as potentially fractional second values). On failure, the empty
		2450	list is returned.
		2451
		2452	=back
		2453
312	=cut	2454	=cut
313		2455
314	# support function to convert a fd into a perl filehandle
315	sub _fd2fh {
316	return undef if $_[0] < 0;
317
318	# try to generate nice filehandles
319	my $sym = "IO::AIO::fd#$_[0]";
320	local *$sym;
321	open *$sym, "+<&=$_[0]"
322	or return undef;
323
324	*$sym
325	}
326
327	min_parallel 4;	2456	min_parallel 8;
328		2457
329	END {	2458	END { flush }
330	max_parallel 0;
331	}
332		2459
333	1;	2460	1;
334		2461
		2462	=head1 EVENT LOOP INTEGRATION
		2463
		2464	It is recommended to use L<AnyEvent::AIO> to integrate IO::AIO
		2465	automatically into many event loops:
		2466
		2467	# AnyEvent integration (EV, Event, Glib, Tk, POE, urxvt, pureperl...)
		2468	use AnyEvent::AIO;
		2469
		2470	You can also integrate IO::AIO manually into many event loops, here are
		2471	some examples of how to do this:
		2472
		2473	# EV integration
		2474	my $aio_w = EV::io IO::AIO::poll_fileno, EV::READ, \&IO::AIO::poll_cb;
		2475
		2476	# Event integration
		2477	Event->io (fd => IO::AIO::poll_fileno,
		2478	poll => 'r',
		2479	cb => \&IO::AIO::poll_cb);
		2480
		2481	# Glib/Gtk2 integration
		2482	add_watch Glib::IO IO::AIO::poll_fileno,
		2483	in => sub { IO::AIO::poll_cb; 1 };
		2484
		2485	# Tk integration
		2486	Tk::Event::IO->fileevent (IO::AIO::poll_fileno, "",
		2487	readable => \&IO::AIO::poll_cb);
		2488
		2489	# Danga::Socket integration
		2490	Danga::Socket->AddOtherFds (IO::AIO::poll_fileno =>
		2491	\&IO::AIO::poll_cb);
		2492
		2493	=head2 FORK BEHAVIOUR
		2494
		2495	Usage of pthreads in a program changes the semantics of fork
		2496	considerably. Specifically, only async-safe functions can be called after
		2497	fork. Perl doesn't know about this, so in general, you cannot call fork
		2498	with defined behaviour in perl if pthreads are involved. IO::AIO uses
		2499	pthreads, so this applies, but many other extensions and (for inexplicable
		2500	reasons) perl itself often is linked against pthreads, so this limitation
		2501	applies to quite a lot of perls.
		2502
		2503	This module no longer tries to fight your OS, or POSIX. That means IO::AIO
		2504	only works in the process that loaded it. Forking is fully supported, but
		2505	using IO::AIO in the child is not.
		2506
		2507	You might get around by not I<using> IO::AIO before (or after)
		2508	forking. You could also try to call the L<IO::AIO::reinit> function in the
		2509	child:
		2510
		2511	=over 4
		2512
		2513	=item IO::AIO::reinit
		2514
		2515	Abandons all current requests and I/O threads and simply reinitialises all
		2516	data structures. This is not an operation supported by any standards, but
		2517	happens to work on GNU/Linux and some newer BSD systems.
		2518
		2519	The only reasonable use for this function is to call it after forking, if
		2520	C<IO::AIO> was used in the parent. Calling it while IO::AIO is active in
		2521	the process will result in undefined behaviour. Calling it at any time
		2522	will also result in any undefined (by POSIX) behaviour.
		2523
		2524	=back
		2525
		2526	=head2 LINUX-SPECIFIC CALLS
		2527
		2528	When a call is documented as "linux-specific" then this means it
		2529	originated on GNU/Linux. C<IO::AIO> will usually try to autodetect the
		2530	availability and compatibility of such calls regardless of the platform
		2531	it is compiled on, so platforms such as FreeBSD which often implement
		2532	these calls will work. When in doubt, call them and see if they fail wth
		2533	C<ENOSYS>.
		2534
		2535	=head2 MEMORY USAGE
		2536
		2537	Per-request usage:
		2538
		2539	Each aio request uses - depending on your architecture - around 100-200
		2540	bytes of memory. In addition, stat requests need a stat buffer (possibly
		2541	a few hundred bytes), readdir requires a result buffer and so on. Perl
		2542	scalars and other data passed into aio requests will also be locked and
		2543	will consume memory till the request has entered the done state.
		2544
		2545	This is not awfully much, so queuing lots of requests is not usually a
		2546	problem.
		2547
		2548	Per-thread usage:
		2549
		2550	In the execution phase, some aio requests require more memory for
		2551	temporary buffers, and each thread requires a stack and other data
		2552	structures (usually around 16k-128k, depending on the OS).
		2553
		2554	=head1 KNOWN BUGS
		2555
		2556	Known bugs will be fixed in the next release :)
		2557
		2558	=head1 KNOWN ISSUES
		2559
		2560	Calls that try to "import" foreign memory areas (such as C<IO::AIO::mmap>
		2561	or C<IO::AIO::aio_slurp>) do not work with generic lvalues, such as
		2562	non-created hash slots or other scalars I didn't think of. It's best to
		2563	avoid such and either use scalar variables or making sure that the scalar
		2564	exists (e.g. by storing C<undef>) and isn't "funny" (e.g. tied).
		2565
		2566	I am not sure anything can be done about this, so this is considered a
		2567	known issue, rather than a bug.
		2568
335	=head1 SEE ALSO	2569	=head1 SEE ALSO
336		2570
337	L<Coro>, L<Linux::AIO>.	2571	L<AnyEvent::AIO> for easy integration into event loops, L<Coro::AIO> for a
		2572	more natural syntax.
338		2573
339	=head1 AUTHOR	2574	=head1 AUTHOR
340		2575
341	Marc Lehmann <schmorp@schmorp.de>	2576	Marc Lehmann <schmorp@schmorp.de>
342	http://home.schmorp.de/	2577	http://home.schmorp.de/

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