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Revision 1.8 by root, Sun Jul 31 17:24:05 2005 UTC vs.
Revision 1.52 by root, Tue Apr 10 05:01:33 2012 UTC

…		…
2	IO::AIO - Asynchronous Input/Output	2	IO::AIO - Asynchronous Input/Output
3		3
4	SYNOPSIS	4	SYNOPSIS
5	use IO::AIO;	5	use IO::AIO;
6		6
7	aio_open "/etc/passwd", O_RDONLY, 0, sub {	7	aio_open "/etc/passwd", IO::AIO::O_RDONLY, 0, sub {
8	my ($fh) = @_;	8	my $fh = shift
		9	or die "/etc/passwd: $!";
9	...	10	...
10	};	11	};
11		12
12	aio_unlink "/tmp/file", sub { };	13	aio_unlink "/tmp/file", sub { };
13		14
14	aio_read $fh, 30000, 1024, $buffer, 0, sub {	15	aio_read $fh, 30000, 1024, $buffer, 0, sub {
15	$_[0] > 0 or die "read error: $!";	16	$_[0] > 0 or die "read error: $!";
16	};	17	};
17		18
18	# Event	19	# version 2+ has request and group objects
19	Event->io (fd => IO::AIO::poll_fileno,	20	use IO::AIO 2;
20	poll => 'r',
21	cb => \&IO::AIO::poll_cb);
22		21
23	# Glib/Gtk2	22	aioreq_pri 4; # give next request a very high priority
24	add_watch Glib::IO IO::AIO::poll_fileno,	23	my $req = aio_unlink "/tmp/file", sub { };
25	in => sub { IO::AIO::poll_cb; 1 };	24	$req->cancel; # cancel request if still in queue
26		25
27	# Tk	26	my $grp = aio_group sub { print "all stats done\n" };
28	Tk::Event::IO->fileevent (IO::AIO::poll_fileno, "",	27	add $grp aio_stat "..." for ...;
29	readable => \&IO::AIO::poll_cb);
30
31	# Danga::Socket
32	Danga::Socket->AddOtherFds (IO::AIO::poll_fileno =>
33	\&IO::AIO::poll_cb);
34		28
35	DESCRIPTION	29	DESCRIPTION
36	This module implements asynchronous I/O using whatever means your	30	This module implements asynchronous I/O using whatever means your
37	operating system supports.	31	operating system supports. It is implemented as an interface to "libeio"
		32	(<http://software.schmorp.de/pkg/libeio.html>).
38		33
		34	Asynchronous means that operations that can normally block your program
		35	(e.g. reading from disk) will be done asynchronously: the operation will
		36	still block, but you can do something else in the meantime. This is
		37	extremely useful for programs that need to stay interactive even when
		38	doing heavy I/O (GUI programs, high performance network servers etc.),
		39	but can also be used to easily do operations in parallel that are
		40	normally done sequentially, e.g. stat'ing many files, which is much
		41	faster on a RAID volume or over NFS when you do a number of stat
		42	operations concurrently.
		43
		44	While most of this works on all types of file descriptors (for example
		45	sockets), using these functions on file descriptors that support
		46	nonblocking operation (again, sockets, pipes etc.) is very inefficient.
		47	Use an event loop for that (such as the EV module): IO::AIO will
		48	naturally fit into such an event loop itself.
		49
39	Currently, a number of threads are started that execute your read/writes	50	In this version, a number of threads are started that execute your
40	and signal their completion. You don't need thread support in your libc	51	requests and signal their completion. You don't need thread support in
41	or perl, and the threads created by this module will not be visible to	52	perl, and the threads created by this module will not be visible to
42	the pthreads library. In the future, this module might make use of the	53	perl. In the future, this module might make use of the native aio
43	native aio functions available on many operating systems. However, they	54	functions available on many operating systems. However, they are often
44	are often not well-supported (Linux doesn't allow them on normal files	55	not well-supported or restricted (GNU/Linux doesn't allow them on normal
45	currently, for example), and they would only support aio_read and	56	files currently, for example), and they would only support aio_read and
46	aio_write, so the remaining functionality would have to be implemented	57	aio_write, so the remaining functionality would have to be implemented
47	using threads anyway.	58	using threads anyway.
48		59
49	Although the module will work with in the presence of other threads, it	60	Although the module will work in the presence of other (Perl-) threads,
50	is currently not reentrant, so use appropriate locking yourself, always	61	it is currently not reentrant in any way, so use appropriate locking
51	call "poll_cb" from within the same thread, or never call "poll_cb" (or	62	yourself, always call "poll_cb" from within the same thread, or never
52	other "aio_" functions) recursively.	63	call "poll_cb" (or other "aio_" functions) recursively.
		64
		65	EXAMPLE
		66	This is a simple example that uses the EV module and loads /etc/passwd
		67	asynchronously:
		68
		69	use Fcntl;
		70	use EV;
		71	use IO::AIO;
		72
		73	# register the IO::AIO callback with EV
		74	my $aio_w = EV::io IO::AIO::poll_fileno, EV::READ, \&IO::AIO::poll_cb;
		75
		76	# queue the request to open /etc/passwd
		77	aio_open "/etc/passwd", IO::AIO::O_RDONLY, 0, sub {
		78	my $fh = shift
		79	or die "error while opening: $!";
		80
		81	# stat'ing filehandles is generally non-blocking
		82	my $size = -s $fh;
		83
		84	# queue a request to read the file
		85	my $contents;
		86	aio_read $fh, 0, $size, $contents, 0, sub {
		87	$_[0] == $size
		88	or die "short read: $!";
		89
		90	close $fh;
		91
		92	# file contents now in $contents
		93	print $contents;
		94
		95	# exit event loop and program
		96	EV::unloop;
		97	};
		98	};
		99
		100	# possibly queue up other requests, or open GUI windows,
		101	# check for sockets etc. etc.
		102
		103	# process events as long as there are some:
		104	EV::loop;
		105
		106	REQUEST ANATOMY AND LIFETIME
		107	Every "aio_*" function creates a request. which is a C data structure
		108	not directly visible to Perl.
		109
		110	If called in non-void context, every request function returns a Perl
		111	object representing the request. In void context, nothing is returned,
		112	which saves a bit of memory.
		113
		114	The perl object is a fairly standard ref-to-hash object. The hash
		115	contents are not used by IO::AIO so you are free to store anything you
		116	like in it.
		117
		118	During their existance, aio requests travel through the following
		119	states, in order:
		120
		121	ready
		122	Immediately after a request is created it is put into the ready
		123	state, waiting for a thread to execute it.
		124
		125	execute
		126	A thread has accepted the request for processing and is currently
		127	executing it (e.g. blocking in read).
		128
		129	pending
		130	The request has been executed and is waiting for result processing.
		131
		132	While request submission and execution is fully asynchronous, result
		133	processing is not and relies on the perl interpreter calling
		134	"poll_cb" (or another function with the same effect).
		135
		136	result
		137	The request results are processed synchronously by "poll_cb".
		138
		139	The "poll_cb" function will process all outstanding aio requests by
		140	calling their callbacks, freeing memory associated with them and
		141	managing any groups they are contained in.
		142
		143	done
		144	Request has reached the end of its lifetime and holds no resources
		145	anymore (except possibly for the Perl object, but its connection to
		146	the actual aio request is severed and calling its methods will
		147	either do nothing or result in a runtime error).
53		148
54	FUNCTIONS	149	FUNCTIONS
55	AIO FUNCTIONS	150	QUICK OVERVIEW
		151	This section simply lists the prototypes of the most important functions
		152	for quick reference. See the following sections for function-by-function
		153	documentation.
		154
		155	aio_wd $pathname, $callback->($wd)
		156	aio_open $pathname, $flags, $mode, $callback->($fh)
		157	aio_close $fh, $callback->($status)
		158	aio_seek $fh,$offset,$whence, $callback->($offs)
		159	aio_read $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
		160	aio_write $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
		161	aio_sendfile $out_fh, $in_fh, $in_offset, $length, $callback->($retval)
		162	aio_readahead $fh,$offset,$length, $callback->($retval)
		163	aio_stat $fh_or_path, $callback->($status)
		164	aio_lstat $fh, $callback->($status)
		165	aio_statvfs $fh_or_path, $callback->($statvfs)
		166	aio_utime $fh_or_path, $atime, $mtime, $callback->($status)
		167	aio_chown $fh_or_path, $uid, $gid, $callback->($status)
		168	aio_chmod $fh_or_path, $mode, $callback->($status)
		169	aio_truncate $fh_or_path, $offset, $callback->($status)
		170	aio_unlink $pathname, $callback->($status)
		171	aio_mknod $pathname, $mode, $dev, $callback->($status)
		172	aio_link $srcpath, $dstpath, $callback->($status)
		173	aio_symlink $srcpath, $dstpath, $callback->($status)
		174	aio_readlink $pathname, $callback->($link)
		175	aio_realpath $pathname, $callback->($link)
		176	aio_rename $srcpath, $dstpath, $callback->($status)
		177	aio_mkdir $pathname, $mode, $callback->($status)
		178	aio_rmdir $pathname, $callback->($status)
		179	aio_readdir $pathname, $callback->($entries)
		180	aio_readdirx $pathname, $flags, $callback->($entries, $flags)
		181	IO::AIO::READDIR_DENTS IO::AIO::READDIR_DIRS_FIRST
		182	IO::AIO::READDIR_STAT_ORDER IO::AIO::READDIR_FOUND_UNKNOWN
		183	aio_scandir $pathname, $maxreq, $callback->($dirs, $nondirs)
		184	aio_load $pathname, $data, $callback->($status)
		185	aio_copy $srcpath, $dstpath, $callback->($status)
		186	aio_move $srcpath, $dstpath, $callback->($status)
		187	aio_rmtree $pathname, $callback->($status)
		188	aio_sync $callback->($status)
		189	aio_syncfs $fh, $callback->($status)
		190	aio_fsync $fh, $callback->($status)
		191	aio_fdatasync $fh, $callback->($status)
		192	aio_sync_file_range $fh, $offset, $nbytes, $flags, $callback->($status)
		193	aio_pathsync $pathname, $callback->($status)
		194	aio_msync $scalar, $offset = 0, $length = undef, flags = 0, $callback->($status)
		195	aio_mtouch $scalar, $offset = 0, $length = undef, flags = 0, $callback->($status)
		196	aio_mlock $scalar, $offset = 0, $length = undef, $callback->($status)
		197	aio_mlockall $flags, $callback->($status)
		198	aio_group $callback->(...)
		199	aio_nop $callback->()
		200
		201	$prev_pri = aioreq_pri [$pri]
		202	aioreq_nice $pri_adjust
		203
		204	IO::AIO::poll_wait
		205	IO::AIO::poll_cb
		206	IO::AIO::poll
		207	IO::AIO::flush
		208	IO::AIO::max_poll_reqs $nreqs
		209	IO::AIO::max_poll_time $seconds
		210	IO::AIO::min_parallel $nthreads
		211	IO::AIO::max_parallel $nthreads
		212	IO::AIO::max_idle $nthreads
		213	IO::AIO::idle_timeout $seconds
		214	IO::AIO::max_outstanding $maxreqs
		215	IO::AIO::nreqs
		216	IO::AIO::nready
		217	IO::AIO::npending
		218
		219	IO::AIO::sendfile $ofh, $ifh, $offset, $count
		220	IO::AIO::fadvise $fh, $offset, $len, $advice
		221	IO::AIO::madvise $scalar, $offset, $length, $advice
		222	IO::AIO::mprotect $scalar, $offset, $length, $protect
		223	IO::AIO::munlock $scalar, $offset = 0, $length = undef
		224	IO::AIO::munlockall
		225
		226	API NOTES
56	All the "aio_*" calls are more or less thin wrappers around the syscall	227	All the "aio_*" calls are more or less thin wrappers around the syscall
57	with the same name (sans "aio_"). The arguments are similar or	228	with the same name (sans "aio_"). The arguments are similar or
58	identical, and they all accept an additional (and optional) $callback	229	identical, and they all accept an additional (and optional) $callback
59	argument which must be a code reference. This code reference will get	230	argument which must be a code reference. This code reference will be
60	called with the syscall return code (e.g. most syscalls return -1 on	231	called after the syscall has been executed in an asynchronous fashion.
61	error, unlike perl, which usually delivers "false") as it's sole	232	The results of the request will be passed as arguments to the callback
62	argument when the given syscall has been executed asynchronously.	233	(and, if an error occured, in $!) - for most requests the syscall return
		234	code (e.g. most syscalls return -1 on error, unlike perl, which usually
		235	delivers "false").
		236
		237	Some requests (such as "aio_readdir") pass the actual results and
		238	communicate failures by passing "undef".
63		239
64	All functions expecting a filehandle keep a copy of the filehandle	240	All functions expecting a filehandle keep a copy of the filehandle
65	internally until the request has finished.	241	internally until the request has finished.
66		242
		243	All functions return request objects of type IO::AIO::REQ that allow
		244	further manipulation of those requests while they are in-flight.
		245
67	The filenames you pass to these routines *must* be absolute. The reason	246	The pathnames you pass to these routines *should* be absolute. The
68	for this is that at the time the request is being executed, the current	247	reason for this is that at the time the request is being executed, the
69	working directory could have changed. Alternatively, you can make sure	248	current working directory could have changed. Alternatively, you can
70	that you never change the current working directory.	249	make sure that you never change the current working directory anywhere
		250	in the program and then use relative paths. You can also take advantage
		251	of IO::AIOs working directory abstraction, that lets you specify paths
		252	relative to some previously-opened "working directory object" - see the
		253	description of the "IO::AIO::WD" class later in this document.
71		254
		255	To encode pathnames as octets, either make sure you either: a) always
		256	pass in filenames you got from outside (command line, readdir etc.)
		257	without tinkering, b) are in your native filesystem encoding, c) use the
		258	Encode module and encode your pathnames to the locale (or other)
		259	encoding in effect in the user environment, d) use
		260	Glib::filename_from_unicode on unicode filenames or e) use something
		261	else to ensure your scalar has the correct contents.
		262
		263	This works, btw. independent of the internal UTF-8 bit, which IO::AIO
		264	handles correctly whether it is set or not.
		265
		266	AIO REQUEST FUNCTIONS
		267	$prev_pri = aioreq_pri [$pri]
		268	Returns the priority value that would be used for the next request
		269	and, if $pri is given, sets the priority for the next aio request.
		270
		271	The default priority is 0, the minimum and maximum priorities are -4
		272	and 4, respectively. Requests with higher priority will be serviced
		273	first.
		274
		275	The priority will be reset to 0 after each call to one of the
		276	"aio_*" functions.
		277
		278	Example: open a file with low priority, then read something from it
		279	with higher priority so the read request is serviced before other
		280	low priority open requests (potentially spamming the cache):
		281
		282	aioreq_pri -3;
		283	aio_open ..., sub {
		284	return unless $_[0];
		285
		286	aioreq_pri -2;
		287	aio_read $_[0], ..., sub {
		288	...
		289	};
		290	};
		291
		292	aioreq_nice $pri_adjust
		293	Similar to "aioreq_pri", but subtracts the given value from the
		294	current priority, so the effect is cumulative.
		295
72	aio_open $pathname, $flags, $mode, $callback	296	aio_open $pathname, $flags, $mode, $callback->($fh)
73	Asynchronously open or create a file and call the callback with a	297	Asynchronously open or create a file and call the callback with a
74	newly created filehandle for the file.	298	newly created filehandle for the file.
75		299
76	The pathname passed to "aio_open" must be absolute. See API NOTES,	300	The pathname passed to "aio_open" must be absolute. See API NOTES,
77	above, for an explanation.	301	above, for an explanation.
…		…
80	They are the same as used by "sysopen".	304	They are the same as used by "sysopen".
81		305
82	Likewise, $mode specifies the mode of the newly created file, if it	306	Likewise, $mode specifies the mode of the newly created file, if it
83	didn't exist and "O_CREAT" has been given, just like perl's	307	didn't exist and "O_CREAT" has been given, just like perl's
84	"sysopen", except that it is mandatory (i.e. use 0 if you don't	308	"sysopen", except that it is mandatory (i.e. use 0 if you don't
85	create new files, and 0666 or 0777 if you do).	309	create new files, and 0666 or 0777 if you do). Note that the $mode
		310	will be modified by the umask in effect then the request is being
		311	executed, so better never change the umask.
86		312
87	Example:	313	Example:
88		314
89	aio_open "/etc/passwd", O_RDONLY, 0, sub {	315	aio_open "/etc/passwd", IO::AIO::O_RDONLY, 0, sub {
90	if ($_[0]) {	316	if ($_[0]) {
91	print "open successful, fh is $_[0]\n";	317	print "open successful, fh is $_[0]\n";
92	...	318	...
93	} else {	319	} else {
94	die "open failed: $!\n";	320	die "open failed: $!\n";
95	}	321	}
96	};	322	};
97		323
		324	In addition to all the common open modes/flags ("O_RDONLY",
		325	"O_WRONLY", "O_RDWR", "O_CREAT", "O_TRUNC", "O_EXCL" and
		326	"O_APPEND"), the following POSIX and non-POSIX constants are
		327	available (missing ones on your system are, as usual, 0):
		328
		329	"O_ASYNC", "O_DIRECT", "O_NOATIME", "O_CLOEXEC", "O_NOCTTY",
		330	"O_NOFOLLOW", "O_NONBLOCK", "O_EXEC", "O_SEARCH", "O_DIRECTORY",
		331	"O_DSYNC", "O_RSYNC", "O_SYNC" and "O_TTY_INIT".
		332
98	aio_close $fh, $callback	333	aio_close $fh, $callback->($status)
99	Asynchronously close a file and call the callback with the result	334	Asynchronously close a file and call the callback with the result
100	code. *WARNING:* although accepted, you should not pass in a perl	335	code.
101	filehandle here, as perl will likely close the file descriptor
102	another time when the filehandle is destroyed. Normally, you can
103	safely call perls "close" or just let filehandles go out of scope.
104		336
105	This is supposed to be a bug in the API, so that might change. It's	337	Unfortunately, you can't do this to perl. Perl *insists* very
106	therefore best to avoid this function.	338	strongly on closing the file descriptor associated with the
		339	filehandle itself.
107		340
		341	Therefore, "aio_close" will not close the filehandle - instead it
		342	will use dup2 to overwrite the file descriptor with the write-end of
		343	a pipe (the pipe fd will be created on demand and will be cached).
		344
		345	Or in other words: the file descriptor will be closed, but it will
		346	not be free for reuse until the perl filehandle is closed.
		347
		348	aio_seek $fh, $offset, $whence, $callback->($offs)
		349	Seeks the filehandle to the new $offset, similarly to perl's
		350	"sysseek". The $whence can use the traditional values (0 for
		351	"IO::AIO::SEEK_SET", 1 for "IO::AIO::SEEK_CUR" or 2 for
		352	"IO::AIO::SEEK_END").
		353
		354	The resulting absolute offset will be passed to the callback, or -1
		355	in case of an error.
		356
		357	In theory, the $whence constants could be different than the
		358	corresponding values from Fcntl, but perl guarantees they are the
		359	same, so don't panic.
		360
		361	As a GNU/Linux (and maybe Solaris) extension, also the constants
		362	"IO::AIO::SEEK_DATA" and "IO::AIO::SEEK_HOLE" are available, if they
		363	could be found. No guarantees about suitability for use in
		364	"aio_seek" or Perl's "sysseek" can be made though, although I would
		365	naively assume they "just work".
		366
108	aio_read $fh,$offset,$length, $data,$dataoffset,$callback	367	aio_read $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
109	aio_write $fh,$offset,$length, $data,$dataoffset,$callback	368	aio_write $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
110	Reads or writes "length" bytes from the specified "fh" and "offset"	369	Reads or writes $length bytes from or to the specified $fh and
111	into the scalar given by "data" and offset "dataoffset" and calls	370	$offset into the scalar given by $data and offset $dataoffset and
112	the callback without the actual number of bytes read (or -1 on	371	calls the callback without the actual number of bytes read (or -1 on
113	error, just like the syscall).	372	error, just like the syscall).
		373
		374	"aio_read" will, like "sysread", shrink or grow the $data scalar to
		375	offset plus the actual number of bytes read.
		376
		377	If $offset is undefined, then the current file descriptor offset
		378	will be used (and updated), otherwise the file descriptor offset
		379	will not be changed by these calls.
		380
		381	If $length is undefined in "aio_write", use the remaining length of
		382	$data.
		383
		384	If $dataoffset is less than zero, it will be counted from the end of
		385	$data.
		386
		387	The $data scalar *MUST NOT* be modified in any way while the request
		388	is outstanding. Modifying it can result in segfaults or World War
		389	III (if the necessary/optional hardware is installed).
114		390
115	Example: Read 15 bytes at offset 7 into scalar $buffer, starting at	391	Example: Read 15 bytes at offset 7 into scalar $buffer, starting at
116	offset 0 within the scalar:	392	offset 0 within the scalar:
117		393
118	aio_read $fh, 7, 15, $buffer, 0, sub {	394	aio_read $fh, 7, 15, $buffer, 0, sub {
119	$_[0] > 0 or die "read error: $!";	395	$_[0] > 0 or die "read error: $!";
120	print "read $_[0] bytes: <$buffer>\n";	396	print "read $_[0] bytes: <$buffer>\n";
121	};	397	};
122		398
		399	aio_sendfile $out_fh, $in_fh, $in_offset, $length, $callback->($retval)
		400	Tries to copy $length bytes from $in_fh to $out_fh. It starts
		401	reading at byte offset $in_offset, and starts writing at the current
		402	file offset of $out_fh. Because of that, it is not safe to issue
		403	more than one "aio_sendfile" per $out_fh, as they will interfere
		404	with each other. The same $in_fh works fine though, as this function
		405	does not move or use the file offset of $in_fh.
		406
		407	Please note that "aio_sendfile" can read more bytes from $in_fh than
		408	are written, and there is no way to find out how many more bytes
		409	have been read from "aio_sendfile" alone, as "aio_sendfile" only
		410	provides the number of bytes written to $out_fh. Only if the result
		411	value equals $length one can assume that $length bytes have been
		412	read.
		413
		414	Unlike with other "aio_" functions, it makes a lot of sense to use
		415	"aio_sendfile" on non-blocking sockets, as long as one end
		416	(typically the $in_fh) is a file - the file I/O will then be
		417	asynchronous, while the socket I/O will be non-blocking. Note,
		418	however, that you can run into a trap where "aio_sendfile" reads
		419	some data with readahead, then fails to write all data, and when the
		420	socket is ready the next time, the data in the cache is already
		421	lost, forcing "aio_sendfile" to again hit the disk. Explicit
		422	"aio_read" + "aio_write" let's you better control resource usage.
		423
		424	This call tries to make use of a native "sendfile"-like syscall to
		425	provide zero-copy operation. For this to work, $out_fh should refer
		426	to a socket, and $in_fh should refer to an mmap'able file.
		427
		428	If a native sendfile cannot be found or it fails with "ENOSYS",
		429	"EINVAL", "ENOTSUP", "EOPNOTSUPP", "EAFNOSUPPORT", "EPROTOTYPE" or
		430	"ENOTSOCK", it will be emulated, so you can call "aio_sendfile" on
		431	any type of filehandle regardless of the limitations of the
		432	operating system.
		433
		434	As native sendfile syscalls (as practically any non-POSIX interface
		435	hacked together in a hurry to improve benchmark numbers) tend to be
		436	rather buggy on many systems, this implementation tries to work
		437	around some known bugs in Linux and FreeBSD kernels (probably
		438	others, too), but that might fail, so you really really should check
		439	the return value of "aio_sendfile" - fewre bytes than expected might
		440	have been transferred.
		441
123	aio_readahead $fh,$offset,$length, $callback	442	aio_readahead $fh,$offset,$length, $callback->($retval)
124	Asynchronously reads the specified byte range into the page cache,
125	using the "readahead" syscall. If that syscall doesn't exist (likely
126	if your OS isn't Linux) the status will be -1 and $! is set to
127	"ENOSYS".
128
129	"aio_readahead" populates the page cache with data from a file so	443	"aio_readahead" populates the page cache with data from a file so
130	that subsequent reads from that file will not block on disk I/O. The	444	that subsequent reads from that file will not block on disk I/O. The
131	$offset argument specifies the starting point from which data is to	445	$offset argument specifies the starting point from which data is to
132	be read and $length specifies the number of bytes to be read. I/O is	446	be read and $length specifies the number of bytes to be read. I/O is
133	performed in whole pages, so that offset is effectively rounded down	447	performed in whole pages, so that offset is effectively rounded down
134	to a page boundary and bytes are read up to the next page boundary	448	to a page boundary and bytes are read up to the next page boundary
135	greater than or equal to (off-set+length). "aio_readahead" does not	449	greater than or equal to (off-set+length). "aio_readahead" does not
136	read beyond the end of the file. The current file offset of the file	450	read beyond the end of the file. The current file offset of the file
137	is left unchanged.	451	is left unchanged.
138		452
		453	If that syscall doesn't exist (likely if your OS isn't Linux) it
		454	will be emulated by simply reading the data, which would have a
		455	similar effect.
		456
139	aio_stat $fh_or_path, $callback	457	aio_stat $fh_or_path, $callback->($status)
140	aio_lstat $fh, $callback	458	aio_lstat $fh, $callback->($status)
141	Works like perl's "stat" or "lstat" in void context. The callback	459	Works like perl's "stat" or "lstat" in void context. The callback
142	will be called after the stat and the results will be available	460	will be called after the stat and the results will be available
143	using "stat _" or "-s _" etc...	461	using "stat _" or "-s _" etc...
144		462
145	The pathname passed to "aio_stat" must be absolute. See API NOTES,	463	The pathname passed to "aio_stat" must be absolute. See API NOTES,
…		…
148	Currently, the stats are always 64-bit-stats, i.e. instead of	466	Currently, the stats are always 64-bit-stats, i.e. instead of
149	returning an error when stat'ing a large file, the results will be	467	returning an error when stat'ing a large file, the results will be
150	silently truncated unless perl itself is compiled with large file	468	silently truncated unless perl itself is compiled with large file
151	support.	469	support.
152		470
		471	To help interpret the mode and dev/rdev stat values, IO::AIO offers
		472	the following constants and functions (if not implemented, the
		473	constants will be 0 and the functions will either "croak" or fall
		474	back on traditional behaviour).
		475
		476	"S_IFMT", "S_IFIFO", "S_IFCHR", "S_IFBLK", "S_IFLNK", "S_IFREG",
		477	"S_IFDIR", "S_IFWHT", "S_IFSOCK", "IO::AIO::major $dev_t",
		478	"IO::AIO::minor $dev_t", "IO::AIO::makedev $major, $minor".
		479
153	Example: Print the length of /etc/passwd:	480	Example: Print the length of /etc/passwd:
154		481
155	aio_stat "/etc/passwd", sub {	482	aio_stat "/etc/passwd", sub {
156	$_[0] and die "stat failed: $!";	483	$_[0] and die "stat failed: $!";
157	print "size is ", -s _, "\n";	484	print "size is ", -s _, "\n";
158	};	485	};
159		486
		487	aio_statvfs $fh_or_path, $callback->($statvfs)
		488	Works like the POSIX "statvfs" or "fstatvfs" syscalls, depending on
		489	whether a file handle or path was passed.
		490
		491	On success, the callback is passed a hash reference with the
		492	following members: "bsize", "frsize", "blocks", "bfree", "bavail",
		493	"files", "ffree", "favail", "fsid", "flag" and "namemax". On
		494	failure, "undef" is passed.
		495
		496	The following POSIX IO::AIO::ST_* constants are defined: "ST_RDONLY"
		497	and "ST_NOSUID".
		498
		499	The following non-POSIX IO::AIO::ST_* flag masks are defined to
		500	their correct value when available, or to 0 on systems that do not
		501	support them: "ST_NODEV", "ST_NOEXEC", "ST_SYNCHRONOUS",
		502	"ST_MANDLOCK", "ST_WRITE", "ST_APPEND", "ST_IMMUTABLE",
		503	"ST_NOATIME", "ST_NODIRATIME" and "ST_RELATIME".
		504
		505	Example: stat "/wd" and dump out the data if successful.
		506
		507	aio_statvfs "/wd", sub {
		508	my $f = $_[0]
		509	or die "statvfs: $!";
		510
		511	use Data::Dumper;
		512	say Dumper $f;
		513	};
		514
		515	# result:
		516	{
		517	bsize => 1024,
		518	bfree => 4333064312,
		519	blocks => 10253828096,
		520	files => 2050765568,
		521	flag => 4096,
		522	favail => 2042092649,
		523	bavail => 4333064312,
		524	ffree => 2042092649,
		525	namemax => 255,
		526	frsize => 1024,
		527	fsid => 1810
		528	}
		529
		530	aio_utime $fh_or_path, $atime, $mtime, $callback->($status)
		531	Works like perl's "utime" function (including the special case of
		532	$atime and $mtime being undef). Fractional times are supported if
		533	the underlying syscalls support them.
		534
		535	When called with a pathname, uses utimes(2) if available, otherwise
		536	utime(2). If called on a file descriptor, uses futimes(2) if
		537	available, otherwise returns ENOSYS, so this is not portable.
		538
		539	Examples:
		540
		541	# set atime and mtime to current time (basically touch(1)):
		542	aio_utime "path", undef, undef;
		543	# set atime to current time and mtime to beginning of the epoch:
		544	aio_utime "path", time, undef; # undef==0
		545
		546	aio_chown $fh_or_path, $uid, $gid, $callback->($status)
		547	Works like perl's "chown" function, except that "undef" for either
		548	$uid or $gid is being interpreted as "do not change" (but -1 can
		549	also be used).
		550
		551	Examples:
		552
		553	# same as "chown root path" in the shell:
		554	aio_chown "path", 0, -1;
		555	# same as above:
		556	aio_chown "path", 0, undef;
		557
		558	aio_truncate $fh_or_path, $offset, $callback->($status)
		559	Works like truncate(2) or ftruncate(2).
		560
		561	aio_chmod $fh_or_path, $mode, $callback->($status)
		562	Works like perl's "chmod" function.
		563
160	aio_unlink $pathname, $callback	564	aio_unlink $pathname, $callback->($status)
161	Asynchronously unlink (delete) a file and call the callback with the	565	Asynchronously unlink (delete) a file and call the callback with the
162	result code.	566	result code.
163		567
		568	aio_mknod $pathname, $mode, $dev, $callback->($status)
		569	[EXPERIMENTAL]
		570
		571	Asynchronously create a device node (or fifo). See mknod(2).
		572
		573	The only (POSIX-) portable way of calling this function is:
		574
		575	aio_mknod $pathname, IO::AIO::S_IFIFO | $mode, 0, sub { ...
		576
		577	See "aio_stat" for info about some potentially helpful extra
		578	constants and functions.
		579
		580	aio_link $srcpath, $dstpath, $callback->($status)
		581	Asynchronously create a new link to the existing object at $srcpath
		582	at the path $dstpath and call the callback with the result code.
		583
		584	aio_symlink $srcpath, $dstpath, $callback->($status)
		585	Asynchronously create a new symbolic link to the existing object at
		586	$srcpath at the path $dstpath and call the callback with the result
		587	code.
		588
		589	aio_readlink $pathname, $callback->($link)
		590	Asynchronously read the symlink specified by $path and pass it to
		591	the callback. If an error occurs, nothing or undef gets passed to
		592	the callback.
		593
		594	aio_realpath $pathname, $callback->($path)
		595	Asynchronously make the path absolute and resolve any symlinks in
		596	$path. The resulting path only consists of directories (Same as
		597	Cwd::realpath).
		598
		599	This request can be used to get the absolute path of the current
		600	working directory by passing it a path of . (a single dot).
		601
		602	aio_rename $srcpath, $dstpath, $callback->($status)
		603	Asynchronously rename the object at $srcpath to $dstpath, just as
		604	rename(2) and call the callback with the result code.
		605
		606	aio_mkdir $pathname, $mode, $callback->($status)
		607	Asynchronously mkdir (create) a directory and call the callback with
		608	the result code. $mode will be modified by the umask at the time the
		609	request is executed, so do not change your umask.
		610
		611	aio_rmdir $pathname, $callback->($status)
		612	Asynchronously rmdir (delete) a directory and call the callback with
		613	the result code.
		614
		615	aio_readdir $pathname, $callback->($entries)
		616	Unlike the POSIX call of the same name, "aio_readdir" reads an
		617	entire directory (i.e. opendir + readdir + closedir). The entries
		618	will not be sorted, and will NOT include the "." and ".." entries.
		619
		620	The callback is passed a single argument which is either "undef" or
		621	an array-ref with the filenames.
		622
		623	aio_readdirx $pathname, $flags, $callback->($entries, $flags)
		624	Quite similar to "aio_readdir", but the $flags argument allows one
		625	to tune behaviour and output format. In case of an error, $entries
		626	will be "undef".
		627
		628	The flags are a combination of the following constants, ORed
		629	together (the flags will also be passed to the callback, possibly
		630	modified):
		631
		632	IO::AIO::READDIR_DENTS
		633	When this flag is off, then the callback gets an arrayref
		634	consisting of names only (as with "aio_readdir"), otherwise it
		635	gets an arrayref with "[$name, $type, $inode]" arrayrefs, each
		636	describing a single directory entry in more detail.
		637
		638	$name is the name of the entry.
		639
		640	$type is one of the "IO::AIO::DT_xxx" constants:
		641
		642	"IO::AIO::DT_UNKNOWN", "IO::AIO::DT_FIFO", "IO::AIO::DT_CHR",
		643	"IO::AIO::DT_DIR", "IO::AIO::DT_BLK", "IO::AIO::DT_REG",
		644	"IO::AIO::DT_LNK", "IO::AIO::DT_SOCK", "IO::AIO::DT_WHT".
		645
		646	"IO::AIO::DT_UNKNOWN" means just that: readdir does not know. If
		647	you need to know, you have to run stat yourself. Also, for speed
		648	reasons, the $type scalars are read-only: you can not modify
		649	them.
		650
		651	$inode is the inode number (which might not be exact on systems
		652	with 64 bit inode numbers and 32 bit perls). This field has
		653	unspecified content on systems that do not deliver the inode
		654	information.
		655
		656	IO::AIO::READDIR_DIRS_FIRST
		657	When this flag is set, then the names will be returned in an
		658	order where likely directories come first, in optimal stat
		659	order. This is useful when you need to quickly find directories,
		660	or you want to find all directories while avoiding to stat()
		661	each entry.
		662
		663	If the system returns type information in readdir, then this is
		664	used to find directories directly. Otherwise, likely directories
		665	are names beginning with ".", or otherwise names with no dots,
		666	of which names with short names are tried first.
		667
		668	IO::AIO::READDIR_STAT_ORDER
		669	When this flag is set, then the names will be returned in an
		670	order suitable for stat()'ing each one. That is, when you plan
		671	to stat() all files in the given directory, then the returned
		672	order will likely be fastest.
		673
		674	If both this flag and "IO::AIO::READDIR_DIRS_FIRST" are
		675	specified, then the likely dirs come first, resulting in a less
		676	optimal stat order.
		677
		678	IO::AIO::READDIR_FOUND_UNKNOWN
		679	This flag should not be set when calling "aio_readdirx".
		680	Instead, it is being set by "aio_readdirx", when any of the
		681	$type's found were "IO::AIO::DT_UNKNOWN". The absence of this
		682	flag therefore indicates that all $type's are known, which can
		683	be used to speed up some algorithms.
		684
		685	aio_load $pathname, $data, $callback->($status)
		686	This is a composite request that tries to fully load the given file
		687	into memory. Status is the same as with aio_read.
		688
		689	aio_copy $srcpath, $dstpath, $callback->($status)
		690	Try to copy the *file* (directories not supported as either source
		691	or destination) from $srcpath to $dstpath and call the callback with
		692	a status of 0 (ok) or -1 (error, see $!).
		693
		694	This is a composite request that creates the destination file with
		695	mode 0200 and copies the contents of the source file into it using
		696	"aio_sendfile", followed by restoring atime, mtime, access mode and
		697	uid/gid, in that order.
		698
		699	If an error occurs, the partial destination file will be unlinked,
		700	if possible, except when setting atime, mtime, access mode and
		701	uid/gid, where errors are being ignored.
		702
		703	aio_move $srcpath, $dstpath, $callback->($status)
		704	Try to move the *file* (directories not supported as either source
		705	or destination) from $srcpath to $dstpath and call the callback with
		706	a status of 0 (ok) or -1 (error, see $!).
		707
		708	This is a composite request that tries to rename(2) the file first;
		709	if rename fails with "EXDEV", it copies the file with "aio_copy"
		710	and, if that is successful, unlinks the $srcpath.
		711
		712	aio_scandir $pathname, $maxreq, $callback->($dirs, $nondirs)
		713	Scans a directory (similar to "aio_readdir") but additionally tries
		714	to efficiently separate the entries of directory $path into two sets
		715	of names, directories you can recurse into (directories), and ones
		716	you cannot recurse into (everything else, including symlinks to
		717	directories).
		718
		719	"aio_scandir" is a composite request that creates of many sub
		720	requests_ $maxreq specifies the maximum number of outstanding aio
		721	requests that this function generates. If it is "<= 0", then a
		722	suitable default will be chosen (currently 4).
		723
		724	On error, the callback is called without arguments, otherwise it
		725	receives two array-refs with path-relative entry names.
		726
		727	Example:
		728
		729	aio_scandir $dir, 0, sub {
		730	my ($dirs, $nondirs) = @_;
		731	print "real directories: @$dirs\n";
		732	print "everything else: @$nondirs\n";
		733	};
		734
		735	Implementation notes.
		736
		737	The "aio_readdir" cannot be avoided, but "stat()"'ing every entry
		738	can.
		739
		740	If readdir returns file type information, then this is used directly
		741	to find directories.
		742
		743	Otherwise, after reading the directory, the modification time, size
		744	etc. of the directory before and after the readdir is checked, and
		745	if they match (and isn't the current time), the link count will be
		746	used to decide how many entries are directories (if >= 2).
		747	Otherwise, no knowledge of the number of subdirectories will be
		748	assumed.
		749
		750	Then entries will be sorted into likely directories a non-initial
		751	dot currently) and likely non-directories (see "aio_readdirx"). Then
		752	every entry plus an appended "/." will be "stat"'ed, likely
		753	directories first, in order of their inode numbers. If that
		754	succeeds, it assumes that the entry is a directory or a symlink to
		755	directory (which will be checked separately). This is often faster
		756	than stat'ing the entry itself because filesystems might detect the
		757	type of the entry without reading the inode data (e.g. ext2fs
		758	filetype feature), even on systems that cannot return the filetype
		759	information on readdir.
		760
		761	If the known number of directories (link count - 2) has been
		762	reached, the rest of the entries is assumed to be non-directories.
		763
		764	This only works with certainty on POSIX (= UNIX) filesystems, which
		765	fortunately are the vast majority of filesystems around.
		766
		767	It will also likely work on non-POSIX filesystems with reduced
		768	efficiency as those tend to return 0 or 1 as link counts, which
		769	disables the directory counting heuristic.
		770
		771	aio_rmtree $pathname, $callback->($status)
		772	Delete a directory tree starting (and including) $path, return the
		773	status of the final "rmdir" only. This is a composite request that
		774	uses "aio_scandir" to recurse into and rmdir directories, and unlink
		775	everything else.
		776
		777	aio_sync $callback->($status)
		778	Asynchronously call sync and call the callback when finished.
		779
164	aio_fsync $fh, $callback	780	aio_fsync $fh, $callback->($status)
165	Asynchronously call fsync on the given filehandle and call the	781	Asynchronously call fsync on the given filehandle and call the
166	callback with the fsync result code.	782	callback with the fsync result code.
167		783
168	aio_fdatasync $fh, $callback	784	aio_fdatasync $fh, $callback->($status)
169	Asynchronously call fdatasync on the given filehandle and call the	785	Asynchronously call fdatasync on the given filehandle and call the
170	callback with the fdatasync result code. Might set $! to "ENOSYS" if	786	callback with the fdatasync result code.
171	"fdatasync" is not available.	787
		788	If this call isn't available because your OS lacks it or it couldn't
		789	be detected, it will be emulated by calling "fsync" instead.
		790
		791	aio_syncfs $fh, $callback->($status)
		792	Asynchronously call the syncfs syscall to sync the filesystem
		793	associated to the given filehandle and call the callback with the
		794	syncfs result code. If syncfs is not available, calls sync(), but
		795	returns -1 and sets errno to "ENOSYS" nevertheless.
		796
		797	aio_sync_file_range $fh, $offset, $nbytes, $flags, $callback->($status)
		798	Sync the data portion of the file specified by $offset and $length
		799	to disk (but NOT the metadata), by calling the Linux-specific
		800	sync_file_range call. If sync_file_range is not available or it
		801	returns ENOSYS, then fdatasync or fsync is being substituted.
		802
		803	$flags can be a combination of
		804	"IO::AIO::SYNC_FILE_RANGE_WAIT_BEFORE",
		805	"IO::AIO::SYNC_FILE_RANGE_WRITE" and
		806	"IO::AIO::SYNC_FILE_RANGE_WAIT_AFTER": refer to the sync_file_range
		807	manpage for details.
		808
		809	aio_pathsync $pathname, $callback->($status)
		810	This request tries to open, fsync and close the given path. This is
		811	a composite request intended to sync directories after directory
		812	operations (E.g. rename). This might not work on all operating
		813	systems or have any specific effect, but usually it makes sure that
		814	directory changes get written to disc. It works for anything that
		815	can be opened for read-only, not just directories.
		816
		817	Future versions of this function might fall back to other methods
		818	when "fsync" on the directory fails (such as calling "sync").
		819
		820	Passes 0 when everything went ok, and -1 on error.
		821
		822	aio_msync $scalar, $offset = 0, $length = undef, flags = 0,
		823	$callback->($status)
		824	This is a rather advanced IO::AIO call, which only works on
		825	mmap(2)ed scalars (see the "IO::AIO::mmap" function, although it
		826	also works on data scalars managed by the Sys::Mmap or Mmap modules,
		827	note that the scalar must only be modified in-place while an aio
		828	operation is pending on it).
		829
		830	It calls the "msync" function of your OS, if available, with the
		831	memory area starting at $offset in the string and ending $length
		832	bytes later. If $length is negative, counts from the end, and if
		833	$length is "undef", then it goes till the end of the string. The
		834	flags can be a combination of "IO::AIO::MS_ASYNC",
		835	"IO::AIO::MS_INVALIDATE" and "IO::AIO::MS_SYNC".
		836
		837	aio_mtouch $scalar, $offset = 0, $length = undef, flags = 0,
		838	$callback->($status)
		839	This is a rather advanced IO::AIO call, which works best on
		840	mmap(2)ed scalars.
		841
		842	It touches (reads or writes) all memory pages in the specified range
		843	inside the scalar. All caveats and parameters are the same as for
		844	"aio_msync", above, except for flags, which must be either 0 (which
		845	reads all pages and ensures they are instantiated) or
		846	"IO::AIO::MT_MODIFY", which modifies the memory page s(by reading
		847	and writing an octet from it, which dirties the page).
		848
		849	aio_mlock $scalar, $offset = 0, $length = undef, $callback->($status)
		850	This is a rather advanced IO::AIO call, which works best on
		851	mmap(2)ed scalars.
		852
		853	It reads in all the pages of the underlying storage into memory (if
		854	any) and locks them, so they are not getting swapped/paged out or
		855	removed.
		856
		857	If $length is undefined, then the scalar will be locked till the
		858	end.
		859
		860	On systems that do not implement "mlock", this function returns -1
		861	and sets errno to "ENOSYS".
		862
		863	Note that the corresponding "munlock" is synchronous and is
		864	documented under "MISCELLANEOUS FUNCTIONS".
		865
		866	Example: open a file, mmap and mlock it - both will be undone when
		867	$data gets destroyed.
		868
		869	open my $fh, "<", $path or die "$path: $!";
		870	my $data;
		871	IO::AIO::mmap $data, -s $fh, IO::AIO::PROT_READ, IO::AIO::MAP_SHARED, $fh;
		872	aio_mlock $data; # mlock in background
		873
		874	aio_mlockall $flags, $callback->($status)
		875	Calls the "mlockall" function with the given $flags (a combination
		876	of "IO::AIO::MCL_CURRENT" and "IO::AIO::MCL_FUTURE").
		877
		878	On systems that do not implement "mlockall", this function returns
		879	-1 and sets errno to "ENOSYS".
		880
		881	Note that the corresponding "munlockall" is synchronous and is
		882	documented under "MISCELLANEOUS FUNCTIONS".
		883
		884	Example: asynchronously lock all current and future pages into
		885	memory.
		886
		887	aio_mlockall IO::AIO::MCL_FUTURE;
		888
		889	aio_fiemap $fh, $start, $length, $flags, $count, $cb->(\@extents)
		890	Queries the extents of the given file (by calling the Linux FIEMAP
		891	ioctl, see <http://cvs.schmorp.de/IO-AIO/doc/fiemap.txt> for
		892	details). If the "ioctl" is not available on your OS, then this
		893	rquiest will fail with "ENOSYS".
		894
		895	$start is the starting offset to query extents for, $length is the
		896	size of the range to query - if it is "undef", then the whole file
		897	will be queried.
		898
		899	$flags is a combination of flags ("IO::AIO::FIEMAP_FLAG_SYNC" or
		900	"IO::AIO::FIEMAP_FLAG_XATTR" - "IO::AIO::FIEMAP_FLAGS_COMPAT" is
		901	also exported), and is normally 0 or "IO::AIO::FIEMAP_FLAG_SYNC" to
		902	query the data portion.
		903
		904	$count is the maximum number of extent records to return. If it is
		905	"undef", then IO::AIO queries all extents of the file. As a very
		906	special case, if it is 0, then the callback receives the number of
		907	extents instead of the extents themselves.
		908
		909	If an error occurs, the callback receives no arguments. The special
		910	"errno" value "IO::AIO::EBADR" is available to test for flag errors.
		911
		912	Otherwise, the callback receives an array reference with extent
		913	structures. Each extent structure is an array reference itself, with
		914	the following members:
		915
		916	[$logical, $physical, $length, $flags]
		917
		918	Flags is any combination of the following flag values (typically
		919	either 0 or "IO::AIO::FIEMAP_EXTENT_LAST"):
		920
		921	"IO::AIO::FIEMAP_EXTENT_LAST", "IO::AIO::FIEMAP_EXTENT_UNKNOWN",
		922	"IO::AIO::FIEMAP_EXTENT_DELALLOC", "IO::AIO::FIEMAP_EXTENT_ENCODED",
		923	"IO::AIO::FIEMAP_EXTENT_DATA_ENCRYPTED",
		924	"IO::AIO::FIEMAP_EXTENT_NOT_ALIGNED",
		925	"IO::AIO::FIEMAP_EXTENT_DATA_INLINE",
		926	"IO::AIO::FIEMAP_EXTENT_DATA_TAIL",
		927	"IO::AIO::FIEMAP_EXTENT_UNWRITTEN", "IO::AIO::FIEMAP_EXTENT_MERGED"
		928	or "IO::AIO::FIEMAP_EXTENT_SHARED".
		929
		930	aio_group $callback->(...)
		931	This is a very special aio request: Instead of doing something, it
		932	is a container for other aio requests, which is useful if you want
		933	to bundle many requests into a single, composite, request with a
		934	definite callback and the ability to cancel the whole request with
		935	its subrequests.
		936
		937	Returns an object of class IO::AIO::GRP. See its documentation below
		938	for more info.
		939
		940	Example:
		941
		942	my $grp = aio_group sub {
		943	print "all stats done\n";
		944	};
		945
		946	add $grp
		947	(aio_stat ...),
		948	(aio_stat ...),
		949	...;
		950
		951	aio_nop $callback->()
		952	This is a special request - it does nothing in itself and is only
		953	used for side effects, such as when you want to add a dummy request
		954	to a group so that finishing the requests in the group depends on
		955	executing the given code.
		956
		957	While this request does nothing, it still goes through the execution
		958	phase and still requires a worker thread. Thus, the callback will
		959	not be executed immediately but only after other requests in the
		960	queue have entered their execution phase. This can be used to
		961	measure request latency.
		962
		963	IO::AIO::aio_busy $fractional_seconds, $callback->() *NOT EXPORTED*
		964	Mainly used for debugging and benchmarking, this aio request puts
		965	one of the request workers to sleep for the given time.
		966
		967	While it is theoretically handy to have simple I/O scheduling
		968	requests like sleep and file handle readable/writable, the overhead
		969	this creates is immense (it blocks a thread for a long time) so do
		970	not use this function except to put your application under
		971	artificial I/O pressure.
		972
		973	IO::AIO::WD - multiple working directories
		974	Your process only has one current working directory, which is used by
		975	all threads. This makes it hard to use relative paths (some other
		976	component could call "chdir" at any time, and it is hard to control when
		977	the path will be used by IO::AIO).
		978
		979	One solution for this is to always use absolute paths. This usually
		980	works, but can be quite slow (the kernel has to walk the whole path on
		981	every access), and can also be a hassle to implement.
		982
		983	Newer POSIX systems have a number of functions (openat, fdopendir,
		984	futimensat and so on) that make it possible to specify working
		985	directories per operation.
		986
		987	For portability, and because the clowns who "designed", or shall I
		988	write, perpetrated this new interface were obviously half-drunk, this
		989	abstraction cannot be perfect, though.
		990
		991	IO::AIO allows you to convert directory paths into a so-called
		992	IO::AIO::WD object. This object stores the canonicalised, absolute
		993	version of the path, and on systems that allow it, also a directory file
		994	descriptor.
		995
		996	Everywhere where a pathname is accepted by IO::AIO (e.g. in "aio_stat"
		997	or "aio_unlink"), one can specify an array reference with an IO::AIO::WD
		998	object and a pathname instead (or the IO::AIO::WD object alone, which
		999	gets interpreted as "[$wd, "."]"). If the pathname is absolute, the
		1000	IO::AIO::WD object is ignored, otherwise the pathname is resolved
		1001	relative to that IO::AIO::WD object.
		1002
		1003	For example, to get a wd object for /etc and then stat passwd inside,
		1004	you would write:
		1005
		1006	aio_wd "/etc", sub {
		1007	my $etcdir = shift;
		1008
		1009	# although $etcdir can be undef on error, there is generally no reason
		1010	# to check for errors here, as aio_stat will fail with ENOENT
		1011	# when $etcdir is undef.
		1012
		1013	aio_stat [$etcdir, "passwd"], sub {
		1014	# yay
		1015	};
		1016	};
		1017
		1018	That "aio_wd" is a request and not a normal function shows that creating
		1019	an IO::AIO::WD object is itself a potentially blocking operation, which
		1020	is why it is done asynchronously.
		1021
		1022	To stat the directory obtained with "aio_wd" above, one could write
		1023	either of the following three request calls:
		1024
		1025	aio_lstat "/etc" , sub { ... # pathname as normal string
		1026	aio_lstat [$wd, "."], sub { ... # "." relative to $wd (i.e. $wd itself)
		1027	aio_lstat $wd , sub { ... # shorthand for the previous
		1028
		1029	As with normal pathnames, IO::AIO keeps a copy of the working directory
		1030	object and the pathname string, so you could write the following without
		1031	causing any issues due to $path getting reused:
		1032
		1033	my $path = [$wd, undef];
		1034
		1035	for my $name (qw(abc def ghi)) {
		1036	$path->[1] = $name;
		1037	aio_stat $path, sub {
		1038	# ...
		1039	};
		1040	}
		1041
		1042	There are some caveats: when directories get renamed (or deleted), the
		1043	pathname string doesn't change, so will point to the new directory (or
		1044	nowhere at all), while the directory fd, if available on the system,
		1045	will still point to the original directory. Most functions accepting a
		1046	pathname will use the directory fd on newer systems, and the string on
		1047	older systems. Some functions (such as realpath) will always rely on the
		1048	string form of the pathname.
		1049
		1050	So this fucntionality is mainly useful to get some protection against
		1051	"chdir", to easily get an absolute path out of a relative path for
		1052	future reference, and to speed up doing many operations in the same
		1053	directory (e.g. when stat'ing all files in a directory).
		1054
		1055	The following functions implement this working directory abstraction:
		1056
		1057	aio_wd $pathname, $callback->($wd)
		1058	Asynchonously canonicalise the given pathname and convert it to an
		1059	IO::AIO::WD object representing it. If possible and supported on the
		1060	system, also open a directory fd to speed up pathname resolution
		1061	relative to this working directory.
		1062
		1063	If something goes wrong, then "undef" is passwd to the callback
		1064	instead of a working directory object and $! is set appropriately.
		1065	Since passing "undef" as working directory component of a pathname
		1066	fails the request with "ENOENT", there is often no need for error
		1067	checking in the "aio_wd" callback, as future requests using the
		1068	value will fail in the expected way.
		1069
		1070	If this call isn't available because your OS lacks it or it couldn't
		1071	be detected, it will be emulated by calling "fsync" instead.
		1072
		1073	IO::AIO::CWD
		1074	This is a compiletime constant (object) that represents the process
		1075	current working directory.
		1076
		1077	Specifying this object as working directory object for a pathname is
		1078	as if the pathname would be specified directly, without a directory
		1079	object, e.g., these calls are functionally identical:
		1080
		1081	aio_stat "somefile", sub { ... };
		1082	aio_stat [IO::AIO::CWD, "somefile"], sub { ... };
		1083
		1084	IO::AIO::REQ CLASS
		1085	All non-aggregate "aio_*" functions return an object of this class when
		1086	called in non-void context.
		1087
		1088	cancel $req
		1089	Cancels the request, if possible. Has the effect of skipping
		1090	execution when entering the execute state and skipping calling the
		1091	callback when entering the the result state, but will leave the
		1092	request otherwise untouched (with the exception of readdir). That
		1093	means that requests that currently execute will not be stopped and
		1094	resources held by the request will not be freed prematurely.
		1095
		1096	cb $req $callback->(...)
		1097	Replace (or simply set) the callback registered to the request.
		1098
		1099	IO::AIO::GRP CLASS
		1100	This class is a subclass of IO::AIO::REQ, so all its methods apply to
		1101	objects of this class, too.
		1102
		1103	A IO::AIO::GRP object is a special request that can contain multiple
		1104	other aio requests.
		1105
		1106	You create one by calling the "aio_group" constructing function with a
		1107	callback that will be called when all contained requests have entered
		1108	the "done" state:
		1109
		1110	my $grp = aio_group sub {
		1111	print "all requests are done\n";
		1112	};
		1113
		1114	You add requests by calling the "add" method with one or more
		1115	"IO::AIO::REQ" objects:
		1116
		1117	$grp->add (aio_unlink "...");
		1118
		1119	add $grp aio_stat "...", sub {
		1120	$_[0] or return $grp->result ("error");
		1121
		1122	# add another request dynamically, if first succeeded
		1123	add $grp aio_open "...", sub {
		1124	$grp->result ("ok");
		1125	};
		1126	};
		1127
		1128	This makes it very easy to create composite requests (see the source of
		1129	"aio_move" for an application) that work and feel like simple requests.
		1130
		1131	* The IO::AIO::GRP objects will be cleaned up during calls to
		1132	"IO::AIO::poll_cb", just like any other request.
		1133
		1134	* They can be canceled like any other request. Canceling will cancel
		1135	not only the request itself, but also all requests it contains.
		1136
		1137	* They can also can also be added to other IO::AIO::GRP objects.
		1138
		1139	* You must not add requests to a group from within the group callback
		1140	(or any later time).
		1141
		1142	Their lifetime, simplified, looks like this: when they are empty, they
		1143	will finish very quickly. If they contain only requests that are in the
		1144	"done" state, they will also finish. Otherwise they will continue to
		1145	exist.
		1146
		1147	That means after creating a group you have some time to add requests
		1148	(precisely before the callback has been invoked, which is only done
		1149	within the "poll_cb"). And in the callbacks of those requests, you can
		1150	add further requests to the group. And only when all those requests have
		1151	finished will the the group itself finish.
		1152
		1153	add $grp ...
		1154	$grp->add (...)
		1155	Add one or more requests to the group. Any type of IO::AIO::REQ can
		1156	be added, including other groups, as long as you do not create
		1157	circular dependencies.
		1158
		1159	Returns all its arguments.
		1160
		1161	$grp->cancel_subs
		1162	Cancel all subrequests and clears any feeder, but not the group
		1163	request itself. Useful when you queued a lot of events but got a
		1164	result early.
		1165
		1166	The group request will finish normally (you cannot add requests to
		1167	the group).
		1168
		1169	$grp->result (...)
		1170	Set the result value(s) that will be passed to the group callback
		1171	when all subrequests have finished and set the groups errno to the
		1172	current value of errno (just like calling "errno" without an error
		1173	number). By default, no argument will be passed and errno is zero.
		1174
		1175	$grp->errno ([$errno])
		1176	Sets the group errno value to $errno, or the current value of errno
		1177	when the argument is missing.
		1178
		1179	Every aio request has an associated errno value that is restored
		1180	when the callback is invoked. This method lets you change this value
		1181	from its default (0).
		1182
		1183	Calling "result" will also set errno, so make sure you either set $!
		1184	before the call to "result", or call c<errno> after it.
		1185
		1186	feed $grp $callback->($grp)
		1187	Sets a feeder/generator on this group: every group can have an
		1188	attached generator that generates requests if idle. The idea behind
		1189	this is that, although you could just queue as many requests as you
		1190	want in a group, this might starve other requests for a potentially
		1191	long time. For example, "aio_scandir" might generate hundreds of
		1192	thousands of "aio_stat" requests, delaying any later requests for a
		1193	long time.
		1194
		1195	To avoid this, and allow incremental generation of requests, you can
		1196	instead a group and set a feeder on it that generates those
		1197	requests. The feed callback will be called whenever there are few
		1198	enough (see "limit", below) requests active in the group itself and
		1199	is expected to queue more requests.
		1200
		1201	The feed callback can queue as many requests as it likes (i.e. "add"
		1202	does not impose any limits).
		1203
		1204	If the feed does not queue more requests when called, it will be
		1205	automatically removed from the group.
		1206
		1207	If the feed limit is 0 when this method is called, it will be set to
		1208	2 automatically.
		1209
		1210	Example:
		1211
		1212	# stat all files in @files, but only ever use four aio requests concurrently:
		1213
		1214	my $grp = aio_group sub { print "finished\n" };
		1215	limit $grp 4;
		1216	feed $grp sub {
		1217	my $file = pop @files
		1218	or return;
		1219
		1220	add $grp aio_stat $file, sub { ... };
		1221	};
		1222
		1223	limit $grp $num
		1224	Sets the feeder limit for the group: The feeder will be called
		1225	whenever the group contains less than this many requests.
		1226
		1227	Setting the limit to 0 will pause the feeding process.
		1228
		1229	The default value for the limit is 0, but note that setting a feeder
		1230	automatically bumps it up to 2.
172		1231
173	SUPPORT FUNCTIONS	1232	SUPPORT FUNCTIONS
		1233	EVENT PROCESSING AND EVENT LOOP INTEGRATION
174	$fileno = IO::AIO::poll_fileno	1234	$fileno = IO::AIO::poll_fileno
175	Return the *request result pipe file descriptor*. This filehandle	1235	Return the *request result pipe file descriptor*. This filehandle
176	must be polled for reading by some mechanism outside this module	1236	must be polled for reading by some mechanism outside this module
177	(e.g. Event or select, see below or the SYNOPSIS). If the pipe	1237	(e.g. EV, Glib, select and so on, see below or the SYNOPSIS). If the
178	becomes readable you have to call "poll_cb" to check the results.	1238	pipe becomes readable you have to call "poll_cb" to check the
		1239	results.
179		1240
180	See "poll_cb" for an example.	1241	See "poll_cb" for an example.
181		1242
182	IO::AIO::poll_cb	1243	IO::AIO::poll_cb
183	Process all outstanding events on the result pipe. You have to call	1244	Process some outstanding events on the result pipe. You have to call
184	this regularly. Returns the number of events processed. Returns	1245	this regularly. Returns 0 if all events could be processed (or there
		1246	were no events to process), or -1 if it returned earlier for
185	immediately when no events are outstanding.	1247	whatever reason. Returns immediately when no events are outstanding.
		1248	The amount of events processed depends on the settings of
		1249	"IO::AIO::max_poll_req" and "IO::AIO::max_poll_time".
		1250
		1251	If not all requests were processed for whatever reason, the
		1252	filehandle will still be ready when "poll_cb" returns, so normally
		1253	you don't have to do anything special to have it called later.
		1254
		1255	Apart from calling "IO::AIO::poll_cb" when the event filehandle
		1256	becomes ready, it can be beneficial to call this function from loops
		1257	which submit a lot of requests, to make sure the results get
		1258	processed when they become available and not just when the loop is
		1259	finished and the event loop takes over again. This function returns
		1260	very fast when there are no outstanding requests.
186		1261
187	Example: Install an Event watcher that automatically calls	1262	Example: Install an Event watcher that automatically calls
188	IO::AIO::poll_cb with high priority:	1263	IO::AIO::poll_cb with high priority (more examples can be found in
		1264	the SYNOPSIS section, at the top of this document):
189		1265
190	Event->io (fd => IO::AIO::poll_fileno,	1266	Event->io (fd => IO::AIO::poll_fileno,
191	poll => 'r', async => 1,	1267	poll => 'r', async => 1,
192	cb => \&IO::AIO::poll_cb);	1268	cb => \&IO::AIO::poll_cb);
193		1269
194	IO::AIO::poll_wait	1270	IO::AIO::poll_wait
		1271	If there are any outstanding requests and none of them in the result
195	Wait till the result filehandle becomes ready for reading (simply	1272	phase, wait till the result filehandle becomes ready for reading
196	does a "select" on the filehandle. This is useful if you want to	1273	(simply does a "select" on the filehandle. This is useful if you
197	synchronously wait for some requests to finish).	1274	want to synchronously wait for some requests to finish).
198		1275
199	See "nreqs" for an example.	1276	See "nreqs" for an example.
200		1277
		1278	IO::AIO::poll
		1279	Waits until some requests have been handled.
		1280
		1281	Returns the number of requests processed, but is otherwise strictly
		1282	equivalent to:
		1283
		1284	IO::AIO::poll_wait, IO::AIO::poll_cb
		1285
201	IO::AIO::nreqs	1286	IO::AIO::flush
202	Returns the number of requests currently outstanding (i.e. for which	1287	Wait till all outstanding AIO requests have been handled.
203	their callback has not been invoked yet).
204		1288
205	Example: wait till there are no outstanding requests anymore:	1289	Strictly equivalent to:
206		1290
207	IO::AIO::poll_wait, IO::AIO::poll_cb	1291	IO::AIO::poll_wait, IO::AIO::poll_cb
208	while IO::AIO::nreqs;	1292	while IO::AIO::nreqs;
209		1293
210	IO::AIO::flush	1294	IO::AIO::max_poll_reqs $nreqs
211	Wait till all outstanding AIO requests have been handled.	1295	IO::AIO::max_poll_time $seconds
		1296	These set the maximum number of requests (default 0, meaning
		1297	infinity) that are being processed by "IO::AIO::poll_cb" in one
		1298	call, respectively the maximum amount of time (default 0, meaning
		1299	infinity) spent in "IO::AIO::poll_cb" to process requests (more
		1300	correctly the mininum amount of time "poll_cb" is allowed to use).
212		1301
213	Strictly equivalent to:	1302	Setting "max_poll_time" to a non-zero value creates an overhead of
		1303	one syscall per request processed, which is not normally a problem
		1304	unless your callbacks are really really fast or your OS is really
		1305	really slow (I am not mentioning Solaris here). Using
		1306	"max_poll_reqs" incurs no overhead.
214		1307
215	IO::AIO::poll_wait, IO::AIO::poll_cb	1308	Setting these is useful if you want to ensure some level of
216	while IO::AIO::nreqs;	1309	interactiveness when perl is not fast enough to process all requests
		1310	in time.
217		1311
218	IO::AIO::poll	1312	For interactive programs, values such as 0.01 to 0.1 should be fine.
219	Waits until some requests have been handled.
220		1313
221	Strictly equivalent to:	1314	Example: Install an Event watcher that automatically calls
		1315	IO::AIO::poll_cb with low priority, to ensure that other parts of
		1316	the program get the CPU sometimes even under high AIO load.
222		1317
223	IO::AIO::poll_wait, IO::AIO::poll_cb	1318	# try not to spend much more than 0.1s in poll_cb
224	if IO::AIO::nreqs;	1319	IO::AIO::max_poll_time 0.1;
225		1320
		1321	# use a low priority so other tasks have priority
		1322	Event->io (fd => IO::AIO::poll_fileno,
		1323	poll => 'r', nice => 1,
		1324	cb => &IO::AIO::poll_cb);
		1325
		1326	CONTROLLING THE NUMBER OF THREADS
226	IO::AIO::min_parallel $nthreads	1327	IO::AIO::min_parallel $nthreads
227	Set the minimum number of AIO threads to $nthreads. The default is	1328	Set the minimum number of AIO threads to $nthreads. The current
228	1, which means a single asynchronous operation can be done at one	1329	default is 8, which means eight asynchronous operations can execute
229	time (the number of outstanding operations, however, is unlimited).	1330	concurrently at any one time (the number of outstanding requests,
		1331	however, is unlimited).
230		1332
		1333	IO::AIO starts threads only on demand, when an AIO request is queued
		1334	and no free thread exists. Please note that queueing up a hundred
		1335	requests can create demand for a hundred threads, even if it turns
		1336	out that everything is in the cache and could have been processed
		1337	faster by a single thread.
		1338
231	It is recommended to keep the number of threads low, as some Linux	1339	It is recommended to keep the number of threads relatively low, as
232	kernel versions will scale negatively with the number of threads	1340	some Linux kernel versions will scale negatively with the number of
233	(higher parallelity => MUCH higher latency). With current Linux 2.6	1341	threads (higher parallelity => MUCH higher latency). With current
234	versions, 4-32 threads should be fine.	1342	Linux 2.6 versions, 4-32 threads should be fine.
235		1343
236	Under normal circumstances you don't need to call this function, as	1344	Under most circumstances you don't need to call this function, as
237	this module automatically starts some threads (the exact number	1345	the module selects a default that is suitable for low to moderate
238	might change, and is currently 4).	1346	load.
239		1347
240	IO::AIO::max_parallel $nthreads	1348	IO::AIO::max_parallel $nthreads
241	Sets the maximum number of AIO threads to $nthreads. If more than	1349	Sets the maximum number of AIO threads to $nthreads. If more than
242	the specified number of threads are currently running, kill them.	1350	the specified number of threads are currently running, this function
243	This function blocks until the limit is reached.	1351	kills them. This function blocks until the limit is reached.
		1352
		1353	While $nthreads are zero, aio requests get queued but not executed
		1354	until the number of threads has been increased again.
244		1355
245	This module automatically runs "max_parallel 0" at program end, to	1356	This module automatically runs "max_parallel 0" at program end, to
246	ensure that all threads are killed and that there are no outstanding	1357	ensure that all threads are killed and that there are no outstanding
247	requests.	1358	requests.
248		1359
249	Under normal circumstances you don't need to call this function.	1360	Under normal circumstances you don't need to call this function.
250		1361
		1362	IO::AIO::max_idle $nthreads
		1363	Limit the number of threads (default: 4) that are allowed to idle
		1364	(i.e., threads that did not get a request to process within the idle
		1365	timeout (default: 10 seconds). That means if a thread becomes idle
		1366	while $nthreads other threads are also idle, it will free its
		1367	resources and exit.
		1368
		1369	This is useful when you allow a large number of threads (e.g. 100 or
		1370	1000) to allow for extremely high load situations, but want to free
		1371	resources under normal circumstances (1000 threads can easily
		1372	consume 30MB of RAM).
		1373
		1374	The default is probably ok in most situations, especially if thread
		1375	creation is fast. If thread creation is very slow on your system you
		1376	might want to use larger values.
		1377
		1378	IO::AIO::idle_timeout $seconds
		1379	Sets the minimum idle timeout (default 10) after which worker
		1380	threads are allowed to exit. SEe "IO::AIO::max_idle".
		1381
251	$oldnreqs = IO::AIO::max_outstanding $nreqs	1382	IO::AIO::max_outstanding $maxreqs
252	Sets the maximum number of outstanding requests to $nreqs. If you	1383	Sets the maximum number of outstanding requests to $nreqs. If you do
253	try to queue up more than this number of requests, the caller will	1384	queue up more than this number of requests, the next call to
		1385	"IO::AIO::poll_cb" (and other functions calling "poll_cb", such as
		1386	"IO::AIO::flush" or "IO::AIO::poll") will block until the limit is
		1387	no longer exceeded.
		1388
		1389	In other words, this setting does not enforce a queue limit, but can
		1390	be used to make poll functions block if the limit is exceeded.
		1391
		1392	This is a very bad function to use in interactive programs because
		1393	it blocks, and a bad way to reduce concurrency because it is
		1394	inexact: Better use an "aio_group" together with a feed callback.
		1395
		1396	It's main use is in scripts without an event loop - when you want to
		1397	stat a lot of files, you can write somehting like this:
		1398
		1399	IO::AIO::max_outstanding 32;
		1400
		1401	for my $path (...) {
		1402	aio_stat $path , ...;
		1403	IO::AIO::poll_cb;
		1404	}
		1405
		1406	IO::AIO::flush;
		1407
		1408	The call to "poll_cb" inside the loop will normally return
		1409	instantly, but as soon as more thna 32 reqeusts are in-flight, it
254	block until some requests have been handled.	1410	will block until some requests have been handled. This keeps the
		1411	loop from pushing a large number of "aio_stat" requests onto the
		1412	queue.
255		1413
256	The default is very large, so normally there is no practical limit.	1414	The default value for "max_outstanding" is very large, so there is
257	If you queue up many requests in a loop it it often improves speed	1415	no practical limit on the number of outstanding requests.
258	if you set this to a relatively low number, such as 100.
259		1416
260	Under normal circumstances you don't need to call this function.	1417	STATISTICAL INFORMATION
		1418	IO::AIO::nreqs
		1419	Returns the number of requests currently in the ready, execute or
		1420	pending states (i.e. for which their callback has not been invoked
		1421	yet).
		1422
		1423	Example: wait till there are no outstanding requests anymore:
		1424
		1425	IO::AIO::poll_wait, IO::AIO::poll_cb
		1426	while IO::AIO::nreqs;
		1427
		1428	IO::AIO::nready
		1429	Returns the number of requests currently in the ready state (not yet
		1430	executed).
		1431
		1432	IO::AIO::npending
		1433	Returns the number of requests currently in the pending state
		1434	(executed, but not yet processed by poll_cb).
		1435
		1436	MISCELLANEOUS FUNCTIONS
		1437	IO::AIO implements some functions that might be useful, but are not
		1438	asynchronous.
		1439
		1440	IO::AIO::sendfile $ofh, $ifh, $offset, $count
		1441	Calls the "eio_sendfile_sync" function, which is like
		1442	"aio_sendfile", but is blocking (this makes most sense if you know
		1443	the input data is likely cached already and the output filehandle is
		1444	set to non-blocking operations).
		1445
		1446	Returns the number of bytes copied, or -1 on error.
		1447
		1448	IO::AIO::fadvise $fh, $offset, $len, $advice
		1449	Simply calls the "posix_fadvise" function (see its manpage for
		1450	details). The following advice constants are available:
		1451	"IO::AIO::FADV_NORMAL", "IO::AIO::FADV_SEQUENTIAL",
		1452	"IO::AIO::FADV_RANDOM", "IO::AIO::FADV_NOREUSE",
		1453	"IO::AIO::FADV_WILLNEED", "IO::AIO::FADV_DONTNEED".
		1454
		1455	On systems that do not implement "posix_fadvise", this function
		1456	returns ENOSYS, otherwise the return value of "posix_fadvise".
		1457
		1458	IO::AIO::madvise $scalar, $offset, $len, $advice
		1459	Simply calls the "posix_madvise" function (see its manpage for
		1460	details). The following advice constants are available:
		1461	"IO::AIO::MADV_NORMAL", "IO::AIO::MADV_SEQUENTIAL",
		1462	"IO::AIO::MADV_RANDOM", "IO::AIO::MADV_WILLNEED",
		1463	"IO::AIO::MADV_DONTNEED".
		1464
		1465	On systems that do not implement "posix_madvise", this function
		1466	returns ENOSYS, otherwise the return value of "posix_madvise".
		1467
		1468	IO::AIO::mprotect $scalar, $offset, $len, $protect
		1469	Simply calls the "mprotect" function on the preferably AIO::mmap'ed
		1470	$scalar (see its manpage for details). The following protect
		1471	constants are available: "IO::AIO::PROT_NONE", "IO::AIO::PROT_READ",
		1472	"IO::AIO::PROT_WRITE", "IO::AIO::PROT_EXEC".
		1473
		1474	On systems that do not implement "mprotect", this function returns
		1475	ENOSYS, otherwise the return value of "mprotect".
		1476
		1477	IO::AIO::mmap $scalar, $length, $prot, $flags, $fh[, $offset]
		1478	Memory-maps a file (or anonymous memory range) and attaches it to
		1479	the given $scalar, which will act like a string scalar.
		1480
		1481	The only operations allowed on the scalar are "substr"/"vec" that
		1482	don't change the string length, and most read-only operations such
		1483	as copying it or searching it with regexes and so on.
		1484
		1485	Anything else is unsafe and will, at best, result in memory leaks.
		1486
		1487	The memory map associated with the $scalar is automatically removed
		1488	when the $scalar is destroyed, or when the "IO::AIO::mmap" or
		1489	"IO::AIO::munmap" functions are called.
		1490
		1491	This calls the "mmap"(2) function internally. See your system's
		1492	manual page for details on the $length, $prot and $flags parameters.
		1493
		1494	The $length must be larger than zero and smaller than the actual
		1495	filesize.
		1496
		1497	$prot is a combination of "IO::AIO::PROT_NONE",
		1498	"IO::AIO::PROT_EXEC", "IO::AIO::PROT_READ" and/or
		1499	"IO::AIO::PROT_WRITE",
		1500
		1501	$flags can be a combination of "IO::AIO::MAP_SHARED" or
		1502	"IO::AIO::MAP_PRIVATE", or a number of system-specific flags (when
		1503	not available, the are defined as 0): "IO::AIO::MAP_ANONYMOUS"
		1504	(which is set to "MAP_ANON" if your system only provides this
		1505	constant), "IO::AIO::MAP_HUGETLB", "IO::AIO::MAP_LOCKED",
		1506	"IO::AIO::MAP_NORESERVE", "IO::AIO::MAP_POPULATE" or
		1507	"IO::AIO::MAP_NONBLOCK"
		1508
		1509	If $fh is "undef", then a file descriptor of -1 is passed.
		1510
		1511	$offset is the offset from the start of the file - it generally must
		1512	be a multiple of "IO::AIO::PAGESIZE" and defaults to 0.
		1513
		1514	Example:
		1515
		1516	use Digest::MD5;
		1517	use IO::AIO;
		1518
		1519	open my $fh, "<verybigfile"
		1520	or die "$!";
		1521
		1522	IO::AIO::mmap my $data, -s $fh, IO::AIO::PROT_READ, IO::AIO::MAP_SHARED, $fh
		1523	or die "verybigfile: $!";
		1524
		1525	my $fast_md5 = md5 $data;
		1526
		1527	IO::AIO::munmap $scalar
		1528	Removes a previous mmap and undefines the $scalar.
		1529
		1530	IO::AIO::munlock $scalar, $offset = 0, $length = undef
		1531	Calls the "munlock" function, undoing the effects of a previous
		1532	"aio_mlock" call (see its description for details).
		1533
		1534	IO::AIO::munlockall
		1535	Calls the "munlockall" function.
		1536
		1537	On systems that do not implement "munlockall", this function returns
		1538	ENOSYS, otherwise the return value of "munlockall".
		1539
		1540	IO::AIO::splice $r_fh, $r_off, $w_fh, $w_off, $length, $flags
		1541	Calls the GNU/Linux splice(2) syscall, if available. If $r_off or
		1542	$w_off are "undef", then "NULL" is passed for these, otherwise they
		1543	should be the file offset.
		1544
		1545	The following symbol flag values are available:
		1546	"IO::AIO::SPLICE_F_MOVE", "IO::AIO::SPLICE_F_NONBLOCK",
		1547	"IO::AIO::SPLICE_F_MORE" and "IO::AIO::SPLICE_F_GIFT".
		1548
		1549	See the splice(2) manpage for details.
		1550
		1551	IO::AIO::tee $r_fh, $w_fh, $length, $flags
		1552	Calls the GNU/Linux tee(2) syscall, see it's manpage and the
		1553	description for "IO::AIO::splice" above for details.
		1554
		1555	EVENT LOOP INTEGRATION
		1556	It is recommended to use AnyEvent::AIO to integrate IO::AIO
		1557	automatically into many event loops:
		1558
		1559	# AnyEvent integration (EV, Event, Glib, Tk, POE, urxvt, pureperl...)
		1560	use AnyEvent::AIO;
		1561
		1562	You can also integrate IO::AIO manually into many event loops, here are
		1563	some examples of how to do this:
		1564
		1565	# EV integration
		1566	my $aio_w = EV::io IO::AIO::poll_fileno, EV::READ, \&IO::AIO::poll_cb;
		1567
		1568	# Event integration
		1569	Event->io (fd => IO::AIO::poll_fileno,
		1570	poll => 'r',
		1571	cb => \&IO::AIO::poll_cb);
		1572
		1573	# Glib/Gtk2 integration
		1574	add_watch Glib::IO IO::AIO::poll_fileno,
		1575	in => sub { IO::AIO::poll_cb; 1 };
		1576
		1577	# Tk integration
		1578	Tk::Event::IO->fileevent (IO::AIO::poll_fileno, "",
		1579	readable => \&IO::AIO::poll_cb);
		1580
		1581	# Danga::Socket integration
		1582	Danga::Socket->AddOtherFds (IO::AIO::poll_fileno =>
		1583	\&IO::AIO::poll_cb);
		1584
		1585	FORK BEHAVIOUR
		1586	Usage of pthreads in a program changes the semantics of fork
		1587	considerably. Specifically, only async-safe functions can be called
		1588	after fork. Perl doesn't know about this, so in general, you cannot call
		1589	fork with defined behaviour in perl if pthreads are involved. IO::AIO
		1590	uses pthreads, so this applies, but many other extensions and (for
		1591	inexplicable reasons) perl itself often is linked against pthreads, so
		1592	this limitation applies to quite a lot of perls.
		1593
		1594	This module no longer tries to fight your OS, or POSIX. That means
		1595	IO::AIO only works in the process that loaded it. Forking is fully
		1596	supported, but using IO::AIO in the child is not.
		1597
		1598	You might get around by not *using* IO::AIO before (or after) forking.
		1599	You could also try to call the IO::AIO::reinit function in the child:
		1600
		1601	IO::AIO::reinit
		1602	Abandons all current requests and I/O threads and simply
		1603	reinitialises all data structures. This is not an operation
		1604	supported by any standards, but happens to work on GNU/Linux and
		1605	some newer BSD systems.
		1606
		1607	The only reasonable use for this function is to call it after
		1608	forking, if "IO::AIO" was used in the parent. Calling it while
		1609	IO::AIO is active in the process will result in undefined behaviour.
		1610	Calling it at any time will also result in any undefined (by POSIX)
		1611	behaviour.
		1612
		1613	MEMORY USAGE
		1614	Per-request usage:
		1615
		1616	Each aio request uses - depending on your architecture - around 100-200
		1617	bytes of memory. In addition, stat requests need a stat buffer (possibly
		1618	a few hundred bytes), readdir requires a result buffer and so on. Perl
		1619	scalars and other data passed into aio requests will also be locked and
		1620	will consume memory till the request has entered the done state.
		1621
		1622	This is not awfully much, so queuing lots of requests is not usually a
		1623	problem.
		1624
		1625	Per-thread usage:
		1626
		1627	In the execution phase, some aio requests require more memory for
		1628	temporary buffers, and each thread requires a stack and other data
		1629	structures (usually around 16k-128k, depending on the OS).
		1630
		1631	KNOWN BUGS
		1632	Known bugs will be fixed in the next release.
261		1633
262	SEE ALSO	1634	SEE ALSO
263	Coro, Linux::AIO.	1635	AnyEvent::AIO for easy integration into event loops, Coro::AIO for a
		1636	more natural syntax.
264		1637
265	AUTHOR	1638	AUTHOR
266	Marc Lehmann <schmorp@schmorp.de>	1639	Marc Lehmann <schmorp@schmorp.de>
267	http://home.schmorp.de/	1640	http://home.schmorp.de/
268		1641

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