[ViewVC] Diff of: cvs/IO-AIO/AIO.pm

Comparing IO-AIO/AIO.pm (file contents):
Revision 1.14 by root, Mon Jul 11 02:53:59 2005 UTC vs.
Revision 1.198 by root, Wed Jun 29 11:25:17 2011 UTC

…		…
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	use IO::AIO;	7	use IO::AIO;
8		8
9	aio_open "/etc/passwd", O_RDONLY, 0, sub {	9	aio_open "/etc/passwd", IO::AIO::O_RDONLY, 0, sub {
10	my ($fh) = @_;	10	my $fh = shift
		11	or die "/etc/passwd: $!";
11	...	12	...
12	};	13	};
13		14
14	aio_unlink "/tmp/file", sub { };	15	aio_unlink "/tmp/file", sub { };
15		16
16	aio_read $fh, 30000, 1024, $buffer, 0, sub {	17	aio_read $fh, 30000, 1024, $buffer, 0, sub {
17	$_[0] > 0 or die "read error: $!";	18	$_[0] > 0 or die "read error: $!";
18	};	19	};
19		20
20	# Event	21	# version 2+ has request and group objects
21	Event->io (fd => IO::AIO::poll_fileno,	22	use IO::AIO 2;
22	poll => 'r',
23	cb => \&IO::AIO::poll_cb);
24		23
25	# Glib/Gtk2	24	aioreq_pri 4; # give next request a very high priority
26	add_watch Glib::IO IO::AIO::poll_fileno,	25	my $req = aio_unlink "/tmp/file", sub { };
27	\&IO::AIO::poll_cb;	26	$req->cancel; # cancel request if still in queue
28		27
29	# Tk	28	my $grp = aio_group sub { print "all stats done\n" };
30	Tk::Event::IO->fileevent (IO::AIO::poll_fileno, "",	29	add $grp aio_stat "..." for ...;
31	readable => \&IO::AIO::poll_cb);
32
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
52	Although the module will work with in the presence of other threads, it is	63	Although the module will work in the presence of other (Perl-) threads,
53	currently not reentrant, so use appropriate locking yourself.	64	it is currently not reentrant in any way, so use appropriate locking
		65	yourself, always call C<poll_cb> from within the same thread, or never
		66	call C<poll_cb> (or other C<aio_> functions) recursively.
		67
		68	=head2 EXAMPLE
		69
		70	This is a simple example that uses the EV module and loads
		71	F</etc/passwd> asynchronously:
		72
		73	use Fcntl;
		74	use EV;
		75	use IO::AIO;
		76
		77	# register the IO::AIO callback with EV
		78	my $aio_w = EV::io IO::AIO::poll_fileno, EV::READ, \&IO::AIO::poll_cb;
		79
		80	# queue the request to open /etc/passwd
		81	aio_open "/etc/passwd", IO::AIO::O_RDONLY, 0, sub {
		82	my $fh = shift
		83	or die "error while opening: $!";
		84
		85	# stat'ing filehandles is generally non-blocking
		86	my $size = -s $fh;
		87
		88	# queue a request to read the file
		89	my $contents;
		90	aio_read $fh, 0, $size, $contents, 0, sub {
		91	$_[0] == $size
		92	or die "short read: $!";
		93
		94	close $fh;
		95
		96	# file contents now in $contents
		97	print $contents;
		98
		99	# exit event loop and program
		100	EV::unloop;
		101	};
		102	};
		103
		104	# possibly queue up other requests, or open GUI windows,
		105	# check for sockets etc. etc.
		106
		107	# process events as long as there are some:
		108	EV::loop;
		109
		110	=head1 REQUEST ANATOMY AND LIFETIME
		111
		112	Every C<aio_*> function creates a request. which is a C data structure not
		113	directly visible to Perl.
		114
		115	If called in non-void context, every request function returns a Perl
		116	object representing the request. In void context, nothing is returned,
		117	which saves a bit of memory.
		118
		119	The perl object is a fairly standard ref-to-hash object. The hash contents
		120	are not used by IO::AIO so you are free to store anything you like in it.
		121
		122	During their existance, aio requests travel through the following states,
		123	in order:
		124
		125	=over 4
		126
		127	=item ready
		128
		129	Immediately after a request is created it is put into the ready state,
		130	waiting for a thread to execute it.
		131
		132	=item execute
		133
		134	A thread has accepted the request for processing and is currently
		135	executing it (e.g. blocking in read).
		136
		137	=item pending
		138
		139	The request has been executed and is waiting for result processing.
		140
		141	While request submission and execution is fully asynchronous, result
		142	processing is not and relies on the perl interpreter calling C<poll_cb>
		143	(or another function with the same effect).
		144
		145	=item result
		146
		147	The request results are processed synchronously by C<poll_cb>.
		148
		149	The C<poll_cb> function will process all outstanding aio requests by
		150	calling their callbacks, freeing memory associated with them and managing
		151	any groups they are contained in.
		152
		153	=item done
		154
		155	Request has reached the end of its lifetime and holds no resources anymore
		156	(except possibly for the Perl object, but its connection to the actual
		157	aio request is severed and calling its methods will either do nothing or
		158	result in a runtime error).
		159
		160	=back
54		161
55	=cut	162	=cut
56		163
57	package IO::AIO;	164	package IO::AIO;
58		165
		166	use Carp ();
		167
		168	use common::sense;
		169
59	use base 'Exporter';	170	use base 'Exporter';
60		171
61	use Fcntl ();
62
63	BEGIN {	172	BEGIN {
64	$VERSION = 0.3;	173	our $VERSION = '3.91';
65		174
66	@EXPORT = qw(aio_read aio_write aio_open aio_close aio_stat aio_lstat aio_unlink	175	our @AIO_REQ = qw(aio_sendfile aio_read aio_write aio_open aio_close
67	aio_fsync aio_fdatasync aio_readahead);	176	aio_stat aio_lstat aio_unlink aio_rmdir aio_readdir aio_readdirx
68	@EXPORT_OK = qw(poll_fileno poll_cb min_parallel max_parallel max_outstanding nreqs);	177	aio_scandir aio_symlink aio_readlink aio_sync aio_fsync
		178	aio_fdatasync aio_sync_file_range aio_pathsync aio_readahead
		179	aio_rename aio_link aio_move aio_copy aio_group
		180	aio_nop aio_mknod aio_load aio_rmtree aio_mkdir aio_chown
		181	aio_chmod aio_utime aio_truncate
		182	aio_msync aio_mtouch aio_mlock aio_mlockall
		183	aio_statvfs);
		184
		185	our @EXPORT = (@AIO_REQ, qw(aioreq_pri aioreq_nice));
		186	our @EXPORT_OK = qw(poll_fileno poll_cb poll_wait flush
		187	min_parallel max_parallel max_idle idle_timeout
		188	nreqs nready npending nthreads
		189	max_poll_time max_poll_reqs
		190	sendfile fadvise madvise
		191	mmap munmap munlock munlockall);
		192
		193	push @AIO_REQ, qw(aio_busy); # not exported
		194
		195	@IO::AIO::GRP::ISA = 'IO::AIO::REQ';
69		196
70	require XSLoader;	197	require XSLoader;
71	XSLoader::load IO::AIO, $VERSION;	198	XSLoader::load ("IO::AIO", $VERSION);
72	}	199	}
73		200
74	=head1 FUNCTIONS	201	=head1 FUNCTIONS
75		202
		203	=head2 QUICK OVERVIEW
		204
		205	This section simply lists the prototypes of the most important functions
		206	for quick reference. See the following sections for function-by-function
		207	documentation.
		208
		209	aio_open $pathname, $flags, $mode, $callback->($fh)
		210	aio_close $fh, $callback->($status)
		211	aio_read $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
		212	aio_write $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
		213	aio_sendfile $out_fh, $in_fh, $in_offset, $length, $callback->($retval)
		214	aio_readahead $fh,$offset,$length, $callback->($retval)
		215	aio_stat $fh_or_path, $callback->($status)
		216	aio_lstat $fh, $callback->($status)
		217	aio_statvfs $fh_or_path, $callback->($statvfs)
		218	aio_utime $fh_or_path, $atime, $mtime, $callback->($status)
		219	aio_chown $fh_or_path, $uid, $gid, $callback->($status)
		220	aio_truncate $fh_or_path, $offset, $callback->($status)
		221	aio_chmod $fh_or_path, $mode, $callback->($status)
		222	aio_unlink $pathname, $callback->($status)
		223	aio_mknod $path, $mode, $dev, $callback->($status)
		224	aio_link $srcpath, $dstpath, $callback->($status)
		225	aio_symlink $srcpath, $dstpath, $callback->($status)
		226	aio_readlink $path, $callback->($link)
		227	aio_rename $srcpath, $dstpath, $callback->($status)
		228	aio_mkdir $pathname, $mode, $callback->($status)
		229	aio_rmdir $pathname, $callback->($status)
		230	aio_readdir $pathname, $callback->($entries)
		231	aio_readdirx $pathname, $flags, $callback->($entries, $flags)
		232	IO::AIO::READDIR_DENTS IO::AIO::READDIR_DIRS_FIRST
		233	IO::AIO::READDIR_STAT_ORDER IO::AIO::READDIR_FOUND_UNKNOWN
		234	aio_load $path, $data, $callback->($status)
		235	aio_copy $srcpath, $dstpath, $callback->($status)
		236	aio_move $srcpath, $dstpath, $callback->($status)
		237	aio_scandir $path, $maxreq, $callback->($dirs, $nondirs)
		238	aio_rmtree $path, $callback->($status)
		239	aio_sync $callback->($status)
		240	aio_fsync $fh, $callback->($status)
		241	aio_fdatasync $fh, $callback->($status)
		242	aio_sync_file_range $fh, $offset, $nbytes, $flags, $callback->($status)
		243	aio_pathsync $path, $callback->($status)
		244	aio_msync $scalar, $offset = 0, $length = undef, flags = 0, $callback->($status)
		245	aio_mtouch $scalar, $offset = 0, $length = undef, flags = 0, $callback->($status)
		246	aio_mlock $scalar, $offset = 0, $length = undef, $callback->($status)
		247	aio_mlockall $flags, $callback->($status)
		248	aio_group $callback->(...)
		249	aio_nop $callback->()
		250
		251	$prev_pri = aioreq_pri [$pri]
		252	aioreq_nice $pri_adjust
		253
		254	IO::AIO::poll_wait
		255	IO::AIO::poll_cb
		256	IO::AIO::poll
		257	IO::AIO::flush
		258	IO::AIO::max_poll_reqs $nreqs
		259	IO::AIO::max_poll_time $seconds
		260	IO::AIO::min_parallel $nthreads
		261	IO::AIO::max_parallel $nthreads
		262	IO::AIO::max_idle $nthreads
		263	IO::AIO::idle_timeout $seconds
		264	IO::AIO::max_outstanding $maxreqs
		265	IO::AIO::nreqs
		266	IO::AIO::nready
		267	IO::AIO::npending
		268
		269	IO::AIO::sendfile $ofh, $ifh, $offset, $count
		270	IO::AIO::fadvise $fh, $offset, $len, $advice
		271	IO::AIO::madvise $scalar, $offset, $length, $advice
		272	IO::AIO::mprotect $scalar, $offset, $length, $protect
		273	IO::AIO::munlock $scalar, $offset = 0, $length = undef
		274	IO::AIO::munlockall
		275
76	=head2 AIO FUNCTIONS	276	=head2 AIO REQUEST FUNCTIONS
77		277
78	All the C<aio_*> calls are more or less thin wrappers around the syscall	278	All the C<aio_*> calls are more or less thin wrappers around the syscall
79	with the same name (sans C<aio_>). The arguments are similar or identical,	279	with the same name (sans C<aio_>). The arguments are similar or identical,
80	and they all accept an additional (and optional) C<$callback> argument	280	and they all accept an additional (and optional) C<$callback> argument
81	which must be a code reference. This code reference will get called with	281	which must be a code reference. This code reference will get called with
82	the syscall return code (e.g. most syscalls return C<-1> on error, unlike	282	the syscall return code (e.g. most syscalls return C<-1> on error, unlike
83	perl, which usually delivers "false") as it's sole argument when the given	283	perl, which usually delivers "false") as its sole argument after the given
84	syscall has been executed asynchronously.	284	syscall has been executed asynchronously.
85		285
86	All functions that expect a filehandle will also accept a file descriptor.	286	All functions expecting a filehandle keep a copy of the filehandle
		287	internally until the request has finished.
87		288
		289	All functions return request objects of type L<IO::AIO::REQ> that allow
		290	further manipulation of those requests while they are in-flight.
		291
88	The filenames you pass to these routines I<must> be absolute. The reason	292	The pathnames you pass to these routines I<must> be absolute and
89	is that at the time the request is being executed, the current working	293	encoded as octets. The reason for the former is that at the time the
90	directory could have changed. Alternatively, you can make sure that you	294	request is being executed, the current working directory could have
91	never change the current working directory.	295	changed. Alternatively, you can make sure that you never change the
		296	current working directory anywhere in the program and then use relative
		297	paths.
		298
		299	To encode pathnames as octets, either make sure you either: a) always pass
		300	in filenames you got from outside (command line, readdir etc.) without
		301	tinkering, b) are ASCII or ISO 8859-1, c) use the Encode module and encode
		302	your pathnames to the locale (or other) encoding in effect in the user
		303	environment, d) use Glib::filename_from_unicode on unicode filenames or e)
		304	use something else to ensure your scalar has the correct contents.
		305
		306	This works, btw. independent of the internal UTF-8 bit, which IO::AIO
		307	handles correctly whether it is set or not.
92		308
93	=over 4	309	=over 4
94		310
		311	=item $prev_pri = aioreq_pri [$pri]
		312
		313	Returns the priority value that would be used for the next request and, if
		314	C<$pri> is given, sets the priority for the next aio request.
		315
		316	The default priority is C<0>, the minimum and maximum priorities are C<-4>
		317	and C<4>, respectively. Requests with higher priority will be serviced
		318	first.
		319
		320	The priority will be reset to C<0> after each call to one of the C<aio_*>
		321	functions.
		322
		323	Example: open a file with low priority, then read something from it with
		324	higher priority so the read request is serviced before other low priority
		325	open requests (potentially spamming the cache):
		326
		327	aioreq_pri -3;
		328	aio_open ..., sub {
		329	return unless $_[0];
		330
		331	aioreq_pri -2;
		332	aio_read $_[0], ..., sub {
		333	...
		334	};
		335	};
		336
		337
		338	=item aioreq_nice $pri_adjust
		339
		340	Similar to C<aioreq_pri>, but subtracts the given value from the current
		341	priority, so the effect is cumulative.
		342
		343
95	=item aio_open $pathname, $flags, $mode, $callback	344	=item aio_open $pathname, $flags, $mode, $callback->($fh)
96		345
97	Asynchronously open or create a file and call the callback with a newly	346	Asynchronously open or create a file and call the callback with a newly
98	created filehandle for the file.	347	created filehandle for the file.
99		348
100	The pathname passed to C<aio_open> must be absolute. See API NOTES, above,	349	The pathname passed to C<aio_open> must be absolute. See API NOTES, above,
101	for an explanation.	350	for an explanation.
102		351
103	The C<$mode> argument is a bitmask. See the C<Fcntl> module for a	352	The C<$flags> argument is a bitmask. See the C<Fcntl> module for a
104	list. They are the same as used in C<sysopen>.	353	list. They are the same as used by C<sysopen>.
		354
		355	Likewise, C<$mode> specifies the mode of the newly created file, if it
		356	didn't exist and C<O_CREAT> has been given, just like perl's C<sysopen>,
		357	except that it is mandatory (i.e. use C<0> if you don't create new files,
		358	and C<0666> or C<0777> if you do). Note that the C<$mode> will be modified
		359	by the umask in effect then the request is being executed, so better never
		360	change the umask.
105		361
106	Example:	362	Example:
107		363
108	aio_open "/etc/passwd", O_RDONLY, 0, sub {	364	aio_open "/etc/passwd", IO::AIO::O_RDONLY, 0, sub {
109	if ($_[0]) {	365	if ($_[0]) {
110	print "open successful, fh is $_[0]\n";	366	print "open successful, fh is $_[0]\n";
111	...	367	...
112	} else {	368	} else {
113	die "open failed: $!\n";	369	die "open failed: $!\n";
114	}	370	}
115	};	371	};
116		372
		373	In addition to all the common open modes/flags (C<O_RDONLY>, C<O_WRONLY>,
		374	C<O_RDWR>, C<O_CREAT>, C<O_TRUNC>, C<O_EXCL> and C<O_APPEND>), the
		375	following POSIX and non-POSIX constants are available (missing ones on
		376	your system are, as usual, C<0>):
		377
		378	C<O_ASYNC>, C<O_DIRECT>, C<O_NOATIME>, C<O_CLOEXEC>, C<O_NOCTTY>, C<O_NOFOLLOW>,
		379	C<O_NONBLOCK>, C<O_EXEC>, C<O_SEARCH>, C<O_DIRECTORY>, C<O_DSYNC>,
		380	C<O_RSYNC>, C<O_SYNC> and C<O_TTY_INIT>.
		381
		382
117	=item aio_close $fh, $callback	383	=item aio_close $fh, $callback->($status)
118		384
119	Asynchronously close a file and call the callback with the result	385	Asynchronously close a file and call the callback with the result
120	code. I<WARNING:> although accepted, you should not pass in a perl	386	code.
121	filehandle here, as perl will likely close the file descriptor itself when
122	the filehandle is destroyed. Normally, you can safely call perls C<close>
123	or just let filehandles go out of scope.
124		387
		388	Unfortunately, you can't do this to perl. Perl I<insists> very strongly on
		389	closing the file descriptor associated with the filehandle itself.
		390
		391	Therefore, C<aio_close> will not close the filehandle - instead it will
		392	use dup2 to overwrite the file descriptor with the write-end of a pipe
		393	(the pipe fd will be created on demand and will be cached).
		394
		395	Or in other words: the file descriptor will be closed, but it will not be
		396	free for reuse until the perl filehandle is closed.
		397
		398	=cut
		399
125	=item aio_read $fh,$offset,$length, $data,$dataoffset,$callback	400	=item aio_read $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
126		401
127	=item aio_write $fh,$offset,$length, $data,$dataoffset,$callback	402	=item aio_write $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
128		403
129	Reads or writes C<length> bytes from the specified C<fh> and C<offset>	404	Reads or writes C<$length> bytes from or to the specified C<$fh> and
130	into the scalar given by C<data> and offset C<dataoffset> and calls the	405	C<$offset> into the scalar given by C<$data> and offset C<$dataoffset>
131	callback without the actual number of bytes read (or -1 on error, just	406	and calls the callback without the actual number of bytes read (or -1 on
132	like the syscall).	407	error, just like the syscall).
133		408
		409	C<aio_read> will, like C<sysread>, shrink or grow the C<$data> scalar to
		410	offset plus the actual number of bytes read.
		411
		412	If C<$offset> is undefined, then the current file descriptor offset will
		413	be used (and updated), otherwise the file descriptor offset will not be
		414	changed by these calls.
		415
		416	If C<$length> is undefined in C<aio_write>, use the remaining length of
		417	C<$data>.
		418
		419	If C<$dataoffset> is less than zero, it will be counted from the end of
		420	C<$data>.
		421
		422	The C<$data> scalar I<MUST NOT> be modified in any way while the request
		423	is outstanding. Modifying it can result in segfaults or World War III (if
		424	the necessary/optional hardware is installed).
		425
134	Example: Read 15 bytes at offset 7 into scalar C<$buffer>, strating at	426	Example: Read 15 bytes at offset 7 into scalar C<$buffer>, starting at
135	offset C<0> within the scalar:	427	offset C<0> within the scalar:
136		428
137	aio_read $fh, 7, 15, $buffer, 0, sub {	429	aio_read $fh, 7, 15, $buffer, 0, sub {
138	$_[0] > 0 or die "read error: $!";	430	$_[0] > 0 or die "read error: $!";
139	print "read $_[0] bytes: <$buffer>\n";	431	print "read $_[0] bytes: <$buffer>\n";
140	};	432	};
141		433
		434
		435	=item aio_sendfile $out_fh, $in_fh, $in_offset, $length, $callback->($retval)
		436
		437	Tries to copy C<$length> bytes from C<$in_fh> to C<$out_fh>. It starts
		438	reading at byte offset C<$in_offset>, and starts writing at the current
		439	file offset of C<$out_fh>. Because of that, it is not safe to issue more
		440	than one C<aio_sendfile> per C<$out_fh>, as they will interfere with each
		441	other. The same C<$in_fh> works fine though, as this function does not
		442	move or use the file offset of C<$in_fh>.
		443
		444	Please note that C<aio_sendfile> can read more bytes from C<$in_fh> than
		445	are written, and there is no way to find out how many more bytes have been
		446	read from C<aio_sendfile> alone, as C<aio_sendfile> only provides the
		447	number of bytes written to C<$out_fh>. Only if the result value equals
		448	C<$length> one can assume that C<$length> bytes have been read.
		449
		450	Unlike with other C<aio_> functions, it makes a lot of sense to use
		451	C<aio_sendfile> on non-blocking sockets, as long as one end (typically
		452	the C<$in_fh>) is a file - the file I/O will then be asynchronous, while
		453	the socket I/O will be non-blocking. Note, however, that you can run
		454	into a trap where C<aio_sendfile> reads some data with readahead, then
		455	fails to write all data, and when the socket is ready the next time, the
		456	data in the cache is already lost, forcing C<aio_sendfile> to again hit
		457	the disk. Explicit C<aio_read> + C<aio_write> let's you better control
		458	resource usage.
		459
		460	This call tries to make use of a native C<sendfile>-like syscall to
		461	provide zero-copy operation. For this to work, C<$out_fh> should refer to
		462	a socket, and C<$in_fh> should refer to an mmap'able file.
		463
		464	If a native sendfile cannot be found or it fails with C<ENOSYS>,
		465	C<EINVAL>, C<ENOTSUP>, C<EOPNOTSUPP>, C<EAFNOSUPPORT>, C<EPROTOTYPE> or
		466	C<ENOTSOCK>, it will be emulated, so you can call C<aio_sendfile> on any
		467	type of filehandle regardless of the limitations of the operating system.
		468
		469	As native sendfile syscalls (as practically any non-POSIX interface hacked
		470	together in a hurry to improve benchmark numbers) tend to be rather buggy
		471	on many systems, this implementation tries to work around some known bugs
		472	in Linux and FreeBSD kernels (probably others, too), but that might fail,
		473	so you really really should check the return value of C<aio_sendfile> -
		474	fewre bytes than expected might have been transferred.
		475
		476
142	=item aio_readahead $fh,$offset,$length, $callback	477	=item aio_readahead $fh,$offset,$length, $callback->($retval)
143		478
144	Asynchronously reads the specified byte range into the page cache, using
145	the C<readahead> syscall. If that syscall doesn't exist the status will be
146	C<-1> and C<$!> is set to ENOSYS.
147
148	readahead() populates the page cache with data from a file so that	479	C<aio_readahead> populates the page cache with data from a file so that
149	subsequent reads from that file will not block on disk I/O. The C<$offset>	480	subsequent reads from that file will not block on disk I/O. The C<$offset>
150	argument specifies the starting point from which data is to be read and	481	argument specifies the starting point from which data is to be read and
151	C<$length> specifies the number of bytes to be read. I/O is performed in	482	C<$length> specifies the number of bytes to be read. I/O is performed in
152	whole pages, so that offset is effectively rounded down to a page boundary	483	whole pages, so that offset is effectively rounded down to a page boundary
153	and bytes are read up to the next page boundary greater than or equal to	484	and bytes are read up to the next page boundary greater than or equal to
154	(off-set+length). aio_readahead() does not read beyond the end of the	485	(off-set+length). C<aio_readahead> does not read beyond the end of the
155	file. The current file offset of the file is left unchanged.	486	file. The current file offset of the file is left unchanged.
156		487
		488	If that syscall doesn't exist (likely if your OS isn't Linux) it will be
		489	emulated by simply reading the data, which would have a similar effect.
		490
		491
157	=item aio_stat $fh_or_path, $callback	492	=item aio_stat $fh_or_path, $callback->($status)
158		493
159	=item aio_lstat $fh, $callback	494	=item aio_lstat $fh, $callback->($status)
160		495
161	Works like perl's C<stat> or C<lstat> in void context. The callback will	496	Works like perl's C<stat> or C<lstat> in void context. The callback will
162	be called after the stat and the results will be available using C<stat _>	497	be called after the stat and the results will be available using C<stat _>
163	or C<-s _> etc...	498	or C<-s _> etc...
164		499
…		…
166	for an explanation.	501	for an explanation.
167		502
168	Currently, the stats are always 64-bit-stats, i.e. instead of returning an	503	Currently, the stats are always 64-bit-stats, i.e. instead of returning an
169	error when stat'ing a large file, the results will be silently truncated	504	error when stat'ing a large file, the results will be silently truncated
170	unless perl itself is compiled with large file support.	505	unless perl itself is compiled with large file support.
		506
		507	To help interpret the mode and dev/rdev stat values, IO::AIO offers the
		508	following constants and functions (if not implemented, the constants will
		509	be C<0> and the functions will either C<croak> or fall back on traditional
		510	behaviour).
		511
		512	C<S_IFMT>, C<S_IFIFO>, C<S_IFCHR>, C<S_IFBLK>, C<S_IFLNK>, C<S_IFREG>,
		513	C<S_IFDIR>, C<S_IFWHT>, C<S_IFSOCK>, C<IO::AIO::major $dev_t>,
		514	C<IO::AIO::minor $dev_t>, C<IO::AIO::makedev $major, $minor>.
171		515
172	Example: Print the length of F</etc/passwd>:	516	Example: Print the length of F</etc/passwd>:
173		517
174	aio_stat "/etc/passwd", sub {	518	aio_stat "/etc/passwd", sub {
175	$_[0] and die "stat failed: $!";	519	$_[0] and die "stat failed: $!";
176	print "size is ", -s _, "\n";	520	print "size is ", -s _, "\n";
177	};	521	};
178		522
		523
		524	=item aio_statvfs $fh_or_path, $callback->($statvfs)
		525
		526	Works like the POSIX C<statvfs> or C<fstatvfs> syscalls, depending on
		527	whether a file handle or path was passed.
		528
		529	On success, the callback is passed a hash reference with the following
		530	members: C<bsize>, C<frsize>, C<blocks>, C<bfree>, C<bavail>, C<files>,
		531	C<ffree>, C<favail>, C<fsid>, C<flag> and C<namemax>. On failure, C<undef>
		532	is passed.
		533
		534	The following POSIX IO::AIO::ST_* constants are defined: C<ST_RDONLY> and
		535	C<ST_NOSUID>.
		536
		537	The following non-POSIX IO::AIO::ST_* flag masks are defined to
		538	their correct value when available, or to C<0> on systems that do
		539	not support them: C<ST_NODEV>, C<ST_NOEXEC>, C<ST_SYNCHRONOUS>,
		540	C<ST_MANDLOCK>, C<ST_WRITE>, C<ST_APPEND>, C<ST_IMMUTABLE>, C<ST_NOATIME>,
		541	C<ST_NODIRATIME> and C<ST_RELATIME>.
		542
		543	Example: stat C</wd> and dump out the data if successful.
		544
		545	aio_statvfs "/wd", sub {
		546	my $f = $_[0]
		547	or die "statvfs: $!";
		548
		549	use Data::Dumper;
		550	say Dumper $f;
		551	};
		552
		553	# result:
		554	{
		555	bsize => 1024,
		556	bfree => 4333064312,
		557	blocks => 10253828096,
		558	files => 2050765568,
		559	flag => 4096,
		560	favail => 2042092649,
		561	bavail => 4333064312,
		562	ffree => 2042092649,
		563	namemax => 255,
		564	frsize => 1024,
		565	fsid => 1810
		566	}
		567
		568
		569	=item aio_utime $fh_or_path, $atime, $mtime, $callback->($status)
		570
		571	Works like perl's C<utime> function (including the special case of $atime
		572	and $mtime being undef). Fractional times are supported if the underlying
		573	syscalls support them.
		574
		575	When called with a pathname, uses utimes(2) if available, otherwise
		576	utime(2). If called on a file descriptor, uses futimes(2) if available,
		577	otherwise returns ENOSYS, so this is not portable.
		578
		579	Examples:
		580
		581	# set atime and mtime to current time (basically touch(1)):
		582	aio_utime "path", undef, undef;
		583	# set atime to current time and mtime to beginning of the epoch:
		584	aio_utime "path", time, undef; # undef==0
		585
		586
		587	=item aio_chown $fh_or_path, $uid, $gid, $callback->($status)
		588
		589	Works like perl's C<chown> function, except that C<undef> for either $uid
		590	or $gid is being interpreted as "do not change" (but -1 can also be used).
		591
		592	Examples:
		593
		594	# same as "chown root path" in the shell:
		595	aio_chown "path", 0, -1;
		596	# same as above:
		597	aio_chown "path", 0, undef;
		598
		599
		600	=item aio_truncate $fh_or_path, $offset, $callback->($status)
		601
		602	Works like truncate(2) or ftruncate(2).
		603
		604
		605	=item aio_chmod $fh_or_path, $mode, $callback->($status)
		606
		607	Works like perl's C<chmod> function.
		608
		609
179	=item aio_unlink $pathname, $callback	610	=item aio_unlink $pathname, $callback->($status)
180		611
181	Asynchronously unlink (delete) a file and call the callback with the	612	Asynchronously unlink (delete) a file and call the callback with the
182	result code.	613	result code.
183		614
		615
		616	=item aio_mknod $path, $mode, $dev, $callback->($status)
		617
		618	[EXPERIMENTAL]
		619
		620	Asynchronously create a device node (or fifo). See mknod(2).
		621
		622	The only (POSIX-) portable way of calling this function is:
		623
		624	aio_mknod $path, IO::AIO::S_IFIFO \| $mode, 0, sub { ...
		625
		626	See C<aio_stat> for info about some potentially helpful extra constants
		627	and functions.
		628
		629	=item aio_link $srcpath, $dstpath, $callback->($status)
		630
		631	Asynchronously create a new link to the existing object at C<$srcpath> at
		632	the path C<$dstpath> and call the callback with the result code.
		633
		634
		635	=item aio_symlink $srcpath, $dstpath, $callback->($status)
		636
		637	Asynchronously create a new symbolic link to the existing object at C<$srcpath> at
		638	the path C<$dstpath> and call the callback with the result code.
		639
		640
		641	=item aio_readlink $path, $callback->($link)
		642
		643	Asynchronously read the symlink specified by C<$path> and pass it to
		644	the callback. If an error occurs, nothing or undef gets passed to the
		645	callback.
		646
		647
		648	=item aio_rename $srcpath, $dstpath, $callback->($status)
		649
		650	Asynchronously rename the object at C<$srcpath> to C<$dstpath>, just as
		651	rename(2) and call the callback with the result code.
		652
		653
		654	=item aio_mkdir $pathname, $mode, $callback->($status)
		655
		656	Asynchronously mkdir (create) a directory and call the callback with
		657	the result code. C<$mode> will be modified by the umask at the time the
		658	request is executed, so do not change your umask.
		659
		660
		661	=item aio_rmdir $pathname, $callback->($status)
		662
		663	Asynchronously rmdir (delete) a directory and call the callback with the
		664	result code.
		665
		666
		667	=item aio_readdir $pathname, $callback->($entries)
		668
		669	Unlike the POSIX call of the same name, C<aio_readdir> reads an entire
		670	directory (i.e. opendir + readdir + closedir). The entries will not be
		671	sorted, and will B<NOT> include the C<.> and C<..> entries.
		672
		673	The callback is passed a single argument which is either C<undef> or an
		674	array-ref with the filenames.
		675
		676
		677	=item aio_readdirx $pathname, $flags, $callback->($entries, $flags)
		678
		679	Quite similar to C<aio_readdir>, but the C<$flags> argument allows to tune
		680	behaviour and output format. In case of an error, C<$entries> will be
		681	C<undef>.
		682
		683	The flags are a combination of the following constants, ORed together (the
		684	flags will also be passed to the callback, possibly modified):
		685
		686	=over 4
		687
		688	=item IO::AIO::READDIR_DENTS
		689
		690	When this flag is off, then the callback gets an arrayref consisting of
		691	names only (as with C<aio_readdir>), otherwise it gets an arrayref with
		692	C<[$name, $type, $inode]> arrayrefs, each describing a single directory
		693	entry in more detail.
		694
		695	C<$name> is the name of the entry.
		696
		697	C<$type> is one of the C<IO::AIO::DT_xxx> constants:
		698
		699	C<IO::AIO::DT_UNKNOWN>, C<IO::AIO::DT_FIFO>, C<IO::AIO::DT_CHR>, C<IO::AIO::DT_DIR>,
		700	C<IO::AIO::DT_BLK>, C<IO::AIO::DT_REG>, C<IO::AIO::DT_LNK>, C<IO::AIO::DT_SOCK>,
		701	C<IO::AIO::DT_WHT>.
		702
		703	C<IO::AIO::DT_UNKNOWN> means just that: readdir does not know. If you need to
		704	know, you have to run stat yourself. Also, for speed reasons, the C<$type>
		705	scalars are read-only: you can not modify them.
		706
		707	C<$inode> is the inode number (which might not be exact on systems with 64
		708	bit inode numbers and 32 bit perls). This field has unspecified content on
		709	systems that do not deliver the inode information.
		710
		711	=item IO::AIO::READDIR_DIRS_FIRST
		712
		713	When this flag is set, then the names will be returned in an order where
		714	likely directories come first, in optimal stat order. This is useful when
		715	you need to quickly find directories, or you want to find all directories
		716	while avoiding to stat() each entry.
		717
		718	If the system returns type information in readdir, then this is used
		719	to find directories directly. Otherwise, likely directories are names
		720	beginning with ".", or otherwise names with no dots, of which names with
		721	short names are tried first.
		722
		723	=item IO::AIO::READDIR_STAT_ORDER
		724
		725	When this flag is set, then the names will be returned in an order
		726	suitable for stat()'ing each one. That is, when you plan to stat()
		727	all files in the given directory, then the returned order will likely
		728	be fastest.
		729
		730	If both this flag and C<IO::AIO::READDIR_DIRS_FIRST> are specified, then
		731	the likely dirs come first, resulting in a less optimal stat order.
		732
		733	=item IO::AIO::READDIR_FOUND_UNKNOWN
		734
		735	This flag should not be set when calling C<aio_readdirx>. Instead, it
		736	is being set by C<aio_readdirx>, when any of the C<$type>'s found were
		737	C<IO::AIO::DT_UNKNOWN>. The absense of this flag therefore indicates that all
		738	C<$type>'s are known, which can be used to speed up some algorithms.
		739
		740	=back
		741
		742
		743	=item aio_load $path, $data, $callback->($status)
		744
		745	This is a composite request that tries to fully load the given file into
		746	memory. Status is the same as with aio_read.
		747
		748	=cut
		749
		750	sub aio_load($$;$) {
		751	my ($path, undef, $cb) = @_;
		752	my $data = \$_[1];
		753
		754	my $pri = aioreq_pri;
		755	my $grp = aio_group $cb;
		756
		757	aioreq_pri $pri;
		758	add $grp aio_open $path, O_RDONLY, 0, sub {
		759	my $fh = shift
		760	or return $grp->result (-1);
		761
		762	aioreq_pri $pri;
		763	add $grp aio_read $fh, 0, (-s $fh), $$data, 0, sub {
		764	$grp->result ($_[0]);
		765	};
		766	};
		767
		768	$grp
		769	}
		770
		771	=item aio_copy $srcpath, $dstpath, $callback->($status)
		772
		773	Try to copy the I<file> (directories not supported as either source or
		774	destination) from C<$srcpath> to C<$dstpath> and call the callback with
		775	a status of C<0> (ok) or C<-1> (error, see C<$!>).
		776
		777	This is a composite request that creates the destination file with
		778	mode 0200 and copies the contents of the source file into it using
		779	C<aio_sendfile>, followed by restoring atime, mtime, access mode and
		780	uid/gid, in that order.
		781
		782	If an error occurs, the partial destination file will be unlinked, if
		783	possible, except when setting atime, mtime, access mode and uid/gid, where
		784	errors are being ignored.
		785
		786	=cut
		787
		788	sub aio_copy($$;$) {
		789	my ($src, $dst, $cb) = @_;
		790
		791	my $pri = aioreq_pri;
		792	my $grp = aio_group $cb;
		793
		794	aioreq_pri $pri;
		795	add $grp aio_open $src, O_RDONLY, 0, sub {
		796	if (my $src_fh = $_[0]) {
		797	my @stat = stat $src_fh; # hmm, might block over nfs?
		798
		799	aioreq_pri $pri;
		800	add $grp aio_open $dst, O_CREAT \| O_WRONLY \| O_TRUNC, 0200, sub {
		801	if (my $dst_fh = $_[0]) {
		802	aioreq_pri $pri;
		803	add $grp aio_sendfile $dst_fh, $src_fh, 0, $stat[7], sub {
		804	if ($_[0] == $stat[7]) {
		805	$grp->result (0);
		806	close $src_fh;
		807
		808	my $ch = sub {
		809	aioreq_pri $pri;
		810	add $grp aio_chmod $dst_fh, $stat[2] & 07777, sub {
		811	aioreq_pri $pri;
		812	add $grp aio_chown $dst_fh, $stat[4], $stat[5], sub {
		813	aioreq_pri $pri;
		814	add $grp aio_close $dst_fh;
		815	}
		816	};
		817	};
		818
		819	aioreq_pri $pri;
		820	add $grp aio_utime $dst_fh, $stat[8], $stat[9], sub {
		821	if ($_[0] < 0 && $! == ENOSYS) {
		822	aioreq_pri $pri;
		823	add $grp aio_utime $dst, $stat[8], $stat[9], $ch;
		824	} else {
		825	$ch->();
		826	}
		827	};
		828	} else {
		829	$grp->result (-1);
		830	close $src_fh;
		831	close $dst_fh;
		832
		833	aioreq $pri;
		834	add $grp aio_unlink $dst;
		835	}
		836	};
		837	} else {
		838	$grp->result (-1);
		839	}
		840	},
		841
		842	} else {
		843	$grp->result (-1);
		844	}
		845	};
		846
		847	$grp
		848	}
		849
		850	=item aio_move $srcpath, $dstpath, $callback->($status)
		851
		852	Try to move the I<file> (directories not supported as either source or
		853	destination) from C<$srcpath> to C<$dstpath> and call the callback with
		854	a status of C<0> (ok) or C<-1> (error, see C<$!>).
		855
		856	This is a composite request that tries to rename(2) the file first; if
		857	rename fails with C<EXDEV>, it copies the file with C<aio_copy> and, if
		858	that is successful, unlinks the C<$srcpath>.
		859
		860	=cut
		861
		862	sub aio_move($$;$) {
		863	my ($src, $dst, $cb) = @_;
		864
		865	my $pri = aioreq_pri;
		866	my $grp = aio_group $cb;
		867
		868	aioreq_pri $pri;
		869	add $grp aio_rename $src, $dst, sub {
		870	if ($_[0] && $! == EXDEV) {
		871	aioreq_pri $pri;
		872	add $grp aio_copy $src, $dst, sub {
		873	$grp->result ($_[0]);
		874
		875	unless ($_[0]) {
		876	aioreq_pri $pri;
		877	add $grp aio_unlink $src;
		878	}
		879	};
		880	} else {
		881	$grp->result ($_[0]);
		882	}
		883	};
		884
		885	$grp
		886	}
		887
		888	=item aio_scandir $path, $maxreq, $callback->($dirs, $nondirs)
		889
		890	Scans a directory (similar to C<aio_readdir>) but additionally tries to
		891	efficiently separate the entries of directory C<$path> into two sets of
		892	names, directories you can recurse into (directories), and ones you cannot
		893	recurse into (everything else, including symlinks to directories).
		894
		895	C<aio_scandir> is a composite request that creates of many sub requests_
		896	C<$maxreq> specifies the maximum number of outstanding aio requests that
		897	this function generates. If it is C<< <= 0 >>, then a suitable default
		898	will be chosen (currently 4).
		899
		900	On error, the callback is called without arguments, otherwise it receives
		901	two array-refs with path-relative entry names.
		902
		903	Example:
		904
		905	aio_scandir $dir, 0, sub {
		906	my ($dirs, $nondirs) = @_;
		907	print "real directories: @$dirs\n";
		908	print "everything else: @$nondirs\n";
		909	};
		910
		911	Implementation notes.
		912
		913	The C<aio_readdir> cannot be avoided, but C<stat()>'ing every entry can.
		914
		915	If readdir returns file type information, then this is used directly to
		916	find directories.
		917
		918	Otherwise, after reading the directory, the modification time, size etc.
		919	of the directory before and after the readdir is checked, and if they
		920	match (and isn't the current time), the link count will be used to decide
		921	how many entries are directories (if >= 2). Otherwise, no knowledge of the
		922	number of subdirectories will be assumed.
		923
		924	Then entries will be sorted into likely directories a non-initial dot
		925	currently) and likely non-directories (see C<aio_readdirx>). Then every
		926	entry plus an appended C</.> will be C<stat>'ed, likely directories first,
		927	in order of their inode numbers. If that succeeds, it assumes that the
		928	entry is a directory or a symlink to directory (which will be checked
		929	seperately). This is often faster than stat'ing the entry itself because
		930	filesystems might detect the type of the entry without reading the inode
		931	data (e.g. ext2fs filetype feature), even on systems that cannot return
		932	the filetype information on readdir.
		933
		934	If the known number of directories (link count - 2) has been reached, the
		935	rest of the entries is assumed to be non-directories.
		936
		937	This only works with certainty on POSIX (= UNIX) filesystems, which
		938	fortunately are the vast majority of filesystems around.
		939
		940	It will also likely work on non-POSIX filesystems with reduced efficiency
		941	as those tend to return 0 or 1 as link counts, which disables the
		942	directory counting heuristic.
		943
		944	=cut
		945
		946	sub aio_scandir($$;$) {
		947	my ($path, $maxreq, $cb) = @_;
		948
		949	my $pri = aioreq_pri;
		950
		951	my $grp = aio_group $cb;
		952
		953	$maxreq = 4 if $maxreq <= 0;
		954
		955	# stat once
		956	aioreq_pri $pri;
		957	add $grp aio_stat $path, sub {
		958	return $grp->result () if $_[0];
		959	my $now = time;
		960	my $hash1 = join ":", (stat _)[0,1,3,7,9];
		961
		962	# read the directory entries
		963	aioreq_pri $pri;
		964	add $grp aio_readdirx $path, READDIR_DIRS_FIRST, sub {
		965	my $entries = shift
		966	or return $grp->result ();
		967
		968	# stat the dir another time
		969	aioreq_pri $pri;
		970	add $grp aio_stat $path, sub {
		971	my $hash2 = join ":", (stat _)[0,1,3,7,9];
		972
		973	my $ndirs;
		974
		975	# take the slow route if anything looks fishy
		976	if ($hash1 ne $hash2 or (stat _)[9] == $now) {
		977	$ndirs = -1;
		978	} else {
		979	# if nlink == 2, we are finished
		980	# for non-posix-fs's, we rely on nlink < 2
		981	$ndirs = (stat _)[3] - 2
		982	or return $grp->result ([], $entries);
		983	}
		984
		985	my (@dirs, @nondirs);
		986
		987	my $statgrp = add $grp aio_group sub {
		988	$grp->result (\@dirs, \@nondirs);
		989	};
		990
		991	limit $statgrp $maxreq;
		992	feed $statgrp sub {
		993	return unless @$entries;
		994	my $entry = shift @$entries;
		995
		996	aioreq_pri $pri;
		997	add $statgrp aio_stat "$path/$entry/.", sub {
		998	if ($_[0] < 0) {
		999	push @nondirs, $entry;
		1000	} else {
		1001	# need to check for real directory
		1002	aioreq_pri $pri;
		1003	add $statgrp aio_lstat "$path/$entry", sub {
		1004	if (-d _) {
		1005	push @dirs, $entry;
		1006
		1007	unless (--$ndirs) {
		1008	push @nondirs, @$entries;
		1009	feed $statgrp;
		1010	}
		1011	} else {
		1012	push @nondirs, $entry;
		1013	}
		1014	}
		1015	}
		1016	};
		1017	};
		1018	};
		1019	};
		1020	};
		1021
		1022	$grp
		1023	}
		1024
		1025	=item aio_rmtree $path, $callback->($status)
		1026
		1027	Delete a directory tree starting (and including) C<$path>, return the
		1028	status of the final C<rmdir> only. This is a composite request that
		1029	uses C<aio_scandir> to recurse into and rmdir directories, and unlink
		1030	everything else.
		1031
		1032	=cut
		1033
		1034	sub aio_rmtree;
		1035	sub aio_rmtree($;$) {
		1036	my ($path, $cb) = @_;
		1037
		1038	my $pri = aioreq_pri;
		1039	my $grp = aio_group $cb;
		1040
		1041	aioreq_pri $pri;
		1042	add $grp aio_scandir $path, 0, sub {
		1043	my ($dirs, $nondirs) = @_;
		1044
		1045	my $dirgrp = aio_group sub {
		1046	add $grp aio_rmdir $path, sub {
		1047	$grp->result ($_[0]);
		1048	};
		1049	};
		1050
		1051	(aioreq_pri $pri), add $dirgrp aio_rmtree "$path/$_" for @$dirs;
		1052	(aioreq_pri $pri), add $dirgrp aio_unlink "$path/$_" for @$nondirs;
		1053
		1054	add $grp $dirgrp;
		1055	};
		1056
		1057	$grp
		1058	}
		1059
		1060	=item aio_sync $callback->($status)
		1061
		1062	Asynchronously call sync and call the callback when finished.
		1063
184	=item aio_fsync $fh, $callback	1064	=item aio_fsync $fh, $callback->($status)
185		1065
186	Asynchronously call fsync on the given filehandle and call the callback	1066	Asynchronously call fsync on the given filehandle and call the callback
187	with the fsync result code.	1067	with the fsync result code.
188		1068
189	=item aio_fdatasync $fh, $callback	1069	=item aio_fdatasync $fh, $callback->($status)
190		1070
191	Asynchronously call fdatasync on the given filehandle and call the	1071	Asynchronously call fdatasync on the given filehandle and call the
192	callback with the fdatasync result code.	1072	callback with the fdatasync result code.
193		1073
		1074	If this call isn't available because your OS lacks it or it couldn't be
		1075	detected, it will be emulated by calling C<fsync> instead.
		1076
		1077	=item aio_sync_file_range $fh, $offset, $nbytes, $flags, $callback->($status)
		1078
		1079	Sync the data portion of the file specified by C<$offset> and C<$length>
		1080	to disk (but NOT the metadata), by calling the Linux-specific
		1081	sync_file_range call. If sync_file_range is not available or it returns
		1082	ENOSYS, then fdatasync or fsync is being substituted.
		1083
		1084	C<$flags> can be a combination of C<IO::AIO::SYNC_FILE_RANGE_WAIT_BEFORE>,
		1085	C<IO::AIO::SYNC_FILE_RANGE_WRITE> and
		1086	C<IO::AIO::SYNC_FILE_RANGE_WAIT_AFTER>: refer to the sync_file_range
		1087	manpage for details.
		1088
		1089	=item aio_pathsync $path, $callback->($status)
		1090
		1091	This request tries to open, fsync and close the given path. This is a
		1092	composite request intended to sync directories after directory operations
		1093	(E.g. rename). This might not work on all operating systems or have any
		1094	specific effect, but usually it makes sure that directory changes get
		1095	written to disc. It works for anything that can be opened for read-only,
		1096	not just directories.
		1097
		1098	Future versions of this function might fall back to other methods when
		1099	C<fsync> on the directory fails (such as calling C<sync>).
		1100
		1101	Passes C<0> when everything went ok, and C<-1> on error.
		1102
		1103	=cut
		1104
		1105	sub aio_pathsync($;$) {
		1106	my ($path, $cb) = @_;
		1107
		1108	my $pri = aioreq_pri;
		1109	my $grp = aio_group $cb;
		1110
		1111	aioreq_pri $pri;
		1112	add $grp aio_open $path, O_RDONLY, 0, sub {
		1113	my ($fh) = @_;
		1114	if ($fh) {
		1115	aioreq_pri $pri;
		1116	add $grp aio_fsync $fh, sub {
		1117	$grp->result ($_[0]);
		1118
		1119	aioreq_pri $pri;
		1120	add $grp aio_close $fh;
		1121	};
		1122	} else {
		1123	$grp->result (-1);
		1124	}
		1125	};
		1126
		1127	$grp
		1128	}
		1129
		1130	=item aio_msync $scalar, $offset = 0, $length = undef, flags = 0, $callback->($status)
		1131
		1132	This is a rather advanced IO::AIO call, which only works on mmap(2)ed
		1133	scalars (see the C<IO::AIO::mmap> function, although it also works on data
		1134	scalars managed by the L<Sys::Mmap> or L<Mmap> modules, note that the
		1135	scalar must only be modified in-place while an aio operation is pending on
		1136	it).
		1137
		1138	It calls the C<msync> function of your OS, if available, with the memory
		1139	area starting at C<$offset> in the string and ending C<$length> bytes
		1140	later. If C<$length> is negative, counts from the end, and if C<$length>
		1141	is C<undef>, then it goes till the end of the string. The flags can be
		1142	a combination of C<IO::AIO::MS_ASYNC>, C<IO::AIO::MS_INVALIDATE> and
		1143	C<IO::AIO::MS_SYNC>.
		1144
		1145	=item aio_mtouch $scalar, $offset = 0, $length = undef, flags = 0, $callback->($status)
		1146
		1147	This is a rather advanced IO::AIO call, which works best on mmap(2)ed
		1148	scalars.
		1149
		1150	It touches (reads or writes) all memory pages in the specified
		1151	range inside the scalar. All caveats and parameters are the same
		1152	as for C<aio_msync>, above, except for flags, which must be either
		1153	C<0> (which reads all pages and ensures they are instantiated) or
		1154	C<IO::AIO::MT_MODIFY>, which modifies the memory page s(by reading and
		1155	writing an octet from it, which dirties the page).
		1156
		1157	=item aio_mlock $scalar, $offset = 0, $length = undef, $callback->($status)
		1158
		1159	This is a rather advanced IO::AIO call, which works best on mmap(2)ed
		1160	scalars.
		1161
		1162	It reads in all the pages of the underlying storage into memory (if any)
		1163	and locks them, so they are not getting swapped/paged out or removed.
		1164
		1165	If C<$length> is undefined, then the scalar will be locked till the end.
		1166
		1167	On systems that do not implement C<mlock>, this function returns C<-1>
		1168	and sets errno to C<ENOSYS>.
		1169
		1170	Note that the corresponding C<munlock> is synchronous and is
		1171	documented under L<MISCELLANEOUS FUNCTIONS>.
		1172
		1173	Example: open a file, mmap and mlock it - both will be undone when
		1174	C<$data> gets destroyed.
		1175
		1176	open my $fh, "<", $path or die "$path: $!";
		1177	my $data;
		1178	IO::AIO::mmap $data, -s $fh, IO::AIO::PROT_READ, IO::AIO::MAP_SHARED, $fh;
		1179	aio_mlock $data; # mlock in background
		1180
		1181	=item aio_mlockall $flags, $callback->($status)
		1182
		1183	Calls the C<mlockall> function with the given C<$flags> (a combination of
		1184	C<IO::AIO::MCL_CURRENT> and C<IO::AIO::MCL_FUTURE>).
		1185
		1186	On systems that do not implement C<mlockall>, this function returns C<-1>
		1187	and sets errno to C<ENOSYS>.
		1188
		1189	Note that the corresponding C<munlockall> is synchronous and is
		1190	documented under L<MISCELLANEOUS FUNCTIONS>.
		1191
		1192	Example: asynchronously lock all current and future pages into memory.
		1193
		1194	aio_mlockall IO::AIO::MCL_FUTURE;
		1195
		1196	=item aio_group $callback->(...)
		1197
		1198	This is a very special aio request: Instead of doing something, it is a
		1199	container for other aio requests, which is useful if you want to bundle
		1200	many requests into a single, composite, request with a definite callback
		1201	and the ability to cancel the whole request with its subrequests.
		1202
		1203	Returns an object of class L<IO::AIO::GRP>. See its documentation below
		1204	for more info.
		1205
		1206	Example:
		1207
		1208	my $grp = aio_group sub {
		1209	print "all stats done\n";
		1210	};
		1211
		1212	add $grp
		1213	(aio_stat ...),
		1214	(aio_stat ...),
		1215	...;
		1216
		1217	=item aio_nop $callback->()
		1218
		1219	This is a special request - it does nothing in itself and is only used for
		1220	side effects, such as when you want to add a dummy request to a group so
		1221	that finishing the requests in the group depends on executing the given
		1222	code.
		1223
		1224	While this request does nothing, it still goes through the execution
		1225	phase and still requires a worker thread. Thus, the callback will not
		1226	be executed immediately but only after other requests in the queue have
		1227	entered their execution phase. This can be used to measure request
		1228	latency.
		1229
		1230	=item IO::AIO::aio_busy $fractional_seconds, $callback->() NOT EXPORTED
		1231
		1232	Mainly used for debugging and benchmarking, this aio request puts one of
		1233	the request workers to sleep for the given time.
		1234
		1235	While it is theoretically handy to have simple I/O scheduling requests
		1236	like sleep and file handle readable/writable, the overhead this creates is
		1237	immense (it blocks a thread for a long time) so do not use this function
		1238	except to put your application under artificial I/O pressure.
		1239
194	=back	1240	=back
195		1241
		1242	=head2 IO::AIO::REQ CLASS
		1243
		1244	All non-aggregate C<aio_*> functions return an object of this class when
		1245	called in non-void context.
		1246
		1247	=over 4
		1248
		1249	=item cancel $req
		1250
		1251	Cancels the request, if possible. Has the effect of skipping execution
		1252	when entering the B<execute> state and skipping calling the callback when
		1253	entering the the B<result> state, but will leave the request otherwise
		1254	untouched (with the exception of readdir). That means that requests that
		1255	currently execute will not be stopped and resources held by the request
		1256	will not be freed prematurely.
		1257
		1258	=item cb $req $callback->(...)
		1259
		1260	Replace (or simply set) the callback registered to the request.
		1261
		1262	=back
		1263
		1264	=head2 IO::AIO::GRP CLASS
		1265
		1266	This class is a subclass of L<IO::AIO::REQ>, so all its methods apply to
		1267	objects of this class, too.
		1268
		1269	A IO::AIO::GRP object is a special request that can contain multiple other
		1270	aio requests.
		1271
		1272	You create one by calling the C<aio_group> constructing function with a
		1273	callback that will be called when all contained requests have entered the
		1274	C<done> state:
		1275
		1276	my $grp = aio_group sub {
		1277	print "all requests are done\n";
		1278	};
		1279
		1280	You add requests by calling the C<add> method with one or more
		1281	C<IO::AIO::REQ> objects:
		1282
		1283	$grp->add (aio_unlink "...");
		1284
		1285	add $grp aio_stat "...", sub {
		1286	$_[0] or return $grp->result ("error");
		1287
		1288	# add another request dynamically, if first succeeded
		1289	add $grp aio_open "...", sub {
		1290	$grp->result ("ok");
		1291	};
		1292	};
		1293
		1294	This makes it very easy to create composite requests (see the source of
		1295	C<aio_move> for an application) that work and feel like simple requests.
		1296
		1297	=over 4
		1298
		1299	=item * The IO::AIO::GRP objects will be cleaned up during calls to
		1300	C<IO::AIO::poll_cb>, just like any other request.
		1301
		1302	=item * They can be canceled like any other request. Canceling will cancel not
		1303	only the request itself, but also all requests it contains.
		1304
		1305	=item * They can also can also be added to other IO::AIO::GRP objects.
		1306
		1307	=item * You must not add requests to a group from within the group callback (or
		1308	any later time).
		1309
		1310	=back
		1311
		1312	Their lifetime, simplified, looks like this: when they are empty, they
		1313	will finish very quickly. If they contain only requests that are in the
		1314	C<done> state, they will also finish. Otherwise they will continue to
		1315	exist.
		1316
		1317	That means after creating a group you have some time to add requests
		1318	(precisely before the callback has been invoked, which is only done within
		1319	the C<poll_cb>). And in the callbacks of those requests, you can add
		1320	further requests to the group. And only when all those requests have
		1321	finished will the the group itself finish.
		1322
		1323	=over 4
		1324
		1325	=item add $grp ...
		1326
		1327	=item $grp->add (...)
		1328
		1329	Add one or more requests to the group. Any type of L<IO::AIO::REQ> can
		1330	be added, including other groups, as long as you do not create circular
		1331	dependencies.
		1332
		1333	Returns all its arguments.
		1334
		1335	=item $grp->cancel_subs
		1336
		1337	Cancel all subrequests and clears any feeder, but not the group request
		1338	itself. Useful when you queued a lot of events but got a result early.
		1339
		1340	The group request will finish normally (you cannot add requests to the
		1341	group).
		1342
		1343	=item $grp->result (...)
		1344
		1345	Set the result value(s) that will be passed to the group callback when all
		1346	subrequests have finished and set the groups errno to the current value
		1347	of errno (just like calling C<errno> without an error number). By default,
		1348	no argument will be passed and errno is zero.
		1349
		1350	=item $grp->errno ([$errno])
		1351
		1352	Sets the group errno value to C<$errno>, or the current value of errno
		1353	when the argument is missing.
		1354
		1355	Every aio request has an associated errno value that is restored when
		1356	the callback is invoked. This method lets you change this value from its
		1357	default (0).
		1358
		1359	Calling C<result> will also set errno, so make sure you either set C<$!>
		1360	before the call to C<result>, or call c<errno> after it.
		1361
		1362	=item feed $grp $callback->($grp)
		1363
		1364	Sets a feeder/generator on this group: every group can have an attached
		1365	generator that generates requests if idle. The idea behind this is that,
		1366	although you could just queue as many requests as you want in a group,
		1367	this might starve other requests for a potentially long time. For example,
		1368	C<aio_scandir> might generate hundreds of thousands C<aio_stat> requests,
		1369	delaying any later requests for a long time.
		1370
		1371	To avoid this, and allow incremental generation of requests, you can
		1372	instead a group and set a feeder on it that generates those requests. The
		1373	feed callback will be called whenever there are few enough (see C<limit>,
		1374	below) requests active in the group itself and is expected to queue more
		1375	requests.
		1376
		1377	The feed callback can queue as many requests as it likes (i.e. C<add> does
		1378	not impose any limits).
		1379
		1380	If the feed does not queue more requests when called, it will be
		1381	automatically removed from the group.
		1382
		1383	If the feed limit is C<0> when this method is called, it will be set to
		1384	C<2> automatically.
		1385
		1386	Example:
		1387
		1388	# stat all files in @files, but only ever use four aio requests concurrently:
		1389
		1390	my $grp = aio_group sub { print "finished\n" };
		1391	limit $grp 4;
		1392	feed $grp sub {
		1393	my $file = pop @files
		1394	or return;
		1395
		1396	add $grp aio_stat $file, sub { ... };
		1397	};
		1398
		1399	=item limit $grp $num
		1400
		1401	Sets the feeder limit for the group: The feeder will be called whenever
		1402	the group contains less than this many requests.
		1403
		1404	Setting the limit to C<0> will pause the feeding process.
		1405
		1406	The default value for the limit is C<0>, but note that setting a feeder
		1407	automatically bumps it up to C<2>.
		1408
		1409	=back
		1410
196	=head2 SUPPORT FUNCTIONS	1411	=head2 SUPPORT FUNCTIONS
197		1412
		1413	=head3 EVENT PROCESSING AND EVENT LOOP INTEGRATION
		1414
198	=over 4	1415	=over 4
199		1416
200	=item $fileno = IO::AIO::poll_fileno	1417	=item $fileno = IO::AIO::poll_fileno
201		1418
202	Return the I<request result pipe filehandle>. This filehandle must be	1419	Return the I<request result pipe file descriptor>. This filehandle must be
203	polled for reading by some mechanism outside this module (e.g. Event	1420	polled for reading by some mechanism outside this module (e.g. EV, Glib,
204	or select, see below). If the pipe becomes readable you have to call	1421	select and so on, see below or the SYNOPSIS). If the pipe becomes readable
205	C<poll_cb> to check the results.	1422	you have to call C<poll_cb> to check the results.
206		1423
207	See C<poll_cb> for an example.	1424	See C<poll_cb> for an example.
208		1425
209	=item IO::AIO::poll_cb	1426	=item IO::AIO::poll_cb
210		1427
211	Process all outstanding events on the result pipe. You have to call this	1428	Process some outstanding events on the result pipe. You have to call
212	regularly. Returns the number of events processed. Returns immediately	1429	this regularly. Returns C<0> if all events could be processed (or there
213	when no events are outstanding.	1430	were no events to process), or C<-1> if it returned earlier for whatever
		1431	reason. Returns immediately when no events are outstanding. The amount of
		1432	events processed depends on the settings of C<IO::AIO::max_poll_req> and
		1433	C<IO::AIO::max_poll_time>.
214		1434
215	You can use Event to multiplex, e.g.:	1435	If not all requests were processed for whatever reason, the filehandle
		1436	will still be ready when C<poll_cb> returns, so normally you don't have to
		1437	do anything special to have it called later.
		1438
		1439	Apart from calling C<IO::AIO::poll_cb> when the event filehandle becomes
		1440	ready, it can be beneficial to call this function from loops which submit
		1441	a lot of requests, to make sure the results get processed when they become
		1442	available and not just when the loop is finished and the event loop takes
		1443	over again. This function returns very fast when there are no outstanding
		1444	requests.
		1445
		1446	Example: Install an Event watcher that automatically calls
		1447	IO::AIO::poll_cb with high priority (more examples can be found in the
		1448	SYNOPSIS section, at the top of this document):
216		1449
217	Event->io (fd => IO::AIO::poll_fileno,	1450	Event->io (fd => IO::AIO::poll_fileno,
218	poll => 'r', async => 1,	1451	poll => 'r', async => 1,
219	cb => \&IO::AIO::poll_cb);	1452	cb => \&IO::AIO::poll_cb);
220		1453
221	=item IO::AIO::poll_wait	1454	=item IO::AIO::poll_wait
222		1455
		1456	If there are any outstanding requests and none of them in the result
223	Wait till the result filehandle becomes ready for reading (simply does a	1457	phase, wait till the result filehandle becomes ready for reading (simply
224	select on the filehandle. This is useful if you want to synchronously wait	1458	does a C<select> on the filehandle. This is useful if you want to
225	for some requests to finish).	1459	synchronously wait for some requests to finish).
226		1460
227	See C<nreqs> for an example.	1461	See C<nreqs> for an example.
228		1462
		1463	=item IO::AIO::poll
		1464
		1465	Waits until some requests have been handled.
		1466
		1467	Returns the number of requests processed, but is otherwise strictly
		1468	equivalent to:
		1469
		1470	IO::AIO::poll_wait, IO::AIO::poll_cb
		1471
229	=item IO::AIO::nreqs	1472	=item IO::AIO::flush
230		1473
231	Returns the number of requests currently outstanding.	1474	Wait till all outstanding AIO requests have been handled.
232		1475
233	Example: wait till there are no outstanding requests anymore:	1476	Strictly equivalent to:
234		1477
235	IO::AIO::poll_wait, IO::AIO::poll_cb	1478	IO::AIO::poll_wait, IO::AIO::poll_cb
236	while IO::AIO::nreqs;	1479	while IO::AIO::nreqs;
237		1480
		1481	=item IO::AIO::max_poll_reqs $nreqs
		1482
		1483	=item IO::AIO::max_poll_time $seconds
		1484
		1485	These set the maximum number of requests (default C<0>, meaning infinity)
		1486	that are being processed by C<IO::AIO::poll_cb> in one call, respectively
		1487	the maximum amount of time (default C<0>, meaning infinity) spent in
		1488	C<IO::AIO::poll_cb> to process requests (more correctly the mininum amount
		1489	of time C<poll_cb> is allowed to use).
		1490
		1491	Setting C<max_poll_time> to a non-zero value creates an overhead of one
		1492	syscall per request processed, which is not normally a problem unless your
		1493	callbacks are really really fast or your OS is really really slow (I am
		1494	not mentioning Solaris here). Using C<max_poll_reqs> incurs no overhead.
		1495
		1496	Setting these is useful if you want to ensure some level of
		1497	interactiveness when perl is not fast enough to process all requests in
		1498	time.
		1499
		1500	For interactive programs, values such as C<0.01> to C<0.1> should be fine.
		1501
		1502	Example: Install an Event watcher that automatically calls
		1503	IO::AIO::poll_cb with low priority, to ensure that other parts of the
		1504	program get the CPU sometimes even under high AIO load.
		1505
		1506	# try not to spend much more than 0.1s in poll_cb
		1507	IO::AIO::max_poll_time 0.1;
		1508
		1509	# use a low priority so other tasks have priority
		1510	Event->io (fd => IO::AIO::poll_fileno,
		1511	poll => 'r', nice => 1,
		1512	cb => &IO::AIO::poll_cb);
		1513
		1514	=back
		1515
		1516	=head3 CONTROLLING THE NUMBER OF THREADS
		1517
		1518	=over
		1519
		1520	=item IO::AIO::min_parallel $nthreads
		1521
		1522	Set the minimum number of AIO threads to C<$nthreads>. The current
		1523	default is C<8>, which means eight asynchronous operations can execute
		1524	concurrently at any one time (the number of outstanding requests,
		1525	however, is unlimited).
		1526
		1527	IO::AIO starts threads only on demand, when an AIO request is queued and
		1528	no free thread exists. Please note that queueing up a hundred requests can
		1529	create demand for a hundred threads, even if it turns out that everything
		1530	is in the cache and could have been processed faster by a single thread.
		1531
		1532	It is recommended to keep the number of threads relatively low, as some
		1533	Linux kernel versions will scale negatively with the number of threads
		1534	(higher parallelity => MUCH higher latency). With current Linux 2.6
		1535	versions, 4-32 threads should be fine.
		1536
		1537	Under most circumstances you don't need to call this function, as the
		1538	module selects a default that is suitable for low to moderate load.
		1539
		1540	=item IO::AIO::max_parallel $nthreads
		1541
		1542	Sets the maximum number of AIO threads to C<$nthreads>. If more than the
		1543	specified number of threads are currently running, this function kills
		1544	them. This function blocks until the limit is reached.
		1545
		1546	While C<$nthreads> are zero, aio requests get queued but not executed
		1547	until the number of threads has been increased again.
		1548
		1549	This module automatically runs C<max_parallel 0> at program end, to ensure
		1550	that all threads are killed and that there are no outstanding requests.
		1551
		1552	Under normal circumstances you don't need to call this function.
		1553
		1554	=item IO::AIO::max_idle $nthreads
		1555
		1556	Limit the number of threads (default: 4) that are allowed to idle
		1557	(i.e., threads that did not get a request to process within the idle
		1558	timeout (default: 10 seconds). That means if a thread becomes idle while
		1559	C<$nthreads> other threads are also idle, it will free its resources and
		1560	exit.
		1561
		1562	This is useful when you allow a large number of threads (e.g. 100 or 1000)
		1563	to allow for extremely high load situations, but want to free resources
		1564	under normal circumstances (1000 threads can easily consume 30MB of RAM).
		1565
		1566	The default is probably ok in most situations, especially if thread
		1567	creation is fast. If thread creation is very slow on your system you might
		1568	want to use larger values.
		1569
		1570	=item IO::AIO::idle_timeout $seconds
		1571
		1572	Sets the minimum idle timeout (default 10) after which worker threads are
		1573	allowed to exit. SEe C<IO::AIO::max_idle>.
		1574
		1575	=item IO::AIO::max_outstanding $maxreqs
		1576
		1577	Sets the maximum number of outstanding requests to C<$nreqs>. If
		1578	you do queue up more than this number of requests, the next call to
		1579	C<IO::AIO::poll_cb> (and other functions calling C<poll_cb>, such as
		1580	C<IO::AIO::flush> or C<IO::AIO::poll>) will block until the limit is no
		1581	longer exceeded.
		1582
		1583	In other words, this setting does not enforce a queue limit, but can be
		1584	used to make poll functions block if the limit is exceeded.
		1585
		1586	This is a very bad function to use in interactive programs because it
		1587	blocks, and a bad way to reduce concurrency because it is inexact: Better
		1588	use an C<aio_group> together with a feed callback.
		1589
		1590	It's main use is in scripts without an event loop - when you want to stat
		1591	a lot of files, you can write somehting like this:
		1592
		1593	IO::AIO::max_outstanding 32;
		1594
		1595	for my $path (...) {
		1596	aio_stat $path , ...;
		1597	IO::AIO::poll_cb;
		1598	}
		1599
		1600	IO::AIO::flush;
		1601
		1602	The call to C<poll_cb> inside the loop will normally return instantly, but
		1603	as soon as more thna C<32> reqeusts are in-flight, it will block until
		1604	some requests have been handled. This keeps the loop from pushing a large
		1605	number of C<aio_stat> requests onto the queue.
		1606
		1607	The default value for C<max_outstanding> is very large, so there is no
		1608	practical limit on the number of outstanding requests.
		1609
		1610	=back
		1611
		1612	=head3 STATISTICAL INFORMATION
		1613
		1614	=over
		1615
238	=item IO::AIO::flush	1616	=item IO::AIO::nreqs
239		1617
240	Wait till all outstanding AIO requests have been handled.	1618	Returns the number of requests currently in the ready, execute or pending
		1619	states (i.e. for which their callback has not been invoked yet).
241		1620
242	Strictly equivalent to:	1621	Example: wait till there are no outstanding requests anymore:
243		1622
244	IO::AIO::poll_wait, IO::AIO::poll_cb	1623	IO::AIO::poll_wait, IO::AIO::poll_cb
245	while IO::AIO::nreqs;	1624	while IO::AIO::nreqs;
246		1625
		1626	=item IO::AIO::nready
		1627
		1628	Returns the number of requests currently in the ready state (not yet
		1629	executed).
		1630
247	=item IO::AIO::poll	1631	=item IO::AIO::npending
248		1632
249	Waits until some requests have been handled.	1633	Returns the number of requests currently in the pending state (executed,
250		1634	but not yet processed by poll_cb).
251	Strictly equivalent to:
252
253	IO::AIO::poll_wait, IO::AIO::poll_cb
254	if IO::AIO::nreqs;
255
256	=item IO::AIO::min_parallel $nthreads
257
258	Set the minimum number of AIO threads to C<$nthreads>. The default is
259	C<1>, which means a single asynchronous operation can be done at one time
260	(the number of outstanding operations, however, is unlimited).
261
262	It is recommended to keep the number of threads low, as some Linux
263	kernel versions will scale negatively with the number of threads (higher
264	parallelity => MUCH higher latency). With current Linux 2.6 versions, 4-32
265	threads should be fine.
266
267	Under normal circumstances you don't need to call this function, as this
268	module automatically starts some threads (the exact number might change,
269	and is currently 4).
270
271	=item IO::AIO::max_parallel $nthreads
272
273	Sets the maximum number of AIO threads to C<$nthreads>. If more than
274	the specified number of threads are currently running, kill them. This
275	function blocks until the limit is reached.
276
277	This module automatically runs C<max_parallel 0> at program end, to ensure
278	that all threads are killed and that there are no outstanding requests.
279
280	Under normal circumstances you don't need to call this function.
281
282	=item $oldnreqs = IO::AIO::max_outstanding $nreqs
283
284	Sets the maximum number of outstanding requests to C<$nreqs>. If you
285	try to queue up more than this number of requests, the caller will block until
286	some requests have been handled.
287
288	The default is very large, so normally there is no practical limit. If you
289	queue up many requests in a loop it it often improves speed if you set
290	this to a relatively low number, such as C<100>.
291
292	Under normal circumstances you don't need to call this function.
293		1635
294	=back	1636	=back
295		1637
		1638	=head3 MISCELLANEOUS FUNCTIONS
		1639
		1640	IO::AIO implements some functions that might be useful, but are not
		1641	asynchronous.
		1642
		1643	=over 4
		1644
		1645	=item IO::AIO::sendfile $ofh, $ifh, $offset, $count
		1646
		1647	Calls the C<eio_sendfile_sync> function, which is like C<aio_sendfile>,
		1648	but is blocking (this makes most sense if you know the input data is
		1649	likely cached already and the output filehandle is set to non-blocking
		1650	operations).
		1651
		1652	Returns the number of bytes copied, or C<-1> on error.
		1653
		1654	=item IO::AIO::fadvise $fh, $offset, $len, $advice
		1655
		1656	Simply calls the C<posix_fadvise> function (see its
		1657	manpage for details). The following advice constants are
		1658	avaiable: C<IO::AIO::FADV_NORMAL>, C<IO::AIO::FADV_SEQUENTIAL>,
		1659	C<IO::AIO::FADV_RANDOM>, C<IO::AIO::FADV_NOREUSE>,
		1660	C<IO::AIO::FADV_WILLNEED>, C<IO::AIO::FADV_DONTNEED>.
		1661
		1662	On systems that do not implement C<posix_fadvise>, this function returns
		1663	ENOSYS, otherwise the return value of C<posix_fadvise>.
		1664
		1665	=item IO::AIO::madvise $scalar, $offset, $len, $advice
		1666
		1667	Simply calls the C<posix_madvise> function (see its
		1668	manpage for details). The following advice constants are
		1669	avaiable: C<IO::AIO::MADV_NORMAL>, C<IO::AIO::MADV_SEQUENTIAL>,
		1670	C<IO::AIO::MADV_RANDOM>, C<IO::AIO::MADV_WILLNEED>, C<IO::AIO::MADV_DONTNEED>.
		1671
		1672	On systems that do not implement C<posix_madvise>, this function returns
		1673	ENOSYS, otherwise the return value of C<posix_madvise>.
		1674
		1675	=item IO::AIO::mprotect $scalar, $offset, $len, $protect
		1676
		1677	Simply calls the C<mprotect> function on the preferably AIO::mmap'ed
		1678	$scalar (see its manpage for details). The following protect
		1679	constants are avaiable: C<IO::AIO::PROT_NONE>, C<IO::AIO::PROT_READ>,
		1680	C<IO::AIO::PROT_WRITE>, C<IO::AIO::PROT_EXEC>.
		1681
		1682	On systems that do not implement C<mprotect>, this function returns
		1683	ENOSYS, otherwise the return value of C<mprotect>.
		1684
		1685	=item IO::AIO::mmap $scalar, $length, $prot, $flags, $fh[, $offset]
		1686
		1687	Memory-maps a file (or anonymous memory range) and attaches it to the
		1688	given C<$scalar>, which will act like a string scalar.
		1689
		1690	The only operations allowed on the scalar are C<substr>/C<vec> that don't
		1691	change the string length, and most read-only operations such as copying it
		1692	or searching it with regexes and so on.
		1693
		1694	Anything else is unsafe and will, at best, result in memory leaks.
		1695
		1696	The memory map associated with the C<$scalar> is automatically removed
		1697	when the C<$scalar> is destroyed, or when the C<IO::AIO::mmap> or
		1698	C<IO::AIO::munmap> functions are called.
		1699
		1700	This calls the C<mmap>(2) function internally. See your system's manual
		1701	page for details on the C<$length>, C<$prot> and C<$flags> parameters.
		1702
		1703	The C<$length> must be larger than zero and smaller than the actual
		1704	filesize.
		1705
		1706	C<$prot> is a combination of C<IO::AIO::PROT_NONE>, C<IO::AIO::PROT_EXEC>,
		1707	C<IO::AIO::PROT_READ> and/or C<IO::AIO::PROT_WRITE>,
		1708
		1709	C<$flags> can be a combination of C<IO::AIO::MAP_SHARED> or
		1710	C<IO::AIO::MAP_PRIVATE>, or a number of system-specific flags (when
		1711	not available, the are defined as 0): C<IO::AIO::MAP_ANONYMOUS>
		1712	(which is set to C<MAP_ANON> if your system only provides this
		1713	constant), C<IO::AIO::MAP_HUGETLB>, C<IO::AIO::MAP_LOCKED>,
		1714	C<IO::AIO::MAP_NORESERVE>, C<IO::AIO::MAP_POPULATE> or
		1715	C<IO::AIO::MAP_NONBLOCK>
		1716
		1717	If C<$fh> is C<undef>, then a file descriptor of C<-1> is passed.
		1718
		1719	C<$offset> is the offset from the start of the file - it generally must be
		1720	a multiple of C<IO::AIO::PAGESIZE> and defaults to C<0>.
		1721
		1722	Example:
		1723
		1724	use Digest::MD5;
		1725	use IO::AIO;
		1726
		1727	open my $fh, "<verybigfile"
		1728	or die "$!";
		1729
		1730	IO::AIO::mmap my $data, -s $fh, IO::AIO::PROT_READ, IO::AIO::MAP_SHARED, $fh
		1731	or die "verybigfile: $!";
		1732
		1733	my $fast_md5 = md5 $data;
		1734
		1735	=item IO::AIO::munmap $scalar
		1736
		1737	Removes a previous mmap and undefines the C<$scalar>.
		1738
		1739	=item IO::AIO::munlock $scalar, $offset = 0, $length = undef
		1740
		1741	Calls the C<munlock> function, undoing the effects of a previous
		1742	C<aio_mlock> call (see its description for details).
		1743
		1744	=item IO::AIO::munlockall
		1745
		1746	Calls the C<munlockall> function.
		1747
		1748	On systems that do not implement C<munlockall>, this function returns
		1749	ENOSYS, otherwise the return value of C<munlockall>.
		1750
		1751	=back
		1752
296	=cut	1753	=cut
297		1754
298	# support function to convert a fd into a perl filehandle
299	sub _fd2fh {
300	return undef if $_[0] < 0;
301
302	# try to be perl5.6-compatible
303	local *AIO_FH;
304	open AIO_FH, "+<&=$_[0]"
305	or return undef;
306
307	*AIO_FH
308	}
309
310	min_parallel 4;	1755	min_parallel 8;
311		1756
312	END {	1757	END { flush }
313	max_parallel 0;
314	}
315		1758
316	1;	1759	1;
317		1760
		1761	=head1 EVENT LOOP INTEGRATION
		1762
		1763	It is recommended to use L<AnyEvent::AIO> to integrate IO::AIO
		1764	automatically into many event loops:
		1765
		1766	# AnyEvent integration (EV, Event, Glib, Tk, POE, urxvt, pureperl...)
		1767	use AnyEvent::AIO;
		1768
		1769	You can also integrate IO::AIO manually into many event loops, here are
		1770	some examples of how to do this:
		1771
		1772	# EV integration
		1773	my $aio_w = EV::io IO::AIO::poll_fileno, EV::READ, \&IO::AIO::poll_cb;
		1774
		1775	# Event integration
		1776	Event->io (fd => IO::AIO::poll_fileno,
		1777	poll => 'r',
		1778	cb => \&IO::AIO::poll_cb);
		1779
		1780	# Glib/Gtk2 integration
		1781	add_watch Glib::IO IO::AIO::poll_fileno,
		1782	in => sub { IO::AIO::poll_cb; 1 };
		1783
		1784	# Tk integration
		1785	Tk::Event::IO->fileevent (IO::AIO::poll_fileno, "",
		1786	readable => \&IO::AIO::poll_cb);
		1787
		1788	# Danga::Socket integration
		1789	Danga::Socket->AddOtherFds (IO::AIO::poll_fileno =>
		1790	\&IO::AIO::poll_cb);
		1791
		1792	=head2 FORK BEHAVIOUR
		1793
		1794	Usage of pthreads in a program changes the semantics of fork
		1795	considerably. Specifically, only async-safe functions can be called after
		1796	fork. Perl doesn't know about this, so in general, you cannot call fork
		1797	with defined behaviour in perl. IO::AIO uses pthreads, so this applies,
		1798	but many other extensions and (for inexplicable reasons) perl itself often
		1799	is linked against pthreads, so this limitation applies.
		1800
		1801	Some operating systems have extensions that allow safe use of fork, and
		1802	this module should do "the right thing" on those, and tries on others. At
		1803	the time of this writing (2011) only GNU/Linux supports these extensions
		1804	to POSIX.
		1805
		1806	=head2 MEMORY USAGE
		1807
		1808	Per-request usage:
		1809
		1810	Each aio request uses - depending on your architecture - around 100-200
		1811	bytes of memory. In addition, stat requests need a stat buffer (possibly
		1812	a few hundred bytes), readdir requires a result buffer and so on. Perl
		1813	scalars and other data passed into aio requests will also be locked and
		1814	will consume memory till the request has entered the done state.
		1815
		1816	This is not awfully much, so queuing lots of requests is not usually a
		1817	problem.
		1818
		1819	Per-thread usage:
		1820
		1821	In the execution phase, some aio requests require more memory for
		1822	temporary buffers, and each thread requires a stack and other data
		1823	structures (usually around 16k-128k, depending on the OS).
		1824
		1825	=head1 KNOWN BUGS
		1826
		1827	Known bugs will be fixed in the next release.
		1828
318	=head1 SEE ALSO	1829	=head1 SEE ALSO
319		1830
320	L<Coro>, L<Linux::AIO>.	1831	L<AnyEvent::AIO> for easy integration into event loops, L<Coro::AIO> for a
		1832	more natural syntax.
321		1833
322	=head1 AUTHOR	1834	=head1 AUTHOR
323		1835
324	Marc Lehmann <schmorp@schmorp.de>	1836	Marc Lehmann <schmorp@schmorp.de>
325	http://home.schmorp.de/	1837	http://home.schmorp.de/

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Revision 1.198 by root, Wed Jun 29 11:25:17 2011 UTC