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Revision 1.30 by root, Wed Aug 17 04:47:38 2005 UTC vs.
Revision 1.169 by root, Sat Jan 2 13:02:20 2010 UTC

…		…
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", 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
		22	use IO::AIO 2;
		23
		24	aioreq_pri 4; # give next request a very high priority
		25	my $req = aio_unlink "/tmp/file", sub { };
		26	$req->cancel; # cancel request if still in queue
		27
		28	my $grp = aio_group sub { print "all stats done\n" };
		29	add $grp aio_stat "..." for ...;
		30
		31	# AnyEvent integration (EV, Event, Glib, Tk, POE, urxvt, pureperl...)
		32	use AnyEvent::AIO;
		33
		34	# EV integration
		35	my $aio_w = EV::io IO::AIO::poll_fileno, EV::READ, \&IO::AIO::poll_cb;
		36
		37	# Event integration
21	Event->io (fd => IO::AIO::poll_fileno,	38	Event->io (fd => IO::AIO::poll_fileno,
22	poll => 'r',	39	poll => 'r',
23	cb => \&IO::AIO::poll_cb);	40	cb => \&IO::AIO::poll_cb);
24		41
25	# Glib/Gtk2	42	# Glib/Gtk2 integration
26	add_watch Glib::IO IO::AIO::poll_fileno,	43	add_watch Glib::IO IO::AIO::poll_fileno,
27	in => sub { IO::AIO::poll_cb; 1 };	44	in => sub { IO::AIO::poll_cb; 1 };
28		45
29	# Tk	46	# Tk integration
30	Tk::Event::IO->fileevent (IO::AIO::poll_fileno, "",	47	Tk::Event::IO->fileevent (IO::AIO::poll_fileno, "",
31	readable => \&IO::AIO::poll_cb);	48	readable => \&IO::AIO::poll_cb);
32		49
33	# Danga::Socket	50	# Danga::Socket integration
34	Danga::Socket->AddOtherFds (IO::AIO::poll_fileno =>	51	Danga::Socket->AddOtherFds (IO::AIO::poll_fileno =>
35	\&IO::AIO::poll_cb);	52	\&IO::AIO::poll_cb);
36		53
37
38	=head1 DESCRIPTION	54	=head1 DESCRIPTION
39		55
40	This module implements asynchronous I/O using whatever means your	56	This module implements asynchronous I/O using whatever means your
41	operating system supports.	57	operating system supports. It is implemented as an interface to C<libeio>
		58	(L<http://software.schmorp.de/pkg/libeio.html>).
42		59
		60	Asynchronous means that operations that can normally block your program
		61	(e.g. reading from disk) will be done asynchronously: the operation
		62	will still block, but you can do something else in the meantime. This
		63	is extremely useful for programs that need to stay interactive even
		64	when doing heavy I/O (GUI programs, high performance network servers
		65	etc.), but can also be used to easily do operations in parallel that are
		66	normally done sequentially, e.g. stat'ing many files, which is much faster
		67	on a RAID volume or over NFS when you do a number of stat operations
		68	concurrently.
		69
		70	While most of this works on all types of file descriptors (for
		71	example sockets), using these functions on file descriptors that
		72	support nonblocking operation (again, sockets, pipes etc.) is
		73	very inefficient. Use an event loop for that (such as the L<EV>
		74	module): IO::AIO will naturally fit into such an event loop itself.
		75
43	Currently, a number of threads are started that execute your read/writes	76	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	77	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	78	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	79	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	80	functions available on many operating systems. However, they are often
48	not well-supported (Linux doesn't allow them on normal files currently,	81	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	82	files currently, for example), and they would only support aio_read and
50	remaining functionality would have to be implemented using threads anyway.	83	aio_write, so the remaining functionality would have to be implemented
		84	using threads anyway.
51		85
52	Although the module will work with in the presence of other threads, it is	86	Although the module will work in the presence of other (Perl-) threads,
53	currently not reentrant, so use appropriate locking yourself, always call	87	it is currently not reentrant in any way, so use appropriate locking
54	C<poll_cb> from within the same thread, or never call C<poll_cb> (or other	88	yourself, always call C<poll_cb> from within the same thread, or never
55	C<aio_> functions) recursively.	89	call C<poll_cb> (or other C<aio_> functions) recursively.
		90
		91	=head2 EXAMPLE
		92
		93	This is a simple example that uses the EV module and loads
		94	F</etc/passwd> asynchronously:
		95
		96	use Fcntl;
		97	use EV;
		98	use IO::AIO;
		99
		100	# register the IO::AIO callback with EV
		101	my $aio_w = EV::io IO::AIO::poll_fileno, EV::READ, \&IO::AIO::poll_cb;
		102
		103	# queue the request to open /etc/passwd
		104	aio_open "/etc/passwd", O_RDONLY, 0, sub {
		105	my $fh = shift
		106	or die "error while opening: $!";
		107
		108	# stat'ing filehandles is generally non-blocking
		109	my $size = -s $fh;
		110
		111	# queue a request to read the file
		112	my $contents;
		113	aio_read $fh, 0, $size, $contents, 0, sub {
		114	$_[0] == $size
		115	or die "short read: $!";
		116
		117	close $fh;
		118
		119	# file contents now in $contents
		120	print $contents;
		121
		122	# exit event loop and program
		123	EV::unloop;
		124	};
		125	};
		126
		127	# possibly queue up other requests, or open GUI windows,
		128	# check for sockets etc. etc.
		129
		130	# process events as long as there are some:
		131	EV::loop;
		132
		133	=head1 REQUEST ANATOMY AND LIFETIME
		134
		135	Every C<aio_*> function creates a request. which is a C data structure not
		136	directly visible to Perl.
		137
		138	If called in non-void context, every request function returns a Perl
		139	object representing the request. In void context, nothing is returned,
		140	which saves a bit of memory.
		141
		142	The perl object is a fairly standard ref-to-hash object. The hash contents
		143	are not used by IO::AIO so you are free to store anything you like in it.
		144
		145	During their existance, aio requests travel through the following states,
		146	in order:
		147
		148	=over 4
		149
		150	=item ready
		151
		152	Immediately after a request is created it is put into the ready state,
		153	waiting for a thread to execute it.
		154
		155	=item execute
		156
		157	A thread has accepted the request for processing and is currently
		158	executing it (e.g. blocking in read).
		159
		160	=item pending
		161
		162	The request has been executed and is waiting for result processing.
		163
		164	While request submission and execution is fully asynchronous, result
		165	processing is not and relies on the perl interpreter calling C<poll_cb>
		166	(or another function with the same effect).
		167
		168	=item result
		169
		170	The request results are processed synchronously by C<poll_cb>.
		171
		172	The C<poll_cb> function will process all outstanding aio requests by
		173	calling their callbacks, freeing memory associated with them and managing
		174	any groups they are contained in.
		175
		176	=item done
		177
		178	Request has reached the end of its lifetime and holds no resources anymore
		179	(except possibly for the Perl object, but its connection to the actual
		180	aio request is severed and calling its methods will either do nothing or
		181	result in a runtime error).
		182
		183	=back
56		184
57	=cut	185	=cut
58		186
59	package IO::AIO;	187	package IO::AIO;
60		188
61	no warnings;	189	use Carp ();
		190
		191	use common::sense;
62		192
63	use base 'Exporter';	193	use base 'Exporter';
64		194
65	use Fcntl ();
66
67	BEGIN {	195	BEGIN {
68	$VERSION = 1.2;	196	our $VERSION = '3.31';
69		197
70	@EXPORT = qw(aio_read aio_write aio_open aio_close aio_stat aio_lstat aio_unlink	198	our @AIO_REQ = qw(aio_sendfile aio_read aio_write aio_open aio_close
71	aio_rmdir aio_symlink aio_fsync aio_fdatasync aio_readahead);	199	aio_stat aio_lstat aio_unlink aio_rmdir aio_readdir aio_readdirx
72	@EXPORT_OK = qw(poll_fileno poll_cb min_parallel max_parallel max_outstanding nreqs);	200	aio_scandir aio_symlink aio_readlink aio_sync aio_fsync
		201	aio_fdatasync aio_sync_file_range aio_pathsync aio_readahead
		202	aio_rename aio_link aio_move aio_copy aio_group
		203	aio_nop aio_mknod aio_load aio_rmtree aio_mkdir aio_chown
		204	aio_chmod aio_utime aio_truncate);
		205
		206	our @EXPORT = (@AIO_REQ, qw(aioreq_pri aioreq_nice));
		207	our @EXPORT_OK = qw(poll_fileno poll_cb poll_wait flush
		208	min_parallel max_parallel max_idle
		209	nreqs nready npending nthreads
		210	max_poll_time max_poll_reqs
		211	sendfile fadvise);
		212
		213	push @AIO_REQ, qw(aio_busy); # not exported
		214
		215	@IO::AIO::GRP::ISA = 'IO::AIO::REQ';
73		216
74	require XSLoader;	217	require XSLoader;
75	XSLoader::load IO::AIO, $VERSION;	218	XSLoader::load ("IO::AIO", $VERSION);
76	}	219	}
77		220
78	=head1 FUNCTIONS	221	=head1 FUNCTIONS
79		222
80	=head2 AIO FUNCTIONS	223	=head2 AIO REQUEST FUNCTIONS
81		224
82	All the C<aio_*> calls are more or less thin wrappers around the syscall	225	All the C<aio_*> calls are more or less thin wrappers around the syscall
83	with the same name (sans C<aio_>). The arguments are similar or identical,	226	with the same name (sans C<aio_>). The arguments are similar or identical,
84	and they all accept an additional (and optional) C<$callback> argument	227	and they all accept an additional (and optional) C<$callback> argument
85	which must be a code reference. This code reference will get called with	228	which must be a code reference. This code reference will get called with
86	the syscall return code (e.g. most syscalls return C<-1> on error, unlike	229	the syscall return code (e.g. most syscalls return C<-1> on error, unlike
87	perl, which usually delivers "false") as it's sole argument when the given	230	perl, which usually delivers "false") as its sole argument after the given
88	syscall has been executed asynchronously.	231	syscall has been executed asynchronously.
89		232
90	All functions expecting a filehandle keep a copy of the filehandle	233	All functions expecting a filehandle keep a copy of the filehandle
91	internally until the request has finished.	234	internally until the request has finished.
92		235
		236	All functions return request objects of type L<IO::AIO::REQ> that allow
		237	further manipulation of those requests while they are in-flight.
		238
93	The pathnames you pass to these routines I<must> be absolute and	239	The pathnames you pass to these routines I<must> be absolute and
94	encoded in byte form. The reason for the former is that at the time the	240	encoded as octets. The reason for the former is that at the time the
95	request is being executed, the current working directory could have	241	request is being executed, the current working directory could have
96	changed. Alternatively, you can make sure that you never change the	242	changed. Alternatively, you can make sure that you never change the
97	current working directory.	243	current working directory anywhere in the program and then use relative
		244	paths.
98		245
99	To encode pathnames to byte form, either make sure you either: a)	246	To encode pathnames as octets, either make sure you either: a) always pass
100	always pass in filenames you got from outside (command line, readdir	247	in filenames you got from outside (command line, readdir etc.) without
101	etc.), b) are ASCII or ISO 8859-1, c) use the Encode module and encode	248	tinkering, b) are ASCII or ISO 8859-1, c) use the Encode module and encode
102	your pathnames to the locale (or other) encoding in effect in the user	249	your pathnames to the locale (or other) encoding in effect in the user
103	environment, d) use Glib::filename_from_unicode on unicode filenames or e)	250	environment, d) use Glib::filename_from_unicode on unicode filenames or e)
104	use something else.	251	use something else to ensure your scalar has the correct contents.
		252
		253	This works, btw. independent of the internal UTF-8 bit, which IO::AIO
		254	handles correctly whether it is set or not.
105		255
106	=over 4	256	=over 4
107		257
		258	=item $prev_pri = aioreq_pri [$pri]
		259
		260	Returns the priority value that would be used for the next request and, if
		261	C<$pri> is given, sets the priority for the next aio request.
		262
		263	The default priority is C<0>, the minimum and maximum priorities are C<-4>
		264	and C<4>, respectively. Requests with higher priority will be serviced
		265	first.
		266
		267	The priority will be reset to C<0> after each call to one of the C<aio_*>
		268	functions.
		269
		270	Example: open a file with low priority, then read something from it with
		271	higher priority so the read request is serviced before other low priority
		272	open requests (potentially spamming the cache):
		273
		274	aioreq_pri -3;
		275	aio_open ..., sub {
		276	return unless $_[0];
		277
		278	aioreq_pri -2;
		279	aio_read $_[0], ..., sub {
		280	...
		281	};
		282	};
		283
		284
		285	=item aioreq_nice $pri_adjust
		286
		287	Similar to C<aioreq_pri>, but subtracts the given value from the current
		288	priority, so the effect is cumulative.
		289
		290
108	=item aio_open $pathname, $flags, $mode, $callback	291	=item aio_open $pathname, $flags, $mode, $callback->($fh)
109		292
110	Asynchronously open or create a file and call the callback with a newly	293	Asynchronously open or create a file and call the callback with a newly
111	created filehandle for the file.	294	created filehandle for the file.
112		295
113	The pathname passed to C<aio_open> must be absolute. See API NOTES, above,	296	The pathname passed to C<aio_open> must be absolute. See API NOTES, above,
…		…
117	list. They are the same as used by C<sysopen>.	300	list. They are the same as used by C<sysopen>.
118		301
119	Likewise, C<$mode> specifies the mode of the newly created file, if it	302	Likewise, C<$mode> specifies the mode of the newly created file, if it
120	didn't exist and C<O_CREAT> has been given, just like perl's C<sysopen>,	303	didn't exist and C<O_CREAT> has been given, just like perl's C<sysopen>,
121	except that it is mandatory (i.e. use C<0> if you don't create new files,	304	except that it is mandatory (i.e. use C<0> if you don't create new files,
122	and C<0666> or C<0777> if you do).	305	and C<0666> or C<0777> if you do). Note that the C<$mode> will be modified
		306	by the umask in effect then the request is being executed, so better never
		307	change the umask.
123		308
124	Example:	309	Example:
125		310
126	aio_open "/etc/passwd", O_RDONLY, 0, sub {	311	aio_open "/etc/passwd", O_RDONLY, 0, sub {
127	if ($_[0]) {	312	if ($_[0]) {
…		…
130	} else {	315	} else {
131	die "open failed: $!\n";	316	die "open failed: $!\n";
132	}	317	}
133	};	318	};
134		319
		320
135	=item aio_close $fh, $callback	321	=item aio_close $fh, $callback->($status)
136		322
137	Asynchronously close a file and call the callback with the result	323	Asynchronously close a file and call the callback with the result
138	code. I<WARNING:> although accepted, you should not pass in a perl	324	code.
139	filehandle here, as perl will likely close the file descriptor another
140	time when the filehandle is destroyed. Normally, you can safely call perls
141	C<close> or just let filehandles go out of scope.
142		325
143	This is supposed to be a bug in the API, so that might change. It's	326	Unfortunately, you can't do this to perl. Perl I<insists> very strongly on
144	therefore best to avoid this function.	327	closing the file descriptor associated with the filehandle itself.
145		328
		329	Therefore, C<aio_close> will not close the filehandle - instead it will
		330	use dup2 to overwrite the file descriptor with the write-end of a pipe
		331	(the pipe fd will be created on demand and will be cached).
		332
		333	Or in other words: the file descriptor will be closed, but it will not be
		334	free for reuse until the perl filehandle is closed.
		335
		336	=cut
		337
146	=item aio_read $fh,$offset,$length, $data,$dataoffset,$callback	338	=item aio_read $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
147		339
148	=item aio_write $fh,$offset,$length, $data,$dataoffset,$callback	340	=item aio_write $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
149		341
150	Reads or writes C<length> bytes from the specified C<fh> and C<offset>	342	Reads or writes C<$length> bytes from or to the specified C<$fh> and
151	into the scalar given by C<data> and offset C<dataoffset> and calls the	343	C<$offset> into the scalar given by C<$data> and offset C<$dataoffset>
152	callback without the actual number of bytes read (or -1 on error, just	344	and calls the callback without the actual number of bytes read (or -1 on
153	like the syscall).	345	error, just like the syscall).
		346
		347	C<aio_read> will, like C<sysread>, shrink or grow the C<$data> scalar to
		348	offset plus the actual number of bytes read.
		349
		350	If C<$offset> is undefined, then the current file descriptor offset will
		351	be used (and updated), otherwise the file descriptor offset will not be
		352	changed by these calls.
		353
		354	If C<$length> is undefined in C<aio_write>, use the remaining length of
		355	C<$data>.
		356
		357	If C<$dataoffset> is less than zero, it will be counted from the end of
		358	C<$data>.
		359
		360	The C<$data> scalar I<MUST NOT> be modified in any way while the request
		361	is outstanding. Modifying it can result in segfaults or World War III (if
		362	the necessary/optional hardware is installed).
154		363
155	Example: Read 15 bytes at offset 7 into scalar C<$buffer>, starting at	364	Example: Read 15 bytes at offset 7 into scalar C<$buffer>, starting at
156	offset C<0> within the scalar:	365	offset C<0> within the scalar:
157		366
158	aio_read $fh, 7, 15, $buffer, 0, sub {	367	aio_read $fh, 7, 15, $buffer, 0, sub {
159	$_[0] > 0 or die "read error: $!";	368	$_[0] > 0 or die "read error: $!";
160	print "read $_[0] bytes: <$buffer>\n";	369	print "read $_[0] bytes: <$buffer>\n";
161	};	370	};
162		371
		372
		373	=item aio_sendfile $out_fh, $in_fh, $in_offset, $length, $callback->($retval)
		374
		375	Tries to copy C<$length> bytes from C<$in_fh> to C<$out_fh>. It starts
		376	reading at byte offset C<$in_offset>, and starts writing at the current
		377	file offset of C<$out_fh>. Because of that, it is not safe to issue more
		378	than one C<aio_sendfile> per C<$out_fh>, as they will interfere with each
		379	other.
		380
		381	This call tries to make use of a native C<sendfile> syscall to provide
		382	zero-copy operation. For this to work, C<$out_fh> should refer to a
		383	socket, and C<$in_fh> should refer to mmap'able file.
		384
		385	If the native sendfile call fails with C<ENOSYS>, C<ENOTSUP>,
		386	C<EOPNOTSUPP> or C<ENOTSOCK>, or is not implemented, it will be emulated,
		387	so you can call C<aio_sendfile> on any type of filehandle regardless of
		388	the limitations of the operating system.
		389
		390	Please note, however, that C<aio_sendfile> can read more bytes from
		391	C<$in_fh> than are written, and there is no way to find out how many
		392	bytes have been read from C<aio_sendfile> alone, as C<aio_sendfile> only
		393	provides the number of bytes written to C<$out_fh>. Only if the result
		394	value equals C<$length> one can assume that C<$length> bytes have been
		395	read.
		396
		397
163	=item aio_readahead $fh,$offset,$length, $callback	398	=item aio_readahead $fh,$offset,$length, $callback->($retval)
164		399
165	C<aio_readahead> populates the page cache with data from a file so that	400	C<aio_readahead> populates the page cache with data from a file so that
166	subsequent reads from that file will not block on disk I/O. The C<$offset>	401	subsequent reads from that file will not block on disk I/O. The C<$offset>
167	argument specifies the starting point from which data is to be read and	402	argument specifies the starting point from which data is to be read and
168	C<$length> specifies the number of bytes to be read. I/O is performed in	403	C<$length> specifies the number of bytes to be read. I/O is performed in
…		…
172	file. The current file offset of the file is left unchanged.	407	file. The current file offset of the file is left unchanged.
173		408
174	If that syscall doesn't exist (likely if your OS isn't Linux) it will be	409	If that syscall doesn't exist (likely if your OS isn't Linux) it will be
175	emulated by simply reading the data, which would have a similar effect.	410	emulated by simply reading the data, which would have a similar effect.
176		411
		412
177	=item aio_stat $fh_or_path, $callback	413	=item aio_stat $fh_or_path, $callback->($status)
178		414
179	=item aio_lstat $fh, $callback	415	=item aio_lstat $fh, $callback->($status)
180		416
181	Works like perl's C<stat> or C<lstat> in void context. The callback will	417	Works like perl's C<stat> or C<lstat> in void context. The callback will
182	be called after the stat and the results will be available using C<stat _>	418	be called after the stat and the results will be available using C<stat _>
183	or C<-s _> etc...	419	or C<-s _> etc...
184		420
…		…
194	aio_stat "/etc/passwd", sub {	430	aio_stat "/etc/passwd", sub {
195	$_[0] and die "stat failed: $!";	431	$_[0] and die "stat failed: $!";
196	print "size is ", -s _, "\n";	432	print "size is ", -s _, "\n";
197	};	433	};
198		434
		435
		436	=item aio_utime $fh_or_path, $atime, $mtime, $callback->($status)
		437
		438	Works like perl's C<utime> function (including the special case of $atime
		439	and $mtime being undef). Fractional times are supported if the underlying
		440	syscalls support them.
		441
		442	When called with a pathname, uses utimes(2) if available, otherwise
		443	utime(2). If called on a file descriptor, uses futimes(2) if available,
		444	otherwise returns ENOSYS, so this is not portable.
		445
		446	Examples:
		447
		448	# set atime and mtime to current time (basically touch(1)):
		449	aio_utime "path", undef, undef;
		450	# set atime to current time and mtime to beginning of the epoch:
		451	aio_utime "path", time, undef; # undef==0
		452
		453
		454	=item aio_chown $fh_or_path, $uid, $gid, $callback->($status)
		455
		456	Works like perl's C<chown> function, except that C<undef> for either $uid
		457	or $gid is being interpreted as "do not change" (but -1 can also be used).
		458
		459	Examples:
		460
		461	# same as "chown root path" in the shell:
		462	aio_chown "path", 0, -1;
		463	# same as above:
		464	aio_chown "path", 0, undef;
		465
		466
		467	=item aio_truncate $fh_or_path, $offset, $callback->($status)
		468
		469	Works like truncate(2) or ftruncate(2).
		470
		471
		472	=item aio_chmod $fh_or_path, $mode, $callback->($status)
		473
		474	Works like perl's C<chmod> function.
		475
		476
199	=item aio_unlink $pathname, $callback	477	=item aio_unlink $pathname, $callback->($status)
200		478
201	Asynchronously unlink (delete) a file and call the callback with the	479	Asynchronously unlink (delete) a file and call the callback with the
202	result code.	480	result code.
203		481
		482
		483	=item aio_mknod $path, $mode, $dev, $callback->($status)
		484
		485	[EXPERIMENTAL]
		486
		487	Asynchronously create a device node (or fifo). See mknod(2).
		488
		489	The only (POSIX-) portable way of calling this function is:
		490
		491	aio_mknod $path, IO::AIO::S_IFIFO | $mode, 0, sub { ...
		492
		493
		494	=item aio_link $srcpath, $dstpath, $callback->($status)
		495
		496	Asynchronously create a new link to the existing object at C<$srcpath> at
		497	the path C<$dstpath> and call the callback with the result code.
		498
		499
		500	=item aio_symlink $srcpath, $dstpath, $callback->($status)
		501
		502	Asynchronously create a new symbolic link to the existing object at C<$srcpath> at
		503	the path C<$dstpath> and call the callback with the result code.
		504
		505
		506	=item aio_readlink $path, $callback->($link)
		507
		508	Asynchronously read the symlink specified by C<$path> and pass it to
		509	the callback. If an error occurs, nothing or undef gets passed to the
		510	callback.
		511
		512
		513	=item aio_rename $srcpath, $dstpath, $callback->($status)
		514
		515	Asynchronously rename the object at C<$srcpath> to C<$dstpath>, just as
		516	rename(2) and call the callback with the result code.
		517
		518
		519	=item aio_mkdir $pathname, $mode, $callback->($status)
		520
		521	Asynchronously mkdir (create) a directory and call the callback with
		522	the result code. C<$mode> will be modified by the umask at the time the
		523	request is executed, so do not change your umask.
		524
		525
204	=item aio_rmdir $pathname, $callback	526	=item aio_rmdir $pathname, $callback->($status)
205		527
206	Asynchronously rmdir (delete) a directory and call the callback with the	528	Asynchronously rmdir (delete) a directory and call the callback with the
207	result code.	529	result code.
208		530
		531
		532	=item aio_readdir $pathname, $callback->($entries)
		533
		534	Unlike the POSIX call of the same name, C<aio_readdir> reads an entire
		535	directory (i.e. opendir + readdir + closedir). The entries will not be
		536	sorted, and will B<NOT> include the C<.> and C<..> entries.
		537
		538	The callback is passed a single argument which is either C<undef> or an
		539	array-ref with the filenames.
		540
		541
		542	=item aio_readdirx $pathname, $flags, $callback->($entries, $flags)
		543
		544	Quite similar to C<aio_readdir>, but the C<$flags> argument allows to tune
		545	behaviour and output format. In case of an error, C<$entries> will be
		546	C<undef>.
		547
		548	The flags are a combination of the following constants, ORed together (the
		549	flags will also be passed to the callback, possibly modified):
		550
		551	=over 4
		552
		553	=item IO::AIO::READDIR_DENTS
		554
		555	When this flag is off, then the callback gets an arrayref with of names
		556	only (as with C<aio_readdir>), otherwise it gets an arrayref with
		557	C<[$name, $type, $inode]> arrayrefs, each describing a single directory
		558	entry in more detail.
		559
		560	C<$name> is the name of the entry.
		561
		562	C<$type> is one of the C<IO::AIO::DT_xxx> constants:
		563
		564	C<IO::AIO::DT_UNKNOWN>, C<IO::AIO::DT_FIFO>, C<IO::AIO::DT_CHR>, C<IO::AIO::DT_DIR>,
		565	C<IO::AIO::DT_BLK>, C<IO::AIO::DT_REG>, C<IO::AIO::DT_LNK>, C<IO::AIO::DT_SOCK>,
		566	C<IO::AIO::DT_WHT>.
		567
		568	C<IO::AIO::DT_UNKNOWN> means just that: readdir does not know. If you need to
		569	know, you have to run stat yourself. Also, for speed reasons, the C<$type>
		570	scalars are read-only: you can not modify them.
		571
		572	C<$inode> is the inode number (which might not be exact on systems with 64
		573	bit inode numbers and 32 bit perls). This field has unspecified content on
		574	systems that do not deliver the inode information.
		575
		576	=item IO::AIO::READDIR_DIRS_FIRST
		577
		578	When this flag is set, then the names will be returned in an order where
		579	likely directories come first. This is useful when you need to quickly
		580	find directories, or you want to find all directories while avoiding to
		581	stat() each entry.
		582
		583	If the system returns type information in readdir, then this is used
		584	to find directories directly. Otherwise, likely directories are files
		585	beginning with ".", or otherwise files with no dots, of which files with
		586	short names are tried first.
		587
		588	=item IO::AIO::READDIR_STAT_ORDER
		589
		590	When this flag is set, then the names will be returned in an order
		591	suitable for stat()'ing each one. That is, when you plan to stat()
		592	all files in the given directory, then the returned order will likely
		593	be fastest.
		594
		595	If both this flag and C<IO::AIO::READDIR_DIRS_FIRST> are specified, then
		596	the likely dirs come first, resulting in a less optimal stat order.
		597
		598	=item IO::AIO::READDIR_FOUND_UNKNOWN
		599
		600	This flag should not be set when calling C<aio_readdirx>. Instead, it
		601	is being set by C<aio_readdirx>, when any of the C<$type>'s found were
		602	C<IO::AIO::DT_UNKNOWN>. The absense of this flag therefore indicates that all
		603	C<$type>'s are known, which can be used to speed up some algorithms.
		604
		605	=back
		606
		607
		608	=item aio_load $path, $data, $callback->($status)
		609
		610	This is a composite request that tries to fully load the given file into
		611	memory. Status is the same as with aio_read.
		612
		613	=cut
		614
		615	sub aio_load($$;$) {
		616	my ($path, undef, $cb) = @_;
		617	my $data = \$_[1];
		618
		619	my $pri = aioreq_pri;
		620	my $grp = aio_group $cb;
		621
		622	aioreq_pri $pri;
		623	add $grp aio_open $path, O_RDONLY, 0, sub {
		624	my $fh = shift
		625	or return $grp->result (-1);
		626
		627	aioreq_pri $pri;
		628	add $grp aio_read $fh, 0, (-s $fh), $$data, 0, sub {
		629	$grp->result ($_[0]);
		630	};
		631	};
		632
		633	$grp
		634	}
		635
		636	=item aio_copy $srcpath, $dstpath, $callback->($status)
		637
		638	Try to copy the I<file> (directories not supported as either source or
		639	destination) from C<$srcpath> to C<$dstpath> and call the callback with
		640	a status of C<0> (ok) or C<-1> (error, see C<$!>).
		641
		642	This is a composite request that creates the destination file with
		643	mode 0200 and copies the contents of the source file into it using
		644	C<aio_sendfile>, followed by restoring atime, mtime, access mode and
		645	uid/gid, in that order.
		646
		647	If an error occurs, the partial destination file will be unlinked, if
		648	possible, except when setting atime, mtime, access mode and uid/gid, where
		649	errors are being ignored.
		650
		651	=cut
		652
		653	sub aio_copy($$;$) {
		654	my ($src, $dst, $cb) = @_;
		655
		656	my $pri = aioreq_pri;
		657	my $grp = aio_group $cb;
		658
		659	aioreq_pri $pri;
		660	add $grp aio_open $src, O_RDONLY, 0, sub {
		661	if (my $src_fh = $_[0]) {
		662	my @stat = stat $src_fh; # hmm, might block over nfs?
		663
		664	aioreq_pri $pri;
		665	add $grp aio_open $dst, O_CREAT | O_WRONLY | O_TRUNC, 0200, sub {
		666	if (my $dst_fh = $_[0]) {
		667	aioreq_pri $pri;
		668	add $grp aio_sendfile $dst_fh, $src_fh, 0, $stat[7], sub {
		669	if ($_[0] == $stat[7]) {
		670	$grp->result (0);
		671	close $src_fh;
		672
		673	my $ch = sub {
		674	aioreq_pri $pri;
		675	add $grp aio_chmod $dst_fh, $stat[2] & 07777, sub {
		676	aioreq_pri $pri;
		677	add $grp aio_chown $dst_fh, $stat[4], $stat[5], sub {
		678	aioreq_pri $pri;
		679	add $grp aio_close $dst_fh;
		680	}
		681	};
		682	};
		683
		684	aioreq_pri $pri;
		685	add $grp aio_utime $dst_fh, $stat[8], $stat[9], sub {
		686	if ($_[0] < 0 && $! == ENOSYS) {
		687	aioreq_pri $pri;
		688	add $grp aio_utime $dst, $stat[8], $stat[9], $ch;
		689	} else {
		690	$ch->();
		691	}
		692	};
		693	} else {
		694	$grp->result (-1);
		695	close $src_fh;
		696	close $dst_fh;
		697
		698	aioreq $pri;
		699	add $grp aio_unlink $dst;
		700	}
		701	};
		702	} else {
		703	$grp->result (-1);
		704	}
		705	},
		706
		707	} else {
		708	$grp->result (-1);
		709	}
		710	};
		711
		712	$grp
		713	}
		714
		715	=item aio_move $srcpath, $dstpath, $callback->($status)
		716
		717	Try to move the I<file> (directories not supported as either source or
		718	destination) from C<$srcpath> to C<$dstpath> and call the callback with
		719	a status of C<0> (ok) or C<-1> (error, see C<$!>).
		720
		721	This is a composite request that tries to rename(2) the file first; if
		722	rename fails with C<EXDEV>, it copies the file with C<aio_copy> and, if
		723	that is successful, unlinks the C<$srcpath>.
		724
		725	=cut
		726
		727	sub aio_move($$;$) {
		728	my ($src, $dst, $cb) = @_;
		729
		730	my $pri = aioreq_pri;
		731	my $grp = aio_group $cb;
		732
		733	aioreq_pri $pri;
		734	add $grp aio_rename $src, $dst, sub {
		735	if ($_[0] && $! == EXDEV) {
		736	aioreq_pri $pri;
		737	add $grp aio_copy $src, $dst, sub {
		738	$grp->result ($_[0]);
		739
		740	if (!$_[0]) {
		741	aioreq_pri $pri;
		742	add $grp aio_unlink $src;
		743	}
		744	};
		745	} else {
		746	$grp->result ($_[0]);
		747	}
		748	};
		749
		750	$grp
		751	}
		752
		753	=item aio_scandir $path, $maxreq, $callback->($dirs, $nondirs)
		754
		755	Scans a directory (similar to C<aio_readdir>) but additionally tries to
		756	efficiently separate the entries of directory C<$path> into two sets of
		757	names, directories you can recurse into (directories), and ones you cannot
		758	recurse into (everything else, including symlinks to directories).
		759
		760	C<aio_scandir> is a composite request that creates of many sub requests_
		761	C<$maxreq> specifies the maximum number of outstanding aio requests that
		762	this function generates. If it is C<< <= 0 >>, then a suitable default
		763	will be chosen (currently 4).
		764
		765	On error, the callback is called without arguments, otherwise it receives
		766	two array-refs with path-relative entry names.
		767
		768	Example:
		769
		770	aio_scandir $dir, 0, sub {
		771	my ($dirs, $nondirs) = @_;
		772	print "real directories: @$dirs\n";
		773	print "everything else: @$nondirs\n";
		774	};
		775
		776	Implementation notes.
		777
		778	The C<aio_readdir> cannot be avoided, but C<stat()>'ing every entry can.
		779
		780	If readdir returns file type information, then this is used directly to
		781	find directories.
		782
		783	Otherwise, after reading the directory, the modification time, size etc.
		784	of the directory before and after the readdir is checked, and if they
		785	match (and isn't the current time), the link count will be used to decide
		786	how many entries are directories (if >= 2). Otherwise, no knowledge of the
		787	number of subdirectories will be assumed.
		788
		789	Then entries will be sorted into likely directories a non-initial dot
		790	currently) and likely non-directories (see C<aio_readdirx>). Then every
		791	entry plus an appended C</.> will be C<stat>'ed, likely directories first,
		792	in order of their inode numbers. If that succeeds, it assumes that the
		793	entry is a directory or a symlink to directory (which will be checked
		794	seperately). This is often faster than stat'ing the entry itself because
		795	filesystems might detect the type of the entry without reading the inode
		796	data (e.g. ext2fs filetype feature), even on systems that cannot return
		797	the filetype information on readdir.
		798
		799	If the known number of directories (link count - 2) has been reached, the
		800	rest of the entries is assumed to be non-directories.
		801
		802	This only works with certainty on POSIX (= UNIX) filesystems, which
		803	fortunately are the vast majority of filesystems around.
		804
		805	It will also likely work on non-POSIX filesystems with reduced efficiency
		806	as those tend to return 0 or 1 as link counts, which disables the
		807	directory counting heuristic.
		808
		809	=cut
		810
		811	sub aio_scandir($$;$) {
		812	my ($path, $maxreq, $cb) = @_;
		813
		814	my $pri = aioreq_pri;
		815
		816	my $grp = aio_group $cb;
		817
		818	$maxreq = 4 if $maxreq <= 0;
		819
		820	# stat once
		821	aioreq_pri $pri;
		822	add $grp aio_stat $path, sub {
		823	return $grp->result () if $_[0];
		824	my $now = time;
		825	my $hash1 = join ":", (stat _)[0,1,3,7,9];
		826
		827	# read the directory entries
		828	aioreq_pri $pri;
		829	add $grp aio_readdirx $path, READDIR_DIRS_FIRST, sub {
		830	my $entries = shift
		831	or return $grp->result ();
		832
		833	# stat the dir another time
		834	aioreq_pri $pri;
		835	add $grp aio_stat $path, sub {
		836	my $hash2 = join ":", (stat _)[0,1,3,7,9];
		837
		838	my $ndirs;
		839
		840	# take the slow route if anything looks fishy
		841	if ($hash1 ne $hash2 or (stat _)[9] == $now) {
		842	$ndirs = -1;
		843	} else {
		844	# if nlink == 2, we are finished
		845	# for non-posix-fs's, we rely on nlink < 2
		846	$ndirs = (stat _)[3] - 2
		847	or return $grp->result ([], $entries);
		848	}
		849
		850	my (@dirs, @nondirs);
		851
		852	my $statgrp = add $grp aio_group sub {
		853	$grp->result (\@dirs, \@nondirs);
		854	};
		855
		856	limit $statgrp $maxreq;
		857	feed $statgrp sub {
		858	return unless @$entries;
		859	my $entry = shift @$entries;
		860
		861	aioreq_pri $pri;
		862	add $statgrp aio_stat "$path/$entry/.", sub {
		863	if ($_[0] < 0) {
		864	push @nondirs, $entry;
		865	} else {
		866	# need to check for real directory
		867	aioreq_pri $pri;
		868	add $statgrp aio_lstat "$path/$entry", sub {
		869	if (-d _) {
		870	push @dirs, $entry;
		871
		872	unless (--$ndirs) {
		873	push @nondirs, @$entries;
		874	feed $statgrp;
		875	}
		876	} else {
		877	push @nondirs, $entry;
		878	}
		879	}
		880	}
		881	};
		882	};
		883	};
		884	};
		885	};
		886
		887	$grp
		888	}
		889
		890	=item aio_rmtree $path, $callback->($status)
		891
		892	Delete a directory tree starting (and including) C<$path>, return the
		893	status of the final C<rmdir> only. This is a composite request that
		894	uses C<aio_scandir> to recurse into and rmdir directories, and unlink
		895	everything else.
		896
		897	=cut
		898
		899	sub aio_rmtree;
		900	sub aio_rmtree($;$) {
		901	my ($path, $cb) = @_;
		902
		903	my $pri = aioreq_pri;
		904	my $grp = aio_group $cb;
		905
		906	aioreq_pri $pri;
		907	add $grp aio_scandir $path, 0, sub {
		908	my ($dirs, $nondirs) = @_;
		909
		910	my $dirgrp = aio_group sub {
		911	add $grp aio_rmdir $path, sub {
		912	$grp->result ($_[0]);
		913	};
		914	};
		915
		916	(aioreq_pri $pri), add $dirgrp aio_rmtree "$path/$_" for @$dirs;
		917	(aioreq_pri $pri), add $dirgrp aio_unlink "$path/$_" for @$nondirs;
		918
		919	add $grp $dirgrp;
		920	};
		921
		922	$grp
		923	}
		924
		925	=item aio_sync $callback->($status)
		926
		927	Asynchronously call sync and call the callback when finished.
		928
209	=item aio_fsync $fh, $callback	929	=item aio_fsync $fh, $callback->($status)
210		930
211	Asynchronously call fsync on the given filehandle and call the callback	931	Asynchronously call fsync on the given filehandle and call the callback
212	with the fsync result code.	932	with the fsync result code.
213		933
214	=item aio_fdatasync $fh, $callback	934	=item aio_fdatasync $fh, $callback->($status)
215		935
216	Asynchronously call fdatasync on the given filehandle and call the	936	Asynchronously call fdatasync on the given filehandle and call the
217	callback with the fdatasync result code.	937	callback with the fdatasync result code.
218		938
219	If this call isn't available because your OS lacks it or it couldn't be	939	If this call isn't available because your OS lacks it or it couldn't be
220	detected, it will be emulated by calling C<fsync> instead.	940	detected, it will be emulated by calling C<fsync> instead.
221		941
		942	=item aio_sync_file_range $fh, $offset, $nbytes, $flags, $callback->($status)
		943
		944	Sync the data portion of the file specified by C<$offset> and C<$length>
		945	to disk (but NOT the metadata), by calling the Linux-specific
		946	sync_file_range call. If sync_file_range is not available or it returns
		947	ENOSYS, then fdatasync or fsync is being substituted.
		948
		949	C<$flags> can be a combination of C<IO::AIO::SYNC_FILE_RANGE_WAIT_BEFORE>,
		950	C<IO::AIO::SYNC_FILE_RANGE_WRITE> and
		951	C<IO::AIO::SYNC_FILE_RANGE_WAIT_AFTER>: refer to the sync_file_range
		952	manpage for details.
		953
		954	=item aio_pathsync $path, $callback->($status)
		955
		956	This request tries to open, fsync and close the given path. This is a
		957	composite request intended to sync directories after directory operations
		958	(E.g. rename). This might not work on all operating systems or have any
		959	specific effect, but usually it makes sure that directory changes get
		960	written to disc. It works for anything that can be opened for read-only,
		961	not just directories.
		962
		963	Future versions of this function might fall back to other methods when
		964	C<fsync> on the directory fails (such as calling C<sync>).
		965
		966	Passes C<0> when everything went ok, and C<-1> on error.
		967
		968	=cut
		969
		970	sub aio_pathsync($;$) {
		971	my ($path, $cb) = @_;
		972
		973	my $pri = aioreq_pri;
		974	my $grp = aio_group $cb;
		975
		976	aioreq_pri $pri;
		977	add $grp aio_open $path, O_RDONLY, 0, sub {
		978	my ($fh) = @_;
		979	if ($fh) {
		980	aioreq_pri $pri;
		981	add $grp aio_fsync $fh, sub {
		982	$grp->result ($_[0]);
		983
		984	aioreq_pri $pri;
		985	add $grp aio_close $fh;
		986	};
		987	} else {
		988	$grp->result (-1);
		989	}
		990	};
		991
		992	$grp
		993	}
		994
		995	=item aio_group $callback->(...)
		996
		997	This is a very special aio request: Instead of doing something, it is a
		998	container for other aio requests, which is useful if you want to bundle
		999	many requests into a single, composite, request with a definite callback
		1000	and the ability to cancel the whole request with its subrequests.
		1001
		1002	Returns an object of class L<IO::AIO::GRP>. See its documentation below
		1003	for more info.
		1004
		1005	Example:
		1006
		1007	my $grp = aio_group sub {
		1008	print "all stats done\n";
		1009	};
		1010
		1011	add $grp
		1012	(aio_stat ...),
		1013	(aio_stat ...),
		1014	...;
		1015
		1016	=item aio_nop $callback->()
		1017
		1018	This is a special request - it does nothing in itself and is only used for
		1019	side effects, such as when you want to add a dummy request to a group so
		1020	that finishing the requests in the group depends on executing the given
		1021	code.
		1022
		1023	While this request does nothing, it still goes through the execution
		1024	phase and still requires a worker thread. Thus, the callback will not
		1025	be executed immediately but only after other requests in the queue have
		1026	entered their execution phase. This can be used to measure request
		1027	latency.
		1028
		1029	=item IO::AIO::aio_busy $fractional_seconds, $callback->() *NOT EXPORTED*
		1030
		1031	Mainly used for debugging and benchmarking, this aio request puts one of
		1032	the request workers to sleep for the given time.
		1033
		1034	While it is theoretically handy to have simple I/O scheduling requests
		1035	like sleep and file handle readable/writable, the overhead this creates is
		1036	immense (it blocks a thread for a long time) so do not use this function
		1037	except to put your application under artificial I/O pressure.
		1038
222	=back	1039	=back
223		1040
		1041	=head2 IO::AIO::REQ CLASS
		1042
		1043	All non-aggregate C<aio_*> functions return an object of this class when
		1044	called in non-void context.
		1045
		1046	=over 4
		1047
		1048	=item cancel $req
		1049
		1050	Cancels the request, if possible. Has the effect of skipping execution
		1051	when entering the B<execute> state and skipping calling the callback when
		1052	entering the the B<result> state, but will leave the request otherwise
		1053	untouched (with the exception of readdir). That means that requests that
		1054	currently execute will not be stopped and resources held by the request
		1055	will not be freed prematurely.
		1056
		1057	=item cb $req $callback->(...)
		1058
		1059	Replace (or simply set) the callback registered to the request.
		1060
		1061	=back
		1062
		1063	=head2 IO::AIO::GRP CLASS
		1064
		1065	This class is a subclass of L<IO::AIO::REQ>, so all its methods apply to
		1066	objects of this class, too.
		1067
		1068	A IO::AIO::GRP object is a special request that can contain multiple other
		1069	aio requests.
		1070
		1071	You create one by calling the C<aio_group> constructing function with a
		1072	callback that will be called when all contained requests have entered the
		1073	C<done> state:
		1074
		1075	my $grp = aio_group sub {
		1076	print "all requests are done\n";
		1077	};
		1078
		1079	You add requests by calling the C<add> method with one or more
		1080	C<IO::AIO::REQ> objects:
		1081
		1082	$grp->add (aio_unlink "...");
		1083
		1084	add $grp aio_stat "...", sub {
		1085	$_[0] or return $grp->result ("error");
		1086
		1087	# add another request dynamically, if first succeeded
		1088	add $grp aio_open "...", sub {
		1089	$grp->result ("ok");
		1090	};
		1091	};
		1092
		1093	This makes it very easy to create composite requests (see the source of
		1094	C<aio_move> for an application) that work and feel like simple requests.
		1095
		1096	=over 4
		1097
		1098	=item * The IO::AIO::GRP objects will be cleaned up during calls to
		1099	C<IO::AIO::poll_cb>, just like any other request.
		1100
		1101	=item * They can be canceled like any other request. Canceling will cancel not
		1102	only the request itself, but also all requests it contains.
		1103
		1104	=item * They can also can also be added to other IO::AIO::GRP objects.
		1105
		1106	=item * You must not add requests to a group from within the group callback (or
		1107	any later time).
		1108
		1109	=back
		1110
		1111	Their lifetime, simplified, looks like this: when they are empty, they
		1112	will finish very quickly. If they contain only requests that are in the
		1113	C<done> state, they will also finish. Otherwise they will continue to
		1114	exist.
		1115
		1116	That means after creating a group you have some time to add requests
		1117	(precisely before the callback has been invoked, which is only done within
		1118	the C<poll_cb>). And in the callbacks of those requests, you can add
		1119	further requests to the group. And only when all those requests have
		1120	finished will the the group itself finish.
		1121
		1122	=over 4
		1123
		1124	=item add $grp ...
		1125
		1126	=item $grp->add (...)
		1127
		1128	Add one or more requests to the group. Any type of L<IO::AIO::REQ> can
		1129	be added, including other groups, as long as you do not create circular
		1130	dependencies.
		1131
		1132	Returns all its arguments.
		1133
		1134	=item $grp->cancel_subs
		1135
		1136	Cancel all subrequests and clears any feeder, but not the group request
		1137	itself. Useful when you queued a lot of events but got a result early.
		1138
		1139	The group request will finish normally (you cannot add requests to the
		1140	group).
		1141
		1142	=item $grp->result (...)
		1143
		1144	Set the result value(s) that will be passed to the group callback when all
		1145	subrequests have finished and set the groups errno to the current value
		1146	of errno (just like calling C<errno> without an error number). By default,
		1147	no argument will be passed and errno is zero.
		1148
		1149	=item $grp->errno ([$errno])
		1150
		1151	Sets the group errno value to C<$errno>, or the current value of errno
		1152	when the argument is missing.
		1153
		1154	Every aio request has an associated errno value that is restored when
		1155	the callback is invoked. This method lets you change this value from its
		1156	default (0).
		1157
		1158	Calling C<result> will also set errno, so make sure you either set C<$!>
		1159	before the call to C<result>, or call c<errno> after it.
		1160
		1161	=item feed $grp $callback->($grp)
		1162
		1163	Sets a feeder/generator on this group: every group can have an attached
		1164	generator that generates requests if idle. The idea behind this is that,
		1165	although you could just queue as many requests as you want in a group,
		1166	this might starve other requests for a potentially long time. For example,
		1167	C<aio_scandir> might generate hundreds of thousands C<aio_stat> requests,
		1168	delaying any later requests for a long time.
		1169
		1170	To avoid this, and allow incremental generation of requests, you can
		1171	instead a group and set a feeder on it that generates those requests. The
		1172	feed callback will be called whenever there are few enough (see C<limit>,
		1173	below) requests active in the group itself and is expected to queue more
		1174	requests.
		1175
		1176	The feed callback can queue as many requests as it likes (i.e. C<add> does
		1177	not impose any limits).
		1178
		1179	If the feed does not queue more requests when called, it will be
		1180	automatically removed from the group.
		1181
		1182	If the feed limit is C<0> when this method is called, it will be set to
		1183	C<2> automatically.
		1184
		1185	Example:
		1186
		1187	# stat all files in @files, but only ever use four aio requests concurrently:
		1188
		1189	my $grp = aio_group sub { print "finished\n" };
		1190	limit $grp 4;
		1191	feed $grp sub {
		1192	my $file = pop @files
		1193	or return;
		1194
		1195	add $grp aio_stat $file, sub { ... };
		1196	};
		1197
		1198	=item limit $grp $num
		1199
		1200	Sets the feeder limit for the group: The feeder will be called whenever
		1201	the group contains less than this many requests.
		1202
		1203	Setting the limit to C<0> will pause the feeding process.
		1204
		1205	The default value for the limit is C<0>, but note that setting a feeder
		1206	automatically bumps it up to C<2>.
		1207
		1208	=back
		1209
224	=head2 SUPPORT FUNCTIONS	1210	=head2 SUPPORT FUNCTIONS
225		1211
		1212	=head3 EVENT PROCESSING AND EVENT LOOP INTEGRATION
		1213
226	=over 4	1214	=over 4
227		1215
228	=item $fileno = IO::AIO::poll_fileno	1216	=item $fileno = IO::AIO::poll_fileno
229		1217
230	Return the I<request result pipe file descriptor>. This filehandle must be	1218	Return the I<request result pipe file descriptor>. This filehandle must be
231	polled for reading by some mechanism outside this module (e.g. Event or	1219	polled for reading by some mechanism outside this module (e.g. EV, Glib,
232	select, see below or the SYNOPSIS). If the pipe becomes readable you have	1220	select and so on, see below or the SYNOPSIS). If the pipe becomes readable
233	to call C<poll_cb> to check the results.	1221	you have to call C<poll_cb> to check the results.
234		1222
235	See C<poll_cb> for an example.	1223	See C<poll_cb> for an example.
236		1224
237	=item IO::AIO::poll_cb	1225	=item IO::AIO::poll_cb
238		1226
239	Process all outstanding events on the result pipe. You have to call this	1227	Process some outstanding events on the result pipe. You have to call this
240	regularly. Returns the number of events processed. Returns immediately	1228	regularly. Returns C<0> if all events could be processed, or C<-1> if it
241	when no events are outstanding.	1229	returned earlier for whatever reason. Returns immediately when no events
		1230	are outstanding. The amount of events processed depends on the settings of
		1231	C<IO::AIO::max_poll_req> and C<IO::AIO::max_poll_time>.
		1232
		1233	If not all requests were processed for whatever reason, the filehandle
		1234	will still be ready when C<poll_cb> returns, so normally you don't have to
		1235	do anything special to have it called later.
242		1236
243	Example: Install an Event watcher that automatically calls	1237	Example: Install an Event watcher that automatically calls
244	IO::AIO::poll_cb with high priority:	1238	IO::AIO::poll_cb with high priority (more examples can be found in the
		1239	SYNOPSIS section, at the top of this document):
245		1240
246	Event->io (fd => IO::AIO::poll_fileno,	1241	Event->io (fd => IO::AIO::poll_fileno,
247	poll => 'r', async => 1,	1242	poll => 'r', async => 1,
248	cb => \&IO::AIO::poll_cb);	1243	cb => \&IO::AIO::poll_cb);
249		1244
		1245	=item IO::AIO::max_poll_reqs $nreqs
		1246
		1247	=item IO::AIO::max_poll_time $seconds
		1248
		1249	These set the maximum number of requests (default C<0>, meaning infinity)
		1250	that are being processed by C<IO::AIO::poll_cb> in one call, respectively
		1251	the maximum amount of time (default C<0>, meaning infinity) spent in
		1252	C<IO::AIO::poll_cb> to process requests (more correctly the mininum amount
		1253	of time C<poll_cb> is allowed to use).
		1254
		1255	Setting C<max_poll_time> to a non-zero value creates an overhead of one
		1256	syscall per request processed, which is not normally a problem unless your
		1257	callbacks are really really fast or your OS is really really slow (I am
		1258	not mentioning Solaris here). Using C<max_poll_reqs> incurs no overhead.
		1259
		1260	Setting these is useful if you want to ensure some level of
		1261	interactiveness when perl is not fast enough to process all requests in
		1262	time.
		1263
		1264	For interactive programs, values such as C<0.01> to C<0.1> should be fine.
		1265
		1266	Example: Install an Event watcher that automatically calls
		1267	IO::AIO::poll_cb with low priority, to ensure that other parts of the
		1268	program get the CPU sometimes even under high AIO load.
		1269
		1270	# try not to spend much more than 0.1s in poll_cb
		1271	IO::AIO::max_poll_time 0.1;
		1272
		1273	# use a low priority so other tasks have priority
		1274	Event->io (fd => IO::AIO::poll_fileno,
		1275	poll => 'r', nice => 1,
		1276	cb => &IO::AIO::poll_cb);
		1277
250	=item IO::AIO::poll_wait	1278	=item IO::AIO::poll_wait
251		1279
		1280	If there are any outstanding requests and none of them in the result
252	Wait till the result filehandle becomes ready for reading (simply does a	1281	phase, wait till the result filehandle becomes ready for reading (simply
253	C<select> on the filehandle. This is useful if you want to synchronously wait	1282	does a C<select> on the filehandle. This is useful if you want to
254	for some requests to finish).	1283	synchronously wait for some requests to finish).
255		1284
256	See C<nreqs> for an example.	1285	See C<nreqs> for an example.
257		1286
		1287	=item IO::AIO::poll
		1288
		1289	Waits until some requests have been handled.
		1290
		1291	Returns the number of requests processed, but is otherwise strictly
		1292	equivalent to:
		1293
		1294	IO::AIO::poll_wait, IO::AIO::poll_cb
		1295
258	=item IO::AIO::nreqs	1296	=item IO::AIO::flush
259		1297
260	Returns the number of requests currently outstanding (i.e. for which their	1298	Wait till all outstanding AIO requests have been handled.
261	callback has not been invoked yet).
262		1299
263	Example: wait till there are no outstanding requests anymore:	1300	Strictly equivalent to:
264		1301
265	IO::AIO::poll_wait, IO::AIO::poll_cb	1302	IO::AIO::poll_wait, IO::AIO::poll_cb
266	while IO::AIO::nreqs;	1303	while IO::AIO::nreqs;
267		1304
		1305	=back
		1306
		1307	=head3 CONTROLLING THE NUMBER OF THREADS
		1308
		1309	=over
		1310
		1311	=item IO::AIO::min_parallel $nthreads
		1312
		1313	Set the minimum number of AIO threads to C<$nthreads>. The current
		1314	default is C<8>, which means eight asynchronous operations can execute
		1315	concurrently at any one time (the number of outstanding requests,
		1316	however, is unlimited).
		1317
		1318	IO::AIO starts threads only on demand, when an AIO request is queued and
		1319	no free thread exists. Please note that queueing up a hundred requests can
		1320	create demand for a hundred threads, even if it turns out that everything
		1321	is in the cache and could have been processed faster by a single thread.
		1322
		1323	It is recommended to keep the number of threads relatively low, as some
		1324	Linux kernel versions will scale negatively with the number of threads
		1325	(higher parallelity => MUCH higher latency). With current Linux 2.6
		1326	versions, 4-32 threads should be fine.
		1327
		1328	Under most circumstances you don't need to call this function, as the
		1329	module selects a default that is suitable for low to moderate load.
		1330
		1331	=item IO::AIO::max_parallel $nthreads
		1332
		1333	Sets the maximum number of AIO threads to C<$nthreads>. If more than the
		1334	specified number of threads are currently running, this function kills
		1335	them. This function blocks until the limit is reached.
		1336
		1337	While C<$nthreads> are zero, aio requests get queued but not executed
		1338	until the number of threads has been increased again.
		1339
		1340	This module automatically runs C<max_parallel 0> at program end, to ensure
		1341	that all threads are killed and that there are no outstanding requests.
		1342
		1343	Under normal circumstances you don't need to call this function.
		1344
		1345	=item IO::AIO::max_idle $nthreads
		1346
		1347	Limit the number of threads (default: 4) that are allowed to idle (i.e.,
		1348	threads that did not get a request to process within 10 seconds). That
		1349	means if a thread becomes idle while C<$nthreads> other threads are also
		1350	idle, it will free its resources and exit.
		1351
		1352	This is useful when you allow a large number of threads (e.g. 100 or 1000)
		1353	to allow for extremely high load situations, but want to free resources
		1354	under normal circumstances (1000 threads can easily consume 30MB of RAM).
		1355
		1356	The default is probably ok in most situations, especially if thread
		1357	creation is fast. If thread creation is very slow on your system you might
		1358	want to use larger values.
		1359
		1360	=item IO::AIO::max_outstanding $maxreqs
		1361
		1362	This is a very bad function to use in interactive programs because it
		1363	blocks, and a bad way to reduce concurrency because it is inexact: Better
		1364	use an C<aio_group> together with a feed callback.
		1365
		1366	Sets the maximum number of outstanding requests to C<$nreqs>. If you
		1367	do queue up more than this number of requests, the next call to the
		1368	C<poll_cb> (and C<poll_some> and other functions calling C<poll_cb>)
		1369	function will block until the limit is no longer exceeded.
		1370
		1371	The default value is very large, so there is no practical limit on the
		1372	number of outstanding requests.
		1373
		1374	You can still queue as many requests as you want. Therefore,
		1375	C<max_outstanding> is mainly useful in simple scripts (with low values) or
		1376	as a stop gap to shield against fatal memory overflow (with large values).
		1377
		1378	=back
		1379
		1380	=head3 STATISTICAL INFORMATION
		1381
		1382	=over
		1383
268	=item IO::AIO::flush	1384	=item IO::AIO::nreqs
269		1385
270	Wait till all outstanding AIO requests have been handled.	1386	Returns the number of requests currently in the ready, execute or pending
		1387	states (i.e. for which their callback has not been invoked yet).
271		1388
272	Strictly equivalent to:	1389	Example: wait till there are no outstanding requests anymore:
273		1390
274	IO::AIO::poll_wait, IO::AIO::poll_cb	1391	IO::AIO::poll_wait, IO::AIO::poll_cb
275	while IO::AIO::nreqs;	1392	while IO::AIO::nreqs;
276		1393
		1394	=item IO::AIO::nready
		1395
		1396	Returns the number of requests currently in the ready state (not yet
		1397	executed).
		1398
277	=item IO::AIO::poll	1399	=item IO::AIO::npending
278		1400
279	Waits until some requests have been handled.	1401	Returns the number of requests currently in the pending state (executed,
280		1402	but not yet processed by poll_cb).
281	Strictly equivalent to:
282
283	IO::AIO::poll_wait, IO::AIO::poll_cb
284	if IO::AIO::nreqs;
285
286	=item IO::AIO::min_parallel $nthreads
287
288	Set the minimum number of AIO threads to C<$nthreads>. The default is
289	C<1>, which means a single asynchronous operation can be done at one time
290	(the number of outstanding operations, however, is unlimited).
291
292	It is recommended to keep the number of threads low, as some Linux
293	kernel versions will scale negatively with the number of threads (higher
294	parallelity => MUCH higher latency). With current Linux 2.6 versions, 4-32
295	threads should be fine.
296
297	Under normal circumstances you don't need to call this function, as this
298	module automatically starts some threads (the exact number might change,
299	and is currently 4).
300
301	=item IO::AIO::max_parallel $nthreads
302
303	Sets the maximum number of AIO threads to C<$nthreads>. If more than
304	the specified number of threads are currently running, kill them. This
305	function blocks until the limit is reached.
306
307	This module automatically runs C<max_parallel 0> at program end, to ensure
308	that all threads are killed and that there are no outstanding requests.
309
310	Under normal circumstances you don't need to call this function.
311
312	=item $oldnreqs = IO::AIO::max_outstanding $nreqs
313
314	Sets the maximum number of outstanding requests to C<$nreqs>. If you
315	try to queue up more than this number of requests, the caller will block until
316	some requests have been handled.
317
318	The default is very large, so normally there is no practical limit. If you
319	queue up many requests in a loop it it often improves speed if you set
320	this to a relatively low number, such as C<100>.
321
322	Under normal circumstances you don't need to call this function.
323		1403
324	=back	1404	=back
325		1405
		1406	=head3 MISCELLANEOUS FUNCTIONS
		1407
		1408	IO::AIO implements some functions that might be useful, but are not
		1409	asynchronous.
		1410
		1411	=over 4
		1412
		1413	=item IO::AIO::sendfile $ofh, $ifh, $offset, $count
		1414
		1415	Calls the C<eio_sendfile_sync> function, which is like C<aio_sendfile>,
		1416	but is blocking (this makes most sense if you know the input data is
		1417	likely cached already and the output filehandle is set to non-blocking
		1418	operations).
		1419
		1420	Returns the number of bytes copied, or C<-1> on error.
		1421
		1422	=item IO::AIO::fadvise $fh, $offset, $len, $advice
		1423
		1424	Simply calls the C<posix_fadvise> function (see it's
		1425	manpage for details). The following advice constants are
		1426	avaiable: C<IO::AIO::FADV_NORMAL>, C<IO::AIO::FADV_SEQUENTIAL>,
		1427	C<IO::AIO::FADV_RANDOM>, C<IO::AIO::FADV_NOREUSE>,
		1428	C<IO::AIO::FADV_WILLNEED>, C<IO::AIO::FADV_DONTNEED>.
		1429
		1430	On systems that do not implement C<posix_fadvise>, this function returns
		1431	ENOSYS, otherwise the return value of C<posix_fadvise>.
		1432
		1433	=back
		1434
326	=cut	1435	=cut
327		1436
328	# support function to convert a fd into a perl filehandle
329	sub _fd2fh {
330	return undef if $_[0] < 0;
331
332	# try to generate nice filehandles
333	my $sym = "IO::AIO::fd#$_[0]";
334	local *$sym;
335
336	open *$sym, "+<&=$_[0]" # usually works under any unix
337	or open *$sym, "<&=$_[0]" # cygwin needs this
338	or open *$sym, ">&=$_[0]" # or this
339	or return undef;
340
341	*$sym
342	}
343
344	min_parallel 4;	1437	min_parallel 8;
345		1438
346	END {	1439	END { flush }
347	max_parallel 0;
348	}
349		1440
350	1;	1441	1;
351		1442
352	=head2 FORK BEHAVIOUR	1443	=head2 FORK BEHAVIOUR
353		1444
354	Before the fork IO::AIO first handles all outstanding requests - if other	1445	This module should do "the right thing" when the process using it forks:
355	threads add requests during this period, this time is prolonged. It then	1446
356	enters a quiescent state where no requests can be added in other threads	1447	Before the fork, IO::AIO enters a quiescent state where no requests
357	and no results will be processed. After the fork the parent simply leaves	1448	can be added in other threads and no results will be processed. After
358	the quiescent state and continues request processing, while the child	1449	the fork the parent simply leaves the quiescent state and continues
359	starts the same number of threads as were in use by the parent.	1450	request/result processing, while the child frees the request/result queue
		1451	(so that the requests started before the fork will only be handled in the
		1452	parent). Threads will be started on demand until the limit set in the
		1453	parent process has been reached again.
		1454
		1455	In short: the parent will, after a short pause, continue as if fork had
		1456	not been called, while the child will act as if IO::AIO has not been used
		1457	yet.
		1458
		1459	=head2 MEMORY USAGE
		1460
		1461	Per-request usage:
		1462
		1463	Each aio request uses - depending on your architecture - around 100-200
		1464	bytes of memory. In addition, stat requests need a stat buffer (possibly
		1465	a few hundred bytes), readdir requires a result buffer and so on. Perl
		1466	scalars and other data passed into aio requests will also be locked and
		1467	will consume memory till the request has entered the done state.
		1468
		1469	This is not awfully much, so queuing lots of requests is not usually a
		1470	problem.
		1471
		1472	Per-thread usage:
		1473
		1474	In the execution phase, some aio requests require more memory for
		1475	temporary buffers, and each thread requires a stack and other data
		1476	structures (usually around 16k-128k, depending on the OS).
		1477
		1478	=head1 KNOWN BUGS
		1479
		1480	Known bugs will be fixed in the next release.
360		1481
361	=head1 SEE ALSO	1482	=head1 SEE ALSO
362		1483
363	L<Coro>, L<Linux::AIO>.	1484	L<AnyEvent::AIO> for easy integration into event loops, L<Coro::AIO> for a
		1485	more natural syntax.
364		1486
365	=head1 AUTHOR	1487	=head1 AUTHOR
366		1488
367	Marc Lehmann <schmorp@schmorp.de>	1489	Marc Lehmann <schmorp@schmorp.de>
368	http://home.schmorp.de/	1490	http://home.schmorp.de/

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