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Comparing IO-AIO/AIO.pm (file contents):
Revision 1.6 by root, Sun Jul 10 22:19:48 2005 UTC vs.
Revision 1.134 by root, Sun Sep 28 03:09:07 2008 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 $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', async => 1,	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	\&IO::AIO::poll_cb;	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
		50	# Danga::Socket integration
		51	Danga::Socket->AddOtherFds (IO::AIO::poll_fileno =>
		52	\&IO::AIO::poll_cb);
		53
33	=head1 DESCRIPTION	54	=head1 DESCRIPTION
34		55
35	This module implements asynchronous I/O using whatever means your	56	This module implements asynchronous I/O using whatever means your
36	operating system supports.	57	operating system supports.
37		58
		59	Asynchronous means that operations that can normally block your program
		60	(e.g. reading from disk) will be done asynchronously: the operation
		61	will still block, but you can do something else in the meantime. This
		62	is extremely useful for programs that need to stay interactive even
		63	when doing heavy I/O (GUI programs, high performance network servers
		64	etc.), but can also be used to easily do operations in parallel that are
		65	normally done sequentially, e.g. stat'ing many files, which is much faster
		66	on a RAID volume or over NFS when you do a number of stat operations
		67	concurrently.
		68
		69	While most of this works on all types of file descriptors (for
		70	example sockets), using these functions on file descriptors that
		71	support nonblocking operation (again, sockets, pipes etc.) is very
		72	inefficient. Use an event loop for that (such as the L<Event|Event>
		73	module): IO::AIO will naturally fit into such an event loop itself.
		74
38	Currently, a number of threads are started that execute your read/writes	75	In this version, a number of threads are started that execute your
39	and signal their completion. You don't need thread support in your libc or	76	requests and signal their completion. You don't need thread support
40	perl, and the threads created by this module will not be visible to the	77	in perl, and the threads created by this module will not be visible
41	pthreads library. In the future, this module might make use of the native	78	to perl. In the future, this module might make use of the native aio
42	aio functions available on many operating systems. However, they are often	79	functions available on many operating systems. However, they are often
43	not well-supported (Linux doesn't allow them on normal files currently,	80	not well-supported or restricted (GNU/Linux doesn't allow them on normal
44	for example), and they would only support aio_read and aio_write, so the	81	files currently, for example), and they would only support aio_read and
45	remaining functionality would have to be implemented using threads anyway.	82	aio_write, so the remaining functionality would have to be implemented
		83	using threads anyway.
46		84
47	Although the module will work with in the presence of other threads, it is	85	Although the module will work in the presence of other (Perl-) threads,
48	currently not reentrant, so use appropriate locking yourself.	86	it is currently not reentrant in any way, so use appropriate locking
		87	yourself, always call C<poll_cb> from within the same thread, or never
		88	call C<poll_cb> (or other C<aio_> functions) recursively.
		89
		90	=head2 EXAMPLE
		91
		92	This is a simple example that uses the Event module and loads
		93	F</etc/passwd> asynchronously:
		94
		95	use Fcntl;
		96	use Event;
		97	use IO::AIO;
		98
		99	# register the IO::AIO callback with Event
		100	Event->io (fd => IO::AIO::poll_fileno,
		101	poll => 'r',
		102	cb => \&IO::AIO::poll_cb);
		103
		104	# queue the request to open /etc/passwd
		105	aio_open "/etc/passwd", O_RDONLY, 0, sub {
		106	my $fh = shift
		107	or die "error while opening: $!";
		108
		109	# stat'ing filehandles is generally non-blocking
		110	my $size = -s $fh;
		111
		112	# queue a request to read the file
		113	my $contents;
		114	aio_read $fh, 0, $size, $contents, 0, sub {
		115	$_[0] == $size
		116	or die "short read: $!";
		117
		118	close $fh;
		119
		120	# file contents now in $contents
		121	print $contents;
		122
		123	# exit event loop and program
		124	Event::unloop;
		125	};
		126	};
		127
		128	# possibly queue up other requests, or open GUI windows,
		129	# check for sockets etc. etc.
		130
		131	# process events as long as there are some:
		132	Event::loop;
		133
		134	=head1 REQUEST ANATOMY AND LIFETIME
		135
		136	Every C<aio_*> function creates a request. which is a C data structure not
		137	directly visible to Perl.
		138
		139	If called in non-void context, every request function returns a Perl
		140	object representing the request. In void context, nothing is returned,
		141	which saves a bit of memory.
		142
		143	The perl object is a fairly standard ref-to-hash object. The hash contents
		144	are not used by IO::AIO so you are free to store anything you like in it.
		145
		146	During their existance, aio requests travel through the following states,
		147	in order:
		148
		149	=over 4
		150
		151	=item ready
		152
		153	Immediately after a request is created it is put into the ready state,
		154	waiting for a thread to execute it.
		155
		156	=item execute
		157
		158	A thread has accepted the request for processing and is currently
		159	executing it (e.g. blocking in read).
		160
		161	=item pending
		162
		163	The request has been executed and is waiting for result processing.
		164
		165	While request submission and execution is fully asynchronous, result
		166	processing is not and relies on the perl interpreter calling C<poll_cb>
		167	(or another function with the same effect).
		168
		169	=item result
		170
		171	The request results are processed synchronously by C<poll_cb>.
		172
		173	The C<poll_cb> function will process all outstanding aio requests by
		174	calling their callbacks, freeing memory associated with them and managing
		175	any groups they are contained in.
		176
		177	=item done
		178
		179	Request has reached the end of its lifetime and holds no resources anymore
		180	(except possibly for the Perl object, but its connection to the actual
		181	aio request is severed and calling its methods will either do nothing or
		182	result in a runtime error).
		183
		184	=back
49		185
50	=cut	186	=cut
51		187
52	package IO::AIO;	188	package IO::AIO;
53		189
		190	use Carp ();
		191
		192	no warnings;
		193	use strict 'vars';
		194
54	use base 'Exporter';	195	use base 'Exporter';
55		196
56	use Fcntl ();
57
58	BEGIN {	197	BEGIN {
59	$VERSION = 0.2;	198	our $VERSION = '3.07';
60		199
61	@EXPORT = qw(aio_read aio_write aio_open aio_close aio_stat aio_lstat aio_unlink	200	our @AIO_REQ = qw(aio_sendfile aio_read aio_write aio_open aio_close
		201	aio_stat aio_lstat aio_unlink aio_rmdir aio_readdir
		202	aio_scandir aio_symlink aio_readlink aio_sync aio_fsync
62	aio_fsync aio_fdatasync aio_readahead);	203	aio_fdatasync aio_pathsync aio_readahead
63	@EXPORT_OK = qw(poll_fileno poll_cb min_parallel max_parallel max_outstanding nreqs);	204	aio_rename aio_link aio_move aio_copy aio_group
		205	aio_nop aio_mknod aio_load aio_rmtree aio_mkdir aio_chown
		206	aio_chmod aio_utime aio_truncate);
		207
		208	our @EXPORT = (@AIO_REQ, qw(aioreq_pri aioreq_nice));
		209	our @EXPORT_OK = qw(poll_fileno poll_cb poll_wait flush
		210	min_parallel max_parallel max_idle
		211	nreqs nready npending nthreads
		212	max_poll_time max_poll_reqs);
		213
		214	@IO::AIO::GRP::ISA = 'IO::AIO::REQ';
64		215
65	require XSLoader;	216	require XSLoader;
66	XSLoader::load IO::AIO, $VERSION;	217	XSLoader::load ("IO::AIO", $VERSION);
67	}	218	}
68		219
69	=head1 FUNCTIONS	220	=head1 FUNCTIONS
70		221
71	=head2 AIO FUNCTIONS	222	=head2 AIO REQUEST FUNCTIONS
72		223
73	All the C<aio_*> calls are more or less thin wrappers around the syscall	224	All the C<aio_*> calls are more or less thin wrappers around the syscall
74	with the same name (sans C<aio_>). The arguments are similar or identical,	225	with the same name (sans C<aio_>). The arguments are similar or identical,
75	and they all accept an additional C<$callback> argument which must be	226	and they all accept an additional (and optional) C<$callback> argument
76	a code reference. This code reference will get called with the syscall	227	which must be a code reference. This code reference will get called with
77	return code (e.g. most syscalls return C<-1> on error, unlike perl, which	228	the syscall return code (e.g. most syscalls return C<-1> on error, unlike
78	usually delivers "false") as it's sole argument when the given syscall has	229	perl, which usually delivers "false") as it's sole argument when the given
79	been executed asynchronously.	230	syscall has been executed asynchronously.
80		231
81	All functions that expect a filehandle will also accept a file descriptor.	232	All functions expecting a filehandle keep a copy of the filehandle
		233	internally until the request has finished.
82		234
		235	All functions return request objects of type L<IO::AIO::REQ> that allow
		236	further manipulation of those requests while they are in-flight.
		237
83	The filenames you pass to these routines I<must> be absolute. The reason	238	The pathnames you pass to these routines I<must> be absolute and
84	is that at the time the request is being executed, the current working	239	encoded as octets. The reason for the former is that at the time the
85	directory could have changed. Alternatively, you can make sure that you	240	request is being executed, the current working directory could have
86	never change the current working directory.	241	changed. Alternatively, you can make sure that you never change the
		242	current working directory anywhere in the program and then use relative
		243	paths.
		244
		245	To encode pathnames as octets, either make sure you either: a) always pass
		246	in filenames you got from outside (command line, readdir etc.) without
		247	tinkering, b) are ASCII or ISO 8859-1, c) use the Encode module and encode
		248	your pathnames to the locale (or other) encoding in effect in the user
		249	environment, d) use Glib::filename_from_unicode on unicode filenames or e)
		250	use something else to ensure your scalar has the correct contents.
		251
		252	This works, btw. independent of the internal UTF-8 bit, which IO::AIO
		253	handles correctly wether it is set or not.
87		254
88	=over 4	255	=over 4
89		256
		257	=item $prev_pri = aioreq_pri [$pri]
		258
		259	Returns the priority value that would be used for the next request and, if
		260	C<$pri> is given, sets the priority for the next aio request.
		261
		262	The default priority is C<0>, the minimum and maximum priorities are C<-4>
		263	and C<4>, respectively. Requests with higher priority will be serviced
		264	first.
		265
		266	The priority will be reset to C<0> after each call to one of the C<aio_*>
		267	functions.
		268
		269	Example: open a file with low priority, then read something from it with
		270	higher priority so the read request is serviced before other low priority
		271	open requests (potentially spamming the cache):
		272
		273	aioreq_pri -3;
		274	aio_open ..., sub {
		275	return unless $_[0];
		276
		277	aioreq_pri -2;
		278	aio_read $_[0], ..., sub {
		279	...
		280	};
		281	};
		282
		283
		284	=item aioreq_nice $pri_adjust
		285
		286	Similar to C<aioreq_pri>, but subtracts the given value from the current
		287	priority, so the effect is cumulative.
		288
		289
90	=item aio_open $pathname, $flags, $mode, $callback	290	=item aio_open $pathname, $flags, $mode, $callback->($fh)
91		291
92	Asynchronously open or create a file and call the callback with a newly	292	Asynchronously open or create a file and call the callback with a newly
93	created filehandle for the file.	293	created filehandle for the file.
94		294
95	The pathname passed to C<aio_open> must be absolute. See API NOTES, above,	295	The pathname passed to C<aio_open> must be absolute. See API NOTES, above,
96	for an explanation.	296	for an explanation.
97		297
98	The C<$mode> argument is a bitmask. See the C<Fcntl> module for a	298	The C<$flags> argument is a bitmask. See the C<Fcntl> module for a
99	list. They are the same as used in C<sysopen>.	299	list. They are the same as used by C<sysopen>.
		300
		301	Likewise, C<$mode> specifies the mode of the newly created file, if it
		302	didn't exist and C<O_CREAT> has been given, just like perl's C<sysopen>,
		303	except that it is mandatory (i.e. use C<0> if you don't create new files,
		304	and C<0666> or C<0777> if you do). Note that the C<$mode> will be modified
		305	by the umask in effect then the request is being executed, so better never
		306	change the umask.
100		307
101	Example:	308	Example:
102		309
103	aio_open "/etc/passwd", O_RDONLY, 0, sub {	310	aio_open "/etc/passwd", O_RDONLY, 0, sub {
104	if ($_[0]) {	311	if ($_[0]) {
…		…
107	} else {	314	} else {
108	die "open failed: $!\n";	315	die "open failed: $!\n";
109	}	316	}
110	};	317	};
111		318
		319
112	=item aio_close $fh, $callback	320	=item aio_close $fh, $callback->($status)
113		321
114	Asynchronously close a file and call the callback with the result	322	Asynchronously close a file and call the callback with the result
115	code. I<WARNING:> although accepted, you should not pass in a perl	323	code.
116	filehandle here, as perl will likely close the file descriptor itself when
117	the filehandle is destroyed. Normally, you can safely call perls C<close>
118	or just let filehandles go out of scope.
119		324
		325	Unfortunately, you can't do this to perl. Perl I<insists> very strongly on
		326	closing the file descriptor associated with the filehandle itself.
		327
		328	Therefore, C<aio_close> will not close the filehandle - instead it will
		329	use dup2 to overwrite the file descriptor with the write-end of a pipe
		330	(the pipe fd will be created on demand and will be cached).
		331
		332	Or in other words: the file descriptor will be closed, but it will not be
		333	free for reuse until the perl filehandle is closed.
		334
		335	=cut
		336
120	=item aio_read $fh,$offset,$length, $data,$dataoffset,$callback	337	=item aio_read $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
121		338
122	=item aio_write $fh,$offset,$length, $data,$dataoffset,$callback	339	=item aio_write $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
123		340
124	Reads or writes C<length> bytes from the specified C<fh> and C<offset>	341	Reads or writes C<$length> bytes from the specified C<$fh> and C<$offset>
125	into the scalar given by C<data> and offset C<dataoffset> and calls the	342	into the scalar given by C<$data> and offset C<$dataoffset> and calls the
126	callback without the actual number of bytes read (or -1 on error, just	343	callback without the actual number of bytes read (or -1 on error, just
127	like the syscall).	344	like the syscall).
128		345
		346	If C<$offset> is undefined, then the current file descriptor offset will
		347	be used (and updated), otherwise the file descriptor offset will not be
		348	changed by these calls.
		349
		350	If C<$length> is undefined in C<aio_write>, use the remaining length of C<$data>.
		351
		352	If C<$dataoffset> is less than zero, it will be counted from the end of
		353	C<$data>.
		354
		355	The C<$data> scalar I<MUST NOT> be modified in any way while the request
		356	is outstanding. Modifying it can result in segfaults or World War III (if
		357	the necessary/optional hardware is installed).
		358
129	Example: Read 15 bytes at offset 7 into scalar C<$buffer>, strating at	359	Example: Read 15 bytes at offset 7 into scalar C<$buffer>, starting at
130	offset C<0> within the scalar:	360	offset C<0> within the scalar:
131		361
132	aio_read $fh, 7, 15, $buffer, 0, sub {	362	aio_read $fh, 7, 15, $buffer, 0, sub {
133	$_[0] >= 0 or die "read error: $!";	363	$_[0] > 0 or die "read error: $!";
134	print "read <$buffer>\n";	364	print "read $_[0] bytes: <$buffer>\n";
135	};	365	};
136		366
		367
		368	=item aio_sendfile $out_fh, $in_fh, $in_offset, $length, $callback->($retval)
		369
		370	Tries to copy C<$length> bytes from C<$in_fh> to C<$out_fh>. It starts
		371	reading at byte offset C<$in_offset>, and starts writing at the current
		372	file offset of C<$out_fh>. Because of that, it is not safe to issue more
		373	than one C<aio_sendfile> per C<$out_fh>, as they will interfere with each
		374	other.
		375
		376	This call tries to make use of a native C<sendfile> syscall to provide
		377	zero-copy operation. For this to work, C<$out_fh> should refer to a
		378	socket, and C<$in_fh> should refer to mmap'able file.
		379
		380	If the native sendfile call fails or is not implemented, it will be
		381	emulated, so you can call C<aio_sendfile> on any type of filehandle
		382	regardless of the limitations of the operating system.
		383
		384	Please note, however, that C<aio_sendfile> can read more bytes from
		385	C<$in_fh> than are written, and there is no way to find out how many
		386	bytes have been read from C<aio_sendfile> alone, as C<aio_sendfile> only
		387	provides the number of bytes written to C<$out_fh>. Only if the result
		388	value equals C<$length> one can assume that C<$length> bytes have been
		389	read.
		390
		391
137	=item aio_readahead $fh,$offset,$length, $callback	392	=item aio_readahead $fh,$offset,$length, $callback->($retval)
138		393
139	Asynchronously reads the specified byte range into the page cache, using
140	the C<readahead> syscall. If that syscall doesn't exist the status will be
141	C<-1> and C<$!> is set to ENOSYS.
142
143	readahead() populates the page cache with data from a file so that	394	C<aio_readahead> populates the page cache with data from a file so that
144	subsequent reads from that file will not block on disk I/O. The C<$offset>	395	subsequent reads from that file will not block on disk I/O. The C<$offset>
145	argument specifies the starting point from which data is to be read and	396	argument specifies the starting point from which data is to be read and
146	C<$length> specifies the number of bytes to be read. I/O is performed in	397	C<$length> specifies the number of bytes to be read. I/O is performed in
147	whole pages, so that offset is effectively rounded down to a page boundary	398	whole pages, so that offset is effectively rounded down to a page boundary
148	and bytes are read up to the next page boundary greater than or equal to	399	and bytes are read up to the next page boundary greater than or equal to
149	(off-set+length). aio_readahead() does not read beyond the end of the	400	(off-set+length). C<aio_readahead> does not read beyond the end of the
150	file. The current file offset of the file is left unchanged.	401	file. The current file offset of the file is left unchanged.
151		402
		403	If that syscall doesn't exist (likely if your OS isn't Linux) it will be
		404	emulated by simply reading the data, which would have a similar effect.
		405
		406
152	=item aio_stat $fh_or_path, $callback	407	=item aio_stat $fh_or_path, $callback->($status)
153		408
154	=item aio_lstat $fh, $callback	409	=item aio_lstat $fh, $callback->($status)
155		410
156	Works like perl's C<stat> or C<lstat> in void context. The callback will	411	Works like perl's C<stat> or C<lstat> in void context. The callback will
157	be called after the stat and the results will be available using C<stat _>	412	be called after the stat and the results will be available using C<stat _>
158	or C<-s _> etc...	413	or C<-s _> etc...
159		414
…		…
169	aio_stat "/etc/passwd", sub {	424	aio_stat "/etc/passwd", sub {
170	$_[0] and die "stat failed: $!";	425	$_[0] and die "stat failed: $!";
171	print "size is ", -s _, "\n";	426	print "size is ", -s _, "\n";
172	};	427	};
173		428
		429
		430	=item aio_utime $fh_or_path, $atime, $mtime, $callback->($status)
		431
		432	Works like perl's C<utime> function (including the special case of $atime
		433	and $mtime being undef). Fractional times are supported if the underlying
		434	syscalls support them.
		435
		436	When called with a pathname, uses utimes(2) if available, otherwise
		437	utime(2). If called on a file descriptor, uses futimes(2) if available,
		438	otherwise returns ENOSYS, so this is not portable.
		439
		440	Examples:
		441
		442	# set atime and mtime to current time (basically touch(1)):
		443	aio_utime "path", undef, undef;
		444	# set atime to current time and mtime to beginning of the epoch:
		445	aio_utime "path", time, undef; # undef==0
		446
		447
		448	=item aio_chown $fh_or_path, $uid, $gid, $callback->($status)
		449
		450	Works like perl's C<chown> function, except that C<undef> for either $uid
		451	or $gid is being interpreted as "do not change" (but -1 can also be used).
		452
		453	Examples:
		454
		455	# same as "chown root path" in the shell:
		456	aio_chown "path", 0, -1;
		457	# same as above:
		458	aio_chown "path", 0, undef;
		459
		460
		461	=item aio_truncate $fh_or_path, $offset, $callback->($status)
		462
		463	Works like truncate(2) or ftruncate(2).
		464
		465
		466	=item aio_chmod $fh_or_path, $mode, $callback->($status)
		467
		468	Works like perl's C<chmod> function.
		469
		470
174	=item aio_unlink $pathname, $callback	471	=item aio_unlink $pathname, $callback->($status)
175		472
176	Asynchronously unlink (delete) a file and call the callback with the	473	Asynchronously unlink (delete) a file and call the callback with the
177	result code.	474	result code.
178		475
		476
		477	=item aio_mknod $path, $mode, $dev, $callback->($status)
		478
		479	[EXPERIMENTAL]
		480
		481	Asynchronously create a device node (or fifo). See mknod(2).
		482
		483	The only (POSIX-) portable way of calling this function is:
		484
		485	aio_mknod $path, IO::AIO::S_IFIFO | $mode, 0, sub { ...
		486
		487
		488	=item aio_link $srcpath, $dstpath, $callback->($status)
		489
		490	Asynchronously create a new link to the existing object at C<$srcpath> at
		491	the path C<$dstpath> and call the callback with the result code.
		492
		493
		494	=item aio_symlink $srcpath, $dstpath, $callback->($status)
		495
		496	Asynchronously create a new symbolic 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_readlink $path, $callback->($link)
		501
		502	Asynchronously read the symlink specified by C<$path> and pass it to
		503	the callback. If an error occurs, nothing or undef gets passed to the
		504	callback.
		505
		506
		507	=item aio_rename $srcpath, $dstpath, $callback->($status)
		508
		509	Asynchronously rename the object at C<$srcpath> to C<$dstpath>, just as
		510	rename(2) and call the callback with the result code.
		511
		512
		513	=item aio_mkdir $pathname, $mode, $callback->($status)
		514
		515	Asynchronously mkdir (create) a directory and call the callback with
		516	the result code. C<$mode> will be modified by the umask at the time the
		517	request is executed, so do not change your umask.
		518
		519
		520	=item aio_rmdir $pathname, $callback->($status)
		521
		522	Asynchronously rmdir (delete) a directory and call the callback with the
		523	result code.
		524
		525
		526	=item aio_readdir $pathname, $callback->($entries)
		527
		528	Unlike the POSIX call of the same name, C<aio_readdir> reads an entire
		529	directory (i.e. opendir + readdir + closedir). The entries will not be
		530	sorted, and will B<NOT> include the C<.> and C<..> entries.
		531
		532	The callback a single argument which is either C<undef> or an array-ref
		533	with the filenames.
		534
		535
		536	=item aio_load $path, $data, $callback->($status)
		537
		538	This is a composite request that tries to fully load the given file into
		539	memory. Status is the same as with aio_read.
		540
		541	=cut
		542
		543	sub aio_load($$;$) {
		544	my ($path, undef, $cb) = @_;
		545	my $data = \$_[1];
		546
		547	my $pri = aioreq_pri;
		548	my $grp = aio_group $cb;
		549
		550	aioreq_pri $pri;
		551	add $grp aio_open $path, O_RDONLY, 0, sub {
		552	my $fh = shift
		553	or return $grp->result (-1);
		554
		555	aioreq_pri $pri;
		556	add $grp aio_read $fh, 0, (-s $fh), $$data, 0, sub {
		557	$grp->result ($_[0]);
		558	};
		559	};
		560
		561	$grp
		562	}
		563
		564	=item aio_copy $srcpath, $dstpath, $callback->($status)
		565
		566	Try to copy the I<file> (directories not supported as either source or
		567	destination) from C<$srcpath> to C<$dstpath> and call the callback with
		568	the C<0> (error) or C<-1> ok.
		569
		570	This is a composite request that creates the destination file with
		571	mode 0200 and copies the contents of the source file into it using
		572	C<aio_sendfile>, followed by restoring atime, mtime, access mode and
		573	uid/gid, in that order.
		574
		575	If an error occurs, the partial destination file will be unlinked, if
		576	possible, except when setting atime, mtime, access mode and uid/gid, where
		577	errors are being ignored.
		578
		579	=cut
		580
		581	sub aio_copy($$;$) {
		582	my ($src, $dst, $cb) = @_;
		583
		584	my $pri = aioreq_pri;
		585	my $grp = aio_group $cb;
		586
		587	aioreq_pri $pri;
		588	add $grp aio_open $src, O_RDONLY, 0, sub {
		589	if (my $src_fh = $_[0]) {
		590	my @stat = stat $src_fh;
		591
		592	aioreq_pri $pri;
		593	add $grp aio_open $dst, O_CREAT | O_WRONLY | O_TRUNC, 0200, sub {
		594	if (my $dst_fh = $_[0]) {
		595	aioreq_pri $pri;
		596	add $grp aio_sendfile $dst_fh, $src_fh, 0, $stat[7], sub {
		597	if ($_[0] == $stat[7]) {
		598	$grp->result (0);
		599	close $src_fh;
		600
		601	# those should not normally block. should. should.
		602	utime $stat[8], $stat[9], $dst;
		603	chmod $stat[2] & 07777, $dst_fh;
		604	chown $stat[4], $stat[5], $dst_fh;
		605
		606	aioreq_pri $pri;
		607	add $grp aio_close $dst_fh;
		608	} else {
		609	$grp->result (-1);
		610	close $src_fh;
		611	close $dst_fh;
		612
		613	aioreq $pri;
		614	add $grp aio_unlink $dst;
		615	}
		616	};
		617	} else {
		618	$grp->result (-1);
		619	}
		620	},
		621
		622	} else {
		623	$grp->result (-1);
		624	}
		625	};
		626
		627	$grp
		628	}
		629
		630	=item aio_move $srcpath, $dstpath, $callback->($status)
		631
		632	Try to move the I<file> (directories not supported as either source or
		633	destination) from C<$srcpath> to C<$dstpath> and call the callback with
		634	the C<0> (error) or C<-1> ok.
		635
		636	This is a composite request that tries to rename(2) the file first. If
		637	rename files with C<EXDEV>, it copies the file with C<aio_copy> and, if
		638	that is successful, unlinking the C<$srcpath>.
		639
		640	=cut
		641
		642	sub aio_move($$;$) {
		643	my ($src, $dst, $cb) = @_;
		644
		645	my $pri = aioreq_pri;
		646	my $grp = aio_group $cb;
		647
		648	aioreq_pri $pri;
		649	add $grp aio_rename $src, $dst, sub {
		650	if ($_[0] && $! == EXDEV) {
		651	aioreq_pri $pri;
		652	add $grp aio_copy $src, $dst, sub {
		653	$grp->result ($_[0]);
		654
		655	if (!$_[0]) {
		656	aioreq_pri $pri;
		657	add $grp aio_unlink $src;
		658	}
		659	};
		660	} else {
		661	$grp->result ($_[0]);
		662	}
		663	};
		664
		665	$grp
		666	}
		667
		668	=item aio_scandir $path, $maxreq, $callback->($dirs, $nondirs)
		669
		670	Scans a directory (similar to C<aio_readdir>) but additionally tries to
		671	efficiently separate the entries of directory C<$path> into two sets of
		672	names, directories you can recurse into (directories), and ones you cannot
		673	recurse into (everything else, including symlinks to directories).
		674
		675	C<aio_scandir> is a composite request that creates of many sub requests_
		676	C<$maxreq> specifies the maximum number of outstanding aio requests that
		677	this function generates. If it is C<< <= 0 >>, then a suitable default
		678	will be chosen (currently 4).
		679
		680	On error, the callback is called without arguments, otherwise it receives
		681	two array-refs with path-relative entry names.
		682
		683	Example:
		684
		685	aio_scandir $dir, 0, sub {
		686	my ($dirs, $nondirs) = @_;
		687	print "real directories: @$dirs\n";
		688	print "everything else: @$nondirs\n";
		689	};
		690
		691	Implementation notes.
		692
		693	The C<aio_readdir> cannot be avoided, but C<stat()>'ing every entry can.
		694
		695	After reading the directory, the modification time, size etc. of the
		696	directory before and after the readdir is checked, and if they match (and
		697	isn't the current time), the link count will be used to decide how many
		698	entries are directories (if >= 2). Otherwise, no knowledge of the number
		699	of subdirectories will be assumed.
		700
		701	Then entries will be sorted into likely directories (everything without
		702	a non-initial dot currently) and likely non-directories (everything
		703	else). Then every entry plus an appended C</.> will be C<stat>'ed,
		704	likely directories first. If that succeeds, it assumes that the entry
		705	is a directory or a symlink to directory (which will be checked
		706	seperately). This is often faster than stat'ing the entry itself because
		707	filesystems might detect the type of the entry without reading the inode
		708	data (e.g. ext2fs filetype feature).
		709
		710	If the known number of directories (link count - 2) has been reached, the
		711	rest of the entries is assumed to be non-directories.
		712
		713	This only works with certainty on POSIX (= UNIX) filesystems, which
		714	fortunately are the vast majority of filesystems around.
		715
		716	It will also likely work on non-POSIX filesystems with reduced efficiency
		717	as those tend to return 0 or 1 as link counts, which disables the
		718	directory counting heuristic.
		719
		720	=cut
		721
		722	sub aio_scandir($$;$) {
		723	my ($path, $maxreq, $cb) = @_;
		724
		725	my $pri = aioreq_pri;
		726
		727	my $grp = aio_group $cb;
		728
		729	$maxreq = 4 if $maxreq <= 0;
		730
		731	# stat once
		732	aioreq_pri $pri;
		733	add $grp aio_stat $path, sub {
		734	return $grp->result () if $_[0];
		735	my $now = time;
		736	my $hash1 = join ":", (stat _)[0,1,3,7,9];
		737
		738	# read the directory entries
		739	aioreq_pri $pri;
		740	add $grp aio_readdir $path, sub {
		741	my $entries = shift
		742	or return $grp->result ();
		743
		744	# stat the dir another time
		745	aioreq_pri $pri;
		746	add $grp aio_stat $path, sub {
		747	my $hash2 = join ":", (stat _)[0,1,3,7,9];
		748
		749	my $ndirs;
		750
		751	# take the slow route if anything looks fishy
		752	if ($hash1 ne $hash2 or (stat _)[9] == $now) {
		753	$ndirs = -1;
		754	} else {
		755	# if nlink == 2, we are finished
		756	# on non-posix-fs's, we rely on nlink < 2
		757	$ndirs = (stat _)[3] - 2
		758	or return $grp->result ([], $entries);
		759	}
		760
		761	# sort into likely dirs and likely nondirs
		762	# dirs == files without ".", short entries first
		763	$entries = [map $_->[0],
		764	sort { $b->[1] cmp $a->[1] }
		765	map [$_, sprintf "%s%04d", (/.\./ ? "1" : "0"), length],
		766	@$entries];
		767
		768	my (@dirs, @nondirs);
		769
		770	my $statgrp = add $grp aio_group sub {
		771	$grp->result (\@dirs, \@nondirs);
		772	};
		773
		774	limit $statgrp $maxreq;
		775	feed $statgrp sub {
		776	return unless @$entries;
		777	my $entry = pop @$entries;
		778
		779	aioreq_pri $pri;
		780	add $statgrp aio_stat "$path/$entry/.", sub {
		781	if ($_[0] < 0) {
		782	push @nondirs, $entry;
		783	} else {
		784	# need to check for real directory
		785	aioreq_pri $pri;
		786	add $statgrp aio_lstat "$path/$entry", sub {
		787	if (-d _) {
		788	push @dirs, $entry;
		789
		790	unless (--$ndirs) {
		791	push @nondirs, @$entries;
		792	feed $statgrp;
		793	}
		794	} else {
		795	push @nondirs, $entry;
		796	}
		797	}
		798	}
		799	};
		800	};
		801	};
		802	};
		803	};
		804
		805	$grp
		806	}
		807
		808	=item aio_rmtree $path, $callback->($status)
		809
		810	Delete a directory tree starting (and including) C<$path>, return the
		811	status of the final C<rmdir> only. This is a composite request that
		812	uses C<aio_scandir> to recurse into and rmdir directories, and unlink
		813	everything else.
		814
		815	=cut
		816
		817	sub aio_rmtree;
		818	sub aio_rmtree($;$) {
		819	my ($path, $cb) = @_;
		820
		821	my $pri = aioreq_pri;
		822	my $grp = aio_group $cb;
		823
		824	aioreq_pri $pri;
		825	add $grp aio_scandir $path, 0, sub {
		826	my ($dirs, $nondirs) = @_;
		827
		828	my $dirgrp = aio_group sub {
		829	add $grp aio_rmdir $path, sub {
		830	$grp->result ($_[0]);
		831	};
		832	};
		833
		834	(aioreq_pri $pri), add $dirgrp aio_rmtree "$path/$_" for @$dirs;
		835	(aioreq_pri $pri), add $dirgrp aio_unlink "$path/$_" for @$nondirs;
		836
		837	add $grp $dirgrp;
		838	};
		839
		840	$grp
		841	}
		842
		843	=item aio_sync $callback->($status)
		844
		845	Asynchronously call sync and call the callback when finished.
		846
179	=item aio_fsync $fh, $callback	847	=item aio_fsync $fh, $callback->($status)
180		848
181	Asynchronously call fsync on the given filehandle and call the callback	849	Asynchronously call fsync on the given filehandle and call the callback
182	with the fsync result code.	850	with the fsync result code.
183		851
184	=item aio_fdatasync $fh, $callback	852	=item aio_fdatasync $fh, $callback->($status)
185		853
186	Asynchronously call fdatasync on the given filehandle and call the	854	Asynchronously call fdatasync on the given filehandle and call the
187	callback with the fdatasync result code.	855	callback with the fdatasync result code.
188		856
		857	If this call isn't available because your OS lacks it or it couldn't be
		858	detected, it will be emulated by calling C<fsync> instead.
		859
		860	=item aio_pathsync $path, $callback->($status)
		861
		862	This request tries to open, fsync and close the given path. This is a
		863	composite request intended tosync directories after directory operations
		864	(E.g. rename). This might not work on all operating systems or have any
		865	specific effect, but usually it makes sure that directory changes get
		866	written to disc. It works for anything that can be opened for read-only,
		867	not just directories.
		868
		869	Passes C<0> when everything went ok, and C<-1> on error.
		870
		871	=cut
		872
		873	sub aio_pathsync($;$) {
		874	my ($path, $cb) = @_;
		875
		876	my $pri = aioreq_pri;
		877	my $grp = aio_group $cb;
		878
		879	aioreq_pri $pri;
		880	add $grp aio_open $path, O_RDONLY, 0, sub {
		881	my ($fh) = @_;
		882	if ($fh) {
		883	aioreq_pri $pri;
		884	add $grp aio_fsync $fh, sub {
		885	$grp->result ($_[0]);
		886
		887	aioreq_pri $pri;
		888	add $grp aio_close $fh;
		889	};
		890	} else {
		891	$grp->result (-1);
		892	}
		893	};
		894
		895	$grp
		896	}
		897
		898	=item aio_group $callback->(...)
		899
		900	This is a very special aio request: Instead of doing something, it is a
		901	container for other aio requests, which is useful if you want to bundle
		902	many requests into a single, composite, request with a definite callback
		903	and the ability to cancel the whole request with its subrequests.
		904
		905	Returns an object of class L<IO::AIO::GRP>. See its documentation below
		906	for more info.
		907
		908	Example:
		909
		910	my $grp = aio_group sub {
		911	print "all stats done\n";
		912	};
		913
		914	add $grp
		915	(aio_stat ...),
		916	(aio_stat ...),
		917	...;
		918
		919	=item aio_nop $callback->()
		920
		921	This is a special request - it does nothing in itself and is only used for
		922	side effects, such as when you want to add a dummy request to a group so
		923	that finishing the requests in the group depends on executing the given
		924	code.
		925
		926	While this request does nothing, it still goes through the execution
		927	phase and still requires a worker thread. Thus, the callback will not
		928	be executed immediately but only after other requests in the queue have
		929	entered their execution phase. This can be used to measure request
		930	latency.
		931
		932	=item IO::AIO::aio_busy $fractional_seconds, $callback->() *NOT EXPORTED*
		933
		934	Mainly used for debugging and benchmarking, this aio request puts one of
		935	the request workers to sleep for the given time.
		936
		937	While it is theoretically handy to have simple I/O scheduling requests
		938	like sleep and file handle readable/writable, the overhead this creates is
		939	immense (it blocks a thread for a long time) so do not use this function
		940	except to put your application under artificial I/O pressure.
		941
189	=back	942	=back
190		943
		944	=head2 IO::AIO::REQ CLASS
		945
		946	All non-aggregate C<aio_*> functions return an object of this class when
		947	called in non-void context.
		948
		949	=over 4
		950
		951	=item cancel $req
		952
		953	Cancels the request, if possible. Has the effect of skipping execution
		954	when entering the B<execute> state and skipping calling the callback when
		955	entering the the B<result> state, but will leave the request otherwise
		956	untouched. That means that requests that currently execute will not be
		957	stopped and resources held by the request will not be freed prematurely.
		958
		959	=item cb $req $callback->(...)
		960
		961	Replace (or simply set) the callback registered to the request.
		962
		963	=back
		964
		965	=head2 IO::AIO::GRP CLASS
		966
		967	This class is a subclass of L<IO::AIO::REQ>, so all its methods apply to
		968	objects of this class, too.
		969
		970	A IO::AIO::GRP object is a special request that can contain multiple other
		971	aio requests.
		972
		973	You create one by calling the C<aio_group> constructing function with a
		974	callback that will be called when all contained requests have entered the
		975	C<done> state:
		976
		977	my $grp = aio_group sub {
		978	print "all requests are done\n";
		979	};
		980
		981	You add requests by calling the C<add> method with one or more
		982	C<IO::AIO::REQ> objects:
		983
		984	$grp->add (aio_unlink "...");
		985
		986	add $grp aio_stat "...", sub {
		987	$_[0] or return $grp->result ("error");
		988
		989	# add another request dynamically, if first succeeded
		990	add $grp aio_open "...", sub {
		991	$grp->result ("ok");
		992	};
		993	};
		994
		995	This makes it very easy to create composite requests (see the source of
		996	C<aio_move> for an application) that work and feel like simple requests.
		997
		998	=over 4
		999
		1000	=item * The IO::AIO::GRP objects will be cleaned up during calls to
		1001	C<IO::AIO::poll_cb>, just like any other request.
		1002
		1003	=item * They can be canceled like any other request. Canceling will cancel not
		1004	only the request itself, but also all requests it contains.
		1005
		1006	=item * They can also can also be added to other IO::AIO::GRP objects.
		1007
		1008	=item * You must not add requests to a group from within the group callback (or
		1009	any later time).
		1010
		1011	=back
		1012
		1013	Their lifetime, simplified, looks like this: when they are empty, they
		1014	will finish very quickly. If they contain only requests that are in the
		1015	C<done> state, they will also finish. Otherwise they will continue to
		1016	exist.
		1017
		1018	That means after creating a group you have some time to add requests
		1019	(precisely before the callback has been invoked, which is only done within
		1020	the C<poll_cb>). And in the callbacks of those requests, you can add
		1021	further requests to the group. And only when all those requests have
		1022	finished will the the group itself finish.
		1023
		1024	=over 4
		1025
		1026	=item add $grp ...
		1027
		1028	=item $grp->add (...)
		1029
		1030	Add one or more requests to the group. Any type of L<IO::AIO::REQ> can
		1031	be added, including other groups, as long as you do not create circular
		1032	dependencies.
		1033
		1034	Returns all its arguments.
		1035
		1036	=item $grp->cancel_subs
		1037
		1038	Cancel all subrequests and clears any feeder, but not the group request
		1039	itself. Useful when you queued a lot of events but got a result early.
		1040
		1041	=item $grp->result (...)
		1042
		1043	Set the result value(s) that will be passed to the group callback when all
		1044	subrequests have finished and set the groups errno to the current value
		1045	of errno (just like calling C<errno> without an error number). By default,
		1046	no argument will be passed and errno is zero.
		1047
		1048	=item $grp->errno ([$errno])
		1049
		1050	Sets the group errno value to C<$errno>, or the current value of errno
		1051	when the argument is missing.
		1052
		1053	Every aio request has an associated errno value that is restored when
		1054	the callback is invoked. This method lets you change this value from its
		1055	default (0).
		1056
		1057	Calling C<result> will also set errno, so make sure you either set C<$!>
		1058	before the call to C<result>, or call c<errno> after it.
		1059
		1060	=item feed $grp $callback->($grp)
		1061
		1062	Sets a feeder/generator on this group: every group can have an attached
		1063	generator that generates requests if idle. The idea behind this is that,
		1064	although you could just queue as many requests as you want in a group,
		1065	this might starve other requests for a potentially long time. For
		1066	example, C<aio_scandir> might generate hundreds of thousands C<aio_stat>
		1067	requests, delaying any later requests for a long time.
		1068
		1069	To avoid this, and allow incremental generation of requests, you can
		1070	instead a group and set a feeder on it that generates those requests. The
		1071	feed callback will be called whenever there are few enough (see C<limit>,
		1072	below) requests active in the group itself and is expected to queue more
		1073	requests.
		1074
		1075	The feed callback can queue as many requests as it likes (i.e. C<add> does
		1076	not impose any limits).
		1077
		1078	If the feed does not queue more requests when called, it will be
		1079	automatically removed from the group.
		1080
		1081	If the feed limit is C<0>, it will be set to C<2> automatically.
		1082
		1083	Example:
		1084
		1085	# stat all files in @files, but only ever use four aio requests concurrently:
		1086
		1087	my $grp = aio_group sub { print "finished\n" };
		1088	limit $grp 4;
		1089	feed $grp sub {
		1090	my $file = pop @files
		1091	or return;
		1092
		1093	add $grp aio_stat $file, sub { ... };
		1094	};
		1095
		1096	=item limit $grp $num
		1097
		1098	Sets the feeder limit for the group: The feeder will be called whenever
		1099	the group contains less than this many requests.
		1100
		1101	Setting the limit to C<0> will pause the feeding process.
		1102
		1103	=back
		1104
191	=head2 SUPPORT FUNCTIONS	1105	=head2 SUPPORT FUNCTIONS
192		1106
		1107	=head3 EVENT PROCESSING AND EVENT LOOP INTEGRATION
		1108
193	=over 4	1109	=over 4
194		1110
195	=item $fileno = IO::AIO::poll_fileno	1111	=item $fileno = IO::AIO::poll_fileno
196		1112
197	Return the I<request result pipe filehandle>. This filehandle must be	1113	Return the I<request result pipe file descriptor>. This filehandle must be
198	polled for reading by some mechanism outside this module (e.g. Event	1114	polled for reading by some mechanism outside this module (e.g. Event or
199	or select, see below). If the pipe becomes readable you have to call	1115	select, see below or the SYNOPSIS). If the pipe becomes readable you have
200	C<poll_cb> to check the results.	1116	to call C<poll_cb> to check the results.
201		1117
202	See C<poll_cb> for an example.	1118	See C<poll_cb> for an example.
203		1119
204	=item IO::AIO::poll_cb	1120	=item IO::AIO::poll_cb
205		1121
206	Process all outstanding events on the result pipe. You have to call this	1122	Process some outstanding events on the result pipe. You have to call this
207	regularly. Returns the number of events processed. Returns immediately	1123	regularly. Returns C<0> if all events could be processed, or C<-1> if it
208	when no events are outstanding.	1124	returned earlier for whatever reason. Returns immediately when no events
		1125	are outstanding. The amount of events processed depends on the settings of
		1126	C<IO::AIO::max_poll_req> and C<IO::AIO::max_poll_time>.
209		1127
210	You can use Event to multiplex, e.g.:	1128	If not all requests were processed for whatever reason, the filehandle
		1129	will still be ready when C<poll_cb> returns, so normally you don't have to
		1130	do anything special to have it called later.
		1131
		1132	Example: Install an Event watcher that automatically calls
		1133	IO::AIO::poll_cb with high priority:
211		1134
212	Event->io (fd => IO::AIO::poll_fileno,	1135	Event->io (fd => IO::AIO::poll_fileno,
213	poll => 'r', async => 1,	1136	poll => 'r', async => 1,
214	cb => \&IO::AIO::poll_cb);	1137	cb => \&IO::AIO::poll_cb);
215		1138
		1139	=item IO::AIO::max_poll_reqs $nreqs
		1140
		1141	=item IO::AIO::max_poll_time $seconds
		1142
		1143	These set the maximum number of requests (default C<0>, meaning infinity)
		1144	that are being processed by C<IO::AIO::poll_cb> in one call, respectively
		1145	the maximum amount of time (default C<0>, meaning infinity) spent in
		1146	C<IO::AIO::poll_cb> to process requests (more correctly the mininum amount
		1147	of time C<poll_cb> is allowed to use).
		1148
		1149	Setting C<max_poll_time> to a non-zero value creates an overhead of one
		1150	syscall per request processed, which is not normally a problem unless your
		1151	callbacks are really really fast or your OS is really really slow (I am
		1152	not mentioning Solaris here). Using C<max_poll_reqs> incurs no overhead.
		1153
		1154	Setting these is useful if you want to ensure some level of
		1155	interactiveness when perl is not fast enough to process all requests in
		1156	time.
		1157
		1158	For interactive programs, values such as C<0.01> to C<0.1> should be fine.
		1159
		1160	Example: Install an Event watcher that automatically calls
		1161	IO::AIO::poll_cb with low priority, to ensure that other parts of the
		1162	program get the CPU sometimes even under high AIO load.
		1163
		1164	# try not to spend much more than 0.1s in poll_cb
		1165	IO::AIO::max_poll_time 0.1;
		1166
		1167	# use a low priority so other tasks have priority
		1168	Event->io (fd => IO::AIO::poll_fileno,
		1169	poll => 'r', nice => 1,
		1170	cb => &IO::AIO::poll_cb);
		1171
216	=item IO::AIO::poll_wait	1172	=item IO::AIO::poll_wait
217		1173
		1174	If there are any outstanding requests and none of them in the result
218	Wait till the result filehandle becomes ready for reading (simply does a	1175	phase, wait till the result filehandle becomes ready for reading (simply
219	select on the filehandle. This is useful if you want to synchronously wait	1176	does a C<select> on the filehandle. This is useful if you want to
220	for some requests to finish).	1177	synchronously wait for some requests to finish).
221		1178
222	See C<nreqs> for an example.	1179	See C<nreqs> for an example.
223		1180
		1181	=item IO::AIO::poll
		1182
		1183	Waits until some requests have been handled.
		1184
		1185	Returns the number of requests processed, but is otherwise strictly
		1186	equivalent to:
		1187
		1188	IO::AIO::poll_wait, IO::AIO::poll_cb
		1189
224	=item IO::AIO::nreqs	1190	=item IO::AIO::flush
225		1191
226	Returns the number of requests currently outstanding.	1192	Wait till all outstanding AIO requests have been handled.
227		1193
228	Example: wait till there are no outstanding requests anymore:	1194	Strictly equivalent to:
229		1195
230	IO::AIO::poll_wait, IO::AIO::poll_cb	1196	IO::AIO::poll_wait, IO::AIO::poll_cb
231	while IO::AIO::nreqs;	1197	while IO::AIO::nreqs;
232		1198
		1199	=back
		1200
		1201	=head3 CONTROLLING THE NUMBER OF THREADS
		1202
		1203	=over
		1204
233	=item IO::AIO::min_parallel $nthreads	1205	=item IO::AIO::min_parallel $nthreads
234		1206
235	Set the minimum number of AIO threads to C<$nthreads>. The default is	1207	Set the minimum number of AIO threads to C<$nthreads>. The current
236	C<1>, which means a single asynchronous operation can be done at one time	1208	default is C<8>, which means eight asynchronous operations can execute
237	(the number of outstanding operations, however, is unlimited).	1209	concurrently at any one time (the number of outstanding requests,
		1210	however, is unlimited).
238		1211
		1212	IO::AIO starts threads only on demand, when an AIO request is queued and
		1213	no free thread exists. Please note that queueing up a hundred requests can
		1214	create demand for a hundred threads, even if it turns out that everything
		1215	is in the cache and could have been processed faster by a single thread.
		1216
239	It is recommended to keep the number of threads low, as some Linux	1217	It is recommended to keep the number of threads relatively low, as some
240	kernel versions will scale negatively with the number of threads (higher	1218	Linux kernel versions will scale negatively with the number of threads
241	parallelity => MUCH higher latency). With current Linux 2.6 versions, 4-32	1219	(higher parallelity => MUCH higher latency). With current Linux 2.6
242	threads should be fine.	1220	versions, 4-32 threads should be fine.
243		1221
244	Under normal circumstances you don't need to call this function, as this	1222	Under most circumstances you don't need to call this function, as the
245	module automatically starts some threads (the exact number might change,	1223	module selects a default that is suitable for low to moderate load.
246	and is currently 4).
247		1224
248	=item IO::AIO::max_parallel $nthreads	1225	=item IO::AIO::max_parallel $nthreads
249		1226
250	Sets the maximum number of AIO threads to C<$nthreads>. If more than	1227	Sets the maximum number of AIO threads to C<$nthreads>. If more than the
251	the specified number of threads are currently running, kill them. This	1228	specified number of threads are currently running, this function kills
252	function blocks until the limit is reached.	1229	them. This function blocks until the limit is reached.
		1230
		1231	While C<$nthreads> are zero, aio requests get queued but not executed
		1232	until the number of threads has been increased again.
253		1233
254	This module automatically runs C<max_parallel 0> at program end, to ensure	1234	This module automatically runs C<max_parallel 0> at program end, to ensure
255	that all threads are killed and that there are no outstanding requests.	1235	that all threads are killed and that there are no outstanding requests.
256		1236
257	Under normal circumstances you don't need to call this function.	1237	Under normal circumstances you don't need to call this function.
258		1238
		1239	=item IO::AIO::max_idle $nthreads
		1240
		1241	Limit the number of threads (default: 4) that are allowed to idle (i.e.,
		1242	threads that did not get a request to process within 10 seconds). That
		1243	means if a thread becomes idle while C<$nthreads> other threads are also
		1244	idle, it will free its resources and exit.
		1245
		1246	This is useful when you allow a large number of threads (e.g. 100 or 1000)
		1247	to allow for extremely high load situations, but want to free resources
		1248	under normal circumstances (1000 threads can easily consume 30MB of RAM).
		1249
		1250	The default is probably ok in most situations, especially if thread
		1251	creation is fast. If thread creation is very slow on your system you might
		1252	want to use larger values.
		1253
259	=item $oldnreqs = IO::AIO::max_outstanding $nreqs	1254	=item IO::AIO::max_outstanding $maxreqs
		1255
		1256	This is a very bad function to use in interactive programs because it
		1257	blocks, and a bad way to reduce concurrency because it is inexact: Better
		1258	use an C<aio_group> together with a feed callback.
260		1259
261	Sets the maximum number of outstanding requests to C<$nreqs>. If you	1260	Sets the maximum number of outstanding requests to C<$nreqs>. If you
262	try to queue up more than this number of requests, the caller will block until	1261	do queue up more than this number of requests, the next call to the
263	some requests have been handled.	1262	C<poll_cb> (and C<poll_some> and other functions calling C<poll_cb>)
		1263	function will block until the limit is no longer exceeded.
264		1264
265	The default is very large, so normally there is no practical limit. If you	1265	The default value is very large, so there is no practical limit on the
266	queue up many requests in a loop it it often improves speed if you set	1266	number of outstanding requests.
267	this to a relatively low number, such as C<100>.
268		1267
269	Under normal circumstances you don't need to call this function.	1268	You can still queue as many requests as you want. Therefore,
		1269	C<max_outstanding> is mainly useful in simple scripts (with low values) or
		1270	as a stop gap to shield against fatal memory overflow (with large values).
270		1271
271	=back	1272	=back
272		1273
		1274	=head3 STATISTICAL INFORMATION
		1275
		1276	=over
		1277
		1278	=item IO::AIO::nreqs
		1279
		1280	Returns the number of requests currently in the ready, execute or pending
		1281	states (i.e. for which their callback has not been invoked yet).
		1282
		1283	Example: wait till there are no outstanding requests anymore:
		1284
		1285	IO::AIO::poll_wait, IO::AIO::poll_cb
		1286	while IO::AIO::nreqs;
		1287
		1288	=item IO::AIO::nready
		1289
		1290	Returns the number of requests currently in the ready state (not yet
		1291	executed).
		1292
		1293	=item IO::AIO::npending
		1294
		1295	Returns the number of requests currently in the pending state (executed,
		1296	but not yet processed by poll_cb).
		1297
		1298	=back
		1299
273	=cut	1300	=cut
274		1301
275	# support function to convert a fd into a perl filehandle
276	sub _fd2fh {
277	return undef if $_[0] < 0;
278
279	# try to be perl5.6-compatible
280	local *AIO_FH;
281	open AIO_FH, "+<&=$_[0]"
282	or return undef;
283
284	*AIO_FH
285	}
286
287	min_parallel 4;	1302	min_parallel 8;
288		1303
289	END {	1304	END { flush }
290	max_parallel 0;
291	}
292		1305
293	1;	1306	1;
294		1307
		1308	=head2 FORK BEHAVIOUR
		1309
		1310	This module should do "the right thing" when the process using it forks:
		1311
		1312	Before the fork, IO::AIO enters a quiescent state where no requests
		1313	can be added in other threads and no results will be processed. After
		1314	the fork the parent simply leaves the quiescent state and continues
		1315	request/result processing, while the child frees the request/result queue
		1316	(so that the requests started before the fork will only be handled in the
		1317	parent). Threads will be started on demand until the limit set in the
		1318	parent process has been reached again.
		1319
		1320	In short: the parent will, after a short pause, continue as if fork had
		1321	not been called, while the child will act as if IO::AIO has not been used
		1322	yet.
		1323
		1324	=head2 MEMORY USAGE
		1325
		1326	Per-request usage:
		1327
		1328	Each aio request uses - depending on your architecture - around 100-200
		1329	bytes of memory. In addition, stat requests need a stat buffer (possibly
		1330	a few hundred bytes), readdir requires a result buffer and so on. Perl
		1331	scalars and other data passed into aio requests will also be locked and
		1332	will consume memory till the request has entered the done state.
		1333
		1334	This is not awfully much, so queuing lots of requests is not usually a
		1335	problem.
		1336
		1337	Per-thread usage:
		1338
		1339	In the execution phase, some aio requests require more memory for
		1340	temporary buffers, and each thread requires a stack and other data
		1341	structures (usually around 16k-128k, depending on the OS).
		1342
		1343	=head1 KNOWN BUGS
		1344
		1345	Known bugs will be fixed in the next release.
		1346
295	=head1 SEE ALSO	1347	=head1 SEE ALSO
296		1348
297	L<Coro>, L<Linux::AIO>.	1349	L<AnyEvent::AIO> for easy integration into event loops, L<Coro::AIO> for a
		1350	more natural syntax.
298		1351
299	=head1 AUTHOR	1352	=head1 AUTHOR
300		1353
301	Marc Lehmann <schmorp@schmorp.de>	1354	Marc Lehmann <schmorp@schmorp.de>
302	http://home.schmorp.de/	1355	http://home.schmorp.de/

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