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Revision 1.16 by root, Mon Jul 11 03:10:08 2005 UTC vs.
Revision 1.119 by root, Sun Dec 2 20:54:33 2007 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, urxvt, pureperl...)
		32	open my $fh, "<&=" . IO::AIO::poll_fileno or die "$!";
		33	my $w = AnyEvent->io (fh => $fh, poll => 'r', cb => sub { IO::AIO::poll_cb });
		34
		35	# EV integration
		36	my $w = EV::io IO::AIO::poll_fileno, EV::READ, \&IO::AIO::poll_cb;
		37
		38	# Event integration
21	Event->io (fd => IO::AIO::poll_fileno,	39	Event->io (fd => IO::AIO::poll_fileno,
22	poll => 'r',	40	poll => 'r',
23	cb => \&IO::AIO::poll_cb);	41	cb => \&IO::AIO::poll_cb);
24		42
25	# Glib/Gtk2	43	# Glib/Gtk2 integration
26	add_watch Glib::IO IO::AIO::poll_fileno,	44	add_watch Glib::IO IO::AIO::poll_fileno,
27	in => sub { IO::AIO::poll_cb, 1 };	45	in => sub { IO::AIO::poll_cb; 1 };
28		46
29	# Tk	47	# Tk integration
30	Tk::Event::IO->fileevent (IO::AIO::poll_fileno, "",	48	Tk::Event::IO->fileevent (IO::AIO::poll_fileno, "",
31	readable => \&IO::AIO::poll_cb);	49	readable => \&IO::AIO::poll_cb);
32		50
33	# Danga::Socket	51	# Danga::Socket integration
34	Danga::Socket->AddOtherFds (IO::AIO::poll_fileno =>	52	Danga::Socket->AddOtherFds (IO::AIO::poll_fileno =>
35	\&IO::AIO::poll_cb);	53	\&IO::AIO::poll_cb);
36		54
37
38	=head1 DESCRIPTION	55	=head1 DESCRIPTION
39		56
40	This module implements asynchronous I/O using whatever means your	57	This module implements asynchronous I/O using whatever means your
41	operating system supports.	58	operating system supports.
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 very
		73	inefficient. Use an event loop for that (such as the L<Event|Event>
		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.	87	it is currently not reentrant in any way, so use appropriate locking
		88	yourself, always call C<poll_cb> from within the same thread, or never
		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 Event module and loads
		94	F</etc/passwd> asynchronously:
		95
		96	use Fcntl;
		97	use Event;
		98	use IO::AIO;
		99
		100	# register the IO::AIO callback with Event
		101	Event->io (fd => IO::AIO::poll_fileno,
		102	poll => 'r',
		103	cb => \&IO::AIO::poll_cb);
		104
		105	# queue the request to open /etc/passwd
		106	aio_open "/etc/passwd", O_RDONLY, 0, sub {
		107	my $fh = shift
		108	or die "error while opening: $!";
		109
		110	# stat'ing filehandles is generally non-blocking
		111	my $size = -s $fh;
		112
		113	# queue a request to read the file
		114	my $contents;
		115	aio_read $fh, 0, $size, $contents, 0, sub {
		116	$_[0] == $size
		117	or die "short read: $!";
		118
		119	close $fh;
		120
		121	# file contents now in $contents
		122	print $contents;
		123
		124	# exit event loop and program
		125	Event::unloop;
		126	};
		127	};
		128
		129	# possibly queue up other requests, or open GUI windows,
		130	# check for sockets etc. etc.
		131
		132	# process events as long as there are some:
		133	Event::loop;
		134
		135	=head1 REQUEST ANATOMY AND LIFETIME
		136
		137	Every C<aio_*> function creates a request. which is a C data structure not
		138	directly visible to Perl.
		139
		140	If called in non-void context, every request function returns a Perl
		141	object representing the request. In void context, nothing is returned,
		142	which saves a bit of memory.
		143
		144	The perl object is a fairly standard ref-to-hash object. The hash contents
		145	are not used by IO::AIO so you are free to store anything you like in it.
		146
		147	During their existance, aio requests travel through the following states,
		148	in order:
		149
		150	=over 4
		151
		152	=item ready
		153
		154	Immediately after a request is created it is put into the ready state,
		155	waiting for a thread to execute it.
		156
		157	=item execute
		158
		159	A thread has accepted the request for processing and is currently
		160	executing it (e.g. blocking in read).
		161
		162	=item pending
		163
		164	The request has been executed and is waiting for result processing.
		165
		166	While request submission and execution is fully asynchronous, result
		167	processing is not and relies on the perl interpreter calling C<poll_cb>
		168	(or another function with the same effect).
		169
		170	=item result
		171
		172	The request results are processed synchronously by C<poll_cb>.
		173
		174	The C<poll_cb> function will process all outstanding aio requests by
		175	calling their callbacks, freeing memory associated with them and managing
		176	any groups they are contained in.
		177
		178	=item done
		179
		180	Request has reached the end of its lifetime and holds no resources anymore
		181	(except possibly for the Perl object, but its connection to the actual
		182	aio request is severed and calling its methods will either do nothing or
		183	result in a runtime error).
		184
		185	=back
54		186
55	=cut	187	=cut
56		188
57	package IO::AIO;	189	package IO::AIO;
58		190
		191	use Carp ();
		192
		193	no warnings;
		194	use strict 'vars';
		195
59	use base 'Exporter';	196	use base 'Exporter';
60		197
61	use Fcntl ();
62
63	BEGIN {	198	BEGIN {
64	$VERSION = 0.3;	199	our $VERSION = '2.6';
65		200
66	@EXPORT = qw(aio_read aio_write aio_open aio_close aio_stat aio_lstat aio_unlink	201	our @AIO_REQ = qw(aio_sendfile aio_read aio_write aio_open aio_close aio_stat
67	aio_fsync aio_fdatasync aio_readahead);	202	aio_lstat aio_unlink aio_rmdir aio_readdir aio_scandir aio_symlink
68	@EXPORT_OK = qw(poll_fileno poll_cb min_parallel max_parallel max_outstanding nreqs);	203	aio_readlink aio_sync aio_fsync aio_fdatasync aio_readahead aio_rename aio_link
		204	aio_move aio_copy aio_group aio_nop aio_mknod aio_load aio_rmtree aio_mkdir
		205	aio_chown aio_chmod aio_utime aio_truncate);
		206	our @EXPORT = (@AIO_REQ, qw(aioreq_pri aioreq_nice aio_block));
		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
		212	@IO::AIO::GRP::ISA = 'IO::AIO::REQ';
69		213
70	require XSLoader;	214	require XSLoader;
71	XSLoader::load IO::AIO, $VERSION;	215	XSLoader::load ("IO::AIO", $VERSION);
72	}	216	}
73		217
74	=head1 FUNCTIONS	218	=head1 FUNCTIONS
75		219
76	=head2 AIO FUNCTIONS	220	=head2 AIO REQUEST FUNCTIONS
77		221
78	All the C<aio_*> calls are more or less thin wrappers around the syscall	222	All the C<aio_*> calls are more or less thin wrappers around the syscall
79	with the same name (sans C<aio_>). The arguments are similar or identical,	223	with the same name (sans C<aio_>). The arguments are similar or identical,
80	and they all accept an additional (and optional) C<$callback> argument	224	and they all accept an additional (and optional) C<$callback> argument
81	which must be a code reference. This code reference will get called with	225	which must be a code reference. This code reference will get called with
82	the syscall return code (e.g. most syscalls return C<-1> on error, unlike	226	the syscall return code (e.g. most syscalls return C<-1> on error, unlike
83	perl, which usually delivers "false") as it's sole argument when the given	227	perl, which usually delivers "false") as it's sole argument when the given
84	syscall has been executed asynchronously.	228	syscall has been executed asynchronously.
85		229
86	All functions that expect a filehandle will also accept a file descriptor.	230	All functions expecting a filehandle keep a copy of the filehandle
		231	internally until the request has finished.
87		232
		233	All functions return request objects of type L<IO::AIO::REQ> that allow
		234	further manipulation of those requests while they are in-flight.
		235
88	The filenames you pass to these routines I<must> be absolute. The reason	236	The pathnames you pass to these routines I<must> be absolute and
89	is that at the time the request is being executed, the current working	237	encoded as octets. The reason for the former is that at the time the
90	directory could have changed. Alternatively, you can make sure that you	238	request is being executed, the current working directory could have
91	never change the current working directory.	239	changed. Alternatively, you can make sure that you never change the
		240	current working directory anywhere in the program and then use relative
		241	paths.
		242
		243	To encode pathnames as octets, either make sure you either: a) always pass
		244	in filenames you got from outside (command line, readdir etc.) without
		245	tinkering, b) are ASCII or ISO 8859-1, c) use the Encode module and encode
		246	your pathnames to the locale (or other) encoding in effect in the user
		247	environment, d) use Glib::filename_from_unicode on unicode filenames or e)
		248	use something else to ensure your scalar has the correct contents.
		249
		250	This works, btw. independent of the internal UTF-8 bit, which IO::AIO
		251	handles correctly wether it is set or not.
92		252
93	=over 4	253	=over 4
94		254
		255	=item $prev_pri = aioreq_pri [$pri]
		256
		257	Returns the priority value that would be used for the next request and, if
		258	C<$pri> is given, sets the priority for the next aio request.
		259
		260	The default priority is C<0>, the minimum and maximum priorities are C<-4>
		261	and C<4>, respectively. Requests with higher priority will be serviced
		262	first.
		263
		264	The priority will be reset to C<0> after each call to one of the C<aio_*>
		265	functions.
		266
		267	Example: open a file with low priority, then read something from it with
		268	higher priority so the read request is serviced before other low priority
		269	open requests (potentially spamming the cache):
		270
		271	aioreq_pri -3;
		272	aio_open ..., sub {
		273	return unless $_[0];
		274
		275	aioreq_pri -2;
		276	aio_read $_[0], ..., sub {
		277	...
		278	};
		279	};
		280
		281
		282	=item aioreq_nice $pri_adjust
		283
		284	Similar to C<aioreq_pri>, but subtracts the given value from the current
		285	priority, so the effect is cumulative.
		286
		287
95	=item aio_open $pathname, $flags, $mode, $callback	288	=item aio_open $pathname, $flags, $mode, $callback->($fh)
96		289
97	Asynchronously open or create a file and call the callback with a newly	290	Asynchronously open or create a file and call the callback with a newly
98	created filehandle for the file.	291	created filehandle for the file.
99		292
100	The pathname passed to C<aio_open> must be absolute. See API NOTES, above,	293	The pathname passed to C<aio_open> must be absolute. See API NOTES, above,
101	for an explanation.	294	for an explanation.
102		295
103	The C<$mode> argument is a bitmask. See the C<Fcntl> module for a	296	The C<$flags> argument is a bitmask. See the C<Fcntl> module for a
104	list. They are the same as used in C<sysopen>.	297	list. They are the same as used by C<sysopen>.
		298
		299	Likewise, C<$mode> specifies the mode of the newly created file, if it
		300	didn't exist and C<O_CREAT> has been given, just like perl's C<sysopen>,
		301	except that it is mandatory (i.e. use C<0> if you don't create new files,
		302	and C<0666> or C<0777> if you do). Note that the C<$mode> will be modified
		303	by the umask in effect then the request is being executed, so better never
		304	change the umask.
105		305
106	Example:	306	Example:
107		307
108	aio_open "/etc/passwd", O_RDONLY, 0, sub {	308	aio_open "/etc/passwd", O_RDONLY, 0, sub {
109	if ($_[0]) {	309	if ($_[0]) {
…		…
112	} else {	312	} else {
113	die "open failed: $!\n";	313	die "open failed: $!\n";
114	}	314	}
115	};	315	};
116		316
		317
117	=item aio_close $fh, $callback	318	=item aio_close $fh, $callback->($status)
118		319
119	Asynchronously close a file and call the callback with the result	320	Asynchronously close a file and call the callback with the result
120	code. I<WARNING:> although accepted, you should not pass in a perl	321	code.
121	filehandle here, as perl will likely close the file descriptor itself when
122	the filehandle is destroyed. Normally, you can safely call perls C<close>
123	or just let filehandles go out of scope.
124		322
		323	Unfortunately, you can't do this to perl. Perl I<insists> very strongly on
		324	closing the file descriptor associated with the filehandle itself. Here is
		325	what aio_close will try:
		326
		327	1. dup()licate the fd
		328	2. asynchronously close() the duplicated fd
		329	3. dup()licate the fd once more
		330	4. let perl close() the filehandle
		331	5. asynchronously close the duplicated fd
		332
		333	The idea is that the first close() flushes stuff to disk that closing an
		334	fd will flush, so when perl closes the fd, nothing much will need to be
		335	flushed. The second async. close() will then flush stuff to disk that
		336	closing the last fd to the file will flush.
		337
		338	Just FYI, SuSv3 has this to say on close:
		339
		340	All outstanding record locks owned by the process on the file
		341	associated with the file descriptor shall be removed.
		342
		343	If fildes refers to a socket, close() shall cause the socket to be
		344	destroyed. ... close() shall block for up to the current linger
		345	interval until all data is transmitted.
		346	[this actually sounds like a specification bug, but who knows]
		347
		348	And at least Linux additionally actually flushes stuff on every close,
		349	even when the file itself is still open.
		350
		351	Sounds enourmously inefficient and complicated? Yes... please show me how
		352	to nuke perl's fd out of existence...
		353
		354	=cut
		355
		356	sub aio_close($;$) {
		357	aio_block {
		358	my ($fh, $cb) = @_;
		359
		360	my $pri = aioreq_pri;
		361	my $grp = aio_group $cb;
		362
		363	my $fd = fileno $fh;
		364
		365	defined $fd or Carp::croak "aio_close called with fd-less filehandle";
		366
		367	# if the dups fail we will simply get EBADF
		368	my $fd2 = _dup $fd;
		369	aioreq_pri $pri;
		370	add $grp _aio_close $fd2, sub {
		371	my $fd2 = _dup $fd;
		372	close $fh;
		373	aioreq_pri $pri;
		374	add $grp _aio_close $fd2, sub {
		375	$grp->result ($_[0]);
		376	};
		377	};
		378
		379	$grp
		380	}
		381	}
		382
		383
125	=item aio_read $fh,$offset,$length, $data,$dataoffset,$callback	384	=item aio_read $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
126		385
127	=item aio_write $fh,$offset,$length, $data,$dataoffset,$callback	386	=item aio_write $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
128		387
129	Reads or writes C<length> bytes from the specified C<fh> and C<offset>	388	Reads or writes C<$length> bytes from the specified C<$fh> and C<$offset>
130	into the scalar given by C<data> and offset C<dataoffset> and calls the	389	into the scalar given by C<$data> and offset C<$dataoffset> and calls the
131	callback without the actual number of bytes read (or -1 on error, just	390	callback without the actual number of bytes read (or -1 on error, just
132	like the syscall).	391	like the syscall).
133		392
		393	If C<$offset> is undefined, then the current file descriptor offset will
		394	be used (and updated), otherwise the file descriptor offset will not be
		395	changed by these calls.
		396
		397	If C<$length> is undefined in C<aio_write>, use the remaining length of C<$data>.
		398
		399	If C<$dataoffset> is less than zero, it will be counted from the end of
		400	C<$data>.
		401
		402	The C<$data> scalar I<MUST NOT> be modified in any way while the request
		403	is outstanding. Modifying it can result in segfaults or World War III (if
		404	the necessary/optional hardware is installed).
		405
134	Example: Read 15 bytes at offset 7 into scalar C<$buffer>, strating at	406	Example: Read 15 bytes at offset 7 into scalar C<$buffer>, starting at
135	offset C<0> within the scalar:	407	offset C<0> within the scalar:
136		408
137	aio_read $fh, 7, 15, $buffer, 0, sub {	409	aio_read $fh, 7, 15, $buffer, 0, sub {
138	$_[0] > 0 or die "read error: $!";	410	$_[0] > 0 or die "read error: $!";
139	print "read $_[0] bytes: <$buffer>\n";	411	print "read $_[0] bytes: <$buffer>\n";
140	};	412	};
141		413
		414
		415	=item aio_sendfile $out_fh, $in_fh, $in_offset, $length, $callback->($retval)
		416
		417	Tries to copy C<$length> bytes from C<$in_fh> to C<$out_fh>. It starts
		418	reading at byte offset C<$in_offset>, and starts writing at the current
		419	file offset of C<$out_fh>. Because of that, it is not safe to issue more
		420	than one C<aio_sendfile> per C<$out_fh>, as they will interfere with each
		421	other.
		422
		423	This call tries to make use of a native C<sendfile> syscall to provide
		424	zero-copy operation. For this to work, C<$out_fh> should refer to a
		425	socket, and C<$in_fh> should refer to mmap'able file.
		426
		427	If the native sendfile call fails or is not implemented, it will be
		428	emulated, so you can call C<aio_sendfile> on any type of filehandle
		429	regardless of the limitations of the operating system.
		430
		431	Please note, however, that C<aio_sendfile> can read more bytes from
		432	C<$in_fh> than are written, and there is no way to find out how many
		433	bytes have been read from C<aio_sendfile> alone, as C<aio_sendfile> only
		434	provides the number of bytes written to C<$out_fh>. Only if the result
		435	value equals C<$length> one can assume that C<$length> bytes have been
		436	read.
		437
		438
142	=item aio_readahead $fh,$offset,$length, $callback	439	=item aio_readahead $fh,$offset,$length, $callback->($retval)
143		440
144	Asynchronously reads the specified byte range into the page cache, using
145	the C<readahead> syscall. If that syscall doesn't exist the status will be
146	C<-1> and C<$!> is set to ENOSYS.
147
148	readahead() populates the page cache with data from a file so that	441	C<aio_readahead> populates the page cache with data from a file so that
149	subsequent reads from that file will not block on disk I/O. The C<$offset>	442	subsequent reads from that file will not block on disk I/O. The C<$offset>
150	argument specifies the starting point from which data is to be read and	443	argument specifies the starting point from which data is to be read and
151	C<$length> specifies the number of bytes to be read. I/O is performed in	444	C<$length> specifies the number of bytes to be read. I/O is performed in
152	whole pages, so that offset is effectively rounded down to a page boundary	445	whole pages, so that offset is effectively rounded down to a page boundary
153	and bytes are read up to the next page boundary greater than or equal to	446	and bytes are read up to the next page boundary greater than or equal to
154	(off-set+length). aio_readahead() does not read beyond the end of the	447	(off-set+length). C<aio_readahead> does not read beyond the end of the
155	file. The current file offset of the file is left unchanged.	448	file. The current file offset of the file is left unchanged.
156		449
		450	If that syscall doesn't exist (likely if your OS isn't Linux) it will be
		451	emulated by simply reading the data, which would have a similar effect.
		452
		453
157	=item aio_stat $fh_or_path, $callback	454	=item aio_stat $fh_or_path, $callback->($status)
158		455
159	=item aio_lstat $fh, $callback	456	=item aio_lstat $fh, $callback->($status)
160		457
161	Works like perl's C<stat> or C<lstat> in void context. The callback will	458	Works like perl's C<stat> or C<lstat> in void context. The callback will
162	be called after the stat and the results will be available using C<stat _>	459	be called after the stat and the results will be available using C<stat _>
163	or C<-s _> etc...	460	or C<-s _> etc...
164		461
…		…
174	aio_stat "/etc/passwd", sub {	471	aio_stat "/etc/passwd", sub {
175	$_[0] and die "stat failed: $!";	472	$_[0] and die "stat failed: $!";
176	print "size is ", -s _, "\n";	473	print "size is ", -s _, "\n";
177	};	474	};
178		475
		476
		477	=item aio_utime $fh_or_path, $atime, $mtime, $callback->($status)
		478
		479	Works like perl's C<utime> function (including the special case of $atime
		480	and $mtime being undef). Fractional times are supported if the underlying
		481	syscalls support them.
		482
		483	When called with a pathname, uses utimes(2) if available, otherwise
		484	utime(2). If called on a file descriptor, uses futimes(2) if available,
		485	otherwise returns ENOSYS, so this is not portable.
		486
		487	Examples:
		488
		489	# set atime and mtime to current time (basically touch(1)):
		490	aio_utime "path", undef, undef;
		491	# set atime to current time and mtime to beginning of the epoch:
		492	aio_utime "path", time, undef; # undef==0
		493
		494
		495	=item aio_chown $fh_or_path, $uid, $gid, $callback->($status)
		496
		497	Works like perl's C<chown> function, except that C<undef> for either $uid
		498	or $gid is being interpreted as "do not change" (but -1 can also be used).
		499
		500	Examples:
		501
		502	# same as "chown root path" in the shell:
		503	aio_chown "path", 0, -1;
		504	# same as above:
		505	aio_chown "path", 0, undef;
		506
		507
		508	=item aio_truncate $fh_or_path, $offset, $callback->($status)
		509
		510	Works like truncate(2) or ftruncate(2).
		511
		512
		513	=item aio_chmod $fh_or_path, $mode, $callback->($status)
		514
		515	Works like perl's C<chmod> function.
		516
		517
179	=item aio_unlink $pathname, $callback	518	=item aio_unlink $pathname, $callback->($status)
180		519
181	Asynchronously unlink (delete) a file and call the callback with the	520	Asynchronously unlink (delete) a file and call the callback with the
182	result code.	521	result code.
183		522
		523
		524	=item aio_mknod $path, $mode, $dev, $callback->($status)
		525
		526	[EXPERIMENTAL]
		527
		528	Asynchronously create a device node (or fifo). See mknod(2).
		529
		530	The only (POSIX-) portable way of calling this function is:
		531
		532	aio_mknod $path, IO::AIO::S_IFIFO | $mode, 0, sub { ...
		533
		534
		535	=item aio_link $srcpath, $dstpath, $callback->($status)
		536
		537	Asynchronously create a new link to the existing object at C<$srcpath> at
		538	the path C<$dstpath> and call the callback with the result code.
		539
		540
		541	=item aio_symlink $srcpath, $dstpath, $callback->($status)
		542
		543	Asynchronously create a new symbolic link to the existing object at C<$srcpath> at
		544	the path C<$dstpath> and call the callback with the result code.
		545
		546
		547	=item aio_readlink $path, $callback->($link)
		548
		549	Asynchronously read the symlink specified by C<$path> and pass it to
		550	the callback. If an error occurs, nothing or undef gets passed to the
		551	callback.
		552
		553
		554	=item aio_rename $srcpath, $dstpath, $callback->($status)
		555
		556	Asynchronously rename the object at C<$srcpath> to C<$dstpath>, just as
		557	rename(2) and call the callback with the result code.
		558
		559
		560	=item aio_mkdir $pathname, $mode, $callback->($status)
		561
		562	Asynchronously mkdir (create) a directory and call the callback with
		563	the result code. C<$mode> will be modified by the umask at the time the
		564	request is executed, so do not change your umask.
		565
		566
		567	=item aio_rmdir $pathname, $callback->($status)
		568
		569	Asynchronously rmdir (delete) a directory and call the callback with the
		570	result code.
		571
		572
		573	=item aio_readdir $pathname, $callback->($entries)
		574
		575	Unlike the POSIX call of the same name, C<aio_readdir> reads an entire
		576	directory (i.e. opendir + readdir + closedir). The entries will not be
		577	sorted, and will B<NOT> include the C<.> and C<..> entries.
		578
		579	The callback a single argument which is either C<undef> or an array-ref
		580	with the filenames.
		581
		582
		583	=item aio_load $path, $data, $callback->($status)
		584
		585	This is a composite request that tries to fully load the given file into
		586	memory. Status is the same as with aio_read.
		587
		588	=cut
		589
		590	sub aio_load($$;$) {
		591	aio_block {
		592	my ($path, undef, $cb) = @_;
		593	my $data = \$_[1];
		594
		595	my $pri = aioreq_pri;
		596	my $grp = aio_group $cb;
		597
		598	aioreq_pri $pri;
		599	add $grp aio_open $path, O_RDONLY, 0, sub {
		600	my $fh = shift
		601	or return $grp->result (-1);
		602
		603	aioreq_pri $pri;
		604	add $grp aio_read $fh, 0, (-s $fh), $$data, 0, sub {
		605	$grp->result ($_[0]);
		606	};
		607	};
		608
		609	$grp
		610	}
		611	}
		612
		613	=item aio_copy $srcpath, $dstpath, $callback->($status)
		614
		615	Try to copy the I<file> (directories not supported as either source or
		616	destination) from C<$srcpath> to C<$dstpath> and call the callback with
		617	the C<0> (error) or C<-1> ok.
		618
		619	This is a composite request that it creates the destination file with
		620	mode 0200 and copies the contents of the source file into it using
		621	C<aio_sendfile>, followed by restoring atime, mtime, access mode and
		622	uid/gid, in that order.
		623
		624	If an error occurs, the partial destination file will be unlinked, if
		625	possible, except when setting atime, mtime, access mode and uid/gid, where
		626	errors are being ignored.
		627
		628	=cut
		629
		630	sub aio_copy($$;$) {
		631	aio_block {
		632	my ($src, $dst, $cb) = @_;
		633
		634	my $pri = aioreq_pri;
		635	my $grp = aio_group $cb;
		636
		637	aioreq_pri $pri;
		638	add $grp aio_open $src, O_RDONLY, 0, sub {
		639	if (my $src_fh = $_[0]) {
		640	my @stat = stat $src_fh;
		641
		642	aioreq_pri $pri;
		643	add $grp aio_open $dst, O_CREAT | O_WRONLY | O_TRUNC, 0200, sub {
		644	if (my $dst_fh = $_[0]) {
		645	aioreq_pri $pri;
		646	add $grp aio_sendfile $dst_fh, $src_fh, 0, $stat[7], sub {
		647	if ($_[0] == $stat[7]) {
		648	$grp->result (0);
		649	close $src_fh;
		650
		651	# those should not normally block. should. should.
		652	utime $stat[8], $stat[9], $dst;
		653	chmod $stat[2] & 07777, $dst_fh;
		654	chown $stat[4], $stat[5], $dst_fh;
		655	close $dst_fh;
		656	} else {
		657	$grp->result (-1);
		658	close $src_fh;
		659	close $dst_fh;
		660
		661	aioreq $pri;
		662	add $grp aio_unlink $dst;
		663	}
		664	};
		665	} else {
		666	$grp->result (-1);
		667	}
		668	},
		669
		670	} else {
		671	$grp->result (-1);
		672	}
		673	};
		674
		675	$grp
		676	}
		677	}
		678
		679	=item aio_move $srcpath, $dstpath, $callback->($status)
		680
		681	Try to move the I<file> (directories not supported as either source or
		682	destination) from C<$srcpath> to C<$dstpath> and call the callback with
		683	the C<0> (error) or C<-1> ok.
		684
		685	This is a composite request that tries to rename(2) the file first. If
		686	rename files with C<EXDEV>, it copies the file with C<aio_copy> and, if
		687	that is successful, unlinking the C<$srcpath>.
		688
		689	=cut
		690
		691	sub aio_move($$;$) {
		692	aio_block {
		693	my ($src, $dst, $cb) = @_;
		694
		695	my $pri = aioreq_pri;
		696	my $grp = aio_group $cb;
		697
		698	aioreq_pri $pri;
		699	add $grp aio_rename $src, $dst, sub {
		700	if ($_[0] && $! == EXDEV) {
		701	aioreq_pri $pri;
		702	add $grp aio_copy $src, $dst, sub {
		703	$grp->result ($_[0]);
		704
		705	if (!$_[0]) {
		706	aioreq_pri $pri;
		707	add $grp aio_unlink $src;
		708	}
		709	};
		710	} else {
		711	$grp->result ($_[0]);
		712	}
		713	};
		714
		715	$grp
		716	}
		717	}
		718
		719	=item aio_scandir $path, $maxreq, $callback->($dirs, $nondirs)
		720
		721	Scans a directory (similar to C<aio_readdir>) but additionally tries to
		722	efficiently separate the entries of directory C<$path> into two sets of
		723	names, directories you can recurse into (directories), and ones you cannot
		724	recurse into (everything else, including symlinks to directories).
		725
		726	C<aio_scandir> is a composite request that creates of many sub requests_
		727	C<$maxreq> specifies the maximum number of outstanding aio requests that
		728	this function generates. If it is C<< <= 0 >>, then a suitable default
		729	will be chosen (currently 4).
		730
		731	On error, the callback is called without arguments, otherwise it receives
		732	two array-refs with path-relative entry names.
		733
		734	Example:
		735
		736	aio_scandir $dir, 0, sub {
		737	my ($dirs, $nondirs) = @_;
		738	print "real directories: @$dirs\n";
		739	print "everything else: @$nondirs\n";
		740	};
		741
		742	Implementation notes.
		743
		744	The C<aio_readdir> cannot be avoided, but C<stat()>'ing every entry can.
		745
		746	After reading the directory, the modification time, size etc. of the
		747	directory before and after the readdir is checked, and if they match (and
		748	isn't the current time), the link count will be used to decide how many
		749	entries are directories (if >= 2). Otherwise, no knowledge of the number
		750	of subdirectories will be assumed.
		751
		752	Then entries will be sorted into likely directories (everything without
		753	a non-initial dot currently) and likely non-directories (everything
		754	else). Then every entry plus an appended C</.> will be C<stat>'ed,
		755	likely directories first. If that succeeds, it assumes that the entry
		756	is a directory or a symlink to directory (which will be checked
		757	seperately). This is often faster than stat'ing the entry itself because
		758	filesystems might detect the type of the entry without reading the inode
		759	data (e.g. ext2fs filetype feature).
		760
		761	If the known number of directories (link count - 2) has been reached, the
		762	rest of the entries is assumed to be non-directories.
		763
		764	This only works with certainty on POSIX (= UNIX) filesystems, which
		765	fortunately are the vast majority of filesystems around.
		766
		767	It will also likely work on non-POSIX filesystems with reduced efficiency
		768	as those tend to return 0 or 1 as link counts, which disables the
		769	directory counting heuristic.
		770
		771	=cut
		772
		773	sub aio_scandir($$;$) {
		774	aio_block {
		775	my ($path, $maxreq, $cb) = @_;
		776
		777	my $pri = aioreq_pri;
		778
		779	my $grp = aio_group $cb;
		780
		781	$maxreq = 4 if $maxreq <= 0;
		782
		783	# stat once
		784	aioreq_pri $pri;
		785	add $grp aio_stat $path, sub {
		786	return $grp->result () if $_[0];
		787	my $now = time;
		788	my $hash1 = join ":", (stat _)[0,1,3,7,9];
		789
		790	# read the directory entries
		791	aioreq_pri $pri;
		792	add $grp aio_readdir $path, sub {
		793	my $entries = shift
		794	or return $grp->result ();
		795
		796	# stat the dir another time
		797	aioreq_pri $pri;
		798	add $grp aio_stat $path, sub {
		799	my $hash2 = join ":", (stat _)[0,1,3,7,9];
		800
		801	my $ndirs;
		802
		803	# take the slow route if anything looks fishy
		804	if ($hash1 ne $hash2 or (stat _)[9] == $now) {
		805	$ndirs = -1;
		806	} else {
		807	# if nlink == 2, we are finished
		808	# on non-posix-fs's, we rely on nlink < 2
		809	$ndirs = (stat _)[3] - 2
		810	or return $grp->result ([], $entries);
		811	}
		812
		813	# sort into likely dirs and likely nondirs
		814	# dirs == files without ".", short entries first
		815	$entries = [map $_->[0],
		816	sort { $b->[1] cmp $a->[1] }
		817	map [$_, sprintf "%s%04d", (/.\./ ? "1" : "0"), length],
		818	@$entries];
		819
		820	my (@dirs, @nondirs);
		821
		822	my $statgrp = add $grp aio_group sub {
		823	$grp->result (\@dirs, \@nondirs);
		824	};
		825
		826	limit $statgrp $maxreq;
		827	feed $statgrp sub {
		828	return unless @$entries;
		829	my $entry = pop @$entries;
		830
		831	aioreq_pri $pri;
		832	add $statgrp aio_stat "$path/$entry/.", sub {
		833	if ($_[0] < 0) {
		834	push @nondirs, $entry;
		835	} else {
		836	# need to check for real directory
		837	aioreq_pri $pri;
		838	add $statgrp aio_lstat "$path/$entry", sub {
		839	if (-d _) {
		840	push @dirs, $entry;
		841
		842	unless (--$ndirs) {
		843	push @nondirs, @$entries;
		844	feed $statgrp;
		845	}
		846	} else {
		847	push @nondirs, $entry;
		848	}
		849	}
		850	}
		851	};
		852	};
		853	};
		854	};
		855	};
		856
		857	$grp
		858	}
		859	}
		860
		861	=item aio_rmtree $path, $callback->($status)
		862
		863	Delete a directory tree starting (and including) C<$path>, return the
		864	status of the final C<rmdir> only. This is a composite request that
		865	uses C<aio_scandir> to recurse into and rmdir directories, and unlink
		866	everything else.
		867
		868	=cut
		869
		870	sub aio_rmtree;
		871	sub aio_rmtree($;$) {
		872	aio_block {
		873	my ($path, $cb) = @_;
		874
		875	my $pri = aioreq_pri;
		876	my $grp = aio_group $cb;
		877
		878	aioreq_pri $pri;
		879	add $grp aio_scandir $path, 0, sub {
		880	my ($dirs, $nondirs) = @_;
		881
		882	my $dirgrp = aio_group sub {
		883	add $grp aio_rmdir $path, sub {
		884	$grp->result ($_[0]);
		885	};
		886	};
		887
		888	(aioreq_pri $pri), add $dirgrp aio_rmtree "$path/$_" for @$dirs;
		889	(aioreq_pri $pri), add $dirgrp aio_unlink "$path/$_" for @$nondirs;
		890
		891	add $grp $dirgrp;
		892	};
		893
		894	$grp
		895	}
		896	}
		897
		898	=item aio_sync $callback->($status)
		899
		900	Asynchronously call sync and call the callback when finished.
		901
184	=item aio_fsync $fh, $callback	902	=item aio_fsync $fh, $callback->($status)
185		903
186	Asynchronously call fsync on the given filehandle and call the callback	904	Asynchronously call fsync on the given filehandle and call the callback
187	with the fsync result code.	905	with the fsync result code.
188		906
189	=item aio_fdatasync $fh, $callback	907	=item aio_fdatasync $fh, $callback->($status)
190		908
191	Asynchronously call fdatasync on the given filehandle and call the	909	Asynchronously call fdatasync on the given filehandle and call the
192	callback with the fdatasync result code.	910	callback with the fdatasync result code.
193		911
		912	If this call isn't available because your OS lacks it or it couldn't be
		913	detected, it will be emulated by calling C<fsync> instead.
		914
		915	=item aio_group $callback->(...)
		916
		917	This is a very special aio request: Instead of doing something, it is a
		918	container for other aio requests, which is useful if you want to bundle
		919	many requests into a single, composite, request with a definite callback
		920	and the ability to cancel the whole request with its subrequests.
		921
		922	Returns an object of class L<IO::AIO::GRP>. See its documentation below
		923	for more info.
		924
		925	Example:
		926
		927	my $grp = aio_group sub {
		928	print "all stats done\n";
		929	};
		930
		931	add $grp
		932	(aio_stat ...),
		933	(aio_stat ...),
		934	...;
		935
		936	=item aio_nop $callback->()
		937
		938	This is a special request - it does nothing in itself and is only used for
		939	side effects, such as when you want to add a dummy request to a group so
		940	that finishing the requests in the group depends on executing the given
		941	code.
		942
		943	While this request does nothing, it still goes through the execution
		944	phase and still requires a worker thread. Thus, the callback will not
		945	be executed immediately but only after other requests in the queue have
		946	entered their execution phase. This can be used to measure request
		947	latency.
		948
		949	=item IO::AIO::aio_busy $fractional_seconds, $callback->() *NOT EXPORTED*
		950
		951	Mainly used for debugging and benchmarking, this aio request puts one of
		952	the request workers to sleep for the given time.
		953
		954	While it is theoretically handy to have simple I/O scheduling requests
		955	like sleep and file handle readable/writable, the overhead this creates is
		956	immense (it blocks a thread for a long time) so do not use this function
		957	except to put your application under artificial I/O pressure.
		958
194	=back	959	=back
195		960
		961	=head2 IO::AIO::REQ CLASS
		962
		963	All non-aggregate C<aio_*> functions return an object of this class when
		964	called in non-void context.
		965
		966	=over 4
		967
		968	=item cancel $req
		969
		970	Cancels the request, if possible. Has the effect of skipping execution
		971	when entering the B<execute> state and skipping calling the callback when
		972	entering the the B<result> state, but will leave the request otherwise
		973	untouched. That means that requests that currently execute will not be
		974	stopped and resources held by the request will not be freed prematurely.
		975
		976	=item cb $req $callback->(...)
		977
		978	Replace (or simply set) the callback registered to the request.
		979
		980	=back
		981
		982	=head2 IO::AIO::GRP CLASS
		983
		984	This class is a subclass of L<IO::AIO::REQ>, so all its methods apply to
		985	objects of this class, too.
		986
		987	A IO::AIO::GRP object is a special request that can contain multiple other
		988	aio requests.
		989
		990	You create one by calling the C<aio_group> constructing function with a
		991	callback that will be called when all contained requests have entered the
		992	C<done> state:
		993
		994	my $grp = aio_group sub {
		995	print "all requests are done\n";
		996	};
		997
		998	You add requests by calling the C<add> method with one or more
		999	C<IO::AIO::REQ> objects:
		1000
		1001	$grp->add (aio_unlink "...");
		1002
		1003	add $grp aio_stat "...", sub {
		1004	$_[0] or return $grp->result ("error");
		1005
		1006	# add another request dynamically, if first succeeded
		1007	add $grp aio_open "...", sub {
		1008	$grp->result ("ok");
		1009	};
		1010	};
		1011
		1012	This makes it very easy to create composite requests (see the source of
		1013	C<aio_move> for an application) that work and feel like simple requests.
		1014
		1015	=over 4
		1016
		1017	=item * The IO::AIO::GRP objects will be cleaned up during calls to
		1018	C<IO::AIO::poll_cb>, just like any other request.
		1019
		1020	=item * They can be canceled like any other request. Canceling will cancel not
		1021	only the request itself, but also all requests it contains.
		1022
		1023	=item * They can also can also be added to other IO::AIO::GRP objects.
		1024
		1025	=item * You must not add requests to a group from within the group callback (or
		1026	any later time).
		1027
		1028	=back
		1029
		1030	Their lifetime, simplified, looks like this: when they are empty, they
		1031	will finish very quickly. If they contain only requests that are in the
		1032	C<done> state, they will also finish. Otherwise they will continue to
		1033	exist.
		1034
		1035	That means after creating a group you have some time to add requests. And
		1036	in the callbacks of those requests, you can add further requests to the
		1037	group. And only when all those requests have finished will the the group
		1038	itself finish.
		1039
		1040	=over 4
		1041
		1042	=item add $grp ...
		1043
		1044	=item $grp->add (...)
		1045
		1046	Add one or more requests to the group. Any type of L<IO::AIO::REQ> can
		1047	be added, including other groups, as long as you do not create circular
		1048	dependencies.
		1049
		1050	Returns all its arguments.
		1051
		1052	=item $grp->cancel_subs
		1053
		1054	Cancel all subrequests and clears any feeder, but not the group request
		1055	itself. Useful when you queued a lot of events but got a result early.
		1056
		1057	=item $grp->result (...)
		1058
		1059	Set the result value(s) that will be passed to the group callback when all
		1060	subrequests have finished and set thre groups errno to the current value
		1061	of errno (just like calling C<errno> without an error number). By default,
		1062	no argument will be passed and errno is zero.
		1063
		1064	=item $grp->errno ([$errno])
		1065
		1066	Sets the group errno value to C<$errno>, or the current value of errno
		1067	when the argument is missing.
		1068
		1069	Every aio request has an associated errno value that is restored when
		1070	the callback is invoked. This method lets you change this value from its
		1071	default (0).
		1072
		1073	Calling C<result> will also set errno, so make sure you either set C<$!>
		1074	before the call to C<result>, or call c<errno> after it.
		1075
		1076	=item feed $grp $callback->($grp)
		1077
		1078	Sets a feeder/generator on this group: every group can have an attached
		1079	generator that generates requests if idle. The idea behind this is that,
		1080	although you could just queue as many requests as you want in a group,
		1081	this might starve other requests for a potentially long time. For
		1082	example, C<aio_scandir> might generate hundreds of thousands C<aio_stat>
		1083	requests, delaying any later requests for a long time.
		1084
		1085	To avoid this, and allow incremental generation of requests, you can
		1086	instead a group and set a feeder on it that generates those requests. The
		1087	feed callback will be called whenever there are few enough (see C<limit>,
		1088	below) requests active in the group itself and is expected to queue more
		1089	requests.
		1090
		1091	The feed callback can queue as many requests as it likes (i.e. C<add> does
		1092	not impose any limits).
		1093
		1094	If the feed does not queue more requests when called, it will be
		1095	automatically removed from the group.
		1096
		1097	If the feed limit is C<0>, it will be set to C<2> automatically.
		1098
		1099	Example:
		1100
		1101	# stat all files in @files, but only ever use four aio requests concurrently:
		1102
		1103	my $grp = aio_group sub { print "finished\n" };
		1104	limit $grp 4;
		1105	feed $grp sub {
		1106	my $file = pop @files
		1107	or return;
		1108
		1109	add $grp aio_stat $file, sub { ... };
		1110	};
		1111
		1112	=item limit $grp $num
		1113
		1114	Sets the feeder limit for the group: The feeder will be called whenever
		1115	the group contains less than this many requests.
		1116
		1117	Setting the limit to C<0> will pause the feeding process.
		1118
		1119	=back
		1120
196	=head2 SUPPORT FUNCTIONS	1121	=head2 SUPPORT FUNCTIONS
197		1122
		1123	=head3 EVENT PROCESSING AND EVENT LOOP INTEGRATION
		1124
198	=over 4	1125	=over 4
199		1126
200	=item $fileno = IO::AIO::poll_fileno	1127	=item $fileno = IO::AIO::poll_fileno
201		1128
202	Return the I<request result pipe filehandle>. This filehandle must be	1129	Return the I<request result pipe file descriptor>. This filehandle must be
203	polled for reading by some mechanism outside this module (e.g. Event	1130	polled for reading by some mechanism outside this module (e.g. Event or
204	or select, see below). If the pipe becomes readable you have to call	1131	select, see below or the SYNOPSIS). If the pipe becomes readable you have
205	C<poll_cb> to check the results.	1132	to call C<poll_cb> to check the results.
206		1133
207	See C<poll_cb> for an example.	1134	See C<poll_cb> for an example.
208		1135
209	=item IO::AIO::poll_cb	1136	=item IO::AIO::poll_cb
210		1137
211	Process all outstanding events on the result pipe. You have to call this	1138	Process some outstanding events on the result pipe. You have to call this
212	regularly. Returns the number of events processed. Returns immediately	1139	regularly. Returns the number of events processed. Returns immediately
213	when no events are outstanding.	1140	when no events are outstanding. The amount of events processed depends on
		1141	the settings of C<IO::AIO::max_poll_req> and C<IO::AIO::max_poll_time>.
214		1142
215	You can use Event to multiplex, e.g.:	1143	If not all requests were processed for whatever reason, the filehandle
		1144	will still be ready when C<poll_cb> returns.
		1145
		1146	Example: Install an Event watcher that automatically calls
		1147	IO::AIO::poll_cb with high priority:
216		1148
217	Event->io (fd => IO::AIO::poll_fileno,	1149	Event->io (fd => IO::AIO::poll_fileno,
218	poll => 'r', async => 1,	1150	poll => 'r', async => 1,
219	cb => \&IO::AIO::poll_cb);	1151	cb => \&IO::AIO::poll_cb);
220		1152
		1153	=item IO::AIO::max_poll_reqs $nreqs
		1154
		1155	=item IO::AIO::max_poll_time $seconds
		1156
		1157	These set the maximum number of requests (default C<0>, meaning infinity)
		1158	that are being processed by C<IO::AIO::poll_cb> in one call, respectively
		1159	the maximum amount of time (default C<0>, meaning infinity) spent in
		1160	C<IO::AIO::poll_cb> to process requests (more correctly the mininum amount
		1161	of time C<poll_cb> is allowed to use).
		1162
		1163	Setting C<max_poll_time> to a non-zero value creates an overhead of one
		1164	syscall per request processed, which is not normally a problem unless your
		1165	callbacks are really really fast or your OS is really really slow (I am
		1166	not mentioning Solaris here). Using C<max_poll_reqs> incurs no overhead.
		1167
		1168	Setting these is useful if you want to ensure some level of
		1169	interactiveness when perl is not fast enough to process all requests in
		1170	time.
		1171
		1172	For interactive programs, values such as C<0.01> to C<0.1> should be fine.
		1173
		1174	Example: Install an Event watcher that automatically calls
		1175	IO::AIO::poll_cb with low priority, to ensure that other parts of the
		1176	program get the CPU sometimes even under high AIO load.
		1177
		1178	# try not to spend much more than 0.1s in poll_cb
		1179	IO::AIO::max_poll_time 0.1;
		1180
		1181	# use a low priority so other tasks have priority
		1182	Event->io (fd => IO::AIO::poll_fileno,
		1183	poll => 'r', nice => 1,
		1184	cb => &IO::AIO::poll_cb);
		1185
221	=item IO::AIO::poll_wait	1186	=item IO::AIO::poll_wait
222		1187
		1188	If there are any outstanding requests and none of them in the result
223	Wait till the result filehandle becomes ready for reading (simply does a	1189	phase, wait till the result filehandle becomes ready for reading (simply
224	select on the filehandle. This is useful if you want to synchronously wait	1190	does a C<select> on the filehandle. This is useful if you want to
225	for some requests to finish).	1191	synchronously wait for some requests to finish).
226		1192
227	See C<nreqs> for an example.	1193	See C<nreqs> for an example.
228		1194
		1195	=item IO::AIO::poll
		1196
		1197	Waits until some requests have been handled.
		1198
		1199	Returns the number of requests processed, but is otherwise strictly
		1200	equivalent to:
		1201
		1202	IO::AIO::poll_wait, IO::AIO::poll_cb
		1203
229	=item IO::AIO::nreqs	1204	=item IO::AIO::flush
230		1205
231	Returns the number of requests currently outstanding.	1206	Wait till all outstanding AIO requests have been handled.
232		1207
233	Example: wait till there are no outstanding requests anymore:	1208	Strictly equivalent to:
234		1209
235	IO::AIO::poll_wait, IO::AIO::poll_cb	1210	IO::AIO::poll_wait, IO::AIO::poll_cb
236	while IO::AIO::nreqs;	1211	while IO::AIO::nreqs;
237		1212
		1213	=back
		1214
		1215	=head3 CONTROLLING THE NUMBER OF THREADS
		1216
		1217	=over
		1218
		1219	=item IO::AIO::min_parallel $nthreads
		1220
		1221	Set the minimum number of AIO threads to C<$nthreads>. The current
		1222	default is C<8>, which means eight asynchronous operations can execute
		1223	concurrently at any one time (the number of outstanding requests,
		1224	however, is unlimited).
		1225
		1226	IO::AIO starts threads only on demand, when an AIO request is queued and
		1227	no free thread exists. Please note that queueing up a hundred requests can
		1228	create demand for a hundred threads, even if it turns out that everything
		1229	is in the cache and could have been processed faster by a single thread.
		1230
		1231	It is recommended to keep the number of threads relatively low, as some
		1232	Linux kernel versions will scale negatively with the number of threads
		1233	(higher parallelity => MUCH higher latency). With current Linux 2.6
		1234	versions, 4-32 threads should be fine.
		1235
		1236	Under most circumstances you don't need to call this function, as the
		1237	module selects a default that is suitable for low to moderate load.
		1238
		1239	=item IO::AIO::max_parallel $nthreads
		1240
		1241	Sets the maximum number of AIO threads to C<$nthreads>. If more than the
		1242	specified number of threads are currently running, this function kills
		1243	them. This function blocks until the limit is reached.
		1244
		1245	While C<$nthreads> are zero, aio requests get queued but not executed
		1246	until the number of threads has been increased again.
		1247
		1248	This module automatically runs C<max_parallel 0> at program end, to ensure
		1249	that all threads are killed and that there are no outstanding requests.
		1250
		1251	Under normal circumstances you don't need to call this function.
		1252
		1253	=item IO::AIO::max_idle $nthreads
		1254
		1255	Limit the number of threads (default: 4) that are allowed to idle (i.e.,
		1256	threads that did not get a request to process within 10 seconds). That
		1257	means if a thread becomes idle while C<$nthreads> other threads are also
		1258	idle, it will free its resources and exit.
		1259
		1260	This is useful when you allow a large number of threads (e.g. 100 or 1000)
		1261	to allow for extremely high load situations, but want to free resources
		1262	under normal circumstances (1000 threads can easily consume 30MB of RAM).
		1263
		1264	The default is probably ok in most situations, especially if thread
		1265	creation is fast. If thread creation is very slow on your system you might
		1266	want to use larger values.
		1267
		1268	=item $oldmaxreqs = IO::AIO::max_outstanding $maxreqs
		1269
		1270	This is a very bad function to use in interactive programs because it
		1271	blocks, and a bad way to reduce concurrency because it is inexact: Better
		1272	use an C<aio_group> together with a feed callback.
		1273
		1274	Sets the maximum number of outstanding requests to C<$nreqs>. If you
		1275	do queue up more than this number of requests, the next call to the
		1276	C<poll_cb> (and C<poll_some> and other functions calling C<poll_cb>)
		1277	function will block until the limit is no longer exceeded.
		1278
		1279	The default value is very large, so there is no practical limit on the
		1280	number of outstanding requests.
		1281
		1282	You can still queue as many requests as you want. Therefore,
		1283	C<max_oustsanding> is mainly useful in simple scripts (with low values) or
		1284	as a stop gap to shield against fatal memory overflow (with large values).
		1285
		1286	=back
		1287
		1288	=head3 STATISTICAL INFORMATION
		1289
		1290	=over
		1291
238	=item IO::AIO::flush	1292	=item IO::AIO::nreqs
239		1293
240	Wait till all outstanding AIO requests have been handled.	1294	Returns the number of requests currently in the ready, execute or pending
		1295	states (i.e. for which their callback has not been invoked yet).
241		1296
242	Strictly equivalent to:	1297	Example: wait till there are no outstanding requests anymore:
243		1298
244	IO::AIO::poll_wait, IO::AIO::poll_cb	1299	IO::AIO::poll_wait, IO::AIO::poll_cb
245	while IO::AIO::nreqs;	1300	while IO::AIO::nreqs;
246		1301
		1302	=item IO::AIO::nready
		1303
		1304	Returns the number of requests currently in the ready state (not yet
		1305	executed).
		1306
247	=item IO::AIO::poll	1307	=item IO::AIO::npending
248		1308
249	Waits until some requests have been handled.	1309	Returns the number of requests currently in the pending state (executed,
250		1310	but not yet processed by poll_cb).
251	Strictly equivalent to:
252
253	IO::AIO::poll_wait, IO::AIO::poll_cb
254	if IO::AIO::nreqs;
255
256	=item IO::AIO::min_parallel $nthreads
257
258	Set the minimum number of AIO threads to C<$nthreads>. The default is
259	C<1>, which means a single asynchronous operation can be done at one time
260	(the number of outstanding operations, however, is unlimited).
261
262	It is recommended to keep the number of threads low, as some Linux
263	kernel versions will scale negatively with the number of threads (higher
264	parallelity => MUCH higher latency). With current Linux 2.6 versions, 4-32
265	threads should be fine.
266
267	Under normal circumstances you don't need to call this function, as this
268	module automatically starts some threads (the exact number might change,
269	and is currently 4).
270
271	=item IO::AIO::max_parallel $nthreads
272
273	Sets the maximum number of AIO threads to C<$nthreads>. If more than
274	the specified number of threads are currently running, kill them. This
275	function blocks until the limit is reached.
276
277	This module automatically runs C<max_parallel 0> at program end, to ensure
278	that all threads are killed and that there are no outstanding requests.
279
280	Under normal circumstances you don't need to call this function.
281
282	=item $oldnreqs = IO::AIO::max_outstanding $nreqs
283
284	Sets the maximum number of outstanding requests to C<$nreqs>. If you
285	try to queue up more than this number of requests, the caller will block until
286	some requests have been handled.
287
288	The default is very large, so normally there is no practical limit. If you
289	queue up many requests in a loop it it often improves speed if you set
290	this to a relatively low number, such as C<100>.
291
292	Under normal circumstances you don't need to call this function.
293		1311
294	=back	1312	=back
295		1313
296	=cut	1314	=cut
297		1315
298	# support function to convert a fd into a perl filehandle
299	sub _fd2fh {
300	return undef if $_[0] < 0;
301
302	# try to be perl5.6-compatible
303	local *AIO_FH;
304	open AIO_FH, "+<&=$_[0]"
305	or return undef;
306
307	*AIO_FH
308	}
309
310	min_parallel 4;	1316	min_parallel 8;
311		1317
312	END {	1318	END { flush }
313	max_parallel 0;
314	}
315		1319
316	1;	1320	1;
317		1321
		1322	=head2 FORK BEHAVIOUR
		1323
		1324	This module should do "the right thing" when the process using it forks:
		1325
		1326	Before the fork, IO::AIO enters a quiescent state where no requests
		1327	can be added in other threads and no results will be processed. After
		1328	the fork the parent simply leaves the quiescent state and continues
		1329	request/result processing, while the child frees the request/result queue
		1330	(so that the requests started before the fork will only be handled in the
		1331	parent). Threads will be started on demand until the limit set in the
		1332	parent process has been reached again.
		1333
		1334	In short: the parent will, after a short pause, continue as if fork had
		1335	not been called, while the child will act as if IO::AIO has not been used
		1336	yet.
		1337
		1338	=head2 MEMORY USAGE
		1339
		1340	Per-request usage:
		1341
		1342	Each aio request uses - depending on your architecture - around 100-200
		1343	bytes of memory. In addition, stat requests need a stat buffer (possibly
		1344	a few hundred bytes), readdir requires a result buffer and so on. Perl
		1345	scalars and other data passed into aio requests will also be locked and
		1346	will consume memory till the request has entered the done state.
		1347
		1348	This is not awfully much, so queuing lots of requests is not usually a
		1349	problem.
		1350
		1351	Per-thread usage:
		1352
		1353	In the execution phase, some aio requests require more memory for
		1354	temporary buffers, and each thread requires a stack and other data
		1355	structures (usually around 16k-128k, depending on the OS).
		1356
		1357	=head1 KNOWN BUGS
		1358
		1359	Known bugs will be fixed in the next release.
		1360
318	=head1 SEE ALSO	1361	=head1 SEE ALSO
319		1362
320	L<Coro>, L<Linux::AIO>.	1363	L<Coro::AIO>.
321		1364
322	=head1 AUTHOR	1365	=head1 AUTHOR
323		1366
324	Marc Lehmann <schmorp@schmorp.de>	1367	Marc Lehmann <schmorp@schmorp.de>
325	http://home.schmorp.de/	1368	http://home.schmorp.de/

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