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Revision 1.9 by root, Sun Jul 10 22:20:55 2005 UTC vs.
Revision 1.147 by root, Wed Jun 3 12:24:49 2009 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',	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 = '3.19';
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
62	aio_fsync aio_fdatasync aio_readahead);	201	aio_stat aio_lstat aio_unlink aio_rmdir aio_readdir
63	@EXPORT_OK = qw(poll_fileno poll_cb min_parallel max_parallel max_outstanding nreqs);	202	aio_scandir aio_symlink aio_readlink aio_sync aio_fsync
		203	aio_fdatasync aio_sync_file_range aio_pathsync aio_readahead
		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	push @AIO_REQ, qw(aio_busy); # not exported
		215
		216	@IO::AIO::GRP::ISA = 'IO::AIO::REQ';
64		217
65	require XSLoader;	218	require XSLoader;
66	XSLoader::load IO::AIO, $VERSION;	219	XSLoader::load ("IO::AIO", $VERSION);
67	}	220	}
68		221
69	=head1 FUNCTIONS	222	=head1 FUNCTIONS
70		223
71	=head2 AIO FUNCTIONS	224	=head2 AIO REQUEST FUNCTIONS
72		225
73	All the C<aio_*> calls are more or less thin wrappers around the syscall	226	All the C<aio_*> calls are more or less thin wrappers around the syscall
74	with the same name (sans C<aio_>). The arguments are similar or identical,	227	with the same name (sans C<aio_>). The arguments are similar or identical,
75	and they all accept an additional C<$callback> argument which must be	228	and they all accept an additional (and optional) C<$callback> argument
76	a code reference. This code reference will get called with the syscall	229	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	230	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	231	perl, which usually delivers "false") as its sole argument after the given
79	been executed asynchronously.	232	syscall has been executed asynchronously.
80		233
81	All functions that expect a filehandle will also accept a file descriptor.	234	All functions expecting a filehandle keep a copy of the filehandle
		235	internally until the request has finished.
82		236
		237	All functions return request objects of type L<IO::AIO::REQ> that allow
		238	further manipulation of those requests while they are in-flight.
		239
83	The filenames you pass to these routines I<must> be absolute. The reason	240	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	241	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	242	request is being executed, the current working directory could have
86	never change the current working directory.	243	changed. Alternatively, you can make sure that you never change the
		244	current working directory anywhere in the program and then use relative
		245	paths.
		246
		247	To encode pathnames as octets, either make sure you either: a) always pass
		248	in filenames you got from outside (command line, readdir etc.) without
		249	tinkering, b) are ASCII or ISO 8859-1, c) use the Encode module and encode
		250	your pathnames to the locale (or other) encoding in effect in the user
		251	environment, d) use Glib::filename_from_unicode on unicode filenames or e)
		252	use something else to ensure your scalar has the correct contents.
		253
		254	This works, btw. independent of the internal UTF-8 bit, which IO::AIO
		255	handles correctly whether it is set or not.
87		256
88	=over 4	257	=over 4
89		258
		259	=item $prev_pri = aioreq_pri [$pri]
		260
		261	Returns the priority value that would be used for the next request and, if
		262	C<$pri> is given, sets the priority for the next aio request.
		263
		264	The default priority is C<0>, the minimum and maximum priorities are C<-4>
		265	and C<4>, respectively. Requests with higher priority will be serviced
		266	first.
		267
		268	The priority will be reset to C<0> after each call to one of the C<aio_*>
		269	functions.
		270
		271	Example: open a file with low priority, then read something from it with
		272	higher priority so the read request is serviced before other low priority
		273	open requests (potentially spamming the cache):
		274
		275	aioreq_pri -3;
		276	aio_open ..., sub {
		277	return unless $_[0];
		278
		279	aioreq_pri -2;
		280	aio_read $_[0], ..., sub {
		281	...
		282	};
		283	};
		284
		285
		286	=item aioreq_nice $pri_adjust
		287
		288	Similar to C<aioreq_pri>, but subtracts the given value from the current
		289	priority, so the effect is cumulative.
		290
		291
90	=item aio_open $pathname, $flags, $mode, $callback	292	=item aio_open $pathname, $flags, $mode, $callback->($fh)
91		293
92	Asynchronously open or create a file and call the callback with a newly	294	Asynchronously open or create a file and call the callback with a newly
93	created filehandle for the file.	295	created filehandle for the file.
94		296
95	The pathname passed to C<aio_open> must be absolute. See API NOTES, above,	297	The pathname passed to C<aio_open> must be absolute. See API NOTES, above,
96	for an explanation.	298	for an explanation.
97		299
98	The C<$mode> argument is a bitmask. See the C<Fcntl> module for a	300	The C<$flags> argument is a bitmask. See the C<Fcntl> module for a
99	list. They are the same as used in C<sysopen>.	301	list. They are the same as used by C<sysopen>.
		302
		303	Likewise, C<$mode> specifies the mode of the newly created file, if it
		304	didn't exist and C<O_CREAT> has been given, just like perl's C<sysopen>,
		305	except that it is mandatory (i.e. use C<0> if you don't create new files,
		306	and C<0666> or C<0777> if you do). Note that the C<$mode> will be modified
		307	by the umask in effect then the request is being executed, so better never
		308	change the umask.
100		309
101	Example:	310	Example:
102		311
103	aio_open "/etc/passwd", O_RDONLY, 0, sub {	312	aio_open "/etc/passwd", O_RDONLY, 0, sub {
104	if ($_[0]) {	313	if ($_[0]) {
…		…
107	} else {	316	} else {
108	die "open failed: $!\n";	317	die "open failed: $!\n";
109	}	318	}
110	};	319	};
111		320
		321
112	=item aio_close $fh, $callback	322	=item aio_close $fh, $callback->($status)
113		323
114	Asynchronously close a file and call the callback with the result	324	Asynchronously close a file and call the callback with the result
115	code. I<WARNING:> although accepted, you should not pass in a perl	325	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		326
		327	Unfortunately, you can't do this to perl. Perl I<insists> very strongly on
		328	closing the file descriptor associated with the filehandle itself.
		329
		330	Therefore, C<aio_close> will not close the filehandle - instead it will
		331	use dup2 to overwrite the file descriptor with the write-end of a pipe
		332	(the pipe fd will be created on demand and will be cached).
		333
		334	Or in other words: the file descriptor will be closed, but it will not be
		335	free for reuse until the perl filehandle is closed.
		336
		337	=cut
		338
120	=item aio_read $fh,$offset,$length, $data,$dataoffset,$callback	339	=item aio_read $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
121		340
122	=item aio_write $fh,$offset,$length, $data,$dataoffset,$callback	341	=item aio_write $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
123		342
124	Reads or writes C<length> bytes from the specified C<fh> and C<offset>	343	Reads or writes C<$length> bytes from or to the specified C<$fh> and
125	into the scalar given by C<data> and offset C<dataoffset> and calls the	344	C<$offset> into the scalar given by C<$data> and offset C<$dataoffset>
126	callback without the actual number of bytes read (or -1 on error, just	345	and calls the callback without the actual number of bytes read (or -1 on
127	like the syscall).	346	error, just like the syscall).
128		347
		348	C<aio_read> will, like C<sysread>, shrink or grow the C<$data> scalar to
		349	offset plus the actual number of bytes read.
		350
		351	If C<$offset> is undefined, then the current file descriptor offset will
		352	be used (and updated), otherwise the file descriptor offset will not be
		353	changed by these calls.
		354
		355	If C<$length> is undefined in C<aio_write>, use the remaining length of
		356	C<$data>.
		357
		358	If C<$dataoffset> is less than zero, it will be counted from the end of
		359	C<$data>.
		360
		361	The C<$data> scalar I<MUST NOT> be modified in any way while the request
		362	is outstanding. Modifying it can result in segfaults or World War III (if
		363	the necessary/optional hardware is installed).
		364
129	Example: Read 15 bytes at offset 7 into scalar C<$buffer>, strating at	365	Example: Read 15 bytes at offset 7 into scalar C<$buffer>, starting at
130	offset C<0> within the scalar:	366	offset C<0> within the scalar:
131		367
132	aio_read $fh, 7, 15, $buffer, 0, sub {	368	aio_read $fh, 7, 15, $buffer, 0, sub {
133	$_[0] > 0 or die "read error: $!";	369	$_[0] > 0 or die "read error: $!";
134	print "read $_[0] bytes: <$buffer>\n";	370	print "read $_[0] bytes: <$buffer>\n";
135	};	371	};
136		372
		373
		374	=item aio_sendfile $out_fh, $in_fh, $in_offset, $length, $callback->($retval)
		375
		376	Tries to copy C<$length> bytes from C<$in_fh> to C<$out_fh>. It starts
		377	reading at byte offset C<$in_offset>, and starts writing at the current
		378	file offset of C<$out_fh>. Because of that, it is not safe to issue more
		379	than one C<aio_sendfile> per C<$out_fh>, as they will interfere with each
		380	other.
		381
		382	This call tries to make use of a native C<sendfile> syscall to provide
		383	zero-copy operation. For this to work, C<$out_fh> should refer to a
		384	socket, and C<$in_fh> should refer to mmap'able file.
		385
		386	If the native sendfile call fails or is not implemented, it will be
		387	emulated, so you can call C<aio_sendfile> on any type of filehandle
		388	regardless of the limitations of the operating system.
		389
		390	Please note, however, that C<aio_sendfile> can read more bytes from
		391	C<$in_fh> than are written, and there is no way to find out how many
		392	bytes have been read from C<aio_sendfile> alone, as C<aio_sendfile> only
		393	provides the number of bytes written to C<$out_fh>. Only if the result
		394	value equals C<$length> one can assume that C<$length> bytes have been
		395	read.
		396
		397
137	=item aio_readahead $fh,$offset,$length, $callback	398	=item aio_readahead $fh,$offset,$length, $callback->($retval)
138		399
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<$!> is set to ENOSYS.
142
143	readahead() populates the page cache with data from a file so that	400	C<aio_readahead> populates the page cache with data from a file so that
144	subsequent reads from that file will not block on disk I/O. The C<$offset>	401	subsequent reads from that file will not block on disk I/O. The C<$offset>
145	argument specifies the starting point from which data is to be read and	402	argument specifies the starting point from which data is to be read and
146	C<$length> specifies the number of bytes to be read. I/O is performed in	403	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	404	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	405	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	406	(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.	407	file. The current file offset of the file is left unchanged.
151		408
		409	If that syscall doesn't exist (likely if your OS isn't Linux) it will be
		410	emulated by simply reading the data, which would have a similar effect.
		411
		412
152	=item aio_stat $fh_or_path, $callback	413	=item aio_stat $fh_or_path, $callback->($status)
153		414
154	=item aio_lstat $fh, $callback	415	=item aio_lstat $fh, $callback->($status)
155		416
156	Works like perl's C<stat> or C<lstat> in void context. The callback will	417	Works like perl's C<stat> or C<lstat> in void context. The callback will
157	be called after the stat and the results will be available using C<stat _>	418	be called after the stat and the results will be available using C<stat _>
158	or C<-s _> etc...	419	or C<-s _> etc...
159		420
…		…
169	aio_stat "/etc/passwd", sub {	430	aio_stat "/etc/passwd", sub {
170	$_[0] and die "stat failed: $!";	431	$_[0] and die "stat failed: $!";
171	print "size is ", -s _, "\n";	432	print "size is ", -s _, "\n";
172	};	433	};
173		434
		435
		436	=item aio_utime $fh_or_path, $atime, $mtime, $callback->($status)
		437
		438	Works like perl's C<utime> function (including the special case of $atime
		439	and $mtime being undef). Fractional times are supported if the underlying
		440	syscalls support them.
		441
		442	When called with a pathname, uses utimes(2) if available, otherwise
		443	utime(2). If called on a file descriptor, uses futimes(2) if available,
		444	otherwise returns ENOSYS, so this is not portable.
		445
		446	Examples:
		447
		448	# set atime and mtime to current time (basically touch(1)):
		449	aio_utime "path", undef, undef;
		450	# set atime to current time and mtime to beginning of the epoch:
		451	aio_utime "path", time, undef; # undef==0
		452
		453
		454	=item aio_chown $fh_or_path, $uid, $gid, $callback->($status)
		455
		456	Works like perl's C<chown> function, except that C<undef> for either $uid
		457	or $gid is being interpreted as "do not change" (but -1 can also be used).
		458
		459	Examples:
		460
		461	# same as "chown root path" in the shell:
		462	aio_chown "path", 0, -1;
		463	# same as above:
		464	aio_chown "path", 0, undef;
		465
		466
		467	=item aio_truncate $fh_or_path, $offset, $callback->($status)
		468
		469	Works like truncate(2) or ftruncate(2).
		470
		471
		472	=item aio_chmod $fh_or_path, $mode, $callback->($status)
		473
		474	Works like perl's C<chmod> function.
		475
		476
174	=item aio_unlink $pathname, $callback	477	=item aio_unlink $pathname, $callback->($status)
175		478
176	Asynchronously unlink (delete) a file and call the callback with the	479	Asynchronously unlink (delete) a file and call the callback with the
177	result code.	480	result code.
178		481
		482
		483	=item aio_mknod $path, $mode, $dev, $callback->($status)
		484
		485	[EXPERIMENTAL]
		486
		487	Asynchronously create a device node (or fifo). See mknod(2).
		488
		489	The only (POSIX-) portable way of calling this function is:
		490
		491	aio_mknod $path, IO::AIO::S_IFIFO | $mode, 0, sub { ...
		492
		493
		494	=item aio_link $srcpath, $dstpath, $callback->($status)
		495
		496	Asynchronously create a new link to the existing object at C<$srcpath> at
		497	the path C<$dstpath> and call the callback with the result code.
		498
		499
		500	=item aio_symlink $srcpath, $dstpath, $callback->($status)
		501
		502	Asynchronously create a new symbolic link to the existing object at C<$srcpath> at
		503	the path C<$dstpath> and call the callback with the result code.
		504
		505
		506	=item aio_readlink $path, $callback->($link)
		507
		508	Asynchronously read the symlink specified by C<$path> and pass it to
		509	the callback. If an error occurs, nothing or undef gets passed to the
		510	callback.
		511
		512
		513	=item aio_rename $srcpath, $dstpath, $callback->($status)
		514
		515	Asynchronously rename the object at C<$srcpath> to C<$dstpath>, just as
		516	rename(2) and call the callback with the result code.
		517
		518
		519	=item aio_mkdir $pathname, $mode, $callback->($status)
		520
		521	Asynchronously mkdir (create) a directory and call the callback with
		522	the result code. C<$mode> will be modified by the umask at the time the
		523	request is executed, so do not change your umask.
		524
		525
		526	=item aio_rmdir $pathname, $callback->($status)
		527
		528	Asynchronously rmdir (delete) a directory and call the callback with the
		529	result code.
		530
		531
		532	=item aio_readdir $pathname, $callback->($entries)
		533
		534	Unlike the POSIX call of the same name, C<aio_readdir> reads an entire
		535	directory (i.e. opendir + readdir + closedir). The entries will not be
		536	sorted, and will B<NOT> include the C<.> and C<..> entries.
		537
		538	The callback a single argument which is either C<undef> or an array-ref
		539	with the filenames.
		540
		541
		542	=item aio_load $path, $data, $callback->($status)
		543
		544	This is a composite request that tries to fully load the given file into
		545	memory. Status is the same as with aio_read.
		546
		547	=cut
		548
		549	sub aio_load($$;$) {
		550	my ($path, undef, $cb) = @_;
		551	my $data = \$_[1];
		552
		553	my $pri = aioreq_pri;
		554	my $grp = aio_group $cb;
		555
		556	aioreq_pri $pri;
		557	add $grp aio_open $path, O_RDONLY, 0, sub {
		558	my $fh = shift
		559	or return $grp->result (-1);
		560
		561	aioreq_pri $pri;
		562	add $grp aio_read $fh, 0, (-s $fh), $$data, 0, sub {
		563	$grp->result ($_[0]);
		564	};
		565	};
		566
		567	$grp
		568	}
		569
		570	=item aio_copy $srcpath, $dstpath, $callback->($status)
		571
		572	Try to copy the I<file> (directories not supported as either source or
		573	destination) from C<$srcpath> to C<$dstpath> and call the callback with
		574	the C<0> (error) or C<-1> ok.
		575
		576	This is a composite request that creates the destination file with
		577	mode 0200 and copies the contents of the source file into it using
		578	C<aio_sendfile>, followed by restoring atime, mtime, access mode and
		579	uid/gid, in that order.
		580
		581	If an error occurs, the partial destination file will be unlinked, if
		582	possible, except when setting atime, mtime, access mode and uid/gid, where
		583	errors are being ignored.
		584
		585	=cut
		586
		587	sub aio_copy($$;$) {
		588	my ($src, $dst, $cb) = @_;
		589
		590	my $pri = aioreq_pri;
		591	my $grp = aio_group $cb;
		592
		593	aioreq_pri $pri;
		594	add $grp aio_open $src, O_RDONLY, 0, sub {
		595	if (my $src_fh = $_[0]) {
		596	my @stat = stat $src_fh; # hmm, might bock over nfs?
		597
		598	aioreq_pri $pri;
		599	add $grp aio_open $dst, O_CREAT | O_WRONLY | O_TRUNC, 0200, sub {
		600	if (my $dst_fh = $_[0]) {
		601	aioreq_pri $pri;
		602	add $grp aio_sendfile $dst_fh, $src_fh, 0, $stat[7], sub {
		603	if ($_[0] == $stat[7]) {
		604	$grp->result (0);
		605	close $src_fh;
		606
		607	my $ch = sub {
		608	aioreq_pri $pri;
		609	add $grp aio_chmod $dst_fh, $stat[2] & 07777, sub {
		610	aioreq_pri $pri;
		611	add $grp aio_chown $dst_fh, $stat[4], $stat[5], sub {
		612	aioreq_pri $pri;
		613	add $grp aio_close $dst_fh;
		614	}
		615	};
		616	};
		617
		618	aioreq_pri $pri;
		619	add $grp aio_utime $dst_fh, $stat[8], $stat[9], sub {
		620	if ($_[0] < 0 && $! == ENOSYS) {
		621	aioreq_pri $pri;
		622	add $grp aio_utime $dst, $stat[8], $stat[9], $ch;
		623	} else {
		624	$ch->();
		625	}
		626	};
		627	} else {
		628	$grp->result (-1);
		629	close $src_fh;
		630	close $dst_fh;
		631
		632	aioreq $pri;
		633	add $grp aio_unlink $dst;
		634	}
		635	};
		636	} else {
		637	$grp->result (-1);
		638	}
		639	},
		640
		641	} else {
		642	$grp->result (-1);
		643	}
		644	};
		645
		646	$grp
		647	}
		648
		649	=item aio_move $srcpath, $dstpath, $callback->($status)
		650
		651	Try to move the I<file> (directories not supported as either source or
		652	destination) from C<$srcpath> to C<$dstpath> and call the callback with
		653	the C<0> (error) or C<-1> ok.
		654
		655	This is a composite request that tries to rename(2) the file first; if
		656	rename fails with C<EXDEV>, it copies the file with C<aio_copy> and, if
		657	that is successful, unlinks the C<$srcpath>.
		658
		659	=cut
		660
		661	sub aio_move($$;$) {
		662	my ($src, $dst, $cb) = @_;
		663
		664	my $pri = aioreq_pri;
		665	my $grp = aio_group $cb;
		666
		667	aioreq_pri $pri;
		668	add $grp aio_rename $src, $dst, sub {
		669	if ($_[0] && $! == EXDEV) {
		670	aioreq_pri $pri;
		671	add $grp aio_copy $src, $dst, sub {
		672	$grp->result ($_[0]);
		673
		674	if (!$_[0]) {
		675	aioreq_pri $pri;
		676	add $grp aio_unlink $src;
		677	}
		678	};
		679	} else {
		680	$grp->result ($_[0]);
		681	}
		682	};
		683
		684	$grp
		685	}
		686
		687	=item aio_scandir $path, $maxreq, $callback->($dirs, $nondirs)
		688
		689	Scans a directory (similar to C<aio_readdir>) but additionally tries to
		690	efficiently separate the entries of directory C<$path> into two sets of
		691	names, directories you can recurse into (directories), and ones you cannot
		692	recurse into (everything else, including symlinks to directories).
		693
		694	C<aio_scandir> is a composite request that creates of many sub requests_
		695	C<$maxreq> specifies the maximum number of outstanding aio requests that
		696	this function generates. If it is C<< <= 0 >>, then a suitable default
		697	will be chosen (currently 4).
		698
		699	On error, the callback is called without arguments, otherwise it receives
		700	two array-refs with path-relative entry names.
		701
		702	Example:
		703
		704	aio_scandir $dir, 0, sub {
		705	my ($dirs, $nondirs) = @_;
		706	print "real directories: @$dirs\n";
		707	print "everything else: @$nondirs\n";
		708	};
		709
		710	Implementation notes.
		711
		712	The C<aio_readdir> cannot be avoided, but C<stat()>'ing every entry can.
		713
		714	After reading the directory, the modification time, size etc. of the
		715	directory before and after the readdir is checked, and if they match (and
		716	isn't the current time), the link count will be used to decide how many
		717	entries are directories (if >= 2). Otherwise, no knowledge of the number
		718	of subdirectories will be assumed.
		719
		720	Then entries will be sorted into likely directories (everything without
		721	a non-initial dot currently) and likely non-directories (everything
		722	else). Then every entry plus an appended C</.> will be C<stat>'ed,
		723	likely directories first. If that succeeds, it assumes that the entry
		724	is a directory or a symlink to directory (which will be checked
		725	seperately). This is often faster than stat'ing the entry itself because
		726	filesystems might detect the type of the entry without reading the inode
		727	data (e.g. ext2fs filetype feature).
		728
		729	If the known number of directories (link count - 2) has been reached, the
		730	rest of the entries is assumed to be non-directories.
		731
		732	This only works with certainty on POSIX (= UNIX) filesystems, which
		733	fortunately are the vast majority of filesystems around.
		734
		735	It will also likely work on non-POSIX filesystems with reduced efficiency
		736	as those tend to return 0 or 1 as link counts, which disables the
		737	directory counting heuristic.
		738
		739	=cut
		740
		741	sub aio_scandir($$;$) {
		742	my ($path, $maxreq, $cb) = @_;
		743
		744	my $pri = aioreq_pri;
		745
		746	my $grp = aio_group $cb;
		747
		748	$maxreq = 4 if $maxreq <= 0;
		749
		750	# stat once
		751	aioreq_pri $pri;
		752	add $grp aio_stat $path, sub {
		753	return $grp->result () if $_[0];
		754	my $now = time;
		755	my $hash1 = join ":", (stat _)[0,1,3,7,9];
		756
		757	# read the directory entries
		758	aioreq_pri $pri;
		759	add $grp aio_readdir $path, sub {
		760	my $entries = shift
		761	or return $grp->result ();
		762
		763	# stat the dir another time
		764	aioreq_pri $pri;
		765	add $grp aio_stat $path, sub {
		766	my $hash2 = join ":", (stat _)[0,1,3,7,9];
		767
		768	my $ndirs;
		769
		770	# take the slow route if anything looks fishy
		771	if ($hash1 ne $hash2 or (stat _)[9] == $now) {
		772	$ndirs = -1;
		773	} else {
		774	# if nlink == 2, we are finished
		775	# on non-posix-fs's, we rely on nlink < 2
		776	$ndirs = (stat _)[3] - 2
		777	or return $grp->result ([], $entries);
		778	}
		779
		780	# sort into likely dirs and likely nondirs
		781	# dirs == files without ".", short entries first
		782	$entries = [map $_->[0],
		783	sort { $b->[1] cmp $a->[1] }
		784	map [$_, sprintf "%s%04d", (/.\./ ? "1" : "0"), length],
		785	@$entries];
		786
		787	my (@dirs, @nondirs);
		788
		789	my $statgrp = add $grp aio_group sub {
		790	$grp->result (\@dirs, \@nondirs);
		791	};
		792
		793	limit $statgrp $maxreq;
		794	feed $statgrp sub {
		795	return unless @$entries;
		796	my $entry = pop @$entries;
		797
		798	aioreq_pri $pri;
		799	add $statgrp aio_stat "$path/$entry/.", sub {
		800	if ($_[0] < 0) {
		801	push @nondirs, $entry;
		802	} else {
		803	# need to check for real directory
		804	aioreq_pri $pri;
		805	add $statgrp aio_lstat "$path/$entry", sub {
		806	if (-d _) {
		807	push @dirs, $entry;
		808
		809	unless (--$ndirs) {
		810	push @nondirs, @$entries;
		811	feed $statgrp;
		812	}
		813	} else {
		814	push @nondirs, $entry;
		815	}
		816	}
		817	}
		818	};
		819	};
		820	};
		821	};
		822	};
		823
		824	$grp
		825	}
		826
		827	=item aio_rmtree $path, $callback->($status)
		828
		829	Delete a directory tree starting (and including) C<$path>, return the
		830	status of the final C<rmdir> only. This is a composite request that
		831	uses C<aio_scandir> to recurse into and rmdir directories, and unlink
		832	everything else.
		833
		834	=cut
		835
		836	sub aio_rmtree;
		837	sub aio_rmtree($;$) {
		838	my ($path, $cb) = @_;
		839
		840	my $pri = aioreq_pri;
		841	my $grp = aio_group $cb;
		842
		843	aioreq_pri $pri;
		844	add $grp aio_scandir $path, 0, sub {
		845	my ($dirs, $nondirs) = @_;
		846
		847	my $dirgrp = aio_group sub {
		848	add $grp aio_rmdir $path, sub {
		849	$grp->result ($_[0]);
		850	};
		851	};
		852
		853	(aioreq_pri $pri), add $dirgrp aio_rmtree "$path/$_" for @$dirs;
		854	(aioreq_pri $pri), add $dirgrp aio_unlink "$path/$_" for @$nondirs;
		855
		856	add $grp $dirgrp;
		857	};
		858
		859	$grp
		860	}
		861
		862	=item aio_sync $callback->($status)
		863
		864	Asynchronously call sync and call the callback when finished.
		865
179	=item aio_fsync $fh, $callback	866	=item aio_fsync $fh, $callback->($status)
180		867
181	Asynchronously call fsync on the given filehandle and call the callback	868	Asynchronously call fsync on the given filehandle and call the callback
182	with the fsync result code.	869	with the fsync result code.
183		870
184	=item aio_fdatasync $fh, $callback	871	=item aio_fdatasync $fh, $callback->($status)
185		872
186	Asynchronously call fdatasync on the given filehandle and call the	873	Asynchronously call fdatasync on the given filehandle and call the
187	callback with the fdatasync result code.	874	callback with the fdatasync result code.
188		875
		876	If this call isn't available because your OS lacks it or it couldn't be
		877	detected, it will be emulated by calling C<fsync> instead.
		878
		879	=item aio_sync_file_range $fh, $offset, $nbytes, $flags, $callback->($status)
		880
		881	Sync the data portion of the file specified by C<$offset> and C<$length>
		882	to disk (but NOT the metadata), by calling the Linux-specific
		883	sync_file_range call. If sync_file_range is not available or it returns
		884	ENOSYS, then fdatasync or fsync is being substituted.
		885
		886	C<$flags> can be a combination of C<IO::AIO::SYNC_FILE_RANGE_WAIT_BEFORE>,
		887	C<IO::AIO::SYNC_FILE_RANGE_WRITE> and
		888	C<IO::AIO::SYNC_FILE_RANGE_WAIT_AFTER>: refer to the sync_file_range
		889	manpage for details.
		890
		891	=item aio_pathsync $path, $callback->($status)
		892
		893	This request tries to open, fsync and close the given path. This is a
		894	composite request intended to sync directories after directory operations
		895	(E.g. rename). This might not work on all operating systems or have any
		896	specific effect, but usually it makes sure that directory changes get
		897	written to disc. It works for anything that can be opened for read-only,
		898	not just directories.
		899
		900	Passes C<0> when everything went ok, and C<-1> on error.
		901
		902	=cut
		903
		904	sub aio_pathsync($;$) {
		905	my ($path, $cb) = @_;
		906
		907	my $pri = aioreq_pri;
		908	my $grp = aio_group $cb;
		909
		910	aioreq_pri $pri;
		911	add $grp aio_open $path, O_RDONLY, 0, sub {
		912	my ($fh) = @_;
		913	if ($fh) {
		914	aioreq_pri $pri;
		915	add $grp aio_fsync $fh, sub {
		916	$grp->result ($_[0]);
		917
		918	aioreq_pri $pri;
		919	add $grp aio_close $fh;
		920	};
		921	} else {
		922	$grp->result (-1);
		923	}
		924	};
		925
		926	$grp
		927	}
		928
		929	=item aio_group $callback->(...)
		930
		931	This is a very special aio request: Instead of doing something, it is a
		932	container for other aio requests, which is useful if you want to bundle
		933	many requests into a single, composite, request with a definite callback
		934	and the ability to cancel the whole request with its subrequests.
		935
		936	Returns an object of class L<IO::AIO::GRP>. See its documentation below
		937	for more info.
		938
		939	Example:
		940
		941	my $grp = aio_group sub {
		942	print "all stats done\n";
		943	};
		944
		945	add $grp
		946	(aio_stat ...),
		947	(aio_stat ...),
		948	...;
		949
		950	=item aio_nop $callback->()
		951
		952	This is a special request - it does nothing in itself and is only used for
		953	side effects, such as when you want to add a dummy request to a group so
		954	that finishing the requests in the group depends on executing the given
		955	code.
		956
		957	While this request does nothing, it still goes through the execution
		958	phase and still requires a worker thread. Thus, the callback will not
		959	be executed immediately but only after other requests in the queue have
		960	entered their execution phase. This can be used to measure request
		961	latency.
		962
		963	=item IO::AIO::aio_busy $fractional_seconds, $callback->() *NOT EXPORTED*
		964
		965	Mainly used for debugging and benchmarking, this aio request puts one of
		966	the request workers to sleep for the given time.
		967
		968	While it is theoretically handy to have simple I/O scheduling requests
		969	like sleep and file handle readable/writable, the overhead this creates is
		970	immense (it blocks a thread for a long time) so do not use this function
		971	except to put your application under artificial I/O pressure.
		972
189	=back	973	=back
190		974
		975	=head2 IO::AIO::REQ CLASS
		976
		977	All non-aggregate C<aio_*> functions return an object of this class when
		978	called in non-void context.
		979
		980	=over 4
		981
		982	=item cancel $req
		983
		984	Cancels the request, if possible. Has the effect of skipping execution
		985	when entering the B<execute> state and skipping calling the callback when
		986	entering the the B<result> state, but will leave the request otherwise
		987	untouched. That means that requests that currently execute will not be
		988	stopped and resources held by the request will not be freed prematurely.
		989
		990	=item cb $req $callback->(...)
		991
		992	Replace (or simply set) the callback registered to the request.
		993
		994	=back
		995
		996	=head2 IO::AIO::GRP CLASS
		997
		998	This class is a subclass of L<IO::AIO::REQ>, so all its methods apply to
		999	objects of this class, too.
		1000
		1001	A IO::AIO::GRP object is a special request that can contain multiple other
		1002	aio requests.
		1003
		1004	You create one by calling the C<aio_group> constructing function with a
		1005	callback that will be called when all contained requests have entered the
		1006	C<done> state:
		1007
		1008	my $grp = aio_group sub {
		1009	print "all requests are done\n";
		1010	};
		1011
		1012	You add requests by calling the C<add> method with one or more
		1013	C<IO::AIO::REQ> objects:
		1014
		1015	$grp->add (aio_unlink "...");
		1016
		1017	add $grp aio_stat "...", sub {
		1018	$_[0] or return $grp->result ("error");
		1019
		1020	# add another request dynamically, if first succeeded
		1021	add $grp aio_open "...", sub {
		1022	$grp->result ("ok");
		1023	};
		1024	};
		1025
		1026	This makes it very easy to create composite requests (see the source of
		1027	C<aio_move> for an application) that work and feel like simple requests.
		1028
		1029	=over 4
		1030
		1031	=item * The IO::AIO::GRP objects will be cleaned up during calls to
		1032	C<IO::AIO::poll_cb>, just like any other request.
		1033
		1034	=item * They can be canceled like any other request. Canceling will cancel not
		1035	only the request itself, but also all requests it contains.
		1036
		1037	=item * They can also can also be added to other IO::AIO::GRP objects.
		1038
		1039	=item * You must not add requests to a group from within the group callback (or
		1040	any later time).
		1041
		1042	=back
		1043
		1044	Their lifetime, simplified, looks like this: when they are empty, they
		1045	will finish very quickly. If they contain only requests that are in the
		1046	C<done> state, they will also finish. Otherwise they will continue to
		1047	exist.
		1048
		1049	That means after creating a group you have some time to add requests
		1050	(precisely before the callback has been invoked, which is only done within
		1051	the C<poll_cb>). And in the callbacks of those requests, you can add
		1052	further requests to the group. And only when all those requests have
		1053	finished will the the group itself finish.
		1054
		1055	=over 4
		1056
		1057	=item add $grp ...
		1058
		1059	=item $grp->add (...)
		1060
		1061	Add one or more requests to the group. Any type of L<IO::AIO::REQ> can
		1062	be added, including other groups, as long as you do not create circular
		1063	dependencies.
		1064
		1065	Returns all its arguments.
		1066
		1067	=item $grp->cancel_subs
		1068
		1069	Cancel all subrequests and clears any feeder, but not the group request
		1070	itself. Useful when you queued a lot of events but got a result early.
		1071
		1072	=item $grp->result (...)
		1073
		1074	Set the result value(s) that will be passed to the group callback when all
		1075	subrequests have finished and set the groups errno to the current value
		1076	of errno (just like calling C<errno> without an error number). By default,
		1077	no argument will be passed and errno is zero.
		1078
		1079	=item $grp->errno ([$errno])
		1080
		1081	Sets the group errno value to C<$errno>, or the current value of errno
		1082	when the argument is missing.
		1083
		1084	Every aio request has an associated errno value that is restored when
		1085	the callback is invoked. This method lets you change this value from its
		1086	default (0).
		1087
		1088	Calling C<result> will also set errno, so make sure you either set C<$!>
		1089	before the call to C<result>, or call c<errno> after it.
		1090
		1091	=item feed $grp $callback->($grp)
		1092
		1093	Sets a feeder/generator on this group: every group can have an attached
		1094	generator that generates requests if idle. The idea behind this is that,
		1095	although you could just queue as many requests as you want in a group,
		1096	this might starve other requests for a potentially long time. For example,
		1097	C<aio_scandir> might generate hundreds of thousands C<aio_stat> requests,
		1098	delaying any later requests for a long time.
		1099
		1100	To avoid this, and allow incremental generation of requests, you can
		1101	instead a group and set a feeder on it that generates those requests. The
		1102	feed callback will be called whenever there are few enough (see C<limit>,
		1103	below) requests active in the group itself and is expected to queue more
		1104	requests.
		1105
		1106	The feed callback can queue as many requests as it likes (i.e. C<add> does
		1107	not impose any limits).
		1108
		1109	If the feed does not queue more requests when called, it will be
		1110	automatically removed from the group.
		1111
		1112	If the feed limit is C<0> when this method is called, it will be set to
		1113	C<2> automatically.
		1114
		1115	Example:
		1116
		1117	# stat all files in @files, but only ever use four aio requests concurrently:
		1118
		1119	my $grp = aio_group sub { print "finished\n" };
		1120	limit $grp 4;
		1121	feed $grp sub {
		1122	my $file = pop @files
		1123	or return;
		1124
		1125	add $grp aio_stat $file, sub { ... };
		1126	};
		1127
		1128	=item limit $grp $num
		1129
		1130	Sets the feeder limit for the group: The feeder will be called whenever
		1131	the group contains less than this many requests.
		1132
		1133	Setting the limit to C<0> will pause the feeding process.
		1134
		1135	The default value for the limit is C<0>, but note that setting a feeder
		1136	automatically bumps it up to C<2>.
		1137
		1138	=back
		1139
191	=head2 SUPPORT FUNCTIONS	1140	=head2 SUPPORT FUNCTIONS
192		1141
		1142	=head3 EVENT PROCESSING AND EVENT LOOP INTEGRATION
		1143
193	=over 4	1144	=over 4
194		1145
195	=item $fileno = IO::AIO::poll_fileno	1146	=item $fileno = IO::AIO::poll_fileno
196		1147
197	Return the I<request result pipe filehandle>. This filehandle must be	1148	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	1149	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	1150	select, see below or the SYNOPSIS). If the pipe becomes readable you have
200	C<poll_cb> to check the results.	1151	to call C<poll_cb> to check the results.
201		1152
202	See C<poll_cb> for an example.	1153	See C<poll_cb> for an example.
203		1154
204	=item IO::AIO::poll_cb	1155	=item IO::AIO::poll_cb
205		1156
206	Process all outstanding events on the result pipe. You have to call this	1157	Process some outstanding events on the result pipe. You have to call this
207	regularly. Returns the number of events processed. Returns immediately	1158	regularly. Returns C<0> if all events could be processed, or C<-1> if it
208	when no events are outstanding.	1159	returned earlier for whatever reason. Returns immediately when no events
		1160	are outstanding. The amount of events processed depends on the settings of
		1161	C<IO::AIO::max_poll_req> and C<IO::AIO::max_poll_time>.
209		1162
210	You can use Event to multiplex, e.g.:	1163	If not all requests were processed for whatever reason, the filehandle
		1164	will still be ready when C<poll_cb> returns, so normally you don't have to
		1165	do anything special to have it called later.
		1166
		1167	Example: Install an Event watcher that automatically calls
		1168	IO::AIO::poll_cb with high priority:
211		1169
212	Event->io (fd => IO::AIO::poll_fileno,	1170	Event->io (fd => IO::AIO::poll_fileno,
213	poll => 'r', async => 1,	1171	poll => 'r', async => 1,
214	cb => \&IO::AIO::poll_cb);	1172	cb => \&IO::AIO::poll_cb);
215		1173
		1174	=item IO::AIO::max_poll_reqs $nreqs
		1175
		1176	=item IO::AIO::max_poll_time $seconds
		1177
		1178	These set the maximum number of requests (default C<0>, meaning infinity)
		1179	that are being processed by C<IO::AIO::poll_cb> in one call, respectively
		1180	the maximum amount of time (default C<0>, meaning infinity) spent in
		1181	C<IO::AIO::poll_cb> to process requests (more correctly the mininum amount
		1182	of time C<poll_cb> is allowed to use).
		1183
		1184	Setting C<max_poll_time> to a non-zero value creates an overhead of one
		1185	syscall per request processed, which is not normally a problem unless your
		1186	callbacks are really really fast or your OS is really really slow (I am
		1187	not mentioning Solaris here). Using C<max_poll_reqs> incurs no overhead.
		1188
		1189	Setting these is useful if you want to ensure some level of
		1190	interactiveness when perl is not fast enough to process all requests in
		1191	time.
		1192
		1193	For interactive programs, values such as C<0.01> to C<0.1> should be fine.
		1194
		1195	Example: Install an Event watcher that automatically calls
		1196	IO::AIO::poll_cb with low priority, to ensure that other parts of the
		1197	program get the CPU sometimes even under high AIO load.
		1198
		1199	# try not to spend much more than 0.1s in poll_cb
		1200	IO::AIO::max_poll_time 0.1;
		1201
		1202	# use a low priority so other tasks have priority
		1203	Event->io (fd => IO::AIO::poll_fileno,
		1204	poll => 'r', nice => 1,
		1205	cb => &IO::AIO::poll_cb);
		1206
216	=item IO::AIO::poll_wait	1207	=item IO::AIO::poll_wait
217		1208
		1209	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	1210	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	1211	does a C<select> on the filehandle. This is useful if you want to
220	for some requests to finish).	1212	synchronously wait for some requests to finish).
221		1213
222	See C<nreqs> for an example.	1214	See C<nreqs> for an example.
223		1215
		1216	=item IO::AIO::poll
		1217
		1218	Waits until some requests have been handled.
		1219
		1220	Returns the number of requests processed, but is otherwise strictly
		1221	equivalent to:
		1222
		1223	IO::AIO::poll_wait, IO::AIO::poll_cb
		1224
224	=item IO::AIO::nreqs	1225	=item IO::AIO::flush
225		1226
226	Returns the number of requests currently outstanding.	1227	Wait till all outstanding AIO requests have been handled.
227		1228
228	Example: wait till there are no outstanding requests anymore:	1229	Strictly equivalent to:
229		1230
230	IO::AIO::poll_wait, IO::AIO::poll_cb	1231	IO::AIO::poll_wait, IO::AIO::poll_cb
231	while IO::AIO::nreqs;	1232	while IO::AIO::nreqs;
232		1233
		1234	=back
		1235
		1236	=head3 CONTROLLING THE NUMBER OF THREADS
		1237
		1238	=over
		1239
233	=item IO::AIO::min_parallel $nthreads	1240	=item IO::AIO::min_parallel $nthreads
234		1241
235	Set the minimum number of AIO threads to C<$nthreads>. The default is	1242	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	1243	default is C<8>, which means eight asynchronous operations can execute
237	(the number of outstanding operations, however, is unlimited).	1244	concurrently at any one time (the number of outstanding requests,
		1245	however, is unlimited).
238		1246
		1247	IO::AIO starts threads only on demand, when an AIO request is queued and
		1248	no free thread exists. Please note that queueing up a hundred requests can
		1249	create demand for a hundred threads, even if it turns out that everything
		1250	is in the cache and could have been processed faster by a single thread.
		1251
239	It is recommended to keep the number of threads low, as some Linux	1252	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	1253	Linux kernel versions will scale negatively with the number of threads
241	parallelity => MUCH higher latency). With current Linux 2.6 versions, 4-32	1254	(higher parallelity => MUCH higher latency). With current Linux 2.6
242	threads should be fine.	1255	versions, 4-32 threads should be fine.
243		1256
244	Under normal circumstances you don't need to call this function, as this	1257	Under most circumstances you don't need to call this function, as the
245	module automatically starts some threads (the exact number might change,	1258	module selects a default that is suitable for low to moderate load.
246	and is currently 4).
247		1259
248	=item IO::AIO::max_parallel $nthreads	1260	=item IO::AIO::max_parallel $nthreads
249		1261
250	Sets the maximum number of AIO threads to C<$nthreads>. If more than	1262	Sets the maximum number of AIO threads to C<$nthreads>. If more than the
251	the specified number of threads are currently running, kill them. This	1263	specified number of threads are currently running, this function kills
252	function blocks until the limit is reached.	1264	them. This function blocks until the limit is reached.
		1265
		1266	While C<$nthreads> are zero, aio requests get queued but not executed
		1267	until the number of threads has been increased again.
253		1268
254	This module automatically runs C<max_parallel 0> at program end, to ensure	1269	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.	1270	that all threads are killed and that there are no outstanding requests.
256		1271
257	Under normal circumstances you don't need to call this function.	1272	Under normal circumstances you don't need to call this function.
258		1273
		1274	=item IO::AIO::max_idle $nthreads
		1275
		1276	Limit the number of threads (default: 4) that are allowed to idle (i.e.,
		1277	threads that did not get a request to process within 10 seconds). That
		1278	means if a thread becomes idle while C<$nthreads> other threads are also
		1279	idle, it will free its resources and exit.
		1280
		1281	This is useful when you allow a large number of threads (e.g. 100 or 1000)
		1282	to allow for extremely high load situations, but want to free resources
		1283	under normal circumstances (1000 threads can easily consume 30MB of RAM).
		1284
		1285	The default is probably ok in most situations, especially if thread
		1286	creation is fast. If thread creation is very slow on your system you might
		1287	want to use larger values.
		1288
259	=item $oldnreqs = IO::AIO::max_outstanding $nreqs	1289	=item IO::AIO::max_outstanding $maxreqs
		1290
		1291	This is a very bad function to use in interactive programs because it
		1292	blocks, and a bad way to reduce concurrency because it is inexact: Better
		1293	use an C<aio_group> together with a feed callback.
260		1294
261	Sets the maximum number of outstanding requests to C<$nreqs>. If you	1295	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	1296	do queue up more than this number of requests, the next call to the
263	some requests have been handled.	1297	C<poll_cb> (and C<poll_some> and other functions calling C<poll_cb>)
		1298	function will block until the limit is no longer exceeded.
264		1299
265	The default is very large, so normally there is no practical limit. If you	1300	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	1301	number of outstanding requests.
267	this to a relatively low number, such as C<100>.
268		1302
269	Under normal circumstances you don't need to call this function.	1303	You can still queue as many requests as you want. Therefore,
		1304	C<max_outstanding> is mainly useful in simple scripts (with low values) or
		1305	as a stop gap to shield against fatal memory overflow (with large values).
270		1306
271	=back	1307	=back
272		1308
		1309	=head3 STATISTICAL INFORMATION
		1310
		1311	=over
		1312
		1313	=item IO::AIO::nreqs
		1314
		1315	Returns the number of requests currently in the ready, execute or pending
		1316	states (i.e. for which their callback has not been invoked yet).
		1317
		1318	Example: wait till there are no outstanding requests anymore:
		1319
		1320	IO::AIO::poll_wait, IO::AIO::poll_cb
		1321	while IO::AIO::nreqs;
		1322
		1323	=item IO::AIO::nready
		1324
		1325	Returns the number of requests currently in the ready state (not yet
		1326	executed).
		1327
		1328	=item IO::AIO::npending
		1329
		1330	Returns the number of requests currently in the pending state (executed,
		1331	but not yet processed by poll_cb).
		1332
		1333	=back
		1334
273	=cut	1335	=cut
274		1336
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;	1337	min_parallel 8;
288		1338
289	END {	1339	END { flush }
290	max_parallel 0;
291	}
292		1340
293	1;	1341	1;
294		1342
		1343	=head2 FORK BEHAVIOUR
		1344
		1345	This module should do "the right thing" when the process using it forks:
		1346
		1347	Before the fork, IO::AIO enters a quiescent state where no requests
		1348	can be added in other threads and no results will be processed. After
		1349	the fork the parent simply leaves the quiescent state and continues
		1350	request/result processing, while the child frees the request/result queue
		1351	(so that the requests started before the fork will only be handled in the
		1352	parent). Threads will be started on demand until the limit set in the
		1353	parent process has been reached again.
		1354
		1355	In short: the parent will, after a short pause, continue as if fork had
		1356	not been called, while the child will act as if IO::AIO has not been used
		1357	yet.
		1358
		1359	=head2 MEMORY USAGE
		1360
		1361	Per-request usage:
		1362
		1363	Each aio request uses - depending on your architecture - around 100-200
		1364	bytes of memory. In addition, stat requests need a stat buffer (possibly
		1365	a few hundred bytes), readdir requires a result buffer and so on. Perl
		1366	scalars and other data passed into aio requests will also be locked and
		1367	will consume memory till the request has entered the done state.
		1368
		1369	This is not awfully much, so queuing lots of requests is not usually a
		1370	problem.
		1371
		1372	Per-thread usage:
		1373
		1374	In the execution phase, some aio requests require more memory for
		1375	temporary buffers, and each thread requires a stack and other data
		1376	structures (usually around 16k-128k, depending on the OS).
		1377
		1378	=head1 KNOWN BUGS
		1379
		1380	Known bugs will be fixed in the next release.
		1381
295	=head1 SEE ALSO	1382	=head1 SEE ALSO
296		1383
297	L<Coro>, L<Linux::AIO>.	1384	L<AnyEvent::AIO> for easy integration into event loops, L<Coro::AIO> for a
		1385	more natural syntax.
298		1386
299	=head1 AUTHOR	1387	=head1 AUTHOR
300		1388
301	Marc Lehmann <schmorp@schmorp.de>	1389	Marc Lehmann <schmorp@schmorp.de>
302	http://home.schmorp.de/	1390	http://home.schmorp.de/

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