ViewVC Help

View File | Revision Log | Show Annotations | Download File

/cvs/IO-AIO/AIO.pm

Comparing IO-AIO/AIO.pm (file contents):
Revision 1.6 by root, Sun Jul 10 22:19:48 2005 UTC vs.
Revision 1.144 by root, Sun Apr 19 19:17:59 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', async => 1,	39	poll => 'r',
23	cb => \&IO::AIO::poll_cb);	40	cb => \&IO::AIO::poll_cb);
24		41
25	# Glib/Gtk2	42	# Glib/Gtk2 integration
26	add_watch Glib::IO IO::AIO::poll_fileno,	43	add_watch Glib::IO IO::AIO::poll_fileno,
27	\&IO::AIO::poll_cb;	44	in => sub { IO::AIO::poll_cb; 1 };
28		45
29	# Tk	46	# Tk integration
30	Tk::Event::IO->fileevent (IO::AIO::poll_fileno, "",	47	Tk::Event::IO->fileevent (IO::AIO::poll_fileno, "",
31	readable => \&IO::AIO::poll_cb);	48	readable => \&IO::AIO::poll_cb);
32		49
		50	# Danga::Socket integration
		51	Danga::Socket->AddOtherFds (IO::AIO::poll_fileno =>
		52	\&IO::AIO::poll_cb);
		53
33	=head1 DESCRIPTION	54	=head1 DESCRIPTION
34		55
35	This module implements asynchronous I/O using whatever means your	56	This module implements asynchronous I/O using whatever means your
36	operating system supports.	57	operating system supports.
37		58
		59	Asynchronous means that operations that can normally block your program
		60	(e.g. reading from disk) will be done asynchronously: the operation
		61	will still block, but you can do something else in the meantime. This
		62	is extremely useful for programs that need to stay interactive even
		63	when doing heavy I/O (GUI programs, high performance network servers
		64	etc.), but can also be used to easily do operations in parallel that are
		65	normally done sequentially, e.g. stat'ing many files, which is much faster
		66	on a RAID volume or over NFS when you do a number of stat operations
		67	concurrently.
		68
		69	While most of this works on all types of file descriptors (for
		70	example sockets), using these functions on file descriptors that
		71	support nonblocking operation (again, sockets, pipes etc.) is very
		72	inefficient. Use an event loop for that (such as the L<Event|Event>
		73	module): IO::AIO will naturally fit into such an event loop itself.
		74
38	Currently, a number of threads are started that execute your read/writes	75	In this version, a number of threads are started that execute your
39	and signal their completion. You don't need thread support in your libc or	76	requests and signal their completion. You don't need thread support
40	perl, and the threads created by this module will not be visible to the	77	in perl, and the threads created by this module will not be visible
41	pthreads library. In the future, this module might make use of the native	78	to perl. In the future, this module might make use of the native aio
42	aio functions available on many operating systems. However, they are often	79	functions available on many operating systems. However, they are often
43	not well-supported (Linux doesn't allow them on normal files currently,	80	not well-supported or restricted (GNU/Linux doesn't allow them on normal
44	for example), and they would only support aio_read and aio_write, so the	81	files currently, for example), and they would only support aio_read and
45	remaining functionality would have to be implemented using threads anyway.	82	aio_write, so the remaining functionality would have to be implemented
		83	using threads anyway.
46		84
47	Although the module will work with in the presence of other threads, it is	85	Although the module will work in the presence of other (Perl-) threads,
48	currently not reentrant, so use appropriate locking yourself.	86	it is currently not reentrant in any way, so use appropriate locking
		87	yourself, always call C<poll_cb> from within the same thread, or never
		88	call C<poll_cb> (or other C<aio_> functions) recursively.
		89
		90	=head2 EXAMPLE
		91
		92	This is a simple example that uses the Event module and loads
		93	F</etc/passwd> asynchronously:
		94
		95	use Fcntl;
		96	use Event;
		97	use IO::AIO;
		98
		99	# register the IO::AIO callback with Event
		100	Event->io (fd => IO::AIO::poll_fileno,
		101	poll => 'r',
		102	cb => \&IO::AIO::poll_cb);
		103
		104	# queue the request to open /etc/passwd
		105	aio_open "/etc/passwd", O_RDONLY, 0, sub {
		106	my $fh = shift
		107	or die "error while opening: $!";
		108
		109	# stat'ing filehandles is generally non-blocking
		110	my $size = -s $fh;
		111
		112	# queue a request to read the file
		113	my $contents;
		114	aio_read $fh, 0, $size, $contents, 0, sub {
		115	$_[0] == $size
		116	or die "short read: $!";
		117
		118	close $fh;
		119
		120	# file contents now in $contents
		121	print $contents;
		122
		123	# exit event loop and program
		124	Event::unloop;
		125	};
		126	};
		127
		128	# possibly queue up other requests, or open GUI windows,
		129	# check for sockets etc. etc.
		130
		131	# process events as long as there are some:
		132	Event::loop;
		133
		134	=head1 REQUEST ANATOMY AND LIFETIME
		135
		136	Every C<aio_*> function creates a request. which is a C data structure not
		137	directly visible to Perl.
		138
		139	If called in non-void context, every request function returns a Perl
		140	object representing the request. In void context, nothing is returned,
		141	which saves a bit of memory.
		142
		143	The perl object is a fairly standard ref-to-hash object. The hash contents
		144	are not used by IO::AIO so you are free to store anything you like in it.
		145
		146	During their existance, aio requests travel through the following states,
		147	in order:
		148
		149	=over 4
		150
		151	=item ready
		152
		153	Immediately after a request is created it is put into the ready state,
		154	waiting for a thread to execute it.
		155
		156	=item execute
		157
		158	A thread has accepted the request for processing and is currently
		159	executing it (e.g. blocking in read).
		160
		161	=item pending
		162
		163	The request has been executed and is waiting for result processing.
		164
		165	While request submission and execution is fully asynchronous, result
		166	processing is not and relies on the perl interpreter calling C<poll_cb>
		167	(or another function with the same effect).
		168
		169	=item result
		170
		171	The request results are processed synchronously by C<poll_cb>.
		172
		173	The C<poll_cb> function will process all outstanding aio requests by
		174	calling their callbacks, freeing memory associated with them and managing
		175	any groups they are contained in.
		176
		177	=item done
		178
		179	Request has reached the end of its lifetime and holds no resources anymore
		180	(except possibly for the Perl object, but its connection to the actual
		181	aio request is severed and calling its methods will either do nothing or
		182	result in a runtime error).
		183
		184	=back
49		185
50	=cut	186	=cut
51		187
52	package IO::AIO;	188	package IO::AIO;
53		189
		190	use Carp ();
		191
		192	no warnings;
		193	use strict 'vars';
		194
54	use base 'Exporter';	195	use base 'Exporter';
55		196
56	use Fcntl ();
57
58	BEGIN {	197	BEGIN {
59	$VERSION = 0.2;	198	our $VERSION = '3.18';
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<$length> bytes from the specified C<$fh> and C<$offset>
125	into the scalar given by C<data> and offset C<dataoffset> and calls the	344	into the scalar given by C<$data> and offset C<$dataoffset> and calls the
126	callback without the actual number of bytes read (or -1 on error, just	345	callback without the actual number of bytes read (or -1 on error, just
127	like the syscall).	346	like the syscall).
128		347
		348	If C<$offset> is undefined, then the current file descriptor offset will
		349	be used (and updated), otherwise the file descriptor offset will not be
		350	changed by these calls.
		351
		352	If C<$length> is undefined in C<aio_write>, use the remaining length of C<$data>.
		353
		354	If C<$dataoffset> is less than zero, it will be counted from the end of
		355	C<$data>.
		356
		357	The C<$data> scalar I<MUST NOT> be modified in any way while the request
		358	is outstanding. Modifying it can result in segfaults or World War III (if
		359	the necessary/optional hardware is installed).
		360
129	Example: Read 15 bytes at offset 7 into scalar C<$buffer>, strating at	361	Example: Read 15 bytes at offset 7 into scalar C<$buffer>, starting at
130	offset C<0> within the scalar:	362	offset C<0> within the scalar:
131		363
132	aio_read $fh, 7, 15, $buffer, 0, sub {	364	aio_read $fh, 7, 15, $buffer, 0, sub {
133	$_[0] >= 0 or die "read error: $!";	365	$_[0] > 0 or die "read error: $!";
134	print "read <$buffer>\n";	366	print "read $_[0] bytes: <$buffer>\n";
135	};	367	};
136		368
		369
		370	=item aio_sendfile $out_fh, $in_fh, $in_offset, $length, $callback->($retval)
		371
		372	Tries to copy C<$length> bytes from C<$in_fh> to C<$out_fh>. It starts
		373	reading at byte offset C<$in_offset>, and starts writing at the current
		374	file offset of C<$out_fh>. Because of that, it is not safe to issue more
		375	than one C<aio_sendfile> per C<$out_fh>, as they will interfere with each
		376	other.
		377
		378	This call tries to make use of a native C<sendfile> syscall to provide
		379	zero-copy operation. For this to work, C<$out_fh> should refer to a
		380	socket, and C<$in_fh> should refer to mmap'able file.
		381
		382	If the native sendfile call fails or is not implemented, it will be
		383	emulated, so you can call C<aio_sendfile> on any type of filehandle
		384	regardless of the limitations of the operating system.
		385
		386	Please note, however, that C<aio_sendfile> can read more bytes from
		387	C<$in_fh> than are written, and there is no way to find out how many
		388	bytes have been read from C<aio_sendfile> alone, as C<aio_sendfile> only
		389	provides the number of bytes written to C<$out_fh>. Only if the result
		390	value equals C<$length> one can assume that C<$length> bytes have been
		391	read.
		392
		393
137	=item aio_readahead $fh,$offset,$length, $callback	394	=item aio_readahead $fh,$offset,$length, $callback->($retval)
138		395
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<$!> is set to ENOSYS.
142
143	readahead() populates the page cache with data from a file so that	396	C<aio_readahead> populates the page cache with data from a file so that
144	subsequent reads from that file will not block on disk I/O. The C<$offset>	397	subsequent reads from that file will not block on disk I/O. The C<$offset>
145	argument specifies the starting point from which data is to be read and	398	argument specifies the starting point from which data is to be read and
146	C<$length> specifies the number of bytes to be read. I/O is performed in	399	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	400	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	401	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	402	(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.	403	file. The current file offset of the file is left unchanged.
151		404
		405	If that syscall doesn't exist (likely if your OS isn't Linux) it will be
		406	emulated by simply reading the data, which would have a similar effect.
		407
		408
152	=item aio_stat $fh_or_path, $callback	409	=item aio_stat $fh_or_path, $callback->($status)
153		410
154	=item aio_lstat $fh, $callback	411	=item aio_lstat $fh, $callback->($status)
155		412
156	Works like perl's C<stat> or C<lstat> in void context. The callback will	413	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 _>	414	be called after the stat and the results will be available using C<stat _>
158	or C<-s _> etc...	415	or C<-s _> etc...
159		416
…		…
169	aio_stat "/etc/passwd", sub {	426	aio_stat "/etc/passwd", sub {
170	$_[0] and die "stat failed: $!";	427	$_[0] and die "stat failed: $!";
171	print "size is ", -s _, "\n";	428	print "size is ", -s _, "\n";
172	};	429	};
173		430
		431
		432	=item aio_utime $fh_or_path, $atime, $mtime, $callback->($status)
		433
		434	Works like perl's C<utime> function (including the special case of $atime
		435	and $mtime being undef). Fractional times are supported if the underlying
		436	syscalls support them.
		437
		438	When called with a pathname, uses utimes(2) if available, otherwise
		439	utime(2). If called on a file descriptor, uses futimes(2) if available,
		440	otherwise returns ENOSYS, so this is not portable.
		441
		442	Examples:
		443
		444	# set atime and mtime to current time (basically touch(1)):
		445	aio_utime "path", undef, undef;
		446	# set atime to current time and mtime to beginning of the epoch:
		447	aio_utime "path", time, undef; # undef==0
		448
		449
		450	=item aio_chown $fh_or_path, $uid, $gid, $callback->($status)
		451
		452	Works like perl's C<chown> function, except that C<undef> for either $uid
		453	or $gid is being interpreted as "do not change" (but -1 can also be used).
		454
		455	Examples:
		456
		457	# same as "chown root path" in the shell:
		458	aio_chown "path", 0, -1;
		459	# same as above:
		460	aio_chown "path", 0, undef;
		461
		462
		463	=item aio_truncate $fh_or_path, $offset, $callback->($status)
		464
		465	Works like truncate(2) or ftruncate(2).
		466
		467
		468	=item aio_chmod $fh_or_path, $mode, $callback->($status)
		469
		470	Works like perl's C<chmod> function.
		471
		472
174	=item aio_unlink $pathname, $callback	473	=item aio_unlink $pathname, $callback->($status)
175		474
176	Asynchronously unlink (delete) a file and call the callback with the	475	Asynchronously unlink (delete) a file and call the callback with the
177	result code.	476	result code.
178		477
		478
		479	=item aio_mknod $path, $mode, $dev, $callback->($status)
		480
		481	[EXPERIMENTAL]
		482
		483	Asynchronously create a device node (or fifo). See mknod(2).
		484
		485	The only (POSIX-) portable way of calling this function is:
		486
		487	aio_mknod $path, IO::AIO::S_IFIFO | $mode, 0, sub { ...
		488
		489
		490	=item aio_link $srcpath, $dstpath, $callback->($status)
		491
		492	Asynchronously create a new link to the existing object at C<$srcpath> at
		493	the path C<$dstpath> and call the callback with the result code.
		494
		495
		496	=item aio_symlink $srcpath, $dstpath, $callback->($status)
		497
		498	Asynchronously create a new symbolic link to the existing object at C<$srcpath> at
		499	the path C<$dstpath> and call the callback with the result code.
		500
		501
		502	=item aio_readlink $path, $callback->($link)
		503
		504	Asynchronously read the symlink specified by C<$path> and pass it to
		505	the callback. If an error occurs, nothing or undef gets passed to the
		506	callback.
		507
		508
		509	=item aio_rename $srcpath, $dstpath, $callback->($status)
		510
		511	Asynchronously rename the object at C<$srcpath> to C<$dstpath>, just as
		512	rename(2) and call the callback with the result code.
		513
		514
		515	=item aio_mkdir $pathname, $mode, $callback->($status)
		516
		517	Asynchronously mkdir (create) a directory and call the callback with
		518	the result code. C<$mode> will be modified by the umask at the time the
		519	request is executed, so do not change your umask.
		520
		521
		522	=item aio_rmdir $pathname, $callback->($status)
		523
		524	Asynchronously rmdir (delete) a directory and call the callback with the
		525	result code.
		526
		527
		528	=item aio_readdir $pathname, $callback->($entries)
		529
		530	Unlike the POSIX call of the same name, C<aio_readdir> reads an entire
		531	directory (i.e. opendir + readdir + closedir). The entries will not be
		532	sorted, and will B<NOT> include the C<.> and C<..> entries.
		533
		534	The callback a single argument which is either C<undef> or an array-ref
		535	with the filenames.
		536
		537
		538	=item aio_load $path, $data, $callback->($status)
		539
		540	This is a composite request that tries to fully load the given file into
		541	memory. Status is the same as with aio_read.
		542
		543	=cut
		544
		545	sub aio_load($$;$) {
		546	my ($path, undef, $cb) = @_;
		547	my $data = \$_[1];
		548
		549	my $pri = aioreq_pri;
		550	my $grp = aio_group $cb;
		551
		552	aioreq_pri $pri;
		553	add $grp aio_open $path, O_RDONLY, 0, sub {
		554	my $fh = shift
		555	or return $grp->result (-1);
		556
		557	aioreq_pri $pri;
		558	add $grp aio_read $fh, 0, (-s $fh), $$data, 0, sub {
		559	$grp->result ($_[0]);
		560	};
		561	};
		562
		563	$grp
		564	}
		565
		566	=item aio_copy $srcpath, $dstpath, $callback->($status)
		567
		568	Try to copy the I<file> (directories not supported as either source or
		569	destination) from C<$srcpath> to C<$dstpath> and call the callback with
		570	the C<0> (error) or C<-1> ok.
		571
		572	This is a composite request that creates the destination file with
		573	mode 0200 and copies the contents of the source file into it using
		574	C<aio_sendfile>, followed by restoring atime, mtime, access mode and
		575	uid/gid, in that order.
		576
		577	If an error occurs, the partial destination file will be unlinked, if
		578	possible, except when setting atime, mtime, access mode and uid/gid, where
		579	errors are being ignored.
		580
		581	=cut
		582
		583	sub aio_copy($$;$) {
		584	my ($src, $dst, $cb) = @_;
		585
		586	my $pri = aioreq_pri;
		587	my $grp = aio_group $cb;
		588
		589	aioreq_pri $pri;
		590	add $grp aio_open $src, O_RDONLY, 0, sub {
		591	if (my $src_fh = $_[0]) {
		592	my @stat = stat $src_fh;
		593
		594	aioreq_pri $pri;
		595	add $grp aio_open $dst, O_CREAT | O_WRONLY | O_TRUNC, 0200, sub {
		596	if (my $dst_fh = $_[0]) {
		597	aioreq_pri $pri;
		598	add $grp aio_sendfile $dst_fh, $src_fh, 0, $stat[7], sub {
		599	if ($_[0] == $stat[7]) {
		600	$grp->result (0);
		601	close $src_fh;
		602
		603	# those should not normally block. should. should.
		604	utime $stat[8], $stat[9], $dst;
		605	chmod $stat[2] & 07777, $dst_fh;
		606	chown $stat[4], $stat[5], $dst_fh;
		607
		608	aioreq_pri $pri;
		609	add $grp aio_close $dst_fh;
		610	} else {
		611	$grp->result (-1);
		612	close $src_fh;
		613	close $dst_fh;
		614
		615	aioreq $pri;
		616	add $grp aio_unlink $dst;
		617	}
		618	};
		619	} else {
		620	$grp->result (-1);
		621	}
		622	},
		623
		624	} else {
		625	$grp->result (-1);
		626	}
		627	};
		628
		629	$grp
		630	}
		631
		632	=item aio_move $srcpath, $dstpath, $callback->($status)
		633
		634	Try to move the I<file> (directories not supported as either source or
		635	destination) from C<$srcpath> to C<$dstpath> and call the callback with
		636	the C<0> (error) or C<-1> ok.
		637
		638	This is a composite request that tries to rename(2) the file first; if
		639	rename fails with C<EXDEV>, it copies the file with C<aio_copy> and, if
		640	that is successful, unlinks the C<$srcpath>.
		641
		642	=cut
		643
		644	sub aio_move($$;$) {
		645	my ($src, $dst, $cb) = @_;
		646
		647	my $pri = aioreq_pri;
		648	my $grp = aio_group $cb;
		649
		650	aioreq_pri $pri;
		651	add $grp aio_rename $src, $dst, sub {
		652	if ($_[0] && $! == EXDEV) {
		653	aioreq_pri $pri;
		654	add $grp aio_copy $src, $dst, sub {
		655	$grp->result ($_[0]);
		656
		657	if (!$_[0]) {
		658	aioreq_pri $pri;
		659	add $grp aio_unlink $src;
		660	}
		661	};
		662	} else {
		663	$grp->result ($_[0]);
		664	}
		665	};
		666
		667	$grp
		668	}
		669
		670	=item aio_scandir $path, $maxreq, $callback->($dirs, $nondirs)
		671
		672	Scans a directory (similar to C<aio_readdir>) but additionally tries to
		673	efficiently separate the entries of directory C<$path> into two sets of
		674	names, directories you can recurse into (directories), and ones you cannot
		675	recurse into (everything else, including symlinks to directories).
		676
		677	C<aio_scandir> is a composite request that creates of many sub requests_
		678	C<$maxreq> specifies the maximum number of outstanding aio requests that
		679	this function generates. If it is C<< <= 0 >>, then a suitable default
		680	will be chosen (currently 4).
		681
		682	On error, the callback is called without arguments, otherwise it receives
		683	two array-refs with path-relative entry names.
		684
		685	Example:
		686
		687	aio_scandir $dir, 0, sub {
		688	my ($dirs, $nondirs) = @_;
		689	print "real directories: @$dirs\n";
		690	print "everything else: @$nondirs\n";
		691	};
		692
		693	Implementation notes.
		694
		695	The C<aio_readdir> cannot be avoided, but C<stat()>'ing every entry can.
		696
		697	After reading the directory, the modification time, size etc. of the
		698	directory before and after the readdir is checked, and if they match (and
		699	isn't the current time), the link count will be used to decide how many
		700	entries are directories (if >= 2). Otherwise, no knowledge of the number
		701	of subdirectories will be assumed.
		702
		703	Then entries will be sorted into likely directories (everything without
		704	a non-initial dot currently) and likely non-directories (everything
		705	else). Then every entry plus an appended C</.> will be C<stat>'ed,
		706	likely directories first. If that succeeds, it assumes that the entry
		707	is a directory or a symlink to directory (which will be checked
		708	seperately). This is often faster than stat'ing the entry itself because
		709	filesystems might detect the type of the entry without reading the inode
		710	data (e.g. ext2fs filetype feature).
		711
		712	If the known number of directories (link count - 2) has been reached, the
		713	rest of the entries is assumed to be non-directories.
		714
		715	This only works with certainty on POSIX (= UNIX) filesystems, which
		716	fortunately are the vast majority of filesystems around.
		717
		718	It will also likely work on non-POSIX filesystems with reduced efficiency
		719	as those tend to return 0 or 1 as link counts, which disables the
		720	directory counting heuristic.
		721
		722	=cut
		723
		724	sub aio_scandir($$;$) {
		725	my ($path, $maxreq, $cb) = @_;
		726
		727	my $pri = aioreq_pri;
		728
		729	my $grp = aio_group $cb;
		730
		731	$maxreq = 4 if $maxreq <= 0;
		732
		733	# stat once
		734	aioreq_pri $pri;
		735	add $grp aio_stat $path, sub {
		736	return $grp->result () if $_[0];
		737	my $now = time;
		738	my $hash1 = join ":", (stat _)[0,1,3,7,9];
		739
		740	# read the directory entries
		741	aioreq_pri $pri;
		742	add $grp aio_readdir $path, sub {
		743	my $entries = shift
		744	or return $grp->result ();
		745
		746	# stat the dir another time
		747	aioreq_pri $pri;
		748	add $grp aio_stat $path, sub {
		749	my $hash2 = join ":", (stat _)[0,1,3,7,9];
		750
		751	my $ndirs;
		752
		753	# take the slow route if anything looks fishy
		754	if ($hash1 ne $hash2 or (stat _)[9] == $now) {
		755	$ndirs = -1;
		756	} else {
		757	# if nlink == 2, we are finished
		758	# on non-posix-fs's, we rely on nlink < 2
		759	$ndirs = (stat _)[3] - 2
		760	or return $grp->result ([], $entries);
		761	}
		762
		763	# sort into likely dirs and likely nondirs
		764	# dirs == files without ".", short entries first
		765	$entries = [map $_->[0],
		766	sort { $b->[1] cmp $a->[1] }
		767	map [$_, sprintf "%s%04d", (/.\./ ? "1" : "0"), length],
		768	@$entries];
		769
		770	my (@dirs, @nondirs);
		771
		772	my $statgrp = add $grp aio_group sub {
		773	$grp->result (\@dirs, \@nondirs);
		774	};
		775
		776	limit $statgrp $maxreq;
		777	feed $statgrp sub {
		778	return unless @$entries;
		779	my $entry = pop @$entries;
		780
		781	aioreq_pri $pri;
		782	add $statgrp aio_stat "$path/$entry/.", sub {
		783	if ($_[0] < 0) {
		784	push @nondirs, $entry;
		785	} else {
		786	# need to check for real directory
		787	aioreq_pri $pri;
		788	add $statgrp aio_lstat "$path/$entry", sub {
		789	if (-d _) {
		790	push @dirs, $entry;
		791
		792	unless (--$ndirs) {
		793	push @nondirs, @$entries;
		794	feed $statgrp;
		795	}
		796	} else {
		797	push @nondirs, $entry;
		798	}
		799	}
		800	}
		801	};
		802	};
		803	};
		804	};
		805	};
		806
		807	$grp
		808	}
		809
		810	=item aio_rmtree $path, $callback->($status)
		811
		812	Delete a directory tree starting (and including) C<$path>, return the
		813	status of the final C<rmdir> only. This is a composite request that
		814	uses C<aio_scandir> to recurse into and rmdir directories, and unlink
		815	everything else.
		816
		817	=cut
		818
		819	sub aio_rmtree;
		820	sub aio_rmtree($;$) {
		821	my ($path, $cb) = @_;
		822
		823	my $pri = aioreq_pri;
		824	my $grp = aio_group $cb;
		825
		826	aioreq_pri $pri;
		827	add $grp aio_scandir $path, 0, sub {
		828	my ($dirs, $nondirs) = @_;
		829
		830	my $dirgrp = aio_group sub {
		831	add $grp aio_rmdir $path, sub {
		832	$grp->result ($_[0]);
		833	};
		834	};
		835
		836	(aioreq_pri $pri), add $dirgrp aio_rmtree "$path/$_" for @$dirs;
		837	(aioreq_pri $pri), add $dirgrp aio_unlink "$path/$_" for @$nondirs;
		838
		839	add $grp $dirgrp;
		840	};
		841
		842	$grp
		843	}
		844
		845	=item aio_sync $callback->($status)
		846
		847	Asynchronously call sync and call the callback when finished.
		848
179	=item aio_fsync $fh, $callback	849	=item aio_fsync $fh, $callback->($status)
180		850
181	Asynchronously call fsync on the given filehandle and call the callback	851	Asynchronously call fsync on the given filehandle and call the callback
182	with the fsync result code.	852	with the fsync result code.
183		853
184	=item aio_fdatasync $fh, $callback	854	=item aio_fdatasync $fh, $callback->($status)
185		855
186	Asynchronously call fdatasync on the given filehandle and call the	856	Asynchronously call fdatasync on the given filehandle and call the
187	callback with the fdatasync result code.	857	callback with the fdatasync result code.
188		858
		859	If this call isn't available because your OS lacks it or it couldn't be
		860	detected, it will be emulated by calling C<fsync> instead.
		861
		862	=item aio_sync_file_range $fh, $offset, $nbytes, $flags, $callback->($status)
		863
		864	Sync the data portion of the file specified by C<$offset> and C<$length>
		865	to disk (but NOT the metadata), by calling the Linux-specific
		866	sync_file_range call. If sync_file_range is not available or it returns
		867	ENOSYS, then fdatasync or fsync is being substituted.
		868
		869	C<$flags> can be a combination of C<IO::AIO::SYNC_FILE_RANGE_WAIT_BEFORE>,
		870	C<IO::AIO::SYNC_FILE_RANGE_WRITE> and
		871	C<IO::AIO::SYNC_FILE_RANGE_WAIT_AFTER>: refer to the sync_file_range
		872	manpage for details.
		873
		874	=item aio_pathsync $path, $callback->($status)
		875
		876	This request tries to open, fsync and close the given path. This is a
		877	composite request intended to sync directories after directory operations
		878	(E.g. rename). This might not work on all operating systems or have any
		879	specific effect, but usually it makes sure that directory changes get
		880	written to disc. It works for anything that can be opened for read-only,
		881	not just directories.
		882
		883	Passes C<0> when everything went ok, and C<-1> on error.
		884
		885	=cut
		886
		887	sub aio_pathsync($;$) {
		888	my ($path, $cb) = @_;
		889
		890	my $pri = aioreq_pri;
		891	my $grp = aio_group $cb;
		892
		893	aioreq_pri $pri;
		894	add $grp aio_open $path, O_RDONLY, 0, sub {
		895	my ($fh) = @_;
		896	if ($fh) {
		897	aioreq_pri $pri;
		898	add $grp aio_fsync $fh, sub {
		899	$grp->result ($_[0]);
		900
		901	aioreq_pri $pri;
		902	add $grp aio_close $fh;
		903	};
		904	} else {
		905	$grp->result (-1);
		906	}
		907	};
		908
		909	$grp
		910	}
		911
		912	=item aio_group $callback->(...)
		913
		914	This is a very special aio request: Instead of doing something, it is a
		915	container for other aio requests, which is useful if you want to bundle
		916	many requests into a single, composite, request with a definite callback
		917	and the ability to cancel the whole request with its subrequests.
		918
		919	Returns an object of class L<IO::AIO::GRP>. See its documentation below
		920	for more info.
		921
		922	Example:
		923
		924	my $grp = aio_group sub {
		925	print "all stats done\n";
		926	};
		927
		928	add $grp
		929	(aio_stat ...),
		930	(aio_stat ...),
		931	...;
		932
		933	=item aio_nop $callback->()
		934
		935	This is a special request - it does nothing in itself and is only used for
		936	side effects, such as when you want to add a dummy request to a group so
		937	that finishing the requests in the group depends on executing the given
		938	code.
		939
		940	While this request does nothing, it still goes through the execution
		941	phase and still requires a worker thread. Thus, the callback will not
		942	be executed immediately but only after other requests in the queue have
		943	entered their execution phase. This can be used to measure request
		944	latency.
		945
		946	=item IO::AIO::aio_busy $fractional_seconds, $callback->() *NOT EXPORTED*
		947
		948	Mainly used for debugging and benchmarking, this aio request puts one of
		949	the request workers to sleep for the given time.
		950
		951	While it is theoretically handy to have simple I/O scheduling requests
		952	like sleep and file handle readable/writable, the overhead this creates is
		953	immense (it blocks a thread for a long time) so do not use this function
		954	except to put your application under artificial I/O pressure.
		955
189	=back	956	=back
190		957
		958	=head2 IO::AIO::REQ CLASS
		959
		960	All non-aggregate C<aio_*> functions return an object of this class when
		961	called in non-void context.
		962
		963	=over 4
		964
		965	=item cancel $req
		966
		967	Cancels the request, if possible. Has the effect of skipping execution
		968	when entering the B<execute> state and skipping calling the callback when
		969	entering the the B<result> state, but will leave the request otherwise
		970	untouched. That means that requests that currently execute will not be
		971	stopped and resources held by the request will not be freed prematurely.
		972
		973	=item cb $req $callback->(...)
		974
		975	Replace (or simply set) the callback registered to the request.
		976
		977	=back
		978
		979	=head2 IO::AIO::GRP CLASS
		980
		981	This class is a subclass of L<IO::AIO::REQ>, so all its methods apply to
		982	objects of this class, too.
		983
		984	A IO::AIO::GRP object is a special request that can contain multiple other
		985	aio requests.
		986
		987	You create one by calling the C<aio_group> constructing function with a
		988	callback that will be called when all contained requests have entered the
		989	C<done> state:
		990
		991	my $grp = aio_group sub {
		992	print "all requests are done\n";
		993	};
		994
		995	You add requests by calling the C<add> method with one or more
		996	C<IO::AIO::REQ> objects:
		997
		998	$grp->add (aio_unlink "...");
		999
		1000	add $grp aio_stat "...", sub {
		1001	$_[0] or return $grp->result ("error");
		1002
		1003	# add another request dynamically, if first succeeded
		1004	add $grp aio_open "...", sub {
		1005	$grp->result ("ok");
		1006	};
		1007	};
		1008
		1009	This makes it very easy to create composite requests (see the source of
		1010	C<aio_move> for an application) that work and feel like simple requests.
		1011
		1012	=over 4
		1013
		1014	=item * The IO::AIO::GRP objects will be cleaned up during calls to
		1015	C<IO::AIO::poll_cb>, just like any other request.
		1016
		1017	=item * They can be canceled like any other request. Canceling will cancel not
		1018	only the request itself, but also all requests it contains.
		1019
		1020	=item * They can also can also be added to other IO::AIO::GRP objects.
		1021
		1022	=item * You must not add requests to a group from within the group callback (or
		1023	any later time).
		1024
		1025	=back
		1026
		1027	Their lifetime, simplified, looks like this: when they are empty, they
		1028	will finish very quickly. If they contain only requests that are in the
		1029	C<done> state, they will also finish. Otherwise they will continue to
		1030	exist.
		1031
		1032	That means after creating a group you have some time to add requests
		1033	(precisely before the callback has been invoked, which is only done within
		1034	the C<poll_cb>). And in the callbacks of those requests, you can add
		1035	further requests to the group. And only when all those requests have
		1036	finished will the the group itself finish.
		1037
		1038	=over 4
		1039
		1040	=item add $grp ...
		1041
		1042	=item $grp->add (...)
		1043
		1044	Add one or more requests to the group. Any type of L<IO::AIO::REQ> can
		1045	be added, including other groups, as long as you do not create circular
		1046	dependencies.
		1047
		1048	Returns all its arguments.
		1049
		1050	=item $grp->cancel_subs
		1051
		1052	Cancel all subrequests and clears any feeder, but not the group request
		1053	itself. Useful when you queued a lot of events but got a result early.
		1054
		1055	=item $grp->result (...)
		1056
		1057	Set the result value(s) that will be passed to the group callback when all
		1058	subrequests have finished and set the groups errno to the current value
		1059	of errno (just like calling C<errno> without an error number). By default,
		1060	no argument will be passed and errno is zero.
		1061
		1062	=item $grp->errno ([$errno])
		1063
		1064	Sets the group errno value to C<$errno>, or the current value of errno
		1065	when the argument is missing.
		1066
		1067	Every aio request has an associated errno value that is restored when
		1068	the callback is invoked. This method lets you change this value from its
		1069	default (0).
		1070
		1071	Calling C<result> will also set errno, so make sure you either set C<$!>
		1072	before the call to C<result>, or call c<errno> after it.
		1073
		1074	=item feed $grp $callback->($grp)
		1075
		1076	Sets a feeder/generator on this group: every group can have an attached
		1077	generator that generates requests if idle. The idea behind this is that,
		1078	although you could just queue as many requests as you want in a group,
		1079	this might starve other requests for a potentially long time. For example,
		1080	C<aio_scandir> might generate hundreds of thousands C<aio_stat> requests,
		1081	delaying any later requests for a long time.
		1082
		1083	To avoid this, and allow incremental generation of requests, you can
		1084	instead a group and set a feeder on it that generates those requests. The
		1085	feed callback will be called whenever there are few enough (see C<limit>,
		1086	below) requests active in the group itself and is expected to queue more
		1087	requests.
		1088
		1089	The feed callback can queue as many requests as it likes (i.e. C<add> does
		1090	not impose any limits).
		1091
		1092	If the feed does not queue more requests when called, it will be
		1093	automatically removed from the group.
		1094
		1095	If the feed limit is C<0> when this method is called, it will be set to
		1096	C<2> automatically.
		1097
		1098	Example:
		1099
		1100	# stat all files in @files, but only ever use four aio requests concurrently:
		1101
		1102	my $grp = aio_group sub { print "finished\n" };
		1103	limit $grp 4;
		1104	feed $grp sub {
		1105	my $file = pop @files
		1106	or return;
		1107
		1108	add $grp aio_stat $file, sub { ... };
		1109	};
		1110
		1111	=item limit $grp $num
		1112
		1113	Sets the feeder limit for the group: The feeder will be called whenever
		1114	the group contains less than this many requests.
		1115
		1116	Setting the limit to C<0> will pause the feeding process.
		1117
		1118	The default value for the limit is C<0>, but note that setting a feeder
		1119	automatically bumps it up to C<2>.
		1120
		1121	=back
		1122
191	=head2 SUPPORT FUNCTIONS	1123	=head2 SUPPORT FUNCTIONS
192		1124
		1125	=head3 EVENT PROCESSING AND EVENT LOOP INTEGRATION
		1126
193	=over 4	1127	=over 4
194		1128
195	=item $fileno = IO::AIO::poll_fileno	1129	=item $fileno = IO::AIO::poll_fileno
196		1130
197	Return the I<request result pipe filehandle>. This filehandle must be	1131	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	1132	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	1133	select, see below or the SYNOPSIS). If the pipe becomes readable you have
200	C<poll_cb> to check the results.	1134	to call C<poll_cb> to check the results.
201		1135
202	See C<poll_cb> for an example.	1136	See C<poll_cb> for an example.
203		1137
204	=item IO::AIO::poll_cb	1138	=item IO::AIO::poll_cb
205		1139
206	Process all outstanding events on the result pipe. You have to call this	1140	Process some outstanding events on the result pipe. You have to call this
207	regularly. Returns the number of events processed. Returns immediately	1141	regularly. Returns C<0> if all events could be processed, or C<-1> if it
208	when no events are outstanding.	1142	returned earlier for whatever reason. Returns immediately when no events
		1143	are outstanding. The amount of events processed depends on the settings of
		1144	C<IO::AIO::max_poll_req> and C<IO::AIO::max_poll_time>.
209		1145
210	You can use Event to multiplex, e.g.:	1146	If not all requests were processed for whatever reason, the filehandle
		1147	will still be ready when C<poll_cb> returns, so normally you don't have to
		1148	do anything special to have it called later.
		1149
		1150	Example: Install an Event watcher that automatically calls
		1151	IO::AIO::poll_cb with high priority:
211		1152
212	Event->io (fd => IO::AIO::poll_fileno,	1153	Event->io (fd => IO::AIO::poll_fileno,
213	poll => 'r', async => 1,	1154	poll => 'r', async => 1,
214	cb => \&IO::AIO::poll_cb);	1155	cb => \&IO::AIO::poll_cb);
215		1156
		1157	=item IO::AIO::max_poll_reqs $nreqs
		1158
		1159	=item IO::AIO::max_poll_time $seconds
		1160
		1161	These set the maximum number of requests (default C<0>, meaning infinity)
		1162	that are being processed by C<IO::AIO::poll_cb> in one call, respectively
		1163	the maximum amount of time (default C<0>, meaning infinity) spent in
		1164	C<IO::AIO::poll_cb> to process requests (more correctly the mininum amount
		1165	of time C<poll_cb> is allowed to use).
		1166
		1167	Setting C<max_poll_time> to a non-zero value creates an overhead of one
		1168	syscall per request processed, which is not normally a problem unless your
		1169	callbacks are really really fast or your OS is really really slow (I am
		1170	not mentioning Solaris here). Using C<max_poll_reqs> incurs no overhead.
		1171
		1172	Setting these is useful if you want to ensure some level of
		1173	interactiveness when perl is not fast enough to process all requests in
		1174	time.
		1175
		1176	For interactive programs, values such as C<0.01> to C<0.1> should be fine.
		1177
		1178	Example: Install an Event watcher that automatically calls
		1179	IO::AIO::poll_cb with low priority, to ensure that other parts of the
		1180	program get the CPU sometimes even under high AIO load.
		1181
		1182	# try not to spend much more than 0.1s in poll_cb
		1183	IO::AIO::max_poll_time 0.1;
		1184
		1185	# use a low priority so other tasks have priority
		1186	Event->io (fd => IO::AIO::poll_fileno,
		1187	poll => 'r', nice => 1,
		1188	cb => &IO::AIO::poll_cb);
		1189
216	=item IO::AIO::poll_wait	1190	=item IO::AIO::poll_wait
217		1191
		1192	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	1193	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	1194	does a C<select> on the filehandle. This is useful if you want to
220	for some requests to finish).	1195	synchronously wait for some requests to finish).
221		1196
222	See C<nreqs> for an example.	1197	See C<nreqs> for an example.
223		1198
		1199	=item IO::AIO::poll
		1200
		1201	Waits until some requests have been handled.
		1202
		1203	Returns the number of requests processed, but is otherwise strictly
		1204	equivalent to:
		1205
		1206	IO::AIO::poll_wait, IO::AIO::poll_cb
		1207
224	=item IO::AIO::nreqs	1208	=item IO::AIO::flush
225		1209
226	Returns the number of requests currently outstanding.	1210	Wait till all outstanding AIO requests have been handled.
227		1211
228	Example: wait till there are no outstanding requests anymore:	1212	Strictly equivalent to:
229		1213
230	IO::AIO::poll_wait, IO::AIO::poll_cb	1214	IO::AIO::poll_wait, IO::AIO::poll_cb
231	while IO::AIO::nreqs;	1215	while IO::AIO::nreqs;
232		1216
		1217	=back
		1218
		1219	=head3 CONTROLLING THE NUMBER OF THREADS
		1220
		1221	=over
		1222
233	=item IO::AIO::min_parallel $nthreads	1223	=item IO::AIO::min_parallel $nthreads
234		1224
235	Set the minimum number of AIO threads to C<$nthreads>. The default is	1225	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	1226	default is C<8>, which means eight asynchronous operations can execute
237	(the number of outstanding operations, however, is unlimited).	1227	concurrently at any one time (the number of outstanding requests,
		1228	however, is unlimited).
238		1229
		1230	IO::AIO starts threads only on demand, when an AIO request is queued and
		1231	no free thread exists. Please note that queueing up a hundred requests can
		1232	create demand for a hundred threads, even if it turns out that everything
		1233	is in the cache and could have been processed faster by a single thread.
		1234
239	It is recommended to keep the number of threads low, as some Linux	1235	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	1236	Linux kernel versions will scale negatively with the number of threads
241	parallelity => MUCH higher latency). With current Linux 2.6 versions, 4-32	1237	(higher parallelity => MUCH higher latency). With current Linux 2.6
242	threads should be fine.	1238	versions, 4-32 threads should be fine.
243		1239
244	Under normal circumstances you don't need to call this function, as this	1240	Under most circumstances you don't need to call this function, as the
245	module automatically starts some threads (the exact number might change,	1241	module selects a default that is suitable for low to moderate load.
246	and is currently 4).
247		1242
248	=item IO::AIO::max_parallel $nthreads	1243	=item IO::AIO::max_parallel $nthreads
249		1244
250	Sets the maximum number of AIO threads to C<$nthreads>. If more than	1245	Sets the maximum number of AIO threads to C<$nthreads>. If more than the
251	the specified number of threads are currently running, kill them. This	1246	specified number of threads are currently running, this function kills
252	function blocks until the limit is reached.	1247	them. This function blocks until the limit is reached.
		1248
		1249	While C<$nthreads> are zero, aio requests get queued but not executed
		1250	until the number of threads has been increased again.
253		1251
254	This module automatically runs C<max_parallel 0> at program end, to ensure	1252	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.	1253	that all threads are killed and that there are no outstanding requests.
256		1254
257	Under normal circumstances you don't need to call this function.	1255	Under normal circumstances you don't need to call this function.
258		1256
		1257	=item IO::AIO::max_idle $nthreads
		1258
		1259	Limit the number of threads (default: 4) that are allowed to idle (i.e.,
		1260	threads that did not get a request to process within 10 seconds). That
		1261	means if a thread becomes idle while C<$nthreads> other threads are also
		1262	idle, it will free its resources and exit.
		1263
		1264	This is useful when you allow a large number of threads (e.g. 100 or 1000)
		1265	to allow for extremely high load situations, but want to free resources
		1266	under normal circumstances (1000 threads can easily consume 30MB of RAM).
		1267
		1268	The default is probably ok in most situations, especially if thread
		1269	creation is fast. If thread creation is very slow on your system you might
		1270	want to use larger values.
		1271
259	=item $oldnreqs = IO::AIO::max_outstanding $nreqs	1272	=item IO::AIO::max_outstanding $maxreqs
		1273
		1274	This is a very bad function to use in interactive programs because it
		1275	blocks, and a bad way to reduce concurrency because it is inexact: Better
		1276	use an C<aio_group> together with a feed callback.
260		1277
261	Sets the maximum number of outstanding requests to C<$nreqs>. If you	1278	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	1279	do queue up more than this number of requests, the next call to the
263	some requests have been handled.	1280	C<poll_cb> (and C<poll_some> and other functions calling C<poll_cb>)
		1281	function will block until the limit is no longer exceeded.
264		1282
265	The default is very large, so normally there is no practical limit. If you	1283	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	1284	number of outstanding requests.
267	this to a relatively low number, such as C<100>.
268		1285
269	Under normal circumstances you don't need to call this function.	1286	You can still queue as many requests as you want. Therefore,
		1287	C<max_outstanding> is mainly useful in simple scripts (with low values) or
		1288	as a stop gap to shield against fatal memory overflow (with large values).
270		1289
271	=back	1290	=back
272		1291
		1292	=head3 STATISTICAL INFORMATION
		1293
		1294	=over
		1295
		1296	=item IO::AIO::nreqs
		1297
		1298	Returns the number of requests currently in the ready, execute or pending
		1299	states (i.e. for which their callback has not been invoked yet).
		1300
		1301	Example: wait till there are no outstanding requests anymore:
		1302
		1303	IO::AIO::poll_wait, IO::AIO::poll_cb
		1304	while IO::AIO::nreqs;
		1305
		1306	=item IO::AIO::nready
		1307
		1308	Returns the number of requests currently in the ready state (not yet
		1309	executed).
		1310
		1311	=item IO::AIO::npending
		1312
		1313	Returns the number of requests currently in the pending state (executed,
		1314	but not yet processed by poll_cb).
		1315
		1316	=back
		1317
273	=cut	1318	=cut
274		1319
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;	1320	min_parallel 8;
288		1321
289	END {	1322	END { flush }
290	max_parallel 0;
291	}
292		1323
293	1;	1324	1;
294		1325
		1326	=head2 FORK BEHAVIOUR
		1327
		1328	This module should do "the right thing" when the process using it forks:
		1329
		1330	Before the fork, IO::AIO enters a quiescent state where no requests
		1331	can be added in other threads and no results will be processed. After
		1332	the fork the parent simply leaves the quiescent state and continues
		1333	request/result processing, while the child frees the request/result queue
		1334	(so that the requests started before the fork will only be handled in the
		1335	parent). Threads will be started on demand until the limit set in the
		1336	parent process has been reached again.
		1337
		1338	In short: the parent will, after a short pause, continue as if fork had
		1339	not been called, while the child will act as if IO::AIO has not been used
		1340	yet.
		1341
		1342	=head2 MEMORY USAGE
		1343
		1344	Per-request usage:
		1345
		1346	Each aio request uses - depending on your architecture - around 100-200
		1347	bytes of memory. In addition, stat requests need a stat buffer (possibly
		1348	a few hundred bytes), readdir requires a result buffer and so on. Perl
		1349	scalars and other data passed into aio requests will also be locked and
		1350	will consume memory till the request has entered the done state.
		1351
		1352	This is not awfully much, so queuing lots of requests is not usually a
		1353	problem.
		1354
		1355	Per-thread usage:
		1356
		1357	In the execution phase, some aio requests require more memory for
		1358	temporary buffers, and each thread requires a stack and other data
		1359	structures (usually around 16k-128k, depending on the OS).
		1360
		1361	=head1 KNOWN BUGS
		1362
		1363	Known bugs will be fixed in the next release.
		1364
295	=head1 SEE ALSO	1365	=head1 SEE ALSO
296		1366
297	L<Coro>, L<Linux::AIO>.	1367	L<AnyEvent::AIO> for easy integration into event loops, L<Coro::AIO> for a
		1368	more natural syntax.
298		1369
299	=head1 AUTHOR	1370	=head1 AUTHOR
300		1371
301	Marc Lehmann <schmorp@schmorp.de>	1372	Marc Lehmann <schmorp@schmorp.de>
302	http://home.schmorp.de/	1373	http://home.schmorp.de/

Diff Legend

–	Removed lines
+	Added lines
<	Changed lines
>	Changed lines