[ViewVC] Diff of: cvs/IO-AIO/AIO.pm

Comparing IO-AIO/AIO.pm (file contents):
Revision 1.21 by root, Wed Jul 13 00:13:09 2005 UTC vs.
Revision 1.155 by root, Sun Jun 14 20:36:59 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',	39	poll => 'r',
23	cb => \&IO::AIO::poll_cb);	40	cb => \&IO::AIO::poll_cb);
24		41
25	# Glib/Gtk2	42	# Glib/Gtk2 integration
26	add_watch Glib::IO IO::AIO::poll_fileno,	43	add_watch Glib::IO IO::AIO::poll_fileno,
27	in => sub { IO::AIO::poll_cb, 1 };	44	in => sub { IO::AIO::poll_cb; 1 };
28		45
29	# Tk	46	# Tk integration
30	Tk::Event::IO->fileevent (IO::AIO::poll_fileno, "",	47	Tk::Event::IO->fileevent (IO::AIO::poll_fileno, "",
31	readable => \&IO::AIO::poll_cb);	48	readable => \&IO::AIO::poll_cb);
32		49
33	# Danga::Socket	50	# Danga::Socket integration
34	Danga::Socket->AddOtherFds (IO::AIO::poll_fileno =>	51	Danga::Socket->AddOtherFds (IO::AIO::poll_fileno =>
35	\&IO::AIO::poll_cb);	52	\&IO::AIO::poll_cb);
36		53
37
38	=head1 DESCRIPTION	54	=head1 DESCRIPTION
39		55
40	This module implements asynchronous I/O using whatever means your	56	This module implements asynchronous I/O using whatever means your
41	operating system supports.	57	operating system supports.
42		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
43	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
44	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
45	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
46	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
47	aio functions available on many operating systems. However, they are often	79	functions available on many operating systems. However, they are often
48	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
49	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
50	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.
51		84
52	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,
53	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
54		185
55	=cut	186	=cut
56		187
57	package IO::AIO;	188	package IO::AIO;
58		189
		190	use Carp ();
		191
		192	no warnings;
		193	use strict 'vars';
		194
59	use base 'Exporter';	195	use base 'Exporter';
60		196
61	use Fcntl ();
62
63	BEGIN {	197	BEGIN {
64	$VERSION = 0.9;	198	our $VERSION = '3.23';
65		199
66	@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
67	aio_fsync aio_fdatasync aio_readahead);	201	aio_stat aio_lstat aio_unlink aio_rmdir aio_readdir aio_readdirx
68	@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';
69		217
70	require XSLoader;	218	require XSLoader;
71	XSLoader::load IO::AIO, $VERSION;	219	XSLoader::load ("IO::AIO", $VERSION);
72	}	220	}
73		221
74	=head1 FUNCTIONS	222	=head1 FUNCTIONS
75		223
76	=head2 AIO FUNCTIONS	224	=head2 AIO REQUEST FUNCTIONS
77		225
78	All the C<aio_*> calls are more or less thin wrappers around the syscall	226	All the C<aio_*> calls are more or less thin wrappers around the syscall
79	with the same name (sans C<aio_>). The arguments are similar or identical,	227	with the same name (sans C<aio_>). The arguments are similar or identical,
80	and they all accept an additional (and optional) C<$callback> argument	228	and they all accept an additional (and optional) C<$callback> argument
81	which must be a code reference. This code reference will get called with	229	which must be a code reference. This code reference will get called with
82	the syscall return code (e.g. most syscalls return C<-1> on error, unlike	230	the syscall return code (e.g. most syscalls return C<-1> on error, unlike
83	perl, which usually delivers "false") as it's sole argument when the given	231	perl, which usually delivers "false") as its sole argument after the given
84	syscall has been executed asynchronously.	232	syscall has been executed asynchronously.
85		233
86	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.
87		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
88	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
89	for this is that at the time the request is being executed, the current	241	encoded as octets. The reason for the former is that at the time the
90	working directory could have changed. Alternatively, you can make sure	242	request is being executed, the current working directory could have
91	that you 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.
92		256
93	=over 4	257	=over 4
94		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
95	=item aio_open $pathname, $flags, $mode, $callback	292	=item aio_open $pathname, $flags, $mode, $callback->($fh)
96		293
97	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
98	created filehandle for the file.	295	created filehandle for the file.
99		296
100	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,
…		…
104	list. They are the same as used by C<sysopen>.	301	list. They are the same as used by C<sysopen>.
105		302
106	Likewise, C<$mode> specifies the mode of the newly created file, if it	303	Likewise, C<$mode> specifies the mode of the newly created file, if it
107	didn't exist and C<O_CREAT> has been given, just like perl's C<sysopen>,	304	didn't exist and C<O_CREAT> has been given, just like perl's C<sysopen>,
108	except that it is mandatory (i.e. use C<0> if you don't create new files,	305	except that it is mandatory (i.e. use C<0> if you don't create new files,
109	and C<0666> or C<0777> if you do).	306	and C<0666> or C<0777> if you do). Note that the C<$mode> will be modified
		307	by the umask in effect then the request is being executed, so better never
		308	change the umask.
110		309
111	Example:	310	Example:
112		311
113	aio_open "/etc/passwd", O_RDONLY, 0, sub {	312	aio_open "/etc/passwd", O_RDONLY, 0, sub {
114	if ($_[0]) {	313	if ($_[0]) {
…		…
117	} else {	316	} else {
118	die "open failed: $!\n";	317	die "open failed: $!\n";
119	}	318	}
120	};	319	};
121		320
		321
122	=item aio_close $fh, $callback	322	=item aio_close $fh, $callback->($status)
123		323
124	Asynchronously close a file and call the callback with the result	324	Asynchronously close a file and call the callback with the result
125	code. I<WARNING:> although accepted, you should not pass in a perl	325	code.
126	filehandle here, as perl will likely close the file descriptor another
127	time when the filehandle is destroyed. Normally, you can safely call perls
128	C<close> or just let filehandles go out of scope.
129		326
130	This is supposed to be a bug in the API, so that might change. It's	327	Unfortunately, you can't do this to perl. Perl I<insists> very strongly on
131	therefore best to avoid this function.	328	closing the file descriptor associated with the filehandle itself.
132		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
133	=item aio_read $fh,$offset,$length, $data,$dataoffset,$callback	339	=item aio_read $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
134		340
135	=item aio_write $fh,$offset,$length, $data,$dataoffset,$callback	341	=item aio_write $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
136		342
137	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
138	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<$dataoffset>
139	callback without the actual number of bytes read (or -1 on error, just	345	and calls the callback without the actual number of bytes read (or -1 on
140	like the syscall).	346	error, just like the syscall).
		347
		348	C<aio_read> will, like C<sysread>, shrink or grow the C<$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).
141		364
142	Example: Read 15 bytes at offset 7 into scalar C<$buffer>, starting at	365	Example: Read 15 bytes at offset 7 into scalar C<$buffer>, starting at
143	offset C<0> within the scalar:	366	offset C<0> within the scalar:
144		367
145	aio_read $fh, 7, 15, $buffer, 0, sub {	368	aio_read $fh, 7, 15, $buffer, 0, sub {
146	$_[0] > 0 or die "read error: $!";	369	$_[0] > 0 or die "read error: $!";
147	print "read $_[0] bytes: <$buffer>\n";	370	print "read $_[0] bytes: <$buffer>\n";
148	};	371	};
149		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
150	=item aio_readahead $fh,$offset,$length, $callback	398	=item aio_readahead $fh,$offset,$length, $callback->($retval)
151
152	Asynchronously reads the specified byte range into the page cache, using
153	the C<readahead> syscall. If that syscall doesn't exist (likely if your OS
154	isn't Linux) the status will be C<-1> and C<$!> is set to C<ENOSYS>.
155		399
156	C<aio_readahead> populates the page cache with data from a file so that	400	C<aio_readahead> populates the page cache with data from a file so that
157	subsequent reads from that file will not block on disk I/O. The C<$offset>	401	subsequent reads from that file will not block on disk I/O. The C<$offset>
158	argument specifies the starting point from which data is to be read and	402	argument specifies the starting point from which data is to be read and
159	C<$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
160	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
161	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
162	(off-set+length). C<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
163	file. The current file offset of the file is left unchanged.	407	file. The current file offset of the file is left unchanged.
164		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
165	=item aio_stat $fh_or_path, $callback	413	=item aio_stat $fh_or_path, $callback->($status)
166		414
167	=item aio_lstat $fh, $callback	415	=item aio_lstat $fh, $callback->($status)
168		416
169	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
170	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 _>
171	or C<-s _> etc...	419	or C<-s _> etc...
172		420
…		…
182	aio_stat "/etc/passwd", sub {	430	aio_stat "/etc/passwd", sub {
183	$_[0] and die "stat failed: $!";	431	$_[0] and die "stat failed: $!";
184	print "size is ", -s _, "\n";	432	print "size is ", -s _, "\n";
185	};	433	};
186		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
187	=item aio_unlink $pathname, $callback	477	=item aio_unlink $pathname, $callback->($status)
188		478
189	Asynchronously unlink (delete) a file and call the callback with the	479	Asynchronously unlink (delete) a file and call the callback with the
190	result code.	480	result code.
191		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 is passed a single argument which is either C<undef> or an
		539	array-ref with the filenames.
		540
		541
		542	=item aio_readdirx $pathname, $flags, $callback->($entries, $flags)
		543
		544	Quite similar to C<aio_readdir>, but the C<$flags> argument allows to tune
		545	behaviour and output format. In case of an error, C<$entries> will be
		546	C<undef>.
		547
		548	The flags are a combination of the following constants, ORed together (the
		549	flags will also be passed to the callback, possibly modified):
		550
		551	=over 4
		552
		553	=item IO::AIO::READDIR_DENTS
		554
		555	When this flag is off, then the callback gets an arrayref with of names
		556	only (as with C<aio_readdir>), otherwise it gets an arrayref with
		557	C<[$name, $type, $inode]> arrayrefs, each describing a single directory
		558	entry in more detail.
		559
		560	C<$name> is the name of the entry.
		561
		562	C<$type> is one of the C<IO::AIO::DT_xxx> constants:
		563
		564	C<IO::AIO::DT_UNKNOWN>, C<IO::AIO::DT_FIFO>, C<IO::AIO::DT_CHR>, C<IO::AIO::DT_DIR>,
		565	C<IO::AIO::DT_BLK>, C<IO::AIO::DT_REG>, C<IO::AIO::DT_LNK>, C<IO::AIO::DT_SOCK>,
		566	C<IO::AIO::DT_WHT>.
		567
		568	C<IO::AIO::DT_UNKNOWN> means just that: readdir does not know. If you need to
		569	know, you have to run stat yourself. Also, for speed reasons, the C<$type>
		570	scalars are read-only: you can not modify them.
		571
		572	C<$inode> is the inode number (which might not be exact on systems with 64
		573	bit inode numbers and 32 bit perls). This field has unspecified content on
		574	systems that do not deliver the inode information.
		575
		576	=item IO::AIO::READDIR_DIRS_FIRST
		577
		578	When this flag is set, then the names will be returned in an order where
		579	likely directories come first. This is useful when you need to quickly
		580	find directories, or you want to find all directories while avoiding to
		581	stat() each entry.
		582
		583	If the system returns type information in readdir, then this is used
		584	to find directories directly. Otherwise, likely directories are files
		585	beginning with ".", or otherwise files with no dots, of which files with
		586	short names are tried first.
		587
		588	=item IO::AIO::READDIR_STAT_ORDER
		589
		590	When this flag is set, then the names will be returned in an order
		591	suitable for stat()'ing each one. That is, when you plan to stat()
		592	all files in the given directory, then the returned order will likely
		593	be fastest.
		594
		595	If both this flag and C<IO::AIO::READDIR_DIRS_FIRST> are specified, then
		596	the likely dirs come first, resulting in a less optimal stat order.
		597
		598	=item IO::AIO::READDIR_FOUND_UNKNOWN
		599
		600	This flag should not be set when calling C<aio_readdirx>. Instead, it
		601	is being set by C<aio_readdirx>, when any of the C<$type>'s found were
		602	C<IO::AIO::DT_UNKNOWN>. The absense of this flag therefore indicates that all
		603	C<$type>'s are known, which can be used to speed up some algorithms.
		604
		605	=back
		606
		607
		608	=item aio_load $path, $data, $callback->($status)
		609
		610	This is a composite request that tries to fully load the given file into
		611	memory. Status is the same as with aio_read.
		612
		613	=cut
		614
		615	sub aio_load($$;$) {
		616	my ($path, undef, $cb) = @_;
		617	my $data = \$_[1];
		618
		619	my $pri = aioreq_pri;
		620	my $grp = aio_group $cb;
		621
		622	aioreq_pri $pri;
		623	add $grp aio_open $path, O_RDONLY, 0, sub {
		624	my $fh = shift
		625	or return $grp->result (-1);
		626
		627	aioreq_pri $pri;
		628	add $grp aio_read $fh, 0, (-s $fh), $$data, 0, sub {
		629	$grp->result ($_[0]);
		630	};
		631	};
		632
		633	$grp
		634	}
		635
		636	=item aio_copy $srcpath, $dstpath, $callback->($status)
		637
		638	Try to copy the I<file> (directories not supported as either source or
		639	destination) from C<$srcpath> to C<$dstpath> and call the callback with
		640	the C<0> (error) or C<-1> ok.
		641
		642	This is a composite request that creates the destination file with
		643	mode 0200 and copies the contents of the source file into it using
		644	C<aio_sendfile>, followed by restoring atime, mtime, access mode and
		645	uid/gid, in that order.
		646
		647	If an error occurs, the partial destination file will be unlinked, if
		648	possible, except when setting atime, mtime, access mode and uid/gid, where
		649	errors are being ignored.
		650
		651	=cut
		652
		653	sub aio_copy($$;$) {
		654	my ($src, $dst, $cb) = @_;
		655
		656	my $pri = aioreq_pri;
		657	my $grp = aio_group $cb;
		658
		659	aioreq_pri $pri;
		660	add $grp aio_open $src, O_RDONLY, 0, sub {
		661	if (my $src_fh = $_[0]) {
		662	my @stat = stat $src_fh; # hmm, might bock over nfs?
		663
		664	aioreq_pri $pri;
		665	add $grp aio_open $dst, O_CREAT \| O_WRONLY \| O_TRUNC, 0200, sub {
		666	if (my $dst_fh = $_[0]) {
		667	aioreq_pri $pri;
		668	add $grp aio_sendfile $dst_fh, $src_fh, 0, $stat[7], sub {
		669	if ($_[0] == $stat[7]) {
		670	$grp->result (0);
		671	close $src_fh;
		672
		673	my $ch = sub {
		674	aioreq_pri $pri;
		675	add $grp aio_chmod $dst_fh, $stat[2] & 07777, sub {
		676	aioreq_pri $pri;
		677	add $grp aio_chown $dst_fh, $stat[4], $stat[5], sub {
		678	aioreq_pri $pri;
		679	add $grp aio_close $dst_fh;
		680	}
		681	};
		682	};
		683
		684	aioreq_pri $pri;
		685	add $grp aio_utime $dst_fh, $stat[8], $stat[9], sub {
		686	if ($_[0] < 0 && $! == ENOSYS) {
		687	aioreq_pri $pri;
		688	add $grp aio_utime $dst, $stat[8], $stat[9], $ch;
		689	} else {
		690	$ch->();
		691	}
		692	};
		693	} else {
		694	$grp->result (-1);
		695	close $src_fh;
		696	close $dst_fh;
		697
		698	aioreq $pri;
		699	add $grp aio_unlink $dst;
		700	}
		701	};
		702	} else {
		703	$grp->result (-1);
		704	}
		705	},
		706
		707	} else {
		708	$grp->result (-1);
		709	}
		710	};
		711
		712	$grp
		713	}
		714
		715	=item aio_move $srcpath, $dstpath, $callback->($status)
		716
		717	Try to move the I<file> (directories not supported as either source or
		718	destination) from C<$srcpath> to C<$dstpath> and call the callback with
		719	the C<0> (error) or C<-1> ok.
		720
		721	This is a composite request that tries to rename(2) the file first; if
		722	rename fails with C<EXDEV>, it copies the file with C<aio_copy> and, if
		723	that is successful, unlinks the C<$srcpath>.
		724
		725	=cut
		726
		727	sub aio_move($$;$) {
		728	my ($src, $dst, $cb) = @_;
		729
		730	my $pri = aioreq_pri;
		731	my $grp = aio_group $cb;
		732
		733	aioreq_pri $pri;
		734	add $grp aio_rename $src, $dst, sub {
		735	if ($_[0] && $! == EXDEV) {
		736	aioreq_pri $pri;
		737	add $grp aio_copy $src, $dst, sub {
		738	$grp->result ($_[0]);
		739
		740	if (!$_[0]) {
		741	aioreq_pri $pri;
		742	add $grp aio_unlink $src;
		743	}
		744	};
		745	} else {
		746	$grp->result ($_[0]);
		747	}
		748	};
		749
		750	$grp
		751	}
		752
		753	=item aio_scandir $path, $maxreq, $callback->($dirs, $nondirs)
		754
		755	Scans a directory (similar to C<aio_readdir>) but additionally tries to
		756	efficiently separate the entries of directory C<$path> into two sets of
		757	names, directories you can recurse into (directories), and ones you cannot
		758	recurse into (everything else, including symlinks to directories).
		759
		760	C<aio_scandir> is a composite request that creates of many sub requests_
		761	C<$maxreq> specifies the maximum number of outstanding aio requests that
		762	this function generates. If it is C<< <= 0 >>, then a suitable default
		763	will be chosen (currently 4).
		764
		765	On error, the callback is called without arguments, otherwise it receives
		766	two array-refs with path-relative entry names.
		767
		768	Example:
		769
		770	aio_scandir $dir, 0, sub {
		771	my ($dirs, $nondirs) = @_;
		772	print "real directories: @$dirs\n";
		773	print "everything else: @$nondirs\n";
		774	};
		775
		776	Implementation notes.
		777
		778	The C<aio_readdir> cannot be avoided, but C<stat()>'ing every entry can.
		779
		780	If readdir returns file type information, then this is used directly to
		781	find directories.
		782
		783	Otherwise, after reading the directory, the modification time, size etc.
		784	of the directory before and after the readdir is checked, and if they
		785	match (and isn't the current time), the link count will be used to decide
		786	how many entries are directories (if >= 2). Otherwise, no knowledge of the
		787	number of subdirectories will be assumed.
		788
		789	Then entries will be sorted into likely directories a non-initial dot
		790	currently) and likely non-directories (see C<aio_readdirx>). Then every
		791	entry plus an appended C</.> will be C<stat>'ed, likely directories first,
		792	in order of their inode numbers. If that succeeds, it assumes that the
		793	entry is a directory or a symlink to directory (which will be checked
		794	seperately). This is often faster than stat'ing the entry itself because
		795	filesystems might detect the type of the entry without reading the inode
		796	data (e.g. ext2fs filetype feature), even on systems that cannot return
		797	the filetype information on readdir.
		798
		799	If the known number of directories (link count - 2) has been reached, the
		800	rest of the entries is assumed to be non-directories.
		801
		802	This only works with certainty on POSIX (= UNIX) filesystems, which
		803	fortunately are the vast majority of filesystems around.
		804
		805	It will also likely work on non-POSIX filesystems with reduced efficiency
		806	as those tend to return 0 or 1 as link counts, which disables the
		807	directory counting heuristic.
		808
		809	=cut
		810
		811	sub aio_scandir($$;$) {
		812	my ($path, $maxreq, $cb) = @_;
		813
		814	my $pri = aioreq_pri;
		815
		816	my $grp = aio_group $cb;
		817
		818	$maxreq = 4 if $maxreq <= 0;
		819
		820	# stat once
		821	aioreq_pri $pri;
		822	add $grp aio_stat $path, sub {
		823	return $grp->result () if $_[0];
		824	my $now = time;
		825	my $hash1 = join ":", (stat _)[0,1,3,7,9];
		826
		827	# read the directory entries
		828	aioreq_pri $pri;
		829	add $grp aio_readdirx $path, READDIR_DIRS_FIRST, sub {
		830	my $entries = shift
		831	or return $grp->result ();
		832
		833	# stat the dir another time
		834	aioreq_pri $pri;
		835	add $grp aio_stat $path, sub {
		836	my $hash2 = join ":", (stat _)[0,1,3,7,9];
		837
		838	my $ndirs;
		839
		840	# take the slow route if anything looks fishy
		841	if ($hash1 ne $hash2 or (stat _)[9] == $now) {
		842	$ndirs = -1;
		843	} else {
		844	# if nlink == 2, we are finished
		845	# for non-posix-fs's, we rely on nlink < 2
		846	$ndirs = (stat _)[3] - 2
		847	or return $grp->result ([], $entries);
		848	}
		849
		850	my (@dirs, @nondirs);
		851
		852	my $statgrp = add $grp aio_group sub {
		853	$grp->result (\@dirs, \@nondirs);
		854	};
		855
		856	limit $statgrp $maxreq;
		857	feed $statgrp sub {
		858	return unless @$entries;
		859	my $entry = shift @$entries;
		860
		861	aioreq_pri $pri;
		862	add $statgrp aio_stat "$path/$entry/.", sub {
		863	if ($_[0] < 0) {
		864	push @nondirs, $entry;
		865	} else {
		866	# need to check for real directory
		867	aioreq_pri $pri;
		868	add $statgrp aio_lstat "$path/$entry", sub {
		869	if (-d _) {
		870	push @dirs, $entry;
		871
		872	unless (--$ndirs) {
		873	push @nondirs, @$entries;
		874	feed $statgrp;
		875	}
		876	} else {
		877	push @nondirs, $entry;
		878	}
		879	}
		880	}
		881	};
		882	};
		883	};
		884	};
		885	};
		886
		887	$grp
		888	}
		889
		890	=item aio_rmtree $path, $callback->($status)
		891
		892	Delete a directory tree starting (and including) C<$path>, return the
		893	status of the final C<rmdir> only. This is a composite request that
		894	uses C<aio_scandir> to recurse into and rmdir directories, and unlink
		895	everything else.
		896
		897	=cut
		898
		899	sub aio_rmtree;
		900	sub aio_rmtree($;$) {
		901	my ($path, $cb) = @_;
		902
		903	my $pri = aioreq_pri;
		904	my $grp = aio_group $cb;
		905
		906	aioreq_pri $pri;
		907	add $grp aio_scandir $path, 0, sub {
		908	my ($dirs, $nondirs) = @_;
		909
		910	my $dirgrp = aio_group sub {
		911	add $grp aio_rmdir $path, sub {
		912	$grp->result ($_[0]);
		913	};
		914	};
		915
		916	(aioreq_pri $pri), add $dirgrp aio_rmtree "$path/$_" for @$dirs;
		917	(aioreq_pri $pri), add $dirgrp aio_unlink "$path/$_" for @$nondirs;
		918
		919	add $grp $dirgrp;
		920	};
		921
		922	$grp
		923	}
		924
		925	=item aio_sync $callback->($status)
		926
		927	Asynchronously call sync and call the callback when finished.
		928
192	=item aio_fsync $fh, $callback	929	=item aio_fsync $fh, $callback->($status)
193		930
194	Asynchronously call fsync on the given filehandle and call the callback	931	Asynchronously call fsync on the given filehandle and call the callback
195	with the fsync result code.	932	with the fsync result code.
196		933
197	=item aio_fdatasync $fh, $callback	934	=item aio_fdatasync $fh, $callback->($status)
198		935
199	Asynchronously call fdatasync on the given filehandle and call the	936	Asynchronously call fdatasync on the given filehandle and call the
200	callback with the fdatasync result code. Might set C<$!> to C<ENOSYS> if	937	callback with the fdatasync result code.
201	C<fdatasync> is not available.	938
		939	If this call isn't available because your OS lacks it or it couldn't be
		940	detected, it will be emulated by calling C<fsync> instead.
		941
		942	=item aio_sync_file_range $fh, $offset, $nbytes, $flags, $callback->($status)
		943
		944	Sync the data portion of the file specified by C<$offset> and C<$length>
		945	to disk (but NOT the metadata), by calling the Linux-specific
		946	sync_file_range call. If sync_file_range is not available or it returns
		947	ENOSYS, then fdatasync or fsync is being substituted.
		948
		949	C<$flags> can be a combination of C<IO::AIO::SYNC_FILE_RANGE_WAIT_BEFORE>,
		950	C<IO::AIO::SYNC_FILE_RANGE_WRITE> and
		951	C<IO::AIO::SYNC_FILE_RANGE_WAIT_AFTER>: refer to the sync_file_range
		952	manpage for details.
		953
		954	=item aio_pathsync $path, $callback->($status)
		955
		956	This request tries to open, fsync and close the given path. This is a
		957	composite request intended to sync directories after directory operations
		958	(E.g. rename). This might not work on all operating systems or have any
		959	specific effect, but usually it makes sure that directory changes get
		960	written to disc. It works for anything that can be opened for read-only,
		961	not just directories.
		962
		963	Passes C<0> when everything went ok, and C<-1> on error.
		964
		965	=cut
		966
		967	sub aio_pathsync($;$) {
		968	my ($path, $cb) = @_;
		969
		970	my $pri = aioreq_pri;
		971	my $grp = aio_group $cb;
		972
		973	aioreq_pri $pri;
		974	add $grp aio_open $path, O_RDONLY, 0, sub {
		975	my ($fh) = @_;
		976	if ($fh) {
		977	aioreq_pri $pri;
		978	add $grp aio_fsync $fh, sub {
		979	$grp->result ($_[0]);
		980
		981	aioreq_pri $pri;
		982	add $grp aio_close $fh;
		983	};
		984	} else {
		985	$grp->result (-1);
		986	}
		987	};
		988
		989	$grp
		990	}
		991
		992	=item aio_group $callback->(...)
		993
		994	This is a very special aio request: Instead of doing something, it is a
		995	container for other aio requests, which is useful if you want to bundle
		996	many requests into a single, composite, request with a definite callback
		997	and the ability to cancel the whole request with its subrequests.
		998
		999	Returns an object of class L<IO::AIO::GRP>. See its documentation below
		1000	for more info.
		1001
		1002	Example:
		1003
		1004	my $grp = aio_group sub {
		1005	print "all stats done\n";
		1006	};
		1007
		1008	add $grp
		1009	(aio_stat ...),
		1010	(aio_stat ...),
		1011	...;
		1012
		1013	=item aio_nop $callback->()
		1014
		1015	This is a special request - it does nothing in itself and is only used for
		1016	side effects, such as when you want to add a dummy request to a group so
		1017	that finishing the requests in the group depends on executing the given
		1018	code.
		1019
		1020	While this request does nothing, it still goes through the execution
		1021	phase and still requires a worker thread. Thus, the callback will not
		1022	be executed immediately but only after other requests in the queue have
		1023	entered their execution phase. This can be used to measure request
		1024	latency.
		1025
		1026	=item IO::AIO::aio_busy $fractional_seconds, $callback->() NOT EXPORTED
		1027
		1028	Mainly used for debugging and benchmarking, this aio request puts one of
		1029	the request workers to sleep for the given time.
		1030
		1031	While it is theoretically handy to have simple I/O scheduling requests
		1032	like sleep and file handle readable/writable, the overhead this creates is
		1033	immense (it blocks a thread for a long time) so do not use this function
		1034	except to put your application under artificial I/O pressure.
202		1035
203	=back	1036	=back
204		1037
		1038	=head2 IO::AIO::REQ CLASS
		1039
		1040	All non-aggregate C<aio_*> functions return an object of this class when
		1041	called in non-void context.
		1042
		1043	=over 4
		1044
		1045	=item cancel $req
		1046
		1047	Cancels the request, if possible. Has the effect of skipping execution
		1048	when entering the B<execute> state and skipping calling the callback when
		1049	entering the the B<result> state, but will leave the request otherwise
		1050	untouched (with the exception of readdir). That means that requests that
		1051	currently execute will not be stopped and resources held by the request
		1052	will not be freed prematurely.
		1053
		1054	=item cb $req $callback->(...)
		1055
		1056	Replace (or simply set) the callback registered to the request.
		1057
		1058	=back
		1059
		1060	=head2 IO::AIO::GRP CLASS
		1061
		1062	This class is a subclass of L<IO::AIO::REQ>, so all its methods apply to
		1063	objects of this class, too.
		1064
		1065	A IO::AIO::GRP object is a special request that can contain multiple other
		1066	aio requests.
		1067
		1068	You create one by calling the C<aio_group> constructing function with a
		1069	callback that will be called when all contained requests have entered the
		1070	C<done> state:
		1071
		1072	my $grp = aio_group sub {
		1073	print "all requests are done\n";
		1074	};
		1075
		1076	You add requests by calling the C<add> method with one or more
		1077	C<IO::AIO::REQ> objects:
		1078
		1079	$grp->add (aio_unlink "...");
		1080
		1081	add $grp aio_stat "...", sub {
		1082	$_[0] or return $grp->result ("error");
		1083
		1084	# add another request dynamically, if first succeeded
		1085	add $grp aio_open "...", sub {
		1086	$grp->result ("ok");
		1087	};
		1088	};
		1089
		1090	This makes it very easy to create composite requests (see the source of
		1091	C<aio_move> for an application) that work and feel like simple requests.
		1092
		1093	=over 4
		1094
		1095	=item * The IO::AIO::GRP objects will be cleaned up during calls to
		1096	C<IO::AIO::poll_cb>, just like any other request.
		1097
		1098	=item * They can be canceled like any other request. Canceling will cancel not
		1099	only the request itself, but also all requests it contains.
		1100
		1101	=item * They can also can also be added to other IO::AIO::GRP objects.
		1102
		1103	=item * You must not add requests to a group from within the group callback (or
		1104	any later time).
		1105
		1106	=back
		1107
		1108	Their lifetime, simplified, looks like this: when they are empty, they
		1109	will finish very quickly. If they contain only requests that are in the
		1110	C<done> state, they will also finish. Otherwise they will continue to
		1111	exist.
		1112
		1113	That means after creating a group you have some time to add requests
		1114	(precisely before the callback has been invoked, which is only done within
		1115	the C<poll_cb>). And in the callbacks of those requests, you can add
		1116	further requests to the group. And only when all those requests have
		1117	finished will the the group itself finish.
		1118
		1119	=over 4
		1120
		1121	=item add $grp ...
		1122
		1123	=item $grp->add (...)
		1124
		1125	Add one or more requests to the group. Any type of L<IO::AIO::REQ> can
		1126	be added, including other groups, as long as you do not create circular
		1127	dependencies.
		1128
		1129	Returns all its arguments.
		1130
		1131	=item $grp->cancel_subs
		1132
		1133	Cancel all subrequests and clears any feeder, but not the group request
		1134	itself. Useful when you queued a lot of events but got a result early.
		1135
		1136	=item $grp->result (...)
		1137
		1138	Set the result value(s) that will be passed to the group callback when all
		1139	subrequests have finished and set the groups errno to the current value
		1140	of errno (just like calling C<errno> without an error number). By default,
		1141	no argument will be passed and errno is zero.
		1142
		1143	=item $grp->errno ([$errno])
		1144
		1145	Sets the group errno value to C<$errno>, or the current value of errno
		1146	when the argument is missing.
		1147
		1148	Every aio request has an associated errno value that is restored when
		1149	the callback is invoked. This method lets you change this value from its
		1150	default (0).
		1151
		1152	Calling C<result> will also set errno, so make sure you either set C<$!>
		1153	before the call to C<result>, or call c<errno> after it.
		1154
		1155	=item feed $grp $callback->($grp)
		1156
		1157	Sets a feeder/generator on this group: every group can have an attached
		1158	generator that generates requests if idle. The idea behind this is that,
		1159	although you could just queue as many requests as you want in a group,
		1160	this might starve other requests for a potentially long time. For example,
		1161	C<aio_scandir> might generate hundreds of thousands C<aio_stat> requests,
		1162	delaying any later requests for a long time.
		1163
		1164	To avoid this, and allow incremental generation of requests, you can
		1165	instead a group and set a feeder on it that generates those requests. The
		1166	feed callback will be called whenever there are few enough (see C<limit>,
		1167	below) requests active in the group itself and is expected to queue more
		1168	requests.
		1169
		1170	The feed callback can queue as many requests as it likes (i.e. C<add> does
		1171	not impose any limits).
		1172
		1173	If the feed does not queue more requests when called, it will be
		1174	automatically removed from the group.
		1175
		1176	If the feed limit is C<0> when this method is called, it will be set to
		1177	C<2> automatically.
		1178
		1179	Example:
		1180
		1181	# stat all files in @files, but only ever use four aio requests concurrently:
		1182
		1183	my $grp = aio_group sub { print "finished\n" };
		1184	limit $grp 4;
		1185	feed $grp sub {
		1186	my $file = pop @files
		1187	or return;
		1188
		1189	add $grp aio_stat $file, sub { ... };
		1190	};
		1191
		1192	=item limit $grp $num
		1193
		1194	Sets the feeder limit for the group: The feeder will be called whenever
		1195	the group contains less than this many requests.
		1196
		1197	Setting the limit to C<0> will pause the feeding process.
		1198
		1199	The default value for the limit is C<0>, but note that setting a feeder
		1200	automatically bumps it up to C<2>.
		1201
		1202	=back
		1203
205	=head2 SUPPORT FUNCTIONS	1204	=head2 SUPPORT FUNCTIONS
		1205
		1206	=head3 EVENT PROCESSING AND EVENT LOOP INTEGRATION
206		1207
207	=over 4	1208	=over 4
208		1209
209	=item $fileno = IO::AIO::poll_fileno	1210	=item $fileno = IO::AIO::poll_fileno
210		1211
…		…
215		1216
216	See C<poll_cb> for an example.	1217	See C<poll_cb> for an example.
217		1218
218	=item IO::AIO::poll_cb	1219	=item IO::AIO::poll_cb
219		1220
220	Process all outstanding events on the result pipe. You have to call this	1221	Process some outstanding events on the result pipe. You have to call this
221	regularly. Returns the number of events processed. Returns immediately	1222	regularly. Returns C<0> if all events could be processed, or C<-1> if it
222	when no events are outstanding.	1223	returned earlier for whatever reason. Returns immediately when no events
		1224	are outstanding. The amount of events processed depends on the settings of
		1225	C<IO::AIO::max_poll_req> and C<IO::AIO::max_poll_time>.
		1226
		1227	If not all requests were processed for whatever reason, the filehandle
		1228	will still be ready when C<poll_cb> returns, so normally you don't have to
		1229	do anything special to have it called later.
223		1230
224	Example: Install an Event watcher that automatically calls	1231	Example: Install an Event watcher that automatically calls
225	IO::AIO::poll_cb with high priority:	1232	IO::AIO::poll_cb with high priority:
226		1233
227	Event->io (fd => IO::AIO::poll_fileno,	1234	Event->io (fd => IO::AIO::poll_fileno,
228	poll => 'r', async => 1,	1235	poll => 'r', async => 1,
229	cb => \&IO::AIO::poll_cb);	1236	cb => \&IO::AIO::poll_cb);
230		1237
		1238	=item IO::AIO::max_poll_reqs $nreqs
		1239
		1240	=item IO::AIO::max_poll_time $seconds
		1241
		1242	These set the maximum number of requests (default C<0>, meaning infinity)
		1243	that are being processed by C<IO::AIO::poll_cb> in one call, respectively
		1244	the maximum amount of time (default C<0>, meaning infinity) spent in
		1245	C<IO::AIO::poll_cb> to process requests (more correctly the mininum amount
		1246	of time C<poll_cb> is allowed to use).
		1247
		1248	Setting C<max_poll_time> to a non-zero value creates an overhead of one
		1249	syscall per request processed, which is not normally a problem unless your
		1250	callbacks are really really fast or your OS is really really slow (I am
		1251	not mentioning Solaris here). Using C<max_poll_reqs> incurs no overhead.
		1252
		1253	Setting these is useful if you want to ensure some level of
		1254	interactiveness when perl is not fast enough to process all requests in
		1255	time.
		1256
		1257	For interactive programs, values such as C<0.01> to C<0.1> should be fine.
		1258
		1259	Example: Install an Event watcher that automatically calls
		1260	IO::AIO::poll_cb with low priority, to ensure that other parts of the
		1261	program get the CPU sometimes even under high AIO load.
		1262
		1263	# try not to spend much more than 0.1s in poll_cb
		1264	IO::AIO::max_poll_time 0.1;
		1265
		1266	# use a low priority so other tasks have priority
		1267	Event->io (fd => IO::AIO::poll_fileno,
		1268	poll => 'r', nice => 1,
		1269	cb => &IO::AIO::poll_cb);
		1270
231	=item IO::AIO::poll_wait	1271	=item IO::AIO::poll_wait
232		1272
		1273	If there are any outstanding requests and none of them in the result
233	Wait till the result filehandle becomes ready for reading (simply does a	1274	phase, wait till the result filehandle becomes ready for reading (simply
234	C<select> on the filehandle. This is useful if you want to synchronously wait	1275	does a C<select> on the filehandle. This is useful if you want to
235	for some requests to finish).	1276	synchronously wait for some requests to finish).
236		1277
237	See C<nreqs> for an example.	1278	See C<nreqs> for an example.
238		1279
		1280	=item IO::AIO::poll
		1281
		1282	Waits until some requests have been handled.
		1283
		1284	Returns the number of requests processed, but is otherwise strictly
		1285	equivalent to:
		1286
		1287	IO::AIO::poll_wait, IO::AIO::poll_cb
		1288
239	=item IO::AIO::nreqs	1289	=item IO::AIO::flush
240		1290
241	Returns the number of requests currently outstanding (i.e. for which their	1291	Wait till all outstanding AIO requests have been handled.
242	callback has not been invoked yet).
243		1292
244	Example: wait till there are no outstanding requests anymore:	1293	Strictly equivalent to:
245		1294
246	IO::AIO::poll_wait, IO::AIO::poll_cb	1295	IO::AIO::poll_wait, IO::AIO::poll_cb
247	while IO::AIO::nreqs;	1296	while IO::AIO::nreqs;
248		1297
		1298	=back
		1299
		1300	=head3 CONTROLLING THE NUMBER OF THREADS
		1301
		1302	=over
		1303
		1304	=item IO::AIO::min_parallel $nthreads
		1305
		1306	Set the minimum number of AIO threads to C<$nthreads>. The current
		1307	default is C<8>, which means eight asynchronous operations can execute
		1308	concurrently at any one time (the number of outstanding requests,
		1309	however, is unlimited).
		1310
		1311	IO::AIO starts threads only on demand, when an AIO request is queued and
		1312	no free thread exists. Please note that queueing up a hundred requests can
		1313	create demand for a hundred threads, even if it turns out that everything
		1314	is in the cache and could have been processed faster by a single thread.
		1315
		1316	It is recommended to keep the number of threads relatively low, as some
		1317	Linux kernel versions will scale negatively with the number of threads
		1318	(higher parallelity => MUCH higher latency). With current Linux 2.6
		1319	versions, 4-32 threads should be fine.
		1320
		1321	Under most circumstances you don't need to call this function, as the
		1322	module selects a default that is suitable for low to moderate load.
		1323
		1324	=item IO::AIO::max_parallel $nthreads
		1325
		1326	Sets the maximum number of AIO threads to C<$nthreads>. If more than the
		1327	specified number of threads are currently running, this function kills
		1328	them. This function blocks until the limit is reached.
		1329
		1330	While C<$nthreads> are zero, aio requests get queued but not executed
		1331	until the number of threads has been increased again.
		1332
		1333	This module automatically runs C<max_parallel 0> at program end, to ensure
		1334	that all threads are killed and that there are no outstanding requests.
		1335
		1336	Under normal circumstances you don't need to call this function.
		1337
		1338	=item IO::AIO::max_idle $nthreads
		1339
		1340	Limit the number of threads (default: 4) that are allowed to idle (i.e.,
		1341	threads that did not get a request to process within 10 seconds). That
		1342	means if a thread becomes idle while C<$nthreads> other threads are also
		1343	idle, it will free its resources and exit.
		1344
		1345	This is useful when you allow a large number of threads (e.g. 100 or 1000)
		1346	to allow for extremely high load situations, but want to free resources
		1347	under normal circumstances (1000 threads can easily consume 30MB of RAM).
		1348
		1349	The default is probably ok in most situations, especially if thread
		1350	creation is fast. If thread creation is very slow on your system you might
		1351	want to use larger values.
		1352
		1353	=item IO::AIO::max_outstanding $maxreqs
		1354
		1355	This is a very bad function to use in interactive programs because it
		1356	blocks, and a bad way to reduce concurrency because it is inexact: Better
		1357	use an C<aio_group> together with a feed callback.
		1358
		1359	Sets the maximum number of outstanding requests to C<$nreqs>. If you
		1360	do queue up more than this number of requests, the next call to the
		1361	C<poll_cb> (and C<poll_some> and other functions calling C<poll_cb>)
		1362	function will block until the limit is no longer exceeded.
		1363
		1364	The default value is very large, so there is no practical limit on the
		1365	number of outstanding requests.
		1366
		1367	You can still queue as many requests as you want. Therefore,
		1368	C<max_outstanding> is mainly useful in simple scripts (with low values) or
		1369	as a stop gap to shield against fatal memory overflow (with large values).
		1370
		1371	=back
		1372
		1373	=head3 STATISTICAL INFORMATION
		1374
		1375	=over
		1376
249	=item IO::AIO::flush	1377	=item IO::AIO::nreqs
250		1378
251	Wait till all outstanding AIO requests have been handled.	1379	Returns the number of requests currently in the ready, execute or pending
		1380	states (i.e. for which their callback has not been invoked yet).
252		1381
253	Strictly equivalent to:	1382	Example: wait till there are no outstanding requests anymore:
254		1383
255	IO::AIO::poll_wait, IO::AIO::poll_cb	1384	IO::AIO::poll_wait, IO::AIO::poll_cb
256	while IO::AIO::nreqs;	1385	while IO::AIO::nreqs;
257		1386
		1387	=item IO::AIO::nready
		1388
		1389	Returns the number of requests currently in the ready state (not yet
		1390	executed).
		1391
258	=item IO::AIO::poll	1392	=item IO::AIO::npending
259		1393
260	Waits until some requests have been handled.	1394	Returns the number of requests currently in the pending state (executed,
261		1395	but not yet processed by poll_cb).
262	Strictly equivalent to:
263
264	IO::AIO::poll_wait, IO::AIO::poll_cb
265	if IO::AIO::nreqs;
266
267	=item IO::AIO::min_parallel $nthreads
268
269	Set the minimum number of AIO threads to C<$nthreads>. The default is
270	C<1>, which means a single asynchronous operation can be done at one time
271	(the number of outstanding operations, however, is unlimited).
272
273	It is recommended to keep the number of threads low, as some Linux
274	kernel versions will scale negatively with the number of threads (higher
275	parallelity => MUCH higher latency). With current Linux 2.6 versions, 4-32
276	threads should be fine.
277
278	Under normal circumstances you don't need to call this function, as this
279	module automatically starts some threads (the exact number might change,
280	and is currently 4).
281
282	=item IO::AIO::max_parallel $nthreads
283
284	Sets the maximum number of AIO threads to C<$nthreads>. If more than
285	the specified number of threads are currently running, kill them. This
286	function blocks until the limit is reached.
287
288	This module automatically runs C<max_parallel 0> at program end, to ensure
289	that all threads are killed and that there are no outstanding requests.
290
291	Under normal circumstances you don't need to call this function.
292
293	=item $oldnreqs = IO::AIO::max_outstanding $nreqs
294
295	Sets the maximum number of outstanding requests to C<$nreqs>. If you
296	try to queue up more than this number of requests, the caller will block until
297	some requests have been handled.
298
299	The default is very large, so normally there is no practical limit. If you
300	queue up many requests in a loop it it often improves speed if you set
301	this to a relatively low number, such as C<100>.
302
303	Under normal circumstances you don't need to call this function.
304		1396
305	=back	1397	=back
306		1398
307	=cut	1399	=cut
308		1400
309	# support function to convert a fd into a perl filehandle
310	sub _fd2fh {
311	return undef if $_[0] < 0;
312
313	# try to be perl5.6-compatible
314	local *AIO_FH;
315	open AIO_FH, "+<&=$_[0]"
316	or return undef;
317
318	*AIO_FH
319	}
320
321	min_parallel 4;	1401	min_parallel 8;
322		1402
323	END {	1403	END { flush }
324	max_parallel 0;
325	}
326		1404
327	1;	1405	1;
328		1406
		1407	=head2 FORK BEHAVIOUR
		1408
		1409	This module should do "the right thing" when the process using it forks:
		1410
		1411	Before the fork, IO::AIO enters a quiescent state where no requests
		1412	can be added in other threads and no results will be processed. After
		1413	the fork the parent simply leaves the quiescent state and continues
		1414	request/result processing, while the child frees the request/result queue
		1415	(so that the requests started before the fork will only be handled in the
		1416	parent). Threads will be started on demand until the limit set in the
		1417	parent process has been reached again.
		1418
		1419	In short: the parent will, after a short pause, continue as if fork had
		1420	not been called, while the child will act as if IO::AIO has not been used
		1421	yet.
		1422
		1423	=head2 MEMORY USAGE
		1424
		1425	Per-request usage:
		1426
		1427	Each aio request uses - depending on your architecture - around 100-200
		1428	bytes of memory. In addition, stat requests need a stat buffer (possibly
		1429	a few hundred bytes), readdir requires a result buffer and so on. Perl
		1430	scalars and other data passed into aio requests will also be locked and
		1431	will consume memory till the request has entered the done state.
		1432
		1433	This is not awfully much, so queuing lots of requests is not usually a
		1434	problem.
		1435
		1436	Per-thread usage:
		1437
		1438	In the execution phase, some aio requests require more memory for
		1439	temporary buffers, and each thread requires a stack and other data
		1440	structures (usually around 16k-128k, depending on the OS).
		1441
		1442	=head1 KNOWN BUGS
		1443
		1444	Known bugs will be fixed in the next release.
		1445
329	=head1 SEE ALSO	1446	=head1 SEE ALSO
330		1447
331	L<Coro>, L<Linux::AIO>.	1448	L<AnyEvent::AIO> for easy integration into event loops, L<Coro::AIO> for a
		1449	more natural syntax.
332		1450
333	=head1 AUTHOR	1451	=head1 AUTHOR
334		1452
335	Marc Lehmann <schmorp@schmorp.de>	1453	Marc Lehmann <schmorp@schmorp.de>
336	http://home.schmorp.de/	1454	http://home.schmorp.de/

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Revision 1.155 by root, Sun Jun 14 20:36:59 2009 UTC