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Revision 1.56 by root, Sun Oct 22 00:53:47 2006 UTC vs.
Revision 1.173 by root, Thu Jan 7 20:25:57 2010 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
…		…
18	};	19	};
19		20
20	# version 2+ has request and group objects	21	# version 2+ has request and group objects
21	use IO::AIO 2;	22	use IO::AIO 2;
22		23
		24	aioreq_pri 4; # give next request a very high priority
23	my $req = aio_unlink "/tmp/file", sub { };	25	my $req = aio_unlink "/tmp/file", sub { };
24	$req->cancel; # cancel request if still in queue	26	$req->cancel; # cancel request if still in queue
25		27
26	my $grp = aio_group sub { print "all stats done\n" };	28	my $grp = aio_group sub { print "all stats done\n" };
27	add $grp aio_stat "..." for ...;	29	add $grp aio_stat "..." for ...;
28		30
		31	# AnyEvent integration (EV, Event, Glib, Tk, POE, urxvt, pureperl...)
		32	use AnyEvent::AIO;
		33
29	# AnyEvent integration	34	# EV integration
30	open my $fh, "<&=" . IO::AIO::poll_fileno or die "$!";	35	my $aio_w = EV::io IO::AIO::poll_fileno, EV::READ, \&IO::AIO::poll_cb;
31	my $w = AnyEvent->io (fh => $fh, poll => 'r', cb => sub { IO::AIO::poll_cb });
32		36
33	# Event integration	37	# Event integration
34	Event->io (fd => IO::AIO::poll_fileno,	38	Event->io (fd => IO::AIO::poll_fileno,
35	poll => 'r',	39	poll => 'r',
36	cb => \&IO::AIO::poll_cb);	40	cb => \&IO::AIO::poll_cb);
…		…
48	\&IO::AIO::poll_cb);	52	\&IO::AIO::poll_cb);
49		53
50	=head1 DESCRIPTION	54	=head1 DESCRIPTION
51		55
52	This module implements asynchronous I/O using whatever means your	56	This module implements asynchronous I/O using whatever means your
53	operating system supports.	57	operating system supports. It is implemented as an interface to C<libeio>
		58	(L<http://software.schmorp.de/pkg/libeio.html>).
54		59
		60	Asynchronous means that operations that can normally block your program
		61	(e.g. reading from disk) will be done asynchronously: the operation
		62	will still block, but you can do something else in the meantime. This
		63	is extremely useful for programs that need to stay interactive even
		64	when doing heavy I/O (GUI programs, high performance network servers
		65	etc.), but can also be used to easily do operations in parallel that are
		66	normally done sequentially, e.g. stat'ing many files, which is much faster
		67	on a RAID volume or over NFS when you do a number of stat operations
		68	concurrently.
		69
		70	While most of this works on all types of file descriptors (for
		71	example sockets), using these functions on file descriptors that
		72	support nonblocking operation (again, sockets, pipes etc.) is
		73	very inefficient. Use an event loop for that (such as the L<EV>
		74	module): IO::AIO will naturally fit into such an event loop itself.
		75
55	Currently, a number of threads are started that execute your read/writes	76	In this version, a number of threads are started that execute your
56	and signal their completion. You don't need thread support in your libc or	77	requests and signal their completion. You don't need thread support
57	perl, and the threads created by this module will not be visible to the	78	in perl, and the threads created by this module will not be visible
58	pthreads library. In the future, this module might make use of the native	79	to perl. In the future, this module might make use of the native aio
59	aio functions available on many operating systems. However, they are often	80	functions available on many operating systems. However, they are often
60	not well-supported (Linux doesn't allow them on normal files currently,	81	not well-supported or restricted (GNU/Linux doesn't allow them on normal
61	for example), and they would only support aio_read and aio_write, so the	82	files currently, for example), and they would only support aio_read and
62	remaining functionality would have to be implemented using threads anyway.	83	aio_write, so the remaining functionality would have to be implemented
		84	using threads anyway.
63		85
64	Although the module will work with in the presence of other threads, it is	86	Although the module will work in the presence of other (Perl-) threads,
65	currently not reentrant, so use appropriate locking yourself, always call	87	it is currently not reentrant in any way, so use appropriate locking
66	C<poll_cb> from within the same thread, or never call C<poll_cb> (or other	88	yourself, always call C<poll_cb> from within the same thread, or never
67	C<aio_> functions) recursively.	89	call C<poll_cb> (or other C<aio_> functions) recursively.
		90
		91	=head2 EXAMPLE
		92
		93	This is a simple example that uses the EV module and loads
		94	F</etc/passwd> asynchronously:
		95
		96	use Fcntl;
		97	use EV;
		98	use IO::AIO;
		99
		100	# register the IO::AIO callback with EV
		101	my $aio_w = EV::io IO::AIO::poll_fileno, EV::READ, \&IO::AIO::poll_cb;
		102
		103	# queue the request to open /etc/passwd
		104	aio_open "/etc/passwd", O_RDONLY, 0, sub {
		105	my $fh = shift
		106	or die "error while opening: $!";
		107
		108	# stat'ing filehandles is generally non-blocking
		109	my $size = -s $fh;
		110
		111	# queue a request to read the file
		112	my $contents;
		113	aio_read $fh, 0, $size, $contents, 0, sub {
		114	$_[0] == $size
		115	or die "short read: $!";
		116
		117	close $fh;
		118
		119	# file contents now in $contents
		120	print $contents;
		121
		122	# exit event loop and program
		123	EV::unloop;
		124	};
		125	};
		126
		127	# possibly queue up other requests, or open GUI windows,
		128	# check for sockets etc. etc.
		129
		130	# process events as long as there are some:
		131	EV::loop;
		132
		133	=head1 REQUEST ANATOMY AND LIFETIME
		134
		135	Every C<aio_*> function creates a request. which is a C data structure not
		136	directly visible to Perl.
		137
		138	If called in non-void context, every request function returns a Perl
		139	object representing the request. In void context, nothing is returned,
		140	which saves a bit of memory.
		141
		142	The perl object is a fairly standard ref-to-hash object. The hash contents
		143	are not used by IO::AIO so you are free to store anything you like in it.
		144
		145	During their existance, aio requests travel through the following states,
		146	in order:
		147
		148	=over 4
		149
		150	=item ready
		151
		152	Immediately after a request is created it is put into the ready state,
		153	waiting for a thread to execute it.
		154
		155	=item execute
		156
		157	A thread has accepted the request for processing and is currently
		158	executing it (e.g. blocking in read).
		159
		160	=item pending
		161
		162	The request has been executed and is waiting for result processing.
		163
		164	While request submission and execution is fully asynchronous, result
		165	processing is not and relies on the perl interpreter calling C<poll_cb>
		166	(or another function with the same effect).
		167
		168	=item result
		169
		170	The request results are processed synchronously by C<poll_cb>.
		171
		172	The C<poll_cb> function will process all outstanding aio requests by
		173	calling their callbacks, freeing memory associated with them and managing
		174	any groups they are contained in.
		175
		176	=item done
		177
		178	Request has reached the end of its lifetime and holds no resources anymore
		179	(except possibly for the Perl object, but its connection to the actual
		180	aio request is severed and calling its methods will either do nothing or
		181	result in a runtime error).
		182
		183	=back
68		184
69	=cut	185	=cut
70		186
71	package IO::AIO;	187	package IO::AIO;
72		188
73	no warnings;	189	use Carp ();
74	use strict 'vars';	190
		191	use common::sense;
75		192
76	use base 'Exporter';	193	use base 'Exporter';
77		194
78	BEGIN {	195	BEGIN {
79	our $VERSION = '2.0';	196	our $VERSION = '3.5';
80		197
81	our @EXPORT = qw(aio_sendfile aio_read aio_write aio_open aio_close aio_stat	198	our @AIO_REQ = qw(aio_sendfile aio_read aio_write aio_open aio_close
82	aio_lstat aio_unlink aio_rmdir aio_readdir aio_scandir aio_symlink	199	aio_stat aio_lstat aio_unlink aio_rmdir aio_readdir aio_readdirx
83	aio_fsync aio_fdatasync aio_readahead aio_rename aio_link aio_move	200	aio_scandir aio_symlink aio_readlink aio_sync aio_fsync
84	aio_group);	201	aio_fdatasync aio_sync_file_range aio_pathsync aio_readahead
85	our @EXPORT_OK = qw(poll_fileno poll_cb min_parallel max_parallel max_outstanding nreqs);	202	aio_rename aio_link aio_move aio_copy aio_group
		203	aio_nop aio_mknod aio_load aio_rmtree aio_mkdir aio_chown
		204	aio_chmod aio_utime aio_truncate
		205	aio_msync aio_mtouch aio_statvfs);
		206
		207	our @EXPORT = (@AIO_REQ, qw(aioreq_pri aioreq_nice));
		208	our @EXPORT_OK = qw(poll_fileno poll_cb poll_wait flush
		209	min_parallel max_parallel max_idle
		210	nreqs nready npending nthreads
		211	max_poll_time max_poll_reqs
		212	sendfile fadvise);
		213
		214	push @AIO_REQ, qw(aio_busy); # not exported
86		215
87	@IO::AIO::GRP::ISA = 'IO::AIO::REQ';	216	@IO::AIO::GRP::ISA = 'IO::AIO::REQ';
88		217
89	require XSLoader;	218	require XSLoader;
90	XSLoader::load ("IO::AIO", $VERSION);	219	XSLoader::load ("IO::AIO", $VERSION);
91	}	220	}
92		221
93	=head1 FUNCTIONS	222	=head1 FUNCTIONS
94		223
95	=head2 AIO FUNCTIONS	224	=head2 AIO REQUEST FUNCTIONS
96		225
97	All the C<aio_*> calls are more or less thin wrappers around the syscall	226	All the C<aio_*> calls are more or less thin wrappers around the syscall
98	with the same name (sans C<aio_>). The arguments are similar or identical,	227	with the same name (sans C<aio_>). The arguments are similar or identical,
99	and they all accept an additional (and optional) C<$callback> argument	228	and they all accept an additional (and optional) C<$callback> argument
100	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
101	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
102	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
103	syscall has been executed asynchronously.	232	syscall has been executed asynchronously.
104		233
105	All functions expecting a filehandle keep a copy of the filehandle	234	All functions expecting a filehandle keep a copy of the filehandle
106	internally until the request has finished.	235	internally until the request has finished.
107		236
108	All requests return objects of type L<IO::AIO::REQ> that allow further	237	All functions return request objects of type L<IO::AIO::REQ> that allow
109	manipulation of those requests while they are in-flight.	238	further manipulation of those requests while they are in-flight.
110		239
111	The pathnames you pass to these routines I<must> be absolute and	240	The pathnames you pass to these routines I<must> be absolute and
112	encoded in byte form. The reason for the former is that at the time the	241	encoded as octets. The reason for the former is that at the time the
113	request is being executed, the current working directory could have	242	request is being executed, the current working directory could have
114	changed. Alternatively, you can make sure that you never change the	243	changed. Alternatively, you can make sure that you never change the
115	current working directory.	244	current working directory anywhere in the program and then use relative
		245	paths.
116		246
117	To encode pathnames to byte form, either make sure you either: a)	247	To encode pathnames as octets, either make sure you either: a) always pass
118	always pass in filenames you got from outside (command line, readdir	248	in filenames you got from outside (command line, readdir etc.) without
119	etc.), b) are ASCII or ISO 8859-1, c) use the Encode module and encode	249	tinkering, b) are ASCII or ISO 8859-1, c) use the Encode module and encode
120	your pathnames to the locale (or other) encoding in effect in the user	250	your pathnames to the locale (or other) encoding in effect in the user
121	environment, d) use Glib::filename_from_unicode on unicode filenames or e)	251	environment, d) use Glib::filename_from_unicode on unicode filenames or e)
122	use something else.	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.
123		256
124	=over 4	257	=over 4
		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
125		291
126	=item aio_open $pathname, $flags, $mode, $callback->($fh)	292	=item aio_open $pathname, $flags, $mode, $callback->($fh)
127		293
128	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
129	created filehandle for the file.	295	created filehandle for the file.
…		…
135	list. They are the same as used by C<sysopen>.	301	list. They are the same as used by C<sysopen>.
136		302
137	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
138	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>,
139	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,
140	and C<0666> or C<0777> if you do).	306	and C<0666> or C<0777> if you do). Note that the C<$mode> will be modified
		307	by the umask in effect then the request is being executed, so better never
		308	change the umask.
141		309
142	Example:	310	Example:
143		311
144	aio_open "/etc/passwd", O_RDONLY, 0, sub {	312	aio_open "/etc/passwd", O_RDONLY, 0, sub {
145	if ($_[0]) {	313	if ($_[0]) {
…		…
148	} else {	316	} else {
149	die "open failed: $!\n";	317	die "open failed: $!\n";
150	}	318	}
151	};	319	};
152		320
		321
153	=item aio_close $fh, $callback->($status)	322	=item aio_close $fh, $callback->($status)
154		323
155	Asynchronously close a file and call the callback with the result	324	Asynchronously close a file and call the callback with the result
156	code. I<WARNING:> although accepted, you should not pass in a perl	325	code.
157	filehandle here, as perl will likely close the file descriptor another
158	time when the filehandle is destroyed. Normally, you can safely call perls
159	C<close> or just let filehandles go out of scope.
160		326
161	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
162	therefore best to avoid this function.	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
163		338
164	=item aio_read $fh,$offset,$length, $data,$dataoffset, $callback->($retval)	339	=item aio_read $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
165		340
166	=item aio_write $fh,$offset,$length, $data,$dataoffset, $callback->($retval)	341	=item aio_write $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
167		342
168	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
169	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<$dataoffset>
170	callback without the actual number of bytes read (or -1 on error, just	345	and calls the callback without the actual number of bytes read (or -1 on
171	like the syscall).	346	error, just like the syscall).
		347
		348	C<aio_read> will, like C<sysread>, shrink or grow the C<$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<$data>.
172		360
173	The C<$data> scalar I<MUST NOT> be modified in any way while the request	361	The C<$data> scalar I<MUST NOT> be modified in any way while the request
174	is outstanding. Modifying it can result in segfaults or WW3 (if the	362	is outstanding. Modifying it can result in segfaults or World War III (if
175	necessary/optional hardware is installed).	363	the necessary/optional hardware is installed).
176		364
177	Example: Read 15 bytes at offset 7 into scalar C<$buffer>, starting at	365	Example: Read 15 bytes at offset 7 into scalar C<$buffer>, starting at
178	offset C<0> within the scalar:	366	offset C<0> within the scalar:
179		367
180	aio_read $fh, 7, 15, $buffer, 0, sub {	368	aio_read $fh, 7, 15, $buffer, 0, sub {
181	$_[0] > 0 or die "read error: $!";	369	$_[0] > 0 or die "read error: $!";
182	print "read $_[0] bytes: <$buffer>\n";	370	print "read $_[0] bytes: <$buffer>\n";
183	};	371	};
184		372
185	=item aio_move $srcpath, $dstpath, $callback->($status)
186
187	Try to move the I<file> (directories not supported as either source or
188	destination) from C<$srcpath> to C<$dstpath> and call the callback with
189	the C<0> (error) or C<-1> ok.
190
191	This is a composite request that tries to rename(2) the file first. If
192	rename files with C<EXDEV>, it creates the destination file with mode 0200
193	and copies the contents of the source file into it using C<aio_sendfile>,
194	followed by restoring atime, mtime, access mode and uid/gid, in that
195	order, and unlinking the C<$srcpath>.
196
197	If an error occurs, the partial destination file will be unlinked, if
198	possible, except when setting atime, mtime, access mode and uid/gid, where
199	errors are being ignored.
200
201	=cut
202
203	sub aio_move($$$) {
204	my ($src, $dst, $cb) = @_;
205
206	my $grp = aio_group;
207
208	add $grp aio_rename $src, $dst, sub {
209	if ($_[0] && $! == EXDEV) {
210	add $grp aio_open $src, O_RDONLY, 0, sub {
211	if (my $src_fh = $_[0]) {
212	my @stat = stat $src_fh;
213
214	add $grp aio_open $dst, O_WRONLY, 0200, sub {
215	if (my $dst_fh = $_[0]) {
216	add $grp aio_sendfile $dst_fh, $src_fh, 0, $stat[7], sub {
217	close $src_fh;
218
219	if ($_[0] == $stat[7]) {
220	utime $stat[8], $stat[9], $dst;
221	chmod $stat[2] & 07777, $dst_fh;
222	chown $stat[4], $stat[5], $dst_fh;
223	close $dst_fh;
224
225	add $grp aio_unlink $src, sub {
226	$cb->($_[0]);
227	};
228	} else {
229	my $errno = $!;
230	add $grp aio_unlink $dst, sub {
231	$! = $errno;
232	$cb->(-1);
233	};
234	}
235	};
236	} else {
237	$cb->(-1);
238	}
239	},
240
241	} else {
242	$cb->(-1);
243	}
244	};
245	} else {
246	$cb->($_[0]);
247	}
248	};
249
250	$grp
251	}
252		373
253	=item aio_sendfile $out_fh, $in_fh, $in_offset, $length, $callback->($retval)	374	=item aio_sendfile $out_fh, $in_fh, $in_offset, $length, $callback->($retval)
254		375
255	Tries to copy C<$length> bytes from C<$in_fh> to C<$out_fh>. It starts	376	Tries to copy C<$length> bytes from C<$in_fh> to C<$out_fh>. It starts
256	reading at byte offset C<$in_offset>, and starts writing at the current	377	reading at byte offset C<$in_offset>, and starts writing at the current
…		…
260		381
261	This call tries to make use of a native C<sendfile> syscall to provide	382	This call tries to make use of a native C<sendfile> syscall to provide
262	zero-copy operation. For this to work, C<$out_fh> should refer to a	383	zero-copy operation. For this to work, C<$out_fh> should refer to a
263	socket, and C<$in_fh> should refer to mmap'able file.	384	socket, and C<$in_fh> should refer to mmap'able file.
264		385
265	If the native sendfile call fails or is not implemented, it will be	386	If a native sendfile cannot be found or it fails with C<ENOSYS>,
		387	C<ENOTSUP>, C<EOPNOTSUPP>, C<EAFNOSUPPORT>, C<EPROTOTYPE> or C<ENOTSOCK>,
266	emulated, so you can call C<aio_sendfile> on any type of filehandle	388	it will be emulated, so you can call C<aio_sendfile> on any type of
267	regardless of the limitations of the operating system.	389	filehandle regardless of the limitations of the operating system.
268		390
269	Please note, however, that C<aio_sendfile> can read more bytes from	391	Please note, however, that C<aio_sendfile> can read more bytes from
270	C<$in_fh> than are written, and there is no way to find out how many	392	C<$in_fh> than are written, and there is no way to find out how many
271	bytes have been read from C<aio_sendfile> alone, as C<aio_sendfile> only	393	bytes have been read from C<aio_sendfile> alone, as C<aio_sendfile> only
272	provides the number of bytes written to C<$out_fh>. Only if the result	394	provides the number of bytes written to C<$out_fh>. Only if the result
273	value equals C<$length> one can assume that C<$length> bytes have been	395	value equals C<$length> one can assume that C<$length> bytes have been
274	read.	396	read.
		397
275		398
276	=item aio_readahead $fh,$offset,$length, $callback->($retval)	399	=item aio_readahead $fh,$offset,$length, $callback->($retval)
277		400
278	C<aio_readahead> populates the page cache with data from a file so that	401	C<aio_readahead> populates the page cache with data from a file so that
279	subsequent reads from that file will not block on disk I/O. The C<$offset>	402	subsequent reads from that file will not block on disk I/O. The C<$offset>
…		…
285	file. The current file offset of the file is left unchanged.	408	file. The current file offset of the file is left unchanged.
286		409
287	If that syscall doesn't exist (likely if your OS isn't Linux) it will be	410	If that syscall doesn't exist (likely if your OS isn't Linux) it will be
288	emulated by simply reading the data, which would have a similar effect.	411	emulated by simply reading the data, which would have a similar effect.
289		412
		413
290	=item aio_stat $fh_or_path, $callback->($status)	414	=item aio_stat $fh_or_path, $callback->($status)
291		415
292	=item aio_lstat $fh, $callback->($status)	416	=item aio_lstat $fh, $callback->($status)
293		417
294	Works like perl's C<stat> or C<lstat> in void context. The callback will	418	Works like perl's C<stat> or C<lstat> in void context. The callback will
…		…
307	aio_stat "/etc/passwd", sub {	431	aio_stat "/etc/passwd", sub {
308	$_[0] and die "stat failed: $!";	432	$_[0] and die "stat failed: $!";
309	print "size is ", -s _, "\n";	433	print "size is ", -s _, "\n";
310	};	434	};
311		435
		436
		437	=item aio_statvfs $fh_or_path, $callback->($statvfs)
		438
		439	Works like the POSIX C<statvfs> or C<fstatvfs> syscalls, depending on
		440	whether a file handle or path was passed.
		441
		442	On success, the callback is passed a hash reference with the following
		443	members: C<bsize>, C<frsize>, C<blocks>, C<bfree>, C<bavail>, C<files>,
		444	C<ffree>, C<favail>, C<fsid>, C<flag> and C<namemax>. On failure, C<undef>
		445	is passed.
		446
		447	The following POSIX IO::AIO::ST_* constants are defined: C<ST_RDONLY> and
		448	C<ST_NOSUID>.
		449
		450	The following non-POSIX IO::AIO::ST_* flag masks are defined to
		451	their correct value when available, or to C<0> on systems that do
		452	not support them: C<ST_NODEV>, C<ST_NOEXEC>, C<ST_SYNCHRONOUS>,
		453	C<ST_MANDLOCK>, C<ST_WRITE>, C<ST_APPEND>, C<ST_IMMUTABLE>, C<ST_NOATIME>,
		454	C<ST_NODIRATIME> and C<ST_RELATIME>.
		455
		456	Example: stat C</wd> and dump out the data if successful.
		457
		458	aio_statvfs "/wd", sub {
		459	my $f = $_[0]
		460	or die "statvfs: $!";
		461
		462	use Data::Dumper;
		463	say Dumper $f;
		464	};
		465
		466	# result:
		467	{
		468	bsize => 1024,
		469	bfree => 4333064312,
		470	blocks => 10253828096,
		471	files => 2050765568,
		472	flag => 4096,
		473	favail => 2042092649,
		474	bavail => 4333064312,
		475	ffree => 2042092649,
		476	namemax => 255,
		477	frsize => 1024,
		478	fsid => 1810
		479	}
		480
		481
		482	=item aio_utime $fh_or_path, $atime, $mtime, $callback->($status)
		483
		484	Works like perl's C<utime> function (including the special case of $atime
		485	and $mtime being undef). Fractional times are supported if the underlying
		486	syscalls support them.
		487
		488	When called with a pathname, uses utimes(2) if available, otherwise
		489	utime(2). If called on a file descriptor, uses futimes(2) if available,
		490	otherwise returns ENOSYS, so this is not portable.
		491
		492	Examples:
		493
		494	# set atime and mtime to current time (basically touch(1)):
		495	aio_utime "path", undef, undef;
		496	# set atime to current time and mtime to beginning of the epoch:
		497	aio_utime "path", time, undef; # undef==0
		498
		499
		500	=item aio_chown $fh_or_path, $uid, $gid, $callback->($status)
		501
		502	Works like perl's C<chown> function, except that C<undef> for either $uid
		503	or $gid is being interpreted as "do not change" (but -1 can also be used).
		504
		505	Examples:
		506
		507	# same as "chown root path" in the shell:
		508	aio_chown "path", 0, -1;
		509	# same as above:
		510	aio_chown "path", 0, undef;
		511
		512
		513	=item aio_truncate $fh_or_path, $offset, $callback->($status)
		514
		515	Works like truncate(2) or ftruncate(2).
		516
		517
		518	=item aio_chmod $fh_or_path, $mode, $callback->($status)
		519
		520	Works like perl's C<chmod> function.
		521
		522
312	=item aio_unlink $pathname, $callback->($status)	523	=item aio_unlink $pathname, $callback->($status)
313		524
314	Asynchronously unlink (delete) a file and call the callback with the	525	Asynchronously unlink (delete) a file and call the callback with the
315	result code.	526	result code.
316		527
		528
		529	=item aio_mknod $path, $mode, $dev, $callback->($status)
		530
		531	[EXPERIMENTAL]
		532
		533	Asynchronously create a device node (or fifo). See mknod(2).
		534
		535	The only (POSIX-) portable way of calling this function is:
		536
		537	aio_mknod $path, IO::AIO::S_IFIFO | $mode, 0, sub { ...
		538
		539
317	=item aio_link $srcpath, $dstpath, $callback->($status)	540	=item aio_link $srcpath, $dstpath, $callback->($status)
318		541
319	Asynchronously create a new link to the existing object at C<$srcpath> at	542	Asynchronously create a new link to the existing object at C<$srcpath> at
320	the path C<$dstpath> and call the callback with the result code.	543	the path C<$dstpath> and call the callback with the result code.
321		544
		545
322	=item aio_symlink $srcpath, $dstpath, $callback->($status)	546	=item aio_symlink $srcpath, $dstpath, $callback->($status)
323		547
324	Asynchronously create a new symbolic link to the existing object at C<$srcpath> at	548	Asynchronously create a new symbolic link to the existing object at C<$srcpath> at
325	the path C<$dstpath> and call the callback with the result code.	549	the path C<$dstpath> and call the callback with the result code.
326		550
		551
		552	=item aio_readlink $path, $callback->($link)
		553
		554	Asynchronously read the symlink specified by C<$path> and pass it to
		555	the callback. If an error occurs, nothing or undef gets passed to the
		556	callback.
		557
		558
327	=item aio_rename $srcpath, $dstpath, $callback->($status)	559	=item aio_rename $srcpath, $dstpath, $callback->($status)
328		560
329	Asynchronously rename the object at C<$srcpath> to C<$dstpath>, just as	561	Asynchronously rename the object at C<$srcpath> to C<$dstpath>, just as
330	rename(2) and call the callback with the result code.	562	rename(2) and call the callback with the result code.
331		563
		564
		565	=item aio_mkdir $pathname, $mode, $callback->($status)
		566
		567	Asynchronously mkdir (create) a directory and call the callback with
		568	the result code. C<$mode> will be modified by the umask at the time the
		569	request is executed, so do not change your umask.
		570
		571
332	=item aio_rmdir $pathname, $callback->($status)	572	=item aio_rmdir $pathname, $callback->($status)
333		573
334	Asynchronously rmdir (delete) a directory and call the callback with the	574	Asynchronously rmdir (delete) a directory and call the callback with the
335	result code.	575	result code.
		576
336		577
337	=item aio_readdir $pathname, $callback->($entries)	578	=item aio_readdir $pathname, $callback->($entries)
338		579
339	Unlike the POSIX call of the same name, C<aio_readdir> reads an entire	580	Unlike the POSIX call of the same name, C<aio_readdir> reads an entire
340	directory (i.e. opendir + readdir + closedir). The entries will not be	581	directory (i.e. opendir + readdir + closedir). The entries will not be
341	sorted, and will B<NOT> include the C<.> and C<..> entries.	582	sorted, and will B<NOT> include the C<.> and C<..> entries.
342		583
343	The callback a single argument which is either C<undef> or an array-ref	584	The callback is passed a single argument which is either C<undef> or an
344	with the filenames.	585	array-ref with the filenames.
		586
		587
		588	=item aio_readdirx $pathname, $flags, $callback->($entries, $flags)
		589
		590	Quite similar to C<aio_readdir>, but the C<$flags> argument allows to tune
		591	behaviour and output format. In case of an error, C<$entries> will be
		592	C<undef>.
		593
		594	The flags are a combination of the following constants, ORed together (the
		595	flags will also be passed to the callback, possibly modified):
		596
		597	=over 4
		598
		599	=item IO::AIO::READDIR_DENTS
		600
		601	When this flag is off, then the callback gets an arrayref with of names
		602	only (as with C<aio_readdir>), otherwise it gets an arrayref with
		603	C<[$name, $type, $inode]> arrayrefs, each describing a single directory
		604	entry in more detail.
		605
		606	C<$name> is the name of the entry.
		607
		608	C<$type> is one of the C<IO::AIO::DT_xxx> constants:
		609
		610	C<IO::AIO::DT_UNKNOWN>, C<IO::AIO::DT_FIFO>, C<IO::AIO::DT_CHR>, C<IO::AIO::DT_DIR>,
		611	C<IO::AIO::DT_BLK>, C<IO::AIO::DT_REG>, C<IO::AIO::DT_LNK>, C<IO::AIO::DT_SOCK>,
		612	C<IO::AIO::DT_WHT>.
		613
		614	C<IO::AIO::DT_UNKNOWN> means just that: readdir does not know. If you need to
		615	know, you have to run stat yourself. Also, for speed reasons, the C<$type>
		616	scalars are read-only: you can not modify them.
		617
		618	C<$inode> is the inode number (which might not be exact on systems with 64
		619	bit inode numbers and 32 bit perls). This field has unspecified content on
		620	systems that do not deliver the inode information.
		621
		622	=item IO::AIO::READDIR_DIRS_FIRST
		623
		624	When this flag is set, then the names will be returned in an order where
		625	likely directories come first. This is useful when you need to quickly
		626	find directories, or you want to find all directories while avoiding to
		627	stat() each entry.
		628
		629	If the system returns type information in readdir, then this is used
		630	to find directories directly. Otherwise, likely directories are files
		631	beginning with ".", or otherwise files with no dots, of which files with
		632	short names are tried first.
		633
		634	=item IO::AIO::READDIR_STAT_ORDER
		635
		636	When this flag is set, then the names will be returned in an order
		637	suitable for stat()'ing each one. That is, when you plan to stat()
		638	all files in the given directory, then the returned order will likely
		639	be fastest.
		640
		641	If both this flag and C<IO::AIO::READDIR_DIRS_FIRST> are specified, then
		642	the likely dirs come first, resulting in a less optimal stat order.
		643
		644	=item IO::AIO::READDIR_FOUND_UNKNOWN
		645
		646	This flag should not be set when calling C<aio_readdirx>. Instead, it
		647	is being set by C<aio_readdirx>, when any of the C<$type>'s found were
		648	C<IO::AIO::DT_UNKNOWN>. The absense of this flag therefore indicates that all
		649	C<$type>'s are known, which can be used to speed up some algorithms.
		650
		651	=back
		652
		653
		654	=item aio_load $path, $data, $callback->($status)
		655
		656	This is a composite request that tries to fully load the given file into
		657	memory. Status is the same as with aio_read.
		658
		659	=cut
		660
		661	sub aio_load($$;$) {
		662	my ($path, undef, $cb) = @_;
		663	my $data = \$_[1];
		664
		665	my $pri = aioreq_pri;
		666	my $grp = aio_group $cb;
		667
		668	aioreq_pri $pri;
		669	add $grp aio_open $path, O_RDONLY, 0, sub {
		670	my $fh = shift
		671	or return $grp->result (-1);
		672
		673	aioreq_pri $pri;
		674	add $grp aio_read $fh, 0, (-s $fh), $$data, 0, sub {
		675	$grp->result ($_[0]);
		676	};
		677	};
		678
		679	$grp
		680	}
		681
		682	=item aio_copy $srcpath, $dstpath, $callback->($status)
		683
		684	Try to copy the I<file> (directories not supported as either source or
		685	destination) from C<$srcpath> to C<$dstpath> and call the callback with
		686	a status of C<0> (ok) or C<-1> (error, see C<$!>).
		687
		688	This is a composite request that creates the destination file with
		689	mode 0200 and copies the contents of the source file into it using
		690	C<aio_sendfile>, followed by restoring atime, mtime, access mode and
		691	uid/gid, in that order.
		692
		693	If an error occurs, the partial destination file will be unlinked, if
		694	possible, except when setting atime, mtime, access mode and uid/gid, where
		695	errors are being ignored.
		696
		697	=cut
		698
		699	sub aio_copy($$;$) {
		700	my ($src, $dst, $cb) = @_;
		701
		702	my $pri = aioreq_pri;
		703	my $grp = aio_group $cb;
		704
		705	aioreq_pri $pri;
		706	add $grp aio_open $src, O_RDONLY, 0, sub {
		707	if (my $src_fh = $_[0]) {
		708	my @stat = stat $src_fh; # hmm, might block over nfs?
		709
		710	aioreq_pri $pri;
		711	add $grp aio_open $dst, O_CREAT | O_WRONLY | O_TRUNC, 0200, sub {
		712	if (my $dst_fh = $_[0]) {
		713	aioreq_pri $pri;
		714	add $grp aio_sendfile $dst_fh, $src_fh, 0, $stat[7], sub {
		715	if ($_[0] == $stat[7]) {
		716	$grp->result (0);
		717	close $src_fh;
		718
		719	my $ch = sub {
		720	aioreq_pri $pri;
		721	add $grp aio_chmod $dst_fh, $stat[2] & 07777, sub {
		722	aioreq_pri $pri;
		723	add $grp aio_chown $dst_fh, $stat[4], $stat[5], sub {
		724	aioreq_pri $pri;
		725	add $grp aio_close $dst_fh;
		726	}
		727	};
		728	};
		729
		730	aioreq_pri $pri;
		731	add $grp aio_utime $dst_fh, $stat[8], $stat[9], sub {
		732	if ($_[0] < 0 && $! == ENOSYS) {
		733	aioreq_pri $pri;
		734	add $grp aio_utime $dst, $stat[8], $stat[9], $ch;
		735	} else {
		736	$ch->();
		737	}
		738	};
		739	} else {
		740	$grp->result (-1);
		741	close $src_fh;
		742	close $dst_fh;
		743
		744	aioreq $pri;
		745	add $grp aio_unlink $dst;
		746	}
		747	};
		748	} else {
		749	$grp->result (-1);
		750	}
		751	},
		752
		753	} else {
		754	$grp->result (-1);
		755	}
		756	};
		757
		758	$grp
		759	}
		760
		761	=item aio_move $srcpath, $dstpath, $callback->($status)
		762
		763	Try to move the I<file> (directories not supported as either source or
		764	destination) from C<$srcpath> to C<$dstpath> and call the callback with
		765	a status of C<0> (ok) or C<-1> (error, see C<$!>).
		766
		767	This is a composite request that tries to rename(2) the file first; if
		768	rename fails with C<EXDEV>, it copies the file with C<aio_copy> and, if
		769	that is successful, unlinks the C<$srcpath>.
		770
		771	=cut
		772
		773	sub aio_move($$;$) {
		774	my ($src, $dst, $cb) = @_;
		775
		776	my $pri = aioreq_pri;
		777	my $grp = aio_group $cb;
		778
		779	aioreq_pri $pri;
		780	add $grp aio_rename $src, $dst, sub {
		781	if ($_[0] && $! == EXDEV) {
		782	aioreq_pri $pri;
		783	add $grp aio_copy $src, $dst, sub {
		784	$grp->result ($_[0]);
		785
		786	if (!$_[0]) {
		787	aioreq_pri $pri;
		788	add $grp aio_unlink $src;
		789	}
		790	};
		791	} else {
		792	$grp->result ($_[0]);
		793	}
		794	};
		795
		796	$grp
		797	}
345		798
346	=item aio_scandir $path, $maxreq, $callback->($dirs, $nondirs)	799	=item aio_scandir $path, $maxreq, $callback->($dirs, $nondirs)
347		800
348	Scans a directory (similar to C<aio_readdir>) but additionally tries to	801	Scans a directory (similar to C<aio_readdir>) but additionally tries to
349	separate the entries of directory C<$path> into two sets of names, ones	802	efficiently separate the entries of directory C<$path> into two sets of
350	you can recurse into (directories or links to them), and ones you cannot	803	names, directories you can recurse into (directories), and ones you cannot
351	recurse into (everything else).	804	recurse into (everything else, including symlinks to directories).
352		805
353	C<aio_scandir> is a composite request that consists of many sub	806	C<aio_scandir> is a composite request that creates of many sub requests_
354	requests. C<$maxreq> specifies the maximum number of outstanding aio	807	C<$maxreq> specifies the maximum number of outstanding aio requests that
355	requests that this function generates. If it is C<< <= 0 >>, then a	808	this function generates. If it is C<< <= 0 >>, then a suitable default
356	suitable default will be chosen (currently 8).	809	will be chosen (currently 4).
357		810
358	On error, the callback is called without arguments, otherwise it receives	811	On error, the callback is called without arguments, otherwise it receives
359	two array-refs with path-relative entry names.	812	two array-refs with path-relative entry names.
360		813
361	Example:	814	Example:
…		…
368		821
369	Implementation notes.	822	Implementation notes.
370		823
371	The C<aio_readdir> cannot be avoided, but C<stat()>'ing every entry can.	824	The C<aio_readdir> cannot be avoided, but C<stat()>'ing every entry can.
372		825
		826	If readdir returns file type information, then this is used directly to
		827	find directories.
		828
373	After reading the directory, the modification time, size etc. of the	829	Otherwise, after reading the directory, the modification time, size etc.
374	directory before and after the readdir is checked, and if they match (and	830	of the directory before and after the readdir is checked, and if they
375	isn't the current time), the link count will be used to decide how many	831	match (and isn't the current time), the link count will be used to decide
376	entries are directories (if >= 2). Otherwise, no knowledge of the number	832	how many entries are directories (if >= 2). Otherwise, no knowledge of the
377	of subdirectories will be assumed.	833	number of subdirectories will be assumed.
378		834
379	Then entries will be sorted into likely directories (everything without	835	Then entries will be sorted into likely directories a non-initial dot
380	a non-initial dot currently) and likely non-directories (everything	836	currently) and likely non-directories (see C<aio_readdirx>). Then every
381	else). Then every entry plus an appended C</.> will be C<stat>'ed,	837	entry plus an appended C</.> will be C<stat>'ed, likely directories first,
382	likely directories first. If that succeeds, it assumes that the entry	838	in order of their inode numbers. If that succeeds, it assumes that the
383	is a directory or a symlink to directory (which will be checked	839	entry is a directory or a symlink to directory (which will be checked
384	seperately). This is often faster than stat'ing the entry itself because	840	seperately). This is often faster than stat'ing the entry itself because
385	filesystems might detect the type of the entry without reading the inode	841	filesystems might detect the type of the entry without reading the inode
386	data (e.g. ext2fs filetype feature).	842	data (e.g. ext2fs filetype feature), even on systems that cannot return
		843	the filetype information on readdir.
387		844
388	If the known number of directories (link count - 2) has been reached, the	845	If the known number of directories (link count - 2) has been reached, the
389	rest of the entries is assumed to be non-directories.	846	rest of the entries is assumed to be non-directories.
390		847
391	This only works with certainty on POSIX (= UNIX) filesystems, which	848	This only works with certainty on POSIX (= UNIX) filesystems, which
…		…
395	as those tend to return 0 or 1 as link counts, which disables the	852	as those tend to return 0 or 1 as link counts, which disables the
396	directory counting heuristic.	853	directory counting heuristic.
397		854
398	=cut	855	=cut
399		856
400	sub aio_scandir($$$) {	857	sub aio_scandir($$;$) {
401	my ($path, $maxreq, $cb) = @_;	858	my ($path, $maxreq, $cb) = @_;
402		859
		860	my $pri = aioreq_pri;
		861
403	my $grp = aio_group;	862	my $grp = aio_group $cb;
404		863
405	$maxreq = 8 if $maxreq <= 0;	864	$maxreq = 4 if $maxreq <= 0;
406		865
407	# stat once	866	# stat once
		867	aioreq_pri $pri;
408	add $grp aio_stat $path, sub {	868	add $grp aio_stat $path, sub {
409	return $cb->() if $_[0];	869	return $grp->result () if $_[0];
410	my $now = time;	870	my $now = time;
411	my $hash1 = join ":", (stat _)[0,1,3,7,9];	871	my $hash1 = join ":", (stat _)[0,1,3,7,9];
412		872
413	# read the directory entries	873	# read the directory entries
		874	aioreq_pri $pri;
414	add $grp aio_readdir $path, sub {	875	add $grp aio_readdirx $path, READDIR_DIRS_FIRST, sub {
415	my $entries = shift	876	my $entries = shift
416	or return $cb->();	877	or return $grp->result ();
417		878
418	# stat the dir another time	879	# stat the dir another time
		880	aioreq_pri $pri;
419	add $grp aio_stat $path, sub {	881	add $grp aio_stat $path, sub {
420	my $hash2 = join ":", (stat _)[0,1,3,7,9];	882	my $hash2 = join ":", (stat _)[0,1,3,7,9];
421		883
422	my $ndirs;	884	my $ndirs;
423		885
424	# take the slow route if anything looks fishy	886	# take the slow route if anything looks fishy
425	if ($hash1 ne $hash2 or (stat _)[9] == $now) {	887	if ($hash1 ne $hash2 or (stat _)[9] == $now) {
426	$ndirs = -1;	888	$ndirs = -1;
427	} else {	889	} else {
428	# if nlink == 2, we are finished	890	# if nlink == 2, we are finished
429	# on non-posix-fs's, we rely on nlink < 2	891	# for non-posix-fs's, we rely on nlink < 2
430	$ndirs = (stat _)[3] - 2	892	$ndirs = (stat _)[3] - 2
431	or return $cb->([], $entries);	893	or return $grp->result ([], $entries);
432	}	894	}
433		895
434	# sort into likely dirs and likely nondirs
435	# dirs == files without ".", short entries first
436	$entries = [map $_->[0],
437	sort { $b->[1] cmp $a->[1] }
438	map [$_, sprintf "%s%04d", (/.\./ ? "1" : "0"), length],
439	@$entries];
440
441	my (@dirs, @nondirs);	896	my (@dirs, @nondirs);
442		897
443	my ($statcb, $schedcb);	898	my $statgrp = add $grp aio_group sub {
444	my $nreq = 0;	899	$grp->result (\@dirs, \@nondirs);
		900	};
445		901
446	$schedcb = sub {	902	limit $statgrp $maxreq;
447	if (@$entries) {	903	feed $statgrp sub {
448	if ($nreq < $maxreq) {	904	return unless @$entries;
449	my $ent = pop @$entries;	905	my $entry = shift @$entries;
		906
		907	aioreq_pri $pri;
		908	add $statgrp aio_stat "$path/$entry/.", sub {
		909	if ($_[0] < 0) {
		910	push @nondirs, $entry;
		911	} else {
		912	# need to check for real directory
		913	aioreq_pri $pri;
		914	add $statgrp aio_lstat "$path/$entry", sub {
		915	if (-d _) {
		916	push @dirs, $entry;
		917
		918	unless (--$ndirs) {
		919	push @nondirs, @$entries;
		920	feed $statgrp;
		921	}
		922	} else {
		923	push @nondirs, $entry;
		924	}
450	$nreq++;	925	}
451	add $grp aio_stat "$path/$ent/.", sub { $statcb->($_[0], $ent) };
452	}	926	}
453	} elsif (!$nreq) {
454	# finished
455	undef $statcb;
456	undef $schedcb;
457	$cb->(\@dirs, \@nondirs) if $cb;
458	undef $cb;
459	}	927	};
460	};	928	};
461	$statcb = sub {
462	my ($status, $entry) = @_;
463
464	if ($status < 0) {
465	$nreq--;
466	push @nondirs, $entry;
467	&$schedcb;
468	} else {
469	# need to check for real directory
470	add $grp aio_lstat "$path/$entry", sub {
471	$nreq--;
472
473	if (-d _) {
474	push @dirs, $entry;
475
476	if (!--$ndirs) {
477	push @nondirs, @$entries;
478	$entries = [];
479	}
480	} else {
481	push @nondirs, $entry;
482	}
483
484	&$schedcb;
485	}
486	}
487	};
488
489	&$schedcb while @$entries && $nreq < $maxreq;
490	};	929	};
491	};	930	};
492	};	931	};
493		932
494	$grp	933	$grp
495	}	934	}
496		935
		936	=item aio_rmtree $path, $callback->($status)
		937
		938	Delete a directory tree starting (and including) C<$path>, return the
		939	status of the final C<rmdir> only. This is a composite request that
		940	uses C<aio_scandir> to recurse into and rmdir directories, and unlink
		941	everything else.
		942
		943	=cut
		944
		945	sub aio_rmtree;
		946	sub aio_rmtree($;$) {
		947	my ($path, $cb) = @_;
		948
		949	my $pri = aioreq_pri;
		950	my $grp = aio_group $cb;
		951
		952	aioreq_pri $pri;
		953	add $grp aio_scandir $path, 0, sub {
		954	my ($dirs, $nondirs) = @_;
		955
		956	my $dirgrp = aio_group sub {
		957	add $grp aio_rmdir $path, sub {
		958	$grp->result ($_[0]);
		959	};
		960	};
		961
		962	(aioreq_pri $pri), add $dirgrp aio_rmtree "$path/$_" for @$dirs;
		963	(aioreq_pri $pri), add $dirgrp aio_unlink "$path/$_" for @$nondirs;
		964
		965	add $grp $dirgrp;
		966	};
		967
		968	$grp
		969	}
		970
		971	=item aio_sync $callback->($status)
		972
		973	Asynchronously call sync and call the callback when finished.
		974
497	=item aio_fsync $fh, $callback->($status)	975	=item aio_fsync $fh, $callback->($status)
498		976
499	Asynchronously call fsync on the given filehandle and call the callback	977	Asynchronously call fsync on the given filehandle and call the callback
500	with the fsync result code.	978	with the fsync result code.
501		979
…		…
505	callback with the fdatasync result code.	983	callback with the fdatasync result code.
506		984
507	If this call isn't available because your OS lacks it or it couldn't be	985	If this call isn't available because your OS lacks it or it couldn't be
508	detected, it will be emulated by calling C<fsync> instead.	986	detected, it will be emulated by calling C<fsync> instead.
509		987
		988	=item aio_sync_file_range $fh, $offset, $nbytes, $flags, $callback->($status)
		989
		990	Sync the data portion of the file specified by C<$offset> and C<$length>
		991	to disk (but NOT the metadata), by calling the Linux-specific
		992	sync_file_range call. If sync_file_range is not available or it returns
		993	ENOSYS, then fdatasync or fsync is being substituted.
		994
		995	C<$flags> can be a combination of C<IO::AIO::SYNC_FILE_RANGE_WAIT_BEFORE>,
		996	C<IO::AIO::SYNC_FILE_RANGE_WRITE> and
		997	C<IO::AIO::SYNC_FILE_RANGE_WAIT_AFTER>: refer to the sync_file_range
		998	manpage for details.
		999
		1000	=item aio_pathsync $path, $callback->($status)
		1001
		1002	This request tries to open, fsync and close the given path. This is a
		1003	composite request intended to sync directories after directory operations
		1004	(E.g. rename). This might not work on all operating systems or have any
		1005	specific effect, but usually it makes sure that directory changes get
		1006	written to disc. It works for anything that can be opened for read-only,
		1007	not just directories.
		1008
		1009	Future versions of this function might fall back to other methods when
		1010	C<fsync> on the directory fails (such as calling C<sync>).
		1011
		1012	Passes C<0> when everything went ok, and C<-1> on error.
		1013
		1014	=cut
		1015
		1016	sub aio_pathsync($;$) {
		1017	my ($path, $cb) = @_;
		1018
		1019	my $pri = aioreq_pri;
		1020	my $grp = aio_group $cb;
		1021
		1022	aioreq_pri $pri;
		1023	add $grp aio_open $path, O_RDONLY, 0, sub {
		1024	my ($fh) = @_;
		1025	if ($fh) {
		1026	aioreq_pri $pri;
		1027	add $grp aio_fsync $fh, sub {
		1028	$grp->result ($_[0]);
		1029
		1030	aioreq_pri $pri;
		1031	add $grp aio_close $fh;
		1032	};
		1033	} else {
		1034	$grp->result (-1);
		1035	}
		1036	};
		1037
		1038	$grp
		1039	}
		1040
		1041	=item aio_msync $scalar, $offset = 0, $length = undef, flags = 0, $callback->($status)
		1042
		1043	This is a rather advanced IO::AIO call, which only works on mmap(2)ed
		1044	scalars (see the L<Sys::Mmap> or L<Mmap> modules for details on this, note
		1045	that the scalar must only be modified in-place while an aio operation is
		1046	pending on it).
		1047
		1048	It calls the C<msync> function of your OS, if available, with the memory
		1049	area starting at C<$offset> in the string and ending C<$length> bytes
		1050	later. If C<$length> is negative, counts from the end, and if C<$length>
		1051	is C<undef>, then it goes till the end of the string. The flags can be
		1052	a combination of C<IO::AIO::MS_ASYNC>, C<IO::AIO::MS_INVALIDATE> and
		1053	C<IO::AIO::MS_SYNC>.
		1054
		1055	=item aio_mtouch $scalar, $offset = 0, $length = undef, flags = 0, $callback->($status)
		1056
		1057	This is a rather advanced IO::AIO call, which works best on mmap(2)ed
		1058	scalars.
		1059
		1060	It touches (reads or writes) all memory pages in the specified
		1061	range inside the scalar. All caveats and parameters are the same
		1062	as for C<aio_msync>, above, except for flags, which must be either
		1063	C<0> (which reads all pages and ensures they are instantiated) or
		1064	C<IO::AIO::MT_MODIFY>, which modifies the memory page s(by reading and
		1065	writing an octet from it, which dirties the page).
		1066
510	=item aio_group $callback->()	1067	=item aio_group $callback->(...)
511
512	[EXPERIMENTAL]
513		1068
514	This is a very special aio request: Instead of doing something, it is a	1069	This is a very special aio request: Instead of doing something, it is a
515	container for other aio requests, which is useful if you want to bundle	1070	container for other aio requests, which is useful if you want to bundle
516	many requests into a single, composite, request.	1071	many requests into a single, composite, request with a definite callback
		1072	and the ability to cancel the whole request with its subrequests.
517		1073
518	Returns an object of class L<IO::AIO::GRP>. See its documentation below	1074	Returns an object of class L<IO::AIO::GRP>. See its documentation below
519	for more info.	1075	for more info.
520		1076
521	Example:	1077	Example:
…		…
527	add $grp	1083	add $grp
528	(aio_stat ...),	1084	(aio_stat ...),
529	(aio_stat ...),	1085	(aio_stat ...),
530	...;	1086	...;
531		1087
		1088	=item aio_nop $callback->()
		1089
		1090	This is a special request - it does nothing in itself and is only used for
		1091	side effects, such as when you want to add a dummy request to a group so
		1092	that finishing the requests in the group depends on executing the given
		1093	code.
		1094
		1095	While this request does nothing, it still goes through the execution
		1096	phase and still requires a worker thread. Thus, the callback will not
		1097	be executed immediately but only after other requests in the queue have
		1098	entered their execution phase. This can be used to measure request
		1099	latency.
		1100
532	=item IO::AIO::aio_sleep $fractional_seconds, $callback->() *NOT EXPORTED*	1101	=item IO::AIO::aio_busy $fractional_seconds, $callback->() *NOT EXPORTED*
533		1102
534	Mainly used for debugging and benchmarking, this aio request puts one of	1103	Mainly used for debugging and benchmarking, this aio request puts one of
535	the request workers to sleep for the given time.	1104	the request workers to sleep for the given time.
536		1105
537	While it is theoretically handy to have simple I/O scheduling requests	1106	While it is theoretically handy to have simple I/O scheduling requests
538	like sleep and file handle readable/writable, the overhead this creates	1107	like sleep and file handle readable/writable, the overhead this creates is
539	is immense, so do not use this function except to put your application	1108	immense (it blocks a thread for a long time) so do not use this function
540	under artificial I/O pressure.	1109	except to put your application under artificial I/O pressure.
541		1110
542	=back	1111	=back
543		1112
544	=head2 IO::AIO::REQ CLASS	1113	=head2 IO::AIO::REQ CLASS
545		1114
546	All non-aggregate C<aio_*> functions return an object of this class when	1115	All non-aggregate C<aio_*> functions return an object of this class when
547	called in non-void context.	1116	called in non-void context.
548		1117
549	A request always moves through the following five states in its lifetime,
550	in order: B<ready> (request has been created, but has not been executed
551	yet), B<execute> (request is currently being executed), B<pending>
552	(request has been executed but callback has not been called yet),
553	B<result> (results are being processed synchronously, includes calling the
554	callback) and B<done> (request has reached the end of its lifetime and
555	holds no resources anymore).
556
557	=over 4	1118	=over 4
558		1119
559	=item $req->cancel	1120	=item cancel $req
560		1121
561	Cancels the request, if possible. Has the effect of skipping execution	1122	Cancels the request, if possible. Has the effect of skipping execution
562	when entering the B<execute> state and skipping calling the callback when	1123	when entering the B<execute> state and skipping calling the callback when
563	entering the the B<result> state, but will leave the request otherwise	1124	entering the the B<result> state, but will leave the request otherwise
564	untouched. That means that requests that currently execute will not be	1125	untouched (with the exception of readdir). That means that requests that
565	stopped and resources held by the request will not be freed prematurely.	1126	currently execute will not be stopped and resources held by the request
		1127	will not be freed prematurely.
		1128
		1129	=item cb $req $callback->(...)
		1130
		1131	Replace (or simply set) the callback registered to the request.
566		1132
567	=back	1133	=back
568		1134
569	=head2 IO::AIO::GRP CLASS	1135	=head2 IO::AIO::GRP CLASS
570		1136
…		…
585	You add requests by calling the C<add> method with one or more	1151	You add requests by calling the C<add> method with one or more
586	C<IO::AIO::REQ> objects:	1152	C<IO::AIO::REQ> objects:
587		1153
588	$grp->add (aio_unlink "...");	1154	$grp->add (aio_unlink "...");
589		1155
590	add $grp aio_stat "...", sub { ... };	1156	add $grp aio_stat "...", sub {
		1157	$_[0] or return $grp->result ("error");
		1158
		1159	# add another request dynamically, if first succeeded
		1160	add $grp aio_open "...", sub {
		1161	$grp->result ("ok");
		1162	};
		1163	};
591		1164
592	This makes it very easy to create composite requests (see the source of	1165	This makes it very easy to create composite requests (see the source of
593	C<aio_move> for an application) that work and feel like simple requests.	1166	C<aio_move> for an application) that work and feel like simple requests.
594		1167
		1168	=over 4
		1169
595	The IO::AIO::GRP objects will be cleaned up during calls to	1170	=item * The IO::AIO::GRP objects will be cleaned up during calls to
596	C<IO::AIO::poll_cb>, just like any other request.	1171	C<IO::AIO::poll_cb>, just like any other request.
597		1172
598	They can be canceled like any other request. Canceling will cancel not	1173	=item * They can be canceled like any other request. Canceling will cancel not
599	just the request itself, but also all requests it contains.	1174	only the request itself, but also all requests it contains.
600		1175
601	They can also can also be added to other IO::AIO::GRP objects.	1176	=item * They can also can also be added to other IO::AIO::GRP objects.
		1177
		1178	=item * You must not add requests to a group from within the group callback (or
		1179	any later time).
		1180
		1181	=back
602		1182
603	Their lifetime, simplified, looks like this: when they are empty, they	1183	Their lifetime, simplified, looks like this: when they are empty, they
604	will finish very quickly. If they contain only requests that are in the	1184	will finish very quickly. If they contain only requests that are in the
605	C<done> state, they will also finish. Otherwise they will continue to	1185	C<done> state, they will also finish. Otherwise they will continue to
606	exist.	1186	exist.
607		1187
		1188	That means after creating a group you have some time to add requests
		1189	(precisely before the callback has been invoked, which is only done within
		1190	the C<poll_cb>). And in the callbacks of those requests, you can add
		1191	further requests to the group. And only when all those requests have
		1192	finished will the the group itself finish.
		1193
608	=over 4	1194	=over 4
609		1195
		1196	=item add $grp ...
		1197
610	=item $grp->add (...)	1198	=item $grp->add (...)
611		1199
612	=item add $grp ...	1200	Add one or more requests to the group. Any type of L<IO::AIO::REQ> can
		1201	be added, including other groups, as long as you do not create circular
		1202	dependencies.
613		1203
614	Add one or more	1204	Returns all its arguments.
615	Cancels the request, if possible. Has the effect of skipping execution	1205
616	when entering the B<execute> state and skipping calling the callback when	1206	=item $grp->cancel_subs
617	entering the the B<result> state, but will leave the request otherwise	1207
618	untouched. That means that requests that currently execute will not be	1208	Cancel all subrequests and clears any feeder, but not the group request
619	stopped and resources held by the request will not be freed prematurely.	1209	itself. Useful when you queued a lot of events but got a result early.
		1210
		1211	The group request will finish normally (you cannot add requests to the
		1212	group).
		1213
		1214	=item $grp->result (...)
		1215
		1216	Set the result value(s) that will be passed to the group callback when all
		1217	subrequests have finished and set the groups errno to the current value
		1218	of errno (just like calling C<errno> without an error number). By default,
		1219	no argument will be passed and errno is zero.
		1220
		1221	=item $grp->errno ([$errno])
		1222
		1223	Sets the group errno value to C<$errno>, or the current value of errno
		1224	when the argument is missing.
		1225
		1226	Every aio request has an associated errno value that is restored when
		1227	the callback is invoked. This method lets you change this value from its
		1228	default (0).
		1229
		1230	Calling C<result> will also set errno, so make sure you either set C<$!>
		1231	before the call to C<result>, or call c<errno> after it.
		1232
		1233	=item feed $grp $callback->($grp)
		1234
		1235	Sets a feeder/generator on this group: every group can have an attached
		1236	generator that generates requests if idle. The idea behind this is that,
		1237	although you could just queue as many requests as you want in a group,
		1238	this might starve other requests for a potentially long time. For example,
		1239	C<aio_scandir> might generate hundreds of thousands C<aio_stat> requests,
		1240	delaying any later requests for a long time.
		1241
		1242	To avoid this, and allow incremental generation of requests, you can
		1243	instead a group and set a feeder on it that generates those requests. The
		1244	feed callback will be called whenever there are few enough (see C<limit>,
		1245	below) requests active in the group itself and is expected to queue more
		1246	requests.
		1247
		1248	The feed callback can queue as many requests as it likes (i.e. C<add> does
		1249	not impose any limits).
		1250
		1251	If the feed does not queue more requests when called, it will be
		1252	automatically removed from the group.
		1253
		1254	If the feed limit is C<0> when this method is called, it will be set to
		1255	C<2> automatically.
		1256
		1257	Example:
		1258
		1259	# stat all files in @files, but only ever use four aio requests concurrently:
		1260
		1261	my $grp = aio_group sub { print "finished\n" };
		1262	limit $grp 4;
		1263	feed $grp sub {
		1264	my $file = pop @files
		1265	or return;
		1266
		1267	add $grp aio_stat $file, sub { ... };
		1268	};
		1269
		1270	=item limit $grp $num
		1271
		1272	Sets the feeder limit for the group: The feeder will be called whenever
		1273	the group contains less than this many requests.
		1274
		1275	Setting the limit to C<0> will pause the feeding process.
		1276
		1277	The default value for the limit is C<0>, but note that setting a feeder
		1278	automatically bumps it up to C<2>.
620		1279
621	=back	1280	=back
622		1281
623	=head2 SUPPORT FUNCTIONS	1282	=head2 SUPPORT FUNCTIONS
624		1283
		1284	=head3 EVENT PROCESSING AND EVENT LOOP INTEGRATION
		1285
625	=over 4	1286	=over 4
626		1287
627	=item $fileno = IO::AIO::poll_fileno	1288	=item $fileno = IO::AIO::poll_fileno
628		1289
629	Return the I<request result pipe file descriptor>. This filehandle must be	1290	Return the I<request result pipe file descriptor>. This filehandle must be
630	polled for reading by some mechanism outside this module (e.g. Event or	1291	polled for reading by some mechanism outside this module (e.g. EV, Glib,
631	select, see below or the SYNOPSIS). If the pipe becomes readable you have	1292	select and so on, see below or the SYNOPSIS). If the pipe becomes readable
632	to call C<poll_cb> to check the results.	1293	you have to call C<poll_cb> to check the results.
633		1294
634	See C<poll_cb> for an example.	1295	See C<poll_cb> for an example.
635		1296
636	=item IO::AIO::poll_cb	1297	=item IO::AIO::poll_cb
637		1298
638	Process all outstanding events on the result pipe. You have to call this	1299	Process some outstanding events on the result pipe. You have to call this
639	regularly. Returns the number of events processed. Returns immediately	1300	regularly. Returns C<0> if all events could be processed, or C<-1> if it
640	when no events are outstanding.	1301	returned earlier for whatever reason. Returns immediately when no events
		1302	are outstanding. The amount of events processed depends on the settings of
		1303	C<IO::AIO::max_poll_req> and C<IO::AIO::max_poll_time>.
		1304
		1305	If not all requests were processed for whatever reason, the filehandle
		1306	will still be ready when C<poll_cb> returns, so normally you don't have to
		1307	do anything special to have it called later.
641		1308
642	Example: Install an Event watcher that automatically calls	1309	Example: Install an Event watcher that automatically calls
643	IO::AIO::poll_cb with high priority:	1310	IO::AIO::poll_cb with high priority (more examples can be found in the
		1311	SYNOPSIS section, at the top of this document):
644		1312
645	Event->io (fd => IO::AIO::poll_fileno,	1313	Event->io (fd => IO::AIO::poll_fileno,
646	poll => 'r', async => 1,	1314	poll => 'r', async => 1,
647	cb => \&IO::AIO::poll_cb);	1315	cb => \&IO::AIO::poll_cb);
648		1316
		1317	=item IO::AIO::max_poll_reqs $nreqs
		1318
		1319	=item IO::AIO::max_poll_time $seconds
		1320
		1321	These set the maximum number of requests (default C<0>, meaning infinity)
		1322	that are being processed by C<IO::AIO::poll_cb> in one call, respectively
		1323	the maximum amount of time (default C<0>, meaning infinity) spent in
		1324	C<IO::AIO::poll_cb> to process requests (more correctly the mininum amount
		1325	of time C<poll_cb> is allowed to use).
		1326
		1327	Setting C<max_poll_time> to a non-zero value creates an overhead of one
		1328	syscall per request processed, which is not normally a problem unless your
		1329	callbacks are really really fast or your OS is really really slow (I am
		1330	not mentioning Solaris here). Using C<max_poll_reqs> incurs no overhead.
		1331
		1332	Setting these is useful if you want to ensure some level of
		1333	interactiveness when perl is not fast enough to process all requests in
		1334	time.
		1335
		1336	For interactive programs, values such as C<0.01> to C<0.1> should be fine.
		1337
		1338	Example: Install an Event watcher that automatically calls
		1339	IO::AIO::poll_cb with low priority, to ensure that other parts of the
		1340	program get the CPU sometimes even under high AIO load.
		1341
		1342	# try not to spend much more than 0.1s in poll_cb
		1343	IO::AIO::max_poll_time 0.1;
		1344
		1345	# use a low priority so other tasks have priority
		1346	Event->io (fd => IO::AIO::poll_fileno,
		1347	poll => 'r', nice => 1,
		1348	cb => &IO::AIO::poll_cb);
		1349
649	=item IO::AIO::poll_wait	1350	=item IO::AIO::poll_wait
650		1351
		1352	If there are any outstanding requests and none of them in the result
651	Wait till the result filehandle becomes ready for reading (simply does a	1353	phase, wait till the result filehandle becomes ready for reading (simply
652	C<select> on the filehandle. This is useful if you want to synchronously wait	1354	does a C<select> on the filehandle. This is useful if you want to
653	for some requests to finish).	1355	synchronously wait for some requests to finish).
654		1356
655	See C<nreqs> for an example.	1357	See C<nreqs> for an example.
656		1358
		1359	=item IO::AIO::poll
		1360
		1361	Waits until some requests have been handled.
		1362
		1363	Returns the number of requests processed, but is otherwise strictly
		1364	equivalent to:
		1365
		1366	IO::AIO::poll_wait, IO::AIO::poll_cb
		1367
657	=item IO::AIO::nreqs	1368	=item IO::AIO::flush
658		1369
659	Returns the number of requests currently outstanding (i.e. for which their	1370	Wait till all outstanding AIO requests have been handled.
660	callback has not been invoked yet).
661		1371
662	Example: wait till there are no outstanding requests anymore:	1372	Strictly equivalent to:
663		1373
664	IO::AIO::poll_wait, IO::AIO::poll_cb	1374	IO::AIO::poll_wait, IO::AIO::poll_cb
665	while IO::AIO::nreqs;	1375	while IO::AIO::nreqs;
666		1376
667	=item IO::AIO::flush	1377	=back
668		1378
669	Wait till all outstanding AIO requests have been handled.	1379	=head3 CONTROLLING THE NUMBER OF THREADS
670		1380
671	Strictly equivalent to:	1381	=over
672
673	IO::AIO::poll_wait, IO::AIO::poll_cb
674	while IO::AIO::nreqs;
675
676	=item IO::AIO::poll
677
678	Waits until some requests have been handled.
679
680	Strictly equivalent to:
681
682	IO::AIO::poll_wait, IO::AIO::poll_cb
683	if IO::AIO::nreqs;
684		1382
685	=item IO::AIO::min_parallel $nthreads	1383	=item IO::AIO::min_parallel $nthreads
686		1384
687	Set the minimum number of AIO threads to C<$nthreads>. The current default	1385	Set the minimum number of AIO threads to C<$nthreads>. The current
688	is C<4>, which means four asynchronous operations can be done at one time	1386	default is C<8>, which means eight asynchronous operations can execute
689	(the number of outstanding operations, however, is unlimited).	1387	concurrently at any one time (the number of outstanding requests,
		1388	however, is unlimited).
690		1389
691	IO::AIO starts threads only on demand, when an AIO request is queued and	1390	IO::AIO starts threads only on demand, when an AIO request is queued and
692	no free thread exists.	1391	no free thread exists. Please note that queueing up a hundred requests can
		1392	create demand for a hundred threads, even if it turns out that everything
		1393	is in the cache and could have been processed faster by a single thread.
693		1394
694	It is recommended to keep the number of threads low, as some Linux	1395	It is recommended to keep the number of threads relatively low, as some
695	kernel versions will scale negatively with the number of threads (higher	1396	Linux kernel versions will scale negatively with the number of threads
696	parallelity => MUCH higher latency). With current Linux 2.6 versions, 4-32	1397	(higher parallelity => MUCH higher latency). With current Linux 2.6
697	threads should be fine.	1398	versions, 4-32 threads should be fine.
698		1399
699	Under most circumstances you don't need to call this function, as the	1400	Under most circumstances you don't need to call this function, as the
700	module selects a default that is suitable for low to moderate load.	1401	module selects a default that is suitable for low to moderate load.
701		1402
702	=item IO::AIO::max_parallel $nthreads	1403	=item IO::AIO::max_parallel $nthreads
…		…
711	This module automatically runs C<max_parallel 0> at program end, to ensure	1412	This module automatically runs C<max_parallel 0> at program end, to ensure
712	that all threads are killed and that there are no outstanding requests.	1413	that all threads are killed and that there are no outstanding requests.
713		1414
714	Under normal circumstances you don't need to call this function.	1415	Under normal circumstances you don't need to call this function.
715		1416
		1417	=item IO::AIO::max_idle $nthreads
		1418
		1419	Limit the number of threads (default: 4) that are allowed to idle (i.e.,
		1420	threads that did not get a request to process within 10 seconds). That
		1421	means if a thread becomes idle while C<$nthreads> other threads are also
		1422	idle, it will free its resources and exit.
		1423
		1424	This is useful when you allow a large number of threads (e.g. 100 or 1000)
		1425	to allow for extremely high load situations, but want to free resources
		1426	under normal circumstances (1000 threads can easily consume 30MB of RAM).
		1427
		1428	The default is probably ok in most situations, especially if thread
		1429	creation is fast. If thread creation is very slow on your system you might
		1430	want to use larger values.
		1431
716	=item $oldnreqs = IO::AIO::max_outstanding $nreqs	1432	=item IO::AIO::max_outstanding $maxreqs
		1433
		1434	This is a very bad function to use in interactive programs because it
		1435	blocks, and a bad way to reduce concurrency because it is inexact: Better
		1436	use an C<aio_group> together with a feed callback.
717		1437
718	Sets the maximum number of outstanding requests to C<$nreqs>. If you	1438	Sets the maximum number of outstanding requests to C<$nreqs>. If you
719	try to queue up more than this number of requests, the caller will block until	1439	do queue up more than this number of requests, the next call to the
720	some requests have been handled.	1440	C<poll_cb> (and C<poll_some> and other functions calling C<poll_cb>)
		1441	function will block until the limit is no longer exceeded.
721		1442
722	The default is very large, so normally there is no practical limit. If you	1443	The default value is very large, so there is no practical limit on the
723	queue up many requests in a loop it often improves speed if you set	1444	number of outstanding requests.
724	this to a relatively low number, such as C<100>.
725		1445
726	Under normal circumstances you don't need to call this function.	1446	You can still queue as many requests as you want. Therefore,
		1447	C<max_outstanding> is mainly useful in simple scripts (with low values) or
		1448	as a stop gap to shield against fatal memory overflow (with large values).
727		1449
728	=back	1450	=back
729		1451
		1452	=head3 STATISTICAL INFORMATION
		1453
		1454	=over
		1455
		1456	=item IO::AIO::nreqs
		1457
		1458	Returns the number of requests currently in the ready, execute or pending
		1459	states (i.e. for which their callback has not been invoked yet).
		1460
		1461	Example: wait till there are no outstanding requests anymore:
		1462
		1463	IO::AIO::poll_wait, IO::AIO::poll_cb
		1464	while IO::AIO::nreqs;
		1465
		1466	=item IO::AIO::nready
		1467
		1468	Returns the number of requests currently in the ready state (not yet
		1469	executed).
		1470
		1471	=item IO::AIO::npending
		1472
		1473	Returns the number of requests currently in the pending state (executed,
		1474	but not yet processed by poll_cb).
		1475
		1476	=back
		1477
		1478	=head3 MISCELLANEOUS FUNCTIONS
		1479
		1480	IO::AIO implements some functions that might be useful, but are not
		1481	asynchronous.
		1482
		1483	=over 4
		1484
		1485	=item IO::AIO::sendfile $ofh, $ifh, $offset, $count
		1486
		1487	Calls the C<eio_sendfile_sync> function, which is like C<aio_sendfile>,
		1488	but is blocking (this makes most sense if you know the input data is
		1489	likely cached already and the output filehandle is set to non-blocking
		1490	operations).
		1491
		1492	Returns the number of bytes copied, or C<-1> on error.
		1493
		1494	=item IO::AIO::fadvise $fh, $offset, $len, $advice
		1495
		1496	Simply calls the C<posix_fadvise> function (see it's
		1497	manpage for details). The following advice constants are
		1498	avaiable: C<IO::AIO::FADV_NORMAL>, C<IO::AIO::FADV_SEQUENTIAL>,
		1499	C<IO::AIO::FADV_RANDOM>, C<IO::AIO::FADV_NOREUSE>,
		1500	C<IO::AIO::FADV_WILLNEED>, C<IO::AIO::FADV_DONTNEED>.
		1501
		1502	On systems that do not implement C<posix_fadvise>, this function returns
		1503	ENOSYS, otherwise the return value of C<posix_fadvise>.
		1504
		1505	=back
		1506
730	=cut	1507	=cut
731		1508
732	# support function to convert a fd into a perl filehandle
733	sub _fd2fh {
734	return undef if $_[0] < 0;
735
736	# try to generate nice filehandles
737	my $sym = "IO::AIO::fd#$_[0]";
738	local *$sym;
739
740	open *$sym, "+<&=$_[0]" # usually works under any unix
741	or open *$sym, "<&=$_[0]" # cygwin needs this
742	or open *$sym, ">&=$_[0]" # or this
743	or return undef;
744
745	*$sym
746	}
747
748	min_parallel 4;	1509	min_parallel 8;
749		1510
750	END {	1511	END { flush }
751	max_parallel 0;
752	}
753		1512
754	1;	1513	1;
755		1514
756	=head2 FORK BEHAVIOUR	1515	=head2 FORK BEHAVIOUR
757		1516
758	This module should do "the right thing" when the process using it forks:	1517	This module should do "the right thing" when the process using it forks:
759		1518
760	Before the fork, IO::AIO enters a quiescent state where no requests	1519	Before the fork, IO::AIO enters a quiescent state where no requests
761	can be added in other threads and no results will be processed. After	1520	can be added in other threads and no results will be processed. After
762	the fork the parent simply leaves the quiescent state and continues	1521	the fork the parent simply leaves the quiescent state and continues
763	request/result processing, while the child clears the request/result	1522	request/result processing, while the child frees the request/result queue
764	queue (so the requests started before the fork will only be handled in	1523	(so that the requests started before the fork will only be handled in the
765	the parent). Threads will be started on demand until the limit ste in the	1524	parent). Threads will be started on demand until the limit set in the
766	parent process has been reached again.	1525	parent process has been reached again.
767		1526
768	In short: the parent will, after a short pause, continue as if fork had	1527	In short: the parent will, after a short pause, continue as if fork had
769	not been called, while the child will act as if IO::AIO has not been used	1528	not been called, while the child will act as if IO::AIO has not been used
770	yet.	1529	yet.
771		1530
		1531	=head2 MEMORY USAGE
		1532
		1533	Per-request usage:
		1534
		1535	Each aio request uses - depending on your architecture - around 100-200
		1536	bytes of memory. In addition, stat requests need a stat buffer (possibly
		1537	a few hundred bytes), readdir requires a result buffer and so on. Perl
		1538	scalars and other data passed into aio requests will also be locked and
		1539	will consume memory till the request has entered the done state.
		1540
		1541	This is not awfully much, so queuing lots of requests is not usually a
		1542	problem.
		1543
		1544	Per-thread usage:
		1545
		1546	In the execution phase, some aio requests require more memory for
		1547	temporary buffers, and each thread requires a stack and other data
		1548	structures (usually around 16k-128k, depending on the OS).
		1549
		1550	=head1 KNOWN BUGS
		1551
		1552	Known bugs will be fixed in the next release.
		1553
772	=head1 SEE ALSO	1554	=head1 SEE ALSO
773		1555
774	L<Coro>, L<Linux::AIO> (obsolete).	1556	L<AnyEvent::AIO> for easy integration into event loops, L<Coro::AIO> for a
		1557	more natural syntax.
775		1558
776	=head1 AUTHOR	1559	=head1 AUTHOR
777		1560
778	Marc Lehmann <schmorp@schmorp.de>	1561	Marc Lehmann <schmorp@schmorp.de>
779	http://home.schmorp.de/	1562	http://home.schmorp.de/

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