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Revision 1.22 by root, Sat Jan 6 02:47:11 2007 UTC vs.
Revision 1.58 by root, Sun May 1 17:19:39 2016 UTC

…		…
2	IO::AIO - Asynchronous Input/Output	2	IO::AIO - Asynchronous Input/Output
3		3
4	SYNOPSIS	4	SYNOPSIS
5	use IO::AIO;	5	use IO::AIO;
6		6
7	aio_open "/etc/passwd", O_RDONLY, 0, sub {	7	aio_open "/etc/passwd", IO::AIO::O_RDONLY, 0, sub {
8	my $fh = shift	8	my $fh = shift
9	or die "/etc/passwd: $!";	9	or die "/etc/passwd: $!";
10	...	10	...
11	};	11	};
12		12
…		…
24	$req->cancel; # cancel request if still in queue	24	$req->cancel; # cancel request if still in queue
25		25
26	my $grp = aio_group sub { print "all stats done\n" };	26	my $grp = aio_group sub { print "all stats done\n" };
27	add $grp aio_stat "..." for ...;	27	add $grp aio_stat "..." for ...;
28		28
29	# AnyEvent integration
30	open my $fh, "<&=" . IO::AIO::poll_fileno or die "$!";
31	my $w = AnyEvent->io (fh => $fh, poll => 'r', cb => sub { IO::AIO::poll_cb });
32
33	# Event integration
34	Event->io (fd => IO::AIO::poll_fileno,
35	poll => 'r',
36	cb => \&IO::AIO::poll_cb);
37
38	# Glib/Gtk2 integration
39	add_watch Glib::IO IO::AIO::poll_fileno,
40	in => sub { IO::AIO::poll_cb; 1 };
41
42	# Tk integration
43	Tk::Event::IO->fileevent (IO::AIO::poll_fileno, "",
44	readable => \&IO::AIO::poll_cb);
45
46	# Danga::Socket integration
47	Danga::Socket->AddOtherFds (IO::AIO::poll_fileno =>
48	\&IO::AIO::poll_cb);
49
50	DESCRIPTION	29	DESCRIPTION
51	This module implements asynchronous I/O using whatever means your	30	This module implements asynchronous I/O using whatever means your
52	operating system supports.	31	operating system supports. It is implemented as an interface to "libeio"
		32	(<http://software.schmorp.de/pkg/libeio.html>).
53		33
54	Asynchronous means that operations that can normally block your program	34	Asynchronous means that operations that can normally block your program
55	(e.g. reading from disk) will be done asynchronously: the operation will	35	(e.g. reading from disk) will be done asynchronously: the operation will
56	still block, but you can do something else in the meantime. This is	36	still block, but you can do something else in the meantime. This is
57	extremely useful for programs that need to stay interactive even when	37	extremely useful for programs that need to stay interactive even when
…		…
61	faster on a RAID volume or over NFS when you do a number of stat	41	faster on a RAID volume or over NFS when you do a number of stat
62	operations concurrently.	42	operations concurrently.
63		43
64	While most of this works on all types of file descriptors (for example	44	While most of this works on all types of file descriptors (for example
65	sockets), using these functions on file descriptors that support	45	sockets), using these functions on file descriptors that support
66	nonblocking operation (again, sockets, pipes etc.) is very inefficient	46	nonblocking operation (again, sockets, pipes etc.) is very inefficient.
67	or might not work (aio_read fails on sockets/pipes/fifos). Use an event
68	loop for that (such as the Event module): IO::AIO will naturally fit	47	Use an event loop for that (such as the EV module): IO::AIO will
69	into such an event loop itself.	48	naturally fit into such an event loop itself.
70		49
71	In this version, a number of threads are started that execute your	50	In this version, a number of threads are started that execute your
72	requests and signal their completion. You don't need thread support in	51	requests and signal their completion. You don't need thread support in
73	perl, and the threads created by this module will not be visible to	52	perl, and the threads created by this module will not be visible to
74	perl. In the future, this module might make use of the native aio	53	perl. In the future, this module might make use of the native aio
…		…
76	not well-supported or restricted (GNU/Linux doesn't allow them on normal	55	not well-supported or restricted (GNU/Linux doesn't allow them on normal
77	files currently, for example), and they would only support aio_read and	56	files currently, for example), and they would only support aio_read and
78	aio_write, so the remaining functionality would have to be implemented	57	aio_write, so the remaining functionality would have to be implemented
79	using threads anyway.	58	using threads anyway.
80		59
81	Although the module will work with in the presence of other (Perl-)	60	Although the module will work in the presence of other (Perl-) threads,
82	threads, it is currently not reentrant in any way, so use appropriate	61	it is currently not reentrant in any way, so use appropriate locking
83	locking yourself, always call "poll_cb" from within the same thread, or	62	yourself, always call "poll_cb" from within the same thread, or never
84	never call "poll_cb" (or other "aio_" functions) recursively.	63	call "poll_cb" (or other "aio_" functions) recursively.
85		64
86	EXAMPLE	65	EXAMPLE
87	This is a simple example that uses the Event module and loads	66	This is a simple example that uses the EV module and loads /etc/passwd
88	/etc/passwd asynchronously:	67	asynchronously:
89		68
90	use Fcntl;
91	use Event;	69	use EV;
92	use IO::AIO;	70	use IO::AIO;
93		71
94	# register the IO::AIO callback with Event	72	# register the IO::AIO callback with EV
95	Event->io (fd => IO::AIO::poll_fileno,	73	my $aio_w = EV::io IO::AIO::poll_fileno, EV::READ, \&IO::AIO::poll_cb;
96	poll => 'r',
97	cb => \&IO::AIO::poll_cb);
98		74
99	# queue the request to open /etc/passwd	75	# queue the request to open /etc/passwd
100	aio_open "/etc/passwd", O_RDONLY, 0, sub {	76	aio_open "/etc/passwd", IO::AIO::O_RDONLY, 0, sub {
101	my $fh = shift	77	my $fh = shift
102	or die "error while opening: $!";	78	or die "error while opening: $!";
103		79
104	# stat'ing filehandles is generally non-blocking	80	# stat'ing filehandles is generally non-blocking
105	my $size = -s $fh;	81	my $size = -s $fh;
…		…
114		90
115	# file contents now in $contents	91	# file contents now in $contents
116	print $contents;	92	print $contents;
117		93
118	# exit event loop and program	94	# exit event loop and program
119	Event::unloop;	95	EV::break;
120	};	96	};
121	};	97	};
122		98
123	# possibly queue up other requests, or open GUI windows,	99	# possibly queue up other requests, or open GUI windows,
124	# check for sockets etc. etc.	100	# check for sockets etc. etc.
125		101
126	# process events as long as there are some:	102	# process events as long as there are some:
127	Event::loop;	103	EV::run;
128		104
129	REQUEST ANATOMY AND LIFETIME	105	REQUEST ANATOMY AND LIFETIME
130	Every "aio_*" function creates a request. which is a C data structure	106	Every "aio_*" function creates a request. which is a C data structure
131	not directly visible to Perl.	107	not directly visible to Perl.
132		108
…		…
168	anymore (except possibly for the Perl object, but its connection to	144	anymore (except possibly for the Perl object, but its connection to
169	the actual aio request is severed and calling its methods will	145	the actual aio request is severed and calling its methods will
170	either do nothing or result in a runtime error).	146	either do nothing or result in a runtime error).
171		147
172	FUNCTIONS	148	FUNCTIONS
173	AIO REQUEST FUNCTIONS	149	QUICK OVERVIEW
		150	This section simply lists the prototypes most of the functions for quick
		151	reference. See the following sections for function-by-function
		152	documentation.
		153
		154	aio_wd $pathname, $callback->($wd)
		155	aio_open $pathname, $flags, $mode, $callback->($fh)
		156	aio_close $fh, $callback->($status)
		157	aio_seek $fh,$offset,$whence, $callback->($offs)
		158	aio_read $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
		159	aio_write $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
		160	aio_sendfile $out_fh, $in_fh, $in_offset, $length, $callback->($retval)
		161	aio_readahead $fh,$offset,$length, $callback->($retval)
		162	aio_stat $fh_or_path, $callback->($status)
		163	aio_lstat $fh, $callback->($status)
		164	aio_statvfs $fh_or_path, $callback->($statvfs)
		165	aio_utime $fh_or_path, $atime, $mtime, $callback->($status)
		166	aio_chown $fh_or_path, $uid, $gid, $callback->($status)
		167	aio_chmod $fh_or_path, $mode, $callback->($status)
		168	aio_truncate $fh_or_path, $offset, $callback->($status)
		169	aio_allocate $fh, $mode, $offset, $len, $callback->($status)
		170	aio_fiemap $fh, $start, $length, $flags, $count, $cb->(\@extents)
		171	aio_unlink $pathname, $callback->($status)
		172	aio_mknod $pathname, $mode, $dev, $callback->($status)
		173	aio_link $srcpath, $dstpath, $callback->($status)
		174	aio_symlink $srcpath, $dstpath, $callback->($status)
		175	aio_readlink $pathname, $callback->($link)
		176	aio_realpath $pathname, $callback->($path)
		177	aio_rename $srcpath, $dstpath, $callback->($status)
		178	aio_mkdir $pathname, $mode, $callback->($status)
		179	aio_rmdir $pathname, $callback->($status)
		180	aio_readdir $pathname, $callback->($entries)
		181	aio_readdirx $pathname, $flags, $callback->($entries, $flags)
		182	IO::AIO::READDIR_DENTS IO::AIO::READDIR_DIRS_FIRST
		183	IO::AIO::READDIR_STAT_ORDER IO::AIO::READDIR_FOUND_UNKNOWN
		184	aio_scandir $pathname, $maxreq, $callback->($dirs, $nondirs)
		185	aio_load $pathname, $data, $callback->($status)
		186	aio_copy $srcpath, $dstpath, $callback->($status)
		187	aio_move $srcpath, $dstpath, $callback->($status)
		188	aio_rmtree $pathname, $callback->($status)
		189	aio_fcntl $fh, $cmd, $arg, $callback->($status)
		190	aio_ioctl $fh, $request, $buf, $callback->($status)
		191	aio_sync $callback->($status)
		192	aio_syncfs $fh, $callback->($status)
		193	aio_fsync $fh, $callback->($status)
		194	aio_fdatasync $fh, $callback->($status)
		195	aio_sync_file_range $fh, $offset, $nbytes, $flags, $callback->($status)
		196	aio_pathsync $pathname, $callback->($status)
		197	aio_msync $scalar, $offset = 0, $length = undef, flags = 0, $callback->($status)
		198	aio_mtouch $scalar, $offset = 0, $length = undef, flags = 0, $callback->($status)
		199	aio_mlock $scalar, $offset = 0, $length = undef, $callback->($status)
		200	aio_mlockall $flags, $callback->($status)
		201	aio_group $callback->(...)
		202	aio_nop $callback->()
		203
		204	$prev_pri = aioreq_pri [$pri]
		205	aioreq_nice $pri_adjust
		206
		207	IO::AIO::poll_wait
		208	IO::AIO::poll_cb
		209	IO::AIO::poll
		210	IO::AIO::flush
		211	IO::AIO::max_poll_reqs $nreqs
		212	IO::AIO::max_poll_time $seconds
		213	IO::AIO::min_parallel $nthreads
		214	IO::AIO::max_parallel $nthreads
		215	IO::AIO::max_idle $nthreads
		216	IO::AIO::idle_timeout $seconds
		217	IO::AIO::max_outstanding $maxreqs
		218	IO::AIO::nreqs
		219	IO::AIO::nready
		220	IO::AIO::npending
		221
		222	IO::AIO::sendfile $ofh, $ifh, $offset, $count
		223	IO::AIO::fadvise $fh, $offset, $len, $advice
		224	IO::AIO::mmap $scalar, $length, $prot, $flags[, $fh[, $offset]]
		225	IO::AIO::munmap $scalar
		226	IO::AIO::madvise $scalar, $offset, $length, $advice
		227	IO::AIO::mprotect $scalar, $offset, $length, $protect
		228	IO::AIO::munlock $scalar, $offset = 0, $length = undef
		229	IO::AIO::munlockall
		230
		231	API NOTES
174	All the "aio_*" calls are more or less thin wrappers around the syscall	232	All the "aio_*" calls are more or less thin wrappers around the syscall
175	with the same name (sans "aio_"). The arguments are similar or	233	with the same name (sans "aio_"). The arguments are similar or
176	identical, and they all accept an additional (and optional) $callback	234	identical, and they all accept an additional (and optional) $callback
177	argument which must be a code reference. This code reference will get	235	argument which must be a code reference. This code reference will be
178	called with the syscall return code (e.g. most syscalls return -1 on	236	called after the syscall has been executed in an asynchronous fashion.
179	error, unlike perl, which usually delivers "false") as it's sole	237	The results of the request will be passed as arguments to the callback
180	argument when the given syscall has been executed asynchronously.	238	(and, if an error occured, in $!) - for most requests the syscall return
		239	code (e.g. most syscalls return -1 on error, unlike perl, which usually
		240	delivers "false").
		241
		242	Some requests (such as "aio_readdir") pass the actual results and
		243	communicate failures by passing "undef".
181		244
182	All functions expecting a filehandle keep a copy of the filehandle	245	All functions expecting a filehandle keep a copy of the filehandle
183	internally until the request has finished.	246	internally until the request has finished.
184		247
185	All functions return request objects of type IO::AIO::REQ that allow	248	All functions return request objects of type IO::AIO::REQ that allow
186	further manipulation of those requests while they are in-flight.	249	further manipulation of those requests while they are in-flight.
187		250
188	The pathnames you pass to these routines *must* be absolute and encoded	251	The pathnames you pass to these routines *should* be absolute. The
189	as octets. The reason for the former is that at the time the request is	252	reason for this is that at the time the request is being executed, the
190	being executed, the current working directory could have changed.	253	current working directory could have changed. Alternatively, you can
191	Alternatively, you can make sure that you never change the current	254	make sure that you never change the current working directory anywhere
192	working directory anywhere in the program and then use relative paths.	255	in the program and then use relative paths. You can also take advantage
		256	of IO::AIOs working directory abstraction, that lets you specify paths
		257	relative to some previously-opened "working directory object" - see the
		258	description of the "IO::AIO::WD" class later in this document.
193		259
194	To encode pathnames as octets, either make sure you either: a) always	260	To encode pathnames as octets, either make sure you either: a) always
195	pass in filenames you got from outside (command line, readdir etc.)	261	pass in filenames you got from outside (command line, readdir etc.)
196	without tinkering, b) are ASCII or ISO 8859-1, c) use the Encode module	262	without tinkering, b) are in your native filesystem encoding, c) use the
197	and encode your pathnames to the locale (or other) encoding in effect in	263	Encode module and encode your pathnames to the locale (or other)
198	the user environment, d) use Glib::filename_from_unicode on unicode	264	encoding in effect in the user environment, d) use
199	filenames or e) use something else to ensure your scalar has the correct	265	Glib::filename_from_unicode on unicode filenames or e) use something
200	contents.	266	else to ensure your scalar has the correct contents.
201		267
202	This works, btw. independent of the internal UTF-8 bit, which IO::AIO	268	This works, btw. independent of the internal UTF-8 bit, which IO::AIO
203	handles correctly wether it is set or not.	269	handles correctly whether it is set or not.
204		270
		271	AIO REQUEST FUNCTIONS
205	$prev_pri = aioreq_pri [$pri]	272	$prev_pri = aioreq_pri [$pri]
206	Returns the priority value that would be used for the next request	273	Returns the priority value that would be used for the next request
207	and, if $pri is given, sets the priority for the next aio request.	274	and, if $pri is given, sets the priority for the next aio request.
208		275
209	The default priority is 0, the minimum and maximum priorities are -4	276	The default priority is 0, the minimum and maximum priorities are -4
…		…
231	Similar to "aioreq_pri", but subtracts the given value from the	298	Similar to "aioreq_pri", but subtracts the given value from the
232	current priority, so the effect is cumulative.	299	current priority, so the effect is cumulative.
233		300
234	aio_open $pathname, $flags, $mode, $callback->($fh)	301	aio_open $pathname, $flags, $mode, $callback->($fh)
235	Asynchronously open or create a file and call the callback with a	302	Asynchronously open or create a file and call the callback with a
236	newly created filehandle for the file.	303	newly created filehandle for the file (or "undef" in case of an
		304	error).
237		305
238	The pathname passed to "aio_open" must be absolute. See API NOTES,	306	The pathname passed to "aio_open" must be absolute. See API NOTES,
239	above, for an explanation.	307	above, for an explanation.
240		308
241	The $flags argument is a bitmask. See the "Fcntl" module for a list.	309	The $flags argument is a bitmask. See the "Fcntl" module for a list.
242	They are the same as used by "sysopen".	310	They are the same as used by "sysopen".
243		311
244	Likewise, $mode specifies the mode of the newly created file, if it	312	Likewise, $mode specifies the mode of the newly created file, if it
245	didn't exist and "O_CREAT" has been given, just like perl's	313	didn't exist and "O_CREAT" has been given, just like perl's
246	"sysopen", except that it is mandatory (i.e. use 0 if you don't	314	"sysopen", except that it is mandatory (i.e. use 0 if you don't
247	create new files, and 0666 or 0777 if you do).	315	create new files, and 0666 or 0777 if you do). Note that the $mode
		316	will be modified by the umask in effect then the request is being
		317	executed, so better never change the umask.
248		318
249	Example:	319	Example:
250		320
251	aio_open "/etc/passwd", O_RDONLY, 0, sub {	321	aio_open "/etc/passwd", IO::AIO::O_RDONLY, 0, sub {
252	if ($_[0]) {	322	if ($_[0]) {
253	print "open successful, fh is $_[0]\n";	323	print "open successful, fh is $_[0]\n";
254	...	324	...
255	} else {	325	} else {
256	die "open failed: $!\n";	326	die "open failed: $!\n";
257	}	327	}
258	};	328	};
259		329
		330	In addition to all the common open modes/flags ("O_RDONLY",
		331	"O_WRONLY", "O_RDWR", "O_CREAT", "O_TRUNC", "O_EXCL" and
		332	"O_APPEND"), the following POSIX and non-POSIX constants are
		333	available (missing ones on your system are, as usual, 0):
		334
		335	"O_ASYNC", "O_DIRECT", "O_NOATIME", "O_CLOEXEC", "O_NOCTTY",
		336	"O_NOFOLLOW", "O_NONBLOCK", "O_EXEC", "O_SEARCH", "O_DIRECTORY",
		337	"O_DSYNC", "O_RSYNC", "O_SYNC", "O_PATH", "O_TMPFILE", and
		338	"O_TTY_INIT".
		339
260	aio_close $fh, $callback->($status)	340	aio_close $fh, $callback->($status)
261	Asynchronously close a file and call the callback with the result	341	Asynchronously close a file and call the callback with the result
262	code. *WARNING:* although accepted, you should not pass in a perl	342	code.
263	filehandle here, as perl will likely close the file descriptor
264	another time when the filehandle is destroyed. Normally, you can
265	safely call perls "close" or just let filehandles go out of scope.
266		343
267	This is supposed to be a bug in the API, so that might change. It's	344	Unfortunately, you can't do this to perl. Perl *insists* very
268	therefore best to avoid this function.	345	strongly on closing the file descriptor associated with the
		346	filehandle itself.
		347
		348	Therefore, "aio_close" will not close the filehandle - instead it
		349	will use dup2 to overwrite the file descriptor with the write-end of
		350	a pipe (the pipe fd will be created on demand and will be cached).
		351
		352	Or in other words: the file descriptor will be closed, but it will
		353	not be free for reuse until the perl filehandle is closed.
		354
		355	aio_seek $fh, $offset, $whence, $callback->($offs)
		356	Seeks the filehandle to the new $offset, similarly to perl's
		357	"sysseek". The $whence can use the traditional values (0 for
		358	"IO::AIO::SEEK_SET", 1 for "IO::AIO::SEEK_CUR" or 2 for
		359	"IO::AIO::SEEK_END").
		360
		361	The resulting absolute offset will be passed to the callback, or -1
		362	in case of an error.
		363
		364	In theory, the $whence constants could be different than the
		365	corresponding values from Fcntl, but perl guarantees they are the
		366	same, so don't panic.
		367
		368	As a GNU/Linux (and maybe Solaris) extension, also the constants
		369	"IO::AIO::SEEK_DATA" and "IO::AIO::SEEK_HOLE" are available, if they
		370	could be found. No guarantees about suitability for use in
		371	"aio_seek" or Perl's "sysseek" can be made though, although I would
		372	naively assume they "just work".
269		373
270	aio_read $fh,$offset,$length, $data,$dataoffset, $callback->($retval)	374	aio_read $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
271	aio_write $fh,$offset,$length, $data,$dataoffset, $callback->($retval)	375	aio_write $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
272	Reads or writes "length" bytes from the specified "fh" and "offset"	376	Reads or writes $length bytes from or to the specified $fh and
273	into the scalar given by "data" and offset "dataoffset" and calls	377	$offset into the scalar given by $data and offset $dataoffset and
274	the callback without the actual number of bytes read (or -1 on	378	calls the callback without the actual number of bytes read (or -1 on
275	error, just like the syscall).	379	error, just like the syscall).
276		380
		381	"aio_read" will, like "sysread", shrink or grow the $data scalar to
		382	offset plus the actual number of bytes read.
		383
		384	If $offset is undefined, then the current file descriptor offset
		385	will be used (and updated), otherwise the file descriptor offset
		386	will not be changed by these calls.
		387
		388	If $length is undefined in "aio_write", use the remaining length of
		389	$data.
		390
		391	If $dataoffset is less than zero, it will be counted from the end of
		392	$data.
		393
277	The $data scalar *MUST NOT* be modified in any way while the request	394	The $data scalar *MUST NOT* be modified in any way while the request
278	is outstanding. Modifying it can result in segfaults or WW3 (if the	395	is outstanding. Modifying it can result in segfaults or World War
279	necessary/optional hardware is installed).	396	III (if the necessary/optional hardware is installed).
280		397
281	Example: Read 15 bytes at offset 7 into scalar $buffer, starting at	398	Example: Read 15 bytes at offset 7 into scalar $buffer, starting at
282	offset 0 within the scalar:	399	offset 0 within the scalar:
283		400
284	aio_read $fh, 7, 15, $buffer, 0, sub {	401	aio_read $fh, 7, 15, $buffer, 0, sub {
…		…
289	aio_sendfile $out_fh, $in_fh, $in_offset, $length, $callback->($retval)	406	aio_sendfile $out_fh, $in_fh, $in_offset, $length, $callback->($retval)
290	Tries to copy $length bytes from $in_fh to $out_fh. It starts	407	Tries to copy $length bytes from $in_fh to $out_fh. It starts
291	reading at byte offset $in_offset, and starts writing at the current	408	reading at byte offset $in_offset, and starts writing at the current
292	file offset of $out_fh. Because of that, it is not safe to issue	409	file offset of $out_fh. Because of that, it is not safe to issue
293	more than one "aio_sendfile" per $out_fh, as they will interfere	410	more than one "aio_sendfile" per $out_fh, as they will interfere
294	with each other.	411	with each other. The same $in_fh works fine though, as this function
		412	does not move or use the file offset of $in_fh.
295		413
		414	Please note that "aio_sendfile" can read more bytes from $in_fh than
		415	are written, and there is no way to find out how many more bytes
		416	have been read from "aio_sendfile" alone, as "aio_sendfile" only
		417	provides the number of bytes written to $out_fh. Only if the result
		418	value equals $length one can assume that $length bytes have been
		419	read.
		420
		421	Unlike with other "aio_" functions, it makes a lot of sense to use
		422	"aio_sendfile" on non-blocking sockets, as long as one end
		423	(typically the $in_fh) is a file - the file I/O will then be
		424	asynchronous, while the socket I/O will be non-blocking. Note,
		425	however, that you can run into a trap where "aio_sendfile" reads
		426	some data with readahead, then fails to write all data, and when the
		427	socket is ready the next time, the data in the cache is already
		428	lost, forcing "aio_sendfile" to again hit the disk. Explicit
		429	"aio_read" + "aio_write" let's you better control resource usage.
		430
296	This call tries to make use of a native "sendfile" syscall to	431	This call tries to make use of a native "sendfile"-like syscall to
297	provide zero-copy operation. For this to work, $out_fh should refer	432	provide zero-copy operation. For this to work, $out_fh should refer
298	to a socket, and $in_fh should refer to mmap'able file.	433	to a socket, and $in_fh should refer to an mmap'able file.
299		434
300	If the native sendfile call fails or is not implemented, it will be	435	If a native sendfile cannot be found or it fails with "ENOSYS",
301	emulated, so you can call "aio_sendfile" on any type of filehandle	436	"EINVAL", "ENOTSUP", "EOPNOTSUPP", "EAFNOSUPPORT", "EPROTOTYPE" or
302	regardless of the limitations of the operating system.	437	"ENOTSOCK", it will be emulated, so you can call "aio_sendfile" on
		438	any type of filehandle regardless of the limitations of the
		439	operating system.
303		440
304	Please note, however, that "aio_sendfile" can read more bytes from	441	As native sendfile syscalls (as practically any non-POSIX interface
305	$in_fh than are written, and there is no way to find out how many	442	hacked together in a hurry to improve benchmark numbers) tend to be
306	bytes have been read from "aio_sendfile" alone, as "aio_sendfile"	443	rather buggy on many systems, this implementation tries to work
307	only provides the number of bytes written to $out_fh. Only if the	444	around some known bugs in Linux and FreeBSD kernels (probably
308	result value equals $length one can assume that $length bytes have	445	others, too), but that might fail, so you really really should check
309	been read.	446	the return value of "aio_sendfile" - fewre bytes than expected might
		447	have been transferred.
310		448
311	aio_readahead $fh,$offset,$length, $callback->($retval)	449	aio_readahead $fh,$offset,$length, $callback->($retval)
312	"aio_readahead" populates the page cache with data from a file so	450	"aio_readahead" populates the page cache with data from a file so
313	that subsequent reads from that file will not block on disk I/O. The	451	that subsequent reads from that file will not block on disk I/O. The
314	$offset argument specifies the starting point from which data is to	452	$offset argument specifies the starting point from which data is to
…		…
335	Currently, the stats are always 64-bit-stats, i.e. instead of	473	Currently, the stats are always 64-bit-stats, i.e. instead of
336	returning an error when stat'ing a large file, the results will be	474	returning an error when stat'ing a large file, the results will be
337	silently truncated unless perl itself is compiled with large file	475	silently truncated unless perl itself is compiled with large file
338	support.	476	support.
339		477
		478	To help interpret the mode and dev/rdev stat values, IO::AIO offers
		479	the following constants and functions (if not implemented, the
		480	constants will be 0 and the functions will either "croak" or fall
		481	back on traditional behaviour).
		482
		483	"S_IFMT", "S_IFIFO", "S_IFCHR", "S_IFBLK", "S_IFLNK", "S_IFREG",
		484	"S_IFDIR", "S_IFWHT", "S_IFSOCK", "IO::AIO::major $dev_t",
		485	"IO::AIO::minor $dev_t", "IO::AIO::makedev $major, $minor".
		486
340	Example: Print the length of /etc/passwd:	487	Example: Print the length of /etc/passwd:
341		488
342	aio_stat "/etc/passwd", sub {	489	aio_stat "/etc/passwd", sub {
343	$_[0] and die "stat failed: $!";	490	$_[0] and die "stat failed: $!";
344	print "size is ", -s _, "\n";	491	print "size is ", -s _, "\n";
345	};	492	};
346		493
		494	aio_statvfs $fh_or_path, $callback->($statvfs)
		495	Works like the POSIX "statvfs" or "fstatvfs" syscalls, depending on
		496	whether a file handle or path was passed.
		497
		498	On success, the callback is passed a hash reference with the
		499	following members: "bsize", "frsize", "blocks", "bfree", "bavail",
		500	"files", "ffree", "favail", "fsid", "flag" and "namemax". On
		501	failure, "undef" is passed.
		502
		503	The following POSIX IO::AIO::ST_* constants are defined: "ST_RDONLY"
		504	and "ST_NOSUID".
		505
		506	The following non-POSIX IO::AIO::ST_* flag masks are defined to
		507	their correct value when available, or to 0 on systems that do not
		508	support them: "ST_NODEV", "ST_NOEXEC", "ST_SYNCHRONOUS",
		509	"ST_MANDLOCK", "ST_WRITE", "ST_APPEND", "ST_IMMUTABLE",
		510	"ST_NOATIME", "ST_NODIRATIME" and "ST_RELATIME".
		511
		512	Example: stat "/wd" and dump out the data if successful.
		513
		514	aio_statvfs "/wd", sub {
		515	my $f = $_[0]
		516	or die "statvfs: $!";
		517
		518	use Data::Dumper;
		519	say Dumper $f;
		520	};
		521
		522	# result:
		523	{
		524	bsize => 1024,
		525	bfree => 4333064312,
		526	blocks => 10253828096,
		527	files => 2050765568,
		528	flag => 4096,
		529	favail => 2042092649,
		530	bavail => 4333064312,
		531	ffree => 2042092649,
		532	namemax => 255,
		533	frsize => 1024,
		534	fsid => 1810
		535	}
		536
		537	Here is a (likely partial - send me updates!) list of fsid values
		538	used by Linux - it is safe to hardcode these when $^O is "linux":
		539
		540	0x0000adf5 adfs
		541	0x0000adff affs
		542	0x5346414f afs
		543	0x09041934 anon-inode filesystem
		544	0x00000187 autofs
		545	0x42465331 befs
		546	0x1badface bfs
		547	0x42494e4d binfmt_misc
		548	0x9123683e btrfs
		549	0x0027e0eb cgroupfs
		550	0xff534d42 cifs
		551	0x73757245 coda
		552	0x012ff7b7 coh
		553	0x28cd3d45 cramfs
		554	0x453dcd28 cramfs-wend (wrong endianness)
		555	0x64626720 debugfs
		556	0x00001373 devfs
		557	0x00001cd1 devpts
		558	0x0000f15f ecryptfs
		559	0x00414a53 efs
		560	0x0000137d ext
		561	0x0000ef53 ext2/ext3/ext4
		562	0x0000ef51 ext2
		563	0xf2f52010 f2fs
		564	0x00004006 fat
		565	0x65735546 fuseblk
		566	0x65735543 fusectl
		567	0x0bad1dea futexfs
		568	0x01161970 gfs2
		569	0x47504653 gpfs
		570	0x00004244 hfs
		571	0xf995e849 hpfs
		572	0x00c0ffee hostfs
		573	0x958458f6 hugetlbfs
		574	0x2bad1dea inotifyfs
		575	0x00009660 isofs
		576	0x000072b6 jffs2
		577	0x3153464a jfs
		578	0x6b414653 k-afs
		579	0x0bd00bd0 lustre
		580	0x0000137f minix
		581	0x0000138f minix 30 char names
		582	0x00002468 minix v2
		583	0x00002478 minix v2 30 char names
		584	0x00004d5a minix v3
		585	0x19800202 mqueue
		586	0x00004d44 msdos
		587	0x0000564c novell
		588	0x00006969 nfs
		589	0x6e667364 nfsd
		590	0x00003434 nilfs
		591	0x5346544e ntfs
		592	0x00009fa1 openprom
		593	0x7461636F ocfs2
		594	0x00009fa0 proc
		595	0x6165676c pstorefs
		596	0x0000002f qnx4
		597	0x68191122 qnx6
		598	0x858458f6 ramfs
		599	0x52654973 reiserfs
		600	0x00007275 romfs
		601	0x67596969 rpc_pipefs
		602	0x73636673 securityfs
		603	0xf97cff8c selinux
		604	0x0000517b smb
		605	0x534f434b sockfs
		606	0x73717368 squashfs
		607	0x62656572 sysfs
		608	0x012ff7b6 sysv2
		609	0x012ff7b5 sysv4
		610	0x01021994 tmpfs
		611	0x15013346 udf
		612	0x00011954 ufs
		613	0x54190100 ufs byteswapped
		614	0x00009fa2 usbdevfs
		615	0x01021997 v9fs
		616	0xa501fcf5 vxfs
		617	0xabba1974 xenfs
		618	0x012ff7b4 xenix
		619	0x58465342 xfs
		620	0x012fd16d xia
		621
		622	aio_utime $fh_or_path, $atime, $mtime, $callback->($status)
		623	Works like perl's "utime" function (including the special case of
		624	$atime and $mtime being undef). Fractional times are supported if
		625	the underlying syscalls support them.
		626
		627	When called with a pathname, uses utimes(2) if available, otherwise
		628	utime(2). If called on a file descriptor, uses futimes(2) if
		629	available, otherwise returns ENOSYS, so this is not portable.
		630
		631	Examples:
		632
		633	# set atime and mtime to current time (basically touch(1)):
		634	aio_utime "path", undef, undef;
		635	# set atime to current time and mtime to beginning of the epoch:
		636	aio_utime "path", time, undef; # undef==0
		637
		638	aio_chown $fh_or_path, $uid, $gid, $callback->($status)
		639	Works like perl's "chown" function, except that "undef" for either
		640	$uid or $gid is being interpreted as "do not change" (but -1 can
		641	also be used).
		642
		643	Examples:
		644
		645	# same as "chown root path" in the shell:
		646	aio_chown "path", 0, -1;
		647	# same as above:
		648	aio_chown "path", 0, undef;
		649
		650	aio_truncate $fh_or_path, $offset, $callback->($status)
		651	Works like truncate(2) or ftruncate(2).
		652
		653	aio_allocate $fh, $mode, $offset, $len, $callback->($status)
		654	Allocates or frees disk space according to the $mode argument. See
		655	the linux "fallocate" documentation for details.
		656
		657	$mode is usually 0 or "IO::AIO::FALLOC_FL_KEEP_SIZE" to allocate
		658	space, or "IO::AIO::FALLOC_FL_PUNCH_HOLE |
		659	IO::AIO::FALLOC_FL_KEEP_SIZE", to deallocate a file range.
		660
		661	IO::AIO also supports "FALLOC_FL_COLLAPSE_RANGE", to remove a range
		662	(without leaving a hole) and "FALLOC_FL_ZERO_RANGE", to zero a range
		663	(see your fallocate(2) manpage).
		664
		665	The file system block size used by "fallocate" is presumably the
		666	"f_bsize" returned by "statvfs".
		667
		668	If "fallocate" isn't available or cannot be emulated (currently no
		669	emulation will be attempted), passes -1 and sets $! to "ENOSYS".
		670
		671	aio_chmod $fh_or_path, $mode, $callback->($status)
		672	Works like perl's "chmod" function.
		673
347	aio_unlink $pathname, $callback->($status)	674	aio_unlink $pathname, $callback->($status)
348	Asynchronously unlink (delete) a file and call the callback with the	675	Asynchronously unlink (delete) a file and call the callback with the
349	result code.	676	result code.
350		677
351	aio_mknod $path, $mode, $dev, $callback->($status)	678	aio_mknod $pathname, $mode, $dev, $callback->($status)
352	[EXPERIMENTAL]	679	[EXPERIMENTAL]
353		680
354	Asynchronously create a device node (or fifo). See mknod(2).	681	Asynchronously create a device node (or fifo). See mknod(2).
355		682
356	The only (POSIX-) portable way of calling this function is:	683	The only (POSIX-) portable way of calling this function is:
357		684
358	aio_mknod $path, IO::AIO::S_IFIFO | $mode, 0, sub { ...	685	aio_mknod $pathname, IO::AIO::S_IFIFO | $mode, 0, sub { ...
		686
		687	See "aio_stat" for info about some potentially helpful extra
		688	constants and functions.
359		689
360	aio_link $srcpath, $dstpath, $callback->($status)	690	aio_link $srcpath, $dstpath, $callback->($status)
361	Asynchronously create a new link to the existing object at $srcpath	691	Asynchronously create a new link to the existing object at $srcpath
362	at the path $dstpath and call the callback with the result code.	692	at the path $dstpath and call the callback with the result code.
363		693
364	aio_symlink $srcpath, $dstpath, $callback->($status)	694	aio_symlink $srcpath, $dstpath, $callback->($status)
365	Asynchronously create a new symbolic link to the existing object at	695	Asynchronously create a new symbolic link to the existing object at
366	$srcpath at the path $dstpath and call the callback with the result	696	$srcpath at the path $dstpath and call the callback with the result
367	code.	697	code.
368		698
369	aio_readlink $path, $callback->($link)	699	aio_readlink $pathname, $callback->($link)
370	Asynchronously read the symlink specified by $path and pass it to	700	Asynchronously read the symlink specified by $path and pass it to
371	the callback. If an error occurs, nothing or undef gets passed to	701	the callback. If an error occurs, nothing or undef gets passed to
372	the callback.	702	the callback.
373		703
		704	aio_realpath $pathname, $callback->($path)
		705	Asynchronously make the path absolute and resolve any symlinks in
		706	$path. The resulting path only consists of directories (same as
		707	Cwd::realpath).
		708
		709	This request can be used to get the absolute path of the current
		710	working directory by passing it a path of . (a single dot).
		711
374	aio_rename $srcpath, $dstpath, $callback->($status)	712	aio_rename $srcpath, $dstpath, $callback->($status)
375	Asynchronously rename the object at $srcpath to $dstpath, just as	713	Asynchronously rename the object at $srcpath to $dstpath, just as
376	rename(2) and call the callback with the result code.	714	rename(2) and call the callback with the result code.
377		715
		716	On systems that support the AIO::WD working directory abstraction
		717	natively, the case "[$wd, "."]" as $srcpath is specialcased -
		718	instead of failing, "rename" is called on the absolute path of $wd.
		719
		720	aio_mkdir $pathname, $mode, $callback->($status)
		721	Asynchronously mkdir (create) a directory and call the callback with
		722	the result code. $mode will be modified by the umask at the time the
		723	request is executed, so do not change your umask.
		724
378	aio_rmdir $pathname, $callback->($status)	725	aio_rmdir $pathname, $callback->($status)
379	Asynchronously rmdir (delete) a directory and call the callback with	726	Asynchronously rmdir (delete) a directory and call the callback with
380	the result code.	727	the result code.
		728
		729	On systems that support the AIO::WD working directory abstraction
		730	natively, the case "[$wd, "."]" is specialcased - instead of
		731	failing, "rmdir" is called on the absolute path of $wd.
381		732
382	aio_readdir $pathname, $callback->($entries)	733	aio_readdir $pathname, $callback->($entries)
383	Unlike the POSIX call of the same name, "aio_readdir" reads an	734	Unlike the POSIX call of the same name, "aio_readdir" reads an
384	entire directory (i.e. opendir + readdir + closedir). The entries	735	entire directory (i.e. opendir + readdir + closedir). The entries
385	will not be sorted, and will NOT include the "." and ".." entries.	736	will not be sorted, and will NOT include the "." and ".." entries.
386		737
387	The callback a single argument which is either "undef" or an	738	The callback is passed a single argument which is either "undef" or
388	array-ref with the filenames.	739	an array-ref with the filenames.
389		740
		741	aio_readdirx $pathname, $flags, $callback->($entries, $flags)
		742	Quite similar to "aio_readdir", but the $flags argument allows one
		743	to tune behaviour and output format. In case of an error, $entries
		744	will be "undef".
		745
		746	The flags are a combination of the following constants, ORed
		747	together (the flags will also be passed to the callback, possibly
		748	modified):
		749
		750	IO::AIO::READDIR_DENTS
		751	When this flag is off, then the callback gets an arrayref
		752	consisting of names only (as with "aio_readdir"), otherwise it
		753	gets an arrayref with "[$name, $type, $inode]" arrayrefs, each
		754	describing a single directory entry in more detail.
		755
		756	$name is the name of the entry.
		757
		758	$type is one of the "IO::AIO::DT_xxx" constants:
		759
		760	"IO::AIO::DT_UNKNOWN", "IO::AIO::DT_FIFO", "IO::AIO::DT_CHR",
		761	"IO::AIO::DT_DIR", "IO::AIO::DT_BLK", "IO::AIO::DT_REG",
		762	"IO::AIO::DT_LNK", "IO::AIO::DT_SOCK", "IO::AIO::DT_WHT".
		763
		764	"IO::AIO::DT_UNKNOWN" means just that: readdir does not know. If
		765	you need to know, you have to run stat yourself. Also, for speed
		766	reasons, the $type scalars are read-only: you can not modify
		767	them.
		768
		769	$inode is the inode number (which might not be exact on systems
		770	with 64 bit inode numbers and 32 bit perls). This field has
		771	unspecified content on systems that do not deliver the inode
		772	information.
		773
		774	IO::AIO::READDIR_DIRS_FIRST
		775	When this flag is set, then the names will be returned in an
		776	order where likely directories come first, in optimal stat
		777	order. This is useful when you need to quickly find directories,
		778	or you want to find all directories while avoiding to stat()
		779	each entry.
		780
		781	If the system returns type information in readdir, then this is
		782	used to find directories directly. Otherwise, likely directories
		783	are names beginning with ".", or otherwise names with no dots,
		784	of which names with short names are tried first.
		785
		786	IO::AIO::READDIR_STAT_ORDER
		787	When this flag is set, then the names will be returned in an
		788	order suitable for stat()'ing each one. That is, when you plan
		789	to stat() all files in the given directory, then the returned
		790	order will likely be fastest.
		791
		792	If both this flag and "IO::AIO::READDIR_DIRS_FIRST" are
		793	specified, then the likely dirs come first, resulting in a less
		794	optimal stat order.
		795
		796	IO::AIO::READDIR_FOUND_UNKNOWN
		797	This flag should not be set when calling "aio_readdirx".
		798	Instead, it is being set by "aio_readdirx", when any of the
		799	$type's found were "IO::AIO::DT_UNKNOWN". The absence of this
		800	flag therefore indicates that all $type's are known, which can
		801	be used to speed up some algorithms.
		802
390	aio_load $path, $data, $callback->($status)	803	aio_load $pathname, $data, $callback->($status)
391	This is a composite request that tries to fully load the given file	804	This is a composite request that tries to fully load the given file
392	into memory. Status is the same as with aio_read.	805	into memory. Status is the same as with aio_read.
393		806
394	aio_copy $srcpath, $dstpath, $callback->($status)	807	aio_copy $srcpath, $dstpath, $callback->($status)
395	Try to copy the *file* (directories not supported as either source	808	Try to copy the *file* (directories not supported as either source
396	or destination) from $srcpath to $dstpath and call the callback with	809	or destination) from $srcpath to $dstpath and call the callback with
397	the 0 (error) or -1 ok.	810	a status of 0 (ok) or -1 (error, see $!).
398		811
399	This is a composite request that it creates the destination file	812	This is a composite request that creates the destination file with
400	with mode 0200 and copies the contents of the source file into it	813	mode 0200 and copies the contents of the source file into it using
401	using "aio_sendfile", followed by restoring atime, mtime, access	814	"aio_sendfile", followed by restoring atime, mtime, access mode and
402	mode and uid/gid, in that order.	815	uid/gid, in that order.
403		816
404	If an error occurs, the partial destination file will be unlinked,	817	If an error occurs, the partial destination file will be unlinked,
405	if possible, except when setting atime, mtime, access mode and	818	if possible, except when setting atime, mtime, access mode and
406	uid/gid, where errors are being ignored.	819	uid/gid, where errors are being ignored.
407		820
408	aio_move $srcpath, $dstpath, $callback->($status)	821	aio_move $srcpath, $dstpath, $callback->($status)
409	Try to move the *file* (directories not supported as either source	822	Try to move the *file* (directories not supported as either source
410	or destination) from $srcpath to $dstpath and call the callback with	823	or destination) from $srcpath to $dstpath and call the callback with
411	the 0 (error) or -1 ok.	824	a status of 0 (ok) or -1 (error, see $!).
412		825
413	This is a composite request that tries to rename(2) the file first.	826	This is a composite request that tries to rename(2) the file first;
414	If rename files with "EXDEV", it copies the file with "aio_copy"	827	if rename fails with "EXDEV", it copies the file with "aio_copy"
415	and, if that is successful, unlinking the $srcpath.	828	and, if that is successful, unlinks the $srcpath.
416		829
417	aio_scandir $path, $maxreq, $callback->($dirs, $nondirs)	830	aio_scandir $pathname, $maxreq, $callback->($dirs, $nondirs)
418	Scans a directory (similar to "aio_readdir") but additionally tries	831	Scans a directory (similar to "aio_readdir") but additionally tries
419	to efficiently separate the entries of directory $path into two sets	832	to efficiently separate the entries of directory $path into two sets
420	of names, directories you can recurse into (directories), and ones	833	of names, directories you can recurse into (directories), and ones
421	you cannot recurse into (everything else, including symlinks to	834	you cannot recurse into (everything else, including symlinks to
422	directories).	835	directories).
…		…
440	Implementation notes.	853	Implementation notes.
441		854
442	The "aio_readdir" cannot be avoided, but "stat()"'ing every entry	855	The "aio_readdir" cannot be avoided, but "stat()"'ing every entry
443	can.	856	can.
444		857
		858	If readdir returns file type information, then this is used directly
		859	to find directories.
		860
445	After reading the directory, the modification time, size etc. of the	861	Otherwise, after reading the directory, the modification time, size
446	directory before and after the readdir is checked, and if they match	862	etc. of the directory before and after the readdir is checked, and
447	(and isn't the current time), the link count will be used to decide	863	if they match (and isn't the current time), the link count will be
448	how many entries are directories (if >= 2). Otherwise, no knowledge	864	used to decide how many entries are directories (if >= 2).
449	of the number of subdirectories will be assumed.	865	Otherwise, no knowledge of the number of subdirectories will be
		866	assumed.
450		867
451	Then entries will be sorted into likely directories (everything	868	Then entries will be sorted into likely directories a non-initial
452	without a non-initial dot currently) and likely non-directories	869	dot currently) and likely non-directories (see "aio_readdirx"). Then
453	(everything else). Then every entry plus an appended "/." will be	870	every entry plus an appended "/." will be "stat"'ed, likely
454	"stat"'ed, likely directories first. If that succeeds, it assumes	871	directories first, in order of their inode numbers. If that
455	that the entry is a directory or a symlink to directory (which will	872	succeeds, it assumes that the entry is a directory or a symlink to
456	be checked seperately). This is often faster than stat'ing the entry	873	directory (which will be checked separately). This is often faster
457	itself because filesystems might detect the type of the entry	874	than stat'ing the entry itself because filesystems might detect the
458	without reading the inode data (e.g. ext2fs filetype feature).	875	type of the entry without reading the inode data (e.g. ext2fs
		876	filetype feature), even on systems that cannot return the filetype
		877	information on readdir.
459		878
460	If the known number of directories (link count - 2) has been	879	If the known number of directories (link count - 2) has been
461	reached, the rest of the entries is assumed to be non-directories.	880	reached, the rest of the entries is assumed to be non-directories.
462		881
463	This only works with certainty on POSIX (= UNIX) filesystems, which	882	This only works with certainty on POSIX (= UNIX) filesystems, which
…		…
465		884
466	It will also likely work on non-POSIX filesystems with reduced	885	It will also likely work on non-POSIX filesystems with reduced
467	efficiency as those tend to return 0 or 1 as link counts, which	886	efficiency as those tend to return 0 or 1 as link counts, which
468	disables the directory counting heuristic.	887	disables the directory counting heuristic.
469		888
		889	aio_rmtree $pathname, $callback->($status)
		890	Delete a directory tree starting (and including) $path, return the
		891	status of the final "rmdir" only. This is a composite request that
		892	uses "aio_scandir" to recurse into and rmdir directories, and unlink
		893	everything else.
		894
		895	aio_fcntl $fh, $cmd, $arg, $callback->($status)
		896	aio_ioctl $fh, $request, $buf, $callback->($status)
		897	These work just like the "fcntl" and "ioctl" built-in functions,
		898	except they execute asynchronously and pass the return value to the
		899	callback.
		900
		901	Both calls can be used for a lot of things, some of which make more
		902	sense to run asynchronously in their own thread, while some others
		903	make less sense. For example, calls that block waiting for external
		904	events, such as locking, will also lock down an I/O thread while it
		905	is waiting, which can deadlock the whole I/O system. At the same
		906	time, there might be no alternative to using a thread to wait.
		907
		908	So in general, you should only use these calls for things that do
		909	(filesystem) I/O, not for things that wait for other events
		910	(network, other processes), although if you are careful and know
		911	what you are doing, you still can.
		912
		913	aio_sync $callback->($status)
		914	Asynchronously call sync and call the callback when finished.
		915
470	aio_fsync $fh, $callback->($status)	916	aio_fsync $fh, $callback->($status)
471	Asynchronously call fsync on the given filehandle and call the	917	Asynchronously call fsync on the given filehandle and call the
472	callback with the fsync result code.	918	callback with the fsync result code.
473		919
474	aio_fdatasync $fh, $callback->($status)	920	aio_fdatasync $fh, $callback->($status)
475	Asynchronously call fdatasync on the given filehandle and call the	921	Asynchronously call fdatasync on the given filehandle and call the
476	callback with the fdatasync result code.	922	callback with the fdatasync result code.
477		923
478	If this call isn't available because your OS lacks it or it couldn't	924	If this call isn't available because your OS lacks it or it couldn't
479	be detected, it will be emulated by calling "fsync" instead.	925	be detected, it will be emulated by calling "fsync" instead.
		926
		927	aio_syncfs $fh, $callback->($status)
		928	Asynchronously call the syncfs syscall to sync the filesystem
		929	associated to the given filehandle and call the callback with the
		930	syncfs result code. If syncfs is not available, calls sync(), but
		931	returns -1 and sets errno to "ENOSYS" nevertheless.
		932
		933	aio_sync_file_range $fh, $offset, $nbytes, $flags, $callback->($status)
		934	Sync the data portion of the file specified by $offset and $length
		935	to disk (but NOT the metadata), by calling the Linux-specific
		936	sync_file_range call. If sync_file_range is not available or it
		937	returns ENOSYS, then fdatasync or fsync is being substituted.
		938
		939	$flags can be a combination of
		940	"IO::AIO::SYNC_FILE_RANGE_WAIT_BEFORE",
		941	"IO::AIO::SYNC_FILE_RANGE_WRITE" and
		942	"IO::AIO::SYNC_FILE_RANGE_WAIT_AFTER": refer to the sync_file_range
		943	manpage for details.
		944
		945	aio_pathsync $pathname, $callback->($status)
		946	This request tries to open, fsync and close the given path. This is
		947	a composite request intended to sync directories after directory
		948	operations (E.g. rename). This might not work on all operating
		949	systems or have any specific effect, but usually it makes sure that
		950	directory changes get written to disc. It works for anything that
		951	can be opened for read-only, not just directories.
		952
		953	Future versions of this function might fall back to other methods
		954	when "fsync" on the directory fails (such as calling "sync").
		955
		956	Passes 0 when everything went ok, and -1 on error.
		957
		958	aio_msync $scalar, $offset = 0, $length = undef, flags = 0,
		959	$callback->($status)
		960	This is a rather advanced IO::AIO call, which only works on
		961	mmap(2)ed scalars (see the "IO::AIO::mmap" function, although it
		962	also works on data scalars managed by the Sys::Mmap or Mmap modules,
		963	note that the scalar must only be modified in-place while an aio
		964	operation is pending on it).
		965
		966	It calls the "msync" function of your OS, if available, with the
		967	memory area starting at $offset in the string and ending $length
		968	bytes later. If $length is negative, counts from the end, and if
		969	$length is "undef", then it goes till the end of the string. The
		970	flags can be a combination of "IO::AIO::MS_ASYNC",
		971	"IO::AIO::MS_INVALIDATE" and "IO::AIO::MS_SYNC".
		972
		973	aio_mtouch $scalar, $offset = 0, $length = undef, flags = 0,
		974	$callback->($status)
		975	This is a rather advanced IO::AIO call, which works best on
		976	mmap(2)ed scalars.
		977
		978	It touches (reads or writes) all memory pages in the specified range
		979	inside the scalar. All caveats and parameters are the same as for
		980	"aio_msync", above, except for flags, which must be either 0 (which
		981	reads all pages and ensures they are instantiated) or
		982	"IO::AIO::MT_MODIFY", which modifies the memory pages (by reading
		983	and writing an octet from it, which dirties the page).
		984
		985	aio_mlock $scalar, $offset = 0, $length = undef, $callback->($status)
		986	This is a rather advanced IO::AIO call, which works best on
		987	mmap(2)ed scalars.
		988
		989	It reads in all the pages of the underlying storage into memory (if
		990	any) and locks them, so they are not getting swapped/paged out or
		991	removed.
		992
		993	If $length is undefined, then the scalar will be locked till the
		994	end.
		995
		996	On systems that do not implement "mlock", this function returns -1
		997	and sets errno to "ENOSYS".
		998
		999	Note that the corresponding "munlock" is synchronous and is
		1000	documented under "MISCELLANEOUS FUNCTIONS".
		1001
		1002	Example: open a file, mmap and mlock it - both will be undone when
		1003	$data gets destroyed.
		1004
		1005	open my $fh, "<", $path or die "$path: $!";
		1006	my $data;
		1007	IO::AIO::mmap $data, -s $fh, IO::AIO::PROT_READ, IO::AIO::MAP_SHARED, $fh;
		1008	aio_mlock $data; # mlock in background
		1009
		1010	aio_mlockall $flags, $callback->($status)
		1011	Calls the "mlockall" function with the given $flags (a combination
		1012	of "IO::AIO::MCL_CURRENT" and "IO::AIO::MCL_FUTURE").
		1013
		1014	On systems that do not implement "mlockall", this function returns
		1015	-1 and sets errno to "ENOSYS".
		1016
		1017	Note that the corresponding "munlockall" is synchronous and is
		1018	documented under "MISCELLANEOUS FUNCTIONS".
		1019
		1020	Example: asynchronously lock all current and future pages into
		1021	memory.
		1022
		1023	aio_mlockall IO::AIO::MCL_FUTURE;
		1024
		1025	aio_fiemap $fh, $start, $length, $flags, $count, $cb->(\@extents)
		1026	Queries the extents of the given file (by calling the Linux "FIEMAP"
		1027	ioctl, see <http://cvs.schmorp.de/IO-AIO/doc/fiemap.txt> for
		1028	details). If the ioctl is not available on your OS, then this
		1029	request will fail with "ENOSYS".
		1030
		1031	$start is the starting offset to query extents for, $length is the
		1032	size of the range to query - if it is "undef", then the whole file
		1033	will be queried.
		1034
		1035	$flags is a combination of flags ("IO::AIO::FIEMAP_FLAG_SYNC" or
		1036	"IO::AIO::FIEMAP_FLAG_XATTR" - "IO::AIO::FIEMAP_FLAGS_COMPAT" is
		1037	also exported), and is normally 0 or "IO::AIO::FIEMAP_FLAG_SYNC" to
		1038	query the data portion.
		1039
		1040	$count is the maximum number of extent records to return. If it is
		1041	"undef", then IO::AIO queries all extents of the range. As a very
		1042	special case, if it is 0, then the callback receives the number of
		1043	extents instead of the extents themselves (which is unreliable, see
		1044	below).
		1045
		1046	If an error occurs, the callback receives no arguments. The special
		1047	"errno" value "IO::AIO::EBADR" is available to test for flag errors.
		1048
		1049	Otherwise, the callback receives an array reference with extent
		1050	structures. Each extent structure is an array reference itself, with
		1051	the following members:
		1052
		1053	[$logical, $physical, $length, $flags]
		1054
		1055	Flags is any combination of the following flag values (typically
		1056	either 0 or "IO::AIO::FIEMAP_EXTENT_LAST" (1)):
		1057
		1058	"IO::AIO::FIEMAP_EXTENT_LAST", "IO::AIO::FIEMAP_EXTENT_UNKNOWN",
		1059	"IO::AIO::FIEMAP_EXTENT_DELALLOC", "IO::AIO::FIEMAP_EXTENT_ENCODED",
		1060	"IO::AIO::FIEMAP_EXTENT_DATA_ENCRYPTED",
		1061	"IO::AIO::FIEMAP_EXTENT_NOT_ALIGNED",
		1062	"IO::AIO::FIEMAP_EXTENT_DATA_INLINE",
		1063	"IO::AIO::FIEMAP_EXTENT_DATA_TAIL",
		1064	"IO::AIO::FIEMAP_EXTENT_UNWRITTEN", "IO::AIO::FIEMAP_EXTENT_MERGED"
		1065	or "IO::AIO::FIEMAP_EXTENT_SHARED".
		1066
		1067	At the time of this writing (Linux 3.2), this requets is unreliable
		1068	unless $count is "undef", as the kernel has all sorts of bugs
		1069	preventing it to return all extents of a range for files with large
		1070	number of extents. The code works around all these issues if $count
		1071	is undef.
480		1072
481	aio_group $callback->(...)	1073	aio_group $callback->(...)
482	This is a very special aio request: Instead of doing something, it	1074	This is a very special aio request: Instead of doing something, it
483	is a container for other aio requests, which is useful if you want	1075	is a container for other aio requests, which is useful if you want
484	to bundle many requests into a single, composite, request with a	1076	to bundle many requests into a single, composite, request with a
…		…
519	requests like sleep and file handle readable/writable, the overhead	1111	requests like sleep and file handle readable/writable, the overhead
520	this creates is immense (it blocks a thread for a long time) so do	1112	this creates is immense (it blocks a thread for a long time) so do
521	not use this function except to put your application under	1113	not use this function except to put your application under
522	artificial I/O pressure.	1114	artificial I/O pressure.
523		1115
		1116	IO::AIO::WD - multiple working directories
		1117	Your process only has one current working directory, which is used by
		1118	all threads. This makes it hard to use relative paths (some other
		1119	component could call "chdir" at any time, and it is hard to control when
		1120	the path will be used by IO::AIO).
		1121
		1122	One solution for this is to always use absolute paths. This usually
		1123	works, but can be quite slow (the kernel has to walk the whole path on
		1124	every access), and can also be a hassle to implement.
		1125
		1126	Newer POSIX systems have a number of functions (openat, fdopendir,
		1127	futimensat and so on) that make it possible to specify working
		1128	directories per operation.
		1129
		1130	For portability, and because the clowns who "designed", or shall I
		1131	write, perpetrated this new interface were obviously half-drunk, this
		1132	abstraction cannot be perfect, though.
		1133
		1134	IO::AIO allows you to convert directory paths into a so-called
		1135	IO::AIO::WD object. This object stores the canonicalised, absolute
		1136	version of the path, and on systems that allow it, also a directory file
		1137	descriptor.
		1138
		1139	Everywhere where a pathname is accepted by IO::AIO (e.g. in "aio_stat"
		1140	or "aio_unlink"), one can specify an array reference with an IO::AIO::WD
		1141	object and a pathname instead (or the IO::AIO::WD object alone, which
		1142	gets interpreted as "[$wd, "."]"). If the pathname is absolute, the
		1143	IO::AIO::WD object is ignored, otherwise the pathname is resolved
		1144	relative to that IO::AIO::WD object.
		1145
		1146	For example, to get a wd object for /etc and then stat passwd inside,
		1147	you would write:
		1148
		1149	aio_wd "/etc", sub {
		1150	my $etcdir = shift;
		1151
		1152	# although $etcdir can be undef on error, there is generally no reason
		1153	# to check for errors here, as aio_stat will fail with ENOENT
		1154	# when $etcdir is undef.
		1155
		1156	aio_stat [$etcdir, "passwd"], sub {
		1157	# yay
		1158	};
		1159	};
		1160
		1161	The fact that "aio_wd" is a request and not a normal function shows that
		1162	creating an IO::AIO::WD object is itself a potentially blocking
		1163	operation, which is why it is done asynchronously.
		1164
		1165	To stat the directory obtained with "aio_wd" above, one could write
		1166	either of the following three request calls:
		1167
		1168	aio_lstat "/etc" , sub { ... # pathname as normal string
		1169	aio_lstat [$wd, "."], sub { ... # "." relative to $wd (i.e. $wd itself)
		1170	aio_lstat $wd , sub { ... # shorthand for the previous
		1171
		1172	As with normal pathnames, IO::AIO keeps a copy of the working directory
		1173	object and the pathname string, so you could write the following without
		1174	causing any issues due to $path getting reused:
		1175
		1176	my $path = [$wd, undef];
		1177
		1178	for my $name (qw(abc def ghi)) {
		1179	$path->[1] = $name;
		1180	aio_stat $path, sub {
		1181	# ...
		1182	};
		1183	}
		1184
		1185	There are some caveats: when directories get renamed (or deleted), the
		1186	pathname string doesn't change, so will point to the new directory (or
		1187	nowhere at all), while the directory fd, if available on the system,
		1188	will still point to the original directory. Most functions accepting a
		1189	pathname will use the directory fd on newer systems, and the string on
		1190	older systems. Some functions (such as realpath) will always rely on the
		1191	string form of the pathname.
		1192
		1193	So this functionality is mainly useful to get some protection against
		1194	"chdir", to easily get an absolute path out of a relative path for
		1195	future reference, and to speed up doing many operations in the same
		1196	directory (e.g. when stat'ing all files in a directory).
		1197
		1198	The following functions implement this working directory abstraction:
		1199
		1200	aio_wd $pathname, $callback->($wd)
		1201	Asynchonously canonicalise the given pathname and convert it to an
		1202	IO::AIO::WD object representing it. If possible and supported on the
		1203	system, also open a directory fd to speed up pathname resolution
		1204	relative to this working directory.
		1205
		1206	If something goes wrong, then "undef" is passwd to the callback
		1207	instead of a working directory object and $! is set appropriately.
		1208	Since passing "undef" as working directory component of a pathname
		1209	fails the request with "ENOENT", there is often no need for error
		1210	checking in the "aio_wd" callback, as future requests using the
		1211	value will fail in the expected way.
		1212
		1213	IO::AIO::CWD
		1214	This is a compiletime constant (object) that represents the process
		1215	current working directory.
		1216
		1217	Specifying this object as working directory object for a pathname is
		1218	as if the pathname would be specified directly, without a directory
		1219	object. For example, these calls are functionally identical:
		1220
		1221	aio_stat "somefile", sub { ... };
		1222	aio_stat [IO::AIO::CWD, "somefile"], sub { ... };
		1223
		1224	To recover the path associated with an IO::AIO::WD object, you can use
		1225	"aio_realpath":
		1226
		1227	aio_realpath $wd, sub {
		1228	warn "path is $_[0]\n";
		1229	};
		1230
		1231	Currently, "aio_statvfs" always, and "aio_rename" and "aio_rmdir"
		1232	sometimes, fall back to using an absolue path.
		1233
524	IO::AIO::REQ CLASS	1234	IO::AIO::REQ CLASS
525	All non-aggregate "aio_*" functions return an object of this class when	1235	All non-aggregate "aio_*" functions return an object of this class when
526	called in non-void context.	1236	called in non-void context.
527		1237
528	cancel $req	1238	cancel $req
529	Cancels the request, if possible. Has the effect of skipping	1239	Cancels the request, if possible. Has the effect of skipping
530	execution when entering the execute state and skipping calling the	1240	execution when entering the execute state and skipping calling the
531	callback when entering the the result state, but will leave the	1241	callback when entering the the result state, but will leave the
532	request otherwise untouched. That means that requests that currently	1242	request otherwise untouched (with the exception of readdir). That
533	execute will not be stopped and resources held by the request will	1243	means that requests that currently execute will not be stopped and
534	not be freed prematurely.	1244	resources held by the request will not be freed prematurely.
535		1245
536	cb $req $callback->(...)	1246	cb $req $callback->(...)
537	Replace (or simply set) the callback registered to the request.	1247	Replace (or simply set) the callback registered to the request.
538		1248
539	IO::AIO::GRP CLASS	1249	IO::AIO::GRP CLASS
…		…
566	};	1276	};
567		1277
568	This makes it very easy to create composite requests (see the source of	1278	This makes it very easy to create composite requests (see the source of
569	"aio_move" for an application) that work and feel like simple requests.	1279	"aio_move" for an application) that work and feel like simple requests.
570		1280
571	* The IO::AIO::GRP objects will be cleaned up during calls to	1281	* The IO::AIO::GRP objects will be cleaned up during calls to
572	"IO::AIO::poll_cb", just like any other request.	1282	"IO::AIO::poll_cb", just like any other request.
		1283
573	* They can be canceled like any other request. Canceling will cancel not	1284	* They can be canceled like any other request. Canceling will cancel
574	only the request itself, but also all requests it contains.	1285	not only the request itself, but also all requests it contains.
		1286
575	* They can also can also be added to other IO::AIO::GRP objects.	1287	* They can also can also be added to other IO::AIO::GRP objects.
		1288
576	* You must not add requests to a group from within the group callback	1289	* You must not add requests to a group from within the group callback
577	(or any later time).	1290	(or any later time).
578		1291
579	Their lifetime, simplified, looks like this: when they are empty, they	1292	Their lifetime, simplified, looks like this: when they are empty, they
580	will finish very quickly. If they contain only requests that are in the	1293	will finish very quickly. If they contain only requests that are in the
581	"done" state, they will also finish. Otherwise they will continue to	1294	"done" state, they will also finish. Otherwise they will continue to
582	exist.	1295	exist.
583		1296
584	That means after creating a group you have some time to add requests.	1297	That means after creating a group you have some time to add requests
585	And in the callbacks of those requests, you can add further requests to	1298	(precisely before the callback has been invoked, which is only done
586	the group. And only when all those requests have finished will the the	1299	within the "poll_cb"). And in the callbacks of those requests, you can
587	group itself finish.	1300	add further requests to the group. And only when all those requests have
		1301	finished will the the group itself finish.
588		1302
589	add $grp ...	1303	add $grp ...
590	$grp->add (...)	1304	$grp->add (...)
591	Add one or more requests to the group. Any type of IO::AIO::REQ can	1305	Add one or more requests to the group. Any type of IO::AIO::REQ can
592	be added, including other groups, as long as you do not create	1306	be added, including other groups, as long as you do not create
…		…
597	$grp->cancel_subs	1311	$grp->cancel_subs
598	Cancel all subrequests and clears any feeder, but not the group	1312	Cancel all subrequests and clears any feeder, but not the group
599	request itself. Useful when you queued a lot of events but got a	1313	request itself. Useful when you queued a lot of events but got a
600	result early.	1314	result early.
601		1315
		1316	The group request will finish normally (you cannot add requests to
		1317	the group).
		1318
602	$grp->result (...)	1319	$grp->result (...)
603	Set the result value(s) that will be passed to the group callback	1320	Set the result value(s) that will be passed to the group callback
604	when all subrequests have finished and set thre groups errno to the	1321	when all subrequests have finished and set the groups errno to the
605	current value of errno (just like calling "errno" without an error	1322	current value of errno (just like calling "errno" without an error
606	number). By default, no argument will be passed and errno is zero.	1323	number). By default, no argument will be passed and errno is zero.
607		1324
608	$grp->errno ([$errno])	1325	$grp->errno ([$errno])
609	Sets the group errno value to $errno, or the current value of errno	1326	Sets the group errno value to $errno, or the current value of errno
…		…
620	Sets a feeder/generator on this group: every group can have an	1337	Sets a feeder/generator on this group: every group can have an
621	attached generator that generates requests if idle. The idea behind	1338	attached generator that generates requests if idle. The idea behind
622	this is that, although you could just queue as many requests as you	1339	this is that, although you could just queue as many requests as you
623	want in a group, this might starve other requests for a potentially	1340	want in a group, this might starve other requests for a potentially
624	long time. For example, "aio_scandir" might generate hundreds of	1341	long time. For example, "aio_scandir" might generate hundreds of
625	thousands "aio_stat" requests, delaying any later requests for a	1342	thousands of "aio_stat" requests, delaying any later requests for a
626	long time.	1343	long time.
627		1344
628	To avoid this, and allow incremental generation of requests, you can	1345	To avoid this, and allow incremental generation of requests, you can
629	instead a group and set a feeder on it that generates those	1346	instead a group and set a feeder on it that generates those
630	requests. The feed callback will be called whenever there are few	1347	requests. The feed callback will be called whenever there are few
…		…
635	does not impose any limits).	1352	does not impose any limits).
636		1353
637	If the feed does not queue more requests when called, it will be	1354	If the feed does not queue more requests when called, it will be
638	automatically removed from the group.	1355	automatically removed from the group.
639		1356
640	If the feed limit is 0, it will be set to 2 automatically.	1357	If the feed limit is 0 when this method is called, it will be set to
		1358	2 automatically.
641		1359
642	Example:	1360	Example:
643		1361
644	# stat all files in @files, but only ever use four aio requests concurrently:	1362	# stat all files in @files, but only ever use four aio requests concurrently:
645		1363
…		…
656	Sets the feeder limit for the group: The feeder will be called	1374	Sets the feeder limit for the group: The feeder will be called
657	whenever the group contains less than this many requests.	1375	whenever the group contains less than this many requests.
658		1376
659	Setting the limit to 0 will pause the feeding process.	1377	Setting the limit to 0 will pause the feeding process.
660		1378
		1379	The default value for the limit is 0, but note that setting a feeder
		1380	automatically bumps it up to 2.
		1381
661	SUPPORT FUNCTIONS	1382	SUPPORT FUNCTIONS
662	EVENT PROCESSING AND EVENT LOOP INTEGRATION	1383	EVENT PROCESSING AND EVENT LOOP INTEGRATION
663	$fileno = IO::AIO::poll_fileno	1384	$fileno = IO::AIO::poll_fileno
664	Return the *request result pipe file descriptor*. This filehandle	1385	Return the *request result pipe file descriptor*. This filehandle
665	must be polled for reading by some mechanism outside this module	1386	must be polled for reading by some mechanism outside this module
666	(e.g. Event or select, see below or the SYNOPSIS). If the pipe	1387	(e.g. EV, Glib, select and so on, see below or the SYNOPSIS). If the
667	becomes readable you have to call "poll_cb" to check the results.	1388	pipe becomes readable you have to call "poll_cb" to check the
		1389	results.
668		1390
669	See "poll_cb" for an example.	1391	See "poll_cb" for an example.
670		1392
671	IO::AIO::poll_cb	1393	IO::AIO::poll_cb
672	Process some outstanding events on the result pipe. You have to call	1394	Process some requests that have reached the result phase (i.e. they
673	this regularly. Returns the number of events processed. Returns	1395	have been executed but the results are not yet reported). You have
		1396	to call this "regularly" to finish outstanding requests.
		1397
		1398	Returns 0 if all events could be processed (or there were no events
		1399	to process), or -1 if it returned earlier for whatever reason.
674	immediately when no events are outstanding. The amount of events	1400	Returns immediately when no events are outstanding. The amount of
675	processed depends on the settings of "IO::AIO::max_poll_req" and	1401	events processed depends on the settings of "IO::AIO::max_poll_req",
676	"IO::AIO::max_poll_time".	1402	"IO::AIO::max_poll_time" and "IO::AIO::max_outstanding".
677		1403
678	If not all requests were processed for whatever reason, the	1404	If not all requests were processed for whatever reason, the poll
679	filehandle will still be ready when "poll_cb" returns.	1405	file descriptor will still be ready when "poll_cb" returns, so
		1406	normally you don't have to do anything special to have it called
		1407	later.
		1408
		1409	Apart from calling "IO::AIO::poll_cb" when the event filehandle
		1410	becomes ready, it can be beneficial to call this function from loops
		1411	which submit a lot of requests, to make sure the results get
		1412	processed when they become available and not just when the loop is
		1413	finished and the event loop takes over again. This function returns
		1414	very fast when there are no outstanding requests.
680		1415
681	Example: Install an Event watcher that automatically calls	1416	Example: Install an Event watcher that automatically calls
682	IO::AIO::poll_cb with high priority:	1417	IO::AIO::poll_cb with high priority (more examples can be found in
		1418	the SYNOPSIS section, at the top of this document):
683		1419
684	Event->io (fd => IO::AIO::poll_fileno,	1420	Event->io (fd => IO::AIO::poll_fileno,
685	poll => 'r', async => 1,	1421	poll => 'r', async => 1,
686	cb => \&IO::AIO::poll_cb);	1422	cb => \&IO::AIO::poll_cb);
		1423
		1424	IO::AIO::poll_wait
		1425	Wait until either at least one request is in the result phase or no
		1426	requests are outstanding anymore.
		1427
		1428	This is useful if you want to synchronously wait for some requests
		1429	to become ready, without actually handling them.
		1430
		1431	See "nreqs" for an example.
		1432
		1433	IO::AIO::poll
		1434	Waits until some requests have been handled.
		1435
		1436	Returns the number of requests processed, but is otherwise strictly
		1437	equivalent to:
		1438
		1439	IO::AIO::poll_wait, IO::AIO::poll_cb
		1440
		1441	IO::AIO::flush
		1442	Wait till all outstanding AIO requests have been handled.
		1443
		1444	Strictly equivalent to:
		1445
		1446	IO::AIO::poll_wait, IO::AIO::poll_cb
		1447	while IO::AIO::nreqs;
687		1448
688	IO::AIO::max_poll_reqs $nreqs	1449	IO::AIO::max_poll_reqs $nreqs
689	IO::AIO::max_poll_time $seconds	1450	IO::AIO::max_poll_time $seconds
690	These set the maximum number of requests (default 0, meaning	1451	These set the maximum number of requests (default 0, meaning
691	infinity) that are being processed by "IO::AIO::poll_cb" in one	1452	infinity) that are being processed by "IO::AIO::poll_cb" in one
…		…
715	# use a low priority so other tasks have priority	1476	# use a low priority so other tasks have priority
716	Event->io (fd => IO::AIO::poll_fileno,	1477	Event->io (fd => IO::AIO::poll_fileno,
717	poll => 'r', nice => 1,	1478	poll => 'r', nice => 1,
718	cb => &IO::AIO::poll_cb);	1479	cb => &IO::AIO::poll_cb);
719		1480
720	IO::AIO::poll_wait
721	If there are any outstanding requests and none of them in the result
722	phase, wait till the result filehandle becomes ready for reading
723	(simply does a "select" on the filehandle. This is useful if you
724	want to synchronously wait for some requests to finish).
725
726	See "nreqs" for an example.
727
728	IO::AIO::poll
729	Waits until some requests have been handled.
730
731	Returns the number of requests processed, but is otherwise strictly
732	equivalent to:
733
734	IO::AIO::poll_wait, IO::AIO::poll_cb
735
736	IO::AIO::flush
737	Wait till all outstanding AIO requests have been handled.
738
739	Strictly equivalent to:
740
741	IO::AIO::poll_wait, IO::AIO::poll_cb
742	while IO::AIO::nreqs;
743
744	CONTROLLING THE NUMBER OF THREADS	1481	CONTROLLING THE NUMBER OF THREADS
745	IO::AIO::min_parallel $nthreads	1482	IO::AIO::min_parallel $nthreads
746	Set the minimum number of AIO threads to $nthreads. The current	1483	Set the minimum number of AIO threads to $nthreads. The current
747	default is 8, which means eight asynchronous operations can execute	1484	default is 8, which means eight asynchronous operations can execute
748	concurrently at any one time (the number of outstanding requests,	1485	concurrently at any one time (the number of outstanding requests,
…		…
777		1514
778	Under normal circumstances you don't need to call this function.	1515	Under normal circumstances you don't need to call this function.
779		1516
780	IO::AIO::max_idle $nthreads	1517	IO::AIO::max_idle $nthreads
781	Limit the number of threads (default: 4) that are allowed to idle	1518	Limit the number of threads (default: 4) that are allowed to idle
782	(i.e., threads that did not get a request to process within 10	1519	(i.e., threads that did not get a request to process within the idle
783	seconds). That means if a thread becomes idle while $nthreads other	1520	timeout (default: 10 seconds). That means if a thread becomes idle
784	threads are also idle, it will free its resources and exit.	1521	while $nthreads other threads are also idle, it will free its
		1522	resources and exit.
785		1523
786	This is useful when you allow a large number of threads (e.g. 100 or	1524	This is useful when you allow a large number of threads (e.g. 100 or
787	1000) to allow for extremely high load situations, but want to free	1525	1000) to allow for extremely high load situations, but want to free
788	resources under normal circumstances (1000 threads can easily	1526	resources under normal circumstances (1000 threads can easily
789	consume 30MB of RAM).	1527	consume 30MB of RAM).
790		1528
791	The default is probably ok in most situations, especially if thread	1529	The default is probably ok in most situations, especially if thread
792	creation is fast. If thread creation is very slow on your system you	1530	creation is fast. If thread creation is very slow on your system you
793	might want to use larger values.	1531	might want to use larger values.
794		1532
		1533	IO::AIO::idle_timeout $seconds
		1534	Sets the minimum idle timeout (default 10) after which worker
		1535	threads are allowed to exit. SEe "IO::AIO::max_idle".
		1536
795	$oldmaxreqs = IO::AIO::max_outstanding $maxreqs	1537	IO::AIO::max_outstanding $maxreqs
		1538	Sets the maximum number of outstanding requests to $nreqs. If you do
		1539	queue up more than this number of requests, the next call to
		1540	"IO::AIO::poll_cb" (and other functions calling "poll_cb", such as
		1541	"IO::AIO::flush" or "IO::AIO::poll") will block until the limit is
		1542	no longer exceeded.
		1543
		1544	In other words, this setting does not enforce a queue limit, but can
		1545	be used to make poll functions block if the limit is exceeded.
		1546
796	This is a very bad function to use in interactive programs because	1547	This is a very bad function to use in interactive programs because
797	it blocks, and a bad way to reduce concurrency because it is	1548	it blocks, and a bad way to reduce concurrency because it is
798	inexact: Better use an "aio_group" together with a feed callback.	1549	inexact: Better use an "aio_group" together with a feed callback.
799		1550
800	Sets the maximum number of outstanding requests to $nreqs. If you to	1551	Its main use is in scripts without an event loop - when you want to
801	queue up more than this number of requests, the next call to the	1552	stat a lot of files, you can write somehting like this:
802	"poll_cb" (and "poll_some" and other functions calling "poll_cb")
803	function will block until the limit is no longer exceeded.
804		1553
805	The default value is very large, so there is no practical limit on	1554	IO::AIO::max_outstanding 32;
		1555
		1556	for my $path (...) {
		1557	aio_stat $path , ...;
		1558	IO::AIO::poll_cb;
		1559	}
		1560
		1561	IO::AIO::flush;
		1562
		1563	The call to "poll_cb" inside the loop will normally return
		1564	instantly, but as soon as more thna 32 reqeusts are in-flight, it
		1565	will block until some requests have been handled. This keeps the
		1566	loop from pushing a large number of "aio_stat" requests onto the
		1567	queue.
		1568
		1569	The default value for "max_outstanding" is very large, so there is
806	the number of outstanding requests.	1570	no practical limit on the number of outstanding requests.
807
808	You can still queue as many requests as you want. Therefore,
809	"max_oustsanding" is mainly useful in simple scripts (with low
810	values) or as a stop gap to shield against fatal memory overflow
811	(with large values).
812		1571
813	STATISTICAL INFORMATION	1572	STATISTICAL INFORMATION
814	IO::AIO::nreqs	1573	IO::AIO::nreqs
815	Returns the number of requests currently in the ready, execute or	1574	Returns the number of requests currently in the ready, execute or
816	pending states (i.e. for which their callback has not been invoked	1575	pending states (i.e. for which their callback has not been invoked
…		…
827		1586
828	IO::AIO::npending	1587	IO::AIO::npending
829	Returns the number of requests currently in the pending state	1588	Returns the number of requests currently in the pending state
830	(executed, but not yet processed by poll_cb).	1589	(executed, but not yet processed by poll_cb).
831		1590
		1591	MISCELLANEOUS FUNCTIONS
		1592	IO::AIO implements some functions that are useful when you want to use
		1593	some "Advanced I/O" function not available to in Perl, without going the
		1594	"Asynchronous I/O" route. Many of these have an asynchronous "aio_*"
		1595	counterpart.
		1596
		1597	IO::AIO::sendfile $ofh, $ifh, $offset, $count
		1598	Calls the "eio_sendfile_sync" function, which is like
		1599	"aio_sendfile", but is blocking (this makes most sense if you know
		1600	the input data is likely cached already and the output filehandle is
		1601	set to non-blocking operations).
		1602
		1603	Returns the number of bytes copied, or -1 on error.
		1604
		1605	IO::AIO::fadvise $fh, $offset, $len, $advice
		1606	Simply calls the "posix_fadvise" function (see its manpage for
		1607	details). The following advice constants are available:
		1608	"IO::AIO::FADV_NORMAL", "IO::AIO::FADV_SEQUENTIAL",
		1609	"IO::AIO::FADV_RANDOM", "IO::AIO::FADV_NOREUSE",
		1610	"IO::AIO::FADV_WILLNEED", "IO::AIO::FADV_DONTNEED".
		1611
		1612	On systems that do not implement "posix_fadvise", this function
		1613	returns ENOSYS, otherwise the return value of "posix_fadvise".
		1614
		1615	IO::AIO::madvise $scalar, $offset, $len, $advice
		1616	Simply calls the "posix_madvise" function (see its manpage for
		1617	details). The following advice constants are available:
		1618	"IO::AIO::MADV_NORMAL", "IO::AIO::MADV_SEQUENTIAL",
		1619	"IO::AIO::MADV_RANDOM", "IO::AIO::MADV_WILLNEED",
		1620	"IO::AIO::MADV_DONTNEED".
		1621
		1622	On systems that do not implement "posix_madvise", this function
		1623	returns ENOSYS, otherwise the return value of "posix_madvise".
		1624
		1625	IO::AIO::mprotect $scalar, $offset, $len, $protect
		1626	Simply calls the "mprotect" function on the preferably AIO::mmap'ed
		1627	$scalar (see its manpage for details). The following protect
		1628	constants are available: "IO::AIO::PROT_NONE", "IO::AIO::PROT_READ",
		1629	"IO::AIO::PROT_WRITE", "IO::AIO::PROT_EXEC".
		1630
		1631	On systems that do not implement "mprotect", this function returns
		1632	ENOSYS, otherwise the return value of "mprotect".
		1633
		1634	IO::AIO::mmap $scalar, $length, $prot, $flags, $fh[, $offset]
		1635	Memory-maps a file (or anonymous memory range) and attaches it to
		1636	the given $scalar, which will act like a string scalar. Returns true
		1637	on success, and false otherwise.
		1638
		1639	The only operations allowed on the scalar are "substr"/"vec" that
		1640	don't change the string length, and most read-only operations such
		1641	as copying it or searching it with regexes and so on.
		1642
		1643	Anything else is unsafe and will, at best, result in memory leaks.
		1644
		1645	The memory map associated with the $scalar is automatically removed
		1646	when the $scalar is destroyed, or when the "IO::AIO::mmap" or
		1647	"IO::AIO::munmap" functions are called.
		1648
		1649	This calls the "mmap"(2) function internally. See your system's
		1650	manual page for details on the $length, $prot and $flags parameters.
		1651
		1652	The $length must be larger than zero and smaller than the actual
		1653	filesize.
		1654
		1655	$prot is a combination of "IO::AIO::PROT_NONE",
		1656	"IO::AIO::PROT_EXEC", "IO::AIO::PROT_READ" and/or
		1657	"IO::AIO::PROT_WRITE",
		1658
		1659	$flags can be a combination of "IO::AIO::MAP_SHARED" or
		1660	"IO::AIO::MAP_PRIVATE", or a number of system-specific flags (when
		1661	not available, the are 0): "IO::AIO::MAP_ANONYMOUS" (which is set to
		1662	"MAP_ANON" if your system only provides this constant),
		1663	"IO::AIO::MAP_LOCKED", "IO::AIO::MAP_NORESERVE",
		1664	"IO::AIO::MAP_POPULATE", "IO::AIO::MAP_NONBLOCK",
		1665	"IO::AIO::MAP_FIXED", "IO::AIO::MAP_GROWSDOWN",
		1666	"IO::AIO::MAP_32BIT", "IO::AIO::MAP_HUGETLB" or
		1667	"IO::AIO::MAP_STACK".
		1668
		1669	If $fh is "undef", then a file descriptor of -1 is passed.
		1670
		1671	$offset is the offset from the start of the file - it generally must
		1672	be a multiple of "IO::AIO::PAGESIZE" and defaults to 0.
		1673
		1674	Example:
		1675
		1676	use Digest::MD5;
		1677	use IO::AIO;
		1678
		1679	open my $fh, "<verybigfile"
		1680	or die "$!";
		1681
		1682	IO::AIO::mmap my $data, -s $fh, IO::AIO::PROT_READ, IO::AIO::MAP_SHARED, $fh
		1683	or die "verybigfile: $!";
		1684
		1685	my $fast_md5 = md5 $data;
		1686
		1687	IO::AIO::munmap $scalar
		1688	Removes a previous mmap and undefines the $scalar.
		1689
		1690	IO::AIO::munlock $scalar, $offset = 0, $length = undef
		1691	Calls the "munlock" function, undoing the effects of a previous
		1692	"aio_mlock" call (see its description for details).
		1693
		1694	IO::AIO::munlockall
		1695	Calls the "munlockall" function.
		1696
		1697	On systems that do not implement "munlockall", this function returns
		1698	ENOSYS, otherwise the return value of "munlockall".
		1699
		1700	IO::AIO::splice $r_fh, $r_off, $w_fh, $w_off, $length, $flags
		1701	Calls the GNU/Linux splice(2) syscall, if available. If $r_off or
		1702	$w_off are "undef", then "NULL" is passed for these, otherwise they
		1703	should be the file offset.
		1704
		1705	$r_fh and $w_fh should not refer to the same file, as splice might
		1706	silently corrupt the data in this case.
		1707
		1708	The following symbol flag values are available:
		1709	"IO::AIO::SPLICE_F_MOVE", "IO::AIO::SPLICE_F_NONBLOCK",
		1710	"IO::AIO::SPLICE_F_MORE" and "IO::AIO::SPLICE_F_GIFT".
		1711
		1712	See the splice(2) manpage for details.
		1713
		1714	IO::AIO::tee $r_fh, $w_fh, $length, $flags
		1715	Calls the GNU/Linux tee(2) syscall, see its manpage and the
		1716	description for "IO::AIO::splice" above for details.
		1717
		1718	$actual_size = IO::AIO::pipesize $r_fh[, $new_size]
		1719	Attempts to query or change the pipe buffer size. Obviously works
		1720	only on pipes, and currently works only on GNU/Linux systems, and
		1721	fails with -1/"ENOSYS" everywhere else. If anybody knows how to
		1722	influence pipe buffer size on other systems, drop me a note.
		1723
		1724	($rfh, $wfh) = IO::AIO::pipe2 [$flags]
		1725	This is a direct interface to the Linux pipe2(2) system call. If
		1726	$flags is missing or 0, then this should be the same as a call to
		1727	perl's built-in "pipe" function and create a new pipe, and works on
		1728	systems that lack the pipe2 syscall. On win32, this case invokes
		1729	"_pipe (..., 4096, O_BINARY)".
		1730
		1731	If $flags is non-zero, it tries to invoke the pipe2 system call with
		1732	the given flags (Linux 2.6.27, glibc 2.9).
		1733
		1734	On success, the read and write file handles are returned.
		1735
		1736	On error, nothing will be returned. If the pipe2 syscall is missing
		1737	and $flags is non-zero, fails with "ENOSYS".
		1738
		1739	Please refer to pipe2(2) for more info on the $flags, but at the
		1740	time of this writing, "IO::AIO::O_CLOEXEC", "IO::AIO::O_NONBLOCK"
		1741	and "IO::AIO::O_DIRECT" (Linux 3.4, for packet-based pipes) were
		1742	supported.
		1743
		1744	EVENT LOOP INTEGRATION
		1745	It is recommended to use AnyEvent::AIO to integrate IO::AIO
		1746	automatically into many event loops:
		1747
		1748	# AnyEvent integration (EV, Event, Glib, Tk, POE, urxvt, pureperl...)
		1749	use AnyEvent::AIO;
		1750
		1751	You can also integrate IO::AIO manually into many event loops, here are
		1752	some examples of how to do this:
		1753
		1754	# EV integration
		1755	my $aio_w = EV::io IO::AIO::poll_fileno, EV::READ, \&IO::AIO::poll_cb;
		1756
		1757	# Event integration
		1758	Event->io (fd => IO::AIO::poll_fileno,
		1759	poll => 'r',
		1760	cb => \&IO::AIO::poll_cb);
		1761
		1762	# Glib/Gtk2 integration
		1763	add_watch Glib::IO IO::AIO::poll_fileno,
		1764	in => sub { IO::AIO::poll_cb; 1 };
		1765
		1766	# Tk integration
		1767	Tk::Event::IO->fileevent (IO::AIO::poll_fileno, "",
		1768	readable => \&IO::AIO::poll_cb);
		1769
		1770	# Danga::Socket integration
		1771	Danga::Socket->AddOtherFds (IO::AIO::poll_fileno =>
		1772	\&IO::AIO::poll_cb);
		1773
832	FORK BEHAVIOUR	1774	FORK BEHAVIOUR
833	This module should do "the right thing" when the process using it forks:	1775	Usage of pthreads in a program changes the semantics of fork
		1776	considerably. Specifically, only async-safe functions can be called
		1777	after fork. Perl doesn't know about this, so in general, you cannot call
		1778	fork with defined behaviour in perl if pthreads are involved. IO::AIO
		1779	uses pthreads, so this applies, but many other extensions and (for
		1780	inexplicable reasons) perl itself often is linked against pthreads, so
		1781	this limitation applies to quite a lot of perls.
834		1782
835	Before the fork, IO::AIO enters a quiescent state where no requests can	1783	This module no longer tries to fight your OS, or POSIX. That means
836	be added in other threads and no results will be processed. After the	1784	IO::AIO only works in the process that loaded it. Forking is fully
837	fork the parent simply leaves the quiescent state and continues	1785	supported, but using IO::AIO in the child is not.
838	request/result processing, while the child frees the request/result
839	queue (so that the requests started before the fork will only be handled
840	in the parent). Threads will be started on demand until the limit set in
841	the parent process has been reached again.
842		1786
843	In short: the parent will, after a short pause, continue as if fork had	1787	You might get around by not *using* IO::AIO before (or after) forking.
844	not been called, while the child will act as if IO::AIO has not been	1788	You could also try to call the IO::AIO::reinit function in the child:
845	used yet.	1789
		1790	IO::AIO::reinit
		1791	Abandons all current requests and I/O threads and simply
		1792	reinitialises all data structures. This is not an operation
		1793	supported by any standards, but happens to work on GNU/Linux and
		1794	some newer BSD systems.
		1795
		1796	The only reasonable use for this function is to call it after
		1797	forking, if "IO::AIO" was used in the parent. Calling it while
		1798	IO::AIO is active in the process will result in undefined behaviour.
		1799	Calling it at any time will also result in any undefined (by POSIX)
		1800	behaviour.
846		1801
847	MEMORY USAGE	1802	MEMORY USAGE
848	Per-request usage:	1803	Per-request usage:
849		1804
850	Each aio request uses - depending on your architecture - around 100-200	1805	Each aio request uses - depending on your architecture - around 100-200
851	bytes of memory. In addition, stat requests need a stat buffer (possibly	1806	bytes of memory. In addition, stat requests need a stat buffer (possibly
852	a few hundred bytes), readdir requires a result buffer and so on. Perl	1807	a few hundred bytes), readdir requires a result buffer and so on. Perl
853	scalars and other data passed into aio requests will also be locked and	1808	scalars and other data passed into aio requests will also be locked and
854	will consume memory till the request has entered the done state.	1809	will consume memory till the request has entered the done state.
855		1810
856	This is now awfully much, so queuing lots of requests is not usually a	1811	This is not awfully much, so queuing lots of requests is not usually a
857	problem.	1812	problem.
858		1813
859	Per-thread usage:	1814	Per-thread usage:
860		1815
861	In the execution phase, some aio requests require more memory for	1816	In the execution phase, some aio requests require more memory for
…		…
864		1819
865	KNOWN BUGS	1820	KNOWN BUGS
866	Known bugs will be fixed in the next release.	1821	Known bugs will be fixed in the next release.
867		1822
868	SEE ALSO	1823	SEE ALSO
869	Coro::AIO.	1824	AnyEvent::AIO for easy integration into event loops, Coro::AIO for a
		1825	more natural syntax.
870		1826
871	AUTHOR	1827	AUTHOR
872	Marc Lehmann <schmorp@schmorp.de>	1828	Marc Lehmann <schmorp@schmorp.de>
873	http://home.schmorp.de/	1829	http://home.schmorp.de/
874		1830

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