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Revision 1.19 by root, Sun Oct 29 01:03:13 2006 UTC vs.
Revision 1.43 by root, Sun Jan 10 23:44:02 2010 UTC

…		…
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", O_RDONLY, 0, sub {
8	my ($fh) = @_;	8	my $fh = shift
		9	or die "/etc/passwd: $!";
9	...	10	...
10	};	11	};
11		12
12	aio_unlink "/tmp/file", sub { };	13	aio_unlink "/tmp/file", sub { };
13		14
…		…
23	$req->cancel; # cancel request if still in queue	24	$req->cancel; # cancel request if still in queue
24		25
25	my $grp = aio_group sub { print "all stats done\n" };	26	my $grp = aio_group sub { print "all stats done\n" };
26	add $grp aio_stat "..." for ...;	27	add $grp aio_stat "..." for ...;
27		28
28	# AnyEvent integration
29	open my $fh, "<&=" . IO::AIO::poll_fileno or die "$!";
30	my $w = AnyEvent->io (fh => $fh, poll => 'r', cb => sub { IO::AIO::poll_cb });
31
32	# Event integration
33	Event->io (fd => IO::AIO::poll_fileno,
34	poll => 'r',
35	cb => \&IO::AIO::poll_cb);
36
37	# Glib/Gtk2 integration
38	add_watch Glib::IO IO::AIO::poll_fileno,
39	in => sub { IO::AIO::poll_cb; 1 };
40
41	# Tk integration
42	Tk::Event::IO->fileevent (IO::AIO::poll_fileno, "",
43	readable => \&IO::AIO::poll_cb);
44
45	# Danga::Socket integration
46	Danga::Socket->AddOtherFds (IO::AIO::poll_fileno =>
47	\&IO::AIO::poll_cb);
48
49	DESCRIPTION	29	DESCRIPTION
50	This module implements asynchronous I/O using whatever means your	30	This module implements asynchronous I/O using whatever means your
51	operating system supports.	31	operating system supports. It is implemented as an interface to "libeio"
		32	(<http://software.schmorp.de/pkg/libeio.html>).
52		33
53	Asynchronous means that operations that can normally block your program	34	Asynchronous means that operations that can normally block your program
54	(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
55	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
56	extremely useful for programs that need to stay interactive even when	37	extremely useful for programs that need to stay interactive even when
…		…
58	but can also be used to easily do operations in parallel that are	39	but can also be used to easily do operations in parallel that are
59	normally done sequentially, e.g. stat'ing many files, which is much	40	normally done sequentially, e.g. stat'ing many files, which is much
60	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
61	operations concurrently.	42	operations concurrently.
62		43
63	While this works on all types of file descriptors (for example sockets),	44	While most of this works on all types of file descriptors (for example
64	using these functions on file descriptors that support nonblocking	45	sockets), using these functions on file descriptors that support
65	operation (again, sockets, pipes etc.) is very inefficient. Use an event	46	nonblocking operation (again, sockets, pipes etc.) is very inefficient.
66	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
67	into such an event loop itself.	48	naturally fit into such an event loop itself.
68		49
69	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
70	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
71	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
72	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
…		…
74	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
75	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
76	aio_write, so the remaining functionality would have to be implemented	57	aio_write, so the remaining functionality would have to be implemented
77	using threads anyway.	58	using threads anyway.
78		59
79	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,
80	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
81	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
82	never call "poll_cb" (or other "aio_" functions) recursively.	63	call "poll_cb" (or other "aio_" functions) recursively.
83		64
84	EXAMPLE	65	EXAMPLE
85	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
86	/etc/passwd asynchronously:	67	asynchronously:
87		68
88	use Fcntl;	69	use Fcntl;
89	use Event;	70	use EV;
90	use IO::AIO;	71	use IO::AIO;
91		72
92	# register the IO::AIO callback with Event	73	# register the IO::AIO callback with EV
93	Event->io (fd => IO::AIO::poll_fileno,	74	my $aio_w = EV::io IO::AIO::poll_fileno, EV::READ, \&IO::AIO::poll_cb;
94	poll => 'r',
95	cb => \&IO::AIO::poll_cb);
96		75
97	# queue the request to open /etc/passwd	76	# queue the request to open /etc/passwd
98	aio_open "/etc/passwd", O_RDONLY, 0, sub {	77	aio_open "/etc/passwd", O_RDONLY, 0, sub {
99	my $fh = $_[0]	78	my $fh = shift
100	or die "error while opening: $!";	79	or die "error while opening: $!";
101		80
102	# stat'ing filehandles is generally non-blocking	81	# stat'ing filehandles is generally non-blocking
103	my $size = -s $fh;	82	my $size = -s $fh;
104		83
…		…
112		91
113	# file contents now in $contents	92	# file contents now in $contents
114	print $contents;	93	print $contents;
115		94
116	# exit event loop and program	95	# exit event loop and program
117	Event::unloop;	96	EV::unloop;
118	};	97	};
119	};	98	};
120		99
121	# possibly queue up other requests, or open GUI windows,	100	# possibly queue up other requests, or open GUI windows,
122	# check for sockets etc. etc.	101	# check for sockets etc. etc.
123		102
124	# process events as long as there are some:	103	# process events as long as there are some:
125	Event::loop;	104	EV::loop;
126		105
127	REQUEST ANATOMY AND LIFETIME	106	REQUEST ANATOMY AND LIFETIME
128	Every "aio_*" function creates a request. which is a C data structure	107	Every "aio_*" function creates a request. which is a C data structure
129	not directly visible to Perl.	108	not directly visible to Perl.
130		109
…		…
166	anymore (except possibly for the Perl object, but its connection to	145	anymore (except possibly for the Perl object, but its connection to
167	the actual aio request is severed and calling its methods will	146	the actual aio request is severed and calling its methods will
168	either do nothing or result in a runtime error).	147	either do nothing or result in a runtime error).
169		148
170	FUNCTIONS	149	FUNCTIONS
		150	QUICK OVERVIEW
		151	This section simply lists the prototypes of the most important functions
		152	for quick reference. See the following sections for function-by-function
		153	documentation.
		154
		155	aio_open $pathname, $flags, $mode, $callback->($fh)
		156	aio_close $fh, $callback->($status)
		157	aio_read $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
		158	aio_write $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
		159	aio_sendfile $out_fh, $in_fh, $in_offset, $length, $callback->($retval)
		160	aio_readahead $fh,$offset,$length, $callback->($retval)
		161	aio_stat $fh_or_path, $callback->($status)
		162	aio_lstat $fh, $callback->($status)
		163	aio_statvfs $fh_or_path, $callback->($statvfs)
		164	aio_utime $fh_or_path, $atime, $mtime, $callback->($status)
		165	aio_chown $fh_or_path, $uid, $gid, $callback->($status)
		166	aio_truncate $fh_or_path, $offset, $callback->($status)
		167	aio_chmod $fh_or_path, $mode, $callback->($status)
		168	aio_unlink $pathname, $callback->($status)
		169	aio_mknod $path, $mode, $dev, $callback->($status)
		170	aio_link $srcpath, $dstpath, $callback->($status)
		171	aio_symlink $srcpath, $dstpath, $callback->($status)
		172	aio_readlink $path, $callback->($link)
		173	aio_rename $srcpath, $dstpath, $callback->($status)
		174	aio_mkdir $pathname, $mode, $callback->($status)
		175	aio_rmdir $pathname, $callback->($status)
		176	aio_readdir $pathname, $callback->($entries)
		177	aio_readdirx $pathname, $flags, $callback->($entries, $flags)
		178	IO::AIO::READDIR_DENTS IO::AIO::READDIR_DIRS_FIRST
		179	IO::AIO::READDIR_STAT_ORDER IO::AIO::READDIR_FOUND_UNKNOWN
		180	aio_load $path, $data, $callback->($status)
		181	aio_copy $srcpath, $dstpath, $callback->($status)
		182	aio_move $srcpath, $dstpath, $callback->($status)
		183	aio_scandir $path, $maxreq, $callback->($dirs, $nondirs)
		184	aio_rmtree $path, $callback->($status)
		185	aio_sync $callback->($status)
		186	aio_fsync $fh, $callback->($status)
		187	aio_fdatasync $fh, $callback->($status)
		188	aio_sync_file_range $fh, $offset, $nbytes, $flags, $callback->($status)
		189	aio_pathsync $path, $callback->($status)
		190	aio_msync $scalar, $offset = 0, $length = undef, flags = 0, $callback->($status)
		191	aio_mtouch $scalar, $offset = 0, $length = undef, flags = 0, $callback->($status)
		192	aio_group $callback->(...)
		193	aio_nop $callback->()
		194
		195	$prev_pri = aioreq_pri [$pri]
		196	aioreq_nice $pri_adjust
		197
		198	IO::AIO::poll_wait
		199	IO::AIO::poll_cb
		200	IO::AIO::poll
		201	IO::AIO::flush
		202	IO::AIO::max_poll_reqs $nreqs
		203	IO::AIO::max_poll_time $seconds
		204	IO::AIO::min_parallel $nthreads
		205	IO::AIO::max_parallel $nthreads
		206	IO::AIO::max_idle $nthreads
		207	IO::AIO::max_outstanding $maxreqs
		208	IO::AIO::nreqs
		209	IO::AIO::nready
		210	IO::AIO::npending
		211
		212	IO::AIO::sendfile $ofh, $ifh, $offset, $count
		213	IO::AIO::fadvise $fh, $offset, $len, $advice
		214	IO::AIO::mlockall $flags
		215	IO::AIO::munlockall
		216
171	AIO REQUEST FUNCTIONS	217	AIO REQUEST FUNCTIONS
172	All the "aio_*" calls are more or less thin wrappers around the	218	All the "aio_*" calls are more or less thin wrappers around the syscall
173	syscall with the same name (sans "aio_"). The arguments are similar	219	with the same name (sans "aio_"). The arguments are similar or
174	or identical, and they all accept an additional (and optional)	220	identical, and they all accept an additional (and optional) $callback
175	$callback argument which must be a code reference. This code	221	argument which must be a code reference. This code reference will get
176	reference will get called with the syscall return code (e.g. most	222	called with the syscall return code (e.g. most syscalls return -1 on
177	syscalls return -1 on error, unlike perl, which usually delivers	223	error, unlike perl, which usually delivers "false") as its sole argument
178	"false") as it's sole argument when the given syscall has been	224	after the given syscall has been executed asynchronously.
179	executed asynchronously.
180		225
181	All functions expecting a filehandle keep a copy of the filehandle	226	All functions expecting a filehandle keep a copy of the filehandle
182	internally until the request has finished.	227	internally until the request has finished.
183		228
184	All functions return request objects of type IO::AIO::REQ that allow	229	All functions return request objects of type IO::AIO::REQ that allow
185	further manipulation of those requests while they are in-flight.	230	further manipulation of those requests while they are in-flight.
186		231
187	The pathnames you pass to these routines *must* be absolute and	232	The pathnames you pass to these routines *must* be absolute and encoded
188	encoded as octets. The reason for the former is that at the time the	233	as octets. The reason for the former is that at the time the request is
189	request is being executed, the current working directory could have	234	being executed, the current working directory could have changed.
190	changed. Alternatively, you can make sure that you never change the	235	Alternatively, you can make sure that you never change the current
191	current working directory anywhere in the program and then use	236	working directory anywhere in the program and then use relative paths.
192	relative paths.
193		237
194	To encode pathnames as octets, either make sure you either: a)	238	To encode pathnames as octets, either make sure you either: a) always
195	always pass in filenames you got from outside (command line, readdir	239	pass in filenames you got from outside (command line, readdir etc.)
196	etc.) without tinkering, b) are ASCII or ISO 8859-1, c) use the	240	without tinkering, b) are ASCII or ISO 8859-1, c) use the Encode module
197	Encode module and encode your pathnames to the locale (or other)	241	and encode your pathnames to the locale (or other) encoding in effect in
198	encoding in effect in the user environment, d) use	242	the user environment, d) use Glib::filename_from_unicode on unicode
199	Glib::filename_from_unicode on unicode filenames or e) use something	243	filenames or e) use something else to ensure your scalar has the correct
200	else to ensure your scalar has the correct contents.	244	contents.
201		245
202	This works, btw. independent of the internal UTF-8 bit, which	246	This works, btw. independent of the internal UTF-8 bit, which IO::AIO
203	IO::AIO handles correctly wether it is set or not.	247	handles correctly whether it is set or not.
204		248
205	$prev_pri = aioreq_pri [$pri]	249	$prev_pri = aioreq_pri [$pri]
206	Returns the priority value that would be used for the next	250	Returns the priority value that would be used for the next request
207	request and, if $pri is given, sets the priority for the next	251	and, if $pri is given, sets the priority for the next aio request.
208	aio request.
209		252
210	The default priority is 0, the minimum and maximum priorities	253	The default priority is 0, the minimum and maximum priorities are -4
211	are -4 and 4, respectively. Requests with higher priority will	254	and 4, respectively. Requests with higher priority will be serviced
212	be serviced first.	255	first.
213		256
214	The priority will be reset to 0 after each call to one of the	257	The priority will be reset to 0 after each call to one of the
215	"aio_*" functions.	258	"aio_*" functions.
216		259
217	Example: open a file with low priority, then read something from	260	Example: open a file with low priority, then read something from it
218	it with higher priority so the read request is serviced before	261	with higher priority so the read request is serviced before other
219	other low priority open requests (potentially spamming the	262	low priority open requests (potentially spamming the cache):
220	cache):
221		263
		264	aioreq_pri -3;
		265	aio_open ..., sub {
		266	return unless $_[0];
		267
222	aioreq_pri -3;	268	aioreq_pri -2;
223	aio_open ..., sub {
224	return unless $_[0];
225
226	aioreq_pri -2;
227	aio_read $_[0], ..., sub {	269	aio_read $_[0], ..., sub {
228	...
229	};
230	};
231
232	aioreq_nice $pri_adjust
233	Similar to "aioreq_pri", but subtracts the given value from the
234	current priority, so the effect is cumulative.
235
236	aio_open $pathname, $flags, $mode, $callback->($fh)
237	Asynchronously open or create a file and call the callback with
238	a newly created filehandle for the file.
239
240	The pathname passed to "aio_open" must be absolute. See API
241	NOTES, above, for an explanation.
242
243	The $flags argument is a bitmask. See the "Fcntl" module for a
244	list. They are the same as used by "sysopen".
245
246	Likewise, $mode specifies the mode of the newly created file, if
247	it didn't exist and "O_CREAT" has been given, just like perl's
248	"sysopen", except that it is mandatory (i.e. use 0 if you don't
249	create new files, and 0666 or 0777 if you do).
250
251	Example:
252
253	aio_open "/etc/passwd", O_RDONLY, 0, sub {
254	if ($_[0]) {
255	print "open successful, fh is $_[0]\n";
256	...
257	} else {
258	die "open failed: $!\n";
259	}
260	};
261
262	aio_close $fh, $callback->($status)
263	Asynchronously close a file and call the callback with the
264	result code. *WARNING:* although accepted, you should not pass
265	in a perl filehandle here, as perl will likely close the file
266	descriptor another time when the filehandle is destroyed.
267	Normally, you can safely call perls "close" or just let
268	filehandles go out of scope.
269
270	This is supposed to be a bug in the API, so that might change.
271	It's therefore best to avoid this function.
272
273	aio_read $fh,$offset,$length, $data,$dataoffset,
274	$callback->($retval)
275	aio_write $fh,$offset,$length, $data,$dataoffset,
276	$callback->($retval)
277	Reads or writes "length" bytes from the specified "fh" and
278	"offset" into the scalar given by "data" and offset "dataoffset"
279	and calls the callback without the actual number of bytes read
280	(or -1 on error, just like the syscall).
281
282	The $data scalar *MUST NOT* be modified in any way while the
283	request is outstanding. Modifying it can result in segfaults or
284	WW3 (if the necessary/optional hardware is installed).
285
286	Example: Read 15 bytes at offset 7 into scalar $buffer, starting
287	at offset 0 within the scalar:
288
289	aio_read $fh, 7, 15, $buffer, 0, sub {
290	$_[0] > 0 or die "read error: $!";
291	print "read $_[0] bytes: <$buffer>\n";
292	};
293
294	aio_sendfile $out_fh, $in_fh, $in_offset, $length,
295	$callback->($retval)
296	Tries to copy $length bytes from $in_fh to $out_fh. It starts
297	reading at byte offset $in_offset, and starts writing at the
298	current file offset of $out_fh. Because of that, it is not safe
299	to issue more than one "aio_sendfile" per $out_fh, as they will
300	interfere with each other.
301
302	This call tries to make use of a native "sendfile" syscall to
303	provide zero-copy operation. For this to work, $out_fh should
304	refer to a socket, and $in_fh should refer to mmap'able file.
305
306	If the native sendfile call fails or is not implemented, it will
307	be emulated, so you can call "aio_sendfile" on any type of
308	filehandle regardless of the limitations of the operating
309	system.
310
311	Please note, however, that "aio_sendfile" can read more bytes
312	from $in_fh than are written, and there is no way to find out
313	how many bytes have been read from "aio_sendfile" alone, as
314	"aio_sendfile" only provides the number of bytes written to
315	$out_fh. Only if the result value equals $length one can assume
316	that $length bytes have been read.
317
318	aio_readahead $fh,$offset,$length, $callback->($retval)
319	"aio_readahead" populates the page cache with data from a file
320	so that subsequent reads from that file will not block on disk
321	I/O. The $offset argument specifies the starting point from
322	which data is to be read and $length specifies the number of
323	bytes to be read. I/O is performed in whole pages, so that
324	offset is effectively rounded down to a page boundary and bytes
325	are read up to the next page boundary greater than or equal to
326	(off-set+length). "aio_readahead" does not read beyond the end
327	of the file. The current file offset of the file is left
328	unchanged.
329
330	If that syscall doesn't exist (likely if your OS isn't Linux) it
331	will be emulated by simply reading the data, which would have a
332	similar effect.
333
334	aio_stat $fh_or_path, $callback->($status)
335	aio_lstat $fh, $callback->($status)
336	Works like perl's "stat" or "lstat" in void context. The
337	callback will be called after the stat and the results will be
338	available using "stat _" or "-s _" etc...
339
340	The pathname passed to "aio_stat" must be absolute. See API
341	NOTES, above, for an explanation.
342
343	Currently, the stats are always 64-bit-stats, i.e. instead of
344	returning an error when stat'ing a large file, the results will
345	be silently truncated unless perl itself is compiled with large
346	file support.
347
348	Example: Print the length of /etc/passwd:
349
350	aio_stat "/etc/passwd", sub {
351	$_[0] and die "stat failed: $!";
352	print "size is ", -s _, "\n";
353	};
354
355	aio_unlink $pathname, $callback->($status)
356	Asynchronously unlink (delete) a file and call the callback with
357	the result code.
358
359	aio_mknod $path, $mode, $dev, $callback->($status)
360	[EXPERIMENTAL]
361
362	Asynchronously create a device node (or fifo). See mknod(2).
363
364	The only (POSIX-) portable way of calling this function is:
365
366	aio_mknod $path, IO::AIO::S_IFIFO | $mode, 0, sub { ...
367
368	aio_link $srcpath, $dstpath, $callback->($status)
369	Asynchronously create a new link to the existing object at
370	$srcpath at the path $dstpath and call the callback with the
371	result code.
372
373	aio_symlink $srcpath, $dstpath, $callback->($status)
374	Asynchronously create a new symbolic link to the existing object
375	at $srcpath at the path $dstpath and call the callback with the
376	result code.
377
378	aio_rename $srcpath, $dstpath, $callback->($status)
379	Asynchronously rename the object at $srcpath to $dstpath, just
380	as rename(2) and call the callback with the result code.
381
382	aio_rmdir $pathname, $callback->($status)
383	Asynchronously rmdir (delete) a directory and call the callback
384	with the result code.
385
386	aio_readdir $pathname, $callback->($entries)
387	Unlike the POSIX call of the same name, "aio_readdir" reads an
388	entire directory (i.e. opendir + readdir + closedir). The
389	entries will not be sorted, and will NOT include the "." and
390	".." entries.
391
392	The callback a single argument which is either "undef" or an
393	array-ref with the filenames.
394
395	aio_copy $srcpath, $dstpath, $callback->($status)
396	Try to copy the *file* (directories not supported as either
397	source or destination) from $srcpath to $dstpath and call the
398	callback with the 0 (error) or -1 ok.
399
400	This is a composite request that it creates the destination file
401	with mode 0200 and copies the contents of the source file into
402	it using "aio_sendfile", followed by restoring atime, mtime,
403	access mode and uid/gid, in that order.
404
405	If an error occurs, the partial destination file will be
406	unlinked, if possible, except when setting atime, mtime, access
407	mode and uid/gid, where errors are being ignored.
408
409	aio_move $srcpath, $dstpath, $callback->($status)
410	Try to move the *file* (directories not supported as either
411	source or destination) from $srcpath to $dstpath and call the
412	callback with the 0 (error) or -1 ok.
413
414	This is a composite request that tries to rename(2) the file
415	first. If rename files with "EXDEV", it copies the file with
416	"aio_copy" and, if that is successful, unlinking the $srcpath.
417
418	aio_scandir $path, $maxreq, $callback->($dirs, $nondirs)
419	Scans a directory (similar to "aio_readdir") but additionally
420	tries to efficiently separate the entries of directory $path
421	into two sets of names, directories you can recurse into
422	(directories), and ones you cannot recurse into (everything
423	else, including symlinks to directories).
424
425	"aio_scandir" is a composite request that creates of many sub
426	requests_ $maxreq specifies the maximum number of outstanding
427	aio requests that this function generates. If it is "<= 0", then
428	a suitable default will be chosen (currently 4).
429
430	On error, the callback is called without arguments, otherwise it
431	receives two array-refs with path-relative entry names.
432
433	Example:
434
435	aio_scandir $dir, 0, sub {
436	my ($dirs, $nondirs) = @_;
437	print "real directories: @$dirs\n";
438	print "everything else: @$nondirs\n";
439	};
440
441	Implementation notes.
442
443	The "aio_readdir" cannot be avoided, but "stat()"'ing every
444	entry can.
445
446	After reading the directory, the modification time, size etc. of
447	the directory before and after the readdir is checked, and if
448	they match (and isn't the current time), the link count will be
449	used to decide how many entries are directories (if >= 2).
450	Otherwise, no knowledge of the number of subdirectories will be
451	assumed.
452
453	Then entries will be sorted into likely directories (everything
454	without a non-initial dot currently) and likely non-directories
455	(everything else). Then every entry plus an appended "/." will
456	be "stat"'ed, likely directories first. If that succeeds, it
457	assumes that the entry is a directory or a symlink to directory
458	(which will be checked seperately). This is often faster than
459	stat'ing the entry itself because filesystems might detect the
460	type of the entry without reading the inode data (e.g. ext2fs
461	filetype feature).
462
463	If the known number of directories (link count - 2) has been
464	reached, the rest of the entries is assumed to be
465	non-directories.
466
467	This only works with certainty on POSIX (= UNIX) filesystems,
468	which fortunately are the vast majority of filesystems around.
469
470	It will also likely work on non-POSIX filesystems with reduced
471	efficiency as those tend to return 0 or 1 as link counts, which
472	disables the directory counting heuristic.
473
474	aio_fsync $fh, $callback->($status)
475	Asynchronously call fsync on the given filehandle and call the
476	callback with the fsync result code.
477
478	aio_fdatasync $fh, $callback->($status)
479	Asynchronously call fdatasync on the given filehandle and call
480	the callback with the fdatasync result code.
481
482	If this call isn't available because your OS lacks it or it
483	couldn't be detected, it will be emulated by calling "fsync"
484	instead.
485
486	aio_group $callback->(...)
487	This is a very special aio request: Instead of doing something,
488	it is a container for other aio requests, which is useful if you
489	want to bundle many requests into a single, composite, request
490	with a definite callback and the ability to cancel the whole
491	request with its subrequests.
492
493	Returns an object of class IO::AIO::GRP. See its documentation
494	below for more info.
495
496	Example:
497
498	my $grp = aio_group sub {
499	print "all stats done\n";
500	};
501
502	add $grp
503	(aio_stat ...),
504	(aio_stat ...),
505	...;	270	...
506
507	aio_nop $callback->()
508	This is a special request - it does nothing in itself and is
509	only used for side effects, such as when you want to add a dummy
510	request to a group so that finishing the requests in the group
511	depends on executing the given code.
512
513	While this request does nothing, it still goes through the
514	execution phase and still requires a worker thread. Thus, the
515	callback will not be executed immediately but only after other
516	requests in the queue have entered their execution phase. This
517	can be used to measure request latency.
518
519	IO::AIO::aio_busy $fractional_seconds, $callback->() *NOT EXPORTED*
520	Mainly used for debugging and benchmarking, this aio request
521	puts one of the request workers to sleep for the given time.
522
523	While it is theoretically handy to have simple I/O scheduling
524	requests like sleep and file handle readable/writable, the
525	overhead this creates is immense (it blocks a thread for a long
526	time) so do not use this function except to put your application
527	under artificial I/O pressure.
528
529	IO::AIO::REQ CLASS
530	All non-aggregate "aio_*" functions return an object of this class
531	when called in non-void context.
532
533	cancel $req
534	Cancels the request, if possible. Has the effect of skipping
535	execution when entering the execute state and skipping calling
536	the callback when entering the the result state, but will leave
537	the request otherwise untouched. That means that requests that
538	currently execute will not be stopped and resources held by the
539	request will not be freed prematurely.
540
541	cb $req $callback->(...)
542	Replace (or simply set) the callback registered to the request.
543
544	IO::AIO::GRP CLASS
545	This class is a subclass of IO::AIO::REQ, so all its methods apply
546	to objects of this class, too.
547
548	A IO::AIO::GRP object is a special request that can contain multiple
549	other aio requests.
550
551	You create one by calling the "aio_group" constructing function with
552	a callback that will be called when all contained requests have
553	entered the "done" state:
554
555	my $grp = aio_group sub {
556	print "all requests are done\n";
557	};
558
559	You add requests by calling the "add" method with one or more
560	"IO::AIO::REQ" objects:
561
562	$grp->add (aio_unlink "...");
563
564	add $grp aio_stat "...", sub {
565	$_[0] or return $grp->result ("error");
566
567	# add another request dynamically, if first succeeded
568	add $grp aio_open "...", sub {
569	$grp->result ("ok");
570	};	271	};
571	};	272	};
572		273
		274	aioreq_nice $pri_adjust
		275	Similar to "aioreq_pri", but subtracts the given value from the
		276	current priority, so the effect is cumulative.
		277
		278	aio_open $pathname, $flags, $mode, $callback->($fh)
		279	Asynchronously open or create a file and call the callback with a
		280	newly created filehandle for the file.
		281
		282	The pathname passed to "aio_open" must be absolute. See API NOTES,
		283	above, for an explanation.
		284
		285	The $flags argument is a bitmask. See the "Fcntl" module for a list.
		286	They are the same as used by "sysopen".
		287
		288	Likewise, $mode specifies the mode of the newly created file, if it
		289	didn't exist and "O_CREAT" has been given, just like perl's
		290	"sysopen", except that it is mandatory (i.e. use 0 if you don't
		291	create new files, and 0666 or 0777 if you do). Note that the $mode
		292	will be modified by the umask in effect then the request is being
		293	executed, so better never change the umask.
		294
		295	Example:
		296
		297	aio_open "/etc/passwd", O_RDONLY, 0, sub {
		298	if ($_[0]) {
		299	print "open successful, fh is $_[0]\n";
		300	...
		301	} else {
		302	die "open failed: $!\n";
		303	}
		304	};
		305
		306	aio_close $fh, $callback->($status)
		307	Asynchronously close a file and call the callback with the result
		308	code.
		309
		310	Unfortunately, you can't do this to perl. Perl *insists* very
		311	strongly on closing the file descriptor associated with the
		312	filehandle itself.
		313
		314	Therefore, "aio_close" will not close the filehandle - instead it
		315	will use dup2 to overwrite the file descriptor with the write-end of
		316	a pipe (the pipe fd will be created on demand and will be cached).
		317
		318	Or in other words: the file descriptor will be closed, but it will
		319	not be free for reuse until the perl filehandle is closed.
		320
		321	aio_read $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
		322	aio_write $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
		323	Reads or writes $length bytes from or to the specified $fh and
		324	$offset into the scalar given by $data and offset $dataoffset and
		325	calls the callback without the actual number of bytes read (or -1 on
		326	error, just like the syscall).
		327
		328	"aio_read" will, like "sysread", shrink or grow the $data scalar to
		329	offset plus the actual number of bytes read.
		330
		331	If $offset is undefined, then the current file descriptor offset
		332	will be used (and updated), otherwise the file descriptor offset
		333	will not be changed by these calls.
		334
		335	If $length is undefined in "aio_write", use the remaining length of
		336	$data.
		337
		338	If $dataoffset is less than zero, it will be counted from the end of
		339	$data.
		340
		341	The $data scalar *MUST NOT* be modified in any way while the request
		342	is outstanding. Modifying it can result in segfaults or World War
		343	III (if the necessary/optional hardware is installed).
		344
		345	Example: Read 15 bytes at offset 7 into scalar $buffer, starting at
		346	offset 0 within the scalar:
		347
		348	aio_read $fh, 7, 15, $buffer, 0, sub {
		349	$_[0] > 0 or die "read error: $!";
		350	print "read $_[0] bytes: <$buffer>\n";
		351	};
		352
		353	aio_sendfile $out_fh, $in_fh, $in_offset, $length, $callback->($retval)
		354	Tries to copy $length bytes from $in_fh to $out_fh. It starts
		355	reading at byte offset $in_offset, and starts writing at the current
		356	file offset of $out_fh. Because of that, it is not safe to issue
		357	more than one "aio_sendfile" per $out_fh, as they will interfere
		358	with each other.
		359
		360	This call tries to make use of a native "sendfile" syscall to
		361	provide zero-copy operation. For this to work, $out_fh should refer
		362	to a socket, and $in_fh should refer to an mmap'able file.
		363
		364	If a native sendfile cannot be found or it fails with "ENOSYS",
		365	"ENOTSUP", "EOPNOTSUPP", "EAFNOSUPPORT", "EPROTOTYPE" or "ENOTSOCK",
		366	it will be emulated, so you can call "aio_sendfile" on any type of
		367	filehandle regardless of the limitations of the operating system.
		368
		369	Please note, however, that "aio_sendfile" can read more bytes from
		370	$in_fh than are written, and there is no way to find out how many
		371	bytes have been read from "aio_sendfile" alone, as "aio_sendfile"
		372	only provides the number of bytes written to $out_fh. Only if the
		373	result value equals $length one can assume that $length bytes have
		374	been read.
		375
		376	aio_readahead $fh,$offset,$length, $callback->($retval)
		377	"aio_readahead" populates the page cache with data from a file so
		378	that subsequent reads from that file will not block on disk I/O. The
		379	$offset argument specifies the starting point from which data is to
		380	be read and $length specifies the number of bytes to be read. I/O is
		381	performed in whole pages, so that offset is effectively rounded down
		382	to a page boundary and bytes are read up to the next page boundary
		383	greater than or equal to (off-set+length). "aio_readahead" does not
		384	read beyond the end of the file. The current file offset of the file
		385	is left unchanged.
		386
		387	If that syscall doesn't exist (likely if your OS isn't Linux) it
		388	will be emulated by simply reading the data, which would have a
		389	similar effect.
		390
		391	aio_stat $fh_or_path, $callback->($status)
		392	aio_lstat $fh, $callback->($status)
		393	Works like perl's "stat" or "lstat" in void context. The callback
		394	will be called after the stat and the results will be available
		395	using "stat _" or "-s _" etc...
		396
		397	The pathname passed to "aio_stat" must be absolute. See API NOTES,
		398	above, for an explanation.
		399
		400	Currently, the stats are always 64-bit-stats, i.e. instead of
		401	returning an error when stat'ing a large file, the results will be
		402	silently truncated unless perl itself is compiled with large file
		403	support.
		404
		405	Example: Print the length of /etc/passwd:
		406
		407	aio_stat "/etc/passwd", sub {
		408	$_[0] and die "stat failed: $!";
		409	print "size is ", -s _, "\n";
		410	};
		411
		412	aio_statvfs $fh_or_path, $callback->($statvfs)
		413	Works like the POSIX "statvfs" or "fstatvfs" syscalls, depending on
		414	whether a file handle or path was passed.
		415
		416	On success, the callback is passed a hash reference with the
		417	following members: "bsize", "frsize", "blocks", "bfree", "bavail",
		418	"files", "ffree", "favail", "fsid", "flag" and "namemax". On
		419	failure, "undef" is passed.
		420
		421	The following POSIX IO::AIO::ST_* constants are defined: "ST_RDONLY"
		422	and "ST_NOSUID".
		423
		424	The following non-POSIX IO::AIO::ST_* flag masks are defined to
		425	their correct value when available, or to 0 on systems that do not
		426	support them: "ST_NODEV", "ST_NOEXEC", "ST_SYNCHRONOUS",
		427	"ST_MANDLOCK", "ST_WRITE", "ST_APPEND", "ST_IMMUTABLE",
		428	"ST_NOATIME", "ST_NODIRATIME" and "ST_RELATIME".
		429
		430	Example: stat "/wd" and dump out the data if successful.
		431
		432	aio_statvfs "/wd", sub {
		433	my $f = $_[0]
		434	or die "statvfs: $!";
		435
		436	use Data::Dumper;
		437	say Dumper $f;
		438	};
		439
		440	# result:
		441	{
		442	bsize => 1024,
		443	bfree => 4333064312,
		444	blocks => 10253828096,
		445	files => 2050765568,
		446	flag => 4096,
		447	favail => 2042092649,
		448	bavail => 4333064312,
		449	ffree => 2042092649,
		450	namemax => 255,
		451	frsize => 1024,
		452	fsid => 1810
		453	}
		454
		455	aio_utime $fh_or_path, $atime, $mtime, $callback->($status)
		456	Works like perl's "utime" function (including the special case of
		457	$atime and $mtime being undef). Fractional times are supported if
		458	the underlying syscalls support them.
		459
		460	When called with a pathname, uses utimes(2) if available, otherwise
		461	utime(2). If called on a file descriptor, uses futimes(2) if
		462	available, otherwise returns ENOSYS, so this is not portable.
		463
		464	Examples:
		465
		466	# set atime and mtime to current time (basically touch(1)):
		467	aio_utime "path", undef, undef;
		468	# set atime to current time and mtime to beginning of the epoch:
		469	aio_utime "path", time, undef; # undef==0
		470
		471	aio_chown $fh_or_path, $uid, $gid, $callback->($status)
		472	Works like perl's "chown" function, except that "undef" for either
		473	$uid or $gid is being interpreted as "do not change" (but -1 can
		474	also be used).
		475
		476	Examples:
		477
		478	# same as "chown root path" in the shell:
		479	aio_chown "path", 0, -1;
		480	# same as above:
		481	aio_chown "path", 0, undef;
		482
		483	aio_truncate $fh_or_path, $offset, $callback->($status)
		484	Works like truncate(2) or ftruncate(2).
		485
		486	aio_chmod $fh_or_path, $mode, $callback->($status)
		487	Works like perl's "chmod" function.
		488
		489	aio_unlink $pathname, $callback->($status)
		490	Asynchronously unlink (delete) a file and call the callback with the
		491	result code.
		492
		493	aio_mknod $path, $mode, $dev, $callback->($status)
		494	[EXPERIMENTAL]
		495
		496	Asynchronously create a device node (or fifo). See mknod(2).
		497
		498	The only (POSIX-) portable way of calling this function is:
		499
		500	aio_mknod $path, IO::AIO::S_IFIFO | $mode, 0, sub { ...
		501
		502	aio_link $srcpath, $dstpath, $callback->($status)
		503	Asynchronously create a new link to the existing object at $srcpath
		504	at the path $dstpath and call the callback with the result code.
		505
		506	aio_symlink $srcpath, $dstpath, $callback->($status)
		507	Asynchronously create a new symbolic link to the existing object at
		508	$srcpath at the path $dstpath and call the callback with the result
		509	code.
		510
		511	aio_readlink $path, $callback->($link)
		512	Asynchronously read the symlink specified by $path and pass it to
		513	the callback. If an error occurs, nothing or undef gets passed to
		514	the callback.
		515
		516	aio_rename $srcpath, $dstpath, $callback->($status)
		517	Asynchronously rename the object at $srcpath to $dstpath, just as
		518	rename(2) and call the callback with the result code.
		519
		520	aio_mkdir $pathname, $mode, $callback->($status)
		521	Asynchronously mkdir (create) a directory and call the callback with
		522	the result code. $mode will be modified by the umask at the time the
		523	request is executed, so do not change your umask.
		524
		525	aio_rmdir $pathname, $callback->($status)
		526	Asynchronously rmdir (delete) a directory and call the callback with
		527	the result code.
		528
		529	aio_readdir $pathname, $callback->($entries)
		530	Unlike the POSIX call of the same name, "aio_readdir" reads an
		531	entire directory (i.e. opendir + readdir + closedir). The entries
		532	will not be sorted, and will NOT include the "." and ".." entries.
		533
		534	The callback is passed a single argument which is either "undef" or
		535	an array-ref with the filenames.
		536
		537	aio_readdirx $pathname, $flags, $callback->($entries, $flags)
		538	Quite similar to "aio_readdir", but the $flags argument allows to
		539	tune behaviour and output format. In case of an error, $entries will
		540	be "undef".
		541
		542	The flags are a combination of the following constants, ORed
		543	together (the flags will also be passed to the callback, possibly
		544	modified):
		545
		546	IO::AIO::READDIR_DENTS
		547	When this flag is off, then the callback gets an arrayref with
		548	of names only (as with "aio_readdir"), otherwise it gets an
		549	arrayref with "[$name, $type, $inode]" arrayrefs, each
		550	describing a single directory entry in more detail.
		551
		552	$name is the name of the entry.
		553
		554	$type is one of the "IO::AIO::DT_xxx" constants:
		555
		556	"IO::AIO::DT_UNKNOWN", "IO::AIO::DT_FIFO", "IO::AIO::DT_CHR",
		557	"IO::AIO::DT_DIR", "IO::AIO::DT_BLK", "IO::AIO::DT_REG",
		558	"IO::AIO::DT_LNK", "IO::AIO::DT_SOCK", "IO::AIO::DT_WHT".
		559
		560	"IO::AIO::DT_UNKNOWN" means just that: readdir does not know. If
		561	you need to know, you have to run stat yourself. Also, for speed
		562	reasons, the $type scalars are read-only: you can not modify
		563	them.
		564
		565	$inode is the inode number (which might not be exact on systems
		566	with 64 bit inode numbers and 32 bit perls). This field has
		567	unspecified content on systems that do not deliver the inode
		568	information.
		569
		570	IO::AIO::READDIR_DIRS_FIRST
		571	When this flag is set, then the names will be returned in an
		572	order where likely directories come first. This is useful when
		573	you need to quickly find directories, or you want to find all
		574	directories while avoiding to stat() each entry.
		575
		576	If the system returns type information in readdir, then this is
		577	used to find directories directly. Otherwise, likely directories
		578	are files beginning with ".", or otherwise files with no dots,
		579	of which files with short names are tried first.
		580
		581	IO::AIO::READDIR_STAT_ORDER
		582	When this flag is set, then the names will be returned in an
		583	order suitable for stat()'ing each one. That is, when you plan
		584	to stat() all files in the given directory, then the returned
		585	order will likely be fastest.
		586
		587	If both this flag and "IO::AIO::READDIR_DIRS_FIRST" are
		588	specified, then the likely dirs come first, resulting in a less
		589	optimal stat order.
		590
		591	IO::AIO::READDIR_FOUND_UNKNOWN
		592	This flag should not be set when calling "aio_readdirx".
		593	Instead, it is being set by "aio_readdirx", when any of the
		594	$type's found were "IO::AIO::DT_UNKNOWN". The absense of this
		595	flag therefore indicates that all $type's are known, which can
		596	be used to speed up some algorithms.
		597
		598	aio_load $path, $data, $callback->($status)
		599	This is a composite request that tries to fully load the given file
		600	into memory. Status is the same as with aio_read.
		601
		602	aio_copy $srcpath, $dstpath, $callback->($status)
		603	Try to copy the *file* (directories not supported as either source
		604	or destination) from $srcpath to $dstpath and call the callback with
		605	a status of 0 (ok) or -1 (error, see $!).
		606
		607	This is a composite request that creates the destination file with
		608	mode 0200 and copies the contents of the source file into it using
		609	"aio_sendfile", followed by restoring atime, mtime, access mode and
		610	uid/gid, in that order.
		611
		612	If an error occurs, the partial destination file will be unlinked,
		613	if possible, except when setting atime, mtime, access mode and
		614	uid/gid, where errors are being ignored.
		615
		616	aio_move $srcpath, $dstpath, $callback->($status)
		617	Try to move the *file* (directories not supported as either source
		618	or destination) from $srcpath to $dstpath and call the callback with
		619	a status of 0 (ok) or -1 (error, see $!).
		620
		621	This is a composite request that tries to rename(2) the file first;
		622	if rename fails with "EXDEV", it copies the file with "aio_copy"
		623	and, if that is successful, unlinks the $srcpath.
		624
		625	aio_scandir $path, $maxreq, $callback->($dirs, $nondirs)
		626	Scans a directory (similar to "aio_readdir") but additionally tries
		627	to efficiently separate the entries of directory $path into two sets
		628	of names, directories you can recurse into (directories), and ones
		629	you cannot recurse into (everything else, including symlinks to
		630	directories).
		631
		632	"aio_scandir" is a composite request that creates of many sub
		633	requests_ $maxreq specifies the maximum number of outstanding aio
		634	requests that this function generates. If it is "<= 0", then a
		635	suitable default will be chosen (currently 4).
		636
		637	On error, the callback is called without arguments, otherwise it
		638	receives two array-refs with path-relative entry names.
		639
		640	Example:
		641
		642	aio_scandir $dir, 0, sub {
		643	my ($dirs, $nondirs) = @_;
		644	print "real directories: @$dirs\n";
		645	print "everything else: @$nondirs\n";
		646	};
		647
		648	Implementation notes.
		649
		650	The "aio_readdir" cannot be avoided, but "stat()"'ing every entry
		651	can.
		652
		653	If readdir returns file type information, then this is used directly
		654	to find directories.
		655
		656	Otherwise, after reading the directory, the modification time, size
		657	etc. of the directory before and after the readdir is checked, and
		658	if they match (and isn't the current time), the link count will be
		659	used to decide how many entries are directories (if >= 2).
		660	Otherwise, no knowledge of the number of subdirectories will be
		661	assumed.
		662
		663	Then entries will be sorted into likely directories a non-initial
		664	dot currently) and likely non-directories (see "aio_readdirx"). Then
		665	every entry plus an appended "/." will be "stat"'ed, likely
		666	directories first, in order of their inode numbers. If that
		667	succeeds, it assumes that the entry is a directory or a symlink to
		668	directory (which will be checked seperately). This is often faster
		669	than stat'ing the entry itself because filesystems might detect the
		670	type of the entry without reading the inode data (e.g. ext2fs
		671	filetype feature), even on systems that cannot return the filetype
		672	information on readdir.
		673
		674	If the known number of directories (link count - 2) has been
		675	reached, the rest of the entries is assumed to be non-directories.
		676
		677	This only works with certainty on POSIX (= UNIX) filesystems, which
		678	fortunately are the vast majority of filesystems around.
		679
		680	It will also likely work on non-POSIX filesystems with reduced
		681	efficiency as those tend to return 0 or 1 as link counts, which
		682	disables the directory counting heuristic.
		683
		684	aio_rmtree $path, $callback->($status)
		685	Delete a directory tree starting (and including) $path, return the
		686	status of the final "rmdir" only. This is a composite request that
		687	uses "aio_scandir" to recurse into and rmdir directories, and unlink
		688	everything else.
		689
		690	aio_sync $callback->($status)
		691	Asynchronously call sync and call the callback when finished.
		692
		693	aio_fsync $fh, $callback->($status)
		694	Asynchronously call fsync on the given filehandle and call the
		695	callback with the fsync result code.
		696
		697	aio_fdatasync $fh, $callback->($status)
		698	Asynchronously call fdatasync on the given filehandle and call the
		699	callback with the fdatasync result code.
		700
		701	If this call isn't available because your OS lacks it or it couldn't
		702	be detected, it will be emulated by calling "fsync" instead.
		703
		704	aio_sync_file_range $fh, $offset, $nbytes, $flags, $callback->($status)
		705	Sync the data portion of the file specified by $offset and $length
		706	to disk (but NOT the metadata), by calling the Linux-specific
		707	sync_file_range call. If sync_file_range is not available or it
		708	returns ENOSYS, then fdatasync or fsync is being substituted.
		709
		710	$flags can be a combination of
		711	"IO::AIO::SYNC_FILE_RANGE_WAIT_BEFORE",
		712	"IO::AIO::SYNC_FILE_RANGE_WRITE" and
		713	"IO::AIO::SYNC_FILE_RANGE_WAIT_AFTER": refer to the sync_file_range
		714	manpage for details.
		715
		716	aio_pathsync $path, $callback->($status)
		717	This request tries to open, fsync and close the given path. This is
		718	a composite request intended to sync directories after directory
		719	operations (E.g. rename). This might not work on all operating
		720	systems or have any specific effect, but usually it makes sure that
		721	directory changes get written to disc. It works for anything that
		722	can be opened for read-only, not just directories.
		723
		724	Future versions of this function might fall back to other methods
		725	when "fsync" on the directory fails (such as calling "sync").
		726
		727	Passes 0 when everything went ok, and -1 on error.
		728
		729	aio_msync $scalar, $offset = 0, $length = undef, flags = 0,
		730	$callback->($status)
		731	This is a rather advanced IO::AIO call, which only works on
		732	mmap(2)ed scalars (see the "IO::AIO::mmap" function, although it
		733	also works on data scalars managed by the Sys::Mmap or Mmap modules,
		734	note that the scalar must only be modified in-place while an aio
		735	operation is pending on it).
		736
		737	It calls the "msync" function of your OS, if available, with the
		738	memory area starting at $offset in the string and ending $length
		739	bytes later. If $length is negative, counts from the end, and if
		740	$length is "undef", then it goes till the end of the string. The
		741	flags can be a combination of "IO::AIO::MS_ASYNC",
		742	"IO::AIO::MS_INVALIDATE" and "IO::AIO::MS_SYNC".
		743
		744	aio_mtouch $scalar, $offset = 0, $length = undef, flags = 0,
		745	$callback->($status)
		746	This is a rather advanced IO::AIO call, which works best on
		747	mmap(2)ed scalars.
		748
		749	It touches (reads or writes) all memory pages in the specified range
		750	inside the scalar. All caveats and parameters are the same as for
		751	"aio_msync", above, except for flags, which must be either 0 (which
		752	reads all pages and ensures they are instantiated) or
		753	"IO::AIO::MT_MODIFY", which modifies the memory page s(by reading
		754	and writing an octet from it, which dirties the page).
		755
		756	aio_group $callback->(...)
		757	This is a very special aio request: Instead of doing something, it
		758	is a container for other aio requests, which is useful if you want
		759	to bundle many requests into a single, composite, request with a
		760	definite callback and the ability to cancel the whole request with
		761	its subrequests.
		762
		763	Returns an object of class IO::AIO::GRP. See its documentation below
		764	for more info.
		765
		766	Example:
		767
		768	my $grp = aio_group sub {
		769	print "all stats done\n";
		770	};
		771
		772	add $grp
		773	(aio_stat ...),
		774	(aio_stat ...),
		775	...;
		776
		777	aio_nop $callback->()
		778	This is a special request - it does nothing in itself and is only
		779	used for side effects, such as when you want to add a dummy request
		780	to a group so that finishing the requests in the group depends on
		781	executing the given code.
		782
		783	While this request does nothing, it still goes through the execution
		784	phase and still requires a worker thread. Thus, the callback will
		785	not be executed immediately but only after other requests in the
		786	queue have entered their execution phase. This can be used to
		787	measure request latency.
		788
		789	IO::AIO::aio_busy $fractional_seconds, $callback->() *NOT EXPORTED*
		790	Mainly used for debugging and benchmarking, this aio request puts
		791	one of the request workers to sleep for the given time.
		792
		793	While it is theoretically handy to have simple I/O scheduling
		794	requests like sleep and file handle readable/writable, the overhead
		795	this creates is immense (it blocks a thread for a long time) so do
		796	not use this function except to put your application under
		797	artificial I/O pressure.
		798
		799	IO::AIO::REQ CLASS
		800	All non-aggregate "aio_*" functions return an object of this class when
		801	called in non-void context.
		802
		803	cancel $req
		804	Cancels the request, if possible. Has the effect of skipping
		805	execution when entering the execute state and skipping calling the
		806	callback when entering the the result state, but will leave the
		807	request otherwise untouched (with the exception of readdir). That
		808	means that requests that currently execute will not be stopped and
		809	resources held by the request will not be freed prematurely.
		810
		811	cb $req $callback->(...)
		812	Replace (or simply set) the callback registered to the request.
		813
		814	IO::AIO::GRP CLASS
		815	This class is a subclass of IO::AIO::REQ, so all its methods apply to
		816	objects of this class, too.
		817
		818	A IO::AIO::GRP object is a special request that can contain multiple
		819	other aio requests.
		820
		821	You create one by calling the "aio_group" constructing function with a
		822	callback that will be called when all contained requests have entered
		823	the "done" state:
		824
		825	my $grp = aio_group sub {
		826	print "all requests are done\n";
		827	};
		828
		829	You add requests by calling the "add" method with one or more
		830	"IO::AIO::REQ" objects:
		831
		832	$grp->add (aio_unlink "...");
		833
		834	add $grp aio_stat "...", sub {
		835	$_[0] or return $grp->result ("error");
		836
		837	# add another request dynamically, if first succeeded
		838	add $grp aio_open "...", sub {
		839	$grp->result ("ok");
		840	};
		841	};
		842
573	This makes it very easy to create composite requests (see the source	843	This makes it very easy to create composite requests (see the source of
574	of "aio_move" for an application) that work and feel like simple	844	"aio_move" for an application) that work and feel like simple requests.
575	requests.
576		845
577	* The IO::AIO::GRP objects will be cleaned up during calls to	846	* The IO::AIO::GRP objects will be cleaned up during calls to
578	"IO::AIO::poll_cb", just like any other request.	847	"IO::AIO::poll_cb", just like any other request.
		848
579	* They can be canceled like any other request. Canceling will cancel	849	* They can be canceled like any other request. Canceling will cancel
580	not only the request itself, but also all requests it contains.	850	not only the request itself, but also all requests it contains.
		851
581	* They can also can also be added to other IO::AIO::GRP objects.	852	* They can also can also be added to other IO::AIO::GRP objects.
		853
582	* You must not add requests to a group from within the group	854	* You must not add requests to a group from within the group callback
583	callback (or any later time).	855	(or any later time).
584		856
585	Their lifetime, simplified, looks like this: when they are empty,	857	Their lifetime, simplified, looks like this: when they are empty, they
586	they will finish very quickly. If they contain only requests that	858	will finish very quickly. If they contain only requests that are in the
587	are in the "done" state, they will also finish. Otherwise they will	859	"done" state, they will also finish. Otherwise they will continue to
588	continue to exist.	860	exist.
589		861
590	That means after creating a group you have some time to add	862	That means after creating a group you have some time to add requests
		863	(precisely before the callback has been invoked, which is only done
591	requests. And in the callbacks of those requests, you can add	864	within the "poll_cb"). And in the callbacks of those requests, you can
592	further requests to the group. And only when all those requests have	865	add further requests to the group. And only when all those requests have
593	finished will the the group itself finish.	866	finished will the the group itself finish.
594		867
595	add $grp ...	868	add $grp ...
596	$grp->add (...)	869	$grp->add (...)
597	Add one or more requests to the group. Any type of IO::AIO::REQ	870	Add one or more requests to the group. Any type of IO::AIO::REQ can
598	can be added, including other groups, as long as you do not	871	be added, including other groups, as long as you do not create
599	create circular dependencies.	872	circular dependencies.
600		873
601	Returns all its arguments.	874	Returns all its arguments.
602		875
603	$grp->cancel_subs	876	$grp->cancel_subs
604	Cancel all subrequests and clears any feeder, but not the group	877	Cancel all subrequests and clears any feeder, but not the group
605	request itself. Useful when you queued a lot of events but got a	878	request itself. Useful when you queued a lot of events but got a
606	result early.	879	result early.
607		880
		881	The group request will finish normally (you cannot add requests to
		882	the group).
		883
608	$grp->result (...)	884	$grp->result (...)
609	Set the result value(s) that will be passed to the group	885	Set the result value(s) that will be passed to the group callback
610	callback when all subrequests have finished and set thre groups	886	when all subrequests have finished and set the groups errno to the
611	errno to the current value of errno (just like calling "errno"	887	current value of errno (just like calling "errno" without an error
612	without an error number). By default, no argument will be passed	888	number). By default, no argument will be passed and errno is zero.
613	and errno is zero.
614		889
615	$grp->errno ([$errno])	890	$grp->errno ([$errno])
616	Sets the group errno value to $errno, or the current value of	891	Sets the group errno value to $errno, or the current value of errno
617	errno when the argument is missing.	892	when the argument is missing.
618		893
619	Every aio request has an associated errno value that is restored	894	Every aio request has an associated errno value that is restored
620	when the callback is invoked. This method lets you change this	895	when the callback is invoked. This method lets you change this value
621	value from its default (0).	896	from its default (0).
622		897
623	Calling "result" will also set errno, so make sure you either	898	Calling "result" will also set errno, so make sure you either set $!
624	set $! before the call to "result", or call c<errno> after it.	899	before the call to "result", or call c<errno> after it.
625		900
626	feed $grp $callback->($grp)	901	feed $grp $callback->($grp)
627	Sets a feeder/generator on this group: every group can have an	902	Sets a feeder/generator on this group: every group can have an
628	attached generator that generates requests if idle. The idea	903	attached generator that generates requests if idle. The idea behind
629	behind this is that, although you could just queue as many	904	this is that, although you could just queue as many requests as you
630	requests as you want in a group, this might starve other	905	want in a group, this might starve other requests for a potentially
631	requests for a potentially long time. For example, "aio_scandir"	906	long time. For example, "aio_scandir" might generate hundreds of
632	might generate hundreds of thousands "aio_stat" requests,	907	thousands "aio_stat" requests, delaying any later requests for a
633	delaying any later requests for a long time.	908	long time.
634		909
635	To avoid this, and allow incremental generation of requests, you	910	To avoid this, and allow incremental generation of requests, you can
636	can instead a group and set a feeder on it that generates those	911	instead a group and set a feeder on it that generates those
637	requests. The feed callback will be called whenever there are	912	requests. The feed callback will be called whenever there are few
638	few enough (see "limit", below) requests active in the group	913	enough (see "limit", below) requests active in the group itself and
639	itself and is expected to queue more requests.	914	is expected to queue more requests.
640		915
641	The feed callback can queue as many requests as it likes (i.e.	916	The feed callback can queue as many requests as it likes (i.e. "add"
642	"add" does not impose any limits).	917	does not impose any limits).
643		918
644	If the feed does not queue more requests when called, it will be	919	If the feed does not queue more requests when called, it will be
645	automatically removed from the group.	920	automatically removed from the group.
646		921
647	If the feed limit is 0, it will be set to 2 automatically.	922	If the feed limit is 0 when this method is called, it will be set to
		923	2 automatically.
648		924
649	Example:	925	Example:
650		926
651	# stat all files in @files, but only ever use four aio requests concurrently:	927	# stat all files in @files, but only ever use four aio requests concurrently:
652		928
653	my $grp = aio_group sub { print "finished\n" };	929	my $grp = aio_group sub { print "finished\n" };
654	limit $grp 4;	930	limit $grp 4;
655	feed $grp sub {	931	feed $grp sub {
656	my $file = pop @files	932	my $file = pop @files
657	or return;	933	or return;
658		934
659	add $grp aio_stat $file, sub { ... };	935	add $grp aio_stat $file, sub { ... };
660	};	936	};
661		937
662	limit $grp $num	938	limit $grp $num
663	Sets the feeder limit for the group: The feeder will be called	939	Sets the feeder limit for the group: The feeder will be called
664	whenever the group contains less than this many requests.	940	whenever the group contains less than this many requests.
665		941
666	Setting the limit to 0 will pause the feeding process.	942	Setting the limit to 0 will pause the feeding process.
		943
		944	The default value for the limit is 0, but note that setting a feeder
		945	automatically bumps it up to 2.
667		946
668	SUPPORT FUNCTIONS	947	SUPPORT FUNCTIONS
669	EVENT PROCESSING AND EVENT LOOP INTEGRATION	948	EVENT PROCESSING AND EVENT LOOP INTEGRATION
670	$fileno = IO::AIO::poll_fileno	949	$fileno = IO::AIO::poll_fileno
671	Return the *request result pipe file descriptor*. This	950	Return the *request result pipe file descriptor*. This filehandle
672	filehandle must be polled for reading by some mechanism outside	951	must be polled for reading by some mechanism outside this module
673	this module (e.g. Event or select, see below or the SYNOPSIS).	952	(e.g. EV, Glib, select and so on, see below or the SYNOPSIS). If the
674	If the pipe becomes readable you have to call "poll_cb" to check	953	pipe becomes readable you have to call "poll_cb" to check the
675	the results.	954	results.
676		955
677	See "poll_cb" for an example.	956	See "poll_cb" for an example.
678		957
679	IO::AIO::poll_cb	958	IO::AIO::poll_cb
680	Process some outstanding events on the result pipe. You have to	959	Process some outstanding events on the result pipe. You have to call
681	call this regularly. Returns the number of events processed.	960	this regularly. Returns 0 if all events could be processed, or -1 if
682	Returns immediately when no events are outstanding. The amount	961	it returned earlier for whatever reason. Returns immediately when no
683	of events processed depends on the settings of	962	events are outstanding. The amount of events processed depends on
684	"IO::AIO::max_poll_req" and "IO::AIO::max_poll_time".	963	the settings of "IO::AIO::max_poll_req" and
		964	"IO::AIO::max_poll_time".
685		965
686	If not all requests were processed for whatever reason, the	966	If not all requests were processed for whatever reason, the
687	filehandle will still be ready when "poll_cb" returns.	967	filehandle will still be ready when "poll_cb" returns, so normally
		968	you don't have to do anything special to have it called later.
688		969
689	Example: Install an Event watcher that automatically calls	970	Example: Install an Event watcher that automatically calls
690	IO::AIO::poll_cb with high priority:	971	IO::AIO::poll_cb with high priority (more examples can be found in
		972	the SYNOPSIS section, at the top of this document):
691		973
692	Event->io (fd => IO::AIO::poll_fileno,	974	Event->io (fd => IO::AIO::poll_fileno,
693	poll => 'r', async => 1,	975	poll => 'r', async => 1,
694	cb => \&IO::AIO::poll_cb);	976	cb => \&IO::AIO::poll_cb);
695		977
696	IO::AIO::max_poll_reqs $nreqs
697	IO::AIO::max_poll_time $seconds
698	These set the maximum number of requests (default 0, meaning
699	infinity) that are being processed by "IO::AIO::poll_cb" in one
700	call, respectively the maximum amount of time (default 0,
701	meaning infinity) spent in "IO::AIO::poll_cb" to process
702	requests (more correctly the mininum amount of time "poll_cb" is
703	allowed to use).
704
705	Setting these is useful if you want to ensure some level of
706	interactiveness when perl is not fast enough to process all
707	requests in time.
708
709	For interactive programs, values such as 0.01 to 0.1 should be
710	fine.
711
712	Example: Install an Event watcher that automatically calls
713	IO::AIO::poll_some with low priority, to ensure that other parts
714	of the program get the CPU sometimes even under high AIO load.
715
716	# try not to spend much more than 0.1s in poll_cb
717	IO::AIO::max_poll_time 0.1;
718
719	# use a low priority so other tasks have priority
720	Event->io (fd => IO::AIO::poll_fileno,
721	poll => 'r', nice => 1,
722	cb => &IO::AIO::poll_cb);
723
724	IO::AIO::poll_wait	978	IO::AIO::poll_wait
		979	If there are any outstanding requests and none of them in the result
725	Wait till the result filehandle becomes ready for reading	980	phase, wait till the result filehandle becomes ready for reading
726	(simply does a "select" on the filehandle. This is useful if you	981	(simply does a "select" on the filehandle. This is useful if you
727	want to synchronously wait for some requests to finish).	982	want to synchronously wait for some requests to finish).
728		983
729	See "nreqs" for an example.	984	See "nreqs" for an example.
730		985
731	IO::AIO::poll	986	IO::AIO::poll
732	Waits until some requests have been handled.	987	Waits until some requests have been handled.
733		988
		989	Returns the number of requests processed, but is otherwise strictly
734	Strictly equivalent to:	990	equivalent to:
735		991
736	IO::AIO::poll_wait, IO::AIO::poll_cb	992	IO::AIO::poll_wait, IO::AIO::poll_cb
737	if IO::AIO::nreqs;
738		993
739	IO::AIO::flush	994	IO::AIO::flush
740	Wait till all outstanding AIO requests have been handled.	995	Wait till all outstanding AIO requests have been handled.
741		996
742	Strictly equivalent to:	997	Strictly equivalent to:
743		998
744	IO::AIO::poll_wait, IO::AIO::poll_cb	999	IO::AIO::poll_wait, IO::AIO::poll_cb
745	while IO::AIO::nreqs;	1000	while IO::AIO::nreqs;
		1001
		1002	IO::AIO::max_poll_reqs $nreqs
		1003	IO::AIO::max_poll_time $seconds
		1004	These set the maximum number of requests (default 0, meaning
		1005	infinity) that are being processed by "IO::AIO::poll_cb" in one
		1006	call, respectively the maximum amount of time (default 0, meaning
		1007	infinity) spent in "IO::AIO::poll_cb" to process requests (more
		1008	correctly the mininum amount of time "poll_cb" is allowed to use).
		1009
		1010	Setting "max_poll_time" to a non-zero value creates an overhead of
		1011	one syscall per request processed, which is not normally a problem
		1012	unless your callbacks are really really fast or your OS is really
		1013	really slow (I am not mentioning Solaris here). Using
		1014	"max_poll_reqs" incurs no overhead.
		1015
		1016	Setting these is useful if you want to ensure some level of
		1017	interactiveness when perl is not fast enough to process all requests
		1018	in time.
		1019
		1020	For interactive programs, values such as 0.01 to 0.1 should be fine.
		1021
		1022	Example: Install an Event watcher that automatically calls
		1023	IO::AIO::poll_cb with low priority, to ensure that other parts of
		1024	the program get the CPU sometimes even under high AIO load.
		1025
		1026	# try not to spend much more than 0.1s in poll_cb
		1027	IO::AIO::max_poll_time 0.1;
		1028
		1029	# use a low priority so other tasks have priority
		1030	Event->io (fd => IO::AIO::poll_fileno,
		1031	poll => 'r', nice => 1,
		1032	cb => &IO::AIO::poll_cb);
746		1033
747	CONTROLLING THE NUMBER OF THREADS	1034	CONTROLLING THE NUMBER OF THREADS
748	IO::AIO::min_parallel $nthreads	1035	IO::AIO::min_parallel $nthreads
749	Set the minimum number of AIO threads to $nthreads. The current	1036	Set the minimum number of AIO threads to $nthreads. The current
750	default is 8, which means eight asynchronous operations can	1037	default is 8, which means eight asynchronous operations can execute
751	execute concurrently at any one time (the number of outstanding	1038	concurrently at any one time (the number of outstanding requests,
752	requests, however, is unlimited).	1039	however, is unlimited).
753		1040
754	IO::AIO starts threads only on demand, when an AIO request is	1041	IO::AIO starts threads only on demand, when an AIO request is queued
755	queued and no free thread exists. Please note that queueing up a	1042	and no free thread exists. Please note that queueing up a hundred
756	hundred requests can create demand for a hundred threads, even	1043	requests can create demand for a hundred threads, even if it turns
757	if it turns out that everything is in the cache and could have	1044	out that everything is in the cache and could have been processed
758	been processed faster by a single thread.	1045	faster by a single thread.
759		1046
760	It is recommended to keep the number of threads relatively low,	1047	It is recommended to keep the number of threads relatively low, as
761	as some Linux kernel versions will scale negatively with the	1048	some Linux kernel versions will scale negatively with the number of
762	number of threads (higher parallelity => MUCH higher latency).	1049	threads (higher parallelity => MUCH higher latency). With current
763	With current Linux 2.6 versions, 4-32 threads should be fine.	1050	Linux 2.6 versions, 4-32 threads should be fine.
764		1051
765	Under most circumstances you don't need to call this function,	1052	Under most circumstances you don't need to call this function, as
766	as the module selects a default that is suitable for low to	1053	the module selects a default that is suitable for low to moderate
767	moderate load.	1054	load.
768		1055
769	IO::AIO::max_parallel $nthreads	1056	IO::AIO::max_parallel $nthreads
770	Sets the maximum number of AIO threads to $nthreads. If more	1057	Sets the maximum number of AIO threads to $nthreads. If more than
771	than the specified number of threads are currently running, this	1058	the specified number of threads are currently running, this function
772	function kills them. This function blocks until the limit is	1059	kills them. This function blocks until the limit is reached.
773	reached.
774		1060
775	While $nthreads are zero, aio requests get queued but not	1061	While $nthreads are zero, aio requests get queued but not executed
776	executed until the number of threads has been increased again.	1062	until the number of threads has been increased again.
777		1063
778	This module automatically runs "max_parallel 0" at program end,	1064	This module automatically runs "max_parallel 0" at program end, to
779	to ensure that all threads are killed and that there are no	1065	ensure that all threads are killed and that there are no outstanding
780	outstanding requests.	1066	requests.
781		1067
782	Under normal circumstances you don't need to call this function.	1068	Under normal circumstances you don't need to call this function.
783		1069
784	IO::AIO::max_idle $nthreads	1070	IO::AIO::max_idle $nthreads
785	Limit the number of threads (default: 4) that are allowed to	1071	Limit the number of threads (default: 4) that are allowed to idle
786	idle (i.e., threads that did not get a request to process within	1072	(i.e., threads that did not get a request to process within 10
787	10 seconds). That means if a thread becomes idle while $nthreads	1073	seconds). That means if a thread becomes idle while $nthreads other
788	other threads are also idle, it will free its resources and	1074	threads are also idle, it will free its resources and exit.
789	exit.
790		1075
791	This is useful when you allow a large number of threads (e.g.	1076	This is useful when you allow a large number of threads (e.g. 100 or
792	100 or 1000) to allow for extremely high load situations, but	1077	1000) to allow for extremely high load situations, but want to free
793	want to free resources under normal circumstances (1000 threads	1078	resources under normal circumstances (1000 threads can easily
794	can easily consume 30MB of RAM).	1079	consume 30MB of RAM).
795		1080
796	The default is probably ok in most situations, especially if	1081	The default is probably ok in most situations, especially if thread
797	thread creation is fast. If thread creation is very slow on your	1082	creation is fast. If thread creation is very slow on your system you
798	system you might want to use larger values.	1083	might want to use larger values.
799		1084
800	$oldmaxreqs = IO::AIO::max_outstanding $maxreqs	1085	IO::AIO::max_outstanding $maxreqs
801	This is a very bad function to use in interactive programs	1086	This is a very bad function to use in interactive programs because
802	because it blocks, and a bad way to reduce concurrency because	1087	it blocks, and a bad way to reduce concurrency because it is
803	it is inexact: Better use an "aio_group" together with a feed	1088	inexact: Better use an "aio_group" together with a feed callback.
804	callback.
805		1089
806	Sets the maximum number of outstanding requests to $nreqs. If	1090	Sets the maximum number of outstanding requests to $nreqs. If you do
807	you to queue up more than this number of requests, the next call	1091	queue up more than this number of requests, the next call to the
808	to the "poll_cb" (and "poll_some" and other functions calling	1092	"poll_cb" (and "poll_some" and other functions calling "poll_cb")
809	"poll_cb") function will block until the limit is no longer	1093	function will block until the limit is no longer exceeded.
810	exceeded.
811		1094
812	The default value is very large, so there is no practical limit	1095	The default value is very large, so there is no practical limit on
813	on the number of outstanding requests.	1096	the number of outstanding requests.
814		1097
815	You can still queue as many requests as you want. Therefore,	1098	You can still queue as many requests as you want. Therefore,
816	"max_oustsanding" is mainly useful in simple scripts (with low	1099	"max_outstanding" is mainly useful in simple scripts (with low
817	values) or as a stop gap to shield against fatal memory overflow	1100	values) or as a stop gap to shield against fatal memory overflow
818	(with large values).	1101	(with large values).
819		1102
820	STATISTICAL INFORMATION	1103	STATISTICAL INFORMATION
821	IO::AIO::nreqs	1104	IO::AIO::nreqs
822	Returns the number of requests currently in the ready, execute	1105	Returns the number of requests currently in the ready, execute or
823	or pending states (i.e. for which their callback has not been	1106	pending states (i.e. for which their callback has not been invoked
824	invoked yet).	1107	yet).
825		1108
826	Example: wait till there are no outstanding requests anymore:	1109	Example: wait till there are no outstanding requests anymore:
827		1110
828	IO::AIO::poll_wait, IO::AIO::poll_cb	1111	IO::AIO::poll_wait, IO::AIO::poll_cb
829	while IO::AIO::nreqs;	1112	while IO::AIO::nreqs;
830		1113
831	IO::AIO::nready	1114	IO::AIO::nready
832	Returns the number of requests currently in the ready state (not	1115	Returns the number of requests currently in the ready state (not yet
833	yet executed).	1116	executed).
834		1117
835	IO::AIO::npending	1118	IO::AIO::npending
836	Returns the number of requests currently in the pending state	1119	Returns the number of requests currently in the pending state
837	(executed, but not yet processed by poll_cb).	1120	(executed, but not yet processed by poll_cb).
		1121
		1122	MISCELLANEOUS FUNCTIONS
		1123	IO::AIO implements some functions that might be useful, but are not
		1124	asynchronous.
		1125
		1126	IO::AIO::sendfile $ofh, $ifh, $offset, $count
		1127	Calls the "eio_sendfile_sync" function, which is like
		1128	"aio_sendfile", but is blocking (this makes most sense if you know
		1129	the input data is likely cached already and the output filehandle is
		1130	set to non-blocking operations).
		1131
		1132	Returns the number of bytes copied, or -1 on error.
		1133
		1134	IO::AIO::fadvise $fh, $offset, $len, $advice
		1135	Simply calls the "posix_fadvise" function (see it's manpage for
		1136	details). The following advice constants are avaiable:
		1137	"IO::AIO::FADV_NORMAL", "IO::AIO::FADV_SEQUENTIAL",
		1138	"IO::AIO::FADV_RANDOM", "IO::AIO::FADV_NOREUSE",
		1139	"IO::AIO::FADV_WILLNEED", "IO::AIO::FADV_DONTNEED".
		1140
		1141	On systems that do not implement "posix_fadvise", this function
		1142	returns ENOSYS, otherwise the return value of "posix_fadvise".
		1143
		1144	IO::AIO::mmap $scalar, $length, $prot, $flags, $fh[, $offset]
		1145	Memory-maps a file (or anonymous memory range) and attaches it to
		1146	the given $scalar, which will act like a string scalar.
		1147
		1148	The only operations allowed on the scalar are "substr"/"vec" that
		1149	don't change the string length, and most read-only operations such
		1150	as copying it or searching it with regexes and so on.
		1151
		1152	Anything else is unsafe and will, at best, result in memory leaks.
		1153
		1154	The memory map associated with the $scalar is automatically removed
		1155	when the $scalar is destroyed, or when the "IO::AIO::mmap" or
		1156	"IO::AIO::munmap" functions are called.
		1157
		1158	This calls the "mmap"(2) function internally. See your system's
		1159	manual page for details on the $length, $prot and $flags parameters.
		1160
		1161	The $length must be larger than zero and smaller than the actual
		1162	filesize.
		1163
		1164	$prot is a combination of "IO::AIO::PROT_NONE",
		1165	"IO::AIO::PROT_EXEC", "IO::AIO::PROT_READ" and/or
		1166	"IO::AIO::PROT_WRITE",
		1167
		1168	$flags can be a combination of "IO::AIO::MAP_SHARED" or
		1169	"IO::AIO::MAP_PRIVATE", or a number of system-specific flags (when
		1170	not available, the are defined as 0): "IO::AIO::MAP_ANONYMOUS"
		1171	(which is set to "MAP_ANON" if your system only provides this
		1172	constant), "IO::AIO::MAP_HUGETLB", "IO::AIO::MAP_LOCKED",
		1173	"IO::AIO::MAP_NORESERVE", "IO::AIO::MAP_POPULATE" or
		1174	"IO::AIO::MAP_NONBLOCK"
		1175
		1176	If $fh is "undef", then a file descriptor of -1 is passed.
		1177
		1178	$offset is the offset from the start of the file - it generally must
		1179	be a multiple of "IO::AIO::PAGESIZE" and defaults to 0.
		1180
		1181	Example:
		1182
		1183	use Digest::MD5;
		1184	use IO::AIO;
		1185
		1186	open my $fh, "<verybigfile"
		1187	or die "$!";
		1188
		1189	IO::AIO::mmap my $data, -s $fh, IO::AIO::PROT_READ, IO::AIO::MAP_SHARED, $fh
		1190	or die "verybigfile: $!";
		1191
		1192	my $fast_md5 = md5 $data;
		1193
		1194	IO::AIO::munmap $scalar
		1195	Removes a previous mmap and undefines the $scalar.
		1196
		1197	IO::AIO::mlockall $flags
		1198	Calls the "mlockall" function with the given $flags (a combination
		1199	of "IO::AIO::MCL_CURRENT" and "IO::AIO::MCL__FUTURE").
		1200
		1201	On systems that do not implement "mlockall", this function returns
		1202	ENOSYS, otherwise the return value of "mlockall".
		1203
		1204	IO::AIO::munlockall
		1205	Calls the "munlockall" function.
		1206
		1207	On systems that do not implement "munlockall", this function returns
		1208	ENOSYS, otherwise the return value of "munlockall".
		1209
		1210	EVENT LOOP INTEGRATION
		1211	It is recommended to use AnyEvent::AIO to integrate IO::AIO
		1212	automatically into many event loops:
		1213
		1214	# AnyEvent integration (EV, Event, Glib, Tk, POE, urxvt, pureperl...)
		1215	use AnyEvent::AIO;
		1216
		1217	You can also integrate IO::AIO manually into many event loops, here are
		1218	some examples of how to do this:
		1219
		1220	# EV integration
		1221	my $aio_w = EV::io IO::AIO::poll_fileno, EV::READ, \&IO::AIO::poll_cb;
		1222
		1223	# Event integration
		1224	Event->io (fd => IO::AIO::poll_fileno,
		1225	poll => 'r',
		1226	cb => \&IO::AIO::poll_cb);
		1227
		1228	# Glib/Gtk2 integration
		1229	add_watch Glib::IO IO::AIO::poll_fileno,
		1230	in => sub { IO::AIO::poll_cb; 1 };
		1231
		1232	# Tk integration
		1233	Tk::Event::IO->fileevent (IO::AIO::poll_fileno, "",
		1234	readable => \&IO::AIO::poll_cb);
		1235
		1236	# Danga::Socket integration
		1237	Danga::Socket->AddOtherFds (IO::AIO::poll_fileno =>
		1238	\&IO::AIO::poll_cb);
838		1239
839	FORK BEHAVIOUR	1240	FORK BEHAVIOUR
840	This module should do "the right thing" when the process using it	1241	This module should do "the right thing" when the process using it forks:
841	forks:
842		1242
843	Before the fork, IO::AIO enters a quiescent state where no requests	1243	Before the fork, IO::AIO enters a quiescent state where no requests can
844	can be added in other threads and no results will be processed.	1244	be added in other threads and no results will be processed. After the
845	After the fork the parent simply leaves the quiescent state and	1245	fork the parent simply leaves the quiescent state and continues
846	continues request/result processing, while the child frees the	1246	request/result processing, while the child frees the request/result
847	request/result queue (so that the requests started before the fork	1247	queue (so that the requests started before the fork will only be handled
848	will only be handled in the parent). Threads will be started on	1248	in the parent). Threads will be started on demand until the limit set in
849	demand until the limit set in the parent process has been reached	1249	the parent process has been reached again.
850	again.
851		1250
852	In short: the parent will, after a short pause, continue as if fork	1251	In short: the parent will, after a short pause, continue as if fork had
853	had not been called, while the child will act as if IO::AIO has not	1252	not been called, while the child will act as if IO::AIO has not been
854	been used yet.	1253	used yet.
855		1254
856	MEMORY USAGE	1255	MEMORY USAGE
857	Per-request usage:	1256	Per-request usage:
858		1257
859	Each aio request uses - depending on your architecture - around	1258	Each aio request uses - depending on your architecture - around 100-200
860	100-200 bytes of memory. In addition, stat requests need a stat	1259	bytes of memory. In addition, stat requests need a stat buffer (possibly
861	buffer (possibly a few hundred bytes), readdir requires a result	1260	a few hundred bytes), readdir requires a result buffer and so on. Perl
862	buffer and so on. Perl scalars and other data passed into aio	1261	scalars and other data passed into aio requests will also be locked and
863	requests will also be locked and will consume memory till the	1262	will consume memory till the request has entered the done state.
864	request has entered the done state.
865		1263
866	This is now awfully much, so queuing lots of requests is not usually	1264	This is not awfully much, so queuing lots of requests is not usually a
867	a problem.	1265	problem.
868		1266
869	Per-thread usage:	1267	Per-thread usage:
870		1268
871	In the execution phase, some aio requests require more memory for	1269	In the execution phase, some aio requests require more memory for
872	temporary buffers, and each thread requires a stack and other data	1270	temporary buffers, and each thread requires a stack and other data
873	structures (usually around 16k-128k, depending on the OS).	1271	structures (usually around 16k-128k, depending on the OS).
874		1272
875	KNOWN BUGS	1273	KNOWN BUGS
876	Known bugs will be fixed in the next release.	1274	Known bugs will be fixed in the next release.
877		1275
878	SEE ALSO	1276	SEE ALSO
879	Coro::AIO.	1277	AnyEvent::AIO for easy integration into event loops, Coro::AIO for a
		1278	more natural syntax.
880		1279
881	AUTHOR	1280	AUTHOR
882	Marc Lehmann <schmorp@schmorp.de>	1281	Marc Lehmann <schmorp@schmorp.de>
883	http://home.schmorp.de/	1282	http://home.schmorp.de/
884		1283

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