[ViewVC] Diff of: cvs/IO-AIO/README

Comparing IO-AIO/README (file contents):
Revision 1.8 by root, Sun Jul 31 17:24:05 2005 UTC vs.
Revision 1.41 by root, Sat Jan 2 14:24:32 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
14	aio_read $fh, 30000, 1024, $buffer, 0, sub {	15	aio_read $fh, 30000, 1024, $buffer, 0, sub {
15	$_[0] > 0 or die "read error: $!";	16	$_[0] > 0 or die "read error: $!";
16	};	17	};
17		18
18	# Event	19	# version 2+ has request and group objects
		20	use IO::AIO 2;
		21
		22	aioreq_pri 4; # give next request a very high priority
		23	my $req = aio_unlink "/tmp/file", sub { };
		24	$req->cancel; # cancel request if still in queue
		25
		26	my $grp = aio_group sub { print "all stats done\n" };
		27	add $grp aio_stat "..." for ...;
		28
		29	# AnyEvent integration (EV, Event, Glib, Tk, POE, urxvt, pureperl...)
		30	use AnyEvent::AIO;
		31
		32	# EV integration
		33	my $aio_w = EV::io IO::AIO::poll_fileno, EV::READ, \&IO::AIO::poll_cb;
		34
		35	# Event integration
19	Event->io (fd => IO::AIO::poll_fileno,	36	Event->io (fd => IO::AIO::poll_fileno,
20	poll => 'r',	37	poll => 'r',
21	cb => \&IO::AIO::poll_cb);	38	cb => \&IO::AIO::poll_cb);
22		39
23	# Glib/Gtk2	40	# Glib/Gtk2 integration
24	add_watch Glib::IO IO::AIO::poll_fileno,	41	add_watch Glib::IO IO::AIO::poll_fileno,
25	in => sub { IO::AIO::poll_cb; 1 };	42	in => sub { IO::AIO::poll_cb; 1 };
26		43
27	# Tk	44	# Tk integration
28	Tk::Event::IO->fileevent (IO::AIO::poll_fileno, "",	45	Tk::Event::IO->fileevent (IO::AIO::poll_fileno, "",
29	readable => \&IO::AIO::poll_cb);	46	readable => \&IO::AIO::poll_cb);
30		47
31	# Danga::Socket	48	# Danga::Socket integration
32	Danga::Socket->AddOtherFds (IO::AIO::poll_fileno =>	49	Danga::Socket->AddOtherFds (IO::AIO::poll_fileno =>
33	\&IO::AIO::poll_cb);	50	\&IO::AIO::poll_cb);
34		51
35	DESCRIPTION	52	DESCRIPTION
36	This module implements asynchronous I/O using whatever means your	53	This module implements asynchronous I/O using whatever means your
37	operating system supports.	54	operating system supports. It is implemented as an interface to "libeio"
		55	(<http://software.schmorp.de/pkg/libeio.html>).
38		56
		57	Asynchronous means that operations that can normally block your program
		58	(e.g. reading from disk) will be done asynchronously: the operation will
		59	still block, but you can do something else in the meantime. This is
		60	extremely useful for programs that need to stay interactive even when
		61	doing heavy I/O (GUI programs, high performance network servers etc.),
		62	but can also be used to easily do operations in parallel that are
		63	normally done sequentially, e.g. stat'ing many files, which is much
		64	faster on a RAID volume or over NFS when you do a number of stat
		65	operations concurrently.
		66
		67	While most of this works on all types of file descriptors (for example
		68	sockets), using these functions on file descriptors that support
		69	nonblocking operation (again, sockets, pipes etc.) is very inefficient.
		70	Use an event loop for that (such as the EV module): IO::AIO will
		71	naturally fit into such an event loop itself.
		72
39	Currently, a number of threads are started that execute your read/writes	73	In this version, a number of threads are started that execute your
40	and signal their completion. You don't need thread support in your libc	74	requests and signal their completion. You don't need thread support in
41	or perl, and the threads created by this module will not be visible to	75	perl, and the threads created by this module will not be visible to
42	the pthreads library. In the future, this module might make use of the	76	perl. In the future, this module might make use of the native aio
43	native aio functions available on many operating systems. However, they	77	functions available on many operating systems. However, they are often
44	are often not well-supported (Linux doesn't allow them on normal files	78	not well-supported or restricted (GNU/Linux doesn't allow them on normal
45	currently, for example), and they would only support aio_read and	79	files currently, for example), and they would only support aio_read and
46	aio_write, so the remaining functionality would have to be implemented	80	aio_write, so the remaining functionality would have to be implemented
47	using threads anyway.	81	using threads anyway.
48		82
49	Although the module will work with in the presence of other threads, it	83	Although the module will work in the presence of other (Perl-) threads,
50	is currently not reentrant, so use appropriate locking yourself, always	84	it is currently not reentrant in any way, so use appropriate locking
51	call "poll_cb" from within the same thread, or never call "poll_cb" (or	85	yourself, always call "poll_cb" from within the same thread, or never
52	other "aio_" functions) recursively.	86	call "poll_cb" (or other "aio_" functions) recursively.
		87
		88	EXAMPLE
		89	This is a simple example that uses the EV module and loads /etc/passwd
		90	asynchronously:
		91
		92	use Fcntl;
		93	use EV;
		94	use IO::AIO;
		95
		96	# register the IO::AIO callback with EV
		97	my $aio_w = EV::io IO::AIO::poll_fileno, EV::READ, \&IO::AIO::poll_cb;
		98
		99	# queue the request to open /etc/passwd
		100	aio_open "/etc/passwd", O_RDONLY, 0, sub {
		101	my $fh = shift
		102	or die "error while opening: $!";
		103
		104	# stat'ing filehandles is generally non-blocking
		105	my $size = -s $fh;
		106
		107	# queue a request to read the file
		108	my $contents;
		109	aio_read $fh, 0, $size, $contents, 0, sub {
		110	$_[0] == $size
		111	or die "short read: $!";
		112
		113	close $fh;
		114
		115	# file contents now in $contents
		116	print $contents;
		117
		118	# exit event loop and program
		119	EV::unloop;
		120	};
		121	};
		122
		123	# possibly queue up other requests, or open GUI windows,
		124	# check for sockets etc. etc.
		125
		126	# process events as long as there are some:
		127	EV::loop;
		128
		129	REQUEST ANATOMY AND LIFETIME
		130	Every "aio_*" function creates a request. which is a C data structure
		131	not directly visible to Perl.
		132
		133	If called in non-void context, every request function returns a Perl
		134	object representing the request. In void context, nothing is returned,
		135	which saves a bit of memory.
		136
		137	The perl object is a fairly standard ref-to-hash object. The hash
		138	contents are not used by IO::AIO so you are free to store anything you
		139	like in it.
		140
		141	During their existance, aio requests travel through the following
		142	states, in order:
		143
		144	ready
		145	Immediately after a request is created it is put into the ready
		146	state, waiting for a thread to execute it.
		147
		148	execute
		149	A thread has accepted the request for processing and is currently
		150	executing it (e.g. blocking in read).
		151
		152	pending
		153	The request has been executed and is waiting for result processing.
		154
		155	While request submission and execution is fully asynchronous, result
		156	processing is not and relies on the perl interpreter calling
		157	"poll_cb" (or another function with the same effect).
		158
		159	result
		160	The request results are processed synchronously by "poll_cb".
		161
		162	The "poll_cb" function will process all outstanding aio requests by
		163	calling their callbacks, freeing memory associated with them and
		164	managing any groups they are contained in.
		165
		166	done
		167	Request has reached the end of its lifetime and holds no resources
		168	anymore (except possibly for the Perl object, but its connection to
		169	the actual aio request is severed and calling its methods will
		170	either do nothing or result in a runtime error).
53		171
54	FUNCTIONS	172	FUNCTIONS
55	AIO FUNCTIONS	173	AIO REQUEST FUNCTIONS
56	All the "aio_*" calls are more or less thin wrappers around the syscall	174	All the "aio_*" calls are more or less thin wrappers around the syscall
57	with the same name (sans "aio_"). The arguments are similar or	175	with the same name (sans "aio_"). The arguments are similar or
58	identical, and they all accept an additional (and optional) $callback	176	identical, and they all accept an additional (and optional) $callback
59	argument which must be a code reference. This code reference will get	177	argument which must be a code reference. This code reference will get
60	called with the syscall return code (e.g. most syscalls return -1 on	178	called with the syscall return code (e.g. most syscalls return -1 on
61	error, unlike perl, which usually delivers "false") as it's sole	179	error, unlike perl, which usually delivers "false") as its sole argument
62	argument when the given syscall has been executed asynchronously.	180	after the given syscall has been executed asynchronously.
63		181
64	All functions expecting a filehandle keep a copy of the filehandle	182	All functions expecting a filehandle keep a copy of the filehandle
65	internally until the request has finished.	183	internally until the request has finished.
66		184
		185	All functions return request objects of type IO::AIO::REQ that allow
		186	further manipulation of those requests while they are in-flight.
		187
67	The filenames you pass to these routines must be absolute. The reason	188	The pathnames you pass to these routines must be absolute and encoded
68	for this is that at the time the request is being executed, the current	189	as octets. The reason for the former is that at the time the request is
69	working directory could have changed. Alternatively, you can make sure	190	being executed, the current working directory could have changed.
70	that you never change the current working directory.	191	Alternatively, you can make sure that you never change the current
		192	working directory anywhere in the program and then use relative paths.
71		193
		194	To encode pathnames as octets, either make sure you either: a) always
		195	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
		197	and encode your pathnames to the locale (or other) encoding in effect in
		198	the user environment, d) use Glib::filename_from_unicode on unicode
		199	filenames or e) use something else to ensure your scalar has the correct
		200	contents.
		201
		202	This works, btw. independent of the internal UTF-8 bit, which IO::AIO
		203	handles correctly whether it is set or not.
		204
		205	$prev_pri = aioreq_pri [$pri]
		206	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.
		208
		209	The default priority is 0, the minimum and maximum priorities are -4
		210	and 4, respectively. Requests with higher priority will be serviced
		211	first.
		212
		213	The priority will be reset to 0 after each call to one of the
		214	"aio_*" functions.
		215
		216	Example: open a file with low priority, then read something from it
		217	with higher priority so the read request is serviced before other
		218	low priority open requests (potentially spamming the cache):
		219
		220	aioreq_pri -3;
		221	aio_open ..., sub {
		222	return unless $_[0];
		223
		224	aioreq_pri -2;
		225	aio_read $_[0], ..., sub {
		226	...
		227	};
		228	};
		229
		230	aioreq_nice $pri_adjust
		231	Similar to "aioreq_pri", but subtracts the given value from the
		232	current priority, so the effect is cumulative.
		233
72	aio_open $pathname, $flags, $mode, $callback	234	aio_open $pathname, $flags, $mode, $callback->($fh)
73	Asynchronously open or create a file and call the callback with a	235	Asynchronously open or create a file and call the callback with a
74	newly created filehandle for the file.	236	newly created filehandle for the file.
75		237
76	The pathname passed to "aio_open" must be absolute. See API NOTES,	238	The pathname passed to "aio_open" must be absolute. See API NOTES,
77	above, for an explanation.	239	above, for an explanation.
…		…
80	They are the same as used by "sysopen".	242	They are the same as used by "sysopen".
81		243
82	Likewise, $mode specifies the mode of the newly created file, if it	244	Likewise, $mode specifies the mode of the newly created file, if it
83	didn't exist and "O_CREAT" has been given, just like perl's	245	didn't exist and "O_CREAT" has been given, just like perl's
84	"sysopen", except that it is mandatory (i.e. use 0 if you don't	246	"sysopen", except that it is mandatory (i.e. use 0 if you don't
85	create new files, and 0666 or 0777 if you do).	247	create new files, and 0666 or 0777 if you do). Note that the $mode
		248	will be modified by the umask in effect then the request is being
		249	executed, so better never change the umask.
86		250
87	Example:	251	Example:
88		252
89	aio_open "/etc/passwd", O_RDONLY, 0, sub {	253	aio_open "/etc/passwd", O_RDONLY, 0, sub {
90	if ($_[0]) {	254	if ($_[0]) {
…		…
93	} else {	257	} else {
94	die "open failed: $!\n";	258	die "open failed: $!\n";
95	}	259	}
96	};	260	};
97		261
98	aio_close $fh, $callback	262	aio_close $fh, $callback->($status)
99	Asynchronously close a file and call the callback with the result	263	Asynchronously close a file and call the callback with the result
100	code. WARNING: although accepted, you should not pass in a perl	264	code.
101	filehandle here, as perl will likely close the file descriptor
102	another time when the filehandle is destroyed. Normally, you can
103	safely call perls "close" or just let filehandles go out of scope.
104		265
105	This is supposed to be a bug in the API, so that might change. It's	266	Unfortunately, you can't do this to perl. Perl insists very
106	therefore best to avoid this function.	267	strongly on closing the file descriptor associated with the
		268	filehandle itself.
107		269
		270	Therefore, "aio_close" will not close the filehandle - instead it
		271	will use dup2 to overwrite the file descriptor with the write-end of
		272	a pipe (the pipe fd will be created on demand and will be cached).
		273
		274	Or in other words: the file descriptor will be closed, but it will
		275	not be free for reuse until the perl filehandle is closed.
		276
108	aio_read $fh,$offset,$length, $data,$dataoffset,$callback	277	aio_read $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
109	aio_write $fh,$offset,$length, $data,$dataoffset,$callback	278	aio_write $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
110	Reads or writes "length" bytes from the specified "fh" and "offset"	279	Reads or writes $length bytes from or to the specified $fh and
111	into the scalar given by "data" and offset "dataoffset" and calls	280	$offset into the scalar given by $data and offset $dataoffset and
112	the callback without the actual number of bytes read (or -1 on	281	calls the callback without the actual number of bytes read (or -1 on
113	error, just like the syscall).	282	error, just like the syscall).
		283
		284	"aio_read" will, like "sysread", shrink or grow the $data scalar to
		285	offset plus the actual number of bytes read.
		286
		287	If $offset is undefined, then the current file descriptor offset
		288	will be used (and updated), otherwise the file descriptor offset
		289	will not be changed by these calls.
		290
		291	If $length is undefined in "aio_write", use the remaining length of
		292	$data.
		293
		294	If $dataoffset is less than zero, it will be counted from the end of
		295	$data.
		296
		297	The $data scalar MUST NOT be modified in any way while the request
		298	is outstanding. Modifying it can result in segfaults or World War
		299	III (if the necessary/optional hardware is installed).
114		300
115	Example: Read 15 bytes at offset 7 into scalar $buffer, starting at	301	Example: Read 15 bytes at offset 7 into scalar $buffer, starting at
116	offset 0 within the scalar:	302	offset 0 within the scalar:
117		303
118	aio_read $fh, 7, 15, $buffer, 0, sub {	304	aio_read $fh, 7, 15, $buffer, 0, sub {
119	$_[0] > 0 or die "read error: $!";	305	$_[0] > 0 or die "read error: $!";
120	print "read $_[0] bytes: <$buffer>\n";	306	print "read $_[0] bytes: <$buffer>\n";
121	};	307	};
122		308
		309	aio_sendfile $out_fh, $in_fh, $in_offset, $length, $callback->($retval)
		310	Tries to copy $length bytes from $in_fh to $out_fh. It starts
		311	reading at byte offset $in_offset, and starts writing at the current
		312	file offset of $out_fh. Because of that, it is not safe to issue
		313	more than one "aio_sendfile" per $out_fh, as they will interfere
		314	with each other.
		315
		316	This call tries to make use of a native "sendfile" syscall to
		317	provide zero-copy operation. For this to work, $out_fh should refer
		318	to a socket, and $in_fh should refer to mmap'able file.
		319
		320	If a native sendfile cannot be found or it fails with "ENOSYS",
		321	"ENOTSUP", "EOPNOTSUPP", "EAFNOSUPPORT", "EPROTOTYPE" or "ENOTSOCK",
		322	it will be emulated, so you can call "aio_sendfile" on any type of
		323	filehandle regardless of the limitations of the operating system.
		324
		325	Please note, however, that "aio_sendfile" can read more bytes from
		326	$in_fh than are written, and there is no way to find out how many
		327	bytes have been read from "aio_sendfile" alone, as "aio_sendfile"
		328	only provides the number of bytes written to $out_fh. Only if the
		329	result value equals $length one can assume that $length bytes have
		330	been read.
		331
123	aio_readahead $fh,$offset,$length, $callback	332	aio_readahead $fh,$offset,$length, $callback->($retval)
124	Asynchronously reads the specified byte range into the page cache,
125	using the "readahead" syscall. If that syscall doesn't exist (likely
126	if your OS isn't Linux) the status will be -1 and $! is set to
127	"ENOSYS".
128
129	"aio_readahead" populates the page cache with data from a file so	333	"aio_readahead" populates the page cache with data from a file so
130	that subsequent reads from that file will not block on disk I/O. The	334	that subsequent reads from that file will not block on disk I/O. The
131	$offset argument specifies the starting point from which data is to	335	$offset argument specifies the starting point from which data is to
132	be read and $length specifies the number of bytes to be read. I/O is	336	be read and $length specifies the number of bytes to be read. I/O is
133	performed in whole pages, so that offset is effectively rounded down	337	performed in whole pages, so that offset is effectively rounded down
134	to a page boundary and bytes are read up to the next page boundary	338	to a page boundary and bytes are read up to the next page boundary
135	greater than or equal to (off-set+length). "aio_readahead" does not	339	greater than or equal to (off-set+length). "aio_readahead" does not
136	read beyond the end of the file. The current file offset of the file	340	read beyond the end of the file. The current file offset of the file
137	is left unchanged.	341	is left unchanged.
138		342
		343	If that syscall doesn't exist (likely if your OS isn't Linux) it
		344	will be emulated by simply reading the data, which would have a
		345	similar effect.
		346
139	aio_stat $fh_or_path, $callback	347	aio_stat $fh_or_path, $callback->($status)
140	aio_lstat $fh, $callback	348	aio_lstat $fh, $callback->($status)
141	Works like perl's "stat" or "lstat" in void context. The callback	349	Works like perl's "stat" or "lstat" in void context. The callback
142	will be called after the stat and the results will be available	350	will be called after the stat and the results will be available
143	using "stat _" or "-s _" etc...	351	using "stat _" or "-s _" etc...
144		352
145	The pathname passed to "aio_stat" must be absolute. See API NOTES,	353	The pathname passed to "aio_stat" must be absolute. See API NOTES,
…		…
155	aio_stat "/etc/passwd", sub {	363	aio_stat "/etc/passwd", sub {
156	$_[0] and die "stat failed: $!";	364	$_[0] and die "stat failed: $!";
157	print "size is ", -s _, "\n";	365	print "size is ", -s _, "\n";
158	};	366	};
159		367
		368	aio_utime $fh_or_path, $atime, $mtime, $callback->($status)
		369	Works like perl's "utime" function (including the special case of
		370	$atime and $mtime being undef). Fractional times are supported if
		371	the underlying syscalls support them.
		372
		373	When called with a pathname, uses utimes(2) if available, otherwise
		374	utime(2). If called on a file descriptor, uses futimes(2) if
		375	available, otherwise returns ENOSYS, so this is not portable.
		376
		377	Examples:
		378
		379	# set atime and mtime to current time (basically touch(1)):
		380	aio_utime "path", undef, undef;
		381	# set atime to current time and mtime to beginning of the epoch:
		382	aio_utime "path", time, undef; # undef==0
		383
		384	aio_chown $fh_or_path, $uid, $gid, $callback->($status)
		385	Works like perl's "chown" function, except that "undef" for either
		386	$uid or $gid is being interpreted as "do not change" (but -1 can
		387	also be used).
		388
		389	Examples:
		390
		391	# same as "chown root path" in the shell:
		392	aio_chown "path", 0, -1;
		393	# same as above:
		394	aio_chown "path", 0, undef;
		395
		396	aio_truncate $fh_or_path, $offset, $callback->($status)
		397	Works like truncate(2) or ftruncate(2).
		398
		399	aio_chmod $fh_or_path, $mode, $callback->($status)
		400	Works like perl's "chmod" function.
		401
160	aio_unlink $pathname, $callback	402	aio_unlink $pathname, $callback->($status)
161	Asynchronously unlink (delete) a file and call the callback with the	403	Asynchronously unlink (delete) a file and call the callback with the
162	result code.	404	result code.
163		405
		406	aio_mknod $path, $mode, $dev, $callback->($status)
		407	[EXPERIMENTAL]
		408
		409	Asynchronously create a device node (or fifo). See mknod(2).
		410
		411	The only (POSIX-) portable way of calling this function is:
		412
		413	aio_mknod $path, IO::AIO::S_IFIFO \| $mode, 0, sub { ...
		414
		415	aio_link $srcpath, $dstpath, $callback->($status)
		416	Asynchronously create a new link to the existing object at $srcpath
		417	at the path $dstpath and call the callback with the result code.
		418
		419	aio_symlink $srcpath, $dstpath, $callback->($status)
		420	Asynchronously create a new symbolic link to the existing object at
		421	$srcpath at the path $dstpath and call the callback with the result
		422	code.
		423
		424	aio_readlink $path, $callback->($link)
		425	Asynchronously read the symlink specified by $path and pass it to
		426	the callback. If an error occurs, nothing or undef gets passed to
		427	the callback.
		428
		429	aio_rename $srcpath, $dstpath, $callback->($status)
		430	Asynchronously rename the object at $srcpath to $dstpath, just as
		431	rename(2) and call the callback with the result code.
		432
		433	aio_mkdir $pathname, $mode, $callback->($status)
		434	Asynchronously mkdir (create) a directory and call the callback with
		435	the result code. $mode will be modified by the umask at the time the
		436	request is executed, so do not change your umask.
		437
		438	aio_rmdir $pathname, $callback->($status)
		439	Asynchronously rmdir (delete) a directory and call the callback with
		440	the result code.
		441
		442	aio_readdir $pathname, $callback->($entries)
		443	Unlike the POSIX call of the same name, "aio_readdir" reads an
		444	entire directory (i.e. opendir + readdir + closedir). The entries
		445	will not be sorted, and will NOT include the "." and ".." entries.
		446
		447	The callback is passed a single argument which is either "undef" or
		448	an array-ref with the filenames.
		449
		450	aio_readdirx $pathname, $flags, $callback->($entries, $flags)
		451	Quite similar to "aio_readdir", but the $flags argument allows to
		452	tune behaviour and output format. In case of an error, $entries will
		453	be "undef".
		454
		455	The flags are a combination of the following constants, ORed
		456	together (the flags will also be passed to the callback, possibly
		457	modified):
		458
		459	IO::AIO::READDIR_DENTS
		460	When this flag is off, then the callback gets an arrayref with
		461	of names only (as with "aio_readdir"), otherwise it gets an
		462	arrayref with "[$name, $type, $inode]" arrayrefs, each
		463	describing a single directory entry in more detail.
		464
		465	$name is the name of the entry.
		466
		467	$type is one of the "IO::AIO::DT_xxx" constants:
		468
		469	"IO::AIO::DT_UNKNOWN", "IO::AIO::DT_FIFO", "IO::AIO::DT_CHR",
		470	"IO::AIO::DT_DIR", "IO::AIO::DT_BLK", "IO::AIO::DT_REG",
		471	"IO::AIO::DT_LNK", "IO::AIO::DT_SOCK", "IO::AIO::DT_WHT".
		472
		473	"IO::AIO::DT_UNKNOWN" means just that: readdir does not know. If
		474	you need to know, you have to run stat yourself. Also, for speed
		475	reasons, the $type scalars are read-only: you can not modify
		476	them.
		477
		478	$inode is the inode number (which might not be exact on systems
		479	with 64 bit inode numbers and 32 bit perls). This field has
		480	unspecified content on systems that do not deliver the inode
		481	information.
		482
		483	IO::AIO::READDIR_DIRS_FIRST
		484	When this flag is set, then the names will be returned in an
		485	order where likely directories come first. This is useful when
		486	you need to quickly find directories, or you want to find all
		487	directories while avoiding to stat() each entry.
		488
		489	If the system returns type information in readdir, then this is
		490	used to find directories directly. Otherwise, likely directories
		491	are files beginning with ".", or otherwise files with no dots,
		492	of which files with short names are tried first.
		493
		494	IO::AIO::READDIR_STAT_ORDER
		495	When this flag is set, then the names will be returned in an
		496	order suitable for stat()'ing each one. That is, when you plan
		497	to stat() all files in the given directory, then the returned
		498	order will likely be fastest.
		499
		500	If both this flag and "IO::AIO::READDIR_DIRS_FIRST" are
		501	specified, then the likely dirs come first, resulting in a less
		502	optimal stat order.
		503
		504	IO::AIO::READDIR_FOUND_UNKNOWN
		505	This flag should not be set when calling "aio_readdirx".
		506	Instead, it is being set by "aio_readdirx", when any of the
		507	$type's found were "IO::AIO::DT_UNKNOWN". The absense of this
		508	flag therefore indicates that all $type's are known, which can
		509	be used to speed up some algorithms.
		510
		511	aio_load $path, $data, $callback->($status)
		512	This is a composite request that tries to fully load the given file
		513	into memory. Status is the same as with aio_read.
		514
		515	aio_copy $srcpath, $dstpath, $callback->($status)
		516	Try to copy the file (directories not supported as either source
		517	or destination) from $srcpath to $dstpath and call the callback with
		518	a status of 0 (ok) or -1 (error, see $!).
		519
		520	This is a composite request that creates the destination file with
		521	mode 0200 and copies the contents of the source file into it using
		522	"aio_sendfile", followed by restoring atime, mtime, access mode and
		523	uid/gid, in that order.
		524
		525	If an error occurs, the partial destination file will be unlinked,
		526	if possible, except when setting atime, mtime, access mode and
		527	uid/gid, where errors are being ignored.
		528
		529	aio_move $srcpath, $dstpath, $callback->($status)
		530	Try to move the file (directories not supported as either source
		531	or destination) from $srcpath to $dstpath and call the callback with
		532	a status of 0 (ok) or -1 (error, see $!).
		533
		534	This is a composite request that tries to rename(2) the file first;
		535	if rename fails with "EXDEV", it copies the file with "aio_copy"
		536	and, if that is successful, unlinks the $srcpath.
		537
		538	aio_scandir $path, $maxreq, $callback->($dirs, $nondirs)
		539	Scans a directory (similar to "aio_readdir") but additionally tries
		540	to efficiently separate the entries of directory $path into two sets
		541	of names, directories you can recurse into (directories), and ones
		542	you cannot recurse into (everything else, including symlinks to
		543	directories).
		544
		545	"aio_scandir" is a composite request that creates of many sub
		546	requests_ $maxreq specifies the maximum number of outstanding aio
		547	requests that this function generates. If it is "<= 0", then a
		548	suitable default will be chosen (currently 4).
		549
		550	On error, the callback is called without arguments, otherwise it
		551	receives two array-refs with path-relative entry names.
		552
		553	Example:
		554
		555	aio_scandir $dir, 0, sub {
		556	my ($dirs, $nondirs) = @_;
		557	print "real directories: @$dirs\n";
		558	print "everything else: @$nondirs\n";
		559	};
		560
		561	Implementation notes.
		562
		563	The "aio_readdir" cannot be avoided, but "stat()"'ing every entry
		564	can.
		565
		566	If readdir returns file type information, then this is used directly
		567	to find directories.
		568
		569	Otherwise, after reading the directory, the modification time, size
		570	etc. of the directory before and after the readdir is checked, and
		571	if they match (and isn't the current time), the link count will be
		572	used to decide how many entries are directories (if >= 2).
		573	Otherwise, no knowledge of the number of subdirectories will be
		574	assumed.
		575
		576	Then entries will be sorted into likely directories a non-initial
		577	dot currently) and likely non-directories (see "aio_readdirx"). Then
		578	every entry plus an appended "/." will be "stat"'ed, likely
		579	directories first, in order of their inode numbers. If that
		580	succeeds, it assumes that the entry is a directory or a symlink to
		581	directory (which will be checked seperately). This is often faster
		582	than stat'ing the entry itself because filesystems might detect the
		583	type of the entry without reading the inode data (e.g. ext2fs
		584	filetype feature), even on systems that cannot return the filetype
		585	information on readdir.
		586
		587	If the known number of directories (link count - 2) has been
		588	reached, the rest of the entries is assumed to be non-directories.
		589
		590	This only works with certainty on POSIX (= UNIX) filesystems, which
		591	fortunately are the vast majority of filesystems around.
		592
		593	It will also likely work on non-POSIX filesystems with reduced
		594	efficiency as those tend to return 0 or 1 as link counts, which
		595	disables the directory counting heuristic.
		596
		597	aio_rmtree $path, $callback->($status)
		598	Delete a directory tree starting (and including) $path, return the
		599	status of the final "rmdir" only. This is a composite request that
		600	uses "aio_scandir" to recurse into and rmdir directories, and unlink
		601	everything else.
		602
		603	aio_sync $callback->($status)
		604	Asynchronously call sync and call the callback when finished.
		605
164	aio_fsync $fh, $callback	606	aio_fsync $fh, $callback->($status)
165	Asynchronously call fsync on the given filehandle and call the	607	Asynchronously call fsync on the given filehandle and call the
166	callback with the fsync result code.	608	callback with the fsync result code.
167		609
168	aio_fdatasync $fh, $callback	610	aio_fdatasync $fh, $callback->($status)
169	Asynchronously call fdatasync on the given filehandle and call the	611	Asynchronously call fdatasync on the given filehandle and call the
170	callback with the fdatasync result code. Might set $! to "ENOSYS" if	612	callback with the fdatasync result code.
171	"fdatasync" is not available.	613
		614	If this call isn't available because your OS lacks it or it couldn't
		615	be detected, it will be emulated by calling "fsync" instead.
		616
		617	aio_sync_file_range $fh, $offset, $nbytes, $flags, $callback->($status)
		618	Sync the data portion of the file specified by $offset and $length
		619	to disk (but NOT the metadata), by calling the Linux-specific
		620	sync_file_range call. If sync_file_range is not available or it
		621	returns ENOSYS, then fdatasync or fsync is being substituted.
		622
		623	$flags can be a combination of
		624	"IO::AIO::SYNC_FILE_RANGE_WAIT_BEFORE",
		625	"IO::AIO::SYNC_FILE_RANGE_WRITE" and
		626	"IO::AIO::SYNC_FILE_RANGE_WAIT_AFTER": refer to the sync_file_range
		627	manpage for details.
		628
		629	aio_pathsync $path, $callback->($status)
		630	This request tries to open, fsync and close the given path. This is
		631	a composite request intended to sync directories after directory
		632	operations (E.g. rename). This might not work on all operating
		633	systems or have any specific effect, but usually it makes sure that
		634	directory changes get written to disc. It works for anything that
		635	can be opened for read-only, not just directories.
		636
		637	Future versions of this function might fall back to other methods
		638	when "fsync" on the directory fails (such as calling "sync").
		639
		640	Passes 0 when everything went ok, and -1 on error.
		641
		642	aio_msync $scalar, $offset = 0, $length = undef, flags = 0,
		643	$callback->($status)
		644	This is a rather advanced IO::AIO call, which only works on
		645	mmap(2)ed scalars (see the Sys::Mmap or Mmap modules for details on
		646	this, note that the scalar must only be modified in-place while an
		647	aio operation is pending on it).
		648
		649	It calls the "msync" function of your OS, if available, with the
		650	memory area starting at $offset in the string and ending $length
		651	bytes later. If $length is negative, counts from the end, and if
		652	$length is "undef", then it goes till the end of the string. The
		653	flags can be a combination of "IO::AIO::MS_ASYNC",
		654	"IO::AIO::MS_INVALIDATE" and "IO::AIO::MS_SYNC".
		655
		656	aio_mtouch $scalar, $offset = 0, $length = undef, flags = 0,
		657	$callback->($status)
		658	This is a rather advanced IO::AIO call, which works best on
		659	mmap(2)ed scalars.
		660
		661	It touches (reads or writes) all memory pages in the specified range
		662	inside the scalar. All caveats and parameters are the same as for
		663	"aio_msync", above, except for flags, which must be either 0 (which
		664	reads all pages and ensures they are instantiated) or
		665	"IO::AIO::MT_MODIFY", which modifies the memory page s(by reading
		666	and writing an octet from it, which dirties the page).
		667
		668	aio_group $callback->(...)
		669	This is a very special aio request: Instead of doing something, it
		670	is a container for other aio requests, which is useful if you want
		671	to bundle many requests into a single, composite, request with a
		672	definite callback and the ability to cancel the whole request with
		673	its subrequests.
		674
		675	Returns an object of class IO::AIO::GRP. See its documentation below
		676	for more info.
		677
		678	Example:
		679
		680	my $grp = aio_group sub {
		681	print "all stats done\n";
		682	};
		683
		684	add $grp
		685	(aio_stat ...),
		686	(aio_stat ...),
		687	...;
		688
		689	aio_nop $callback->()
		690	This is a special request - it does nothing in itself and is only
		691	used for side effects, such as when you want to add a dummy request
		692	to a group so that finishing the requests in the group depends on
		693	executing the given code.
		694
		695	While this request does nothing, it still goes through the execution
		696	phase and still requires a worker thread. Thus, the callback will
		697	not be executed immediately but only after other requests in the
		698	queue have entered their execution phase. This can be used to
		699	measure request latency.
		700
		701	IO::AIO::aio_busy $fractional_seconds, $callback->() NOT EXPORTED
		702	Mainly used for debugging and benchmarking, this aio request puts
		703	one of the request workers to sleep for the given time.
		704
		705	While it is theoretically handy to have simple I/O scheduling
		706	requests like sleep and file handle readable/writable, the overhead
		707	this creates is immense (it blocks a thread for a long time) so do
		708	not use this function except to put your application under
		709	artificial I/O pressure.
		710
		711	IO::AIO::REQ CLASS
		712	All non-aggregate "aio_*" functions return an object of this class when
		713	called in non-void context.
		714
		715	cancel $req
		716	Cancels the request, if possible. Has the effect of skipping
		717	execution when entering the execute state and skipping calling the
		718	callback when entering the the result state, but will leave the
		719	request otherwise untouched (with the exception of readdir). That
		720	means that requests that currently execute will not be stopped and
		721	resources held by the request will not be freed prematurely.
		722
		723	cb $req $callback->(...)
		724	Replace (or simply set) the callback registered to the request.
		725
		726	IO::AIO::GRP CLASS
		727	This class is a subclass of IO::AIO::REQ, so all its methods apply to
		728	objects of this class, too.
		729
		730	A IO::AIO::GRP object is a special request that can contain multiple
		731	other aio requests.
		732
		733	You create one by calling the "aio_group" constructing function with a
		734	callback that will be called when all contained requests have entered
		735	the "done" state:
		736
		737	my $grp = aio_group sub {
		738	print "all requests are done\n";
		739	};
		740
		741	You add requests by calling the "add" method with one or more
		742	"IO::AIO::REQ" objects:
		743
		744	$grp->add (aio_unlink "...");
		745
		746	add $grp aio_stat "...", sub {
		747	$_[0] or return $grp->result ("error");
		748
		749	# add another request dynamically, if first succeeded
		750	add $grp aio_open "...", sub {
		751	$grp->result ("ok");
		752	};
		753	};
		754
		755	This makes it very easy to create composite requests (see the source of
		756	"aio_move" for an application) that work and feel like simple requests.
		757
		758	* The IO::AIO::GRP objects will be cleaned up during calls to
		759	"IO::AIO::poll_cb", just like any other request.
		760
		761	* They can be canceled like any other request. Canceling will cancel
		762	not only the request itself, but also all requests it contains.
		763
		764	* They can also can also be added to other IO::AIO::GRP objects.
		765
		766	* You must not add requests to a group from within the group callback
		767	(or any later time).
		768
		769	Their lifetime, simplified, looks like this: when they are empty, they
		770	will finish very quickly. If they contain only requests that are in the
		771	"done" state, they will also finish. Otherwise they will continue to
		772	exist.
		773
		774	That means after creating a group you have some time to add requests
		775	(precisely before the callback has been invoked, which is only done
		776	within the "poll_cb"). And in the callbacks of those requests, you can
		777	add further requests to the group. And only when all those requests have
		778	finished will the the group itself finish.
		779
		780	add $grp ...
		781	$grp->add (...)
		782	Add one or more requests to the group. Any type of IO::AIO::REQ can
		783	be added, including other groups, as long as you do not create
		784	circular dependencies.
		785
		786	Returns all its arguments.
		787
		788	$grp->cancel_subs
		789	Cancel all subrequests and clears any feeder, but not the group
		790	request itself. Useful when you queued a lot of events but got a
		791	result early.
		792
		793	The group request will finish normally (you cannot add requests to
		794	the group).
		795
		796	$grp->result (...)
		797	Set the result value(s) that will be passed to the group callback
		798	when all subrequests have finished and set the groups errno to the
		799	current value of errno (just like calling "errno" without an error
		800	number). By default, no argument will be passed and errno is zero.
		801
		802	$grp->errno ([$errno])
		803	Sets the group errno value to $errno, or the current value of errno
		804	when the argument is missing.
		805
		806	Every aio request has an associated errno value that is restored
		807	when the callback is invoked. This method lets you change this value
		808	from its default (0).
		809
		810	Calling "result" will also set errno, so make sure you either set $!
		811	before the call to "result", or call c<errno> after it.
		812
		813	feed $grp $callback->($grp)
		814	Sets a feeder/generator on this group: every group can have an
		815	attached generator that generates requests if idle. The idea behind
		816	this is that, although you could just queue as many requests as you
		817	want in a group, this might starve other requests for a potentially
		818	long time. For example, "aio_scandir" might generate hundreds of
		819	thousands "aio_stat" requests, delaying any later requests for a
		820	long time.
		821
		822	To avoid this, and allow incremental generation of requests, you can
		823	instead a group and set a feeder on it that generates those
		824	requests. The feed callback will be called whenever there are few
		825	enough (see "limit", below) requests active in the group itself and
		826	is expected to queue more requests.
		827
		828	The feed callback can queue as many requests as it likes (i.e. "add"
		829	does not impose any limits).
		830
		831	If the feed does not queue more requests when called, it will be
		832	automatically removed from the group.
		833
		834	If the feed limit is 0 when this method is called, it will be set to
		835	2 automatically.
		836
		837	Example:
		838
		839	# stat all files in @files, but only ever use four aio requests concurrently:
		840
		841	my $grp = aio_group sub { print "finished\n" };
		842	limit $grp 4;
		843	feed $grp sub {
		844	my $file = pop @files
		845	or return;
		846
		847	add $grp aio_stat $file, sub { ... };
		848	};
		849
		850	limit $grp $num
		851	Sets the feeder limit for the group: The feeder will be called
		852	whenever the group contains less than this many requests.
		853
		854	Setting the limit to 0 will pause the feeding process.
		855
		856	The default value for the limit is 0, but note that setting a feeder
		857	automatically bumps it up to 2.
172		858
173	SUPPORT FUNCTIONS	859	SUPPORT FUNCTIONS
		860	EVENT PROCESSING AND EVENT LOOP INTEGRATION
174	$fileno = IO::AIO::poll_fileno	861	$fileno = IO::AIO::poll_fileno
175	Return the request result pipe file descriptor. This filehandle	862	Return the request result pipe file descriptor. This filehandle
176	must be polled for reading by some mechanism outside this module	863	must be polled for reading by some mechanism outside this module
177	(e.g. Event or select, see below or the SYNOPSIS). If the pipe	864	(e.g. EV, Glib, select and so on, see below or the SYNOPSIS). If the
178	becomes readable you have to call "poll_cb" to check the results.	865	pipe becomes readable you have to call "poll_cb" to check the
		866	results.
179		867
180	See "poll_cb" for an example.	868	See "poll_cb" for an example.
181		869
182	IO::AIO::poll_cb	870	IO::AIO::poll_cb
183	Process all outstanding events on the result pipe. You have to call	871	Process some outstanding events on the result pipe. You have to call
184	this regularly. Returns the number of events processed. Returns	872	this regularly. Returns 0 if all events could be processed, or -1 if
185	immediately when no events are outstanding.	873	it returned earlier for whatever reason. Returns immediately when no
		874	events are outstanding. The amount of events processed depends on
		875	the settings of "IO::AIO::max_poll_req" and
		876	"IO::AIO::max_poll_time".
		877
		878	If not all requests were processed for whatever reason, the
		879	filehandle will still be ready when "poll_cb" returns, so normally
		880	you don't have to do anything special to have it called later.
186		881
187	Example: Install an Event watcher that automatically calls	882	Example: Install an Event watcher that automatically calls
188	IO::AIO::poll_cb with high priority:	883	IO::AIO::poll_cb with high priority (more examples can be found in
		884	the SYNOPSIS section, at the top of this document):
189		885
190	Event->io (fd => IO::AIO::poll_fileno,	886	Event->io (fd => IO::AIO::poll_fileno,
191	poll => 'r', async => 1,	887	poll => 'r', async => 1,
192	cb => \&IO::AIO::poll_cb);	888	cb => \&IO::AIO::poll_cb);
193		889
		890	IO::AIO::max_poll_reqs $nreqs
		891	IO::AIO::max_poll_time $seconds
		892	These set the maximum number of requests (default 0, meaning
		893	infinity) that are being processed by "IO::AIO::poll_cb" in one
		894	call, respectively the maximum amount of time (default 0, meaning
		895	infinity) spent in "IO::AIO::poll_cb" to process requests (more
		896	correctly the mininum amount of time "poll_cb" is allowed to use).
		897
		898	Setting "max_poll_time" to a non-zero value creates an overhead of
		899	one syscall per request processed, which is not normally a problem
		900	unless your callbacks are really really fast or your OS is really
		901	really slow (I am not mentioning Solaris here). Using
		902	"max_poll_reqs" incurs no overhead.
		903
		904	Setting these is useful if you want to ensure some level of
		905	interactiveness when perl is not fast enough to process all requests
		906	in time.
		907
		908	For interactive programs, values such as 0.01 to 0.1 should be fine.
		909
		910	Example: Install an Event watcher that automatically calls
		911	IO::AIO::poll_cb with low priority, to ensure that other parts of
		912	the program get the CPU sometimes even under high AIO load.
		913
		914	# try not to spend much more than 0.1s in poll_cb
		915	IO::AIO::max_poll_time 0.1;
		916
		917	# use a low priority so other tasks have priority
		918	Event->io (fd => IO::AIO::poll_fileno,
		919	poll => 'r', nice => 1,
		920	cb => &IO::AIO::poll_cb);
		921
194	IO::AIO::poll_wait	922	IO::AIO::poll_wait
		923	If there are any outstanding requests and none of them in the result
195	Wait till the result filehandle becomes ready for reading (simply	924	phase, wait till the result filehandle becomes ready for reading
196	does a "select" on the filehandle. This is useful if you want to	925	(simply does a "select" on the filehandle. This is useful if you
197	synchronously wait for some requests to finish).	926	want to synchronously wait for some requests to finish).
198		927
199	See "nreqs" for an example.	928	See "nreqs" for an example.
200		929
		930	IO::AIO::poll
		931	Waits until some requests have been handled.
		932
		933	Returns the number of requests processed, but is otherwise strictly
		934	equivalent to:
		935
		936	IO::AIO::poll_wait, IO::AIO::poll_cb
		937
201	IO::AIO::nreqs	938	IO::AIO::flush
202	Returns the number of requests currently outstanding (i.e. for which	939	Wait till all outstanding AIO requests have been handled.
203	their callback has not been invoked yet).
204		940
205	Example: wait till there are no outstanding requests anymore:	941	Strictly equivalent to:
206		942
207	IO::AIO::poll_wait, IO::AIO::poll_cb	943	IO::AIO::poll_wait, IO::AIO::poll_cb
208	while IO::AIO::nreqs;	944	while IO::AIO::nreqs;
209		945
210	IO::AIO::flush	946	CONTROLLING THE NUMBER OF THREADS
211	Wait till all outstanding AIO requests have been handled.
212
213	Strictly equivalent to:
214
215	IO::AIO::poll_wait, IO::AIO::poll_cb
216	while IO::AIO::nreqs;
217
218	IO::AIO::poll
219	Waits until some requests have been handled.
220
221	Strictly equivalent to:
222
223	IO::AIO::poll_wait, IO::AIO::poll_cb
224	if IO::AIO::nreqs;
225
226	IO::AIO::min_parallel $nthreads	947	IO::AIO::min_parallel $nthreads
227	Set the minimum number of AIO threads to $nthreads. The default is	948	Set the minimum number of AIO threads to $nthreads. The current
228	1, which means a single asynchronous operation can be done at one	949	default is 8, which means eight asynchronous operations can execute
229	time (the number of outstanding operations, however, is unlimited).	950	concurrently at any one time (the number of outstanding requests,
		951	however, is unlimited).
230		952
		953	IO::AIO starts threads only on demand, when an AIO request is queued
		954	and no free thread exists. Please note that queueing up a hundred
		955	requests can create demand for a hundred threads, even if it turns
		956	out that everything is in the cache and could have been processed
		957	faster by a single thread.
		958
231	It is recommended to keep the number of threads low, as some Linux	959	It is recommended to keep the number of threads relatively low, as
232	kernel versions will scale negatively with the number of threads	960	some Linux kernel versions will scale negatively with the number of
233	(higher parallelity => MUCH higher latency). With current Linux 2.6	961	threads (higher parallelity => MUCH higher latency). With current
234	versions, 4-32 threads should be fine.	962	Linux 2.6 versions, 4-32 threads should be fine.
235		963
236	Under normal circumstances you don't need to call this function, as	964	Under most circumstances you don't need to call this function, as
237	this module automatically starts some threads (the exact number	965	the module selects a default that is suitable for low to moderate
238	might change, and is currently 4).	966	load.
239		967
240	IO::AIO::max_parallel $nthreads	968	IO::AIO::max_parallel $nthreads
241	Sets the maximum number of AIO threads to $nthreads. If more than	969	Sets the maximum number of AIO threads to $nthreads. If more than
242	the specified number of threads are currently running, kill them.	970	the specified number of threads are currently running, this function
243	This function blocks until the limit is reached.	971	kills them. This function blocks until the limit is reached.
		972
		973	While $nthreads are zero, aio requests get queued but not executed
		974	until the number of threads has been increased again.
244		975
245	This module automatically runs "max_parallel 0" at program end, to	976	This module automatically runs "max_parallel 0" at program end, to
246	ensure that all threads are killed and that there are no outstanding	977	ensure that all threads are killed and that there are no outstanding
247	requests.	978	requests.
248		979
249	Under normal circumstances you don't need to call this function.	980	Under normal circumstances you don't need to call this function.
250		981
		982	IO::AIO::max_idle $nthreads
		983	Limit the number of threads (default: 4) that are allowed to idle
		984	(i.e., threads that did not get a request to process within 10
		985	seconds). That means if a thread becomes idle while $nthreads other
		986	threads are also idle, it will free its resources and exit.
		987
		988	This is useful when you allow a large number of threads (e.g. 100 or
		989	1000) to allow for extremely high load situations, but want to free
		990	resources under normal circumstances (1000 threads can easily
		991	consume 30MB of RAM).
		992
		993	The default is probably ok in most situations, especially if thread
		994	creation is fast. If thread creation is very slow on your system you
		995	might want to use larger values.
		996
251	$oldnreqs = IO::AIO::max_outstanding $nreqs	997	IO::AIO::max_outstanding $maxreqs
		998	This is a very bad function to use in interactive programs because
		999	it blocks, and a bad way to reduce concurrency because it is
		1000	inexact: Better use an "aio_group" together with a feed callback.
		1001
252	Sets the maximum number of outstanding requests to $nreqs. If you	1002	Sets the maximum number of outstanding requests to $nreqs. If you do
253	try to queue up more than this number of requests, the caller will	1003	queue up more than this number of requests, the next call to the
254	block until some requests have been handled.	1004	"poll_cb" (and "poll_some" and other functions calling "poll_cb")
		1005	function will block until the limit is no longer exceeded.
255		1006
256	The default is very large, so normally there is no practical limit.	1007	The default value is very large, so there is no practical limit on
257	If you queue up many requests in a loop it it often improves speed	1008	the number of outstanding requests.
258	if you set this to a relatively low number, such as 100.
259		1009
260	Under normal circumstances you don't need to call this function.	1010	You can still queue as many requests as you want. Therefore,
		1011	"max_outstanding" is mainly useful in simple scripts (with low
		1012	values) or as a stop gap to shield against fatal memory overflow
		1013	(with large values).
		1014
		1015	STATISTICAL INFORMATION
		1016	IO::AIO::nreqs
		1017	Returns the number of requests currently in the ready, execute or
		1018	pending states (i.e. for which their callback has not been invoked
		1019	yet).
		1020
		1021	Example: wait till there are no outstanding requests anymore:
		1022
		1023	IO::AIO::poll_wait, IO::AIO::poll_cb
		1024	while IO::AIO::nreqs;
		1025
		1026	IO::AIO::nready
		1027	Returns the number of requests currently in the ready state (not yet
		1028	executed).
		1029
		1030	IO::AIO::npending
		1031	Returns the number of requests currently in the pending state
		1032	(executed, but not yet processed by poll_cb).
		1033
		1034	MISCELLANEOUS FUNCTIONS
		1035	IO::AIO implements some functions that might be useful, but are not
		1036	asynchronous.
		1037
		1038	IO::AIO::sendfile $ofh, $ifh, $offset, $count
		1039	Calls the "eio_sendfile_sync" function, which is like
		1040	"aio_sendfile", but is blocking (this makes most sense if you know
		1041	the input data is likely cached already and the output filehandle is
		1042	set to non-blocking operations).
		1043
		1044	Returns the number of bytes copied, or -1 on error.
		1045
		1046	IO::AIO::fadvise $fh, $offset, $len, $advice
		1047	Simply calls the "posix_fadvise" function (see it's manpage for
		1048	details). The following advice constants are avaiable:
		1049	"IO::AIO::FADV_NORMAL", "IO::AIO::FADV_SEQUENTIAL",
		1050	"IO::AIO::FADV_RANDOM", "IO::AIO::FADV_NOREUSE",
		1051	"IO::AIO::FADV_WILLNEED", "IO::AIO::FADV_DONTNEED".
		1052
		1053	On systems that do not implement "posix_fadvise", this function
		1054	returns ENOSYS, otherwise the return value of "posix_fadvise".
		1055
		1056	FORK BEHAVIOUR
		1057	This module should do "the right thing" when the process using it forks:
		1058
		1059	Before the fork, IO::AIO enters a quiescent state where no requests can
		1060	be added in other threads and no results will be processed. After the
		1061	fork the parent simply leaves the quiescent state and continues
		1062	request/result processing, while the child frees the request/result
		1063	queue (so that the requests started before the fork will only be handled
		1064	in the parent). Threads will be started on demand until the limit set in
		1065	the parent process has been reached again.
		1066
		1067	In short: the parent will, after a short pause, continue as if fork had
		1068	not been called, while the child will act as if IO::AIO has not been
		1069	used yet.
		1070
		1071	MEMORY USAGE
		1072	Per-request usage:
		1073
		1074	Each aio request uses - depending on your architecture - around 100-200
		1075	bytes of memory. In addition, stat requests need a stat buffer (possibly
		1076	a few hundred bytes), readdir requires a result buffer and so on. Perl
		1077	scalars and other data passed into aio requests will also be locked and
		1078	will consume memory till the request has entered the done state.
		1079
		1080	This is not awfully much, so queuing lots of requests is not usually a
		1081	problem.
		1082
		1083	Per-thread usage:
		1084
		1085	In the execution phase, some aio requests require more memory for
		1086	temporary buffers, and each thread requires a stack and other data
		1087	structures (usually around 16k-128k, depending on the OS).
		1088
		1089	KNOWN BUGS
		1090	Known bugs will be fixed in the next release.
261		1091
262	SEE ALSO	1092	SEE ALSO
263	Coro, Linux::AIO.	1093	AnyEvent::AIO for easy integration into event loops, Coro::AIO for a
		1094	more natural syntax.
264		1095
265	AUTHOR	1096	AUTHOR
266	Marc Lehmann <schmorp@schmorp.de>	1097	Marc Lehmann <schmorp@schmorp.de>
267	http://home.schmorp.de/	1098	http://home.schmorp.de/
268		1099

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Revision 1.8 by root, Sun Jul 31 17:24:05 2005 UTC vs.
Revision 1.41 by root, Sat Jan 2 14:24:32 2010 UTC