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

Comparing IO-AIO/README (file contents):
Revision 1.11 by root, Sat Aug 20 00:32:42 2005 UTC vs.
Revision 1.39 by root, Wed Aug 5 11:53:16 2009 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 pathnames you pass to these routines must be absolute and encoded	188	The pathnames you pass to these routines must be absolute and encoded
68	in byte form. The reason for the former is that at the time the request	189	as octets. The reason for the former is that at the time the request is
69	is being executed, the current working directory could have changed.	190	being executed, the current working directory could have changed.
70	Alternatively, you can make sure that you never change the current	191	Alternatively, you can make sure that you never change the current
71	working directory.	192	working directory anywhere in the program and then use relative paths.
72		193
73	To encode pathnames to byte form, either make sure you either: a) always	194	To encode pathnames as octets, either make sure you either: a) always
74	pass in filenames you got from outside (command line, readdir etc.), b)	195	pass in filenames you got from outside (command line, readdir etc.)
75	are ASCII or ISO 8859-1, c) use the Encode module and encode your	196	without tinkering, b) are ASCII or ISO 8859-1, c) use the Encode module
76	pathnames to the locale (or other) encoding in effect in the user	197	and encode your pathnames to the locale (or other) encoding in effect in
77	environment, d) use Glib::filename_from_unicode on unicode filenames or	198	the user environment, d) use Glib::filename_from_unicode on unicode
78	e) use something else.	199	filenames or e) use something else to ensure your scalar has the correct
		200	contents.
79		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
80	aio_open $pathname, $flags, $mode, $callback	234	aio_open $pathname, $flags, $mode, $callback->($fh)
81	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
82	newly created filehandle for the file.	236	newly created filehandle for the file.
83		237
84	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,
85	above, for an explanation.	239	above, for an explanation.
…		…
88	They are the same as used by "sysopen".	242	They are the same as used by "sysopen".
89		243
90	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
91	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
92	"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
93	create new files, and 0666 or 0777 if you do).	247	create new files, and 0666 or 0777 if you do). Note that the $mode
		248	will be modified by the umask in effect then the request is being
		249	executed, so better never change the umask.
94		250
95	Example:	251	Example:
96		252
97	aio_open "/etc/passwd", O_RDONLY, 0, sub {	253	aio_open "/etc/passwd", O_RDONLY, 0, sub {
98	if ($_[0]) {	254	if ($_[0]) {
…		…
101	} else {	257	} else {
102	die "open failed: $!\n";	258	die "open failed: $!\n";
103	}	259	}
104	};	260	};
105		261
106	aio_close $fh, $callback	262	aio_close $fh, $callback->($status)
107	Asynchronously close a file and call the callback with the result	263	Asynchronously close a file and call the callback with the result
108	code. WARNING: although accepted, you should not pass in a perl	264	code.
109	filehandle here, as perl will likely close the file descriptor
110	another time when the filehandle is destroyed. Normally, you can
111	safely call perls "close" or just let filehandles go out of scope.
112		265
113	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
114	therefore best to avoid this function.	267	strongly on closing the file descriptor associated with the
		268	filehandle itself.
115		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
116	aio_read $fh,$offset,$length, $data,$dataoffset,$callback	277	aio_read $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
117	aio_write $fh,$offset,$length, $data,$dataoffset,$callback	278	aio_write $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
118	Reads or writes "length" bytes from the specified "fh" and "offset"	279	Reads or writes $length bytes from or to the specified $fh and
119	into the scalar given by "data" and offset "dataoffset" and calls	280	$offset into the scalar given by $data and offset $dataoffset and
120	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
121	error, just like the syscall).	282	error, just like the syscall).
122		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
123	The $data scalar MUST NOT be modified in any way while the request	297	The $data scalar MUST NOT be modified in any way while the request
124	is outstanding. Modifying it can result in segfaults or WW3 (if the	298	is outstanding. Modifying it can result in segfaults or World War
125	necessary/optional hardware is installed).	299	III (if the necessary/optional hardware is installed).
126		300
127	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
128	offset 0 within the scalar:	302	offset 0 within the scalar:
129		303
130	aio_read $fh, 7, 15, $buffer, 0, sub {	304	aio_read $fh, 7, 15, $buffer, 0, sub {
131	$_[0] > 0 or die "read error: $!";	305	$_[0] > 0 or die "read error: $!";
132	print "read $_[0] bytes: <$buffer>\n";	306	print "read $_[0] bytes: <$buffer>\n";
133	};	307	};
134		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 the native sendfile call fails or is not implemented, it will be
		321	emulated, so you can call "aio_sendfile" on any type of filehandle
		322	regardless of the limitations of the operating system.
		323
		324	Please note, however, that "aio_sendfile" can read more bytes from
		325	$in_fh than are written, and there is no way to find out how many
		326	bytes have been read from "aio_sendfile" alone, as "aio_sendfile"
		327	only provides the number of bytes written to $out_fh. Only if the
		328	result value equals $length one can assume that $length bytes have
		329	been read.
		330
135	aio_readahead $fh,$offset,$length, $callback	331	aio_readahead $fh,$offset,$length, $callback->($retval)
136	"aio_readahead" populates the page cache with data from a file so	332	"aio_readahead" populates the page cache with data from a file so
137	that subsequent reads from that file will not block on disk I/O. The	333	that subsequent reads from that file will not block on disk I/O. The
138	$offset argument specifies the starting point from which data is to	334	$offset argument specifies the starting point from which data is to
139	be read and $length specifies the number of bytes to be read. I/O is	335	be read and $length specifies the number of bytes to be read. I/O is
140	performed in whole pages, so that offset is effectively rounded down	336	performed in whole pages, so that offset is effectively rounded down
…		…
145		341
146	If that syscall doesn't exist (likely if your OS isn't Linux) it	342	If that syscall doesn't exist (likely if your OS isn't Linux) it
147	will be emulated by simply reading the data, which would have a	343	will be emulated by simply reading the data, which would have a
148	similar effect.	344	similar effect.
149		345
150	aio_stat $fh_or_path, $callback	346	aio_stat $fh_or_path, $callback->($status)
151	aio_lstat $fh, $callback	347	aio_lstat $fh, $callback->($status)
152	Works like perl's "stat" or "lstat" in void context. The callback	348	Works like perl's "stat" or "lstat" in void context. The callback
153	will be called after the stat and the results will be available	349	will be called after the stat and the results will be available
154	using "stat _" or "-s _" etc...	350	using "stat _" or "-s _" etc...
155		351
156	The pathname passed to "aio_stat" must be absolute. See API NOTES,	352	The pathname passed to "aio_stat" must be absolute. See API NOTES,
…		…
166	aio_stat "/etc/passwd", sub {	362	aio_stat "/etc/passwd", sub {
167	$_[0] and die "stat failed: $!";	363	$_[0] and die "stat failed: $!";
168	print "size is ", -s _, "\n";	364	print "size is ", -s _, "\n";
169	};	365	};
170		366
		367	aio_utime $fh_or_path, $atime, $mtime, $callback->($status)
		368	Works like perl's "utime" function (including the special case of
		369	$atime and $mtime being undef). Fractional times are supported if
		370	the underlying syscalls support them.
		371
		372	When called with a pathname, uses utimes(2) if available, otherwise
		373	utime(2). If called on a file descriptor, uses futimes(2) if
		374	available, otherwise returns ENOSYS, so this is not portable.
		375
		376	Examples:
		377
		378	# set atime and mtime to current time (basically touch(1)):
		379	aio_utime "path", undef, undef;
		380	# set atime to current time and mtime to beginning of the epoch:
		381	aio_utime "path", time, undef; # undef==0
		382
		383	aio_chown $fh_or_path, $uid, $gid, $callback->($status)
		384	Works like perl's "chown" function, except that "undef" for either
		385	$uid or $gid is being interpreted as "do not change" (but -1 can
		386	also be used).
		387
		388	Examples:
		389
		390	# same as "chown root path" in the shell:
		391	aio_chown "path", 0, -1;
		392	# same as above:
		393	aio_chown "path", 0, undef;
		394
		395	aio_truncate $fh_or_path, $offset, $callback->($status)
		396	Works like truncate(2) or ftruncate(2).
		397
		398	aio_chmod $fh_or_path, $mode, $callback->($status)
		399	Works like perl's "chmod" function.
		400
171	aio_unlink $pathname, $callback	401	aio_unlink $pathname, $callback->($status)
172	Asynchronously unlink (delete) a file and call the callback with the	402	Asynchronously unlink (delete) a file and call the callback with the
173	result code.	403	result code.
174		404
		405	aio_mknod $path, $mode, $dev, $callback->($status)
		406	[EXPERIMENTAL]
		407
		408	Asynchronously create a device node (or fifo). See mknod(2).
		409
		410	The only (POSIX-) portable way of calling this function is:
		411
		412	aio_mknod $path, IO::AIO::S_IFIFO \| $mode, 0, sub { ...
		413
		414	aio_link $srcpath, $dstpath, $callback->($status)
		415	Asynchronously create a new link to the existing object at $srcpath
		416	at the path $dstpath and call the callback with the result code.
		417
		418	aio_symlink $srcpath, $dstpath, $callback->($status)
		419	Asynchronously create a new symbolic link to the existing object at
		420	$srcpath at the path $dstpath and call the callback with the result
		421	code.
		422
		423	aio_readlink $path, $callback->($link)
		424	Asynchronously read the symlink specified by $path and pass it to
		425	the callback. If an error occurs, nothing or undef gets passed to
		426	the callback.
		427
		428	aio_rename $srcpath, $dstpath, $callback->($status)
		429	Asynchronously rename the object at $srcpath to $dstpath, just as
		430	rename(2) and call the callback with the result code.
		431
		432	aio_mkdir $pathname, $mode, $callback->($status)
		433	Asynchronously mkdir (create) a directory and call the callback with
		434	the result code. $mode will be modified by the umask at the time the
		435	request is executed, so do not change your umask.
		436
175	aio_rmdir $pathname, $callback	437	aio_rmdir $pathname, $callback->($status)
176	Asynchronously rmdir (delete) a directory and call the callback with	438	Asynchronously rmdir (delete) a directory and call the callback with
177	the result code.	439	the result code.
178		440
		441	aio_readdir $pathname, $callback->($entries)
		442	Unlike the POSIX call of the same name, "aio_readdir" reads an
		443	entire directory (i.e. opendir + readdir + closedir). The entries
		444	will not be sorted, and will NOT include the "." and ".." entries.
		445
		446	The callback is passed a single argument which is either "undef" or
		447	an array-ref with the filenames.
		448
		449	aio_readdirx $pathname, $flags, $callback->($entries, $flags)
		450	Quite similar to "aio_readdir", but the $flags argument allows to
		451	tune behaviour and output format. In case of an error, $entries will
		452	be "undef".
		453
		454	The flags are a combination of the following constants, ORed
		455	together (the flags will also be passed to the callback, possibly
		456	modified):
		457
		458	IO::AIO::READDIR_DENTS
		459	When this flag is off, then the callback gets an arrayref with
		460	of names only (as with "aio_readdir"), otherwise it gets an
		461	arrayref with "[$name, $type, $inode]" arrayrefs, each
		462	describing a single directory entry in more detail.
		463
		464	$name is the name of the entry.
		465
		466	$type is one of the "IO::AIO::DT_xxx" constants:
		467
		468	"IO::AIO::DT_UNKNOWN", "IO::AIO::DT_FIFO", "IO::AIO::DT_CHR",
		469	"IO::AIO::DT_DIR", "IO::AIO::DT_BLK", "IO::AIO::DT_REG",
		470	"IO::AIO::DT_LNK", "IO::AIO::DT_SOCK", "IO::AIO::DT_WHT".
		471
		472	"IO::AIO::DT_UNKNOWN" means just that: readdir does not know. If
		473	you need to know, you have to run stat yourself. Also, for speed
		474	reasons, the $type scalars are read-only: you can not modify
		475	them.
		476
		477	$inode is the inode number (which might not be exact on systems
		478	with 64 bit inode numbers and 32 bit perls). This field has
		479	unspecified content on systems that do not deliver the inode
		480	information.
		481
		482	IO::AIO::READDIR_DIRS_FIRST
		483	When this flag is set, then the names will be returned in an
		484	order where likely directories come first. This is useful when
		485	you need to quickly find directories, or you want to find all
		486	directories while avoiding to stat() each entry.
		487
		488	If the system returns type information in readdir, then this is
		489	used to find directories directly. Otherwise, likely directories
		490	are files beginning with ".", or otherwise files with no dots,
		491	of which files with short names are tried first.
		492
		493	IO::AIO::READDIR_STAT_ORDER
		494	When this flag is set, then the names will be returned in an
		495	order suitable for stat()'ing each one. That is, when you plan
		496	to stat() all files in the given directory, then the returned
		497	order will likely be fastest.
		498
		499	If both this flag and "IO::AIO::READDIR_DIRS_FIRST" are
		500	specified, then the likely dirs come first, resulting in a less
		501	optimal stat order.
		502
		503	IO::AIO::READDIR_FOUND_UNKNOWN
		504	This flag should not be set when calling "aio_readdirx".
		505	Instead, it is being set by "aio_readdirx", when any of the
		506	$type's found were "IO::AIO::DT_UNKNOWN". The absense of this
		507	flag therefore indicates that all $type's are known, which can
		508	be used to speed up some algorithms.
		509
		510	aio_load $path, $data, $callback->($status)
		511	This is a composite request that tries to fully load the given file
		512	into memory. Status is the same as with aio_read.
		513
		514	aio_copy $srcpath, $dstpath, $callback->($status)
		515	Try to copy the file (directories not supported as either source
		516	or destination) from $srcpath to $dstpath and call the callback with
		517	the 0 (error) or -1 ok.
		518
		519	This is a composite request that creates the destination file with
		520	mode 0200 and copies the contents of the source file into it using
		521	"aio_sendfile", followed by restoring atime, mtime, access mode and
		522	uid/gid, in that order.
		523
		524	If an error occurs, the partial destination file will be unlinked,
		525	if possible, except when setting atime, mtime, access mode and
		526	uid/gid, where errors are being ignored.
		527
		528	aio_move $srcpath, $dstpath, $callback->($status)
		529	Try to move the file (directories not supported as either source
		530	or destination) from $srcpath to $dstpath and call the callback with
		531	the 0 (error) or -1 ok.
		532
		533	This is a composite request that tries to rename(2) the file first;
		534	if rename fails with "EXDEV", it copies the file with "aio_copy"
		535	and, if that is successful, unlinks the $srcpath.
		536
		537	aio_scandir $path, $maxreq, $callback->($dirs, $nondirs)
		538	Scans a directory (similar to "aio_readdir") but additionally tries
		539	to efficiently separate the entries of directory $path into two sets
		540	of names, directories you can recurse into (directories), and ones
		541	you cannot recurse into (everything else, including symlinks to
		542	directories).
		543
		544	"aio_scandir" is a composite request that creates of many sub
		545	requests_ $maxreq specifies the maximum number of outstanding aio
		546	requests that this function generates. If it is "<= 0", then a
		547	suitable default will be chosen (currently 4).
		548
		549	On error, the callback is called without arguments, otherwise it
		550	receives two array-refs with path-relative entry names.
		551
		552	Example:
		553
		554	aio_scandir $dir, 0, sub {
		555	my ($dirs, $nondirs) = @_;
		556	print "real directories: @$dirs\n";
		557	print "everything else: @$nondirs\n";
		558	};
		559
		560	Implementation notes.
		561
		562	The "aio_readdir" cannot be avoided, but "stat()"'ing every entry
		563	can.
		564
		565	If readdir returns file type information, then this is used directly
		566	to find directories.
		567
		568	Otherwise, after reading the directory, the modification time, size
		569	etc. of the directory before and after the readdir is checked, and
		570	if they match (and isn't the current time), the link count will be
		571	used to decide how many entries are directories (if >= 2).
		572	Otherwise, no knowledge of the number of subdirectories will be
		573	assumed.
		574
		575	Then entries will be sorted into likely directories a non-initial
		576	dot currently) and likely non-directories (see "aio_readdirx"). Then
		577	every entry plus an appended "/." will be "stat"'ed, likely
		578	directories first, in order of their inode numbers. If that
		579	succeeds, it assumes that the entry is a directory or a symlink to
		580	directory (which will be checked seperately). This is often faster
		581	than stat'ing the entry itself because filesystems might detect the
		582	type of the entry without reading the inode data (e.g. ext2fs
		583	filetype feature), even on systems that cannot return the filetype
		584	information on readdir.
		585
		586	If the known number of directories (link count - 2) has been
		587	reached, the rest of the entries is assumed to be non-directories.
		588
		589	This only works with certainty on POSIX (= UNIX) filesystems, which
		590	fortunately are the vast majority of filesystems around.
		591
		592	It will also likely work on non-POSIX filesystems with reduced
		593	efficiency as those tend to return 0 or 1 as link counts, which
		594	disables the directory counting heuristic.
		595
		596	aio_rmtree $path, $callback->($status)
		597	Delete a directory tree starting (and including) $path, return the
		598	status of the final "rmdir" only. This is a composite request that
		599	uses "aio_scandir" to recurse into and rmdir directories, and unlink
		600	everything else.
		601
		602	aio_sync $callback->($status)
		603	Asynchronously call sync and call the callback when finished.
		604
179	aio_fsync $fh, $callback	605	aio_fsync $fh, $callback->($status)
180	Asynchronously call fsync on the given filehandle and call the	606	Asynchronously call fsync on the given filehandle and call the
181	callback with the fsync result code.	607	callback with the fsync result code.
182		608
183	aio_fdatasync $fh, $callback	609	aio_fdatasync $fh, $callback->($status)
184	Asynchronously call fdatasync on the given filehandle and call the	610	Asynchronously call fdatasync on the given filehandle and call the
185	callback with the fdatasync result code.	611	callback with the fdatasync result code.
186		612
187	If this call isn't available because your OS lacks it or it couldn't	613	If this call isn't available because your OS lacks it or it couldn't
188	be detected, it will be emulated by calling "fsync" instead.	614	be detected, it will be emulated by calling "fsync" instead.
189		615
		616	aio_sync_file_range $fh, $offset, $nbytes, $flags, $callback->($status)
		617	Sync the data portion of the file specified by $offset and $length
		618	to disk (but NOT the metadata), by calling the Linux-specific
		619	sync_file_range call. If sync_file_range is not available or it
		620	returns ENOSYS, then fdatasync or fsync is being substituted.
		621
		622	$flags can be a combination of
		623	"IO::AIO::SYNC_FILE_RANGE_WAIT_BEFORE",
		624	"IO::AIO::SYNC_FILE_RANGE_WRITE" and
		625	"IO::AIO::SYNC_FILE_RANGE_WAIT_AFTER": refer to the sync_file_range
		626	manpage for details.
		627
		628	aio_pathsync $path, $callback->($status)
		629	This request tries to open, fsync and close the given path. This is
		630	a composite request intended to sync directories after directory
		631	operations (E.g. rename). This might not work on all operating
		632	systems or have any specific effect, but usually it makes sure that
		633	directory changes get written to disc. It works for anything that
		634	can be opened for read-only, not just directories.
		635
		636	Future versions of this function might fall back to other methods
		637	when "fsync" on the directory fails (such as calling "sync").
		638
		639	Passes 0 when everything went ok, and -1 on error.
		640
		641	aio_group $callback->(...)
		642	This is a very special aio request: Instead of doing something, it
		643	is a container for other aio requests, which is useful if you want
		644	to bundle many requests into a single, composite, request with a
		645	definite callback and the ability to cancel the whole request with
		646	its subrequests.
		647
		648	Returns an object of class IO::AIO::GRP. See its documentation below
		649	for more info.
		650
		651	Example:
		652
		653	my $grp = aio_group sub {
		654	print "all stats done\n";
		655	};
		656
		657	add $grp
		658	(aio_stat ...),
		659	(aio_stat ...),
		660	...;
		661
		662	aio_nop $callback->()
		663	This is a special request - it does nothing in itself and is only
		664	used for side effects, such as when you want to add a dummy request
		665	to a group so that finishing the requests in the group depends on
		666	executing the given code.
		667
		668	While this request does nothing, it still goes through the execution
		669	phase and still requires a worker thread. Thus, the callback will
		670	not be executed immediately but only after other requests in the
		671	queue have entered their execution phase. This can be used to
		672	measure request latency.
		673
		674	IO::AIO::aio_busy $fractional_seconds, $callback->() NOT EXPORTED
		675	Mainly used for debugging and benchmarking, this aio request puts
		676	one of the request workers to sleep for the given time.
		677
		678	While it is theoretically handy to have simple I/O scheduling
		679	requests like sleep and file handle readable/writable, the overhead
		680	this creates is immense (it blocks a thread for a long time) so do
		681	not use this function except to put your application under
		682	artificial I/O pressure.
		683
		684	IO::AIO::REQ CLASS
		685	All non-aggregate "aio_*" functions return an object of this class when
		686	called in non-void context.
		687
		688	cancel $req
		689	Cancels the request, if possible. Has the effect of skipping
		690	execution when entering the execute state and skipping calling the
		691	callback when entering the the result state, but will leave the
		692	request otherwise untouched (with the exception of readdir). That
		693	means that requests that currently execute will not be stopped and
		694	resources held by the request will not be freed prematurely.
		695
		696	cb $req $callback->(...)
		697	Replace (or simply set) the callback registered to the request.
		698
		699	IO::AIO::GRP CLASS
		700	This class is a subclass of IO::AIO::REQ, so all its methods apply to
		701	objects of this class, too.
		702
		703	A IO::AIO::GRP object is a special request that can contain multiple
		704	other aio requests.
		705
		706	You create one by calling the "aio_group" constructing function with a
		707	callback that will be called when all contained requests have entered
		708	the "done" state:
		709
		710	my $grp = aio_group sub {
		711	print "all requests are done\n";
		712	};
		713
		714	You add requests by calling the "add" method with one or more
		715	"IO::AIO::REQ" objects:
		716
		717	$grp->add (aio_unlink "...");
		718
		719	add $grp aio_stat "...", sub {
		720	$_[0] or return $grp->result ("error");
		721
		722	# add another request dynamically, if first succeeded
		723	add $grp aio_open "...", sub {
		724	$grp->result ("ok");
		725	};
		726	};
		727
		728	This makes it very easy to create composite requests (see the source of
		729	"aio_move" for an application) that work and feel like simple requests.
		730
		731	* The IO::AIO::GRP objects will be cleaned up during calls to
		732	"IO::AIO::poll_cb", just like any other request.
		733
		734	* They can be canceled like any other request. Canceling will cancel
		735	not only the request itself, but also all requests it contains.
		736
		737	* They can also can also be added to other IO::AIO::GRP objects.
		738
		739	* You must not add requests to a group from within the group callback
		740	(or any later time).
		741
		742	Their lifetime, simplified, looks like this: when they are empty, they
		743	will finish very quickly. If they contain only requests that are in the
		744	"done" state, they will also finish. Otherwise they will continue to
		745	exist.
		746
		747	That means after creating a group you have some time to add requests
		748	(precisely before the callback has been invoked, which is only done
		749	within the "poll_cb"). And in the callbacks of those requests, you can
		750	add further requests to the group. And only when all those requests have
		751	finished will the the group itself finish.
		752
		753	add $grp ...
		754	$grp->add (...)
		755	Add one or more requests to the group. Any type of IO::AIO::REQ can
		756	be added, including other groups, as long as you do not create
		757	circular dependencies.
		758
		759	Returns all its arguments.
		760
		761	$grp->cancel_subs
		762	Cancel all subrequests and clears any feeder, but not the group
		763	request itself. Useful when you queued a lot of events but got a
		764	result early.
		765
		766	$grp->result (...)
		767	Set the result value(s) that will be passed to the group callback
		768	when all subrequests have finished and set the groups errno to the
		769	current value of errno (just like calling "errno" without an error
		770	number). By default, no argument will be passed and errno is zero.
		771
		772	$grp->errno ([$errno])
		773	Sets the group errno value to $errno, or the current value of errno
		774	when the argument is missing.
		775
		776	Every aio request has an associated errno value that is restored
		777	when the callback is invoked. This method lets you change this value
		778	from its default (0).
		779
		780	Calling "result" will also set errno, so make sure you either set $!
		781	before the call to "result", or call c<errno> after it.
		782
		783	feed $grp $callback->($grp)
		784	Sets a feeder/generator on this group: every group can have an
		785	attached generator that generates requests if idle. The idea behind
		786	this is that, although you could just queue as many requests as you
		787	want in a group, this might starve other requests for a potentially
		788	long time. For example, "aio_scandir" might generate hundreds of
		789	thousands "aio_stat" requests, delaying any later requests for a
		790	long time.
		791
		792	To avoid this, and allow incremental generation of requests, you can
		793	instead a group and set a feeder on it that generates those
		794	requests. The feed callback will be called whenever there are few
		795	enough (see "limit", below) requests active in the group itself and
		796	is expected to queue more requests.
		797
		798	The feed callback can queue as many requests as it likes (i.e. "add"
		799	does not impose any limits).
		800
		801	If the feed does not queue more requests when called, it will be
		802	automatically removed from the group.
		803
		804	If the feed limit is 0 when this method is called, it will be set to
		805	2 automatically.
		806
		807	Example:
		808
		809	# stat all files in @files, but only ever use four aio requests concurrently:
		810
		811	my $grp = aio_group sub { print "finished\n" };
		812	limit $grp 4;
		813	feed $grp sub {
		814	my $file = pop @files
		815	or return;
		816
		817	add $grp aio_stat $file, sub { ... };
		818	};
		819
		820	limit $grp $num
		821	Sets the feeder limit for the group: The feeder will be called
		822	whenever the group contains less than this many requests.
		823
		824	Setting the limit to 0 will pause the feeding process.
		825
		826	The default value for the limit is 0, but note that setting a feeder
		827	automatically bumps it up to 2.
		828
190	SUPPORT FUNCTIONS	829	SUPPORT FUNCTIONS
		830	EVENT PROCESSING AND EVENT LOOP INTEGRATION
191	$fileno = IO::AIO::poll_fileno	831	$fileno = IO::AIO::poll_fileno
192	Return the request result pipe file descriptor. This filehandle	832	Return the request result pipe file descriptor. This filehandle
193	must be polled for reading by some mechanism outside this module	833	must be polled for reading by some mechanism outside this module
194	(e.g. Event or select, see below or the SYNOPSIS). If the pipe	834	(e.g. EV, Glib, select and so on, see below or the SYNOPSIS). If the
195	becomes readable you have to call "poll_cb" to check the results.	835	pipe becomes readable you have to call "poll_cb" to check the
		836	results.
196		837
197	See "poll_cb" for an example.	838	See "poll_cb" for an example.
198		839
199	IO::AIO::poll_cb	840	IO::AIO::poll_cb
200	Process all outstanding events on the result pipe. You have to call	841	Process some outstanding events on the result pipe. You have to call
201	this regularly. Returns the number of events processed. Returns	842	this regularly. Returns 0 if all events could be processed, or -1 if
202	immediately when no events are outstanding.	843	it returned earlier for whatever reason. Returns immediately when no
		844	events are outstanding. The amount of events processed depends on
		845	the settings of "IO::AIO::max_poll_req" and
		846	"IO::AIO::max_poll_time".
		847
		848	If not all requests were processed for whatever reason, the
		849	filehandle will still be ready when "poll_cb" returns, so normally
		850	you don't have to do anything special to have it called later.
203		851
204	Example: Install an Event watcher that automatically calls	852	Example: Install an Event watcher that automatically calls
205	IO::AIO::poll_cb with high priority:	853	IO::AIO::poll_cb with high priority (more examples can be found in
		854	the SYNOPSIS section, at the top of this document):
206		855
207	Event->io (fd => IO::AIO::poll_fileno,	856	Event->io (fd => IO::AIO::poll_fileno,
208	poll => 'r', async => 1,	857	poll => 'r', async => 1,
209	cb => \&IO::AIO::poll_cb);	858	cb => \&IO::AIO::poll_cb);
210		859
		860	IO::AIO::max_poll_reqs $nreqs
		861	IO::AIO::max_poll_time $seconds
		862	These set the maximum number of requests (default 0, meaning
		863	infinity) that are being processed by "IO::AIO::poll_cb" in one
		864	call, respectively the maximum amount of time (default 0, meaning
		865	infinity) spent in "IO::AIO::poll_cb" to process requests (more
		866	correctly the mininum amount of time "poll_cb" is allowed to use).
		867
		868	Setting "max_poll_time" to a non-zero value creates an overhead of
		869	one syscall per request processed, which is not normally a problem
		870	unless your callbacks are really really fast or your OS is really
		871	really slow (I am not mentioning Solaris here). Using
		872	"max_poll_reqs" incurs no overhead.
		873
		874	Setting these is useful if you want to ensure some level of
		875	interactiveness when perl is not fast enough to process all requests
		876	in time.
		877
		878	For interactive programs, values such as 0.01 to 0.1 should be fine.
		879
		880	Example: Install an Event watcher that automatically calls
		881	IO::AIO::poll_cb with low priority, to ensure that other parts of
		882	the program get the CPU sometimes even under high AIO load.
		883
		884	# try not to spend much more than 0.1s in poll_cb
		885	IO::AIO::max_poll_time 0.1;
		886
		887	# use a low priority so other tasks have priority
		888	Event->io (fd => IO::AIO::poll_fileno,
		889	poll => 'r', nice => 1,
		890	cb => &IO::AIO::poll_cb);
		891
211	IO::AIO::poll_wait	892	IO::AIO::poll_wait
		893	If there are any outstanding requests and none of them in the result
212	Wait till the result filehandle becomes ready for reading (simply	894	phase, wait till the result filehandle becomes ready for reading
213	does a "select" on the filehandle. This is useful if you want to	895	(simply does a "select" on the filehandle. This is useful if you
214	synchronously wait for some requests to finish).	896	want to synchronously wait for some requests to finish).
215		897
216	See "nreqs" for an example.	898	See "nreqs" for an example.
217		899
		900	IO::AIO::poll
		901	Waits until some requests have been handled.
		902
		903	Returns the number of requests processed, but is otherwise strictly
		904	equivalent to:
		905
		906	IO::AIO::poll_wait, IO::AIO::poll_cb
		907
218	IO::AIO::nreqs	908	IO::AIO::flush
219	Returns the number of requests currently outstanding (i.e. for which	909	Wait till all outstanding AIO requests have been handled.
220	their callback has not been invoked yet).
221		910
222	Example: wait till there are no outstanding requests anymore:	911	Strictly equivalent to:
223		912
224	IO::AIO::poll_wait, IO::AIO::poll_cb	913	IO::AIO::poll_wait, IO::AIO::poll_cb
225	while IO::AIO::nreqs;	914	while IO::AIO::nreqs;
226		915
227	IO::AIO::flush	916	CONTROLLING THE NUMBER OF THREADS
228	Wait till all outstanding AIO requests have been handled.
229
230	Strictly equivalent to:
231
232	IO::AIO::poll_wait, IO::AIO::poll_cb
233	while IO::AIO::nreqs;
234
235	IO::AIO::poll
236	Waits until some requests have been handled.
237
238	Strictly equivalent to:
239
240	IO::AIO::poll_wait, IO::AIO::poll_cb
241	if IO::AIO::nreqs;
242
243	IO::AIO::min_parallel $nthreads	917	IO::AIO::min_parallel $nthreads
244	Set the minimum number of AIO threads to $nthreads. The current	918	Set the minimum number of AIO threads to $nthreads. The current
245	default is 4, which means four asynchronous operations can be done	919	default is 8, which means eight asynchronous operations can execute
246	at one time (the number of outstanding operations, however, is	920	concurrently at any one time (the number of outstanding requests,
247	unlimited).	921	however, is unlimited).
248		922
249	IO::AIO starts threads only on demand, when an AIO request is queued	923	IO::AIO starts threads only on demand, when an AIO request is queued
250	and no free thread exists.	924	and no free thread exists. Please note that queueing up a hundred
		925	requests can create demand for a hundred threads, even if it turns
		926	out that everything is in the cache and could have been processed
		927	faster by a single thread.
251		928
252	It is recommended to keep the number of threads low, as some Linux	929	It is recommended to keep the number of threads relatively low, as
253	kernel versions will scale negatively with the number of threads	930	some Linux kernel versions will scale negatively with the number of
254	(higher parallelity => MUCH higher latency). With current Linux 2.6	931	threads (higher parallelity => MUCH higher latency). With current
255	versions, 4-32 threads should be fine.	932	Linux 2.6 versions, 4-32 threads should be fine.
256		933
257	Under most circumstances you don't need to call this function, as	934	Under most circumstances you don't need to call this function, as
258	the module selects a default that is suitable for low to moderate	935	the module selects a default that is suitable for low to moderate
259	load.	936	load.
260		937
…		…
270	ensure that all threads are killed and that there are no outstanding	947	ensure that all threads are killed and that there are no outstanding
271	requests.	948	requests.
272		949
273	Under normal circumstances you don't need to call this function.	950	Under normal circumstances you don't need to call this function.
274		951
		952	IO::AIO::max_idle $nthreads
		953	Limit the number of threads (default: 4) that are allowed to idle
		954	(i.e., threads that did not get a request to process within 10
		955	seconds). That means if a thread becomes idle while $nthreads other
		956	threads are also idle, it will free its resources and exit.
		957
		958	This is useful when you allow a large number of threads (e.g. 100 or
		959	1000) to allow for extremely high load situations, but want to free
		960	resources under normal circumstances (1000 threads can easily
		961	consume 30MB of RAM).
		962
		963	The default is probably ok in most situations, especially if thread
		964	creation is fast. If thread creation is very slow on your system you
		965	might want to use larger values.
		966
275	$oldnreqs = IO::AIO::max_outstanding $nreqs	967	IO::AIO::max_outstanding $maxreqs
		968	This is a very bad function to use in interactive programs because
		969	it blocks, and a bad way to reduce concurrency because it is
		970	inexact: Better use an "aio_group" together with a feed callback.
		971
276	Sets the maximum number of outstanding requests to $nreqs. If you	972	Sets the maximum number of outstanding requests to $nreqs. If you do
277	try to queue up more than this number of requests, the caller will	973	queue up more than this number of requests, the next call to the
278	block until some requests have been handled.	974	"poll_cb" (and "poll_some" and other functions calling "poll_cb")
		975	function will block until the limit is no longer exceeded.
279		976
280	The default is very large, so normally there is no practical limit.	977	The default value is very large, so there is no practical limit on
281	If you queue up many requests in a loop it often improves speed if	978	the number of outstanding requests.
282	you set this to a relatively low number, such as 100.
283		979
284	Under normal circumstances you don't need to call this function.	980	You can still queue as many requests as you want. Therefore,
		981	"max_outstanding" is mainly useful in simple scripts (with low
		982	values) or as a stop gap to shield against fatal memory overflow
		983	(with large values).
		984
		985	STATISTICAL INFORMATION
		986	IO::AIO::nreqs
		987	Returns the number of requests currently in the ready, execute or
		988	pending states (i.e. for which their callback has not been invoked
		989	yet).
		990
		991	Example: wait till there are no outstanding requests anymore:
		992
		993	IO::AIO::poll_wait, IO::AIO::poll_cb
		994	while IO::AIO::nreqs;
		995
		996	IO::AIO::nready
		997	Returns the number of requests currently in the ready state (not yet
		998	executed).
		999
		1000	IO::AIO::npending
		1001	Returns the number of requests currently in the pending state
		1002	(executed, but not yet processed by poll_cb).
		1003
		1004	MISCELLANEOUS FUNCTIONS
		1005	IO::AIO implements some functions that might be useful, but are not
		1006	asynchronous.
		1007
		1008	IO::AIO::sendfile $ofh, $ifh, $offset, $count
		1009	Calls the "eio_sendfile_sync" function, which is like
		1010	"aio_sendfile", but is blocking (this makes most sense if you know
		1011	the input data is likely cached already and the output filehandle is
		1012	set to non-blocking operations).
		1013
		1014	Returns the number of bytes copied, or -1 on error.
		1015
		1016	IO::AIO::fadvise $fh, $offset, $len, $advice
		1017	Simply calls the "posix_fadvise" function (see it's manpage for
		1018	details). The following advice constants are avaiable:
		1019	"IO::AIO::FADV_NORMAL", "IO::AIO::FADV_SEQUENTIAL",
		1020	"IO::AIO::FADV_RANDOM", "IO::AIO::FADV_NOREUSE",
		1021	"IO::AIO::FADV_WILLNEED", "IO::AIO::FADV_DONTNEED".
		1022
		1023	On systems that do not implement "posix_fadvise", this function
		1024	returns ENOSYS, otherwise the return value of "posix_fadvise".
285		1025
286	FORK BEHAVIOUR	1026	FORK BEHAVIOUR
		1027	This module should do "the right thing" when the process using it forks:
		1028
287	Before the fork, IO::AIO enters a quiescent state where no requests can	1029	Before the fork, IO::AIO enters a quiescent state where no requests can
288	be added in other threads and no results will be processed. After the	1030	be added in other threads and no results will be processed. After the
289	fork the parent simply leaves the quiescent state and continues	1031	fork the parent simply leaves the quiescent state and continues
290	request/result processing, while the child clears the request/result	1032	request/result processing, while the child frees the request/result
291	queue (so the requests started before the fork will only be handled in	1033	queue (so that the requests started before the fork will only be handled
292	the parent). Threats will be started on demand until the limit ste in	1034	in the parent). Threads will be started on demand until the limit set in
293	the parent process has been reached again.	1035	the parent process has been reached again.
294		1036
		1037	In short: the parent will, after a short pause, continue as if fork had
		1038	not been called, while the child will act as if IO::AIO has not been
		1039	used yet.
		1040
		1041	MEMORY USAGE
		1042	Per-request usage:
		1043
		1044	Each aio request uses - depending on your architecture - around 100-200
		1045	bytes of memory. In addition, stat requests need a stat buffer (possibly
		1046	a few hundred bytes), readdir requires a result buffer and so on. Perl
		1047	scalars and other data passed into aio requests will also be locked and
		1048	will consume memory till the request has entered the done state.
		1049
		1050	This is not awfully much, so queuing lots of requests is not usually a
		1051	problem.
		1052
		1053	Per-thread usage:
		1054
		1055	In the execution phase, some aio requests require more memory for
		1056	temporary buffers, and each thread requires a stack and other data
		1057	structures (usually around 16k-128k, depending on the OS).
		1058
		1059	KNOWN BUGS
		1060	Known bugs will be fixed in the next release.
		1061
295	SEE ALSO	1062	SEE ALSO
296	Coro, Linux::AIO.	1063	AnyEvent::AIO for easy integration into event loops, Coro::AIO for a
		1064	more natural syntax.
297		1065
298	AUTHOR	1066	AUTHOR
299	Marc Lehmann <schmorp@schmorp.de>	1067	Marc Lehmann <schmorp@schmorp.de>
300	http://home.schmorp.de/	1068	http://home.schmorp.de/
301		1069

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Revision 1.11 by root, Sat Aug 20 00:32:42 2005 UTC vs.
Revision 1.39 by root, Wed Aug 5 11:53:16 2009 UTC