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

Comparing IO-AIO/README (file contents):
Revision 1.4 by root, Sun Jul 10 21:04:46 2005 UTC vs.
Revision 1.22 by root, Sat Jan 6 02:47:11 2007 UTC

…		…
1	NAME	1	NAME
2	IO::AIO - Asynchronous Input/Output	2	IO::AIO - Asynchronous Input/Output
3		3
4	SYNOPSIS	4	SYNOPSIS
5	use IO::AIO;	5	use IO::AIO;
		6
		7	aio_open "/etc/passwd", O_RDONLY, 0, sub {
		8	my $fh = shift
		9	or die "/etc/passwd: $!";
		10	...
		11	};
		12
		13	aio_unlink "/tmp/file", sub { };
		14
		15	aio_read $fh, 30000, 1024, $buffer, 0, sub {
		16	$_[0] > 0 or die "read error: $!";
		17	};
		18
		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
		30	open my $fh, "<&=" . IO::AIO::poll_fileno or die "$!";
		31	my $w = AnyEvent->io (fh => $fh, poll => 'r', cb => sub { IO::AIO::poll_cb });
		32
		33	# Event integration
		34	Event->io (fd => IO::AIO::poll_fileno,
		35	poll => 'r',
		36	cb => \&IO::AIO::poll_cb);
		37
		38	# Glib/Gtk2 integration
		39	add_watch Glib::IO IO::AIO::poll_fileno,
		40	in => sub { IO::AIO::poll_cb; 1 };
		41
		42	# Tk integration
		43	Tk::Event::IO->fileevent (IO::AIO::poll_fileno, "",
		44	readable => \&IO::AIO::poll_cb);
		45
		46	# Danga::Socket integration
		47	Danga::Socket->AddOtherFds (IO::AIO::poll_fileno =>
		48	\&IO::AIO::poll_cb);
6		49
7	DESCRIPTION	50	DESCRIPTION
8	This module implements asynchronous I/O using whatever means your	51	This module implements asynchronous I/O using whatever means your
9	operating system supports.	52	operating system supports.
10		53
		54	Asynchronous means that operations that can normally block your program
		55	(e.g. reading from disk) will be done asynchronously: the operation will
		56	still block, but you can do something else in the meantime. This is
		57	extremely useful for programs that need to stay interactive even when
		58	doing heavy I/O (GUI programs, high performance network servers etc.),
		59	but can also be used to easily do operations in parallel that are
		60	normally done sequentially, e.g. stat'ing many files, which is much
		61	faster on a RAID volume or over NFS when you do a number of stat
		62	operations concurrently.
		63
		64	While most of this works on all types of file descriptors (for example
		65	sockets), using these functions on file descriptors that support
		66	nonblocking operation (again, sockets, pipes etc.) is very inefficient
		67	or might not work (aio_read fails on sockets/pipes/fifos). Use an event
		68	loop for that (such as the Event module): IO::AIO will naturally fit
		69	into such an event loop itself.
		70
11	Currently, a number of threads are started that execute your read/writes	71	In this version, a number of threads are started that execute your
12	and signal their completion. You don't need thread support in your libc	72	requests and signal their completion. You don't need thread support in
13	or perl, and the threads created by this module will not be visible to	73	perl, and the threads created by this module will not be visible to
14	the pthreads library. In the future, this module might make use of the	74	perl. In the future, this module might make use of the native aio
15	native aio functions available on many operating systems. However, they	75	functions available on many operating systems. However, they are often
16	are often not well-supported (Linux doesn't allow them on normal files	76	not well-supported or restricted (GNU/Linux doesn't allow them on normal
17	currently, for example), and they would only support aio_read and	77	files currently, for example), and they would only support aio_read and
18	aio_write, so the remaining functionality would have to be implemented	78	aio_write, so the remaining functionality would have to be implemented
19	using threads anyway.	79	using threads anyway.
20		80
21	Although the module will work with in the presence of other threads, it	81	Although the module will work with in the presence of other (Perl-)
22	is currently not reentrant, so use appropriate locking yourself.	82	threads, it is currently not reentrant in any way, so use appropriate
		83	locking yourself, always call "poll_cb" from within the same thread, or
		84	never call "poll_cb" (or other "aio_" functions) recursively.
		85
		86	EXAMPLE
		87	This is a simple example that uses the Event module and loads
		88	/etc/passwd asynchronously:
		89
		90	use Fcntl;
		91	use Event;
		92	use IO::AIO;
		93
		94	# register the IO::AIO callback with Event
		95	Event->io (fd => IO::AIO::poll_fileno,
		96	poll => 'r',
		97	cb => \&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	Event::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	Event::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).
23		171
24	FUNCTIONS	172	FUNCTIONS
25	AIO FUNCTIONS	173	AIO REQUEST FUNCTIONS
26	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
27	with the same name (sans "aio_"). The arguments are similar or	175	with the same name (sans "aio_"). The arguments are similar or
28	identical, and they all accept an additional $callback argument which	176	identical, and they all accept an additional (and optional) $callback
29	must be a code reference. This code reference will get called with the	177	argument which must be a code reference. This code reference will get
30	syscall return code (e.g. most syscalls return -1 on error, unlike perl,	178	called with the syscall return code (e.g. most syscalls return -1 on
31	which usually delivers "false") as it's sole argument when the given	179	error, unlike perl, which usually delivers "false") as it's sole
32	syscall has been executed asynchronously.	180	argument when the given syscall has been executed asynchronously.
33		181
34	All functions that expect a filehandle will also accept a file	182	All functions expecting a filehandle keep a copy of the filehandle
35	descriptor.	183	internally until the request has finished.
36		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
37	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
38	is that at the time the request is being executed, the current working	189	as octets. The reason for the former is that at the time the request is
39	directory could have changed. Alternatively, you can make sure that you	190	being executed, the current working directory could have changed.
40	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.
41		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 wether 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
42	aio_open $pathname, $flags, $mode, $callback	234	aio_open $pathname, $flags, $mode, $callback->($fh)
43	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
44	newly created filehandle for the file.	236	newly created filehandle for the file.
45		237
46	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,
47	above, for an explanation.	239	above, for an explanation.
48		240
49	The $mode argument is a bitmask. See the "Fcntl" module for a list.	241	The $flags argument is a bitmask. See the "Fcntl" module for a list.
50	They are the same as used in "sysopen".	242	They are the same as used by "sysopen".
		243
		244	Likewise, $mode specifies the mode of the newly created file, if it
		245	didn't exist and "O_CREAT" has been given, just like perl's
		246	"sysopen", except that it is mandatory (i.e. use 0 if you don't
		247	create new files, and 0666 or 0777 if you do).
51		248
52	Example:	249	Example:
53		250
54	aio_open "/etc/passwd", O_RDONLY, 0, sub {	251	aio_open "/etc/passwd", O_RDONLY, 0, sub {
55	if ($_[0]) {	252	if ($_[0]) {
58	} else {	255	} else {
59	die "open failed: $!\n";	256	die "open failed: $!\n";
60	}	257	}
61	};	258	};
62		259
63	aio_close $fh, $callback	260	aio_close $fh, $callback->($status)
64	Asynchronously close a file and call the callback with the result	261	Asynchronously close a file and call the callback with the result
65	code. WARNING: although accepted, you should not pass in a perl	262	code. WARNING: although accepted, you should not pass in a perl
66	filehandle here, as perl will likely close the file descriptor	263	filehandle here, as perl will likely close the file descriptor
67	itself when the filehandle is destroyed. Normally, you can safely	264	another time when the filehandle is destroyed. Normally, you can
68	call perls "close" or just let filehandles go out of scope.	265	safely call perls "close" or just let filehandles go out of scope.
69		266
		267	This is supposed to be a bug in the API, so that might change. It's
		268	therefore best to avoid this function.
		269
70	aio_read $fh,$offset,$length, $data,$dataoffset,$callback	270	aio_read $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
71	aio_write $fh,$offset,$length, $data,$dataoffset,$callback	271	aio_write $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
72	Reads or writes "length" bytes from the specified "fh" and "offset"	272	Reads or writes "length" bytes from the specified "fh" and "offset"
73	into the scalar given by "data" and offset "dataoffset" and calls	273	into the scalar given by "data" and offset "dataoffset" and calls
74	the callback without the actual number of bytes read (or -1 on	274	the callback without the actual number of bytes read (or -1 on
75	error, just like the syscall).	275	error, just like the syscall).
76		276
		277	The $data scalar MUST NOT be modified in any way while the request
		278	is outstanding. Modifying it can result in segfaults or WW3 (if the
		279	necessary/optional hardware is installed).
		280
77	Example: Read 15 bytes at offset 7 into scalar $buffer, strating at	281	Example: Read 15 bytes at offset 7 into scalar $buffer, starting at
78	offset 0 within the scalar:	282	offset 0 within the scalar:
79		283
80	aio_read $fh, 7, 15, $buffer, 0, sub {	284	aio_read $fh, 7, 15, $buffer, 0, sub {
81	$_[0] >= 0 or die "read error: $!";	285	$_[0] > 0 or die "read error: $!";
82	print "read <$buffer>\n";	286	print "read $_[0] bytes: <$buffer>\n";
83	};	287	};
84		288
		289	aio_sendfile $out_fh, $in_fh, $in_offset, $length, $callback->($retval)
		290	Tries to copy $length bytes from $in_fh to $out_fh. It starts
		291	reading at byte offset $in_offset, and starts writing at the current
		292	file offset of $out_fh. Because of that, it is not safe to issue
		293	more than one "aio_sendfile" per $out_fh, as they will interfere
		294	with each other.
		295
		296	This call tries to make use of a native "sendfile" syscall to
		297	provide zero-copy operation. For this to work, $out_fh should refer
		298	to a socket, and $in_fh should refer to mmap'able file.
		299
		300	If the native sendfile call fails or is not implemented, it will be
		301	emulated, so you can call "aio_sendfile" on any type of filehandle
		302	regardless of the limitations of the operating system.
		303
		304	Please note, however, that "aio_sendfile" can read more bytes from
		305	$in_fh than are written, and there is no way to find out how many
		306	bytes have been read from "aio_sendfile" alone, as "aio_sendfile"
		307	only provides the number of bytes written to $out_fh. Only if the
		308	result value equals $length one can assume that $length bytes have
		309	been read.
		310
85	aio_readahead $fh,$offset,$length, $callback	311	aio_readahead $fh,$offset,$length, $callback->($retval)
86	Asynchronously reads the specified byte range into the page cache,
87	using the "readahead" syscall. If that syscall doesn't exist the
88	status will be -1 and $! is set to ENOSYS.
89
90	readahead() populates the page cache with data from a file so that	312	"aio_readahead" populates the page cache with data from a file so
91	subsequent reads from that file will not block on disk I/O. The	313	that subsequent reads from that file will not block on disk I/O. The
92	$offset argument specifies the starting point from which data is to	314	$offset argument specifies the starting point from which data is to
93	be read and $length specifies the number of bytes to be read. I/O is	315	be read and $length specifies the number of bytes to be read. I/O is
94	performed in whole pages, so that offset is effectively rounded down	316	performed in whole pages, so that offset is effectively rounded down
95	to a page boundary and bytes are read up to the next page boundary	317	to a page boundary and bytes are read up to the next page boundary
96	greater than or equal to (off-set+length). aio_readahead() does not	318	greater than or equal to (off-set+length). "aio_readahead" does not
97	read beyond the end of the file. The current file offset of the file	319	read beyond the end of the file. The current file offset of the file
98	is left unchanged.	320	is left unchanged.
99		321
		322	If that syscall doesn't exist (likely if your OS isn't Linux) it
		323	will be emulated by simply reading the data, which would have a
		324	similar effect.
		325
100	aio_stat $fh_or_path, $callback	326	aio_stat $fh_or_path, $callback->($status)
101	aio_lstat $fh, $callback	327	aio_lstat $fh, $callback->($status)
102	Works like perl's "stat" or "lstat" in void context. The callback	328	Works like perl's "stat" or "lstat" in void context. The callback
103	will be called after the stat and the results will be available	329	will be called after the stat and the results will be available
104	using "stat _" or "-s _" etc...	330	using "stat _" or "-s _" etc...
105		331
106	The pathname passed to "aio_stat" must be absolute. See API NOTES,	332	The pathname passed to "aio_stat" must be absolute. See API NOTES,
…		…
116	aio_stat "/etc/passwd", sub {	342	aio_stat "/etc/passwd", sub {
117	$_[0] and die "stat failed: $!";	343	$_[0] and die "stat failed: $!";
118	print "size is ", -s _, "\n";	344	print "size is ", -s _, "\n";
119	};	345	};
120		346
121	aio_unlink $pathname, $callback	347	aio_unlink $pathname, $callback->($status)
122	Asynchronously unlink (delete) a file and call the callback with the	348	Asynchronously unlink (delete) a file and call the callback with the
123	result code.	349	result code.
124		350
		351	aio_mknod $path, $mode, $dev, $callback->($status)
		352	[EXPERIMENTAL]
		353
		354	Asynchronously create a device node (or fifo). See mknod(2).
		355
		356	The only (POSIX-) portable way of calling this function is:
		357
		358	aio_mknod $path, IO::AIO::S_IFIFO \| $mode, 0, sub { ...
		359
		360	aio_link $srcpath, $dstpath, $callback->($status)
		361	Asynchronously create a new link to the existing object at $srcpath
		362	at the path $dstpath and call the callback with the result code.
		363
		364	aio_symlink $srcpath, $dstpath, $callback->($status)
		365	Asynchronously create a new symbolic link to the existing object at
		366	$srcpath at the path $dstpath and call the callback with the result
		367	code.
		368
		369	aio_readlink $path, $callback->($link)
		370	Asynchronously read the symlink specified by $path and pass it to
		371	the callback. If an error occurs, nothing or undef gets passed to
		372	the callback.
		373
		374	aio_rename $srcpath, $dstpath, $callback->($status)
		375	Asynchronously rename the object at $srcpath to $dstpath, just as
		376	rename(2) and call the callback with the result code.
		377
		378	aio_rmdir $pathname, $callback->($status)
		379	Asynchronously rmdir (delete) a directory and call the callback with
		380	the result code.
		381
		382	aio_readdir $pathname, $callback->($entries)
		383	Unlike the POSIX call of the same name, "aio_readdir" reads an
		384	entire directory (i.e. opendir + readdir + closedir). The entries
		385	will not be sorted, and will NOT include the "." and ".." entries.
		386
		387	The callback a single argument which is either "undef" or an
		388	array-ref with the filenames.
		389
		390	aio_load $path, $data, $callback->($status)
		391	This is a composite request that tries to fully load the given file
		392	into memory. Status is the same as with aio_read.
		393
		394	aio_copy $srcpath, $dstpath, $callback->($status)
		395	Try to copy the file (directories not supported as either source
		396	or destination) from $srcpath to $dstpath and call the callback with
		397	the 0 (error) or -1 ok.
		398
		399	This is a composite request that it creates the destination file
		400	with mode 0200 and copies the contents of the source file into it
		401	using "aio_sendfile", followed by restoring atime, mtime, access
		402	mode and uid/gid, in that order.
		403
		404	If an error occurs, the partial destination file will be unlinked,
		405	if possible, except when setting atime, mtime, access mode and
		406	uid/gid, where errors are being ignored.
		407
		408	aio_move $srcpath, $dstpath, $callback->($status)
		409	Try to move the file (directories not supported as either source
		410	or destination) from $srcpath to $dstpath and call the callback with
		411	the 0 (error) or -1 ok.
		412
		413	This is a composite request that tries to rename(2) the file first.
		414	If rename files with "EXDEV", it copies the file with "aio_copy"
		415	and, if that is successful, unlinking the $srcpath.
		416
		417	aio_scandir $path, $maxreq, $callback->($dirs, $nondirs)
		418	Scans a directory (similar to "aio_readdir") but additionally tries
		419	to efficiently separate the entries of directory $path into two sets
		420	of names, directories you can recurse into (directories), and ones
		421	you cannot recurse into (everything else, including symlinks to
		422	directories).
		423
		424	"aio_scandir" is a composite request that creates of many sub
		425	requests_ $maxreq specifies the maximum number of outstanding aio
		426	requests that this function generates. If it is "<= 0", then a
		427	suitable default will be chosen (currently 4).
		428
		429	On error, the callback is called without arguments, otherwise it
		430	receives two array-refs with path-relative entry names.
		431
		432	Example:
		433
		434	aio_scandir $dir, 0, sub {
		435	my ($dirs, $nondirs) = @_;
		436	print "real directories: @$dirs\n";
		437	print "everything else: @$nondirs\n";
		438	};
		439
		440	Implementation notes.
		441
		442	The "aio_readdir" cannot be avoided, but "stat()"'ing every entry
		443	can.
		444
		445	After reading the directory, the modification time, size etc. of the
		446	directory before and after the readdir is checked, and if they match
		447	(and isn't the current time), the link count will be used to decide
		448	how many entries are directories (if >= 2). Otherwise, no knowledge
		449	of the number of subdirectories will be assumed.
		450
		451	Then entries will be sorted into likely directories (everything
		452	without a non-initial dot currently) and likely non-directories
		453	(everything else). Then every entry plus an appended "/." will be
		454	"stat"'ed, likely directories first. If that succeeds, it assumes
		455	that the entry is a directory or a symlink to directory (which will
		456	be checked seperately). This is often faster than stat'ing the entry
		457	itself because filesystems might detect the type of the entry
		458	without reading the inode data (e.g. ext2fs filetype feature).
		459
		460	If the known number of directories (link count - 2) has been
		461	reached, the rest of the entries is assumed to be non-directories.
		462
		463	This only works with certainty on POSIX (= UNIX) filesystems, which
		464	fortunately are the vast majority of filesystems around.
		465
		466	It will also likely work on non-POSIX filesystems with reduced
		467	efficiency as those tend to return 0 or 1 as link counts, which
		468	disables the directory counting heuristic.
		469
125	aio_fsync $fh, $callback	470	aio_fsync $fh, $callback->($status)
126	Asynchronously call fsync on the given filehandle and call the	471	Asynchronously call fsync on the given filehandle and call the
127	callback with the fsync result code.	472	callback with the fsync result code.
128		473
129	aio_fdatasync $fh, $callback	474	aio_fdatasync $fh, $callback->($status)
130	Asynchronously call fdatasync on the given filehandle and call the	475	Asynchronously call fdatasync on the given filehandle and call the
131	callback with the fdatasync result code.	476	callback with the fdatasync result code.
132		477
		478	If this call isn't available because your OS lacks it or it couldn't
		479	be detected, it will be emulated by calling "fsync" instead.
		480
		481	aio_group $callback->(...)
		482	This is a very special aio request: Instead of doing something, it
		483	is a container for other aio requests, which is useful if you want
		484	to bundle many requests into a single, composite, request with a
		485	definite callback and the ability to cancel the whole request with
		486	its subrequests.
		487
		488	Returns an object of class IO::AIO::GRP. See its documentation below
		489	for more info.
		490
		491	Example:
		492
		493	my $grp = aio_group sub {
		494	print "all stats done\n";
		495	};
		496
		497	add $grp
		498	(aio_stat ...),
		499	(aio_stat ...),
		500	...;
		501
		502	aio_nop $callback->()
		503	This is a special request - it does nothing in itself and is only
		504	used for side effects, such as when you want to add a dummy request
		505	to a group so that finishing the requests in the group depends on
		506	executing the given code.
		507
		508	While this request does nothing, it still goes through the execution
		509	phase and still requires a worker thread. Thus, the callback will
		510	not be executed immediately but only after other requests in the
		511	queue have entered their execution phase. This can be used to
		512	measure request latency.
		513
		514	IO::AIO::aio_busy $fractional_seconds, $callback->() NOT EXPORTED
		515	Mainly used for debugging and benchmarking, this aio request puts
		516	one of the request workers to sleep for the given time.
		517
		518	While it is theoretically handy to have simple I/O scheduling
		519	requests like sleep and file handle readable/writable, the overhead
		520	this creates is immense (it blocks a thread for a long time) so do
		521	not use this function except to put your application under
		522	artificial I/O pressure.
		523
		524	IO::AIO::REQ CLASS
		525	All non-aggregate "aio_*" functions return an object of this class when
		526	called in non-void context.
		527
		528	cancel $req
		529	Cancels the request, if possible. Has the effect of skipping
		530	execution when entering the execute state and skipping calling the
		531	callback when entering the the result state, but will leave the
		532	request otherwise untouched. That means that requests that currently
		533	execute will not be stopped and resources held by the request will
		534	not be freed prematurely.
		535
		536	cb $req $callback->(...)
		537	Replace (or simply set) the callback registered to the request.
		538
		539	IO::AIO::GRP CLASS
		540	This class is a subclass of IO::AIO::REQ, so all its methods apply to
		541	objects of this class, too.
		542
		543	A IO::AIO::GRP object is a special request that can contain multiple
		544	other aio requests.
		545
		546	You create one by calling the "aio_group" constructing function with a
		547	callback that will be called when all contained requests have entered
		548	the "done" state:
		549
		550	my $grp = aio_group sub {
		551	print "all requests are done\n";
		552	};
		553
		554	You add requests by calling the "add" method with one or more
		555	"IO::AIO::REQ" objects:
		556
		557	$grp->add (aio_unlink "...");
		558
		559	add $grp aio_stat "...", sub {
		560	$_[0] or return $grp->result ("error");
		561
		562	# add another request dynamically, if first succeeded
		563	add $grp aio_open "...", sub {
		564	$grp->result ("ok");
		565	};
		566	};
		567
		568	This makes it very easy to create composite requests (see the source of
		569	"aio_move" for an application) that work and feel like simple requests.
		570
		571	* The IO::AIO::GRP objects will be cleaned up during calls to
		572	"IO::AIO::poll_cb", just like any other request.
		573	* They can be canceled like any other request. Canceling will cancel not
		574	only the request itself, but also all requests it contains.
		575	* They can also can also be added to other IO::AIO::GRP objects.
		576	* You must not add requests to a group from within the group callback
		577	(or any later time).
		578
		579	Their lifetime, simplified, looks like this: when they are empty, they
		580	will finish very quickly. If they contain only requests that are in the
		581	"done" state, they will also finish. Otherwise they will continue to
		582	exist.
		583
		584	That means after creating a group you have some time to add requests.
		585	And in the callbacks of those requests, you can add further requests to
		586	the group. And only when all those requests have finished will the the
		587	group itself finish.
		588
		589	add $grp ...
		590	$grp->add (...)
		591	Add one or more requests to the group. Any type of IO::AIO::REQ can
		592	be added, including other groups, as long as you do not create
		593	circular dependencies.
		594
		595	Returns all its arguments.
		596
		597	$grp->cancel_subs
		598	Cancel all subrequests and clears any feeder, but not the group
		599	request itself. Useful when you queued a lot of events but got a
		600	result early.
		601
		602	$grp->result (...)
		603	Set the result value(s) that will be passed to the group callback
		604	when all subrequests have finished and set thre groups errno to the
		605	current value of errno (just like calling "errno" without an error
		606	number). By default, no argument will be passed and errno is zero.
		607
		608	$grp->errno ([$errno])
		609	Sets the group errno value to $errno, or the current value of errno
		610	when the argument is missing.
		611
		612	Every aio request has an associated errno value that is restored
		613	when the callback is invoked. This method lets you change this value
		614	from its default (0).
		615
		616	Calling "result" will also set errno, so make sure you either set $!
		617	before the call to "result", or call c<errno> after it.
		618
		619	feed $grp $callback->($grp)
		620	Sets a feeder/generator on this group: every group can have an
		621	attached generator that generates requests if idle. The idea behind
		622	this is that, although you could just queue as many requests as you
		623	want in a group, this might starve other requests for a potentially
		624	long time. For example, "aio_scandir" might generate hundreds of
		625	thousands "aio_stat" requests, delaying any later requests for a
		626	long time.
		627
		628	To avoid this, and allow incremental generation of requests, you can
		629	instead a group and set a feeder on it that generates those
		630	requests. The feed callback will be called whenever there are few
		631	enough (see "limit", below) requests active in the group itself and
		632	is expected to queue more requests.
		633
		634	The feed callback can queue as many requests as it likes (i.e. "add"
		635	does not impose any limits).
		636
		637	If the feed does not queue more requests when called, it will be
		638	automatically removed from the group.
		639
		640	If the feed limit is 0, it will be set to 2 automatically.
		641
		642	Example:
		643
		644	# stat all files in @files, but only ever use four aio requests concurrently:
		645
		646	my $grp = aio_group sub { print "finished\n" };
		647	limit $grp 4;
		648	feed $grp sub {
		649	my $file = pop @files
		650	or return;
		651
		652	add $grp aio_stat $file, sub { ... };
		653	};
		654
		655	limit $grp $num
		656	Sets the feeder limit for the group: The feeder will be called
		657	whenever the group contains less than this many requests.
		658
		659	Setting the limit to 0 will pause the feeding process.
		660
133	SUPPORT FUNCTIONS	661	SUPPORT FUNCTIONS
		662	EVENT PROCESSING AND EVENT LOOP INTEGRATION
134	$fileno = IO::AIO::poll_fileno	663	$fileno = IO::AIO::poll_fileno
135	Return the request result pipe filehandle. This filehandle must be	664	Return the request result pipe file descriptor. This filehandle
136	polled for reading by some mechanism outside this module (e.g. Event	665	must be polled for reading by some mechanism outside this module
137	or select, see below). If the pipe becomes readable you have to call	666	(e.g. Event or select, see below or the SYNOPSIS). If the pipe
138	"poll_cb" to check the results.	667	becomes readable you have to call "poll_cb" to check the results.
139		668
140	See "poll_cb" for an example.	669	See "poll_cb" for an example.
141		670
142	IO::AIO::poll_cb	671	IO::AIO::poll_cb
143	Process all outstanding events on the result pipe. You have to call	672	Process some outstanding events on the result pipe. You have to call
144	this regularly. Returns the number of events processed. Returns	673	this regularly. Returns the number of events processed. Returns
145	immediately when no events are outstanding.	674	immediately when no events are outstanding. The amount of events
		675	processed depends on the settings of "IO::AIO::max_poll_req" and
		676	"IO::AIO::max_poll_time".
146		677
147	You can use Event to multiplex, e.g.:	678	If not all requests were processed for whatever reason, the
		679	filehandle will still be ready when "poll_cb" returns.
		680
		681	Example: Install an Event watcher that automatically calls
		682	IO::AIO::poll_cb with high priority:
148		683
149	Event->io (fd => IO::AIO::poll_fileno,	684	Event->io (fd => IO::AIO::poll_fileno,
150	poll => 'r', async => 1,	685	poll => 'r', async => 1,
151	cb => \&IO::AIO::poll_cb);	686	cb => \&IO::AIO::poll_cb);
152		687
		688	IO::AIO::max_poll_reqs $nreqs
		689	IO::AIO::max_poll_time $seconds
		690	These set the maximum number of requests (default 0, meaning
		691	infinity) that are being processed by "IO::AIO::poll_cb" in one
		692	call, respectively the maximum amount of time (default 0, meaning
		693	infinity) spent in "IO::AIO::poll_cb" to process requests (more
		694	correctly the mininum amount of time "poll_cb" is allowed to use).
		695
		696	Setting "max_poll_time" to a non-zero value creates an overhead of
		697	one syscall per request processed, which is not normally a problem
		698	unless your callbacks are really really fast or your OS is really
		699	really slow (I am not mentioning Solaris here). Using
		700	"max_poll_reqs" incurs no overhead.
		701
		702	Setting these is useful if you want to ensure some level of
		703	interactiveness when perl is not fast enough to process all requests
		704	in time.
		705
		706	For interactive programs, values such as 0.01 to 0.1 should be fine.
		707
		708	Example: Install an Event watcher that automatically calls
		709	IO::AIO::poll_cb with low priority, to ensure that other parts of
		710	the program get the CPU sometimes even under high AIO load.
		711
		712	# try not to spend much more than 0.1s in poll_cb
		713	IO::AIO::max_poll_time 0.1;
		714
		715	# use a low priority so other tasks have priority
		716	Event->io (fd => IO::AIO::poll_fileno,
		717	poll => 'r', nice => 1,
		718	cb => &IO::AIO::poll_cb);
		719
153	IO::AIO::poll_wait	720	IO::AIO::poll_wait
		721	If there are any outstanding requests and none of them in the result
154	Wait till the result filehandle becomes ready for reading (simply	722	phase, wait till the result filehandle becomes ready for reading
155	does a select on the filehandle. This is useful if you want to	723	(simply does a "select" on the filehandle. This is useful if you
156	synchronously wait for some requests to finish).	724	want to synchronously wait for some requests to finish).
157		725
158	See "nreqs" for an example.	726	See "nreqs" for an example.
159		727
		728	IO::AIO::poll
		729	Waits until some requests have been handled.
		730
		731	Returns the number of requests processed, but is otherwise strictly
		732	equivalent to:
		733
		734	IO::AIO::poll_wait, IO::AIO::poll_cb
		735
160	IO::AIO::nreqs	736	IO::AIO::flush
161	Returns the number of requests currently outstanding.	737	Wait till all outstanding AIO requests have been handled.
162		738
163	Example: wait till there are no outstanding requests anymore:	739	Strictly equivalent to:
164		740
165	IO::AIO::poll_wait, IO::AIO::poll_cb	741	IO::AIO::poll_wait, IO::AIO::poll_cb
166	while IO::AIO::nreqs;	742	while IO::AIO::nreqs;
167		743
		744	CONTROLLING THE NUMBER OF THREADS
168	IO::AIO::min_parallel $nthreads	745	IO::AIO::min_parallel $nthreads
169	Set the minimum number of AIO threads to $nthreads. The default is	746	Set the minimum number of AIO threads to $nthreads. The current
170	1, which means a single asynchronous operation can be done at one	747	default is 8, which means eight asynchronous operations can execute
171	time (the number of outstanding operations, however, is unlimited).	748	concurrently at any one time (the number of outstanding requests,
		749	however, is unlimited).
172		750
		751	IO::AIO starts threads only on demand, when an AIO request is queued
		752	and no free thread exists. Please note that queueing up a hundred
		753	requests can create demand for a hundred threads, even if it turns
		754	out that everything is in the cache and could have been processed
		755	faster by a single thread.
		756
173	It is recommended to keep the number of threads low, as some Linux	757	It is recommended to keep the number of threads relatively low, as
174	kernel versions will scale negatively with the number of threads	758	some Linux kernel versions will scale negatively with the number of
175	(higher parallelity => MUCH higher latency). With current Linux 2.6	759	threads (higher parallelity => MUCH higher latency). With current
176	versions, 4-32 threads should be fine.	760	Linux 2.6 versions, 4-32 threads should be fine.
177		761
178	Under normal circumstances you don't need to call this function, as	762	Under most circumstances you don't need to call this function, as
179	this module automatically starts some threads (the exact number	763	the module selects a default that is suitable for low to moderate
180	might change, and is currently 4).	764	load.
181		765
182	IO::AIO::max_parallel $nthreads	766	IO::AIO::max_parallel $nthreads
183	Sets the maximum number of AIO threads to $nthreads. If more than	767	Sets the maximum number of AIO threads to $nthreads. If more than
184	the specified number of threads are currently running, kill them.	768	the specified number of threads are currently running, this function
185	This function blocks until the limit is reached.	769	kills them. This function blocks until the limit is reached.
		770
		771	While $nthreads are zero, aio requests get queued but not executed
		772	until the number of threads has been increased again.
186		773
187	This module automatically runs "max_parallel 0" at program end, to	774	This module automatically runs "max_parallel 0" at program end, to
188	ensure that all threads are killed and that there are no outstanding	775	ensure that all threads are killed and that there are no outstanding
189	requests.	776	requests.
190		777
191	Under normal circumstances you don't need to call this function.	778	Under normal circumstances you don't need to call this function.
192		779
		780	IO::AIO::max_idle $nthreads
		781	Limit the number of threads (default: 4) that are allowed to idle
		782	(i.e., threads that did not get a request to process within 10
		783	seconds). That means if a thread becomes idle while $nthreads other
		784	threads are also idle, it will free its resources and exit.
		785
		786	This is useful when you allow a large number of threads (e.g. 100 or
		787	1000) to allow for extremely high load situations, but want to free
		788	resources under normal circumstances (1000 threads can easily
		789	consume 30MB of RAM).
		790
		791	The default is probably ok in most situations, especially if thread
		792	creation is fast. If thread creation is very slow on your system you
		793	might want to use larger values.
		794
193	$oldnreqs = IO::AIO::max_outstanding $nreqs	795	$oldmaxreqs = IO::AIO::max_outstanding $maxreqs
		796	This is a very bad function to use in interactive programs because
		797	it blocks, and a bad way to reduce concurrency because it is
		798	inexact: Better use an "aio_group" together with a feed callback.
		799
194	Sets the maximum number of outstanding requests to $nreqs. If you	800	Sets the maximum number of outstanding requests to $nreqs. If you to
195	try to queue up more than this number of requests, the caller will	801	queue up more than this number of requests, the next call to the
196	block until some requests have been handled.	802	"poll_cb" (and "poll_some" and other functions calling "poll_cb")
		803	function will block until the limit is no longer exceeded.
197		804
198	The default is very large, so normally there is no practical limit.	805	The default value is very large, so there is no practical limit on
199	If you queue up many requests in a loop it it often improves speed	806	the number of outstanding requests.
200	if you set this to a relatively low number, such as 100.
201		807
202	Under normal circumstances you don't need to call this function.	808	You can still queue as many requests as you want. Therefore,
		809	"max_oustsanding" is mainly useful in simple scripts (with low
		810	values) or as a stop gap to shield against fatal memory overflow
		811	(with large values).
		812
		813	STATISTICAL INFORMATION
		814	IO::AIO::nreqs
		815	Returns the number of requests currently in the ready, execute or
		816	pending states (i.e. for which their callback has not been invoked
		817	yet).
		818
		819	Example: wait till there are no outstanding requests anymore:
		820
		821	IO::AIO::poll_wait, IO::AIO::poll_cb
		822	while IO::AIO::nreqs;
		823
		824	IO::AIO::nready
		825	Returns the number of requests currently in the ready state (not yet
		826	executed).
		827
		828	IO::AIO::npending
		829	Returns the number of requests currently in the pending state
		830	(executed, but not yet processed by poll_cb).
		831
		832	FORK BEHAVIOUR
		833	This module should do "the right thing" when the process using it forks:
		834
		835	Before the fork, IO::AIO enters a quiescent state where no requests can
		836	be added in other threads and no results will be processed. After the
		837	fork the parent simply leaves the quiescent state and continues
		838	request/result processing, while the child frees the request/result
		839	queue (so that the requests started before the fork will only be handled
		840	in the parent). Threads will be started on demand until the limit set in
		841	the parent process has been reached again.
		842
		843	In short: the parent will, after a short pause, continue as if fork had
		844	not been called, while the child will act as if IO::AIO has not been
		845	used yet.
		846
		847	MEMORY USAGE
		848	Per-request usage:
		849
		850	Each aio request uses - depending on your architecture - around 100-200
		851	bytes of memory. In addition, stat requests need a stat buffer (possibly
		852	a few hundred bytes), readdir requires a result buffer and so on. Perl
		853	scalars and other data passed into aio requests will also be locked and
		854	will consume memory till the request has entered the done state.
		855
		856	This is now awfully much, so queuing lots of requests is not usually a
		857	problem.
		858
		859	Per-thread usage:
		860
		861	In the execution phase, some aio requests require more memory for
		862	temporary buffers, and each thread requires a stack and other data
		863	structures (usually around 16k-128k, depending on the OS).
		864
		865	KNOWN BUGS
		866	Known bugs will be fixed in the next release.
203		867
204	SEE ALSO	868	SEE ALSO
205	Coro, Linux::AIO.	869	Coro::AIO.
206		870
207	AUTHOR	871	AUTHOR
208	Marc Lehmann <schmorp@schmorp.de>	872	Marc Lehmann <schmorp@schmorp.de>
209	http://home.schmorp.de/	873	http://home.schmorp.de/
210		874

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Revision 1.22 by root, Sat Jan 6 02:47:11 2007 UTC