[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 1.27 by root, Sat Oct 6 14:05:37 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	Use an event loop for that (such as the Event module): IO::AIO will
		68	naturally fit into such an event loop itself.
		69
11	Currently, a number of threads are started that execute your read/writes	70	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	71	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	72	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	73	perl. In the future, this module might make use of the native aio
15	native aio functions available on many operating systems. However, they	74	functions available on many operating systems. However, they are often
16	are often not well-supported (Linux doesn't allow them on normal files	75	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	76	files currently, for example), and they would only support aio_read and
18	aio_write, so the remaining functionality would have to be implemented	77	aio_write, so the remaining functionality would have to be implemented
19	using threads anyway.	78	using threads anyway.
20		79
21	Although the module will work with in the presence of other threads, it	80	Although the module will work in the presence of other (Perl-) threads,
22	is currently not reentrant, so use appropriate locking yourself.	81	it is currently not reentrant in any way, so use appropriate locking
		82	yourself, always call "poll_cb" from within the same thread, or never
		83	call "poll_cb" (or other "aio_" functions) recursively.
		84
		85	EXAMPLE
		86	This is a simple example that uses the Event module and loads
		87	/etc/passwd asynchronously:
		88
		89	use Fcntl;
		90	use Event;
		91	use IO::AIO;
		92
		93	# register the IO::AIO callback with Event
		94	Event->io (fd => IO::AIO::poll_fileno,
		95	poll => 'r',
		96	cb => \&IO::AIO::poll_cb);
		97
		98	# queue the request to open /etc/passwd
		99	aio_open "/etc/passwd", O_RDONLY, 0, sub {
		100	my $fh = shift
		101	or die "error while opening: $!";
		102
		103	# stat'ing filehandles is generally non-blocking
		104	my $size = -s $fh;
		105
		106	# queue a request to read the file
		107	my $contents;
		108	aio_read $fh, 0, $size, $contents, 0, sub {
		109	$_[0] == $size
		110	or die "short read: $!";
		111
		112	close $fh;
		113
		114	# file contents now in $contents
		115	print $contents;
		116
		117	# exit event loop and program
		118	Event::unloop;
		119	};
		120	};
		121
		122	# possibly queue up other requests, or open GUI windows,
		123	# check for sockets etc. etc.
		124
		125	# process events as long as there are some:
		126	Event::loop;
		127
		128	REQUEST ANATOMY AND LIFETIME
		129	Every "aio_*" function creates a request. which is a C data structure
		130	not directly visible to Perl.
		131
		132	If called in non-void context, every request function returns a Perl
		133	object representing the request. In void context, nothing is returned,
		134	which saves a bit of memory.
		135
		136	The perl object is a fairly standard ref-to-hash object. The hash
		137	contents are not used by IO::AIO so you are free to store anything you
		138	like in it.
		139
		140	During their existance, aio requests travel through the following
		141	states, in order:
		142
		143	ready
		144	Immediately after a request is created it is put into the ready
		145	state, waiting for a thread to execute it.
		146
		147	execute
		148	A thread has accepted the request for processing and is currently
		149	executing it (e.g. blocking in read).
		150
		151	pending
		152	The request has been executed and is waiting for result processing.
		153
		154	While request submission and execution is fully asynchronous, result
		155	processing is not and relies on the perl interpreter calling
		156	"poll_cb" (or another function with the same effect).
		157
		158	result
		159	The request results are processed synchronously by "poll_cb".
		160
		161	The "poll_cb" function will process all outstanding aio requests by
		162	calling their callbacks, freeing memory associated with them and
		163	managing any groups they are contained in.
		164
		165	done
		166	Request has reached the end of its lifetime and holds no resources
		167	anymore (except possibly for the Perl object, but its connection to
		168	the actual aio request is severed and calling its methods will
		169	either do nothing or result in a runtime error).
23		170
24	FUNCTIONS	171	FUNCTIONS
25	AIO FUNCTIONS	172	AIO REQUEST FUNCTIONS
26	All the "aio_*" calls are more or less thin wrappers around the syscall	173	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	174	with the same name (sans "aio_"). The arguments are similar or
28	identical, and they all accept an additional $callback argument which	175	identical, and they all accept an additional (and optional) $callback
29	must be a code reference. This code reference will get called with the	176	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,	177	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	178	error, unlike perl, which usually delivers "false") as it's sole
32	syscall has been executed asynchronously.	179	argument when the given syscall has been executed asynchronously.
33		180
34	All functions that expect a filehandle will also accept a file	181	All functions expecting a filehandle keep a copy of the filehandle
35	descriptor.	182	internally until the request has finished.
36		183
		184	All functions return request objects of type IO::AIO::REQ that allow
		185	further manipulation of those requests while they are in-flight.
		186
37	The filenames you pass to these routines must be absolute. The reason	187	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	188	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	189	being executed, the current working directory could have changed.
40	never change the current working directory.	190	Alternatively, you can make sure that you never change the current
		191	working directory anywhere in the program and then use relative paths.
41		192
		193	To encode pathnames as octets, either make sure you either: a) always
		194	pass in filenames you got from outside (command line, readdir etc.)
		195	without tinkering, b) are ASCII or ISO 8859-1, c) use the Encode module
		196	and encode your pathnames to the locale (or other) encoding in effect in
		197	the user environment, d) use Glib::filename_from_unicode on unicode
		198	filenames or e) use something else to ensure your scalar has the correct
		199	contents.
		200
		201	This works, btw. independent of the internal UTF-8 bit, which IO::AIO
		202	handles correctly wether it is set or not.
		203
		204	$prev_pri = aioreq_pri [$pri]
		205	Returns the priority value that would be used for the next request
		206	and, if $pri is given, sets the priority for the next aio request.
		207
		208	The default priority is 0, the minimum and maximum priorities are -4
		209	and 4, respectively. Requests with higher priority will be serviced
		210	first.
		211
		212	The priority will be reset to 0 after each call to one of the
		213	"aio_*" functions.
		214
		215	Example: open a file with low priority, then read something from it
		216	with higher priority so the read request is serviced before other
		217	low priority open requests (potentially spamming the cache):
		218
		219	aioreq_pri -3;
		220	aio_open ..., sub {
		221	return unless $_[0];
		222
		223	aioreq_pri -2;
		224	aio_read $_[0], ..., sub {
		225	...
		226	};
		227	};
		228
		229	aioreq_nice $pri_adjust
		230	Similar to "aioreq_pri", but subtracts the given value from the
		231	current priority, so the effect is cumulative.
		232
42	aio_open $pathname, $flags, $mode, $callback	233	aio_open $pathname, $flags, $mode, $callback->($fh)
43	Asynchronously open or create a file and call the callback with a	234	Asynchronously open or create a file and call the callback with a
44	newly created filehandle for the file.	235	newly created filehandle for the file.
45		236
46	The pathname passed to "aio_open" must be absolute. See API NOTES,	237	The pathname passed to "aio_open" must be absolute. See API NOTES,
47	above, for an explanation.	238	above, for an explanation.
48		239
49	The $mode argument is a bitmask. See the "Fcntl" module for a list.	240	The $flags argument is a bitmask. See the "Fcntl" module for a list.
50	They are the same as used in "sysopen".	241	They are the same as used by "sysopen".
		242
		243	Likewise, $mode specifies the mode of the newly created file, if it
		244	didn't exist and "O_CREAT" has been given, just like perl's
		245	"sysopen", except that it is mandatory (i.e. use 0 if you don't
		246	create new files, and 0666 or 0777 if you do). Note that the $mode
		247	will be modified by the umask in effect then the request is being
		248	executed, so better never change the umask.
51		249
52	Example:	250	Example:
53		251
54	aio_open "/etc/passwd", O_RDONLY, 0, sub {	252	aio_open "/etc/passwd", O_RDONLY, 0, sub {
55	if ($_[0]) {	253	if ($_[0]) {
58	} else {	256	} else {
59	die "open failed: $!\n";	257	die "open failed: $!\n";
60	}	258	}
61	};	259	};
62		260
63	aio_close $fh, $callback	261	aio_close $fh, $callback->($status)
64	Asynchronously close a file and call the callback with the result	262	Asynchronously close a file and call the callback with the result
65	code. WARNING: although accepted, you should not pass in a perl	263	code.
66	filehandle here, as perl will likely close the file descriptor
67	itself when the filehandle is destroyed. Normally, you can safely
68	call perls "close" or just let filehandles go out of scope.
69		264
		265	Unfortunately, you can't do this to perl. Perl insists very
		266	strongly on closing the file descriptor associated with the
		267	filehandle itself. Here is what aio_close will try:
		268
		269	1. dup()licate the fd
		270	2. asynchronously close() the duplicated fd
		271	3. dup()licate the fd once more
		272	4. let perl close() the filehandle
		273	5. asynchronously close the duplicated fd
		274
		275	The idea is that the first close() flushes stuff to disk that
		276	closing an fd will flush, so when perl closes the fd, nothing much
		277	will need to be flushed. The second async. close() will then flush
		278	stuff to disk that closing the last fd to the file will flush.
		279
		280	Just FYI, SuSv3 has this to say on close:
		281
		282	All outstanding record locks owned by the process on the file
		283	associated with the file descriptor shall be removed.
		284
		285	If fildes refers to a socket, close() shall cause the socket to be
		286	destroyed. ... close() shall block for up to the current linger
		287	interval until all data is transmitted.
		288	[this actually sounds like a specification bug, but who knows]
		289
		290	And at least Linux additionally actually flushes stuff on every
		291	close, even when the file itself is still open.
		292
		293	Sounds enourmously inefficient and complicated? Yes... please show
		294	me how to nuke perl's fd out of existence...
		295
70	aio_read $fh,$offset,$length, $data,$dataoffset,$callback	296	aio_read $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
71	aio_write $fh,$offset,$length, $data,$dataoffset,$callback	297	aio_write $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
72	Reads or writes "length" bytes from the specified "fh" and "offset"	298	Reads or writes $length bytes from the specified $fh and $offset
73	into the scalar given by "data" and offset "dataoffset" and calls	299	into the scalar given by $data and offset $dataoffset and calls the
74	the callback without the actual number of bytes read (or -1 on	300	callback without the actual number of bytes read (or -1 on error,
75	error, just like the syscall).	301	just like the syscall).
76		302
		303	If $offset is undefined, then the current file descriptor offset
		304	will be used (and updated), otherwise the file descriptor offset
		305	will not be changed by these calls.
		306
		307	If $length is undefined in "aio_write", use the remaining length of
		308	$data.
		309
		310	If $dataoffset is less than zero, it will be counted from the end of
		311	$data.
		312
		313	The $data scalar MUST NOT be modified in any way while the request
		314	is outstanding. Modifying it can result in segfaults or World War
		315	III (if the necessary/optional hardware is installed).
		316
77	Example: Read 15 bytes at offset 7 into scalar $buffer, strating at	317	Example: Read 15 bytes at offset 7 into scalar $buffer, starting at
78	offset 0 within the scalar:	318	offset 0 within the scalar:
79		319
80	aio_read $fh, 7, 15, $buffer, 0, sub {	320	aio_read $fh, 7, 15, $buffer, 0, sub {
81	$_[0] >= 0 or die "read error: $!";	321	$_[0] > 0 or die "read error: $!";
82	print "read <$buffer>\n";	322	print "read $_[0] bytes: <$buffer>\n";
83	};	323	};
84		324
		325	aio_sendfile $out_fh, $in_fh, $in_offset, $length, $callback->($retval)
		326	Tries to copy $length bytes from $in_fh to $out_fh. It starts
		327	reading at byte offset $in_offset, and starts writing at the current
		328	file offset of $out_fh. Because of that, it is not safe to issue
		329	more than one "aio_sendfile" per $out_fh, as they will interfere
		330	with each other.
		331
		332	This call tries to make use of a native "sendfile" syscall to
		333	provide zero-copy operation. For this to work, $out_fh should refer
		334	to a socket, and $in_fh should refer to mmap'able file.
		335
		336	If the native sendfile call fails or is not implemented, it will be
		337	emulated, so you can call "aio_sendfile" on any type of filehandle
		338	regardless of the limitations of the operating system.
		339
		340	Please note, however, that "aio_sendfile" can read more bytes from
		341	$in_fh than are written, and there is no way to find out how many
		342	bytes have been read from "aio_sendfile" alone, as "aio_sendfile"
		343	only provides the number of bytes written to $out_fh. Only if the
		344	result value equals $length one can assume that $length bytes have
		345	been read.
		346
85	aio_readahead $fh,$offset,$length, $callback	347	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	348	"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	349	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	350	$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	351	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	352	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	353	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	354	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	355	read beyond the end of the file. The current file offset of the file
98	is left unchanged.	356	is left unchanged.
99		357
		358	If that syscall doesn't exist (likely if your OS isn't Linux) it
		359	will be emulated by simply reading the data, which would have a
		360	similar effect.
		361
100	aio_stat $fh_or_path, $callback	362	aio_stat $fh_or_path, $callback->($status)
101	aio_lstat $fh, $callback	363	aio_lstat $fh, $callback->($status)
102	Works like perl's "stat" or "lstat" in void context. The callback	364	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	365	will be called after the stat and the results will be available
104	using "stat _" or "-s _" etc...	366	using "stat _" or "-s _" etc...
105		367
106	The pathname passed to "aio_stat" must be absolute. See API NOTES,	368	The pathname passed to "aio_stat" must be absolute. See API NOTES,
…		…
116	aio_stat "/etc/passwd", sub {	378	aio_stat "/etc/passwd", sub {
117	$_[0] and die "stat failed: $!";	379	$_[0] and die "stat failed: $!";
118	print "size is ", -s _, "\n";	380	print "size is ", -s _, "\n";
119	};	381	};
120		382
		383	aio_utime $fh_or_path, $atime, $mtime, $callback->($status)
		384	Works like perl's "utime" function (including the special case of
		385	$atime and $mtime being undef). Fractional times are supported if
		386	the underlying syscalls support them.
		387
		388	When called with a pathname, uses utimes(2) if available, otherwise
		389	utime(2). If called on a file descriptor, uses futimes(2) if
		390	available, otherwise returns ENOSYS, so this is not portable.
		391
		392	Examples:
		393
		394	# set atime and mtime to current time (basically touch(1)):
		395	aio_utime "path", undef, undef;
		396	# set atime to current time and mtime to beginning of the epoch:
		397	aio_utime "path", time, undef; # undef==0
		398
		399	aio_chown $fh_or_path, $uid, $gid, $callback->($status)
		400	Works like perl's "chown" function, except that "undef" for either
		401	$uid or $gid is being interpreted as "do not change" (but -1 can
		402	also be used).
		403
		404	Examples:
		405
		406	# same as "chown root path" in the shell:
		407	aio_chown "path", 0, -1;
		408	# same as above:
		409	aio_chown "path", 0, undef;
		410
		411	aio_truncate $fh_or_path, $offset, $callback->($status)
		412	Works like truncate(2) or ftruncate(2).
		413
		414	aio_chmod $fh_or_path, $mode, $callback->($status)
		415	Works like perl's "chmod" function.
		416
121	aio_unlink $pathname, $callback	417	aio_unlink $pathname, $callback->($status)
122	Asynchronously unlink (delete) a file and call the callback with the	418	Asynchronously unlink (delete) a file and call the callback with the
123	result code.	419	result code.
124		420
		421	aio_mknod $path, $mode, $dev, $callback->($status)
		422	[EXPERIMENTAL]
		423
		424	Asynchronously create a device node (or fifo). See mknod(2).
		425
		426	The only (POSIX-) portable way of calling this function is:
		427
		428	aio_mknod $path, IO::AIO::S_IFIFO \| $mode, 0, sub { ...
		429
		430	aio_link $srcpath, $dstpath, $callback->($status)
		431	Asynchronously create a new link to the existing object at $srcpath
		432	at the path $dstpath and call the callback with the result code.
		433
		434	aio_symlink $srcpath, $dstpath, $callback->($status)
		435	Asynchronously create a new symbolic link to the existing object at
		436	$srcpath at the path $dstpath and call the callback with the result
		437	code.
		438
		439	aio_readlink $path, $callback->($link)
		440	Asynchronously read the symlink specified by $path and pass it to
		441	the callback. If an error occurs, nothing or undef gets passed to
		442	the callback.
		443
		444	aio_rename $srcpath, $dstpath, $callback->($status)
		445	Asynchronously rename the object at $srcpath to $dstpath, just as
		446	rename(2) and call the callback with the result code.
		447
		448	aio_mkdir $pathname, $mode, $callback->($status)
		449	Asynchronously mkdir (create) a directory and call the callback with
		450	the result code. $mode will be modified by the umask at the time the
		451	request is executed, so do not change your umask.
		452
		453	aio_rmdir $pathname, $callback->($status)
		454	Asynchronously rmdir (delete) a directory and call the callback with
		455	the result code.
		456
		457	aio_readdir $pathname, $callback->($entries)
		458	Unlike the POSIX call of the same name, "aio_readdir" reads an
		459	entire directory (i.e. opendir + readdir + closedir). The entries
		460	will not be sorted, and will NOT include the "." and ".." entries.
		461
		462	The callback a single argument which is either "undef" or an
		463	array-ref with the filenames.
		464
		465	aio_load $path, $data, $callback->($status)
		466	This is a composite request that tries to fully load the given file
		467	into memory. Status is the same as with aio_read.
		468
		469	aio_copy $srcpath, $dstpath, $callback->($status)
		470	Try to copy the file (directories not supported as either source
		471	or destination) from $srcpath to $dstpath and call the callback with
		472	the 0 (error) or -1 ok.
		473
		474	This is a composite request that it creates the destination file
		475	with mode 0200 and copies the contents of the source file into it
		476	using "aio_sendfile", followed by restoring atime, mtime, access
		477	mode and uid/gid, in that order.
		478
		479	If an error occurs, the partial destination file will be unlinked,
		480	if possible, except when setting atime, mtime, access mode and
		481	uid/gid, where errors are being ignored.
		482
		483	aio_move $srcpath, $dstpath, $callback->($status)
		484	Try to move the file (directories not supported as either source
		485	or destination) from $srcpath to $dstpath and call the callback with
		486	the 0 (error) or -1 ok.
		487
		488	This is a composite request that tries to rename(2) the file first.
		489	If rename files with "EXDEV", it copies the file with "aio_copy"
		490	and, if that is successful, unlinking the $srcpath.
		491
		492	aio_scandir $path, $maxreq, $callback->($dirs, $nondirs)
		493	Scans a directory (similar to "aio_readdir") but additionally tries
		494	to efficiently separate the entries of directory $path into two sets
		495	of names, directories you can recurse into (directories), and ones
		496	you cannot recurse into (everything else, including symlinks to
		497	directories).
		498
		499	"aio_scandir" is a composite request that creates of many sub
		500	requests_ $maxreq specifies the maximum number of outstanding aio
		501	requests that this function generates. If it is "<= 0", then a
		502	suitable default will be chosen (currently 4).
		503
		504	On error, the callback is called without arguments, otherwise it
		505	receives two array-refs with path-relative entry names.
		506
		507	Example:
		508
		509	aio_scandir $dir, 0, sub {
		510	my ($dirs, $nondirs) = @_;
		511	print "real directories: @$dirs\n";
		512	print "everything else: @$nondirs\n";
		513	};
		514
		515	Implementation notes.
		516
		517	The "aio_readdir" cannot be avoided, but "stat()"'ing every entry
		518	can.
		519
		520	After reading the directory, the modification time, size etc. of the
		521	directory before and after the readdir is checked, and if they match
		522	(and isn't the current time), the link count will be used to decide
		523	how many entries are directories (if >= 2). Otherwise, no knowledge
		524	of the number of subdirectories will be assumed.
		525
		526	Then entries will be sorted into likely directories (everything
		527	without a non-initial dot currently) and likely non-directories
		528	(everything else). Then every entry plus an appended "/." will be
		529	"stat"'ed, likely directories first. If that succeeds, it assumes
		530	that the entry is a directory or a symlink to directory (which will
		531	be checked seperately). This is often faster than stat'ing the entry
		532	itself because filesystems might detect the type of the entry
		533	without reading the inode data (e.g. ext2fs filetype feature).
		534
		535	If the known number of directories (link count - 2) has been
		536	reached, the rest of the entries is assumed to be non-directories.
		537
		538	This only works with certainty on POSIX (= UNIX) filesystems, which
		539	fortunately are the vast majority of filesystems around.
		540
		541	It will also likely work on non-POSIX filesystems with reduced
		542	efficiency as those tend to return 0 or 1 as link counts, which
		543	disables the directory counting heuristic.
		544
		545	aio_rmtree $path, $callback->($status)
		546	Delete a directory tree starting (and including) $path, return the
		547	status of the final "rmdir" only. This is a composite request that
		548	uses "aio_scandir" to recurse into and rmdir directories, and unlink
		549	everything else.
		550
125	aio_fsync $fh, $callback	551	aio_fsync $fh, $callback->($status)
126	Asynchronously call fsync on the given filehandle and call the	552	Asynchronously call fsync on the given filehandle and call the
127	callback with the fsync result code.	553	callback with the fsync result code.
128		554
129	aio_fdatasync $fh, $callback	555	aio_fdatasync $fh, $callback->($status)
130	Asynchronously call fdatasync on the given filehandle and call the	556	Asynchronously call fdatasync on the given filehandle and call the
131	callback with the fdatasync result code.	557	callback with the fdatasync result code.
132		558
		559	If this call isn't available because your OS lacks it or it couldn't
		560	be detected, it will be emulated by calling "fsync" instead.
		561
		562	aio_group $callback->(...)
		563	This is a very special aio request: Instead of doing something, it
		564	is a container for other aio requests, which is useful if you want
		565	to bundle many requests into a single, composite, request with a
		566	definite callback and the ability to cancel the whole request with
		567	its subrequests.
		568
		569	Returns an object of class IO::AIO::GRP. See its documentation below
		570	for more info.
		571
		572	Example:
		573
		574	my $grp = aio_group sub {
		575	print "all stats done\n";
		576	};
		577
		578	add $grp
		579	(aio_stat ...),
		580	(aio_stat ...),
		581	...;
		582
		583	aio_nop $callback->()
		584	This is a special request - it does nothing in itself and is only
		585	used for side effects, such as when you want to add a dummy request
		586	to a group so that finishing the requests in the group depends on
		587	executing the given code.
		588
		589	While this request does nothing, it still goes through the execution
		590	phase and still requires a worker thread. Thus, the callback will
		591	not be executed immediately but only after other requests in the
		592	queue have entered their execution phase. This can be used to
		593	measure request latency.
		594
		595	IO::AIO::aio_busy $fractional_seconds, $callback->() NOT EXPORTED
		596	Mainly used for debugging and benchmarking, this aio request puts
		597	one of the request workers to sleep for the given time.
		598
		599	While it is theoretically handy to have simple I/O scheduling
		600	requests like sleep and file handle readable/writable, the overhead
		601	this creates is immense (it blocks a thread for a long time) so do
		602	not use this function except to put your application under
		603	artificial I/O pressure.
		604
		605	IO::AIO::REQ CLASS
		606	All non-aggregate "aio_*" functions return an object of this class when
		607	called in non-void context.
		608
		609	cancel $req
		610	Cancels the request, if possible. Has the effect of skipping
		611	execution when entering the execute state and skipping calling the
		612	callback when entering the the result state, but will leave the
		613	request otherwise untouched. That means that requests that currently
		614	execute will not be stopped and resources held by the request will
		615	not be freed prematurely.
		616
		617	cb $req $callback->(...)
		618	Replace (or simply set) the callback registered to the request.
		619
		620	IO::AIO::GRP CLASS
		621	This class is a subclass of IO::AIO::REQ, so all its methods apply to
		622	objects of this class, too.
		623
		624	A IO::AIO::GRP object is a special request that can contain multiple
		625	other aio requests.
		626
		627	You create one by calling the "aio_group" constructing function with a
		628	callback that will be called when all contained requests have entered
		629	the "done" state:
		630
		631	my $grp = aio_group sub {
		632	print "all requests are done\n";
		633	};
		634
		635	You add requests by calling the "add" method with one or more
		636	"IO::AIO::REQ" objects:
		637
		638	$grp->add (aio_unlink "...");
		639
		640	add $grp aio_stat "...", sub {
		641	$_[0] or return $grp->result ("error");
		642
		643	# add another request dynamically, if first succeeded
		644	add $grp aio_open "...", sub {
		645	$grp->result ("ok");
		646	};
		647	};
		648
		649	This makes it very easy to create composite requests (see the source of
		650	"aio_move" for an application) that work and feel like simple requests.
		651
		652	* The IO::AIO::GRP objects will be cleaned up during calls to
		653	"IO::AIO::poll_cb", just like any other request.
		654	* They can be canceled like any other request. Canceling will cancel not
		655	only the request itself, but also all requests it contains.
		656	* They can also can also be added to other IO::AIO::GRP objects.
		657	* You must not add requests to a group from within the group callback
		658	(or any later time).
		659
		660	Their lifetime, simplified, looks like this: when they are empty, they
		661	will finish very quickly. If they contain only requests that are in the
		662	"done" state, they will also finish. Otherwise they will continue to
		663	exist.
		664
		665	That means after creating a group you have some time to add requests.
		666	And in the callbacks of those requests, you can add further requests to
		667	the group. And only when all those requests have finished will the the
		668	group itself finish.
		669
		670	add $grp ...
		671	$grp->add (...)
		672	Add one or more requests to the group. Any type of IO::AIO::REQ can
		673	be added, including other groups, as long as you do not create
		674	circular dependencies.
		675
		676	Returns all its arguments.
		677
		678	$grp->cancel_subs
		679	Cancel all subrequests and clears any feeder, but not the group
		680	request itself. Useful when you queued a lot of events but got a
		681	result early.
		682
		683	$grp->result (...)
		684	Set the result value(s) that will be passed to the group callback
		685	when all subrequests have finished and set thre groups errno to the
		686	current value of errno (just like calling "errno" without an error
		687	number). By default, no argument will be passed and errno is zero.
		688
		689	$grp->errno ([$errno])
		690	Sets the group errno value to $errno, or the current value of errno
		691	when the argument is missing.
		692
		693	Every aio request has an associated errno value that is restored
		694	when the callback is invoked. This method lets you change this value
		695	from its default (0).
		696
		697	Calling "result" will also set errno, so make sure you either set $!
		698	before the call to "result", or call c<errno> after it.
		699
		700	feed $grp $callback->($grp)
		701	Sets a feeder/generator on this group: every group can have an
		702	attached generator that generates requests if idle. The idea behind
		703	this is that, although you could just queue as many requests as you
		704	want in a group, this might starve other requests for a potentially
		705	long time. For example, "aio_scandir" might generate hundreds of
		706	thousands "aio_stat" requests, delaying any later requests for a
		707	long time.
		708
		709	To avoid this, and allow incremental generation of requests, you can
		710	instead a group and set a feeder on it that generates those
		711	requests. The feed callback will be called whenever there are few
		712	enough (see "limit", below) requests active in the group itself and
		713	is expected to queue more requests.
		714
		715	The feed callback can queue as many requests as it likes (i.e. "add"
		716	does not impose any limits).
		717
		718	If the feed does not queue more requests when called, it will be
		719	automatically removed from the group.
		720
		721	If the feed limit is 0, it will be set to 2 automatically.
		722
		723	Example:
		724
		725	# stat all files in @files, but only ever use four aio requests concurrently:
		726
		727	my $grp = aio_group sub { print "finished\n" };
		728	limit $grp 4;
		729	feed $grp sub {
		730	my $file = pop @files
		731	or return;
		732
		733	add $grp aio_stat $file, sub { ... };
		734	};
		735
		736	limit $grp $num
		737	Sets the feeder limit for the group: The feeder will be called
		738	whenever the group contains less than this many requests.
		739
		740	Setting the limit to 0 will pause the feeding process.
		741
133	SUPPORT FUNCTIONS	742	SUPPORT FUNCTIONS
		743	EVENT PROCESSING AND EVENT LOOP INTEGRATION
134	$fileno = IO::AIO::poll_fileno	744	$fileno = IO::AIO::poll_fileno
135	Return the request result pipe filehandle. This filehandle must be	745	Return the request result pipe file descriptor. This filehandle
136	polled for reading by some mechanism outside this module (e.g. Event	746	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	747	(e.g. Event or select, see below or the SYNOPSIS). If the pipe
138	"poll_cb" to check the results.	748	becomes readable you have to call "poll_cb" to check the results.
139		749
140	See "poll_cb" for an example.	750	See "poll_cb" for an example.
141		751
142	IO::AIO::poll_cb	752	IO::AIO::poll_cb
143	Process all outstanding events on the result pipe. You have to call	753	Process some outstanding events on the result pipe. You have to call
144	this regularly. Returns the number of events processed. Returns	754	this regularly. Returns the number of events processed. Returns
145	immediately when no events are outstanding.	755	immediately when no events are outstanding. The amount of events
		756	processed depends on the settings of "IO::AIO::max_poll_req" and
		757	"IO::AIO::max_poll_time".
146		758
147	You can use Event to multiplex, e.g.:	759	If not all requests were processed for whatever reason, the
		760	filehandle will still be ready when "poll_cb" returns.
		761
		762	Example: Install an Event watcher that automatically calls
		763	IO::AIO::poll_cb with high priority:
148		764
149	Event->io (fd => IO::AIO::poll_fileno,	765	Event->io (fd => IO::AIO::poll_fileno,
150	poll => 'r', async => 1,	766	poll => 'r', async => 1,
151	cb => \&IO::AIO::poll_cb);	767	cb => \&IO::AIO::poll_cb);
152		768
		769	IO::AIO::max_poll_reqs $nreqs
		770	IO::AIO::max_poll_time $seconds
		771	These set the maximum number of requests (default 0, meaning
		772	infinity) that are being processed by "IO::AIO::poll_cb" in one
		773	call, respectively the maximum amount of time (default 0, meaning
		774	infinity) spent in "IO::AIO::poll_cb" to process requests (more
		775	correctly the mininum amount of time "poll_cb" is allowed to use).
		776
		777	Setting "max_poll_time" to a non-zero value creates an overhead of
		778	one syscall per request processed, which is not normally a problem
		779	unless your callbacks are really really fast or your OS is really
		780	really slow (I am not mentioning Solaris here). Using
		781	"max_poll_reqs" incurs no overhead.
		782
		783	Setting these is useful if you want to ensure some level of
		784	interactiveness when perl is not fast enough to process all requests
		785	in time.
		786
		787	For interactive programs, values such as 0.01 to 0.1 should be fine.
		788
		789	Example: Install an Event watcher that automatically calls
		790	IO::AIO::poll_cb with low priority, to ensure that other parts of
		791	the program get the CPU sometimes even under high AIO load.
		792
		793	# try not to spend much more than 0.1s in poll_cb
		794	IO::AIO::max_poll_time 0.1;
		795
		796	# use a low priority so other tasks have priority
		797	Event->io (fd => IO::AIO::poll_fileno,
		798	poll => 'r', nice => 1,
		799	cb => &IO::AIO::poll_cb);
		800
153	IO::AIO::poll_wait	801	IO::AIO::poll_wait
		802	If there are any outstanding requests and none of them in the result
154	Wait till the result filehandle becomes ready for reading (simply	803	phase, wait till the result filehandle becomes ready for reading
155	does a select on the filehandle. This is useful if you want to	804	(simply does a "select" on the filehandle. This is useful if you
156	synchronously wait for some requests to finish).	805	want to synchronously wait for some requests to finish).
157		806
158	See "nreqs" for an example.	807	See "nreqs" for an example.
159		808
		809	IO::AIO::poll
		810	Waits until some requests have been handled.
		811
		812	Returns the number of requests processed, but is otherwise strictly
		813	equivalent to:
		814
		815	IO::AIO::poll_wait, IO::AIO::poll_cb
		816
160	IO::AIO::nreqs	817	IO::AIO::flush
161	Returns the number of requests currently outstanding.	818	Wait till all outstanding AIO requests have been handled.
162		819
163	Example: wait till there are no outstanding requests anymore:	820	Strictly equivalent to:
164		821
165	IO::AIO::poll_wait, IO::AIO::poll_cb	822	IO::AIO::poll_wait, IO::AIO::poll_cb
166	while IO::AIO::nreqs;	823	while IO::AIO::nreqs;
167		824
		825	CONTROLLING THE NUMBER OF THREADS
168	IO::AIO::min_parallel $nthreads	826	IO::AIO::min_parallel $nthreads
169	Set the minimum number of AIO threads to $nthreads. The default is	827	Set the minimum number of AIO threads to $nthreads. The current
170	1, which means a single asynchronous operation can be done at one	828	default is 8, which means eight asynchronous operations can execute
171	time (the number of outstanding operations, however, is unlimited).	829	concurrently at any one time (the number of outstanding requests,
		830	however, is unlimited).
172		831
		832	IO::AIO starts threads only on demand, when an AIO request is queued
		833	and no free thread exists. Please note that queueing up a hundred
		834	requests can create demand for a hundred threads, even if it turns
		835	out that everything is in the cache and could have been processed
		836	faster by a single thread.
		837
173	It is recommended to keep the number of threads low, as some Linux	838	It is recommended to keep the number of threads relatively low, as
174	kernel versions will scale negatively with the number of threads	839	some Linux kernel versions will scale negatively with the number of
175	(higher parallelity => MUCH higher latency). With current Linux 2.6	840	threads (higher parallelity => MUCH higher latency). With current
176	versions, 4-32 threads should be fine.	841	Linux 2.6 versions, 4-32 threads should be fine.
177		842
178	Under normal circumstances you don't need to call this function, as	843	Under most circumstances you don't need to call this function, as
179	this module automatically starts some threads (the exact number	844	the module selects a default that is suitable for low to moderate
180	might change, and is currently 4).	845	load.
181		846
182	IO::AIO::max_parallel $nthreads	847	IO::AIO::max_parallel $nthreads
183	Sets the maximum number of AIO threads to $nthreads. If more than	848	Sets the maximum number of AIO threads to $nthreads. If more than
184	the specified number of threads are currently running, kill them.	849	the specified number of threads are currently running, this function
185	This function blocks until the limit is reached.	850	kills them. This function blocks until the limit is reached.
		851
		852	While $nthreads are zero, aio requests get queued but not executed
		853	until the number of threads has been increased again.
186		854
187	This module automatically runs "max_parallel 0" at program end, to	855	This module automatically runs "max_parallel 0" at program end, to
188	ensure that all threads are killed and that there are no outstanding	856	ensure that all threads are killed and that there are no outstanding
189	requests.	857	requests.
190		858
191	Under normal circumstances you don't need to call this function.	859	Under normal circumstances you don't need to call this function.
192		860
		861	IO::AIO::max_idle $nthreads
		862	Limit the number of threads (default: 4) that are allowed to idle
		863	(i.e., threads that did not get a request to process within 10
		864	seconds). That means if a thread becomes idle while $nthreads other
		865	threads are also idle, it will free its resources and exit.
		866
		867	This is useful when you allow a large number of threads (e.g. 100 or
		868	1000) to allow for extremely high load situations, but want to free
		869	resources under normal circumstances (1000 threads can easily
		870	consume 30MB of RAM).
		871
		872	The default is probably ok in most situations, especially if thread
		873	creation is fast. If thread creation is very slow on your system you
		874	might want to use larger values.
		875
193	$oldnreqs = IO::AIO::max_outstanding $nreqs	876	$oldmaxreqs = IO::AIO::max_outstanding $maxreqs
		877	This is a very bad function to use in interactive programs because
		878	it blocks, and a bad way to reduce concurrency because it is
		879	inexact: Better use an "aio_group" together with a feed callback.
		880
194	Sets the maximum number of outstanding requests to $nreqs. If you	881	Sets the maximum number of outstanding requests to $nreqs. If you do
195	try to queue up more than this number of requests, the caller will	882	queue up more than this number of requests, the next call to the
196	block until some requests have been handled.	883	"poll_cb" (and "poll_some" and other functions calling "poll_cb")
		884	function will block until the limit is no longer exceeded.
197		885
198	The default is very large, so normally there is no practical limit.	886	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	887	the number of outstanding requests.
200	if you set this to a relatively low number, such as 100.
201		888
202	Under normal circumstances you don't need to call this function.	889	You can still queue as many requests as you want. Therefore,
		890	"max_oustsanding" is mainly useful in simple scripts (with low
		891	values) or as a stop gap to shield against fatal memory overflow
		892	(with large values).
		893
		894	STATISTICAL INFORMATION
		895	IO::AIO::nreqs
		896	Returns the number of requests currently in the ready, execute or
		897	pending states (i.e. for which their callback has not been invoked
		898	yet).
		899
		900	Example: wait till there are no outstanding requests anymore:
		901
		902	IO::AIO::poll_wait, IO::AIO::poll_cb
		903	while IO::AIO::nreqs;
		904
		905	IO::AIO::nready
		906	Returns the number of requests currently in the ready state (not yet
		907	executed).
		908
		909	IO::AIO::npending
		910	Returns the number of requests currently in the pending state
		911	(executed, but not yet processed by poll_cb).
		912
		913	FORK BEHAVIOUR
		914	This module should do "the right thing" when the process using it forks:
		915
		916	Before the fork, IO::AIO enters a quiescent state where no requests can
		917	be added in other threads and no results will be processed. After the
		918	fork the parent simply leaves the quiescent state and continues
		919	request/result processing, while the child frees the request/result
		920	queue (so that the requests started before the fork will only be handled
		921	in the parent). Threads will be started on demand until the limit set in
		922	the parent process has been reached again.
		923
		924	In short: the parent will, after a short pause, continue as if fork had
		925	not been called, while the child will act as if IO::AIO has not been
		926	used yet.
		927
		928	MEMORY USAGE
		929	Per-request usage:
		930
		931	Each aio request uses - depending on your architecture - around 100-200
		932	bytes of memory. In addition, stat requests need a stat buffer (possibly
		933	a few hundred bytes), readdir requires a result buffer and so on. Perl
		934	scalars and other data passed into aio requests will also be locked and
		935	will consume memory till the request has entered the done state.
		936
		937	This is not awfully much, so queuing lots of requests is not usually a
		938	problem.
		939
		940	Per-thread usage:
		941
		942	In the execution phase, some aio requests require more memory for
		943	temporary buffers, and each thread requires a stack and other data
		944	structures (usually around 16k-128k, depending on the OS).
		945
		946	KNOWN BUGS
		947	Known bugs will be fixed in the next release.
203		948
204	SEE ALSO	949	SEE ALSO
205	Coro, Linux::AIO.	950	Coro::AIO.
206		951
207	AUTHOR	952	AUTHOR
208	Marc Lehmann <schmorp@schmorp.de>	953	Marc Lehmann <schmorp@schmorp.de>
209	http://home.schmorp.de/	954	http://home.schmorp.de/
210		955

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Comparing IO-AIO/README (file contents): Revision 1.4 by root, Sun Jul 10 21:04:46 2005 UTC vs. Revision 1.27 by root, Sat Oct 6 14:05:37 2007 UTC

Diff Legend

Comparing IO-AIO/README (file contents):
Revision 1.4 by root, Sun Jul 10 21:04:46 2005 UTC vs.
Revision 1.27 by root, Sat Oct 6 14:05:37 2007 UTC