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

Comparing IO-AIO/README (file contents):
Revision 1.14 by root, Mon Dec 26 18:31:12 2005 UTC vs.
Revision 1.24 by root, Sun Aug 5 16:45:54 2007 UTC

…		…
3		3
4	SYNOPSIS	4	SYNOPSIS
5	use IO::AIO;	5	use IO::AIO;
6		6
7	aio_open "/etc/passwd", O_RDONLY, 0, sub {	7	aio_open "/etc/passwd", O_RDONLY, 0, sub {
8	my ($fh) = @_;	8	my $fh = shift
		9	or die "/etc/passwd: $!";
9	...	10	...
10	};	11	};
11		12
12	aio_unlink "/tmp/file", sub { };	13	aio_unlink "/tmp/file", sub { };
13		14
14	aio_read $fh, 30000, 1024, $buffer, 0, sub {	15	aio_read $fh, 30000, 1024, $buffer, 0, sub {
15	$_[0] > 0 or die "read error: $!";	16	$_[0] > 0 or die "read error: $!";
16	};	17	};
17		18
18	# AnyEvent	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
19	open my $fh, "<&=" . IO::AIO::poll_fileno or die "$!";	30	open my $fh, "<&=" . IO::AIO::poll_fileno or die "$!";
20	my $w = AnyEvent->io (fh => $fh, poll => 'r', cb => sub { IO::AIO::poll_cb });	31	my $w = AnyEvent->io (fh => $fh, poll => 'r', cb => sub { IO::AIO::poll_cb });
21		32
22	# Event	33	# Event integration
23	Event->io (fd => IO::AIO::poll_fileno,	34	Event->io (fd => IO::AIO::poll_fileno,
24	poll => 'r',	35	poll => 'r',
25	cb => \&IO::AIO::poll_cb);	36	cb => \&IO::AIO::poll_cb);
26		37
27	# Glib/Gtk2	38	# Glib/Gtk2 integration
28	add_watch Glib::IO IO::AIO::poll_fileno,	39	add_watch Glib::IO IO::AIO::poll_fileno,
29	in => sub { IO::AIO::poll_cb; 1 };	40	in => sub { IO::AIO::poll_cb; 1 };
30		41
31	# Tk	42	# Tk integration
32	Tk::Event::IO->fileevent (IO::AIO::poll_fileno, "",	43	Tk::Event::IO->fileevent (IO::AIO::poll_fileno, "",
33	readable => \&IO::AIO::poll_cb);	44	readable => \&IO::AIO::poll_cb);
34		45
35	# Danga::Socket	46	# Danga::Socket integration
36	Danga::Socket->AddOtherFds (IO::AIO::poll_fileno =>	47	Danga::Socket->AddOtherFds (IO::AIO::poll_fileno =>
37	\&IO::AIO::poll_cb);	48	\&IO::AIO::poll_cb);
38		49
39	DESCRIPTION	50	DESCRIPTION
40	This module implements asynchronous I/O using whatever means your	51	This module implements asynchronous I/O using whatever means your
41	operating system supports.	52	operating system supports.
42		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
43	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
44	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
45	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
46	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
47	native aio functions available on many operating systems. However, they	74	functions available on many operating systems. However, they are often
48	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
49	currently, for example), and they would only support aio_read and	76	files currently, for example), and they would only support aio_read and
50	aio_write, so the remaining functionality would have to be implemented	77	aio_write, so the remaining functionality would have to be implemented
51	using threads anyway.	78	using threads anyway.
52		79
53	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,
54	is currently not reentrant, so use appropriate locking yourself, always	81	it is currently not reentrant in any way, so use appropriate locking
55	call "poll_cb" from within the same thread, or never call "poll_cb" (or	82	yourself, always call "poll_cb" from within the same thread, or never
56	other "aio_" functions) recursively.	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).
57		170
58	FUNCTIONS	171	FUNCTIONS
59	AIO FUNCTIONS	172	AIO REQUEST FUNCTIONS
60	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
61	with the same name (sans "aio_"). The arguments are similar or	174	with the same name (sans "aio_"). The arguments are similar or
62	identical, and they all accept an additional (and optional) $callback	175	identical, and they all accept an additional (and optional) $callback
63	argument which must be a code reference. This code reference will get	176	argument which must be a code reference. This code reference will get
64	called with the syscall return code (e.g. most syscalls return -1 on	177	called with the syscall return code (e.g. most syscalls return -1 on
…		…
66	argument when the given syscall has been executed asynchronously.	179	argument when the given syscall has been executed asynchronously.
67		180
68	All functions expecting a filehandle keep a copy of the filehandle	181	All functions expecting a filehandle keep a copy of the filehandle
69	internally until the request has finished.	182	internally until the request has finished.
70		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
71	The pathnames you pass to these routines must be absolute and encoded	187	The pathnames you pass to these routines must be absolute and encoded
72	in byte form. The reason for the former is that at the time the request	188	as octets. The reason for the former is that at the time the request is
73	is being executed, the current working directory could have changed.	189	being executed, the current working directory could have changed.
74	Alternatively, you can make sure that you never change the current	190	Alternatively, you can make sure that you never change the current
75	working directory.	191	working directory anywhere in the program and then use relative paths.
76		192
77	To encode pathnames to byte form, either make sure you either: a) always	193	To encode pathnames as octets, either make sure you either: a) always
78	pass in filenames you got from outside (command line, readdir etc.), b)	194	pass in filenames you got from outside (command line, readdir etc.)
79	are ASCII or ISO 8859-1, c) use the Encode module and encode your	195	without tinkering, b) are ASCII or ISO 8859-1, c) use the Encode module
80	pathnames to the locale (or other) encoding in effect in the user	196	and encode your pathnames to the locale (or other) encoding in effect in
81	environment, d) use Glib::filename_from_unicode on unicode filenames or	197	the user environment, d) use Glib::filename_from_unicode on unicode
82	e) use something else.	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.
83		232
84	aio_open $pathname, $flags, $mode, $callback->($fh)	233	aio_open $pathname, $flags, $mode, $callback->($fh)
85	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
86	newly created filehandle for the file.	235	newly created filehandle for the file.
87		236
…		…
92	They are the same as used by "sysopen".	241	They are the same as used by "sysopen".
93		242
94	Likewise, $mode specifies the mode of the newly created file, if it	243	Likewise, $mode specifies the mode of the newly created file, if it
95	didn't exist and "O_CREAT" has been given, just like perl's	244	didn't exist and "O_CREAT" has been given, just like perl's
96	"sysopen", except that it is mandatory (i.e. use 0 if you don't	245	"sysopen", except that it is mandatory (i.e. use 0 if you don't
97	create new files, and 0666 or 0777 if you do).	246	create new files, and 0666 or 0777 if you do). Note that the $mode
		247	will be modified by the umask in effect then the request is being
		248	executed, so better never change the umask.
98		249
99	Example:	250	Example:
100		251
101	aio_open "/etc/passwd", O_RDONLY, 0, sub {	252	aio_open "/etc/passwd", O_RDONLY, 0, sub {
102	if ($_[0]) {	253	if ($_[0]) {
…		…
117	This is supposed to be a bug in the API, so that might change. It's	268	This is supposed to be a bug in the API, so that might change. It's
118	therefore best to avoid this function.	269	therefore best to avoid this function.
119		270
120	aio_read $fh,$offset,$length, $data,$dataoffset, $callback->($retval)	271	aio_read $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
121	aio_write $fh,$offset,$length, $data,$dataoffset, $callback->($retval)	272	aio_write $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
122	Reads or writes "length" bytes from the specified "fh" and "offset"	273	Reads or writes $length bytes from the specified $fh and $offset
123	into the scalar given by "data" and offset "dataoffset" and calls	274	into the scalar given by $data and offset $dataoffset and calls the
124	the callback without the actual number of bytes read (or -1 on	275	callback without the actual number of bytes read (or -1 on error,
125	error, just like the syscall).	276	just like the syscall).
		277
		278	If $offset is undefined, then the current file offset will be used
		279	(and updated), otherwise the file offset will not be changed by
		280	these calls.
		281
		282	If $length is undefined in "aio_write", use the remaining length of
		283	$data.
		284
		285	If $dataoffset is less than zero, it will be counted from the end of
		286	$data.
126		287
127	The $data scalar MUST NOT be modified in any way while the request	288	The $data scalar MUST NOT be modified in any way while the request
128	is outstanding. Modifying it can result in segfaults or WW3 (if the	289	is outstanding. Modifying it can result in segfaults or World War
129	necessary/optional hardware is installed).	290	III (if the necessary/optional hardware is installed).
130		291
131	Example: Read 15 bytes at offset 7 into scalar $buffer, starting at	292	Example: Read 15 bytes at offset 7 into scalar $buffer, starting at
132	offset 0 within the scalar:	293	offset 0 within the scalar:
133		294
134	aio_read $fh, 7, 15, $buffer, 0, sub {	295	aio_read $fh, 7, 15, $buffer, 0, sub {
…		…
192	aio_stat "/etc/passwd", sub {	353	aio_stat "/etc/passwd", sub {
193	$_[0] and die "stat failed: $!";	354	$_[0] and die "stat failed: $!";
194	print "size is ", -s _, "\n";	355	print "size is ", -s _, "\n";
195	};	356	};
196		357
		358	aio_utime $fh_or_path, $atime, $mtime, $callback->($status)
		359	Works like perl's "utime" function (including the special case of
		360	$atime and $mtime being undef). Fractional times are supported if
		361	the underlying syscalls support them.
		362
		363	When called with a pathname, uses utimes(2) if available, otherwise
		364	utime(2). If called on a file descriptor, uses futimes(2) if
		365	available, otherwise returns ENOSYS, so this is not portable.
		366
		367	Examples:
		368
		369	# set atime and mtime to current time (basically touch(1)):
		370	aio_utime "path", undef, undef;
		371	# set atime to current time and mtime to beginning of the epoch:
		372	aio_utime "path", time, undef; # undef==0
		373
		374	aio_chown $fh_or_path, $uid, $gid, $callback->($status)
		375	Works like perl's "chown" function, except that "undef" for either
		376	$uid or $gid is being interpreted as "do not change" (but -1 can
		377	also be used).
		378
		379	Examples:
		380
		381	# same as "chown root path" in the shell:
		382	aio_chown "path", 0, -1;
		383	# same as above:
		384	aio_chown "path", 0, undef;
		385
		386	aio_truncate $fh_or_path, $offset, $callback->($status)
		387	Works like truncate(2) or ftruncate(2).
		388
		389	aio_chmod $fh_or_path, $mode, $callback->($status)
		390	Works like perl's "chmod" function.
		391
197	aio_unlink $pathname, $callback->($status)	392	aio_unlink $pathname, $callback->($status)
198	Asynchronously unlink (delete) a file and call the callback with the	393	Asynchronously unlink (delete) a file and call the callback with the
199	result code.	394	result code.
200		395
		396	aio_mknod $path, $mode, $dev, $callback->($status)
		397	[EXPERIMENTAL]
		398
		399	Asynchronously create a device node (or fifo). See mknod(2).
		400
		401	The only (POSIX-) portable way of calling this function is:
		402
		403	aio_mknod $path, IO::AIO::S_IFIFO \| $mode, 0, sub { ...
		404
		405	aio_link $srcpath, $dstpath, $callback->($status)
		406	Asynchronously create a new link to the existing object at $srcpath
		407	at the path $dstpath and call the callback with the result code.
		408
		409	aio_symlink $srcpath, $dstpath, $callback->($status)
		410	Asynchronously create a new symbolic link to the existing object at
		411	$srcpath at the path $dstpath and call the callback with the result
		412	code.
		413
		414	aio_readlink $path, $callback->($link)
		415	Asynchronously read the symlink specified by $path and pass it to
		416	the callback. If an error occurs, nothing or undef gets passed to
		417	the callback.
		418
		419	aio_rename $srcpath, $dstpath, $callback->($status)
		420	Asynchronously rename the object at $srcpath to $dstpath, just as
		421	rename(2) and call the callback with the result code.
		422
		423	aio_mkdir $pathname, $mode, $callback->($status)
		424	Asynchronously mkdir (create) a directory and call the callback with
		425	the result code. $mode will be modified by the umask at the time the
		426	request is executed, so do not change your umask.
		427
201	aio_rmdir $pathname, $callback->($status)	428	aio_rmdir $pathname, $callback->($status)
202	Asynchronously rmdir (delete) a directory and call the callback with	429	Asynchronously rmdir (delete) a directory and call the callback with
203	the result code.	430	the result code.
204		431
205	aio_readdir $pathname $callback->($entries)	432	aio_readdir $pathname, $callback->($entries)
206	Unlike the POSIX call of the same name, "aio_readdir" reads an	433	Unlike the POSIX call of the same name, "aio_readdir" reads an
207	entire directory (i.e. opendir + readdir + closedir). The entries	434	entire directory (i.e. opendir + readdir + closedir). The entries
208	will not be sorted, and will NOT include the "." and ".." entries.	435	will not be sorted, and will NOT include the "." and ".." entries.
209		436
210	The callback a single argument which is either "undef" or an	437	The callback a single argument which is either "undef" or an
211	array-ref with the filenames.	438	array-ref with the filenames.
212		439
		440	aio_load $path, $data, $callback->($status)
		441	This is a composite request that tries to fully load the given file
		442	into memory. Status is the same as with aio_read.
		443
		444	aio_copy $srcpath, $dstpath, $callback->($status)
		445	Try to copy the file (directories not supported as either source
		446	or destination) from $srcpath to $dstpath and call the callback with
		447	the 0 (error) or -1 ok.
		448
		449	This is a composite request that it creates the destination file
		450	with mode 0200 and copies the contents of the source file into it
		451	using "aio_sendfile", followed by restoring atime, mtime, access
		452	mode and uid/gid, in that order.
		453
		454	If an error occurs, the partial destination file will be unlinked,
		455	if possible, except when setting atime, mtime, access mode and
		456	uid/gid, where errors are being ignored.
		457
		458	aio_move $srcpath, $dstpath, $callback->($status)
		459	Try to move the file (directories not supported as either source
		460	or destination) from $srcpath to $dstpath and call the callback with
		461	the 0 (error) or -1 ok.
		462
		463	This is a composite request that tries to rename(2) the file first.
		464	If rename files with "EXDEV", it copies the file with "aio_copy"
		465	and, if that is successful, unlinking the $srcpath.
		466
213	aio_scandir $path, $maxreq, $callback->($dirs, $nondirs)	467	aio_scandir $path, $maxreq, $callback->($dirs, $nondirs)
214	Scans a directory (similar to "aio_readdir") and tries to separate	468	Scans a directory (similar to "aio_readdir") but additionally tries
215	the entries of directory $path into two sets of names, ones you can	469	to efficiently separate the entries of directory $path into two sets
216	recurse into (directories), and ones you cannot recurse into	470	of names, directories you can recurse into (directories), and ones
217	(everything else).	471	you cannot recurse into (everything else, including symlinks to
		472	directories).
218		473
219	"aio_scandir" is a composite request that consists of many	474	"aio_scandir" is a composite request that creates of many sub
220	aio-primitives. $maxreq specifies the maximum number of outstanding	475	requests_ $maxreq specifies the maximum number of outstanding aio
221	aio requests that this function generates. If it is "<= 0", then a	476	requests that this function generates. If it is "<= 0", then a
222	suitable default will be chosen (currently 8).	477	suitable default will be chosen (currently 4).
223		478
224	On error, the callback is called without arguments, otherwise it	479	On error, the callback is called without arguments, otherwise it
225	receives two array-refs with path-relative entry names.	480	receives two array-refs with path-relative entry names.
226		481
227	Example:	482	Example:
…		…
236		491
237	The "aio_readdir" cannot be avoided, but "stat()"'ing every entry	492	The "aio_readdir" cannot be avoided, but "stat()"'ing every entry
238	can.	493	can.
239		494
240	After reading the directory, the modification time, size etc. of the	495	After reading the directory, the modification time, size etc. of the
241	directory before and after the readdir is checked, and if they	496	directory before and after the readdir is checked, and if they match
242	match, the link count will be used to decide how many entries are	497	(and isn't the current time), the link count will be used to decide
243	directories (if >= 2). Otherwise, no knowledge of the number of	498	how many entries are directories (if >= 2). Otherwise, no knowledge
244	subdirectories will be assumed.	499	of the number of subdirectories will be assumed.
245		500
246	Then entires will be sorted into likely directories (everything	501	Then entries will be sorted into likely directories (everything
247	without a non-initial dot) and likely non-directories (everything	502	without a non-initial dot currently) and likely non-directories
248	else). Then every entry + "/." will be "stat"'ed, likely directories	503	(everything else). Then every entry plus an appended "/." will be
249	first. This is often faster because filesystems might detect the	504	"stat"'ed, likely directories first. If that succeeds, it assumes
250	type of the entry without reading the inode data (e.g. ext2s
251	filetype feature). If that succeeds, it assumes that the entry is a
252	directory or a symlink to directory (which will be checked	505	that the entry is a directory or a symlink to directory (which will
253	seperately).	506	be checked seperately). This is often faster than stat'ing the entry
		507	itself because filesystems might detect the type of the entry
		508	without reading the inode data (e.g. ext2fs filetype feature).
254		509
255	If the known number of directories has been reached, the rest of the	510	If the known number of directories (link count - 2) has been
256	entries is assumed to be non-directories.	511	reached, the rest of the entries is assumed to be non-directories.
		512
		513	This only works with certainty on POSIX (= UNIX) filesystems, which
		514	fortunately are the vast majority of filesystems around.
		515
		516	It will also likely work on non-POSIX filesystems with reduced
		517	efficiency as those tend to return 0 or 1 as link counts, which
		518	disables the directory counting heuristic.
		519
		520	aio_rmtree $path, $callback->($status)
		521	Delete a directory tree starting (and including) $path, return the
		522	status of the final "rmdir" only. This is a composite request that
		523	uses "aio_scandir" to recurse into and rmdir directories, and unlink
		524	everything else.
257		525
258	aio_fsync $fh, $callback->($status)	526	aio_fsync $fh, $callback->($status)
259	Asynchronously call fsync on the given filehandle and call the	527	Asynchronously call fsync on the given filehandle and call the
260	callback with the fsync result code.	528	callback with the fsync result code.
261		529
…		…
264	callback with the fdatasync result code.	532	callback with the fdatasync result code.
265		533
266	If this call isn't available because your OS lacks it or it couldn't	534	If this call isn't available because your OS lacks it or it couldn't
267	be detected, it will be emulated by calling "fsync" instead.	535	be detected, it will be emulated by calling "fsync" instead.
268		536
		537	aio_group $callback->(...)
		538	This is a very special aio request: Instead of doing something, it
		539	is a container for other aio requests, which is useful if you want
		540	to bundle many requests into a single, composite, request with a
		541	definite callback and the ability to cancel the whole request with
		542	its subrequests.
		543
		544	Returns an object of class IO::AIO::GRP. See its documentation below
		545	for more info.
		546
		547	Example:
		548
		549	my $grp = aio_group sub {
		550	print "all stats done\n";
		551	};
		552
		553	add $grp
		554	(aio_stat ...),
		555	(aio_stat ...),
		556	...;
		557
		558	aio_nop $callback->()
		559	This is a special request - it does nothing in itself and is only
		560	used for side effects, such as when you want to add a dummy request
		561	to a group so that finishing the requests in the group depends on
		562	executing the given code.
		563
		564	While this request does nothing, it still goes through the execution
		565	phase and still requires a worker thread. Thus, the callback will
		566	not be executed immediately but only after other requests in the
		567	queue have entered their execution phase. This can be used to
		568	measure request latency.
		569
		570	IO::AIO::aio_busy $fractional_seconds, $callback->() NOT EXPORTED
		571	Mainly used for debugging and benchmarking, this aio request puts
		572	one of the request workers to sleep for the given time.
		573
		574	While it is theoretically handy to have simple I/O scheduling
		575	requests like sleep and file handle readable/writable, the overhead
		576	this creates is immense (it blocks a thread for a long time) so do
		577	not use this function except to put your application under
		578	artificial I/O pressure.
		579
		580	IO::AIO::REQ CLASS
		581	All non-aggregate "aio_*" functions return an object of this class when
		582	called in non-void context.
		583
		584	cancel $req
		585	Cancels the request, if possible. Has the effect of skipping
		586	execution when entering the execute state and skipping calling the
		587	callback when entering the the result state, but will leave the
		588	request otherwise untouched. That means that requests that currently
		589	execute will not be stopped and resources held by the request will
		590	not be freed prematurely.
		591
		592	cb $req $callback->(...)
		593	Replace (or simply set) the callback registered to the request.
		594
		595	IO::AIO::GRP CLASS
		596	This class is a subclass of IO::AIO::REQ, so all its methods apply to
		597	objects of this class, too.
		598
		599	A IO::AIO::GRP object is a special request that can contain multiple
		600	other aio requests.
		601
		602	You create one by calling the "aio_group" constructing function with a
		603	callback that will be called when all contained requests have entered
		604	the "done" state:
		605
		606	my $grp = aio_group sub {
		607	print "all requests are done\n";
		608	};
		609
		610	You add requests by calling the "add" method with one or more
		611	"IO::AIO::REQ" objects:
		612
		613	$grp->add (aio_unlink "...");
		614
		615	add $grp aio_stat "...", sub {
		616	$_[0] or return $grp->result ("error");
		617
		618	# add another request dynamically, if first succeeded
		619	add $grp aio_open "...", sub {
		620	$grp->result ("ok");
		621	};
		622	};
		623
		624	This makes it very easy to create composite requests (see the source of
		625	"aio_move" for an application) that work and feel like simple requests.
		626
		627	* The IO::AIO::GRP objects will be cleaned up during calls to
		628	"IO::AIO::poll_cb", just like any other request.
		629	* They can be canceled like any other request. Canceling will cancel not
		630	only the request itself, but also all requests it contains.
		631	* They can also can also be added to other IO::AIO::GRP objects.
		632	* You must not add requests to a group from within the group callback
		633	(or any later time).
		634
		635	Their lifetime, simplified, looks like this: when they are empty, they
		636	will finish very quickly. If they contain only requests that are in the
		637	"done" state, they will also finish. Otherwise they will continue to
		638	exist.
		639
		640	That means after creating a group you have some time to add requests.
		641	And in the callbacks of those requests, you can add further requests to
		642	the group. And only when all those requests have finished will the the
		643	group itself finish.
		644
		645	add $grp ...
		646	$grp->add (...)
		647	Add one or more requests to the group. Any type of IO::AIO::REQ can
		648	be added, including other groups, as long as you do not create
		649	circular dependencies.
		650
		651	Returns all its arguments.
		652
		653	$grp->cancel_subs
		654	Cancel all subrequests and clears any feeder, but not the group
		655	request itself. Useful when you queued a lot of events but got a
		656	result early.
		657
		658	$grp->result (...)
		659	Set the result value(s) that will be passed to the group callback
		660	when all subrequests have finished and set thre groups errno to the
		661	current value of errno (just like calling "errno" without an error
		662	number). By default, no argument will be passed and errno is zero.
		663
		664	$grp->errno ([$errno])
		665	Sets the group errno value to $errno, or the current value of errno
		666	when the argument is missing.
		667
		668	Every aio request has an associated errno value that is restored
		669	when the callback is invoked. This method lets you change this value
		670	from its default (0).
		671
		672	Calling "result" will also set errno, so make sure you either set $!
		673	before the call to "result", or call c<errno> after it.
		674
		675	feed $grp $callback->($grp)
		676	Sets a feeder/generator on this group: every group can have an
		677	attached generator that generates requests if idle. The idea behind
		678	this is that, although you could just queue as many requests as you
		679	want in a group, this might starve other requests for a potentially
		680	long time. For example, "aio_scandir" might generate hundreds of
		681	thousands "aio_stat" requests, delaying any later requests for a
		682	long time.
		683
		684	To avoid this, and allow incremental generation of requests, you can
		685	instead a group and set a feeder on it that generates those
		686	requests. The feed callback will be called whenever there are few
		687	enough (see "limit", below) requests active in the group itself and
		688	is expected to queue more requests.
		689
		690	The feed callback can queue as many requests as it likes (i.e. "add"
		691	does not impose any limits).
		692
		693	If the feed does not queue more requests when called, it will be
		694	automatically removed from the group.
		695
		696	If the feed limit is 0, it will be set to 2 automatically.
		697
		698	Example:
		699
		700	# stat all files in @files, but only ever use four aio requests concurrently:
		701
		702	my $grp = aio_group sub { print "finished\n" };
		703	limit $grp 4;
		704	feed $grp sub {
		705	my $file = pop @files
		706	or return;
		707
		708	add $grp aio_stat $file, sub { ... };
		709	};
		710
		711	limit $grp $num
		712	Sets the feeder limit for the group: The feeder will be called
		713	whenever the group contains less than this many requests.
		714
		715	Setting the limit to 0 will pause the feeding process.
		716
269	SUPPORT FUNCTIONS	717	SUPPORT FUNCTIONS
		718	EVENT PROCESSING AND EVENT LOOP INTEGRATION
270	$fileno = IO::AIO::poll_fileno	719	$fileno = IO::AIO::poll_fileno
271	Return the request result pipe file descriptor. This filehandle	720	Return the request result pipe file descriptor. This filehandle
272	must be polled for reading by some mechanism outside this module	721	must be polled for reading by some mechanism outside this module
273	(e.g. Event or select, see below or the SYNOPSIS). If the pipe	722	(e.g. Event or select, see below or the SYNOPSIS). If the pipe
274	becomes readable you have to call "poll_cb" to check the results.	723	becomes readable you have to call "poll_cb" to check the results.
275		724
276	See "poll_cb" for an example.	725	See "poll_cb" for an example.
277		726
278	IO::AIO::poll_cb	727	IO::AIO::poll_cb
279	Process all outstanding events on the result pipe. You have to call	728	Process some outstanding events on the result pipe. You have to call
280	this regularly. Returns the number of events processed. Returns	729	this regularly. Returns the number of events processed. Returns
281	immediately when no events are outstanding.	730	immediately when no events are outstanding. The amount of events
		731	processed depends on the settings of "IO::AIO::max_poll_req" and
		732	"IO::AIO::max_poll_time".
		733
		734	If not all requests were processed for whatever reason, the
		735	filehandle will still be ready when "poll_cb" returns.
282		736
283	Example: Install an Event watcher that automatically calls	737	Example: Install an Event watcher that automatically calls
284	IO::AIO::poll_cb with high priority:	738	IO::AIO::poll_cb with high priority:
285		739
286	Event->io (fd => IO::AIO::poll_fileno,	740	Event->io (fd => IO::AIO::poll_fileno,
287	poll => 'r', async => 1,	741	poll => 'r', async => 1,
288	cb => \&IO::AIO::poll_cb);	742	cb => \&IO::AIO::poll_cb);
289		743
		744	IO::AIO::max_poll_reqs $nreqs
		745	IO::AIO::max_poll_time $seconds
		746	These set the maximum number of requests (default 0, meaning
		747	infinity) that are being processed by "IO::AIO::poll_cb" in one
		748	call, respectively the maximum amount of time (default 0, meaning
		749	infinity) spent in "IO::AIO::poll_cb" to process requests (more
		750	correctly the mininum amount of time "poll_cb" is allowed to use).
		751
		752	Setting "max_poll_time" to a non-zero value creates an overhead of
		753	one syscall per request processed, which is not normally a problem
		754	unless your callbacks are really really fast or your OS is really
		755	really slow (I am not mentioning Solaris here). Using
		756	"max_poll_reqs" incurs no overhead.
		757
		758	Setting these is useful if you want to ensure some level of
		759	interactiveness when perl is not fast enough to process all requests
		760	in time.
		761
		762	For interactive programs, values such as 0.01 to 0.1 should be fine.
		763
		764	Example: Install an Event watcher that automatically calls
		765	IO::AIO::poll_cb with low priority, to ensure that other parts of
		766	the program get the CPU sometimes even under high AIO load.
		767
		768	# try not to spend much more than 0.1s in poll_cb
		769	IO::AIO::max_poll_time 0.1;
		770
		771	# use a low priority so other tasks have priority
		772	Event->io (fd => IO::AIO::poll_fileno,
		773	poll => 'r', nice => 1,
		774	cb => &IO::AIO::poll_cb);
		775
290	IO::AIO::poll_wait	776	IO::AIO::poll_wait
		777	If there are any outstanding requests and none of them in the result
291	Wait till the result filehandle becomes ready for reading (simply	778	phase, wait till the result filehandle becomes ready for reading
292	does a "select" on the filehandle. This is useful if you want to	779	(simply does a "select" on the filehandle. This is useful if you
293	synchronously wait for some requests to finish).	780	want to synchronously wait for some requests to finish).
294		781
295	See "nreqs" for an example.	782	See "nreqs" for an example.
296		783
		784	IO::AIO::poll
		785	Waits until some requests have been handled.
		786
		787	Returns the number of requests processed, but is otherwise strictly
		788	equivalent to:
		789
		790	IO::AIO::poll_wait, IO::AIO::poll_cb
		791
297	IO::AIO::nreqs	792	IO::AIO::flush
298	Returns the number of requests currently outstanding (i.e. for which	793	Wait till all outstanding AIO requests have been handled.
299	their callback has not been invoked yet).
300		794
301	Example: wait till there are no outstanding requests anymore:	795	Strictly equivalent to:
302		796
303	IO::AIO::poll_wait, IO::AIO::poll_cb	797	IO::AIO::poll_wait, IO::AIO::poll_cb
304	while IO::AIO::nreqs;	798	while IO::AIO::nreqs;
305		799
306	IO::AIO::flush	800	CONTROLLING THE NUMBER OF THREADS
307	Wait till all outstanding AIO requests have been handled.
308
309	Strictly equivalent to:
310
311	IO::AIO::poll_wait, IO::AIO::poll_cb
312	while IO::AIO::nreqs;
313
314	IO::AIO::poll
315	Waits until some requests have been handled.
316
317	Strictly equivalent to:
318
319	IO::AIO::poll_wait, IO::AIO::poll_cb
320	if IO::AIO::nreqs;
321
322	IO::AIO::min_parallel $nthreads	801	IO::AIO::min_parallel $nthreads
323	Set the minimum number of AIO threads to $nthreads. The current	802	Set the minimum number of AIO threads to $nthreads. The current
324	default is 4, which means four asynchronous operations can be done	803	default is 8, which means eight asynchronous operations can execute
325	at one time (the number of outstanding operations, however, is	804	concurrently at any one time (the number of outstanding requests,
326	unlimited).	805	however, is unlimited).
327		806
328	IO::AIO starts threads only on demand, when an AIO request is queued	807	IO::AIO starts threads only on demand, when an AIO request is queued
329	and no free thread exists.	808	and no free thread exists. Please note that queueing up a hundred
		809	requests can create demand for a hundred threads, even if it turns
		810	out that everything is in the cache and could have been processed
		811	faster by a single thread.
330		812
331	It is recommended to keep the number of threads low, as some Linux	813	It is recommended to keep the number of threads relatively low, as
332	kernel versions will scale negatively with the number of threads	814	some Linux kernel versions will scale negatively with the number of
333	(higher parallelity => MUCH higher latency). With current Linux 2.6	815	threads (higher parallelity => MUCH higher latency). With current
334	versions, 4-32 threads should be fine.	816	Linux 2.6 versions, 4-32 threads should be fine.
335		817
336	Under most circumstances you don't need to call this function, as	818	Under most circumstances you don't need to call this function, as
337	the module selects a default that is suitable for low to moderate	819	the module selects a default that is suitable for low to moderate
338	load.	820	load.
339		821
…		…
349	ensure that all threads are killed and that there are no outstanding	831	ensure that all threads are killed and that there are no outstanding
350	requests.	832	requests.
351		833
352	Under normal circumstances you don't need to call this function.	834	Under normal circumstances you don't need to call this function.
353		835
		836	IO::AIO::max_idle $nthreads
		837	Limit the number of threads (default: 4) that are allowed to idle
		838	(i.e., threads that did not get a request to process within 10
		839	seconds). That means if a thread becomes idle while $nthreads other
		840	threads are also idle, it will free its resources and exit.
		841
		842	This is useful when you allow a large number of threads (e.g. 100 or
		843	1000) to allow for extremely high load situations, but want to free
		844	resources under normal circumstances (1000 threads can easily
		845	consume 30MB of RAM).
		846
		847	The default is probably ok in most situations, especially if thread
		848	creation is fast. If thread creation is very slow on your system you
		849	might want to use larger values.
		850
354	$oldnreqs = IO::AIO::max_outstanding $nreqs	851	$oldmaxreqs = IO::AIO::max_outstanding $maxreqs
		852	This is a very bad function to use in interactive programs because
		853	it blocks, and a bad way to reduce concurrency because it is
		854	inexact: Better use an "aio_group" together with a feed callback.
		855
355	Sets the maximum number of outstanding requests to $nreqs. If you	856	Sets the maximum number of outstanding requests to $nreqs. If you to
356	try to queue up more than this number of requests, the caller will	857	queue up more than this number of requests, the next call to the
357	block until some requests have been handled.	858	"poll_cb" (and "poll_some" and other functions calling "poll_cb")
		859	function will block until the limit is no longer exceeded.
358		860
359	The default is very large, so normally there is no practical limit.	861	The default value is very large, so there is no practical limit on
360	If you queue up many requests in a loop it often improves speed if	862	the number of outstanding requests.
361	you set this to a relatively low number, such as 100.
362		863
363	Under normal circumstances you don't need to call this function.	864	You can still queue as many requests as you want. Therefore,
		865	"max_oustsanding" is mainly useful in simple scripts (with low
		866	values) or as a stop gap to shield against fatal memory overflow
		867	(with large values).
		868
		869	STATISTICAL INFORMATION
		870	IO::AIO::nreqs
		871	Returns the number of requests currently in the ready, execute or
		872	pending states (i.e. for which their callback has not been invoked
		873	yet).
		874
		875	Example: wait till there are no outstanding requests anymore:
		876
		877	IO::AIO::poll_wait, IO::AIO::poll_cb
		878	while IO::AIO::nreqs;
		879
		880	IO::AIO::nready
		881	Returns the number of requests currently in the ready state (not yet
		882	executed).
		883
		884	IO::AIO::npending
		885	Returns the number of requests currently in the pending state
		886	(executed, but not yet processed by poll_cb).
364		887
365	FORK BEHAVIOUR	888	FORK BEHAVIOUR
		889	This module should do "the right thing" when the process using it forks:
		890
366	Before the fork, IO::AIO enters a quiescent state where no requests can	891	Before the fork, IO::AIO enters a quiescent state where no requests can
367	be added in other threads and no results will be processed. After the	892	be added in other threads and no results will be processed. After the
368	fork the parent simply leaves the quiescent state and continues	893	fork the parent simply leaves the quiescent state and continues
369	request/result processing, while the child clears the request/result	894	request/result processing, while the child frees the request/result
370	queue (so the requests started before the fork will only be handled in	895	queue (so that the requests started before the fork will only be handled
371	the parent). Threats will be started on demand until the limit ste in	896	in the parent). Threads will be started on demand until the limit set in
372	the parent process has been reached again.	897	the parent process has been reached again.
373		898
		899	In short: the parent will, after a short pause, continue as if fork had
		900	not been called, while the child will act as if IO::AIO has not been
		901	used yet.
		902
		903	MEMORY USAGE
		904	Per-request usage:
		905
		906	Each aio request uses - depending on your architecture - around 100-200
		907	bytes of memory. In addition, stat requests need a stat buffer (possibly
		908	a few hundred bytes), readdir requires a result buffer and so on. Perl
		909	scalars and other data passed into aio requests will also be locked and
		910	will consume memory till the request has entered the done state.
		911
		912	This is now awfully much, so queuing lots of requests is not usually a
		913	problem.
		914
		915	Per-thread usage:
		916
		917	In the execution phase, some aio requests require more memory for
		918	temporary buffers, and each thread requires a stack and other data
		919	structures (usually around 16k-128k, depending on the OS).
		920
		921	KNOWN BUGS
		922	Known bugs will be fixed in the next release.
		923
374	SEE ALSO	924	SEE ALSO
375	Coro, Linux::AIO.	925	Coro::AIO.
376		926
377	AUTHOR	927	AUTHOR
378	Marc Lehmann <schmorp@schmorp.de>	928	Marc Lehmann <schmorp@schmorp.de>
379	http://home.schmorp.de/	929	http://home.schmorp.de/
380		930

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Revision 1.24 by root, Sun Aug 5 16:45:54 2007 UTC