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

Comparing IO-AIO/README (file contents):
Revision 1.17 by root, Mon Jun 26 14:53:55 2006 UTC vs.
Revision 1.21 by root, Fri Dec 22 04:05:50 2006 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	or might not work (aio_read fails on sockets/pipes/fifos). Use an event
		68	loop for that (such as the Event module): IO::AIO will naturally fit
		69	into such an event loop itself.
		70
43	Currently, a number of threads are started that execute your read/writes	71	In this version, a number of threads are started that execute your
44	and signal their completion. You don't need thread support in your libc	72	requests and signal their completion. You don't need thread support in
45	or perl, and the threads created by this module will not be visible to	73	perl, and the threads created by this module will not be visible to
46	the pthreads library. In the future, this module might make use of the	74	perl. In the future, this module might make use of the native aio
47	native aio functions available on many operating systems. However, they	75	functions available on many operating systems. However, they are often
48	are often not well-supported (Linux doesn't allow them on normal files	76	not well-supported or restricted (GNU/Linux doesn't allow them on normal
49	currently, for example), and they would only support aio_read and	77	files currently, for example), and they would only support aio_read and
50	aio_write, so the remaining functionality would have to be implemented	78	aio_write, so the remaining functionality would have to be implemented
51	using threads anyway.	79	using threads anyway.
52		80
53	Although the module will work with in the presence of other threads, it	81	Although the module will work with in the presence of other (Perl-)
54	is currently not reentrant, so use appropriate locking yourself, always	82	threads, it is currently not reentrant in any way, so use appropriate
55	call "poll_cb" from within the same thread, or never call "poll_cb" (or	83	locking yourself, always call "poll_cb" from within the same thread, or
56	other "aio_" functions) recursively.	84	never call "poll_cb" (or other "aio_" functions) recursively.
		85
		86	EXAMPLE
		87	This is a simple example that uses the Event module and loads
		88	/etc/passwd asynchronously:
		89
		90	use Fcntl;
		91	use Event;
		92	use IO::AIO;
		93
		94	# register the IO::AIO callback with Event
		95	Event->io (fd => IO::AIO::poll_fileno,
		96	poll => 'r',
		97	cb => \&IO::AIO::poll_cb);
		98
		99	# queue the request to open /etc/passwd
		100	aio_open "/etc/passwd", O_RDONLY, 0, sub {
		101	my $fh = shift
		102	or die "error while opening: $!";
		103
		104	# stat'ing filehandles is generally non-blocking
		105	my $size = -s $fh;
		106
		107	# queue a request to read the file
		108	my $contents;
		109	aio_read $fh, 0, $size, $contents, 0, sub {
		110	$_[0] == $size
		111	or die "short read: $!";
		112
		113	close $fh;
		114
		115	# file contents now in $contents
		116	print $contents;
		117
		118	# exit event loop and program
		119	Event::unloop;
		120	};
		121	};
		122
		123	# possibly queue up other requests, or open GUI windows,
		124	# check for sockets etc. etc.
		125
		126	# process events as long as there are some:
		127	Event::loop;
		128
		129	REQUEST ANATOMY AND LIFETIME
		130	Every "aio_*" function creates a request. which is a C data structure
		131	not directly visible to Perl.
		132
		133	If called in non-void context, every request function returns a Perl
		134	object representing the request. In void context, nothing is returned,
		135	which saves a bit of memory.
		136
		137	The perl object is a fairly standard ref-to-hash object. The hash
		138	contents are not used by IO::AIO so you are free to store anything you
		139	like in it.
		140
		141	During their existance, aio requests travel through the following
		142	states, in order:
		143
		144	ready
		145	Immediately after a request is created it is put into the ready
		146	state, waiting for a thread to execute it.
		147
		148	execute
		149	A thread has accepted the request for processing and is currently
		150	executing it (e.g. blocking in read).
		151
		152	pending
		153	The request has been executed and is waiting for result processing.
		154
		155	While request submission and execution is fully asynchronous, result
		156	processing is not and relies on the perl interpreter calling
		157	"poll_cb" (or another function with the same effect).
		158
		159	result
		160	The request results are processed synchronously by "poll_cb".
		161
		162	The "poll_cb" function will process all outstanding aio requests by
		163	calling their callbacks, freeing memory associated with them and
		164	managing any groups they are contained in.
		165
		166	done
		167	Request has reached the end of its lifetime and holds no resources
		168	anymore (except possibly for the Perl object, but its connection to
		169	the actual aio request is severed and calling its methods will
		170	either do nothing or result in a runtime error).
57		171
58	FUNCTIONS	172	FUNCTIONS
59	AIO FUNCTIONS	173	AIO REQUEST FUNCTIONS
60	All the "aio_*" calls are more or less thin wrappers around the syscall	174	All the "aio_*" calls are more or less thin wrappers around the syscall
61	with the same name (sans "aio_"). The arguments are similar or	175	with the same name (sans "aio_"). The arguments are similar or
62	identical, and they all accept an additional (and optional) $callback	176	identical, and they all accept an additional (and optional) $callback
63	argument which must be a code reference. This code reference will get	177	argument which must be a code reference. This code reference will get
64	called with the syscall return code (e.g. most syscalls return -1 on	178	called with the syscall return code (e.g. most syscalls return -1 on
…		…
66	argument when the given syscall has been executed asynchronously.	180	argument when the given syscall has been executed asynchronously.
67		181
68	All functions expecting a filehandle keep a copy of the filehandle	182	All functions expecting a filehandle keep a copy of the filehandle
69	internally until the request has finished.	183	internally until the request has finished.
70		184
		185	All functions return request objects of type IO::AIO::REQ that allow
		186	further manipulation of those requests while they are in-flight.
		187
71	The pathnames you pass to these routines must be absolute and encoded	188	The pathnames you pass to these routines must be absolute and encoded
72	in byte form. The reason for the former is that at the time the request	189	as octets. The reason for the former is that at the time the request is
73	is being executed, the current working directory could have changed.	190	being executed, the current working directory could have changed.
74	Alternatively, you can make sure that you never change the current	191	Alternatively, you can make sure that you never change the current
75	working directory.	192	working directory anywhere in the program and then use relative paths.
76		193
77	To encode pathnames to byte form, either make sure you either: a) always	194	To encode pathnames as octets, either make sure you either: a) always
78	pass in filenames you got from outside (command line, readdir etc.), b)	195	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	196	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	197	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	198	the user environment, d) use Glib::filename_from_unicode on unicode
82	e) use something else.	199	filenames or e) use something else to ensure your scalar has the correct
		200	contents.
		201
		202	This works, btw. independent of the internal UTF-8 bit, which IO::AIO
		203	handles correctly wether it is set or not.
		204
		205	$prev_pri = aioreq_pri [$pri]
		206	Returns the priority value that would be used for the next request
		207	and, if $pri is given, sets the priority for the next aio request.
		208
		209	The default priority is 0, the minimum and maximum priorities are -4
		210	and 4, respectively. Requests with higher priority will be serviced
		211	first.
		212
		213	The priority will be reset to 0 after each call to one of the
		214	"aio_*" functions.
		215
		216	Example: open a file with low priority, then read something from it
		217	with higher priority so the read request is serviced before other
		218	low priority open requests (potentially spamming the cache):
		219
		220	aioreq_pri -3;
		221	aio_open ..., sub {
		222	return unless $_[0];
		223
		224	aioreq_pri -2;
		225	aio_read $_[0], ..., sub {
		226	...
		227	};
		228	};
		229
		230	aioreq_nice $pri_adjust
		231	Similar to "aioreq_pri", but subtracts the given value from the
		232	current priority, so the effect is cumulative.
83		233
84	aio_open $pathname, $flags, $mode, $callback->($fh)	234	aio_open $pathname, $flags, $mode, $callback->($fh)
85	Asynchronously open or create a file and call the callback with a	235	Asynchronously open or create a file and call the callback with a
86	newly created filehandle for the file.	236	newly created filehandle for the file.
87		237
…		…
133		283
134	aio_read $fh, 7, 15, $buffer, 0, sub {	284	aio_read $fh, 7, 15, $buffer, 0, sub {
135	$_[0] > 0 or die "read error: $!";	285	$_[0] > 0 or die "read error: $!";
136	print "read $_[0] bytes: <$buffer>\n";	286	print "read $_[0] bytes: <$buffer>\n";
137	};	287	};
138
139	aio_move $srcpath, $dstpath, $callback->($status)
140	[EXPERIMENTAL]
141
142	Try to move the file (directories not supported as either source
143	or destination) from $srcpath to $dstpath and call the callback with
144	the 0 (error) or -1 ok.
145
146	This is a composite request that tries to rename(2) the file first.
147	If rename files with "EXDEV", it creates the destination file with
148	mode 0200 and copies the contents of the source file into it using
149	"aio_sendfile", followed by restoring atime, mtime, access mode and
150	uid/gid, in that order, and unlinking the $srcpath.
151
152	If an error occurs, the partial destination file will be unlinked,
153	if possible, except when setting atime, mtime, access mode and
154	uid/gid, where errors are being ignored.
155		288
156	aio_sendfile $out_fh, $in_fh, $in_offset, $length, $callback->($retval)	289	aio_sendfile $out_fh, $in_fh, $in_offset, $length, $callback->($retval)
157	Tries to copy $length bytes from $in_fh to $out_fh. It starts	290	Tries to copy $length bytes from $in_fh to $out_fh. It starts
158	reading at byte offset $in_offset, and starts writing at the current	291	reading at byte offset $in_offset, and starts writing at the current
159	file offset of $out_fh. Because of that, it is not safe to issue	292	file offset of $out_fh. Because of that, it is not safe to issue
…		…
213		346
214	aio_unlink $pathname, $callback->($status)	347	aio_unlink $pathname, $callback->($status)
215	Asynchronously unlink (delete) a file and call the callback with the	348	Asynchronously unlink (delete) a file and call the callback with the
216	result code.	349	result code.
217		350
		351	aio_mknod $path, $mode, $dev, $callback->($status)
		352	[EXPERIMENTAL]
		353
		354	Asynchronously create a device node (or fifo). See mknod(2).
		355
		356	The only (POSIX-) portable way of calling this function is:
		357
		358	aio_mknod $path, IO::AIO::S_IFIFO \| $mode, 0, sub { ...
		359
218	aio_link $srcpath, $dstpath, $callback->($status)	360	aio_link $srcpath, $dstpath, $callback->($status)
219	Asynchronously create a new link to the existing object at $srcpath	361	Asynchronously create a new link to the existing object at $srcpath
220	at the path $dstpath and call the callback with the result code.	362	at the path $dstpath and call the callback with the result code.
221		363
222	aio_symlink $srcpath, $dstpath, $callback->($status)	364	aio_symlink $srcpath, $dstpath, $callback->($status)
223	Asynchronously create a new symbolic link to the existing object at	365	Asynchronously create a new symbolic link to the existing object at
224	$srcpath at the path $dstpath and call the callback with the result	366	$srcpath at the path $dstpath and call the callback with the result
225	code.	367	code.
226		368
		369	aio_readlink $path, $callback->($link)
		370	Asynchronously read the symlink specified by $path and pass it to
		371	the callback. If an error occurs, nothing or undef gets passed to
		372	the callback.
		373
227	aio_rename $srcpath, $dstpath, $callback->($status)	374	aio_rename $srcpath, $dstpath, $callback->($status)
228	Asynchronously rename the object at $srcpath to $dstpath, just as	375	Asynchronously rename the object at $srcpath to $dstpath, just as
229	rename(2) and call the callback with the result code.	376	rename(2) and call the callback with the result code.
230		377
231	aio_rmdir $pathname, $callback->($status)	378	aio_rmdir $pathname, $callback->($status)
…		…
238	will not be sorted, and will NOT include the "." and ".." entries.	385	will not be sorted, and will NOT include the "." and ".." entries.
239		386
240	The callback a single argument which is either "undef" or an	387	The callback a single argument which is either "undef" or an
241	array-ref with the filenames.	388	array-ref with the filenames.
242		389
		390	aio_copy $srcpath, $dstpath, $callback->($status)
		391	Try to copy the file (directories not supported as either source
		392	or destination) from $srcpath to $dstpath and call the callback with
		393	the 0 (error) or -1 ok.
		394
		395	This is a composite request that it creates the destination file
		396	with mode 0200 and copies the contents of the source file into it
		397	using "aio_sendfile", followed by restoring atime, mtime, access
		398	mode and uid/gid, in that order.
		399
		400	If an error occurs, the partial destination file will be unlinked,
		401	if possible, except when setting atime, mtime, access mode and
		402	uid/gid, where errors are being ignored.
		403
		404	aio_move $srcpath, $dstpath, $callback->($status)
		405	Try to move the file (directories not supported as either source
		406	or destination) from $srcpath to $dstpath and call the callback with
		407	the 0 (error) or -1 ok.
		408
		409	This is a composite request that tries to rename(2) the file first.
		410	If rename files with "EXDEV", it copies the file with "aio_copy"
		411	and, if that is successful, unlinking the $srcpath.
		412
243	aio_scandir $path, $maxreq, $callback->($dirs, $nondirs)	413	aio_scandir $path, $maxreq, $callback->($dirs, $nondirs)
244	Scans a directory (similar to "aio_readdir") and tries to separate	414	Scans a directory (similar to "aio_readdir") but additionally tries
245	the entries of directory $path into two sets of names, ones you can	415	to efficiently separate the entries of directory $path into two sets
246	recurse into (directories), and ones you cannot recurse into	416	of names, directories you can recurse into (directories), and ones
247	(everything else).	417	you cannot recurse into (everything else, including symlinks to
		418	directories).
248		419
249	"aio_scandir" is a composite request that consists of many	420	"aio_scandir" is a composite request that creates of many sub
250	aio-primitives. $maxreq specifies the maximum number of outstanding	421	requests_ $maxreq specifies the maximum number of outstanding aio
251	aio requests that this function generates. If it is "<= 0", then a	422	requests that this function generates. If it is "<= 0", then a
252	suitable default will be chosen (currently 8).	423	suitable default will be chosen (currently 4).
253		424
254	On error, the callback is called without arguments, otherwise it	425	On error, the callback is called without arguments, otherwise it
255	receives two array-refs with path-relative entry names.	426	receives two array-refs with path-relative entry names.
256		427
257	Example:	428	Example:
…		…
266		437
267	The "aio_readdir" cannot be avoided, but "stat()"'ing every entry	438	The "aio_readdir" cannot be avoided, but "stat()"'ing every entry
268	can.	439	can.
269		440
270	After reading the directory, the modification time, size etc. of the	441	After reading the directory, the modification time, size etc. of the
271	directory before and after the readdir is checked, and if they	442	directory before and after the readdir is checked, and if they match
272	match, the link count will be used to decide how many entries are	443	(and isn't the current time), the link count will be used to decide
273	directories (if >= 2). Otherwise, no knowledge of the number of	444	how many entries are directories (if >= 2). Otherwise, no knowledge
274	subdirectories will be assumed.	445	of the number of subdirectories will be assumed.
275		446
276	Then entires will be sorted into likely directories (everything	447	Then entries will be sorted into likely directories (everything
277	without a non-initial dot) and likely non-directories (everything	448	without a non-initial dot currently) and likely non-directories
278	else). Then every entry + "/." will be "stat"'ed, likely directories	449	(everything else). Then every entry plus an appended "/." will be
279	first. This is often faster because filesystems might detect the	450	"stat"'ed, likely directories first. If that succeeds, it assumes
280	type of the entry without reading the inode data (e.g. ext2fs
281	filetype feature). If that succeeds, it assumes that the entry is a
282	directory or a symlink to directory (which will be checked	451	that the entry is a directory or a symlink to directory (which will
283	seperately).	452	be checked seperately). This is often faster than stat'ing the entry
		453	itself because filesystems might detect the type of the entry
		454	without reading the inode data (e.g. ext2fs filetype feature).
284		455
285	If the known number of directories has been reached, the rest of the	456	If the known number of directories (link count - 2) has been
286	entries is assumed to be non-directories.	457	reached, the rest of the entries is assumed to be non-directories.
		458
		459	This only works with certainty on POSIX (= UNIX) filesystems, which
		460	fortunately are the vast majority of filesystems around.
		461
		462	It will also likely work on non-POSIX filesystems with reduced
		463	efficiency as those tend to return 0 or 1 as link counts, which
		464	disables the directory counting heuristic.
287		465
288	aio_fsync $fh, $callback->($status)	466	aio_fsync $fh, $callback->($status)
289	Asynchronously call fsync on the given filehandle and call the	467	Asynchronously call fsync on the given filehandle and call the
290	callback with the fsync result code.	468	callback with the fsync result code.
291		469
…		…
294	callback with the fdatasync result code.	472	callback with the fdatasync result code.
295		473
296	If this call isn't available because your OS lacks it or it couldn't	474	If this call isn't available because your OS lacks it or it couldn't
297	be detected, it will be emulated by calling "fsync" instead.	475	be detected, it will be emulated by calling "fsync" instead.
298		476
		477	aio_group $callback->(...)
		478	This is a very special aio request: Instead of doing something, it
		479	is a container for other aio requests, which is useful if you want
		480	to bundle many requests into a single, composite, request with a
		481	definite callback and the ability to cancel the whole request with
		482	its subrequests.
		483
		484	Returns an object of class IO::AIO::GRP. See its documentation below
		485	for more info.
		486
		487	Example:
		488
		489	my $grp = aio_group sub {
		490	print "all stats done\n";
		491	};
		492
		493	add $grp
		494	(aio_stat ...),
		495	(aio_stat ...),
		496	...;
		497
		498	aio_nop $callback->()
		499	This is a special request - it does nothing in itself and is only
		500	used for side effects, such as when you want to add a dummy request
		501	to a group so that finishing the requests in the group depends on
		502	executing the given code.
		503
		504	While this request does nothing, it still goes through the execution
		505	phase and still requires a worker thread. Thus, the callback will
		506	not be executed immediately but only after other requests in the
		507	queue have entered their execution phase. This can be used to
		508	measure request latency.
		509
		510	IO::AIO::aio_busy $fractional_seconds, $callback->() NOT EXPORTED
		511	Mainly used for debugging and benchmarking, this aio request puts
		512	one of the request workers to sleep for the given time.
		513
		514	While it is theoretically handy to have simple I/O scheduling
		515	requests like sleep and file handle readable/writable, the overhead
		516	this creates is immense (it blocks a thread for a long time) so do
		517	not use this function except to put your application under
		518	artificial I/O pressure.
		519
		520	IO::AIO::REQ CLASS
		521	All non-aggregate "aio_*" functions return an object of this class when
		522	called in non-void context.
		523
		524	cancel $req
		525	Cancels the request, if possible. Has the effect of skipping
		526	execution when entering the execute state and skipping calling the
		527	callback when entering the the result state, but will leave the
		528	request otherwise untouched. That means that requests that currently
		529	execute will not be stopped and resources held by the request will
		530	not be freed prematurely.
		531
		532	cb $req $callback->(...)
		533	Replace (or simply set) the callback registered to the request.
		534
		535	IO::AIO::GRP CLASS
		536	This class is a subclass of IO::AIO::REQ, so all its methods apply to
		537	objects of this class, too.
		538
		539	A IO::AIO::GRP object is a special request that can contain multiple
		540	other aio requests.
		541
		542	You create one by calling the "aio_group" constructing function with a
		543	callback that will be called when all contained requests have entered
		544	the "done" state:
		545
		546	my $grp = aio_group sub {
		547	print "all requests are done\n";
		548	};
		549
		550	You add requests by calling the "add" method with one or more
		551	"IO::AIO::REQ" objects:
		552
		553	$grp->add (aio_unlink "...");
		554
		555	add $grp aio_stat "...", sub {
		556	$_[0] or return $grp->result ("error");
		557
		558	# add another request dynamically, if first succeeded
		559	add $grp aio_open "...", sub {
		560	$grp->result ("ok");
		561	};
		562	};
		563
		564	This makes it very easy to create composite requests (see the source of
		565	"aio_move" for an application) that work and feel like simple requests.
		566
		567	* The IO::AIO::GRP objects will be cleaned up during calls to
		568	"IO::AIO::poll_cb", just like any other request.
		569	* They can be canceled like any other request. Canceling will cancel not
		570	only the request itself, but also all requests it contains.
		571	* They can also can also be added to other IO::AIO::GRP objects.
		572	* You must not add requests to a group from within the group callback
		573	(or any later time).
		574
		575	Their lifetime, simplified, looks like this: when they are empty, they
		576	will finish very quickly. If they contain only requests that are in the
		577	"done" state, they will also finish. Otherwise they will continue to
		578	exist.
		579
		580	That means after creating a group you have some time to add requests.
		581	And in the callbacks of those requests, you can add further requests to
		582	the group. And only when all those requests have finished will the the
		583	group itself finish.
		584
		585	add $grp ...
		586	$grp->add (...)
		587	Add one or more requests to the group. Any type of IO::AIO::REQ can
		588	be added, including other groups, as long as you do not create
		589	circular dependencies.
		590
		591	Returns all its arguments.
		592
		593	$grp->cancel_subs
		594	Cancel all subrequests and clears any feeder, but not the group
		595	request itself. Useful when you queued a lot of events but got a
		596	result early.
		597
		598	$grp->result (...)
		599	Set the result value(s) that will be passed to the group callback
		600	when all subrequests have finished and set thre groups errno to the
		601	current value of errno (just like calling "errno" without an error
		602	number). By default, no argument will be passed and errno is zero.
		603
		604	$grp->errno ([$errno])
		605	Sets the group errno value to $errno, or the current value of errno
		606	when the argument is missing.
		607
		608	Every aio request has an associated errno value that is restored
		609	when the callback is invoked. This method lets you change this value
		610	from its default (0).
		611
		612	Calling "result" will also set errno, so make sure you either set $!
		613	before the call to "result", or call c<errno> after it.
		614
		615	feed $grp $callback->($grp)
		616	Sets a feeder/generator on this group: every group can have an
		617	attached generator that generates requests if idle. The idea behind
		618	this is that, although you could just queue as many requests as you
		619	want in a group, this might starve other requests for a potentially
		620	long time. For example, "aio_scandir" might generate hundreds of
		621	thousands "aio_stat" requests, delaying any later requests for a
		622	long time.
		623
		624	To avoid this, and allow incremental generation of requests, you can
		625	instead a group and set a feeder on it that generates those
		626	requests. The feed callback will be called whenever there are few
		627	enough (see "limit", below) requests active in the group itself and
		628	is expected to queue more requests.
		629
		630	The feed callback can queue as many requests as it likes (i.e. "add"
		631	does not impose any limits).
		632
		633	If the feed does not queue more requests when called, it will be
		634	automatically removed from the group.
		635
		636	If the feed limit is 0, it will be set to 2 automatically.
		637
		638	Example:
		639
		640	# stat all files in @files, but only ever use four aio requests concurrently:
		641
		642	my $grp = aio_group sub { print "finished\n" };
		643	limit $grp 4;
		644	feed $grp sub {
		645	my $file = pop @files
		646	or return;
		647
		648	add $grp aio_stat $file, sub { ... };
		649	};
		650
		651	limit $grp $num
		652	Sets the feeder limit for the group: The feeder will be called
		653	whenever the group contains less than this many requests.
		654
		655	Setting the limit to 0 will pause the feeding process.
		656
299	SUPPORT FUNCTIONS	657	SUPPORT FUNCTIONS
		658	EVENT PROCESSING AND EVENT LOOP INTEGRATION
300	$fileno = IO::AIO::poll_fileno	659	$fileno = IO::AIO::poll_fileno
301	Return the request result pipe file descriptor. This filehandle	660	Return the request result pipe file descriptor. This filehandle
302	must be polled for reading by some mechanism outside this module	661	must be polled for reading by some mechanism outside this module
303	(e.g. Event or select, see below or the SYNOPSIS). If the pipe	662	(e.g. Event or select, see below or the SYNOPSIS). If the pipe
304	becomes readable you have to call "poll_cb" to check the results.	663	becomes readable you have to call "poll_cb" to check the results.
305		664
306	See "poll_cb" for an example.	665	See "poll_cb" for an example.
307		666
308	IO::AIO::poll_cb	667	IO::AIO::poll_cb
309	Process all outstanding events on the result pipe. You have to call	668	Process some outstanding events on the result pipe. You have to call
310	this regularly. Returns the number of events processed. Returns	669	this regularly. Returns the number of events processed. Returns
311	immediately when no events are outstanding.	670	immediately when no events are outstanding. The amount of events
		671	processed depends on the settings of "IO::AIO::max_poll_req" and
		672	"IO::AIO::max_poll_time".
		673
		674	If not all requests were processed for whatever reason, the
		675	filehandle will still be ready when "poll_cb" returns.
312		676
313	Example: Install an Event watcher that automatically calls	677	Example: Install an Event watcher that automatically calls
314	IO::AIO::poll_cb with high priority:	678	IO::AIO::poll_cb with high priority:
315		679
316	Event->io (fd => IO::AIO::poll_fileno,	680	Event->io (fd => IO::AIO::poll_fileno,
317	poll => 'r', async => 1,	681	poll => 'r', async => 1,
318	cb => \&IO::AIO::poll_cb);	682	cb => \&IO::AIO::poll_cb);
319		683
		684	IO::AIO::max_poll_reqs $nreqs
		685	IO::AIO::max_poll_time $seconds
		686	These set the maximum number of requests (default 0, meaning
		687	infinity) that are being processed by "IO::AIO::poll_cb" in one
		688	call, respectively the maximum amount of time (default 0, meaning
		689	infinity) spent in "IO::AIO::poll_cb" to process requests (more
		690	correctly the mininum amount of time "poll_cb" is allowed to use).
		691
		692	Setting "max_poll_time" to a non-zero value creates an overhead of
		693	one syscall per request processed, which is not normally a problem
		694	unless your callbacks are really really fast or your OS is really
		695	really slow (I am not mentioning Solaris here). Using
		696	"max_poll_reqs" incurs no overhead.
		697
		698	Setting these is useful if you want to ensure some level of
		699	interactiveness when perl is not fast enough to process all requests
		700	in time.
		701
		702	For interactive programs, values such as 0.01 to 0.1 should be fine.
		703
		704	Example: Install an Event watcher that automatically calls
		705	IO::AIO::poll_cb with low priority, to ensure that other parts of
		706	the program get the CPU sometimes even under high AIO load.
		707
		708	# try not to spend much more than 0.1s in poll_cb
		709	IO::AIO::max_poll_time 0.1;
		710
		711	# use a low priority so other tasks have priority
		712	Event->io (fd => IO::AIO::poll_fileno,
		713	poll => 'r', nice => 1,
		714	cb => &IO::AIO::poll_cb);
		715
320	IO::AIO::poll_wait	716	IO::AIO::poll_wait
		717	If there are any outstanding requests and none of them in the result
321	Wait till the result filehandle becomes ready for reading (simply	718	phase, wait till the result filehandle becomes ready for reading
322	does a "select" on the filehandle. This is useful if you want to	719	(simply does a "select" on the filehandle. This is useful if you
323	synchronously wait for some requests to finish).	720	want to synchronously wait for some requests to finish).
324		721
325	See "nreqs" for an example.	722	See "nreqs" for an example.
326		723
		724	IO::AIO::poll
		725	Waits until some requests have been handled.
		726
		727	Returns the number of requests processed, but is otherwise strictly
		728	equivalent to:
		729
		730	IO::AIO::poll_wait, IO::AIO::poll_cb
		731
327	IO::AIO::nreqs	732	IO::AIO::flush
328	Returns the number of requests currently outstanding (i.e. for which	733	Wait till all outstanding AIO requests have been handled.
329	their callback has not been invoked yet).
330		734
331	Example: wait till there are no outstanding requests anymore:	735	Strictly equivalent to:
332		736
333	IO::AIO::poll_wait, IO::AIO::poll_cb	737	IO::AIO::poll_wait, IO::AIO::poll_cb
334	while IO::AIO::nreqs;	738	while IO::AIO::nreqs;
335		739
336	IO::AIO::flush	740	CONTROLLING THE NUMBER OF THREADS
337	Wait till all outstanding AIO requests have been handled.
338
339	Strictly equivalent to:
340
341	IO::AIO::poll_wait, IO::AIO::poll_cb
342	while IO::AIO::nreqs;
343
344	IO::AIO::poll
345	Waits until some requests have been handled.
346
347	Strictly equivalent to:
348
349	IO::AIO::poll_wait, IO::AIO::poll_cb
350	if IO::AIO::nreqs;
351
352	IO::AIO::min_parallel $nthreads	741	IO::AIO::min_parallel $nthreads
353	Set the minimum number of AIO threads to $nthreads. The current	742	Set the minimum number of AIO threads to $nthreads. The current
354	default is 4, which means four asynchronous operations can be done	743	default is 8, which means eight asynchronous operations can execute
355	at one time (the number of outstanding operations, however, is	744	concurrently at any one time (the number of outstanding requests,
356	unlimited).	745	however, is unlimited).
357		746
358	IO::AIO starts threads only on demand, when an AIO request is queued	747	IO::AIO starts threads only on demand, when an AIO request is queued
359	and no free thread exists.	748	and no free thread exists. Please note that queueing up a hundred
		749	requests can create demand for a hundred threads, even if it turns
		750	out that everything is in the cache and could have been processed
		751	faster by a single thread.
360		752
361	It is recommended to keep the number of threads low, as some Linux	753	It is recommended to keep the number of threads relatively low, as
362	kernel versions will scale negatively with the number of threads	754	some Linux kernel versions will scale negatively with the number of
363	(higher parallelity => MUCH higher latency). With current Linux 2.6	755	threads (higher parallelity => MUCH higher latency). With current
364	versions, 4-32 threads should be fine.	756	Linux 2.6 versions, 4-32 threads should be fine.
365		757
366	Under most circumstances you don't need to call this function, as	758	Under most circumstances you don't need to call this function, as
367	the module selects a default that is suitable for low to moderate	759	the module selects a default that is suitable for low to moderate
368	load.	760	load.
369		761
…		…
379	ensure that all threads are killed and that there are no outstanding	771	ensure that all threads are killed and that there are no outstanding
380	requests.	772	requests.
381		773
382	Under normal circumstances you don't need to call this function.	774	Under normal circumstances you don't need to call this function.
383		775
		776	IO::AIO::max_idle $nthreads
		777	Limit the number of threads (default: 4) that are allowed to idle
		778	(i.e., threads that did not get a request to process within 10
		779	seconds). That means if a thread becomes idle while $nthreads other
		780	threads are also idle, it will free its resources and exit.
		781
		782	This is useful when you allow a large number of threads (e.g. 100 or
		783	1000) to allow for extremely high load situations, but want to free
		784	resources under normal circumstances (1000 threads can easily
		785	consume 30MB of RAM).
		786
		787	The default is probably ok in most situations, especially if thread
		788	creation is fast. If thread creation is very slow on your system you
		789	might want to use larger values.
		790
384	$oldnreqs = IO::AIO::max_outstanding $nreqs	791	$oldmaxreqs = IO::AIO::max_outstanding $maxreqs
		792	This is a very bad function to use in interactive programs because
		793	it blocks, and a bad way to reduce concurrency because it is
		794	inexact: Better use an "aio_group" together with a feed callback.
		795
385	Sets the maximum number of outstanding requests to $nreqs. If you	796	Sets the maximum number of outstanding requests to $nreqs. If you to
386	try to queue up more than this number of requests, the caller will	797	queue up more than this number of requests, the next call to the
387	block until some requests have been handled.	798	"poll_cb" (and "poll_some" and other functions calling "poll_cb")
		799	function will block until the limit is no longer exceeded.
388		800
389	The default is very large, so normally there is no practical limit.	801	The default value is very large, so there is no practical limit on
390	If you queue up many requests in a loop it often improves speed if	802	the number of outstanding requests.
391	you set this to a relatively low number, such as 100.
392		803
393	Under normal circumstances you don't need to call this function.	804	You can still queue as many requests as you want. Therefore,
		805	"max_oustsanding" is mainly useful in simple scripts (with low
		806	values) or as a stop gap to shield against fatal memory overflow
		807	(with large values).
		808
		809	STATISTICAL INFORMATION
		810	IO::AIO::nreqs
		811	Returns the number of requests currently in the ready, execute or
		812	pending states (i.e. for which their callback has not been invoked
		813	yet).
		814
		815	Example: wait till there are no outstanding requests anymore:
		816
		817	IO::AIO::poll_wait, IO::AIO::poll_cb
		818	while IO::AIO::nreqs;
		819
		820	IO::AIO::nready
		821	Returns the number of requests currently in the ready state (not yet
		822	executed).
		823
		824	IO::AIO::npending
		825	Returns the number of requests currently in the pending state
		826	(executed, but not yet processed by poll_cb).
394		827
395	FORK BEHAVIOUR	828	FORK BEHAVIOUR
		829	This module should do "the right thing" when the process using it forks:
		830
396	Before the fork, IO::AIO enters a quiescent state where no requests can	831	Before the fork, IO::AIO enters a quiescent state where no requests can
397	be added in other threads and no results will be processed. After the	832	be added in other threads and no results will be processed. After the
398	fork the parent simply leaves the quiescent state and continues	833	fork the parent simply leaves the quiescent state and continues
399	request/result processing, while the child clears the request/result	834	request/result processing, while the child frees the request/result
400	queue (so the requests started before the fork will only be handled in	835	queue (so that the requests started before the fork will only be handled
401	the parent). Threats will be started on demand until the limit ste in	836	in the parent). Threads will be started on demand until the limit set in
402	the parent process has been reached again.	837	the parent process has been reached again.
403		838
		839	In short: the parent will, after a short pause, continue as if fork had
		840	not been called, while the child will act as if IO::AIO has not been
		841	used yet.
		842
		843	MEMORY USAGE
		844	Per-request usage:
		845
		846	Each aio request uses - depending on your architecture - around 100-200
		847	bytes of memory. In addition, stat requests need a stat buffer (possibly
		848	a few hundred bytes), readdir requires a result buffer and so on. Perl
		849	scalars and other data passed into aio requests will also be locked and
		850	will consume memory till the request has entered the done state.
		851
		852	This is now awfully much, so queuing lots of requests is not usually a
		853	problem.
		854
		855	Per-thread usage:
		856
		857	In the execution phase, some aio requests require more memory for
		858	temporary buffers, and each thread requires a stack and other data
		859	structures (usually around 16k-128k, depending on the OS).
		860
		861	KNOWN BUGS
		862	Known bugs will be fixed in the next release.
		863
404	SEE ALSO	864	SEE ALSO
405	Coro, Linux::AIO.	865	Coro::AIO.
406		866
407	AUTHOR	867	AUTHOR
408	Marc Lehmann <schmorp@schmorp.de>	868	Marc Lehmann <schmorp@schmorp.de>
409	http://home.schmorp.de/	869	http://home.schmorp.de/
410		870

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Revision 1.21 by root, Fri Dec 22 04:05:50 2006 UTC