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Revision 1.19 by root, Sun Oct 29 01:03:13 2006 UTC vs.
Revision 1.40 by root, Thu Nov 12 00:01:52 2009 UTC

…		…
3		3
4	SYNOPSIS	4	SYNOPSIS
5	use IO::AIO;	5	use IO::AIO;
6		6
7	aio_open "/etc/passwd", O_RDONLY, 0, sub {	7	aio_open "/etc/passwd", O_RDONLY, 0, sub {
8	my ($fh) = @_;	8	my $fh = shift
		9	or die "/etc/passwd: $!";
9	...	10	...
10	};	11	};
11		12
12	aio_unlink "/tmp/file", sub { };	13	aio_unlink "/tmp/file", sub { };
13		14
…		…
23	$req->cancel; # cancel request if still in queue	24	$req->cancel; # cancel request if still in queue
24		25
25	my $grp = aio_group sub { print "all stats done\n" };	26	my $grp = aio_group sub { print "all stats done\n" };
26	add $grp aio_stat "..." for ...;	27	add $grp aio_stat "..." for ...;
27		28
		29	# AnyEvent integration (EV, Event, Glib, Tk, POE, urxvt, pureperl...)
		30	use AnyEvent::AIO;
		31
28	# AnyEvent integration	32	# EV integration
29	open my $fh, "<&=" . IO::AIO::poll_fileno or die "$!";	33	my $aio_w = EV::io IO::AIO::poll_fileno, EV::READ, \&IO::AIO::poll_cb;
30	my $w = AnyEvent->io (fh => $fh, poll => 'r', cb => sub { IO::AIO::poll_cb });
31		34
32	# Event integration	35	# Event integration
33	Event->io (fd => IO::AIO::poll_fileno,	36	Event->io (fd => IO::AIO::poll_fileno,
34	poll => 'r',	37	poll => 'r',
35	cb => \&IO::AIO::poll_cb);	38	cb => \&IO::AIO::poll_cb);
…		…
46	Danga::Socket->AddOtherFds (IO::AIO::poll_fileno =>	49	Danga::Socket->AddOtherFds (IO::AIO::poll_fileno =>
47	\&IO::AIO::poll_cb);	50	\&IO::AIO::poll_cb);
48		51
49	DESCRIPTION	52	DESCRIPTION
50	This module implements asynchronous I/O using whatever means your	53	This module implements asynchronous I/O using whatever means your
51	operating system supports.	54	operating system supports. It is implemented as an interface to "libeio"
		55	(<http://software.schmorp.de/pkg/libeio.html>).
52		56
53	Asynchronous means that operations that can normally block your program	57	Asynchronous means that operations that can normally block your program
54	(e.g. reading from disk) will be done asynchronously: the operation will	58	(e.g. reading from disk) will be done asynchronously: the operation will
55	still block, but you can do something else in the meantime. This is	59	still block, but you can do something else in the meantime. This is
56	extremely useful for programs that need to stay interactive even when	60	extremely useful for programs that need to stay interactive even when
…		…
58	but can also be used to easily do operations in parallel that are	62	but can also be used to easily do operations in parallel that are
59	normally done sequentially, e.g. stat'ing many files, which is much	63	normally done sequentially, e.g. stat'ing many files, which is much
60	faster on a RAID volume or over NFS when you do a number of stat	64	faster on a RAID volume or over NFS when you do a number of stat
61	operations concurrently.	65	operations concurrently.
62		66
63	While this works on all types of file descriptors (for example sockets),	67	While most of this works on all types of file descriptors (for example
64	using these functions on file descriptors that support nonblocking	68	sockets), using these functions on file descriptors that support
65	operation (again, sockets, pipes etc.) is very inefficient. Use an event	69	nonblocking operation (again, sockets, pipes etc.) is very inefficient.
66	loop for that (such as the Event module): IO::AIO will naturally fit	70	Use an event loop for that (such as the EV module): IO::AIO will
67	into such an event loop itself.	71	naturally fit into such an event loop itself.
68		72
69	In this version, a number of threads are started that execute your	73	In this version, a number of threads are started that execute your
70	requests and signal their completion. You don't need thread support in	74	requests and signal their completion. You don't need thread support in
71	perl, and the threads created by this module will not be visible to	75	perl, and the threads created by this module will not be visible to
72	perl. In the future, this module might make use of the native aio	76	perl. In the future, this module might make use of the native aio
…		…
74	not well-supported or restricted (GNU/Linux doesn't allow them on normal	78	not well-supported or restricted (GNU/Linux doesn't allow them on normal
75	files currently, for example), and they would only support aio_read and	79	files currently, for example), and they would only support aio_read and
76	aio_write, so the remaining functionality would have to be implemented	80	aio_write, so the remaining functionality would have to be implemented
77	using threads anyway.	81	using threads anyway.
78		82
79	Although the module will work with in the presence of other (Perl-)	83	Although the module will work in the presence of other (Perl-) threads,
80	threads, it is currently not reentrant in any way, so use appropriate	84	it is currently not reentrant in any way, so use appropriate locking
81	locking yourself, always call "poll_cb" from within the same thread, or	85	yourself, always call "poll_cb" from within the same thread, or never
82	never call "poll_cb" (or other "aio_" functions) recursively.	86	call "poll_cb" (or other "aio_" functions) recursively.
83		87
84	EXAMPLE	88	EXAMPLE
85	This is a simple example that uses the Event module and loads	89	This is a simple example that uses the EV module and loads /etc/passwd
86	/etc/passwd asynchronously:	90	asynchronously:
87		91
88	use Fcntl;	92	use Fcntl;
89	use Event;	93	use EV;
90	use IO::AIO;	94	use IO::AIO;
91		95
92	# register the IO::AIO callback with Event	96	# register the IO::AIO callback with EV
93	Event->io (fd => IO::AIO::poll_fileno,	97	my $aio_w = EV::io IO::AIO::poll_fileno, EV::READ, \&IO::AIO::poll_cb;
94	poll => 'r',
95	cb => \&IO::AIO::poll_cb);
96		98
97	# queue the request to open /etc/passwd	99	# queue the request to open /etc/passwd
98	aio_open "/etc/passwd", O_RDONLY, 0, sub {	100	aio_open "/etc/passwd", O_RDONLY, 0, sub {
99	my $fh = $_[0]	101	my $fh = shift
100	or die "error while opening: $!";	102	or die "error while opening: $!";
101		103
102	# stat'ing filehandles is generally non-blocking	104	# stat'ing filehandles is generally non-blocking
103	my $size = -s $fh;	105	my $size = -s $fh;
104		106
…		…
112		114
113	# file contents now in $contents	115	# file contents now in $contents
114	print $contents;	116	print $contents;
115		117
116	# exit event loop and program	118	# exit event loop and program
117	Event::unloop;	119	EV::unloop;
118	};	120	};
119	};	121	};
120		122
121	# possibly queue up other requests, or open GUI windows,	123	# possibly queue up other requests, or open GUI windows,
122	# check for sockets etc. etc.	124	# check for sockets etc. etc.
123		125
124	# process events as long as there are some:	126	# process events as long as there are some:
125	Event::loop;	127	EV::loop;
126		128
127	REQUEST ANATOMY AND LIFETIME	129	REQUEST ANATOMY AND LIFETIME
128	Every "aio_*" function creates a request. which is a C data structure	130	Every "aio_*" function creates a request. which is a C data structure
129	not directly visible to Perl.	131	not directly visible to Perl.
130		132
…		…
167	the actual aio request is severed and calling its methods will	169	the actual aio request is severed and calling its methods will
168	either do nothing or result in a runtime error).	170	either do nothing or result in a runtime error).
169		171
170	FUNCTIONS	172	FUNCTIONS
171	AIO REQUEST FUNCTIONS	173	AIO REQUEST FUNCTIONS
172	All the "aio_*" calls are more or less thin wrappers around the	174	All the "aio_*" calls are more or less thin wrappers around the syscall
173	syscall with the same name (sans "aio_"). The arguments are similar	175	with the same name (sans "aio_"). The arguments are similar or
174	or identical, and they all accept an additional (and optional)	176	identical, and they all accept an additional (and optional) $callback
175	$callback argument which must be a code reference. This code	177	argument which must be a code reference. This code reference will get
176	reference will get called with the syscall return code (e.g. most	178	called with the syscall return code (e.g. most syscalls return -1 on
177	syscalls return -1 on error, unlike perl, which usually delivers	179	error, unlike perl, which usually delivers "false") as its sole argument
178	"false") as it's sole argument when the given syscall has been	180	after the given syscall has been executed asynchronously.
179	executed asynchronously.
180		181
181	All functions expecting a filehandle keep a copy of the filehandle	182	All functions expecting a filehandle keep a copy of the filehandle
182	internally until the request has finished.	183	internally until the request has finished.
183		184
184	All functions return request objects of type IO::AIO::REQ that allow	185	All functions return request objects of type IO::AIO::REQ that allow
185	further manipulation of those requests while they are in-flight.	186	further manipulation of those requests while they are in-flight.
186		187
187	The pathnames you pass to these routines *must* be absolute and	188	The pathnames you pass to these routines *must* be absolute and encoded
188	encoded as octets. The reason for the former is that at the time the	189	as octets. The reason for the former is that at the time the request is
189	request is being executed, the current working directory could have	190	being executed, the current working directory could have changed.
190	changed. Alternatively, you can make sure that you never change the	191	Alternatively, you can make sure that you never change the current
191	current working directory anywhere in the program and then use	192	working directory anywhere in the program and then use relative paths.
192	relative paths.
193		193
194	To encode pathnames as octets, either make sure you either: a)	194	To encode pathnames as octets, either make sure you either: a) always
195	always pass in filenames you got from outside (command line, readdir	195	pass in filenames you got from outside (command line, readdir etc.)
196	etc.) without tinkering, b) are ASCII or ISO 8859-1, c) use the	196	without tinkering, b) are ASCII or ISO 8859-1, c) use the Encode module
197	Encode module and encode your pathnames to the locale (or other)	197	and encode your pathnames to the locale (or other) encoding in effect in
198	encoding in effect in the user environment, d) use	198	the user environment, d) use Glib::filename_from_unicode on unicode
199	Glib::filename_from_unicode on unicode filenames or e) use something	199	filenames or e) use something else to ensure your scalar has the correct
200	else to ensure your scalar has the correct contents.	200	contents.
201		201
202	This works, btw. independent of the internal UTF-8 bit, which	202	This works, btw. independent of the internal UTF-8 bit, which IO::AIO
203	IO::AIO handles correctly wether it is set or not.	203	handles correctly whether it is set or not.
204		204
205	$prev_pri = aioreq_pri [$pri]	205	$prev_pri = aioreq_pri [$pri]
206	Returns the priority value that would be used for the next	206	Returns the priority value that would be used for the next request
207	request and, if $pri is given, sets the priority for the next	207	and, if $pri is given, sets the priority for the next aio request.
208	aio request.
209		208
210	The default priority is 0, the minimum and maximum priorities	209	The default priority is 0, the minimum and maximum priorities are -4
211	are -4 and 4, respectively. Requests with higher priority will	210	and 4, respectively. Requests with higher priority will be serviced
212	be serviced first.	211	first.
213		212
214	The priority will be reset to 0 after each call to one of the	213	The priority will be reset to 0 after each call to one of the
215	"aio_*" functions.	214	"aio_*" functions.
216		215
217	Example: open a file with low priority, then read something from	216	Example: open a file with low priority, then read something from it
218	it with higher priority so the read request is serviced before	217	with higher priority so the read request is serviced before other
219	other low priority open requests (potentially spamming the	218	low priority open requests (potentially spamming the cache):
220	cache):
221		219
		220	aioreq_pri -3;
		221	aio_open ..., sub {
		222	return unless $_[0];
		223
222	aioreq_pri -3;	224	aioreq_pri -2;
223	aio_open ..., sub {
224	return unless $_[0];
225
226	aioreq_pri -2;
227	aio_read $_[0], ..., sub {	225	aio_read $_[0], ..., sub {
228	...
229	};
230	};
231
232	aioreq_nice $pri_adjust
233	Similar to "aioreq_pri", but subtracts the given value from the
234	current priority, so the effect is cumulative.
235
236	aio_open $pathname, $flags, $mode, $callback->($fh)
237	Asynchronously open or create a file and call the callback with
238	a newly created filehandle for the file.
239
240	The pathname passed to "aio_open" must be absolute. See API
241	NOTES, above, for an explanation.
242
243	The $flags argument is a bitmask. See the "Fcntl" module for a
244	list. They are the same as used by "sysopen".
245
246	Likewise, $mode specifies the mode of the newly created file, if
247	it didn't exist and "O_CREAT" has been given, just like perl's
248	"sysopen", except that it is mandatory (i.e. use 0 if you don't
249	create new files, and 0666 or 0777 if you do).
250
251	Example:
252
253	aio_open "/etc/passwd", O_RDONLY, 0, sub {
254	if ($_[0]) {
255	print "open successful, fh is $_[0]\n";
256	...
257	} else {
258	die "open failed: $!\n";
259	}
260	};
261
262	aio_close $fh, $callback->($status)
263	Asynchronously close a file and call the callback with the
264	result code. *WARNING:* although accepted, you should not pass
265	in a perl filehandle here, as perl will likely close the file
266	descriptor another time when the filehandle is destroyed.
267	Normally, you can safely call perls "close" or just let
268	filehandles go out of scope.
269
270	This is supposed to be a bug in the API, so that might change.
271	It's therefore best to avoid this function.
272
273	aio_read $fh,$offset,$length, $data,$dataoffset,
274	$callback->($retval)
275	aio_write $fh,$offset,$length, $data,$dataoffset,
276	$callback->($retval)
277	Reads or writes "length" bytes from the specified "fh" and
278	"offset" into the scalar given by "data" and offset "dataoffset"
279	and calls the callback without the actual number of bytes read
280	(or -1 on error, just like the syscall).
281
282	The $data scalar *MUST NOT* be modified in any way while the
283	request is outstanding. Modifying it can result in segfaults or
284	WW3 (if the necessary/optional hardware is installed).
285
286	Example: Read 15 bytes at offset 7 into scalar $buffer, starting
287	at offset 0 within the scalar:
288
289	aio_read $fh, 7, 15, $buffer, 0, sub {
290	$_[0] > 0 or die "read error: $!";
291	print "read $_[0] bytes: <$buffer>\n";
292	};
293
294	aio_sendfile $out_fh, $in_fh, $in_offset, $length,
295	$callback->($retval)
296	Tries to copy $length bytes from $in_fh to $out_fh. It starts
297	reading at byte offset $in_offset, and starts writing at the
298	current file offset of $out_fh. Because of that, it is not safe
299	to issue more than one "aio_sendfile" per $out_fh, as they will
300	interfere with each other.
301
302	This call tries to make use of a native "sendfile" syscall to
303	provide zero-copy operation. For this to work, $out_fh should
304	refer to a socket, and $in_fh should refer to mmap'able file.
305
306	If the native sendfile call fails or is not implemented, it will
307	be emulated, so you can call "aio_sendfile" on any type of
308	filehandle regardless of the limitations of the operating
309	system.
310
311	Please note, however, that "aio_sendfile" can read more bytes
312	from $in_fh than are written, and there is no way to find out
313	how many bytes have been read from "aio_sendfile" alone, as
314	"aio_sendfile" only provides the number of bytes written to
315	$out_fh. Only if the result value equals $length one can assume
316	that $length bytes have been read.
317
318	aio_readahead $fh,$offset,$length, $callback->($retval)
319	"aio_readahead" populates the page cache with data from a file
320	so that subsequent reads from that file will not block on disk
321	I/O. The $offset argument specifies the starting point from
322	which data is to be read and $length specifies the number of
323	bytes to be read. I/O is performed in whole pages, so that
324	offset is effectively rounded down to a page boundary and bytes
325	are read up to the next page boundary greater than or equal to
326	(off-set+length). "aio_readahead" does not read beyond the end
327	of the file. The current file offset of the file is left
328	unchanged.
329
330	If that syscall doesn't exist (likely if your OS isn't Linux) it
331	will be emulated by simply reading the data, which would have a
332	similar effect.
333
334	aio_stat $fh_or_path, $callback->($status)
335	aio_lstat $fh, $callback->($status)
336	Works like perl's "stat" or "lstat" in void context. The
337	callback will be called after the stat and the results will be
338	available using "stat _" or "-s _" etc...
339
340	The pathname passed to "aio_stat" must be absolute. See API
341	NOTES, above, for an explanation.
342
343	Currently, the stats are always 64-bit-stats, i.e. instead of
344	returning an error when stat'ing a large file, the results will
345	be silently truncated unless perl itself is compiled with large
346	file support.
347
348	Example: Print the length of /etc/passwd:
349
350	aio_stat "/etc/passwd", sub {
351	$_[0] and die "stat failed: $!";
352	print "size is ", -s _, "\n";
353	};
354
355	aio_unlink $pathname, $callback->($status)
356	Asynchronously unlink (delete) a file and call the callback with
357	the result code.
358
359	aio_mknod $path, $mode, $dev, $callback->($status)
360	[EXPERIMENTAL]
361
362	Asynchronously create a device node (or fifo). See mknod(2).
363
364	The only (POSIX-) portable way of calling this function is:
365
366	aio_mknod $path, IO::AIO::S_IFIFO | $mode, 0, sub { ...
367
368	aio_link $srcpath, $dstpath, $callback->($status)
369	Asynchronously create a new link to the existing object at
370	$srcpath at the path $dstpath and call the callback with the
371	result code.
372
373	aio_symlink $srcpath, $dstpath, $callback->($status)
374	Asynchronously create a new symbolic link to the existing object
375	at $srcpath at the path $dstpath and call the callback with the
376	result code.
377
378	aio_rename $srcpath, $dstpath, $callback->($status)
379	Asynchronously rename the object at $srcpath to $dstpath, just
380	as rename(2) and call the callback with the result code.
381
382	aio_rmdir $pathname, $callback->($status)
383	Asynchronously rmdir (delete) a directory and call the callback
384	with the result code.
385
386	aio_readdir $pathname, $callback->($entries)
387	Unlike the POSIX call of the same name, "aio_readdir" reads an
388	entire directory (i.e. opendir + readdir + closedir). The
389	entries will not be sorted, and will NOT include the "." and
390	".." entries.
391
392	The callback a single argument which is either "undef" or an
393	array-ref with the filenames.
394
395	aio_copy $srcpath, $dstpath, $callback->($status)
396	Try to copy the *file* (directories not supported as either
397	source or destination) from $srcpath to $dstpath and call the
398	callback with the 0 (error) or -1 ok.
399
400	This is a composite request that it creates the destination file
401	with mode 0200 and copies the contents of the source file into
402	it using "aio_sendfile", followed by restoring atime, mtime,
403	access mode and uid/gid, in that order.
404
405	If an error occurs, the partial destination file will be
406	unlinked, if possible, except when setting atime, mtime, access
407	mode and uid/gid, where errors are being ignored.
408
409	aio_move $srcpath, $dstpath, $callback->($status)
410	Try to move the *file* (directories not supported as either
411	source or destination) from $srcpath to $dstpath and call the
412	callback with the 0 (error) or -1 ok.
413
414	This is a composite request that tries to rename(2) the file
415	first. If rename files with "EXDEV", it copies the file with
416	"aio_copy" and, if that is successful, unlinking the $srcpath.
417
418	aio_scandir $path, $maxreq, $callback->($dirs, $nondirs)
419	Scans a directory (similar to "aio_readdir") but additionally
420	tries to efficiently separate the entries of directory $path
421	into two sets of names, directories you can recurse into
422	(directories), and ones you cannot recurse into (everything
423	else, including symlinks to directories).
424
425	"aio_scandir" is a composite request that creates of many sub
426	requests_ $maxreq specifies the maximum number of outstanding
427	aio requests that this function generates. If it is "<= 0", then
428	a suitable default will be chosen (currently 4).
429
430	On error, the callback is called without arguments, otherwise it
431	receives two array-refs with path-relative entry names.
432
433	Example:
434
435	aio_scandir $dir, 0, sub {
436	my ($dirs, $nondirs) = @_;
437	print "real directories: @$dirs\n";
438	print "everything else: @$nondirs\n";
439	};
440
441	Implementation notes.
442
443	The "aio_readdir" cannot be avoided, but "stat()"'ing every
444	entry can.
445
446	After reading the directory, the modification time, size etc. of
447	the directory before and after the readdir is checked, and if
448	they match (and isn't the current time), the link count will be
449	used to decide how many entries are directories (if >= 2).
450	Otherwise, no knowledge of the number of subdirectories will be
451	assumed.
452
453	Then entries will be sorted into likely directories (everything
454	without a non-initial dot currently) and likely non-directories
455	(everything else). Then every entry plus an appended "/." will
456	be "stat"'ed, likely directories first. If that succeeds, it
457	assumes that the entry is a directory or a symlink to directory
458	(which will be checked seperately). This is often faster than
459	stat'ing the entry itself because filesystems might detect the
460	type of the entry without reading the inode data (e.g. ext2fs
461	filetype feature).
462
463	If the known number of directories (link count - 2) has been
464	reached, the rest of the entries is assumed to be
465	non-directories.
466
467	This only works with certainty on POSIX (= UNIX) filesystems,
468	which fortunately are the vast majority of filesystems around.
469
470	It will also likely work on non-POSIX filesystems with reduced
471	efficiency as those tend to return 0 or 1 as link counts, which
472	disables the directory counting heuristic.
473
474	aio_fsync $fh, $callback->($status)
475	Asynchronously call fsync on the given filehandle and call the
476	callback with the fsync result code.
477
478	aio_fdatasync $fh, $callback->($status)
479	Asynchronously call fdatasync on the given filehandle and call
480	the callback with the fdatasync result code.
481
482	If this call isn't available because your OS lacks it or it
483	couldn't be detected, it will be emulated by calling "fsync"
484	instead.
485
486	aio_group $callback->(...)
487	This is a very special aio request: Instead of doing something,
488	it is a container for other aio requests, which is useful if you
489	want to bundle many requests into a single, composite, request
490	with a definite callback and the ability to cancel the whole
491	request with its subrequests.
492
493	Returns an object of class IO::AIO::GRP. See its documentation
494	below for more info.
495
496	Example:
497
498	my $grp = aio_group sub {
499	print "all stats done\n";
500	};
501
502	add $grp
503	(aio_stat ...),
504	(aio_stat ...),
505	...;	226	...
506
507	aio_nop $callback->()
508	This is a special request - it does nothing in itself and is
509	only used for side effects, such as when you want to add a dummy
510	request to a group so that finishing the requests in the group
511	depends on executing the given code.
512
513	While this request does nothing, it still goes through the
514	execution phase and still requires a worker thread. Thus, the
515	callback will not be executed immediately but only after other
516	requests in the queue have entered their execution phase. This
517	can be used to measure request latency.
518
519	IO::AIO::aio_busy $fractional_seconds, $callback->() *NOT EXPORTED*
520	Mainly used for debugging and benchmarking, this aio request
521	puts one of the request workers to sleep for the given time.
522
523	While it is theoretically handy to have simple I/O scheduling
524	requests like sleep and file handle readable/writable, the
525	overhead this creates is immense (it blocks a thread for a long
526	time) so do not use this function except to put your application
527	under artificial I/O pressure.
528
529	IO::AIO::REQ CLASS
530	All non-aggregate "aio_*" functions return an object of this class
531	when called in non-void context.
532
533	cancel $req
534	Cancels the request, if possible. Has the effect of skipping
535	execution when entering the execute state and skipping calling
536	the callback when entering the the result state, but will leave
537	the request otherwise untouched. That means that requests that
538	currently execute will not be stopped and resources held by the
539	request will not be freed prematurely.
540
541	cb $req $callback->(...)
542	Replace (or simply set) the callback registered to the request.
543
544	IO::AIO::GRP CLASS
545	This class is a subclass of IO::AIO::REQ, so all its methods apply
546	to objects of this class, too.
547
548	A IO::AIO::GRP object is a special request that can contain multiple
549	other aio requests.
550
551	You create one by calling the "aio_group" constructing function with
552	a callback that will be called when all contained requests have
553	entered the "done" state:
554
555	my $grp = aio_group sub {
556	print "all requests are done\n";
557	};
558
559	You add requests by calling the "add" method with one or more
560	"IO::AIO::REQ" objects:
561
562	$grp->add (aio_unlink "...");
563
564	add $grp aio_stat "...", sub {
565	$_[0] or return $grp->result ("error");
566
567	# add another request dynamically, if first succeeded
568	add $grp aio_open "...", sub {
569	$grp->result ("ok");
570	};	227	};
571	};	228	};
572		229
		230	aioreq_nice $pri_adjust
		231	Similar to "aioreq_pri", but subtracts the given value from the
		232	current priority, so the effect is cumulative.
		233
		234	aio_open $pathname, $flags, $mode, $callback->($fh)
		235	Asynchronously open or create a file and call the callback with a
		236	newly created filehandle for the file.
		237
		238	The pathname passed to "aio_open" must be absolute. See API NOTES,
		239	above, for an explanation.
		240
		241	The $flags argument is a bitmask. See the "Fcntl" module for a list.
		242	They are the same as used by "sysopen".
		243
		244	Likewise, $mode specifies the mode of the newly created file, if it
		245	didn't exist and "O_CREAT" has been given, just like perl's
		246	"sysopen", except that it is mandatory (i.e. use 0 if you don't
		247	create new files, and 0666 or 0777 if you do). Note that the $mode
		248	will be modified by the umask in effect then the request is being
		249	executed, so better never change the umask.
		250
		251	Example:
		252
		253	aio_open "/etc/passwd", O_RDONLY, 0, sub {
		254	if ($_[0]) {
		255	print "open successful, fh is $_[0]\n";
		256	...
		257	} else {
		258	die "open failed: $!\n";
		259	}
		260	};
		261
		262	aio_close $fh, $callback->($status)
		263	Asynchronously close a file and call the callback with the result
		264	code.
		265
		266	Unfortunately, you can't do this to perl. Perl *insists* very
		267	strongly on closing the file descriptor associated with the
		268	filehandle itself.
		269
		270	Therefore, "aio_close" will not close the filehandle - instead it
		271	will use dup2 to overwrite the file descriptor with the write-end of
		272	a pipe (the pipe fd will be created on demand and will be cached).
		273
		274	Or in other words: the file descriptor will be closed, but it will
		275	not be free for reuse until the perl filehandle is closed.
		276
		277	aio_read $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
		278	aio_write $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
		279	Reads or writes $length bytes from or to the specified $fh and
		280	$offset into the scalar given by $data and offset $dataoffset and
		281	calls the callback without the actual number of bytes read (or -1 on
		282	error, just like the syscall).
		283
		284	"aio_read" will, like "sysread", shrink or grow the $data scalar to
		285	offset plus the actual number of bytes read.
		286
		287	If $offset is undefined, then the current file descriptor offset
		288	will be used (and updated), otherwise the file descriptor offset
		289	will not be changed by these calls.
		290
		291	If $length is undefined in "aio_write", use the remaining length of
		292	$data.
		293
		294	If $dataoffset is less than zero, it will be counted from the end of
		295	$data.
		296
		297	The $data scalar *MUST NOT* be modified in any way while the request
		298	is outstanding. Modifying it can result in segfaults or World War
		299	III (if the necessary/optional hardware is installed).
		300
		301	Example: Read 15 bytes at offset 7 into scalar $buffer, starting at
		302	offset 0 within the scalar:
		303
		304	aio_read $fh, 7, 15, $buffer, 0, sub {
		305	$_[0] > 0 or die "read error: $!";
		306	print "read $_[0] bytes: <$buffer>\n";
		307	};
		308
		309	aio_sendfile $out_fh, $in_fh, $in_offset, $length, $callback->($retval)
		310	Tries to copy $length bytes from $in_fh to $out_fh. It starts
		311	reading at byte offset $in_offset, and starts writing at the current
		312	file offset of $out_fh. Because of that, it is not safe to issue
		313	more than one "aio_sendfile" per $out_fh, as they will interfere
		314	with each other.
		315
		316	This call tries to make use of a native "sendfile" syscall to
		317	provide zero-copy operation. For this to work, $out_fh should refer
		318	to a socket, and $in_fh should refer to mmap'able file.
		319
		320	If the native sendfile call fails or is not implemented, it will be
		321	emulated, so you can call "aio_sendfile" on any type of filehandle
		322	regardless of the limitations of the operating system.
		323
		324	Please note, however, that "aio_sendfile" can read more bytes from
		325	$in_fh than are written, and there is no way to find out how many
		326	bytes have been read from "aio_sendfile" alone, as "aio_sendfile"
		327	only provides the number of bytes written to $out_fh. Only if the
		328	result value equals $length one can assume that $length bytes have
		329	been read.
		330
		331	aio_readahead $fh,$offset,$length, $callback->($retval)
		332	"aio_readahead" populates the page cache with data from a file so
		333	that subsequent reads from that file will not block on disk I/O. The
		334	$offset argument specifies the starting point from which data is to
		335	be read and $length specifies the number of bytes to be read. I/O is
		336	performed in whole pages, so that offset is effectively rounded down
		337	to a page boundary and bytes are read up to the next page boundary
		338	greater than or equal to (off-set+length). "aio_readahead" does not
		339	read beyond the end of the file. The current file offset of the file
		340	is left unchanged.
		341
		342	If that syscall doesn't exist (likely if your OS isn't Linux) it
		343	will be emulated by simply reading the data, which would have a
		344	similar effect.
		345
		346	aio_stat $fh_or_path, $callback->($status)
		347	aio_lstat $fh, $callback->($status)
		348	Works like perl's "stat" or "lstat" in void context. The callback
		349	will be called after the stat and the results will be available
		350	using "stat _" or "-s _" etc...
		351
		352	The pathname passed to "aio_stat" must be absolute. See API NOTES,
		353	above, for an explanation.
		354
		355	Currently, the stats are always 64-bit-stats, i.e. instead of
		356	returning an error when stat'ing a large file, the results will be
		357	silently truncated unless perl itself is compiled with large file
		358	support.
		359
		360	Example: Print the length of /etc/passwd:
		361
		362	aio_stat "/etc/passwd", sub {
		363	$_[0] and die "stat failed: $!";
		364	print "size is ", -s _, "\n";
		365	};
		366
		367	aio_utime $fh_or_path, $atime, $mtime, $callback->($status)
		368	Works like perl's "utime" function (including the special case of
		369	$atime and $mtime being undef). Fractional times are supported if
		370	the underlying syscalls support them.
		371
		372	When called with a pathname, uses utimes(2) if available, otherwise
		373	utime(2). If called on a file descriptor, uses futimes(2) if
		374	available, otherwise returns ENOSYS, so this is not portable.
		375
		376	Examples:
		377
		378	# set atime and mtime to current time (basically touch(1)):
		379	aio_utime "path", undef, undef;
		380	# set atime to current time and mtime to beginning of the epoch:
		381	aio_utime "path", time, undef; # undef==0
		382
		383	aio_chown $fh_or_path, $uid, $gid, $callback->($status)
		384	Works like perl's "chown" function, except that "undef" for either
		385	$uid or $gid is being interpreted as "do not change" (but -1 can
		386	also be used).
		387
		388	Examples:
		389
		390	# same as "chown root path" in the shell:
		391	aio_chown "path", 0, -1;
		392	# same as above:
		393	aio_chown "path", 0, undef;
		394
		395	aio_truncate $fh_or_path, $offset, $callback->($status)
		396	Works like truncate(2) or ftruncate(2).
		397
		398	aio_chmod $fh_or_path, $mode, $callback->($status)
		399	Works like perl's "chmod" function.
		400
		401	aio_unlink $pathname, $callback->($status)
		402	Asynchronously unlink (delete) a file and call the callback with the
		403	result code.
		404
		405	aio_mknod $path, $mode, $dev, $callback->($status)
		406	[EXPERIMENTAL]
		407
		408	Asynchronously create a device node (or fifo). See mknod(2).
		409
		410	The only (POSIX-) portable way of calling this function is:
		411
		412	aio_mknod $path, IO::AIO::S_IFIFO | $mode, 0, sub { ...
		413
		414	aio_link $srcpath, $dstpath, $callback->($status)
		415	Asynchronously create a new link to the existing object at $srcpath
		416	at the path $dstpath and call the callback with the result code.
		417
		418	aio_symlink $srcpath, $dstpath, $callback->($status)
		419	Asynchronously create a new symbolic link to the existing object at
		420	$srcpath at the path $dstpath and call the callback with the result
		421	code.
		422
		423	aio_readlink $path, $callback->($link)
		424	Asynchronously read the symlink specified by $path and pass it to
		425	the callback. If an error occurs, nothing or undef gets passed to
		426	the callback.
		427
		428	aio_rename $srcpath, $dstpath, $callback->($status)
		429	Asynchronously rename the object at $srcpath to $dstpath, just as
		430	rename(2) and call the callback with the result code.
		431
		432	aio_mkdir $pathname, $mode, $callback->($status)
		433	Asynchronously mkdir (create) a directory and call the callback with
		434	the result code. $mode will be modified by the umask at the time the
		435	request is executed, so do not change your umask.
		436
		437	aio_rmdir $pathname, $callback->($status)
		438	Asynchronously rmdir (delete) a directory and call the callback with
		439	the result code.
		440
		441	aio_readdir $pathname, $callback->($entries)
		442	Unlike the POSIX call of the same name, "aio_readdir" reads an
		443	entire directory (i.e. opendir + readdir + closedir). The entries
		444	will not be sorted, and will NOT include the "." and ".." entries.
		445
		446	The callback is passed a single argument which is either "undef" or
		447	an array-ref with the filenames.
		448
		449	aio_readdirx $pathname, $flags, $callback->($entries, $flags)
		450	Quite similar to "aio_readdir", but the $flags argument allows to
		451	tune behaviour and output format. In case of an error, $entries will
		452	be "undef".
		453
		454	The flags are a combination of the following constants, ORed
		455	together (the flags will also be passed to the callback, possibly
		456	modified):
		457
		458	IO::AIO::READDIR_DENTS
		459	When this flag is off, then the callback gets an arrayref with
		460	of names only (as with "aio_readdir"), otherwise it gets an
		461	arrayref with "[$name, $type, $inode]" arrayrefs, each
		462	describing a single directory entry in more detail.
		463
		464	$name is the name of the entry.
		465
		466	$type is one of the "IO::AIO::DT_xxx" constants:
		467
		468	"IO::AIO::DT_UNKNOWN", "IO::AIO::DT_FIFO", "IO::AIO::DT_CHR",
		469	"IO::AIO::DT_DIR", "IO::AIO::DT_BLK", "IO::AIO::DT_REG",
		470	"IO::AIO::DT_LNK", "IO::AIO::DT_SOCK", "IO::AIO::DT_WHT".
		471
		472	"IO::AIO::DT_UNKNOWN" means just that: readdir does not know. If
		473	you need to know, you have to run stat yourself. Also, for speed
		474	reasons, the $type scalars are read-only: you can not modify
		475	them.
		476
		477	$inode is the inode number (which might not be exact on systems
		478	with 64 bit inode numbers and 32 bit perls). This field has
		479	unspecified content on systems that do not deliver the inode
		480	information.
		481
		482	IO::AIO::READDIR_DIRS_FIRST
		483	When this flag is set, then the names will be returned in an
		484	order where likely directories come first. This is useful when
		485	you need to quickly find directories, or you want to find all
		486	directories while avoiding to stat() each entry.
		487
		488	If the system returns type information in readdir, then this is
		489	used to find directories directly. Otherwise, likely directories
		490	are files beginning with ".", or otherwise files with no dots,
		491	of which files with short names are tried first.
		492
		493	IO::AIO::READDIR_STAT_ORDER
		494	When this flag is set, then the names will be returned in an
		495	order suitable for stat()'ing each one. That is, when you plan
		496	to stat() all files in the given directory, then the returned
		497	order will likely be fastest.
		498
		499	If both this flag and "IO::AIO::READDIR_DIRS_FIRST" are
		500	specified, then the likely dirs come first, resulting in a less
		501	optimal stat order.
		502
		503	IO::AIO::READDIR_FOUND_UNKNOWN
		504	This flag should not be set when calling "aio_readdirx".
		505	Instead, it is being set by "aio_readdirx", when any of the
		506	$type's found were "IO::AIO::DT_UNKNOWN". The absense of this
		507	flag therefore indicates that all $type's are known, which can
		508	be used to speed up some algorithms.
		509
		510	aio_load $path, $data, $callback->($status)
		511	This is a composite request that tries to fully load the given file
		512	into memory. Status is the same as with aio_read.
		513
		514	aio_copy $srcpath, $dstpath, $callback->($status)
		515	Try to copy the *file* (directories not supported as either source
		516	or destination) from $srcpath to $dstpath and call the callback with
		517	a status of 0 (ok) or -1 (error, see $!).
		518
		519	This is a composite request that creates the destination file with
		520	mode 0200 and copies the contents of the source file into it using
		521	"aio_sendfile", followed by restoring atime, mtime, access mode and
		522	uid/gid, in that order.
		523
		524	If an error occurs, the partial destination file will be unlinked,
		525	if possible, except when setting atime, mtime, access mode and
		526	uid/gid, where errors are being ignored.
		527
		528	aio_move $srcpath, $dstpath, $callback->($status)
		529	Try to move the *file* (directories not supported as either source
		530	or destination) from $srcpath to $dstpath and call the callback with
		531	a status of 0 (ok) or -1 (error, see $!).
		532
		533	This is a composite request that tries to rename(2) the file first;
		534	if rename fails with "EXDEV", it copies the file with "aio_copy"
		535	and, if that is successful, unlinks the $srcpath.
		536
		537	aio_scandir $path, $maxreq, $callback->($dirs, $nondirs)
		538	Scans a directory (similar to "aio_readdir") but additionally tries
		539	to efficiently separate the entries of directory $path into two sets
		540	of names, directories you can recurse into (directories), and ones
		541	you cannot recurse into (everything else, including symlinks to
		542	directories).
		543
		544	"aio_scandir" is a composite request that creates of many sub
		545	requests_ $maxreq specifies the maximum number of outstanding aio
		546	requests that this function generates. If it is "<= 0", then a
		547	suitable default will be chosen (currently 4).
		548
		549	On error, the callback is called without arguments, otherwise it
		550	receives two array-refs with path-relative entry names.
		551
		552	Example:
		553
		554	aio_scandir $dir, 0, sub {
		555	my ($dirs, $nondirs) = @_;
		556	print "real directories: @$dirs\n";
		557	print "everything else: @$nondirs\n";
		558	};
		559
		560	Implementation notes.
		561
		562	The "aio_readdir" cannot be avoided, but "stat()"'ing every entry
		563	can.
		564
		565	If readdir returns file type information, then this is used directly
		566	to find directories.
		567
		568	Otherwise, after reading the directory, the modification time, size
		569	etc. of the directory before and after the readdir is checked, and
		570	if they match (and isn't the current time), the link count will be
		571	used to decide how many entries are directories (if >= 2).
		572	Otherwise, no knowledge of the number of subdirectories will be
		573	assumed.
		574
		575	Then entries will be sorted into likely directories a non-initial
		576	dot currently) and likely non-directories (see "aio_readdirx"). Then
		577	every entry plus an appended "/." will be "stat"'ed, likely
		578	directories first, in order of their inode numbers. If that
		579	succeeds, it assumes that the entry is a directory or a symlink to
		580	directory (which will be checked seperately). This is often faster
		581	than stat'ing the entry itself because filesystems might detect the
		582	type of the entry without reading the inode data (e.g. ext2fs
		583	filetype feature), even on systems that cannot return the filetype
		584	information on readdir.
		585
		586	If the known number of directories (link count - 2) has been
		587	reached, the rest of the entries is assumed to be non-directories.
		588
		589	This only works with certainty on POSIX (= UNIX) filesystems, which
		590	fortunately are the vast majority of filesystems around.
		591
		592	It will also likely work on non-POSIX filesystems with reduced
		593	efficiency as those tend to return 0 or 1 as link counts, which
		594	disables the directory counting heuristic.
		595
		596	aio_rmtree $path, $callback->($status)
		597	Delete a directory tree starting (and including) $path, return the
		598	status of the final "rmdir" only. This is a composite request that
		599	uses "aio_scandir" to recurse into and rmdir directories, and unlink
		600	everything else.
		601
		602	aio_sync $callback->($status)
		603	Asynchronously call sync and call the callback when finished.
		604
		605	aio_fsync $fh, $callback->($status)
		606	Asynchronously call fsync on the given filehandle and call the
		607	callback with the fsync result code.
		608
		609	aio_fdatasync $fh, $callback->($status)
		610	Asynchronously call fdatasync on the given filehandle and call the
		611	callback with the fdatasync result code.
		612
		613	If this call isn't available because your OS lacks it or it couldn't
		614	be detected, it will be emulated by calling "fsync" instead.
		615
		616	aio_sync_file_range $fh, $offset, $nbytes, $flags, $callback->($status)
		617	Sync the data portion of the file specified by $offset and $length
		618	to disk (but NOT the metadata), by calling the Linux-specific
		619	sync_file_range call. If sync_file_range is not available or it
		620	returns ENOSYS, then fdatasync or fsync is being substituted.
		621
		622	$flags can be a combination of
		623	"IO::AIO::SYNC_FILE_RANGE_WAIT_BEFORE",
		624	"IO::AIO::SYNC_FILE_RANGE_WRITE" and
		625	"IO::AIO::SYNC_FILE_RANGE_WAIT_AFTER": refer to the sync_file_range
		626	manpage for details.
		627
		628	aio_pathsync $path, $callback->($status)
		629	This request tries to open, fsync and close the given path. This is
		630	a composite request intended to sync directories after directory
		631	operations (E.g. rename). This might not work on all operating
		632	systems or have any specific effect, but usually it makes sure that
		633	directory changes get written to disc. It works for anything that
		634	can be opened for read-only, not just directories.
		635
		636	Future versions of this function might fall back to other methods
		637	when "fsync" on the directory fails (such as calling "sync").
		638
		639	Passes 0 when everything went ok, and -1 on error.
		640
		641	aio_group $callback->(...)
		642	This is a very special aio request: Instead of doing something, it
		643	is a container for other aio requests, which is useful if you want
		644	to bundle many requests into a single, composite, request with a
		645	definite callback and the ability to cancel the whole request with
		646	its subrequests.
		647
		648	Returns an object of class IO::AIO::GRP. See its documentation below
		649	for more info.
		650
		651	Example:
		652
		653	my $grp = aio_group sub {
		654	print "all stats done\n";
		655	};
		656
		657	add $grp
		658	(aio_stat ...),
		659	(aio_stat ...),
		660	...;
		661
		662	aio_nop $callback->()
		663	This is a special request - it does nothing in itself and is only
		664	used for side effects, such as when you want to add a dummy request
		665	to a group so that finishing the requests in the group depends on
		666	executing the given code.
		667
		668	While this request does nothing, it still goes through the execution
		669	phase and still requires a worker thread. Thus, the callback will
		670	not be executed immediately but only after other requests in the
		671	queue have entered their execution phase. This can be used to
		672	measure request latency.
		673
		674	IO::AIO::aio_busy $fractional_seconds, $callback->() *NOT EXPORTED*
		675	Mainly used for debugging and benchmarking, this aio request puts
		676	one of the request workers to sleep for the given time.
		677
		678	While it is theoretically handy to have simple I/O scheduling
		679	requests like sleep and file handle readable/writable, the overhead
		680	this creates is immense (it blocks a thread for a long time) so do
		681	not use this function except to put your application under
		682	artificial I/O pressure.
		683
		684	IO::AIO::REQ CLASS
		685	All non-aggregate "aio_*" functions return an object of this class when
		686	called in non-void context.
		687
		688	cancel $req
		689	Cancels the request, if possible. Has the effect of skipping
		690	execution when entering the execute state and skipping calling the
		691	callback when entering the the result state, but will leave the
		692	request otherwise untouched (with the exception of readdir). That
		693	means that requests that currently execute will not be stopped and
		694	resources held by the request will not be freed prematurely.
		695
		696	cb $req $callback->(...)
		697	Replace (or simply set) the callback registered to the request.
		698
		699	IO::AIO::GRP CLASS
		700	This class is a subclass of IO::AIO::REQ, so all its methods apply to
		701	objects of this class, too.
		702
		703	A IO::AIO::GRP object is a special request that can contain multiple
		704	other aio requests.
		705
		706	You create one by calling the "aio_group" constructing function with a
		707	callback that will be called when all contained requests have entered
		708	the "done" state:
		709
		710	my $grp = aio_group sub {
		711	print "all requests are done\n";
		712	};
		713
		714	You add requests by calling the "add" method with one or more
		715	"IO::AIO::REQ" objects:
		716
		717	$grp->add (aio_unlink "...");
		718
		719	add $grp aio_stat "...", sub {
		720	$_[0] or return $grp->result ("error");
		721
		722	# add another request dynamically, if first succeeded
		723	add $grp aio_open "...", sub {
		724	$grp->result ("ok");
		725	};
		726	};
		727
573	This makes it very easy to create composite requests (see the source	728	This makes it very easy to create composite requests (see the source of
574	of "aio_move" for an application) that work and feel like simple	729	"aio_move" for an application) that work and feel like simple requests.
575	requests.
576		730
577	* The IO::AIO::GRP objects will be cleaned up during calls to	731	* The IO::AIO::GRP objects will be cleaned up during calls to
578	"IO::AIO::poll_cb", just like any other request.	732	"IO::AIO::poll_cb", just like any other request.
		733
579	* They can be canceled like any other request. Canceling will cancel	734	* They can be canceled like any other request. Canceling will cancel
580	not only the request itself, but also all requests it contains.	735	not only the request itself, but also all requests it contains.
		736
581	* They can also can also be added to other IO::AIO::GRP objects.	737	* They can also can also be added to other IO::AIO::GRP objects.
		738
582	* You must not add requests to a group from within the group	739	* You must not add requests to a group from within the group callback
583	callback (or any later time).	740	(or any later time).
584		741
585	Their lifetime, simplified, looks like this: when they are empty,	742	Their lifetime, simplified, looks like this: when they are empty, they
586	they will finish very quickly. If they contain only requests that	743	will finish very quickly. If they contain only requests that are in the
587	are in the "done" state, they will also finish. Otherwise they will	744	"done" state, they will also finish. Otherwise they will continue to
588	continue to exist.	745	exist.
589		746
590	That means after creating a group you have some time to add	747	That means after creating a group you have some time to add requests
		748	(precisely before the callback has been invoked, which is only done
591	requests. And in the callbacks of those requests, you can add	749	within the "poll_cb"). And in the callbacks of those requests, you can
592	further requests to the group. And only when all those requests have	750	add further requests to the group. And only when all those requests have
593	finished will the the group itself finish.	751	finished will the the group itself finish.
594		752
595	add $grp ...	753	add $grp ...
596	$grp->add (...)	754	$grp->add (...)
597	Add one or more requests to the group. Any type of IO::AIO::REQ	755	Add one or more requests to the group. Any type of IO::AIO::REQ can
598	can be added, including other groups, as long as you do not	756	be added, including other groups, as long as you do not create
599	create circular dependencies.	757	circular dependencies.
600		758
601	Returns all its arguments.	759	Returns all its arguments.
602		760
603	$grp->cancel_subs	761	$grp->cancel_subs
604	Cancel all subrequests and clears any feeder, but not the group	762	Cancel all subrequests and clears any feeder, but not the group
605	request itself. Useful when you queued a lot of events but got a	763	request itself. Useful when you queued a lot of events but got a
606	result early.	764	result early.
607		765
608	$grp->result (...)	766	$grp->result (...)
609	Set the result value(s) that will be passed to the group	767	Set the result value(s) that will be passed to the group callback
610	callback when all subrequests have finished and set thre groups	768	when all subrequests have finished and set the groups errno to the
611	errno to the current value of errno (just like calling "errno"	769	current value of errno (just like calling "errno" without an error
612	without an error number). By default, no argument will be passed	770	number). By default, no argument will be passed and errno is zero.
613	and errno is zero.
614		771
615	$grp->errno ([$errno])	772	$grp->errno ([$errno])
616	Sets the group errno value to $errno, or the current value of	773	Sets the group errno value to $errno, or the current value of errno
617	errno when the argument is missing.	774	when the argument is missing.
618		775
619	Every aio request has an associated errno value that is restored	776	Every aio request has an associated errno value that is restored
620	when the callback is invoked. This method lets you change this	777	when the callback is invoked. This method lets you change this value
621	value from its default (0).	778	from its default (0).
622		779
623	Calling "result" will also set errno, so make sure you either	780	Calling "result" will also set errno, so make sure you either set $!
624	set $! before the call to "result", or call c<errno> after it.	781	before the call to "result", or call c<errno> after it.
625		782
626	feed $grp $callback->($grp)	783	feed $grp $callback->($grp)
627	Sets a feeder/generator on this group: every group can have an	784	Sets a feeder/generator on this group: every group can have an
628	attached generator that generates requests if idle. The idea	785	attached generator that generates requests if idle. The idea behind
629	behind this is that, although you could just queue as many	786	this is that, although you could just queue as many requests as you
630	requests as you want in a group, this might starve other	787	want in a group, this might starve other requests for a potentially
631	requests for a potentially long time. For example, "aio_scandir"	788	long time. For example, "aio_scandir" might generate hundreds of
632	might generate hundreds of thousands "aio_stat" requests,	789	thousands "aio_stat" requests, delaying any later requests for a
633	delaying any later requests for a long time.	790	long time.
634		791
635	To avoid this, and allow incremental generation of requests, you	792	To avoid this, and allow incremental generation of requests, you can
636	can instead a group and set a feeder on it that generates those	793	instead a group and set a feeder on it that generates those
637	requests. The feed callback will be called whenever there are	794	requests. The feed callback will be called whenever there are few
638	few enough (see "limit", below) requests active in the group	795	enough (see "limit", below) requests active in the group itself and
639	itself and is expected to queue more requests.	796	is expected to queue more requests.
640		797
641	The feed callback can queue as many requests as it likes (i.e.	798	The feed callback can queue as many requests as it likes (i.e. "add"
642	"add" does not impose any limits).	799	does not impose any limits).
643		800
644	If the feed does not queue more requests when called, it will be	801	If the feed does not queue more requests when called, it will be
645	automatically removed from the group.	802	automatically removed from the group.
646		803
647	If the feed limit is 0, it will be set to 2 automatically.	804	If the feed limit is 0 when this method is called, it will be set to
		805	2 automatically.
648		806
649	Example:	807	Example:
650		808
651	# stat all files in @files, but only ever use four aio requests concurrently:	809	# stat all files in @files, but only ever use four aio requests concurrently:
652		810
653	my $grp = aio_group sub { print "finished\n" };	811	my $grp = aio_group sub { print "finished\n" };
654	limit $grp 4;	812	limit $grp 4;
655	feed $grp sub {	813	feed $grp sub {
656	my $file = pop @files	814	my $file = pop @files
657	or return;	815	or return;
658		816
659	add $grp aio_stat $file, sub { ... };	817	add $grp aio_stat $file, sub { ... };
660	};	818	};
661		819
662	limit $grp $num	820	limit $grp $num
663	Sets the feeder limit for the group: The feeder will be called	821	Sets the feeder limit for the group: The feeder will be called
664	whenever the group contains less than this many requests.	822	whenever the group contains less than this many requests.
665		823
666	Setting the limit to 0 will pause the feeding process.	824	Setting the limit to 0 will pause the feeding process.
		825
		826	The default value for the limit is 0, but note that setting a feeder
		827	automatically bumps it up to 2.
667		828
668	SUPPORT FUNCTIONS	829	SUPPORT FUNCTIONS
669	EVENT PROCESSING AND EVENT LOOP INTEGRATION	830	EVENT PROCESSING AND EVENT LOOP INTEGRATION
670	$fileno = IO::AIO::poll_fileno	831	$fileno = IO::AIO::poll_fileno
671	Return the *request result pipe file descriptor*. This	832	Return the *request result pipe file descriptor*. This filehandle
672	filehandle must be polled for reading by some mechanism outside	833	must be polled for reading by some mechanism outside this module
673	this module (e.g. Event or select, see below or the SYNOPSIS).	834	(e.g. EV, Glib, select and so on, see below or the SYNOPSIS). If the
674	If the pipe becomes readable you have to call "poll_cb" to check	835	pipe becomes readable you have to call "poll_cb" to check the
675	the results.	836	results.
676		837
677	See "poll_cb" for an example.	838	See "poll_cb" for an example.
678		839
679	IO::AIO::poll_cb	840	IO::AIO::poll_cb
680	Process some outstanding events on the result pipe. You have to	841	Process some outstanding events on the result pipe. You have to call
681	call this regularly. Returns the number of events processed.	842	this regularly. Returns 0 if all events could be processed, or -1 if
682	Returns immediately when no events are outstanding. The amount	843	it returned earlier for whatever reason. Returns immediately when no
683	of events processed depends on the settings of	844	events are outstanding. The amount of events processed depends on
684	"IO::AIO::max_poll_req" and "IO::AIO::max_poll_time".	845	the settings of "IO::AIO::max_poll_req" and
		846	"IO::AIO::max_poll_time".
685		847
686	If not all requests were processed for whatever reason, the	848	If not all requests were processed for whatever reason, the
687	filehandle will still be ready when "poll_cb" returns.	849	filehandle will still be ready when "poll_cb" returns, so normally
		850	you don't have to do anything special to have it called later.
688		851
689	Example: Install an Event watcher that automatically calls	852	Example: Install an Event watcher that automatically calls
690	IO::AIO::poll_cb with high priority:	853	IO::AIO::poll_cb with high priority (more examples can be found in
		854	the SYNOPSIS section, at the top of this document):
691		855
692	Event->io (fd => IO::AIO::poll_fileno,	856	Event->io (fd => IO::AIO::poll_fileno,
693	poll => 'r', async => 1,	857	poll => 'r', async => 1,
694	cb => \&IO::AIO::poll_cb);	858	cb => \&IO::AIO::poll_cb);
695		859
696	IO::AIO::max_poll_reqs $nreqs	860	IO::AIO::max_poll_reqs $nreqs
697	IO::AIO::max_poll_time $seconds	861	IO::AIO::max_poll_time $seconds
698	These set the maximum number of requests (default 0, meaning	862	These set the maximum number of requests (default 0, meaning
699	infinity) that are being processed by "IO::AIO::poll_cb" in one	863	infinity) that are being processed by "IO::AIO::poll_cb" in one
700	call, respectively the maximum amount of time (default 0,	864	call, respectively the maximum amount of time (default 0, meaning
701	meaning infinity) spent in "IO::AIO::poll_cb" to process	865	infinity) spent in "IO::AIO::poll_cb" to process requests (more
702	requests (more correctly the mininum amount of time "poll_cb" is	866	correctly the mininum amount of time "poll_cb" is allowed to use).
703	allowed to use).
704		867
		868	Setting "max_poll_time" to a non-zero value creates an overhead of
		869	one syscall per request processed, which is not normally a problem
		870	unless your callbacks are really really fast or your OS is really
		871	really slow (I am not mentioning Solaris here). Using
		872	"max_poll_reqs" incurs no overhead.
		873
705	Setting these is useful if you want to ensure some level of	874	Setting these is useful if you want to ensure some level of
706	interactiveness when perl is not fast enough to process all	875	interactiveness when perl is not fast enough to process all requests
707	requests in time.	876	in time.
708		877
709	For interactive programs, values such as 0.01 to 0.1 should be	878	For interactive programs, values such as 0.01 to 0.1 should be fine.
710	fine.
711		879
712	Example: Install an Event watcher that automatically calls	880	Example: Install an Event watcher that automatically calls
713	IO::AIO::poll_some with low priority, to ensure that other parts	881	IO::AIO::poll_cb with low priority, to ensure that other parts of
714	of the program get the CPU sometimes even under high AIO load.	882	the program get the CPU sometimes even under high AIO load.
715		883
716	# try not to spend much more than 0.1s in poll_cb	884	# try not to spend much more than 0.1s in poll_cb
717	IO::AIO::max_poll_time 0.1;	885	IO::AIO::max_poll_time 0.1;
718		886
719	# use a low priority so other tasks have priority	887	# use a low priority so other tasks have priority
720	Event->io (fd => IO::AIO::poll_fileno,	888	Event->io (fd => IO::AIO::poll_fileno,
721	poll => 'r', nice => 1,	889	poll => 'r', nice => 1,
722	cb => &IO::AIO::poll_cb);	890	cb => &IO::AIO::poll_cb);
723		891
724	IO::AIO::poll_wait	892	IO::AIO::poll_wait
		893	If there are any outstanding requests and none of them in the result
725	Wait till the result filehandle becomes ready for reading	894	phase, wait till the result filehandle becomes ready for reading
726	(simply does a "select" on the filehandle. This is useful if you	895	(simply does a "select" on the filehandle. This is useful if you
727	want to synchronously wait for some requests to finish).	896	want to synchronously wait for some requests to finish).
728		897
729	See "nreqs" for an example.	898	See "nreqs" for an example.
730		899
731	IO::AIO::poll	900	IO::AIO::poll
732	Waits until some requests have been handled.	901	Waits until some requests have been handled.
733		902
		903	Returns the number of requests processed, but is otherwise strictly
734	Strictly equivalent to:	904	equivalent to:
735		905
736	IO::AIO::poll_wait, IO::AIO::poll_cb	906	IO::AIO::poll_wait, IO::AIO::poll_cb
737	if IO::AIO::nreqs;
738		907
739	IO::AIO::flush	908	IO::AIO::flush
740	Wait till all outstanding AIO requests have been handled.	909	Wait till all outstanding AIO requests have been handled.
741		910
742	Strictly equivalent to:	911	Strictly equivalent to:
743		912
744	IO::AIO::poll_wait, IO::AIO::poll_cb	913	IO::AIO::poll_wait, IO::AIO::poll_cb
745	while IO::AIO::nreqs;	914	while IO::AIO::nreqs;
746		915
747	CONTROLLING THE NUMBER OF THREADS	916	CONTROLLING THE NUMBER OF THREADS
748	IO::AIO::min_parallel $nthreads	917	IO::AIO::min_parallel $nthreads
749	Set the minimum number of AIO threads to $nthreads. The current	918	Set the minimum number of AIO threads to $nthreads. The current
750	default is 8, which means eight asynchronous operations can	919	default is 8, which means eight asynchronous operations can execute
751	execute concurrently at any one time (the number of outstanding	920	concurrently at any one time (the number of outstanding requests,
752	requests, however, is unlimited).	921	however, is unlimited).
753		922
754	IO::AIO starts threads only on demand, when an AIO request is	923	IO::AIO starts threads only on demand, when an AIO request is queued
755	queued and no free thread exists. Please note that queueing up a	924	and no free thread exists. Please note that queueing up a hundred
756	hundred requests can create demand for a hundred threads, even	925	requests can create demand for a hundred threads, even if it turns
757	if it turns out that everything is in the cache and could have	926	out that everything is in the cache and could have been processed
758	been processed faster by a single thread.	927	faster by a single thread.
759		928
760	It is recommended to keep the number of threads relatively low,	929	It is recommended to keep the number of threads relatively low, as
761	as some Linux kernel versions will scale negatively with the	930	some Linux kernel versions will scale negatively with the number of
762	number of threads (higher parallelity => MUCH higher latency).	931	threads (higher parallelity => MUCH higher latency). With current
763	With current Linux 2.6 versions, 4-32 threads should be fine.	932	Linux 2.6 versions, 4-32 threads should be fine.
764		933
765	Under most circumstances you don't need to call this function,	934	Under most circumstances you don't need to call this function, as
766	as the module selects a default that is suitable for low to	935	the module selects a default that is suitable for low to moderate
767	moderate load.	936	load.
768		937
769	IO::AIO::max_parallel $nthreads	938	IO::AIO::max_parallel $nthreads
770	Sets the maximum number of AIO threads to $nthreads. If more	939	Sets the maximum number of AIO threads to $nthreads. If more than
771	than the specified number of threads are currently running, this	940	the specified number of threads are currently running, this function
772	function kills them. This function blocks until the limit is	941	kills them. This function blocks until the limit is reached.
773	reached.
774		942
775	While $nthreads are zero, aio requests get queued but not	943	While $nthreads are zero, aio requests get queued but not executed
776	executed until the number of threads has been increased again.	944	until the number of threads has been increased again.
777		945
778	This module automatically runs "max_parallel 0" at program end,	946	This module automatically runs "max_parallel 0" at program end, to
779	to ensure that all threads are killed and that there are no	947	ensure that all threads are killed and that there are no outstanding
780	outstanding requests.	948	requests.
781		949
782	Under normal circumstances you don't need to call this function.	950	Under normal circumstances you don't need to call this function.
783		951
784	IO::AIO::max_idle $nthreads	952	IO::AIO::max_idle $nthreads
785	Limit the number of threads (default: 4) that are allowed to	953	Limit the number of threads (default: 4) that are allowed to idle
786	idle (i.e., threads that did not get a request to process within	954	(i.e., threads that did not get a request to process within 10
787	10 seconds). That means if a thread becomes idle while $nthreads	955	seconds). That means if a thread becomes idle while $nthreads other
788	other threads are also idle, it will free its resources and	956	threads are also idle, it will free its resources and exit.
789	exit.
790		957
791	This is useful when you allow a large number of threads (e.g.	958	This is useful when you allow a large number of threads (e.g. 100 or
792	100 or 1000) to allow for extremely high load situations, but	959	1000) to allow for extremely high load situations, but want to free
793	want to free resources under normal circumstances (1000 threads	960	resources under normal circumstances (1000 threads can easily
794	can easily consume 30MB of RAM).	961	consume 30MB of RAM).
795		962
796	The default is probably ok in most situations, especially if	963	The default is probably ok in most situations, especially if thread
797	thread creation is fast. If thread creation is very slow on your	964	creation is fast. If thread creation is very slow on your system you
798	system you might want to use larger values.	965	might want to use larger values.
799		966
800	$oldmaxreqs = IO::AIO::max_outstanding $maxreqs	967	IO::AIO::max_outstanding $maxreqs
801	This is a very bad function to use in interactive programs	968	This is a very bad function to use in interactive programs because
802	because it blocks, and a bad way to reduce concurrency because	969	it blocks, and a bad way to reduce concurrency because it is
803	it is inexact: Better use an "aio_group" together with a feed	970	inexact: Better use an "aio_group" together with a feed callback.
804	callback.
805		971
806	Sets the maximum number of outstanding requests to $nreqs. If	972	Sets the maximum number of outstanding requests to $nreqs. If you do
807	you to queue up more than this number of requests, the next call	973	queue up more than this number of requests, the next call to the
808	to the "poll_cb" (and "poll_some" and other functions calling	974	"poll_cb" (and "poll_some" and other functions calling "poll_cb")
809	"poll_cb") function will block until the limit is no longer	975	function will block until the limit is no longer exceeded.
810	exceeded.
811		976
812	The default value is very large, so there is no practical limit	977	The default value is very large, so there is no practical limit on
813	on the number of outstanding requests.	978	the number of outstanding requests.
814		979
815	You can still queue as many requests as you want. Therefore,	980	You can still queue as many requests as you want. Therefore,
816	"max_oustsanding" is mainly useful in simple scripts (with low	981	"max_outstanding" is mainly useful in simple scripts (with low
817	values) or as a stop gap to shield against fatal memory overflow	982	values) or as a stop gap to shield against fatal memory overflow
818	(with large values).	983	(with large values).
819		984
820	STATISTICAL INFORMATION	985	STATISTICAL INFORMATION
821	IO::AIO::nreqs	986	IO::AIO::nreqs
822	Returns the number of requests currently in the ready, execute	987	Returns the number of requests currently in the ready, execute or
823	or pending states (i.e. for which their callback has not been	988	pending states (i.e. for which their callback has not been invoked
824	invoked yet).	989	yet).
825		990
826	Example: wait till there are no outstanding requests anymore:	991	Example: wait till there are no outstanding requests anymore:
827		992
828	IO::AIO::poll_wait, IO::AIO::poll_cb	993	IO::AIO::poll_wait, IO::AIO::poll_cb
829	while IO::AIO::nreqs;	994	while IO::AIO::nreqs;
830		995
831	IO::AIO::nready	996	IO::AIO::nready
832	Returns the number of requests currently in the ready state (not	997	Returns the number of requests currently in the ready state (not yet
833	yet executed).	998	executed).
834		999
835	IO::AIO::npending	1000	IO::AIO::npending
836	Returns the number of requests currently in the pending state	1001	Returns the number of requests currently in the pending state
837	(executed, but not yet processed by poll_cb).	1002	(executed, but not yet processed by poll_cb).
		1003
		1004	MISCELLANEOUS FUNCTIONS
		1005	IO::AIO implements some functions that might be useful, but are not
		1006	asynchronous.
		1007
		1008	IO::AIO::sendfile $ofh, $ifh, $offset, $count
		1009	Calls the "eio_sendfile_sync" function, which is like
		1010	"aio_sendfile", but is blocking (this makes most sense if you know
		1011	the input data is likely cached already and the output filehandle is
		1012	set to non-blocking operations).
		1013
		1014	Returns the number of bytes copied, or -1 on error.
		1015
		1016	IO::AIO::fadvise $fh, $offset, $len, $advice
		1017	Simply calls the "posix_fadvise" function (see it's manpage for
		1018	details). The following advice constants are avaiable:
		1019	"IO::AIO::FADV_NORMAL", "IO::AIO::FADV_SEQUENTIAL",
		1020	"IO::AIO::FADV_RANDOM", "IO::AIO::FADV_NOREUSE",
		1021	"IO::AIO::FADV_WILLNEED", "IO::AIO::FADV_DONTNEED".
		1022
		1023	On systems that do not implement "posix_fadvise", this function
		1024	returns ENOSYS, otherwise the return value of "posix_fadvise".
838		1025
839	FORK BEHAVIOUR	1026	FORK BEHAVIOUR
840	This module should do "the right thing" when the process using it	1027	This module should do "the right thing" when the process using it forks:
841	forks:
842		1028
843	Before the fork, IO::AIO enters a quiescent state where no requests	1029	Before the fork, IO::AIO enters a quiescent state where no requests can
844	can be added in other threads and no results will be processed.	1030	be added in other threads and no results will be processed. After the
845	After the fork the parent simply leaves the quiescent state and	1031	fork the parent simply leaves the quiescent state and continues
846	continues request/result processing, while the child frees the	1032	request/result processing, while the child frees the request/result
847	request/result queue (so that the requests started before the fork	1033	queue (so that the requests started before the fork will only be handled
848	will only be handled in the parent). Threads will be started on	1034	in the parent). Threads will be started on demand until the limit set in
849	demand until the limit set in the parent process has been reached	1035	the parent process has been reached again.
850	again.
851		1036
852	In short: the parent will, after a short pause, continue as if fork	1037	In short: the parent will, after a short pause, continue as if fork had
853	had not been called, while the child will act as if IO::AIO has not	1038	not been called, while the child will act as if IO::AIO has not been
854	been used yet.	1039	used yet.
855		1040
856	MEMORY USAGE	1041	MEMORY USAGE
857	Per-request usage:	1042	Per-request usage:
858		1043
859	Each aio request uses - depending on your architecture - around	1044	Each aio request uses - depending on your architecture - around 100-200
860	100-200 bytes of memory. In addition, stat requests need a stat	1045	bytes of memory. In addition, stat requests need a stat buffer (possibly
861	buffer (possibly a few hundred bytes), readdir requires a result	1046	a few hundred bytes), readdir requires a result buffer and so on. Perl
862	buffer and so on. Perl scalars and other data passed into aio	1047	scalars and other data passed into aio requests will also be locked and
863	requests will also be locked and will consume memory till the	1048	will consume memory till the request has entered the done state.
864	request has entered the done state.
865		1049
866	This is now awfully much, so queuing lots of requests is not usually	1050	This is not awfully much, so queuing lots of requests is not usually a
867	a problem.	1051	problem.
868		1052
869	Per-thread usage:	1053	Per-thread usage:
870		1054
871	In the execution phase, some aio requests require more memory for	1055	In the execution phase, some aio requests require more memory for
872	temporary buffers, and each thread requires a stack and other data	1056	temporary buffers, and each thread requires a stack and other data
873	structures (usually around 16k-128k, depending on the OS).	1057	structures (usually around 16k-128k, depending on the OS).
874		1058
875	KNOWN BUGS	1059	KNOWN BUGS
876	Known bugs will be fixed in the next release.	1060	Known bugs will be fixed in the next release.
877		1061
878	SEE ALSO	1062	SEE ALSO
879	Coro::AIO.	1063	AnyEvent::AIO for easy integration into event loops, Coro::AIO for a
		1064	more natural syntax.
880		1065
881	AUTHOR	1066	AUTHOR
882	Marc Lehmann <schmorp@schmorp.de>	1067	Marc Lehmann <schmorp@schmorp.de>
883	http://home.schmorp.de/	1068	http://home.schmorp.de/
884		1069

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