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Revision 1.18 by root, Thu Oct 26 16:28:33 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
…		…
47	\&IO::AIO::poll_cb);	48	\&IO::AIO::poll_cb);
48		49
49	DESCRIPTION	50	DESCRIPTION
50	This module implements asynchronous I/O using whatever means your	51	This module implements asynchronous I/O using whatever means your
51	operating system supports.	52	operating system supports.
		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.
52		70
53	In this version, a number of threads are started that execute your	71	In this version, a number of threads are started that execute your
54	requests and signal their completion. You don't need thread support in	72	requests and signal their completion. You don't need thread support in
55	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
56	perl. In the future, this module might make use of the native aio	74	perl. In the future, this module might make use of the native aio
57	functions available on many operating systems. However, they are often	75	functions available on many operating systems. However, they are often
58	not well-supported or restricted (Linux doesn't allow them on normal	76	not well-supported or restricted (GNU/Linux doesn't allow them on normal
59	files currently, for example), and they would only support aio_read and	77	files currently, for example), and they would only support aio_read and
60	aio_write, so the remaining functionality would have to be implemented	78	aio_write, so the remaining functionality would have to be implemented
61	using threads anyway.	79	using threads anyway.
62		80
63	Although the module will work with in the presence of other (Perl-)	81	Although the module will work with in the presence of other (Perl-)
64	threads, it is currently not reentrant in any way, so use appropriate	82	threads, it is currently not reentrant in any way, so use appropriate
65	locking yourself, always call "poll_cb" from within the same thread, or	83	locking yourself, always call "poll_cb" from within the same thread, or
66	never call "poll_cb" (or 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;
67		128
68	REQUEST ANATOMY AND LIFETIME	129	REQUEST ANATOMY AND LIFETIME
69	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
70	not directly visible to Perl.	131	not directly visible to Perl.
71		132
…		…
107	anymore (except possibly for the Perl object, but its connection to	168	anymore (except possibly for the Perl object, but its connection to
108	the actual aio request is severed and calling its methods will	169	the actual aio request is severed and calling its methods will
109	either do nothing or result in a runtime error).	170	either do nothing or result in a runtime error).
110		171
111	FUNCTIONS	172	FUNCTIONS
112	AIO FUNCTIONS	173	AIO REQUEST FUNCTIONS
113	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
114	syscall with the same name (sans "aio_"). The arguments are similar	175	with the same name (sans "aio_"). The arguments are similar or
115	or identical, and they all accept an additional (and optional)	176	identical, and they all accept an additional (and optional) $callback
116	$callback argument which must be a code reference. This code	177	argument which must be a code reference. This code reference will get
117	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
118	syscalls return -1 on error, unlike perl, which usually delivers	179	error, unlike perl, which usually delivers "false") as it's sole
119	"false") as it's sole argument when the given syscall has been	180	argument when the given syscall has been executed asynchronously.
120	executed asynchronously.
121		181
122	All functions expecting a filehandle keep a copy of the filehandle	182	All functions expecting a filehandle keep a copy of the filehandle
123	internally until the request has finished.	183	internally until the request has finished.
124		184
125	All requests return objects of type IO::AIO::REQ that allow further	185	All functions return request objects of type IO::AIO::REQ that allow
126	manipulation of those requests while they are in-flight.	186	further manipulation of those requests while they are in-flight.
127		187
128	The pathnames you pass to these routines *must* be absolute and	188	The pathnames you pass to these routines *must* be absolute and encoded
129	encoded in byte form. The reason for the former is that at the time	189	as octets. The reason for the former is that at the time the request is
130	the request is being executed, the current working directory could	190	being executed, the current working directory could have changed.
131	have changed. Alternatively, you can make sure that you never change	191	Alternatively, you can make sure that you never change the current
132	the current working directory.	192	working directory anywhere in the program and then use relative paths.
133		193
134	To encode pathnames to byte form, either make sure you either: a)	194	To encode pathnames as octets, either make sure you either: a) always
135	always pass in filenames you got from outside (command line, readdir	195	pass in filenames you got from outside (command line, readdir etc.)
136	etc.), b) are ASCII or ISO 8859-1, c) use the Encode module and	196	without tinkering, b) are ASCII or ISO 8859-1, c) use the Encode module
137	encode your pathnames to the locale (or other) encoding in effect in	197	and encode your pathnames to the locale (or other) encoding in effect in
138	the user environment, d) use Glib::filename_from_unicode on unicode	198	the user environment, d) use Glib::filename_from_unicode on unicode
139	filenames or e) use something else.	199	filenames or e) use something else to ensure your scalar has the correct
		200	contents.
140		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
141	$prev_pri = aioreq_pri [$pri]	205	$prev_pri = aioreq_pri [$pri]
142	Returns the priority value that would be used for the next	206	Returns the priority value that would be used for the next request
143	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.
144	aio request.
145		208
146	The default priority is 0, the minimum and maximum priorities	209	The default priority is 0, the minimum and maximum priorities are -4
147	are -4 and 4, respectively. Requests with higher priority will	210	and 4, respectively. Requests with higher priority will be serviced
148	be serviced first.	211	first.
149		212
150	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
151	"aio_*" functions.	214	"aio_*" functions.
152		215
153	Example: open a file with low priority, then read something from	216	Example: open a file with low priority, then read something from it
154	it with higher priority so the read request is serviced before	217	with higher priority so the read request is serviced before other
155	other low priority open requests (potentially spamming the	218	low priority open requests (potentially spamming the cache):
156	cache):
157		219
		220	aioreq_pri -3;
		221	aio_open ..., sub {
		222	return unless $_[0];
		223
158	aioreq_pri -3;	224	aioreq_pri -2;
159	aio_open ..., sub {
160	return unless $_[0];
161
162	aioreq_pri -2;
163	aio_read $_[0], ..., sub {	225	aio_read $_[0], ..., sub {
164	...
165	};
166	};
167
168	aioreq_nice $pri_adjust
169	Similar to "aioreq_pri", but subtracts the given value from the
170	current priority, so effects are cumulative.
171
172	aio_open $pathname, $flags, $mode, $callback->($fh)
173	Asynchronously open or create a file and call the callback with
174	a newly created filehandle for the file.
175
176	The pathname passed to "aio_open" must be absolute. See API
177	NOTES, above, for an explanation.
178
179	The $flags argument is a bitmask. See the "Fcntl" module for a
180	list. They are the same as used by "sysopen".
181
182	Likewise, $mode specifies the mode of the newly created file, if
183	it didn't exist and "O_CREAT" has been given, just like perl's
184	"sysopen", except that it is mandatory (i.e. use 0 if you don't
185	create new files, and 0666 or 0777 if you do).
186
187	Example:
188
189	aio_open "/etc/passwd", O_RDONLY, 0, sub {
190	if ($_[0]) {
191	print "open successful, fh is $_[0]\n";
192	...
193	} else {
194	die "open failed: $!\n";
195	}
196	};
197
198	aio_close $fh, $callback->($status)
199	Asynchronously close a file and call the callback with the
200	result code. *WARNING:* although accepted, you should not pass
201	in a perl filehandle here, as perl will likely close the file
202	descriptor another time when the filehandle is destroyed.
203	Normally, you can safely call perls "close" or just let
204	filehandles go out of scope.
205
206	This is supposed to be a bug in the API, so that might change.
207	It's therefore best to avoid this function.
208
209	aio_read $fh,$offset,$length, $data,$dataoffset,
210	$callback->($retval)
211	aio_write $fh,$offset,$length, $data,$dataoffset,
212	$callback->($retval)
213	Reads or writes "length" bytes from the specified "fh" and
214	"offset" into the scalar given by "data" and offset "dataoffset"
215	and calls the callback without the actual number of bytes read
216	(or -1 on error, just like the syscall).
217
218	The $data scalar *MUST NOT* be modified in any way while the
219	request is outstanding. Modifying it can result in segfaults or
220	WW3 (if the necessary/optional hardware is installed).
221
222	Example: Read 15 bytes at offset 7 into scalar $buffer, starting
223	at offset 0 within the scalar:
224
225	aio_read $fh, 7, 15, $buffer, 0, sub {
226	$_[0] > 0 or die "read error: $!";
227	print "read $_[0] bytes: <$buffer>\n";
228	};
229
230	aio_move $srcpath, $dstpath, $callback->($status)
231	Try to move the *file* (directories not supported as either
232	source or destination) from $srcpath to $dstpath and call the
233	callback with the 0 (error) or -1 ok.
234
235	This is a composite request that tries to rename(2) the file
236	first. If rename files with "EXDEV", it creates the destination
237	file with mode 0200 and copies the contents of the source file
238	into it using "aio_sendfile", followed by restoring atime,
239	mtime, access mode and uid/gid, in that order, and unlinking the
240	$srcpath.
241
242	If an error occurs, the partial destination file will be
243	unlinked, if possible, except when setting atime, mtime, access
244	mode and uid/gid, where errors are being ignored.
245
246	aio_sendfile $out_fh, $in_fh, $in_offset, $length,
247	$callback->($retval)
248	Tries to copy $length bytes from $in_fh to $out_fh. It starts
249	reading at byte offset $in_offset, and starts writing at the
250	current file offset of $out_fh. Because of that, it is not safe
251	to issue more than one "aio_sendfile" per $out_fh, as they will
252	interfere with each other.
253
254	This call tries to make use of a native "sendfile" syscall to
255	provide zero-copy operation. For this to work, $out_fh should
256	refer to a socket, and $in_fh should refer to mmap'able file.
257
258	If the native sendfile call fails or is not implemented, it will
259	be emulated, so you can call "aio_sendfile" on any type of
260	filehandle regardless of the limitations of the operating
261	system.
262
263	Please note, however, that "aio_sendfile" can read more bytes
264	from $in_fh than are written, and there is no way to find out
265	how many bytes have been read from "aio_sendfile" alone, as
266	"aio_sendfile" only provides the number of bytes written to
267	$out_fh. Only if the result value equals $length one can assume
268	that $length bytes have been read.
269
270	aio_readahead $fh,$offset,$length, $callback->($retval)
271	"aio_readahead" populates the page cache with data from a file
272	so that subsequent reads from that file will not block on disk
273	I/O. The $offset argument specifies the starting point from
274	which data is to be read and $length specifies the number of
275	bytes to be read. I/O is performed in whole pages, so that
276	offset is effectively rounded down to a page boundary and bytes
277	are read up to the next page boundary greater than or equal to
278	(off-set+length). "aio_readahead" does not read beyond the end
279	of the file. The current file offset of the file is left
280	unchanged.
281
282	If that syscall doesn't exist (likely if your OS isn't Linux) it
283	will be emulated by simply reading the data, which would have a
284	similar effect.
285
286	aio_stat $fh_or_path, $callback->($status)
287	aio_lstat $fh, $callback->($status)
288	Works like perl's "stat" or "lstat" in void context. The
289	callback will be called after the stat and the results will be
290	available using "stat _" or "-s _" etc...
291
292	The pathname passed to "aio_stat" must be absolute. See API
293	NOTES, above, for an explanation.
294
295	Currently, the stats are always 64-bit-stats, i.e. instead of
296	returning an error when stat'ing a large file, the results will
297	be silently truncated unless perl itself is compiled with large
298	file support.
299
300	Example: Print the length of /etc/passwd:
301
302	aio_stat "/etc/passwd", sub {
303	$_[0] and die "stat failed: $!";
304	print "size is ", -s _, "\n";
305	};
306
307	aio_unlink $pathname, $callback->($status)
308	Asynchronously unlink (delete) a file and call the callback with
309	the result code.
310
311	aio_link $srcpath, $dstpath, $callback->($status)
312	Asynchronously create a new link to the existing object at
313	$srcpath at the path $dstpath and call the callback with the
314	result code.
315
316	aio_symlink $srcpath, $dstpath, $callback->($status)
317	Asynchronously create a new symbolic link to the existing object
318	at $srcpath at the path $dstpath and call the callback with the
319	result code.
320
321	aio_rename $srcpath, $dstpath, $callback->($status)
322	Asynchronously rename the object at $srcpath to $dstpath, just
323	as rename(2) and call the callback with the result code.
324
325	aio_rmdir $pathname, $callback->($status)
326	Asynchronously rmdir (delete) a directory and call the callback
327	with the result code.
328
329	aio_readdir $pathname, $callback->($entries)
330	Unlike the POSIX call of the same name, "aio_readdir" reads an
331	entire directory (i.e. opendir + readdir + closedir). The
332	entries will not be sorted, and will NOT include the "." and
333	".." entries.
334
335	The callback a single argument which is either "undef" or an
336	array-ref with the filenames.
337
338	aio_scandir $path, $maxreq, $callback->($dirs, $nondirs)
339	Scans a directory (similar to "aio_readdir") but additionally
340	tries to efficiently separate the entries of directory $path
341	into two sets of names, directories you can recurse into
342	(directories), and ones you cannot recurse into (everything
343	else, including symlinks to directories).
344
345	"aio_scandir" is a composite request that creates of many sub
346	requests_ $maxreq specifies the maximum number of outstanding
347	aio requests that this function generates. If it is "<= 0", then
348	a suitable default will be chosen (currently 6).
349
350	On error, the callback is called without arguments, otherwise it
351	receives two array-refs with path-relative entry names.
352
353	Example:
354
355	aio_scandir $dir, 0, sub {
356	my ($dirs, $nondirs) = @_;
357	print "real directories: @$dirs\n";
358	print "everything else: @$nondirs\n";
359	};
360
361	Implementation notes.
362
363	The "aio_readdir" cannot be avoided, but "stat()"'ing every
364	entry can.
365
366	After reading the directory, the modification time, size etc. of
367	the directory before and after the readdir is checked, and if
368	they match (and isn't the current time), the link count will be
369	used to decide how many entries are directories (if >= 2).
370	Otherwise, no knowledge of the number of subdirectories will be
371	assumed.
372
373	Then entries will be sorted into likely directories (everything
374	without a non-initial dot currently) and likely non-directories
375	(everything else). Then every entry plus an appended "/." will
376	be "stat"'ed, likely directories first. If that succeeds, it
377	assumes that the entry is a directory or a symlink to directory
378	(which will be checked seperately). This is often faster than
379	stat'ing the entry itself because filesystems might detect the
380	type of the entry without reading the inode data (e.g. ext2fs
381	filetype feature).
382
383	If the known number of directories (link count - 2) has been
384	reached, the rest of the entries is assumed to be
385	non-directories.
386
387	This only works with certainty on POSIX (= UNIX) filesystems,
388	which fortunately are the vast majority of filesystems around.
389
390	It will also likely work on non-POSIX filesystems with reduced
391	efficiency as those tend to return 0 or 1 as link counts, which
392	disables the directory counting heuristic.
393
394	aio_fsync $fh, $callback->($status)
395	Asynchronously call fsync on the given filehandle and call the
396	callback with the fsync result code.
397
398	aio_fdatasync $fh, $callback->($status)
399	Asynchronously call fdatasync on the given filehandle and call
400	the callback with the fdatasync result code.
401
402	If this call isn't available because your OS lacks it or it
403	couldn't be detected, it will be emulated by calling "fsync"
404	instead.
405
406	aio_group $callback->(...)
407	This is a very special aio request: Instead of doing something,
408	it is a container for other aio requests, which is useful if you
409	want to bundle many requests into a single, composite, request
410	with a definite callback and the ability to cancel the whole
411	request with its subrequests.
412
413	Returns an object of class IO::AIO::GRP. See its documentation
414	below for more info.
415
416	Example:
417
418	my $grp = aio_group sub {
419	print "all stats done\n";
420	};
421
422	add $grp
423	(aio_stat ...),
424	(aio_stat ...),
425	...;	226	...
426
427	aio_nop $callback->()
428	This is a special request - it does nothing in itself and is
429	only used for side effects, such as when you want to add a dummy
430	request to a group so that finishing the requests in the group
431	depends on executing the given code.
432
433	While this request does nothing, it still goes through the
434	execution phase and still requires a worker thread. Thus, the
435	callback will not be executed immediately but only after other
436	requests in the queue have entered their execution phase. This
437	can be used to measure request latency.
438
439	IO::AIO::aio_busy $fractional_seconds, $callback->() *NOT EXPORTED*
440	Mainly used for debugging and benchmarking, this aio request
441	puts one of the request workers to sleep for the given time.
442
443	While it is theoretically handy to have simple I/O scheduling
444	requests like sleep and file handle readable/writable, the
445	overhead this creates is immense (it blocks a thread for a long
446	time) so do not use this function except to put your application
447	under artificial I/O pressure.
448
449	IO::AIO::REQ CLASS
450	All non-aggregate "aio_*" functions return an object of this class
451	when called in non-void context.
452
453	cancel $req
454	Cancels the request, if possible. Has the effect of skipping
455	execution when entering the execute state and skipping calling
456	the callback when entering the the result state, but will leave
457	the request otherwise untouched. That means that requests that
458	currently execute will not be stopped and resources held by the
459	request will not be freed prematurely.
460
461	cb $req $callback->(...)
462	Replace (or simply set) the callback registered to the request.
463
464	IO::AIO::GRP CLASS
465	This class is a subclass of IO::AIO::REQ, so all its methods apply
466	to objects of this class, too.
467
468	A IO::AIO::GRP object is a special request that can contain multiple
469	other aio requests.
470
471	You create one by calling the "aio_group" constructing function with
472	a callback that will be called when all contained requests have
473	entered the "done" state:
474
475	my $grp = aio_group sub {
476	print "all requests are done\n";
477	};
478
479	You add requests by calling the "add" method with one or more
480	"IO::AIO::REQ" objects:
481
482	$grp->add (aio_unlink "...");
483
484	add $grp aio_stat "...", sub {
485	$_[0] or return $grp->result ("error");
486
487	# add another request dynamically, if first succeeded
488	add $grp aio_open "...", sub {
489	$grp->result ("ok");
490	};	227	};
491	};	228	};
492		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, $mode specifies the mode of the newly created file, if it
		245	didn't exist and "O_CREAT" has been given, just like perl's
		246	"sysopen", except that it is mandatory (i.e. use 0 if you don't
		247	create new files, and 0666 or 0777 if you do).
		248
		249	Example:
		250
		251	aio_open "/etc/passwd", O_RDONLY, 0, sub {
		252	if ($_[0]) {
		253	print "open successful, fh is $_[0]\n";
		254	...
		255	} else {
		256	die "open failed: $!\n";
		257	}
		258	};
		259
		260	aio_close $fh, $callback->($status)
		261	Asynchronously close a file and call the callback with the result
		262	code. *WARNING:* although accepted, you should not pass in a perl
		263	filehandle here, as perl will likely close the file descriptor
		264	another time when the filehandle is destroyed. Normally, you can
		265	safely call perls "close" or just let filehandles go out of scope.
		266
		267	This is supposed to be a bug in the API, so that might change. It's
		268	therefore best to avoid this function.
		269
		270	aio_read $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
		271	aio_write $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
		272	Reads or writes "length" bytes from the specified "fh" and "offset"
		273	into the scalar given by "data" and offset "dataoffset" and calls
		274	the callback without the actual number of bytes read (or -1 on
		275	error, just like the syscall).
		276
		277	The $data scalar *MUST NOT* be modified in any way while the request
		278	is outstanding. Modifying it can result in segfaults or WW3 (if the
		279	necessary/optional hardware is installed).
		280
		281	Example: Read 15 bytes at offset 7 into scalar $buffer, starting at
		282	offset 0 within the scalar:
		283
		284	aio_read $fh, 7, 15, $buffer, 0, sub {
		285	$_[0] > 0 or die "read error: $!";
		286	print "read $_[0] bytes: <$buffer>\n";
		287	};
		288
		289	aio_sendfile $out_fh, $in_fh, $in_offset, $length, $callback->($retval)
		290	Tries to copy $length bytes from $in_fh to $out_fh. It starts
		291	reading at byte offset $in_offset, and starts writing at the current
		292	file offset of $out_fh. Because of that, it is not safe to issue
		293	more than one "aio_sendfile" per $out_fh, as they will interfere
		294	with each other.
		295
		296	This call tries to make use of a native "sendfile" syscall to
		297	provide zero-copy operation. For this to work, $out_fh should refer
		298	to a socket, and $in_fh should refer to mmap'able file.
		299
		300	If the native sendfile call fails or is not implemented, it will be
		301	emulated, so you can call "aio_sendfile" on any type of filehandle
		302	regardless of the limitations of the operating system.
		303
		304	Please note, however, that "aio_sendfile" can read more bytes from
		305	$in_fh than are written, and there is no way to find out how many
		306	bytes have been read from "aio_sendfile" alone, as "aio_sendfile"
		307	only provides the number of bytes written to $out_fh. Only if the
		308	result value equals $length one can assume that $length bytes have
		309	been read.
		310
		311	aio_readahead $fh,$offset,$length, $callback->($retval)
		312	"aio_readahead" populates the page cache with data from a file so
		313	that subsequent reads from that file will not block on disk I/O. The
		314	$offset argument specifies the starting point from which data is to
		315	be read and $length specifies the number of bytes to be read. I/O is
		316	performed in whole pages, so that offset is effectively rounded down
		317	to a page boundary and bytes are read up to the next page boundary
		318	greater than or equal to (off-set+length). "aio_readahead" does not
		319	read beyond the end of the file. The current file offset of the file
		320	is left unchanged.
		321
		322	If that syscall doesn't exist (likely if your OS isn't Linux) it
		323	will be emulated by simply reading the data, which would have a
		324	similar effect.
		325
		326	aio_stat $fh_or_path, $callback->($status)
		327	aio_lstat $fh, $callback->($status)
		328	Works like perl's "stat" or "lstat" in void context. The callback
		329	will be called after the stat and the results will be available
		330	using "stat _" or "-s _" etc...
		331
		332	The pathname passed to "aio_stat" must be absolute. See API NOTES,
		333	above, for an explanation.
		334
		335	Currently, the stats are always 64-bit-stats, i.e. instead of
		336	returning an error when stat'ing a large file, the results will be
		337	silently truncated unless perl itself is compiled with large file
		338	support.
		339
		340	Example: Print the length of /etc/passwd:
		341
		342	aio_stat "/etc/passwd", sub {
		343	$_[0] and die "stat failed: $!";
		344	print "size is ", -s _, "\n";
		345	};
		346
		347	aio_unlink $pathname, $callback->($status)
		348	Asynchronously unlink (delete) a file and call the callback with the
		349	result code.
		350
		351	aio_mknod $path, $mode, $dev, $callback->($status)
		352	[EXPERIMENTAL]
		353
		354	Asynchronously create a device node (or fifo). See mknod(2).
		355
		356	The only (POSIX-) portable way of calling this function is:
		357
		358	aio_mknod $path, IO::AIO::S_IFIFO | $mode, 0, sub { ...
		359
		360	aio_link $srcpath, $dstpath, $callback->($status)
		361	Asynchronously create a new link to the existing object at $srcpath
		362	at the path $dstpath and call the callback with the result code.
		363
		364	aio_symlink $srcpath, $dstpath, $callback->($status)
		365	Asynchronously create a new symbolic link to the existing object at
		366	$srcpath at the path $dstpath and call the callback with the result
		367	code.
		368
		369	aio_readlink $path, $callback->($link)
		370	Asynchronously read the symlink specified by $path and pass it to
		371	the callback. If an error occurs, nothing or undef gets passed to
		372	the callback.
		373
		374	aio_rename $srcpath, $dstpath, $callback->($status)
		375	Asynchronously rename the object at $srcpath to $dstpath, just as
		376	rename(2) and call the callback with the result code.
		377
		378	aio_rmdir $pathname, $callback->($status)
		379	Asynchronously rmdir (delete) a directory and call the callback with
		380	the result code.
		381
		382	aio_readdir $pathname, $callback->($entries)
		383	Unlike the POSIX call of the same name, "aio_readdir" reads an
		384	entire directory (i.e. opendir + readdir + closedir). The entries
		385	will not be sorted, and will NOT include the "." and ".." entries.
		386
		387	The callback a single argument which is either "undef" or an
		388	array-ref with the filenames.
		389
		390	aio_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
		413	aio_scandir $path, $maxreq, $callback->($dirs, $nondirs)
		414	Scans a directory (similar to "aio_readdir") but additionally tries
		415	to efficiently separate the entries of directory $path into two sets
		416	of names, directories you can recurse into (directories), and ones
		417	you cannot recurse into (everything else, including symlinks to
		418	directories).
		419
		420	"aio_scandir" is a composite request that creates of many sub
		421	requests_ $maxreq specifies the maximum number of outstanding aio
		422	requests that this function generates. If it is "<= 0", then a
		423	suitable default will be chosen (currently 4).
		424
		425	On error, the callback is called without arguments, otherwise it
		426	receives two array-refs with path-relative entry names.
		427
		428	Example:
		429
		430	aio_scandir $dir, 0, sub {
		431	my ($dirs, $nondirs) = @_;
		432	print "real directories: @$dirs\n";
		433	print "everything else: @$nondirs\n";
		434	};
		435
		436	Implementation notes.
		437
		438	The "aio_readdir" cannot be avoided, but "stat()"'ing every entry
		439	can.
		440
		441	After reading the directory, the modification time, size etc. of the
		442	directory before and after the readdir is checked, and if they match
		443	(and isn't the current time), the link count will be used to decide
		444	how many entries are directories (if >= 2). Otherwise, no knowledge
		445	of the number of subdirectories will be assumed.
		446
		447	Then entries will be sorted into likely directories (everything
		448	without a non-initial dot currently) and likely non-directories
		449	(everything else). Then every entry plus an appended "/." will be
		450	"stat"'ed, likely directories first. If that succeeds, it assumes
		451	that the entry is a directory or a symlink to directory (which will
		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).
		455
		456	If the known number of directories (link count - 2) has been
		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.
		465
		466	aio_fsync $fh, $callback->($status)
		467	Asynchronously call fsync on the given filehandle and call the
		468	callback with the fsync result code.
		469
		470	aio_fdatasync $fh, $callback->($status)
		471	Asynchronously call fdatasync on the given filehandle and call the
		472	callback with the fdatasync result code.
		473
		474	If this call isn't available because your OS lacks it or it couldn't
		475	be detected, it will be emulated by calling "fsync" instead.
		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
493	This makes it very easy to create composite requests (see the source	564	This makes it very easy to create composite requests (see the source of
494	of "aio_move" for an application) that work and feel like simple	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
		657	SUPPORT FUNCTIONS
		658	EVENT PROCESSING AND EVENT LOOP INTEGRATION
		659	$fileno = IO::AIO::poll_fileno
		660	Return the *request result pipe file descriptor*. This filehandle
		661	must be polled for reading by some mechanism outside this module
		662	(e.g. Event or select, see below or the SYNOPSIS). If the pipe
		663	becomes readable you have to call "poll_cb" to check the results.
		664
		665	See "poll_cb" for an example.
		666
		667	IO::AIO::poll_cb
		668	Process some outstanding events on the result pipe. You have to call
		669	this regularly. Returns the number of events processed. Returns
		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.
		676
		677	Example: Install an Event watcher that automatically calls
		678	IO::AIO::poll_cb with high priority:
		679
		680	Event->io (fd => IO::AIO::poll_fileno,
		681	poll => 'r', async => 1,
		682	cb => \&IO::AIO::poll_cb);
		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
		716	IO::AIO::poll_wait
		717	If there are any outstanding requests and none of them in the result
		718	phase, wait till the result filehandle becomes ready for reading
		719	(simply does a "select" on the filehandle. This is useful if you
		720	want to synchronously wait for some requests to finish).
		721
		722	See "nreqs" for an example.
		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
		732	IO::AIO::flush
		733	Wait till all outstanding AIO requests have been handled.
		734
		735	Strictly equivalent to:
		736
		737	IO::AIO::poll_wait, IO::AIO::poll_cb
		738	while IO::AIO::nreqs;
		739
		740	CONTROLLING THE NUMBER OF THREADS
		741	IO::AIO::min_parallel $nthreads
		742	Set the minimum number of AIO threads to $nthreads. The current
		743	default is 8, which means eight asynchronous operations can execute
		744	concurrently at any one time (the number of outstanding requests,
		745	however, is unlimited).
		746
		747	IO::AIO starts threads only on demand, when an AIO request is queued
		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.
		752
		753	It is recommended to keep the number of threads relatively low, as
		754	some Linux kernel versions will scale negatively with the number of
		755	threads (higher parallelity => MUCH higher latency). With current
		756	Linux 2.6 versions, 4-32 threads should be fine.
		757
		758	Under most circumstances you don't need to call this function, as
		759	the module selects a default that is suitable for low to moderate
		760	load.
		761
		762	IO::AIO::max_parallel $nthreads
		763	Sets the maximum number of AIO threads to $nthreads. If more than
		764	the specified number of threads are currently running, this function
		765	kills them. This function blocks until the limit is reached.
		766
		767	While $nthreads are zero, aio requests get queued but not executed
		768	until the number of threads has been increased again.
		769
		770	This module automatically runs "max_parallel 0" at program end, to
		771	ensure that all threads are killed and that there are no outstanding
495	requests.	772	requests.
496		773
497	* The IO::AIO::GRP objects will be cleaned up during calls to
498	"IO::AIO::poll_cb", just like any other request.
499	* They can be canceled like any other request. Canceling will cancel
500	not only the request itself, but also all requests it contains.
501	* They can also can also be added to other IO::AIO::GRP objects.
502	* You must not add requests to a group from within the group
503	callback (or any later time).
504
505	Their lifetime, simplified, looks like this: when they are empty,
506	they will finish very quickly. If they contain only requests that
507	are in the "done" state, they will also finish. Otherwise they will
508	continue to exist.
509
510	That means after creating a group you have some time to add
511	requests. And in the callbacks of those requests, you can add
512	further requests to the group. And only when all those requests have
513	finished will the the group itself finish.
514
515	add $grp ...
516	$grp->add (...)
517	Add one or more requests to the group. Any type of IO::AIO::REQ
518	can be added, including other groups, as long as you do not
519	create circular dependencies.
520
521	Returns all its arguments.
522
523	$grp->cancel_subs
524	Cancel all subrequests and clears any feeder, but not the group
525	request itself. Useful when you queued a lot of events but got a
526	result early.
527
528	$grp->result (...)
529	Set the result value(s) that will be passed to the group
530	callback when all subrequests have finished and set thre groups
531	errno to the current value of errno (just like calling "errno"
532	without an error number). By default, no argument will be passed
533	and errno is zero.
534
535	$grp->errno ([$errno])
536	Sets the group errno value to $errno, or the current value of
537	errno when the argument is missing.
538
539	Every aio request has an associated errno value that is restored
540	when the callback is invoked. This method lets you change this
541	value from its default (0).
542
543	Calling "result" will also set errno, so make sure you either
544	set $! before the call to "result", or call c<errno> after it.
545
546	feed $grp $callback->($grp)
547	Sets a feeder/generator on this group: every group can have an
548	attached generator that generates requests if idle. The idea
549	behind this is that, although you could just queue as many
550	requests as you want in a group, this might starve other
551	requests for a potentially long time. For example, "aio_scandir"
552	might generate hundreds of thousands "aio_stat" requests,
553	delaying any later requests for a long time.
554
555	To avoid this, and allow incremental generation of requests, you
556	can instead a group and set a feeder on it that generates those
557	requests. The feed callback will be called whenever there are
558	few enough (see "limit", below) requests active in the group
559	itself and is expected to queue more requests.
560
561	The feed callback can queue as many requests as it likes (i.e.
562	"add" does not impose any limits).
563
564	If the feed does not queue more requests when called, it will be
565	automatically removed from the group.
566
567	If the feed limit is 0, it will be set to 2 automatically.
568
569	Example:
570
571	# stat all files in @files, but only ever use four aio requests concurrently:
572
573	my $grp = aio_group sub { print "finished\n" };
574	limit $grp 4;
575	feed $grp sub {
576	my $file = pop @files
577	or return;
578
579	add $grp aio_stat $file, sub { ... };
580	};
581
582	limit $grp $num
583	Sets the feeder limit for the group: The feeder will be called
584	whenever the group contains less than this many requests.
585
586	Setting the limit to 0 will pause the feeding process.
587
588	SUPPORT FUNCTIONS
589	$fileno = IO::AIO::poll_fileno
590	Return the *request result pipe file descriptor*. This
591	filehandle must be polled for reading by some mechanism outside
592	this module (e.g. Event or select, see below or the SYNOPSIS).
593	If the pipe becomes readable you have to call "poll_cb" to check
594	the results.
595
596	See "poll_cb" for an example.
597
598	IO::AIO::poll_cb
599	Process all outstanding events on the result pipe. You have to
600	call this regularly. Returns the number of events processed.
601	Returns immediately when no events are outstanding.
602
603	If not all requests were processed for whatever reason, the
604	filehandle will still be ready when "poll_cb" returns.
605
606	Example: Install an Event watcher that automatically calls
607	IO::AIO::poll_cb with high priority:
608
609	Event->io (fd => IO::AIO::poll_fileno,
610	poll => 'r', async => 1,
611	cb => \&IO::AIO::poll_cb);
612
613	IO::AIO::poll_some $max_requests
614	Similar to "poll_cb", but only processes up to $max_requests
615	requests at a time.
616
617	Useful if you want to ensure some level of interactiveness when
618	perl is not fast enough to process all requests in time.
619
620	Example: Install an Event watcher that automatically calls
621	IO::AIO::poll_some with low priority, to ensure that other parts
622	of the program get the CPU sometimes even under high AIO load.
623
624	Event->io (fd => IO::AIO::poll_fileno,
625	poll => 'r', nice => 1,
626	cb => sub { IO::AIO::poll_some 256 });
627
628	IO::AIO::poll_wait
629	Wait till the result filehandle becomes ready for reading
630	(simply does a "select" on the filehandle. This is useful if you
631	want to synchronously wait for some requests to finish).
632
633	See "nreqs" for an example.
634
635	IO::AIO::nreqs
636	Returns the number of requests currently in the ready, execute
637	or pending states (i.e. for which their callback has not been
638	invoked yet).
639
640	Example: wait till there are no outstanding requests anymore:
641
642	IO::AIO::poll_wait, IO::AIO::poll_cb
643	while IO::AIO::nreqs;
644
645	IO::AIO::nready
646	Returns the number of requests currently in the ready state (not
647	yet executed).
648
649	IO::AIO::npending
650	Returns the number of requests currently in the pending state
651	(executed, but not yet processed by poll_cb).
652
653	IO::AIO::flush
654	Wait till all outstanding AIO requests have been handled.
655
656	Strictly equivalent to:
657
658	IO::AIO::poll_wait, IO::AIO::poll_cb
659	while IO::AIO::nreqs;
660
661	IO::AIO::poll
662	Waits until some requests have been handled.
663
664	Strictly equivalent to:
665
666	IO::AIO::poll_wait, IO::AIO::poll_cb
667	if IO::AIO::nreqs;
668
669	IO::AIO::min_parallel $nthreads
670	Set the minimum number of AIO threads to $nthreads. The current
671	default is 8, which means eight asynchronous operations can
672	execute concurrently at any one time (the number of outstanding
673	requests, however, is unlimited).
674
675	IO::AIO starts threads only on demand, when an AIO request is
676	queued and no free thread exists.
677
678	It is recommended to keep the number of threads relatively low,
679	as some Linux kernel versions will scale negatively with the
680	number of threads (higher parallelity => MUCH higher latency).
681	With current Linux 2.6 versions, 4-32 threads should be fine.
682
683	Under most circumstances you don't need to call this function,
684	as the module selects a default that is suitable for low to
685	moderate load.
686
687	IO::AIO::max_parallel $nthreads
688	Sets the maximum number of AIO threads to $nthreads. If more
689	than the specified number of threads are currently running, this
690	function kills them. This function blocks until the limit is
691	reached.
692
693	While $nthreads are zero, aio requests get queued but not
694	executed until the number of threads has been increased again.
695
696	This module automatically runs "max_parallel 0" at program end,
697	to ensure that all threads are killed and that there are no
698	outstanding requests.
699
700	Under normal circumstances you don't need to call this function.	774	Under normal circumstances you don't need to call this function.
701		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
702	$oldmaxreqs = IO::AIO::max_outstanding $maxreqs	791	$oldmaxreqs = IO::AIO::max_outstanding $maxreqs
703	This is a very bad function to use in interactive programs	792	This is a very bad function to use in interactive programs because
704	because it blocks, and a bad way to reduce concurrency because	793	it blocks, and a bad way to reduce concurrency because it is
705	it is inexact: Better use an "aio_group" together with a feed	794	inexact: Better use an "aio_group" together with a feed callback.
706	callback.
707		795
708	Sets the maximum number of outstanding requests to $nreqs. If	796	Sets the maximum number of outstanding requests to $nreqs. If you to
709	you to queue up more than this number of requests, the next call	797	queue up more than this number of requests, the next call to the
710	to the "poll_cb" (and "poll_some" and other functions calling	798	"poll_cb" (and "poll_some" and other functions calling "poll_cb")
711	"poll_cb") function will block until the limit is no longer	799	function will block until the limit is no longer exceeded.
712	exceeded.
713		800
714	The default value is very large, so there is no practical limit	801	The default value is very large, so there is no practical limit on
715	on the number of outstanding requests.	802	the number of outstanding requests.
716		803
717	You can still queue as many requests as you want. Therefore,	804	You can still queue as many requests as you want. Therefore,
718	"max_oustsanding" is mainly useful in simple scripts (with low	805	"max_oustsanding" is mainly useful in simple scripts (with low
719	values) or as a stop gap to shield against fatal memory overflow	806	values) or as a stop gap to shield against fatal memory overflow
720	(with large values).	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).
721		827
722	FORK BEHAVIOUR	828	FORK BEHAVIOUR
723	This module should do "the right thing" when the process using it	829	This module should do "the right thing" when the process using it forks:
724	forks:
725		830
726	Before the fork, IO::AIO enters a quiescent state where no requests	831	Before the fork, IO::AIO enters a quiescent state where no requests can
727	can be added in other threads and no results will be processed.	832	be added in other threads and no results will be processed. After the
728	After the fork the parent simply leaves the quiescent state and	833	fork the parent simply leaves the quiescent state and continues
729	continues request/result processing, while the child frees the	834	request/result processing, while the child frees the request/result
730	request/result queue (so that the requests started before the fork	835	queue (so that the requests started before the fork will only be handled
731	will only be handled in the parent). Threads will be started on	836	in the parent). Threads will be started on demand until the limit set in
732	demand until the limit set in the parent process has been reached	837	the parent process has been reached again.
733	again.
734		838
735	In short: the parent will, after a short pause, continue as if fork	839	In short: the parent will, after a short pause, continue as if fork had
736	had not been called, while the child will act as if IO::AIO has not	840	not been called, while the child will act as if IO::AIO has not been
737	been used yet.	841	used yet.
738		842
739	MEMORY USAGE	843	MEMORY USAGE
740	Per-request usage:	844	Per-request usage:
741		845
742	Each aio request uses - depending on your architecture - around	846	Each aio request uses - depending on your architecture - around 100-200
743	100-200 bytes of memory. In addition, stat requests need a stat	847	bytes of memory. In addition, stat requests need a stat buffer (possibly
744	buffer (possibly a few hundred bytes), readdir requires a result	848	a few hundred bytes), readdir requires a result buffer and so on. Perl
745	buffer and so on. Perl scalars and other data passed into aio	849	scalars and other data passed into aio requests will also be locked and
746	requests will also be locked and will consume memory till the	850	will consume memory till the request has entered the done state.
747	request has entered the done state.
748		851
749	This is now awfully much, so queuing lots of requests is not usually	852	This is now awfully much, so queuing lots of requests is not usually a
750	a problem.	853	problem.
751		854
752	Per-thread usage:	855	Per-thread usage:
753		856
754	In the execution phase, some aio requests require more memory for	857	In the execution phase, some aio requests require more memory for
755	temporary buffers, and each thread requires a stack and other data	858	temporary buffers, and each thread requires a stack and other data
756	structures (usually around 16k-128k, depending on the OS).	859	structures (usually around 16k-128k, depending on the OS).
757		860
758	KNOWN BUGS	861	KNOWN BUGS
759	Known bugs will be fixed in the next release.	862	Known bugs will be fixed in the next release.
760		863
761	SEE ALSO	864	SEE ALSO
762	Coro::AIO.	865	Coro::AIO.
763		866
764	AUTHOR	867	AUTHOR
765	Marc Lehmann <schmorp@schmorp.de>	868	Marc Lehmann <schmorp@schmorp.de>
766	http://home.schmorp.de/	869	http://home.schmorp.de/
767		870

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