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Revision 1.18 by root, Thu Oct 26 16:28:33 2006 UTC vs.
Revision 1.22 by root, Sat Jan 6 02:47:11 2007 UTC

…		…
3		3
4	SYNOPSIS	4	SYNOPSIS
5	use IO::AIO;	5	use IO::AIO;
6		6
7	aio_open "/etc/passwd", O_RDONLY, 0, sub {	7	aio_open "/etc/passwd", O_RDONLY, 0, sub {
8	my ($fh) = @_;	8	my $fh = shift
		9	or die "/etc/passwd: $!";
9	...	10	...
10	};	11	};
11		12
12	aio_unlink "/tmp/file", sub { };	13	aio_unlink "/tmp/file", sub { };
13		14
…		…
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_load $path, $data, $callback->($status)
		391	This is a composite request that tries to fully load the given file
		392	into memory. Status is the same as with aio_read.
		393
		394	aio_copy $srcpath, $dstpath, $callback->($status)
		395	Try to copy the *file* (directories not supported as either source
		396	or destination) from $srcpath to $dstpath and call the callback with
		397	the 0 (error) or -1 ok.
		398
		399	This is a composite request that it creates the destination file
		400	with mode 0200 and copies the contents of the source file into it
		401	using "aio_sendfile", followed by restoring atime, mtime, access
		402	mode and uid/gid, in that order.
		403
		404	If an error occurs, the partial destination file will be unlinked,
		405	if possible, except when setting atime, mtime, access mode and
		406	uid/gid, where errors are being ignored.
		407
		408	aio_move $srcpath, $dstpath, $callback->($status)
		409	Try to move the *file* (directories not supported as either source
		410	or destination) from $srcpath to $dstpath and call the callback with
		411	the 0 (error) or -1 ok.
		412
		413	This is a composite request that tries to rename(2) the file first.
		414	If rename files with "EXDEV", it copies the file with "aio_copy"
		415	and, if that is successful, unlinking the $srcpath.
		416
		417	aio_scandir $path, $maxreq, $callback->($dirs, $nondirs)
		418	Scans a directory (similar to "aio_readdir") but additionally tries
		419	to efficiently separate the entries of directory $path into two sets
		420	of names, directories you can recurse into (directories), and ones
		421	you cannot recurse into (everything else, including symlinks to
		422	directories).
		423
		424	"aio_scandir" is a composite request that creates of many sub
		425	requests_ $maxreq specifies the maximum number of outstanding aio
		426	requests that this function generates. If it is "<= 0", then a
		427	suitable default will be chosen (currently 4).
		428
		429	On error, the callback is called without arguments, otherwise it
		430	receives two array-refs with path-relative entry names.
		431
		432	Example:
		433
		434	aio_scandir $dir, 0, sub {
		435	my ($dirs, $nondirs) = @_;
		436	print "real directories: @$dirs\n";
		437	print "everything else: @$nondirs\n";
		438	};
		439
		440	Implementation notes.
		441
		442	The "aio_readdir" cannot be avoided, but "stat()"'ing every entry
		443	can.
		444
		445	After reading the directory, the modification time, size etc. of the
		446	directory before and after the readdir is checked, and if they match
		447	(and isn't the current time), the link count will be used to decide
		448	how many entries are directories (if >= 2). Otherwise, no knowledge
		449	of the number of subdirectories will be assumed.
		450
		451	Then entries will be sorted into likely directories (everything
		452	without a non-initial dot currently) and likely non-directories
		453	(everything else). Then every entry plus an appended "/." will be
		454	"stat"'ed, likely directories first. If that succeeds, it assumes
		455	that the entry is a directory or a symlink to directory (which will
		456	be checked seperately). This is often faster than stat'ing the entry
		457	itself because filesystems might detect the type of the entry
		458	without reading the inode data (e.g. ext2fs filetype feature).
		459
		460	If the known number of directories (link count - 2) has been
		461	reached, the rest of the entries is assumed to be non-directories.
		462
		463	This only works with certainty on POSIX (= UNIX) filesystems, which
		464	fortunately are the vast majority of filesystems around.
		465
		466	It will also likely work on non-POSIX filesystems with reduced
		467	efficiency as those tend to return 0 or 1 as link counts, which
		468	disables the directory counting heuristic.
		469
		470	aio_fsync $fh, $callback->($status)
		471	Asynchronously call fsync on the given filehandle and call the
		472	callback with the fsync result code.
		473
		474	aio_fdatasync $fh, $callback->($status)
		475	Asynchronously call fdatasync on the given filehandle and call the
		476	callback with the fdatasync result code.
		477
		478	If this call isn't available because your OS lacks it or it couldn't
		479	be detected, it will be emulated by calling "fsync" instead.
		480
		481	aio_group $callback->(...)
		482	This is a very special aio request: Instead of doing something, it
		483	is a container for other aio requests, which is useful if you want
		484	to bundle many requests into a single, composite, request with a
		485	definite callback and the ability to cancel the whole request with
		486	its subrequests.
		487
		488	Returns an object of class IO::AIO::GRP. See its documentation below
		489	for more info.
		490
		491	Example:
		492
		493	my $grp = aio_group sub {
		494	print "all stats done\n";
		495	};
		496
		497	add $grp
		498	(aio_stat ...),
		499	(aio_stat ...),
		500	...;
		501
		502	aio_nop $callback->()
		503	This is a special request - it does nothing in itself and is only
		504	used for side effects, such as when you want to add a dummy request
		505	to a group so that finishing the requests in the group depends on
		506	executing the given code.
		507
		508	While this request does nothing, it still goes through the execution
		509	phase and still requires a worker thread. Thus, the callback will
		510	not be executed immediately but only after other requests in the
		511	queue have entered their execution phase. This can be used to
		512	measure request latency.
		513
		514	IO::AIO::aio_busy $fractional_seconds, $callback->() *NOT EXPORTED*
		515	Mainly used for debugging and benchmarking, this aio request puts
		516	one of the request workers to sleep for the given time.
		517
		518	While it is theoretically handy to have simple I/O scheduling
		519	requests like sleep and file handle readable/writable, the overhead
		520	this creates is immense (it blocks a thread for a long time) so do
		521	not use this function except to put your application under
		522	artificial I/O pressure.
		523
		524	IO::AIO::REQ CLASS
		525	All non-aggregate "aio_*" functions return an object of this class when
		526	called in non-void context.
		527
		528	cancel $req
		529	Cancels the request, if possible. Has the effect of skipping
		530	execution when entering the execute state and skipping calling the
		531	callback when entering the the result state, but will leave the
		532	request otherwise untouched. That means that requests that currently
		533	execute will not be stopped and resources held by the request will
		534	not be freed prematurely.
		535
		536	cb $req $callback->(...)
		537	Replace (or simply set) the callback registered to the request.
		538
		539	IO::AIO::GRP CLASS
		540	This class is a subclass of IO::AIO::REQ, so all its methods apply to
		541	objects of this class, too.
		542
		543	A IO::AIO::GRP object is a special request that can contain multiple
		544	other aio requests.
		545
		546	You create one by calling the "aio_group" constructing function with a
		547	callback that will be called when all contained requests have entered
		548	the "done" state:
		549
		550	my $grp = aio_group sub {
		551	print "all requests are done\n";
		552	};
		553
		554	You add requests by calling the "add" method with one or more
		555	"IO::AIO::REQ" objects:
		556
		557	$grp->add (aio_unlink "...");
		558
		559	add $grp aio_stat "...", sub {
		560	$_[0] or return $grp->result ("error");
		561
		562	# add another request dynamically, if first succeeded
		563	add $grp aio_open "...", sub {
		564	$grp->result ("ok");
		565	};
		566	};
		567
493	This makes it very easy to create composite requests (see the source	568	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	569	"aio_move" for an application) that work and feel like simple requests.
		570
		571	* The IO::AIO::GRP objects will be cleaned up during calls to
		572	"IO::AIO::poll_cb", just like any other request.
		573	* They can be canceled like any other request. Canceling will cancel not
		574	only the request itself, but also all requests it contains.
		575	* They can also can also be added to other IO::AIO::GRP objects.
		576	* You must not add requests to a group from within the group callback
		577	(or any later time).
		578
		579	Their lifetime, simplified, looks like this: when they are empty, they
		580	will finish very quickly. If they contain only requests that are in the
		581	"done" state, they will also finish. Otherwise they will continue to
		582	exist.
		583
		584	That means after creating a group you have some time to add requests.
		585	And in the callbacks of those requests, you can add further requests to
		586	the group. And only when all those requests have finished will the the
		587	group itself finish.
		588
		589	add $grp ...
		590	$grp->add (...)
		591	Add one or more requests to the group. Any type of IO::AIO::REQ can
		592	be added, including other groups, as long as you do not create
		593	circular dependencies.
		594
		595	Returns all its arguments.
		596
		597	$grp->cancel_subs
		598	Cancel all subrequests and clears any feeder, but not the group
		599	request itself. Useful when you queued a lot of events but got a
		600	result early.
		601
		602	$grp->result (...)
		603	Set the result value(s) that will be passed to the group callback
		604	when all subrequests have finished and set thre groups errno to the
		605	current value of errno (just like calling "errno" without an error
		606	number). By default, no argument will be passed and errno is zero.
		607
		608	$grp->errno ([$errno])
		609	Sets the group errno value to $errno, or the current value of errno
		610	when the argument is missing.
		611
		612	Every aio request has an associated errno value that is restored
		613	when the callback is invoked. This method lets you change this value
		614	from its default (0).
		615
		616	Calling "result" will also set errno, so make sure you either set $!
		617	before the call to "result", or call c<errno> after it.
		618
		619	feed $grp $callback->($grp)
		620	Sets a feeder/generator on this group: every group can have an
		621	attached generator that generates requests if idle. The idea behind
		622	this is that, although you could just queue as many requests as you
		623	want in a group, this might starve other requests for a potentially
		624	long time. For example, "aio_scandir" might generate hundreds of
		625	thousands "aio_stat" requests, delaying any later requests for a
		626	long time.
		627
		628	To avoid this, and allow incremental generation of requests, you can
		629	instead a group and set a feeder on it that generates those
		630	requests. The feed callback will be called whenever there are few
		631	enough (see "limit", below) requests active in the group itself and
		632	is expected to queue more requests.
		633
		634	The feed callback can queue as many requests as it likes (i.e. "add"
		635	does not impose any limits).
		636
		637	If the feed does not queue more requests when called, it will be
		638	automatically removed from the group.
		639
		640	If the feed limit is 0, it will be set to 2 automatically.
		641
		642	Example:
		643
		644	# stat all files in @files, but only ever use four aio requests concurrently:
		645
		646	my $grp = aio_group sub { print "finished\n" };
		647	limit $grp 4;
		648	feed $grp sub {
		649	my $file = pop @files
		650	or return;
		651
		652	add $grp aio_stat $file, sub { ... };
		653	};
		654
		655	limit $grp $num
		656	Sets the feeder limit for the group: The feeder will be called
		657	whenever the group contains less than this many requests.
		658
		659	Setting the limit to 0 will pause the feeding process.
		660
		661	SUPPORT FUNCTIONS
		662	EVENT PROCESSING AND EVENT LOOP INTEGRATION
		663	$fileno = IO::AIO::poll_fileno
		664	Return the *request result pipe file descriptor*. This filehandle
		665	must be polled for reading by some mechanism outside this module
		666	(e.g. Event or select, see below or the SYNOPSIS). If the pipe
		667	becomes readable you have to call "poll_cb" to check the results.
		668
		669	See "poll_cb" for an example.
		670
		671	IO::AIO::poll_cb
		672	Process some outstanding events on the result pipe. You have to call
		673	this regularly. Returns the number of events processed. Returns
		674	immediately when no events are outstanding. The amount of events
		675	processed depends on the settings of "IO::AIO::max_poll_req" and
		676	"IO::AIO::max_poll_time".
		677
		678	If not all requests were processed for whatever reason, the
		679	filehandle will still be ready when "poll_cb" returns.
		680
		681	Example: Install an Event watcher that automatically calls
		682	IO::AIO::poll_cb with high priority:
		683
		684	Event->io (fd => IO::AIO::poll_fileno,
		685	poll => 'r', async => 1,
		686	cb => \&IO::AIO::poll_cb);
		687
		688	IO::AIO::max_poll_reqs $nreqs
		689	IO::AIO::max_poll_time $seconds
		690	These set the maximum number of requests (default 0, meaning
		691	infinity) that are being processed by "IO::AIO::poll_cb" in one
		692	call, respectively the maximum amount of time (default 0, meaning
		693	infinity) spent in "IO::AIO::poll_cb" to process requests (more
		694	correctly the mininum amount of time "poll_cb" is allowed to use).
		695
		696	Setting "max_poll_time" to a non-zero value creates an overhead of
		697	one syscall per request processed, which is not normally a problem
		698	unless your callbacks are really really fast or your OS is really
		699	really slow (I am not mentioning Solaris here). Using
		700	"max_poll_reqs" incurs no overhead.
		701
		702	Setting these is useful if you want to ensure some level of
		703	interactiveness when perl is not fast enough to process all requests
		704	in time.
		705
		706	For interactive programs, values such as 0.01 to 0.1 should be fine.
		707
		708	Example: Install an Event watcher that automatically calls
		709	IO::AIO::poll_cb with low priority, to ensure that other parts of
		710	the program get the CPU sometimes even under high AIO load.
		711
		712	# try not to spend much more than 0.1s in poll_cb
		713	IO::AIO::max_poll_time 0.1;
		714
		715	# use a low priority so other tasks have priority
		716	Event->io (fd => IO::AIO::poll_fileno,
		717	poll => 'r', nice => 1,
		718	cb => &IO::AIO::poll_cb);
		719
		720	IO::AIO::poll_wait
		721	If there are any outstanding requests and none of them in the result
		722	phase, wait till the result filehandle becomes ready for reading
		723	(simply does a "select" on the filehandle. This is useful if you
		724	want to synchronously wait for some requests to finish).
		725
		726	See "nreqs" for an example.
		727
		728	IO::AIO::poll
		729	Waits until some requests have been handled.
		730
		731	Returns the number of requests processed, but is otherwise strictly
		732	equivalent to:
		733
		734	IO::AIO::poll_wait, IO::AIO::poll_cb
		735
		736	IO::AIO::flush
		737	Wait till all outstanding AIO requests have been handled.
		738
		739	Strictly equivalent to:
		740
		741	IO::AIO::poll_wait, IO::AIO::poll_cb
		742	while IO::AIO::nreqs;
		743
		744	CONTROLLING THE NUMBER OF THREADS
		745	IO::AIO::min_parallel $nthreads
		746	Set the minimum number of AIO threads to $nthreads. The current
		747	default is 8, which means eight asynchronous operations can execute
		748	concurrently at any one time (the number of outstanding requests,
		749	however, is unlimited).
		750
		751	IO::AIO starts threads only on demand, when an AIO request is queued
		752	and no free thread exists. Please note that queueing up a hundred
		753	requests can create demand for a hundred threads, even if it turns
		754	out that everything is in the cache and could have been processed
		755	faster by a single thread.
		756
		757	It is recommended to keep the number of threads relatively low, as
		758	some Linux kernel versions will scale negatively with the number of
		759	threads (higher parallelity => MUCH higher latency). With current
		760	Linux 2.6 versions, 4-32 threads should be fine.
		761
		762	Under most circumstances you don't need to call this function, as
		763	the module selects a default that is suitable for low to moderate
		764	load.
		765
		766	IO::AIO::max_parallel $nthreads
		767	Sets the maximum number of AIO threads to $nthreads. If more than
		768	the specified number of threads are currently running, this function
		769	kills them. This function blocks until the limit is reached.
		770
		771	While $nthreads are zero, aio requests get queued but not executed
		772	until the number of threads has been increased again.
		773
		774	This module automatically runs "max_parallel 0" at program end, to
		775	ensure that all threads are killed and that there are no outstanding
495	requests.	776	requests.
496		777
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.	778	Under normal circumstances you don't need to call this function.
701		779
		780	IO::AIO::max_idle $nthreads
		781	Limit the number of threads (default: 4) that are allowed to idle
		782	(i.e., threads that did not get a request to process within 10
		783	seconds). That means if a thread becomes idle while $nthreads other
		784	threads are also idle, it will free its resources and exit.
		785
		786	This is useful when you allow a large number of threads (e.g. 100 or
		787	1000) to allow for extremely high load situations, but want to free
		788	resources under normal circumstances (1000 threads can easily
		789	consume 30MB of RAM).
		790
		791	The default is probably ok in most situations, especially if thread
		792	creation is fast. If thread creation is very slow on your system you
		793	might want to use larger values.
		794
702	$oldmaxreqs = IO::AIO::max_outstanding $maxreqs	795	$oldmaxreqs = IO::AIO::max_outstanding $maxreqs
703	This is a very bad function to use in interactive programs	796	This is a very bad function to use in interactive programs because
704	because it blocks, and a bad way to reduce concurrency because	797	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	798	inexact: Better use an "aio_group" together with a feed callback.
706	callback.
707		799
708	Sets the maximum number of outstanding requests to $nreqs. If	800	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	801	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	802	"poll_cb" (and "poll_some" and other functions calling "poll_cb")
711	"poll_cb") function will block until the limit is no longer	803	function will block until the limit is no longer exceeded.
712	exceeded.
713		804
714	The default value is very large, so there is no practical limit	805	The default value is very large, so there is no practical limit on
715	on the number of outstanding requests.	806	the number of outstanding requests.
716		807
717	You can still queue as many requests as you want. Therefore,	808	You can still queue as many requests as you want. Therefore,
718	"max_oustsanding" is mainly useful in simple scripts (with low	809	"max_oustsanding" is mainly useful in simple scripts (with low
719	values) or as a stop gap to shield against fatal memory overflow	810	values) or as a stop gap to shield against fatal memory overflow
720	(with large values).	811	(with large values).
		812
		813	STATISTICAL INFORMATION
		814	IO::AIO::nreqs
		815	Returns the number of requests currently in the ready, execute or
		816	pending states (i.e. for which their callback has not been invoked
		817	yet).
		818
		819	Example: wait till there are no outstanding requests anymore:
		820
		821	IO::AIO::poll_wait, IO::AIO::poll_cb
		822	while IO::AIO::nreqs;
		823
		824	IO::AIO::nready
		825	Returns the number of requests currently in the ready state (not yet
		826	executed).
		827
		828	IO::AIO::npending
		829	Returns the number of requests currently in the pending state
		830	(executed, but not yet processed by poll_cb).
721		831
722	FORK BEHAVIOUR	832	FORK BEHAVIOUR
723	This module should do "the right thing" when the process using it	833	This module should do "the right thing" when the process using it forks:
724	forks:
725		834
726	Before the fork, IO::AIO enters a quiescent state where no requests	835	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.	836	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	837	fork the parent simply leaves the quiescent state and continues
729	continues request/result processing, while the child frees the	838	request/result processing, while the child frees the request/result
730	request/result queue (so that the requests started before the fork	839	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	840	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	841	the parent process has been reached again.
733	again.
734		842
735	In short: the parent will, after a short pause, continue as if fork	843	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	844	not been called, while the child will act as if IO::AIO has not been
737	been used yet.	845	used yet.
738		846
739	MEMORY USAGE	847	MEMORY USAGE
740	Per-request usage:	848	Per-request usage:
741		849
742	Each aio request uses - depending on your architecture - around	850	Each aio request uses - depending on your architecture - around 100-200
743	100-200 bytes of memory. In addition, stat requests need a stat	851	bytes of memory. In addition, stat requests need a stat buffer (possibly
744	buffer (possibly a few hundred bytes), readdir requires a result	852	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	853	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	854	will consume memory till the request has entered the done state.
747	request has entered the done state.
748		855
749	This is now awfully much, so queuing lots of requests is not usually	856	This is now awfully much, so queuing lots of requests is not usually a
750	a problem.	857	problem.
751		858
752	Per-thread usage:	859	Per-thread usage:
753		860
754	In the execution phase, some aio requests require more memory for	861	In the execution phase, some aio requests require more memory for
755	temporary buffers, and each thread requires a stack and other data	862	temporary buffers, and each thread requires a stack and other data
756	structures (usually around 16k-128k, depending on the OS).	863	structures (usually around 16k-128k, depending on the OS).
757		864
758	KNOWN BUGS	865	KNOWN BUGS
759	Known bugs will be fixed in the next release.	866	Known bugs will be fixed in the next release.
760		867
761	SEE ALSO	868	SEE ALSO
762	Coro::AIO.	869	Coro::AIO.
763		870
764	AUTHOR	871	AUTHOR
765	Marc Lehmann <schmorp@schmorp.de>	872	Marc Lehmann <schmorp@schmorp.de>
766	http://home.schmorp.de/	873	http://home.schmorp.de/
767		874

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