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Revision 1.18 by root, Thu Oct 26 16:28:33 2006 UTC vs.
Revision 1.26 by root, Thu Oct 4 12:50:35 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	Use an event loop for that (such as the Event module): IO::AIO will
		68	naturally fit into such an event loop itself.
52		69
53	In this version, a number of threads are started that execute your	70	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	71	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	72	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	73	perl. In the future, this module might make use of the native aio
57	functions available on many operating systems. However, they are often	74	functions available on many operating systems. However, they are often
58	not well-supported or restricted (Linux doesn't allow them on normal	75	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	76	files currently, for example), and they would only support aio_read and
60	aio_write, so the remaining functionality would have to be implemented	77	aio_write, so the remaining functionality would have to be implemented
61	using threads anyway.	78	using threads anyway.
62		79
63	Although the module will work with in the presence of other (Perl-)	80	Although the module will work in the presence of other (Perl-) threads,
64	threads, it is currently not reentrant in any way, so use appropriate	81	it is currently not reentrant in any way, so use appropriate locking
65	locking yourself, always call "poll_cb" from within the same thread, or	82	yourself, always call "poll_cb" from within the same thread, or never
66	never call "poll_cb" (or other "aio_" functions) recursively.	83	call "poll_cb" (or other "aio_" functions) recursively.
		84
		85	EXAMPLE
		86	This is a simple example that uses the Event module and loads
		87	/etc/passwd asynchronously:
		88
		89	use Fcntl;
		90	use Event;
		91	use IO::AIO;
		92
		93	# register the IO::AIO callback with Event
		94	Event->io (fd => IO::AIO::poll_fileno,
		95	poll => 'r',
		96	cb => \&IO::AIO::poll_cb);
		97
		98	# queue the request to open /etc/passwd
		99	aio_open "/etc/passwd", O_RDONLY, 0, sub {
		100	my $fh = shift
		101	or die "error while opening: $!";
		102
		103	# stat'ing filehandles is generally non-blocking
		104	my $size = -s $fh;
		105
		106	# queue a request to read the file
		107	my $contents;
		108	aio_read $fh, 0, $size, $contents, 0, sub {
		109	$_[0] == $size
		110	or die "short read: $!";
		111
		112	close $fh;
		113
		114	# file contents now in $contents
		115	print $contents;
		116
		117	# exit event loop and program
		118	Event::unloop;
		119	};
		120	};
		121
		122	# possibly queue up other requests, or open GUI windows,
		123	# check for sockets etc. etc.
		124
		125	# process events as long as there are some:
		126	Event::loop;
67		127
68	REQUEST ANATOMY AND LIFETIME	128	REQUEST ANATOMY AND LIFETIME
69	Every "aio_*" function creates a request. which is a C data structure	129	Every "aio_*" function creates a request. which is a C data structure
70	not directly visible to Perl.	130	not directly visible to Perl.
71		131
…		…
107	anymore (except possibly for the Perl object, but its connection to	167	anymore (except possibly for the Perl object, but its connection to
108	the actual aio request is severed and calling its methods will	168	the actual aio request is severed and calling its methods will
109	either do nothing or result in a runtime error).	169	either do nothing or result in a runtime error).
110		170
111	FUNCTIONS	171	FUNCTIONS
112	AIO FUNCTIONS	172	AIO REQUEST FUNCTIONS
113	All the "aio_*" calls are more or less thin wrappers around the	173	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	174	with the same name (sans "aio_"). The arguments are similar or
115	or identical, and they all accept an additional (and optional)	175	identical, and they all accept an additional (and optional) $callback
116	$callback argument which must be a code reference. This code	176	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	177	called with the syscall return code (e.g. most syscalls return -1 on
118	syscalls return -1 on error, unlike perl, which usually delivers	178	error, unlike perl, which usually delivers "false") as it's sole
119	"false") as it's sole argument when the given syscall has been	179	argument when the given syscall has been executed asynchronously.
120	executed asynchronously.
121		180
122	All functions expecting a filehandle keep a copy of the filehandle	181	All functions expecting a filehandle keep a copy of the filehandle
123	internally until the request has finished.	182	internally until the request has finished.
124		183
125	All requests return objects of type IO::AIO::REQ that allow further	184	All functions return request objects of type IO::AIO::REQ that allow
126	manipulation of those requests while they are in-flight.	185	further manipulation of those requests while they are in-flight.
127		186
128	The pathnames you pass to these routines *must* be absolute and	187	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	188	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	189	being executed, the current working directory could have changed.
131	have changed. Alternatively, you can make sure that you never change	190	Alternatively, you can make sure that you never change the current
132	the current working directory.	191	working directory anywhere in the program and then use relative paths.
133		192
134	To encode pathnames to byte form, either make sure you either: a)	193	To encode pathnames as octets, either make sure you either: a) always
135	always pass in filenames you got from outside (command line, readdir	194	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	195	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	196	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	197	the user environment, d) use Glib::filename_from_unicode on unicode
139	filenames or e) use something else.	198	filenames or e) use something else to ensure your scalar has the correct
		199	contents.
140		200
		201	This works, btw. independent of the internal UTF-8 bit, which IO::AIO
		202	handles correctly wether it is set or not.
		203
141	$prev_pri = aioreq_pri [$pri]	204	$prev_pri = aioreq_pri [$pri]
142	Returns the priority value that would be used for the next	205	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	206	and, if $pri is given, sets the priority for the next aio request.
144	aio request.
145		207
146	The default priority is 0, the minimum and maximum priorities	208	The default priority is 0, the minimum and maximum priorities are -4
147	are -4 and 4, respectively. Requests with higher priority will	209	and 4, respectively. Requests with higher priority will be serviced
148	be serviced first.	210	first.
149		211
150	The priority will be reset to 0 after each call to one of the	212	The priority will be reset to 0 after each call to one of the
151	"aio_*" functions.	213	"aio_*" functions.
152		214
153	Example: open a file with low priority, then read something from	215	Example: open a file with low priority, then read something from it
154	it with higher priority so the read request is serviced before	216	with higher priority so the read request is serviced before other
155	other low priority open requests (potentially spamming the	217	low priority open requests (potentially spamming the cache):
156	cache):
157		218
		219	aioreq_pri -3;
		220	aio_open ..., sub {
		221	return unless $_[0];
		222
158	aioreq_pri -3;	223	aioreq_pri -2;
159	aio_open ..., sub {
160	return unless $_[0];
161
162	aioreq_pri -2;
163	aio_read $_[0], ..., sub {	224	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	...;	225	...
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	};	226	};
491	};	227	};
492		228
		229	aioreq_nice $pri_adjust
		230	Similar to "aioreq_pri", but subtracts the given value from the
		231	current priority, so the effect is cumulative.
		232
		233	aio_open $pathname, $flags, $mode, $callback->($fh)
		234	Asynchronously open or create a file and call the callback with a
		235	newly created filehandle for the file.
		236
		237	The pathname passed to "aio_open" must be absolute. See API NOTES,
		238	above, for an explanation.
		239
		240	The $flags argument is a bitmask. See the "Fcntl" module for a list.
		241	They are the same as used by "sysopen".
		242
		243	Likewise, $mode specifies the mode of the newly created file, if it
		244	didn't exist and "O_CREAT" has been given, just like perl's
		245	"sysopen", except that it is mandatory (i.e. use 0 if you don't
		246	create new files, and 0666 or 0777 if you do). Note that the $mode
		247	will be modified by the umask in effect then the request is being
		248	executed, so better never change the umask.
		249
		250	Example:
		251
		252	aio_open "/etc/passwd", O_RDONLY, 0, sub {
		253	if ($_[0]) {
		254	print "open successful, fh is $_[0]\n";
		255	...
		256	} else {
		257	die "open failed: $!\n";
		258	}
		259	};
		260
		261	aio_close $fh, $callback->($status)
		262	Asynchronously close a file and call the callback with the result
		263	code.
		264
		265	Unlike the other functions operating on files, this function uses
		266	the PerlIO layer to close the filehandle. The reason is that the
		267	PerlIO API insists on closing the underlying fd itself, no matter
		268	what, and doesn't allow modifications to the fd. Unfortunately, it
		269	is not clear that you can call PerlIO from different threads
		270	(actually, its quite clear that this won't work in some cases), so
		271	while it likely works perfectly with simple file handles (such as
		272	the ones created by "aio_open") it might fail in interesting ways
		273	for others.
		274
		275	Having said that, aio_close tries to clean up the filehandle as much
		276	as possible before handing it to an io thread, and generally does
		277	work.
		278
		279	aio_read $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
		280	aio_write $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
		281	Reads or writes $length bytes from the specified $fh and $offset
		282	into the scalar given by $data and offset $dataoffset and calls the
		283	callback without the actual number of bytes read (or -1 on error,
		284	just like the syscall).
		285
		286	If $offset is undefined, then the current file descriptor offset
		287	will be used (and updated), otherwise the file descriptor offset
		288	will not be changed by these calls.
		289
		290	If $length is undefined in "aio_write", use the remaining length of
		291	$data.
		292
		293	If $dataoffset is less than zero, it will be counted from the end of
		294	$data.
		295
		296	The $data scalar *MUST NOT* be modified in any way while the request
		297	is outstanding. Modifying it can result in segfaults or World War
		298	III (if the necessary/optional hardware is installed).
		299
		300	Example: Read 15 bytes at offset 7 into scalar $buffer, starting at
		301	offset 0 within the scalar:
		302
		303	aio_read $fh, 7, 15, $buffer, 0, sub {
		304	$_[0] > 0 or die "read error: $!";
		305	print "read $_[0] bytes: <$buffer>\n";
		306	};
		307
		308	aio_sendfile $out_fh, $in_fh, $in_offset, $length, $callback->($retval)
		309	Tries to copy $length bytes from $in_fh to $out_fh. It starts
		310	reading at byte offset $in_offset, and starts writing at the current
		311	file offset of $out_fh. Because of that, it is not safe to issue
		312	more than one "aio_sendfile" per $out_fh, as they will interfere
		313	with each other.
		314
		315	This call tries to make use of a native "sendfile" syscall to
		316	provide zero-copy operation. For this to work, $out_fh should refer
		317	to a socket, and $in_fh should refer to mmap'able file.
		318
		319	If the native sendfile call fails or is not implemented, it will be
		320	emulated, so you can call "aio_sendfile" on any type of filehandle
		321	regardless of the limitations of the operating system.
		322
		323	Please note, however, that "aio_sendfile" can read more bytes from
		324	$in_fh than are written, and there is no way to find out how many
		325	bytes have been read from "aio_sendfile" alone, as "aio_sendfile"
		326	only provides the number of bytes written to $out_fh. Only if the
		327	result value equals $length one can assume that $length bytes have
		328	been read.
		329
		330	aio_readahead $fh,$offset,$length, $callback->($retval)
		331	"aio_readahead" populates the page cache with data from a file so
		332	that subsequent reads from that file will not block on disk I/O. The
		333	$offset argument specifies the starting point from which data is to
		334	be read and $length specifies the number of bytes to be read. I/O is
		335	performed in whole pages, so that offset is effectively rounded down
		336	to a page boundary and bytes are read up to the next page boundary
		337	greater than or equal to (off-set+length). "aio_readahead" does not
		338	read beyond the end of the file. The current file offset of the file
		339	is left unchanged.
		340
		341	If that syscall doesn't exist (likely if your OS isn't Linux) it
		342	will be emulated by simply reading the data, which would have a
		343	similar effect.
		344
		345	aio_stat $fh_or_path, $callback->($status)
		346	aio_lstat $fh, $callback->($status)
		347	Works like perl's "stat" or "lstat" in void context. The callback
		348	will be called after the stat and the results will be available
		349	using "stat _" or "-s _" etc...
		350
		351	The pathname passed to "aio_stat" must be absolute. See API NOTES,
		352	above, for an explanation.
		353
		354	Currently, the stats are always 64-bit-stats, i.e. instead of
		355	returning an error when stat'ing a large file, the results will be
		356	silently truncated unless perl itself is compiled with large file
		357	support.
		358
		359	Example: Print the length of /etc/passwd:
		360
		361	aio_stat "/etc/passwd", sub {
		362	$_[0] and die "stat failed: $!";
		363	print "size is ", -s _, "\n";
		364	};
		365
		366	aio_utime $fh_or_path, $atime, $mtime, $callback->($status)
		367	Works like perl's "utime" function (including the special case of
		368	$atime and $mtime being undef). Fractional times are supported if
		369	the underlying syscalls support them.
		370
		371	When called with a pathname, uses utimes(2) if available, otherwise
		372	utime(2). If called on a file descriptor, uses futimes(2) if
		373	available, otherwise returns ENOSYS, so this is not portable.
		374
		375	Examples:
		376
		377	# set atime and mtime to current time (basically touch(1)):
		378	aio_utime "path", undef, undef;
		379	# set atime to current time and mtime to beginning of the epoch:
		380	aio_utime "path", time, undef; # undef==0
		381
		382	aio_chown $fh_or_path, $uid, $gid, $callback->($status)
		383	Works like perl's "chown" function, except that "undef" for either
		384	$uid or $gid is being interpreted as "do not change" (but -1 can
		385	also be used).
		386
		387	Examples:
		388
		389	# same as "chown root path" in the shell:
		390	aio_chown "path", 0, -1;
		391	# same as above:
		392	aio_chown "path", 0, undef;
		393
		394	aio_truncate $fh_or_path, $offset, $callback->($status)
		395	Works like truncate(2) or ftruncate(2).
		396
		397	aio_chmod $fh_or_path, $mode, $callback->($status)
		398	Works like perl's "chmod" function.
		399
		400	aio_unlink $pathname, $callback->($status)
		401	Asynchronously unlink (delete) a file and call the callback with the
		402	result code.
		403
		404	aio_mknod $path, $mode, $dev, $callback->($status)
		405	[EXPERIMENTAL]
		406
		407	Asynchronously create a device node (or fifo). See mknod(2).
		408
		409	The only (POSIX-) portable way of calling this function is:
		410
		411	aio_mknod $path, IO::AIO::S_IFIFO | $mode, 0, sub { ...
		412
		413	aio_link $srcpath, $dstpath, $callback->($status)
		414	Asynchronously create a new link to the existing object at $srcpath
		415	at the path $dstpath and call the callback with the result code.
		416
		417	aio_symlink $srcpath, $dstpath, $callback->($status)
		418	Asynchronously create a new symbolic link to the existing object at
		419	$srcpath at the path $dstpath and call the callback with the result
		420	code.
		421
		422	aio_readlink $path, $callback->($link)
		423	Asynchronously read the symlink specified by $path and pass it to
		424	the callback. If an error occurs, nothing or undef gets passed to
		425	the callback.
		426
		427	aio_rename $srcpath, $dstpath, $callback->($status)
		428	Asynchronously rename the object at $srcpath to $dstpath, just as
		429	rename(2) and call the callback with the result code.
		430
		431	aio_mkdir $pathname, $mode, $callback->($status)
		432	Asynchronously mkdir (create) a directory and call the callback with
		433	the result code. $mode will be modified by the umask at the time the
		434	request is executed, so do not change your umask.
		435
		436	aio_rmdir $pathname, $callback->($status)
		437	Asynchronously rmdir (delete) a directory and call the callback with
		438	the result code.
		439
		440	aio_readdir $pathname, $callback->($entries)
		441	Unlike the POSIX call of the same name, "aio_readdir" reads an
		442	entire directory (i.e. opendir + readdir + closedir). The entries
		443	will not be sorted, and will NOT include the "." and ".." entries.
		444
		445	The callback a single argument which is either "undef" or an
		446	array-ref with the filenames.
		447
		448	aio_load $path, $data, $callback->($status)
		449	This is a composite request that tries to fully load the given file
		450	into memory. Status is the same as with aio_read.
		451
		452	aio_copy $srcpath, $dstpath, $callback->($status)
		453	Try to copy the *file* (directories not supported as either source
		454	or destination) from $srcpath to $dstpath and call the callback with
		455	the 0 (error) or -1 ok.
		456
		457	This is a composite request that it creates the destination file
		458	with mode 0200 and copies the contents of the source file into it
		459	using "aio_sendfile", followed by restoring atime, mtime, access
		460	mode and uid/gid, in that order.
		461
		462	If an error occurs, the partial destination file will be unlinked,
		463	if possible, except when setting atime, mtime, access mode and
		464	uid/gid, where errors are being ignored.
		465
		466	aio_move $srcpath, $dstpath, $callback->($status)
		467	Try to move the *file* (directories not supported as either source
		468	or destination) from $srcpath to $dstpath and call the callback with
		469	the 0 (error) or -1 ok.
		470
		471	This is a composite request that tries to rename(2) the file first.
		472	If rename files with "EXDEV", it copies the file with "aio_copy"
		473	and, if that is successful, unlinking the $srcpath.
		474
		475	aio_scandir $path, $maxreq, $callback->($dirs, $nondirs)
		476	Scans a directory (similar to "aio_readdir") but additionally tries
		477	to efficiently separate the entries of directory $path into two sets
		478	of names, directories you can recurse into (directories), and ones
		479	you cannot recurse into (everything else, including symlinks to
		480	directories).
		481
		482	"aio_scandir" is a composite request that creates of many sub
		483	requests_ $maxreq specifies the maximum number of outstanding aio
		484	requests that this function generates. If it is "<= 0", then a
		485	suitable default will be chosen (currently 4).
		486
		487	On error, the callback is called without arguments, otherwise it
		488	receives two array-refs with path-relative entry names.
		489
		490	Example:
		491
		492	aio_scandir $dir, 0, sub {
		493	my ($dirs, $nondirs) = @_;
		494	print "real directories: @$dirs\n";
		495	print "everything else: @$nondirs\n";
		496	};
		497
		498	Implementation notes.
		499
		500	The "aio_readdir" cannot be avoided, but "stat()"'ing every entry
		501	can.
		502
		503	After reading the directory, the modification time, size etc. of the
		504	directory before and after the readdir is checked, and if they match
		505	(and isn't the current time), the link count will be used to decide
		506	how many entries are directories (if >= 2). Otherwise, no knowledge
		507	of the number of subdirectories will be assumed.
		508
		509	Then entries will be sorted into likely directories (everything
		510	without a non-initial dot currently) and likely non-directories
		511	(everything else). Then every entry plus an appended "/." will be
		512	"stat"'ed, likely directories first. If that succeeds, it assumes
		513	that the entry is a directory or a symlink to directory (which will
		514	be checked seperately). This is often faster than stat'ing the entry
		515	itself because filesystems might detect the type of the entry
		516	without reading the inode data (e.g. ext2fs filetype feature).
		517
		518	If the known number of directories (link count - 2) has been
		519	reached, the rest of the entries is assumed to be non-directories.
		520
		521	This only works with certainty on POSIX (= UNIX) filesystems, which
		522	fortunately are the vast majority of filesystems around.
		523
		524	It will also likely work on non-POSIX filesystems with reduced
		525	efficiency as those tend to return 0 or 1 as link counts, which
		526	disables the directory counting heuristic.
		527
		528	aio_rmtree $path, $callback->($status)
		529	Delete a directory tree starting (and including) $path, return the
		530	status of the final "rmdir" only. This is a composite request that
		531	uses "aio_scandir" to recurse into and rmdir directories, and unlink
		532	everything else.
		533
		534	aio_fsync $fh, $callback->($status)
		535	Asynchronously call fsync on the given filehandle and call the
		536	callback with the fsync result code.
		537
		538	aio_fdatasync $fh, $callback->($status)
		539	Asynchronously call fdatasync on the given filehandle and call the
		540	callback with the fdatasync result code.
		541
		542	If this call isn't available because your OS lacks it or it couldn't
		543	be detected, it will be emulated by calling "fsync" instead.
		544
		545	aio_group $callback->(...)
		546	This is a very special aio request: Instead of doing something, it
		547	is a container for other aio requests, which is useful if you want
		548	to bundle many requests into a single, composite, request with a
		549	definite callback and the ability to cancel the whole request with
		550	its subrequests.
		551
		552	Returns an object of class IO::AIO::GRP. See its documentation below
		553	for more info.
		554
		555	Example:
		556
		557	my $grp = aio_group sub {
		558	print "all stats done\n";
		559	};
		560
		561	add $grp
		562	(aio_stat ...),
		563	(aio_stat ...),
		564	...;
		565
		566	aio_nop $callback->()
		567	This is a special request - it does nothing in itself and is only
		568	used for side effects, such as when you want to add a dummy request
		569	to a group so that finishing the requests in the group depends on
		570	executing the given code.
		571
		572	While this request does nothing, it still goes through the execution
		573	phase and still requires a worker thread. Thus, the callback will
		574	not be executed immediately but only after other requests in the
		575	queue have entered their execution phase. This can be used to
		576	measure request latency.
		577
		578	IO::AIO::aio_busy $fractional_seconds, $callback->() *NOT EXPORTED*
		579	Mainly used for debugging and benchmarking, this aio request puts
		580	one of the request workers to sleep for the given time.
		581
		582	While it is theoretically handy to have simple I/O scheduling
		583	requests like sleep and file handle readable/writable, the overhead
		584	this creates is immense (it blocks a thread for a long time) so do
		585	not use this function except to put your application under
		586	artificial I/O pressure.
		587
		588	IO::AIO::REQ CLASS
		589	All non-aggregate "aio_*" functions return an object of this class when
		590	called in non-void context.
		591
		592	cancel $req
		593	Cancels the request, if possible. Has the effect of skipping
		594	execution when entering the execute state and skipping calling the
		595	callback when entering the the result state, but will leave the
		596	request otherwise untouched. That means that requests that currently
		597	execute will not be stopped and resources held by the request will
		598	not be freed prematurely.
		599
		600	cb $req $callback->(...)
		601	Replace (or simply set) the callback registered to the request.
		602
		603	IO::AIO::GRP CLASS
		604	This class is a subclass of IO::AIO::REQ, so all its methods apply to
		605	objects of this class, too.
		606
		607	A IO::AIO::GRP object is a special request that can contain multiple
		608	other aio requests.
		609
		610	You create one by calling the "aio_group" constructing function with a
		611	callback that will be called when all contained requests have entered
		612	the "done" state:
		613
		614	my $grp = aio_group sub {
		615	print "all requests are done\n";
		616	};
		617
		618	You add requests by calling the "add" method with one or more
		619	"IO::AIO::REQ" objects:
		620
		621	$grp->add (aio_unlink "...");
		622
		623	add $grp aio_stat "...", sub {
		624	$_[0] or return $grp->result ("error");
		625
		626	# add another request dynamically, if first succeeded
		627	add $grp aio_open "...", sub {
		628	$grp->result ("ok");
		629	};
		630	};
		631
493	This makes it very easy to create composite requests (see the source	632	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	633	"aio_move" for an application) that work and feel like simple requests.
		634
		635	* The IO::AIO::GRP objects will be cleaned up during calls to
		636	"IO::AIO::poll_cb", just like any other request.
		637	* They can be canceled like any other request. Canceling will cancel not
		638	only the request itself, but also all requests it contains.
		639	* They can also can also be added to other IO::AIO::GRP objects.
		640	* You must not add requests to a group from within the group callback
		641	(or any later time).
		642
		643	Their lifetime, simplified, looks like this: when they are empty, they
		644	will finish very quickly. If they contain only requests that are in the
		645	"done" state, they will also finish. Otherwise they will continue to
		646	exist.
		647
		648	That means after creating a group you have some time to add requests.
		649	And in the callbacks of those requests, you can add further requests to
		650	the group. And only when all those requests have finished will the the
		651	group itself finish.
		652
		653	add $grp ...
		654	$grp->add (...)
		655	Add one or more requests to the group. Any type of IO::AIO::REQ can
		656	be added, including other groups, as long as you do not create
		657	circular dependencies.
		658
		659	Returns all its arguments.
		660
		661	$grp->cancel_subs
		662	Cancel all subrequests and clears any feeder, but not the group
		663	request itself. Useful when you queued a lot of events but got a
		664	result early.
		665
		666	$grp->result (...)
		667	Set the result value(s) that will be passed to the group callback
		668	when all subrequests have finished and set thre groups errno to the
		669	current value of errno (just like calling "errno" without an error
		670	number). By default, no argument will be passed and errno is zero.
		671
		672	$grp->errno ([$errno])
		673	Sets the group errno value to $errno, or the current value of errno
		674	when the argument is missing.
		675
		676	Every aio request has an associated errno value that is restored
		677	when the callback is invoked. This method lets you change this value
		678	from its default (0).
		679
		680	Calling "result" will also set errno, so make sure you either set $!
		681	before the call to "result", or call c<errno> after it.
		682
		683	feed $grp $callback->($grp)
		684	Sets a feeder/generator on this group: every group can have an
		685	attached generator that generates requests if idle. The idea behind
		686	this is that, although you could just queue as many requests as you
		687	want in a group, this might starve other requests for a potentially
		688	long time. For example, "aio_scandir" might generate hundreds of
		689	thousands "aio_stat" requests, delaying any later requests for a
		690	long time.
		691
		692	To avoid this, and allow incremental generation of requests, you can
		693	instead a group and set a feeder on it that generates those
		694	requests. The feed callback will be called whenever there are few
		695	enough (see "limit", below) requests active in the group itself and
		696	is expected to queue more requests.
		697
		698	The feed callback can queue as many requests as it likes (i.e. "add"
		699	does not impose any limits).
		700
		701	If the feed does not queue more requests when called, it will be
		702	automatically removed from the group.
		703
		704	If the feed limit is 0, it will be set to 2 automatically.
		705
		706	Example:
		707
		708	# stat all files in @files, but only ever use four aio requests concurrently:
		709
		710	my $grp = aio_group sub { print "finished\n" };
		711	limit $grp 4;
		712	feed $grp sub {
		713	my $file = pop @files
		714	or return;
		715
		716	add $grp aio_stat $file, sub { ... };
		717	};
		718
		719	limit $grp $num
		720	Sets the feeder limit for the group: The feeder will be called
		721	whenever the group contains less than this many requests.
		722
		723	Setting the limit to 0 will pause the feeding process.
		724
		725	SUPPORT FUNCTIONS
		726	EVENT PROCESSING AND EVENT LOOP INTEGRATION
		727	$fileno = IO::AIO::poll_fileno
		728	Return the *request result pipe file descriptor*. This filehandle
		729	must be polled for reading by some mechanism outside this module
		730	(e.g. Event or select, see below or the SYNOPSIS). If the pipe
		731	becomes readable you have to call "poll_cb" to check the results.
		732
		733	See "poll_cb" for an example.
		734
		735	IO::AIO::poll_cb
		736	Process some outstanding events on the result pipe. You have to call
		737	this regularly. Returns the number of events processed. Returns
		738	immediately when no events are outstanding. The amount of events
		739	processed depends on the settings of "IO::AIO::max_poll_req" and
		740	"IO::AIO::max_poll_time".
		741
		742	If not all requests were processed for whatever reason, the
		743	filehandle will still be ready when "poll_cb" returns.
		744
		745	Example: Install an Event watcher that automatically calls
		746	IO::AIO::poll_cb with high priority:
		747
		748	Event->io (fd => IO::AIO::poll_fileno,
		749	poll => 'r', async => 1,
		750	cb => \&IO::AIO::poll_cb);
		751
		752	IO::AIO::max_poll_reqs $nreqs
		753	IO::AIO::max_poll_time $seconds
		754	These set the maximum number of requests (default 0, meaning
		755	infinity) that are being processed by "IO::AIO::poll_cb" in one
		756	call, respectively the maximum amount of time (default 0, meaning
		757	infinity) spent in "IO::AIO::poll_cb" to process requests (more
		758	correctly the mininum amount of time "poll_cb" is allowed to use).
		759
		760	Setting "max_poll_time" to a non-zero value creates an overhead of
		761	one syscall per request processed, which is not normally a problem
		762	unless your callbacks are really really fast or your OS is really
		763	really slow (I am not mentioning Solaris here). Using
		764	"max_poll_reqs" incurs no overhead.
		765
		766	Setting these is useful if you want to ensure some level of
		767	interactiveness when perl is not fast enough to process all requests
		768	in time.
		769
		770	For interactive programs, values such as 0.01 to 0.1 should be fine.
		771
		772	Example: Install an Event watcher that automatically calls
		773	IO::AIO::poll_cb with low priority, to ensure that other parts of
		774	the program get the CPU sometimes even under high AIO load.
		775
		776	# try not to spend much more than 0.1s in poll_cb
		777	IO::AIO::max_poll_time 0.1;
		778
		779	# use a low priority so other tasks have priority
		780	Event->io (fd => IO::AIO::poll_fileno,
		781	poll => 'r', nice => 1,
		782	cb => &IO::AIO::poll_cb);
		783
		784	IO::AIO::poll_wait
		785	If there are any outstanding requests and none of them in the result
		786	phase, wait till the result filehandle becomes ready for reading
		787	(simply does a "select" on the filehandle. This is useful if you
		788	want to synchronously wait for some requests to finish).
		789
		790	See "nreqs" for an example.
		791
		792	IO::AIO::poll
		793	Waits until some requests have been handled.
		794
		795	Returns the number of requests processed, but is otherwise strictly
		796	equivalent to:
		797
		798	IO::AIO::poll_wait, IO::AIO::poll_cb
		799
		800	IO::AIO::flush
		801	Wait till all outstanding AIO requests have been handled.
		802
		803	Strictly equivalent to:
		804
		805	IO::AIO::poll_wait, IO::AIO::poll_cb
		806	while IO::AIO::nreqs;
		807
		808	CONTROLLING THE NUMBER OF THREADS
		809	IO::AIO::min_parallel $nthreads
		810	Set the minimum number of AIO threads to $nthreads. The current
		811	default is 8, which means eight asynchronous operations can execute
		812	concurrently at any one time (the number of outstanding requests,
		813	however, is unlimited).
		814
		815	IO::AIO starts threads only on demand, when an AIO request is queued
		816	and no free thread exists. Please note that queueing up a hundred
		817	requests can create demand for a hundred threads, even if it turns
		818	out that everything is in the cache and could have been processed
		819	faster by a single thread.
		820
		821	It is recommended to keep the number of threads relatively low, as
		822	some Linux kernel versions will scale negatively with the number of
		823	threads (higher parallelity => MUCH higher latency). With current
		824	Linux 2.6 versions, 4-32 threads should be fine.
		825
		826	Under most circumstances you don't need to call this function, as
		827	the module selects a default that is suitable for low to moderate
		828	load.
		829
		830	IO::AIO::max_parallel $nthreads
		831	Sets the maximum number of AIO threads to $nthreads. If more than
		832	the specified number of threads are currently running, this function
		833	kills them. This function blocks until the limit is reached.
		834
		835	While $nthreads are zero, aio requests get queued but not executed
		836	until the number of threads has been increased again.
		837
		838	This module automatically runs "max_parallel 0" at program end, to
		839	ensure that all threads are killed and that there are no outstanding
495	requests.	840	requests.
496		841
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.	842	Under normal circumstances you don't need to call this function.
701		843
		844	IO::AIO::max_idle $nthreads
		845	Limit the number of threads (default: 4) that are allowed to idle
		846	(i.e., threads that did not get a request to process within 10
		847	seconds). That means if a thread becomes idle while $nthreads other
		848	threads are also idle, it will free its resources and exit.
		849
		850	This is useful when you allow a large number of threads (e.g. 100 or
		851	1000) to allow for extremely high load situations, but want to free
		852	resources under normal circumstances (1000 threads can easily
		853	consume 30MB of RAM).
		854
		855	The default is probably ok in most situations, especially if thread
		856	creation is fast. If thread creation is very slow on your system you
		857	might want to use larger values.
		858
702	$oldmaxreqs = IO::AIO::max_outstanding $maxreqs	859	$oldmaxreqs = IO::AIO::max_outstanding $maxreqs
703	This is a very bad function to use in interactive programs	860	This is a very bad function to use in interactive programs because
704	because it blocks, and a bad way to reduce concurrency because	861	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	862	inexact: Better use an "aio_group" together with a feed callback.
706	callback.
707		863
708	Sets the maximum number of outstanding requests to $nreqs. If	864	Sets the maximum number of outstanding requests to $nreqs. If you do
709	you to queue up more than this number of requests, the next call	865	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	866	"poll_cb" (and "poll_some" and other functions calling "poll_cb")
711	"poll_cb") function will block until the limit is no longer	867	function will block until the limit is no longer exceeded.
712	exceeded.
713		868
714	The default value is very large, so there is no practical limit	869	The default value is very large, so there is no practical limit on
715	on the number of outstanding requests.	870	the number of outstanding requests.
716		871
717	You can still queue as many requests as you want. Therefore,	872	You can still queue as many requests as you want. Therefore,
718	"max_oustsanding" is mainly useful in simple scripts (with low	873	"max_oustsanding" is mainly useful in simple scripts (with low
719	values) or as a stop gap to shield against fatal memory overflow	874	values) or as a stop gap to shield against fatal memory overflow
720	(with large values).	875	(with large values).
		876
		877	STATISTICAL INFORMATION
		878	IO::AIO::nreqs
		879	Returns the number of requests currently in the ready, execute or
		880	pending states (i.e. for which their callback has not been invoked
		881	yet).
		882
		883	Example: wait till there are no outstanding requests anymore:
		884
		885	IO::AIO::poll_wait, IO::AIO::poll_cb
		886	while IO::AIO::nreqs;
		887
		888	IO::AIO::nready
		889	Returns the number of requests currently in the ready state (not yet
		890	executed).
		891
		892	IO::AIO::npending
		893	Returns the number of requests currently in the pending state
		894	(executed, but not yet processed by poll_cb).
721		895
722	FORK BEHAVIOUR	896	FORK BEHAVIOUR
723	This module should do "the right thing" when the process using it	897	This module should do "the right thing" when the process using it forks:
724	forks:
725		898
726	Before the fork, IO::AIO enters a quiescent state where no requests	899	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.	900	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	901	fork the parent simply leaves the quiescent state and continues
729	continues request/result processing, while the child frees the	902	request/result processing, while the child frees the request/result
730	request/result queue (so that the requests started before the fork	903	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	904	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	905	the parent process has been reached again.
733	again.
734		906
735	In short: the parent will, after a short pause, continue as if fork	907	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	908	not been called, while the child will act as if IO::AIO has not been
737	been used yet.	909	used yet.
738		910
739	MEMORY USAGE	911	MEMORY USAGE
740	Per-request usage:	912	Per-request usage:
741		913
742	Each aio request uses - depending on your architecture - around	914	Each aio request uses - depending on your architecture - around 100-200
743	100-200 bytes of memory. In addition, stat requests need a stat	915	bytes of memory. In addition, stat requests need a stat buffer (possibly
744	buffer (possibly a few hundred bytes), readdir requires a result	916	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	917	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	918	will consume memory till the request has entered the done state.
747	request has entered the done state.
748		919
749	This is now awfully much, so queuing lots of requests is not usually	920	This is not awfully much, so queuing lots of requests is not usually a
750	a problem.	921	problem.
751		922
752	Per-thread usage:	923	Per-thread usage:
753		924
754	In the execution phase, some aio requests require more memory for	925	In the execution phase, some aio requests require more memory for
755	temporary buffers, and each thread requires a stack and other data	926	temporary buffers, and each thread requires a stack and other data
756	structures (usually around 16k-128k, depending on the OS).	927	structures (usually around 16k-128k, depending on the OS).
757		928
758	KNOWN BUGS	929	KNOWN BUGS
759	Known bugs will be fixed in the next release.	930	Known bugs will be fixed in the next release.
760		931
761	SEE ALSO	932	SEE ALSO
762	Coro::AIO.	933	Coro::AIO.
763		934
764	AUTHOR	935	AUTHOR
765	Marc Lehmann <schmorp@schmorp.de>	936	Marc Lehmann <schmorp@schmorp.de>
766	http://home.schmorp.de/	937	http://home.schmorp.de/
767		938

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