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Revision 1.20 by root, Tue Oct 31 00:45:41 2006 UTC

…		…
47	\&IO::AIO::poll_cb);	47	\&IO::AIO::poll_cb);
48		48
49	DESCRIPTION	49	DESCRIPTION
50	This module implements asynchronous I/O using whatever means your	50	This module implements asynchronous I/O using whatever means your
51	operating system supports.	51	operating system supports.
		52
		53	Asynchronous means that operations that can normally block your program
		54	(e.g. reading from disk) will be done asynchronously: the operation will
		55	still block, but you can do something else in the meantime. This is
		56	extremely useful for programs that need to stay interactive even when
		57	doing heavy I/O (GUI programs, high performance network servers etc.),
		58	but can also be used to easily do operations in parallel that are
		59	normally done sequentially, e.g. stat'ing many files, which is much
		60	faster on a RAID volume or over NFS when you do a number of stat
		61	operations concurrently.
		62
		63	While most of this works on all types of file descriptors (for example
		64	sockets), using these functions on file descriptors that support
		65	nonblocking operation (again, sockets, pipes etc.) is very inefficient
		66	or might not work (aio_read fails on sockets/pipes/fifos). Use an event
		67	loop for that (such as the Event module): IO::AIO will naturally fit
		68	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 with in the presence of other (Perl-)
64	threads, it is currently not reentrant in any way, so use appropriate	81	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	82	locking yourself, always call "poll_cb" from within the same thread, or
66	never call "poll_cb" (or other "aio_" functions) recursively.	83	never 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 = $_[0]
		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, $mode specifies the mode of the newly created file, if it
		244	didn't exist and "O_CREAT" has been given, just like perl's
		245	"sysopen", except that it is mandatory (i.e. use 0 if you don't
		246	create new files, and 0666 or 0777 if you do).
		247
		248	Example:
		249
		250	aio_open "/etc/passwd", O_RDONLY, 0, sub {
		251	if ($_[0]) {
		252	print "open successful, fh is $_[0]\n";
		253	...
		254	} else {
		255	die "open failed: $!\n";
		256	}
		257	};
		258
		259	aio_close $fh, $callback->($status)
		260	Asynchronously close a file and call the callback with the result
		261	code. *WARNING:* although accepted, you should not pass in a perl
		262	filehandle here, as perl will likely close the file descriptor
		263	another time when the filehandle is destroyed. Normally, you can
		264	safely call perls "close" or just let filehandles go out of scope.
		265
		266	This is supposed to be a bug in the API, so that might change. It's
		267	therefore best to avoid this function.
		268
		269	aio_read $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
		270	aio_write $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
		271	Reads or writes "length" bytes from the specified "fh" and "offset"
		272	into the scalar given by "data" and offset "dataoffset" and calls
		273	the callback without the actual number of bytes read (or -1 on
		274	error, just like the syscall).
		275
		276	The $data scalar *MUST NOT* be modified in any way while the request
		277	is outstanding. Modifying it can result in segfaults or WW3 (if the
		278	necessary/optional hardware is installed).
		279
		280	Example: Read 15 bytes at offset 7 into scalar $buffer, starting at
		281	offset 0 within the scalar:
		282
		283	aio_read $fh, 7, 15, $buffer, 0, sub {
		284	$_[0] > 0 or die "read error: $!";
		285	print "read $_[0] bytes: <$buffer>\n";
		286	};
		287
		288	aio_sendfile $out_fh, $in_fh, $in_offset, $length, $callback->($retval)
		289	Tries to copy $length bytes from $in_fh to $out_fh. It starts
		290	reading at byte offset $in_offset, and starts writing at the current
		291	file offset of $out_fh. Because of that, it is not safe to issue
		292	more than one "aio_sendfile" per $out_fh, as they will interfere
		293	with each other.
		294
		295	This call tries to make use of a native "sendfile" syscall to
		296	provide zero-copy operation. For this to work, $out_fh should refer
		297	to a socket, and $in_fh should refer to mmap'able file.
		298
		299	If the native sendfile call fails or is not implemented, it will be
		300	emulated, so you can call "aio_sendfile" on any type of filehandle
		301	regardless of the limitations of the operating system.
		302
		303	Please note, however, that "aio_sendfile" can read more bytes from
		304	$in_fh than are written, and there is no way to find out how many
		305	bytes have been read from "aio_sendfile" alone, as "aio_sendfile"
		306	only provides the number of bytes written to $out_fh. Only if the
		307	result value equals $length one can assume that $length bytes have
		308	been read.
		309
		310	aio_readahead $fh,$offset,$length, $callback->($retval)
		311	"aio_readahead" populates the page cache with data from a file so
		312	that subsequent reads from that file will not block on disk I/O. The
		313	$offset argument specifies the starting point from which data is to
		314	be read and $length specifies the number of bytes to be read. I/O is
		315	performed in whole pages, so that offset is effectively rounded down
		316	to a page boundary and bytes are read up to the next page boundary
		317	greater than or equal to (off-set+length). "aio_readahead" does not
		318	read beyond the end of the file. The current file offset of the file
		319	is left unchanged.
		320
		321	If that syscall doesn't exist (likely if your OS isn't Linux) it
		322	will be emulated by simply reading the data, which would have a
		323	similar effect.
		324
		325	aio_stat $fh_or_path, $callback->($status)
		326	aio_lstat $fh, $callback->($status)
		327	Works like perl's "stat" or "lstat" in void context. The callback
		328	will be called after the stat and the results will be available
		329	using "stat _" or "-s _" etc...
		330
		331	The pathname passed to "aio_stat" must be absolute. See API NOTES,
		332	above, for an explanation.
		333
		334	Currently, the stats are always 64-bit-stats, i.e. instead of
		335	returning an error when stat'ing a large file, the results will be
		336	silently truncated unless perl itself is compiled with large file
		337	support.
		338
		339	Example: Print the length of /etc/passwd:
		340
		341	aio_stat "/etc/passwd", sub {
		342	$_[0] and die "stat failed: $!";
		343	print "size is ", -s _, "\n";
		344	};
		345
		346	aio_unlink $pathname, $callback->($status)
		347	Asynchronously unlink (delete) a file and call the callback with the
		348	result code.
		349
		350	aio_mknod $path, $mode, $dev, $callback->($status)
		351	[EXPERIMENTAL]
		352
		353	Asynchronously create a device node (or fifo). See mknod(2).
		354
		355	The only (POSIX-) portable way of calling this function is:
		356
		357	aio_mknod $path, IO::AIO::S_IFIFO | $mode, 0, sub { ...
		358
		359	aio_link $srcpath, $dstpath, $callback->($status)
		360	Asynchronously create a new link to the existing object at $srcpath
		361	at the path $dstpath and call the callback with the result code.
		362
		363	aio_symlink $srcpath, $dstpath, $callback->($status)
		364	Asynchronously create a new symbolic link to the existing object at
		365	$srcpath at the path $dstpath and call the callback with the result
		366	code.
		367
		368	aio_readlink $path, $callback->($link)
		369	Asynchronously read the symlink specified by $path and pass it to
		370	the callback. If an error occurs, nothing or undef gets passed to
		371	the callback.
		372
		373	aio_rename $srcpath, $dstpath, $callback->($status)
		374	Asynchronously rename the object at $srcpath to $dstpath, just as
		375	rename(2) and call the callback with the result code.
		376
		377	aio_rmdir $pathname, $callback->($status)
		378	Asynchronously rmdir (delete) a directory and call the callback with
		379	the result code.
		380
		381	aio_readdir $pathname, $callback->($entries)
		382	Unlike the POSIX call of the same name, "aio_readdir" reads an
		383	entire directory (i.e. opendir + readdir + closedir). The entries
		384	will not be sorted, and will NOT include the "." and ".." entries.
		385
		386	The callback a single argument which is either "undef" or an
		387	array-ref with the filenames.
		388
		389	aio_copy $srcpath, $dstpath, $callback->($status)
		390	Try to copy the *file* (directories not supported as either source
		391	or destination) from $srcpath to $dstpath and call the callback with
		392	the 0 (error) or -1 ok.
		393
		394	This is a composite request that it creates the destination file
		395	with mode 0200 and copies the contents of the source file into it
		396	using "aio_sendfile", followed by restoring atime, mtime, access
		397	mode and uid/gid, in that order.
		398
		399	If an error occurs, the partial destination file will be unlinked,
		400	if possible, except when setting atime, mtime, access mode and
		401	uid/gid, where errors are being ignored.
		402
		403	aio_move $srcpath, $dstpath, $callback->($status)
		404	Try to move the *file* (directories not supported as either source
		405	or destination) from $srcpath to $dstpath and call the callback with
		406	the 0 (error) or -1 ok.
		407
		408	This is a composite request that tries to rename(2) the file first.
		409	If rename files with "EXDEV", it copies the file with "aio_copy"
		410	and, if that is successful, unlinking the $srcpath.
		411
		412	aio_scandir $path, $maxreq, $callback->($dirs, $nondirs)
		413	Scans a directory (similar to "aio_readdir") but additionally tries
		414	to efficiently separate the entries of directory $path into two sets
		415	of names, directories you can recurse into (directories), and ones
		416	you cannot recurse into (everything else, including symlinks to
		417	directories).
		418
		419	"aio_scandir" is a composite request that creates of many sub
		420	requests_ $maxreq specifies the maximum number of outstanding aio
		421	requests that this function generates. If it is "<= 0", then a
		422	suitable default will be chosen (currently 4).
		423
		424	On error, the callback is called without arguments, otherwise it
		425	receives two array-refs with path-relative entry names.
		426
		427	Example:
		428
		429	aio_scandir $dir, 0, sub {
		430	my ($dirs, $nondirs) = @_;
		431	print "real directories: @$dirs\n";
		432	print "everything else: @$nondirs\n";
		433	};
		434
		435	Implementation notes.
		436
		437	The "aio_readdir" cannot be avoided, but "stat()"'ing every entry
		438	can.
		439
		440	After reading the directory, the modification time, size etc. of the
		441	directory before and after the readdir is checked, and if they match
		442	(and isn't the current time), the link count will be used to decide
		443	how many entries are directories (if >= 2). Otherwise, no knowledge
		444	of the number of subdirectories will be assumed.
		445
		446	Then entries will be sorted into likely directories (everything
		447	without a non-initial dot currently) and likely non-directories
		448	(everything else). Then every entry plus an appended "/." will be
		449	"stat"'ed, likely directories first. If that succeeds, it assumes
		450	that the entry is a directory or a symlink to directory (which will
		451	be checked seperately). This is often faster than stat'ing the entry
		452	itself because filesystems might detect the type of the entry
		453	without reading the inode data (e.g. ext2fs filetype feature).
		454
		455	If the known number of directories (link count - 2) has been
		456	reached, the rest of the entries is assumed to be non-directories.
		457
		458	This only works with certainty on POSIX (= UNIX) filesystems, which
		459	fortunately are the vast majority of filesystems around.
		460
		461	It will also likely work on non-POSIX filesystems with reduced
		462	efficiency as those tend to return 0 or 1 as link counts, which
		463	disables the directory counting heuristic.
		464
		465	aio_fsync $fh, $callback->($status)
		466	Asynchronously call fsync on the given filehandle and call the
		467	callback with the fsync result code.
		468
		469	aio_fdatasync $fh, $callback->($status)
		470	Asynchronously call fdatasync on the given filehandle and call the
		471	callback with the fdatasync result code.
		472
		473	If this call isn't available because your OS lacks it or it couldn't
		474	be detected, it will be emulated by calling "fsync" instead.
		475
		476	aio_group $callback->(...)
		477	This is a very special aio request: Instead of doing something, it
		478	is a container for other aio requests, which is useful if you want
		479	to bundle many requests into a single, composite, request with a
		480	definite callback and the ability to cancel the whole request with
		481	its subrequests.
		482
		483	Returns an object of class IO::AIO::GRP. See its documentation below
		484	for more info.
		485
		486	Example:
		487
		488	my $grp = aio_group sub {
		489	print "all stats done\n";
		490	};
		491
		492	add $grp
		493	(aio_stat ...),
		494	(aio_stat ...),
		495	...;
		496
		497	aio_nop $callback->()
		498	This is a special request - it does nothing in itself and is only
		499	used for side effects, such as when you want to add a dummy request
		500	to a group so that finishing the requests in the group depends on
		501	executing the given code.
		502
		503	While this request does nothing, it still goes through the execution
		504	phase and still requires a worker thread. Thus, the callback will
		505	not be executed immediately but only after other requests in the
		506	queue have entered their execution phase. This can be used to
		507	measure request latency.
		508
		509	IO::AIO::aio_busy $fractional_seconds, $callback->() *NOT EXPORTED*
		510	Mainly used for debugging and benchmarking, this aio request puts
		511	one of the request workers to sleep for the given time.
		512
		513	While it is theoretically handy to have simple I/O scheduling
		514	requests like sleep and file handle readable/writable, the overhead
		515	this creates is immense (it blocks a thread for a long time) so do
		516	not use this function except to put your application under
		517	artificial I/O pressure.
		518
		519	IO::AIO::REQ CLASS
		520	All non-aggregate "aio_*" functions return an object of this class when
		521	called in non-void context.
		522
		523	cancel $req
		524	Cancels the request, if possible. Has the effect of skipping
		525	execution when entering the execute state and skipping calling the
		526	callback when entering the the result state, but will leave the
		527	request otherwise untouched. That means that requests that currently
		528	execute will not be stopped and resources held by the request will
		529	not be freed prematurely.
		530
		531	cb $req $callback->(...)
		532	Replace (or simply set) the callback registered to the request.
		533
		534	IO::AIO::GRP CLASS
		535	This class is a subclass of IO::AIO::REQ, so all its methods apply to
		536	objects of this class, too.
		537
		538	A IO::AIO::GRP object is a special request that can contain multiple
		539	other aio requests.
		540
		541	You create one by calling the "aio_group" constructing function with a
		542	callback that will be called when all contained requests have entered
		543	the "done" state:
		544
		545	my $grp = aio_group sub {
		546	print "all requests are done\n";
		547	};
		548
		549	You add requests by calling the "add" method with one or more
		550	"IO::AIO::REQ" objects:
		551
		552	$grp->add (aio_unlink "...");
		553
		554	add $grp aio_stat "...", sub {
		555	$_[0] or return $grp->result ("error");
		556
		557	# add another request dynamically, if first succeeded
		558	add $grp aio_open "...", sub {
		559	$grp->result ("ok");
		560	};
		561	};
		562
493	This makes it very easy to create composite requests (see the source	563	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	564	"aio_move" for an application) that work and feel like simple requests.
		565
		566	* The IO::AIO::GRP objects will be cleaned up during calls to
		567	"IO::AIO::poll_cb", just like any other request.
		568	* They can be canceled like any other request. Canceling will cancel not
		569	only the request itself, but also all requests it contains.
		570	* They can also can also be added to other IO::AIO::GRP objects.
		571	* You must not add requests to a group from within the group callback
		572	(or any later time).
		573
		574	Their lifetime, simplified, looks like this: when they are empty, they
		575	will finish very quickly. If they contain only requests that are in the
		576	"done" state, they will also finish. Otherwise they will continue to
		577	exist.
		578
		579	That means after creating a group you have some time to add requests.
		580	And in the callbacks of those requests, you can add further requests to
		581	the group. And only when all those requests have finished will the the
		582	group itself finish.
		583
		584	add $grp ...
		585	$grp->add (...)
		586	Add one or more requests to the group. Any type of IO::AIO::REQ can
		587	be added, including other groups, as long as you do not create
		588	circular dependencies.
		589
		590	Returns all its arguments.
		591
		592	$grp->cancel_subs
		593	Cancel all subrequests and clears any feeder, but not the group
		594	request itself. Useful when you queued a lot of events but got a
		595	result early.
		596
		597	$grp->result (...)
		598	Set the result value(s) that will be passed to the group callback
		599	when all subrequests have finished and set thre groups errno to the
		600	current value of errno (just like calling "errno" without an error
		601	number). By default, no argument will be passed and errno is zero.
		602
		603	$grp->errno ([$errno])
		604	Sets the group errno value to $errno, or the current value of errno
		605	when the argument is missing.
		606
		607	Every aio request has an associated errno value that is restored
		608	when the callback is invoked. This method lets you change this value
		609	from its default (0).
		610
		611	Calling "result" will also set errno, so make sure you either set $!
		612	before the call to "result", or call c<errno> after it.
		613
		614	feed $grp $callback->($grp)
		615	Sets a feeder/generator on this group: every group can have an
		616	attached generator that generates requests if idle. The idea behind
		617	this is that, although you could just queue as many requests as you
		618	want in a group, this might starve other requests for a potentially
		619	long time. For example, "aio_scandir" might generate hundreds of
		620	thousands "aio_stat" requests, delaying any later requests for a
		621	long time.
		622
		623	To avoid this, and allow incremental generation of requests, you can
		624	instead a group and set a feeder on it that generates those
		625	requests. The feed callback will be called whenever there are few
		626	enough (see "limit", below) requests active in the group itself and
		627	is expected to queue more requests.
		628
		629	The feed callback can queue as many requests as it likes (i.e. "add"
		630	does not impose any limits).
		631
		632	If the feed does not queue more requests when called, it will be
		633	automatically removed from the group.
		634
		635	If the feed limit is 0, it will be set to 2 automatically.
		636
		637	Example:
		638
		639	# stat all files in @files, but only ever use four aio requests concurrently:
		640
		641	my $grp = aio_group sub { print "finished\n" };
		642	limit $grp 4;
		643	feed $grp sub {
		644	my $file = pop @files
		645	or return;
		646
		647	add $grp aio_stat $file, sub { ... };
		648	};
		649
		650	limit $grp $num
		651	Sets the feeder limit for the group: The feeder will be called
		652	whenever the group contains less than this many requests.
		653
		654	Setting the limit to 0 will pause the feeding process.
		655
		656	SUPPORT FUNCTIONS
		657	EVENT PROCESSING AND EVENT LOOP INTEGRATION
		658	$fileno = IO::AIO::poll_fileno
		659	Return the *request result pipe file descriptor*. This filehandle
		660	must be polled for reading by some mechanism outside this module
		661	(e.g. Event or select, see below or the SYNOPSIS). If the pipe
		662	becomes readable you have to call "poll_cb" to check the results.
		663
		664	See "poll_cb" for an example.
		665
		666	IO::AIO::poll_cb
		667	Process some outstanding events on the result pipe. You have to call
		668	this regularly. Returns the number of events processed. Returns
		669	immediately when no events are outstanding. The amount of events
		670	processed depends on the settings of "IO::AIO::max_poll_req" and
		671	"IO::AIO::max_poll_time".
		672
		673	If not all requests were processed for whatever reason, the
		674	filehandle will still be ready when "poll_cb" returns.
		675
		676	Example: Install an Event watcher that automatically calls
		677	IO::AIO::poll_cb with high priority:
		678
		679	Event->io (fd => IO::AIO::poll_fileno,
		680	poll => 'r', async => 1,
		681	cb => \&IO::AIO::poll_cb);
		682
		683	IO::AIO::max_poll_reqs $nreqs
		684	IO::AIO::max_poll_time $seconds
		685	These set the maximum number of requests (default 0, meaning
		686	infinity) that are being processed by "IO::AIO::poll_cb" in one
		687	call, respectively the maximum amount of time (default 0, meaning
		688	infinity) spent in "IO::AIO::poll_cb" to process requests (more
		689	correctly the mininum amount of time "poll_cb" is allowed to use).
		690
		691	Setting "max_poll_time" to a non-zero value creates an overhead of
		692	one syscall per request processed, which is not normally a problem
		693	unless your callbacks are really really fast or your OS is really
		694	really slow (I am not mentioning Solaris here). Using
		695	"max_poll_reqs" incurs no overhead.
		696
		697	Setting these is useful if you want to ensure some level of
		698	interactiveness when perl is not fast enough to process all requests
		699	in time.
		700
		701	For interactive programs, values such as 0.01 to 0.1 should be fine.
		702
		703	Example: Install an Event watcher that automatically calls
		704	IO::AIO::poll_cb with low priority, to ensure that other parts of
		705	the program get the CPU sometimes even under high AIO load.
		706
		707	# try not to spend much more than 0.1s in poll_cb
		708	IO::AIO::max_poll_time 0.1;
		709
		710	# use a low priority so other tasks have priority
		711	Event->io (fd => IO::AIO::poll_fileno,
		712	poll => 'r', nice => 1,
		713	cb => &IO::AIO::poll_cb);
		714
		715	IO::AIO::poll_wait
		716	Wait till the result filehandle becomes ready for reading (simply
		717	does a "select" on the filehandle. This is useful if you want to
		718	synchronously wait for some requests to finish).
		719
		720	See "nreqs" for an example.
		721
		722	IO::AIO::poll
		723	Waits until some requests have been handled.
		724
		725	Strictly equivalent to:
		726
		727	IO::AIO::poll_wait, IO::AIO::poll_cb
		728	if IO::AIO::nreqs;
		729
		730	IO::AIO::flush
		731	Wait till all outstanding AIO requests have been handled.
		732
		733	Strictly equivalent to:
		734
		735	IO::AIO::poll_wait, IO::AIO::poll_cb
		736	while IO::AIO::nreqs;
		737
		738	CONTROLLING THE NUMBER OF THREADS
		739	IO::AIO::min_parallel $nthreads
		740	Set the minimum number of AIO threads to $nthreads. The current
		741	default is 8, which means eight asynchronous operations can execute
		742	concurrently at any one time (the number of outstanding requests,
		743	however, is unlimited).
		744
		745	IO::AIO starts threads only on demand, when an AIO request is queued
		746	and no free thread exists. Please note that queueing up a hundred
		747	requests can create demand for a hundred threads, even if it turns
		748	out that everything is in the cache and could have been processed
		749	faster by a single thread.
		750
		751	It is recommended to keep the number of threads relatively low, as
		752	some Linux kernel versions will scale negatively with the number of
		753	threads (higher parallelity => MUCH higher latency). With current
		754	Linux 2.6 versions, 4-32 threads should be fine.
		755
		756	Under most circumstances you don't need to call this function, as
		757	the module selects a default that is suitable for low to moderate
		758	load.
		759
		760	IO::AIO::max_parallel $nthreads
		761	Sets the maximum number of AIO threads to $nthreads. If more than
		762	the specified number of threads are currently running, this function
		763	kills them. This function blocks until the limit is reached.
		764
		765	While $nthreads are zero, aio requests get queued but not executed
		766	until the number of threads has been increased again.
		767
		768	This module automatically runs "max_parallel 0" at program end, to
		769	ensure that all threads are killed and that there are no outstanding
495	requests.	770	requests.
496		771
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.	772	Under normal circumstances you don't need to call this function.
701		773
		774	IO::AIO::max_idle $nthreads
		775	Limit the number of threads (default: 4) that are allowed to idle
		776	(i.e., threads that did not get a request to process within 10
		777	seconds). That means if a thread becomes idle while $nthreads other
		778	threads are also idle, it will free its resources and exit.
		779
		780	This is useful when you allow a large number of threads (e.g. 100 or
		781	1000) to allow for extremely high load situations, but want to free
		782	resources under normal circumstances (1000 threads can easily
		783	consume 30MB of RAM).
		784
		785	The default is probably ok in most situations, especially if thread
		786	creation is fast. If thread creation is very slow on your system you
		787	might want to use larger values.
		788
702	$oldmaxreqs = IO::AIO::max_outstanding $maxreqs	789	$oldmaxreqs = IO::AIO::max_outstanding $maxreqs
703	This is a very bad function to use in interactive programs	790	This is a very bad function to use in interactive programs because
704	because it blocks, and a bad way to reduce concurrency because	791	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	792	inexact: Better use an "aio_group" together with a feed callback.
706	callback.
707		793
708	Sets the maximum number of outstanding requests to $nreqs. If	794	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	795	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	796	"poll_cb" (and "poll_some" and other functions calling "poll_cb")
711	"poll_cb") function will block until the limit is no longer	797	function will block until the limit is no longer exceeded.
712	exceeded.
713		798
714	The default value is very large, so there is no practical limit	799	The default value is very large, so there is no practical limit on
715	on the number of outstanding requests.	800	the number of outstanding requests.
716		801
717	You can still queue as many requests as you want. Therefore,	802	You can still queue as many requests as you want. Therefore,
718	"max_oustsanding" is mainly useful in simple scripts (with low	803	"max_oustsanding" is mainly useful in simple scripts (with low
719	values) or as a stop gap to shield against fatal memory overflow	804	values) or as a stop gap to shield against fatal memory overflow
720	(with large values).	805	(with large values).
		806
		807	STATISTICAL INFORMATION
		808	IO::AIO::nreqs
		809	Returns the number of requests currently in the ready, execute or
		810	pending states (i.e. for which their callback has not been invoked
		811	yet).
		812
		813	Example: wait till there are no outstanding requests anymore:
		814
		815	IO::AIO::poll_wait, IO::AIO::poll_cb
		816	while IO::AIO::nreqs;
		817
		818	IO::AIO::nready
		819	Returns the number of requests currently in the ready state (not yet
		820	executed).
		821
		822	IO::AIO::npending
		823	Returns the number of requests currently in the pending state
		824	(executed, but not yet processed by poll_cb).
721		825
722	FORK BEHAVIOUR	826	FORK BEHAVIOUR
723	This module should do "the right thing" when the process using it	827	This module should do "the right thing" when the process using it forks:
724	forks:
725		828
726	Before the fork, IO::AIO enters a quiescent state where no requests	829	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.	830	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	831	fork the parent simply leaves the quiescent state and continues
729	continues request/result processing, while the child frees the	832	request/result processing, while the child frees the request/result
730	request/result queue (so that the requests started before the fork	833	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	834	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	835	the parent process has been reached again.
733	again.
734		836
735	In short: the parent will, after a short pause, continue as if fork	837	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	838	not been called, while the child will act as if IO::AIO has not been
737	been used yet.	839	used yet.
738		840
739	MEMORY USAGE	841	MEMORY USAGE
740	Per-request usage:	842	Per-request usage:
741		843
742	Each aio request uses - depending on your architecture - around	844	Each aio request uses - depending on your architecture - around 100-200
743	100-200 bytes of memory. In addition, stat requests need a stat	845	bytes of memory. In addition, stat requests need a stat buffer (possibly
744	buffer (possibly a few hundred bytes), readdir requires a result	846	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	847	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	848	will consume memory till the request has entered the done state.
747	request has entered the done state.
748		849
749	This is now awfully much, so queuing lots of requests is not usually	850	This is now awfully much, so queuing lots of requests is not usually a
750	a problem.	851	problem.
751		852
752	Per-thread usage:	853	Per-thread usage:
753		854
754	In the execution phase, some aio requests require more memory for	855	In the execution phase, some aio requests require more memory for
755	temporary buffers, and each thread requires a stack and other data	856	temporary buffers, and each thread requires a stack and other data
756	structures (usually around 16k-128k, depending on the OS).	857	structures (usually around 16k-128k, depending on the OS).
757		858
758	KNOWN BUGS	859	KNOWN BUGS
759	Known bugs will be fixed in the next release.	860	Known bugs will be fixed in the next release.
760		861
761	SEE ALSO	862	SEE ALSO
762	Coro::AIO.	863	Coro::AIO.
763		864
764	AUTHOR	865	AUTHOR
765	Marc Lehmann <schmorp@schmorp.de>	866	Marc Lehmann <schmorp@schmorp.de>
766	http://home.schmorp.de/	867	http://home.schmorp.de/
767		868

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