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Revision 1.18 by root, Thu Oct 26 16:28:33 2006 UTC vs.
Revision 1.27 by root, Sat Oct 6 14:05:37 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	Unfortunately, you can't do this to perl. Perl *insists* very
		266	strongly on closing the file descriptor associated with the
		267	filehandle itself. Here is what aio_close will try:
		268
		269	1. dup()licate the fd
		270	2. asynchronously close() the duplicated fd
		271	3. dup()licate the fd once more
		272	4. let perl close() the filehandle
		273	5. asynchronously close the duplicated fd
		274
		275	The idea is that the first close() flushes stuff to disk that
		276	closing an fd will flush, so when perl closes the fd, nothing much
		277	will need to be flushed. The second async. close() will then flush
		278	stuff to disk that closing the last fd to the file will flush.
		279
		280	Just FYI, SuSv3 has this to say on close:
		281
		282	All outstanding record locks owned by the process on the file
		283	associated with the file descriptor shall be removed.
		284
		285	If fildes refers to a socket, close() shall cause the socket to be
		286	destroyed. ... close() shall block for up to the current linger
		287	interval until all data is transmitted.
		288	[this actually sounds like a specification bug, but who knows]
		289
		290	And at least Linux additionally actually flushes stuff on every
		291	close, even when the file itself is still open.
		292
		293	Sounds enourmously inefficient and complicated? Yes... please show
		294	me how to nuke perl's fd out of existence...
		295
		296	aio_read $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
		297	aio_write $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
		298	Reads or writes $length bytes from the specified $fh and $offset
		299	into the scalar given by $data and offset $dataoffset and calls the
		300	callback without the actual number of bytes read (or -1 on error,
		301	just like the syscall).
		302
		303	If $offset is undefined, then the current file descriptor offset
		304	will be used (and updated), otherwise the file descriptor offset
		305	will not be changed by these calls.
		306
		307	If $length is undefined in "aio_write", use the remaining length of
		308	$data.
		309
		310	If $dataoffset is less than zero, it will be counted from the end of
		311	$data.
		312
		313	The $data scalar *MUST NOT* be modified in any way while the request
		314	is outstanding. Modifying it can result in segfaults or World War
		315	III (if the necessary/optional hardware is installed).
		316
		317	Example: Read 15 bytes at offset 7 into scalar $buffer, starting at
		318	offset 0 within the scalar:
		319
		320	aio_read $fh, 7, 15, $buffer, 0, sub {
		321	$_[0] > 0 or die "read error: $!";
		322	print "read $_[0] bytes: <$buffer>\n";
		323	};
		324
		325	aio_sendfile $out_fh, $in_fh, $in_offset, $length, $callback->($retval)
		326	Tries to copy $length bytes from $in_fh to $out_fh. It starts
		327	reading at byte offset $in_offset, and starts writing at the current
		328	file offset of $out_fh. Because of that, it is not safe to issue
		329	more than one "aio_sendfile" per $out_fh, as they will interfere
		330	with each other.
		331
		332	This call tries to make use of a native "sendfile" syscall to
		333	provide zero-copy operation. For this to work, $out_fh should refer
		334	to a socket, and $in_fh should refer to mmap'able file.
		335
		336	If the native sendfile call fails or is not implemented, it will be
		337	emulated, so you can call "aio_sendfile" on any type of filehandle
		338	regardless of the limitations of the operating system.
		339
		340	Please note, however, that "aio_sendfile" can read more bytes from
		341	$in_fh than are written, and there is no way to find out how many
		342	bytes have been read from "aio_sendfile" alone, as "aio_sendfile"
		343	only provides the number of bytes written to $out_fh. Only if the
		344	result value equals $length one can assume that $length bytes have
		345	been read.
		346
		347	aio_readahead $fh,$offset,$length, $callback->($retval)
		348	"aio_readahead" populates the page cache with data from a file so
		349	that subsequent reads from that file will not block on disk I/O. The
		350	$offset argument specifies the starting point from which data is to
		351	be read and $length specifies the number of bytes to be read. I/O is
		352	performed in whole pages, so that offset is effectively rounded down
		353	to a page boundary and bytes are read up to the next page boundary
		354	greater than or equal to (off-set+length). "aio_readahead" does not
		355	read beyond the end of the file. The current file offset of the file
		356	is left unchanged.
		357
		358	If that syscall doesn't exist (likely if your OS isn't Linux) it
		359	will be emulated by simply reading the data, which would have a
		360	similar effect.
		361
		362	aio_stat $fh_or_path, $callback->($status)
		363	aio_lstat $fh, $callback->($status)
		364	Works like perl's "stat" or "lstat" in void context. The callback
		365	will be called after the stat and the results will be available
		366	using "stat _" or "-s _" etc...
		367
		368	The pathname passed to "aio_stat" must be absolute. See API NOTES,
		369	above, for an explanation.
		370
		371	Currently, the stats are always 64-bit-stats, i.e. instead of
		372	returning an error when stat'ing a large file, the results will be
		373	silently truncated unless perl itself is compiled with large file
		374	support.
		375
		376	Example: Print the length of /etc/passwd:
		377
		378	aio_stat "/etc/passwd", sub {
		379	$_[0] and die "stat failed: $!";
		380	print "size is ", -s _, "\n";
		381	};
		382
		383	aio_utime $fh_or_path, $atime, $mtime, $callback->($status)
		384	Works like perl's "utime" function (including the special case of
		385	$atime and $mtime being undef). Fractional times are supported if
		386	the underlying syscalls support them.
		387
		388	When called with a pathname, uses utimes(2) if available, otherwise
		389	utime(2). If called on a file descriptor, uses futimes(2) if
		390	available, otherwise returns ENOSYS, so this is not portable.
		391
		392	Examples:
		393
		394	# set atime and mtime to current time (basically touch(1)):
		395	aio_utime "path", undef, undef;
		396	# set atime to current time and mtime to beginning of the epoch:
		397	aio_utime "path", time, undef; # undef==0
		398
		399	aio_chown $fh_or_path, $uid, $gid, $callback->($status)
		400	Works like perl's "chown" function, except that "undef" for either
		401	$uid or $gid is being interpreted as "do not change" (but -1 can
		402	also be used).
		403
		404	Examples:
		405
		406	# same as "chown root path" in the shell:
		407	aio_chown "path", 0, -1;
		408	# same as above:
		409	aio_chown "path", 0, undef;
		410
		411	aio_truncate $fh_or_path, $offset, $callback->($status)
		412	Works like truncate(2) or ftruncate(2).
		413
		414	aio_chmod $fh_or_path, $mode, $callback->($status)
		415	Works like perl's "chmod" function.
		416
		417	aio_unlink $pathname, $callback->($status)
		418	Asynchronously unlink (delete) a file and call the callback with the
		419	result code.
		420
		421	aio_mknod $path, $mode, $dev, $callback->($status)
		422	[EXPERIMENTAL]
		423
		424	Asynchronously create a device node (or fifo). See mknod(2).
		425
		426	The only (POSIX-) portable way of calling this function is:
		427
		428	aio_mknod $path, IO::AIO::S_IFIFO | $mode, 0, sub { ...
		429
		430	aio_link $srcpath, $dstpath, $callback->($status)
		431	Asynchronously create a new link to the existing object at $srcpath
		432	at the path $dstpath and call the callback with the result code.
		433
		434	aio_symlink $srcpath, $dstpath, $callback->($status)
		435	Asynchronously create a new symbolic link to the existing object at
		436	$srcpath at the path $dstpath and call the callback with the result
		437	code.
		438
		439	aio_readlink $path, $callback->($link)
		440	Asynchronously read the symlink specified by $path and pass it to
		441	the callback. If an error occurs, nothing or undef gets passed to
		442	the callback.
		443
		444	aio_rename $srcpath, $dstpath, $callback->($status)
		445	Asynchronously rename the object at $srcpath to $dstpath, just as
		446	rename(2) and call the callback with the result code.
		447
		448	aio_mkdir $pathname, $mode, $callback->($status)
		449	Asynchronously mkdir (create) a directory and call the callback with
		450	the result code. $mode will be modified by the umask at the time the
		451	request is executed, so do not change your umask.
		452
		453	aio_rmdir $pathname, $callback->($status)
		454	Asynchronously rmdir (delete) a directory and call the callback with
		455	the result code.
		456
		457	aio_readdir $pathname, $callback->($entries)
		458	Unlike the POSIX call of the same name, "aio_readdir" reads an
		459	entire directory (i.e. opendir + readdir + closedir). The entries
		460	will not be sorted, and will NOT include the "." and ".." entries.
		461
		462	The callback a single argument which is either "undef" or an
		463	array-ref with the filenames.
		464
		465	aio_load $path, $data, $callback->($status)
		466	This is a composite request that tries to fully load the given file
		467	into memory. Status is the same as with aio_read.
		468
		469	aio_copy $srcpath, $dstpath, $callback->($status)
		470	Try to copy the *file* (directories not supported as either source
		471	or destination) from $srcpath to $dstpath and call the callback with
		472	the 0 (error) or -1 ok.
		473
		474	This is a composite request that it creates the destination file
		475	with mode 0200 and copies the contents of the source file into it
		476	using "aio_sendfile", followed by restoring atime, mtime, access
		477	mode and uid/gid, in that order.
		478
		479	If an error occurs, the partial destination file will be unlinked,
		480	if possible, except when setting atime, mtime, access mode and
		481	uid/gid, where errors are being ignored.
		482
		483	aio_move $srcpath, $dstpath, $callback->($status)
		484	Try to move the *file* (directories not supported as either source
		485	or destination) from $srcpath to $dstpath and call the callback with
		486	the 0 (error) or -1 ok.
		487
		488	This is a composite request that tries to rename(2) the file first.
		489	If rename files with "EXDEV", it copies the file with "aio_copy"
		490	and, if that is successful, unlinking the $srcpath.
		491
		492	aio_scandir $path, $maxreq, $callback->($dirs, $nondirs)
		493	Scans a directory (similar to "aio_readdir") but additionally tries
		494	to efficiently separate the entries of directory $path into two sets
		495	of names, directories you can recurse into (directories), and ones
		496	you cannot recurse into (everything else, including symlinks to
		497	directories).
		498
		499	"aio_scandir" is a composite request that creates of many sub
		500	requests_ $maxreq specifies the maximum number of outstanding aio
		501	requests that this function generates. If it is "<= 0", then a
		502	suitable default will be chosen (currently 4).
		503
		504	On error, the callback is called without arguments, otherwise it
		505	receives two array-refs with path-relative entry names.
		506
		507	Example:
		508
		509	aio_scandir $dir, 0, sub {
		510	my ($dirs, $nondirs) = @_;
		511	print "real directories: @$dirs\n";
		512	print "everything else: @$nondirs\n";
		513	};
		514
		515	Implementation notes.
		516
		517	The "aio_readdir" cannot be avoided, but "stat()"'ing every entry
		518	can.
		519
		520	After reading the directory, the modification time, size etc. of the
		521	directory before and after the readdir is checked, and if they match
		522	(and isn't the current time), the link count will be used to decide
		523	how many entries are directories (if >= 2). Otherwise, no knowledge
		524	of the number of subdirectories will be assumed.
		525
		526	Then entries will be sorted into likely directories (everything
		527	without a non-initial dot currently) and likely non-directories
		528	(everything else). Then every entry plus an appended "/." will be
		529	"stat"'ed, likely directories first. If that succeeds, it assumes
		530	that the entry is a directory or a symlink to directory (which will
		531	be checked seperately). This is often faster than stat'ing the entry
		532	itself because filesystems might detect the type of the entry
		533	without reading the inode data (e.g. ext2fs filetype feature).
		534
		535	If the known number of directories (link count - 2) has been
		536	reached, the rest of the entries is assumed to be non-directories.
		537
		538	This only works with certainty on POSIX (= UNIX) filesystems, which
		539	fortunately are the vast majority of filesystems around.
		540
		541	It will also likely work on non-POSIX filesystems with reduced
		542	efficiency as those tend to return 0 or 1 as link counts, which
		543	disables the directory counting heuristic.
		544
		545	aio_rmtree $path, $callback->($status)
		546	Delete a directory tree starting (and including) $path, return the
		547	status of the final "rmdir" only. This is a composite request that
		548	uses "aio_scandir" to recurse into and rmdir directories, and unlink
		549	everything else.
		550
		551	aio_fsync $fh, $callback->($status)
		552	Asynchronously call fsync on the given filehandle and call the
		553	callback with the fsync result code.
		554
		555	aio_fdatasync $fh, $callback->($status)
		556	Asynchronously call fdatasync on the given filehandle and call the
		557	callback with the fdatasync result code.
		558
		559	If this call isn't available because your OS lacks it or it couldn't
		560	be detected, it will be emulated by calling "fsync" instead.
		561
		562	aio_group $callback->(...)
		563	This is a very special aio request: Instead of doing something, it
		564	is a container for other aio requests, which is useful if you want
		565	to bundle many requests into a single, composite, request with a
		566	definite callback and the ability to cancel the whole request with
		567	its subrequests.
		568
		569	Returns an object of class IO::AIO::GRP. See its documentation below
		570	for more info.
		571
		572	Example:
		573
		574	my $grp = aio_group sub {
		575	print "all stats done\n";
		576	};
		577
		578	add $grp
		579	(aio_stat ...),
		580	(aio_stat ...),
		581	...;
		582
		583	aio_nop $callback->()
		584	This is a special request - it does nothing in itself and is only
		585	used for side effects, such as when you want to add a dummy request
		586	to a group so that finishing the requests in the group depends on
		587	executing the given code.
		588
		589	While this request does nothing, it still goes through the execution
		590	phase and still requires a worker thread. Thus, the callback will
		591	not be executed immediately but only after other requests in the
		592	queue have entered their execution phase. This can be used to
		593	measure request latency.
		594
		595	IO::AIO::aio_busy $fractional_seconds, $callback->() *NOT EXPORTED*
		596	Mainly used for debugging and benchmarking, this aio request puts
		597	one of the request workers to sleep for the given time.
		598
		599	While it is theoretically handy to have simple I/O scheduling
		600	requests like sleep and file handle readable/writable, the overhead
		601	this creates is immense (it blocks a thread for a long time) so do
		602	not use this function except to put your application under
		603	artificial I/O pressure.
		604
		605	IO::AIO::REQ CLASS
		606	All non-aggregate "aio_*" functions return an object of this class when
		607	called in non-void context.
		608
		609	cancel $req
		610	Cancels the request, if possible. Has the effect of skipping
		611	execution when entering the execute state and skipping calling the
		612	callback when entering the the result state, but will leave the
		613	request otherwise untouched. That means that requests that currently
		614	execute will not be stopped and resources held by the request will
		615	not be freed prematurely.
		616
		617	cb $req $callback->(...)
		618	Replace (or simply set) the callback registered to the request.
		619
		620	IO::AIO::GRP CLASS
		621	This class is a subclass of IO::AIO::REQ, so all its methods apply to
		622	objects of this class, too.
		623
		624	A IO::AIO::GRP object is a special request that can contain multiple
		625	other aio requests.
		626
		627	You create one by calling the "aio_group" constructing function with a
		628	callback that will be called when all contained requests have entered
		629	the "done" state:
		630
		631	my $grp = aio_group sub {
		632	print "all requests are done\n";
		633	};
		634
		635	You add requests by calling the "add" method with one or more
		636	"IO::AIO::REQ" objects:
		637
		638	$grp->add (aio_unlink "...");
		639
		640	add $grp aio_stat "...", sub {
		641	$_[0] or return $grp->result ("error");
		642
		643	# add another request dynamically, if first succeeded
		644	add $grp aio_open "...", sub {
		645	$grp->result ("ok");
		646	};
		647	};
		648
493	This makes it very easy to create composite requests (see the source	649	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	650	"aio_move" for an application) that work and feel like simple requests.
		651
		652	* The IO::AIO::GRP objects will be cleaned up during calls to
		653	"IO::AIO::poll_cb", just like any other request.
		654	* They can be canceled like any other request. Canceling will cancel not
		655	only the request itself, but also all requests it contains.
		656	* They can also can also be added to other IO::AIO::GRP objects.
		657	* You must not add requests to a group from within the group callback
		658	(or any later time).
		659
		660	Their lifetime, simplified, looks like this: when they are empty, they
		661	will finish very quickly. If they contain only requests that are in the
		662	"done" state, they will also finish. Otherwise they will continue to
		663	exist.
		664
		665	That means after creating a group you have some time to add requests.
		666	And in the callbacks of those requests, you can add further requests to
		667	the group. And only when all those requests have finished will the the
		668	group itself finish.
		669
		670	add $grp ...
		671	$grp->add (...)
		672	Add one or more requests to the group. Any type of IO::AIO::REQ can
		673	be added, including other groups, as long as you do not create
		674	circular dependencies.
		675
		676	Returns all its arguments.
		677
		678	$grp->cancel_subs
		679	Cancel all subrequests and clears any feeder, but not the group
		680	request itself. Useful when you queued a lot of events but got a
		681	result early.
		682
		683	$grp->result (...)
		684	Set the result value(s) that will be passed to the group callback
		685	when all subrequests have finished and set thre groups errno to the
		686	current value of errno (just like calling "errno" without an error
		687	number). By default, no argument will be passed and errno is zero.
		688
		689	$grp->errno ([$errno])
		690	Sets the group errno value to $errno, or the current value of errno
		691	when the argument is missing.
		692
		693	Every aio request has an associated errno value that is restored
		694	when the callback is invoked. This method lets you change this value
		695	from its default (0).
		696
		697	Calling "result" will also set errno, so make sure you either set $!
		698	before the call to "result", or call c<errno> after it.
		699
		700	feed $grp $callback->($grp)
		701	Sets a feeder/generator on this group: every group can have an
		702	attached generator that generates requests if idle. The idea behind
		703	this is that, although you could just queue as many requests as you
		704	want in a group, this might starve other requests for a potentially
		705	long time. For example, "aio_scandir" might generate hundreds of
		706	thousands "aio_stat" requests, delaying any later requests for a
		707	long time.
		708
		709	To avoid this, and allow incremental generation of requests, you can
		710	instead a group and set a feeder on it that generates those
		711	requests. The feed callback will be called whenever there are few
		712	enough (see "limit", below) requests active in the group itself and
		713	is expected to queue more requests.
		714
		715	The feed callback can queue as many requests as it likes (i.e. "add"
		716	does not impose any limits).
		717
		718	If the feed does not queue more requests when called, it will be
		719	automatically removed from the group.
		720
		721	If the feed limit is 0, it will be set to 2 automatically.
		722
		723	Example:
		724
		725	# stat all files in @files, but only ever use four aio requests concurrently:
		726
		727	my $grp = aio_group sub { print "finished\n" };
		728	limit $grp 4;
		729	feed $grp sub {
		730	my $file = pop @files
		731	or return;
		732
		733	add $grp aio_stat $file, sub { ... };
		734	};
		735
		736	limit $grp $num
		737	Sets the feeder limit for the group: The feeder will be called
		738	whenever the group contains less than this many requests.
		739
		740	Setting the limit to 0 will pause the feeding process.
		741
		742	SUPPORT FUNCTIONS
		743	EVENT PROCESSING AND EVENT LOOP INTEGRATION
		744	$fileno = IO::AIO::poll_fileno
		745	Return the *request result pipe file descriptor*. This filehandle
		746	must be polled for reading by some mechanism outside this module
		747	(e.g. Event or select, see below or the SYNOPSIS). If the pipe
		748	becomes readable you have to call "poll_cb" to check the results.
		749
		750	See "poll_cb" for an example.
		751
		752	IO::AIO::poll_cb
		753	Process some outstanding events on the result pipe. You have to call
		754	this regularly. Returns the number of events processed. Returns
		755	immediately when no events are outstanding. The amount of events
		756	processed depends on the settings of "IO::AIO::max_poll_req" and
		757	"IO::AIO::max_poll_time".
		758
		759	If not all requests were processed for whatever reason, the
		760	filehandle will still be ready when "poll_cb" returns.
		761
		762	Example: Install an Event watcher that automatically calls
		763	IO::AIO::poll_cb with high priority:
		764
		765	Event->io (fd => IO::AIO::poll_fileno,
		766	poll => 'r', async => 1,
		767	cb => \&IO::AIO::poll_cb);
		768
		769	IO::AIO::max_poll_reqs $nreqs
		770	IO::AIO::max_poll_time $seconds
		771	These set the maximum number of requests (default 0, meaning
		772	infinity) that are being processed by "IO::AIO::poll_cb" in one
		773	call, respectively the maximum amount of time (default 0, meaning
		774	infinity) spent in "IO::AIO::poll_cb" to process requests (more
		775	correctly the mininum amount of time "poll_cb" is allowed to use).
		776
		777	Setting "max_poll_time" to a non-zero value creates an overhead of
		778	one syscall per request processed, which is not normally a problem
		779	unless your callbacks are really really fast or your OS is really
		780	really slow (I am not mentioning Solaris here). Using
		781	"max_poll_reqs" incurs no overhead.
		782
		783	Setting these is useful if you want to ensure some level of
		784	interactiveness when perl is not fast enough to process all requests
		785	in time.
		786
		787	For interactive programs, values such as 0.01 to 0.1 should be fine.
		788
		789	Example: Install an Event watcher that automatically calls
		790	IO::AIO::poll_cb with low priority, to ensure that other parts of
		791	the program get the CPU sometimes even under high AIO load.
		792
		793	# try not to spend much more than 0.1s in poll_cb
		794	IO::AIO::max_poll_time 0.1;
		795
		796	# use a low priority so other tasks have priority
		797	Event->io (fd => IO::AIO::poll_fileno,
		798	poll => 'r', nice => 1,
		799	cb => &IO::AIO::poll_cb);
		800
		801	IO::AIO::poll_wait
		802	If there are any outstanding requests and none of them in the result
		803	phase, wait till the result filehandle becomes ready for reading
		804	(simply does a "select" on the filehandle. This is useful if you
		805	want to synchronously wait for some requests to finish).
		806
		807	See "nreqs" for an example.
		808
		809	IO::AIO::poll
		810	Waits until some requests have been handled.
		811
		812	Returns the number of requests processed, but is otherwise strictly
		813	equivalent to:
		814
		815	IO::AIO::poll_wait, IO::AIO::poll_cb
		816
		817	IO::AIO::flush
		818	Wait till all outstanding AIO requests have been handled.
		819
		820	Strictly equivalent to:
		821
		822	IO::AIO::poll_wait, IO::AIO::poll_cb
		823	while IO::AIO::nreqs;
		824
		825	CONTROLLING THE NUMBER OF THREADS
		826	IO::AIO::min_parallel $nthreads
		827	Set the minimum number of AIO threads to $nthreads. The current
		828	default is 8, which means eight asynchronous operations can execute
		829	concurrently at any one time (the number of outstanding requests,
		830	however, is unlimited).
		831
		832	IO::AIO starts threads only on demand, when an AIO request is queued
		833	and no free thread exists. Please note that queueing up a hundred
		834	requests can create demand for a hundred threads, even if it turns
		835	out that everything is in the cache and could have been processed
		836	faster by a single thread.
		837
		838	It is recommended to keep the number of threads relatively low, as
		839	some Linux kernel versions will scale negatively with the number of
		840	threads (higher parallelity => MUCH higher latency). With current
		841	Linux 2.6 versions, 4-32 threads should be fine.
		842
		843	Under most circumstances you don't need to call this function, as
		844	the module selects a default that is suitable for low to moderate
		845	load.
		846
		847	IO::AIO::max_parallel $nthreads
		848	Sets the maximum number of AIO threads to $nthreads. If more than
		849	the specified number of threads are currently running, this function
		850	kills them. This function blocks until the limit is reached.
		851
		852	While $nthreads are zero, aio requests get queued but not executed
		853	until the number of threads has been increased again.
		854
		855	This module automatically runs "max_parallel 0" at program end, to
		856	ensure that all threads are killed and that there are no outstanding
495	requests.	857	requests.
496		858
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.	859	Under normal circumstances you don't need to call this function.
701		860
		861	IO::AIO::max_idle $nthreads
		862	Limit the number of threads (default: 4) that are allowed to idle
		863	(i.e., threads that did not get a request to process within 10
		864	seconds). That means if a thread becomes idle while $nthreads other
		865	threads are also idle, it will free its resources and exit.
		866
		867	This is useful when you allow a large number of threads (e.g. 100 or
		868	1000) to allow for extremely high load situations, but want to free
		869	resources under normal circumstances (1000 threads can easily
		870	consume 30MB of RAM).
		871
		872	The default is probably ok in most situations, especially if thread
		873	creation is fast. If thread creation is very slow on your system you
		874	might want to use larger values.
		875
702	$oldmaxreqs = IO::AIO::max_outstanding $maxreqs	876	$oldmaxreqs = IO::AIO::max_outstanding $maxreqs
703	This is a very bad function to use in interactive programs	877	This is a very bad function to use in interactive programs because
704	because it blocks, and a bad way to reduce concurrency because	878	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	879	inexact: Better use an "aio_group" together with a feed callback.
706	callback.
707		880
708	Sets the maximum number of outstanding requests to $nreqs. If	881	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	882	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	883	"poll_cb" (and "poll_some" and other functions calling "poll_cb")
711	"poll_cb") function will block until the limit is no longer	884	function will block until the limit is no longer exceeded.
712	exceeded.
713		885
714	The default value is very large, so there is no practical limit	886	The default value is very large, so there is no practical limit on
715	on the number of outstanding requests.	887	the number of outstanding requests.
716		888
717	You can still queue as many requests as you want. Therefore,	889	You can still queue as many requests as you want. Therefore,
718	"max_oustsanding" is mainly useful in simple scripts (with low	890	"max_oustsanding" is mainly useful in simple scripts (with low
719	values) or as a stop gap to shield against fatal memory overflow	891	values) or as a stop gap to shield against fatal memory overflow
720	(with large values).	892	(with large values).
		893
		894	STATISTICAL INFORMATION
		895	IO::AIO::nreqs
		896	Returns the number of requests currently in the ready, execute or
		897	pending states (i.e. for which their callback has not been invoked
		898	yet).
		899
		900	Example: wait till there are no outstanding requests anymore:
		901
		902	IO::AIO::poll_wait, IO::AIO::poll_cb
		903	while IO::AIO::nreqs;
		904
		905	IO::AIO::nready
		906	Returns the number of requests currently in the ready state (not yet
		907	executed).
		908
		909	IO::AIO::npending
		910	Returns the number of requests currently in the pending state
		911	(executed, but not yet processed by poll_cb).
721		912
722	FORK BEHAVIOUR	913	FORK BEHAVIOUR
723	This module should do "the right thing" when the process using it	914	This module should do "the right thing" when the process using it forks:
724	forks:
725		915
726	Before the fork, IO::AIO enters a quiescent state where no requests	916	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.	917	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	918	fork the parent simply leaves the quiescent state and continues
729	continues request/result processing, while the child frees the	919	request/result processing, while the child frees the request/result
730	request/result queue (so that the requests started before the fork	920	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	921	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	922	the parent process has been reached again.
733	again.
734		923
735	In short: the parent will, after a short pause, continue as if fork	924	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	925	not been called, while the child will act as if IO::AIO has not been
737	been used yet.	926	used yet.
738		927
739	MEMORY USAGE	928	MEMORY USAGE
740	Per-request usage:	929	Per-request usage:
741		930
742	Each aio request uses - depending on your architecture - around	931	Each aio request uses - depending on your architecture - around 100-200
743	100-200 bytes of memory. In addition, stat requests need a stat	932	bytes of memory. In addition, stat requests need a stat buffer (possibly
744	buffer (possibly a few hundred bytes), readdir requires a result	933	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	934	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	935	will consume memory till the request has entered the done state.
747	request has entered the done state.
748		936
749	This is now awfully much, so queuing lots of requests is not usually	937	This is not awfully much, so queuing lots of requests is not usually a
750	a problem.	938	problem.
751		939
752	Per-thread usage:	940	Per-thread usage:
753		941
754	In the execution phase, some aio requests require more memory for	942	In the execution phase, some aio requests require more memory for
755	temporary buffers, and each thread requires a stack and other data	943	temporary buffers, and each thread requires a stack and other data
756	structures (usually around 16k-128k, depending on the OS).	944	structures (usually around 16k-128k, depending on the OS).
757		945
758	KNOWN BUGS	946	KNOWN BUGS
759	Known bugs will be fixed in the next release.	947	Known bugs will be fixed in the next release.
760		948
761	SEE ALSO	949	SEE ALSO
762	Coro::AIO.	950	Coro::AIO.
763		951
764	AUTHOR	952	AUTHOR
765	Marc Lehmann <schmorp@schmorp.de>	953	Marc Lehmann <schmorp@schmorp.de>
766	http://home.schmorp.de/	954	http://home.schmorp.de/
767		955

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