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Revision 1.18 by root, Thu Oct 26 16:28:33 2006 UTC vs.
Revision 1.23 by root, Mon Jan 22 15:59:52 2007 UTC

…		…
3		3
4	SYNOPSIS	4	SYNOPSIS
5	use IO::AIO;	5	use IO::AIO;
6		6
7	aio_open "/etc/passwd", O_RDONLY, 0, sub {	7	aio_open "/etc/passwd", O_RDONLY, 0, sub {
8	my ($fh) = @_;	8	my $fh = shift
		9	or die "/etc/passwd: $!";
9	...	10	...
10	};	11	};
11		12
12	aio_unlink "/tmp/file", sub { };	13	aio_unlink "/tmp/file", sub { };
13		14
…		…
47	\&IO::AIO::poll_cb);	48	\&IO::AIO::poll_cb);
48		49
49	DESCRIPTION	50	DESCRIPTION
50	This module implements asynchronous I/O using whatever means your	51	This module implements asynchronous I/O using whatever means your
51	operating system supports.	52	operating system supports.
		53
		54	Asynchronous means that operations that can normally block your program
		55	(e.g. reading from disk) will be done asynchronously: the operation will
		56	still block, but you can do something else in the meantime. This is
		57	extremely useful for programs that need to stay interactive even when
		58	doing heavy I/O (GUI programs, high performance network servers etc.),
		59	but can also be used to easily do operations in parallel that are
		60	normally done sequentially, e.g. stat'ing many files, which is much
		61	faster on a RAID volume or over NFS when you do a number of stat
		62	operations concurrently.
		63
		64	While most of this works on all types of file descriptors (for example
		65	sockets), using these functions on file descriptors that support
		66	nonblocking operation (again, sockets, pipes etc.) is very inefficient
		67	or might not work (aio_read fails on sockets/pipes/fifos). Use an event
		68	loop for that (such as the Event module): IO::AIO will naturally fit
		69	into such an event loop itself.
52		70
53	In this version, a number of threads are started that execute your	71	In this version, a number of threads are started that execute your
54	requests and signal their completion. You don't need thread support in	72	requests and signal their completion. You don't need thread support in
55	perl, and the threads created by this module will not be visible to	73	perl, and the threads created by this module will not be visible to
56	perl. In the future, this module might make use of the native aio	74	perl. In the future, this module might make use of the native aio
57	functions available on many operating systems. However, they are often	75	functions available on many operating systems. However, they are often
58	not well-supported or restricted (Linux doesn't allow them on normal	76	not well-supported or restricted (GNU/Linux doesn't allow them on normal
59	files currently, for example), and they would only support aio_read and	77	files currently, for example), and they would only support aio_read and
60	aio_write, so the remaining functionality would have to be implemented	78	aio_write, so the remaining functionality would have to be implemented
61	using threads anyway.	79	using threads anyway.
62		80
63	Although the module will work with in the presence of other (Perl-)	81	Although the module will work with in the presence of other (Perl-)
64	threads, it is currently not reentrant in any way, so use appropriate	82	threads, it is currently not reentrant in any way, so use appropriate
65	locking yourself, always call "poll_cb" from within the same thread, or	83	locking yourself, always call "poll_cb" from within the same thread, or
66	never call "poll_cb" (or other "aio_" functions) recursively.	84	never call "poll_cb" (or other "aio_" functions) recursively.
		85
		86	EXAMPLE
		87	This is a simple example that uses the Event module and loads
		88	/etc/passwd asynchronously:
		89
		90	use Fcntl;
		91	use Event;
		92	use IO::AIO;
		93
		94	# register the IO::AIO callback with Event
		95	Event->io (fd => IO::AIO::poll_fileno,
		96	poll => 'r',
		97	cb => \&IO::AIO::poll_cb);
		98
		99	# queue the request to open /etc/passwd
		100	aio_open "/etc/passwd", O_RDONLY, 0, sub {
		101	my $fh = shift
		102	or die "error while opening: $!";
		103
		104	# stat'ing filehandles is generally non-blocking
		105	my $size = -s $fh;
		106
		107	# queue a request to read the file
		108	my $contents;
		109	aio_read $fh, 0, $size, $contents, 0, sub {
		110	$_[0] == $size
		111	or die "short read: $!";
		112
		113	close $fh;
		114
		115	# file contents now in $contents
		116	print $contents;
		117
		118	# exit event loop and program
		119	Event::unloop;
		120	};
		121	};
		122
		123	# possibly queue up other requests, or open GUI windows,
		124	# check for sockets etc. etc.
		125
		126	# process events as long as there are some:
		127	Event::loop;
67		128
68	REQUEST ANATOMY AND LIFETIME	129	REQUEST ANATOMY AND LIFETIME
69	Every "aio_*" function creates a request. which is a C data structure	130	Every "aio_*" function creates a request. which is a C data structure
70	not directly visible to Perl.	131	not directly visible to Perl.
71		132
…		…
107	anymore (except possibly for the Perl object, but its connection to	168	anymore (except possibly for the Perl object, but its connection to
108	the actual aio request is severed and calling its methods will	169	the actual aio request is severed and calling its methods will
109	either do nothing or result in a runtime error).	170	either do nothing or result in a runtime error).
110		171
111	FUNCTIONS	172	FUNCTIONS
112	AIO FUNCTIONS	173	AIO REQUEST FUNCTIONS
113	All the "aio_*" calls are more or less thin wrappers around the	174	All the "aio_*" calls are more or less thin wrappers around the syscall
114	syscall with the same name (sans "aio_"). The arguments are similar	175	with the same name (sans "aio_"). The arguments are similar or
115	or identical, and they all accept an additional (and optional)	176	identical, and they all accept an additional (and optional) $callback
116	$callback argument which must be a code reference. This code	177	argument which must be a code reference. This code reference will get
117	reference will get called with the syscall return code (e.g. most	178	called with the syscall return code (e.g. most syscalls return -1 on
118	syscalls return -1 on error, unlike perl, which usually delivers	179	error, unlike perl, which usually delivers "false") as it's sole
119	"false") as it's sole argument when the given syscall has been	180	argument when the given syscall has been executed asynchronously.
120	executed asynchronously.
121		181
122	All functions expecting a filehandle keep a copy of the filehandle	182	All functions expecting a filehandle keep a copy of the filehandle
123	internally until the request has finished.	183	internally until the request has finished.
124		184
125	All requests return objects of type IO::AIO::REQ that allow further	185	All functions return request objects of type IO::AIO::REQ that allow
126	manipulation of those requests while they are in-flight.	186	further manipulation of those requests while they are in-flight.
127		187
128	The pathnames you pass to these routines *must* be absolute and	188	The pathnames you pass to these routines *must* be absolute and encoded
129	encoded in byte form. The reason for the former is that at the time	189	as octets. The reason for the former is that at the time the request is
130	the request is being executed, the current working directory could	190	being executed, the current working directory could have changed.
131	have changed. Alternatively, you can make sure that you never change	191	Alternatively, you can make sure that you never change the current
132	the current working directory.	192	working directory anywhere in the program and then use relative paths.
133		193
134	To encode pathnames to byte form, either make sure you either: a)	194	To encode pathnames as octets, either make sure you either: a) always
135	always pass in filenames you got from outside (command line, readdir	195	pass in filenames you got from outside (command line, readdir etc.)
136	etc.), b) are ASCII or ISO 8859-1, c) use the Encode module and	196	without tinkering, b) are ASCII or ISO 8859-1, c) use the Encode module
137	encode your pathnames to the locale (or other) encoding in effect in	197	and encode your pathnames to the locale (or other) encoding in effect in
138	the user environment, d) use Glib::filename_from_unicode on unicode	198	the user environment, d) use Glib::filename_from_unicode on unicode
139	filenames or e) use something else.	199	filenames or e) use something else to ensure your scalar has the correct
		200	contents.
140		201
		202	This works, btw. independent of the internal UTF-8 bit, which IO::AIO
		203	handles correctly wether it is set or not.
		204
141	$prev_pri = aioreq_pri [$pri]	205	$prev_pri = aioreq_pri [$pri]
142	Returns the priority value that would be used for the next	206	Returns the priority value that would be used for the next request
143	request and, if $pri is given, sets the priority for the next	207	and, if $pri is given, sets the priority for the next aio request.
144	aio request.
145		208
146	The default priority is 0, the minimum and maximum priorities	209	The default priority is 0, the minimum and maximum priorities are -4
147	are -4 and 4, respectively. Requests with higher priority will	210	and 4, respectively. Requests with higher priority will be serviced
148	be serviced first.	211	first.
149		212
150	The priority will be reset to 0 after each call to one of the	213	The priority will be reset to 0 after each call to one of the
151	"aio_*" functions.	214	"aio_*" functions.
152		215
153	Example: open a file with low priority, then read something from	216	Example: open a file with low priority, then read something from it
154	it with higher priority so the read request is serviced before	217	with higher priority so the read request is serviced before other
155	other low priority open requests (potentially spamming the	218	low priority open requests (potentially spamming the cache):
156	cache):
157		219
		220	aioreq_pri -3;
		221	aio_open ..., sub {
		222	return unless $_[0];
		223
158	aioreq_pri -3;	224	aioreq_pri -2;
159	aio_open ..., sub {
160	return unless $_[0];
161
162	aioreq_pri -2;
163	aio_read $_[0], ..., sub {	225	aio_read $_[0], ..., sub {
164	...
165	};
166	};
167
168	aioreq_nice $pri_adjust
169	Similar to "aioreq_pri", but subtracts the given value from the
170	current priority, so effects are cumulative.
171
172	aio_open $pathname, $flags, $mode, $callback->($fh)
173	Asynchronously open or create a file and call the callback with
174	a newly created filehandle for the file.
175
176	The pathname passed to "aio_open" must be absolute. See API
177	NOTES, above, for an explanation.
178
179	The $flags argument is a bitmask. See the "Fcntl" module for a
180	list. They are the same as used by "sysopen".
181
182	Likewise, $mode specifies the mode of the newly created file, if
183	it didn't exist and "O_CREAT" has been given, just like perl's
184	"sysopen", except that it is mandatory (i.e. use 0 if you don't
185	create new files, and 0666 or 0777 if you do).
186
187	Example:
188
189	aio_open "/etc/passwd", O_RDONLY, 0, sub {
190	if ($_[0]) {
191	print "open successful, fh is $_[0]\n";
192	...
193	} else {
194	die "open failed: $!\n";
195	}
196	};
197
198	aio_close $fh, $callback->($status)
199	Asynchronously close a file and call the callback with the
200	result code. *WARNING:* although accepted, you should not pass
201	in a perl filehandle here, as perl will likely close the file
202	descriptor another time when the filehandle is destroyed.
203	Normally, you can safely call perls "close" or just let
204	filehandles go out of scope.
205
206	This is supposed to be a bug in the API, so that might change.
207	It's therefore best to avoid this function.
208
209	aio_read $fh,$offset,$length, $data,$dataoffset,
210	$callback->($retval)
211	aio_write $fh,$offset,$length, $data,$dataoffset,
212	$callback->($retval)
213	Reads or writes "length" bytes from the specified "fh" and
214	"offset" into the scalar given by "data" and offset "dataoffset"
215	and calls the callback without the actual number of bytes read
216	(or -1 on error, just like the syscall).
217
218	The $data scalar *MUST NOT* be modified in any way while the
219	request is outstanding. Modifying it can result in segfaults or
220	WW3 (if the necessary/optional hardware is installed).
221
222	Example: Read 15 bytes at offset 7 into scalar $buffer, starting
223	at offset 0 within the scalar:
224
225	aio_read $fh, 7, 15, $buffer, 0, sub {
226	$_[0] > 0 or die "read error: $!";
227	print "read $_[0] bytes: <$buffer>\n";
228	};
229
230	aio_move $srcpath, $dstpath, $callback->($status)
231	Try to move the *file* (directories not supported as either
232	source or destination) from $srcpath to $dstpath and call the
233	callback with the 0 (error) or -1 ok.
234
235	This is a composite request that tries to rename(2) the file
236	first. If rename files with "EXDEV", it creates the destination
237	file with mode 0200 and copies the contents of the source file
238	into it using "aio_sendfile", followed by restoring atime,
239	mtime, access mode and uid/gid, in that order, and unlinking the
240	$srcpath.
241
242	If an error occurs, the partial destination file will be
243	unlinked, if possible, except when setting atime, mtime, access
244	mode and uid/gid, where errors are being ignored.
245
246	aio_sendfile $out_fh, $in_fh, $in_offset, $length,
247	$callback->($retval)
248	Tries to copy $length bytes from $in_fh to $out_fh. It starts
249	reading at byte offset $in_offset, and starts writing at the
250	current file offset of $out_fh. Because of that, it is not safe
251	to issue more than one "aio_sendfile" per $out_fh, as they will
252	interfere with each other.
253
254	This call tries to make use of a native "sendfile" syscall to
255	provide zero-copy operation. For this to work, $out_fh should
256	refer to a socket, and $in_fh should refer to mmap'able file.
257
258	If the native sendfile call fails or is not implemented, it will
259	be emulated, so you can call "aio_sendfile" on any type of
260	filehandle regardless of the limitations of the operating
261	system.
262
263	Please note, however, that "aio_sendfile" can read more bytes
264	from $in_fh than are written, and there is no way to find out
265	how many bytes have been read from "aio_sendfile" alone, as
266	"aio_sendfile" only provides the number of bytes written to
267	$out_fh. Only if the result value equals $length one can assume
268	that $length bytes have been read.
269
270	aio_readahead $fh,$offset,$length, $callback->($retval)
271	"aio_readahead" populates the page cache with data from a file
272	so that subsequent reads from that file will not block on disk
273	I/O. The $offset argument specifies the starting point from
274	which data is to be read and $length specifies the number of
275	bytes to be read. I/O is performed in whole pages, so that
276	offset is effectively rounded down to a page boundary and bytes
277	are read up to the next page boundary greater than or equal to
278	(off-set+length). "aio_readahead" does not read beyond the end
279	of the file. The current file offset of the file is left
280	unchanged.
281
282	If that syscall doesn't exist (likely if your OS isn't Linux) it
283	will be emulated by simply reading the data, which would have a
284	similar effect.
285
286	aio_stat $fh_or_path, $callback->($status)
287	aio_lstat $fh, $callback->($status)
288	Works like perl's "stat" or "lstat" in void context. The
289	callback will be called after the stat and the results will be
290	available using "stat _" or "-s _" etc...
291
292	The pathname passed to "aio_stat" must be absolute. See API
293	NOTES, above, for an explanation.
294
295	Currently, the stats are always 64-bit-stats, i.e. instead of
296	returning an error when stat'ing a large file, the results will
297	be silently truncated unless perl itself is compiled with large
298	file support.
299
300	Example: Print the length of /etc/passwd:
301
302	aio_stat "/etc/passwd", sub {
303	$_[0] and die "stat failed: $!";
304	print "size is ", -s _, "\n";
305	};
306
307	aio_unlink $pathname, $callback->($status)
308	Asynchronously unlink (delete) a file and call the callback with
309	the result code.
310
311	aio_link $srcpath, $dstpath, $callback->($status)
312	Asynchronously create a new link to the existing object at
313	$srcpath at the path $dstpath and call the callback with the
314	result code.
315
316	aio_symlink $srcpath, $dstpath, $callback->($status)
317	Asynchronously create a new symbolic link to the existing object
318	at $srcpath at the path $dstpath and call the callback with the
319	result code.
320
321	aio_rename $srcpath, $dstpath, $callback->($status)
322	Asynchronously rename the object at $srcpath to $dstpath, just
323	as rename(2) and call the callback with the result code.
324
325	aio_rmdir $pathname, $callback->($status)
326	Asynchronously rmdir (delete) a directory and call the callback
327	with the result code.
328
329	aio_readdir $pathname, $callback->($entries)
330	Unlike the POSIX call of the same name, "aio_readdir" reads an
331	entire directory (i.e. opendir + readdir + closedir). The
332	entries will not be sorted, and will NOT include the "." and
333	".." entries.
334
335	The callback a single argument which is either "undef" or an
336	array-ref with the filenames.
337
338	aio_scandir $path, $maxreq, $callback->($dirs, $nondirs)
339	Scans a directory (similar to "aio_readdir") but additionally
340	tries to efficiently separate the entries of directory $path
341	into two sets of names, directories you can recurse into
342	(directories), and ones you cannot recurse into (everything
343	else, including symlinks to directories).
344
345	"aio_scandir" is a composite request that creates of many sub
346	requests_ $maxreq specifies the maximum number of outstanding
347	aio requests that this function generates. If it is "<= 0", then
348	a suitable default will be chosen (currently 6).
349
350	On error, the callback is called without arguments, otherwise it
351	receives two array-refs with path-relative entry names.
352
353	Example:
354
355	aio_scandir $dir, 0, sub {
356	my ($dirs, $nondirs) = @_;
357	print "real directories: @$dirs\n";
358	print "everything else: @$nondirs\n";
359	};
360
361	Implementation notes.
362
363	The "aio_readdir" cannot be avoided, but "stat()"'ing every
364	entry can.
365
366	After reading the directory, the modification time, size etc. of
367	the directory before and after the readdir is checked, and if
368	they match (and isn't the current time), the link count will be
369	used to decide how many entries are directories (if >= 2).
370	Otherwise, no knowledge of the number of subdirectories will be
371	assumed.
372
373	Then entries will be sorted into likely directories (everything
374	without a non-initial dot currently) and likely non-directories
375	(everything else). Then every entry plus an appended "/." will
376	be "stat"'ed, likely directories first. If that succeeds, it
377	assumes that the entry is a directory or a symlink to directory
378	(which will be checked seperately). This is often faster than
379	stat'ing the entry itself because filesystems might detect the
380	type of the entry without reading the inode data (e.g. ext2fs
381	filetype feature).
382
383	If the known number of directories (link count - 2) has been
384	reached, the rest of the entries is assumed to be
385	non-directories.
386
387	This only works with certainty on POSIX (= UNIX) filesystems,
388	which fortunately are the vast majority of filesystems around.
389
390	It will also likely work on non-POSIX filesystems with reduced
391	efficiency as those tend to return 0 or 1 as link counts, which
392	disables the directory counting heuristic.
393
394	aio_fsync $fh, $callback->($status)
395	Asynchronously call fsync on the given filehandle and call the
396	callback with the fsync result code.
397
398	aio_fdatasync $fh, $callback->($status)
399	Asynchronously call fdatasync on the given filehandle and call
400	the callback with the fdatasync result code.
401
402	If this call isn't available because your OS lacks it or it
403	couldn't be detected, it will be emulated by calling "fsync"
404	instead.
405
406	aio_group $callback->(...)
407	This is a very special aio request: Instead of doing something,
408	it is a container for other aio requests, which is useful if you
409	want to bundle many requests into a single, composite, request
410	with a definite callback and the ability to cancel the whole
411	request with its subrequests.
412
413	Returns an object of class IO::AIO::GRP. See its documentation
414	below for more info.
415
416	Example:
417
418	my $grp = aio_group sub {
419	print "all stats done\n";
420	};
421
422	add $grp
423	(aio_stat ...),
424	(aio_stat ...),
425	...;	226	...
426
427	aio_nop $callback->()
428	This is a special request - it does nothing in itself and is
429	only used for side effects, such as when you want to add a dummy
430	request to a group so that finishing the requests in the group
431	depends on executing the given code.
432
433	While this request does nothing, it still goes through the
434	execution phase and still requires a worker thread. Thus, the
435	callback will not be executed immediately but only after other
436	requests in the queue have entered their execution phase. This
437	can be used to measure request latency.
438
439	IO::AIO::aio_busy $fractional_seconds, $callback->() *NOT EXPORTED*
440	Mainly used for debugging and benchmarking, this aio request
441	puts one of the request workers to sleep for the given time.
442
443	While it is theoretically handy to have simple I/O scheduling
444	requests like sleep and file handle readable/writable, the
445	overhead this creates is immense (it blocks a thread for a long
446	time) so do not use this function except to put your application
447	under artificial I/O pressure.
448
449	IO::AIO::REQ CLASS
450	All non-aggregate "aio_*" functions return an object of this class
451	when called in non-void context.
452
453	cancel $req
454	Cancels the request, if possible. Has the effect of skipping
455	execution when entering the execute state and skipping calling
456	the callback when entering the the result state, but will leave
457	the request otherwise untouched. That means that requests that
458	currently execute will not be stopped and resources held by the
459	request will not be freed prematurely.
460
461	cb $req $callback->(...)
462	Replace (or simply set) the callback registered to the request.
463
464	IO::AIO::GRP CLASS
465	This class is a subclass of IO::AIO::REQ, so all its methods apply
466	to objects of this class, too.
467
468	A IO::AIO::GRP object is a special request that can contain multiple
469	other aio requests.
470
471	You create one by calling the "aio_group" constructing function with
472	a callback that will be called when all contained requests have
473	entered the "done" state:
474
475	my $grp = aio_group sub {
476	print "all requests are done\n";
477	};
478
479	You add requests by calling the "add" method with one or more
480	"IO::AIO::REQ" objects:
481
482	$grp->add (aio_unlink "...");
483
484	add $grp aio_stat "...", sub {
485	$_[0] or return $grp->result ("error");
486
487	# add another request dynamically, if first succeeded
488	add $grp aio_open "...", sub {
489	$grp->result ("ok");
490	};	227	};
491	};	228	};
492		229
		230	aioreq_nice $pri_adjust
		231	Similar to "aioreq_pri", but subtracts the given value from the
		232	current priority, so the effect is cumulative.
		233
		234	aio_open $pathname, $flags, $mode, $callback->($fh)
		235	Asynchronously open or create a file and call the callback with a
		236	newly created filehandle for the file.
		237
		238	The pathname passed to "aio_open" must be absolute. See API NOTES,
		239	above, for an explanation.
		240
		241	The $flags argument is a bitmask. See the "Fcntl" module for a list.
		242	They are the same as used by "sysopen".
		243
		244	Likewise, $mode specifies the mode of the newly created file, if it
		245	didn't exist and "O_CREAT" has been given, just like perl's
		246	"sysopen", except that it is mandatory (i.e. use 0 if you don't
		247	create new files, and 0666 or 0777 if you do). Note that the $mode
		248	will be modified by the umask in effect then the request is being
		249	executed, so better never change the umask.
		250
		251	Example:
		252
		253	aio_open "/etc/passwd", O_RDONLY, 0, sub {
		254	if ($_[0]) {
		255	print "open successful, fh is $_[0]\n";
		256	...
		257	} else {
		258	die "open failed: $!\n";
		259	}
		260	};
		261
		262	aio_close $fh, $callback->($status)
		263	Asynchronously close a file and call the callback with the result
		264	code. *WARNING:* although accepted, you should not pass in a perl
		265	filehandle here, as perl will likely close the file descriptor
		266	another time when the filehandle is destroyed. Normally, you can
		267	safely call perls "close" or just let filehandles go out of scope.
		268
		269	This is supposed to be a bug in the API, so that might change. It's
		270	therefore best to avoid this function.
		271
		272	aio_read $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
		273	aio_write $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
		274	Reads or writes "length" bytes from the specified "fh" and "offset"
		275	into the scalar given by "data" and offset "dataoffset" and calls
		276	the callback without the actual number of bytes read (or -1 on
		277	error, just like the syscall).
		278
		279	The $data scalar *MUST NOT* be modified in any way while the request
		280	is outstanding. Modifying it can result in segfaults or WW3 (if the
		281	necessary/optional hardware is installed).
		282
		283	Example: Read 15 bytes at offset 7 into scalar $buffer, starting at
		284	offset 0 within the scalar:
		285
		286	aio_read $fh, 7, 15, $buffer, 0, sub {
		287	$_[0] > 0 or die "read error: $!";
		288	print "read $_[0] bytes: <$buffer>\n";
		289	};
		290
		291	aio_sendfile $out_fh, $in_fh, $in_offset, $length, $callback->($retval)
		292	Tries to copy $length bytes from $in_fh to $out_fh. It starts
		293	reading at byte offset $in_offset, and starts writing at the current
		294	file offset of $out_fh. Because of that, it is not safe to issue
		295	more than one "aio_sendfile" per $out_fh, as they will interfere
		296	with each other.
		297
		298	This call tries to make use of a native "sendfile" syscall to
		299	provide zero-copy operation. For this to work, $out_fh should refer
		300	to a socket, and $in_fh should refer to mmap'able file.
		301
		302	If the native sendfile call fails or is not implemented, it will be
		303	emulated, so you can call "aio_sendfile" on any type of filehandle
		304	regardless of the limitations of the operating system.
		305
		306	Please note, however, that "aio_sendfile" can read more bytes from
		307	$in_fh than are written, and there is no way to find out how many
		308	bytes have been read from "aio_sendfile" alone, as "aio_sendfile"
		309	only provides the number of bytes written to $out_fh. Only if the
		310	result value equals $length one can assume that $length bytes have
		311	been read.
		312
		313	aio_readahead $fh,$offset,$length, $callback->($retval)
		314	"aio_readahead" populates the page cache with data from a file so
		315	that subsequent reads from that file will not block on disk I/O. The
		316	$offset argument specifies the starting point from which data is to
		317	be read and $length specifies the number of bytes to be read. I/O is
		318	performed in whole pages, so that offset is effectively rounded down
		319	to a page boundary and bytes are read up to the next page boundary
		320	greater than or equal to (off-set+length). "aio_readahead" does not
		321	read beyond the end of the file. The current file offset of the file
		322	is left unchanged.
		323
		324	If that syscall doesn't exist (likely if your OS isn't Linux) it
		325	will be emulated by simply reading the data, which would have a
		326	similar effect.
		327
		328	aio_stat $fh_or_path, $callback->($status)
		329	aio_lstat $fh, $callback->($status)
		330	Works like perl's "stat" or "lstat" in void context. The callback
		331	will be called after the stat and the results will be available
		332	using "stat _" or "-s _" etc...
		333
		334	The pathname passed to "aio_stat" must be absolute. See API NOTES,
		335	above, for an explanation.
		336
		337	Currently, the stats are always 64-bit-stats, i.e. instead of
		338	returning an error when stat'ing a large file, the results will be
		339	silently truncated unless perl itself is compiled with large file
		340	support.
		341
		342	Example: Print the length of /etc/passwd:
		343
		344	aio_stat "/etc/passwd", sub {
		345	$_[0] and die "stat failed: $!";
		346	print "size is ", -s _, "\n";
		347	};
		348
		349	aio_unlink $pathname, $callback->($status)
		350	Asynchronously unlink (delete) a file and call the callback with the
		351	result code.
		352
		353	aio_mknod $path, $mode, $dev, $callback->($status)
		354	[EXPERIMENTAL]
		355
		356	Asynchronously create a device node (or fifo). See mknod(2).
		357
		358	The only (POSIX-) portable way of calling this function is:
		359
		360	aio_mknod $path, IO::AIO::S_IFIFO | $mode, 0, sub { ...
		361
		362	aio_link $srcpath, $dstpath, $callback->($status)
		363	Asynchronously create a new link to the existing object at $srcpath
		364	at the path $dstpath and call the callback with the result code.
		365
		366	aio_symlink $srcpath, $dstpath, $callback->($status)
		367	Asynchronously create a new symbolic link to the existing object at
		368	$srcpath at the path $dstpath and call the callback with the result
		369	code.
		370
		371	aio_readlink $path, $callback->($link)
		372	Asynchronously read the symlink specified by $path and pass it to
		373	the callback. If an error occurs, nothing or undef gets passed to
		374	the callback.
		375
		376	aio_rename $srcpath, $dstpath, $callback->($status)
		377	Asynchronously rename the object at $srcpath to $dstpath, just as
		378	rename(2) and call the callback with the result code.
		379
		380	aio_mkdir $pathname, $mode, $callback->($status)
		381	Asynchronously mkdir (create) a directory and call the callback with
		382	the result code. $mode will be modified by the umask at the time the
		383	request is executed, so do not change your umask.
		384
		385	aio_rmdir $pathname, $callback->($status)
		386	Asynchronously rmdir (delete) a directory and call the callback with
		387	the result code.
		388
		389	aio_readdir $pathname, $callback->($entries)
		390	Unlike the POSIX call of the same name, "aio_readdir" reads an
		391	entire directory (i.e. opendir + readdir + closedir). The entries
		392	will not be sorted, and will NOT include the "." and ".." entries.
		393
		394	The callback a single argument which is either "undef" or an
		395	array-ref with the filenames.
		396
		397	aio_load $path, $data, $callback->($status)
		398	This is a composite request that tries to fully load the given file
		399	into memory. Status is the same as with aio_read.
		400
		401	aio_copy $srcpath, $dstpath, $callback->($status)
		402	Try to copy the *file* (directories not supported as either source
		403	or destination) from $srcpath to $dstpath and call the callback with
		404	the 0 (error) or -1 ok.
		405
		406	This is a composite request that it creates the destination file
		407	with mode 0200 and copies the contents of the source file into it
		408	using "aio_sendfile", followed by restoring atime, mtime, access
		409	mode and uid/gid, in that order.
		410
		411	If an error occurs, the partial destination file will be unlinked,
		412	if possible, except when setting atime, mtime, access mode and
		413	uid/gid, where errors are being ignored.
		414
		415	aio_move $srcpath, $dstpath, $callback->($status)
		416	Try to move the *file* (directories not supported as either source
		417	or destination) from $srcpath to $dstpath and call the callback with
		418	the 0 (error) or -1 ok.
		419
		420	This is a composite request that tries to rename(2) the file first.
		421	If rename files with "EXDEV", it copies the file with "aio_copy"
		422	and, if that is successful, unlinking the $srcpath.
		423
		424	aio_scandir $path, $maxreq, $callback->($dirs, $nondirs)
		425	Scans a directory (similar to "aio_readdir") but additionally tries
		426	to efficiently separate the entries of directory $path into two sets
		427	of names, directories you can recurse into (directories), and ones
		428	you cannot recurse into (everything else, including symlinks to
		429	directories).
		430
		431	"aio_scandir" is a composite request that creates of many sub
		432	requests_ $maxreq specifies the maximum number of outstanding aio
		433	requests that this function generates. If it is "<= 0", then a
		434	suitable default will be chosen (currently 4).
		435
		436	On error, the callback is called without arguments, otherwise it
		437	receives two array-refs with path-relative entry names.
		438
		439	Example:
		440
		441	aio_scandir $dir, 0, sub {
		442	my ($dirs, $nondirs) = @_;
		443	print "real directories: @$dirs\n";
		444	print "everything else: @$nondirs\n";
		445	};
		446
		447	Implementation notes.
		448
		449	The "aio_readdir" cannot be avoided, but "stat()"'ing every entry
		450	can.
		451
		452	After reading the directory, the modification time, size etc. of the
		453	directory before and after the readdir is checked, and if they match
		454	(and isn't the current time), the link count will be used to decide
		455	how many entries are directories (if >= 2). Otherwise, no knowledge
		456	of the number of subdirectories will be assumed.
		457
		458	Then entries will be sorted into likely directories (everything
		459	without a non-initial dot currently) and likely non-directories
		460	(everything else). Then every entry plus an appended "/." will be
		461	"stat"'ed, likely directories first. If that succeeds, it assumes
		462	that the entry is a directory or a symlink to directory (which will
		463	be checked seperately). This is often faster than stat'ing the entry
		464	itself because filesystems might detect the type of the entry
		465	without reading the inode data (e.g. ext2fs filetype feature).
		466
		467	If the known number of directories (link count - 2) has been
		468	reached, the rest of the entries is assumed to be non-directories.
		469
		470	This only works with certainty on POSIX (= UNIX) filesystems, which
		471	fortunately are the vast majority of filesystems around.
		472
		473	It will also likely work on non-POSIX filesystems with reduced
		474	efficiency as those tend to return 0 or 1 as link counts, which
		475	disables the directory counting heuristic.
		476
		477	aio_rmtree $path, $callback->($status)
		478	Delete a directory tree starting (and including) $path, return the
		479	status of the final "rmdir" only. This is a composite request that
		480	uses "aio_scandir" to recurse into and rmdir directories, and unlink
		481	everything else.
		482
		483	aio_fsync $fh, $callback->($status)
		484	Asynchronously call fsync on the given filehandle and call the
		485	callback with the fsync result code.
		486
		487	aio_fdatasync $fh, $callback->($status)
		488	Asynchronously call fdatasync on the given filehandle and call the
		489	callback with the fdatasync result code.
		490
		491	If this call isn't available because your OS lacks it or it couldn't
		492	be detected, it will be emulated by calling "fsync" instead.
		493
		494	aio_group $callback->(...)
		495	This is a very special aio request: Instead of doing something, it
		496	is a container for other aio requests, which is useful if you want
		497	to bundle many requests into a single, composite, request with a
		498	definite callback and the ability to cancel the whole request with
		499	its subrequests.
		500
		501	Returns an object of class IO::AIO::GRP. See its documentation below
		502	for more info.
		503
		504	Example:
		505
		506	my $grp = aio_group sub {
		507	print "all stats done\n";
		508	};
		509
		510	add $grp
		511	(aio_stat ...),
		512	(aio_stat ...),
		513	...;
		514
		515	aio_nop $callback->()
		516	This is a special request - it does nothing in itself and is only
		517	used for side effects, such as when you want to add a dummy request
		518	to a group so that finishing the requests in the group depends on
		519	executing the given code.
		520
		521	While this request does nothing, it still goes through the execution
		522	phase and still requires a worker thread. Thus, the callback will
		523	not be executed immediately but only after other requests in the
		524	queue have entered their execution phase. This can be used to
		525	measure request latency.
		526
		527	IO::AIO::aio_busy $fractional_seconds, $callback->() *NOT EXPORTED*
		528	Mainly used for debugging and benchmarking, this aio request puts
		529	one of the request workers to sleep for the given time.
		530
		531	While it is theoretically handy to have simple I/O scheduling
		532	requests like sleep and file handle readable/writable, the overhead
		533	this creates is immense (it blocks a thread for a long time) so do
		534	not use this function except to put your application under
		535	artificial I/O pressure.
		536
		537	IO::AIO::REQ CLASS
		538	All non-aggregate "aio_*" functions return an object of this class when
		539	called in non-void context.
		540
		541	cancel $req
		542	Cancels the request, if possible. Has the effect of skipping
		543	execution when entering the execute state and skipping calling the
		544	callback when entering the the result state, but will leave the
		545	request otherwise untouched. That means that requests that currently
		546	execute will not be stopped and resources held by the request will
		547	not be freed prematurely.
		548
		549	cb $req $callback->(...)
		550	Replace (or simply set) the callback registered to the request.
		551
		552	IO::AIO::GRP CLASS
		553	This class is a subclass of IO::AIO::REQ, so all its methods apply to
		554	objects of this class, too.
		555
		556	A IO::AIO::GRP object is a special request that can contain multiple
		557	other aio requests.
		558
		559	You create one by calling the "aio_group" constructing function with a
		560	callback that will be called when all contained requests have entered
		561	the "done" state:
		562
		563	my $grp = aio_group sub {
		564	print "all requests are done\n";
		565	};
		566
		567	You add requests by calling the "add" method with one or more
		568	"IO::AIO::REQ" objects:
		569
		570	$grp->add (aio_unlink "...");
		571
		572	add $grp aio_stat "...", sub {
		573	$_[0] or return $grp->result ("error");
		574
		575	# add another request dynamically, if first succeeded
		576	add $grp aio_open "...", sub {
		577	$grp->result ("ok");
		578	};
		579	};
		580
493	This makes it very easy to create composite requests (see the source	581	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	582	"aio_move" for an application) that work and feel like simple requests.
		583
		584	* The IO::AIO::GRP objects will be cleaned up during calls to
		585	"IO::AIO::poll_cb", just like any other request.
		586	* They can be canceled like any other request. Canceling will cancel not
		587	only the request itself, but also all requests it contains.
		588	* They can also can also be added to other IO::AIO::GRP objects.
		589	* You must not add requests to a group from within the group callback
		590	(or any later time).
		591
		592	Their lifetime, simplified, looks like this: when they are empty, they
		593	will finish very quickly. If they contain only requests that are in the
		594	"done" state, they will also finish. Otherwise they will continue to
		595	exist.
		596
		597	That means after creating a group you have some time to add requests.
		598	And in the callbacks of those requests, you can add further requests to
		599	the group. And only when all those requests have finished will the the
		600	group itself finish.
		601
		602	add $grp ...
		603	$grp->add (...)
		604	Add one or more requests to the group. Any type of IO::AIO::REQ can
		605	be added, including other groups, as long as you do not create
		606	circular dependencies.
		607
		608	Returns all its arguments.
		609
		610	$grp->cancel_subs
		611	Cancel all subrequests and clears any feeder, but not the group
		612	request itself. Useful when you queued a lot of events but got a
		613	result early.
		614
		615	$grp->result (...)
		616	Set the result value(s) that will be passed to the group callback
		617	when all subrequests have finished and set thre groups errno to the
		618	current value of errno (just like calling "errno" without an error
		619	number). By default, no argument will be passed and errno is zero.
		620
		621	$grp->errno ([$errno])
		622	Sets the group errno value to $errno, or the current value of errno
		623	when the argument is missing.
		624
		625	Every aio request has an associated errno value that is restored
		626	when the callback is invoked. This method lets you change this value
		627	from its default (0).
		628
		629	Calling "result" will also set errno, so make sure you either set $!
		630	before the call to "result", or call c<errno> after it.
		631
		632	feed $grp $callback->($grp)
		633	Sets a feeder/generator on this group: every group can have an
		634	attached generator that generates requests if idle. The idea behind
		635	this is that, although you could just queue as many requests as you
		636	want in a group, this might starve other requests for a potentially
		637	long time. For example, "aio_scandir" might generate hundreds of
		638	thousands "aio_stat" requests, delaying any later requests for a
		639	long time.
		640
		641	To avoid this, and allow incremental generation of requests, you can
		642	instead a group and set a feeder on it that generates those
		643	requests. The feed callback will be called whenever there are few
		644	enough (see "limit", below) requests active in the group itself and
		645	is expected to queue more requests.
		646
		647	The feed callback can queue as many requests as it likes (i.e. "add"
		648	does not impose any limits).
		649
		650	If the feed does not queue more requests when called, it will be
		651	automatically removed from the group.
		652
		653	If the feed limit is 0, it will be set to 2 automatically.
		654
		655	Example:
		656
		657	# stat all files in @files, but only ever use four aio requests concurrently:
		658
		659	my $grp = aio_group sub { print "finished\n" };
		660	limit $grp 4;
		661	feed $grp sub {
		662	my $file = pop @files
		663	or return;
		664
		665	add $grp aio_stat $file, sub { ... };
		666	};
		667
		668	limit $grp $num
		669	Sets the feeder limit for the group: The feeder will be called
		670	whenever the group contains less than this many requests.
		671
		672	Setting the limit to 0 will pause the feeding process.
		673
		674	SUPPORT FUNCTIONS
		675	EVENT PROCESSING AND EVENT LOOP INTEGRATION
		676	$fileno = IO::AIO::poll_fileno
		677	Return the *request result pipe file descriptor*. This filehandle
		678	must be polled for reading by some mechanism outside this module
		679	(e.g. Event or select, see below or the SYNOPSIS). If the pipe
		680	becomes readable you have to call "poll_cb" to check the results.
		681
		682	See "poll_cb" for an example.
		683
		684	IO::AIO::poll_cb
		685	Process some outstanding events on the result pipe. You have to call
		686	this regularly. Returns the number of events processed. Returns
		687	immediately when no events are outstanding. The amount of events
		688	processed depends on the settings of "IO::AIO::max_poll_req" and
		689	"IO::AIO::max_poll_time".
		690
		691	If not all requests were processed for whatever reason, the
		692	filehandle will still be ready when "poll_cb" returns.
		693
		694	Example: Install an Event watcher that automatically calls
		695	IO::AIO::poll_cb with high priority:
		696
		697	Event->io (fd => IO::AIO::poll_fileno,
		698	poll => 'r', async => 1,
		699	cb => \&IO::AIO::poll_cb);
		700
		701	IO::AIO::max_poll_reqs $nreqs
		702	IO::AIO::max_poll_time $seconds
		703	These set the maximum number of requests (default 0, meaning
		704	infinity) that are being processed by "IO::AIO::poll_cb" in one
		705	call, respectively the maximum amount of time (default 0, meaning
		706	infinity) spent in "IO::AIO::poll_cb" to process requests (more
		707	correctly the mininum amount of time "poll_cb" is allowed to use).
		708
		709	Setting "max_poll_time" to a non-zero value creates an overhead of
		710	one syscall per request processed, which is not normally a problem
		711	unless your callbacks are really really fast or your OS is really
		712	really slow (I am not mentioning Solaris here). Using
		713	"max_poll_reqs" incurs no overhead.
		714
		715	Setting these is useful if you want to ensure some level of
		716	interactiveness when perl is not fast enough to process all requests
		717	in time.
		718
		719	For interactive programs, values such as 0.01 to 0.1 should be fine.
		720
		721	Example: Install an Event watcher that automatically calls
		722	IO::AIO::poll_cb with low priority, to ensure that other parts of
		723	the program get the CPU sometimes even under high AIO load.
		724
		725	# try not to spend much more than 0.1s in poll_cb
		726	IO::AIO::max_poll_time 0.1;
		727
		728	# use a low priority so other tasks have priority
		729	Event->io (fd => IO::AIO::poll_fileno,
		730	poll => 'r', nice => 1,
		731	cb => &IO::AIO::poll_cb);
		732
		733	IO::AIO::poll_wait
		734	If there are any outstanding requests and none of them in the result
		735	phase, wait till the result filehandle becomes ready for reading
		736	(simply does a "select" on the filehandle. This is useful if you
		737	want to synchronously wait for some requests to finish).
		738
		739	See "nreqs" for an example.
		740
		741	IO::AIO::poll
		742	Waits until some requests have been handled.
		743
		744	Returns the number of requests processed, but is otherwise strictly
		745	equivalent to:
		746
		747	IO::AIO::poll_wait, IO::AIO::poll_cb
		748
		749	IO::AIO::flush
		750	Wait till all outstanding AIO requests have been handled.
		751
		752	Strictly equivalent to:
		753
		754	IO::AIO::poll_wait, IO::AIO::poll_cb
		755	while IO::AIO::nreqs;
		756
		757	CONTROLLING THE NUMBER OF THREADS
		758	IO::AIO::min_parallel $nthreads
		759	Set the minimum number of AIO threads to $nthreads. The current
		760	default is 8, which means eight asynchronous operations can execute
		761	concurrently at any one time (the number of outstanding requests,
		762	however, is unlimited).
		763
		764	IO::AIO starts threads only on demand, when an AIO request is queued
		765	and no free thread exists. Please note that queueing up a hundred
		766	requests can create demand for a hundred threads, even if it turns
		767	out that everything is in the cache and could have been processed
		768	faster by a single thread.
		769
		770	It is recommended to keep the number of threads relatively low, as
		771	some Linux kernel versions will scale negatively with the number of
		772	threads (higher parallelity => MUCH higher latency). With current
		773	Linux 2.6 versions, 4-32 threads should be fine.
		774
		775	Under most circumstances you don't need to call this function, as
		776	the module selects a default that is suitable for low to moderate
		777	load.
		778
		779	IO::AIO::max_parallel $nthreads
		780	Sets the maximum number of AIO threads to $nthreads. If more than
		781	the specified number of threads are currently running, this function
		782	kills them. This function blocks until the limit is reached.
		783
		784	While $nthreads are zero, aio requests get queued but not executed
		785	until the number of threads has been increased again.
		786
		787	This module automatically runs "max_parallel 0" at program end, to
		788	ensure that all threads are killed and that there are no outstanding
495	requests.	789	requests.
496		790
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.	791	Under normal circumstances you don't need to call this function.
701		792
		793	IO::AIO::max_idle $nthreads
		794	Limit the number of threads (default: 4) that are allowed to idle
		795	(i.e., threads that did not get a request to process within 10
		796	seconds). That means if a thread becomes idle while $nthreads other
		797	threads are also idle, it will free its resources and exit.
		798
		799	This is useful when you allow a large number of threads (e.g. 100 or
		800	1000) to allow for extremely high load situations, but want to free
		801	resources under normal circumstances (1000 threads can easily
		802	consume 30MB of RAM).
		803
		804	The default is probably ok in most situations, especially if thread
		805	creation is fast. If thread creation is very slow on your system you
		806	might want to use larger values.
		807
702	$oldmaxreqs = IO::AIO::max_outstanding $maxreqs	808	$oldmaxreqs = IO::AIO::max_outstanding $maxreqs
703	This is a very bad function to use in interactive programs	809	This is a very bad function to use in interactive programs because
704	because it blocks, and a bad way to reduce concurrency because	810	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	811	inexact: Better use an "aio_group" together with a feed callback.
706	callback.
707		812
708	Sets the maximum number of outstanding requests to $nreqs. If	813	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	814	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	815	"poll_cb" (and "poll_some" and other functions calling "poll_cb")
711	"poll_cb") function will block until the limit is no longer	816	function will block until the limit is no longer exceeded.
712	exceeded.
713		817
714	The default value is very large, so there is no practical limit	818	The default value is very large, so there is no practical limit on
715	on the number of outstanding requests.	819	the number of outstanding requests.
716		820
717	You can still queue as many requests as you want. Therefore,	821	You can still queue as many requests as you want. Therefore,
718	"max_oustsanding" is mainly useful in simple scripts (with low	822	"max_oustsanding" is mainly useful in simple scripts (with low
719	values) or as a stop gap to shield against fatal memory overflow	823	values) or as a stop gap to shield against fatal memory overflow
720	(with large values).	824	(with large values).
		825
		826	STATISTICAL INFORMATION
		827	IO::AIO::nreqs
		828	Returns the number of requests currently in the ready, execute or
		829	pending states (i.e. for which their callback has not been invoked
		830	yet).
		831
		832	Example: wait till there are no outstanding requests anymore:
		833
		834	IO::AIO::poll_wait, IO::AIO::poll_cb
		835	while IO::AIO::nreqs;
		836
		837	IO::AIO::nready
		838	Returns the number of requests currently in the ready state (not yet
		839	executed).
		840
		841	IO::AIO::npending
		842	Returns the number of requests currently in the pending state
		843	(executed, but not yet processed by poll_cb).
721		844
722	FORK BEHAVIOUR	845	FORK BEHAVIOUR
723	This module should do "the right thing" when the process using it	846	This module should do "the right thing" when the process using it forks:
724	forks:
725		847
726	Before the fork, IO::AIO enters a quiescent state where no requests	848	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.	849	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	850	fork the parent simply leaves the quiescent state and continues
729	continues request/result processing, while the child frees the	851	request/result processing, while the child frees the request/result
730	request/result queue (so that the requests started before the fork	852	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	853	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	854	the parent process has been reached again.
733	again.
734		855
735	In short: the parent will, after a short pause, continue as if fork	856	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	857	not been called, while the child will act as if IO::AIO has not been
737	been used yet.	858	used yet.
738		859
739	MEMORY USAGE	860	MEMORY USAGE
740	Per-request usage:	861	Per-request usage:
741		862
742	Each aio request uses - depending on your architecture - around	863	Each aio request uses - depending on your architecture - around 100-200
743	100-200 bytes of memory. In addition, stat requests need a stat	864	bytes of memory. In addition, stat requests need a stat buffer (possibly
744	buffer (possibly a few hundred bytes), readdir requires a result	865	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	866	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	867	will consume memory till the request has entered the done state.
747	request has entered the done state.
748		868
749	This is now awfully much, so queuing lots of requests is not usually	869	This is now awfully much, so queuing lots of requests is not usually a
750	a problem.	870	problem.
751		871
752	Per-thread usage:	872	Per-thread usage:
753		873
754	In the execution phase, some aio requests require more memory for	874	In the execution phase, some aio requests require more memory for
755	temporary buffers, and each thread requires a stack and other data	875	temporary buffers, and each thread requires a stack and other data
756	structures (usually around 16k-128k, depending on the OS).	876	structures (usually around 16k-128k, depending on the OS).
757		877
758	KNOWN BUGS	878	KNOWN BUGS
759	Known bugs will be fixed in the next release.	879	Known bugs will be fixed in the next release.
760		880
761	SEE ALSO	881	SEE ALSO
762	Coro::AIO.	882	Coro::AIO.
763		883
764	AUTHOR	884	AUTHOR
765	Marc Lehmann <schmorp@schmorp.de>	885	Marc Lehmann <schmorp@schmorp.de>
766	http://home.schmorp.de/	886	http://home.schmorp.de/
767		887

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