IO-AIO/AIO.pm

=head1 NAME

IO::AIO - Asynchronous Input/Output

=head1 SYNOPSIS

 use IO::AIO;

 aio_open "/etc/passwd", O_RDONLY, 0, sub {
    my ($fh) = @_;
    ...
 };

 aio_unlink "/tmp/file", sub { };

 aio_read $fh, 30000, 1024, $buffer, 0, sub {
    $_[0] > 0 or die "read error: $!";
 };

 # Event
 Event->io (fd => IO::AIO::poll_fileno,
            poll => 'r',
            cb => \&IO::AIO::poll_cb);

 # Glib/Gtk2
 add_watch Glib::IO IO::AIO::poll_fileno,
           \&IO::AIO::poll_cb;

 # Tk
 Tk::Event::IO->fileevent (IO::AIO::poll_fileno, "",
                           readable => \&IO::AIO::poll_cb);

 # Danga::Socket
 Danga::Socket->AddOtherFds (IO::AIO::poll_fileno =>
                             \&IO::AIO::poll_cb);


=head1 DESCRIPTION

This module implements asynchronous I/O using whatever means your
operating system supports.

Currently, a number of threads are started that execute your read/writes
and signal their completion. You don't need thread support in your libc or
perl, and the threads created by this module will not be visible to the
pthreads library. In the future, this module might make use of the native
aio functions available on many operating systems. However, they are often
not well-supported (Linux doesn't allow them on normal files currently,
for example), and they would only support aio_read and aio_write, so the
remaining functionality would have to be implemented using threads anyway.

Although the module will work with in the presence of other threads, it is
currently not reentrant, so use appropriate locking yourself.

=cut

package IO::AIO;

use base 'Exporter';

use Fcntl ();

BEGIN {
   $VERSION = 0.3;

   @EXPORT = qw(aio_read aio_write aio_open aio_close aio_stat aio_lstat aio_unlink
                aio_fsync aio_fdatasync aio_readahead);
   @EXPORT_OK = qw(poll_fileno poll_cb min_parallel max_parallel max_outstanding nreqs);

   require XSLoader;
   XSLoader::load IO::AIO, $VERSION;
}

=head1 FUNCTIONS

=head2 AIO FUNCTIONS

All the C<aio_*> calls are more or less thin wrappers around the syscall
with the same name (sans C<aio_>). The arguments are similar or identical,
and they all accept an additional C<$callback> argument which must be
a code reference. This code reference will get called with the syscall
return code (e.g. most syscalls return C<-1> on error, unlike perl, which
usually delivers "false") as it's sole argument when the given syscall has
been executed asynchronously.

All functions that expect a filehandle will also accept a file descriptor.

The filenames you pass to these routines I<must> be absolute. The reason
is that at the time the request is being executed, the current working
directory could have changed. Alternatively, you can make sure that you
never change the current working directory.

=over 4

=item aio_open $pathname, $flags, $mode, $callback

Asynchronously open or create a file and call the callback with a newly
created filehandle for the file.

The pathname passed to C<aio_open> must be absolute. See API NOTES, above,
for an explanation.

The C<$mode> argument is a bitmask. See the C<Fcntl> module for a
list. They are the same as used in C<sysopen>.

Example:

   aio_open "/etc/passwd", O_RDONLY, 0, sub {
      if ($_[0]) {
         print "open successful, fh is $_[0]\n";
         ...
      } else {
         die "open failed: $!\n";
      }
   };

=item aio_close $fh, $callback

Asynchronously close a file and call the callback with the result
code. I<WARNING:> although accepted, you should not pass in a perl
filehandle here, as perl will likely close the file descriptor itself when
the filehandle is destroyed. Normally, you can safely call perls C<close>
or just let filehandles go out of scope.

=item aio_read  $fh,$offset,$length, $data,$dataoffset,$callback

=item aio_write $fh,$offset,$length, $data,$dataoffset,$callback

Reads or writes C<length> bytes from the specified C<fh> and C<offset>
into the scalar given by C<data> and offset C<dataoffset> and calls the
callback without the actual number of bytes read (or -1 on error, just
like the syscall).

Example: Read 15 bytes at offset 7 into scalar C<$buffer>, strating at
offset C<0> within the scalar:

   aio_read $fh, 7, 15, $buffer, 0, sub {
      $_[0] > 0 or die "read error: $!";
      print "read $_[0] bytes: <$buffer>\n";
   };

=item aio_readahead $fh,$offset,$length, $callback

Asynchronously reads the specified byte range into the page cache, using
the C<readahead> syscall. If that syscall doesn't exist the status will be
C<-1> and C<$!> is set to ENOSYS.

readahead() populates the page cache with data from a file so that
subsequent reads from that file will not block on disk I/O. The C<$offset>
argument specifies the starting point from which data is to be read and
C<$length> specifies the number of bytes to be read. I/O is performed in
whole pages, so that offset is effectively rounded down to a page boundary
and bytes are read up to the next page boundary greater than or equal to
(off-set+length). aio_readahead() does not read beyond the end of the
file. The current file offset of the file is left unchanged.

=item aio_stat  $fh_or_path, $callback

=item aio_lstat $fh, $callback

Works like perl's C<stat> or C<lstat> in void context. The callback will
be called after the stat and the results will be available using C<stat _>
or C<-s _> etc...

The pathname passed to C<aio_stat> must be absolute. See API NOTES, above,
for an explanation.

Currently, the stats are always 64-bit-stats, i.e. instead of returning an
error when stat'ing a large file, the results will be silently truncated
unless perl itself is compiled with large file support.

Example: Print the length of F</etc/passwd>:

   aio_stat "/etc/passwd", sub {
      $_[0] and die "stat failed: $!";
      print "size is ", -s _, "\n";
   };

=item aio_unlink $pathname, $callback

Asynchronously unlink (delete) a file and call the callback with the
result code.

=item aio_fsync $fh, $callback

Asynchronously call fsync on the given filehandle and call the callback
with the fsync result code.

=item aio_fdatasync $fh, $callback

Asynchronously call fdatasync on the given filehandle and call the
callback with the fdatasync result code.

=back

=head2 SUPPORT FUNCTIONS

=over 4

=item $fileno = IO::AIO::poll_fileno

Return the I<request result pipe filehandle>. This filehandle must be
polled for reading by some mechanism outside this module (e.g. Event
or select, see below). If the pipe becomes readable you have to call
C<poll_cb> to check the results.

See C<poll_cb> for an example.

=item IO::AIO::poll_cb

Process all outstanding events on the result pipe. You have to call this
regularly. Returns the number of events processed. Returns immediately
when no events are outstanding.

You can use Event to multiplex, e.g.:

   Event->io (fd => IO::AIO::poll_fileno,
              poll => 'r', async => 1,
              cb => \&IO::AIO::poll_cb);

=item IO::AIO::poll_wait

Wait till the result filehandle becomes ready for reading (simply does a
select on the filehandle. This is useful if you want to synchronously wait
for some requests to finish).

See C<nreqs> for an example.

=item IO::AIO::nreqs

Returns the number of requests currently outstanding.

Example: wait till there are no outstanding requests anymore:

   IO::AIO::poll_wait, IO::AIO::poll_cb
      while IO::AIO::nreqs;

=item IO::AIO::min_parallel $nthreads

Set the minimum number of AIO threads to C<$nthreads>. The default is
C<1>, which means a single asynchronous operation can be done at one time
(the number of outstanding operations, however, is unlimited).

It is recommended to keep the number of threads low, as some Linux
kernel versions will scale negatively with the number of threads (higher
parallelity => MUCH higher latency). With current Linux 2.6 versions, 4-32
threads should be fine.

Under normal circumstances you don't need to call this function, as this
module automatically starts some threads (the exact number might change,
and is currently 4).

=item IO::AIO::max_parallel $nthreads

Sets the maximum number of AIO threads to C<$nthreads>. If more than
the specified number of threads are currently running, kill them. This
function blocks until the limit is reached.

This module automatically runs C<max_parallel 0> at program end, to ensure
that all threads are killed and that there are no outstanding requests.

Under normal circumstances you don't need to call this function.

=item $oldnreqs = IO::AIO::max_outstanding $nreqs

Sets the maximum number of outstanding requests to C<$nreqs>. If you
try to queue up more than this number of requests, the caller will block until
some requests have been handled.

The default is very large, so normally there is no practical limit. If you
queue up many requests in a loop it it often improves speed if you set
this to a relatively low number, such as C<100>.

Under normal circumstances you don't need to call this function.

=back

=cut

# support function to convert a fd into a perl filehandle
sub _fd2fh {
   return undef if $_[0] < 0;

   # try to be perl5.6-compatible
   local *AIO_FH;
   open AIO_FH, "+<&=$_[0]"
      or return undef;

   *AIO_FH
}

min_parallel 4;

END {
   max_parallel 0;
}

1;

=head1 SEE ALSO

L<Coro>, L<Linux::AIO>.

=head1 AUTHOR

 Marc Lehmann <schmorp@schmorp.de>
 http://home.schmorp.de/

=cut

Revision:	1.11
Committed:	Mon Jul 11 00:51:32 2005 UTC (18 years, 10 months ago) by root
Branch:	MAIN
Changes since 1.10:	+5 -0 lines
Log Message:	* empty log message *
#	Content
1	=head1 NAME
2
3	IO::AIO - Asynchronous Input/Output
4
5	=head1 SYNOPSIS
6
7	use IO::AIO;
8
9	aio_open "/etc/passwd", O_RDONLY, 0, sub {
10	my ($fh) = @_;
11	...
12	};
13
14	aio_unlink "/tmp/file", sub { };
15
16	aio_read $fh, 30000, 1024, $buffer, 0, sub {
17	$_[0] > 0 or die "read error: $!";
18	};
19
20	# Event
21	Event->io (fd => IO::AIO::poll_fileno,
22	poll => 'r',
23	cb => \&IO::AIO::poll_cb);
24
25	# Glib/Gtk2
26	add_watch Glib::IO IO::AIO::poll_fileno,
27	\&IO::AIO::poll_cb;
28
29	# Tk
30	Tk::Event::IO->fileevent (IO::AIO::poll_fileno, "",
31	readable => \&IO::AIO::poll_cb);
32
33	# Danga::Socket
34	Danga::Socket->AddOtherFds (IO::AIO::poll_fileno =>
35	\&IO::AIO::poll_cb);
36
37
38	=head1 DESCRIPTION
39
40	This module implements asynchronous I/O using whatever means your
41	operating system supports.
42
43	Currently, a number of threads are started that execute your read/writes
44	and signal their completion. You don't need thread support in your libc or
45	perl, and the threads created by this module will not be visible to the
46	pthreads library. In the future, this module might make use of the native
47	aio functions available on many operating systems. However, they are often
48	not well-supported (Linux doesn't allow them on normal files currently,
49	for example), and they would only support aio_read and aio_write, so the
50	remaining functionality would have to be implemented using threads anyway.
51
52	Although the module will work with in the presence of other threads, it is
53	currently not reentrant, so use appropriate locking yourself.
54
55	=cut
56
57	package IO::AIO;
58
59	use base 'Exporter';
60
61	use Fcntl ();
62
63	BEGIN {
64	$VERSION = 0.3;
65
66	@EXPORT = qw(aio_read aio_write aio_open aio_close aio_stat aio_lstat aio_unlink
67	aio_fsync aio_fdatasync aio_readahead);
68	@EXPORT_OK = qw(poll_fileno poll_cb min_parallel max_parallel max_outstanding nreqs);
69
70	require XSLoader;
71	XSLoader::load IO::AIO, $VERSION;
72	}
73
74	=head1 FUNCTIONS
75
76	=head2 AIO FUNCTIONS
77
78	All the C<aio_*> calls are more or less thin wrappers around the syscall
79	with the same name (sans C<aio_>). The arguments are similar or identical,
80	and they all accept an additional C<$callback> argument which must be
81	a code reference. This code reference will get called with the syscall
82	return code (e.g. most syscalls return C<-1> on error, unlike perl, which
83	usually delivers "false") as it's sole argument when the given syscall has
84	been executed asynchronously.
85
86	All functions that expect a filehandle will also accept a file descriptor.
87
88	The filenames you pass to these routines I<must> be absolute. The reason
89	is that at the time the request is being executed, the current working
90	directory could have changed. Alternatively, you can make sure that you
91	never change the current working directory.
92
93	=over 4
94
95	=item aio_open $pathname, $flags, $mode, $callback
96
97	Asynchronously open or create a file and call the callback with a newly
98	created filehandle for the file.
99
100	The pathname passed to C<aio_open> must be absolute. See API NOTES, above,
101	for an explanation.
102
103	The C<$mode> argument is a bitmask. See the C<Fcntl> module for a
104	list. They are the same as used in C<sysopen>.
105
106	Example:
107
108	aio_open "/etc/passwd", O_RDONLY, 0, sub {
109	if ($_[0]) {
110	print "open successful, fh is $_[0]\n";
111	...
112	} else {
113	die "open failed: $!\n";
114	}
115	};
116
117	=item aio_close $fh, $callback
118
119	Asynchronously close a file and call the callback with the result
120	code. I<WARNING:> although accepted, you should not pass in a perl
121	filehandle here, as perl will likely close the file descriptor itself when
122	the filehandle is destroyed. Normally, you can safely call perls C<close>
123	or just let filehandles go out of scope.
124
125	=item aio_read $fh,$offset,$length, $data,$dataoffset,$callback
126
127	=item aio_write $fh,$offset,$length, $data,$dataoffset,$callback
128
129	Reads or writes C<length> bytes from the specified C<fh> and C<offset>
130	into the scalar given by C<data> and offset C<dataoffset> and calls the
131	callback without the actual number of bytes read (or -1 on error, just
132	like the syscall).
133
134	Example: Read 15 bytes at offset 7 into scalar C<$buffer>, strating at
135	offset C<0> within the scalar:
136
137	aio_read $fh, 7, 15, $buffer, 0, sub {
138	$_[0] > 0 or die "read error: $!";
139	print "read $_[0] bytes: <$buffer>\n";
140	};
141
142	=item aio_readahead $fh,$offset,$length, $callback
143
144	Asynchronously reads the specified byte range into the page cache, using
145	the C<readahead> syscall. If that syscall doesn't exist the status will be
146	C<-1> and C<$!> is set to ENOSYS.
147
148	readahead() populates the page cache with data from a file so that
149	subsequent reads from that file will not block on disk I/O. The C<$offset>
150	argument specifies the starting point from which data is to be read and
151	C<$length> specifies the number of bytes to be read. I/O is performed in
152	whole pages, so that offset is effectively rounded down to a page boundary
153	and bytes are read up to the next page boundary greater than or equal to
154	(off-set+length). aio_readahead() does not read beyond the end of the
155	file. The current file offset of the file is left unchanged.
156
157	=item aio_stat $fh_or_path, $callback
158
159	=item aio_lstat $fh, $callback
160
161	Works like perl's C<stat> or C<lstat> in void context. The callback will
162	be called after the stat and the results will be available using C<stat _>
163	or C<-s _> etc...
164
165	The pathname passed to C<aio_stat> must be absolute. See API NOTES, above,
166	for an explanation.
167
168	Currently, the stats are always 64-bit-stats, i.e. instead of returning an
169	error when stat'ing a large file, the results will be silently truncated
170	unless perl itself is compiled with large file support.
171
172	Example: Print the length of F</etc/passwd>:
173
174	aio_stat "/etc/passwd", sub {
175	$_[0] and die "stat failed: $!";
176	print "size is ", -s _, "\n";
177	};
178
179	=item aio_unlink $pathname, $callback
180
181	Asynchronously unlink (delete) a file and call the callback with the
182	result code.
183
184	=item aio_fsync $fh, $callback
185
186	Asynchronously call fsync on the given filehandle and call the callback
187	with the fsync result code.
188
189	=item aio_fdatasync $fh, $callback
190
191	Asynchronously call fdatasync on the given filehandle and call the
192	callback with the fdatasync result code.
193
194	=back
195
196	=head2 SUPPORT FUNCTIONS
197
198	=over 4
199
200	=item $fileno = IO::AIO::poll_fileno
201
202	Return the I<request result pipe filehandle>. This filehandle must be
203	polled for reading by some mechanism outside this module (e.g. Event
204	or select, see below). If the pipe becomes readable you have to call
205	C<poll_cb> to check the results.
206
207	See C<poll_cb> for an example.
208
209	=item IO::AIO::poll_cb
210
211	Process all outstanding events on the result pipe. You have to call this
212	regularly. Returns the number of events processed. Returns immediately
213	when no events are outstanding.
214
215	You can use Event to multiplex, e.g.:
216
217	Event->io (fd => IO::AIO::poll_fileno,
218	poll => 'r', async => 1,
219	cb => \&IO::AIO::poll_cb);
220
221	=item IO::AIO::poll_wait
222
223	Wait till the result filehandle becomes ready for reading (simply does a
224	select on the filehandle. This is useful if you want to synchronously wait
225	for some requests to finish).
226
227	See C<nreqs> for an example.
228
229	=item IO::AIO::nreqs
230
231	Returns the number of requests currently outstanding.
232
233	Example: wait till there are no outstanding requests anymore:
234
235	IO::AIO::poll_wait, IO::AIO::poll_cb
236	while IO::AIO::nreqs;
237
238	=item IO::AIO::min_parallel $nthreads
239
240	Set the minimum number of AIO threads to C<$nthreads>. The default is
241	C<1>, which means a single asynchronous operation can be done at one time
242	(the number of outstanding operations, however, is unlimited).
243
244	It is recommended to keep the number of threads low, as some Linux
245	kernel versions will scale negatively with the number of threads (higher
246	parallelity => MUCH higher latency). With current Linux 2.6 versions, 4-32
247	threads should be fine.
248
249	Under normal circumstances you don't need to call this function, as this
250	module automatically starts some threads (the exact number might change,
251	and is currently 4).
252
253	=item IO::AIO::max_parallel $nthreads
254
255	Sets the maximum number of AIO threads to C<$nthreads>. If more than
256	the specified number of threads are currently running, kill them. This
257	function blocks until the limit is reached.
258
259	This module automatically runs C<max_parallel 0> at program end, to ensure
260	that all threads are killed and that there are no outstanding requests.
261
262	Under normal circumstances you don't need to call this function.
263
264	=item $oldnreqs = IO::AIO::max_outstanding $nreqs
265
266	Sets the maximum number of outstanding requests to C<$nreqs>. If you
267	try to queue up more than this number of requests, the caller will block until
268	some requests have been handled.
269
270	The default is very large, so normally there is no practical limit. If you
271	queue up many requests in a loop it it often improves speed if you set
272	this to a relatively low number, such as C<100>.
273
274	Under normal circumstances you don't need to call this function.
275
276	=back
277
278	=cut
279
280	# support function to convert a fd into a perl filehandle
281	sub _fd2fh {
282	return undef if $_[0] < 0;
283
284	# try to be perl5.6-compatible
285	local *AIO_FH;
286	open AIO_FH, "+<&=$_[0]"
287	or return undef;
288
289	*AIO_FH
290	}
291
292	min_parallel 4;
293
294	END {
295	max_parallel 0;
296	}
297
298	1;
299
300	=head1 SEE ALSO
301
302	L<Coro>, L<Linux::AIO>.
303
304	=head1 AUTHOR
305
306	Marc Lehmann <schmorp@schmorp.de>
307	http://home.schmorp.de/
308
309	=cut
310