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', async => 1,
            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);

=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 = 0.2;

   @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: $!";
      print "read <$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:	1.6
Committed:	Sun Jul 10 22:19:48 2005 UTC (18 years, 10 months ago) by root
Branch:	MAIN
Changes since 1.5:	+24 -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', async => 1,
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	=head1 DESCRIPTION
34
35	This module implements asynchronous I/O using whatever means your
36	operating system supports.
37
38	Currently, a number of threads are started that execute your read/writes
39	and signal their completion. You don't need thread support in your libc or
40	perl, and the threads created by this module will not be visible to the
41	pthreads library. In the future, this module might make use of the native
42	aio functions available on many operating systems. However, they are often
43	not well-supported (Linux doesn't allow them on normal files currently,
44	for example), and they would only support aio_read and aio_write, so the
45	remaining functionality would have to be implemented using threads anyway.
46
47	Although the module will work with in the presence of other threads, it is
48	currently not reentrant, so use appropriate locking yourself.
49
50	=cut
51
52	package IO::AIO;
53
54	use base 'Exporter';
55
56	use Fcntl ();
57
58	BEGIN {
59	$VERSION = 0.2;
60
61	@EXPORT = qw(aio_read aio_write aio_open aio_close aio_stat aio_lstat aio_unlink
62	aio_fsync aio_fdatasync aio_readahead);
63	@EXPORT_OK = qw(poll_fileno poll_cb min_parallel max_parallel max_outstanding nreqs);
64
65	require XSLoader;
66	XSLoader::load IO::AIO, $VERSION;
67	}
68
69	=head1 FUNCTIONS
70
71	=head2 AIO FUNCTIONS
72
73	All the C<aio_*> calls are more or less thin wrappers around the syscall
74	with the same name (sans C<aio_>). The arguments are similar or identical,
75	and they all accept an additional C<$callback> argument which must be
76	a code reference. This code reference will get called with the syscall
77	return code (e.g. most syscalls return C<-1> on error, unlike perl, which
78	usually delivers "false") as it's sole argument when the given syscall has
79	been executed asynchronously.
80
81	All functions that expect a filehandle will also accept a file descriptor.
82
83	The filenames you pass to these routines I<must> be absolute. The reason
84	is that at the time the request is being executed, the current working
85	directory could have changed. Alternatively, you can make sure that you
86	never change the current working directory.
87
88	=over 4
89
90	=item aio_open $pathname, $flags, $mode, $callback
91
92	Asynchronously open or create a file and call the callback with a newly
93	created filehandle for the file.
94
95	The pathname passed to C<aio_open> must be absolute. See API NOTES, above,
96	for an explanation.
97
98	The C<$mode> argument is a bitmask. See the C<Fcntl> module for a
99	list. They are the same as used in C<sysopen>.
100
101	Example:
102
103	aio_open "/etc/passwd", O_RDONLY, 0, sub {
104	if ($_[0]) {
105	print "open successful, fh is $_[0]\n";
106	...
107	} else {
108	die "open failed: $!\n";
109	}
110	};
111
112	=item aio_close $fh, $callback
113
114	Asynchronously close a file and call the callback with the result
115	code. I<WARNING:> although accepted, you should not pass in a perl
116	filehandle here, as perl will likely close the file descriptor itself when
117	the filehandle is destroyed. Normally, you can safely call perls C<close>
118	or just let filehandles go out of scope.
119
120	=item aio_read $fh,$offset,$length, $data,$dataoffset,$callback
121
122	=item aio_write $fh,$offset,$length, $data,$dataoffset,$callback
123
124	Reads or writes C<length> bytes from the specified C<fh> and C<offset>
125	into the scalar given by C<data> and offset C<dataoffset> and calls the
126	callback without the actual number of bytes read (or -1 on error, just
127	like the syscall).
128
129	Example: Read 15 bytes at offset 7 into scalar C<$buffer>, strating at
130	offset C<0> within the scalar:
131
132	aio_read $fh, 7, 15, $buffer, 0, sub {
133	$_[0] >= 0 or die "read error: $!";
134	print "read <$buffer>\n";
135	};
136
137	=item aio_readahead $fh,$offset,$length, $callback
138
139	Asynchronously reads the specified byte range into the page cache, using
140	the C<readahead> syscall. If that syscall doesn't exist the status will be
141	C<-1> and C<$!> is set to ENOSYS.
142
143	readahead() populates the page cache with data from a file so that
144	subsequent reads from that file will not block on disk I/O. The C<$offset>
145	argument specifies the starting point from which data is to be read and
146	C<$length> specifies the number of bytes to be read. I/O is performed in
147	whole pages, so that offset is effectively rounded down to a page boundary
148	and bytes are read up to the next page boundary greater than or equal to
149	(off-set+length). aio_readahead() does not read beyond the end of the
150	file. The current file offset of the file is left unchanged.
151
152	=item aio_stat $fh_or_path, $callback
153
154	=item aio_lstat $fh, $callback
155
156	Works like perl's C<stat> or C<lstat> in void context. The callback will
157	be called after the stat and the results will be available using C<stat _>
158	or C<-s _> etc...
159
160	The pathname passed to C<aio_stat> must be absolute. See API NOTES, above,
161	for an explanation.
162
163	Currently, the stats are always 64-bit-stats, i.e. instead of returning an
164	error when stat'ing a large file, the results will be silently truncated
165	unless perl itself is compiled with large file support.
166
167	Example: Print the length of F</etc/passwd>:
168
169	aio_stat "/etc/passwd", sub {
170	$_[0] and die "stat failed: $!";
171	print "size is ", -s _, "\n";
172	};
173
174	=item aio_unlink $pathname, $callback
175
176	Asynchronously unlink (delete) a file and call the callback with the
177	result code.
178
179	=item aio_fsync $fh, $callback
180
181	Asynchronously call fsync on the given filehandle and call the callback
182	with the fsync result code.
183
184	=item aio_fdatasync $fh, $callback
185
186	Asynchronously call fdatasync on the given filehandle and call the
187	callback with the fdatasync result code.
188
189	=back
190
191	=head2 SUPPORT FUNCTIONS
192
193	=over 4
194
195	=item $fileno = IO::AIO::poll_fileno
196
197	Return the I<request result pipe filehandle>. This filehandle must be
198	polled for reading by some mechanism outside this module (e.g. Event
199	or select, see below). If the pipe becomes readable you have to call
200	C<poll_cb> to check the results.
201
202	See C<poll_cb> for an example.
203
204	=item IO::AIO::poll_cb
205
206	Process all outstanding events on the result pipe. You have to call this
207	regularly. Returns the number of events processed. Returns immediately
208	when no events are outstanding.
209
210	You can use Event to multiplex, e.g.:
211
212	Event->io (fd => IO::AIO::poll_fileno,
213	poll => 'r', async => 1,
214	cb => \&IO::AIO::poll_cb);
215
216	=item IO::AIO::poll_wait
217
218	Wait till the result filehandle becomes ready for reading (simply does a
219	select on the filehandle. This is useful if you want to synchronously wait
220	for some requests to finish).
221
222	See C<nreqs> for an example.
223
224	=item IO::AIO::nreqs
225
226	Returns the number of requests currently outstanding.
227
228	Example: wait till there are no outstanding requests anymore:
229
230	IO::AIO::poll_wait, IO::AIO::poll_cb
231	while IO::AIO::nreqs;
232
233	=item IO::AIO::min_parallel $nthreads
234
235	Set the minimum number of AIO threads to C<$nthreads>. The default is
236	C<1>, which means a single asynchronous operation can be done at one time
237	(the number of outstanding operations, however, is unlimited).
238
239	It is recommended to keep the number of threads low, as some Linux
240	kernel versions will scale negatively with the number of threads (higher
241	parallelity => MUCH higher latency). With current Linux 2.6 versions, 4-32
242	threads should be fine.
243
244	Under normal circumstances you don't need to call this function, as this
245	module automatically starts some threads (the exact number might change,
246	and is currently 4).
247
248	=item IO::AIO::max_parallel $nthreads
249
250	Sets the maximum number of AIO threads to C<$nthreads>. If more than
251	the specified number of threads are currently running, kill them. This
252	function blocks until the limit is reached.
253
254	This module automatically runs C<max_parallel 0> at program end, to ensure
255	that all threads are killed and that there are no outstanding requests.
256
257	Under normal circumstances you don't need to call this function.
258
259	=item $oldnreqs = IO::AIO::max_outstanding $nreqs
260
261	Sets the maximum number of outstanding requests to C<$nreqs>. If you
262	try to queue up more than this number of requests, the caller will block until
263	some requests have been handled.
264
265	The default is very large, so normally there is no practical limit. If you
266	queue up many requests in a loop it it often improves speed if you set
267	this to a relatively low number, such as C<100>.
268
269	Under normal circumstances you don't need to call this function.
270
271	=back
272
273	=cut
274
275	# support function to convert a fd into a perl filehandle
276	sub _fd2fh {
277	return undef if $_[0] < 0;
278
279	# try to be perl5.6-compatible
280	local *AIO_FH;
281	open AIO_FH, "+<&=$_[0]"
282	or return undef;
283
284	*AIO_FH
285	}
286
287	min_parallel 4;
288
289	END {
290	max_parallel 0;
291	}
292
293	1;
294
295	=head1 SEE ALSO
296
297	L<Coro>, L<Linux::AIO>.
298
299	=head1 AUTHOR
300
301	Marc Lehmann <schmorp@schmorp.de>
302	http://home.schmorp.de/
303
304	=cut
305