IO-AIO/AIO.pm

=head1 NAME

IO::AIO - Asynchronous Input/Output

=head1 SYNOPSIS

 use IO::AIO;

=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.

=head2 API NOTES

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

=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 nreqs);

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

=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).

Under normal circumstances you don't need to call this function, as this
module automatically starts a single async thread.

=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 $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 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.

=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;

=back

=head1 BUGS

   - could be optimized to use more semaphores instead of filehandles.

=head1 SEE ALSO

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

=head1 AUTHOR

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

=cut

Revision:	1.3
Committed:	Sun Jul 10 20:07:11 2005 UTC (18 years, 10 months ago) by root
Branch:	MAIN
Changes since 1.2:	+1 -1 lines
Log Message:	* empty log message *
#	User	Rev	Content
1	root	1.1	=head1 NAME
2
3			IO::AIO - Asynchronous Input/Output
4
5			=head1 SYNOPSIS
6
7			use IO::AIO;
8
9			=head1 DESCRIPTION
10
11			This module implements asynchronous I/O using whatever means your
12	root	1.2	operating system supports.
13	root	1.1
14	root	1.2	Currently, a number of threads are started that execute your read/writes
15			and signal their completion. You don't need thread support in your libc or
16			perl, and the threads created by this module will not be visible to the
17			pthreads library. In the future, this module might make use of the native
18			aio functions available on many operating systems. However, they are often
19			not well-supported (Linux doesn't allow them on normal files currently,
20			for example), and they would only support aio_read and aio_write, so the
21			remaining functionality would have to be implemented using threads anyway.
22	root	1.1
23			Although the module will work with in the presence of other threads, it is
24	root	1.2	currently not reentrant, so use appropriate locking yourself.
25	root	1.1
26			=head2 API NOTES
27
28			All the C<aio_*> calls are more or less thin wrappers around the syscall
29			with the same name (sans C<aio_>). The arguments are similar or identical,
30			and they all accept an additional C<$callback> argument which must be
31			a code reference. This code reference will get called with the syscall
32			return code (e.g. most syscalls return C<-1> on error, unlike perl, which
33			usually delivers "false") as it's sole argument when the given syscall has
34			been executed asynchronously.
35
36			All functions that expect a filehandle will also accept a file descriptor.
37
38			The filenames you pass to these routines I<must> be absolute. The reason
39			is that at the time the request is being executed, the current working
40			directory could have changed. Alternatively, you can make sure that you
41			never change the current working directory.
42
43			=over 4
44
45			=cut
46
47			package IO::AIO;
48
49			use base 'Exporter';
50
51	root	1.2	use Fcntl ();
52
53	root	1.1	BEGIN {
54	root	1.3	$VERSION = 0.2;
55	root	1.1
56			@EXPORT = qw(aio_read aio_write aio_open aio_close aio_stat aio_lstat aio_unlink
57			aio_fsync aio_fdatasync aio_readahead);
58			@EXPORT_OK = qw(poll_fileno poll_cb min_parallel max_parallel nreqs);
59
60			require XSLoader;
61			XSLoader::load IO::AIO, $VERSION;
62			}
63
64			=item IO::AIO::min_parallel $nthreads
65
66			Set the minimum number of AIO threads to C<$nthreads>. The default is
67			C<1>, which means a single asynchronous operation can be done at one time
68			(the number of outstanding operations, however, is unlimited).
69
70			It is recommended to keep the number of threads low, as some linux
71			kernel versions will scale negatively with the number of threads (higher
72			parallelity => MUCH higher latency).
73
74			Under normal circumstances you don't need to call this function, as this
75			module automatically starts a single async thread.
76
77			=item IO::AIO::max_parallel $nthreads
78
79			Sets the maximum number of AIO threads to C<$nthreads>. If more than
80			the specified number of threads are currently running, kill them. This
81			function blocks until the limit is reached.
82
83			This module automatically runs C<max_parallel 0> at program end, to ensure
84			that all threads are killed and that there are no outstanding requests.
85
86			Under normal circumstances you don't need to call this function.
87
88			=item $fileno = IO::AIO::poll_fileno
89
90			Return the I<request result pipe filehandle>. This filehandle must be
91			polled for reading by some mechanism outside this module (e.g. Event
92			or select, see below). If the pipe becomes readable you have to call
93			C<poll_cb> to check the results.
94
95			See C<poll_cb> for an example.
96
97			=item IO::AIO::poll_cb
98
99			Process all outstanding events on the result pipe. You have to call this
100			regularly. Returns the number of events processed. Returns immediately
101			when no events are outstanding.
102
103			You can use Event to multiplex, e.g.:
104
105			Event->io (fd => IO::AIO::poll_fileno,
106			poll => 'r', async => 1,
107			cb => \&IO::AIO::poll_cb);
108
109			=item IO::AIO::poll_wait
110
111			Wait till the result filehandle becomes ready for reading (simply does a
112			select on the filehandle. This is useful if you want to synchronously wait
113			for some requests to finish).
114
115			See C<nreqs> for an example.
116
117			=item IO::AIO::nreqs
118
119			Returns the number of requests currently outstanding.
120
121			Example: wait till there are no outstanding requests anymore:
122
123			IO::AIO::poll_wait, IO::AIO::poll_cb
124			while IO::AIO::nreqs;
125
126			=item aio_open $pathname, $flags, $mode, $callback
127
128	root	1.2	Asynchronously open or create a file and call the callback with a newly
129			created filehandle for the file.
130	root	1.1
131			The pathname passed to C<aio_open> must be absolute. See API NOTES, above,
132			for an explanation.
133
134			The C<$mode> argument is a bitmask. See the C<Fcntl> module for a
135			list. They are the same as used in C<sysopen>.
136
137			Example:
138
139			aio_open "/etc/passwd", O_RDONLY, 0, sub {
140	root	1.2	if ($_[0]) {
141			print "open successful, fh is $_[0]\n";
142	root	1.1	...
143			} else {
144			die "open failed: $!\n";
145			}
146			};
147
148			=item aio_close $fh, $callback
149
150	root	1.2	Asynchronously close a file and call the callback with the result
151			code. I<WARNING:> although accepted, you should not pass in a perl
152			filehandle here, as perl will likely close the file descriptor itself when
153			the filehandle is destroyed. Normally, you can safely call perls C<close>
154			or just let filehandles go out of scope.
155	root	1.1
156			=item aio_read $fh,$offset,$length, $data,$dataoffset,$callback
157
158			=item aio_write $fh,$offset,$length, $data,$dataoffset,$callback
159
160			Reads or writes C<length> bytes from the specified C<fh> and C<offset>
161			into the scalar given by C<data> and offset C<dataoffset> and calls the
162			callback without the actual number of bytes read (or -1 on error, just
163			like the syscall).
164
165			Example: Read 15 bytes at offset 7 into scalar C<$buffer>, strating at
166			offset C<0> within the scalar:
167
168			aio_read $fh, 7, 15, $buffer, 0, sub {
169			$_[0] >= 0 or die "read error: $!";
170			print "read <$buffer>\n";
171			};
172
173			=item aio_readahead $fh,$offset,$length, $callback
174
175			Asynchronously reads the specified byte range into the page cache, using
176			the C<readahead> syscall. If that syscall doesn't exist the status will be
177			C<-1> and C<$!> is set to ENOSYS.
178
179			readahead() populates the page cache with data from a file so that
180			subsequent reads from that file will not block on disk I/O. The C<$offset>
181			argument specifies the starting point from which data is to be read and
182			C<$length> specifies the number of bytes to be read. I/O is performed in
183			whole pages, so that offset is effectively rounded down to a page boundary
184			and bytes are read up to the next page boundary greater than or equal to
185			(off-set+length). aio_readahead() does not read beyond the end of the
186			file. The current file offset of the file is left unchanged.
187
188			=item aio_stat $fh_or_path, $callback
189
190			=item aio_lstat $fh, $callback
191
192			Works like perl's C<stat> or C<lstat> in void context. The callback will
193			be called after the stat and the results will be available using C<stat _>
194			or C<-s _> etc...
195
196			The pathname passed to C<aio_stat> must be absolute. See API NOTES, above,
197			for an explanation.
198
199			Currently, the stats are always 64-bit-stats, i.e. instead of returning an
200			error when stat'ing a large file, the results will be silently truncated
201			unless perl itself is compiled with large file support.
202
203			Example: Print the length of F</etc/passwd>:
204
205			aio_stat "/etc/passwd", sub {
206			$_[0] and die "stat failed: $!";
207			print "size is ", -s _, "\n";
208			};
209
210			=item aio_unlink $pathname, $callback
211
212			Asynchronously unlink (delete) a file and call the callback with the
213			result code.
214
215			=item aio_fsync $fh, $callback
216
217			Asynchronously call fsync on the given filehandle and call the callback
218			with the fsync result code.
219
220			=item aio_fdatasync $fh, $callback
221
222			Asynchronously call fdatasync on the given filehandle and call the
223			callback with the fdatasync result code.
224
225			=cut
226
227	root	1.2	# support function to convert a fd into a perl filehandle
228			sub _fd2fh {
229			return undef if $_[0] < 0;
230
231			# try to be perl5.6-compatible
232			local *AIO_FH;
233			open AIO_FH, "+<&=$_[0]"
234			or return undef;
235
236			*AIO_FH
237			}
238
239	root	1.1	min_parallel 4;
240
241			END {
242			max_parallel 0;
243			}
244
245			1;
246
247			=back
248
249			=head1 BUGS
250
251	root	1.2	- could be optimized to use more semaphores instead of filehandles.
252	root	1.1
253			=head1 SEE ALSO
254
255			L<Coro>, L<Linux::AIO>.
256
257			=head1 AUTHOR
258
259			Marc Lehmann <schmorp@schmorp.de>
260			http://home.schmorp.de/
261
262			=cut
263