Linux-AIO/AIO.pm

=head1 NAME

Linux::AIO - linux-specific aio implemented using clone

=head1 SYNOPSIS

 use Linux::AIO;

=head1 DESCRIPTION

This module implements asynchronous I/O using the means available to Linux
- clone. It does not hook into the POSIX aio_* functions because Linux
does not yet support these in the kernel (even as of 2.6.12, only O_DIRECT
files are supported) and even if, it would only allow aio_read and write,
not open, stat and so on.

Instead, in this module a number of (non-posix) 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.

NOTICE: the threads created by this module will automatically be killed
when the thread calling min_parallel exits. Make sure you only ever call
min_parallel from the same thread that loaded this module.

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

=over 4

=cut

package Linux::AIO;

use base 'Exporter';

BEGIN {
   $VERSION = 1.7;

   @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 Linux::AIO, $VERSION;
}

=item Linux::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).

=item Linux::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.

=item $fileno = Linux::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.

=item Linux::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 => Linux::AIO::poll_fileno,
              poll => 'r', async => 1,
              cb => \&Linux::AIO::poll_cb );

=item Linux::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).

=item Linux::AIO::nreqs

Returns the number of requests currently outstanding.

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

Asynchronously open or create a file and call the callback with the
filedescriptor (NOT a perl filehandle, sorry for that, but watch out, this
might change in the future).

=item aio_close $fh, $callback

Asynchronously close a file and call the callback with the result code.

=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 C<undef> on error).

=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...

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.

=item aio_unlink  $pathname, $callback

Asynchronously unlink a file.

=cut

min_parallel 1;

END {
   max_parallel 0;
}

1;

=back

=head1 BUGS

This module has been extensively tested in a large and very busy webserver
for many years now.

   - aio_open gives a fd, but all other functions expect a perl filehandle.

=head1 SEE ALSO

L<Coro>.

=head1 AUTHOR

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

=cut

Revision:	1.29
Committed:	Sat Jul 9 22:45:05 2005 UTC (18 years, 10 months ago) by root
Branch:	MAIN
Changes since 1.28:	+3 -2 lines
Log Message:	* empty log message *
#	User	Rev	Content
1	root	1.1	=head1 NAME
2
3			Linux::AIO - linux-specific aio implemented using clone
4
5			=head1 SYNOPSIS
6
7			use Linux::AIO;
8
9			=head1 DESCRIPTION
10
11	root	1.27	This module implements asynchronous I/O using the means available to Linux
12			- clone. It does not hook into the POSIX aio_* functions because Linux
13			does not yet support these in the kernel (even as of 2.6.12, only O_DIRECT
14			files are supported) and even if, it would only allow aio_read and write,
15			not open, stat and so on.
16	root	1.14
17			Instead, in this module a number of (non-posix) threads are started that
18			execute your read/writes and signal their completion. You don't need
19			thread support in your libc or perl, and the threads created by this
20			module will not be visible to the pthreads library.
21	root	1.3
22	root	1.17	NOTICE: the threads created by this module will automatically be killed
23			when the thread calling min_parallel exits. Make sure you only ever call
24			min_parallel from the same thread that loaded this module.
25
26	root	1.27	Although the module will work with in the presence of other threads, it is
27			not reentrant, so use appropriate locking yourself.
28	root	1.16
29	root	1.1	=over 4
30
31			=cut
32
33			package Linux::AIO;
34
35	root	1.2	use base 'Exporter';
36
37	root	1.1	BEGIN {
38	root	1.29	$VERSION = 1.7;
39	root	1.1
40	root	1.29	@EXPORT = qw(aio_read aio_write aio_open aio_close aio_stat aio_lstat aio_unlink
41			aio_fsync aio_fdatasync aio_readahead);
42	root	1.2	@EXPORT_OK = qw(poll_fileno poll_cb min_parallel max_parallel nreqs);
43
44	root	1.1	require XSLoader;
45			XSLoader::load Linux::AIO, $VERSION;
46			}
47
48	root	1.14	=item Linux::AIO::min_parallel $nthreads
49	root	1.1
50	root	1.16	Set the minimum number of AIO threads to C<$nthreads>. The default is
51			C<1>, which means a single asynchronous operation can be done at one time
52			(the number of outstanding operations, however, is unlimited).
53	root	1.1
54	root	1.24	It is recommended to keep the number of threads low, as some linux
55	root	1.14	kernel versions will scale negatively with the number of threads (higher
56			parallelity => MUCH higher latency).
57
58	root	1.24	=item Linux::AIO::max_parallel $nthreads
59
60			Sets the maximum number of AIO threads to C<$nthreads>. If more than
61			the specified number of threads are currently running, kill them. This
62			function blocks until the limit is reached.
63
64			This module automatically runs C<max_parallel 0> at program end, to ensure
65			that all threads are killed and that there are no outstanding requests.
66
67	root	1.2	=item $fileno = Linux::AIO::poll_fileno
68
69	root	1.14	Return the I<request result pipe filehandle>. This filehandle must be
70			polled for reading by some mechanism outside this module (e.g. Event
71			or select, see below). If the pipe becomes readable you have to call
72			C<poll_cb> to check the results.
73	root	1.2
74			=item Linux::AIO::poll_cb
75
76			Process all outstanding events on the result pipe. You have to call this
77	root	1.14	regularly. Returns the number of events processed. Returns immediately
78			when no events are outstanding.
79	root	1.2
80	root	1.3	You can use Event to multiplex, e.g.:
81
82	root	1.14	Event->io (fd => Linux::AIO::poll_fileno,
83			poll => 'r', async => 1,
84			cb => \&Linux::AIO::poll_cb );
85	root	1.3
86	root	1.24	=item Linux::AIO::poll_wait
87
88			Wait till the result filehandle becomes ready for reading (simply does a
89			select on the filehandle. This is useful if you want to synchronously wait
90			for some requests to finish).
91
92	root	1.2	=item Linux::AIO::nreqs
93
94			Returns the number of requests currently outstanding.
95	root	1.4
96	root	1.14	=item aio_open $pathname, $flags, $mode, $callback
97	root	1.10
98			Asynchronously open or create a file and call the callback with the
99	root	1.14	filedescriptor (NOT a perl filehandle, sorry for that, but watch out, this
100			might change in the future).
101	root	1.10
102	root	1.14	=item aio_close $fh, $callback
103	root	1.10
104			Asynchronously close a file and call the callback with the result code.
105
106	root	1.14	=item aio_read $fh,$offset,$length, $data,$dataoffset,$callback
107	root	1.9
108	root	1.14	=item aio_write $fh,$offset,$length, $data,$dataoffset,$callback
109	root	1.4
110			Reads or writes C<length> bytes from the specified C<fh> and C<offset>
111			into the scalar given by C<data> and offset C<dataoffset> and calls the
112	root	1.14	callback without the actual number of bytes read (or C<undef> on error).
113	root	1.4
114	root	1.14	=item aio_stat $fh_or_path, $callback
115	root	1.4
116	root	1.14	=item aio_lstat $fh, $callback
117	root	1.5
118	root	1.14	Works like perl's C<stat> or C<lstat> in void context. The callback will
119			be called after the stat and the results will be available using C<stat _>
120			or C<-s _> etc...
121	root	1.5
122	root	1.10	Currently, the stats are always 64-bit-stats, i.e. instead of returning an
123			error when stat'ing a large file, the results will be silently truncated
124			unless perl itself is compiled with large file support.
125	root	1.17
126			=item aio_unlink $pathname, $callback
127
128	root	1.18	Asynchronously unlink a file.
129	root	1.2
130	root	1.1	=cut
131	root	1.16
132			min_parallel 1;
133	root	1.2
134			END {
135			max_parallel 0;
136			}
137	root	1.1
138			1;
139
140			=back
141
142			=head1 BUGS
143
144	root	1.14	This module has been extensively tested in a large and very busy webserver
145			for many years now.
146	root	1.1
147	root	1.14	- aio_open gives a fd, but all other functions expect a perl filehandle.
148	root	1.6
149	root	1.1	=head1 SEE ALSO
150
151			L<Coro>.
152
153			=head1 AUTHOR
154
155	root	1.22	Marc Lehmann <schmorp@schmorp.de>
156	root	1.20	http://home.schmorp.de/
157	root	1.1
158			=cut
159