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, it falls back to Linux::AIO if that
module is available, or uses pthreads to emulato aio functionality.

Currently, in this module 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.

Although the module will work with in the presence of other threads, it is
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';

BEGIN {
   $VERSION = 0.1;

   @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 the
filedescriptor (NOT a perl filehandle, sorry for that, but watch out, this
might change in the future).

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] >= 0) {
         open my $fh, "<&$_[0]";   # create a copy for perl
         aio_close $_[0], sub { }; # close the aio handle
         print "open successful, fh is $fh\n";
         ...
      } else {
         die "open failed: $!\n";
      }
   };

=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 -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

min_parallel 4;

END {
   max_parallel 0;
}

1;

=back

=head1 BUGS

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

=head1 SEE ALSO

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

=head1 AUTHOR

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

=cut

Revision:	1.1
Committed:	Sun Jul 10 17:07:44 2005 UTC (18 years, 10 months ago) by root
Branch:	MAIN
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			operating system supports. Currently, it falls back to Linux::AIO if that
13			module is available, or uses pthreads to emulato aio functionality.
14
15			Currently, in this module a number of threads are started that execute
16			your read/writes and signal their completion. You don't need thread
17			support in your libc or perl, and the threads created by this module will
18			not be visible to the pthreads library.
19
20			Although the module will work with in the presence of other threads, it is
21			not reentrant, so use appropriate locking yourself.
22
23			=head2 API NOTES
24
25			All the C<aio_*> calls are more or less thin wrappers around the syscall
26			with the same name (sans C<aio_>). The arguments are similar or identical,
27			and they all accept an additional C<$callback> argument which must be
28			a code reference. This code reference will get called with the syscall
29			return code (e.g. most syscalls return C<-1> on error, unlike perl, which
30			usually delivers "false") as it's sole argument when the given syscall has
31			been executed asynchronously.
32
33			All functions that expect a filehandle will also accept a file descriptor.
34
35			The filenames you pass to these routines I<must> be absolute. The reason
36			is that at the time the request is being executed, the current working
37			directory could have changed. Alternatively, you can make sure that you
38			never change the current working directory.
39
40			=over 4
41
42			=cut
43
44			package IO::AIO;
45
46			use base 'Exporter';
47
48			BEGIN {
49			$VERSION = 0.1;
50
51			@EXPORT = qw(aio_read aio_write aio_open aio_close aio_stat aio_lstat aio_unlink
52			aio_fsync aio_fdatasync aio_readahead);
53			@EXPORT_OK = qw(poll_fileno poll_cb min_parallel max_parallel nreqs);
54
55			require XSLoader;
56			XSLoader::load IO::AIO, $VERSION;
57			}
58
59			=item IO::AIO::min_parallel $nthreads
60
61			Set the minimum number of AIO threads to C<$nthreads>. The default is
62			C<1>, which means a single asynchronous operation can be done at one time
63			(the number of outstanding operations, however, is unlimited).
64
65			It is recommended to keep the number of threads low, as some linux
66			kernel versions will scale negatively with the number of threads (higher
67			parallelity => MUCH higher latency).
68
69			Under normal circumstances you don't need to call this function, as this
70			module automatically starts a single async thread.
71
72			=item IO::AIO::max_parallel $nthreads
73
74			Sets the maximum number of AIO threads to C<$nthreads>. If more than
75			the specified number of threads are currently running, kill them. This
76			function blocks until the limit is reached.
77
78			This module automatically runs C<max_parallel 0> at program end, to ensure
79			that all threads are killed and that there are no outstanding requests.
80
81			Under normal circumstances you don't need to call this function.
82
83			=item $fileno = IO::AIO::poll_fileno
84
85			Return the I<request result pipe filehandle>. This filehandle must be
86			polled for reading by some mechanism outside this module (e.g. Event
87			or select, see below). If the pipe becomes readable you have to call
88			C<poll_cb> to check the results.
89
90			See C<poll_cb> for an example.
91
92			=item IO::AIO::poll_cb
93
94			Process all outstanding events on the result pipe. You have to call this
95			regularly. Returns the number of events processed. Returns immediately
96			when no events are outstanding.
97
98			You can use Event to multiplex, e.g.:
99
100			Event->io (fd => IO::AIO::poll_fileno,
101			poll => 'r', async => 1,
102			cb => \&IO::AIO::poll_cb);
103
104			=item IO::AIO::poll_wait
105
106			Wait till the result filehandle becomes ready for reading (simply does a
107			select on the filehandle. This is useful if you want to synchronously wait
108			for some requests to finish).
109
110			See C<nreqs> for an example.
111
112			=item IO::AIO::nreqs
113
114			Returns the number of requests currently outstanding.
115
116			Example: wait till there are no outstanding requests anymore:
117
118			IO::AIO::poll_wait, IO::AIO::poll_cb
119			while IO::AIO::nreqs;
120
121			=item aio_open $pathname, $flags, $mode, $callback
122
123			Asynchronously open or create a file and call the callback with the
124			filedescriptor (NOT a perl filehandle, sorry for that, but watch out, this
125			might change in the future).
126
127			The pathname passed to C<aio_open> must be absolute. See API NOTES, above,
128			for an explanation.
129
130			The C<$mode> argument is a bitmask. See the C<Fcntl> module for a
131			list. They are the same as used in C<sysopen>.
132
133			Example:
134
135			aio_open "/etc/passwd", O_RDONLY, 0, sub {
136			if ($_[0] >= 0) {
137			open my $fh, "<&$_[0]"; # create a copy for perl
138			aio_close $_[0], sub { }; # close the aio handle
139			print "open successful, fh is $fh\n";
140			...
141			} else {
142			die "open failed: $!\n";
143			}
144			};
145
146			=item aio_close $fh, $callback
147
148			Asynchronously close a file and call the callback with the result code.
149
150			=item aio_read $fh,$offset,$length, $data,$dataoffset,$callback
151
152			=item aio_write $fh,$offset,$length, $data,$dataoffset,$callback
153
154			Reads or writes C<length> bytes from the specified C<fh> and C<offset>
155			into the scalar given by C<data> and offset C<dataoffset> and calls the
156			callback without the actual number of bytes read (or -1 on error, just
157			like the syscall).
158
159			Example: Read 15 bytes at offset 7 into scalar C<$buffer>, strating at
160			offset C<0> within the scalar:
161
162			aio_read $fh, 7, 15, $buffer, 0, sub {
163			$_[0] >= 0 or die "read error: $!";
164			print "read <$buffer>\n";
165			};
166
167			=item aio_readahead $fh,$offset,$length, $callback
168
169			Asynchronously reads the specified byte range into the page cache, using
170			the C<readahead> syscall. If that syscall doesn't exist the status will be
171			C<-1> and C<$!> is set to ENOSYS.
172
173			readahead() populates the page cache with data from a file so that
174			subsequent reads from that file will not block on disk I/O. The C<$offset>
175			argument specifies the starting point from which data is to be read and
176			C<$length> specifies the number of bytes to be read. I/O is performed in
177			whole pages, so that offset is effectively rounded down to a page boundary
178			and bytes are read up to the next page boundary greater than or equal to
179			(off-set+length). aio_readahead() does not read beyond the end of the
180			file. The current file offset of the file is left unchanged.
181
182			=item aio_stat $fh_or_path, $callback
183
184			=item aio_lstat $fh, $callback
185
186			Works like perl's C<stat> or C<lstat> in void context. The callback will
187			be called after the stat and the results will be available using C<stat _>
188			or C<-s _> etc...
189
190			The pathname passed to C<aio_stat> must be absolute. See API NOTES, above,
191			for an explanation.
192
193			Currently, the stats are always 64-bit-stats, i.e. instead of returning an
194			error when stat'ing a large file, the results will be silently truncated
195			unless perl itself is compiled with large file support.
196
197			Example: Print the length of F</etc/passwd>:
198
199			aio_stat "/etc/passwd", sub {
200			$_[0] and die "stat failed: $!";
201			print "size is ", -s _, "\n";
202			};
203
204			=item aio_unlink $pathname, $callback
205
206			Asynchronously unlink (delete) a file and call the callback with the
207			result code.
208
209			=item aio_fsync $fh, $callback
210
211			Asynchronously call fsync on the given filehandle and call the callback
212			with the fsync result code.
213
214			=item aio_fdatasync $fh, $callback
215
216			Asynchronously call fdatasync on the given filehandle and call the
217			callback with the fdatasync result code.
218
219			=cut
220
221			min_parallel 4;
222
223			END {
224			max_parallel 0;
225			}
226
227			1;
228
229			=back
230
231			=head1 BUGS
232
233			- aio_open gives a fd, but all other functions expect a perl filehandle.
234
235			=head1 SEE ALSO
236
237			L<Coro>, L<Linux::AIO>.
238
239			=head1 AUTHOR
240
241			Marc Lehmann <schmorp@schmorp.de>
242			http://home.schmorp.de/
243
244			=cut
245