Linux-AIO/AIO.pm

=head1 NAME

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

=head1 SYNOPSIS

 use Linux::AIO;

 # This module has been mostly superseded by IO::AIO.

=head1 DESCRIPTION

I<This module has been mostly superseded by IO::AIO, which is API 
compatible.>

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.

=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 Linux::AIO;

use base 'Exporter';

BEGIN {
   $VERSION = 1.9;

   @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).

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

=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.

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

=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.

See C<poll_cb> for an example.

=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).

See C<nreqs> for an example.

=item Linux::AIO::nreqs

Returns the number of requests currently outstanding.

Example: wait till there are no outstanding requests anymore:

   Linux::AIO::poll_wait, Linux::AIO::poll_cb
      while Linux::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]";
         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.

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 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>, L<IO::AIO>.

=head1 AUTHOR

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

=cut

Revision:	1.37
Committed:	Wed Feb 1 23:47:26 2006 UTC (18 years, 3 months ago) by root
Branch:	MAIN
CVS Tags:	rel-1_9, HEAD
Changes since 1.36:	+1 -1 lines
Log Message:	* empty log message *
#	Content
1	=head1 NAME
2
3	Linux::AIO - linux-specific aio implemented using clone
4
5	=head1 SYNOPSIS
6
7	use Linux::AIO;
8
9	# This module has been mostly superseded by IO::AIO.
10
11	=head1 DESCRIPTION
12
13	I<This module has been mostly superseded by IO::AIO, which is API
14	compatible.>
15
16	This module implements asynchronous I/O using the means available to Linux
17	- clone. It does not hook into the POSIX aio_* functions because Linux
18	does not yet support these in the kernel (even as of 2.6.12, only O_DIRECT
19	files are supported) and even if, it would only allow aio_read and write,
20	not open, stat and so on.
21
22	Instead, in this module a number of (non-posix) threads are started that
23	execute your read/writes and signal their completion. You don't need
24	thread support in your libc or perl, and the threads created by this
25	module will not be visible to the pthreads library.
26
27	NOTICE: the threads created by this module will automatically be killed
28	when the thread calling min_parallel exits. Make sure you only ever call
29	min_parallel from the same thread that loaded this module.
30
31	Although the module will work with in the presence of other threads, it is
32	not reentrant, so use appropriate locking yourself.
33
34	=head2 API NOTES
35
36	All the C<aio_*> calls are more or less thin wrappers around the syscall
37	with the same name (sans C<aio_>). The arguments are similar or identical,
38	and they all accept an additional C<$callback> argument which must be
39	a code reference. This code reference will get called with the syscall
40	return code (e.g. most syscalls return C<-1> on error, unlike perl, which
41	usually delivers "false") as it's sole argument when the given syscall has
42	been executed asynchronously.
43
44	All functions that expect a filehandle will also accept a file descriptor.
45
46	The filenames you pass to these routines I<must> be absolute. The reason
47	is that at the time the request is being executed, the current working
48	directory could have changed. Alternatively, you can make sure that you
49	never change the current working directory.
50
51	=over 4
52
53	=cut
54
55	package Linux::AIO;
56
57	use base 'Exporter';
58
59	BEGIN {
60	$VERSION = 1.9;
61
62	@EXPORT = qw(aio_read aio_write aio_open aio_close aio_stat aio_lstat aio_unlink
63	aio_fsync aio_fdatasync aio_readahead);
64	@EXPORT_OK = qw(poll_fileno poll_cb min_parallel max_parallel nreqs);
65
66	require XSLoader;
67	XSLoader::load Linux::AIO, $VERSION;
68	}
69
70	=item Linux::AIO::min_parallel $nthreads
71
72	Set the minimum number of AIO threads to C<$nthreads>. The default is
73	C<1>, which means a single asynchronous operation can be done at one time
74	(the number of outstanding operations, however, is unlimited).
75
76	It is recommended to keep the number of threads low, as some linux
77	kernel versions will scale negatively with the number of threads (higher
78	parallelity => MUCH higher latency).
79
80	Under normal circumstances you don't need to call this function, as this
81	module automatically starts a single async thread.
82
83	=item Linux::AIO::max_parallel $nthreads
84
85	Sets the maximum number of AIO threads to C<$nthreads>. If more than
86	the specified number of threads are currently running, kill them. This
87	function blocks until the limit is reached.
88
89	This module automatically runs C<max_parallel 0> at program end, to ensure
90	that all threads are killed and that there are no outstanding requests.
91
92	Under normal circumstances you don't need to call this function.
93
94	=item $fileno = Linux::AIO::poll_fileno
95
96	Return the I<request result pipe filehandle>. This filehandle must be
97	polled for reading by some mechanism outside this module (e.g. Event
98	or select, see below). If the pipe becomes readable you have to call
99	C<poll_cb> to check the results.
100
101	See C<poll_cb> for an example.
102
103	=item Linux::AIO::poll_cb
104
105	Process all outstanding events on the result pipe. You have to call this
106	regularly. Returns the number of events processed. Returns immediately
107	when no events are outstanding.
108
109	You can use Event to multiplex, e.g.:
110
111	Event->io (fd => Linux::AIO::poll_fileno,
112	poll => 'r', async => 1,
113	cb => \&Linux::AIO::poll_cb);
114
115	=item Linux::AIO::poll_wait
116
117	Wait till the result filehandle becomes ready for reading (simply does a
118	select on the filehandle. This is useful if you want to synchronously wait
119	for some requests to finish).
120
121	See C<nreqs> for an example.
122
123	=item Linux::AIO::nreqs
124
125	Returns the number of requests currently outstanding.
126
127	Example: wait till there are no outstanding requests anymore:
128
129	Linux::AIO::poll_wait, Linux::AIO::poll_cb
130	while Linux::AIO::nreqs;
131
132	=item aio_open $pathname, $flags, $mode, $callback
133
134	Asynchronously open or create a file and call the callback with the
135	filedescriptor (NOT a perl filehandle, sorry for that, but watch out, this
136	might change in the future).
137
138	The pathname passed to C<aio_open> must be absolute. See API NOTES, above,
139	for an explanation.
140
141	The C<$mode> argument is a bitmask. See the C<Fcntl> module for a
142	list. They are the same as used in C<sysopen>.
143
144	Example:
145
146	aio_open "/etc/passwd", O_RDONLY, 0, sub {
147	if ($_[0] >= 0) {
148	open my $fh, "<&=$_[0]";
149	print "open successful, fh is $fh\n";
150	...
151	} else {
152	die "open failed: $!\n";
153	}
154	};
155
156	=item aio_close $fh, $callback
157
158	Asynchronously close a file and call the callback with the result code.
159
160	=item aio_read $fh,$offset,$length, $data,$dataoffset,$callback
161
162	=item aio_write $fh,$offset,$length, $data,$dataoffset,$callback
163
164	Reads or writes C<length> bytes from the specified C<fh> and C<offset>
165	into the scalar given by C<data> and offset C<dataoffset> and calls the
166	callback without the actual number of bytes read (or -1 on error, just
167	like the syscall).
168
169	Example: Read 15 bytes at offset 7 into scalar C<$buffer>, strating at
170	offset C<0> within the scalar:
171
172	aio_read $fh, 7, 15, $buffer, 0, sub {
173	$_[0] >= 0 or die "read error: $!";
174	print "read <$buffer>\n";
175	};
176
177	=item aio_readahead $fh,$offset,$length, $callback
178
179	Asynchronously reads the specified byte range into the page cache, using
180	the C<readahead> syscall.
181
182	readahead() populates the page cache with data from a file so that
183	subsequent reads from that file will not block on disk I/O. The C<$offset>
184	argument specifies the starting point from which data is to be read and
185	C<$length> specifies the number of bytes to be read. I/O is performed in
186	whole pages, so that offset is effectively rounded down to a page boundary
187	and bytes are read up to the next page boundary greater than or equal to
188	(off-set+length). aio_readahead() does not read beyond the end of the
189	file. The current file offset of the file is left unchanged.
190
191	=item aio_stat $fh_or_path, $callback
192
193	=item aio_lstat $fh, $callback
194
195	Works like perl's C<stat> or C<lstat> in void context. The callback will
196	be called after the stat and the results will be available using C<stat _>
197	or C<-s _> etc...
198
199	The pathname passed to C<aio_stat> must be absolute. See API NOTES, above,
200	for an explanation.
201
202	Currently, the stats are always 64-bit-stats, i.e. instead of returning an
203	error when stat'ing a large file, the results will be silently truncated
204	unless perl itself is compiled with large file support.
205
206	Example: Print the length of F</etc/passwd>:
207
208	aio_stat "/etc/passwd", sub {
209	$_[0] and die "stat failed: $!";
210	print "size is ", -s _, "\n";
211	};
212
213	=item aio_unlink $pathname, $callback
214
215	Asynchronously unlink (delete) a file and call the callback with the
216	result code.
217
218	=item aio_fsync $fh, $callback
219
220	Asynchronously call fsync on the given filehandle and call the callback
221	with the fsync result code.
222
223	=item aio_fdatasync $fh, $callback
224
225	Asynchronously call fdatasync on the given filehandle and call the
226	callback with the fdatasync result code.
227
228	=cut
229
230	min_parallel 1;
231
232	END {
233	max_parallel 0;
234	}
235
236	1;
237
238	=back
239
240	=head1 BUGS
241
242	This module has been extensively tested in a large and very busy webserver
243	for many years now.
244
245	- aio_open gives a fd, but all other functions expect a perl filehandle.
246
247	=head1 SEE ALSO
248
249	L<Coro>, L<IO::AIO>.
250
251	=head1 AUTHOR
252
253	Marc Lehmann <schmorp@schmorp.de>
254	http://home.schmorp.de/
255
256	=cut
257