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',
            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);

 # Danga::Socket
 Danga::Socket->AddOtherFds (IO::AIO::poll_fileno =>
                             \&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 = 0.3;

   @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 $_[0] bytes: <$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::flush

Wait till all outstanding AIO requests have been handled.

Strictly equivalent to:

   IO::AIO::poll_wait, IO::AIO::poll_cb
      while IO::AIO::nreqs;

=item IO::AIO::poll

Waits until some requests have been handled.

Strictly equivalent to:

   IO::AIO::poll_wait, IO::AIO::poll_cb
      if 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:	1.13
Committed:	Mon Jul 11 01:49:14 2005 UTC (18 years, 10 months ago) by root
Branch:	MAIN
Changes since 1.12:	+14 -0 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	root	1.6	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	root	1.8	$_[0] > 0 or die "read error: $!";
18	root	1.6	};
19
20			# Event
21			Event->io (fd => IO::AIO::poll_fileno,
22	root	1.7	poll => 'r',
23	root	1.6	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	root	1.11	# Danga::Socket
34			Danga::Socket->AddOtherFds (IO::AIO::poll_fileno =>
35			\&IO::AIO::poll_cb);
36
37
38	root	1.1	=head1 DESCRIPTION
39
40			This module implements asynchronous I/O using whatever means your
41	root	1.2	operating system supports.
42	root	1.1
43	root	1.2	Currently, a number of threads are started that execute your read/writes
44			and signal their completion. You don't need thread support in your libc or
45			perl, and the threads created by this module will not be visible to the
46			pthreads library. In the future, this module might make use of the native
47			aio functions available on many operating systems. However, they are often
48			not well-supported (Linux doesn't allow them on normal files currently,
49			for example), and they would only support aio_read and aio_write, so the
50			remaining functionality would have to be implemented using threads anyway.
51	root	1.1
52			Although the module will work with in the presence of other threads, it is
53	root	1.2	currently not reentrant, so use appropriate locking yourself.
54	root	1.1
55			=cut
56
57			package IO::AIO;
58
59			use base 'Exporter';
60
61	root	1.2	use Fcntl ();
62
63	root	1.1	BEGIN {
64	root	1.10	$VERSION = 0.3;
65	root	1.1
66			@EXPORT = qw(aio_read aio_write aio_open aio_close aio_stat aio_lstat aio_unlink
67			aio_fsync aio_fdatasync aio_readahead);
68	root	1.4	@EXPORT_OK = qw(poll_fileno poll_cb min_parallel max_parallel max_outstanding nreqs);
69	root	1.1
70			require XSLoader;
71			XSLoader::load IO::AIO, $VERSION;
72			}
73
74	root	1.5	=head1 FUNCTIONS
75	root	1.1
76	root	1.5	=head2 AIO FUNCTIONS
77	root	1.1
78	root	1.5	All the C<aio_*> calls are more or less thin wrappers around the syscall
79			with the same name (sans C<aio_>). The arguments are similar or identical,
80			and they all accept an additional C<$callback> argument which must be
81			a code reference. This code reference will get called with the syscall
82			return code (e.g. most syscalls return C<-1> on error, unlike perl, which
83			usually delivers "false") as it's sole argument when the given syscall has
84			been executed asynchronously.
85	root	1.1
86	root	1.5	All functions that expect a filehandle will also accept a file descriptor.
87	root	1.1
88	root	1.5	The filenames you pass to these routines I<must> be absolute. The reason
89			is that at the time the request is being executed, the current working
90			directory could have changed. Alternatively, you can make sure that you
91			never change the current working directory.
92	root	1.1
93	root	1.5	=over 4
94	root	1.1
95			=item aio_open $pathname, $flags, $mode, $callback
96
97	root	1.2	Asynchronously open or create a file and call the callback with a newly
98			created filehandle for the file.
99	root	1.1
100			The pathname passed to C<aio_open> must be absolute. See API NOTES, above,
101			for an explanation.
102
103			The C<$mode> argument is a bitmask. See the C<Fcntl> module for a
104			list. They are the same as used in C<sysopen>.
105
106			Example:
107
108			aio_open "/etc/passwd", O_RDONLY, 0, sub {
109	root	1.2	if ($_[0]) {
110			print "open successful, fh is $_[0]\n";
111	root	1.1	...
112			} else {
113			die "open failed: $!\n";
114			}
115			};
116
117			=item aio_close $fh, $callback
118
119	root	1.2	Asynchronously close a file and call the callback with the result
120			code. I<WARNING:> although accepted, you should not pass in a perl
121			filehandle here, as perl will likely close the file descriptor itself when
122			the filehandle is destroyed. Normally, you can safely call perls C<close>
123			or just let filehandles go out of scope.
124	root	1.1
125			=item aio_read $fh,$offset,$length, $data,$dataoffset,$callback
126
127			=item aio_write $fh,$offset,$length, $data,$dataoffset,$callback
128
129			Reads or writes C<length> bytes from the specified C<fh> and C<offset>
130			into the scalar given by C<data> and offset C<dataoffset> and calls the
131			callback without the actual number of bytes read (or -1 on error, just
132			like the syscall).
133
134			Example: Read 15 bytes at offset 7 into scalar C<$buffer>, strating at
135			offset C<0> within the scalar:
136
137			aio_read $fh, 7, 15, $buffer, 0, sub {
138	root	1.9	$_[0] > 0 or die "read error: $!";
139			print "read $_[0] bytes: <$buffer>\n";
140	root	1.1	};
141
142			=item aio_readahead $fh,$offset,$length, $callback
143
144			Asynchronously reads the specified byte range into the page cache, using
145			the C<readahead> syscall. If that syscall doesn't exist the status will be
146			C<-1> and C<$!> is set to ENOSYS.
147
148			readahead() populates the page cache with data from a file so that
149			subsequent reads from that file will not block on disk I/O. The C<$offset>
150			argument specifies the starting point from which data is to be read and
151			C<$length> specifies the number of bytes to be read. I/O is performed in
152			whole pages, so that offset is effectively rounded down to a page boundary
153			and bytes are read up to the next page boundary greater than or equal to
154			(off-set+length). aio_readahead() does not read beyond the end of the
155			file. The current file offset of the file is left unchanged.
156
157			=item aio_stat $fh_or_path, $callback
158
159			=item aio_lstat $fh, $callback
160
161			Works like perl's C<stat> or C<lstat> in void context. The callback will
162			be called after the stat and the results will be available using C<stat _>
163			or C<-s _> etc...
164
165			The pathname passed to C<aio_stat> must be absolute. See API NOTES, above,
166			for an explanation.
167
168			Currently, the stats are always 64-bit-stats, i.e. instead of returning an
169			error when stat'ing a large file, the results will be silently truncated
170			unless perl itself is compiled with large file support.
171
172			Example: Print the length of F</etc/passwd>:
173
174			aio_stat "/etc/passwd", sub {
175			$_[0] and die "stat failed: $!";
176			print "size is ", -s _, "\n";
177			};
178
179			=item aio_unlink $pathname, $callback
180
181			Asynchronously unlink (delete) a file and call the callback with the
182			result code.
183
184			=item aio_fsync $fh, $callback
185
186			Asynchronously call fsync on the given filehandle and call the callback
187			with the fsync result code.
188
189			=item aio_fdatasync $fh, $callback
190
191			Asynchronously call fdatasync on the given filehandle and call the
192			callback with the fdatasync result code.
193
194	root	1.5	=back
195
196			=head2 SUPPORT FUNCTIONS
197
198			=over 4
199
200			=item $fileno = IO::AIO::poll_fileno
201
202			Return the I<request result pipe filehandle>. This filehandle must be
203			polled for reading by some mechanism outside this module (e.g. Event
204			or select, see below). If the pipe becomes readable you have to call
205			C<poll_cb> to check the results.
206
207			See C<poll_cb> for an example.
208
209			=item IO::AIO::poll_cb
210
211			Process all outstanding events on the result pipe. You have to call this
212			regularly. Returns the number of events processed. Returns immediately
213			when no events are outstanding.
214
215			You can use Event to multiplex, e.g.:
216
217			Event->io (fd => IO::AIO::poll_fileno,
218			poll => 'r', async => 1,
219			cb => \&IO::AIO::poll_cb);
220
221			=item IO::AIO::poll_wait
222
223			Wait till the result filehandle becomes ready for reading (simply does a
224			select on the filehandle. This is useful if you want to synchronously wait
225			for some requests to finish).
226
227			See C<nreqs> for an example.
228
229			=item IO::AIO::nreqs
230
231			Returns the number of requests currently outstanding.
232
233			Example: wait till there are no outstanding requests anymore:
234
235			IO::AIO::poll_wait, IO::AIO::poll_cb
236			while IO::AIO::nreqs;
237
238	root	1.12	=item IO::AIO::flush
239
240			Wait till all outstanding AIO requests have been handled.
241
242	root	1.13	Strictly equivalent to:
243
244			IO::AIO::poll_wait, IO::AIO::poll_cb
245			while IO::AIO::nreqs;
246
247			=item IO::AIO::poll
248
249			Waits until some requests have been handled.
250
251			Strictly equivalent to:
252
253			IO::AIO::poll_wait, IO::AIO::poll_cb
254			if IO::AIO::nreqs;
255
256	root	1.5	=item IO::AIO::min_parallel $nthreads
257
258			Set the minimum number of AIO threads to C<$nthreads>. The default is
259			C<1>, which means a single asynchronous operation can be done at one time
260			(the number of outstanding operations, however, is unlimited).
261
262			It is recommended to keep the number of threads low, as some Linux
263			kernel versions will scale negatively with the number of threads (higher
264			parallelity => MUCH higher latency). With current Linux 2.6 versions, 4-32
265			threads should be fine.
266
267			Under normal circumstances you don't need to call this function, as this
268			module automatically starts some threads (the exact number might change,
269			and is currently 4).
270
271			=item IO::AIO::max_parallel $nthreads
272
273			Sets the maximum number of AIO threads to C<$nthreads>. If more than
274			the specified number of threads are currently running, kill them. This
275			function blocks until the limit is reached.
276
277			This module automatically runs C<max_parallel 0> at program end, to ensure
278			that all threads are killed and that there are no outstanding requests.
279
280			Under normal circumstances you don't need to call this function.
281
282			=item $oldnreqs = IO::AIO::max_outstanding $nreqs
283
284			Sets the maximum number of outstanding requests to C<$nreqs>. If you
285			try to queue up more than this number of requests, the caller will block until
286			some requests have been handled.
287
288			The default is very large, so normally there is no practical limit. If you
289			queue up many requests in a loop it it often improves speed if you set
290			this to a relatively low number, such as C<100>.
291
292			Under normal circumstances you don't need to call this function.
293
294			=back
295
296	root	1.1	=cut
297
298	root	1.2	# support function to convert a fd into a perl filehandle
299			sub _fd2fh {
300			return undef if $_[0] < 0;
301
302			# try to be perl5.6-compatible
303			local *AIO_FH;
304			open AIO_FH, "+<&=$_[0]"
305			or return undef;
306
307			*AIO_FH
308			}
309
310	root	1.1	min_parallel 4;
311
312			END {
313			max_parallel 0;
314			}
315
316			1;
317
318			=head1 SEE ALSO
319
320			L<Coro>, L<Linux::AIO>.
321
322			=head1 AUTHOR
323
324			Marc Lehmann <schmorp@schmorp.de>
325			http://home.schmorp.de/
326
327			=cut
328