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,
           in => sub { IO::AIO::poll_cb, 1 };

 # 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 = 0.9;

   @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 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 (and optional) 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
for this 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<$flags> argument is a bitmask. See the C<Fcntl> module for a
list. They are the same as used by C<sysopen>.

Likewise, C<$mode> specifies the mode of the newly created file, if it
didn't exist and C<O_CREAT> has been given, just like perl's C<sysopen>,
except that it is mandatory (i.e. use C<0> if you don't create new files,
and C<0666> or C<0777> if you do).

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 another
time when the filehandle is destroyed. Normally, you can safely call perls
C<close> or just let filehandles go out of scope.

This is supposed to be a bug in the API, so that might change. It's
therefore best to avoid this function.

=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>, starting 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 (likely if your OS
isn't Linux) the status will be C<-1> and C<$!> is set to C<ENOSYS>.

C<aio_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). C<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. Might set C<$!> to C<ENOSYS> if
C<fdatasync> is not available.

=back

=head2 SUPPORT FUNCTIONS

=over 4

=item $fileno = IO::AIO::poll_fileno

Return the I<request result pipe file descriptor>. This filehandle must be
polled for reading by some mechanism outside this module (e.g. Event or
select, see below or the SYNOPSIS). 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.

Example: Install an Event watcher that automatically calls
IO::AIO::poll_cb with high priority:

   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
C<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 (i.e. for which their
callback has not been invoked yet).

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:	1.21
Committed:	Wed Jul 13 00:13:09 2005 UTC (18 years, 10 months ago) by root
Branch:	MAIN
Changes since 1.20:	+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	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	root	1.16	in => sub { IO::AIO::poll_cb, 1 };
28	root	1.6
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	1.21	$VERSION = 0.9;
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, $VERSION;
72			}
73
74	root	1.5	=head1 FUNCTIONS
75	root	1.1
76	root	1.5	=head2 AIO FUNCTIONS
77	root	1.1
78	root	1.5	All the C<aio_*> calls are more or less thin wrappers around the syscall
79			with the same name (sans C<aio_>). The arguments are similar or identical,
80	root	1.14	and they all accept an additional (and optional) C<$callback> argument
81			which must be a code reference. This code reference will get called with
82			the syscall return code (e.g. most syscalls return C<-1> on error, unlike
83			perl, which usually delivers "false") as it's sole argument when the given
84			syscall has 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	root	1.20	for this is that at the time the request is being executed, the current
90			working directory could have changed. Alternatively, you can make sure
91			that you 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, $callback
96
97	root	1.2	Asynchronously open or create a file and call the callback with a newly
98			created filehandle for the file.
99	root	1.1
100			The pathname passed to C<aio_open> must be absolute. See API NOTES, above,
101			for an explanation.
102
103	root	1.20	The C<$flags> argument is a bitmask. See the C<Fcntl> module for a
104			list. They are the same as used by C<sysopen>.
105
106			Likewise, C<$mode> specifies the mode of the newly created file, if it
107			didn't exist and C<O_CREAT> has been given, just like perl's C<sysopen>,
108			except that it is mandatory (i.e. use C<0> if you don't create new files,
109			and C<0666> or C<0777> if you do).
110	root	1.1
111			Example:
112
113			aio_open "/etc/passwd", O_RDONLY, 0, sub {
114	root	1.2	if ($_[0]) {
115			print "open successful, fh is $_[0]\n";
116	root	1.1	...
117			} else {
118			die "open failed: $!\n";
119			}
120			};
121
122			=item aio_close $fh, $callback
123
124	root	1.2	Asynchronously close a file and call the callback with the result
125			code. I<WARNING:> although accepted, you should not pass in a perl
126	root	1.20	filehandle here, as perl will likely close the file descriptor another
127			time when the filehandle is destroyed. Normally, you can safely call perls
128			C<close> or just let filehandles go out of scope.
129
130			This is supposed to be a bug in the API, so that might change. It's
131			therefore best to avoid this function.
132	root	1.1
133			=item aio_read $fh,$offset,$length, $data,$dataoffset,$callback
134
135			=item aio_write $fh,$offset,$length, $data,$dataoffset,$callback
136
137			Reads or writes C<length> bytes from the specified C<fh> and C<offset>
138			into the scalar given by C<data> and offset C<dataoffset> and calls the
139			callback without the actual number of bytes read (or -1 on error, just
140			like the syscall).
141
142	root	1.17	Example: Read 15 bytes at offset 7 into scalar C<$buffer>, starting at
143	root	1.1	offset C<0> within the scalar:
144
145			aio_read $fh, 7, 15, $buffer, 0, sub {
146	root	1.9	$_[0] > 0 or die "read error: $!";
147			print "read $_[0] bytes: <$buffer>\n";
148	root	1.1	};
149
150			=item aio_readahead $fh,$offset,$length, $callback
151
152			Asynchronously reads the specified byte range into the page cache, using
153	root	1.17	the C<readahead> syscall. If that syscall doesn't exist (likely if your OS
154	root	1.20	isn't Linux) the status will be C<-1> and C<$!> is set to C<ENOSYS>.
155	root	1.1
156	root	1.20	C<aio_readahead> populates the page cache with data from a file so that
157	root	1.1	subsequent reads from that file will not block on disk I/O. The C<$offset>
158			argument specifies the starting point from which data is to be read and
159			C<$length> specifies the number of bytes to be read. I/O is performed in
160			whole pages, so that offset is effectively rounded down to a page boundary
161			and bytes are read up to the next page boundary greater than or equal to
162	root	1.20	(off-set+length). C<aio_readahead> does not read beyond the end of the
163	root	1.1	file. The current file offset of the file is left unchanged.
164
165			=item aio_stat $fh_or_path, $callback
166
167			=item aio_lstat $fh, $callback
168
169			Works like perl's C<stat> or C<lstat> in void context. The callback will
170			be called after the stat and the results will be available using C<stat _>
171			or C<-s _> etc...
172
173			The pathname passed to C<aio_stat> must be absolute. See API NOTES, above,
174			for an explanation.
175
176			Currently, the stats are always 64-bit-stats, i.e. instead of returning an
177			error when stat'ing a large file, the results will be silently truncated
178			unless perl itself is compiled with large file support.
179
180			Example: Print the length of F</etc/passwd>:
181
182			aio_stat "/etc/passwd", sub {
183			$_[0] and die "stat failed: $!";
184			print "size is ", -s _, "\n";
185			};
186
187			=item aio_unlink $pathname, $callback
188
189			Asynchronously unlink (delete) a file and call the callback with the
190			result code.
191
192			=item aio_fsync $fh, $callback
193
194			Asynchronously call fsync on the given filehandle and call the callback
195			with the fsync result code.
196
197			=item aio_fdatasync $fh, $callback
198
199			Asynchronously call fdatasync on the given filehandle and call the
200	root	1.20	callback with the fdatasync result code. Might set C<$!> to C<ENOSYS> if
201			C<fdatasync> is not available.
202	root	1.1
203	root	1.5	=back
204
205			=head2 SUPPORT FUNCTIONS
206
207			=over 4
208
209			=item $fileno = IO::AIO::poll_fileno
210
211	root	1.20	Return the I<request result pipe file descriptor>. This filehandle must be
212			polled for reading by some mechanism outside this module (e.g. Event or
213			select, see below or the SYNOPSIS). If the pipe becomes readable you have
214			to call C<poll_cb> to check the results.
215	root	1.5
216			See C<poll_cb> for an example.
217
218			=item IO::AIO::poll_cb
219
220			Process all outstanding events on the result pipe. You have to call this
221			regularly. Returns the number of events processed. Returns immediately
222			when no events are outstanding.
223
224	root	1.20	Example: Install an Event watcher that automatically calls
225			IO::AIO::poll_cb with high priority:
226	root	1.5
227			Event->io (fd => IO::AIO::poll_fileno,
228			poll => 'r', async => 1,
229			cb => \&IO::AIO::poll_cb);
230
231			=item IO::AIO::poll_wait
232
233			Wait till the result filehandle becomes ready for reading (simply does a
234	root	1.20	C<select> on the filehandle. This is useful if you want to synchronously wait
235	root	1.5	for some requests to finish).
236
237			See C<nreqs> for an example.
238
239			=item IO::AIO::nreqs
240
241	root	1.20	Returns the number of requests currently outstanding (i.e. for which their
242			callback has not been invoked yet).
243	root	1.5
244			Example: wait till there are no outstanding requests anymore:
245
246			IO::AIO::poll_wait, IO::AIO::poll_cb
247			while IO::AIO::nreqs;
248
249	root	1.12	=item IO::AIO::flush
250
251			Wait till all outstanding AIO requests have been handled.
252
253	root	1.13	Strictly equivalent to:
254
255			IO::AIO::poll_wait, IO::AIO::poll_cb
256			while IO::AIO::nreqs;
257
258			=item IO::AIO::poll
259
260			Waits until some requests have been handled.
261
262			Strictly equivalent to:
263
264			IO::AIO::poll_wait, IO::AIO::poll_cb
265			if IO::AIO::nreqs;
266
267	root	1.5	=item IO::AIO::min_parallel $nthreads
268
269			Set the minimum number of AIO threads to C<$nthreads>. The default is
270			C<1>, which means a single asynchronous operation can be done at one time
271			(the number of outstanding operations, however, is unlimited).
272
273			It is recommended to keep the number of threads low, as some Linux
274			kernel versions will scale negatively with the number of threads (higher
275			parallelity => MUCH higher latency). With current Linux 2.6 versions, 4-32
276			threads should be fine.
277
278			Under normal circumstances you don't need to call this function, as this
279			module automatically starts some threads (the exact number might change,
280			and is currently 4).
281
282			=item IO::AIO::max_parallel $nthreads
283
284			Sets the maximum number of AIO threads to C<$nthreads>. If more than
285			the specified number of threads are currently running, kill them. This
286			function blocks until the limit is reached.
287
288			This module automatically runs C<max_parallel 0> at program end, to ensure
289			that all threads are killed and that there are no outstanding requests.
290
291			Under normal circumstances you don't need to call this function.
292
293			=item $oldnreqs = IO::AIO::max_outstanding $nreqs
294
295			Sets the maximum number of outstanding requests to C<$nreqs>. If you
296			try to queue up more than this number of requests, the caller will block until
297			some requests have been handled.
298
299			The default is very large, so normally there is no practical limit. If you
300			queue up many requests in a loop it it often improves speed if you set
301			this to a relatively low number, such as C<100>.
302
303			Under normal circumstances you don't need to call this function.
304
305			=back
306
307	root	1.1	=cut
308
309	root	1.2	# support function to convert a fd into a perl filehandle
310			sub _fd2fh {
311			return undef if $_[0] < 0;
312
313			# try to be perl5.6-compatible
314			local *AIO_FH;
315			open AIO_FH, "+<&=$_[0]"
316			or return undef;
317
318			*AIO_FH
319			}
320
321	root	1.1	min_parallel 4;
322
323			END {
324			max_parallel 0;
325			}
326
327			1;
328
329			=head1 SEE ALSO
330
331			L<Coro>, L<Linux::AIO>.
332
333			=head1 AUTHOR
334
335			Marc Lehmann <schmorp@schmorp.de>
336			http://home.schmorp.de/
337
338			=cut
339