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, always call
C<poll_cb> from within the same thread, or never call C<poll_cb> (or other
C<aio_> functions) recursively.

=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:	1.22
Committed:	Wed Jul 20 21:55:27 2005 UTC (18 years, 10 months ago) by root
Branch:	MAIN
CVS Tags:	rel-0_9
Changes since 1.21:	+4 -2 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	1.22	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	1.22	currently not reentrant, so use appropriate locking yourself, always call
54			C<poll_cb> from within the same thread, or never call C<poll_cb> (or other
55			C<aio_> functions) recursively.
56	root	1.1
57			=cut
58
59			package IO::AIO;
60
61			use base 'Exporter';
62
63	root	1.2	use Fcntl ();
64
65	root	1.1	BEGIN {
66	root	1.21	$VERSION = 0.9;
67	root	1.1
68			@EXPORT = qw(aio_read aio_write aio_open aio_close aio_stat aio_lstat aio_unlink
69			aio_fsync aio_fdatasync aio_readahead);
70	root	1.4	@EXPORT_OK = qw(poll_fileno poll_cb min_parallel max_parallel max_outstanding nreqs);
71	root	1.1
72			require XSLoader;
73			XSLoader::load IO::AIO, $VERSION;
74			}
75
76	root	1.5	=head1 FUNCTIONS
77	root	1.1
78	root	1.5	=head2 AIO FUNCTIONS
79	root	1.1
80	root	1.5	All the C<aio_*> calls are more or less thin wrappers around the syscall
81			with the same name (sans C<aio_>). The arguments are similar or identical,
82	root	1.14	and they all accept an additional (and optional) C<$callback> argument
83			which must be a code reference. This code reference will get called with
84			the syscall return code (e.g. most syscalls return C<-1> on error, unlike
85			perl, which usually delivers "false") as it's sole argument when the given
86			syscall has been executed asynchronously.
87	root	1.1
88	root	1.5	All functions that expect a filehandle will also accept a file descriptor.
89	root	1.1
90	root	1.5	The filenames you pass to these routines I<must> be absolute. The reason
91	root	1.20	for this is that at the time the request is being executed, the current
92			working directory could have changed. Alternatively, you can make sure
93			that you never change the current working directory.
94	root	1.1
95	root	1.5	=over 4
96	root	1.1
97			=item aio_open $pathname, $flags, $mode, $callback
98
99	root	1.2	Asynchronously open or create a file and call the callback with a newly
100			created filehandle for the file.
101	root	1.1
102			The pathname passed to C<aio_open> must be absolute. See API NOTES, above,
103			for an explanation.
104
105	root	1.20	The C<$flags> argument is a bitmask. See the C<Fcntl> module for a
106			list. They are the same as used by C<sysopen>.
107
108			Likewise, C<$mode> specifies the mode of the newly created file, if it
109			didn't exist and C<O_CREAT> has been given, just like perl's C<sysopen>,
110			except that it is mandatory (i.e. use C<0> if you don't create new files,
111			and C<0666> or C<0777> if you do).
112	root	1.1
113			Example:
114
115			aio_open "/etc/passwd", O_RDONLY, 0, sub {
116	root	1.2	if ($_[0]) {
117			print "open successful, fh is $_[0]\n";
118	root	1.1	...
119			} else {
120			die "open failed: $!\n";
121			}
122			};
123
124			=item aio_close $fh, $callback
125
126	root	1.2	Asynchronously close a file and call the callback with the result
127			code. I<WARNING:> although accepted, you should not pass in a perl
128	root	1.20	filehandle here, as perl will likely close the file descriptor another
129			time when the filehandle is destroyed. Normally, you can safely call perls
130			C<close> or just let filehandles go out of scope.
131
132			This is supposed to be a bug in the API, so that might change. It's
133			therefore best to avoid this function.
134	root	1.1
135			=item aio_read $fh,$offset,$length, $data,$dataoffset,$callback
136
137			=item aio_write $fh,$offset,$length, $data,$dataoffset,$callback
138
139			Reads or writes C<length> bytes from the specified C<fh> and C<offset>
140			into the scalar given by C<data> and offset C<dataoffset> and calls the
141			callback without the actual number of bytes read (or -1 on error, just
142			like the syscall).
143
144	root	1.17	Example: Read 15 bytes at offset 7 into scalar C<$buffer>, starting at
145	root	1.1	offset C<0> within the scalar:
146
147			aio_read $fh, 7, 15, $buffer, 0, sub {
148	root	1.9	$_[0] > 0 or die "read error: $!";
149			print "read $_[0] bytes: <$buffer>\n";
150	root	1.1	};
151
152			=item aio_readahead $fh,$offset,$length, $callback
153
154			Asynchronously reads the specified byte range into the page cache, using
155	root	1.17	the C<readahead> syscall. If that syscall doesn't exist (likely if your OS
156	root	1.20	isn't Linux) the status will be C<-1> and C<$!> is set to C<ENOSYS>.
157	root	1.1
158	root	1.20	C<aio_readahead> populates the page cache with data from a file so that
159	root	1.1	subsequent reads from that file will not block on disk I/O. The C<$offset>
160			argument specifies the starting point from which data is to be read and
161			C<$length> specifies the number of bytes to be read. I/O is performed in
162			whole pages, so that offset is effectively rounded down to a page boundary
163			and bytes are read up to the next page boundary greater than or equal to
164	root	1.20	(off-set+length). C<aio_readahead> does not read beyond the end of the
165	root	1.1	file. The current file offset of the file is left unchanged.
166
167			=item aio_stat $fh_or_path, $callback
168
169			=item aio_lstat $fh, $callback
170
171			Works like perl's C<stat> or C<lstat> in void context. The callback will
172			be called after the stat and the results will be available using C<stat _>
173			or C<-s _> etc...
174
175			The pathname passed to C<aio_stat> must be absolute. See API NOTES, above,
176			for an explanation.
177
178			Currently, the stats are always 64-bit-stats, i.e. instead of returning an
179			error when stat'ing a large file, the results will be silently truncated
180			unless perl itself is compiled with large file support.
181
182			Example: Print the length of F</etc/passwd>:
183
184			aio_stat "/etc/passwd", sub {
185			$_[0] and die "stat failed: $!";
186			print "size is ", -s _, "\n";
187			};
188
189			=item aio_unlink $pathname, $callback
190
191			Asynchronously unlink (delete) a file and call the callback with the
192			result code.
193
194			=item aio_fsync $fh, $callback
195
196			Asynchronously call fsync on the given filehandle and call the callback
197			with the fsync result code.
198
199			=item aio_fdatasync $fh, $callback
200
201			Asynchronously call fdatasync on the given filehandle and call the
202	root	1.20	callback with the fdatasync result code. Might set C<$!> to C<ENOSYS> if
203			C<fdatasync> is not available.
204	root	1.1
205	root	1.5	=back
206
207			=head2 SUPPORT FUNCTIONS
208
209			=over 4
210
211			=item $fileno = IO::AIO::poll_fileno
212
213	root	1.20	Return the I<request result pipe file descriptor>. This filehandle must be
214			polled for reading by some mechanism outside this module (e.g. Event or
215			select, see below or the SYNOPSIS). If the pipe becomes readable you have
216			to call C<poll_cb> to check the results.
217	root	1.5
218			See C<poll_cb> for an example.
219
220			=item IO::AIO::poll_cb
221
222			Process all outstanding events on the result pipe. You have to call this
223			regularly. Returns the number of events processed. Returns immediately
224			when no events are outstanding.
225
226	root	1.20	Example: Install an Event watcher that automatically calls
227			IO::AIO::poll_cb with high priority:
228	root	1.5
229			Event->io (fd => IO::AIO::poll_fileno,
230			poll => 'r', async => 1,
231			cb => \&IO::AIO::poll_cb);
232
233			=item IO::AIO::poll_wait
234
235			Wait till the result filehandle becomes ready for reading (simply does a
236	root	1.20	C<select> on the filehandle. This is useful if you want to synchronously wait
237	root	1.5	for some requests to finish).
238
239			See C<nreqs> for an example.
240
241			=item IO::AIO::nreqs
242
243	root	1.20	Returns the number of requests currently outstanding (i.e. for which their
244			callback has not been invoked yet).
245	root	1.5
246			Example: wait till there are no outstanding requests anymore:
247
248			IO::AIO::poll_wait, IO::AIO::poll_cb
249			while IO::AIO::nreqs;
250
251	root	1.12	=item IO::AIO::flush
252
253			Wait till all outstanding AIO requests have been handled.
254
255	root	1.13	Strictly equivalent to:
256
257			IO::AIO::poll_wait, IO::AIO::poll_cb
258			while IO::AIO::nreqs;
259
260			=item IO::AIO::poll
261
262			Waits until some requests have been handled.
263
264			Strictly equivalent to:
265
266			IO::AIO::poll_wait, IO::AIO::poll_cb
267			if IO::AIO::nreqs;
268
269	root	1.5	=item IO::AIO::min_parallel $nthreads
270
271			Set the minimum number of AIO threads to C<$nthreads>. The default is
272			C<1>, which means a single asynchronous operation can be done at one time
273			(the number of outstanding operations, however, is unlimited).
274
275			It is recommended to keep the number of threads low, as some Linux
276			kernel versions will scale negatively with the number of threads (higher
277			parallelity => MUCH higher latency). With current Linux 2.6 versions, 4-32
278			threads should be fine.
279
280			Under normal circumstances you don't need to call this function, as this
281			module automatically starts some threads (the exact number might change,
282			and is currently 4).
283
284			=item IO::AIO::max_parallel $nthreads
285
286			Sets the maximum number of AIO threads to C<$nthreads>. If more than
287			the specified number of threads are currently running, kill them. This
288			function blocks until the limit is reached.
289
290			This module automatically runs C<max_parallel 0> at program end, to ensure
291			that all threads are killed and that there are no outstanding requests.
292
293			Under normal circumstances you don't need to call this function.
294
295			=item $oldnreqs = IO::AIO::max_outstanding $nreqs
296
297			Sets the maximum number of outstanding requests to C<$nreqs>. If you
298			try to queue up more than this number of requests, the caller will block until
299			some requests have been handled.
300
301			The default is very large, so normally there is no practical limit. If you
302			queue up many requests in a loop it it often improves speed if you set
303			this to a relatively low number, such as C<100>.
304
305			Under normal circumstances you don't need to call this function.
306
307			=back
308
309	root	1.1	=cut
310
311	root	1.2	# support function to convert a fd into a perl filehandle
312			sub _fd2fh {
313			return undef if $_[0] < 0;
314
315			# try to be perl5.6-compatible
316			local *AIO_FH;
317			open AIO_FH, "+<&=$_[0]"
318			or return undef;
319
320			*AIO_FH
321			}
322
323	root	1.1	min_parallel 4;
324
325			END {
326			max_parallel 0;
327			}
328
329			1;
330
331			=head1 SEE ALSO
332
333			L<Coro>, L<Linux::AIO>.
334
335			=head1 AUTHOR
336
337			Marc Lehmann <schmorp@schmorp.de>
338			http://home.schmorp.de/
339
340			=cut
341