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 *
#	Content
1	=head1 NAME
2
3	IO::AIO - Asynchronous Input/Output
4
5	=head1 SYNOPSIS
6
7	use IO::AIO;
8
9	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	$_[0] > 0 or die "read error: $!";
18	};
19
20	# Event
21	Event->io (fd => IO::AIO::poll_fileno,
22	poll => 'r',
23	cb => \&IO::AIO::poll_cb);
24
25	# Glib/Gtk2
26	add_watch Glib::IO IO::AIO::poll_fileno,
27	in => sub { IO::AIO::poll_cb, 1 };
28
29	# Tk
30	Tk::Event::IO->fileevent (IO::AIO::poll_fileno, "",
31	readable => \&IO::AIO::poll_cb);
32
33	# Danga::Socket
34	Danga::Socket->AddOtherFds (IO::AIO::poll_fileno =>
35	\&IO::AIO::poll_cb);
36
37
38	=head1 DESCRIPTION
39
40	This module implements asynchronous I/O using whatever means your
41	operating system supports.
42
43	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
52	Although the module will work with in the presence of other threads, it is
53	currently not reentrant, so use appropriate locking yourself.
54
55	=cut
56
57	package IO::AIO;
58
59	use base 'Exporter';
60
61	use Fcntl ();
62
63	BEGIN {
64	$VERSION = 0.9;
65
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	@EXPORT_OK = qw(poll_fileno poll_cb min_parallel max_parallel max_outstanding nreqs);
69
70	require XSLoader;
71	XSLoader::load IO::AIO, $VERSION;
72	}
73
74	=head1 FUNCTIONS
75
76	=head2 AIO FUNCTIONS
77
78	All the C<aio_*> calls are more or less thin wrappers around the syscall
79	with the same name (sans C<aio_>). The arguments are similar or identical,
80	and they all accept an additional (and optional) C<$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
86	All functions that expect a filehandle will also accept a file descriptor.
87
88	The filenames you pass to these routines I<must> be absolute. The reason
89	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
93	=over 4
94
95	=item aio_open $pathname, $flags, $mode, $callback
96
97	Asynchronously open or create a file and call the callback with a newly
98	created filehandle for the file.
99
100	The pathname passed to C<aio_open> must be absolute. See API NOTES, above,
101	for an explanation.
102
103	The C<$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<$mode> specifies the mode of the newly created file, if it
107	didn't exist and C<O_CREAT> has been given, just like perl's C<sysopen>,
108	except that it is mandatory (i.e. use C<0> if you don't create new files,
109	and C<0666> or C<0777> if you do).
110
111	Example:
112
113	aio_open "/etc/passwd", O_RDONLY, 0, sub {
114	if ($_[0]) {
115	print "open successful, fh is $_[0]\n";
116	...
117	} else {
118	die "open failed: $!\n";
119	}
120	};
121
122	=item aio_close $fh, $callback
123
124	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	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
133	=item aio_read $fh,$offset,$length, $data,$dataoffset,$callback
134
135	=item aio_write $fh,$offset,$length, $data,$dataoffset,$callback
136
137	Reads or writes C<length> bytes from the specified C<fh> and C<offset>
138	into the scalar given by C<data> and offset C<dataoffset> and calls the
139	callback without the actual number of bytes read (or -1 on error, just
140	like the syscall).
141
142	Example: Read 15 bytes at offset 7 into scalar C<$buffer>, starting at
143	offset C<0> within the scalar:
144
145	aio_read $fh, 7, 15, $buffer, 0, sub {
146	$_[0] > 0 or die "read error: $!";
147	print "read $_[0] bytes: <$buffer>\n";
148	};
149
150	=item aio_readahead $fh,$offset,$length, $callback
151
152	Asynchronously reads the specified byte range into the page cache, using
153	the C<readahead> syscall. If that syscall doesn't exist (likely if your OS
154	isn't Linux) the status will be C<-1> and C<$!> is set to C<ENOSYS>.
155
156	C<aio_readahead> populates the page cache with data from a file so that
157	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	(off-set+length). C<aio_readahead> does not read beyond the end of the
163	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, $callback
198
199	Asynchronously call fdatasync on the given filehandle and call the
200	callback with the fdatasync result code. Might set C<$!> to C<ENOSYS> if
201	C<fdatasync> is not available.
202
203	=back
204
205	=head2 SUPPORT FUNCTIONS
206
207	=over 4
208
209	=item $fileno = IO::AIO::poll_fileno
210
211	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
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	Example: Install an Event watcher that automatically calls
225	IO::AIO::poll_cb with high priority:
226
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	C<select> on the filehandle. This is useful if you want to synchronously wait
235	for some requests to finish).
236
237	See C<nreqs> for an example.
238
239	=item IO::AIO::nreqs
240
241	Returns the number of requests currently outstanding (i.e. for which their
242	callback has not been invoked yet).
243
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	=item IO::AIO::flush
250
251	Wait till all outstanding AIO requests have been handled.
252
253	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	=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	=cut
308
309	# 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	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