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;

no warnings;

use base 'Exporter';

use Fcntl ();

BEGIN {
   $VERSION = 1.1;

   @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 expecting a filehandle keep a copy of the filehandle
internally until the request has finished.

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 generate nice filehandles
   my $sym = "IO::AIO::fd#$_[0]";
   local *$sym;

   open *$sym, "+<&$_[0]"      # usually under any unix
      or open *$sym, "<&$_[0]" # cygwin needs this
      or open *$sym, ">&$_[0]" # cygwin needs this
      or return undef;

   *$sym
}

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:	1.25
Committed:	Sun Jul 31 21:21:12 2005 UTC (18 years, 9 months ago) by root
Branch:	MAIN
CVS Tags:	rel-1_1
Changes since 1.24:	+4 -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	1.22	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	root	1.23	no warnings;
62
63	root	1.1	use base 'Exporter';
64
65	root	1.2	use Fcntl ();
66
67	root	1.1	BEGIN {
68	root	1.24	$VERSION = 1.1;
69	root	1.1
70			@EXPORT = qw(aio_read aio_write aio_open aio_close aio_stat aio_lstat aio_unlink
71			aio_fsync aio_fdatasync aio_readahead);
72	root	1.4	@EXPORT_OK = qw(poll_fileno poll_cb min_parallel max_parallel max_outstanding nreqs);
73	root	1.1
74			require XSLoader;
75			XSLoader::load IO::AIO, $VERSION;
76			}
77
78	root	1.5	=head1 FUNCTIONS
79	root	1.1
80	root	1.5	=head2 AIO FUNCTIONS
81	root	1.1
82	root	1.5	All the C<aio_*> calls are more or less thin wrappers around the syscall
83			with the same name (sans C<aio_>). The arguments are similar or identical,
84	root	1.14	and they all accept an additional (and optional) C<$callback> argument
85			which must be a code reference. This code reference will get called with
86			the syscall return code (e.g. most syscalls return C<-1> on error, unlike
87			perl, which usually delivers "false") as it's sole argument when the given
88			syscall has been executed asynchronously.
89	root	1.1
90	root	1.23	All functions expecting a filehandle keep a copy of the filehandle
91			internally until the request has finished.
92	root	1.1
93	root	1.5	The filenames you pass to these routines I<must> be absolute. The reason
94	root	1.20	for this is that at the time the request is being executed, the current
95			working directory could have changed. Alternatively, you can make sure
96			that you never change the current working directory.
97	root	1.1
98	root	1.5	=over 4
99	root	1.1
100			=item aio_open $pathname, $flags, $mode, $callback
101
102	root	1.2	Asynchronously open or create a file and call the callback with a newly
103			created filehandle for the file.
104	root	1.1
105			The pathname passed to C<aio_open> must be absolute. See API NOTES, above,
106			for an explanation.
107
108	root	1.20	The C<$flags> argument is a bitmask. See the C<Fcntl> module for a
109			list. They are the same as used by C<sysopen>.
110
111			Likewise, C<$mode> specifies the mode of the newly created file, if it
112			didn't exist and C<O_CREAT> has been given, just like perl's C<sysopen>,
113			except that it is mandatory (i.e. use C<0> if you don't create new files,
114			and C<0666> or C<0777> if you do).
115	root	1.1
116			Example:
117
118			aio_open "/etc/passwd", O_RDONLY, 0, sub {
119	root	1.2	if ($_[0]) {
120			print "open successful, fh is $_[0]\n";
121	root	1.1	...
122			} else {
123			die "open failed: $!\n";
124			}
125			};
126
127			=item aio_close $fh, $callback
128
129	root	1.2	Asynchronously close a file and call the callback with the result
130			code. I<WARNING:> although accepted, you should not pass in a perl
131	root	1.20	filehandle here, as perl will likely close the file descriptor another
132			time when the filehandle is destroyed. Normally, you can safely call perls
133			C<close> or just let filehandles go out of scope.
134
135			This is supposed to be a bug in the API, so that might change. It's
136			therefore best to avoid this function.
137	root	1.1
138			=item aio_read $fh,$offset,$length, $data,$dataoffset,$callback
139
140			=item aio_write $fh,$offset,$length, $data,$dataoffset,$callback
141
142			Reads or writes C<length> bytes from the specified C<fh> and C<offset>
143			into the scalar given by C<data> and offset C<dataoffset> and calls the
144			callback without the actual number of bytes read (or -1 on error, just
145			like the syscall).
146
147	root	1.17	Example: Read 15 bytes at offset 7 into scalar C<$buffer>, starting at
148	root	1.1	offset C<0> within the scalar:
149
150			aio_read $fh, 7, 15, $buffer, 0, sub {
151	root	1.9	$_[0] > 0 or die "read error: $!";
152			print "read $_[0] bytes: <$buffer>\n";
153	root	1.1	};
154
155			=item aio_readahead $fh,$offset,$length, $callback
156
157			Asynchronously reads the specified byte range into the page cache, using
158	root	1.17	the C<readahead> syscall. If that syscall doesn't exist (likely if your OS
159	root	1.20	isn't Linux) the status will be C<-1> and C<$!> is set to C<ENOSYS>.
160	root	1.1
161	root	1.20	C<aio_readahead> populates the page cache with data from a file so that
162	root	1.1	subsequent reads from that file will not block on disk I/O. The C<$offset>
163			argument specifies the starting point from which data is to be read and
164			C<$length> specifies the number of bytes to be read. I/O is performed in
165			whole pages, so that offset is effectively rounded down to a page boundary
166			and bytes are read up to the next page boundary greater than or equal to
167	root	1.20	(off-set+length). C<aio_readahead> does not read beyond the end of the
168	root	1.1	file. The current file offset of the file is left unchanged.
169
170			=item aio_stat $fh_or_path, $callback
171
172			=item aio_lstat $fh, $callback
173
174			Works like perl's C<stat> or C<lstat> in void context. The callback will
175			be called after the stat and the results will be available using C<stat _>
176			or C<-s _> etc...
177
178			The pathname passed to C<aio_stat> must be absolute. See API NOTES, above,
179			for an explanation.
180
181			Currently, the stats are always 64-bit-stats, i.e. instead of returning an
182			error when stat'ing a large file, the results will be silently truncated
183			unless perl itself is compiled with large file support.
184
185			Example: Print the length of F</etc/passwd>:
186
187			aio_stat "/etc/passwd", sub {
188			$_[0] and die "stat failed: $!";
189			print "size is ", -s _, "\n";
190			};
191
192			=item aio_unlink $pathname, $callback
193
194			Asynchronously unlink (delete) a file and call the callback with the
195			result code.
196
197			=item aio_fsync $fh, $callback
198
199			Asynchronously call fsync on the given filehandle and call the callback
200			with the fsync result code.
201
202			=item aio_fdatasync $fh, $callback
203
204			Asynchronously call fdatasync on the given filehandle and call the
205	root	1.20	callback with the fdatasync result code. Might set C<$!> to C<ENOSYS> if
206			C<fdatasync> is not available.
207	root	1.1
208	root	1.5	=back
209
210			=head2 SUPPORT FUNCTIONS
211
212			=over 4
213
214			=item $fileno = IO::AIO::poll_fileno
215
216	root	1.20	Return the I<request result pipe file descriptor>. This filehandle must be
217			polled for reading by some mechanism outside this module (e.g. Event or
218			select, see below or the SYNOPSIS). If the pipe becomes readable you have
219			to call C<poll_cb> to check the results.
220	root	1.5
221			See C<poll_cb> for an example.
222
223			=item IO::AIO::poll_cb
224
225			Process all outstanding events on the result pipe. You have to call this
226			regularly. Returns the number of events processed. Returns immediately
227			when no events are outstanding.
228
229	root	1.20	Example: Install an Event watcher that automatically calls
230			IO::AIO::poll_cb with high priority:
231	root	1.5
232			Event->io (fd => IO::AIO::poll_fileno,
233			poll => 'r', async => 1,
234			cb => \&IO::AIO::poll_cb);
235
236			=item IO::AIO::poll_wait
237
238			Wait till the result filehandle becomes ready for reading (simply does a
239	root	1.20	C<select> on the filehandle. This is useful if you want to synchronously wait
240	root	1.5	for some requests to finish).
241
242			See C<nreqs> for an example.
243
244			=item IO::AIO::nreqs
245
246	root	1.20	Returns the number of requests currently outstanding (i.e. for which their
247			callback has not been invoked yet).
248	root	1.5
249			Example: wait till there are no outstanding requests anymore:
250
251			IO::AIO::poll_wait, IO::AIO::poll_cb
252			while IO::AIO::nreqs;
253
254	root	1.12	=item IO::AIO::flush
255
256			Wait till all outstanding AIO requests have been handled.
257
258	root	1.13	Strictly equivalent to:
259
260			IO::AIO::poll_wait, IO::AIO::poll_cb
261			while IO::AIO::nreqs;
262
263			=item IO::AIO::poll
264
265			Waits until some requests have been handled.
266
267			Strictly equivalent to:
268
269			IO::AIO::poll_wait, IO::AIO::poll_cb
270			if IO::AIO::nreqs;
271
272	root	1.5	=item IO::AIO::min_parallel $nthreads
273
274			Set the minimum number of AIO threads to C<$nthreads>. The default is
275			C<1>, which means a single asynchronous operation can be done at one time
276			(the number of outstanding operations, however, is unlimited).
277
278			It is recommended to keep the number of threads low, as some Linux
279			kernel versions will scale negatively with the number of threads (higher
280			parallelity => MUCH higher latency). With current Linux 2.6 versions, 4-32
281			threads should be fine.
282
283			Under normal circumstances you don't need to call this function, as this
284			module automatically starts some threads (the exact number might change,
285			and is currently 4).
286
287			=item IO::AIO::max_parallel $nthreads
288
289			Sets the maximum number of AIO threads to C<$nthreads>. If more than
290			the specified number of threads are currently running, kill them. This
291			function blocks until the limit is reached.
292
293			This module automatically runs C<max_parallel 0> at program end, to ensure
294			that all threads are killed and that there are no outstanding requests.
295
296			Under normal circumstances you don't need to call this function.
297
298			=item $oldnreqs = IO::AIO::max_outstanding $nreqs
299
300			Sets the maximum number of outstanding requests to C<$nreqs>. If you
301			try to queue up more than this number of requests, the caller will block until
302			some requests have been handled.
303
304			The default is very large, so normally there is no practical limit. If you
305			queue up many requests in a loop it it often improves speed if you set
306			this to a relatively low number, such as C<100>.
307
308			Under normal circumstances you don't need to call this function.
309
310			=back
311
312	root	1.1	=cut
313
314	root	1.2	# support function to convert a fd into a perl filehandle
315			sub _fd2fh {
316			return undef if $_[0] < 0;
317
318	root	1.23	# try to generate nice filehandles
319			my $sym = "IO::AIO::fd#$_[0]";
320			local *$sym;
321	root	1.25
322			open *$sym, "+<&$_[0]" # usually under any unix
323			or open *$sym, "<&$_[0]" # cygwin needs this
324			or open *$sym, ">&$_[0]" # cygwin needs this
325	root	1.2	or return undef;
326
327	root	1.23	*$sym
328	root	1.2	}
329
330	root	1.1	min_parallel 4;
331
332			END {
333			max_parallel 0;
334			}
335
336			1;
337
338			=head1 SEE ALSO
339
340			L<Coro>, L<Linux::AIO>.
341
342			=head1 AUTHOR
343
344			Marc Lehmann <schmorp@schmorp.de>
345			http://home.schmorp.de/
346
347			=cut
348