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_rmdir aio_symlink 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

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.

If that syscall doesn't exist (likely if your OS isn't Linux) it will be
emulated by simply reading the data, which would have a similar effect.

=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_rmdir $pathname, $callback

Asynchronously rmdir (delete) a directory 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.

If this call isn't available because your OS lacks it or it couldn't be
detected, it will be emulated by calling C<fsync> instead.

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

   *$sym
}

min_parallel 4;

END {
   max_parallel 0;
}

1;

=head2 FORK BEHAVIOUR

IO::AIO handles all outstanding AIO requests before the fork, destroys all
AIO threads, and recreates them in both the parent and the child after the
fork.


=head1 SEE ALSO

L<Coro>, L<Linux::AIO>.

=head1 AUTHOR

 Marc Lehmann <schmorp@schmorp.de>
 http://home.schmorp.de/

=cut

Revision:	1.27
Committed:	Tue Aug 16 22:22:18 2005 UTC (18 years, 9 months ago) by root
Branch:	MAIN
Changes since 1.26:	+16 -4 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	root	1.27	aio_rmdir aio_symlink 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, $callback
156
157	root	1.20	C<aio_readahead> populates the page cache with data from a file so that
158	root	1.1	subsequent reads from that file will not block on disk I/O. The C<$offset>
159			argument specifies the starting point from which data is to be read and
160			C<$length> specifies the number of bytes to be read. I/O is performed in
161			whole pages, so that offset is effectively rounded down to a page boundary
162			and bytes are read up to the next page boundary greater than or equal to
163	root	1.20	(off-set+length). C<aio_readahead> does not read beyond the end of the
164	root	1.1	file. The current file offset of the file is left unchanged.
165
166	root	1.26	If that syscall doesn't exist (likely if your OS isn't Linux) it will be
167			emulated by simply reading the data, which would have a similar effect.
168
169	root	1.1	=item aio_stat $fh_or_path, $callback
170
171			=item aio_lstat $fh, $callback
172
173			Works like perl's C<stat> or C<lstat> in void context. The callback will
174			be called after the stat and the results will be available using C<stat _>
175			or C<-s _> etc...
176
177			The pathname passed to C<aio_stat> must be absolute. See API NOTES, above,
178			for an explanation.
179
180			Currently, the stats are always 64-bit-stats, i.e. instead of returning an
181			error when stat'ing a large file, the results will be silently truncated
182			unless perl itself is compiled with large file support.
183
184			Example: Print the length of F</etc/passwd>:
185
186			aio_stat "/etc/passwd", sub {
187			$_[0] and die "stat failed: $!";
188			print "size is ", -s _, "\n";
189			};
190
191			=item aio_unlink $pathname, $callback
192
193			Asynchronously unlink (delete) a file and call the callback with the
194			result code.
195
196	root	1.27	=item aio_rmdir $pathname, $callback
197
198			Asynchronously rmdir (delete) a directory and call the callback with the
199			result code.
200
201	root	1.1	=item aio_fsync $fh, $callback
202
203			Asynchronously call fsync on the given filehandle and call the callback
204			with the fsync result code.
205
206			=item aio_fdatasync $fh, $callback
207
208			Asynchronously call fdatasync on the given filehandle and call the
209	root	1.26	callback with the fdatasync result code.
210
211			If this call isn't available because your OS lacks it or it couldn't be
212			detected, it will be emulated by calling C<fsync> instead.
213	root	1.1
214	root	1.5	=back
215
216			=head2 SUPPORT FUNCTIONS
217
218			=over 4
219
220			=item $fileno = IO::AIO::poll_fileno
221
222	root	1.20	Return the I<request result pipe file descriptor>. This filehandle must be
223			polled for reading by some mechanism outside this module (e.g. Event or
224			select, see below or the SYNOPSIS). If the pipe becomes readable you have
225			to call C<poll_cb> to check the results.
226	root	1.5
227			See C<poll_cb> for an example.
228
229			=item IO::AIO::poll_cb
230
231			Process all outstanding events on the result pipe. You have to call this
232			regularly. Returns the number of events processed. Returns immediately
233			when no events are outstanding.
234
235	root	1.20	Example: Install an Event watcher that automatically calls
236			IO::AIO::poll_cb with high priority:
237	root	1.5
238			Event->io (fd => IO::AIO::poll_fileno,
239			poll => 'r', async => 1,
240			cb => \&IO::AIO::poll_cb);
241
242			=item IO::AIO::poll_wait
243
244			Wait till the result filehandle becomes ready for reading (simply does a
245	root	1.20	C<select> on the filehandle. This is useful if you want to synchronously wait
246	root	1.5	for some requests to finish).
247
248			See C<nreqs> for an example.
249
250			=item IO::AIO::nreqs
251
252	root	1.20	Returns the number of requests currently outstanding (i.e. for which their
253			callback has not been invoked yet).
254	root	1.5
255			Example: wait till there are no outstanding requests anymore:
256
257			IO::AIO::poll_wait, IO::AIO::poll_cb
258			while IO::AIO::nreqs;
259
260	root	1.12	=item IO::AIO::flush
261
262			Wait till all outstanding AIO requests have been handled.
263
264	root	1.13	Strictly equivalent to:
265
266			IO::AIO::poll_wait, IO::AIO::poll_cb
267			while IO::AIO::nreqs;
268
269			=item IO::AIO::poll
270
271			Waits until some requests have been handled.
272
273			Strictly equivalent to:
274
275			IO::AIO::poll_wait, IO::AIO::poll_cb
276			if IO::AIO::nreqs;
277
278	root	1.5	=item IO::AIO::min_parallel $nthreads
279
280			Set the minimum number of AIO threads to C<$nthreads>. The default is
281			C<1>, which means a single asynchronous operation can be done at one time
282			(the number of outstanding operations, however, is unlimited).
283
284			It is recommended to keep the number of threads low, as some Linux
285			kernel versions will scale negatively with the number of threads (higher
286			parallelity => MUCH higher latency). With current Linux 2.6 versions, 4-32
287			threads should be fine.
288
289			Under normal circumstances you don't need to call this function, as this
290			module automatically starts some threads (the exact number might change,
291			and is currently 4).
292
293			=item IO::AIO::max_parallel $nthreads
294
295			Sets the maximum number of AIO threads to C<$nthreads>. If more than
296			the specified number of threads are currently running, kill them. This
297			function blocks until the limit is reached.
298
299			This module automatically runs C<max_parallel 0> at program end, to ensure
300			that all threads are killed and that there are no outstanding requests.
301
302			Under normal circumstances you don't need to call this function.
303
304			=item $oldnreqs = IO::AIO::max_outstanding $nreqs
305
306			Sets the maximum number of outstanding requests to C<$nreqs>. If you
307			try to queue up more than this number of requests, the caller will block until
308			some requests have been handled.
309
310			The default is very large, so normally there is no practical limit. If you
311			queue up many requests in a loop it it often improves speed if you set
312			this to a relatively low number, such as C<100>.
313
314			Under normal circumstances you don't need to call this function.
315
316			=back
317
318	root	1.1	=cut
319
320	root	1.2	# support function to convert a fd into a perl filehandle
321			sub _fd2fh {
322			return undef if $_[0] < 0;
323
324	root	1.23	# try to generate nice filehandles
325			my $sym = "IO::AIO::fd#$_[0]";
326			local *$sym;
327	root	1.25
328	root	1.27	open *$sym, "+<&=$_[0]" # usually works under any unix
329			or open *$sym, "<&=$_[0]" # cygwin needs this
330			or open *$sym, ">&=$_[0]" # or this
331	root	1.2	or return undef;
332
333	root	1.23	*$sym
334	root	1.2	}
335
336	root	1.1	min_parallel 4;
337
338			END {
339			max_parallel 0;
340			}
341
342			1;
343
344	root	1.27	=head2 FORK BEHAVIOUR
345
346			IO::AIO handles all outstanding AIO requests before the fork, destroys all
347			AIO threads, and recreates them in both the parent and the child after the
348			fork.
349
350
351	root	1.1	=head1 SEE ALSO
352
353			L<Coro>, L<Linux::AIO>.
354
355			=head1 AUTHOR
356
357			Marc Lehmann <schmorp@schmorp.de>
358			http://home.schmorp.de/
359
360			=cut
361