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

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_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 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:	1.26
Committed:	Sun Aug 7 03:34:07 2005 UTC (18 years, 10 months ago) by root
Branch:	MAIN
Changes since 1.25:	+7 -6 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, 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
57	=cut
58
59	package IO::AIO;
60
61	no warnings;
62
63	use base 'Exporter';
64
65	use Fcntl ();
66
67	BEGIN {
68	$VERSION = 1.1;
69
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	@EXPORT_OK = qw(poll_fileno poll_cb min_parallel max_parallel max_outstanding nreqs);
73
74	require XSLoader;
75	XSLoader::load IO::AIO, $VERSION;
76	}
77
78	=head1 FUNCTIONS
79
80	=head2 AIO FUNCTIONS
81
82	All the C<aio_*> calls are more or less thin wrappers around the syscall
83	with the same name (sans C<aio_>). The arguments are similar or identical,
84	and they all accept an additional (and optional) C<$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
90	All functions expecting a filehandle keep a copy of the filehandle
91	internally until the request has finished.
92
93	The filenames you pass to these routines I<must> be absolute. The reason
94	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
98	=over 4
99
100	=item aio_open $pathname, $flags, $mode, $callback
101
102	Asynchronously open or create a file and call the callback with a newly
103	created filehandle for the file.
104
105	The pathname passed to C<aio_open> must be absolute. See API NOTES, above,
106	for an explanation.
107
108	The C<$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<$mode> specifies the mode of the newly created file, if it
112	didn't exist and C<O_CREAT> has been given, just like perl's C<sysopen>,
113	except that it is mandatory (i.e. use C<0> if you don't create new files,
114	and C<0666> or C<0777> if you do).
115
116	Example:
117
118	aio_open "/etc/passwd", O_RDONLY, 0, sub {
119	if ($_[0]) {
120	print "open successful, fh is $_[0]\n";
121	...
122	} else {
123	die "open failed: $!\n";
124	}
125	};
126
127	=item aio_close $fh, $callback
128
129	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	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
138	=item aio_read $fh,$offset,$length, $data,$dataoffset,$callback
139
140	=item aio_write $fh,$offset,$length, $data,$dataoffset,$callback
141
142	Reads or writes C<length> bytes from the specified C<fh> and C<offset>
143	into the scalar given by C<data> and offset C<dataoffset> and calls the
144	callback without the actual number of bytes read (or -1 on error, just
145	like the syscall).
146
147	Example: Read 15 bytes at offset 7 into scalar C<$buffer>, starting at
148	offset C<0> within the scalar:
149
150	aio_read $fh, 7, 15, $buffer, 0, sub {
151	$_[0] > 0 or die "read error: $!";
152	print "read $_[0] bytes: <$buffer>\n";
153	};
154
155	=item aio_readahead $fh,$offset,$length, $callback
156
157	C<aio_readahead> populates the page cache with data from a file so that
158	subsequent reads from that file will not block on disk I/O. The C<$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	(off-set+length). C<aio_readahead> does not read beyond the end of the
164	file. The current file offset of the file is left unchanged.
165
166	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	=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	=item aio_fsync $fh, $callback
197
198	Asynchronously call fsync on the given filehandle and call the callback
199	with the fsync result code.
200
201	=item aio_fdatasync $fh, $callback
202
203	Asynchronously call fdatasync on the given filehandle and call the
204	callback with the fdatasync result code.
205
206	If this call isn't available because your OS lacks it or it couldn't be
207	detected, it will be emulated by calling C<fsync> instead.
208
209	=back
210
211	=head2 SUPPORT FUNCTIONS
212
213	=over 4
214
215	=item $fileno = IO::AIO::poll_fileno
216
217	Return the I<request result pipe file descriptor>. This filehandle must be
218	polled for reading by some mechanism outside this module (e.g. Event or
219	select, see below or the SYNOPSIS). If the pipe becomes readable you have
220	to call C<poll_cb> to check the results.
221
222	See C<poll_cb> for an example.
223
224	=item IO::AIO::poll_cb
225
226	Process all outstanding events on the result pipe. You have to call this
227	regularly. Returns the number of events processed. Returns immediately
228	when no events are outstanding.
229
230	Example: Install an Event watcher that automatically calls
231	IO::AIO::poll_cb with high priority:
232
233	Event->io (fd => IO::AIO::poll_fileno,
234	poll => 'r', async => 1,
235	cb => \&IO::AIO::poll_cb);
236
237	=item IO::AIO::poll_wait
238
239	Wait till the result filehandle becomes ready for reading (simply does a
240	C<select> on the filehandle. This is useful if you want to synchronously wait
241	for some requests to finish).
242
243	See C<nreqs> for an example.
244
245	=item IO::AIO::nreqs
246
247	Returns the number of requests currently outstanding (i.e. for which their
248	callback has not been invoked yet).
249
250	Example: wait till there are no outstanding requests anymore:
251
252	IO::AIO::poll_wait, IO::AIO::poll_cb
253	while IO::AIO::nreqs;
254
255	=item IO::AIO::flush
256
257	Wait till all outstanding AIO requests have been handled.
258
259	Strictly equivalent to:
260
261	IO::AIO::poll_wait, IO::AIO::poll_cb
262	while IO::AIO::nreqs;
263
264	=item IO::AIO::poll
265
266	Waits until some requests have been handled.
267
268	Strictly equivalent to:
269
270	IO::AIO::poll_wait, IO::AIO::poll_cb
271	if IO::AIO::nreqs;
272
273	=item IO::AIO::min_parallel $nthreads
274
275	Set the minimum number of AIO threads to C<$nthreads>. The default is
276	C<1>, which means a single asynchronous operation can be done at one time
277	(the number of outstanding operations, however, is unlimited).
278
279	It is recommended to keep the number of threads low, as some Linux
280	kernel versions will scale negatively with the number of threads (higher
281	parallelity => MUCH higher latency). With current Linux 2.6 versions, 4-32
282	threads should be fine.
283
284	Under normal circumstances you don't need to call this function, as this
285	module automatically starts some threads (the exact number might change,
286	and is currently 4).
287
288	=item IO::AIO::max_parallel $nthreads
289
290	Sets the maximum number of AIO threads to C<$nthreads>. If more than
291	the specified number of threads are currently running, kill them. This
292	function blocks until the limit is reached.
293
294	This module automatically runs C<max_parallel 0> at program end, to ensure
295	that all threads are killed and that there are no outstanding requests.
296
297	Under normal circumstances you don't need to call this function.
298
299	=item $oldnreqs = IO::AIO::max_outstanding $nreqs
300
301	Sets the maximum number of outstanding requests to C<$nreqs>. If you
302	try to queue up more than this number of requests, the caller will block until
303	some requests have been handled.
304
305	The default is very large, so normally there is no practical limit. If you
306	queue up many requests in a loop it it often improves speed if you set
307	this to a relatively low number, such as C<100>.
308
309	Under normal circumstances you don't need to call this function.
310
311	=back
312
313	=cut
314
315	# support function to convert a fd into a perl filehandle
316	sub _fd2fh {
317	return undef if $_[0] < 0;
318
319	# try to generate nice filehandles
320	my $sym = "IO::AIO::fd#$_[0]";
321	local *$sym;
322
323	open *$sym, "+<&$_[0]" # usually under any unix
324	or open *$sym, "<&$_[0]" # cygwin needs this
325	or open *$sym, ">&$_[0]" # cygwin needs this
326	or return undef;
327
328	*$sym
329	}
330
331	min_parallel 4;
332
333	END {
334	max_parallel 0;
335	}
336
337	1;
338
339	=head1 SEE ALSO
340
341	L<Coro>, L<Linux::AIO>.
342
343	=head1 AUTHOR
344
345	Marc Lehmann <schmorp@schmorp.de>
346	http://home.schmorp.de/
347
348	=cut
349