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 *
#	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_rmdir aio_symlink 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_rmdir $pathname, $callback
197
198	Asynchronously rmdir (delete) a directory and call the callback with the
199	result code.
200
201	=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	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
214	=back
215
216	=head2 SUPPORT FUNCTIONS
217
218	=over 4
219
220	=item $fileno = IO::AIO::poll_fileno
221
222	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
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	Example: Install an Event watcher that automatically calls
236	IO::AIO::poll_cb with high priority:
237
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	C<select> on the filehandle. This is useful if you want to synchronously wait
246	for some requests to finish).
247
248	See C<nreqs> for an example.
249
250	=item IO::AIO::nreqs
251
252	Returns the number of requests currently outstanding (i.e. for which their
253	callback has not been invoked yet).
254
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	=item IO::AIO::flush
261
262	Wait till all outstanding AIO requests have been handled.
263
264	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	=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	=cut
319
320	# support function to convert a fd into a perl filehandle
321	sub _fd2fh {
322	return undef if $_[0] < 0;
323
324	# try to generate nice filehandles
325	my $sym = "IO::AIO::fd#$_[0]";
326	local *$sym;
327
328	open *$sym, "+<&=$_[0]" # usually works under any unix
329	or open *$sym, "<&=$_[0]" # cygwin needs this
330	or open *$sym, ">&=$_[0]" # or this
331	or return undef;
332
333	*$sym
334	}
335
336	min_parallel 4;
337
338	END {
339	max_parallel 0;
340	}
341
342	1;
343
344	=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	=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