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 = 1.3;


   @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 pathnames you pass to these routines I<must> be absolute and
encoded in byte form. The reason for the former 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.

To encode pathnames to byte form, either make sure you either: a)
always pass in filenames you got from outside (command line, readdir
etc.), b) are ASCII or ISO 8859-1, c) use the Encode module and encode
your pathnames to the locale (or other) encoding in effect in the user
environment, d) use Glib::filename_from_unicode on unicode filenames or e)
use something else.

=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).

The C<$data> scalar I<MUST NOT> be modified in any way while the request
is outstanding. Modifying it can result in segfaults or WW3 (if the
necessary/optional hardware is installed).

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

Before the fork IO::AIO enters a quiescent state where no requests can be
added in other threads and no results will be processed. After the fork
the parent simply leaves the quiescent state and continues request/result
processing, while the child clears the request/result queue and starts the
same number of threads as were in use by the parent.

=head1 SEE ALSO

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

=head1 AUTHOR

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

=cut

Revision:	1.32
Committed:	Wed Aug 17 05:26:20 2005 UTC (18 years, 9 months ago) by root
Branch:	MAIN
CVS Tags:	rel-1_3
Changes since 1.31:	+2 -1 lines
Log Message:	* empty log message *
#	Content
1	=head1 NAME
2
3	IO::AIO - Asynchronous Input/Output
4
5	=head1 SYNOPSIS
6
7	use IO::AIO;
8
9	aio_open "/etc/passwd", O_RDONLY, 0, sub {
10	my ($fh) = @_;
11	...
12	};
13
14	aio_unlink "/tmp/file", sub { };
15
16	aio_read $fh, 30000, 1024, $buffer, 0, sub {
17	$_[0] > 0 or die "read error: $!";
18	};
19
20	# Event
21	Event->io (fd => IO::AIO::poll_fileno,
22	poll => 'r',
23	cb => \&IO::AIO::poll_cb);
24
25	# Glib/Gtk2
26	add_watch Glib::IO IO::AIO::poll_fileno,
27	in => sub { IO::AIO::poll_cb; 1 };
28
29	# Tk
30	Tk::Event::IO->fileevent (IO::AIO::poll_fileno, "",
31	readable => \&IO::AIO::poll_cb);
32
33	# Danga::Socket
34	Danga::Socket->AddOtherFds (IO::AIO::poll_fileno =>
35	\&IO::AIO::poll_cb);
36
37
38	=head1 DESCRIPTION
39
40	This module implements asynchronous I/O using whatever means your
41	operating system supports.
42
43	Currently, a number of threads are started that execute your read/writes
44	and signal their completion. You don't need thread support in your libc or
45	perl, and the threads created by this module will not be visible to the
46	pthreads library. In the future, this module might make use of the native
47	aio functions available on many operating systems. However, they are often
48	not well-supported (Linux doesn't allow them on normal files currently,
49	for example), and they would only support aio_read and aio_write, so the
50	remaining functionality would have to be implemented using threads anyway.
51
52	Although the module will work with in the presence of other threads, it is
53	currently not reentrant, so use appropriate locking yourself, 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 = 1.3;
69
70
71	@EXPORT = qw(aio_read aio_write aio_open aio_close aio_stat aio_lstat aio_unlink
72	aio_rmdir aio_symlink aio_fsync aio_fdatasync aio_readahead);
73	@EXPORT_OK = qw(poll_fileno poll_cb min_parallel max_parallel max_outstanding nreqs);
74
75	require XSLoader;
76	XSLoader::load IO::AIO, $VERSION;
77	}
78
79	=head1 FUNCTIONS
80
81	=head2 AIO FUNCTIONS
82
83	All the C<aio_*> calls are more or less thin wrappers around the syscall
84	with the same name (sans C<aio_>). The arguments are similar or identical,
85	and they all accept an additional (and optional) C<$callback> argument
86	which must be a code reference. This code reference will get called with
87	the syscall return code (e.g. most syscalls return C<-1> on error, unlike
88	perl, which usually delivers "false") as it's sole argument when the given
89	syscall has been executed asynchronously.
90
91	All functions expecting a filehandle keep a copy of the filehandle
92	internally until the request has finished.
93
94	The pathnames you pass to these routines I<must> be absolute and
95	encoded in byte form. The reason for the former is that at the time the
96	request is being executed, the current working directory could have
97	changed. Alternatively, you can make sure that you never change the
98	current working directory.
99
100	To encode pathnames to byte form, either make sure you either: a)
101	always pass in filenames you got from outside (command line, readdir
102	etc.), b) are ASCII or ISO 8859-1, c) use the Encode module and encode
103	your pathnames to the locale (or other) encoding in effect in the user
104	environment, d) use Glib::filename_from_unicode on unicode filenames or e)
105	use something else.
106
107	=over 4
108
109	=item aio_open $pathname, $flags, $mode, $callback
110
111	Asynchronously open or create a file and call the callback with a newly
112	created filehandle for the file.
113
114	The pathname passed to C<aio_open> must be absolute. See API NOTES, above,
115	for an explanation.
116
117	The C<$flags> argument is a bitmask. See the C<Fcntl> module for a
118	list. They are the same as used by C<sysopen>.
119
120	Likewise, C<$mode> specifies the mode of the newly created file, if it
121	didn't exist and C<O_CREAT> has been given, just like perl's C<sysopen>,
122	except that it is mandatory (i.e. use C<0> if you don't create new files,
123	and C<0666> or C<0777> if you do).
124
125	Example:
126
127	aio_open "/etc/passwd", O_RDONLY, 0, sub {
128	if ($_[0]) {
129	print "open successful, fh is $_[0]\n";
130	...
131	} else {
132	die "open failed: $!\n";
133	}
134	};
135
136	=item aio_close $fh, $callback
137
138	Asynchronously close a file and call the callback with the result
139	code. I<WARNING:> although accepted, you should not pass in a perl
140	filehandle here, as perl will likely close the file descriptor another
141	time when the filehandle is destroyed. Normally, you can safely call perls
142	C<close> or just let filehandles go out of scope.
143
144	This is supposed to be a bug in the API, so that might change. It's
145	therefore best to avoid this function.
146
147	=item aio_read $fh,$offset,$length, $data,$dataoffset,$callback
148
149	=item aio_write $fh,$offset,$length, $data,$dataoffset,$callback
150
151	Reads or writes C<length> bytes from the specified C<fh> and C<offset>
152	into the scalar given by C<data> and offset C<dataoffset> and calls the
153	callback without the actual number of bytes read (or -1 on error, just
154	like the syscall).
155
156	The C<$data> scalar I<MUST NOT> be modified in any way while the request
157	is outstanding. Modifying it can result in segfaults or WW3 (if the
158	necessary/optional hardware is installed).
159
160	Example: Read 15 bytes at offset 7 into scalar C<$buffer>, starting at
161	offset C<0> within the scalar:
162
163	aio_read $fh, 7, 15, $buffer, 0, sub {
164	$_[0] > 0 or die "read error: $!";
165	print "read $_[0] bytes: <$buffer>\n";
166	};
167
168	=item aio_readahead $fh,$offset,$length, $callback
169
170	C<aio_readahead> populates the page cache with data from a file so that
171	subsequent reads from that file will not block on disk I/O. The C<$offset>
172	argument specifies the starting point from which data is to be read and
173	C<$length> specifies the number of bytes to be read. I/O is performed in
174	whole pages, so that offset is effectively rounded down to a page boundary
175	and bytes are read up to the next page boundary greater than or equal to
176	(off-set+length). C<aio_readahead> does not read beyond the end of the
177	file. The current file offset of the file is left unchanged.
178
179	If that syscall doesn't exist (likely if your OS isn't Linux) it will be
180	emulated by simply reading the data, which would have a similar effect.
181
182	=item aio_stat $fh_or_path, $callback
183
184	=item aio_lstat $fh, $callback
185
186	Works like perl's C<stat> or C<lstat> in void context. The callback will
187	be called after the stat and the results will be available using C<stat _>
188	or C<-s _> etc...
189
190	The pathname passed to C<aio_stat> must be absolute. See API NOTES, above,
191	for an explanation.
192
193	Currently, the stats are always 64-bit-stats, i.e. instead of returning an
194	error when stat'ing a large file, the results will be silently truncated
195	unless perl itself is compiled with large file support.
196
197	Example: Print the length of F</etc/passwd>:
198
199	aio_stat "/etc/passwd", sub {
200	$_[0] and die "stat failed: $!";
201	print "size is ", -s _, "\n";
202	};
203
204	=item aio_unlink $pathname, $callback
205
206	Asynchronously unlink (delete) a file and call the callback with the
207	result code.
208
209	=item aio_rmdir $pathname, $callback
210
211	Asynchronously rmdir (delete) a directory and call the callback with the
212	result code.
213
214	=item aio_fsync $fh, $callback
215
216	Asynchronously call fsync on the given filehandle and call the callback
217	with the fsync result code.
218
219	=item aio_fdatasync $fh, $callback
220
221	Asynchronously call fdatasync on the given filehandle and call the
222	callback with the fdatasync result code.
223
224	If this call isn't available because your OS lacks it or it couldn't be
225	detected, it will be emulated by calling C<fsync> instead.
226
227	=back
228
229	=head2 SUPPORT FUNCTIONS
230
231	=over 4
232
233	=item $fileno = IO::AIO::poll_fileno
234
235	Return the I<request result pipe file descriptor>. This filehandle must be
236	polled for reading by some mechanism outside this module (e.g. Event or
237	select, see below or the SYNOPSIS). If the pipe becomes readable you have
238	to call C<poll_cb> to check the results.
239
240	See C<poll_cb> for an example.
241
242	=item IO::AIO::poll_cb
243
244	Process all outstanding events on the result pipe. You have to call this
245	regularly. Returns the number of events processed. Returns immediately
246	when no events are outstanding.
247
248	Example: Install an Event watcher that automatically calls
249	IO::AIO::poll_cb with high priority:
250
251	Event->io (fd => IO::AIO::poll_fileno,
252	poll => 'r', async => 1,
253	cb => \&IO::AIO::poll_cb);
254
255	=item IO::AIO::poll_wait
256
257	Wait till the result filehandle becomes ready for reading (simply does a
258	C<select> on the filehandle. This is useful if you want to synchronously wait
259	for some requests to finish).
260
261	See C<nreqs> for an example.
262
263	=item IO::AIO::nreqs
264
265	Returns the number of requests currently outstanding (i.e. for which their
266	callback has not been invoked yet).
267
268	Example: wait till there are no outstanding requests anymore:
269
270	IO::AIO::poll_wait, IO::AIO::poll_cb
271	while IO::AIO::nreqs;
272
273	=item IO::AIO::flush
274
275	Wait till all outstanding AIO requests have been handled.
276
277	Strictly equivalent to:
278
279	IO::AIO::poll_wait, IO::AIO::poll_cb
280	while IO::AIO::nreqs;
281
282	=item IO::AIO::poll
283
284	Waits until some requests have been handled.
285
286	Strictly equivalent to:
287
288	IO::AIO::poll_wait, IO::AIO::poll_cb
289	if IO::AIO::nreqs;
290
291	=item IO::AIO::min_parallel $nthreads
292
293	Set the minimum number of AIO threads to C<$nthreads>. The default is
294	C<1>, which means a single asynchronous operation can be done at one time
295	(the number of outstanding operations, however, is unlimited).
296
297	It is recommended to keep the number of threads low, as some Linux
298	kernel versions will scale negatively with the number of threads (higher
299	parallelity => MUCH higher latency). With current Linux 2.6 versions, 4-32
300	threads should be fine.
301
302	Under normal circumstances you don't need to call this function, as this
303	module automatically starts some threads (the exact number might change,
304	and is currently 4).
305
306	=item IO::AIO::max_parallel $nthreads
307
308	Sets the maximum number of AIO threads to C<$nthreads>. If more than
309	the specified number of threads are currently running, kill them. This
310	function blocks until the limit is reached.
311
312	This module automatically runs C<max_parallel 0> at program end, to ensure
313	that all threads are killed and that there are no outstanding requests.
314
315	Under normal circumstances you don't need to call this function.
316
317	=item $oldnreqs = IO::AIO::max_outstanding $nreqs
318
319	Sets the maximum number of outstanding requests to C<$nreqs>. If you
320	try to queue up more than this number of requests, the caller will block until
321	some requests have been handled.
322
323	The default is very large, so normally there is no practical limit. If you
324	queue up many requests in a loop it it often improves speed if you set
325	this to a relatively low number, such as C<100>.
326
327	Under normal circumstances you don't need to call this function.
328
329	=back
330
331	=cut
332
333	# support function to convert a fd into a perl filehandle
334	sub _fd2fh {
335	return undef if $_[0] < 0;
336
337	# try to generate nice filehandles
338	my $sym = "IO::AIO::fd#$_[0]";
339	local *$sym;
340
341	open *$sym, "+<&=$_[0]" # usually works under any unix
342	or open *$sym, "<&=$_[0]" # cygwin needs this
343	or open *$sym, ">&=$_[0]" # or this
344	or return undef;
345
346	*$sym
347	}
348
349	min_parallel 4;
350
351	END {
352	max_parallel 0;
353	}
354
355	1;
356
357	=head2 FORK BEHAVIOUR
358
359	Before the fork IO::AIO enters a quiescent state where no requests can be
360	added in other threads and no results will be processed. After the fork
361	the parent simply leaves the quiescent state and continues request/result
362	processing, while the child clears the request/result queue and starts the
363	same number of threads as were in use by the parent.
364
365	=head1 SEE ALSO
366
367	L<Coro>, L<Linux::AIO>.
368
369	=head1 AUTHOR
370
371	Marc Lehmann <schmorp@schmorp.de>
372	http://home.schmorp.de/
373
374	=cut
375