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 = 1.4;

   @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:	1.33
Committed:	Wed Aug 17 06:12:10 2005 UTC (18 years, 9 months ago) by root
Branch:	MAIN
CVS Tags:	rel-1_4
Changes since 1.32:	+1 -2 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 = 1.4;
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 pathnames you pass to these routines I<must> be absolute and
94	encoded in byte form. The reason for the former is that at the time the
95	request is being executed, the current working directory could have
96	changed. Alternatively, you can make sure that you never change the
97	current working directory.
98
99	To encode pathnames to byte form, either make sure you either: a)
100	always pass in filenames you got from outside (command line, readdir
101	etc.), b) are ASCII or ISO 8859-1, c) use the Encode module and encode
102	your pathnames to the locale (or other) encoding in effect in the user
103	environment, d) use Glib::filename_from_unicode on unicode filenames or e)
104	use something else.
105
106	=over 4
107
108	=item aio_open $pathname, $flags, $mode, $callback
109
110	Asynchronously open or create a file and call the callback with a newly
111	created filehandle for the file.
112
113	The pathname passed to C<aio_open> must be absolute. See API NOTES, above,
114	for an explanation.
115
116	The C<$flags> argument is a bitmask. See the C<Fcntl> module for a
117	list. They are the same as used by C<sysopen>.
118
119	Likewise, C<$mode> specifies the mode of the newly created file, if it
120	didn't exist and C<O_CREAT> has been given, just like perl's C<sysopen>,
121	except that it is mandatory (i.e. use C<0> if you don't create new files,
122	and C<0666> or C<0777> if you do).
123
124	Example:
125
126	aio_open "/etc/passwd", O_RDONLY, 0, sub {
127	if ($_[0]) {
128	print "open successful, fh is $_[0]\n";
129	...
130	} else {
131	die "open failed: $!\n";
132	}
133	};
134
135	=item aio_close $fh, $callback
136
137	Asynchronously close a file and call the callback with the result
138	code. I<WARNING:> although accepted, you should not pass in a perl
139	filehandle here, as perl will likely close the file descriptor another
140	time when the filehandle is destroyed. Normally, you can safely call perls
141	C<close> or just let filehandles go out of scope.
142
143	This is supposed to be a bug in the API, so that might change. It's
144	therefore best to avoid this function.
145
146	=item aio_read $fh,$offset,$length, $data,$dataoffset,$callback
147
148	=item aio_write $fh,$offset,$length, $data,$dataoffset,$callback
149
150	Reads or writes C<length> bytes from the specified C<fh> and C<offset>
151	into the scalar given by C<data> and offset C<dataoffset> and calls the
152	callback without the actual number of bytes read (or -1 on error, just
153	like the syscall).
154
155	The C<$data> scalar I<MUST NOT> be modified in any way while the request
156	is outstanding. Modifying it can result in segfaults or WW3 (if the
157	necessary/optional hardware is installed).
158
159	Example: Read 15 bytes at offset 7 into scalar C<$buffer>, starting at
160	offset C<0> within the scalar:
161
162	aio_read $fh, 7, 15, $buffer, 0, sub {
163	$_[0] > 0 or die "read error: $!";
164	print "read $_[0] bytes: <$buffer>\n";
165	};
166
167	=item aio_readahead $fh,$offset,$length, $callback
168
169	C<aio_readahead> populates the page cache with data from a file so that
170	subsequent reads from that file will not block on disk I/O. The C<$offset>
171	argument specifies the starting point from which data is to be read and
172	C<$length> specifies the number of bytes to be read. I/O is performed in
173	whole pages, so that offset is effectively rounded down to a page boundary
174	and bytes are read up to the next page boundary greater than or equal to
175	(off-set+length). C<aio_readahead> does not read beyond the end of the
176	file. The current file offset of the file is left unchanged.
177
178	If that syscall doesn't exist (likely if your OS isn't Linux) it will be
179	emulated by simply reading the data, which would have a similar effect.
180
181	=item aio_stat $fh_or_path, $callback
182
183	=item aio_lstat $fh, $callback
184
185	Works like perl's C<stat> or C<lstat> in void context. The callback will
186	be called after the stat and the results will be available using C<stat _>
187	or C<-s _> etc...
188
189	The pathname passed to C<aio_stat> must be absolute. See API NOTES, above,
190	for an explanation.
191
192	Currently, the stats are always 64-bit-stats, i.e. instead of returning an
193	error when stat'ing a large file, the results will be silently truncated
194	unless perl itself is compiled with large file support.
195
196	Example: Print the length of F</etc/passwd>:
197
198	aio_stat "/etc/passwd", sub {
199	$_[0] and die "stat failed: $!";
200	print "size is ", -s _, "\n";
201	};
202
203	=item aio_unlink $pathname, $callback
204
205	Asynchronously unlink (delete) a file and call the callback with the
206	result code.
207
208	=item aio_rmdir $pathname, $callback
209
210	Asynchronously rmdir (delete) a directory and call the callback with the
211	result code.
212
213	=item aio_fsync $fh, $callback
214
215	Asynchronously call fsync on the given filehandle and call the callback
216	with the fsync result code.
217
218	=item aio_fdatasync $fh, $callback
219
220	Asynchronously call fdatasync on the given filehandle and call the
221	callback with the fdatasync result code.
222
223	If this call isn't available because your OS lacks it or it couldn't be
224	detected, it will be emulated by calling C<fsync> instead.
225
226	=back
227
228	=head2 SUPPORT FUNCTIONS
229
230	=over 4
231
232	=item $fileno = IO::AIO::poll_fileno
233
234	Return the I<request result pipe file descriptor>. This filehandle must be
235	polled for reading by some mechanism outside this module (e.g. Event or
236	select, see below or the SYNOPSIS). If the pipe becomes readable you have
237	to call C<poll_cb> to check the results.
238
239	See C<poll_cb> for an example.
240
241	=item IO::AIO::poll_cb
242
243	Process all outstanding events on the result pipe. You have to call this
244	regularly. Returns the number of events processed. Returns immediately
245	when no events are outstanding.
246
247	Example: Install an Event watcher that automatically calls
248	IO::AIO::poll_cb with high priority:
249
250	Event->io (fd => IO::AIO::poll_fileno,
251	poll => 'r', async => 1,
252	cb => \&IO::AIO::poll_cb);
253
254	=item IO::AIO::poll_wait
255
256	Wait till the result filehandle becomes ready for reading (simply does a
257	C<select> on the filehandle. This is useful if you want to synchronously wait
258	for some requests to finish).
259
260	See C<nreqs> for an example.
261
262	=item IO::AIO::nreqs
263
264	Returns the number of requests currently outstanding (i.e. for which their
265	callback has not been invoked yet).
266
267	Example: wait till there are no outstanding requests anymore:
268
269	IO::AIO::poll_wait, IO::AIO::poll_cb
270	while IO::AIO::nreqs;
271
272	=item IO::AIO::flush
273
274	Wait till all outstanding AIO requests have been handled.
275
276	Strictly equivalent to:
277
278	IO::AIO::poll_wait, IO::AIO::poll_cb
279	while IO::AIO::nreqs;
280
281	=item IO::AIO::poll
282
283	Waits until some requests have been handled.
284
285	Strictly equivalent to:
286
287	IO::AIO::poll_wait, IO::AIO::poll_cb
288	if IO::AIO::nreqs;
289
290	=item IO::AIO::min_parallel $nthreads
291
292	Set the minimum number of AIO threads to C<$nthreads>. The default is
293	C<1>, which means a single asynchronous operation can be done at one time
294	(the number of outstanding operations, however, is unlimited).
295
296	It is recommended to keep the number of threads low, as some Linux
297	kernel versions will scale negatively with the number of threads (higher
298	parallelity => MUCH higher latency). With current Linux 2.6 versions, 4-32
299	threads should be fine.
300
301	Under normal circumstances you don't need to call this function, as this
302	module automatically starts some threads (the exact number might change,
303	and is currently 4).
304
305	=item IO::AIO::max_parallel $nthreads
306
307	Sets the maximum number of AIO threads to C<$nthreads>. If more than
308	the specified number of threads are currently running, kill them. This
309	function blocks until the limit is reached.
310
311	This module automatically runs C<max_parallel 0> at program end, to ensure
312	that all threads are killed and that there are no outstanding requests.
313
314	Under normal circumstances you don't need to call this function.
315
316	=item $oldnreqs = IO::AIO::max_outstanding $nreqs
317
318	Sets the maximum number of outstanding requests to C<$nreqs>. If you
319	try to queue up more than this number of requests, the caller will block until
320	some requests have been handled.
321
322	The default is very large, so normally there is no practical limit. If you
323	queue up many requests in a loop it it often improves speed if you set
324	this to a relatively low number, such as C<100>.
325
326	Under normal circumstances you don't need to call this function.
327
328	=back
329
330	=cut
331
332	# support function to convert a fd into a perl filehandle
333	sub _fd2fh {
334	return undef if $_[0] < 0;
335
336	# try to generate nice filehandles
337	my $sym = "IO::AIO::fd#$_[0]";
338	local *$sym;
339
340	open *$sym, "+<&=$_[0]" # usually works under any unix
341	or open *$sym, "<&=$_[0]" # cygwin needs this
342	or open *$sym, ">&=$_[0]" # or this
343	or return undef;
344
345	*$sym
346	}
347
348	min_parallel 4;
349
350	END {
351	max_parallel 0;
352	}
353
354	1;
355
356	=head2 FORK BEHAVIOUR
357
358	Before the fork IO::AIO enters a quiescent state where no requests can be
359	added in other threads and no results will be processed. After the fork
360	the parent simply leaves the quiescent state and continues request/result
361	processing, while the child clears the request/result queue and starts the
362	same number of threads as were in use by the parent.
363
364	=head1 SEE ALSO
365
366	L<Coro>, L<Linux::AIO>.
367
368	=head1 AUTHOR
369
370	Marc Lehmann <schmorp@schmorp.de>
371	http://home.schmorp.de/
372
373	=cut
374