Re: [LAD] a *simple* ring buffer, comments pls?

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To: <linux-audio-dev@...>
Date: Friday, July 8, 2011 - 11:27 pm

On Sat, Jul 09, 2011 at 02:03:34AM +0300, Dan Muresan wrote:

Depends. If both ends are periodic processes no other synchronisation
is required. And e.g. Jack callback is such a process, and likely to
be one end.

> So I think it would be better to drop the volatile's, and leave safety

You may be right about the (HW as opposed to compiler) re-ordering of
data w.r.t. pointers on some architectures. But AFAIK, at least on Intel
and AMD writes are not re-ordered w.r.t. other writes from the same CPU,
same for reads.

Regarding the volatile declarations, at least on my version (which
is slightly different from Jack's) there is no performance penalty.
So I keep them just as reminders that these data are shared and may
change in unexpected ways.

You are wrong in saying that 'volatile' has no place in multi-threading.
It is the correct way to go if you want to ensure that a value is e.g.
read/written just once even if it is used many times:

extern volatile int xval; // Written by other thread(s)

void f (void)
{
int x;

x = xval;

// use x many times, it won't change.
}

Without the 'volatile', the compiler is free to read
the memory value xval as many times as it wants, even
if it has a local copy, and it probably will do so if
you have many local variables.

Ciao,

--
FA

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Messages in current thread:
[LAD] a *simple* ring buffer, comments pls?, James Morris, (Thu Jul 7, 12:10 pm)
Re: [LAD] a *simple* ring buffer, comments pls?, James Morris, (Fri Jul 8, 12:51 am)
Re: [LAD] a *simple* ring buffer, comments pls?, James Morris, (Fri Jul 8, 11:24 am)
Re: [LAD] a *simple* ring buffer, comments pls?, Paul Davis, (Fri Jul 8, 1:22 pm)
Re: [LAD] a *simple* ring buffer, comments pls?, Fons Adriaensen, (Fri Jul 8, 5:17 pm)
Re: [LAD] a *simple* ring buffer, comments pls?, Gabriel M. Beddingfield, (Fri Jul 8, 6:12 pm)
Re: [LAD] a *simple* ring buffer, comments pls?, Arnold Krille, (Fri Jul 8, 7:06 pm)
Re: [LAD] a *simple* ring buffer, comments pls?, Fons Adriaensen, (Fri Jul 8, 7:53 pm)
Re: [LAD] a *simple* ring buffer, comments pls?, Paul Davis, (Fri Jul 8, 8:41 pm)
Re: [LAD] a *simple* ring buffer, comments pls?, Fons Adriaensen, (Fri Jul 8, 9:01 pm)
Re: [LAD] a *simple* ring buffer, comments pls?, Arnold Krille, (Fri Jul 8, 8:59 pm)
Re: [LAD] a *simple* ring buffer, comments pls?, Fons Adriaensen, (Fri Jul 8, 9:11 pm)
Re: [LAD] a *simple* ring buffer, comments pls?, Dan Muresan, (Fri Jul 8, 7:23 pm)
Re: [LAD] a *simple* ring buffer, comments pls?, Dan Muresan, (Mon Jul 11, 6:59 pm)
Re: [LAD] a *simple* ring buffer, comments pls?, Fons Adriaensen, (Mon Jul 11, 8:53 pm)
Re: [LAD] a *simple* ring buffer, comments pls?, Dan Muresan, (Tue Jul 12, 5:41 am)
Re: [LAD] a *simple* ring buffer, comments pls?, Dan Kegel, (Fri Jul 8, 7:29 pm)
Re: [LAD] a *simple* ring buffer, comments pls?, Paul Davis, (Fri Jul 8, 8:49 pm)
Re: [LAD] a *simple* ring buffer, comments pls?, Sean Bolton, (Fri Jul 8, 9:57 pm)
Re: [LAD] a *simple* ring buffer, comments pls?, Dan Muresan, (Fri Jul 8, 11:03 pm)
Re: [LAD] a *simple* ring buffer, comments pls?, Fons Adriaensen, (Fri Jul 8, 11:27 pm)
Re: [LAD] a *simple* ring buffer, comments pls?, Dan Muresan, (Sat Jul 9, 1:25 pm)
Re: [LAD] a *simple* ring buffer, comments pls?, Fons Adriaensen, (Sat Jul 9, 2:38 pm)
Re: [LAD] a *simple* ring buffer, comments pls?, Dan Muresan, (Sun Jul 10, 3:05 pm)
Re: [LAD] a *simple* ring buffer, comments pls?, Fons Adriaensen, (Sun Jul 10, 9:15 pm)
Re: [LAD] a *simple* ring buffer, comments pls?, Dan Muresan, (Mon Jul 11, 12:03 pm)
Re: [LAD] a *simple* ring buffer, comments pls?, Fons Adriaensen, (Mon Jul 11, 8:44 pm)
Re: [LAD] a *simple* ring buffer, comments pls?, Dan Kegel, (Sun Jul 10, 10:34 pm)
Re: [LAD] a *simple* ring buffer, comments pls?, Paul Davis, (Sun Jul 10, 9:41 pm)
Re: [LAD] a *simple* ring buffer, comments pls?, Sean Bolton, (Mon Jul 11, 1:34 am)
Re: [LAD] a *simple* ring buffer, comments pls?, Sean Bolton, (Mon Jul 11, 1:44 am)
Re: [LAD] a *simple* ring buffer, comments pls?, Olivier Guilyardi, (Mon Jul 11, 7:19 pm)
Re: [LAD] a *simple* ring buffer, comments pls?, James Morris, (Mon Jul 11, 8:32 pm)
Re: [LAD] a *simple* ring buffer, comments pls?, Chris Cannam, (Mon Jul 11, 8:50 pm)
Re: [LAD] a *simple* ring buffer, comments pls?, Tim E. Real, (Mon Jul 11, 9:38 pm)
Re: [LAD] a *simple* ring buffer, comments pls?, Robin Gareus, (Mon Jul 11, 10:27 pm)
Re: [LAD] a *simple* ring buffer, comments pls?, Arnold Krille, (Mon Jul 11, 10:12 pm)
Re: [LAD] a *simple* ring buffer, comments pls?, Robin Gareus, (Mon Jul 11, 10:28 pm)
Re: [LAD] a *simple* ring buffer, comments pls?, Paul Davis, (Mon Jul 11, 10:34 pm)
Re: [LAD] a *simple* ring buffer, comments pls?, Dan Mills, (Mon Jul 11, 10:24 pm)
Re: [LAD] a *simple* ring buffer, comments pls?, Fons Adriaensen, (Mon Jul 11, 10:06 pm)
Re: [LAD] a *simple* ring buffer, comments pls?, Olivier Guilyardi, (Mon Jul 11, 11:06 pm)
Re: [LAD] a *simple* ring buffer, comments pls?, Dan Muresan, (Mon Jul 11, 10:17 pm)
Re: [LAD] a *simple* ring buffer, comments pls?, Paul Davis, (Mon Jul 11, 8:58 pm)
Re: [LAD] a *simple* ring buffer, comments pls?, Chris Cannam, (Tue Jul 12, 7:07 am)
Re: [LAD] a *simple* ring buffer, comments pls?, Dan Muresan, (Tue Jul 12, 12:44 pm)
Re: [LAD] a *simple* ring buffer, comments pls?, Kai Vehmanen, (Wed Jul 20, 9:25 pm)
Re: [LAD] a *simple* ring buffer, comments pls?, Emanuel Rumpf, (Sat Aug 20, 6:24 pm)
Re: [LAD] a *simple* ring buffer, comments pls?, Emanuel Rumpf, (Sat Aug 27, 7:21 am)
Re: [LAD] a *simple* ring buffer, comments pls?, Gabriel Beddingfield, (Sat Aug 20, 7:16 pm)
Re: [LAD] a *simple* ring buffer, comments pls?, Chris Cannam, (Tue Jul 12, 7:46 pm)
Re: [LAD] a *simple* ring buffer, comments pls?, Olivier Guilyardi, (Tue Jul 12, 8:20 pm)
Re: [LAD] a *simple* ring buffer, comments pls?, Arnold Krille, (Tue Jul 12, 11:31 pm)
Re: [LAD] a *simple* ring buffer, comments pls?, Paul Davis, (Tue Jul 12, 11:56 pm)
Re: [LAD] a *simple* ring buffer, comments pls?, Olivier Guilyardi, (Wed Jul 13, 12:27 am)
Re: [LAD] a *simple* ring buffer, comments pls?, Chris Cannam, (Tue Jul 12, 9:07 pm)
Re: [LAD] a *simple* ring buffer, comments pls?, Olivier Guilyardi, (Tue Jul 12, 9:26 pm)
Re: [LAD] a *simple* ring buffer, comments pls?, Paul Davis, (Tue Jul 12, 8:36 pm)
Re: [LAD] a *simple* ring buffer, comments pls?, Olivier Guilyardi, (Tue Jul 12, 9:32 pm)
Re: [LAD] a *simple* ring buffer, comments pls?, Dan Kegel, (Tue Jul 12, 10:23 pm)
Re: [LAD] a *simple* ring buffer, comments pls?, Olivier Guilyardi, (Tue Jul 12, 11:50 pm)
Re: [LAD] a *simple* ring buffer, comments pls?, Fred Gleason, (Wed Jul 13, 12:08 am)
Re: [LAD] a *simple* ring buffer, comments pls?, Olivier Guilyardi, (Wed Jul 13, 12:25 am)
Re: [LAD] a *simple* ring buffer, comments pls?, Chris Cannam, (Tue Jul 12, 9:37 pm)
Re: [LAD] a *simple* ring buffer, comments pls?, Olivier Guilyardi, (Tue Jul 12, 10:00 pm)
Re: [LAD] a *simple* ring buffer, comments pls?, Chris Cannam, (Tue Jul 12, 9:16 pm)
Re: [LAD] a *simple* ring buffer, comments pls?, Emanuel Rumpf, (Tue Jul 12, 5:20 pm)
Re: [LAD] a *simple* ring buffer, comments pls?, Chris Cannam, (Mon Jul 11, 8:50 pm)
Re: [LAD] a *simple* ring buffer, comments pls?, David Olofson, (Mon Jul 11, 8:47 pm)
Re: [LAD] a *simple* ring buffer, comments pls?, Dan Kegel, (Fri Jul 8, 9:52 pm)
Re: [LAD] a *simple* ring buffer, comments pls?, Fons Adriaensen, (Fri Jul 8, 6:39 pm)
Re: [LAD] a *simple* ring buffer, comments pls?, James Morris, (Fri Jul 8, 12:21 pm)
Re: [LAD] a *simple* ring buffer, comments pls?, Olivier Guilyardi, (Fri Jul 8, 12:56 pm)
Re: [LAD] a *simple* ring buffer, comments pls?, Gabriel M. Beddingfield, (Fri Jul 8, 1:04 am)
Re: [LAD] a *simple* ring buffer, comments pls?, David Robillard, (Fri Jul 8, 2:23 pm)
Re: [LAD] a *simple* ring buffer, comments pls?, James Morris, (Fri Jul 8, 8:45 am)
Re: [LAD] a *simple* ring buffer, comments pls?, James Morris, (Fri Jul 8, 8:40 am)