Re: [LAU] Simple, easy multithreaded circular buffer library for Linux?

On Fri, Oct 17, 2008 at 8:46 AM, Paul Davis <paul@email-addr-hidden> wrote:
> On Fri, 2008-10-17 at 14:13 +0200, Olivier Guilyardi wrote:
>
>> Okay, I wrote such a test. It fails with Jack's ringbuffer (jack1 r3004) but
>> succeeds with Portaudio's one (r1240).
>
> Nice work. Nobody ask why we didn't do this 5 years ago!
>
>> The Portaudio code looks more and more robust to me. It's also surprisingly
>> short. Maybe that the best would be to replace jack's ringbuffer with it? I
>> think it should be possible to keep the jack_ringbuffer api unchanged.
>
> I'd rather add the memory barriers to the JACK code, but this could be a
> race to see who does what first. A memory barrier is typically single
> instruction. The complication tends to be defining them in a
> sufficiently portable way.
>

Why do you suspect you need memory barriers? My concern with
ringbuffer.c is the non-atomic ops on the read and write pointers.
They're marked volatile, but what I think you really want is make all
ops on those fields atomic. Stuff like this:

rb->read_ptr += n1;
rb->read_ptr &= rb->size_mask;

Looks like a problem to me. What happens if there's a context switch
in between those 2 statements?

NB: I only took a cursory glance at the code.
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Received on Fri Oct 17 16:15:03 2008