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

[Olivier Guilyardi]

Paul Coccoli wrote:
> On Fri, Oct 17, 2008 at 8:46 AM, Paul Davis <paul at linuxaudiosystems.com> wrote:
>>
>> 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.

Well, it looks like you had a fast but great insight here. I've turned all
statements of this kind into one-liners, and the jack ringbuffer now
(apparently) passes the test.

Here's the patch against jack1 r3007:
http://svn.samalyse.com/misc/rbtest/patches/jack-r3007-rb-fix.diff

And thanks everyone for the tests ! I've updated the test suite, it now contains
an additional test with this patch. Please continue testing :)

-- 
  Olivier Guilyardi / Samalyse