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

On 07/13/2011 03:51 PM, Paul Davis wrote:
> On Wed, Jul 13, 2011 at 9:46 AM, Olivier Guilyardi <list@email-addr-hidden> wrote:
>> On 07/13/2011 11:09 AM, Tim Blechmann wrote:
>>
>>> in fact, testing is not the best approach for verifying lock-free data
>>> structures: an implementation may work for years, if a certain condition is
>>> never triggered. the only reasonable way to ensure the correctness is a formal
>>> proof. unfortunately, most publications assume a sequencially consistent memory
>>> model and sometimes even avoid dealing with the ABA problem.
>> To me, testing on real devices is needed, it's a pragmatic approach. But I agree
>> it doesn't solve the entire problem.
>>
>> That said, what about simulation? One could for example implement a minimal
>> emulator for the abstract CPU and memory model described in
>> linux/Documentation/memory-barriers.txt, and test lock-free algorithms on this.
>
> i don't see why this is needed. its trivial to demonstrate on a piece
> of paper that in a system with weak memory ordering constraints,
> absence of a memory barrier is incorrect for any code with coupled
> data values (e.g. a read index and read data). it doesn't matter if
> this doesn't happen very often. you don't need a simulator of any
> given CPU+memory model - its just demonstrably incorrect.

I see your point, although sometimes it's unclear what kind of barriers to use
and where to place them.

--
  Olivier
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