More on memory barriers

[Jason Merrill]

On Wed, 15 Sep 2004 13:11:41 -0700, Richard Henderson <rth@redhat.com> wrote:

> On Wed, Sep 15, 2004 at 12:20:53PM -0700, Geoffrey Keating wrote:
>> So you have to do something to prevent a processor from 
>> speculatively executing that code path while the code protected by the 
>> mutex is running in a different processor.
>
> Has nothing to do with speculation.

On the Alpha the problem has to do with its wacky cache-coherence rules,
but on other architectures the problem has everything to do with
speculation.  If the memory model allows the processor to execute loads out
of order, you can run into the same problem by loading the contents of the
guarded object before the flag.

Jason