Subj : Re: posix and lock-free algorithms
To   : comp.programming.threads
From : Sean Kelly
Date : Fri Aug 12 2005 01:38 pm

David Hopwood wrote:
>
> In context, it *is* clear that whatever "synchronizing memory" means, it must
> mean something that can be used to avoid reading or modifying a memory location
> (that is, *each* memory location that could potentially be accessed from more
> than one thread) while another thread of control may be modifying it. But that
> doesn't have to be a global memory barrier -- because there patently are other
> ways to satisfy the requirement that only involve constraints on ordering of
> accesses to particular subsets of locations, not global constraints. There's
> nothing here to say that a global memory barrier even has to be implementable,
> or well-defined, on the target architecture.

Exactly.  To make this point easier to understand, I suggest applying
it to a clustered system--each machine might implement synchronization
via message-passing.  In such an environment, it's obviously far more
efficient to only synchronize data altered within the critical section.


Sean

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