atomic accesses

[Andrew Haley]

Paul Koning wrote:
> I'm really wondering why this is being considered.
> 
> A documented property of the form "GCC will use a single instruction
> to do X when possible" means exactly nothing.  In particular, to call
> such a statement a "guarantee" is seriously misleading.

I agree.

> If Linux needs the single-instruction property for atomicity, and it
> thinks it can rely on this supposed property, then Linux has a bug.
> To do atomic operations, you have to use primitives that are
> guaranteed always to have the necessary atomicity properties.

Yes.

> Typically those would be found in asm statements.

> I suspect it would be valuable to have standardized primitives for
> atomic actions (semaphores, spinlocks, test-and-set primitives,
> circular buffers, pick one).

We already have these in gcc, and they're even documented.

Andrew.