RFR #2 (M) 8148146: Integrate new internal Unsafe entry points, and basic intrinsic support for VarHandles

[David Holmes]

On 5/07/2016 7:09 PM, Andrew Haley wrote:
> On 04/07/16 22:09, David Holmes wrote:
>> Surely cmpxchg already ensures the store (if it happens) is visible in
>> other threads - else the cmpxchg would not even operate correctly.
>
> No, it doesn't.  Semantically, the cmpxchg is no more than an atomic
> operation on a single word: it has no other memory ordering effects.
> If you want the store to be observed before some other memory access
> you have to do something to make that happen.

You seem to be confusing ordering with visibility. The cmpxchg must be 
visible to other threads else cmpxchg can't function. But that doesn't 
imply any ordering constraints with anything before/after the cmpxchg.

Cheers,
David

> Andrew.
>