2d8
Subj : Re: [.NET] Volatile Fields [correction]
To   : comp.programming.threads
From : Chris Thomasson
Date : Thu Sep 22 2005 03:25 am

> Start with F (fence) == Y == Z == 0.
>
> P1:  F = 1; Y = 1;
> P2:  if (Y == 1) { (void) F; F = 1; Z = 1; }
> P3:  if (Z == 1) { (void) F; assert(Y == 1); }
>
> can fail, e.g. in this execution:

Right. The fence is in the wrong place. You store to the fence "after" 
storing to Y or Z. This acts as a release barrier. You would then load from 
the fence to get an acquire barrier:

Processor 1:  Y = 1; Fence.rel = 1;
Processor 2:  if (Fence.acq == 1 ) { Z = 1; Fence.rel = 2; }
Processor 3:  if (Fence.acq == 2) { assert( Y == 1 && Z == 1 ); }


Simple...

;)

.

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