Re: Uses for memory barriers

[Alan Stern <stern@rowland.harvard.edu>]

On Fri, 8 Sep 2006, Oliver Neukum wrote:

> It seems you are correct.
> Therefore the correct code on CPU 1 would be:
> 
> y = -1;
> b = 1;
> //mb();
> //x = a;
> while (y < 0) relax();
> 
> mb();
> x = a;
> 
> assert(x==1 || y==1);   //???
> 
> And yes, it is confusing. I've been forced to change my mind twice.

Again you have misunderstood.  The original code was _not_ incorrect.  I 
was asking: Given the code as stated, would the assertion ever fail?

The code _was_ correct for my purposes, namely, to illustrate a technical 
point about the behavior of memory barriers.

Alan

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