Subj : Re: [.NET] Volatile Fields [correction]
To   : comp.programming.threads
From : Joe Seigh
Date : Tue Sep 20 2005 08:30 am

Chris Thomasson wrote:
>>If you want to do global memory barriers just using PC and nothing else,
>>you can.  Just use a common memory location to "sync" everything with. 
>>E.g.
> 
> [...]
> 
> Yup. This works in x86:
> 
> Processor 1:  Y = 1; L = 1;
> Processor 2:  if (L == 1) { Z = 1; L = 2; }
> Processor 3:  if (L == 2) { assert( Z == 1 && Y == 1 ); }
> 
> http://groups.google.com/group/comp.programming.threads/msg/68ba70e66d6b6ee9?hl=en
> 
> L is a lightweight memory barrier. 
> 
> 
You don't need the load on the "memory barrier".

W = X = Y = Z = 0;

Processor 1:   W = 1; L = 1; X = 1
Processor 2:   if (X == 1) { Y = 1; L = 1; Z = 1; }
Processor 3:   if (Z == 1) { assert (W == 1 && Y == 1); }

W and Y are stored by two different processors and are seen in order.

-- 
Joe Seigh

When you get lemons, you make lemonade.
When you get hardware, you make software.

.