Subj : Re: [.NET] Volatile Fields [correction]
To   : comp.programming.threads
From : David Hopwood
Date : Mon Sep 19 2005 03:35 pm

Oops, wrong example. This is the example I meant:

  Strictly speaking, though, adding memory barriers is not always sufficient to
  simulate sequentially consistent behaviour. For instance, you might think that in
  this example:

    Start with Y == Z == 0.

    Processor 1:  Y = 1;
    Processor 2:  if (Y == 1) { Z = 1; }
    Processor 3:  if (Z == 1) { assert(Y == 1); }

  the assert cannot fail (because Z = 1 can only happen after Y = 1).
  But in some memory models, including the model used by x86
  (as far as it's possible to tell from the documentation), and probably also the
  one used by .NET, it *is* possible for the assert to fail. This can happen no
  matter what memory barriers are added, and even if Y and Z are volatile in the
  case of .NET.

-- 
David Hopwood <david.nospam.hopwood@blueyonder.co.uk>

.