Re: JavaMemoryModel: Executions I find profoundly troubling

Date: Mon Jul 28 2003 - 13:05:49 EDT

I do find Example 1 pretty strange because it's almost an
out-of-thin-air occurence. I find Bill's argument against
allowing "additional redundant reads of shared variables"
quite persuasive: it's definitely not acceptable in other

I'm less sure about Example 2, because offhand, it seems like
a simple case of allowing reordering. (Isn't it sufficient to
reorder Thread 1's first two statements after its last two,
rather than Jerry's more complicated transformation?) However,
that example seems exactly analogous to the following example:

Initially, X = 0, Y = 0, A = 1

   Thread 1 Thread 2
   r1 = X r3 = Y
   if (r1 == 0) X = r3
     A = 0
   r2 = A
   Y = r2

But in this case, I think Sarita's model may not allow
r1 == r2 == r3 == 1. (Is this true?)

One argument about why this example should not be allowed
but Bill's Example 2 should be allowed is because the *name*
of the variable is the same in this example. I like this
distinction: I'm in favor of enforcing orders between
accesses to the same named variable but not to two different
variables that happen to be aliased, though I'm not sure what
all the implications are. I'm mostly in favor because the
programmer can readily see that two statements use identical
variables, but not that they might be aliased.

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