Re: JavaMemoryModel: Draft JMM Synopsis

From: Vijay Saraswat (
Date: Mon Mar 01 2004 - 10:00:10 EST

Doug Lea wrote:

>>If I understand your synopsis correctly, it will allow programmers to assume
>>that r2=1, r5=0 is not allowed. However, this outcome is allowed since there
>>is no inter-thread happens-before relationship here.
>Thanks! I forgot that you can't condense it so far as to avoid
>mentioning the fact that happens-before edges only occur when
>volatile reads and writes are to same variable. I'll add this.

This is true but not relevant to the current example. Even if you assume
that all volatile events must be totally ordered in the happens-before
relationship (irrespective of the variable they are directed at), you
can still get r2=1, r5=0. Here is the ordering:

    r1=V2 --hb-> V3=1

With this, you still get that r2=B NOT--hb-> B=1, so the read of B can
see B=1, and of course r5 could be zero because of intialization.

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