RE: JavaMemoryModel: New Unified JMM Description

From: David Holmes (
Date: Thu Apr 15 2004 - 19:53:48 EDT

Sylvia wrote:
> I think this way lies madness. The model simply isn't defined in terms of
> permitted or non-permitted reorderings.

Well it is and it isn't. ...

> If you want to make some assertion in your lock free algorithm
> you need to find a combination of happens-before and synchronization
> orderings that supports it.

But that is not sufficient. Identifying the happens-before relationships
doesn't guarantee that A will happen before B. The system is allowed to
reorder actions in a happens-before relationship as long as it is not
detectable by anything that happens-after. So to determine that A will
actually happen before B you have to show that A happening after B would be
detectable by something that happens-after, and so the reordering would not
be allowed.

David Holmes

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