RE: JavaMemoryModel: proposal for semantics & implementation on relaxed memory model machines

From: David Holmes (
Date: Wed Jul 14 1999 - 22:21:49 EDT

> -----Original Message-----
> From:
> []On Behalf Of Dan Scales
> 5) One way to support the initialize-once idiom so that it is
> reasonably efficient on all types of machines is to add a new
> keyword 'sync' that qualifies variables. Any read of a 'sync'
> variable acts as an acquire and any write of a 'sync' variable
> acts as a release. If a reference to a newly constructed object
> is stored in a sync variable, then other processors reading the
> variable will be guaranteed to see the correct contents of the new
> object.

Instead of adding a new keyword we could simply hijack 'volatile' to mean
this. After all our general rule for accessing mutable fields is that it
must be done under synchronisation or the field must be declared volatile.
For object references having the reference a volatile doesn't achieve any
useful guarantees about the state of the object's fields, so enhancing
volatile in this way would seem to be a good thing to do and fairly clean.

Overall I find the proposal to be a good compromise on programmability and
implementation cost.


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