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Subject: Re: AtomicReferenceArray writes and visibility
Date: Thu, 31 Mar 2011 21:22:56 -0700
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On 3/30/2011 10:43 PM, Volker Borchert wrote:
> Hello all,
>
> reading on the "new" memory model and AtomicReferenceArray, it
> seems that anything done before a .set() on an AtomicReferenceArray
> "happens-before" anything done after a .get() on the same
> AtomicReferenceArray.
>
> Two questions:
>
> 1. Am I right?


No. I know how the assembly language compare-and-swap instructions work, 
and there's little chance that they would be implemented with a memory 
barrier.  It could happen, on certain systems, but in general there's no 
synchronization, and no happens-before.


Read the source code for the AtomicReferenceArray.  set() doesn't use 
any synchronization.  It calls sun.misc.Unsafe#putObjectVolatile().  I 
don't see how that's going to create a happens-before.