Groups > comp.lang.java.programmer > #2688

Re: AtomicReferenceArray writes and visibility

From	markspace <-@.>
Newsgroups	comp.lang.java.programmer
Subject	Re: AtomicReferenceArray writes and visibility
Date	2011-03-31 21:22 -0700
Organization	A noiseless patient Spider
Message-ID	<in3jv4$1so$1@dont-email.me> (permalink)
References	<in14ae$qap$1@Gaia.teknon.de>

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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.

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Thread

AtomicReferenceArray writes and visibility v_borchert@despammed.com (Volker Borchert) - 2011-03-31 05:43 +0000
  Re: AtomicReferenceArray writes and visibility Peter Duniho <NpOeStPeAdM@NnOwSlPiAnMk.com> - 2011-03-31 00:52 -0700
    Re: AtomicReferenceArray writes and visibility v_borchert@despammed.com (Volker Borchert) - 2011-04-02 06:28 +0000
  Re: AtomicReferenceArray writes and visibility Kevin McMurtrie <mcmurtrie@pixelmemory.us> - 2011-03-31 20:55 -0700
  Re: AtomicReferenceArray writes and visibility markspace <-@.> - 2011-03-31 21:22 -0700
    Re: AtomicReferenceArray writes and visibility Peter Duniho <NpOeStPeAdM@NnOwSlPiAnMk.com> - 2011-03-31 21:54 -0700
      Re: AtomicReferenceArray writes and visibility markspace <-@.> - 2011-03-31 21:58 -0700
        Re: AtomicReferenceArray writes and visibility Patricia Shanahan <pats@acm.org> - 2011-03-31 22:24 -0700
          Re: AtomicReferenceArray writes and visibility markspace <-@.> - 2011-03-31 22:55 -0700
  Re: AtomicReferenceArray writes and visibility Lew <lew@lewscanon.com> - 2011-04-01 11:40 -0700

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