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Re: AtomicReferenceArray writes and visibility

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In article <in14ae$qap$1@Gaia.teknon.de>,
 v_borchert@despammed.com (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?
> 2. If so, does this hold true if the write does not actually change
>    the value, in other words, if the write only "refreshes" the
>    memory location?
> 
> Thank you
> 
> 	V.B.

For the weakCompareAndSet methods, it's not a matter of values being set 
then destroyed by collisions.  The difference is that when you're 
operating on multiple values, threads may see those values change in a 
different order than they are set.  A multithreaded operation which 
requires a sequence of changes to multiple values may fail.  The weak 
methods may also return false more often than expected.

At least in my source code, the weakCompareAndSet versions have no 
special operation.  It looks like Sun may expect that some systems can 
run faster when memory syncing rules are relaxed.  On a multi-core Intel 
x86 CPU, multiple threads can't write to the same CPU block of memory at 
once.  The only performance difference between the 'atomic' package and 
a 'synchronized' block is that a synchronized block caries a high risk 
of a thread losing it's CPU time (quanta runs out) while the lock is 
held.  The 'atomic' operations have no such risk.
-- 
I will not see posts from Google or e-mails from Yahoo because I must
filter them as spam

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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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