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Subject: Re: Robert Dewar's great article about the Strengths of Ada over
 other langauges in multiprocessing!
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From: Ole-Hjalmar Kristensen
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Date: 01 Apr 2008 11:02:39 +0200
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>>>>> "(b" == (see below) <yaldnif.w@blueyonder.co.uk> writes:

<snip>

    (b> I think the wording is trying to cover all the bases.
    (b> One clue is the phrase "_full_ cache consistency".
    (b> The caches certainly need to be consistent with respect to the
    (b> protected data, even for protected functions and procedures,
    (b> but only entries ensure global consistency and so provide
    (b> synchronization of data that is not local to the protected object.

Yes, that seems reasonable.

    >> Btw., I ran a simple test on a SPRAC multiprocessor with an entryless
    >> protected object containing a single integer versus an integer
    >> declared with pragma atomic, and as expected the pragma atomic
    >> solution was much (40x) faster.

    (b> Unfortunately, we can't usefully apply that pragma even
    (b> to a pair of integers. (I don't mean the pair's components!)

Agreed, but you may able to cheat and pack a pair of integers into
a 64-bit atomic, and a compare-and-swap is also much cheaper than a
protected object it seems.

    (b> -- 
    (b> Bill Findlay
    (b> <surname><forename> chez blueyonder.co.uk



-- 
   C++: The power, elegance and simplicity of a hand grenade.