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Newsgroups: comp.lang.ada
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: 02 Apr 2008 09:22:54 +0200
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Date: 2008-04-02T09:22:54+02:00
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>>>>> "(b" == (see below) <yaldnif.w@blueyonder.co.uk> writes:

<snip>

    (b> Also, simply declaring a variable atomic does not in itself
    (b> ensure global consistency of view. For that you also need
    (b> to execute appropriate memory barrier operations for the
    (b> architecture. (I'm sure you know that.)

Yes, I know. So pragma atomic does not help very much by itself in
implementing lock-free algorithms.
 
    >> 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> Yes, but this is completely implementation-dependent.
    (b> Not much above the semantic level of assembly.
    (b> I would take a lot of convincing that the performance
    (b> improvement was actually necessary.

I agree that it rarely should be necessary. It would have been nice to
have a way of implementing lock-free algorithms in Ada efficiently,
but entryless protected objects seems to be the best solution if
you want a portable program.

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


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