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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: PAR (Was: Embedded languages based on early Ada)
Newsgroups: comp.lang.ada
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Date: Wed, 7 Mar 2007 20:55:35 +0100
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Date: 2007-03-07T20:55:26+01:00
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On Wed, 07 Mar 2007 18:26:08 GMT, Ray Blaak wrote:

> "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> writes:
>> Hmm, but checking is really the key issue here. I fail to see it in bare
>> PAR. It is just absent there. What would be the semantics of:
>> 
>> declare
>>    I : Integer := 0;
>> begin in parallel
>>    I := I + 1;
>>    I := I - 1;
>> end;  -- What is the postcondition here?
> 
> That would be bad programming, just as if you expressed it equivalently with
> expicit task bodies.

Why is it bad programming? Consider this:

declare
   Sum : Numeric := 0.0;
begin in parallel
   Sum := Sum + Integrate (Series (1..N);
   Sum := Sum + Integrate (Series (N+1..2*N);
   Sum := Sum + Integrate (Series (2*N+1..3*N);
   ...
end;

> Ada already has synchronization constructs that need to be used to allow
> dependent concurrent items to coordinate properly.

If so, then what would be the contribution of PAR? One important
proposition is that there is no any use in PAR running absolutely
independent code. So the question arise, what *exactly* PAR does with:

1. ":=" x 2 times
2. "+"
3. "-"
4. "I" x 4 times

?

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de