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Newsgroups: comp.lang.ada
Subject: Re: PAR (Was: Embedded languages based on early Ada)
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From: Ray Blaak <rAYblaaK@STRIPCAPStelus.net>
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Date: Tue, 06 Mar 2007 07:07:07 GMT
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Date: 2007-03-06T07:07:07+00:00
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"Dr. Adrian Wrigley" <amtw@linuxchip.demon.co.uk.uk.uk> writes:
> If you can persuade programmers to use "par" unless they explicitly
> *need* sequential execution, a great many statements will be marked
> as concurrent.  Numeric codes will use "par" in the computational
> core, as well as outer layers of execution.

I would strongly discourage this practice. Getting sequential programs correct
is hard enough. Parallel programs are vastly more difficult and subtle.

All concurrency constructs should be very explicit, clear, and robust. Ada has
the fundamentals right, if only a little verbose to specify.

This is also why I dislike the notion of special concurrency pragmas that
suggest concurrency only a possibility. It should instead of made clearly
obvious in the source, so as to aid the programmer to a maximum effect in
their reasonings about the control flow.

> Mandating sequential execution except where the "pragma" is used
> puts parallel statements at an immediate disadvantage - it makes
> them seem to be second class citizens, added on afterwards
> in an attempt to speed things up. 

It is only 2nd class because our brains our wired that way, at least in terms
of how we know how to program.

The point is to choose one way or the other, and to have the source be clear
about that decision.

-- 
Cheers,                                        The Rhythm is around me,
                                               The Rhythm has control.
Ray Blaak                                      The Rhythm is inside me,
rAYblaaK@STRIPCAPStelus.net                    The Rhythm has my soul.