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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: GNAT and Tasklets
Date: Fri, 19 Dec 2014 19:05:45 -0600
Organization: Jacob Sparre Andersen Research & Innovation
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Date: 2014-12-19T19:05:45-06:00
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"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message 
news:1gfkkgi7ukoj3$.1pqtchynzp9rc$.dlg@40tude.net...
> On Fri, 19 Dec 2014 11:35:05 -0700, Brad Moore wrote:
...
>> I haven't listed all the semantics but for the questions you ask,
>> each arm of the parallel block is a separate thread of execution (which
>> we have been calling a tasklet).
>>
>> Each tasklet starts off with its own local declaration of Total,
>> initialized to 0, which is the Identity value for the reduction.
>>
>> So, for the top Total, you end up with {Top_}Total := 1 + A + B;
>> for the bottom Total, you end up with {Bottom_}Total := C + D;
>>
>> Then during the reduction phase, those two results get reduced using the
>> reduction operation, which in this case is "+".
>>
>> So the end result is Total = 1 + A + B + C + D;
>
> I think that the block should have explicit parameters, e.g. Total must be
> an in-out parameter of the block. The syntax should be similar to the
> selective accept. Each arm must also have parameters, and only those and 
> of
> the block must be visible within an arm. E.g. A, B must be parameters.
> Nothing else should be visible.

Interesting. This does sound like a better approach to me. (The whole 
reduction object idea seems to me to be the worst part of the parallel 
proposals -- something needs to be available, but that doesn't seem to be 
the way to do it.)

OTOH, the syntax to specify such parameters doesn't seem natural. We surely 
don't want to force a parallel block or loop to be the only contents of a 
subprogram.

More thought required.

                                             Randy.