Re: GNAT and Tasklets

[Dennis Lee Bieber <wlfraed@ix.netcom.com>]

On Fri, 19 Dec 2014 11:35:05 -0700, Brad Moore <brad.moore@shaw.ca>
declaimed the following:

>
>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;

	There is no way I would ever interpret /that/ result... I'd actually
expect an optimizing compiler to see that the result of incrementing Total
is thrown away by the next statement in the block.

>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;
>

	So your reduction phase becomes the equivalent of a summing
operation...

	par_sum(	1,
				A + B,
				C + D	)	{of course, to do this right requires deferred
								evaluation of the parameters}

What if you want the result to be a product?
-- 
	Wulfraed                 Dennis Lee Bieber         AF6VN
    wlfraed@ix.netcom.com    HTTP://wlfraed.home.netcom.com/