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From: Gustaf Thorslund <gustaf@thorslund.org>
Newsgroups: comp.lang.ada
Subject: Re: What would you like in Ada202X?
Date: Tue, 15 May 2012 08:15:03 +0200
Organization: gustaf.thorslund.org
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Date: 2012-05-15T08:15:03+02:00
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On 2012-05-15 00:49, tmoran@acm.org wrote:

>> I suppose somewhere there need to be a way to set max concurrency.
>    This ability to say something about the resources to use on the target
> machine is normally done with compilation parameters, which is pretty
> limiting.  Specifying the max concurrency for a piece of code is analogous
> to specifying that certain arrays are rarely accessed and are good
> candidates for swapping, while others really need to stay in RAM.  I've
> not seen that in a language either.

I agree it would be kind of stupid setting it at compilation time. Was 
thinking of some way setting it at runtime. Then this could be given as 
a command line argument or in a configuration file, but this would be up 
to the user to do. With a database (DBMS) (or browser, or email 
client...) you would not want to set the size of buffers and memory used 
at compilation time, but you would still want to have it configurable.


Looking at "I in 1..5" vs "X in 1..50000" one might expect the first one 
to run with full concurrency, but most of us wouldn't want it on the 
second one (at least not today, but maybe 202X). Nested/recursive calls 
could also result in a bit too much concurrency.

If there should be a global limit and/or local limit I'd leave for 
others to discuss.

For local concurrency control one might still prefer to do

with all I in 1 .. 10 do
   for J in I .. 1000*I loop
     { stmt }
   end loop;
end do all; -- or end with all;

instead of

with all J in 1 .. 10000 do
   { stmt }
end do all; -- or end with all;

But that would be up to the user to decide and could be related to 
resource allocation needed for each concurrent sequence of statements or 
aggregating of the results.

Regards,
Gustaf
-- 
http://gustaf.thorslund.org