Re: Termination of tasks waiting on a protected queue

[Jeffrey Carter <spam.jrcarter.not@spam.not.acm.org>]

On 05/18/2014 12:32 AM, Natasha Kerensikova wrote:
>
> I have been having a task termination issue, and I'm wondering whether I
> got my design wrong or whether I'm missing something, so I ask you to
> help me on that.
>
> The basic need is delegating potentially long jobs to a dedicated task
> (or pool of tasks) so that the program flow generating the jobs and
> continue quickly. I furthermore assume that the jobs are "fire and
> forget", that there is no need to report anything about completion (or
> lack of thereof) to the code that generated the jobs (or more
> realistically, that reporting is performed through channels outside of
> the scope of the problem).

I have done something similar for pools of worker tasks. I used an instance of 
PragmARC.Queue_Unbounded_Blocking to hold the job requests rather than rolling 
my own for each task pool. The solution to termination was to use a timed entry 
call to the queue, with another protected object with a function to indicate if 
the pool tasks should end. The tasks looked like

Forever : loop
    select
       Job_Queue.Get (Item => Info);

       Process (Info => Info);
    or
       delay Check_Interval;

       exit Forever when Control.Finalizing;
    end select;
end loop Forever;

Obviously not Ravenscar compliant.

Check_Interval was quite long, 2 seconds.

-- 
Jeff Carter
"If I could find a sheriff who so offends the citizens of Rock
Ridge that his very appearance would drive them out of town ...
but where would I find such a man? Why am I asking you?"
Blazing Saddles
37