Re: Freezing a task

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

On 11/17/2011 06:23 PM, Rego, P. wrote:
>
> So I can use
>
> Paused : Boolean := False;
> begin
>      accept Start;
>      loop
>         if Paused then
>            accept Release;
>            Paused := False;
>         else
>            select
>               accept Pause;
>               Paused := True;
>            else
>               ... -- Do stuff
>            end select;
>         end if;
>      end loop;
>
> and if I would want to add an abort entry? What should I do?

Depends on when you want to be able to stop the task. I'd guess

select
    accept Pause;
    Paused := True;
or
    accept Stop;

    exit;
else
    -- Do stuff.
end select;

"abort" is a reserved word, so it can't be the name of the entry. A protected 
object seems cleaner, though:

protected Control is
    procedure Process;
    -- Instruct the task to start processing, or to resume processing after
    -- being paused.

    procedure Stop;
    -- Tell the task to terminate.

    procedure Pause;
    -- Tell the task to pause processing.

    entry Get (Stop : out Boolean);
    -- Used by the task to wait until it should do something.
    -- Stop will be True if the task should terminate; False if it should
    -- do stuff.
private -- Control
    ...
end Control;

task body T is
    Stop : Boolean;
begin -- T
    loop
       Control.Get (Stop => Stop);

       exit when Stop;

       -- Do stuff.
    end loop;
end T;

-- 
Jeff Carter
"You can never forget too much about C++."
115