Re: Tasking problem (delay)

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

Gerd wrote:
> 
> Would this be a good solution for my problem or are there any other
> traps?

I don't see any traps. This design for Worker implies that you need to 
change the WD timeout value repeatedly, to arbitrary values, but what 
you've presented indicates that it only needs to be changed once to a 
fixed value. If that's the case, it would probably be better for the 
design to reflect it, encapsulating all information about the timeout 
value in the Worker task.

However, this design may have the Worker doing too much. In addition to 
the work its supposed to do, it's also doing the work of the watchdog. 
It might be better to separate them:

protected WD_Station is
    procedure Startup_Completed;

    procedure Check_In;
    -- Called periodically by monitored task.

    entry Wait_For_Startup;

    entry Wait;
    -- Called by WD task to wait for the monitored task to check in.
private -- WD_Station
    ...
end WD_Station;

The startup task calls WD_Station.Startup_Complete at the appropriate 
time. The worker task would look like

begin -- Worker
    Forever : loop
       select
          accept Data ...;
          WD_Station.Check_In;
       or
          terminate;
       end select;
    end loop Forever;
end Worker;

There would also be a task WD_Timer:

task body WD_Timer is
begin -- WD_Timer
    WD_Station.Wait_For_Startup;

    Forever : loop
       select
          WD_Station.Wait;
       or
          delay 1.0;
          -- Watchdog processing here.
       end select;
    end loop Forever;
end WD_Timer;

You would need a way for WD_Station to inform WD_Timer that it should 
end, if that is a possibility.

-- 
Jeff Carter
"You empty-headed animal-food-trough wiper."
Monty Python & the Holy Grail
04