Re: Abortable Timed Action

[Anh Vo <anhvofrcaus@gmail.com>]

On Thursday, December 31, 2015 at 10:09:30 AM UTC-8, T.G. wrote:
> On 2015-12-31, Anh Vo <anhvofrcaus@gmail.com> wrote:
> > I think accuracy more important than better/simpler way. There is a
> > drifting issue in your codes in term of time since delay statement
> > is involved. In addition, timer has no problem of this kind. If you
> > decide to use timer, take look at
> > http://www.adacore.com/adaanswers/gems/ada-gem-15/. Let me know if
> > have any question.
> >
> > Anh Vo
> 
> Very nice example. I didn't know about Ada.Real_Time.Timing_Events,
> I'll probably go with that. Thanks for the pointer.

After looking at your original post again, I believe your code should work after replacing delay statement by delay until statement. The delay until statement does not have time drifting issue. In addition, then Entry Finish can be replaced by the terminate alternative. The modified version is shown below.

   with Ada.Calendar; use type Ada.Calendar.Time;
   with Ada.Text_Io;  use Ada.Text_Io;
   -- ...

   -- ...
   task type Timed_Action_Task is 
     entry Exec_After (T : Duration); 
     entry Cancel; 
   end Timed_Action_Task; 

   task body Timed_Action_Task is 
      Timeout : Duration; 
   begin 
      loop 
         select 
            accept Exec_After (T : Duration) do 
               Timeout := T; 
            end Exec_After; 
            select 
               accept Cancel; 
            or 
               delay until (Ada.Calendar.Clock + Timeout); 
               Put_Line ("Do Something"); 
            end select; 
         or 
            terminate;
         end select; 
      end loop; 
   end Timed_Action_Task;