task time-out&abort

["e.coli" <maurizio.ferracini@gmail.com>]

here the code...
------------------------------------
with Ada.Text_Io;
with Ada.Task_Identification;

procedure Semplice2 is --processo genitore

   task Un_Task is--specifica
      entry Uno;
      entry Due;
   end Un_Task;

   task body Un_Task is
   begin
      loop
         select
            accept Uno do
               Ada.Text_Io.Put_Line("foo");
            end Uno;
         or
            accept Due do
               Ada.Text_Io.Put_Line("buffering");
               loop           -- ;)
                  delay(0.0);
               end loop;
               Ada.Text_Io.Put_Line("bar");
            end Due;
         end select;
      end loop;
   end Un_Task;

begin --corpo genitore
   Un_Task.Uno;
   Ada.Text_Io.Put_Line ("wait Horribly long calculation");
   select
      delay 5.0;
      Ada.Text_Io.Put_Line ("Horribly long calculation abandoned");
   then abort
      un_task.due;
   end select;
end Semplice2;
-----------------------------------------

but don't work...
how i can do the five second time out?
thanks