guideline

For mutual exclusion, when measured performance indicates, use protected types as an alternative to tasking rendezvous.

To implement an interrupt handler, when performance measurement indicates, use a protected procedure.

   -- (1) Using protected objects
   --     (See ACES V2.0, test "a9_pt_prot_access_02")
   protected Object is
      function Read return Float;
      procedure Write (Value : in Float);
   private
      Data : Float;
   end Object;
   protected body Object is
      function Read return Float is
      begin
         return Data;
      end Read;
      procedure Write (Value : in Float) is
      begin
         Data := Value;
      end Write;
   end Object;
   task type Modify is
   end Modify;
   type Mod_Bunch is array (1 .. 5) of Modify;
   task body Modify is
      ...
   begin -- Modify
      for I in 1 .. 200 loop
         The_Value := Object.Read;
         Object.Write (The_Value - 0.125);
         if The_Value < -1.0E7 then
            The_Value := 1.0;
         end if;
      end loop;
   end Modify;
   ...
   -- Block statement to be timed
   declare
      Contending_Tasks : array (1 .. 5) of Modify;
   begin
      null;  -- 5 tasks contend for access to protected data
   end;
   ------------------------------------------------------------------------------
   -- (2) Using monitor task
   --     (See ACES V2.0, test "tk_rz_entry_access_02")
   Task Object is
      entry Write (Value : in     Float);
      entry Read  (Value :    out Float);
   end Object;
   task body Object is
      Data : Float;
   begin -- Object
      loop
         select
            accept Write (Value : in     Float) do
               Data := Value;
            end Write;
         or
            accept Read  (Value :    out Float) do
               Value := Data;
            end Read;
         or
            terminate;
         end select;
      end loop;
   end Object;
   -- Task type Modify declared as above
   -- Block statement to be timed as above

rationale