Ada protected types

Question

I've got a simple package in Ada with procedures and functions. I'd like to have all the functions and procedures in a protected type.

eg for a simple .adb file

package body Pack is

  procedure procedure1 (B : in out Integer) is
  begin
    B := new Integer;
  end procedure1;

  procedure procedure2 (B: in out Integer) is
  begin
    B.Cont(B.First-1) := 1;
  end procedure2;

  function procedure3 (B : Integer) return Boolean is
  begin
    return B.First = B.Last;
  end procedure3;

end pack;

and or a simple .ads

package body Pack is

   procedure procedure1 (B : in out Integer);

   procedure procedure2 (B: in out Integer);

   function procedure3 (B : Integer) return Boolean;

end pack;

How would I go about it?

Answer 1

The thing about a protected type is that it protects something (against concurrent access). It's hard to see from your code what it is you want to protect.

If, say, you wanted to do a thread-safe increment, you might have a spec like

package Pack is
   protected type T is
      procedure Set (To : Integer);
      procedure Increment (By : Integer);
      function Get return Integer;
   private
      Value : Integer := 0;
   end T;
end Pack;

(this is far from perfect; you'd like to be able to specify the initial Value when you declare a T , but that's starting to get complicated).

In this case, the thing to be protected is the Value . You want to be sure that if two tasks call Increment at the “same” time, one with By => 3 and one with By => 4 , the Value ends up being incremented by 7.

The body could look like

package body Pack is
   protected body T is
      procedure Set (To : Integer) is
      begin
         Value := To;
      end Set;
      procedure Increment (By : Integer) is
      begin
         Value := Value + By;
      end Increment;
      function Get return Integer is
      begin
         return Value;
      end Get;
   end T;
end Pack;

Recommended reading: the Wikibooks section on protected types.