-- Modified from John Barnes, "Programming in Ada 95".
-- Readers/Writers synchronization with tracing and artificial delays.

with text_io;

package body readerwriter is
 use text_io;
 package int_io is new integer_io(integer);
 use int_io;

  V : integer;  -- V is the data
  Test : Boolean := True;

  task Control is
    entry Start;
    entry Stop;
    entry Write(X: in integer; N: in Count);
   end;

  task body Control is
      Readers: Integer := 0; -- number of active readers
      begin
        accept Write(X: in integer; N: in Count) do -- Write initial value of V;
           if Test then Set_Col(N); Put("Start Write "); Put(X,2); 
                        New_Line; end if;
           V := X;
           if Test then delay 0.05;   
                        Set_Col(N); Put("End   write "); Put(X,2); 
                        New_Line; end if;
        end Write;
      loop
       select
         accept Start do   
           Readers := Readers + 1; 
         end Start;
       or 
        accept Stop do
           Readers := Readers - 1;
         end Stop;
       or
        when Readers = 0 =>
           accept Write(X: in integer; N: in Count) do
              if Test then Set_Col(N); Put("Start Write "); Put(X,2); New_Line; 
               end if;
              V := X;
              if Test then delay 0.05; Set_Col(N); Put("End   Write "); 
                           Put(X,2); New_Line; end if;
            end Write;
       end select;
    end loop;
end Control;

procedure Read(X: out Integer; N: in Count) is
  begin Control.Start;
        X := V;
        if Test then Set_Col(N); Put("Start Read "); Put(X,2); New_Line; end if;
        if Test then delay 0.04;  
                     Set_Col(N); Put("End  Read  "); Put(X,2); New_Line; end if;
        Control.Stop;
  end Read;

procedure Write(X: in Integer; N: in Count) is
   begin Control.Write(X,N);
   end Write;

end readerwriter;