-- test_prot_83.adb

with Text_IO;
procedure Test_Prot_83 is -- like Ada 95 protected Buffer
                          -- FIFO on floating point numbers

  F1, F2, F3 : Float;              -- just temporaries
  Size   : constant := 100;        -- buffer size
  subtype Indices is natural range 0..Size-1;   -- modular type in Ada 95
  type Pool_Type is array(Indices) of Float;

  task Buffer is
    entry Read(C : out Float);   -- mutually exclusive because of select
    entry Write(C : in Float);
  end Buffer;

  task body Buffer is
    Pool : Pool_Type;            -- the protected data items
    Count : Natural := 0;        
    In_Index, Out_Index : Indices := 0;
  begin
    loop
      select
        when Count < Pool'Length =>      -- guard holds up writer when full
          accept Write(C : in Float) do
            Pool(In_Index) := C;
            In_Index := In_Index mod Pool'Length; 
            Count := Count + 1;
          end;
      or
        when Count > 0 =>                -- guard holds up reader when empty
          accept Read(C : out Float) do
            C := Pool(Out_Index);
            Out_Index := Out_Index mod Pool'Length;
            Count := Count - 1;
          end;
      or
        terminate;
      end select;
    end loop;
  end Buffer;
begin
  Buffer.Write(1.5);        -- these calls would normally be in tasks
  Buffer.Read(F1);          -- here in main program, must avoid deadlock
  Buffer.Write(2.6);
  Buffer.Write(3.7);
  Buffer.Read(F2);
  Buffer.Read(F3);
  Text_io.Put_line("Write and Read gives " & Integer'Image(Integer(F1)) & "  " &
                    Integer'Image(Integer(F2)) & "  " &
                    Integer'Image(Integer(F3)));
  for I in 1..250 loop
    Buffer.Write(Float(I));  -- loop through buffer several times
    Buffer.Read(F1);
  end loop;
  Buffer.Write(4.8);
  Buffer.Read(F1);
  Text_io.Put_line("Write and Read gives " & Integer'Image(Integer(F1)));
end Test_Prot_83;