# File ruby/comm_bstream.rb, line 16
        def get_port_number(opt_proc)
          if @port.nil? then
                ap = opt_proc.call(:bstream_bridge_port)
                if ap then
                  @port = ap
                else
                  s = TCPServer.open(0)
                  @port = s.addr[1]
                  s.close
                end
          end
          return @port
        end