def dt_logger
      if instance_variable_defined?(k = :@dt_logger)
        instance_variable_get(k)
      else
        instance_variable_set(k, begin
          Logger.new(conf.root_path + "log/dt.log")
        rescue Errno::ENOENT
          nil
        end)
      end
    end
def dt_logger
      if instance_variable_defined?(k = :@dt_logger)
        instance_variable_get(k)
      else
        instance_variable_set(k, begin
          Logger.new(conf.root_path + "log/dt.log")
        rescue Errno::ENOENT
          nil
        end)
      end
    end
File logger, an instance of Ruby's <tt>Logger</tt>.
 @return [Logger] Default is a <tt>Logger</tt> writing to <tt>log/dt.log</tt>.