code: def wake_deadline(start_time, timeout)
        timeout = process_timeout(timeout)
        deadline = start_time + timeout if timeout
      end
docs: Calculate the desired time to wake up.
   @api private
   @param start_time [nil,Time] time when the thread is put to sleep
   @param timeout [Numeric] desired time to sleep in seconds, +nil+ for forever
   @raise [TypeError] if +start_time+ is not +nil+ or a +Numeric+
   @raise [ArgumentError] if +start_time+ is negative
   @return [Time]