code: protected long computeNext(long last) {
      long currentTick = clock.currentTimeMicros();
      if (last >= currentTick) {
        maybeLog(currentTick, last);
        return last + 1;
      }
      return currentTick;
    }
docs: Compute the next timestamp, given the current clock tick and the last timestamp returned.
  
  <p>If timestamps have to drift ahead of the current clock tick to guarantee monotonicity, a
  warning will be logged according to the rules defined in the configuration.