apollo-core/src/main/java/com/ctrip/framework/apollo/core/schedule/ExponentialSchedulePolicy.java/ExponentialSchedulePolicy/fail
class ExponentialSchedulePolicy:  @Override
  public long fail() {
    long delayTime = lastDelayTime;

    if (delayTime == 0) {
      delayTime = delayTimeLowerBound;
    } else {
      delayTime = Math.min(lastDelayTime << 1, delayTimeUpperBound);
    }

    lastDelayTime = delayTime;

    return delayTime;
  }