DLedgerLeaderElector.maintainAsFollower

[YalikWang]

源代码：

private void maintainAsFollower() {
        if (DLedgerUtils.elapsed(lastLeaderHeartBeatTime) > 2 * heartBeatTimeIntervalMs) {
            synchronized (memberState) {
                if (memberState.isFollower() && (DLedgerUtils.elapsed(lastLeaderHeartBeatTime) > maxHeartBeatLeak * heartBeatTimeIntervalMs)) {
                    logger.info("[{}][HeartBeatTimeOut] lastLeaderHeartBeatTime: {} heartBeatTimeIntervalMs: {} lastLeader={}", memberState.getSelfId(), new Timestamp(lastLeaderHeartBeatTime), heartBeatTimeIntervalMs, memberState.getLeaderId());
                    changeRoleToCandidate(memberState.currTerm());
                }
            }
        }
    }

为什么需要进行两次超时判断，而不是直接将最终的超时判断放到锁外，就像下面这样：

private void maintainAsFollower() {
        if (DLedgerUtils.elapsed(lastLeaderHeartBeatTime) > maxHeartBeatLeak * heartBeatTimeIntervalMs) {
            synchronized (memberState) {
                if (memberState.isFollower()) {
                    logger.info("[{}][HeartBeatTimeOut] lastLeaderHeartBeatTime: {} heartBeatTimeIntervalMs: {} lastLeader={}", memberState.getSelfId(), new Timestamp(lastLeaderHeartBeatTime), heartBeatTimeIntervalMs, memberState.getLeaderId());
                    changeRoleToCandidate(memberState.currTerm());
                }
            }
        }
    }

是考虑性能还是什么其他原因

[supervate]

It look like its for improve system stability.
Reduce the probability of follower upgrade to candidate.

The first judgement is 2 * heartBeatTimeIntervalMs
The second judgement is 3(max) * heartBeatTimeIntervalMs

It give a chance to current term's leader that it can send a heartbeat to follower to prevent it upgrade to candidate, when we found it will be timeout.