关于Zookeeper框架Curator中的主从选举框架LeaderLatch的坑

根据网上给的LeaderLatch的示例代码写的业务代码，这里面用到的serverId是从配置中读取的（每个新部署的实例自动生成，之后一直不变）

@PostConstructpublic void setUp() throws Exception {    RetryPolicy retryPolicy = new ExponentialBackoffRetry(1000, 3);    client = CuratorFrameworkFactory.builder()            .connectString(zkConnectString)            .retryPolicy(retryPolicy)            .sessionTimeoutMs(60000)            .connectionTimeoutMs(3000)            .namespace(Constants.GLOBAL_NAME_SPACE)            .build();    client.start();    leaderLatch = new LeaderLatch(client, QUORUM_PATH, serverId);    leaderLatch.addListener(new LeaderLatchListener() {        @Override        public void isLeader() {            log.info("Currently run as leader");        }        @Override        public void notLeader() {            log.info("Currently run as slave");        }    });    leaderLatch.start();}

这段代码达到的预期效果应该是当前实例在运行为leader的时候，日志打印Currently run as leader；当丢失leader的时候，日志打印Currently run as leader。
多实例运行时，刚开始选主是没问题的，只有一个为leader。但是丢失主的实例不能切换Slave方式运行；我这里测试丢失主的方式有两种，一是断开实例与zk之间的连接，二是删除zk上面的该实例锁住的数据（例如leaderlatch路径为/test，那么每个实例会在/test这个路径下生成一个临时节点，将这个临时节点手动删除）。
而且这么写代码，很难做主从切换缓冲时间来防止主从来回切换。

所以，将代码中的listener去掉，修改为主动轮询监听：

@PostConstructpublic void setUp() throws Exception {    RetryPolicy retryPolicy = new ExponentialBackoffRetry(1000, 3);    client = CuratorFrameworkFactory.builder()            .connectString(zkConnectString)            .retryPolicy(retryPolicy)            .sessionTimeoutMs(60000)            .connectionTimeoutMs(3000)            .namespace(Constants.GLOBAL_NAME_SPACE)            .build();    client.start();    leaderLatch = new LeaderLatch(client, QUORUM_PATH, serverId);    leaderLatch.start();}@Scheduled(fixedDelay = 3000)public void checkLeader() throws Exception {    //首先利用serverId检查自己是否还存在于leaderlatch选举结果集中    //考虑网络阻塞，zk数据异常丢失等情况    boolean isExist = false;    Collection<Participant> participants = leaderLatch.getParticipants();    for (Participant participant : participants) {        if (serverId.equals(participant.getId())) {            isExist = true;            break;        }    }    //如果不存在，则重新加入选举    if (!isExist) {        log.info("Current server does not exist on zk, reset leaderlatch");        leaderLatch.close();        leaderLatch = new LeaderLatch(client, QUORUM_PATH, serverId);        leaderLatch.start();        log.info("Successfully reset leaderlatch");    }    //查看当前leader是否是自己    //注意，不能用leaderLatch.hasLeadership()因为有zk数据丢失的不确定性    //利用serverId对比确认是否主为自己    Participant leader = leaderLatch.getLeader();    boolean hashLeaderShip = serverId.equals(leader.getId());    if (log.isInfoEnabled()) {        log.info("Current Participant: {}", JSON.toJSONString(participants));        log.info("Current Leader: {}", leader);    }    //主从切换缓冲    if(hashLeaderShip) {        isLeaderCount++;        isSlaveCount = 0;    } else {        isLeaderCount = 0;        isSlaveCount ++;    }    if (isLeaderCount > 3 && !isLeader) {        log.info("Currently run as leader");    }    if (isSlaveCount > 3 && isLeader) {        log.info("Currently run as slave");    }}