Github user lvfangmin commented on the issue: https://github.com/apache/zookeeper/pull/689 @anmolnar that's a good point, I think the reason we didn't use ZooKeeperThread or ZooKeeperCriticalThread is because we don't expect to exit abnormally from the WatcherCleaner thread, which is true for now. But I think it's better to use ZooKeeperThread or even ZooKeeperCriticalThread to cover future changes which might cause the thread exit abnormally.
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