Major Description
We have client A which create a znode ,and its path is /zk/lock/100000. Another client B thread is acquiring for the lock, so it calls the exist command with watch periodically to check if it is available. Then Client A has finished this work, and delete this znode. Client b still calls exist command with watch. Because the code doesn't check node existence, when the Watch add operation comes , it will add to non-exist node path.
This problem may be cause by the follow code.
public Stat statNode(String path, Watcher watcher) throws KeeperException.NoNodeException { Stat stat = new Stat(); DataNode n = nodes.get(path); if (watcher != null) { dataWatches.addWatch(path, watcher); } if (n == null) { throw new KeeperException.NoNodeException(); } synchronized (n) { n.copyStat(stat); return stat; } }
The zk version we use is 3.4.5. We meet a problem that is the zk client try to reestablish to zk cluster failed after disconnect for some reason.We find it causes by ZOOKEEPER-706. But we try to know why there are so many watches. Then we find this problem.
