zookeeper 3.3.3 hangs on exists() calls

[Zhen Zhang]

Hi all, we see a few threads hang on exists() calls. The client side runs 
zookeeper 3.3.3, and the server side runs zookeeper 3.3.4. Here are the call 
stacks:

"shutdown thread for container: 1408093949" daemon prio=10 
tid=0x00007ebf14206000 nid=0x6428 in Object.wait() [0x00007f0058135000]
   java.lang.Thread.State: WAITING (on object monitor)
    at java.lang.Object.wait(Native Method)
    at java.lang.Object.wait(Object.java:485)
    at org.apache.zookeeper.ClientCnxn.submitRequest(ClientCnxn.java:1317)
    - locked <0x00007f009170b3b8> (a org.apache.zookeeper.ClientCnxn$Packet)
    at org.apache.zookeeper.ZooKeeper.exists(ZooKeeper.java:804)
    at org.apache.zookeeper.ZooKeeper.exists(ZooKeeper.java:837)
....


"ZkClient-EventThread-72-eat1-app207.stg.linkedin.com:12913,eat1-app208.stg.linkedin.com:12913,eat1-app209.stg.linkedin.com:12913"
 daemon prio=10 tid=0x00007effa0039000 nid=0x4569 in Object.wait() 
[0x00007f0058438000]
   java.lang.Thread.State: WAITING (on object monitor)
    at java.lang.Object.wait(Native Method)
    at java.lang.Object.wait(Object.java:485)
    at org.apache.zookeeper.ClientCnxn.submitRequest(ClientCnxn.java:1317)
    - locked <0x00007f0090e9c688> (a org.apache.zookeeper.ClientCnxn$Packet)
    at org.apache.zookeeper.ZooKeeper.exists(ZooKeeper.java:804)
    at org.apache.zookeeper.ZooKeeper.exists(ZooKeeper.java:837)
...

Appreciate your help!

Thanks
Zhen Zhang