Rohith commented on YARN-2946:

Thanks [~jianhe] and [~varun_saxena] for your suggestions.

[~jianhe] , I am trying to understand before implementing state machine for DT 
keys updates on store,  is there any specific reason why state machine was not 
implemented? Does state machine for updating DT keys cause any potential issues?

> DeadLocks in RMStateStore<->ZKRMStateStore
> ------------------------------------------
>                 Key: YARN-2946
>                 URL: https://issues.apache.org/jira/browse/YARN-2946
>             Project: Hadoop YARN
>          Issue Type: Bug
>          Components: resourcemanager
>    Affects Versions: 2.7.0
>            Reporter: Rohith
>            Assignee: Rohith
>            Priority: Blocker
>         Attachments: 0001-YARN-2946.patch, 0002-YARN-2946.patch, 
> RM_BeforeFix_Deadlock_cycle_1.png, RM_BeforeFix_Deadlock_cycle_2.png, 
> TestYARN2946.java
> Found one deadlock in ZKRMStateStore.
> # Initial stage zkClient is null because of zk disconnected event.
> # When ZKRMstatestore#runWithCheck()  wait(zkSessionTimeout) for zkClient to 
> re establish zookeeper connection either via synconnected or expired event, 
> it is highly possible that any other thred can obtain lock on 
> {{ZKRMStateStore.this}} from state machine transition events. This cause 
> Deadlock in ZKRMStateStore.

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