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https://issues.apache.org/jira/browse/YARN-2946?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14244142#comment-14244142
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Varun Saxena commented on YARN-2946:
------------------------------------
[~rohithsharma], good catch. As you said {{synchronized}} can be removed from
{{RMStateStore#isFencedState()}}.
Regarding the methods you listed out, I think we can avoid reverse locking i.e.
*ZKRMStateStore.class -> StateMachine.doTransition()* by making the following
changes.
# Remove {{synchronized}} keyword from each one of the methods listed above.
# Separate out State machine synchronization(invoked by call to
{{isFencedState}} & {{notifyStoreOperationFailed}}) and ZKRMStateStore
synchronization by putting the relevant code in a synchronized block.
For example, code for RMStateStore#storeRMDTMasterKey() can be changed as under
:
{code:title=RMStateStore.java|borderStyle=solid}
public void storeRMDTMasterKey(DelegationKey delegationKey) {
if(isFencedState()) {
LOG.info("State store is in Fenced state. Can't store RM Delegation " +
"Token Master key.");
return;
}
try {
synchronized(this) {
storeRMDTMasterKeyState(delegationKey);
}
} catch (Exception e) {
notifyStoreOperationFailed(e);
}
}
{code}
> DeadLock's 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,
> 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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