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https://issues.apache.org/jira/browse/YARN-2030?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13998635#comment-13998635
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Tsuyoshi OZAWA commented on YARN-2030:
--------------------------------------

+1 for this idea too. Using state machine makes the code cleaner and simpler.

> Use StateMachine to simplify handleStoreEvent() in RMStateStore
> ---------------------------------------------------------------
>
>                 Key: YARN-2030
>                 URL: https://issues.apache.org/jira/browse/YARN-2030
>             Project: Hadoop YARN
>          Issue Type: Improvement
>            Reporter: Junping Du
>
> Now the logic to handle different store events in handleStoreEvent() is as 
> following:
> {code}
> if (event.getType().equals(RMStateStoreEventType.STORE_APP)
>         || event.getType().equals(RMStateStoreEventType.UPDATE_APP)) {
>       ...
>       if (event.getType().equals(RMStateStoreEventType.STORE_APP)) {
>         ...
>       } else {
>         ...
>       }
>       ...
>       try {
>         if (event.getType().equals(RMStateStoreEventType.STORE_APP)) {
>           ...
>         } else {
>           ...
>         }
>       } 
>       ...
>     } else if (event.getType().equals(RMStateStoreEventType.STORE_APP_ATTEMPT)
>         || event.getType().equals(RMStateStoreEventType.UPDATE_APP_ATTEMPT)) {
>       ...
>       if (event.getType().equals(RMStateStoreEventType.STORE_APP_ATTEMPT)) {
>         ...
>       } else {
>         ...
>       }
>         ...
>         if (event.getType().equals(RMStateStoreEventType.STORE_APP_ATTEMPT)) {
>           ...
>         } else {
>           ...
>         }
>       }
>       ...
>     } else if (event.getType().equals(RMStateStoreEventType.REMOVE_APP)) {
>     ...
>     } else {
>       ...
>     }
> }
> {code}
> This is not only confuse people but also led to mistake easily. We may 
> leverage state machine to simply this even no state transitions.



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