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https://issues.apache.org/jira/browse/YARN-2910?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14237379#comment-14237379
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Tsuyoshi OZAWA commented on YARN-2910:
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Ah, that's the reason... [~rchiang], do you mind updating the test?
> FSLeafQueue can throw ConcurrentModificationException
> -----------------------------------------------------
>
> Key: YARN-2910
> URL: https://issues.apache.org/jira/browse/YARN-2910
> Project: Hadoop YARN
> Issue Type: Bug
> Components: fairscheduler
> Affects Versions: 2.5.0
> Reporter: Wilfred Spiegelenburg
> Assignee: Ray Chiang
> Attachments: FSLeafQueue_concurrent_exception.txt, YARN-2910.1.patch,
> YARN-2910.2.patch, YARN-2910.patch
>
>
> The list that maintains the runnable and the non runnable apps are a standard
> ArrayList but there is no guarantee that it will only be manipulated by one
> thread in the system. This can lead to the following exception:
> {noformat}
> 2014-11-12 02:29:01,169 ERROR [RMCommunicator Allocator]
> org.apache.hadoop.mapreduce.v2.app.rm.RMContainerAllocator: ERROR IN
> CONTACTING RM.
> java.util.ConcurrentModificationException:
> java.util.ConcurrentModificationException
> at java.util.ArrayList$Itr.checkForComodification(ArrayList.java:859)
> at java.util.ArrayList$Itr.next(ArrayList.java:831)
> at
> org.apache.hadoop.yarn.server.resourcemanager.scheduler.fair.FSLeafQueue.getResourceUsage(FSLeafQueue.java:147)
> at
> org.apache.hadoop.yarn.server.resourcemanager.scheduler.fair.FSAppAttempt.getHeadroom(FSAppAttempt.java:180)
> at
> org.apache.hadoop.yarn.server.resourcemanager.scheduler.fair.FairScheduler.allocate(FairScheduler.java:923)
> at
> org.apache.hadoop.yarn.server.resourcemanager.ApplicationMasterService.allocate(ApplicationMasterService.java:516)
> {noformat}
> Full stack trace in the attached file.
> We should guard against that by using a thread safe version from
> java.util.concurrent.CopyOnWriteArrayList
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