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https://issues.apache.org/jira/browse/YARN-2910?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14237420#comment-14237420
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Tsuyoshi OZAWA commented on YARN-2910:
--------------------------------------

Thanks for updating, Akira. But now Ray is the assignee of this JIRA and he is 
doing this issue, so let's wait for the update by him :-)

[~rchiang], could you update following things based on v3 patch?
{code}
+        for (int i=0; i <200; i++) {
{code}

{code}
+        for (int i=0; i <200; i++) {
{code}

On my local, the probability of failure is low with Akira's patch since the 
number of iteration is too small. How about making the iteration larger(e.g. 
10000)?
Additionally, this is minor nits, but please add space to after < like {code}< 
10000{code}.

> 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-2910.3.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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