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https://issues.apache.org/jira/browse/HADOOP-4232?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12636030#action_12636030
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Hudson commented on HADOOP-4232:
--------------------------------
Integrated in Hadoop-trunk #620 (See
[http://hudson.zones.apache.org/hudson/job/Hadoop-trunk/620/])
. Fix race condition in JVM reuse when multiple slots become free.
Contributed by Devaraj Das.
> Race condition in JVM reuse when more than one slot becomes free
> ----------------------------------------------------------------
>
> Key: HADOOP-4232
> URL: https://issues.apache.org/jira/browse/HADOOP-4232
> Project: Hadoop Core
> Issue Type: Bug
> Components: mapred
> Affects Versions: 0.19.0
> Reporter: Devaraj Das
> Assignee: Devaraj Das
> Priority: Blocker
> Fix For: 0.19.0
>
> Attachments: 4232-after-review.patch, 4232.patch
>
>
> A race condition exists where there are two or more slots free and there are
> two or more tasks waiting to run. As an example, consider a case where there
> are two free slots and there are two tasks waiting to run. JVM_job1 and
> JVM_job2 are the two idle jvms in memory. A waiting task, task job1_t1, kills
> the JVM_job2 and spawns a new one, JVM_1_job1. While JVM_1_job1 is
> initializing (it is marked busy during initialization), JVM_job1 picks this
> task up and hence this becomes busy as well. Another waiting task, job3_t1
> finds both the JVMs busy and doesn't spawn a new JVM.
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