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https://issues.apache.org/jira/browse/MAPREDUCE-5166?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13640476#comment-13640476
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Arun C Murthy commented on MAPREDUCE-5166:
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Furthermore, iterating over Counters isn't thread-safe (copy-safe) since the
map-thread might be modifying the Counter, the RPC layer saves us since it
makes a safe (sync) copy.
I wonder what else exhibits this problem in LJR, I mean other than Counters...
> ConcurrentModificationException in LocalJobRunner
> -------------------------------------------------
>
> Key: MAPREDUCE-5166
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-5166
> Project: Hadoop Map/Reduce
> Issue Type: Bug
> Affects Versions: 1.2.0
> Reporter: Gunther Hagleitner
> Priority: Critical
>
> With the latest version hive unit tests fail in various places with the
> following stack trace. The problem seems related to: MAPREDUCE-2931
> {noformat}
> [junit] java.util.ConcurrentModificationException
> [junit] at java.util.HashMap$HashIterator.nextEntry(HashMap.java:793)
> [junit] at java.util.HashMap$ValueIterator.next(HashMap.java:822)
> [junit] at
> org.apache.hadoop.mapred.Counters.incrAllCounters(Counters.java:505)
> [junit] at org.apache.hadoop.mapred.Counters.sum(Counters.java:528)
> [junit] at
> org.apache.hadoop.mapred.LocalJobRunner$Job.getCurrentCounters(LocalJobRunner.java:490)
> [junit] at
> org.apache.hadoop.mapred.LocalJobRunner.getJobCounters(LocalJobRunner.java:634)
> [junit] at
> org.apache.hadoop.mapred.JobClient$NetworkedJob.getCounters(JobClient.java:418)
> [junit] at
> org.apache.hadoop.hive.ql.exec.HadoopJobExecHelper$ExecDriverTaskHandle.getCounters(HadoopJobExecHelper.java:465)
> [junit] at
> org.apache.hadoop.hive.ql.exec.HadoopJobExecHelper.progress(HadoopJobExecHelper.java:300)
> [junit] at
> org.apache.hadoop.hive.ql.exec.HadoopJobExecHelper.progress(HadoopJobExecHelper.java:532)
> [junit] at
> org.apache.hadoop.hive.ql.exec.ExecDriver.execute(ExecDriver.java:453)
> [junit] at
> org.apache.hadoop.hive.ql.exec.ExecDriver.main(ExecDriver.java:681)
> [junit] at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
> [junit] at
> sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
> [junit] at
> sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
> [junit] at java.lang.reflect.Method.invoke(Method.java:597)
> [junit] at org.apache.hadoop.util.RunJar.main(RunJar.java:160)
> {noformat}
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