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https://issues.apache.org/jira/browse/HDDS-6060?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17452098#comment-17452098
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George Huang commented on HDDS-6060:
------------------------------------
>From @Bharat Viswanadham,
I think what might be happening here is
The containerID's set which we get is UnModifiableNavigableSet wrapping
original NavigableSet, so the returned object cannot be modified by caller, but
other threads can modify this while map phase happening(during collect). So,
ContainerAttribute#getCollection need to return a NavigableSet which is truly
cloned UnmodifableNavigableSet, not just a wrapped Set.
{code:java}
Collections.unmodifiableList(ints).stream().map(a -> a + 1).map(a ->
addSomething(1, ints)).collect(Collectors.toList());
private int addSomething(int current, List<Integer> ints) {
ints.add(1);
return current;
}
{code}
Here in above example when 2nd map phase modifies original set we get same
ConcurrentModificationException.
> ERROR MetricsSourceAdapter: Error getting metrics from source
> SCMContainerMetrics java.util.ConcurrentModificationException
> ---------------------------------------------------------------------------------------------------------------------------
>
> Key: HDDS-6060
> URL: https://issues.apache.org/jira/browse/HDDS-6060
> Project: Apache Ozone
> Issue Type: Bug
> Components: SCM
> Reporter: George Huang
> Assignee: George Huang
> Priority: Major
>
> |1:23:33.841 PM|ERROR|MetricsSourceAdapter|Error getting metrics from source
> SCMContainerMetrics
> java.util.ConcurrentModificationException
> at java.util.TreeMap$KeySpliterator.forEachRemaining(TreeMap.java:2757)
> at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:482)
> at
> java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:472)
> at java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:708)
> at java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
> at java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:566)
> at
> org.apache.hadoop.hdds.scm.container.ContainerManagerImpl.getContainers(ContainerManagerImpl.java:172)
> at
> org.apache.hadoop.hdds.scm.server.StorageContainerManager.getContainerStateCount(StorageContainerManager.java:1769)
> at
> org.apache.hadoop.hdds.scm.server.SCMContainerMetrics.getMetrics(SCMContainerMetrics.java:68)
> at
> org.apache.hadoop.metrics2.impl.MetricsSourceAdapter.getMetrics(MetricsSourceAdapter.java:200)
> at
> org.apache.hadoop.metrics2.impl.MetricsSystemImpl.snapshotMetrics(MetricsSystemImpl.java:419)
> at
> org.apache.hadoop.metrics2.impl.MetricsSystemImpl.sampleMetrics(MetricsSystemImpl.java:406)
> at
> org.apache.hadoop.metrics2.impl.MetricsSystemImpl.onTimerEvent(MetricsSystemImpl.java:381)
> at
> org.apache.hadoop.metrics2.impl.MetricsSystemImpl$4.run(MetricsSystemImpl.java:368)
> at java.util.TimerThread.mainLoop(Timer.java:555)
> at java.util.TimerThread.run(Timer.java:505)|
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