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https://issues.apache.org/jira/browse/HADOOP-11361?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15363120#comment-15363120
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Yongjun Zhang commented on HADOOP-11361:
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Hi [~brahmareddy],
I took a quick look at your latest patch,
You removed
{code}
lastRecs = null; // in case regular interval update is not running
{code}
and added
{code}
189 // Not making LastRecs null due to Race between multiple readers
and
190 // updater
190 lastRecsCleared = true;
{code}
Given that the code is doing {{lastRecsCleared = true;}}, the comment "Not
making LastRecs null ..." is a bit contradictory.
It looks to me that it's actually not a race condition issue (otherwise please
would you please explain what race condition you are seeing), because it looks
that a single thread would run into the same problem as explained in my comment
linked above. So seems to me that the solution would be to fix
{{MetricsSourceAdapter#updateAttrCache}} to let it check whether lastRecs is
NULL, and not to access it if so.
Does it make sense to you?
Thanks.
> Fix a race condition in MetricsSourceAdapter.updateJmxCache
> -----------------------------------------------------------
>
> Key: HADOOP-11361
> URL: https://issues.apache.org/jira/browse/HADOOP-11361
> Project: Hadoop Common
> Issue Type: Bug
> Affects Versions: 2.4.1, 2.5.1, 2.6.0
> Reporter: Brahma Reddy Battula
> Assignee: Brahma Reddy Battula
> Attachments: HADOOP-111361-003.patch, HADOOP-11361-002.patch,
> HADOOP-11361-004.patch, HADOOP-11361.patch, HDFS-7487.patch
>
>
> {noformat}
> Caused by: java.lang.NullPointerException
> at
> org.apache.hadoop.metrics2.impl.MetricsSourceAdapter.updateAttrCache(MetricsSourceAdapter.java:247)
> at
> org.apache.hadoop.metrics2.impl.MetricsSourceAdapter.updateJmxCache(MetricsSourceAdapter.java:177)
> at
> org.apache.hadoop.metrics2.impl.MetricsSourceAdapter.getAttribute(MetricsSourceAdapter.java:102)
> at
> com.sun.jmx.interceptor.DefaultMBeanServerInterceptor.getAttribute(DefaultMBeanServerInterceptor.java:647)
> {noformat}
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