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https://issues.apache.org/jira/browse/HADOOP-11274?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14201477#comment-14201477
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Vinod Kumar Vavilapalli commented on HADOOP-11274:
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Tx for the clarification Jing, yes, my analysis is wrong.
Still, locking the entire object for updateResources is plain bad along with
locking during read and write conf operations. We should NOT be making these
changes without careful analysis and testing - this Configuration class is the
center piece of ten's of projects.
> ConcurrentModificationException in Configuration Copy Constructor
> -----------------------------------------------------------------
>
> Key: HADOOP-11274
> URL: https://issues.apache.org/jira/browse/HADOOP-11274
> Project: Hadoop Common
> Issue Type: Bug
> Components: conf
> Reporter: Junping Du
> Assignee: Junping Du
> Priority: Blocker
> Fix For: 2.6.0
>
> Attachments: HADOOP-11274-v2.patch, HADOOP-11274.003.patch,
> HADOOP-11274.patch
>
>
> Exception as below happens in doing some configuration update in parallel:
> {noformat}
> java.util.ConcurrentModificationException
> at java.util.HashMap$HashIterator.nextEntry(HashMap.java:922)
> at java.util.HashMap$EntryIterator.next(HashMap.java:962)
> at java.util.HashMap$EntryIterator.next(HashMap.java:960)
> at java.util.HashMap.putAllForCreate(HashMap.java:554)
> at java.util.HashMap.<init>(HashMap.java:298)
> at org.apache.hadoop.conf.Configuration.<init>(Configuration.java:703)
> {noformat}
> In a constructor of Configuration - public Configuration(Configuration
> other), the copy of updatingResource data structure in copy constructor is
> not synchronized properly.
> Configuration.get() eventually calls loadProperty() where updatingResource
> gets updated. So, whats happening here is one thread is trying to do copy of
> Configuration as demonstrated in stack trace and other thread is doing
> Configuration.get(key) and than ConcurrentModificationException occurs
> because copying of updatingResource is not synchronized in constructor.
> We should make the update to updatingResource get synchronized, and also fix
> other tiny synchronized issues there.
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