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https://issues.apache.org/jira/browse/HADOOP-11274?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14201458#comment-14201458
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Jing Zhao commented on HADOOP-11274:
------------------------------------
Oops, I did not notice that setQuietly also takes the lock. The deadlock looks
very hard to hit though, since the two configuration objects need to use each
other for construction. However, considering this is a very critical part of
the code, maybe we should revert the patch from trunk, branch-2 and branch-2.6
before we have a clear solution.
> 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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