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From "Junping Du (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HADOOP-11274) ConcurrentModificationException in Configuration Copy Constructor
Date Wed, 05 Nov 2014 16:24:35 GMT
Junping Du created HADOOP-11274:

             Summary: 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: Critical

Exception as below happens in doing some configuration update in parallel:
	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)
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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