[jira] [Created] (HADOOP-11274) ConcurrentModificationException in Configuration Copy Constructor

["Junping Du (JIRA)" <ji...@apache.org>]

Junping Du created HADOOP-11274:
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             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:
{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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