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From "Zhijie Shen (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-11274) ConcurrentModificationException in Configuration Copy Constructor
Date Wed, 05 Nov 2014 19:57:34 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-11274?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14198965#comment-14198965
] 

Zhijie Shen commented on HADOOP-11274:
--------------------------------------

[~djp], I'm afraid read and write access to other.updatingResource is still not completely
synchronized after the patch.
{code}
     this.updatingResource = new HashMap<String, String[]>(other.updatingResource);
     this.finalParameters = new HashSet<String>(other.finalParameters);
{code}

updatingResource can be also modified by {{set(String name, String value, String source)}}
and {{readFields(DataInput in)}}.

> 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
>         Attachments: 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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