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From "Vinod Kumar Vavilapalli (JIRA)" <j...@apache.org>
Subject [jira] [Reopened] (HADOOP-11274) ConcurrentModificationException in Configuration Copy Constructor
Date Fri, 07 Nov 2014 02:09:34 GMT

     [ https://issues.apache.org/jira/browse/HADOOP-11274?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Vinod Kumar Vavilapalli reopened HADOOP-11274:
----------------------------------------------

I don't know the behavior of locking this in a constructor, but assuming so, I think there
is a deadlock already.


Thread 1: Copy constructor takes lock on object 2, and then calls setQuietly which waits on
locking on itself
Thread 2: Same but the locking in reverse order.

> 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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