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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