[HADOOP-11274] ConcurrentModificationException in Configuration Copy Constructor

• Type: Bug
• Status: Closed
• Priority: Blocker
• Resolution: Duplicate
• Component/s: conf
• Target Version/s: 2.7.0
• Assignee: Vinod Kumar Vavilapalli
• Reporter: Junping Du
• Created: 05/Nov/14 16:24
• Updated: 25/Oct/19 20:25
• Resolved: 01/Mar/15 20:36

Description

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

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)

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.

Issue Links

• breaks: HIVE-8760 Pass a copy of HiveConf to hooks
• is duplicated by: HADOOP-11209 Configuration#updatingResource/finalParameters are not thread-safe
• relates to: HADOOP-15331 Fix a race condition causing parsing error of java.io.BufferedInputStream in class org.apache.hadoop.conf.Configuration