[ZOOKEEPER-783] committedLog in ZKDatabase is not properly synchronized

• Type: Bug
• Status: Closed
• Priority: Critical
• Resolution: Fixed
• Affects Version/s: 3.3.1
• Fix Version/s: 3.3.2, 3.4.0
• Component/s: server
• Hadoop Flags: Reviewed
• Assignee: Henry Robinson
• Reporter: Henry Robinson
• Created: 01/Jun/10 19:22
• Updated: 23/Nov/11 19:22
• Resolved: 26/Jul/10 22:45

Description

ZKDatabase.getCommittedLog() returns a reference to the LinkedList<Proposal> committedLog in ZKDatabase. This is then iterated over by at least one caller.

I have seen a bug that causes a NPE in LinkedList.clear on committedLog, which I am pretty sure is due to the lack of synchronization. This bug has not been apparent in normal ZK operation, but in code that I have that starts and stops a ZK server in process repeatedly (clear() is called from ZooKeeperServerMain.shutdown()).

It's better style to defensively copy the list in getCommittedLog, and to synchronize on the list in ZKDatabase.clear.