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From "Henry Robinson (JIRA)" <j...@apache.org>
Subject [jira] Updated: (ZOOKEEPER-783) committedLog in ZKDatabase is not properly synchronized
Date Tue, 01 Jun 2010 19:42:36 GMT

     [ https://issues.apache.org/jira/browse/ZOOKEEPER-783?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Henry Robinson updated ZOOKEEPER-783:
-------------------------------------

    Attachment: ZOOKEEPER-783.patch

Defensive copying added to getCommittedLog() and synchronization during clear(). 

No tests added; really not sure how best to test for this. It does fix my test case but it's
very difficult to distill that into a test (plus it only fails once in about 100 runs). 

> committedLog in ZKDatabase is not properly synchronized
> -------------------------------------------------------
>
>                 Key: ZOOKEEPER-783
>                 URL: https://issues.apache.org/jira/browse/ZOOKEEPER-783
>             Project: Zookeeper
>          Issue Type: Bug
>          Components: server
>    Affects Versions: 3.3.1
>            Reporter: Henry Robinson
>            Priority: Critical
>         Attachments: ZOOKEEPER-783.patch
>
>
> 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.

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