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Date: Mon, 3 Sep 2012 22:37:08 +1100 (NCT)
From: "Claus Ibsen (JIRA)" <jira@apache.org>
To: dev@activemq.apache.org
Message-ID: <529669254.30063.1346672228285.JavaMail.jiratomcat@arcas>
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Subject: [jira] [Commented] (AMQ-3982) Overlapping PList iterators can read
 wrong data or throw exceptions about chunk streams not existing.
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    [ https://issues.apache.org/jira/browse/AMQ-3982?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13447228#comment-13447228 ] 

Claus Ibsen commented on AMQ-3982:
----------------------------------

And today I got this on trunk code on the PListTest

{code}
2012-09-03 13:08:59,043 [IRM:0          ] - WARN  PListTest                      - Job[0] caught exception: null
java.lang.NullPointerException
	at org.apache.kahadb.util.LinkedNode.isTailNode(LinkedNode.java:68)
	at org.apache.kahadb.util.LinkedNode.getNext(LinkedNode.java:48)
	at org.apache.kahadb.index.ListNode$ListIterator.next(ListNode.java:184)
	at org.apache.kahadb.index.ListNode$ListIterator.next(ListNode.java:129)
	at org.apache.activemq.store.kahadb.plist.PList$PListIterator.next(PList.java:210)
	at org.apache.activemq.store.kahadb.plist.PList$PListIterator.next(PList.java:192)
	at org.apache.activemq.store.kahadb.plist.PListTest$Job.run(PListTest.java:578)
	at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
	at java.lang.Thread.run(Thread.java:680)
{code}
                
> Overlapping PList iterators can read wrong data or throw exceptions about chunk streams not existing.
> -----------------------------------------------------------------------------------------------------
>
>                 Key: AMQ-3982
>                 URL: https://issues.apache.org/jira/browse/AMQ-3982
>             Project: ActiveMQ
>          Issue Type: Bug
>          Components: Broker
>    Affects Versions: 5.6.0
>            Reporter: Timothy Bish
>            Assignee: Timothy Bish
>            Priority: Critical
>             Fix For: 5.7.0
>
>         Attachments: new.txt
>
>
> When multiple PList iterators are in use and happen have an overlapping read of PageFile data on disk they can reset each others seek offset and cause an exception to be thrown about "chunk stream does not exist" or read of a page in the Free list.  The reason is that the hasNext of PList iterator needs to by sync'd on the index lock to prevent two iterators from entering into a readPage call concurrently.  

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