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From "Michael Dick (JIRA)" <j...@apache.org>
Subject [jira] Commented: (OPENJPA-1168) NPE in UUIDGenerator.initializeForType1()
Date Thu, 09 Jul 2009 01:30:15 GMT

    [ https://issues.apache.org/jira/browse/OPENJPA-1168?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12728994#action_12728994
] 

Michael Dick commented on OPENJPA-1168:
---------------------------------------

Hi Rick,

I'm unable to hit the timing window you mention on my system, but your explanation is sound.


That said there's still a window where IP can be initialized (non null) but not copied. Another
thread could hit this window when IP was empty and get a non-unique id. It's probably safer
to set a different flag at the end of the method and key off that instead of IP or RANDOM.

Thanks for the patch though - I doubt this was easy to find.  

> NPE in UUIDGenerator.initializeForType1()
> -----------------------------------------
>
>                 Key: OPENJPA-1168
>                 URL: https://issues.apache.org/jira/browse/OPENJPA-1168
>             Project: OpenJPA
>          Issue Type: Bug
>          Components: lib
>            Reporter: Rick Curtis
>             Fix For: 1.3.0, 2.0.0
>
>         Attachments: OPENJPA-1168.patch
>
>
> When UUIDGenerator.createType1() is called by more than one thread at *nearly* the same
time AND UUIDGenerator.createType1() wasn't called previously, a small timing window exists
where a NPE will result.
> Scenario:
> Thread 1 calls UUIDGenerator.createType1() and RANDOM == null so initializeForType1()
is called. While that thread is in initializeForType1(), it sets the static variable RANDOM
so that value is no longer null. Now Thread 2 calls UUIDGenerator.createType1() and RANDOM
is no longer null, so it proceeds to the call System.arraycopy(IP, 0, uuid, 10, IP.length);.
At this point Thread 1 hasn't got to initializing IP yet, so Thread 2 gets hits a NPE.

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