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From "Sahoo (JIRA)" <j...@apache.org>
Subject [jira] Updated: (FELIX-2791) NPE in getStartLevel due to race condition
Date Thu, 20 Jan 2011 06:38:43 GMT

     [ https://issues.apache.org/jira/browse/FELIX-2791?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Sahoo updated FELIX-2791:
-------------------------

    Attachment: patch.txt

PFA a patch that solves the issue. It introduces a barrier and a flag to make sure watcher
threads don't run until fileinstall has finished initialisation. Please review if you want
to, as I plan to commit and make a new release of fileinstall ASAP. Thanks.

> NPE in getStartLevel due to race condition
> ------------------------------------------
>
>                 Key: FELIX-2791
>                 URL: https://issues.apache.org/jira/browse/FELIX-2791
>             Project: Felix
>          Issue Type: Bug
>          Components: File Install
>    Affects Versions: fileinstall-3.1.4
>            Reporter: Sahoo
>            Assignee: Sahoo
>            Priority: Blocker
>             Fix For: fileinstall-3.1.6
>
>         Attachments: patch.txt
>
>
> We are using FileInstall 3.1.4 and one of our user is seeing the following exception
repeated in the directory watcher main loop continuously:
> java.lang.NullPointerException
>         at org.apache.felix.fileinstall.internal.FileInstall.getStartLevel(FileInstall.java:283)
>         at org.apache.felix.fileinstall.internal.FileInstall.getStartLevel(FileInstall.java:276)
>         at org.apache.felix.fileinstall.internal.DirectoryWatcher.run(DirectoryWatcher.java:237)
> In main loop, we have serious trouble: java.lang.NullPointerException
> NPE comes from FileInstall.java:283, which looks like this:
>             return (StartLevel) startLevel.waitForService(timeout);
> It looks like a concurrency bug to me in FileInstall. The only explanation that I have
so far is that in the target environment, code is getting reordered and hence directory watcher
thread is spwaned before startLevel is initialzed.. Since startLevel is not declared volatile,
nor is it accessed from a synchronized block, DirectoryWatcher thread continues to see the
stale value.
> So, I suggest we change startLevel to a volatile field. Any comments?

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