[FELIX-2791] NPE in getStartLevel due to race condition

• Type: Bug
• Status: Closed
• Priority: Blocker
• Resolution: Fixed
• Affects Version/s: fileinstall-3.1.4
• Fix Version/s: fileinstall-3.1.6
• Component/s: File Install
• Assignee: Sanjeeb Kumar Sahoo
• Reporter: Sanjeeb Kumar Sahoo
• Created: 19/Jan/11 16:11
• Updated: 17/Mar/15 07:01
• Resolved: 21/Jan/11 01:08

Description

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?