Description Rumen Georgiev 2011-08-31 07:28:59 EDT

Build Identifier: I20100608-0911

When getInstallLocation() is invoked from multiple concurrent threads it may return "null". The problem seems to be missing synchronization 
 in the org.eclipse.core.internal.runtime.InternalPlatform. When multiple thread s invoke getInstallLocation() and it was not called since the platform start-up, there is a chance that the first thread creates ServiceTracker and invoke open() and just before calling getService(), another thread assigns new ServiceTracker instance to the "installLocation" field, so the first thread ends up calling getService() on a tracker that is not tracking services (open() has not been called). This leads to "null" returned by the method. 
This is the same for most of the methods in org.eclipse.core.internal.runtime.InternalPlatform.

The problem occurred in a code that executes on project open. This code does the following:

manager = IResource.getPathVariableManager()
manager.getURIValue("someVariableName")

So when multiple projects are opened at the same time, multiple threads execute the snippet above and sometimes the described race condition happens.

Here's a stack trace of the exception we get:
java.lang.NullPointerException
at org.eclipse.core.internal.resources.projectvariables.EclipseHomeProjectVariable.getValue(EclipseHomeProjectVariable.java:38)
at org.eclipse.core.internal.resources.ProjectVariableProviderManager$Descriptor.getValue(ProjectVariableProviderManager.java:58)
at org.eclipse.core.internal.resources.ProjectPathVariableManager.internalGetValue(ProjectPathVariableManager.java:151)
at org.eclipse.core.internal.resources.ProjectPathVariableManager.getURIValue(ProjectPathVariableManager.java:110)
...

Reproducible: Always

Steps to Reproduce:
the problem easily can be reproduced with breakpoints and running two concurrent threads that invokes Platform.getInstallLocation(). 
1. Install breakpoint at org.eclipse.core.internal.runtime.InternalPlatform.getInstallLocation() at line 356 "installLocation = new ServiceTracker(context, filter, null);"
2. Run two threads that invokes Platform.getInstallLocation()
3. Start debug and wait to suspend both threads at installed breakpoint. 
4. In the first thread perform "Step Over" to line 359   "return (Location) installLocation.getService();"
5. In second thread perform "Step Over" to line 357 "installLocation.open();"
6. Go back to first thread and perform "Step Over" to invoke installLocation.getService()
7. method will return "null"