David Jencks created FELIX-4223:
-----------------------------------
Summary: [DS] DependencyManager filter should be set up in enable,
not activate, to avoid race conditions
Key: FELIX-4223
URL: https://issues.apache.org/jira/browse/FELIX-4223
Project: Felix
Issue Type: Bug
Components: Declarative Services (SCR)
Affects Versions: scr-1.8.0
Reporter: David Jencks
Assignee: David Jencks
Fix For: scr-1.8.0
Currently target filters on DependencyManager are set during activation. This
can cause a race condition between a thread on which a service dependency is
registered and a thread requesting a service. A simple solution to this is to
set up the filters during enable (and of course modify them on configuration
updates). This makes sense to me since activation can never by itself change
the target filter.
The symptoms we saw of the race condition were
Caused by: java.lang.NullPointerException
at
org.apache.felix.scr.impl.manager.DependencyManager.open(DependencyManager.java:1454)
at
org.apache.felix.scr.impl.manager.ImmediateComponentManager.createImplementationObject(ImmediateComponentManager.java:266)
at
org.apache.felix.scr.impl.manager.ImmediateComponentManager.createComponent(ImmediateComponentManager.java:123)
at
org.apache.felix.scr.impl.manager.ImmediateComponentManager.getService(ImmediateComponentManager.java:800)
at
org.apache.felix.scr.impl.manager.ImmediateComponentManager.getServiceInternal(ImmediateComponentManager.java:767)
at
org.apache.felix.scr.impl.manager.ImmediateComponentManager.getService(ImmediateComponentManager.java:706)
at
org.eclipse.osgi.internal.serviceregistry.ServiceUse$1.run(ServiceUse.java:141)
In this code base the NPE is from trackerRef.get() == null.
I don't entirely understand how the NPE occurs, it appears to require the jvm
to reorder some instructions that don't look to me reorderable, but there is
obviously a problem with concurrent access to setTarget if a second thread
calls it while the first thread is in this block:
customizer.setTracker( tracker );
registered = true;
//first thread parked here
tracker.open( m_componentManager.getTrackingCount() );
customizer.setTrackerOpened();
the second thread will use the registered flag to not actually open the
tracker, there is a code block earlier that exits if registered == true and
there is no filter change.
--
This message is automatically generated by JIRA.
If you think it was sent incorrectly, please contact your JIRA administrators
For more information on JIRA, see: http://www.atlassian.com/software/jira
