[jira] [Created] (FELIX-4597) Race issue causing ConcurrentModificationException in org.apache.felix.http.whiteboard.internal.manager.ExtenderManager.add(ExtenderManager.java:111)

["Xander Uiterlinden (JIRA)" <ji...@apache.org>]

Xander Uiterlinden created FELIX-4597:
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             Summary: Race issue causing ConcurrentModificationException in org.apache.felix.http.whiteboard.internal.manager.ExtenderManager.add(ExtenderManager.java:111)
                 Key: FELIX-4597
                 URL: https://issues.apache.org/jira/browse/FELIX-4597
             Project: Felix
          Issue Type: Bug
          Components: HTTP Service
    Affects Versions: http-2.3.0
            Reporter: Xander Uiterlinden


Quite frequently when launching our application we're getting a ConcurrentModificationException, see the following stacktrace:

java.util.ConcurrentModificationException
	at java.util.HashMap$HashIterator.nextNode(HashMap.java:1429)
	at java.util.HashMap$KeyIterator.next(HashMap.java:1453)
	at org.apache.felix.http.whiteboard.internal.manager.ExtenderManager.add(ExtenderManager.java:111)
	at org.apache.felix.http.whiteboard.internal.tracker.HttpContextTracker.added(HttpContextTracker.java:37)
	at org.apache.felix.http.whiteboard.internal.tracker.HttpContextTracker.added(HttpContextTracker.java:24)
	at org.apache.felix.http.whiteboard.internal.tracker.AbstractTracker.addingService(AbstractTracker.java:36)
	at org.osgi.util.tracker.ServiceTracker$Tracked.customizerAdding(ServiceTracker.java:932)
	at org.osgi.util.tracker.ServiceTracker$Tracked.customizerAdding(ServiceTracker.java:864)
	at org.osgi.util.tracker.AbstractTracked.trackAdding(AbstractTracked.java:256)
	at org.osgi.util.tracker.AbstractTracked.track(AbstractTracked.java:229)
	at org.osgi.util.tracker.ServiceTracker$Tracked.serviceChanged(ServiceTracker.java:8

This is caused by a race issue where one thread is adding HttpContext where another thread is adding a servlet for this context at the same time.

Thread A:
In ExtenderManager.addHttpContext(service, ref) the http context is added to the context manager which returns a collection of mappings. This collection is the actual collection as administered by the HttpContextHolder.
In a for loop* on these mappings the mappings are registered with the HttpService.

Collection<AbstractMapping> mappings = this.contextManager.addHttpContext(bundle, contextId, service);

Thread B:
When adding a servlet on the other thread, getHttpContext(mapping, ref) is called which calls getHttpContext(bundle, contextId, mapping). Here the HttpContextHolder is obtained by HttpContextHolder holder = this.idMap.get(id). After which holder.addMapping(mapping) is called. This addMapping is called while thread A is still in it's for loop iterating over the mappings.

This requires synchronization. It would actually be nice to be able to synchronize on a particular HttpContext. This would require some method refactoring.



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