[issues] Created: (PAXWEB-191) When a bundle registered with Pax Web is uninstalled, references to that bundle's objects are not properly cleaned up causing a memory leak.

[John Trimble (JIRA)]

When a bundle registered with Pax Web is uninstalled, references to that 
bundle's objects are not properly cleaned up causing a memory leak.
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                 Key: PAXWEB-191
                 URL: http://issues.ops4j.org/browse/PAXWEB-191
             Project: Pax Web
          Issue Type: Bug
          Components: Http Service, War Extender, Web Container
    Affects Versions: 0.7.2
         Environment: Apache Felix Karaf 1.2.0 and Pax Web 0.7.2
            Reporter: John Trimble
            Assignee: Alin Dreghiciu
         Attachments: bundle_uninstallation_leak_fix.patch, memoryhogwebapp.zip

Pax Web continues to hold object references to uninstalled bundles that had 
registered with the Pax Web WebContainer service or were extended by the Pax 
Web War Extender. This causes a memory leak leading to permanent generation and 
heap space issues if bundles, which interact with Pax Web in the aforementioned 
ways, are routinely installed and uninstalled. 

With regard to the WebContainer service, instances of 
org.ops4j.pax.web.service.internal.HttpServiceStarted are never garbage 
collected once instantiated and potentially continue to hold references to 
various objects from uninstalled bundles, such as ServletContextListener 
instances, if they were not explicitly unregistered. The cause of this is that 
newly instantiated instances of HttpServiceStarted add a ServerListener 
instance, implemented as an anonymous inner class of HttpServiceStarted, to the 
ServerController, but never remove it. This listener holds an implicit 
reference to the HttpServiceStarted instance preventing its garbage collection, 
and the garbage collection of anything it references.

The Pax Web War Extender's WebXmlObserver holds references to instances of 
org.ops4j.pax.web.extender.war.internal.model.WebApp even after the associated 
WAR has been uninstalled. This leads to the same issue regarding permanent 
generation and heap space.

I've attached a patch that should plug both of these leaks. First, it adds the 
ability to remove ServerListener instances from a ServerController, and 
modifies the HttpServiceStarted's stop() method to remove the appropriate 
ServerListener instance from the ServerController. Secondly, it modifies the 
WebXmlObserver's removingEntries() method to remove the appropriate WebApp 
reference.

In addition to the patch, I've included a small example webapp to help 
illustrate the problem. Simply install and uninstall the WAR serveral times, 
allowing the Pax Web War Extender to extend it, and an OutOfMemory exception 
will soon follow. If you examine the heap space, using a tool like YourKit, you 
will find outstanding references to MemoryHogServletContextListener instances, 
as well as extraneous WebApp and HttpServiceStarted instances.


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