In order to move to simpler module assembly and deployment in our web
applications, I decided to give the META-INF/services a try. That would
allow us to deploy different implementations (jars) to different customers,
each having the implementation that fits them best. Originally I used the
JDK ServiceLoader, but that API is rather limited, for example lacking
notification of changes.

So I switched to the Lookup API, although I know it was designed for
desktop applications, not for long-running server software. This change
immediately caused a memory leak when the webapp was unloaded. Within a few
reloads we got a PermGen OutOfMemory exception. That turned out to be a
Timer thread that could never be cancel()-ed. We were still using an older
version of the lookup library, so I switched to the new one, from NetBeans
7, platform/lib/org-openide-util-lookup.jar and org-openide-util.jar.
Unfortunately, the RequestProcessor class from org-openide-util.jar still
suffers from the same problem.

It turned out this is caused by my LookupListener. Adding a LookupListener
caused several threads to start (and never end). One thread is a Timer
thread (Timer-0, Timer-1 etc), another one is called "Active Reference
Queue Daemon". As long as I avoid the event notification functionality of
Lookup, everything is working fine. Is there anything I can do to end those
threads?