Affects Version/s: None
Fix Version/s: None
A typical Servlet container services requests from a pool of threads. The Servlet container controls the lifecycle of those threads.
This creates a problem when my servlet (or a library which my servlet relies on) uses Threadlocal variables. For Tomcat, it means that when the context is undeployed, it has to check the viability of the threads in the pool to see if my code has 'polluted' them with Threadlocals. For example, it gives a warning like the following:
SEVERE: The web application  created a ThreadLocal with key of type [org.apache.xmlbeans.impl.store.CharUtil$1] (value [org.apache.xmlbeans.impl.store.CharUtil$1@2aace7a7]) and a value of type [java.lang.ref.SoftReference] (value [java.lang.ref.SoftReference@3d9c9ad4]) but failed to remove it when the web application was stopped. Threads are going to be renewed over time to try and avoid a probable memory leak. Dec 13, 2012 12:54:30 PM org.apache.catalina.loader.WebappClassLoader checkThreadLocalMapForLeaks
Is this really an exceptional situation though? Can't I expect that the container will do as Tomcat has done, without feeling the need to blame me for it? Even if I did have the opportunity to provide some kind of 'thread-will-no-longer-perform-work-for-this-webapp' hook, I wouldn't necessarily be able to clean up - sometimes it is 3rd-party libraries which use Threadlocal.
See the question here for more discussion if you like.