Server warning when removing showcase from Tomcat 8. I was able to produce these warnings by testing only the native demos such as camera, camcorder, fetch-contact etc. then removing the .war file from the server. This appears different from the usual server warnings occasionally seen when removing showcase from the server.
21-Dec-2015 10:41:07.544 WARNING [ContainerBackgroundProcessor[StandardEngine[Ca
talina]]] org.apache.catalina.loader.WebappClassLoaderBase.clearReferencesThread
s The web application [showcase] appears to have started a thread named [pool-1-
thread-1] but has failed to stop it. This is very likely to create a memory leak
. Stack trace of thread:
 sun.misc.Unsafe.park(Native Method)
 java.util.concurrent.locks.LockSupport.park(LockSupport.java:186)
 java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(Abs
tractQueuedSynchronizer.java:2043)
 java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(Schedule
dThreadPoolExecutor.java:1079)
 java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(Schedule
dThreadPoolExecutor.java:807)
 java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1068)
 java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1130)

 java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)

 java.lang.Thread.run(Thread.java:745)
21-Dec-2015 10:41:07.544 WARNING [ContainerBackgroundProcessor[StandardEngine[Ca
talina]]] org.apache.catalina.loader.WebappClassLoaderBase.clearReferencesThread
s The web application [showcase] appears to have started a thread named [pool-1-
thread-2] but has failed to stop it. This is very likely to create a memory leak
. Stack trace of thread:
 sun.misc.Unsafe.park(Native Method)
 java.util.concurrent.locks.LockSupport.park(LockSupport.java:186)
 java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(Abs
tractQueuedSynchronizer.java:2043)
 java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(Schedule
dThreadPoolExecutor.java:1079)
 java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(Schedule
dThreadPoolExecutor.java:807)
 java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1068)
 java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1130)

 java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)

 java.lang.Thread.run(Thread.java:745)
21-Dec-2015 10:41:07.544 WARNING [ContainerBackgroundProcessor[StandardEngine[Ca
talina]]] org.apache.catalina.loader.WebappClassLoaderBase.clearReferencesThread
s The web application [showcase] appears to have started a thread named [pool-1-
thread-3] but has failed to stop it. This is very likely to create a memory leak
. Stack trace of thread:
 sun.misc.Unsafe.park(Native Method)
 java.util.concurrent.locks.LockSupport.park(LockSupport.java:186)
 java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(Abs
tractQueuedSynchronizer.java:2043)
 java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(Schedule
dThreadPoolExecutor.java:1085)
 java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(Schedule
dThreadPoolExecutor.java:807)
 java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1068)
 java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1130)

 java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)

 java.lang.Thread.run(Thread.java:745)