Drools failed to stop worker threads when shutting down web application in Tomcat 8

[Puhong You-c]

We use Drools 7.2.0.Final in our RulesEnhine web application which is deployed to Tomcat 8. When shutting down the web application, the following messages are logged into the Tomcat catalina.log --

26-Aug-2017 15:14:55.602 WARNING [http-nio-8080-exec-2] org.apache.catalina.loader.WebappClassLoaderBase.clearReferencesThreads The web application [RulesEngine] appears to have started a thread named [drools-worker-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:175)

 java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:2039)

 java.util.concurrent.LinkedBlockingQueue.take(LinkedBlockingQueue.java:442)

 java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1067)

 java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1127)

 java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)

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

26-Aug-2017 15:14:55.606 WARNING [http-nio-8080-exec-2] org.apache.catalina.loader.WebappClassLoaderBase.clearReferencesThreads The web application [RulesEngine] appears to have started a thread named [drools-worker-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:175)

 java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:2039)

 java.util.concurrent.LinkedBlockingQueue.take(LinkedBlockingQueue.java:442)

 java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1067)

 java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1127)

 java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)

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

26-Aug-2017 15:14:55.610 WARNING [http-nio-8080-exec-2] org.apache.catalina.loader.WebappClassLoaderBase.clearReferencesThreads The web application [RulesEngine] appears to have started a thread named [drools-worker-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:175)

 java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:2039)

 java.util.concurrent.LinkedBlockingQueue.take(LinkedBlockingQueue.java:442)

 java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1067)

 java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1127)

 java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)

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

26-Aug-2017 15:14:55.613 WARNING [http-nio-8080-exec-2] org.apache.catalina.loader.WebappClassLoaderBase.clearReferencesThreads The web application [RulesEngine] appears to have started a thread named [drools-worker-4] 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:175)

 java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:2039)

 java.util.concurrent.LinkedBlockingQueue.take(LinkedBlockingQueue.java:442)

 java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1067)

 java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1127)

 java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)

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

There was a bug report related to this problem --

https://issues.jboss.org/browse/DROOLS-1156

This bug was marked as fixed in 7.0.0.Beta1, but the problem still exists in 7.2.0.Final.

=======

Our application obtains a handle to KieBase via the following calls during initialization phase --

   private KieContainer kieContainer = null;

   public KieBase loadCrashRulesKnowledgeBase() {

        try {

        if (kieContainer == null) {

        kieContainer = KieServices.Factory.get().getKieClasspathContainer();

        }

    KieBase kieBase = kieContainer.getKieBase(CRASH_RULES_KBASE_NAME);

        kieBase.addEventListener(new RulesEngineConfigurationEventListener(this));

        return kieBase;

        } catch (Exception e){

            throw new RulesEngineRuntimeException("Could Not Load CrashRulesKnowledgeBase from Drools Package.");

        }

  }

During application shutdown, we try to clean up the KieContainer like this -- 

     if (kieContainer != null) {

     kieContainer.dispose();

    }

Anyone know how to properly stop the drools worker threads during web application shutdown?