Hello, Using Drools 5.1.0.M1. I am running into a blocking problem when I concurrently try to update a fact in my knowledge session, which is fireUntilHalt() in its own thread, from another thread, an updator thread. I know that only these 2 threads are ever accessing each knowledge session. Has anyone else run into this problem? I am including the relavant details and can provide a working example if need be. The block happens randomly anywhere from 20 - 1000's of sessions. I consistantly get this stack trace from the blocked thread: org.drools.common.AbstractWorkingMemory.executeQueuedActions(AbstractWorkingMemory.java:1540) org.drools.common.AbstractWorkingMemory.update(AbstractWorkingMemory.java:1529) org.drools.common.AbstractWorkingMemory.update(AbstractWorkingMemory.java:1403) org.drools.impl.StatefulKnowledgeSessionImpl.update(StatefulKnowledgeSessionImpl.java:248) ... I have a simple drools knowledge base that is a basic rule flow [Start -> Rule Flow Group -> Event Wait -> Rule Flow Group -> End] I build a knowledge base like this: KnowledgeBaseConfiguration knowledgeBaseConfiguration = KnowledgeBaseFactory.newKnowledgeBaseConfiguration(); knowledgeBaseConfiguration.setOption(AssertBehaviorOption.EQUALITY); knowledgeBaseConfiguration.setOption(MBeansOption.ENABLED); KnowledgeBase knowledgeBase = KnowledgeBaseFactory.newKnowledgeBase(knowledgeBaseConfiguration); KnowledgeBuilder kbuilder = KnowledgeBuilderFactory.newKnowledgeBuilder(); kbuilder.add(ResourceFactory.newClassPathResource(CHANGE_SET_XML, getClass()), ResourceType.CHANGE_SET); if (kbuilder.hasErrors()) { throw new IllegalArgumentException("Unable to build knowledge"); } knowledgeBase.addKnowledgePackages(kbuilder.getKnowledgePackages()); My basic test fact is: public class Fact() { String name; boolean isReady; //getters and setters } I have a fixed thread pool (Sun's ExecutorService.newFixedThreadPool() with 20 threads). Each session is submitted from a for loop of 0 to 100000 where it generates a simple fact with Fact.name = "fact"+i and Fact.isReady = false, then puts it in an array like so: final Object[] facts... fixedPoolExecutor.submit(new Runnable() { @Override public void run() { StatefulKnowledgeSession knowledgeSession = null; try { knowledgeSession = knowledgeBase.newStatefulKnowledgeSession(); //put it in a ConcurrentHashMap keyed by session id. ... for (Object fact : facts) { knowledgeSession.insert(fact); } //add session completion halt event - omiting other unused methods knowledgeSession.addEventListener(new ProcessEventListener() { @Override public void afterProcessCompleted(ProcessCompletedEvent event) { knowledgeSession.halt(); } }); knowledgeSession.startProcess(PROCESS_ID); knowledgeSession.fireUntilHalt(); } finally { if (knowledgeSession != null) { knowledgeSession.dispose(); } } }); I have a single thread executor (Sun's ExecutorService.newSingleThreadExecutor()) that is used to update these sessions (basically set the Fact.isReady from false to true for the EventWait in my rule flow): final int sessionId... final Object[] facts... singleThreadExecutor.submit(new Runnable() { @Override public void run() { StatefulKnowledgeSession knowledgeSession = null; try { knowledgeSession = ... from ConcurrentHashMap based on sessionId FactHandle factHandle = knowledgeSession.getFactHandle(fact); if (null != factHandle) { knowledgeSession.update(factHandle, fact);//This is where it blocks and never returns } else { knowledgeSession.insert(fact); } }); -Heath -- View this message in context: http://n3.nabble.com/StatefulKnowledgeSession-synchronization-problem-tp1... Sent from the Drools - User mailing list archive at Nabble.com. _______________________________________________ rules-users mailing list rules-users(a)lists.jboss.org https://lists.jboss.org/mailman/listinfo/rules-users