2010/2/8 heldeen <heldeen@overstock.com>

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
--
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