Thomas Leung created DROOLS-1000: ------------------------------------ Summary: Race condition occured when executing Drools Key: DROOLS-1000 URL: https://issues.jboss.org/browse/DROOLS-1000 Project: Drools Issue Type: Bug Components: core engine Affects Versions: 6.2.0.Final Reporter: Thomas Leung Assignee: Mario Fusco We encountered soft timeout on threads executing Drools in our production environment. Below is the trimmed thread dump: "DSLFpmlUniversalContainerCacheWorker:2" id=988 State:RUNNABLE at java.util.HashMap.getEntry(HashMap.java:446) at java.util.HashMap.containsKey(HashMap.java:434) at java.util.HashSet.contains(HashSet.java:201) at org.drools.core.impl.KnowledgeBaseImpl.addEventListener(KnowledgeBaseImpl.java:252) at org.jbpm.process.instance.ProcessRuntimeImpl.initProcessEventListeners(ProcessRuntimeImpl.java:303) at org.jbpm.process.instance.ProcessRuntimeImpl.<init>(ProcessRuntimeImpl.java:115) at org.jbpm.process.instance.ProcessRuntimeFactoryServiceImpl.newProcessRuntime(ProcessRuntimeFactoryServiceImpl.java:10) at org.jbpm.process.instance.ProcessRuntimeFactoryServiceImpl.newProcessRuntime(ProcessRuntimeFactoryServiceImpl.java:7) at org.drools.core.runtime.process.ProcessRuntimeFactory.newProcessRuntime(ProcessRuntimeFactory.java:16) at org.drools.core.impl.StatefulKnowledgeSessionImpl.createProcessRuntime(StatefulKnowledgeSessionImpl.java:757) at org.drools.core.impl.StatefulKnowledgeSessionImpl.<init>(StatefulKnowledgeSessionImpl.java:393) at org.drools.core.impl.StatefulKnowledgeSessionImpl.<init>(StatefulKnowledgeSessionImpl.java:286) at org.drools.core.common.PhreakWorkingMemoryFactory.createWorkingMemory(PhreakWorkingMemoryFactory.java:21) at org.drools.core.impl.StatelessKnowledgeSessionImpl.newWorkingMemory(StatelessKnowledgeSessionImpl.java:127) at org.drools.core.impl.StatelessKnowledgeSessionImpl.execute(StatelessKnowledgeSessionImpl.java:302) Analysis on the Drools code reveals a possible thread safety issue. A single instance of KnowledgeBaseImpl is shared amongst multiple kSessions but inside KnowledgeBaseImpl, it contains a HashSet storing the listeners: public final Set<KieBaseEventListener> kieBaseListeners = new HashSet<KieBaseEventListener>(); public void addEventListener(KieBaseEventListener listener) { if (!kieBaseListeners.contains(listener)) { eventSupport.addEventListener(listener); kieBaseListeners.add(listener); } } When 2 threads try to put into a hashmap at the same time and both trigger the map to be resized there is a small chance of created a corrupt internal data structure which results in infinite loops. There are a bunch of references on the net for this, here is one example: [http://stackoverflow.com/questions/13695832/explain-the-timing-causing-ha...]. Our system heavily rely on Drools and we have high volume everyday, we really need help from Drools dev team and much appreciate if you can provide a patch for us. Thanks in advance. -- This message was sent by Atlassian JIRA (v6.4.11#64026)