java.lang.LinkageError, but only sometimes (multithreading issue) ----------------------------------------------------------------- Key: JBRULES-3675 URL: https://issues.jboss.org/browse/JBRULES-3675 Project: JBRULES Issue Type: Bug Security Level: Public(Everyone can see) Components: drools-core Affects Versions: 5.4.0.Final Environment: - JBoss 7.1.1 - drools 5.4.0.Final - jdk 1.6u30 - Windows 7 64 bit Reporter: kenneth westelinck Assignee: Mario Fusco Fix For: 6.0.0.Alpha1 See mail on mailinglist: {noformat} We have an application (A) deployed on JBoss 7.1.1 accepting commands (CQRS, but only C and Q :) ). A console application (B) is sending a large volume of commands to create entities in A. Entities in A are validated by Drools (plain drl files, configured in spring using drools-spring). Most of the time this works just fine. But sometimes, we get the following exception: java.lang.LinkageError: loader (instance of org/drools/rule/JavaDialectRuntimeData$PackageClassLoader): attempted duplicate class definition for name: "a/b/c/Rule_person_unique___name_656ee3db19d34e689d95e2d6b2be67b6" at java.lang.ClassLoader.defineClass1(Native Method) [rt.jar:1.6.0_30] at java.lang.ClassLoader.defineClassCond(ClassLoader.java:631) [rt.jar:1.6.0_30] at java.lang.ClassLoader.defineClass(ClassLoader.java:615) [rt.jar:1.6.0_30] at org.drools.rule.JavaDialectRuntimeData$PackageClassLoader.fastFindClass(JavaDialectRuntimeData.java:615) [drools-core-5.4.0.Final.jar:5.4.0.Final] at org.drools.util.CompositeClassLoader$CachingLoader.load(CompositeClassLoader.java:254) [knowledge-api-5.4.0.Final.jar:5.4.0.Final] at org.drools.util.CompositeClassLoader$CachingLoader.load(CompositeClassLoader.java:237) [knowledge-api-5.4.0.Final.jar:5.4.0.Final] at org.drools.util.CompositeClassLoader.loadClass(CompositeClassLoader.java:88) [knowledge-api-5.4.0.Final.jar:5.4.0.Final] at java.lang.ClassLoader.loadClass(ClassLoader.java:295) [rt.jar:1.6.0_30] at java.lang.ClassLoader.loadClass(ClassLoader.java:247) [rt.jar:1.6.0_30] at a.b.c.Rule_person___unique___name_656ee3db19d34e689d95e2d6b2be67b6Eval0InvokerGenerated.evaluate(Unknown Source) at a.b.c.Rule_person___unique___name_656ee3db19d34e689d95e2d6b2be67b6Eval0Invoker.evaluate(Unknown Source) at org.drools.rule.EvalCondition.isAllowed(EvalCondition.java:114) [drools-core-5.4.0.Final.jar:5.4.0.Final] Any idea where this is coming from or what's causing this. {noformat} And the answer: {noformat} I have never experienced this myself, but after having a quick look at the code I believe this could be a multi-threading problem. In the abstract class java.lang.ClassLoader the method loadClass(String, boolean) is synchronized, but both org.drools.util.CompositeClassLoader and org.drools.rule.JavaDialectRuntimeData$PackageClassLoader override this method without the use of "synchronized". I would suggest you create a JIRA issue for this. {noformat} We are now trying 5.5.0.CR1 and so far, we have not encountered this issue. I'll keep you posted should the same issue appear on 5.5.0.CR1