LinkageError exception during multi-threaded execution ------------------------------------------------------ Key: DROOLS-144 URL: https://issues.jboss.org/browse/DROOLS-144 Project: Drools Issue Type: Bug Security Level: Public(Everyone can see) Affects Versions: 5.5.0.Final, 6.0.0.Beta2 Environment: Linux Ubuntu 12.10, OpenJDK 1.7 Reporter: Davide Sottara Assignee: Mark Proctor Priority: Blocker The exception is thrown in org.drools.rule.JavaRuntimeDialectData, when the CompositeClassLoader tries to define the class implementing a rule consequence. The method fastFindClass, which does the lazy initialization, is not thread-safe. It is possible for two threads to call findLoadedClass(..), get null and thus start the definition process which eventually results in the exception. The situation is indeed very rare