public synchronized void cleanup() {
    // the logwriter holds onto a distribution config, which holds onto
    // the InternalDistributedSystem, which holds onto the
    // DistributionManager, which holds onto ... you get the idea
    logger = null;
    logWriter = null;
  }
clean up the threadgroup, releasing resources that could be problematic (bug 35388)

@since GemFire 4.2.3
geode-core/src/main/java/org/apache/geode/internal/logging/LoggingThreadGroup.java