@Override
        public void run() {
            try {
                handleEvents();
            } catch (Throwable e) {
                log.warn("event handler thread exiting with exception", e);
            }
            try {
                cleanupEvent.run();
            } catch (Throwable e) {
                log.warn("cleanup event threw exception", e);
            }
        }
A condition variable for waking up the event handler thread.
server-common/src/main/java/org/apache/kafka/queue/KafkaEventQueue.java