@Override
    public void beginShutdown(String source) {
        lock.lock();
        try {
            if (shuttingDown) {
                log.debug("{}: Event queue is already shutting down.", source);
                return;
            }
            log.info("{}: shutting down event queue.", source);
            shuttingDown = true;
            eventHandler.cond.signal();
        } finally {
            lock.unlock();
        }
    }
True if the event handler thread was interrupted. Protected by the lock.
server-common/src/main/java/org/apache/kafka/queue/KafkaEventQueue.java