public void start() {
    pauseLock.lock();
    try {
      isStopped = false;
      unpaused.signalAll();
    } finally {
      pauseLock.unlock();
    }
  }
ThreadPoolExecutor extension which is stopped by default and can be started & stopped.
ambari-server/src/main/java/org/apache/ambari/server/utils/ManagedThreadPoolExecutor.java