@Override
    public void onSuccess(Object result) {
      if (isShutdown.get()) {
        LOG.info("Wait queue scheduler worker exited with success!");
      } else {
        LOG.error("Wait queue scheduler worker exited with success!");
        Thread.getDefaultUncaughtExceptionHandler().uncaughtException(Thread.currentThread(),
            new IllegalStateException("WaitQueue worked exited before shutdown"));
      }
    }
Worker that takes tasks from wait queue and schedule it for execution.
llap-server/src/java/org/apache/hadoop/hive/llap/daemon/impl/TaskExecutorService.java