code: public static ExecutorService getValidExecutor() {
          ExecutorService executorToUse;
          if (EXECUTOR.isTerminating() || EXECUTOR.isShutdown() || EXECUTOR.isTerminated()) {
              executorToUse = Executors.newSingleThreadExecutor();
              LOG.info("由于线程池" + ThreadPoolManager.class.getSimpleName() + "不可用，因此使用临时线程提交此任务");
          } else {
              executorToUse = EXECUTOR;
          }
          return executorToUse;
      }
docs: 获取有效的线程池