code: public static ExecutorService newSingleThreadPoolExecutor() {
          ExecutorService singleThreadPoolExecutor = Executors.newSingleThreadExecutor();
          EXECUTORS.add(singleThreadPoolExecutor);
          return singleThreadPoolExecutor;
      }
docs: 新建一个受管理的单线程池，你不需要注定关闭线程池，管理器会帮你关闭的
  注意：请复用，而不要频繁构造线程池