code: public static int queueSize() {
          int queueSize = 0;
          for (ExecutorService pool : EXECUTORS) {
              if (pool instanceof ThreadPoolExecutor) {
                  queueSize += ((ThreadPoolExecutor) pool).getQueue().size();
              }
          }
          for (ExecutorService pool : EXPLICIT_EXECUTORS) {
              if (pool instanceof ThreadPoolExecutor) {
                  queueSize += ((ThreadPoolExecutor) pool).getQueue().size();
              }
          }
          return queueSize;
      }
docs: 监控api