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