docs: public static Executor getExecutor() {
          synchronized (LOCK) {
              if (Settings.executor == null) {
                  Executor executor = getAsyncTaskExecutor();
                  if (executor == null) {
                      executor = new ThreadPoolExecutor(DEFAULT_CORE_POOL_SIZE, DEFAULT_MAXIMUM_POOL_SIZE,
                              DEFAULT_KEEP_ALIVE, TimeUnit.SECONDS, DEFAULT_WORK_QUEUE, DEFAULT_THREAD_FACTORY);
                  }
                  Settings.executor = executor;
              }
          }
          return Settings.executor;
      }