public boolean pause(final int id) {
    final FileDownloadModel model = mHelper.find(id);
    if (model == null) {
      return false;
    }

    if (FileDownloadLog.NEED_LOG) {
      FileDownloadLog.d(this, "paused %d", id);
    }

    mThreadPool.cancel(id);
    /**
     * 耦合 by {@link FileDownloadRunnable#run()} 中的 {@link
     * com.squareup.okhttp.Request.Builder#tag(Object)} 目前在okHttp里还是每个单独任务
     */
    // 之所以注释掉,不想这里回调error,okHttp中会根据okHttp所在被cancel的情况抛error
    //        client.cancel(id);
    return true;
  }