code: public int pause(final int id) {
          List<BaseDownloadTask.IRunningTask> taskList = FileDownloadList.getImpl()
                  .getDownloadingList(id);
          if (null == taskList || taskList.isEmpty()) {
              FileDownloadLog.w(this, "request pause but not exist %d", id);
              return 0;
          }
  
          for (BaseDownloadTask.IRunningTask task : taskList) {
              task.getOrigin().pause();
          }
  
          return taskList.size();
      }
docs: Pause downloading tasks with the {@code id}.
  
  @param id the {@code id} .
  @return The size of tasks has been paused.
  @see #pause(FileDownloadListener)