code: public void pause() {
      synchronized (taskInfo) {
        if (taskInfo.getStatus() == HttpDownStatus.PAUSE
            || taskInfo.getStatus() == HttpDownStatus.DONE) {
          return;
        }
        long time = System.currentTimeMillis();
        taskInfo.setStatus(HttpDownStatus.PAUSE);
        taskInfo.setLastPauseTime(time);
        for (ChunkInfo chunkInfo : taskInfo.getChunkInfoList()) {
          if (chunkInfo.getStatus() != HttpDownStatus.DONE) {
            chunkInfo.setStatus(HttpDownStatus.PAUSE);
            chunkInfo.setLastPauseTime(time);
          }
        }
        close();
      }
      if (callback != null) {
        callback.onPause(this);
      }
    }
docs: 暂停下载