code: public synchronized void pause() {
          if (paused) {
              Util.w(TAG, "require pause this queue(remain " + taskList.size() + "), but"
                      + "it has already been paused");
              return;
          }
          paused = true;
  
          if (runningTask != null) {
              runningTask.cancel();
              taskList.add(0, runningTask);
              runningTask = null;
          }
      }
docs: Pause the queue.
  
  @see #resume()