private synchronized void asyncExecute(
     int type, final Runnable runnable, final TaskCallBack callback) {
   if (mTaskList.size() >= 10) {
     FileManageTask task = mTaskList.remove(0);
     task.cancel();
   }
   FileManageTask task = new FileManageTask(type, runnable, callback);
   mTaskList.add(task);
   task.execute();
 }