- thread + handler
- 暴露唯一接口onHandleIntent给子类实现
- 消息队列保证任务的顺序性
- 巧妙的自动退出机制，其关键点
Stop the service if the most recent time it was started was startId.```
startId is A unique integer representing this specific request to start.
Use with {@link #stopSelfResult(int)}.```