To understand, consider the following scenario: The user has instructed input to die; input synchronously notifies all subscribers to die and signals our main thread to die.

• 需要理解的是,我们假设的情况是这样的:用户指示输入任务单元结束,然后输入任务单元同步通知所有的事件关注者结束,然后发送结束信号使得主线程结束。