This method is called to wait for an event completion on the indicated semaphore, with a specified time.

调用这个方法来等待所需要信号上某个事件的完成，等待指定的一段时间。

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If an event occurs during the specified time period, this method exits, returning the relevant WatchKey.

如果在特定时间范围内，有任何事件发生，这一方法存在，会返回相应的WatchKey。

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At some unspecified later time, when the subject's state changes, the subject notifies the observer of the change event with the update method callback.

在随后某个未知的时候，目标对象的状态发生了更改，目标对象会使用update回调方法，通知观察者，告知已经发生了状态更改事件。

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