观察器对象订阅那些报告所监视实体中任何状态更改的事件，然后基于那些事件中的信息更新自己的状态。
The observer object subscribes to events that report any state changes in the monitored entity, and then updates its own state based on information in those events.
多数定制清理器都会观察某些模型对象，并根据更改击发逻辑来使一个或多个缓存页面到期失效。
Most custom sweepers observe some model object, and based on changes, fire logic to expire one or more cache pages.
通知事件通过回调型显式接口以及与之对应的代理和调用程序对象，与观察器进行通信。
Notification events were communicated to observers with call-back explicit interfaces and their respective proxy and invoker objects.
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