然后，如果策略消费者需要策略提供者执行特定的策略，策略消费者作为被观察对象，回调提供者，以执行策略操作。
Later, when consumers of the strategy providers need the providers to perform the particular strategy, the consumers, as observables, call back to the providers to perform the strategy operation.
服务请求者发出请求消息，并随后向服务轮询响应，或者向请求者发出回调。
The service requestor dispatches the request message and subsequently polls the service for the response, or a callback is dispatched to the requestor.
在update调用期间，目标对象发起了对观察者的回调；因此，从这一点上来说，目标对象是服务请求者，观察者对象是服务提供者。
During the update call, the subject is initiating a callback to the observer; thus, at that point, the subject is the service requester and the observer is the service provider.
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