Since the beginning of the Internet, if you wanted to sync services between two servers the most common solution was to have the client ping the host at regular intervals, which his known as polling.

自从互联网开始起来，如果你想要同步两个服务器之间的服务，最通常的解决方案是让客户端以规律的间隔来ping服务器，这就是人们所知的轮询。

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