| 摘要 |
Subscribers connected to a publish/subscribe message broker receive messages on topic names to which they have subscribed. The subscribers receive any number of messages on each topic to which they have subscribed. When the broker receives a message on a second, pre-specified, topic, associated with a first topic, the broker removes any existing retained message related to the first topic. Thus any subsequent subscribers to the first topic do not receive the retained message when they subscribe, and thus do not receive out-of-date information. If, at a later date, a new message is published on the first topic subscribers will receive the new message if they are still subscribed.
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