StackOverflow2013

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POImplement durable pub/sub?
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copied!<p>Let's say I have a publisher and mutiple listeners. When the publisher sends a message, it has to be received by all listeners. If one of the listeners is down, he should get the message as soon he is back up again.</p> <p>How can I implement this?</p> <p>I was thinking about using queues: Each listener makes it's own queue and sends a subscrtiption message to the publisher with the location of it's queue. The publisher saves the location to a file or DB, and starts sending it's messages to that queue.</p> <p>So, this would be the timeline:</p> <p>Publisher is started. No listeners yet.</p> <p>Publisher sends message 1.</p> <p>Publisher sends message 2.</p> <p>Publisher sends message 3.</p> <p>Listener 1 starts and subscribes with publisher.</p> <p>Publisher sends message 4.</p> <p>Listener 1 receives message 4.</p> <p>Listener 2 starts and subscribes with publisher.</p> <p>Publisher sends message 5.</p> <p>Listener 1 receives message 5.</p> <p>Listener 2 receives message 5.</p> <p>Listener 2 chrashes.</p> <p>Publisher sends message 6.</p> <p>Listener 1 receives message 6.</p> <p>Publisher sends message 7.</p> <p>Listener 1 receives message 7.</p> <p>Listener 2 comes back up, no need to subscribe again.</p> <p>Listener 2 receives message 6.</p> <p>Listener 2 receives message 7.</p> <p>The bottom line is I need one queue per listener, and one queue or channel to send and receive messages for 'start listening' and 'stop listening'. Am I thinking in the right direction, or am I completely wrong?</p>

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