Distributed Semaphore and Fairness

[shivam fialok]

Hi,

I needed to implement distributed semaphore in one of the applications and I found this rabbitmq blog which describes a way of how this can be implemented using rabbitmq.

But I am concerned regarding the fairness.

So, when we have multiple consumers bound to the same queue, rabbitmq dispatches messages to them in round-robin order. But does rabbitmq gurantee that when new consumers join a queue, then any existing consumers which had already been waiting for a message (or resource) (they are waiting because a resource/message is not yet available) will get the message first (whenever the resource/message becomes available) before any new consumers? In simpler terms, does rabbitmq take into account how long a consumer has been waiting to decide which consumer gets the next message?

Let me know if something is unclear in the question.

Thanks in advance.

[Wes Peng]

No, the round robin policy can’t promise that.

A new consumer has the same chance to get messages as the older ones.

Thanks 

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[shivam fialok]

Okay. Thanks for the quick response.

Is there a way to achieve this kind of fairness in rabbitmq?

By the way, I tried the above using rabbitmq and it seems to make sure that older consumers get the message first. But I cound not find it in the documentation anywhere. I guess it is because the round robin policy does not gurantee that it will remain the case always.