[rabbitmq-discuss] data being fetched from other queues too(that are not named in basicConsume)

Tue Apr 12 07:48:49 BST 2011

Hi Mustafa,

Thanks for your help...

Infact, I need an asynchronous version only so that my code doesn't keep on polling the server for new messages..

My query is, if we have done something like this:

boolean autoAck = false;

            System.out.println("fetching message from the Q: " + queueName + "\n");
            this.channel.basicConsume(queueName, autoAck, this.queueingConsumer);   // We are trying to fetch the data from the specified queue name only

            QueueingConsumer.Delivery delivery;

            try {
                  delivery = this.queueingConsumer.nextDelivery(timeout);     //Shouldn't this fetch the data from the specified queue only and not some other queue(s); FYI, the same channel has been bound to a no. of queues; I hope this is not the culprit???

            } catch (InterruptedException ie) {
                  return null;
            }
            if(delivery != null)
            {
                  channel.basicAck(delivery.getEnvelope().getDeliveryTag(), false);
                  byte[] body = delivery.getBody();
                  return body;
            }
            else
            {
                  return null;
            }

Since, in "channel.basicConsume", I have passed the name of the queue from which data has to be fetched (and not other queues too to which the channel is bound to), the why do we get data from other queues too when we do "this.queueingConsumer.nextDelivery(timeout);".

Initially, I had used "basicGet", but that will be synchronous and that's the reason why I decided to use "basicConsume".

Please also see my comments in "RED".

Also, you can see a trimmed down version of my code here:
http://pastebin.com/zLJpUFHA

Thanks & Regards,
Kamal

From: rabbitmq-discuss-bounces at lists.rabbitmq.com [mailto:rabbitmq-discuss-bounces at lists.rabbitmq.com] On Behalf Of Amr Mostafa
Sent: Monday, April 11, 2011 7:32 PM
To: Kamal
Cc: rabbitmq-discuss at lists.rabbitmq.com
Subject: Re: [rabbitmq-discuss] data being fetched from other queues too(that are not named in basicConsume)

Hi Kamal,

It looks like you are mistaking Channel.basicConsume for Channel.basicGet. The first (which you are using) is asynchronous and what it does is subscribe a consumer with the messaging server on a given queue. All incoming messages to do that queue will be directly sent by the messaging server to that subscribed consumer. In the QueuingConsumer implementation, those received messages are held in an internal queue and you fetch them using nextDelivery.

This model is called subscription-based, another simpler approach is using Channel.basicGet. I advise you to check this for details:

http://www.rabbitmq.com/api-guide.html
On Mon, Apr 11, 2011 at 3:19 PM, Kamal <kamal.nandan at gmail.com<mailto:kamal.nandan at gmail.com>> wrote:
Hi,

I am facing a strange problem while using RabbitMq.

I have a consumer that creates 3 queues(just for name sake HIGH/MEDIUM/
LOW priority queues) on the RabbitMQ server and consumes data from the
3 queues in this order:
5 messages from HIGH
3 messages from MEDIUM
2 messages from LOW.

This keeps on happening in round-robin fashion.
If there is no data available on the respective queue, the data from
the next queue is fetched.

I am using "Channel.basicConsume(queueName, ACK, QueueingConsumer)"
and "QueueingConsumer.nextDelivery(timeout)" to fetch the data.

What I see here is: I see that the data is fetched from the other
queues too. i.e. Even though I have passed the queuename as "HIGH",
then too i see that the data is being fetched from the queue "LOW" or
"MEDIUM" and vice versa. I am finding this behaviour quite strange.
Can someone plz help me out with this.

Following is a snippet of my code.:
http://pastebin.com/s03dP91z

Thanks in advance..

Regards,
Kamal
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Amr Mostafa
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