[rabbitmq-discuss] queue subscription + sending to some exchange

[Emile Joubert]

Hi Petar,

I assume that queueHandlers in your snippet establishes a new channel
when the error occurs. Is it possible that queueHandlers is using the
wrong channel by mistake? Can you supply a minimal self-contained
example that illustrates the problem? Is there any additional
information in the broker logfile at the time of the error?


-Emile


On 21/06/11 01:17, Petar Shomov wrote:
> Hi Simone,
> 
> Thanx for the suggestion! I have read that section about threading
> many times but my understanding is that channels can be shared among
> threads as long as they are not used concurrently. I am not doing that
> and I even went ahead and created that channel in the thread that is
> doing the consumption just to be on the safe side. No dice, same
> error.
> 
> What worries me in that section is this paragraph:
> 
> "Application callback handlers must not invoke blocking AMQP operations (such as
> IModel.QueueDeclare, IModel.BasicCancel or IModel.BasicPublish). If
> they do, the channel
> will deadlock"
> 
> Now, does that mean I should not be doing what I intended to be doing
> (I use IModel.BasicPublish)? I find that hard to believe.
> I am taking care to open a different channel for the publishing of my
> messages but I wonder is that enough?
> My channel did not deadlock just looks like things got mixed up ;(
> 
> ---------------------------------
> Regards,
> 
> Petar
> 
> 
> 
> On Mon, Jun 20, 2011 at 9:57 PM, Simone Busoli <simone.busoli at gmail.com> wrote:
>> Hi Petar,
>>
>> I think you are violating one of the assumption that the C# client does on
>> channel usage. Channels should not be shared among threads (read the pdf
>> user guide for details), and it appears you are using the channel on a
>> different thread than that where the channel was created.
>>
>> On Mon, Jun 20, 2011 at 23:41, Petar Shomov <pshomov at gmail.com> wrote:
>>>
>>> Hi guys,
>>>
>>> I have a situation which I do not completely understand and I was
>>> hoping someone more acquainted with AMQP and RabbitMQ might point me
>>> in the right direction.
>>>
>>> I have a console app that needs to subscribe to a message queue where
>>> the process of handling a message is rather lengthy. During this
>>> lengthy process I need to send out messages to some exchange which
>>> represent information about the progress of the operation.
>>> The subscription to the queue has to be asynchronous too, since I am
>>> doing something else on the main thread. So I have running in a thread
>>> this code (C#):
>>>
>>>                var job = new Thread(() =>
>>>                                         {
>>>                                             var consumer = new
>>> QueueingBasicConsumer(channel);
>>>
>>> channel.BasicConsume(queueName, false, consumer);
>>>                                             while (true)
>>>                                             {
>>>                                                 BasicDeliverEventArgs e =
>>> null;
>>>                                                 e =
>>> (BasicDeliverEventArgs) consumer.Queue.Dequeue();
>>>
>>> queueHandlers[queueName][e.Exchange](e);
>>>
>>> channel.BasicAck(e.DeliveryTag, false);
>>>                                              }
>>>                                         }
>>>
>>>  Unfortunately when I try to send messages within the message handler
>>> (I am opening a different channel on the same connection, tried even
>>> opening a different connection with no better luck) I am getting these
>>> kind of exceptions, usually when attempting to send the *second*
>>> message:
>>>
>>> -               $exception      {"The AMQP operation was interrupted: AMQP
>>> close-reason,
>>> initiated by Library, code=504, text=\"Frame received for invalid
>>> channel 2\", classId=0, methodId=0,
>>> cause=RabbitMQ.Client.Impl.ChannelErrorException: Frame received for
>>> invalid channel 2\r\n   at ...
>>>
>>>
>>> Thoughts, ideas, anything?