[rabbitmq-discuss] queue subscription + sending to some exchange
Petar Shomov
pshomov at gmail.com
Wed Jun 22 22:41:30 BST 2011
forgot to CC the mailing list
---------------------------------
Regards,
Petar
On Wed, Jun 22, 2011 at 9:39 PM, Petar Shomov <pshomov at gmail.com> wrote:
> Hi Simone,
>
> I assumed (based on the .NET API) that the operations were
> synchronous. I will verify that assumption.
> Thanx for the tip on NUnit delayed polling! I did not know that.
> Although my helper does more then catching assertion exceptions (in my
> "full" version of the test) I will definitely check it out.
>
> ---------------------------------
> Regards,
>
> Petar
>
>
>
> On Wed, Jun 22, 2011 at 8:44 AM, Busoli, Simone
> <Simone.Busoli at ferrari.com> wrote:
>> Hi Petar,
>>
>> looking at the code I am under the impression that you may have a race condition between the subscription and the first publish, in that the second may try to publish to the exchange before the first declares it, although I believed the exchange declaration was a synchronous operation.
>>
>> Side note: instead of your assertion helpers, you can leverage NUnit's support for delayed (polling) assertions:
>>
>> Assert.That(() => done, Is.EqualTo(3).After(delay))
>>
>> NUnit will verify the assertion at intervals until delay has expired, at which point it will fail if the constraint is not satisfied yet.
>>
>> -----Original Message-----
>> From: rabbitmq-discuss-bounces at lists.rabbitmq.com [mailto:rabbitmq-discuss-bounces at lists.rabbitmq.com] On Behalf Of Petar Shomov
>> Sent: Wednesday, June 22, 2011 3:20 AM
>> To: Emile Joubert
>> Cc: rabbitmq-discuss at lists.rabbitmq.com
>> Subject: Re: [rabbitmq-discuss] queue subscription + sending to some exchange
>>
>> Hi Emile,
>>
>> What a great suggestion: look into the log file ;). Indeed I looked and found the problem: the exchange I was posting to did not exist.
>> Somehow the first posting succeeded but on the second attempt did not go through or something like that.
>>
>> I am going to post the mini-example just in case since I prepared it anyways so it might be useful to someone. I find the error message in the rabbitmq server log very helpful but the one that I got in the client was very confusing - 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
>>
>> Thank you and Simone for reaching out!
>>
>> ---------------------------------
>> Regards,
>>
>> Petar
>>
>>
>>
>> On Tue, Jun 21, 2011 at 9:40 AM, Emile Joubert <emile at rabbitmq.com> wrote:
>>> 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?
>>>
>>
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