如何在WCF端点上延迟从MSMQ挑选消息

Question

Can anyone suggest me a solution for a scenario where I want the msmq message from the queue to be picked up after some delay as there are workflows which need to trigger in the database before I pickup the msmq message for processing and I am seeing some delay there in the workflow processing. Is there some setting or built in features as Sleep and all that is not the solution I am looking for or delaying at the client end as there is a transaction running on the client end which needs to execute all at once and cannot delay process just the call to the Queue.

Thanks, Bala

Answer 1

I solved this by creating another queue as Pending queue. Once I received the message at the endpoint, I queued appropriate message which do not require immediate processing to another queue using below queue.

PendingQueue.Send(queuedMessage);

The message was removed in Active queue automatically.

There is another Timer service which parses this Pending queue and re-queues the message to active as and when required.

However remember to add custom xmlformatter to the pending queue when initializing queue in timer, as in below queue, as the queue will not know how to de-serialize the contract object otherwise.

//Create a Formatter that can deserialize the Messages.
XmlMessageFormatter xmlMessageFormatter = new XmlMessageFormatter
    {
        TargetTypes = new[]
            {typeof (DataContract)}
    };
_pendingQueue.Formatter = xmlMessageFormatter;

Then I used the following code to retrieve object at appropriate time.

List<Message> messages = PendingQueue.GetAllMessages().ToList();
foreach (Message x in messages)
{
    DataContract y = x.Body as DataContract;
    if (!<some condition>) 
        continue;    
    //Remove the object from pending queue.
    PendingQueue.ReceiveById(x.Id);
    _mproxy.QueueMessage(y)
}

Above did the trick for me. Also do remember that the active queue should not be transactional, otherwise, if the message execution fails when re queued, the original caller can not be notified. Please feel free to improve the solution.