C# MQ Api How to fetch message without getting exception in case of empty queue

Question

I have to periodically check messages in a queue within Websphere MQ. I haven't found better approach rather than try getting a message and handle 2033 reason code (which is NO_MSG_AVAILABLE) like this:

try
{
    // ...
    inQueue.Get(message);
}
catch (MQException exception)
{
    if (exception.ReasonCode != 2033)
        throw;
}

Is there better way to get message from queue? I think that there might be some openOptions flag that I'm not aware of, that wouldn't throw exception when no message available, but return null instead.

Answer 1

There are three ways to avoid or reduce this polling mechanism. Here they are in oder of elegance(the higher the better):

1. MQGET with wait interval UNLIMITED and MQGMO_FAIL_IF_QUIESCING
2. Get your application be triggered by MQServer
3. Callback function - new with MQ V7 on both sides

Answer 2

You are missing the MQC.MQGMO_WAIT flag on MQGetMessageOptions.Options . Change it this way:

getOptions = new MQGetMessageOptions {WaitInterval = MQC.MQWI_UNLIMITED, Options = MQC.MQGMO_WAIT | MQC.MQGMO_FAIL_IF_QUIESCING}

Please note that this would make the calling thread to be blocked till a message arrives at the queue or some connection exception occurs. MQ has another client called IBM Message Service Client (aka XMS .NET) that provides a JMS specification implementation in .NET. This has a nice little Message Listener which gets automatically invoked whenever a message arrives in a queue. Unlike in the above example, the calling thread will not be blocked when Message Listener is used.

More details on XMS .NET can be found here . Samples are also shipped with MQ and for message listener sample, please refer "SampleAsyncConsumer.cs" source file.

Answer 3

I was getting this. I solved it by putting the Message initiator inside the loop:

_queueManager = new MQQueueManager(Queuemanager, _mqProperties);

MQQueue queue = _queueManager.AccessQueue(
    Queuename, 
    MQC.MQOO_INPUT_AS_Q_DEF + MQC.MQOO_FAIL_IF_QUIESCING + MQC.MQOO_INQUIRE);            

string xml = "";

while (queue.CurrentDepth > 0)
{
    MQMessage message = new MQMessage();                
    queue.Get(message);
    xml = message.ReadString(message.MessageLength);
    MsgQueue.Enqueue(xml);                    
    message.ClearMessage();                                
}

There must be something in the Message internally that errors when reusing it for another get.