Question

I get the exception when executing the following code. Any ideas what is wrong?

string queueName = "FormatName:Direct=TCP:1.1.1.1\\Private$\\test";
MessageQueue queue;

if (MessageQueue.Exists(queueName))
     queue = new System.Messaging.MessageQueue(queueName);
else queue = MessageQueue.Create(queueName);

queue.Send(sWriter.ToString());

Edit:
Here is the exception message and first line of stacktrace

Cannot determine whether a queue with the specified format name
exists.
at System.Messaging.MessageQueue.Exists(String path)

It works for a local queue by the way.

Answer 1

From your sample, it looks like you’re trying to check whether a remote private queue exists, but as the MessageQueue.Exists documentation says:

Exists cannot be called to verify the
existence of a remote private queue.

Trying to do so will produce an InvalidOperationException.

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If you really need this information for your workflow, you can use the MessageQueue. GetPrivateQueuesByMachine method and iterate the results to find a match. If you do, I recommend reading Are Remote MSMQ Queues Reliable?, which discusses this approach in some depth.

This post from the excellent “MSMQ from the plumber’s mate” blog suggests another alternative: don’t even check whether your queues exist, “but instead handle the non-delivery of the message should it turn out that the queue doesn’t exist.” (You’ll need to track administration queues and/or dead-letter queues, but you should probably be doing that anyway.)