Can I peek into empty MSMQ without getting exception?

Question

As far as I can see from the documentation, the way you are supposed to check if there are messages in a message queue is to use the Peek method. You then rely on it failing with a MessageQueueException to tell you that the queue was empty.

    public bool IsQueueEmpty()
    {
        bool isQueueEmpty = false;
        MessageQueue myQueue = new MessageQueue(".\\myQueue");

        try
        {
            myQueue.Peek(new TimeSpan(0));
            isQueueEmpty = false;
        }

        catch(MessageQueueException e)
        {
            if (e.MessageQueueErrorCode == 
                MessageQueueErrorCode.IOTimeout)
            {
                isQueueEmpty = true;
            }
        }
        return isQueueEmpty;
    }

I've always been told - and have experienced - that Exeptions are costly, and should not be used for normal operations. So my questions are:

• Are my assumptions that relying on catching the MessageQueueException is a costly operation correct?

• Are there any way to synchronously check if there are messages in a queue without having to rely on exceptions?

I'm working with the System.Messaging namespace in C#, but if I would need to go unmanaged to solve this that could be an option. And note that I want a solution without using WCF with MSMQ.

Answer 1

• Yes you are correct in the assumption that exceptions are costly. Actually it is the throwing that is expensive, not the catching. It is normal for a queue to be empty at times and a normal state should not lead to an exception being thrown.

• By using MessageQueue.GetMessageEnumerator2 we could use the enumerator to determine if a queue is empty or not without loading all messages. With this approach we would never load more than one message.

Example:

private static bool IsQueueEmpty(MessageQueue queue)
{
    using (var enumerator = queue.GetMessageEnumerator2())
    {
        return !enumerator.MoveNext();
    }
}

or to implement Peek which returns null if the message queue is empty (untested, but should work)

private static Message Peek(MessageQueue queue)
{
    using (var enumerator = queue.GetMessageEnumerator2())
    {
        return enumerator.MoveNext() ? enumerator.Current : null;
    }
}

We used code like the original to check about twenty different queues. Since we changed from the original implementation to the one I suggest, the speed of our imports increased drastically since the CPU could be used more to process messages instead of processing throws.