How do I exhaust a thread's message queue?

[Andrej Mitrovic]

Note this is just pseudocode:

// worker thread
void doWork()
{
    // while there's still stuff in the message queue
    while (messagesInQueue)
    {
         result = receiveOnly!int(); 
         switch(result)
         {
             // main thread could be enabling or disabling features this way,
             // and sending some commands..
         }
    }

    // now that we have all of our commands, do some hard work..
}

// background Thread
void main()
{
    while (userHasMoreInputs())
    {
         // send switches to the worker thread, via e.g.:
         workerThread.send(userValue);
    }
}

So I'm really interested in how to implement that line:
while (messagesInQueue)

Perhaps I have to use receiveTimeout?