def subscribe(*args, &block)
      @mutex.synchronize do
        listener = Listener.new(*args)
        listener.on_delivery(&block)
        @listeners << listener
      end
    end
def subscribe(*args, &block)
      @mutex.synchronize do
        listener = Listener.new(*args)
        listener.on_delivery(&block)
        @listeners << listener
      end
    end
Add listener to the queue to receive messages

 @api public