Remove up to the specified maxNumItems from the front of this queue. Optionally specify a buffer into which the items removed from the queue are loaded. If buffer is non‐null, the removed items are appended to it as if by repeated application of buffer‐>push_back(popFront()) while the queue is not empty and maxNumItems have not yet been removed. The behavior is undefined unless maxNumItems >= 0. This method never blocks.