public Marker getMarker(String name) {
        if (name == null) {
            throw new IllegalArgumentException("Marker name cannot be null");
        }

        Marker marker = markerMap.get(name);
        if (marker == null) {
            marker = new BasicMarker(name);
            Marker oldMarker = markerMap.putIfAbsent(name, marker);
            if (oldMarker != null) {
                marker = oldMarker;
            }
        }
        return marker;
    }
Manufacture a {@link BasicMarker} instance by name. If the instance has been 
created earlier, return the previously created instance. 

@param name the name of the marker to be created
@return a Marker instance
slf4j-api/src/main/java/org/slf4j/helpers/BasicMarkerFactory.java