public void use(Allocation allocation) {
        String key = allocation.key();
        if (byKeys.containsKey(key)) {
            if (byKeys.get(key).port == allocation.port) {
                return; // already OK
            }
            Allocation toRemove = byKeys.remove(key);
            byPorts.remove(toRemove.port);
        }
        if (byPorts.containsKey(allocation.port)) {
            Allocation toRemove = byPorts.remove(allocation.port);
            byKeys.remove(toRemove.key());
        }
        byPorts.put(allocation.port, allocation);
        byKeys.put(key, allocation);
    }
force add the given allocation, removing any conflicting ones
config-model/src/main/java/com/yahoo/vespa/model/PortFinder.java