public synchronized void orderParts() {
        if (!orderIdByPartType.isEmpty()) {
            for (Map.Entry<PartType, Long> entry : orderIdByPartType.entrySet()) {
                Long orderId = entry.getValue();
                if (orderId == null) {
                    orderId = supplier.orderPart(entry.getKey(), 5);
                    entry.setValue(orderId);
                } 
            }
        }
    }