public void addListener(BuildOperationListener listener) {
        listenersLock.lock();
        try {
            List<ProgressShieldingBuildOperationListener> listeners = new ArrayList<ProgressShieldingBuildOperationListener>(this.listeners);
            listeners.add(new ProgressShieldingBuildOperationListener(listener));
            this.listeners = listeners;
        } finally {
            listenersLock.unlock();
        }
    }