#vulnerable code 
                                protected void fireInstancesAdded(int... instanceIds) {
        if (listener != null) {
            listener.objectInstancesAdded(this, instanceIds);
        }
    } 
                            #location 3 
                            #vulnerability type THREAD_SAFETY_VIOLATION
#fixed code
                                protected void fireInstancesAdded(int... instanceIds) {
        transactionalListener.objectInstancesAdded(this, instanceIds);
    }