#fixed code
                                void internalClose() throws IOException {
        if (!closed) {
            closed = true;
            backend.rrdClose();
        }
    }
#vulnerable code 
                                void realClose() throws IOException {
        if (!closed) {
            closed = true;
            backend.rrdClose();
        }
    } 
                            #location 3 
                            #vulnerability type THREAD_SAFETY_VIOLATION