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