#vulnerable code 
                              @SuppressWarnings("unchecked")
  @Override
  public void run() {
    // restart the clock.
    lastResponseMs = clock.currentTimeMillis();
    this.rowMerger = new RowMerger(rowObserver);
    synchronized (callLock) {
      super.run();
      // pre-fetch one more result, for performance reasons.
      adapter = new CallToStreamObserverAdapter<ReadRowsRequest>(call);
      adapter.request(1);
      if (rowObserver instanceof ClientResponseObserver) {
        ((ClientResponseObserver<ReadRowsRequest, FlatRow>) rowObserver).beforeStart(adapter);
      }
    }
  } 
                            #location 5 
                            #vulnerability type THREAD_SAFETY_VIOLATION
#fixed code
                              @SuppressWarnings("unchecked")
  @Override
  public void run() {
    // restart the clock.
    this.rowMerger = new RowMerger(rowObserver);
    adapter = new CallToStreamObserverAdapter();
    synchronized (callLock) {
      super.run();
      // pre-fetch one more result, for performance reasons.
      adapter.request(1);
      if (rowObserver instanceof ClientResponseObserver) {
        ((ClientResponseObserver<ReadRowsRequest, FlatRow>) rowObserver).beforeStart(adapter);
      }
      lastResponseMs = clock.currentTimeMillis();
    }
  }