#vulnerable code 
                              @Override
  public void onClose(Status status, Metadata trailers) {
    synchronized (callLock) {
      call = null;
    }
    rpcTimerContext.close();

    // OK
    if (status.isOk()) {
      if (onOK(trailers)) {
        operationTimerContext.close();
      }
    } else {
      onError(status, trailers);
    }
  } 
                            #location 11 
                            #vulnerability type THREAD_SAFETY_VIOLATION
#fixed code
                              @Override
  public void onClose(Status status, Metadata trailers) {
    try (NonThrowingCloseable s = TRACER.withSpan(operationSpan)) {
      synchronized (callLock) {
        call = null;
      }
      rpcTimerContext.close();
      // OK
      if (status.isOk()) {
        if (onOK(trailers)) {
          finalizeStats(status);
        }
      } else {
        onError(status, trailers);
      }
    }
  }