message: GPU buffers support only sync mode
diff: @@ -26,6 +26,10 @@ void BP5Writer::PutCommon(Variable<T> &variable, const T *values, bool sync)
  BeginStep(StepMode::Update);
  }
  variable.SetData(values);
  + // if the user buffer is allocated on the GPU always use sync mode
  + bool isCudaBuffer = (variable.m_MemorySpace == MemorySpace::CUDA);
  + if (isCudaBuffer)
  + sync = true;
  size_t *Shape = NULL;
  size_t *Start = NULL;
  