opencv c++ gpumat mat(cpu) memory share

refer to code:

..

size_t frameByteSize = initMat.step[0] * initMat.rows;

#ifndef USE_UNIFIED_MEM

    /* Pinned memory. No cache */

    std::cout << "Using pinned memory" << std::endl;

    void* device_ptr, * host_ptr;

    cudaSetDeviceFlags(cudaDeviceMapHost);

    cudaHostAlloc((void**)&host_ptr, frameByteSize, cudaHostAllocMapped);

    cudaHostGetDevicePointer((void**)&device_ptr, (void*)host_ptr, 0);

    cv::Mat frame_out(height, width, CV_8UC3, host_ptr);

    cv::cuda::GpuMat d_frame_out(height, width, CV_8UC3, device_ptr);

#else

    /* Unified memory */

    std::cout << "Using unified memory" << std::endl;

    void* unified_ptr;

    cudaMallocManaged(&unified_ptr, frameByteSize);

    cv::Mat frame_out(height, width, CV_8UC3, unified_ptr);

    cv::cuda::GpuMat d_frame_out(height, width, CV_8UC3, unified_ptr);

#endif

..

another example

..

void* m_device_ptr = NULL;

void* m_host_ptr = NULL;

//memory share frame -> cuda_frame

cudaSetDeviceFlags(cudaDeviceMapHost);

size_t frameByteSize = initMat.step[0] * initMat.rows;

cudaHostAlloc((void**)&m_host_ptr, frameByteSize, cudaHostAllocMapped);

cudaHostGetDevicePointer((void**)&m_device_ptr, (void*)m_host_ptr, 0);

cv::Mat m_frame = cv::Mat(initMat.rows, initMat.cols, CV_8UC3, m_host_ptr);

cv::cuda::GpuMat m_cuda_frame = cv::cuda::GpuMat(initMat.rows, initMat.cols, CV_8UC3, m_device_ptr);

//initiation

iframes.copyTo(m_frame);

..