如何在OpenCL中从内核打印结果？

Question

I am new to OpenCL. I am trying to use OpenCL c++ kernel language extension http://amd-dev.wpengine.netdna-cdn.com/wordpress/media/2012/10/CPP_kernel_language.pdf . I am trying to print results using page 10 code of this document. Please find the code below from this documentation and correct me if am wrong anywhere.

class Test{
public:
    void setX(int value){ x = value;}
    int getX(){ return x;}
private:
    int x;
};

int main() {
    cl_mem classObj = clCreateBuffer(context, CL_MEM_USE_HOST_PTR, sizeof(Test), &tempClass, &ret);
    void* dm_idata = clEnqueueMapBuffer(command_queue, classObj, CL_TRUE, CL_MAP_WRITE, 0 , sizeof(Test), 0, NULL, NULL, &ret);
    tempClass.setX(10); //prints this value
    clEnqueueUnmapMemObject(command_queue, classObj, dm_idata, 0, NULL, NULL);//class is passed to the device
    ret = clEnqueueNDRangeKernel(command_queue, kernel, 1, NULL, &global_item_size, &local_item_size, 0, NULL, NULL);
    clEnqueueMapBuffer(command_queue, classObj, CL_TRUE, CL_MAP_WRITE, 0, sizeof(Test), 0, NULL, NULL, &ret);//class is passed back to the host
    printf("\n temp value: %d\n", tempClass.getX());
}

Here is the kernel code.

class Test {
    setX (int value);
private:
     int x;
};

__kernel void foo(__global Test* Inclass){   

if(get_global_id(0) == 0)
    Inclass->setX(6);
}

It prints the value from host code. I need to get the result from kernel. Any help is highly appreciated.

The result I got is

temp value = 10

Answer 1

对clEnqueueMapBuffer第二次调用应传递CL_MAP_READ ，而不是CL_MAP_WRITE ，因为您要读取数据。