c++ - 如何 thrust::make_transform_iterator 取消引用 device_ptr？

Question

C++ 和 CUDA 的新手。使用 MSVS 2015 社区和 CUDA 9.2。

我尝试制作一个仅取消引用 device_ptr 的 transform_iterator。

我收到编译错误:无法使用给定的参数列表调用函数“dereference_device_double_functor::operator()”

我还制作了一个使用 host_vector 和普通双指针的版本，以确保我的仿函数使用正确。

    #include <iostream>
    #include "thrust\device_vector.h"
    #include "thrust\host_vector.h"

    struct dereference_device_double_functor
    {
        dereference_device_double_functor() {}

        typedef thrust::device_reference<thrust::device_ptr<double>> argument_type;
        typedef double result_type;

        __host__ __device__
            double operator()(thrust::device_reference<thrust::device_ptr<double>> xDpRef) const {
            thrust::device_ptr<double> xDp = (thrust::device_ptr<double>)xDpRef;
            return *xDp;
        }
    };

    struct dereference_host_double_functor
    {
        dereference_host_double_functor() {}

        typedef double* argument_type;
        typedef double result_type;

        __host__ __device__
            double operator()(double* const& xPtr) const {
            return *xPtr;
        }
    };

    int main()
    {
        // Create double
        thrust::device_vector<double> dv(1, 5);
        thrust::host_vector<double> hv(1, 6);

        // Make sure its there
        std::cout << dv[0] << std::endl;
        std::cout << hv[0] << std::endl;

        // Create pointers to doubles
        thrust::device_vector<thrust::device_ptr<double>> dvPtr(1);
        thrust::device_vector<double*> hvPtr(1);

        // Assign pointers to doubles
        dvPtr[0] = &(dv[0]);
        hvPtr[0] = &(hv[0]);

        // Make sure pointers point correctly
        std::cout << *((thrust::device_ptr<double>)dvPtr[0]) << std::endl;
        std::cout << *(hvPtr[0]) << std::endl;

        // Test functor with iterator
        auto dvi = dvPtr.begin();
        double dvd = dereference_device_double_functor()(*dvi);
        auto hvi = hvPtr.begin();
        double hvd = dereference_host_double_functor()(*hvi);

        // Make sure it worked with iterator
        std::cout << dvd << std::endl;
        std::cout << hvd << std::endl;

        // Make dereferencing transfom iterators
        auto tik = thrust::make_transform_iterator(dvPtr.begin(), dereference_device_double_functor());
        auto tij = thrust::make_transform_iterator(hvPtr.begin(), dereference_host_double_functor());

        // Check that transform iterators work
        //std::cout << *tik << std::endl; // Will cause compile error: function "dereference_device_double_functor::operator()" cannot be called with the given argument list
        std::cout << *tij << std::endl;

        return 0;
    }

感谢您的帮助!

Answer 1

在你的问题中，你这样说:

I tried making a transform_iterator that just dereferences a device_ptr.

然而，这不是我在您的代码中看到的:

    __host__ __device__
        double operator()(thrust::device_reference<thrust::device_ptr<double>> xDpRef) const {

当我在 linux 上编译你的代码时，我得到以下信息(摘自编译错误 spew):

$ nvcc -std=c++11 -o t351 t351.cu
/usr/local/cuda/bin/..//include/thrust/iterator/transform_iterator.h(312): error: function "dereference_device_double_functor::operator()" cannot be called with the given argument list
            argument types are: (thrust::device_ptr<double>)
            object type is: dereference_device_double_functor
...

所以推力传递给你 thrust::device_ptr<double> .但是您的仿函数运算符配置为采用 thrust::device_reference<thrust::device_ptr<double>>

当我修改你的代码时:

    __host__ __device__
        double operator()(thrust::device_reference<thrust::device_ptr<double>> xDpRef) const {

为此:

    __host__ __device__
        double operator()(thrust::device_ptr<double> xDpRef) const {

它为我正确编译和运行(在 linux 上):

$ cat t351.cu
 #include <iostream>
    #include <thrust/device_vector.h>
    #include <thrust/host_vector.h>

    struct dereference_device_double_functor
    {
        dereference_device_double_functor() {}

        typedef thrust::device_reference<thrust::device_ptr<double>> argument_type;
        typedef double result_type;

        __host__ __device__
            double operator()(thrust::device_ptr<double> xDpRef) const {
            thrust::device_ptr<double> xDp = (thrust::device_ptr<double>)xDpRef;
            return *xDp;
        }
    };

    struct dereference_host_double_functor
    {
        dereference_host_double_functor() {}

        typedef double* argument_type;
        typedef double result_type;

        __host__ __device__
            double operator()(double* const& xPtr) const {
            return *xPtr;
        }
    };

    int main()
    {
        // Create double
        thrust::device_vector<double> dv(1, 5);
        thrust::host_vector<double> hv(1, 6);

        // Make sure its there
        std::cout << dv[0] << std::endl;
        std::cout << hv[0] << std::endl;

        // Create pointers to doubles
        thrust::device_vector<thrust::device_ptr<double>> dvPtr(1);
        thrust::device_vector<double*> hvPtr(1);

        // Assign pointers to doubles
        dvPtr[0] = &(dv[0]);
        hvPtr[0] = &(hv[0]);

        // Make sure pointers point correctly
        std::cout << *((thrust::device_ptr<double>)dvPtr[0]) << std::endl;
        std::cout << *(hvPtr[0]) << std::endl;

        // Test functor with iterator
        auto dvi = dvPtr.begin();
        double dvd = dereference_device_double_functor()(*dvi);
        auto hvi = hvPtr.begin();
        double hvd = dereference_host_double_functor()(*hvi);

        // Make sure it worked with iterator
        std::cout << dvd << std::endl;
        std::cout << hvd << std::endl;

        // Make dereferencing transfom iterators
        auto tik = thrust::make_transform_iterator(dvPtr.begin(), dereference_device_double_functor());
        auto tij = thrust::make_transform_iterator(hvPtr.begin(), dereference_host_double_functor());

        // Check that transform iterators work
        std::cout << *tik << std::endl; // Will cause compile error: function "dereference_device_double_functor::operator()" cannot be called with the given argument list
        std::cout << *tij << std::endl;

        return 0;
    }
$ nvcc -std=c++11 -o t351 t351.cu
$ cuda-memcheck ./t351
========= CUDA-MEMCHECK
5
6
5
6
5
6
5
6
========= ERROR SUMMARY: 0 errors
$