採用迭代器元組併產生基本類型的一元函數

我有一個指向迭代器元組的zip迭代器。我想用一個函子提供thrust :: transform，它將使用元組來抓取元素併產生一個標量輸出。採用迭代器元組併產生基本類型的一元函數

我的程序不工作，我不知道爲什麼。

我認爲這可能與某些事情有關： CUDA thrust zip_iterator tuple transform_reduce，但更改仿函數的模板參數並沒有成功。

下面的代碼編譯：

#include <iostream> 
#include <thrust/transform.h> 
#include <thrust/functional.h> 
#include <thrust/device_vector.h> 
#include <thrust/device_ptr.h> 
#include <thrust/iterator/zip_iterator.h> 
#include <thrust/tuple.h> 

typedef thrust::device_vector<double>::iterator realIter; 
typedef thrust::tuple<realIter,realIter> Tup; 
typedef thrust::zip_iterator<Tup> Zip; 
typedef thrust::tuple<double,double> Tup2; //I tried replacing Tup with this in the functor 

struct dummyOp : public thrust::unary_function<Tup, double> { 
__host__ __device__ double operator()(Tup &tup){ 
    double result = *thrust::get<0>(tup); 
    return result; 
} 
}; 

int main(){ 
    thrust::device_vector<double> A(4); 
    thrust::device_vector<double> B(4); 
    thrust::device_vector<double> C(4); 

    A[0] = 1.; A[1] = 2.; 
    A[2] = 3.; A[3] = 4.; 

    B[0] = 4.; B[1] = 3.; 
    B[2] = 2.; B[3] = 1.; 

    Tup tup = thrust::tuple<realIter,realIter>(A.begin(),B.begin()); 
    Zip zippy = thrust::zip_iterator<Tup>(tup); 
    dummyOp f; 

    // The following does not work: 
    //thrust::transform(zippy, zippy + 4, C.begin(), f); 

    std::cout << "A:\n"; 
    thrust::copy(A.begin(), A.end(), std::ostream_iterator<double>(std::cout, " ")); 
    std::cout << "\nB:\n"; 
    thrust::copy(B.begin(), B.end(), std::ostream_iterator<double>(std::cout, " ")); 
    std::cout << "\nC:\n"; 
    thrust::copy(C.begin(), C.end(), std::ostream_iterator<double>(std::cout, " ")); 
    std::cout << std::endl; 
    std::cout <<"get<0>(zippy[0]) returns:\n" << thrust::get<0>(zippy[0]) << std::endl; 
    std::cout <<"get<1>(zippy[1]) returns:\n" << thrust::get<1>(zippy[1]) << std::endl; 

    return 0; 
}

並運行它給：

$ ./so2 
A: 
1 2 3 4 
B: 
4 3 2 1 
C: 
0 0 0 0 
get<0>(zippy[0]) returns: 
1 
get<1>(zippy[1]) returns: 
3

隨着問題的行註釋掉，我們有：

$ nvcc -arch=compute_35 so2.cu -o so2 
/usr/local/cuda/bin/../targets/x86_64-linux/include/thrust/detail/internal_functional.h(322): error: function "dummyOp::operator()" cannot be called with the given argument list 
      argument types are: (thrust::detail::tuple_of_iterator_references<double &, double &, thrust::null_type, thrust::null_type, thrust::null_type, thrust::null_type, thrust::null_type, thrust::null_type, thrust::null_type, thrust::null_type>) 
      object type is: dummyOp 
      detected during: 
      instantiation of "thrust::detail::enable_if_non_const_reference_or_tuple_of_iterator_references<thrust::tuple_element<1, Tuple>::type>::type thrust::detail::unary_transform_functor<UnaryFunction>::operator()(Tuple) [with UnaryFunction=dummyOp, Tuple=thrust::detail::tuple_of_iterator_references<thrust::detail::tuple_of_iterator_references<double &, double &, thrust::null_type, thrust::null_type, thrust::null_type, thrust::null_type, thrust::null_type, thrust::null_type, thrust::null_type, thrust::null_type>, double &, thrust::null_type, thrust::null_type, thrust::null_type, thrust::null_type, thrust::null_type, thrust::null_type, thrust::null_type, thrust::null_type>]" 
/usr/local/cuda/bin/../targets/x86_64-linux/include/thrust/detail/function.h(60): here 
      instantiation of "Result thrust::detail::wrapped_function<Function, Result>::operator()(const Argument &) const [with Function=thrust::detail::unary_transform_functor<dummyOp>, Result=void, Argument=thrust::detail::tuple_of_iterator_references<thrust::detail::tuple_of_iterator_references<thrust::device_reference<double>, thrust::device_reference<double>, thrust::null_type, thrust::null_type, thrust::null_type, thrust::null_type, thrust::null_type, thrust::null_type, thrust::null_type, thrust::null_type>, thrust::device_reference<double>, thrust::null_type, thrust::null_type, thrust::null_type, thrust::null_type, thrust::null_type, thrust::null_type, thrust::null_type, thrust::null_type>]" 
/usr/local/cuda/bin/../targets/x86_64-linux/include/thrust/system/cuda/detail/for_each.inl(57): here 
      instantiation of "void thrust::system::cuda::detail::for_each_n_detail::for_each_kernel::operator()(thrust::system::cuda::detail::bulk_::parallel_group<thrust::system::cuda::detail::bulk_::concurrent_group<thrust::system::cuda::detail::bulk_::agent<1UL>, 0UL>, 0UL> &, Iterator, Function, Size) [with Iterator=thrust::zip_iterator<thrust::tuple<Zip, thrust::detail::normal_iterator<thrust::device_ptr<double>>, thrust::null_type, thrust::null_type, thrust::null_type, thrust::null_type, thrust::null_type, thrust::null_type, thrust::null_type, thrust::null_type>>, Function=thrust::detail::wrapped_function<thrust::detail::unary_transform_functor<dummyOp>, void>, Size=unsigned int]" 
/usr/local/cuda/bin/../targets/x86_64-linux/include/thrust/system/cuda/detail/bulk/detail/apply_from_tuple.hpp(71): here 
      instantiation of "void thrust::system::cuda::detail::bulk_::detail::apply_from_tuple(Function, const thrust::tuple<Arg1, Arg2, Arg3, Arg4, thrust::null_type, thrust::null_type, thrust::null_type, thrust::null_type, thrust::null_type, thrust::null_type> &) [with Function=thrust::system::cuda::detail::for_each_n_detail::for_each_kernel, Arg1=thrust::system::cuda::detail::bulk_::parallel_group<thrust::system::cuda::detail::bulk_::concurrent_group<thrust::system::cuda::detail::bulk_::agent<1UL>, 0UL>, 0UL> &, Arg2=thrust::zip_iterator<thrust::tuple<Zip, thrust::detail::normal_iterator<thrust::device_ptr<double>>, thrust::null_type, thrust::null_type, thrust::null_type, thrust::null_type, thrust::null_type, thrust::null_type, thrust::null_type, thrust::null_type>>, Arg3=thrust::detail::wrapped_function<thrust::detail::unary_transform_functor<dummyOp>, void>, Arg4=unsigned int]" 
/usr/local/cuda/bin/../targets/x86_64-linux/include/thrust/system/cuda/detail/bulk/detail/closure.hpp(50): here 
      instantiation of "void thrust::system::cuda::detail::bulk_::detail::closure<Function, Tuple>::operator()() [with Function=thrust::system::cuda::detail::for_each_n_detail::for_each_kernel, Tuple=thrust::tuple<thrust::system::cuda::detail::bulk_::parallel_group<thrust::system::cuda::detail::bulk_::concurrent_group<thrust::system::cuda::detail::bulk_::agent<1UL>, 0UL>, 0UL> &, thrust::zip_iterator<thrust::tuple<Zip, thrust::detail::normal_iterator<thrust::device_ptr<double>>, thrust::null_type, thrust::null_type, thrust::null_type, thrust::null_type, thrust::null_type, thrust::null_type, thrust::null_type, thrust::null_type>>, thrust::detail::wrapped_function<thrust::detail::unary_transform_functor<dummyOp>, void>, unsigned int, thrust::null_type, thrust::null_type, thrust::null_type, thrust::null_type, thrust::null_type, thrust::null_type>]" 
/usr/local/cuda/bin/../targets/x86_64-linux/include/thrust/system/cuda/detail/bulk/detail/cuda_task.hpp(58): here 
      [ 9 instantiation contexts not shown ] 
      instantiation of "RandomAccessIterator thrust::system::cuda::detail::for_each(thrust::system::cuda::detail::execution_policy<DerivedPolicy> &, RandomAccessIterator, RandomAccessIterator, UnaryFunction) [with DerivedPolicy=thrust::system::cuda::detail::tag, RandomAccessIterator=thrust::zip_iterator<thrust::tuple<Zip, thrust::detail::normal_iterator<thrust::device_ptr<double>>, thrust::null_type, thrust::null_type, thrust::null_type, thrust::null_type, thrust::null_type, thrust::null_type, thrust::null_type, thrust::null_type>>, UnaryFunction=thrust::detail::unary_transform_functor<dummyOp>]" 
/usr/local/cuda/bin/../targets/x86_64-linux/include/thrust/detail/for_each.inl(44): here 
      instantiation of "InputIterator thrust::for_each(const thrust::detail::execution_policy_base<DerivedPolicy> &, InputIterator, InputIterator, UnaryFunction) [with DerivedPolicy=thrust::system::cuda::detail::tag, InputIterator=thrust::zip_iterator<thrust::tuple<Zip, thrust::detail::normal_iterator<thrust::device_ptr<double>>, thrust::null_type, thrust::null_type, thrust::null_type, thrust::null_type, thrust::null_type, thrust::null_type, thrust::null_type, thrust::null_type>>, UnaryFunction=thrust::detail::unary_transform_functor<dummyOp>]" 
/usr/local/cuda/bin/../targets/x86_64-linux/include/thrust/system/detail/generic/transform.inl(57): here 
      instantiation of "OutputIterator thrust::system::detail::generic::transform(thrust::execution_policy<DerivedPolicy> &, InputIterator, InputIterator, OutputIterator, UnaryFunction) [with DerivedPolicy=thrust::system::cuda::detail::tag, InputIterator=Zip, OutputIterator=thrust::detail::normal_iterator<thrust::device_ptr<double>>, UnaryFunction=dummyOp]" 
/usr/local/cuda/bin/../targets/x86_64-linux/include/thrust/detail/transform.inl(44): here 
      instantiation of "OutputIterator thrust::transform(const thrust::detail::execution_policy_base<DerivedPolicy> &, InputIterator, InputIterator, OutputIterator, UnaryFunction) [with DerivedPolicy=thrust::system::cuda::detail::tag, InputIterator=Zip, OutputIterator=thrust::detail::normal_iterator<thrust::device_ptr<double>>, UnaryFunction=dummyOp]" 
/usr/local/cuda/bin/../targets/x86_64-linux/include/thrust/detail/transform.inl(142): here 
      instantiation of "OutputIterator thrust::transform(InputIterator, InputIterator, OutputIterator, UnaryFunction) [with InputIterator=Zip, OutputIterator=thrust::detail::normal_iterator<thrust::device_ptr<double>>, UnaryFunction=dummyOp]" 
so2.cu(36): here

更新：雖然我還是真的很想幫助理解上面的代碼中的問題，下面的工作：

struct dummyOp { 
template <typename Tuple> 
__host__ __device__ double operator()(Tuple tup){ 
    double result = thrust::get<0>(tup); 
    return result; 
} 
};

的想法是從這裏被盜：https://github.com/thrust/thrust/blob/master/examples/arbitrary_transformation.cu

這並不構成回答我自己的問題，因爲我還是不明白什麼是錯的原始代碼中的類型。

另外：它不能使參數成爲明確的參考（Tuple &）。這是否意味着tup通過價值傳遞？

來源

2016-09-30 Eric Mittman

一般來說，當一個zip迭代器作爲推力算法的一部分取消引用時，它會創建一個基本類型的元組（即不是迭代器或指針），該元組被傳遞給有問題的函子。

當我們分析從你的代碼輸出的編譯器與「進攻路線」：

argument types are: (thrust::detail::tuple_of_iterator_references<double &, double &,

我們觀察到，當推力取消引用zippy拉鍊迭代器，它產生的引用到double項目的元組。我們可以用它來通知我們預期的仿函數，即輸入型：

thrust::tuple<double &, double &>

因爲這些都是基本類型的引用，就沒有必要爲我們解引用這些（就好像它們是指針，或迭代器）在函子中取得它們的價值。

以下修改後的代碼結合這些觀點，沒有錯誤編譯：

$ cat t4.cu 
#include <iostream> 
#include <thrust/transform.h> 
#include <thrust/functional.h> 
#include <thrust/device_vector.h> 
#include <thrust/device_ptr.h> 
#include <thrust/iterator/zip_iterator.h> 
#include <thrust/tuple.h> 

typedef thrust::device_vector<double>::iterator realIter; 
typedef thrust::tuple<realIter,realIter> Tup; 
typedef thrust::zip_iterator<Tup> Zip; 
typedef thrust::tuple<double &,double &> Tup2; //I tried replacing Tup with this in the functor 

struct dummyOp : public thrust::unary_function<Tup2, double> { 
__host__ __device__ double operator()(Tup2 &tup){ 
    double result = thrust::get<0>(tup); 
    return result; 
} 
}; 

int main(){ 
    thrust::device_vector<double> A(4); 
    thrust::device_vector<double> B(4); 
    thrust::device_vector<double> C(4); 

    A[0] = 1.; A[1] = 2.; 
    A[2] = 3.; A[3] = 4.; 

    B[0] = 4.; B[1] = 3.; 
    B[2] = 2.; B[3] = 1.; 

    Tup tup = thrust::tuple<realIter,realIter>(A.begin(),B.begin()); 
    Zip zippy = thrust::zip_iterator<Tup>(tup); 
    dummyOp f; 

    // The following does not work: 
    thrust::transform(zippy, zippy + 4, C.begin(), f); 

    std::cout << "A:\n"; 
    thrust::copy(A.begin(), A.end(), std::ostream_iterator<double>(std::cout, " ")); 
    std::cout << "\nB:\n"; 
    thrust::copy(B.begin(), B.end(), std::ostream_iterator<double>(std::cout, " ")); 
    std::cout << "\nC:\n"; 
    thrust::copy(C.begin(), C.end(), std::ostream_iterator<double>(std::cout, " ")); 
    std::cout << std::endl; 
    std::cout <<"get<0>(zippy[0]) returns:\n" << thrust::get<0>(zippy[0]) << std::endl; 
    std::cout <<"get<1>(zippy[1]) returns:\n" << thrust::get<1>(zippy[1]) << std::endl; 

    return 0; 
} 
$ nvcc -arch=sm_61 -o t4 t4.cu 
$ ./t4 
A: 
1 2 3 4 
B: 
4 3 2 1 
C: 
1 2 3 4 
get<0>(zippy[0]) returns: 
1 
get<1>(zippy[1]) returns: 
3 
$

作爲替代，模板化的元組類型的作品的仿函數算子，當然，因爲編譯器推斷出必要類型的細節和實例化函子操作符的適當版本。

來源

2016-10-02 00:51:50

採用迭代器元組併產生基本類型的一元函數

回答

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