自定义迭代器与std :: sort工作，但不与tbb :: parallel_sort？ [英] Custom iterator works with std::sort but not with tbb::parallel_sort?

问题描述

我试图使用 tbb :: parallel_sort 同时对2个数组排序。这里的Intel文档说明了 https://software.intel.com/en-us/node/506167 对迭代器和序列的要求与std :: sort相同。。这似乎不是这样的。我的自定义迭代器与 std :: sort 完美地工作，但产生一个编译错误与 tbb :: parallel_sort 。请参阅下面的代码：

I am trying to use tbb::parallel_sort to sort 2 arrays at the same time. Intel's documentation here says https://software.intel.com/en-us/node/506167 The requirements on the iterator and sequence are the same as for std::sort.. This doesn't seem to be the case. My custom iterator works perfectly fine with std::sort but produces a compilation error with tbb::parallel_sort. Please see the code bellow:

int main()//needs boost and tbb to compile
{
    int values_size = 6;
    int nums1[] = {5, 8, 7, 89, 56, 4};
    int nums2[] = {2, 1, 1, 4, 9, 2};

    //WORKS!
    std::sort(do_dual_sort.make_iter(nums1, nums2), 
    do_dual_sort.make_iter(nums1+values_size, nums2+values_size),
    do_dual_sort.make_comp_desc(nums1, nums2));

    //DOESN'T COMPILE
    tbb::parallel_sort(do_dual_sort.make_iter(nums1, nums2), 
    do_dual_sort.make_iter(nums1+values_size, nums2+values_size),
    do_dual_sort.make_comp_desc(nums1, nums2));

    for(unsigned int i = 0; i < values_size; i++) cout << "nums1[" << i << "] " << nums1[i] << " | nums2[" << i << "] "  << nums2[i] << "\n";
    return 0;
}

class dual_sort
{
public:
    template <class T, class T2>
    struct helper_type {
        public:
            typedef boost::tuple<typename iterator_traits<T>::value_type, typename iterator_traits<T2>::value_type> value_type;
            typedef boost::tuple<typename iterator_traits<T>::value_type&, typename iterator_traits<T2>::value_type&> ref_type;
    };

    template <typename T1, typename T2>
    class dual_iterator : public boost::iterator_facade<dual_iterator<T1, T2>,
                                                        typename helper_type<T1, T2>::value_type,
                                                        boost::random_access_traversal_tag,
                                                        typename helper_type<T1, T2>::ref_type> {
    public:
        explicit dual_iterator(T1 iter1, T2 iter2) : mIter1(iter1), mIter2(iter2) {}
        typedef typename iterator_traits<T1>::difference_type difference_type;
    private:
        void increment() { ++mIter1; ++mIter2; }
        void decrement() { --mIter1; --mIter2; }
        bool equal(dual_iterator const& other) const { return mIter1 == other.mIter1; }
        typename helper_type<T1, T2>::ref_type dereference() const { return (typename helper_type<T1, T2>::ref_type(*mIter1, *mIter2)); }
        difference_type distance_to(dual_iterator const& other) const { return other.mIter1 - mIter1; }
        void advance(difference_type n) { mIter1 += n; mIter2 += n; }

        T1 mIter1;
        T2 mIter2;
        friend class boost::iterator_core_access;
    };

    template <typename T1, typename T2>
    dual_iterator<T1, T2> make_iter(T1 t1, T2 t2) { return dual_iterator<T1, T2>(t1, t2); }

    template <class T1, class T2> struct iter_comp_desc {
        typedef typename helper_type<T1, T2>::value_type T;
        bool operator()(const T& t1, const T& t2) const { return get<0>(t1) > get<0>(t2); }
        bool operator()(const char*& t1, const char*& t2) const { return strcmp(get<0>(t1), get<0>(t2)) == 1; }
    };

    template <class T1, class T2> iter_comp_desc<T1, T2> make_comp_desc(T1 t1, T2 t2) { return iter_comp_desc<T1, T2>(); }

} do_dual_sort;

我得到的编译错误是：

error C2512: 'dual_sort::dual_iterator<T1,T2>' : no appropriate default constructor available
with
[
    T1=int *,
    T2=int *
]
tbb44_20150728oss\include\tbb/parallel_sort.h(201) : see reference to function template instantiation 'void tbb::internal::parallel_quick_sort<RandomAccessIterator,Compare>(RandomAccessIterator,RandomAccessIterator,const Compare &)' being compiled
with
[
    RandomAccessIterator=dual_sort::dual_iterator<int *,int *>,
    Compare=dual_sort::iter_comp_desc<int *,int *>
]
main.cpp(1125) : see reference to function template instantiation 'void tbb::parallel_sort<dual_sort::dual_iterator<T1,T2>,dual_sort::iter_comp_desc<T1,T2>>(RandomAccessIterator,RandomAccessIterator,const Compare &)' being compiled
with
[
    T1=int *,
    T2=int *,
    RandomAccessIterator=dual_sort::dual_iterator<int *,int *>,
    Compare=dual_sort::iter_comp_desc<int *,int *>
]

编辑：我使用的编译器是 Visual Studio 2012 。你可以尝试用 std 替换一些boost函数，使它在 g ++ 上工作。

Edit: The compiler I used is Visual Studio 2012. You can try to replace some boost functions with std ones to get it work on g++.

推荐答案

类quick_sort_range 在 tbb / parallel_sort.h 包含 RandomAccessIterator begin; 成员在其构造函数中进行复制初始化，并在其他构造函数中进行默认初始化和分配。因此，它需要默认和可复制构造和可分配的迭代器。

The class quick_sort_range in tbb/parallel_sort.h contains RandomAccessIterator begin; member which is copy-initialized in one its constructor and default-initialized and then assigned in the other constructor. Thus it requires iterators which are default&copy-constructable and assignable.

因此，TBB文档不正确，声明了与 std :: sort 相同的要求，因为稍后需要随机访问迭代器，其中不需要 是可分配的，而TBB实现需要版本< = 4.4。

So, the TBB documentation is not correct claiming the same requirements as std::sort since the later requires just random-access iterators which are not required to be assignable while TBB implementation requires it for versions <= 4.4.

默认可构造和可分配的需求可以是固定的，但是移动或可复制构造可能仍然存在（使文档中的声明正确）。您可以在 TBB论坛上报告此问题。

The default-constructable and assignable requirements can be fixed but move or copy-constructable will likely remain (making the claim in the documentation correct). You can report this issue on TBB Forum.

您可以安全地将默认和复制构造函数和赋值运算符添加到代码中，以使用 tbb :: parallel_sort

You can safely add default&copy constructors and assignment operator to your code to compile it with tbb::parallel_sort as far as I can see.

以下是您的代码片段的在线编译器： http://coliru.stacked-crooked.com/a/47dafd091d36a9c4

Here is the online compiler with your snippet: http://coliru.stacked-crooked.com/a/47dafd091d36a9c4

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