c++ - 这个奇怪的 clang 编译错误

Question

我有一个解决那些二维迷宫的程序，它对我来说工作得很好，但是我用 gprof (和@jrfonseca 的花式 gprof2dot )对它进行了分析，在我看来它是在一些操作上遇到困难，并决定进行一些并行化尝试。

基本上，在一个消耗 50%(cpu？)时间的函数中，我有两种并行化选择(单个队列的多个消费者和使用相似但不相等的参数并行调用同一函数) 但一开始我想独立地做这两件事来检查一个初始假设哪个更好，我并不总是做 C++ 代码，并通过在互联网上搜索如何获得 std::thread 返回一个值 我在 std::future 上读到一个很好的答案和建议，然后我将它复制到我的代码中，所以请你知道这意味着什么......

bash-4.3$ sh build.sh
In file included from find_path.cpp:6:
In file included from /Applications/Xcode.app/Contents/Developer/Toolchains/Xco
deDefault.xctoolchain/usr/bin/../include/c++/v1/future:371:
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/
usr/bin/../include/c++/v1/thread:337:5: error:
      attempt to use a deleted function
    __invoke(_VSTD::move(_VSTD::get<0>(__t)), _VSTD::move(_VSTD::get<_In...
    ^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/
usr/bin/../include/c++/v1/thread:347:5:
      in instantiation of function template specialization
      'std::__1::__thread_execute<void
      (*)(std::__1::priority_queue<std::__1::vector<std::__1::pair<int, int>,
      std::__1::allocator<std::__1::pair<int, int> > >,
      std::__1::vector<std::__1::vector<std::__1::pair<int, int>,
      std::__1::allocator<std::__1::pair<int, int> > >,
      std::__1::allocator<std::__1::vector<std::__1::pair<int, int>,
      std::__1::allocator<std::__1::pair<int, int> > > > >, NearerTarget> &,
      std::__1::vector<std::__1::pair<int, int>,
      std::__1::allocator<std::__1::pair<int, int> > > &, std::__1::pair<int,
      int> &, int, int, int, int, unsigned char *,
      std::__1::vector<std::__1::pair<int, int>,
      std::__1::allocator<std::__1::pair<int, int> > > &, int, int,
      std::__1::promise<bool> &&),
      std::__1::reference_wrapper<std::__1::priority_queue<std::__1::vector<std
::__1::pair<int,
      int>, std::__1::allocator<std::__1::pair<int, int> > >,
      std::__1::vector<std::__1::vector<std::__1::pair<int, int>,
      std::__1::allocator<std::__1::pair<int, int> > >,
      std::__1::allocator<std::__1::vector<std::__1::pair<int, int>,
      std::__1::allocator<std::__1::pair<int, int> > > > >, NearerTarget> >,
      std::__1::reference_wrapper<std::__1::vector<std::__1::pair<int, int>,
      std::__1::allocator<std::__1::pair<int, int> > > >,
      std::__1::reference_wrapper<std::__1::pair<int, int> >, int, int, int,
      int, const unsigned char *,
      std::__1::reference_wrapper<std::__1::vector<std::__1::pair<int, int>,
      std::__1::allocator<std::__1::pair<int, int> > > >, int, int,
      std::__1::promise<bool> , 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12>'
      requested here
    __thread_execute(*__p, _Index());
    ^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/
usr/bin/../include/c++/v1/thread:359:42: note:
      in instantiation of function template specialization
      'std::__1::__thread_proxy<std::__1::tuple<void
      (*)(std::__1::priority_queue<std::__1::vector<std::__1::pair<int, int>,
      std::__1::allocator<std::__1::pair<int, int> > >,
      std::__1::vector<std::__1::vector<std::__1::pair<int, int>,
      std::__1::allocator<std::__1::pair<int, int> > >,
      std::__1::allocator<std::__1::vector<std::__1::pair<int, int>,
      std::__1::allocator<std::__1::pair<int, int> > > > >, NearerTarget> &,
      std::__1::vector<std::__1::pair<int, int>,
      std::__1::allocator<std::__1::pair<int, int> > > &, std::__1::pair<int,
      int> &, int, int, int, int, unsigned char *,
      std::__1::vector<std::__1::pair<int, int>,
      std::__1::allocator<std::__1::pair<int, int> > > &, int, int,
      std::__1::promise<bool> &&),
      std::__1::reference_wrapper<std::__1::priority_queue<std::__1::vector<std
::__1::pair<int,
      int>, std::__1::allocator<std::__1::pair<int, int> > >,
      std::__1::vector<std::__1::vector<std::__1::pair<int, int>,
      std::__1::allocator<std::__1::pair<int, int> > >,
      std::__1::allocator<std::__1::vector<std::__1::pair<int, int>,
      std::__1::allocator<std::__1::pair<int, int> > > > >, NearerTarget> >,
      std::__1::reference_wrapper<std::__1::vector<std::__1::pair<int, int>,
      std::__1::allocator<std::__1::pair<int, int> > > >,
      std::__1::reference_wrapper<std::__1::pair<int, int> >, int, int, int,
      int, const unsigned char *,
      std::__1::reference_wrapper<std::__1::vector<std::__1::pair<int, int>,
      std::__1::allocator<std::__1::pair<int, int> > > >, int, int,
      std::__1::promise<bool> > >' requested here
    int __ec = pthread_create(&__t_, 0, &__thread_proxy<_Gp>, __p.get());
                                         ^
find_path.cpp:258:25: note: in instantiation of function template specializatio
n
      'std::__1::thread::thread<void
      (*)(std::__1::priority_queue<std::__1::vector<std::__1::pair<int, int>,
      std::__1::allocator<std::__1::pair<int, int> > >,
      std::__1::vector<std::__1::vector<std::__1::pair<int, int>,
      std::__1::allocator<std::__1::pair<int, int> > >,
      std::__1::allocator<std::__1::vector<std::__1::pair<int, int>,
      std::__1::allocator<std::__1::pair<int, int> > > > >, NearerTarget> &,
      std::__1::vector<std::__1::pair<int, int>,
      std::__1::allocator<std::__1::pair<int, int> > > &, std::__1::pair<int,
      int> &, int, int, int, int, unsigned char *,
      std::__1::vector<std::__1::pair<int, int>,
      std::__1::allocator<std::__1::pair<int, int> > > &, int, int,
      std::__1::promise<bool> &&),
      std::__1::reference_wrapper<std::__1::priority_queue<std::__1::vector<std
::__1::pair<int,
      int>, std::__1::allocator<std::__1::pair<int, int> > >,
      std::__1::vector<std::__1::vector<std::__1::pair<int, int>,
      std::__1::allocator<std::__1::pair<int, int> > >,
      std::__1::allocator<std::__1::vector<std::__1::pair<int, int>,
      std::__1::allocator<std::__1::pair<int, int> > > > >, NearerTarget> >,
      std::__1::reference_wrapper<std::__1::vector<std::__1::pair<int, int>,
      std::__1::allocator<std::__1::pair<int, int> > > >,
      std::__1::reference_wrapper<std::__1::pair<int, int> >, int &, int &,
      const int &, const int &, const unsigned char *&,
      std::__1::reference_wrapper<std::__1::vector<std::__1::pair<int, int>,
      std::__1::allocator<std::__1::pair<int, int> > > >, const int &, int,
      std::__1::promise<bool> , void>' requested here
            std::thread n(&move, std::ref(active_paths),
                        ^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/
usr/bin/../include/c++/v1/type_traits:1043:5: note:
      '~__nat' has been explicitly marked deleted here
    ~__nat() = delete;
    ^
1 error generated.
bash-4.3$

...在这种情况下？

一些find_path.cpp:

 1  //   For 'assert(expression)'.
 2  #include <cassert>
 3  //   For 'std::abs' (absolute value function, integers version)'.
 4  #include <cstdlib>
 5  //   For 'std::promise' and 'std::future'.
 6  #include <future>  // <--
 7  //   For 'std::mutex'.
 8  #include <mutex>
 9  //   For 'std::priority_queue'.
10  #include <queue>
11  //   For 'std::move'.
12  #include <utility>
13  //   For 'std::vector'.
14  #include <vector>
15  //   For 'std::thread'.
16  #include <thread>
17  //   For 'std::get', 'std::make_tuple' and 'std::tuple'.
18  #include <tuple>

还有一些:

242             //   Do not add new paths unless deemed necessary.
243             bool add_north_move, add_west_move, add_south_move, add_east_move;
244             add_north_move = add_west_move = add_south_move = add_east_move =
245                 0;
246 
247             //   Another helper.
248             std::vector < std::pair < int, int > > active_paths_top =
249                 active_paths.top();
250             std::pair < int, int > active_paths_top_back =
251                 active_paths_top.back();
252 
253             //   Directions clockwise (0: 'N', 1: 'E', 2: 'S', 3: 'W').
254             int direction = 0;
255 
256             std::promise < bool > n_p;
257             auto n_f = n_p.get_future();
258             std::thread n(&move, std::ref(active_paths),  // <--
259                           std::ref(active_paths_top),
260                           std::ref(active_paths_top_back), new_move_back_x, new_move_back_y,
261               nMapWidth, nMapHeight, pMap, std::ref(north_move), nOutBufferSize, direction++, std::move(n_p)
262             );
263             std::promise < bool > e_p;
264             auto e_f = e_p.get_future();
265             std::thread e(&move, std::ref(active_paths),
266                           std::ref(active_paths_top),
267                           std::ref(active_paths_top_back), new_move_back_x, new_move_back_y,
268               nMapWidth, nMapHeight, pMap, std::ref(east_move), nOutBufferSize, direction++, std::move(e_p)
269             );

void move(12) 中的内容:

108 void move(std::priority_queue <
109         std::vector < std::pair < int, int > >,
110         std::vector < std::vector < std::pair < int, int > > >,
111         NearerTarget
112     > & active_paths,
113     std::vector < std::pair < int, int > > & active_paths_top,
114     std::pair < int, int > & active_paths_top_back, int new_move_back_x, int new_move_back_y,
115     int map_width, int map_height, unsigned char * map, std::vector < std::pair < int, int > > & move,
116     int out_buffer_size, int direction,
117     std::promise < bool > && add_move) {
118     assert(-1 < direction && 4 > direction);
119     std::pair < int, int > new_coord;
120     switch (direction) {
121     case 0:
122             //   Add move 'N'.
123             new_coord = std::make_pair(
124                     active_paths_top_back.first,
125                     active_paths_top_back.second + 1);
126             break;
127     case 1:
128             //   Add move 'E'.
129             new_coord = std::make_pair(
130                     active_paths_top_back.first + 1,
131                     active_paths_top_back.second);
132             break;
133     case 2:
134             //   Add move 'S'.
135             new_coord = std::make_pair(
136                     active_paths_top_back.first,
137                     active_paths_top_back.second - 1);
138             break;
139     case 3:
140             //   Add move 'W'.
141             new_coord = std::make_pair(
142                     active_paths_top_back.first - 1,
143                     active_paths_top_back.second);
144             break;
145     }
146 
147             //   Push it to the queue of paths only if the movement
148             // makes sense.
149             new_move_back_x = new_coord.first;
150             new_move_back_y = new_coord.second;
151             if (new_move_back_x > -1 && new_move_back_x < map_width &&
152                     new_move_back_y > -1 && new_move_back_y < map_height)
153             {
154                 //   Move is inside bounds.
155 
156                 //   Check collision detection.
157                 if (map[new_move_back_y * map_width + new_move_back_x])
158                 {
159                     //   Check not visited.
160                     if (! visited(
161                                 new_move_back_x,
162                                 new_move_back_y,
163                                 active_paths.top()))
164                     {
165                         move = active_paths_top;
166                         move.reserve(out_buffer_size);
167                         move.push_back(new_coord);
168                         add_move.set_value(true);
169                     }
170                 }
171             }
172 }

它告诉我明确标记为已删除 ~__nat，我什至不记得做过这样的事情。

我有点习惯 pthreads、Python 线程、Java 并行模型……不太了解不确定的选择、一般的异步、promises……我应该放弃努力离开 std::future有什么用？

Answer 1

该错误消息与一个新的 C++ 功能有关，即“删除”默认运算符以使其不可访问(以前，通常的技术是将它们设为私有(private))。

在您的情况下，它表示线程构造函数的参数存在问题。您的代码非常复杂，但您可能遇到过这个问题:C++ std::thread "Attempt to use a deleted function"

我肯定会建议继续使用 std:future。作为介绍，强烈推荐 Herb Sutter 关于新的 C++ 并发特性的以下演讲:https://channel9.msdn.com/Shows/Going+Deep/C-and-Beyond-2012-Herb-Sutter-Concurrency-and-Parallelism