问答博客资讯标签用户活动
logo极客观点logo项目管理logoHarmonyOS
javascript
前端
python
node.js
react
vue.js
php
laravel
go
人工智能
mysql
linux
ios
java
android
css
typescript
spring
程序员
logoONES 研发管理logo思否企业问答logo安谋科技 XPU

如何在 C 中声明原子向量

社区维基
1
新手上路，请多包涵

我打算声明一个原子变量向量，用作多线程程序中的计数器。这是我尝试过的：

 #include <atomic>
#include <vector>

int main(void)
{
  std::vector<std::atomic<int>> v_a;
  std::atomic<int> a_i(1);
  v_a.push_back(a_i);
  return 0;
}

这是 gcc 4.6.3 烦人的冗长错误消息：

 In file included from /usr/include/c++/4.6/x86_64-linux-gnu/./bits/c++allocator.h:34:0,
             from /usr/include/c++/4.6/bits/allocator.h:48,
             from /usr/include/c++/4.6/vector:62,
             from test_atomic_vec.h:2,
             from test_atomic_vec.cc:1:
/usr/include/c++/4.6/ext/new_allocator.h: In member function ‘void __gnu_cxx::new_allocator<_Tp>::construct(__gnu_cxx::new_allocator<_Tp>::pointer, const _Tp&) [with _Tp = std::atomic<int>, __gnu_cxx::new_allocator<_Tp>::pointer = std::atomic<int>*]’:
/usr/include/c++/4.6/bits/stl_vector.h:830:6:   instantiated from ‘void std::vector<_Tp, _Alloc>::push_back(const value_type&) [with _Tp = std::atomic<int>, _Alloc = std::allocator<std::atomic<int> >, std::vector<_Tp, _Alloc>::value_type = std::atomic<int>]’
test_atomic_vec.cc:10:20:   instantiated from here
/usr/include/c++/4.6/ext/new_allocator.h:108:9: error: use of deleted function ‘std::atomic<int>::atomic(const std::atomic<int>&)’
/usr/include/c++/4.6/atomic:538:7: error: declared here
In file included from /usr/include/c++/4.6/vector:70:0,
             from test_atomic_vec.h:2,
             from test_atomic_vec.cc:1:
/usr/include/c++/4.6/bits/vector.tcc: In member function ‘void std::vector<_Tp, _Alloc>::_M_insert_aux(std::vector<_Tp, _Alloc>::iterator, _Args&& ...) [with _Args = {const std::atomic<int>&}, _Tp = std::atomic<int>, _Alloc = std::allocator<std::atomic<int> >, std::vector<_Tp, _Alloc>::iterator = __gnu_cxx::__normal_iterator<std::atomic<int>*, std::vector<std::atomic<int> > >, typename std::_Vector_base<_Tp, _Alloc>::_Tp_alloc_type::pointer = std::atomic<int>*]’:
/usr/include/c++/4.6/bits/stl_vector.h:834:4:   instantiated from ‘void std::vector<_Tp, _Alloc>::push_back(const value_type&) [with _Tp = std::atomic<int>, _Alloc = std::allocator<std::atomic<int> >, std::vector<_Tp, _Alloc>::value_type = std::atomic<int>]’
test_atomic_vec.cc:10:20:   instantiated from here
/usr/include/c++/4.6/bits/vector.tcc:319:4: error: use of deleted function ‘std::atomic<int>::atomic(const std::atomic<int>&)’
/usr/include/c++/4.6/atomic:538:7: error: declared here
/usr/include/c++/4.6/bits/stl_vector.h:834:4:   instantiated from ‘void std::vector<_Tp, _Alloc>::push_back(const value_type&) [with _Tp = std::atomic<int>, _Alloc = std::allocator<std::atomic<int> >, std::vector<_Tp, _Alloc>::value_type = std::atomic<int>]’
test_atomic_vec.cc:10:20:   instantiated from here
/usr/include/c++/4.6/bits/vector.tcc:319:4: error: use of deleted function ‘std::atomic<int>& std::atomic<int>::operator=(const std::atomic<int>&)’
/usr/include/c++/4.6/atomic:539:15: error: declared here
In file included from /usr/include/c++/4.6/x86_64-linux-gnu/./bits/c++allocator.h:34:0,
             from /usr/include/c++/4.6/bits/allocator.h:48,
             from /usr/include/c++/4.6/vector:62,
             from test_atomic_vec.h:2,
             from test_atomic_vec.cc:1:
/usr/include/c++/4.6/ext/new_allocator.h: In member function ‘void __gnu_cxx::new_allocator<_Tp>::construct(__gnu_cxx::new_allocator<_Tp>::pointer, _Args&& ...) [with _Args = {std::atomic<int>}, _Tp = std::atomic<int>, __gnu_cxx::new_allocator<_Tp>::pointer = std::atomic<int>*]’:
/usr/include/c++/4.6/bits/vector.tcc:306:4:   instantiated from ‘void std::vector<_Tp, _Alloc>::_M_insert_aux(std::vector<_Tp, _Alloc>::iterator, _Args&& ...) [with _Args = {const std::atomic<int>&}, _Tp = std::atomic<int>, _Alloc = std::allocator<std::atomic<int> >, std::vector<_Tp, _Alloc>::iterator = __gnu_cxx::__normal_iterator<std::atomic<int>*, std::vector<std::atomic<int> > >, typename std::_Vector_base<_Tp, _Alloc>::_Tp_alloc_type::pointer = std::atomic<int>*]’
/usr/include/c++/4.6/bits/stl_vector.h:834:4:   instantiated from ‘void std::vector<_Tp, _Alloc>::push_back(const value_type&) [with _Tp = std::atomic<int>, _Alloc = std::allocator<std::atomic<int> >, std::vector<_Tp, _Alloc>::value_type = std::atomic<int>]’
test_atomic_vec.cc:10:20:   instantiated from here
/usr/include/c++/4.6/ext/new_allocator.h:114:4: error: use of deleted function ‘std::atomic<int>::atomic(const std::atomic<int>&)’
/usr/include/c++/4.6/atomic:538:7: error: declared here
In file included from /usr/include/c++/4.6/vector:61:0,
             from test_atomic_vec.h:2,
             from test_atomic_vec.cc:1:
/usr/include/c++/4.6/bits/stl_algobase.h: In static member function ‘static _BI2 std::__copy_move_backward<true, false, std::random_access_iterator_tag>::__copy_move_b(_BI1, _BI1, _BI2) [with _BI1 = std::atomic<int>*, _BI2 = std::atomic<int>*]’:
/usr/include/c++/4.6/bits/stl_algobase.h:581:18:   instantiated from ‘_BI2 std::__copy_move_backward_a(_BI1, _BI1, _BI2) [with bool _IsMove = true, _BI1 = std::atomic<int>*, _BI2 = std::atomic<int>*]’
/usr/include/c++/4.6/bits/stl_algobase.h:590:34:   instantiated from ‘_BI2 std::__copy_move_backward_a2(_BI1, _BI1, _BI2) [with bool _IsMove = true, _BI1 = std::atomic<int>*, _BI2 = std::atomic<int>*]’
/usr/include/c++/4.6/bits/stl_algobase.h:661:15:   instantiated from ‘_BI2 std::move_backward(_BI1, _BI1, _BI2) [with _BI1 = std::atomic<int>*, _BI2 = std::atomic<int>*]’
/usr/include/c++/4.6/bits/vector.tcc:313:4:   instantiated from ‘void std::vector<_Tp, _Alloc>::_M_insert_aux(std::vector<_Tp, _Alloc>::iterator, _Args&& ...) [with _Args = {const std::atomic<int>&}, _Tp = std::atomic<int>, _Alloc = std::allocator<std::atomic<int> >, std::vector<_Tp, _Alloc>::iterator = __gnu_cxx::__normal_iterator<std::atomic<int>*, std::vector<std::atomic<int> > >, typename std::_Vector_base<_Tp, _Alloc>::_Tp_alloc_type::pointer = std::atomic<int>*]’
/usr/include/c++/4.6/bits/stl_vector.h:834:4:   instantiated from ‘void std::vector<_Tp, _Alloc>::push_back(const value_type&) [with _Tp = std::atomic<int>, _Alloc = std::allocator<std::atomic<int> >, std::vector<_Tp, _Alloc>::value_type = std::atomic<int>]’
test_atomic_vec.cc:10:20:   instantiated from here
/usr/include/c++/4.6/bits/stl_algobase.h:546:6: error: use of deleted function ‘std::atomic<int>& std::atomic<int>::operator=(const std::atomic<int>&)’
/usr/include/c++/4.6/atomic:539:15: error: declared here
In file included from /usr/include/c++/4.6/vector:63:0,
             from test_atomic_vec.h:2,
             from test_atomic_vec.cc:1:
/usr/include/c++/4.6/bits/stl_construct.h: In function ‘void std::_Construct(_T1*, _Args&& ...) [with _T1 = std::atomic<int>, _Args = {std::atomic<int>}]’:
/usr/include/c++/4.6/bits/stl_uninitialized.h:77:3:   instantiated from ‘static _ForwardIterator std::__uninitialized_copy<_TrivialValueTypes>::__uninit_copy(_InputIterator, _InputIterator, _ForwardIterator) [with _InputIterator = std::move_iterator<std::atomic<int>*>, _ForwardIterator = std::atomic<int>*, bool _TrivialValueTypes = false]’
/usr/include/c++/4.6/bits/stl_uninitialized.h:119:41:   instantiated from ‘_ForwardIterator std::uninitialized_copy(_InputIterator, _InputIterator, _ForwardIterator) [with _InputIterator = std::move_iterator<std::atomic<int>*>, _ForwardIterator = std::atomic<int>*]’
/usr/include/c++/4.6/bits/stl_uninitialized.h:259:63:   instantiated from ‘_ForwardIterator std::__uninitialized_copy_a(_InputIterator, _InputIterator, _ForwardIterator, std::allocator<_Tp>&) [with _InputIterator = std::move_iterator<std::atomic<int>*>, _ForwardIterator = std::atomic<int>*, _Tp = std::atomic<int>]’
/usr/include/c++/4.6/bits/stl_uninitialized.h:269:24:   instantiated from ‘_ForwardIterator std::__uninitialized_move_a(_InputIterator, _InputIterator, _ForwardIterator, _Allocator&) [with _InputIterator = std::atomic<int>*, _ForwardIterator = std::atomic<int>*, _Allocator = std::allocator<std::atomic<int> >]’
/usr/include/c++/4.6/bits/vector.tcc:343:8:   instantiated from ‘void std::vector<_Tp, _Alloc>::_M_insert_aux(std::vector<_Tp, _Alloc>::iterator, _Args&& ...) [with _Args = {const std::atomic<int>&}, _Tp = std::atomic<int>, _Alloc = std::allocator<std::atomic<int> >, std::vector<_Tp, _Alloc>::iterator = __gnu_cxx::__normal_iterator<std::atomic<int>*, std::vector<std::atomic<int> > >, typename std::_Vector_base<_Tp, _Alloc>::_Tp_alloc_type::pointer = std::atomic<int>*]’
/usr/include/c++/4.6/bits/stl_vector.h:834:4:   instantiated from ‘void std::vector<_Tp, _Alloc>::push_back(const value_type&) [with _Tp = std::atomic<int>, _Alloc = std::allocator<std::atomic<int> >, std::vector<_Tp, _Alloc>::value_type = std::atomic<int>]’
test_atomic_vec.cc:10:20:   instantiated from here
/usr/include/c++/4.6/bits/stl_construct.h:76:7: error: use of deleted function ‘std::atomic<int>::atomic(const std::atomic<int>&)’
/usr/include/c++/4.6/atomic:538:7: error: declared here

我该如何解决这个问题？

当我用 push_back() 注释掉该行时，错误消失了。

编辑： 我编辑了帖子…对于那些看到第一篇帖子的人来说，错误是令人尴尬的是我使用了 gcc 而不是 g++ ：

原文由 steffen 发布，翻译遵循 CC BY-SA 4.0 许可协议

Stack Overflow 翻译c++stlc++11atomic
阅读 647
2 个回答
得票最新
社区维基
1
✓ 已被采纳

正如评论中提到的这个 密切相关的问题 中所述， std::atomic<T> 不是可复制构造的，也不是可复制分配的。

不具有这些属性的对象类型不能用作 std::vector 的元素。

但是，应该可以在 std::atomic<T> 元素周围创建一个可复制构造和可复制分配的包装器。它将必须使用 load() 和 store() 成员函数 std::atomic<T> 来提供构造和分配（这是上述问题的公认答案所描述的想法以上）：

 #include <atomic>
#include <vector>

template <typename T>
struct atomwrapper
{
  std::atomic<T> _a;

  atomwrapper()
    :_a()
  {}

  atomwrapper(const std::atomic<T> &a)
    :_a(a.load())
  {}

  atomwrapper(const atomwrapper &other)
    :_a(other._a.load())
  {}

  atomwrapper &operator=(const atomwrapper &other)
  {
    _a.store(other._a.load());
  }
};

int main(void)
{
  std::vector<atomwrapper<int>> v_a;
  std::atomic<int> a_i(1);
  v_a.push_back(a_i);
  return 0;
}

编辑：正如 Bo Persson 正确指出的那样，包装器执行的复制操作不是原子的。它使您能够复制原子对象，但副本本身不是原子的。这意味着对原子的任何并发访问都不能使用复制操作。这意味着不能同时执行对向量本身的操作（例如添加或删除元素）。

示例：如果一个线程修改了一个原子中存储的值，而另一个线程将新元素添加到向量中，则可能会发生向量重新分配，并且第一个线程修改的对象可能会从向量中的一个位置复制到另一个位置.在这种情况下，第一个线程执行的元素访问和第二个线程触发的复制操作之间将存在数据竞争。

原文由 jogojapan 发布，翻译遵循 CC BY-SA 3.0 许可协议

社区维基
1

在我看来 atomic<T> 没有复制构造函数。据我所知，也不是移动构造函数。

一种解决方法可能是使用 vector<T>::emplace_back() 在向量中就地构造原子。唉，我现在没有 C++11 编译器，否则我会去测试它。

原文由 Kaz Dragon 发布，翻译遵循 CC BY-SA 3.0 许可协议

撰写回答
你尚未登录，登录后可以
  • 和开发者交流问题的细节
  • 关注并接收问题和回答的更新提醒
  • 参与内容的编辑和改进，让解决方法与时俱进
推荐问题