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我正在尝试从 std::thread 获取 std::future ，似乎唯一的方法（？）这样做是使用 std::packaged_task 。嗯，另外，我想在std::thread中调用的函数是一个类成员函数。我可以找到这个线程Use member function in std::packaged_task但他们使用 std::async 而不是 std::thread。我试图根据该帖子进行编译，但是当我尝试在此处编译此代码时：

#include <iostream>
#include <future>
#include <thread>

class test
{
    int fthread(int b)
    {
        return a + b;
    }

    int a;
public:
    test(int a_) : a(a_) {}

    int run(int b)
    {
        std::packaged_task<int(int)>
            task(std::bind(&test::fthread, this));

        //std::thread a(std::move(std::ref(task)), 5, 1);
        std::thread th(std::move(std::ref(task)), b);//<--Edit typo...

        std::future<int> fut = task.get_future();

        return fut.get();
    }
};

int main()
{
    int a = 5, b = 1;
    test t(a);

    int c = t.run(b);

    if (c != (a+b))
        return 1;
    return 0;
}

我在 MSVC 2013 上收到以下错误：

error C2064: term does not evaluate to a function taking 1 arguments
class does not define an 'operator()' or a user defined conversion operator to a pointer-to-function or reference-to-function that takes appropriate number of arguments

1>          C:\MesProgs\Microsoft Visual Studio 12.0\VC\include\functional(1137) : see reference to function template instantiation 'int std::_Bind<true,int,std::_Pmf_wrap<int (__cdecl test::* )(int),int,test,int>,test *const >::_Do_call<_Ty,0x00>(std::tuple<_Ty &>,std::_Arg_idx<0x00>)' being compiled
1>          with
1>          [
1>              _Ty=int
1>          ]
1>          C:\MesProgs\Microsoft Visual Studio 12.0\VC\include\functional(1137) : see reference to function template instantiation 'int std::_Bind<true,int,std::_Pmf_wrap<int (__cdecl test::* )(int),int,test,int>,test *const >::_Do_call<_Ty,0x00>(std::tuple<_Ty &>,std::_Arg_idx<0x00>)' being compiled
1>          with
1>          [
1>              _Ty=int
1>          ]
1>          C:\MesProgs\Microsoft Visual Studio 12.0\VC\include\xrefwrap(283) : see reference to function template instantiation 'int std::_Bind<true,int,std::_Pmf_wrap<int (__cdecl test::* )(int),int,test,int>,test *const >::operator ()<_Ty>(_Ty &&)' being compiled
1>          with
1>          [
1>              _Ty=int
1>          ]
1>          C:\MesProgs\Microsoft Visual Studio 12.0\VC\include\xrefwrap(283) : see reference to function template instantiation 'int std::_Bind<true,int,std::_Pmf_wrap<int (__cdecl test::* )(int),int,test,int>,test *const >::operator ()<_Ty>(_Ty &&)' being compiled
1>          with
1>          [
1>              _Ty=int
1>          ]
1>          C:\MesProgs\Microsoft Visual Studio 12.0\VC\include\functional(228) : see reference to function template instantiation '_Ret std::_Callable_obj<std::_Bind<true,_Ret,std::_Pmf_wrap<int (__cdecl test::* )(int),int,test,int>,test *const >,false>::_ApplyX<_Rx,_Ty>(_Ty &&)' being compiled
1>          with
1>          [
1>              _Ret=int
1>  ,            _Rx=int
1>  ,            _Ty=int
1>          ]
1>          C:\MesProgs\Microsoft Visual Studio 12.0\VC\include\functional(228) : see reference to function template instantiation '_Ret std::_Callable_obj<std::_Bind<true,_Ret,std::_Pmf_wrap<int (__cdecl test::* )(int),int,test,int>,test *const >,false>::_ApplyX<_Rx,_Ty>(_Ty &&)' being compiled
1>          with
1>          [
1>              _Ret=int
1>  ,            _Rx=int
1>  ,            _Ty=int
1>          ]
1>          C:\MesProgs\Microsoft Visual Studio 12.0\VC\include\functional(226) : while compiling class template member function 'int std::_Func_impl<_MyWrapper,_Alloc,_Ret,int>::_Do_call(int &&)'
1>          with
1>          [
1>              _Alloc=std::allocator<std::_Func_class<int,int>>
1>  ,            _Ret=int
1>          ]
1>          C:\MesProgs\Microsoft Visual Studio 12.0\VC\include\functional(495) : see reference to class template instantiation 'std::_Func_impl<_MyWrapper,_Alloc,_Ret,int>' being compiled
1>          with
1>          [
1>              _Alloc=std::allocator<std::_Func_class<int,int>>
1>  ,            _Ret=int
1>          ]
1>          C:\MesProgs\Microsoft Visual Studio 12.0\VC\include\functional(396) : see reference to function template instantiation 'void std::_Func_class<_Ret,int>::_Do_alloc<_Myimpl,_Ty,_Alloc>(_Fty &&,_Alloc)' being compiled
1>          with
1>          [
1>              _Ret=int
1>  ,            _Ty=std::_Bind<true,int,std::_Pmf_wrap<int (__cdecl test::* )(int),int,test,int>,test *const >
1>  ,            _Alloc=std::allocator<std::_Func_class<int,int>>
1>  ,            _Fty=std::_Bind<true,int,std::_Pmf_wrap<int (__cdecl test::* )(int),int,test,int>,test *const >
1>          ]
1>          C:\MesProgs\Microsoft Visual Studio 12.0\VC\include\functional(396) : see reference to function template instantiation 'void std::_Func_class<_Ret,int>::_Do_alloc<_Myimpl,_Ty,_Alloc>(_Fty &&,_Alloc)' being compiled
1>          with
1>          [
1>              _Ret=int
1>  ,            _Ty=std::_Bind<true,int,std::_Pmf_wrap<int (__cdecl test::* )(int),int,test,int>,test *const >
1>  ,            _Alloc=std::allocator<std::_Func_class<int,int>>
1>  ,            _Fty=std::_Bind<true,int,std::_Pmf_wrap<int (__cdecl test::* )(int),int,test,int>,test *const >
1>          ]
1>          C:\MesProgs\Microsoft Visual Studio 12.0\VC\include\functional(385) : see reference to function template instantiation 'void std::_Func_class<_Ret,int>::_Reset_alloc<_Ty,std::allocator<std::_Func_class<_Ret,int>>>(_Fty &&,_Alloc)' being compiled
1>          with
1>          [
1>              _Ret=int
1>  ,            _Ty=std::_Bind<true,int,std::_Pmf_wrap<int (__cdecl test::* )(int),int,test,int>,test *const >
1>  ,            _Fty=std::_Bind<true,int,std::_Pmf_wrap<int (__cdecl test::* )(int),int,test,int>,test *const >
1>  ,            _Alloc=std::allocator<std::_Func_class<int,int>>
1>          ]
1>          C:\MesProgs\Microsoft Visual Studio 12.0\VC\include\functional(385) : see reference to function template instantiation 'void std::_Func_class<_Ret,int>::_Reset_alloc<_Ty,std::allocator<std::_Func_class<_Ret,int>>>(_Fty &&,_Alloc)' being compiled
1>          with
1>          [
1>              _Ret=int
1>  ,            _Ty=std::_Bind<true,int,std::_Pmf_wrap<int (__cdecl test::* )(int),int,test,int>,test *const >
1>  ,            _Fty=std::_Bind<true,int,std::_Pmf_wrap<int (__cdecl test::* )(int),int,test,int>,test *const >
1>  ,            _Alloc=std::allocator<std::_Func_class<int,int>>
1>          ]
1>          C:\MesProgs\Microsoft Visual Studio 12.0\VC\include\functional(671) : see reference to function template instantiation 'void std::_Func_class<_Ret,int>::_Reset<_Ty>(_Fty &&)' being compiled
1>          with
1>          [
1>              _Ret=int
1>  ,            _Ty=std::_Bind<true,int,std::_Pmf_wrap<int (__cdecl test::* )(int),int,test,int>,test *const >
1>  ,            _Fty=std::_Bind<true,int,std::_Pmf_wrap<int (__cdecl test::* )(int),int,test,int>,test *const >
1>          ]
1>          C:\MesProgs\Microsoft Visual Studio 12.0\VC\include\functional(671) : see reference to function template instantiation 'void std::_Func_class<_Ret,int>::_Reset<_Ty>(_Fty &&)' being compiled
1>          with
1>          [
1>              _Ret=int
1>  ,            _Ty=std::_Bind<true,int,std::_Pmf_wrap<int (__cdecl test::* )(int),int,test,int>,test *const >
1>  ,            _Fty=std::_Bind<true,int,std::_Pmf_wrap<int (__cdecl test::* )(int),int,test,int>,test *const >
1>          ]
1>          C:\MesProgs\Microsoft Visual Studio 12.0\VC\include\future(588) : see reference to function template instantiation 'std::function<_Ret (int)>::function<_Ty>(_Fx &&)' being compiled
1>          with
1>          [
1>              _Ret=int
1>  ,            _Ty=std::_Bind<true,int,std::_Pmf_wrap<int (__cdecl test::* )(int),int,test,int>,test *const >
1>  ,            _Fx=std::_Bind<true,int,std::_Pmf_wrap<int (__cdecl test::* )(int),int,test,int>,test *const >
1>          ]
1>          C:\MesProgs\Microsoft Visual Studio 12.0\VC\include\future(588) : see reference to function template instantiation 'std::function<_Ret (int)>::function<_Ty>(_Fx &&)' being compiled
1>          with
1>          [
1>              _Ret=int
1>  ,            _Ty=std::_Bind<true,int,std::_Pmf_wrap<int (__cdecl test::* )(int),int,test,int>,test *const >
1>  ,            _Fx=std::_Bind<true,int,std::_Pmf_wrap<int (__cdecl test::* )(int),int,test,int>,test *const >
1>          ]
1>          C:\MesProgs\Microsoft Visual Studio 12.0\VC\include\future(1742) : see reference to function template instantiation 'std::_Packaged_state<_Ret (int)>::_Packaged_state<_Ty>(_Fty2 &&)' being compiled
1>          with
1>          [
1>              _Ret=int
1>  ,            _Ty=std::_Bind<true,int,std::_Pmf_wrap<int (__cdecl test::* )(int),int,test,int>,test *const >
1>  ,            _Fty2=std::_Bind<true,int,std::_Pmf_wrap<int (__cdecl test::* )(int),int,test,int>,test *const >
1>          ]
1>          C:\MesProgs\Microsoft Visual Studio 12.0\VC\include\future(1744) : see reference to function template instantiation 'std::_Packaged_state<_Ret (int)>::_Packaged_state<_Ty>(_Fty2 &&)' being compiled
1>          with
1>          [
1>              _Ret=int
1>  ,            _Ty=std::_Bind<true,int,std::_Pmf_wrap<int (__cdecl test::* )(int),int,test,int>,test *const >
1>  ,            _Fty2=std::_Bind<true,int,std::_Pmf_wrap<int (__cdecl test::* )(int),int,test,int>,test *const >
1>          ]
1>          main.cpp(51) : see reference to function template instantiation 'std::packaged_task<int (int)>::packaged_task<std::_Bind<true,int,std::_Pmf_wrap<int (__cdecl test::* )(int),int,test,int>,test *const >>(_Fty2 &&)' being compiled
1>          with
1>          [
1>              _Fty2=std::_Bind<true,int,std::_Pmf_wrap<int (__cdecl test::* )(int),int,test,int>,test *const >
1>          ]
1>          main.cpp(51) : see reference to function template instantiation 'std::packaged_task<int (int)>::packaged_task<std::_Bind<true,int,std::_Pmf_wrap<int (__cdecl test::* )(int),int,test,int>,test *const >>(_Fty2 &&)' being compiled
1>          with
1>          [
1>              _Fty2=std::_Bind<true,int,std::_Pmf_wrap<int (__cdecl test::* )(int),int,test,int>,test *const >
1>          ]

我会很感激任何帮助！谢谢

4

1 回答 1

2

你有几个问题：

  • 您没有在bind. 应该是std::bind(&test::fthread, this, std::placeholders::_1)，或者更好[this](int i){ return fthread(i); }。

  • 当您应该直接移动reference_wrappera或通过值传递 a 时，您正试图移动 a 。如果将其移动到线程中，请务必在移动之前将其提取出来。std::threadpackaged_taskstd::thread a(std::move(task), ...reference_wrapperstd::thread a(std::ref(task), ....packaged_taskfuture

  • 当只有一个参数时，您将两个参数 - 5 和 1 - 传递给std::thread构造函数。packaged_task通过对 中的测试的检查main，您希望该论点是b：std::thread a(std::move(task), b);

  • 您不加入或分离线程，因此其析构函数将调用std::terminate.

解决所有这些结果：

int run(int b)
{
    std::packaged_task<int(int)>
            task(std::bind(&test::fthread, this, std::placeholders::_1));
    std::future<int> fut = task.get_future();

    std::thread(std::move(task), b).join();

    return fut.get();
}

这在语义上等同于：

int run(int b)
{
    return std::async(std::launch::async, [this,b]{ return fthread(b); }).get();
}

在 Coliru 演示

于 2014-10-24T18:32:31.143 回答