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std::thread から std::future を取得しようとしていますが、そうする唯一の方法 (?) は std::packaged_task を使用することです。さて、さらに std::thread で呼び出したい関数はクラスメンバ関数です。このスレッドUse member function in std::packaged_task を見つけることができましたが、 std::thread の代わりに std::async を使用しています。その投稿に基づいて何かをコンパイルしようとしましたが、ここでこのコードをコンパイルしようとすると:

#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;
}

MSVC 2013 で次のエラーが発生します。

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>          ]

助けていただければ幸いです！ありがとうございました

4

1 に答える 1

2

いくつかの問題があります:

  • で予想される引数のプレースホルダーを指定しませんbind。それはあるべきかstd::bind(&test::fthread, this, std::placeholders::_1)、それ以上です[this](int i){ return fthread(i); }。

  • 単純に直接移動する必要があるときにareference_wrapperを移動しようとしています:または値によって a を渡します: 。をねじ山に移動する場合は、移動する前に必ず抜き出してください。std::threadpackaged_taskstd::thread a(std::move(task), ...reference_wrapperstd::thread a(std::ref(task), ....packaged_taskfuture

  • が引数を 1 つしかとらない場合、 2 つの引数 (5 と 1) をstd::threadコンストラクターに渡します。packaged_taskのテストの調査から、mainその引数を次のようにする必要がありますb。std::thread a(std::move(task), b);

  • スレッドに参加したり切り離したりしないため、そのデストラクタは を呼び出しますstd::terminate。

これらすべてに対処すると、次の結果が得られます。

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();
}

これは意味的に次のものと同じです:

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

Coliruでのデモ

于 2014-10-24T18:32:31.143 に答える