我正在尝试从std :: thread获取std :: future，似乎唯一的方法（？）是使用std :: packaged_task。那么，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。我尝试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> ]
我很感激任何帮助！谢谢
答案 0 :(得分：1)
你有几个问题：
您没有为bind中的预期参数指定占位符。它应该是std::bind(&test::fthread, this, std::placeholders::_1)，或者更好[this](int i){ return fthread(i); }。
当您只是直接移动reference_wrapper：std::thread或传递packaged_task时，您正试图将std::thread a(std::move(task), ...移至reference_wrapper }按值：std::thread a(std::ref(task), ....。如果您将packaged_task移动到主题中，请确保在移动之前提取其future。
当std::thread只接受一个参数时，将两个参数--5和1 - 传递给packaged_task构造函数。通过检查main中的测试，您希望该参数为b：std::thread a(std::move(task), b);
您不加入或分离该主题，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();
}
在语义上与：
相同int run(int b)
{
return std::async(std::launch::async, [this,b]{ return fthread(b); }).get();
}
<强> Demo at Coliru