c++ - 包装 std::thread 调用函数

Question

我想控制线程，所以每个新发出的线程都会先通过我的代码。
这样，在下面的示例中使用 runThread() 发出的每个新线程将首先调用下面的函数 runInnerThread()(我在其中进行了某种初始化)并且然后调用所需的函数。

我试过这样写:

#include <iostream>
#include <thread>

template<typename _Callable, typename... _Args>
void runThreadInner(_Callable&& __f, _Args&&... __args) {
    // My initializations...
    __f(__args...);
    // My finishing...
};

template<typename _Callable, typename... _Args>
bool runThread(_Callable&& __f, _Args&&... __args) {
    std::thread t(std::bind(&runThreadInner,
                            std::forward<_Callable>(__f),
                            std::forward<_Args>(__args)...));
}

int main() {
    runThread([]() {
        std::cout << std::this_thread::get_id() << "Threading...\n";
    });
    return 0;
}

我从编译器那里得到一个错误，它提示推导 runThreadInner() 模板

main.cpp: In instantiation of ‘bool runThread(_Callable&&, _Args&& ...) [with _Callable = main()::__lambda0; _Args = {}]’:
main.cpp:43:3:   required from here
main.cpp:27:38: error: no matching function for call to ‘bind(<unresolved overloaded function type>, main()::__lambda0)’
        std::forward<_Args>(__args)...));
                                      ^
main.cpp:27:38: note: candidates are:
In file included from /usr/include/c++/4.8/memory:79:0,
                 from main.cpp:2:
/usr/include/c++/4.8/functional:1655:5: note: template<class _Func, class ... _BoundArgs> typename std::_Bind_helper<std::__or_<std::is_integral<typename std::decay<_Tp>::type>, std::is_enum<typename std::decay<_Tp>::type> >::value, _Func, _BoundArgs ...>::type std::bind(_Func&&, _BoundArgs&& ...)
     bind(_Func&& __f, _BoundArgs&&... __args)
     ^
/usr/include/c++/4.8/functional:1655:5: note:   template argument deduction/substitution failed:
main.cpp:27:38: note:   couldn't deduce template parameter ‘_Func’
        std::forward<_Args>(__args)...));
                                      ^
In file included from /usr/include/c++/4.8/memory:79:0,
                 from main.cpp:2:
/usr/include/c++/4.8/functional:1682:5: note: template<class _Result, class _Func, class ... _BoundArgs> typename std::_Bindres_helper<_Result, _Func, _BoundArgs>::type std::bind(_Func&&, _BoundArgs&& ...)
     bind(_Func&& __f, _BoundArgs&&... __args)
     ^
/usr/include/c++/4.8/functional:1682:5: note:   template argument deduction/substitution failed:
main.cpp:27:38: note:   couldn't deduce template parameter ‘_Result’
        std::forward<_Args>(__args)...));

我尝试显式定义模板，但没有成功:

template<typename _Callable, typename... _Args>
bool runThread(_Callable&& __f, _Args&&... __args) {
    std::thread t(std::bind(&runThreadInner<_Callable, _Args>,
                            std::forward<_Callable>(__f),
                            std::forward<_Args>(__args)...));
}

这可能吗？谢谢。

Answer 1

简单易行。

#include <thread>
#include <iostream>

template<typename Callable, typename... Args>
void runThreadInner(Callable&& f, Args&&... args) {
    // My initializations...
    f(args...);
    // My finishing...
};

template<typename Callable, typename... Args>
std::thread runThread(Callable&& f, Args&&... args) {
    std::thread t(&runThreadInner<Callable, Args...>, 
         std::forward<Callable> (f), std::forward<Args>(args)...);
    return t;
}
int main() {
    auto t = runThread([]() {
        std::cout << "Threading..." << std::endl;
    });
    t.join();
    return 0;
}