指向成员对象的指针 - 中断线程

Question

这是对a question I got answered yesterday的跟进。

我试图让成员函数中断线程，但我不知道是什么，这些错误是：

[vagrant@localhost projects]$ g++ -o test test.cpp -lpthread 
test.cpp: In instantiation of ‘InterruptibleThread::InterruptibleThread(Function&&, Args&& ...)::<lambda(std::atomic_bool&, std::atomic_bool&, auto:1&&, Args&& ...)> [with auto:1 = void (MyClass::*)(int); Function = void (MyClass::*)(int); Args = {MyClass*, int}; std::atomic_bool = std::atomic<bool>]’: 
/usr/local/include/c++/6.3.0/type_traits:2481:26: required by substitution of ‘template<class _Fn, class ... _Args> static std::__result_of_success<decltype (declval<_Fn>()((declval<_Args>)()...)), std::__invoke_other> std::__result_of_other_impl::_S_test(int) [with _Fn = InterruptibleThread::InterruptibleThread(Function&&, Args&& ...) [with Function = void (MyClass::*)(int); Args = {MyClass*, int}]::<lambda(std::atomic_bool&, std::atomic_bool&, auto:1&&, MyClass*&&, int&&)>; _Args = {std::reference_wrapper<std::atomic<bool> >, std::reference_wrapper<std::atomic<bool> >, void (MyClass::*)(int), MyClass*, int}]’ 
/usr/local/include/c++/6.3.0/type_traits:2492:55: required from ‘struct std::__result_of_impl<false, false, InterruptibleThread::InterruptibleThread(Function&&, Args&& ...) [with Function = void (MyClass::*)(int); Args = {MyClass*, int}]::<lambda(std::atomic_bool&, std::atomic_bool&, auto:1&&, MyClass*&&, int&&)>, std::reference_wrapper<std::atomic<bool> >, std::reference_wrapper<std::atomic<bool> >, void (MyClass::*)(int), MyClass*, int>’ 
/usr/local/include/c++/6.3.0/type_traits:2496:12: required from ‘class std::result_of<InterruptibleThread::InterruptibleThread(Function&&, Args&& ...) [with Function = void (MyClass::*)(int); Args = {MyClass*, int}]::<lambda(std::atomic_bool&, std::atomic_bool&, auto:1&&, MyClass*&&, int&&)>(std::reference_wrapper<std::atomic<bool> >, std::reference_wrapper<std::atomic<bool> >, void (MyClass::*)(int), MyClass*, int)>’ 
/usr/local/include/c++/6.3.0/functional:1365:61: required from ‘struct std::_Bind_simple<InterruptibleThread::InterruptibleThread(Function&&, Args&& ...) [with Function = void (MyClass::*)(int); Args = {MyClass*, int}]::<lambda(std::atomic_bool&, std::atomic_bool&, auto:1&&, MyClass*&&, int&&)>(std::reference_wrapper<std::atomic<bool> >, std::reference_wrapper<std::atomic<bool> >, void (MyClass::*)(int), MyClass*, int)>’ 
/usr/local/include/c++/6.3.0/thread:137:26: required from ‘std::thread::thread(_Callable&&, _Args&& ...) [with _Callable = InterruptibleThread::InterruptibleThread(Function&&, Args&& ...) [with Function = void (MyClass::*)(int); Args = {MyClass*, int}]::<lambda(std::atomic_bool&, std::atomic_bool&, auto:1&&, MyClass*&&, int&&)>; _Args = {std::reference_wrapper<std::atomic<bool> >, std::reference_wrapper<std::atomic<bool> >, void (MyClass::*)(int), MyClass*, int}]’ 
test.cpp:41:33: required from ‘InterruptibleThread::InterruptibleThread(Function&&, Args&& ...) [with Function = void (MyClass::*)(int); Args = {MyClass*, int}]’ 
test.cpp:111:53: required from here 
test.cpp:36:9: error: must use ‘.*’ or ‘->*’ to call pointer-to-member function in ‘fxn (...)’, e.g. ‘(... ->* fxn) (...)’ 
     fxn(forward<Args>(args)...); 

当前代码：

using namespace std; 

class InterruptThreadException {}; 

class InterruptibleThread { 
private: 
    static thread_local atomic_bool* stopRef; 
    static thread_local atomic_bool* pauseRef; 
    atomic_bool stopFlag{false}; 
    atomic_bool pauseFlag{false}; 
    thread thrd; 

public: 
    friend void checkForInterrupt(); 
    template < typename Function, typename... Args > 
    InterruptibleThread(Function&& _fxn, Args&&... _args) 
     : thrd(
       [](atomic_bool& sr, atomic_bool& pr, auto&& fxn, Args&&... args) { 
        stopRef = &sr; 
        pauseRef = &pr; 
        fxn(forward<Args>(args)...); 
       }, 
       ref(stopFlag), 
       ref(pauseFlag), 
       forward<Function>(_fxn), 
       forward<Args>(_args)...) { 
     thrd.detach(); 
    } 
    bool stopping() const { 
     return stopFlag.load(); 
    } 

    void stop() { 
     stopFlag.store(true); 
    } 

    void pause() { 
     pauseFlag.store(true); 
     cout << "setting pause flag: " << pauseFlag.load() << endl; 
    } 

    void start() { 
     pauseFlag.store(false); 
    } 
}; 

void checkForInterrupt() { 
    cout << "Pause flag: " << InterruptibleThread::pauseRef->load() << endl; 
    cout << "Stop flag: " << InterruptibleThread::stopRef->load() << endl; 
    while (InterruptibleThread::pauseRef->load()) { 
     cout << "Paused\n"; 
     this_thread::sleep_for(chrono::seconds(1)); 
    } 
    if (!InterruptibleThread::stopRef->load()) { 
     return; 
    } 
    throw InterruptThreadException(); 
} 

thread_local atomic_bool* InterruptibleThread::stopRef = nullptr; 
thread_local atomic_bool* InterruptibleThread::pauseRef = nullptr; 

void doWork() { 
    int i = 0; 
    try { 
     while (true) { 
      cout << "Checking for interrupt: " << i++ << endl; 
      checkForInterrupt(); 
      this_thread::sleep_for(chrono::seconds(1)); 
     } 
    } catch (InterruptThreadException) { 
     cout << "Interrupted\n\n"; 
    } 
} 

class MyClass { 
private: 
    int myInt; 
    void setInt(int i) { 
     myInt = i; 
    } 

public: 
    MyClass() : myInt(1) { 
    } 
    void myWork(int i); 
    void doWork(); 
}; 

void MyClass::myWork(int i) { 
    setInt(i); 
    cout << "myInt value: " << myInt << endl; 
} 

void MyClass::doWork() { 
    InterruptibleThread t(&MyClass::myWork, this, 666); 
} 

int main() { 
    MyClass mc; 
    mc.doWork(); 

    cout << "Press enter to exit" << endl; 
    getchar(); 
    return 0; 
} 

我试过编译器的建议，得到了之后的错误与fold表达式有关（afaik是C++ 17，我不会使用超过14的任何东西）。任何想法如何让这个工作？

我有一个没有使用lambdas的工作版本，但我真的好奇如何让这与原始代码一起工作。

Answer 1

指向成员函数的指针使用与指向非成员函数或其他函数的指针不同的语法来调用。由于您的案例中的Function是void (MyClass::*)(int)，因此您需要使用语法(object.*fxn)(arg)或(objectPtr->*fxn)(arg)来调用它。

如果你有访问C++ 17层的功能，你可以使用std::invoke均匀拨打不同类型的可调用的：

InterruptibleThread(Function&& _fxn, Args&&... _args) 
    : thrd(
      [](atomic_bool& sr, atomic_bool& pr, auto&& fxn, auto&&... args) { 
       stopRef = &sr; 
       pauseRef = ≺ 
       std::invoke(std::move(fxn), std::move(args)...); 
      }, 
      //... 

注：我改变Args&&... args到auto&&... args因为Args&&...可能会导致问题。

如果您没有访问C++ 17，你可以自己实现invoke相当容易：

template <typename Callable, 
      typename... Args, 
      typename = std::enable_if_t<!std::is_member_function_pointer<Callable>::value>> 
decltype(auto) invoke(Callable&& c, Args&&... args) { 
    return std::forward<Callable>(c)(std::forward<Args>(args)...); 
} 

template <typename T, 
      typename T2, 
      typename Ret, 
      typename... FuncArgs, 
      typename... Args, 
      typename = std::enable_if_t<!std::is_pointer<T2>::value>> 
decltype(auto) invoke(Ret (T::*c)(FuncArgs...), T2&& t, Args&&... args) { 
    return (std::forward<T>(t).*c)(std::forward<Args>(args)...); 
} 

template <typename T, 
      typename T2, 
      typename Ret, 
      typename... FuncArgs, 
      typename... Args> 
decltype(auto) invoke(Ret (T::*c)(FuncArgs...), T2* t, Args&&... args) { 
    return (t->*c)(std::forward<Args>(args)...); 
} 

这并不尽一切std::invoke做，但它的一切，你需要它。