将参数传递给std :: thread包装器 [英] Pass parameters to std::thread wrapper

问题描述

我想实现一个小的线程包装器，该包装器在线程仍处于活动状态或线程已完成其工作时提供信息。为此，我需要将要由线程类执行的函数及其参数传递给另一个函数。我有一个简单的实现方法，该方法应该可以工作，但无法对其进行编译，而且我不知道该怎么做才能使其工作。

I want to implement a small thread wrapper that provides the information if a thread is still active, or if the thread has finished its work. For this I need to pass the function and its parameters to be executed by the thread class to another function. I have a simple implementation that should work but cannot get it to compile, and I can't figure out what to do to make it work.

这是我的代码：

#include <unistd.h>
#include <iomanip>
#include <iostream>
#include <thread>
#include <utility>

class ManagedThread
{
public:
   template< class Function, class... Args> explicit ManagedThread( Function&& f, Args&&... args);
   bool isActive() const { return mActive; }
private:
   volatile bool  mActive;
   std::thread    mThread;
};

template< class Function, class... Args>
   void threadFunction( volatile bool& active_flag, Function&& f, Args&&... args)
{
   active_flag = true;
   f( args...);
   active_flag = false;
}

template< class Function, class... Args>
   ManagedThread::ManagedThread( Function&& f, Args&&... args):
      mActive( false),
      mThread( threadFunction< Function, Args...>, std::ref( mActive), f, args...)
{
}

static void func() { std::cout << "thread 1" << std::endl; }

int main() {
   ManagedThread  mt1( func);
   std::cout << "thread 1 active = " << std::boolalpha << mt1.isActive() << std::endl;
   ::sleep( 1);
   std::cout << "thread 1 active = " << std::boolalpha << mt1.isActive() << std::endl;

   return 0;
}

我得到的编译器错误：

In file included from /usr/include/c++/5/thread:39:0,
                 from prog.cpp:4:
/usr/include/c++/5/functional: In instantiation of 'struct std::_Bind_simple<void (*(std::reference_wrapper<volatile bool>, void (*)()))(volatile bool&, void (&)())>':
/usr/include/c++/5/thread:137:59:   required from 'std::thread::thread(_Callable&&, _Args&& ...) [with _Callable = void (&)(volatile bool&, void (&)()); _Args = {std::reference_wrapper<volatile bool>, void (&)()}]'
prog.cpp:28:82:   required from 'ManagedThread::ManagedThread(Function&&, Args&& ...) [with Function = void (&)(); Args = {}]'
prog.cpp:35:28:   required from here
/usr/include/c++/5/functional:1505:61: error: no type named 'type' in 'class std::result_of<void (*(std::reference_wrapper<volatile bool>, void (*)()))(volatile bool&, void (&)())>'
       typedef typename result_of<_Callable(_Args...)>::type result_type;
                                                             ^
/usr/include/c++/5/functional:1526:9: error: no type named 'type' in 'class std::result_of<void (*(std::reference_wrapper<volatile bool>, void (*)()))(volatile bool&, void (&)())>'
         _M_invoke(_Index_tuple<_Indices...>)
         ^

此处提供实时示例： https://ideone.com/jhBF1q

推荐答案

在错误消息中，您可以看到 void（*）（）与 void（&）（）之差。这是因为 std :: thread的构造函数参数是 std :: decay ed 。

In the error message, you can see the difference void (*)() vs void (&)(). That's because std::thread's constructor parameters are std::decayed.

还添加 std :: ref 到 f ：

template< class Function, class... Args>
   ManagedThread::ManagedThread( Function&& f, Args&&... args):
      mActive( false),
      mThread( threadFunction< Function, Args...>, std::ref(mActive), std::ref(f), std::forward<Args>(args)...)
{
}

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