Storing an std::thread object as a class member

Question

I'm trying to keep an std::thread object inside a class.

class GenericWindow
{
    public:
        void Create()
        {
            // ...
            MessageLoopThread = std::thread(&GenericWindow::MessageLoop, *this);
        }
    private:
        std::thread MessageLoopThread;
        void GenericWindow::Destroy()   // Called from the destructor
        {
            SendMessageW(m_hWnd, WM_DESTROY, NULL, NULL);
            UnregisterClassW(m_ClassName.c_str(), m_WindowClass.hInstance);
            MessageLoopThread.join();
        } 
        void GenericWindow::MessageLoop()
        {
            MSG Msg;
            while (GetMessageW(&Msg, NULL, 0, 0))
            {
                if (!IsDialogMessageW(m_hWnd, &Msg))
                {
                    TranslateMessage(&Msg);
                    DispatchMessageW(&Msg);
                }
            }
        }
};      // LINE 66

Error given:

[Line 66] Error C2248: 'std::thread::thread' : cannot access private member declared in class 'std::thread'

This error message doesn't help me, I'm not trying to access any private member of the std::thread class.

What is wrong in my code? How do I fix it?

Answer 1

On this line:

MessageLoopThread = std::thread(&GenericWindow::MessageLoop, *this);

You are passing *this by value to the std::thread constructor, which will try to make a copy to pass to the newly spawned thread. *this is of course noncopyable, since it has a std::thread member. If you want to pass a reference, you need to put it in a std::reference_wrapper:

MessageLoopThread = std::thread(&GenericWindow::MessageLoop,
                                std::ref(*this));