C++ Thread Inside a Class

Question

I'm trying to do a timer class in c++ and I ran into this problem:

I have a start method which creates a thread over a main loop:

    static DWORD WINAPI Timer::MainLoop(LPVOID param)
    {
        Timer* TP = reinterpret_cast<Timer*>(param);
        while (true)
        {

            clock_t now = clock();
            unsigned long timeSinceLastExecution = (unsigned long)(now - TP->lastExecution);
            if (timeSinceLastExecution >= TP->interval && TP->tick_callback != NULL)
            {
                TimerMesssage msg;
                msg.caller = TP;
                msg.timeLastLastCall = timeSinceLastExecution;
                TP->tick_callback(1);
                TP->lastExecution = clock();
            }
        }
        return 0;
    }
    void Timer::Start()
    {
        if (this->mainLoop != NULL)
        {
            this->Stop();
        }
        this->currentValue = 0;
        this->lastExecution = clock();
        mainLoop = CreateThread(NULL, 0, MainLoop, reinterpret_cast<LPVOID>(this), 0, 0);
    }

The problem is that

DWORD WINAPI Timer::MainLoop(LPVOID param)

Is not the same as

DWORD WINAPI MainLoop(LPVOID param)

So I can't use the first declaration to crate a thread with that function. I found that I can set it as static as it is in the example above, but then I loss acces to the private members, do you know which is the right way to do this?

Thank you!

Edit: Sorry, typo!

Answer 1

The idea is to use the static method only as a launchpad for the non-static member:

static DWORD WINAPI Timer::MainLoop(LPVOID param)
{
    Timer* TP = reinterpret_cast<Timer*>(param);
    return TP->MainLoop();
}

// Non-static method
DWORD Timer::MainLoop()
{
    while (true)
    {
        clock_t now = clock();
        unsigned long timeSinceLastExecution = (unsigned long)(now - lastExecution);
        if (timeSinceLastExecution >= interval && tick_callback != NULL)
        {
            TimerMesssage msg;
            msg.caller = this;
            msg.timeLastLastCall = timeSinceLastExecution;
            tick_callback(1);
            lastExecution = clock();
        }
    }
    return 0;
}

void Timer::Start()
{
    if (this->mainLoop != NULL)
    {
        this->Stop();
    }
    this->currentValue = 0;
    this->lastExecution = clock();
    mainLoop = CreateThread(NULL, 0, MainLoop, reinterpret_cast<LPVOID>(this), 0, 0);
}