C++ mutiple joining thread

I want to define two of std::thread in my function, than join() them multiple times in a loop. I googled for it but I only found questions like "C++ multiple joining on the same function".

Code:

void Func()
{
    thread t1 {ThreadFunc1};
    thread t2 {ThreadFunc2};
    while(true)
    {
        if(t1.joinable()) 
            t1.join();
        if(t2.joinable()) 
            t2.join();
        // Do someting else.
    }
}

As I expected, the threads are running just once at the first cycle. I want to make it very fast. I wonder if I can reset them or 'make it joinable' again. Do you have any solutions?

Thanks!