Question

I have the following:

   class DThread
   {
      virtual void run()=0;

    _beginthreadex(NULL,0,tfunc,this,0,&m_UIThreadID);  // class itself being passed as param to thread function...

    static unsigned int __stdcall tfunc(void* thisptr) 
        {
            static_cast<DThread*>(thisptr)->run();
            return 0;
        }

//other stuff

}

The run function is implemented in a derived class.

Why is the function that’s being called in the thread being called through a cast this pointer? Is this good practise?

Can’t it just be called directly?

The actual function needing to run is in the derived class.

My question is

Answer 1

Most platform-level thread APIs are bare-bones C and take a plain pointer to function to run in new thread. This means in C++ that function has to be either a free function or a static member. Neither of these give access to any class instance. The workaround for building statefull thread classes is to exploit additional “pass-through” argument of the thread creation call (that’s usually a pointer that is later passed to the function executed in the new thread) and give it a pointer to the class itself, i.e. this. The static function could then call a [virtual] member, say run() or something like that.