Function Pointer Not Working

[Marcone via Digitalmars-d-learn]

// Function threadingw()
void threadingw(HWND hwn, void delegate() fun) nothrow {
        try {
                // Function _fun()
                extern(Windows)
                uint _fun(void * arg){
			(*(cast(void delegate()*) arg))(); // Do not show "Hello 
World!" :(
                        return 0;
                }
                CreateThread(null, 0, &_fun, &fun, 0, null);
        } catch(Throwable){}
}
void main(){
        null.threadingw({writeln("Hello World!");});

}