Is it safe for multiple threads to call the same function?

Question

Is it safe to for example do:

void AddTwo(int &num)
{
  num +=2;
}


void ThreadProc(lpvoid arg)
{
AddTwo((int)arg);

}

Would it be saf

Answer 1

The function itself is safe to call. It becomes dangerous if they're all trying to operate on the same variable.