EmptyCrate Software. Travel. Stuff.

I would put to use RAII management of my thread: (this is covered in Multithreaded C++: Part 3: RAII And Threads)

I would update the destructor of this class to automatically shutdown the thread when it is called:

 ~threaded_class()
    {
      //Warning this stop call will fail if stop had been called previously, 
      //see Multithreaded C++: Part 3: RAII And Threads for a more robust
      //example
      stop(); 
    }

Then I would place the object at the appropriate scope so that its lifetime was what I needed it to be.

int main()
{
  threaded_class fibcalc;
 
  //Do stuff
  doSomethingWithFibCalc(fibcalc);
 
  //When main() exits fibcalc is popped from the stack, its destructor is called and the
  //Thread is automatically stopped and joined.
}

I feel compelled to point out that this example is mostly academic. It's a fun way to illustrate the use of boost threads and mutexes, but it's a very inefficient way of calculating the Fibonacci sequence. A method utilising a cache or even calculating the sequence statically at compile time is a much better option.