C++: A threaded timer

/* copyright Benjamin Collins 2006
 * please contact for licensing information */
#include <iostream>
 
#include <boost/thread/condition.hpp>
#include <boost/thread/mutex.hpp>
#include <boost/thread/recursive_mutex.hpp>
#include <boost/thread/thread.hpp>
#include <boost/thread/xtime.hpp>
 
typedef boost::recursive_mutex::scoped_lock rt_slock;
 
namespace
{
  bool _start = false;
  boost::recursive_mutex start_mutex;
  boost::condition start_condition;
 
  bool started()
  {
    return _start;
  }
  void start()
  {
    rt_slock lk(start_mutex);
    _start = true;
  }
  void stop()
  {
    rt_slock lk(start_mutex);
    _start = false;
  }
}
 
class timer_func
{
public:
  timer_func()
  {
    boost::xtime_get(&_time, boost::TIME_UTC);
  }
 
  void operator()()
  {
    while(true)
      {
        {
          rt_slock lk(start_mutex);
          start_condition.wait(lk);
        }
 
        while(started())
          {
            _time.sec += 1;
            boost::thread::sleep(_time);
            if(started())
              std::cout << "." << std::flush;
          }
      }
  }
 
private:
  boost::xtime _time;
};
 
int main()
{
  timer_func timer;
  boost::thread t(timer);
  while(true)
    {
      if(!started())
        {
          std::cout << "press enter to start: " << std::flush;
          std::cin.get();
          start();
          std::cout << "starting" << std::endl;
          start_condition.notify_one();
        }
      else
        {
          std::cout << "press enter to stop: " << std::flush;
          std::cin.get();
          stop();
          std::cout << "stopping" << std::endl;
        }
    }
 
  return 0;
}