Here's a typical implementation of a clock:

class Clock {  public:    Clock() : offset_( 0 ) {}    double time();    void adjustTime( double dt );  private:    double offset_;};double Clock::time() {  struct timeval tv;  gettimeofday( &tv, 0 );  return (double)tv.tv_sec + 1e-6*(double)tv.tv_usec - offset_;}void Clock::adjustTime( double dt ) {  offset_ -= dt;}

At start-up, the server will call clock->adjustTime(-clock->time()) to re-set it to 0. serverLogicalTime() would return clock->time() after that adjustment.

On Windows, you typically use QueryPerformanceCounter() instead -- although it has some bugs. In fact, all the PC hardware timers have bugs -- see this article.