title: measuring time of multi-threading program
body: <p>I measured time with function clock() but it gave bad results. I mean it gives the same results for program with one thread and for the same program running with OpenMP with many threads. But in fact, I notice with my watch that with many threads program counts faster.
  So I need some wall-clock timer...</p>
  
  <p>My question is: What is better function for this issue? 
  clock_gettime() or mb gettimeofday() ? or mb something else?</p>
  
  <p>if clock_gettime(),then with which clock? CLOCK_REALTIME or CLOCK_MONOTONIC?</p>
  
  <p>using mac os x (snow leopard)</p>