Okay, then I am interpreting things correctly, and my internal timer seems to be consistent with the output of the "time" command that you refer to. To restate, the sum of "real" and "system" time is the pertinent measure. The results you posted then indicate that there is no speedup associated with increasing the number of threads. I am now seeing the same thing...
No, the "real" time is the pertinent measure. I'm saying the program took 4.991s to complete with 2 threads and 9.668s to complete with 1 thread. You might be less confused if you increase the number of loops in operator() so the program is slow enough you can measure the execution time by watching a clock.
Frank, Thank you for your patience with me. I am now understanding this correctly. I did not realize that the clock() function would double- count in multithreaded applications. I took your suggestion of increasing the loop count and that clarified it for me. It appears that I do have scalability after all... James