-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On Wednesday 14 May 2008 16:36 pm, Frank Mori Hess wrote:
On Wednesday 14 May 2008 16:24 pm, James Sutherland wrote:
Phil, Thank you for your suggestions - I am hunting in the dark here...
for( int itask=0; itask<nTasks; ++itask ){ boost::thread_group threads; for( int i=0; i<nThreads; ++i ){ threads.create_thread( MyStruct(itask++ + 100) ); } threads.join_all(); }
Did you really want the ++itask in the first for() ? Isn't it being incremented enough in the create_thread line?
This was intentional. This highly contrived example creates a fixed amount of work (nTasks) and divides them up among nThreads threads. As a thread takes a task, I increment itask. Strange, I know...
No, if you also increment itask in the outer loop, you are doing fewer tasks when nThreads is smaller. Although, what I said before about creating more threads than you think was wrong (I misunderstood your program).
Also, your program appears to output the cpu time spent on the program, not the real time it took. What I see (after fixing the itask increment): $time ./a.out Executing 12 tasks using 1 threads. time: 9.64 real 0m9.668s user 0m9.641s sys 0m0.004s $ time ./a.out Executing 12 tasks using 2 threads. time: 9.91 real 0m4.991s user 0m9.909s sys 0m0.012s - -- Frank -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.6 (GNU/Linux) iD8DBQFIK05B5vihyNWuA4URAkAbAKCWSBb0kLmh61BLesNiBRCDm8rdhACgp0Wi SR1/9LEMLdcr8K4eSOeOA+o= =mGQ4 -----END PGP SIGNATURE-----