Re: GThreads and GThreadPool help for a dummy

[Øystein Schønning-Johansen <oystein gnubg org>]

> However back to my code:
>  pool = g_thread_pool_new( my_calc, (gpointer) &common, 8, FALSE, &err );
>
>  for (i = 0; i < n_tot; i++ )
>          g_thread_pool_push( pool, &store[i], &err );
>
>  g_thread_pool_free( pool, FALSE, TRUE );
>
> Why doesn't the g_thread_pool_free function stop and wait for all
> threads. I really specify this to wait (the third parameter is wait_
> and set TRUE). In my understanding this must then be a bug in glib.
> Should I fill in a bug report?

Oh my! What a blunder. I got the parameters in my_calc() swapped. It
then just returned without calculating anything. I fixed this, and it
now seems to work. The documentation on this is a bit unclear, and may
need some polishing, but there is no bug.

Scaling is a bit strange though! I'm working on a box with 2 intel
xeon quad core processors and would therefore expect to get a close
linear speed up from 1 -8 threads. Here's the results:

Threads  execution time [sec]
   1         14.38
   2         11.73
   3          7.59
   4          6.42
   5          5.89
   6         14.91
   7         33.94
   8         35.00

Is it the mutex lock and unlock that gives all this overhead when
there's many threads. I'll try splitting the array and see if that
gives better scalability.

-Øystein