Re: Does Ada tasking profit from multi-core cpus?

[Jeffrey Creem <jeff@thecreems.com>]

Colin Paul Gloster wrote:
> Tom Moran posted on Mon, 05 Mar 2007 23:33:31 -0600:
>           
> "> 1. Whether protected object's functions are indeed executed concurrently
>> when come from the tasks running on different cores?
> 
>    A quick test with a single protected object containing a single,
> long-duration, function appears to have just one call of the function
> active at a time, even if the function is called from two different tasks.
> 
>   global_flag : integer := 0;
> 
>   protected body pt is
>     function f(id : integer) return natural is
>       change_count : natural := 0;
>     begin
>       global_flag := id;
>       for i in 1 .. 10_000_000 loop
>         if global_flag /= id then
>           change_count := change_count;
>           global_flag := id;
>         end if;
>       end loop;
>       return change_count;
>     end f;
>   end pt;
> 
> One task calls pt.f(id=>1) and the other calls pt.f(id=>2).  They both get
> a result of zero back from their function call.  This was with Gnat 3.15p
> Windows 2000 on a dual core Pentium.  If I change it from a single
> protected object to two instances of a protected type, then the function
> calls are overlapped and return non-zero results.
> 
> [..]"
> 
> 
> I am grateful to Thomas Moran for such a brilliant demonstration of
> how poor the so-called GNU Ada Translator can be.


I don't think this proves that the two tasks are not overlapping. It 
probably proves that if you specifically write broken code it is indeed 
sometimes broken.