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

[Colin Paul Gloster <Colin_Paul_Gloster@ACM.org>]

Tom Moran posted on Mon, 05 Mar 2007 23:33:31 -0600:

"[..]

  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.

[..]"


Tom Moran posted on Tue, 06 Mar 2007 12:58:34 -0600:
"[..]

  Sorry.  That's a typo in trying to pretty-up the code for posting.
The actual code that ran was:
        if pt_flag /= id then
          result := result+1;
          pt_flag := id;
        end if;
which, as you see, does indeed do an increment.  Which is why

> > 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.

[..]"


Was the return statement
      return change_count;
or some other item whose value was never changed according to the
semantics of Ada as in your original post in which case the behavior
is still not valid Ada, or did the return statement return something
like result or pt_flag?

Regards,
Colin Paul Gloster