[erlang-questions] Parallel Shootout & a style question

[Mats Cronqvist]

Kevin Scaldeferri wrote:
> First,  I don't think it's been mentioned here, but the language  
> benchmarks shootout finally got some multi-core hardware!
>
> http://shootout.alioth.debian.org/u64q/
>
> At the moment, though, there are almost no submissions of parallelized  
> code, so the results are about the same as the existing hardware.
>
> I figured (slightly spurred on by the Haskell community) that we  
> should try to submit some modified versions that actually use the  
> multiple cores.  So, for example, I made a slight change to the binary  
> trees code and got a nearly 2x speedup on my 2-core machine.  In doing  
> so, I did run into one of those little things that I've never really  
> known the preferred approach for.  My modified function looks like this:
>
> depthLoop(D,M) when D > M -> ok;
> depthLoop(D,M) ->
>      Self = self(),
>      spawn(fun() ->
>                    N = 1 bsl (M-D + ?Min),
>                    io:fwrite("~w\t trees of depth ~w\t check: ~w~n",
>                              [ 2*N, D, sumLoop(N,D,0) ]),
>                    Self ! done
>            end),
>      depthLoop (D+2,M),
>      receive done -> done end.
>
>
>   
  i'm partial to the monitor-exit idiom. gets rid of the Self for one thing.

  mats

 depthLoop(D,M) when D > M -> ok;
 depthLoop(D,M) ->
   erlang:spawn_monitor(fun()-> slave(D, M) end),
   depthLoop (D+2,M),
   receive {'DOWN',_,_,_,done} -> done end.

 slave(D, M) ->
   N = 1 bsl (M-D + ?Min),
   io:fwrite("~w\t trees of depth ~w\t check: ~w~n",
         [ 2*N, D, sumLoop(N,D,0) ]),
   exit(done).