Fold in Parallelism

[Russel Winder]

Ali,

Shouldn't this be a pull request for std.parallelism to be extended? 

If the function is in std.algorithm, then people should not have to
write it for themselves in std.parallelism.


On Mon, 2017-12-18 at 11:01 -0800, Ali Çehreli via Digitalmars-d-learn
wrote:
> 
[…]
> > Hi Ali,
> > 
> >    Thank you very much, may we know if possible as to when this
> > would be 
> > added.
> > 
> > From,
> > Vino.B
> 
> The implementation is almost a copy+paste from std.algorithm.fold.
> You 
> can simply copy the following fold template to your project and
> start 
> using it:
> 
> import std.parallelism;
> import std.stdio;
> 
> int adder(int result, int element) {
>      return result + element;
> }
> 
> template fold(fun...)
> if (fun.length >= 1)
> {
>      import std.parallelism : TaskPool;
>      auto fold(R, S...)(TaskPool t, R r, S seed)
>      {
>          static if (S.length < 2)
>          {
>              return t.reduce!fun(seed, r);
>          }
>          else
>          {
>              import std.typecons : tuple;
>              return t.reduce!fun(tuple(seed), r);
>          }
>      }
> }
> 
> unittest {
>      import std.range;
> 
>      const N = 10_000;
>      const expected = N * (N - 1) / 2;
> 
>      foreach (numThreads; 1 .. 100) {
>          auto t = new TaskPool(numThreads);
>          const result = t.fold!adder(N.iota);
>          assert(result == expected);
>          t.finish();
>      }
> }
> 
> void main() {
> }
> 
> If you want to provide an explicit seed value, good luck making sense
> of 
> how it affects the final result. :) (The documentation of 
> TaskPool.reduce explains it but I find it too involved to
> understand.)
> 
> Ali
-- 
Russel.
===========================================
Dr Russel Winder      t: +44 20 7585 2200
41 Buckmaster Road    m: +44 7770 465 077
London SW11 1EN, UK   w: www.russel.org.uk
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