Skynet 1M Fiber microbenchmark in D

[Biotronic]

On Wednesday, 18 October 2017 at 11:34:57 UTC, Nordlöw wrote:
> Another thing...how should the synchronization between the 
> fibers figure out when the total number of fibers have reached 
> one million?...via an atomic counter fed by reference to the 
> constructor...or are there better ways? Because I do need an 
> atomic reference counter here, right?

This is how I did it:
import core.thread : Fiber;

class MyFiber : Fiber {
     int _depth;
     ulong _index;
     ulong _value;

     this(int depth, ulong index) {
         super(&run);
         _depth = depth;
         _index = index;
     }

     void run() {
         if (_depth == 6) { // 10^6 == 1 million, so stop here.
             _value = _index;
             return;
         }

         _value = 0;
         foreach (i; 0..10) { // Line 23
             auto e = new MyFiber(_depth+1, _index * 10 + i);
             e.call();
             _value += e._value;
         }
     }
}

unittest {
     import std.stdio : writeln;
     import std.datetime.stopwatch : StopWatch, AutoStart;
     auto sw = StopWatch(AutoStart.yes);
     auto a = new MyFiber(0, 0);
     a.call();
     sw.stop();
     assert(a._value == 499999500000);
     writeln(a._value, " after ", sw.peek);
}


> And how do I parallelize this over multiple worker threads? 
> AFAICT fibers are by default all spawned in the same main 
> thread, right?

True. Well, they're not really spawned on any thread - they're 
allocated on the heap, have their own stack, and are run on 
whichever thread happens to invoke their call() method.

I experimented a little bit with parallelism, and the easiest 
definitely is to replace line 23 with this:

foreach (i; taskPool.parallel(10.iota, 1)) {

It seems to make very little difference in terms of run time, 
though. I tried using a mix of these approaches - parallel at low 
depth, basically just to fill up the cores, and serial closer to 
the leaves. The difference is still negligible, so I assume the 
losses are elsewhere.

--
   Biotronic