How can I use TTask.WaitForAny from the new threading library?

Question

In an attempt to use the threading library in Delphi to calculate tasks in parallel and using TTask.WaitForAny() to get the first calculated result, an exceptio

Answer 1

Here is an example using TParallel.For to stop the execution when an answer is produced. It uses the TParallel.LoopState to signal other members of the parallel for loop. By using the .Stop signal, all current and pending iterations should stop. Current iterations should check loopState.Stopped.

procedure Parallel3(CS: TCriticalSection);
var
  Ticks: Cardinal;
  i,ix: Integer;  // variables that are only touched once in the Parallel.For loop
begin
  i := 0;
  Ticks := TThread.GetTickCount;
  TParallel.For(1,WorkerCount,
    procedure(index:Integer; loopState: TParallel.TLoopState)
    var
      k,l,m: Integer;
    begin
      // Do something complex
      k := (1000 - index)*1000;
      for l := 0 to Pred(k) do
        m := k div 1000;
      // If criteria to stop fulfilled:
      CS.Enter;
      Try
        if loopState.Stopped then // A solution was already found
          Exit;
        loopState.Stop;  // Signal 
        Inc(i);
        ix := index;
      Finally
        CS.Leave;
      End;
    end
  );
  Ticks := TThread.GetTickCount - Ticks;
  WriteLn('Parallel time ' + Ticks.ToString + ' ticks', ' i :',i,' index:',ix);
end;

The critical section protects the calculated results, here for simplicity i,ix.

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Disclaimer, given the state of bugs galore within the System.Threading library, I would recommend another solution using the OTL framework. At least until the library has reached a stable foundation.