Why same code executes faster in the thread?

Question

Consider this very simple piece of code:

uses Diagnostics;

const
  ITER_COUNT = 100000000;

procedure TForm1.btn2Click(Sender: TObject);
var
  val: Double;
  i: Integer;
begin
  sw := TStopwatch.StartNew;

  val := 1;
  for i := 0 to ITER_COUNT - 1 do
  begin
    val := val + i;
    val := val - i;
    val := val * 10;
    val := val / 10;
  end;

  sw.Stop;

  mmo1.Lines.Add(Format('Simple completed in %D ms. Result: %G',
    [sw.ElapsedMilliseconds, val]));
end;

This simple loop executes in 4027 ms on my PC. Now if I write the same code, only using different thread:

procedure TForm1.btn3Click(Sender: TObject);
begin
  sw := TStopwatch.StartNew;
  TThread.CreateAnonymousThread(
    procedure
    var
      val: Double;
      i: Integer;
    begin
      val := 1;
      for i := 0 to ITER_COUNT- 1 do
      begin
        val := val + i;
        val := val - i;
        val := val * 10;
        val := val / 10;
      end;

      sw.Stop;

      TThread.Queue(nil, procedure
        begin
          mmo1.Lines.Add(Format('Async completed in %D ms. Result: %G',
            [sw.ElapsedMilliseconds, val]));
        end);
    end
  ).Start;
end;

This method which does the same but in the different thread executes in 2910 ms! (Compiled in Delphi XE with Release configuration active) I noticed ~25% gain in the thread no matter how many iterations I have. Why this is so? Shouldn't it be the same results?

EDIT: After further investigations I found that probably the reason for this is Windows 7 OS. On Windows 7 machine simple loop in the main thread executes ~25% slower than async version! I've even tried to run this same project on the same Windows 7 PC using Windows XP mode and then both results were equal - ~3000ms! I'm completely lost here...What is Windows 7 doing with the main thread that it is slower?

Answer 1

Strange indeed, but maybe it is because of some offset c.q. alignment.

Maybe the variables in the anonymous thread are proper aligned, and the other one not. You could try to add some dummy variables to change to offset or if you have Delphi XE2, try some different code alignment.