New class TCountdownEventEx for versions prior to XE2

I've discovered some new handy classes in XE2 and I said to myself why not implement them into prior versions via my own class?

TCountdownEventEx = class
  private
    FCurrent,
    FInitial: integer;
    FEvent: TEventEx;
  public
    constructor Create(aSize: integer);
    destructor Destroy; override;
    procedure Add(aSize: integer);
    function IsFinish: boolean;
    procedure Reset;
    procedure Signal;
    procedure Wait(aTimeout: cardinal);

    property Current: integer read FCurrent;
    property Initial: integer read FInitial;
  end;


{ TCountdownEventEx }

procedure TCountdownEventEx.Add(aSize: integer);
begin
  if IsFinish then
    raise Exception.Create('Already signalled');

  TInterlockedEx.Add(FCurrent, aSize);
end;

constructor TCountdownEventEx.Create(aSize: integer);
begin
  FInitial := aSize;
  FEvent := TEventEx.Create;

  Reset;
end;

destructor TCountdownEventEx.Destroy;
begin
  FEvent.Free;

  inherited;
end;

procedure TCountdownEventEx.Reset;
begin
  FEvent.Reset;
  FCurrent := FInitial;
end;


procedure TCountdownEventEx.Signal;
begin
  TInterlockedEx.Dec(FCurrent);
  if FCurrent = 0 then
    FEvent.Sign;
end;


function TCountdownEventEx.IsFinish: boolean;
begin
  Exit(FCurrent <= 0);
end;

procedure TCountdownEventEx.Wait(aTimeout: cardinal);
begin
  FEvent.Wait(aTimeout);
end;

I've used the same example as in Delphi help and it seems to work...

program TCountdownEvent_example;

{$APPTYPE CONSOLE}

uses
  SysUtils,
  BB.Sync,
  Classes;

var
  RunwayFlag: TCountdownEventEx;

type
  TThreadIgnite = class(TThread)
  private
    procedure Execute; override;
  end;

procedure TThreadIgnite.Execute;
begin
  RunwayFlag.Wait(INFINITE);
  Writeln('Ignited');
end;

var
  Thread: TThreadIgnite;

begin
  RunwayFlag := TCountdownEventEx.Create(200);

  Thread := TThreadIgnite.Create(True);
  Thread.Start;

  while not RunwayFlag.IsFinish do
  begin
    RunwayFlag.Signal;
    Writeln(RunwayFlag.Current);
  end;

end. { Put breakpoint here to see the console output. }