procedure WaitForFlag(Flag : PBoolean ; TimeOutSeconds : integer = 10);
var EndTime : Extended;
begin
  Flag^ := True;
  EndTime := Now() + TimeOutSeconds * OneSecond;

  while (Flag^ = True) and (Now() < EndTime) do
    Application.ProcessMessages;
  //if Flag^ then raise ETimeOut.Create;
end;

  while (Flag^ = True) and (Now() < EndTime) do
  begin
    Sleep(1);
    Application.ProcessMessages;
  end;

type
  TForm1 = class(TForm)
    CheckBox1: TCheckBox;
    Label1: TLabel;
    Button1: TButton;
    procedure Button1Click(Sender: TObject);
    procedure FormClose(Sender: TObject; var Action: TCloseAction);
    procedure CheckBox1Click(Sender: TObject);
  private
    { Private-Deklarationen }
    Flag: Boolean;
    procedure WaitForFlag(TimeOutSeconds: DWORD = 10);
  public
    { Public-Deklarationen }
  end;

var
  Form1 : TForm1;

implementation

{$R *.dfm}

procedure TForm1.WaitForFlag(TimeOutSeconds: DWORD = 10);
var
  EndTime : DWORD;
begin
  Flag := True;
  EndTime := GetTickCount + TimeOutSeconds * 1000;

  while (Flag = True) and (GetTickCount < EndTime) do
  begin
    Sleep(1);
    Application.ProcessMessages;
  end;

end;

procedure TForm1.Button1Click(Sender: TObject);
begin
  Flag := True;
  WaitForFlag;
  Label1.Caption := 'Done ...';
end;

procedure TForm1.FormClose(Sender: TObject; var Action: TCloseAction);
begin
  Flag := False;
end;

procedure TForm1.CheckBox1Click(Sender: TObject);
begin
  Flag := not CheckBox1.Checked;
end;

Type
  TMyThread = Class (TThread)
  <Lokale Werte>
  Protected
     Procedure Execute; Override;
  Public
     Constructor Create (<Werte für den Thread>);
  End;

Constructor TMyThread.Create(<Werte für den Thread>);
Begin
  Inherited Create (True);
  <Lokale Werte> := <Werte für den Thread>
  <Sonstige Vorbereitungen>
  Resume; // Jetzt geht lo-hos!
End;

Procedure TMyThread.Execute;
Begin
  Try
    <Hier steht der Code drin, den der Thread ausführen soll>
    <Dazwischen immer mal wieder ein :>
    If Terminated Then Exit;
  Finally
    <Etwaige Speicheranforderungen, Objekte etc. wieder freigeben>
  End
End;