Q:如何限制應用程式一次只執行一份 instance ?
A:參考下列程式碼:

type
  TForm1 = class(TForm)
    procedure FormCreate(Sender: TObject);
    procedure FormDestroy(Sender: TObject);
  private
    FAtom: ATOM;
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.DFM}

procedure TForm1.FormCreate(Sender: TObject);
begin
  { Searchs table to see if the program is already running }
  if GlobalFindAtom('PROGRAM_RUNNING') = 0 then
    { If not found then add it }
    FAtom := GlobalAddAtom('PROGRAM_RUNNING')
  else
  begin
    { If program is already running the show message and halt }
    ShowMessage('There is already an instance of this program running.');
    Application.Terminate;
  end;
end;

procedure TForm1.FormDestroy(Sender: TObject);
begin
  GlobalDeleteAtom(FAtom);
end;