对象互斥

var
  MutexHandle: Integer;

begin
  if OpenMutex(MUTEX_ALL_ACCESS, FALSE, 'RunOnceMutex') <> 0 then
  begin
     ShowMessage('This application is already open!');
     Exit;
  end;
  MutexHandle := CreateMutex(nil, TRUE, 'RunOnceMutex');

  Application.Initialize;
  Application.CreateForm(TForm1, Form1);
  Application.Run;

  ReleaseMutex(MutexHandle); 

end;