Delphi 里防止程序多次运行

在dpr里加入以下红色部分代码

program Main;

uses
  Vcl.Forms,
  Windows,
  SysUtils,
  uMain in 'uMain.pas' {MainForm};

{$R *.res}

Var
hMutex:HWND; 
Ret:Integer;

begin
  Application.Initialize;
  Application.MainFormOnTaskbar := True;
  Application.Title := '测试系统';
  hMutex:=CreateMutex(nil,False,'测试系统');
  Ret:=GetLastError;
  If Ret = ERROR_ALREADY_EXISTS Then
  begin
    Application.MessageBox('程序已经运行!','测试系统',MB_OK);
    ReleaseMutex(hMutex);//释放程序
    Application.Terminate;
  end;

  Application.CreateForm(TMainForm, MainForm);
  Application.Run;

end.