只允许运行一个程序

避免程序运行两个，一般后台服务都需要这个功能，工程文件修改事例如下：

 

program printService;

uses
  Forms,
  u_main in 'u_main.pas' {Form1};

{$R *.res}
var //避免程序的二次运行;
//  h: HWND;
  hMutex: THandle;
begin
  hMutex := OpenMutex(MUTEX_ALL_ACCESS, True, 'printService');
  if hMutex <> 0 then
  begin
    showmessage('后台程序已经在运行，请看有下角的图标！');
//    MessageBox(handle, '后台程序已经在运行，请看有下角的图标！', '温馨提示', MB_OK
//    + MB_ICONINFORMATION);
    Exit;
  end;
  hMutex := CreateMutex(nil, False, 'printService');
  if hMutex = 0 then
  begin
    Exit;
  end;

  try
  Application.Initialize;
  Application.CreateForm(TForm1, Form1);
  Application.Run;
  finally
    ReleaseMutex(hMutex);
  end;
end.