windows service problem

[Austin]

class HelloService(win32serviceutil.ServiceFramework):
    _svc_name_ = "HelloService"
    _svc_display_name_ = "Hello Service"
    def __init__(self,args):
        win32serviceutil.ServiceFramework.__init__(self,args)
        self.hWaitStop = win32event.CreateEvent(None, 0, 0, None)
        self.check = 1

    def SvcStop(self):
        self.ReportServiceStatus(win32service.SERVICE_STOP_PENDING)
        win32event.SetEvent(self.hWaitStop)
        self.check = 0

    def SvcDoRun(self):
        win32event.WaitForSingleObject(self.hWaitStop, win32event.INFINITE)
        while True:
            CheckPoint('SvcDoRun')
            if self.check == 0:
                break

if __name__ == '__main__':
    win32serviceutil.HandleCommandLine(HelloService)

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I modified the demo code from Python Programming on Win32.
CheckPoint is a class to open a file and write some words.
But the problem is that no matter how I re-start the service and the
CheckPoint() doesn't work.
Anything wrong?