当不应用程序框架时，可以通过定义互斥变量来判断是否已运行实例：

Sub Main()
    Dim isNotRunning As Boolean = True
    Static run As New System.Threading.Mutex(True,"SampleForm",isNotRunning)
    If isNotRunning Then
        run.ReleaseMutex()
        Application.Run(New SampleForm)
    End If
End Sub