Public Class M
        Private Locked As Boolean
 
        Private Sub DoSth()
            '...
            Locked = True
            '...
        End Sub
 
        Public Class S
            Private Parent As M
 
            Public Sub New(ByVal SInst As M)
                Parent = SInst
            End Sub
 
            Private Sub DoSth()
                If Not Parent.Locked Then
                    '...
                End If
            End Sub
        End Class
    End Class