敬请各位高手解决vb.net（VS2010）多线程的问题。谢谢。

以下代码在（VS2010）测试正常。
Private a As Integer
    Private b As Integer
    Private Sub setA()
        a = 1
    End Sub
    Private Sub setB()
        b = 2
    End Sub
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Dim t1 As Threading.Thread
        Dim t2 As Threading.Thread
        t1 = New Threading.Thread(AddressOf setA)
        t2 = New Threading.Thread(AddressOf setB)
        t1.Start()
        t2.Start()
    End Sub
Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
        MessageBox.Show ("a=" & a & ",b=" & b)
    End Sub
问题：如何只用一个按钮可以实现以上代码的功能？以下代码不能实现以上代码的功能。
Private a As Integer
    Private b As Integer
    Private Sub setA()
        a = 1
    End Sub
    Private Sub setB()
        b = 2
    End Sub
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Dim t1 As Threading.Thread
        Dim t2 As Threading.Thread
        t1 = New Threading.Thread(AddressOf setA)
        t2 = New Threading.Thread(AddressOf setB)
        t1.Start()
        t2.Start()
         MessageBox.Show ("a=" & a & ",b=" & b)
    End Sub