启动和停止循环，而按钮单击

我使用下面的代码来启动和停止foreach循环的执行。但start运行良好。当停止按钮点击时，我无法停止循环执行。请帮我做这件事。

private void btn_start_Click(object sender, EventArgs e)
{
    if (txt_rows.Text != "") {
        thread = new System.Threading.Thread(new System.Threading.ThreadStart(update));
        thread.IsBackground = true;
        thread.Start();
    }
}
private void Update()
{
    //My logic here
}
private void btn_stop_Click(object sender, EventArgs e)
{
    lbl_appstatus.Text = "Stop"; // Button click event not fired while run the loop
    lbl_appstatus.Update();
    lbl_appstatus.ForeColor = System.Drawing.Color.Red;
    if (thread != null && thread.IsAlive)
        thread.Abort();
}