//实例未被创建时加锁（双重锁定，多线程安全）
public static Tool2 GetInstance()
{
if (instance == null || instance.IsDisposed)
{
lock (syncRoot)
{
if (instance == null || instance.IsDisposed)
{
instance = new Tool2();
}
}
}
instance.MdiParent = Form1.ActiveForm;
return(instance);
}
private void toolStripLabel2_Click(object sender, EventArgs e)
{
Tool2.GetInstance().Show();
}