private void button4_Click(object sender, EventArgs e)
        {
            DateTime dt1 = DateTime.Now;
            if (textBox3.Text == "")
                richTextBox3.Text += "2的0次方为1";
            else
            {
                ManualResetEvent[] mr = new ManualResetEvent[int.Parse(textBox3.Text)];
                for (int i = 1; i <= int.Parse(textBox3.Text); i++)
                {
                    //int poolnum = i;
                    int temp = new int();
                    temp = i;
                    Control.CheckForIllegalCrossThreadCalls = false;
                    mr[temp - 1] = new ManualResetEvent(false);
                    ThreadPool.QueueUserWorkItem(delegate(object num)
                    {
                        long pre = 1;
                        for (int n = 1; n <= temp; n++)
                        {
                            Thread.Sleep(1);
                            pre *= 2;
                        }

                        richTextBox3.AppendText("2的" + temp.ToString() + "次方为：  " + pre.ToString() + "\r\n");
                        mr[temp - 1].Set();
                    });
                }
                WaitHandle.WaitAll(mr);
            }
            DateTime dt2 = DateTime.Now;
            label8.Text = (dt2 - dt1).TotalSeconds.ToString();
        }