当我启动计时器时我的程序锁定，并且我'；I’我不知道为什么

我已经创建了两个程序。两者都使用间隔设置为250毫秒的计时器。

问题是，我的第一个程序没有锁定，然后我运行它，第二个程序锁定了out，让我可以点击停止按钮。所谓锁，我的意思是程序运行完成它的工作，直到我从VS停止它。

我不明白为什么我不能停止我的第一个程序，而基本相同的方式为其他程序工作。有什么想法吗？

锁定程序：

    private void btnScan_Click(object sender, EventArgs e)
    {
        tmrInterval.Interval = (int)nudInterval.Value;
        tmrInterval.Start();
    }
    private void ScanPort(IPAddress address, int port)
    {
        using (TcpClient client = new TcpClient())
        {
            IAsyncResult result = client.BeginConnect(address, port, null, null);
            if (result.AsyncWaitHandle.WaitOne((int)nudTimeout.Value, false)) txtDisplay.AppendText("Port: " + port + " is open." + Environment.NewLine);
            else txtDisplay.AppendText("Port: " + port + " is closed." + Environment.NewLine);
        }
    }
    private void btnStop_Click(object sender, EventArgs e)
    {
        tmrInterval.Stop();
    }
    private void tmrInterval_Tick(object sender, EventArgs e)
    {
        ScanPort(IPAddress.Parse(txtIP.Text), currentPort);
        currentPort++;
        if (currentPort == nudTo.Value) tmrInterval.Stop();
    }

不锁定的程序：

    void tmrPingInterval_Tick(object sender, EventArgs e)
    {
        if (txtTo.Text == string.Empty) Ping(IPAddress.Parse(ip2str(startIP)));
        else
        {
            if (currentIP >= endIP) tmrPingInterval.Stop();
            Ping(IPAddress.Parse(ip2str(currentIP)));
            currentIP++;
        }
    }
    private void btnPing_Click(object sender, EventArgs e)
    {
        if (txtFrom.Text != string.Empty)
        {
            txtFrom.Enabled = false;
            txtTo.Enabled = false;
            txtDisplay.Text = string.Empty;
            tsslPingCount.Text = string.Empty;
            count = 0;
            open = 0;
            closed = 0;
            tmrPingInterval.Interval = int.Parse(nudInterval.Value.ToString());
            try
            {
                startIP = str2ip(txtFrom.Text);
                if (txtTo.Text != string.Empty) endIP = str2ip(txtTo.Text);
                currentIP = startIP;
                tmrPingInterval.Start();
            }
            catch
            {
                MessageBox.Show("Input must be in IP format: 100.100.100.100", "Information", MessageBoxButtons.OK, MessageBoxIcon.Information);
                txtFrom.Enabled = true;
                txtTo.Enabled = true;
            }
        }
        else MessageBox.Show("IP field cannot be empty!", "Information", MessageBoxButtons.OK, MessageBoxIcon.Information);
    }
    private void btnStop_Click(object sender, EventArgs e)
    {
        txtFrom.Enabled = true;
        txtTo.Enabled = true;
        tmrPingInterval.Stop();
    }
    private void Ping(IPAddress address)
    {
        Ping pingSender = new Ping();
        PingOptions options = new PingOptions();
        if (cbDontFragment.Checked) options.DontFragment = true;
        else options.DontFragment = false;
        string data = string.Empty;
        int dataCounter = 0;
        options.Ttl = (int)nudTTL.Value;
        for (int i = 0; i < nudData.Value; i++)
        {
            dataCounter++;
            if (dataCounter == 10) dataCounter = 0;
            data += dataCounter.ToString();
        }
        byte[] buffer = Encoding.ASCII.GetBytes(data);
        int timeout = 120;
        try
        {
            PingReply reply = pingSender.Send(address, timeout, buffer, options);
            if (reply.Status == IPStatus.Success)
            {
            }
            else
            {
            }
        }
        catch (Exception ex)
        {
            txtDisplay.SelectedText += Environment.NewLine + ex.Message;
        }
    }