C#关于线程间控键调用的问题

using System;
using System.Collections.Generic;
using System.Text;
using System.Drawing;
using System.Windows.Forms;
using System.Threading;
namespace WindowsApplication1
{
    class Class1
    {
        private Panel l;
        Label la;
        public Class1(Panel a)
        {
            this.l = a;
        }
        delegate void DAdd();
        public void add()
        {            if (this.l.InvokeRequired)//-----同下
            {
                this.l.Invoke(new DAdd(add));//------------帮忙解释下这句什么意思
            }
            else
            {
                int x = 0, y = 25;
                la = new Label();
                Random rand = new Random();
                int r = rand.Next(97, 123);
                x = rand.Next(0, 100);
                la.Text = ((char)r).ToString();
                this.l.Controls.Add(la);
                la.Location = new Point(x, y);
                while (true)
                {
                    la.Location = new Point(x, y);
                    y++;
                    Thread.Sleep(500);
                }            }
        }
    }
}
--------------------------------------------------
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using System.Threading;
namespace WindowsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
            Control.CheckForIllegalCrossThreadCalls = false;
        }
        private void Form1_Load(object sender, EventArgs e)
        {
            Class1 cc = new Class1(this.panel1);
            new Thread(new ThreadStart(cc.add)).Start();
            
        }        private void panel1_Paint(object sender, PaintEventArgs e)
        {        }        private void timer1_Tick(object sender, EventArgs e)
        {
           
        }    }
}
为什么一运行窗口程序就死机??错哪?不加while循环的时候就可以运行..