c# 多线程 无法获取参数 我想知道哪个线程在做什么 获取不成功

[c2a2o2]

 public partial class Form1 : Form
    {
        public int num;
        public void BeginbbsUrlFind()
        {

            for (int j = 0; j < 500; j++)
            {
                System.Threading.Thread.Sleep(100);//没什么意思，单纯的执行延时 
                AddListUrl(j.ToString());
            }

        }
        private delegate void AddListUrlCallback(string url);

        private void AddListUrl(string url)
        {
            int p = num;

            if (this.InvokeRequired)
            {
                AddListUrlCallback method = new AddListUrlCallback(this.AddListUrl);
                this.Invoke(method, new object[] { url });
            }
            else
            {
                listBox1.Items.Add(url.ToString());

                //label1.Items.Add(url.ToString());
                label1.Text = "线程" + p + "正在输出" + url;
            }
        }

        public Form1()
        {
            InitializeComponent();
        }


        private void Form1_Load(object sender, EventArgs e)
        {

        }

        private void button1_Click(object sender, EventArgs e)
        {
            this.listBox1.Items.Clear();
            for (int i = 1; i <= 10; i++)
            {//这里开启了10个线程
                num = i;
                ThreadStart start = new ThreadStart(BeginbbsUrlFind);
                Thread thread = new Thread(start);
                thread.Name = i.ToString();

                thread.Start();



            }


        }
    }