在做threading.timer測試時,發現在thread callback拿到1個ID以上.
理解上,應該只拿到自己的thread ID,怎麼會拿到一個以上呢?

using System.Threading;
        private  Timer timer;
        private void Form1_Load(object sender, EventArgs e)
        {
             TimerCallback callback = new  TimerCallback(Do);
             timer = new  Timer(callback, null, 0, 1000);

        }
        private void Do(object state)
        {
            //這裡會拿到不同的ID,為什麼?
            string val =  Thread.CurrentThread.ManagedThreadId.ToString();
            this.BeginInvoke(new dSetList(_setList), new object[] { val }); 

        }
        delegate void dSetList(string val);
        private void _setList(string val)
        {
            if (listBox1.Items.Contains(val) == false)
            {
                listBox1.Items.Add(val);
            }
        }
        
        private void button1_Click(object sender, EventArgs e)
        {
            string val = System.Threading.Thread.CurrentThread.ManagedThreadId.ToString();
            textBox1.Text = val;
        }