ตัวอย่างนี้ผมให้ thread เขียน TextBox นะครับ ทดสอบแล้วใช้งานได้ครับ แต่ code อาจจะไม่ค่อยดีนะครับ
ชี้แนะได้นะครับ

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Threading;


namespace TestThread
{
    public partial class Form1 : Form
    {
        delegate void SetTextCallback(string text);


        public Form1()
        {
            InitializeComponent();
        }

        class MyObject
        {
            public string myName;
            public TextBox txtbox;

            public MyObject(ref TextBox txtBox)
            {
                this.txtbox = txtBox;
            }

            private void SetText(string text)
            {
                // InvokeRequired required compares the thread ID of the
                // calling thread to the thread ID of the creating thread.
                // If these threads are different, it returns true.
                if (this.txtbox.InvokeRequired)
                {
                    SetTextCallback d = new SetTextCallback(SetText);
                    txtbox.Invoke(d, new object[] { text });
                }
                else
                {
                    this.txtbox.Text = text;
                }
            }

            public void Start()
            {
                while (true)
                {
                    Mutex objMutex = new Mutex(false, "ThreadLock");
                    try
                    {
                        objMutex.WaitOne();
                        //Console.WriteLine("I am >> " + this.myName);
                        //this.txtbox.Text = "I am >> " + this.myName;
                        this.SetText("I am >> " + this.myName);
                       
                    }
                    finally
                    {
                        objMutex.ReleaseMutex();
                    }
                    Random random = new Random();
                    Thread.Sleep(random.Next(1000, 3000));
                }
            }
        }

        private void button1_Click(object sender, EventArgs e)
        {
            MyObject obj = new MyObject(ref this.textBox1);
            obj.myName = "Chiwa";
            Thread thread = new Thread(new ThreadStart(obj.Start));
            thread.Start();

            obj = new MyObject(ref this.textBox1);
            obj.myName = "Pee";
            thread = new Thread(new ThreadStart(obj.Start));
            thread.Start();


            obj = new MyObject(ref this.textBox1);
            obj.myName = "Nok";
            thread = new Thread(new ThreadStart(obj.Start));
            thread.Start();
        }

        private void Form1_Load(object sender, EventArgs e)
        {

        }
    }
}