VS 2008 Formマルチスレッドインスタンス

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 WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
        public int iou = 0;
        public int i =-1;
        private void button1_Click(object sender, EventArgs e)
        {
            iou =-1;
            Thread t1 = new Thread(Print1);
            t1.IsBackground = true;// 
            t1.Start();
            Thread t2 = new Thread(Print2);
            t2.IsBackground = true;
            t2.Start();
            Thread t3 = new Thread(Print3);
            t3.IsBackground = true;
            t3.Start();
            
        }

    
        public void Print1()
        {
            for (int i = 1; i <= 99999; i++)
            {
                if (iou == 0)
                {
                    textBox1.Text = i.ToString();
                }
                else
                {
                    i = 1000000;
                }
            }

        }
        public void Print2()
        {
            for (i = 9999999; i >=0; i--)
            {
                
                if (iou ==-1)
                {
                    textBox2.Text = i.ToString();
                }
                else
                {
                    iou = i; i = 0;
                }
            }
        }
        public void Print3()
        {
            for (int i = 1; i <= 999; i++)
            {
               // textBox3.Text = (int.Parse(textBox2.Text.Trim()) - int.Parse(textBox1.Text.Trim())).ToString();
            }
        }
        private void Form1_Load(object sender, EventArgs e)
        {
            Control.CheckForIllegalCrossThreadCalls = false;
            // 
        }

        private void button2_Click(object sender, EventArgs e)
        {
            iou = 1;
        }

        private void button3_Click(object sender, EventArgs e)
        {
            iou = -0;
        }
// 
        private void button4_Click(object sender, EventArgs e)
        {
            i = iou;
            iou = -1;
            Thread t2 = new Thread(Print2);
            t2.IsBackground = true;
            t2.Start();
        }


    }
}

以上、Formsバックグラウンドマルチスレッドコード
フロントには、開始、停止、一時停止、起動、などの制御ボタンがあり、それぞれグローバル変数を使用して状態を制御します.