C#

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 MTWindowsTestApp
{
    public partial class Form1 : Form
    {
        int m_nThreadCount;
        bool m_bExit;
        
        public Form1()
        {
            InitializeComponent();
            m_nThreadCount = 0;
            m_bExit = false;
        }

        private void button1_Click( object sender, EventArgs e )
        {
            Thread t;
            int i;

            // 4 Threads starten
            for( i = 0; i < 4; ++i )
            {
                t = new Thread( new ParameterizedThreadStart( MyThread ) );
                t.Priority = ThreadPriority.BelowNormal;
                t.Start( new ThreadData( m_nThreadCount++ ) );
                //Thread.Sleep( 500 );
            }
        }

        public delegate void SetTextDelegate( string strText,
            ThreadData td );
        public void SetText( string strText, ThreadData td )
        {
            switch( td.m_nNr )
            {
                case 0:
                {
                    textBox1.Text = strText;
                    break;
                }
                case 1:
                {
                    textBox2.Text = strText;
                    break;
                }
                case 2:
                {
                    textBox3.Text = strText;
                    break;
                }
                case 3:
                {
                    textBox4.Text = strText;
                    break;
                }
            }
        }
        
        public void MyThread( object Data )
        {
            int nCount;
            int nData = ( (ThreadData)Data ).m_nNr;
            string strTemp;

            nCount = 0;
            strTemp = nData.ToString();
            //while( !m_bExit )
            while( true )
            {
                strTemp = "Thread " + nData.ToString() + ": " +
                    nCount.ToString();
                BeginInvoke( new SetTextDelegate( SetText ),
                    new object[] { strTemp, Data } );
                nCount++;
                Thread.Sleep( 10 );
            }
        }

        private void Form1_FormClosing( object sender, FormClosingEventArgs e )
        {
            m_bExit = true;
        }

    }

    public class ThreadData
    {
        public int m_nNr;
        public ThreadData( int nNr )
        {
            m_nNr = nNr;
        }
    }
}