Calling Your Main Thread From A Worker Thread In C#

using System;
using System.Threading;
using System.Windows.Forms;

namespace WindowsApplication1
{       
   public class Counter
   {       
      private Label LabeltoUpdate;
      private int MaxCount;
      private CallBack CallBackMethod;
       
      public Counter(Label l,int max, CallBack cb)
      {
          LabeltoUpdate = l;
          MaxCount = max;
          CallBackMethod = cb;
      }

      public void BeginProcessing()
      {
          int i;

          for(i=1;i < MaxCount; i  )
          {
             LabeltoUpdate.Text = i.ToString();
             LabeltoUpdate.Refresh();
          }

          //Tell the main thread we have completed
          CallBackMethod(i,Thread.CurrentThread.Name);
      }
   }
}

using System.Threading;

private void button1_Click(object sender, System.EventArgs e)
{
   Counter c1 = new Counter(label1,3000,new CallBack(ThreadCompleted));
   Counter c2 = new Counter(label2,1500,new CallBack(ThreadCompleted));

   Thread t1 = new Thread(new ThreadStart(c1.BeginProcessing));
   Thread t2 = new Thread(new ThreadStart(c2.BeginProcessing));

   t1.Name = "Counter Thread 1";
   t2.Name = "Counter Thread 2";

   t1.Start();
   t2.Start();
}

private void ThreadCompleted(int intTotal,string strName)
{
   MessageBox.Show("Thread "   strName  
                      " has completed at "   intTotal.ToString());
}