passing data to and from threads

using System;
using System.Threading;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            Multiply m = new Multiply("Hello, world!", 13, new ResultDelegate(ResultCallback));

            Thread t = new Thread(new ThreadStart(m.ThreadProc));
            t.Start();
            Console.WriteLine("Main thread does some work, then waits.");
            t.Join();
            Console.WriteLine("Thread completed.");

            Console.ReadLine();
        }
        public static void ResultCallback(int retValue)
        {
            Console.WriteLine("Returned value: {0}", retValue);
        }
    }

    public delegate void ResultDelegate(int value);

    public class Multiply
    {
        private string greeting;
        private int value;

        private ResultDelegate callback;

        public Multiply(string _greeting, int _value, ResultDelegate _callback)
        {
            greeting = _greeting;
            value = _value;
            callback = _callback;
        }

        public void ThreadProc()
        {
            Console.WriteLine(greeting);
            if (callback != null)
            {
                callback(value * 2);
            }
        }
    }
}