using System;

using System.Threading;

public class Program

{

    public static void Main()

    {

        // The asynchronous method puts the thread id here.

            int threadId;

​

            // Create an instance of the test class.

            AsyncDemo ad = new AsyncDemo();

​

            // Create the delegate.

            AsyncMethodCaller caller = new AsyncMethodCaller(ad.TestMethod);

​

            // Initiate the asychronous call.

            IAsyncResult result = caller.BeginInvoke(3000, out threadId, null, null);

​

            Thread.Sleep(10);

            Console.WriteLine("Main thread {0} does some work.s",

                Thread.CurrentThread.ManagedThreadId);

​

            // Call EndInvoke to wait for the asynchronous call to complete,

            // and to retrieve the results.

            string returnValue = caller.EndInvoke(out threadId, result);

​

            Console.WriteLine("The call executed on thread {0}, with return value \"{1}\".", threadId, returnValue);

    }

     public class AsyncDemo 

    {

        // The method to be executed asynchronously.

        public string TestMethod(int callDuration, out int threadId) 

        {

            Console.WriteLine("Test method begins.");

            Thread.Sleep(callDuration);

            threadId = Thread.CurrentThread.ManagedThreadId;

            return String.Format("My call time was {0}.", callDuration.ToString());

        }

    }

    // The delegate must have the same signature as the method

    // it will call asynchronously.

    public delegate string AsyncMethodCaller(int callDuration, out int threadId);

}