using System;

using System.Threading;

​

public class Program

{

    public static void Main()

    {

        Func<int, int, int> funcDelegate = (int num1, int num2) =>

        {

            Console.WriteLine($"Test method begins in thread {Thread.CurrentThread.ManagedThreadId}");

            Thread.Sleep(TimeSpan.FromSeconds(3));

            return num1 + num2;

        };

        IAsyncResult asyncResult = funcDelegate.BeginInvoke(30, 20, null, null);

        Console.WriteLine($"Main thread {Thread.CurrentThread.ManagedThreadId} does some work.\n");

        while (!asyncResult.IsCompleted)

        {

            Thread.Sleep(250);

            Console.Write(".");

        }

​

        //This wil return result without delay. Because, WaitOne() lets finishing child operation.

        int result = funcDelegate.EndInvoke(asyncResult);

        Console.WriteLine($"\nDoWork(30, 20) returned {result}");

    }

}