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.");

        Thread.Sleep(TimeSpan.FromSeconds(2));

        //Wait main thread for the child thread

        asyncResult.AsyncWaitHandle.WaitOne();

        Console.WriteLine("You can do other operations");

        asyncResult.AsyncWaitHandle.Close();

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

        int result = funcDelegate.EndInvoke(asyncResult);

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

    }

}