using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApp1
{
class Program
{
public delegate void MyFunction(string msg);

public static void Main(string[] args)
{
MyFunction fn = StartA;
fn.BeginInvoke("【B】要开始运行了！", asyncCallback=> {
for (int i = 1; i <= 1000; i++)
{
Console.WriteLine("\t\t\t【B】运行了" + i + "‰");
};
},null);

Console.WriteLine("【A】要开始运行了！");
for (int i = 1; i <= 1000; i++)
{
Console.WriteLine("\t【A】运行了" + i + "‰");
};

Console.ReadKey();
}

public static void StartA(string msg)
{
Console.WriteLine(msg);
}
}
}

运行结果

   public delegate void AsyncDelegate();
        private AsyncDelegate asyncDl;

                  asyncDl = new AsyncDelegate(() =>
                {
                   //todo
                });

                AsyncCallback callBack = new AsyncCallback((s) =>
                {

                         //todo
                });

              asyncDl.BeginInvoke(callBack, null); //启动执行

            当异步方法执行完毕会调用callBack方法