一个例子看懂异步代码执行效率

  class OutHelper
    {
        public DateTime Method1()
        {
            Thread.Sleep(1000);
            return DateTime.Now;
        }

        public DateTime Method2()
        {
            Thread.Sleep(1500);
            return DateTime.Now;
        }

        public DateTime Method3()
        {
            Thread.Sleep(1800);
            return DateTime.Now;
        }

        public async Task<DateTime> AMethod1()
        {
            await Task.Delay(1000);
            return DateTime.Now;
        }

        public async Task<DateTime> AMethod2()
        {
            await Task.Delay(1500);
            return DateTime.Now;
        }

        public async Task<DateTime> AMethod3()
        {
            await Task.Delay(1800);
            return DateTime.Now;
        }
    }

class Program
    {
        static void Main(string[] args)
        {
            OutHelper oh = new OutHelper();

            Console.WriteLine("同步调用开始……");
            Stopwatch sw = new Stopwatch();
            sw.Start();

            DateTime d1 = oh.Method1();
            DateTime d2 = oh.Method2();
            DateTime d3 = oh.Method3();
            Console.WriteLine("同步：d1={0}, d2={1}, d3={2}", d1, d2, d3);
            Console.Out.Flush();
            sw.Stop();
            Console.WriteLine("同步调用耗时:{0}", sw.ElapsedMilliseconds);


            Console.WriteLine("异步调用开始……");

            sw.Reset();
            sw.Start();

            var ad1 = oh.AMethod1();
            var ad2 = oh.AMethod2();
            var ad3 = oh.AMethod3();

           Task.WhenAll(ad1, ad2, ad3);
            Console.WriteLine("同步：d1={0}, d2={1}, d3={2}", ad1.Result, ad2.Result, ad3.Result);
            Console.Out.Flush();
            sw.Stop();

            Console.WriteLine("异步调用耗时:{0}", sw.ElapsedMilliseconds);

            Console.ReadLine();
        }
    }