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遇到真正的await后，由新线程接管，即操作开始异步。

不阻塞主线程

class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine($"主线程{Thread.CurrentThread.ManagedThreadId}");
            Console.WriteLine($"主线程{Thread.CurrentThread.ManagedThreadId}:{SayAsync().Status}");
            Console.WriteLine($"主线程{Thread.CurrentThread.ManagedThreadId}");
            Console.ReadKey(true);
        }

        public static async Task<string> SayAsync()
        {
            Console.WriteLine($"主线程{Thread.CurrentThread.ManagedThreadId}_SayAsync");

            var s = await Task<string>.Run(async () =>
            {
                await Task.Delay(TimeSpan.FromSeconds(2));
                Console.WriteLine("---------------两秒后----------------");
                Console.WriteLine($"子线程{Thread.CurrentThread.ManagedThreadId}");
                return "vvull";
            });
            Console.WriteLine($"子线程{Thread.CurrentThread.ManagedThreadId}:{s}");
            Console.WriteLine($"子线程{Thread.CurrentThread.ManagedThreadId}");
            return s;
        }

    }

阻塞主线程

class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine($"主线程{Thread.CurrentThread.ManagedThreadId}");
            Console.WriteLine($"主线程{Thread.CurrentThread.ManagedThreadId}:{SayAsync().Result}");//阻塞主线程
            Console.WriteLine($"主线程{Thread.CurrentThread.ManagedThreadId}");
            Console.ReadKey(true);
        }

        public static async Task<string> SayAsync()
        {
            Console.WriteLine($"主线程{Thread.CurrentThread.ManagedThreadId}_SayAsync");

            var s = await Task<string>.Run(async () =>
            {
                await Task.Delay(TimeSpan.FromSeconds(2));
                Console.WriteLine("---------------两秒后----------------");
                Console.WriteLine($"子线程{Thread.CurrentThread.ManagedThreadId}");
                return "vvull";
            });
            Console.WriteLine($"子线程{Thread.CurrentThread.ManagedThreadId}:{s}");
            Console.WriteLine($"子线程{Thread.CurrentThread.ManagedThreadId}");
            return s;
        }

    }

进阶版

class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine($"{Thread.CurrentThread.ManagedThreadId}->主线程");
            giaoAsync();
            Thread.Sleep(3000);
            Console.WriteLine("---------------三秒后----------------");
            Console.WriteLine($"{Thread.CurrentThread.ManagedThreadId}->主线程");
            Console.ReadKey();
        }
        static async Task giaoAsync()
        {
            Console.WriteLine($"{Thread.CurrentThread.ManagedThreadId}->giao");

            //Console.WriteLine($"{Thread.CurrentThread.ManagedThreadId}->giao:{await SayAsync()}");//本句以后由新线程接管
            //Console.WriteLine($"{Thread.CurrentThread.ManagedThreadId}->giao*");

            var s = await SayAsync();//由新线接管
            Console.WriteLine($"{Thread.CurrentThread.ManagedThreadId}->giao**_{s}");
            Console.WriteLine($"{Thread.CurrentThread.ManagedThreadId}->giao**");

            var ss = await SayAsync();//由新线接管
            Console.WriteLine($"{Thread.CurrentThread.ManagedThreadId}->giao***_{ss}");
            Console.WriteLine($"{Thread.CurrentThread.ManagedThreadId}->giao***");
        }

        public static async Task<string> SayAsync()
        {
            Console.WriteLine($"{Thread.CurrentThread.ManagedThreadId}->SayAsync");

            var s = await Task<string>.Run(async () =>
            {                
                Console.WriteLine($"{Thread.CurrentThread.ManagedThreadId}->SayAsync*");
                await Task.Delay(TimeSpan.FromSeconds(0.001));
                Console.WriteLine("---------------两秒后----------------");
                Console.WriteLine($"{Thread.CurrentThread.ManagedThreadId}->SayAsync**");
                return "vvull";
            });
            Console.WriteLine($"{Thread.CurrentThread.ManagedThreadId}->SayAsync**_{s}");
            Console.WriteLine($"{Thread.CurrentThread.ManagedThreadId}->SayAsync**");
            return s;
        }

    }

使用Async和Await的异步编程

原文：https://www.cnblogs.com/vvull/p/13218369.html