async和await

 class Program
    {
        static void Main(string[] args)
        {
            //AwaitAsyncClass.NoReturnNoAwait();
            //AwaitAsyncClass.NoReturn();
            //{
            //    Task t = AwaitAsyncClass.NoReturnTask();
            //    Console.WriteLine($"Main Thread Task ManagedThreadId={Thread.CurrentThread.ManagedThreadId}");
            //    t.Wait();//主线程等待Task的完成  阻塞的
            //    await t;//await后的代码会由线程池的线程执行  非阻塞
            //}
            {
                Task<long> t = AwaitAsyncClass.SumAsync();
                Console.WriteLine($"Main Thread Task ManagedThreadId={Thread.CurrentThread.ManagedThreadId}");
                long lResult = t.Result;//访问result   主线程等待Task的完成
                t.Wait();//等价于上一行
                Console.WriteLine(lResult);
            }
            Console.WriteLine($"Main Thread Task ManagedThreadId={Thread.CurrentThread.ManagedThreadId}");
            Console.ReadLine();
        }
    }

    class AwaitAsyncClass
    {
        /// <summary>
        /// 只有async没有await，会有个warn
        /// 跟普通方法没有区别
        /// </summary>
        public static async void NoReturnNoAwait()
        {
            //主线程执行
            Console.WriteLine($"NoReturnNoAwait Sleep before Task,ThreadId={Thread.CurrentThread.ManagedThreadId}");
            Task task = Task.Run(() =>//启动新线程完成任务
            {
                Console.WriteLine($"NoReturnNoAwait Sleep before,ThreadId={Thread.CurrentThread.ManagedThreadId}");
                Thread.Sleep(3000);
                Console.WriteLine($"NoReturnNoAwait Sleep after,ThreadId={Thread.CurrentThread.ManagedThreadId}");
            });

            //主线程执行
            Console.WriteLine($"NoReturnNoAwait Sleep after Task,ThreadId={Thread.CurrentThread.ManagedThreadId}");
        }

        /// <summary>
        /// async/await 
        /// 不能单独await
        /// await 只能放在task前面
        /// 不推荐void返回值，使用Task来代替
        /// Task和Task<T>能够使用await, Task.WhenAny, Task.WhenAll等方式组合使用。Async Void 不行
        /// </summary>
        public static async void NoReturn()
        {
            //主线程执行
            Console.WriteLine($"NoReturn Sleep before await,ThreadId={Thread.CurrentThread.ManagedThreadId}");
            TaskFactory taskFactory = new TaskFactory();
            Task task = taskFactory.StartNew(() =>
            {
                Console.WriteLine($"NoReturn Sleep before,ThreadId={Thread.CurrentThread.ManagedThreadId}");
                Thread.Sleep(3000);
                Console.WriteLine($"NoReturn Sleep after,ThreadId={Thread.CurrentThread.ManagedThreadId}");
            });

            //task.ContinueWith(t =>
            //{
            //    Console.WriteLine($"NoReturn Sleep after await,ThreadId={Thread.CurrentThread.ManagedThreadId}");
            //});
            await task;//主线程到这里就返回了，执行主线程任务
            Console.WriteLine($"NoReturn Sleep after await,ThreadId={Thread.CurrentThread.ManagedThreadId}");
            //await 后面的代码 和task.ContinueWith() 中回调方法类似
            //这个回调的线程是不确定的：可能是主线程  可能是子线程  也可能是其他线程
        }


        /// <summary>
        /// 无返回值  async Task == async void
        /// Task和Task<T>能够使用await, Task.WhenAny, Task.WhenAll等方式组合使用。Async Void 不行
        /// </summary>
        /// <returns></returns>
        public static async Task NoReturnTask()
        {
            //这里还是主线程的id
            Console.WriteLine($"NoReturnTask Sleep before await,ThreadId={Thread.CurrentThread.ManagedThreadId}");

            Task task = Task.Run(() =>
            {
                Console.WriteLine($"NoReturnTask Sleep before,ThreadId={Thread.CurrentThread.ManagedThreadId}");
                Thread.Sleep(3000);
                Console.WriteLine($"NoReturnTask Sleep after,ThreadId={Thread.CurrentThread.ManagedThreadId}");
            });
            await task;
            Console.WriteLine($"NoReturnTask Sleep after await,ThreadId={Thread.CurrentThread.ManagedThreadId}");

            //return new TaskFactory().StartNew(() => { });  //不能return  没有async才行
        }



        /// <summary>
        /// 带返回值的Task  
        /// 要使用返回值就一定要等子线程计算完毕
        /// </summary>
        /// <returns>async 就只返回long</returns>
        public static async Task<long> SumAsync()
        {
            Console.WriteLine($"SumAsync 111 start ManagedThreadId={Thread.CurrentThread.ManagedThreadId}");
            long result = 0;

            await Task.Run(() =>
            {
                for (int k = 0; k < 10; k++)
                {
                    Console.WriteLine($"SumAsync {k} await Task.Run ManagedThreadId={Thread.CurrentThread.ManagedThreadId}");
                    Thread.Sleep(1000);
                }
                for (long i = 0; i < 999_999_999; i++)
                {
                    result += i;
                }
            });

            Console.WriteLine($"SumFactory 111   end ManagedThreadId={Thread.CurrentThread.ManagedThreadId}");

            return result;
        }
    }