C# 中Async 和 Await 的用法，异步等待执行结果

using System;
using System.Threading;
using System.Threading.Tasks;

namespace ConsoleApp1
{
    class Program
    {
        public static async Task Main(string[] args)
        {
            //异步等待执行结果
            //int result = await DoTask();

            Task task2 = Task.Run(() =>
            {
                for (int i = 0; i < 5; ++i)
                {
                    Console.WriteLine("做其它的事");
                    Thread.Sleep(100);
                }

            });
            Console.WriteLine("全部执行完成 结果：{0}", await DoTask());
            await GetValueAsync();
            Console.WriteLine("结束");
            Console.ReadKey();
        }

        public static async Task GetValueAsync()
        {
            Console.WriteLine("GetValueAsync Task start");
            await Task.Run(() =>
            {
                Thread.Sleep(1000);
                for (int i = 0; i < 5; ++i)
                {
                    Console.WriteLine("GetValueAsync Task : {0}", i);
                }
            });
            Console.WriteLine("GetValueAsync Task  End");
        } 

        private static async Task DoTask()
        {
            Console.WriteLine("DoTask Task start");
            int length = 0;
            await Task.Run(() =>
            {
                for (int i = 0; i < 100; i++)
                {
                    length++;
                    Console.WriteLine("DoTask Task {0}", length);
                    Thread.Sleep(10);
                }
            });
            Console.WriteLine("DoTask Task end");
            return length;
        }
    }
}