c# 异步方法不起作用

考虑以下使用vs 2015编写的控制台应用程序的代码：

using System;
using System.Threading.Tasks;
public class Example
{
    public static void Main()
    {
        Console.WriteLine("请稍等....");
        DateTime time1 = DateTime.Now;
        Task task1 = MyAsyncFun1();
        Task task2 = MyAsyncFun2();
        task1.Wait();
        task2.Wait();
        DateTime time2 = DateTime.Now;
        Console.WriteLine("耗时: " + 
        (time2 -  time1).TotalSeconds);
        Console.ReadLine();
    }
    private static async Task MyAsyncFun1()
    {
        await Task.Yield();
        System.Threading.Thread.Sleep(2000);
    }
    private static async Task MyAsyncFun2()
    {
        await Task.Yield();
        System.Threading.Thread.Sleep(2000);
    }
}

这里有两个异步调用的方法，所有都正常工作，因为执行是并行的，所以“耗时”没有超过2秒。

但是当我将这段代码写在一个ApiController的Action方法中，像这样：

public class MyController : ApiController
{
    private static async Task MyAsyncFun1()
    {
        await Task.Yield();
        System.Threading.Thread.Sleep(2000);
    }
    private static async Task MyAsyncFun2()
    {
        await Task.Yield();
        System.Threading.Thread.Sleep(2000);
    }
    public async Task MyAction([FromBody] Mymodel model)
    {
        DateTime time1 = DateTime.Now;
        Task task1 = MyAsyncFun1();
        Task task2 = MyAsyncFun2();
        task1.Wait();
        task2.Wait();
        DateTime time2 = DateTime.Now;
        double d=(time2 - time1).TotalSeconds;
        return .....;
    }
}

执行在task1.Wait()语句上无限期地挂起。