通过回答中的方法，反射拿到的 m_action 值总是 null

var task = RequestCnblogsQ();
var fieldInfo = typeof(Task).GetField("m_action", BindingFlags.Instance | BindingFlags.NonPublic);
var action = fieldInfo.GetValue(task);

@dudu: 一旦 Task 运行完毕，m_action 就是 null 了，可以改成这样：

Task t = new Task<Task>(DoSomething);

var fieldInfo = typeof(Task).GetField("m_action", BindingFlags.Instance | BindingFlags.NonPublic);
Delegate action = fieldInfo.GetValue(t) as Delegate;
Console.WriteLine(action.Method.Name);

t.Start();

@沈星繁: t.Start() 会抛异常：

Unhandled Exception: System.InvalidOperationException: Start may not be called on a task that hascompleted.
   at System.Threading.Tasks.Task.Start(TaskScheduler scheduler)

@dudu:

先把 Task new 出来（此时没有运行里面的方法），取方法名（可能是用来写 Log 的？），再运行 Task。

我的测试代码是这样的，运行是没有问题的：

using System;
using System.Net.Http;
using System.Reflection;
using System.Threading.Tasks;

namespace ConsoleApp1
{
    class Program
    {
        static void Main(string[] args)
        {
            var task = new Task<Task>(RequestCnblogsQ);

            var fieldInfo = typeof(Task).GetField("m_action", BindingFlags.Instance | BindingFlags.NonPublic);
            Delegate action = fieldInfo.GetValue(task) as Delegate;
            Console.WriteLine(action.Method.Name);

            task.Start();
        }

        private static async Task RequestCnblogsQ()
        {
            await new HttpClient().GetAsync("https://q.cnblogs.com/");
        }
    }
}

@沈星繁: 赞！的确可以