Task.run为什么子线程里的设置“TaskCreationOptions.AttachedToParent”无效

            //TaskCreationOptions.AttachedToParent不起作用
            Task task = Task.Run(() =>
            {
                var task1 = new Task(() =>
                {
                    Thread.Sleep(1000);
                    Console.WriteLine("11111");
                }, TaskCreationOptions.AttachedToParent);
                task1.Start();

            });

            task.ContinueWith(t =>
            {
                Console.WriteLine("222222");
            });
            task.Wait();
            Console.WriteLine("主线程执行完毕");    

执行结果：

 TaskCreationOptions.AttachedToParent，这里的设置不起作用

//TaskCreationOptions.AttachedToParent起作用
            Task task = new Task(() =>
            {
                var task1 = new Task(() =>
                {
                    Thread.Sleep(1000);
                    Console.WriteLine("11111");
                }, TaskCreationOptions.AttachedToParent);
                task1.Start();

            });

            task.ContinueWith(t =>
            {
                Console.WriteLine("222222");
            });

            task.Start();
            task.Wait();
            Console.WriteLine("主线程执行完毕");

  TaskCreationOptions.AttachedToParent，起到了想要的结果。

通过reflector发现Task.run的底层代码

 public static Task Run(Func<Task> function, CancellationToken cancellationToken)
    {
      if (function == null)
        throw new ArgumentNullException(nameof (function));
      if (AppContextSwitches.ThrowExceptionIfDisposedCancellationTokenSource)
        cancellationToken.ThrowIfSourceDisposed();
      return cancellationToken.IsCancellationRequested ? Task.FromCancellation(cancellationToken) : (Task) new UnwrapPromise<VoidTaskResult>((Task) Task<Task>.Factory.StartNew(function, cancellationToken, TaskCreationOptions.DenyChildAttach, TaskScheduler.Default), true);
    }

其中有TaskCreationOptions.DenyChildAttach，解释了为什么Task.run的  TaskCreationOptions.AttachedToParent为什么无效了