c# – 两个线程之间的共享变量与共享属性的行为不同

在他关于C#中线程的优秀论文中,Joseph Albahari提出了以下简单程序来演示为什么我们需要对多个线程读取和写入的数据使用某种形式的内存屏障.如果您在发布模式下编译它并在没有调试器的情况下自由运行它,程序永远不会结束：

static void Main()
  {
     bool complete = false;
     var t = new Thread(() =>
     {
        bool toggle = false;
        while (!complete) toggle = !toggle;
     });
     t.Start();
     Thread.Sleep(1000);
     complete = true;                  
     t.Join(); // Blocks indefinitely
  }

我的问题是,为什么以上稍微修改过的上述程序版本不再无限期地阻塞？

class Foo
{
  public bool Complete { get; set; }
}

class Program
{
  static void Main()
  {
     var foo = new Foo();
     var t = new Thread(() =>
     {
        bool toggle = false;
        while (!foo.Complete) toggle = !toggle;
     });
     t.Start();
     Thread.Sleep(1000);
     foo.Complete = true;                  
     t.Join(); // No longer blocks indefinitely!!!
  }
}

以下仍然无限期地阻止：

class Foo
{
  public bool Complete;// { get; set; }
}

class Program
{
  static void Main()
  {
     var foo = new Foo();
     var t = new Thread(() =>
     {
        bool toggle = false;
        while (!foo.Complete) toggle = !toggle;
     });
     t.Start();
     Thread.Sleep(1000);
     foo.Complete = true;                  
     t.Join(); // Still blocks indefinitely!!!
  }
}

如下所示：

class Program
{
  static bool Complete { get; set; }

  static void Main()
  {
     var t = new Thread(() =>
     {
        bool toggle = false;
        while (!Complete) toggle = !toggle;
     });
     t.Start();
     Thread.Sleep(1000);
     Complete = true;                  
     t.Join(); // Still blocks indefinitely!!!
  }
}