.NET ExecutionContext如何实际工作？

我试图发现 ExecutionContext如何在.NET Framework 4.0及更高版本中实际运行.文档说当使用Thread.Start和大多数线程池操作时,托管原则,同步,区域设置和用户上下文都流向新线程.但我不能在实践中看到这一点.

这是一个简单的控制台应用程序,用于测试启动新线程时同步上下文和托管原则是否流动…

static void Main(string[] args)
    {
        SynchronizationContext.SetSynchronizationContext(new SynchronizationContext());
        Thread.CurrentPrincipal = new GenericPrincipal(new GenericIdentity("One"),null);

        Thread t1 = new Thread(new ThreadStart(ThreadRun));
        t1.Start();
        t1.Join();

        SynchronizationContext.SetSynchronizationContext(new SynchronizationContext());
        Thread.CurrentPrincipal = new GenericPrincipal(new GenericIdentity("Two"),null);

        AsyncFlowControl aFC = ExecutionContext.SuppressFlow();
        Thread t2 = new Thread(new ThreadStart(ThreadRun));
        t2.Start();
        t2.Join();
        aFC.Undo();

        Console.Read();
    }

    static void ThreadRun()
    {
        Console.WriteLine("ThreadRun Id={0} Context={1} Principle={2}",Thread.CurrentThread.ManagedThreadId,(SynchronizationContext.Current != null),Thread.CurrentPrincipal.Identity.Name);
    }

结果是……

ThreadRun Id=11 Context=False Principle=One
    ThreadRun Id=12 Context=False Principle=Two

因此,同步上下文永远不会流动,并且即使在您指定它时,托管原则也始终会流动.基本上文档是完全错误的.那么是否描述了ExecutionContext在现实中的作用以及它为何有用？

[SecuritySafeCritical]
    private void Start(ref StackCrawlMark stackMark)
    {
      this.StartupSetApartmentStateInternal();
      if (this.m_Delegate != null)
        ((ThreadHelper) this.m_Delegate.Target).SetExecutionContextHelper(ExecutionContext.Capture(ref stackMark,ExecutionContext.CaptureOptions.IgnoreSyncCtx));
      this.StartInternal(CallContext.Principal,ref stackMark);
    }