c# – 为什么从“Async CTP / Release”中删除“SwitchTo”？

然后我发现这个blurb here：

The reason we got rid of it was because it was so dangerous. The alternative is to bundle up your code inside TaskEx.Run…

我的问题是简单的：为什么是危险的？使用什么特定的危险会导致？

请注意,我已经阅读了其余的帖子,所以我明白这里有技术上的限制.我的问题是,如果我知道这一点,为什么会很危险？

我正在考虑重新执行帮助方法给我指定的功能,但如果有一些根本的破坏,除了有人认为这是危险的,我不会这样做.

具体来说,非常天真,我将如何考虑实现所需的方法：

public static class ContextSwitcher
{
    public static ThreadPoolContextSwitcher SwitchToThreadPool()
    {
        return new ThreadPoolContextSwitcher();
    }

    public static SynchronizationContextSwitcher SwitchTo(this SynchronizationContext synchronizationContext)
    {
        return new SynchronizationContextSwitcher(synchronizationContext);
    }
}

public class SynchronizationContextSwitcher : INotifyCompletion
{
    private readonly SynchronizationContext _SynchronizationContext;

    public SynchronizationContextSwitcher(SynchronizationContext synchronizationContext)
    {
        _SynchronizationContext = synchronizationContext;
    }

    public SynchronizationContextSwitcher GetAwaiter()
    {
        return this;
    }

    public bool IsCompleted
    {
        get
        {
            return false;
        }
    }

    public void OnCompleted(Action action)
    {
        _SynchronizationContext.Post(_ => action(),null);
    }

    public void GetResult()
    {
    }
}

public class ThreadPoolContextSwitcher : INotifyCompletion
{
    public ThreadPoolContextSwitcher GetAwaiter()
    {
        return this;
    }

    public bool IsCompleted
    {
        get
        {
            return false;
        }
    }

    public void OnCompleted(Action action)
    {
        ThreadPool.QueueUserWorkItem(_ => action(),null);
    }

    public void GetResult()
    {
    }
}

这将允许我编写如下代码：

public async void Test()
{
    await ContextSwitcher.SwitchToThreadPool(); // ensure we're not bogging down the UI thread
    // do some heavy processing
    await _UIContext.SwitchTo(); // presumably saved from the main thread
    // update UI with new data
}