捕獲產生內部任務的任務的異常

Question

給出以下簡化代碼

    /// <summary>
    /// Within the VS2010 debugger, the following test will cease with an 
    /// "Exception was unhandled by user code". 
    /// (Debug window reports a "A first chance exception of type 
    /// 'System.Exception' ..." BEFORE the exception is caught 
    /// further down in the execution path.)
    /// OUTSIDE the VS2010 debugger, the exception is caught by the tComplete 
    /// task that follows the tOpen task, just as expected.
    /// </summary>
    public void StartToOpen_Simple()
    {
        Task tOpen = Task.Factory.StartNew(() => {
            //do some work before spawning another task here
            try
            {
                return Task.Factory.StartNew(() => {
                    Thread.Sleep(2000);
                    //First chance exception occurs here:
                    throw new Exception("Some generic exception");
                }, TaskCreationOptions.AttachedToParent);
            } catch (Exception ex)
            {
                //never fires
                var source = new TaskCompletionSource<object>();
                source.TrySetException(ex);
                return source.Task;
            }
        }).Unwrap();

        Task tComplete = tOpen.ContinueWith(t => {
            if (t.Exception != null)
            {
                Exception LastOpenException = t.Exception.Flatten().GetBaseException();
                if (LastOpenException is OperationCanceledException)
                {
                    Console.WriteLine("OperationCanceledEx: " + LastOpenException.Message);
                } else
                {
                    Console.WriteLine("Some exception occured in the tOpen task, but we're prepared for it here in the tComplete task.");
                    Console.WriteLine("The exception message was: {0}", LastOpenException.Message);
                }
            } else
            {
                //do something if no exception occured (doesn't happen in this example)
            }
        }, CancellationToken.None, TaskContinuationOptions.ExecuteSynchronously | TaskContinuationOptions.AttachedToParent, TaskScheduler.Default);
    }

並測試它，例如通過

    static void Main(string[] args)
    {
        AsyncTest test = new AsyncTest();
        test.StartToOpen_Simple();

        Console.WriteLine("Started async task. Waiting for exception");
        Console.ReadKey();
    }

我在VS2010調試器中運行時遇到一個非常煩人的問題：就像“摘要”狀態一樣，調試器在'tOpen'任務中拋出，相信我沒有捕獲異常（我在下面進一步說明） “在'tComplete'任務中）。 只有當我繼續調試會話時，才會看到異常“冒泡”並因此按需處理。 如果這個方法是在一個固定的時間間隔（它是！）上運行的，那么調試就變成了一場噩夢，因為調試器會在每個時間間隔內中斷。

在控制台上運行該程序，不會出現此行為。

1. 有人可以向我解釋為什么調試器在這一行中斷，即它沒有看到
2. 有哪些能夠合理調試VS2010中存在此類代碼的代碼？

Answer 1

第一次機會異常消息通常並不意味着代碼中存在問題。 對於優雅處理異常的應用程序/組件，第一次機會異常消息讓開發人員知道遇到並處理了異常情況。

請參考這個