使用async/await和TaskCompletionSource进行奇怪的堆栈跟踪增长

Question

以下C#代码:

class Program
{
    static readonly List<TaskCompletionSource<bool>> buffer = 
                new List<TaskCompletionSource<bool>>();
    static Timer timer;

    public static void Main()
    {
        var outstanding = Enumerable.Range(1, 10)
            .Select(Enqueue)
            .ToArray();

        timer = new Timer(x => Flush(), null, 
                         TimeSpan.FromSeconds(1),
                         TimeSpan.FromMilliseconds(-1));
        try
        {
            Task.WaitAll(outstanding);
        }
        catch {}

        Console.ReadKey();
    }

    static Task Enqueue(int i)
    {
        var task = new TaskCompletionSource<bool>();
        buffer.Add(task);
        return task.Task;
    }

    static void Flush()
    {
        try
        {
            throw new ArgumentException("test");
        }
        catch (Exception e)
        {
            foreach (var each in buffer)
            {
                var lenBefore = e.StackTrace.Length;
                each.TrySetException(e);
                var lenAfter = e.StackTrace.Length;
                Console.WriteLine($"Before - After: {lenBefore} - {lenAfter}");
                Console.WriteLine(e.StackTrace);

            }
        }
    }
}

生产:

Before - After: 149 - 149
Before - After: 149 - 149
Before - After: 149 - 149
Before - After: 149 - 149
Before - After: 149 - 149
Before - After: 149 - 149
Before - After: 149 - 149
Before - After: 149 - 149
Before - After: 149 - 149
Before - After: 149 - 149

但是当我将Enqueue方法更改为异步时:

static async Task Enqueue(int i)
{
    var task = new TaskCompletionSource<bool>();
    buffer.Add(task);
    return await task.Task;
}

结果是:

Before - After: 149 - 643
Before - After: 643 - 1137
Before - After: 1137 - 1631
Before - After: 1631 - 2125
Before - After: 2125 - 2619
Before - After: 2619 - 3113
Before - After: 3113 - 3607
Before - After: 3607 - 4101
Before - After: 4101 - 4595
Before - After: 4595 - 5089

对于每个缓冲的项,它看起来像递归堆栈跟踪增长.对于第一项异常堆栈跟踪将是:

   at Program.Flush() in C:\src\Program.cs:line 41
   --- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotificati...
   at System.Runtime.CompilerServices.TaskAwaiter`1.GetResult()
   at Program.<Enqueue>d__3.MoveNext() in C:\src\Program.cs:line 34

第二个看起来像下面等等:

   at Program.Flush() in C:\src\Program.cs:line 41
   --- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotificati...
   at System.Runtime.CompilerServices.TaskAwaiter`1.GetResult()
   at Program.<Enqueue>d__3.MoveNext() in C:\src\Program.cs:line 34
   --- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotificati...
   at System.Runtime.CompilerServices.TaskAwaiter`1.GetResult()
   at Program.<Enqueue>d__3.MoveNext() in C:\src\Program.cs:line 34

这里发生了什么以及如何解决它？

Answer 1

简答:await尝试打开结果,而方法withod await不尝试访问任务结果.

更长的回答:

1. 调用堆栈的重复部分具有以下外观:

2. 该ValidateEnd的方法TaskAwaiter正在被内联,并且HandleNonSuccessAndDebuggerNotification导致一个呼叫ThrowForNonSuccess这似乎是太内联和作为唯一的例外是用于为10个设置结果TaskCompletionSourceS, 即异常的生长堆叠的原因这里可以看到.

简单的解决方案是new Exception("Some descriptive message", originalException) 在每次TrySetException通话时使用.