Question

现在我知道首先使用Marshal.GetExceptionCode()是一个hack，但问题不在于它（Visual Studio调试器也检测到活动异常）

private static async Task TestAsync()
{
    Log("TestAsync.Before");

    await HandleExceptionAsync();

    Log("TestAsync.After");
}

private static async Task HandleExceptionAsync()
{
    try
    {
        Log("HandleExceptionAsync.Try");
        await ThrowAsync();
    }
    catch (InvalidOperationException)
    {
        Log("HandleExceptionAsync.Catch");
    }

    Log("HandleExceptionAsync.AfterCatch");
}

private static async Task ThrowAsync()
{
    await Task.Delay(1000);
    throw new InvalidOperationException("Delayed exception");
}

private static void Log(string step)
{
    Console.WriteLine($"{step}: {Marshal.GetExceptionCode()}");
}

输出

TestAsync.Before: 0
HandleExceptionAsync.Try: 0
Exception thrown: 'System.InvalidOperationException' in Interactive.dll
Exception thrown: 'System.InvalidOperationException' in System.Private.CoreLib.ni.dll
HandleExceptionAsync.Catch: -532462766
HandleExceptionAsync.AfterCatch: -532462766
TestAsync.After: -532462766
The thread 9292 has exited with code 0 (0x0).

该异常在整个等待链中保持活动状态，即使它已被捕获。 我检查了生成的代码，它没有提供为什么会发生这种情况的相关部分（为MoveNext状态机生成HandleExceptionAsync）：

  void IAsyncStateMachine.MoveNext()
  {
    int num1 = this.\u003C\u003E1__state;
    try
    {
      if (num1 == 0)
        ;
      try
      {
        TaskAwaiter awaiter;
        int num2;
        if (num1 != 0)
        {
          Program.Log("HandleExceptionAsync.Try");
          awaiter = Program.ThrowAsync().GetAwaiter();
          if (!awaiter.IsCompleted)
          {
            this.\u003C\u003E1__state = num2 = 0;
            this.\u003C\u003Eu__1 = awaiter;
            Program.\u003CHandleExceptionAsync\u003Ed__1 stateMachine = this;
            this.\u003C\u003Et__builder.AwaitUnsafeOnCompleted<TaskAwaiter, Program.\u003CHandleExceptionAsync\u003Ed__1>(ref awaiter, ref stateMachine);
            return;
          }
        }
        else
        {
          awaiter = this.\u003C\u003Eu__1;
          this.\u003C\u003Eu__1 = new TaskAwaiter();
          this.\u003C\u003E1__state = num2 = -1;
        }
        awaiter.GetResult();
        awaiter = new TaskAwaiter();
      }
      catch (InvalidOperationException ex)
      {
        Program.Log("HandleExceptionAsync.Catch");
      }
      Program.Log("HandleExceptionAsync.AfterCatch");
    }
    catch (Exception ex)
    {
      this.\u003C\u003E1__state = -2;
      this.\u003C\u003Et__builder.SetException(ex);
      return;
    }
    this.\u003C\u003E1__state = -2;
    this.\u003C\u003Et__builder.SetResult();
  }

我没有看到这与同步上下文有关（在这种情况下它是一个控制台应用程序，所以在池上安排了延续），我最好的猜测是有一些调用堆栈操作发生，但我找不到任何很好的信息。

如果有人能够解释为什么会这样，我会很感激并提供文档的链接，解释如何在CLR /编译器中实现它

UPD1 ：添加了VS调试器的屏幕截图，显示异步中的活动异常，未显示任何内容同步

异步

同步

Answer 1

如果你在Log("HandleExceptionAsync.AfterCatch");放置一个断点，那么callstack会解释这个诀窍：

ConsoleApp1.exe!ConsoleApp1.Program.Log(string step) Line 107   C#
ConsoleApp1.exe!ConsoleApp1.Program.HandleExceptionAsync() Line 95  C#
mscorlib.dll!System.Runtime.CompilerServices.AsyncMethodBuilderCore.MoveNextRunner.InvokeMoveNext(object stateMachine)  Unknown
mscorlib.dll!System.Threading.ExecutionContext.RunInternal(System.Threading.ExecutionContext executionContext, System.Threading.ContextCallback callback, object state, bool preserveSyncCtx)   Unknown
mscorlib.dll!System.Threading.ExecutionContext.Run(System.Threading.ExecutionContext executionContext, System.Threading.ContextCallback callback, object state, bool preserveSyncCtx)   Unknown
mscorlib.dll!System.Runtime.CompilerServices.AsyncMethodBuilderCore.MoveNextRunner.Run()    Unknown
mscorlib.dll!System.Threading.Tasks.AwaitTaskContinuation.RunOrScheduleAction(System.Action action, bool allowInlining, ref System.Threading.Tasks.Task currentTask)    Unknown
mscorlib.dll!System.Threading.Tasks.Task.FinishContinuations()  Unknown
mscorlib.dll!System.Threading.Tasks.Task.FinishStageThree() Unknown
mscorlib.dll!System.Threading.Tasks.Task.FinishStageTwo()   Unknown
mscorlib.dll!System.Threading.Tasks.Task.Finish(bool bUserDelegateExecuted) Unknown
mscorlib.dll!System.Threading.Tasks.Task<System.Threading.Tasks.VoidTaskResult>.TrySetException(object exceptionObject) Unknown
mscorlib.dll!System.Runtime.CompilerServices.AsyncTaskMethodBuilder<System.Threading.Tasks.VoidTaskResult>.SetException(System.Exception exception) Unknown
mscorlib.dll!System.Runtime.CompilerServices.AsyncTaskMethodBuilder.SetException(System.Exception exception)    Unknown
ConsoleApp1.exe!ConsoleApp1.Program.ThrowAsync() Line 101   C#
... (continues until the timer of Task.Delay)

看到底部框架？尽管我们正在HandleExceptionAsync进行日志记录，但我们仍处于ThrowAsync状态。怎么可能？答案也在callstack中：

mscorlib.dll!System.Threading.Tasks.Task<System.Threading.Tasks.VoidTaskResult>.TrySetException(object exceptionObject) Unknown

简单来说，由于await关键字，您的HandleExceptionAsync方法会被切断，如下所示：

void HandleExceptionAsync1()
{
    Log("HandleExceptionAsync.Try");
}

void HandleExceptionAsync2()
{
    Log("HandleExceptionAsync.AfterCatch");
}

当然，这比这更复杂。事实上，这种方法并没有被切断，只是简单地转化为状态机。但是，对于这个演示，这是明智的等价。

HandleExceptionAsync2需要在ThrowAsync之后执行。因此，HandleExceptionAsync2将被链接为延续。类似的东西：

ThrowAsync().ContinueWith(HandleExceptionAsync2);

（同样，这比那更复杂。我只是简化了解释）

＆＃34;问题＆＃34;是，当运行时完成ThrowAsync返回的任务时：

System.Threading.Tasks.Task<System.Threading.Tasks.VoidTaskResult>.TrySetException(object exceptionObject)

继续实际上将内联，并在同一个callstack中执行（参见上面的框架）。出于性能原因，这是TPL经常进行的优化。因此，在调用Log("HandleExceptionAsync.AfterCatch");，时，您实际上仍然在ThrowAsync 的捕获区中，因此您看到了这种行为。

在异步方法中捕获异常后的异常

1 个答案: