使用未观察到的异常查找任务的最佳策略

Question

假设我有以下代码:

private static void Run()
{
    TaskScheduler.UnobservedTaskException += delegate { Console.WriteLine("Unobserved task exception!"); };

    try
    {
        RunAsync().Wait();
    }
    catch (Exception)
    {
    }

    GC.Collect();
    GC.WaitForPendingFinalizers();
    GC.Collect();

    Thread.Sleep(Timeout.InfiniteTimeSpan);
}

private static async Task RunAsync()
{
    var task1 = ThrowAsync();
    var task2 = ThrowAsync();

    await task1;
    await task2;
}

private static async Task ThrowAsync()
{
    throw new Exception("Test exception");
}

此代码输出,Unobserved task exception!因为task2未观察到异常.

我的问题如下:有没有办法以编程方式确定哪个任务有未观察到的异常？例如,我想获取一个调用任务或类似的方法的堆栈跟踪:

Unobserved exception: task2 in RunAsync()

遗憾的是,异常堆栈跟踪是不够的.上面的代码只是一个演示,在实际的应用程序中,我有时会有一些未观察到的任务异常,其堆栈跟踪如下:

System.AggregateException: A Task's exception(s) were not observed either by Waiting on the Task or accessing its Exception property. As a result, the unobserved exception was rethrown by the finalizer thread. ---> System.NullReferenceException: Object reference not set to an instance of an object.
   at System.Web.HttpApplication.get_CurrentModuleContainer()
   at System.Web.HttpApplication.PipelineStepManager.ResumeSteps(Exception error)

Answer 1

人们将能够判断哪个任务实例有未观察到的异常。那将在task2第二个下await

await task1;
await task2;

因为第一个await“观察”的结果task1。

TaskScheduler.UnobservedTaskException然后，如果事件处理程序被修改为呈现提供的实际任务异常

    TaskScheduler.UnobservedTaskException += delegate(object o, UnobservedTaskExceptionEventArgs ea)
    {
        Console.WriteLine($"Unobserved task exception! {ea.Exception.ToString()}");
    };

然后可以通过观察异常的堆栈跟踪来跟踪任务代码的失败区域：

Unobserved task exception!
System.AggregateException: A Task's exception(s) were not observed either by Waiting on the Task or accessing its Exception property. As a result, the unobserved exception was rethrown by the finalizer thread. (Test exception)
---> System.Exception: Test exception
   at ConsoleApp1.Program.ThrowAsync() in C:\Users\sergepavlov\Desktop\ConsoleApp1\ConsoleApp1\Program.cs:line 42
   --- End of inner exception stack trace ---
---> (Inner Exception #0) System.Exception: Test exception
   at ConsoleApp1.Program.ThrowAsync() in C:\Users\sergepavlov\Desktop\ConsoleApp1\ConsoleApp1\Program.cs:line 42
<--- 

希望这是有道理的。