处理未等待任务的异常

Question

Let's assume I have a console application with Main method, something like this:

public static void Main(string[] args)
{
    AppDomain.CurrentDomain.UnhandledException += (sender, eventArgs) =>
    {
        Console.WriteLine("App Unobserved");
    };
    TaskScheduler.UnobservedTaskException += (sender, eventArgs) =>
    {
        Console.WriteLine("Task Unobserved");
    };
    Task.Run(async () => await MyAwesomeMethod());
    // other awesome code...
    Console.ReadLine();
}

public static async Task MyAwesomeMethod()
{
    // some useful work
    if (something_went_wrong)
        throw new Exception();
    // other some useful work
}

So, I just run MyAwesomeMethod (fire-and-forget), and want to do some other job, but I also want to know if there any unhandled exceptions. But application finishes successfully without any sign of problem (exception is just swallowed).

How can I handle exception from MyAwesomeMethod(), without awaiting it or using Task.Run(...).Wait()?

Answer 1

So, I just run MyAwesomeMethod (fire-and-forget)... but I also want to know if there any unhandled exceptions. But application finishes successfully without any sign of problem (exception is just swallowed).

That's not "fire and forget", then. "Fire and forget" literally means that you don't care when (or whether) the task completes (or errors).

How can I handle exception from MyAwesomeMethod(), without awaiting it or using Task.Run(...).Wait()?

Use await anyway:

Task.Run(async () => {
  try {
    await MyAwesomeMethod();
  } catch (Exception ex) {
    Console.WriteLine(ex);
  }
});

Answer 2

You can check the status of your task once it's done.

Task.Run(() => MyAwesomeMethod()).ContinueWith((task) =>
{
    if (task.Status == TaskStatus.RanToCompletion && task.Result != null)
    {

    }
    else
    {
        try
        {
            Logger.LogError(task.Exception.ToString());
            Logger.LogMessage("something_went_wrong");
        }
        catch { }
    }
});

Answer 3

You could for example wrap the code in the background task in a try...catch block and raise an event as soon as you enter the catch block (if you do).

Like

event EventHandler<Exception> exceptionInWorker;

and in the task do

try
{
    //do something
}
catch (Exception e)
{
    exceptionInWorker?.Invoke(this, e);
}

Answer 4

您可以像执行操作一样订阅TaskScheduler.UnobservedTaskException事件，但是使用将UnobservedTaskExceptionEventArgs作为其第二个参数的处理程序，通过该处理程序，您可以通过其Exception属性访问未处理的异常并记录有关该异常的所有信息。