Handling exception thrown by handlers

I am evaluating the library for an internal use at my company.

One issue I have currently is that if any handler throws an exception, it will prevent other handlers from receiving the same event. While that is currently the same behavior of normal .NET events, it can cause issues.

Would you consider an overloaded method for WeakEventSource<TEventArgs>.Raise that takes a delegate that can handle any exception and decide whether event notification should continue or not.

Something like:

public void Raise(object? sender, TEventArgs args, Func<Exception, bool> exceptionHandler)
{
    var validHandlers = GetValidHandlers(_handlers);
    foreach (var handler in validHandlers)
    {
        try
        {
            handler.Invoke(sender, args);
        }
        catch (Exception ex)
        {
            if (exceptionHandler(ex))
                continue;
            throw;
        }
    }
}

I was also thinking of a more advanced handler that returns a state so that bad subscriber can be automatically unsubscribed:

[Flags]
public enum ErrorHandlingFlags
{
    None = 0,
    NotThrow = 1,
    Unsubscribe = 2,
}

public void Raise(object? sender, TEventArgs args, Func<Exception, ErrorHandlingFlags> exceptionHandler)
{
    var validHandlers = GetValidHandlers(_handlers);
    foreach (var handler in validHandlers)
    {
        try
        {
            handler.Invoke(sender, args);
        }
        catch (Exception ex)
        {
            var flag = exceptionHandler(ex);
            if (flag.HasFlag(ErrorHandlingFlags.Unsubscribe))
            {
                // find a way to unsubscribe
            }

            if (flag.HasFlag(ErrorHandlingFlags.NotThrow))
                continue;

            throw;
        }
    }
}

But I’m not sure how the unsubscription can work without the original EventHandler<TEventArgs>.

[thomaslevesque]

Hi @Kryptos-FR,

I have most of the code sitting on my laptop, but I haven’t had time to come back to it since last week. I’ll try to finish it in the next few days.

[thomaslevesque]

Anyway, the good news is that I found a way to unsubscribe automatically (still need to test, though). It involves significant internal changes, but I think they’re good ones.