Logging the final exception?

Hello,

In order to log the final exception after all retries have failed we are currently using the fallback event:

var fallbackPolicy = builder.FallbackAsync((token, context) => { return Task.CompletedTask; }, (ex, context) => LogFinalError(ex, context));

As suggested in another thread. However since the last update this operation now longer works, we are getting an exception:

You have executed the generic .Execute<TResult> method on a non-generic FallbackPolicy. A non-generic FallbackPolicy only defines a fallback action which returns void; it can never return a substitute TResult value. To use FallbackPolicy to provide fallback TResult values you must define a generic fallback policy FallbackPolicy<TResult>. For example, define the policy as Policy<TResult>.Handle<Whatever>.Fallback<TResult>(/* some TResult value or Func<..., TResult> */);

I suppose this is linked to the fix https://github.com/App-vNext/Polly/issues/294 ?

Is there a way to attach an event on fallback without having to handle the return type?

By the way this library is great, keep on the good work!

[reisenberger]

Is it safe to rethrow the exception from onFallback, after logging of course?

Throwing an exception from within either onFallback or fallbackAction will cause that exception to propagate further outwards; the FallbackPolicy will not swallow or govern it in any way. (Policies govern the delegate passed to Execute(...), or all actions of a policy deeper inside a PolicyWrap. Policies do not guard their own actions (fallbackAction; onFallback; onRetry etc); that could lead to all manner of recursion.)

wouldn’t .Fallback with an Action prevent the Exception from actually bubbling?

FallbackPolicy catches the exceptions it is configured to handle and passes control to the configured fallbackAction after calling onFallback. FallbackPolicy does not rethrow the exception it handled. If fallbackAction or onFallback rethrow it will bubble; if they do not, it will not.

[thurfir]

Hello @reisenberger , wouldn’t .Fallback with an Action prevent the Exception from actually bubbling?

Is it safe to rethrow the exception from onFallback, after logging of course?

Thank you.