I have an MVC+SignalR application that has a lot of Reactive Extensions subscriptions flying around, all of which are projections of data coming from a Socket in realtime. Some of these subscriptions are not working as expected, and when they raise an exception it just goes into the void unless I'm debugging.
I had hoped that I could use Elmah to automatically log these unhandled exceptions, but it seems that unless the exception occurs on the same thread that's processing the request/response, eg it causes a yellow screen of death, Elmah isn't touching it. So my question is twofold:
Can I get Elmah to automatically log exceptions on background/worker processes?
If the answer to #1 is "no", what's my next best option, other than wrapping my subscriptions in try/catch blocks at a very high level?
Ad 1) If it doesn't happen already it probably doesn't.
I don't know how exactly you use background threads, but I will try to explain were ELMAH handling is working. ELMAH is integrated into ASP.NET pipeline, and when the error occurs it is handled by ASP.NET pipeline, which shows error page (like http error 500) and invoke ErrorLogModule. Moreover quoting Using HTTP Modules and Handlers to Create Pluggable ASP.NET Components -> Adding ELMAH to an ASP.NET Web Application
The section adds the ErrorLogModule HTTP module to the ASP.NET HTTP pipeline. Make sure you include this setting, otherwise ELMAH won't be listening for the Error event, and therefore won't be logging any unhandled exceptions.
Ad 2) Because you are using Reactive Extensions you can handle onError in which you can automatically log into Elmah. If you don't want to writer everywhere error hangling in OnError, just create your own function or method extension which will wrap it automatically for you. Writing into ELMAH manually is simple just call:
Elmah.ErrorSignal.FromCurrentContext().Raise(ex);