A debugging experience with "highly compatible" ASP.NET 4.5

posted by Jeff | Sunday, August 26, 2012, 1:56 PM | comments: 0

I have to admit that I will pretty much upgrade software for no reason other than being on the latest version. I won't do it if it's super expensive (Adobe gets money from me about once every three or four years at best), but particularly with frameworks and stuff generally available as part of my MSDN subscription, I'll be bleeding edge. CoasterBuzz was running on the MVC 4 framework pretty much as soon as they did a "go live" license for it.

I didn't really jump in head-first with Windows 8 and Visual Studio 2012, in part because I just wasn't interested in doing the reinstalls for each new version. Turns out there weren't that many revisions anyway. But when the final versions were released a week and a half ago, I jumped in.

I saw on one of the Microsoft sites that .Net 4.5 was a "highly compatible in-place update" to the framework. Good enough for me. I was obviously running it by default in Windows 8, and installed it on my production server. I suppose it's "highly compatible," except when it isn't.

Three of my sites are running with various flavors of the MVC version of POP Forums. All of them stopped working under ASP.NET 4.5. It was not immediately obvious what the problem might be beyond an exception indicating that there were no repository classes registered with Ninject, which I use for dependency injection in the forums. This was made all the more weird by the fact that it ran fine locally in the dev Web host.

My first instinct was to spin up a Windows Server VM on my local box and put the remote debugger on it. (Side note: running multiple VM's on a Retina MacBook Pro with 16 gigs of RAM is pretty much the most awesome thing ever. I can't believe this computer is for real, and not a 50-pound tower under my desk.) What might have been going on in IIS that doesn't happen in Visual Studio?

In the debugging process, I realized that I might be looking in the wrong place. POP Forums creates a Ninject container using a method called from a PreApplicationStartMethod attribute, and at that time registers a module (what Ninject uses to map interfaces to implementations) that maps all of the core dependencies. It also creates an instance of an HttpModule that originally hosted the "services" (search indexing, mailer, etc.), but now just records errors.

That's all well and good, but the actual repository mapping, where data is actually read or persisted, happens in Application_Start() in global.asax. The idea there is that you can swap out the SqlSingleWebServer repos for something tuned for multiple servers, Oracle or something else. Of course, if I used something like StructureMap, which does convention-based mapping for dependency injection (a class implementing ISettingsRepository called SettingsRepository is automagically mapped), I wouldn't have to worry about it.

In any case, the HttpModule, being instantiated before Application_Start() gets to run, would throw because there was no repo mapped where it could get settings from the database. This makes total sense. The fix is sort of a hack, where I don't setup the innards of the HttpModule until a call to its BeginRequest is made. I say it's a hack, because its primary function, logging exceptions, won't work until the app has warmed up.

Still, this brings up an interesting question about the race condition, and what changed in 4.5 when it's running in IIS. In ASP.NET 4, it would appear that the code called via the PreApplicationStartMethod was either failing silently, and running again later, or it was getting to that code after Application_Start was called.

In any case, weird thing. The real pain point I'm experiencing now is a bug in MVC 4 that is extremely serious because it renders the mobile/alternate view functionality very much broken.


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