Question

I’m not talking about asynchronous pages or asynchronous handlers, I just want to know if I should be afraid of any side effect when I invoke an asynchronous method that will end after the page is finished rendering.

Example given: Each time that a user do login, I have to launch a heavy and time consuming SQL operation, but the user doesn’t need to know the result of that operation, so I can execute the query using BeginExecuteNonQuery without pass any callback, and finish rendering the page.

My concern is, what happen if the HTTP call ends (because the page is served) and whatever I’ve executed asynchronously is already running? is ASP.NET or IIS going to cut, destroy, void anything?

Cheers.

Answer 1

That operation will run, even when the request has finished. However, please note that the ASP.NET host aggressively kills threads. When IIS has any reason for unloading or recycling the AppDomain, your background thread will be killed. Unloading happens in several situations. For instance when no new requests have come in for a certain period of time. Or when too many exceptions are fired from the application within a certain period of time. Or when the memory pressure gets too high.

If you need the guarantee, that the operation will finish, I think there are three things you can do:

1. Speed up the operation so that it can run synchronously, or
2. Move that that heavy operation to a Windows Service and let that execute it, or
3. You can hook onto the HostingEnvironment.RegisterObject method (as Phill Haack explains here) (demands full trust) to prevent the AppDomain to go down while that thread is running.