Prevent IIS from reusing worker processes for separate ASP.Net AppDomains

Question

When IIS restarts an ASP.Net (2.0) web application, it can either:

• Recycle the AppDomain: Unload the AppDomain and load a new AppDomain on the same process (e.g. when HttpRuntime.UnloadAppDomain() is called, when web.config is changed).
• Recycle the process: unload the AppDomain and load a new one on a new process (e.g. when invoking Recycle command on an AppPool via inetmgr, or when memory limit is reached).

Due to some internal reasons (trouble with legacy native code we depend upon), we cannot allow the first option. We just can't load the application twice on the same process.

Can IIS be somehow told to never allow worker process reuse?

I've tried preventing it myself by tracking whether an application has already started on a process once using a Mutex, and if so - throwing an exception during Application_Start()); I've also tried terminating the process by calling Environment.Exit() during Application_End(). The problem with both methods is that it causes any requests that arrive during Application_End or Application_Start to fail (unlike a manual process recycle, which fails absolutely no requests because they are redirected to the new process right away).

Answer 1

I believe that "Recycle the AppDomain" comes under preview of ASP.NET runtime and IIS is not really involved anywhere (I am not 100% sure about this in case of integrated pipeline of IIS7). So I don't think that what you want is feasible. But there are couple of workaround that you may consider for your problem:

1. Ensure that you run start-up code (manipulating legacy code) to run only once - this should be possible via named system semaphores. Once system semaphore is created by app start-up in worker process, it will exists till process is recycled so you can have per process initialization.

2. If #1 is not possible then consider hosting code manipulating legacy code in a separate process all together - this process can expose relevant functionality via WCF services over named pipes. ASP.NET will consume them to use legacy code.

Answer 2

Couldn't find a way to tell IIS that worker processes are not to be reused. Can't afford fixing the underlying problem that forbids process reuse. Therefore, ended up calling Environment.Exit(0) in Application_End, although it may cause a small number of requests to fail with a connection reset.