Detect when Visual Studio is test-firing the website for intellisense

Question

There's a lot of exposition here - but it's needed.

Not sure how many people are aware of this, but, the Razor code editor in Visual Studio causes your website to be 'test-fired' up to just before the Application_Start event - and this is causing some annoying issues in my current project, which uses WebActivator to do a lot of the site initialisation.

Update - On closer inspection it's not just Razor - it looks like it's Visual Studio-wide - hence the change of title

I need to be able to detect when website code is being run by Visual Studio and not by a web server.

To demonstrate - do the following (exactly as written to ensure it reproduces):

• Create a new MVC 4 site, I used the Internet Application template so there were some pages there on creation.
• Add the WebActivator package from nuget
• Add a class to the App_Start folder called RazorPageBugTest
• Paste this code (changing the relevant namespace):

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using MvcApplication6.App_Start;
using System.IO;

[assembly: WebActivator.PreApplicationStartMethod(
  typeof(RazorPageBugTest), "Start", Order = 0)]

namespace MvcApplication6.App_Start
{
  public static class RazorPageBugTest
  {
    public static void Start()
    {
      using (var writer = File.Open(@"c:\trace.txt", FileMode.Create))
      {
        using (var tw = new StreamWriter(writer))
        {
          tw.AutoFlush = true;
          tw.WriteLine("Written at {0}", DateTime.Now);
        }
      }
    }
  }
}

Notice that this code is not something that would usually work on a web server anyway - given that it's writing to drive C: (indeed this might not work on your machine if you don't run VS as administrator).

• Now build the project.
• This next bit works best if you already have Explorer open on C: Once that's completed, find a Razor view and open it
• Wait for all the C#/VB bits to be highlighted
• Take a look at drive C - oh look, there's a file called 'trace.txt' and the date is within the last few seconds!

So that demonstrates the problem here - the Razor code editor is firing up an AppDomain and, effectively, shelling the website in order to get intellisense (including things like stuff in the App_Helpers folder etc). Now it doesn't actually trigger the Application_Start method - but when you have WebActivator in the project as well, any of its pre-application-start methods are triggered.

In my case this is causing huge issues - high CPU usage and memory usage in devenv.exe (equivalent to the website having just been started) because I initialise DI containers and god-knows what else at this point, but one in particular is proving really annoying.

My website has a component that listens on the network for status and cache-invalidation messages from other machines in the web farm. In QA and Live environments this listener never fails to open the port and listen - on my dev machine, however, it frequently fails - saying the port's already in use. When I look for the process that's holding it open - it's always devenv.exe.

You guessed it - I start this listener in a WebActivator-initialised boot-strapping call.

So the question is - does anyone know of a way to detect that the code isn't being run by a 'proper' web host so I can stop it being run? I'm particularly hopeful for this as it'll also mean that my Visual Studio and Razor editing experience will become a damn-site faster as a result!

As a bonus, any fix could legitimately be sent to David Ebbo - author of WebActivator - so he can stick it earlier in his stack to prevent the problem completely!

Update

I have just added an issue to the WebActivator page on GitHub to see if David Ebbo can push either my fix, or a better one, down into the WebActivator component.

Answer 1

Guess what the value of Process.GetCurrentProcess().ProcessName will be in this case?

Answer: Microsoft.VisualStudio.Web.Host.

So if there's a VisualStudio in the name of the process, you could safely scrape it.

Also check this article out about the hosting process.