App pool recycle uses incorrect directory under stress

[natemcmaster]

Under high load, app pool recycling causes IIS to use the wrong directory when recycling applications within a website.

Repro

1. Create three small ASP.NET Core 1.0 applications under one website.

   websiteroot/
       web.config
   apps/
       testapp1/
           web.config
       testapp2/
           web.config
       testapp3/
           web.config
   

   using System.IO;
   using System.Threading.Tasks;
   using Microsoft.AspNetCore.Builder;
   using Microsoft.AspNetCore.Hosting;
   using Microsoft.AspNetCore.Http;
   
   public class Startup
   {
       public void Configure(IApplicationBuilder app)
       {
           app.Run(async context =>
           {
               await Task.Delay(1000);
               await context.Response.WriteAsync("Echo");
           });
       }
   
       public static void Main(string[] args)
       {
           var host = new WebHostBuilder()
                   .UseContentRoot(Directory.GetCurrentDirectory())
                   .UseKestrel()
                   .UseIISIntegration()
                   .UseStartup<Startup>()
                   .Build();
   
           host.Run();
       }
   }

   <configuration>
       <system.webServer>
           <handlers>
               <add name='aspnetCore' path="*" verb="*" modules="AspNetCoreModule" resourceType="Unspecified" />
           </handlers>
           <aspNetCore processPath="dotnet" arguments='.\testapp1.dll' stdoutLogEnabled="false" forwardWindowsAuthToken="false"/>
       </system.webServer>
   </configuration>

2. Create high load. I got this to repro with 10 threads constantly pulling at the three apps within the website.

3. Wait for an app pool recycle to trigger (such as using the # of requests trigger, or time interval trigger).

Expected

ANCM should always use the appropriate app/testappN/ folder to start the app.

Actual

Not always, but somethings IIS uses websiteroot/ instead of app/testappN/ as the current working directory when starting the app. This causes perpetual 502.5 errors.

The application to execute does not exist: 'C:\inetpub\websiteroot\testapp1.dll'

[natemcmaster]

cc @shirhatti @muratg this is the root cause of @wpostma's issue aspnet/IISIntegration#245 (comment), and may be a conflating factor in other IIS + ANCM perf bugs we've received.

[shirhatti]

Fixed in a private build. Will ship in 1.1.0