Getting the assembly name for a process started within an app domain

Question

I have a service that creates an app domain and starts it:

this._appDomain = AppDomain.CreateDomain(this._appName, AppDomain.CurrentDomain.Evidence, appDomainSetup);
this._startStopControllerToRun = (IStartStop)this._appDomain.CreateInstanceFromAndUnwrap(assemblyName, this._fullyQualifiedClassName);
this._startStopControllerToRun.Start();

That has been running well for a long time now. The issue is when the controller, started within this app domain, calls a framework logging class. The logger gets the entry assembly name and records that as the source in the event log. This is how the logger gets the source (caller) name:

private static string GetSource()
{
    try
    {
        var assembly = Assembly.GetEntryAssembly();

        // GetEntryAssembly() can return null when called in the context of a unit test project.
        // That can also happen when called from an app hosted in IIS, or even a windows service.
        if (assembly == null)
        {
            // From http://stackoverflow.com/a/14165787/279516:
            assembly = new StackTrace().GetFrames().Last().GetMethod().Module.Assembly;
        }

        return assembly.GetName().Name;
    }
    catch
    {
        return "Unknown";
    }
}

Before adding that if check, the logger would record "Unknown" for the source. After some research, I added that attempt in the if block. Now the logger records "mscorlib" as the source (entry assembly name).

This is the overview: Host -> Controller (running within app domain)

How can I get the name of the assembly (that has the controller) running within the domain?

Note: I also tried this (below), but it gives me the name of the framework where the logging class exists (not the name of the assembly in which the controller is running within the app domain):

assembly = Assembly.GetExecutingAssembly();

Answer 1

I ran into a situation where somewhere buried in the .net code, it was relying on Assembly.GetEntryAssembly(). It would take the returned assembly and inspect it for an assembly level attribute. Which is going to fail if code is in an app domain.

Long story short, I had to work around this same issue. The solution is ugly, I hate that I needed to do this but it worked...

If you read the docs here - Assembly.GetEntryAssembly() Method

It contains this section:

Return Value

Type: System.Reflection.Assembly

The assembly that is the process executable in the default application domain, or the first executable that was executed by AppDomain.ExecuteAssembly. Can return null when called from unmanaged code.

To get around this, I added some code to my exe which makes the process exit if "/initializingappdomain" is passed as an argument.

Here is some code to do this...

// 1. Create your new app domain...
var newDomain = AppDomain.CreateDomain(...);
            
// 2. call domain.ExecuteAssembly, passing in this process and the "/initializingappdomain" argument which will cause the process to exit right away
newDomain.ExecuteAssembly(GetProcessName(), new[] { "/initializingappdomain" });

private static string GetProcessName()
{
   return System.IO.Path.GetFileName(Process.GetCurrentProcess().MainModule.FileName.Replace(".vshost", ""));
}

// 3. Use your app domain as you see fit, Assembly.GetEntryAssembly will now return this hosting .net exe.

Again, this is far from ideal. There are better solutions if you can avoid this but if you find yourself in a situation where you don't own the code relying on Assembly.GetEntryAssembly(), this will get you by in a pinch.

Answer 2

This is perhaps one way to do what you want. What I'm demonstrating here is passing and receiving metadata to the created AppDomain via SetData and GetData methods so disregard how I am creating the actual remote type.

using System;
using System.Reflection;

namespace ConsoleApplication13
{
    class Program
    {
        static void Main(string[] args)
        {
            AppDomain appDomain = AppDomain.CreateDomain("foo");

            appDomain.SetData(FooUtility.SourceKey, FooUtility.SourceValue);

            IFoo foo = (IFoo)appDomain.CreateInstanceFromAndUnwrap(Assembly.GetEntryAssembly().Location, typeof(Foo).FullName);

            foo.DoSomething();
        }
    }

    public static class FooUtility
    {
        public const string SourceKey = "Source";
        public const string SourceValue = "Foo Host";
    }

    public interface IFoo
    {
        void DoSomething();
    }

    public class Foo : MarshalByRefObject, IFoo
    {
        public void DoSomething()
        {
            string source = AppDomain.CurrentDomain.GetData(FooUtility.SourceKey) as string;

            if (String.IsNullOrWhiteSpace(source))
                source = "some default";

            Console.WriteLine(source);
        }
    }
}

Which outputs:

Foo Host
Press any key to continue ...

So in your case, you could pass whatever source metadata to the AppDomain:

this._appDomain = AppDomain.CreateDomain(this._appName, AppDomain.CurrentDomain.Evidence, appDomainSetup);

this._appDomain.SetData("Source", "MyController");

this._startStopControllerToRun = (IStartStop)this._appDomain.CreateInstanceFromAndUnwrap(assemblyName, this._fullyQualifiedClassName);
this._startStopControllerToRun.Start();

and in your GetSource method check for its existence.

private static string GetSource()
{
    try
    {
        string source = AppDomain.CurrentDomain.GetData("Source") as string;

        if (!String.IsNullOrWhiteSpace(source))
            return source;

        var assembly = Assembly.GetEntryAssembly();

        // GetEntryAssembly() can return null when called in the context of a unit test project.
        // That can also happen when called from an app hosted in IIS, or even a windows service.
        if (assembly == null)
        {
            // From http://stackoverflow.com/a/14165787/279516:
            assembly = new StackTrace().GetFrames().Last().GetMethod().Module.Assembly;
        }

        return assembly.GetName().Name;
    }
    catch
    {
        return "Unknown";
    }
}

UPDATE ALTERNATIVE

You could also declare a public interface method for setting the source on a static location in the target domain as well.

using System;
using System.Reflection;

namespace ConsoleApplication13
{
    class Program
    {
        static void Main(string[] args)
        {
            AppDomain appDomain = AppDomain.CreateDomain("foo");

            IFoo foo = (IFoo)appDomain.CreateInstanceFromAndUnwrap(Assembly.GetEntryAssembly().Location, typeof(Foo).FullName);

            foo.SetSource("Foo Host");

            foo.DoSomething();
        }
    }

    public interface IFoo
    {
        void DoSomething();
        void SetSource(string source);
    }

    public class Foo : MarshalByRefObject, IFoo
    {
        public void DoSomething()
        {
            string source = Foo.Source;

            if (String.IsNullOrWhiteSpace(source))
                source = "some default";

            Console.WriteLine(source);
        }

        public static string Source{get; private set;}

        public void SetSource(string source)
        {
            Foo.Source = source;
        }
    }
}