I am currently writing an application suite with a plugin system that loads plugins at runtime using the MEF framework.
I have currently setup one of my top level WPF applications to embed it's referenced DLLs as embedded resources and load them at runtime using the method described here.
This works fine and I get my single file WPF application that runs fine.
However, another of my top level console applications uses the MEF framework to load plugins at runtime (the WPF application is fixed and includes the plugins explicitly). My plugins have several dependencies themselves on various libraries and the extensions folder that the console application loads the plugins from is littered with all the various library dlls.
I would like to embed the dependencies of each plugin within itself so that my extensions directory contains only the top level DLL files. The method that I have used above does not cater for this approach as the plugin component cannot find the required dependency as it is only the executing assembly that is being searched for these embedded resources.
My current OnResolveAssembly method looks like this:
public static Assembly OnResolveAssembly(object sender, ResolveEventArgs args)
{
Assembly executingAssembly = Assembly.GetExecutingAssembly();
var assemblyName = new AssemblyName(args.Name);
string path = assemblyName.Name + ".dll";
if (assemblyName.CultureInfo.Equals(CultureInfo.InvariantCulture) == false)
{
path = String.Format(#"{0}\{1}", assemblyName.CultureInfo, path);
}
using (Stream stream = executingAssembly.GetManifestResourceStream(path))
{
if (stream == null)
return null;
var assemblyRawBytes = new byte[stream.Length];
stream.Read(assemblyRawBytes, 0, assemblyRawBytes.Length);
return Assembly.Load(assemblyRawBytes);
}
}
I'm thinking that the best way to proceed would be to add in functionality to keep track of all assemblies loaded in a list and once a new assembly has been loaded in this way, recursively do the same; load any embedded DLLs within those as you go. You can then add these DLLs to the list which will act as a cache.
Is there perhaps a better way to proceed with this?
I have implemented a very similar solution to yours and it works very fine for me. As you can see I keep track of already loaded assemblies in a _references dictionary.
In my case, I do not need to "eagerly" load all embedded dependencies in any recursive way, but rather my embedded assemblies do register themselves with the application host on-demand.
public static class ApplicationHost
{
private static readonly Dictionary<string, Assembly> _references = new Dictionary<string, Assembly>();
[STAThread]
private static void Main()
{
AppDomain.CurrentDomain.AssemblyResolve += (sender, args) => _references.ContainsKey(args.Name) ? _references[args.Name] : null;
RegisterAssemblyAndEmbeddedDependencies();
// continue application bootstrapping...
}
public static void RegisterAssemblyAndEmbeddedDependencies()
{
var assembly = Assembly.GetCallingAssembly();
_references[assembly.FullName] = assembly;
foreach (var resourceName in assembly.GetManifestResourceNames())
{
using (var resourceStream = assembly.GetManifestResourceStream(resourceName))
{
var rawAssembly = new byte[resourceStream.Length];
resourceStream.Read(rawAssembly, 0, rawAssembly.Length);
var reference = Assembly.Load(rawAssembly);
_references[reference.FullName] = reference;
}
}
}
}
Related
I have a .Net Framework WPF application that I'm currently migrating to .Net6. At startup it examines certain assemblies in the executable folder looking for any with a custom assembly attribute. Those that have this are then loaded into the current appdomain. (Note that some of these assemblies may already be in the appdomain, as they are projects in the running application's solution).
This is the 4.x code:
private void LoadAssemblies(string folder)
{
AppDomain.CurrentDomain.ReflectionOnlyAssemblyResolve +=
(s, e) => Assembly.ReflectionOnlyLoad(e.Name);
var assemblyFiles = Directory.GetFiles(folder, "*.Client.dll");
foreach (var assemblyFile in assemblyFiles)
{
var reflectionOnlyAssembly = Assembly.ReflectionOnlyLoadFrom(assemblyFile);
if (ContainsCustomAttr(reflectionOnlyAssembly))
{
var assembly = Assembly.LoadFrom(assemblyFile);
ProcessAssembly(assembly);
}
}
}
The custom assembly attribute (that this code is looking for) has a string property containing a path to a XAML resource file within that assembly. The ProcessAssembly() method adds this resource file to the application's merged dictionary, something like this:
var resourceUri = string.Format(
"pack://application:,,,/{0};component/{1}",
assembly.GetName().Name,
mimicAssemblyAttribute.DataTemplatePath);
var uri = new Uri(resourceUri, UriKind.RelativeOrAbsolute);
application.Resources.MergedDictionaries.Add(new ResourceDictionary { Source = uri });
Just to reiterate, all this works as it should in the .Net 4.x application.
.Net6 on the other hand doesn't support reflection-only loading, nor can you create a second app domain in which to load the assemblies. I rewrote the above code by loading the assemblies being examined into what I understand is a temporary, unloadable context:
private void LoadAssemblies(string folder)
{
var assemblyFiles = Directory.GetFiles(folder, "*.Client.dll");
using (var ctx = new TempAssemblyLoadContext(AppDomain.CurrentDomain.BaseDirectory))
{
foreach (var assemblyFile in assemblyFiles)
{
var assm = ctx.LoadFromAssemblyPath(assemblyFile);
if (ContainsCustomAttr(assm))
{
var assm2 = Assembly.LoadFrom(assemblyFile);
ProcessAssembly(assm2);
}
}
}
}
private class TempAssemblyLoadContext : AssemblyLoadContext, IDisposable
{
private AssemblyDependencyResolver _resolver;
public TempAssemblyLoadContext(string readerLocation)
: base(isCollectible: true)
{
_resolver = new AssemblyDependencyResolver(readerLocation);
}
public void Dispose()
{
Unload();
}
protected override Assembly Load(AssemblyName assemblyName)
{
var path = _resolver.ResolveAssemblyToPath(assemblyName);
if (path != null)
{
return LoadFromAssemblyPath(path);
}
return null;
}
protected override IntPtr LoadUnmanagedDll(string unmanagedDllName)
{
var path = _resolver.ResolveUnmanagedDllToPath(unmanagedDllName);
if (path != null)
{
return LoadUnmanagedDllFromPath(path);
}
return IntPtr.Zero;
}
}
(Note the ProcessAssembly() method is unchanged).
This code "works" in so much as it goes through the motions without crashing. However at a later point when the application starts creating the views, I get the following exception:
The component '..ModeSelectorView' does not have a resource identified by the URI '/.;component/views/modeselector/modeselectorview.xaml'.
This particular view resides in a project of this application's solution, so the assembly will already be in the appdomain. The assembly also contains that custom attribute so the above code will be trying to load it, although I believe that Assembly.LoadFrom() should not load the same assembly again?
Just in case, I modified the "if" block in my LoadAssemblies() method to ignore assemblies already in the app domain:
if (ContainsCustomAttr(assm) && !AppDomain.CurrentDomain.GetAssemblies().Contains(assm))
Sure enough, a breakpoint shows that the assembly in question (containing that view) is ignored and not loaded into the app domain. However I still get the same exception further down the line.
In fact I can comment out the entire "if" block so no assemblies are being loaded into the app domain, and I still get the exception, suggesting that it's caused by loading the assembly into that AssemblyLoadContext.
Also, a breakpoint shows that context is being unloaded via its Dispose() method, upon dropping out of the "using" block in the LoadAssemblies() method.
Edit: even with the "if" block commented out, a breakpoint at the end of the method shows that all the assemblies being loaded by ctx.LoadFromAssemblyPath() are ending up in AppDomain.Current. What am I not understanding? Is the context part of the appdomain and not a separate "area"? How can I achieve this "isolated" loading of assemblies in a similar way to the "reflection only" approach that I was using in .Net 4.x?
Okay, so I found the answer, which is to use MetadataLoadContext. This is essentially the .Net Core replacement for reflection-only loading:
private void LoadAssemblies(string folder)
{
// The load context needs access to the .Net "core" assemblies...
var allAssemblies = Directory.GetFiles(RuntimeEnvironment.GetRuntimeDirectory(), "*.Client.dll").ToList();
// .. and the assemblies that I need to examine.
var assembliesToExamine = Directory.GetFiles(folder, "NuIns.CoDaq.*.Client.dll");
allAssemblies.AddRange(assembliesToExamine);
var resolver = new PathAssemblyResolver(allAssemblies);
using (var mlc = new MetadataLoadContext(resolver))
{
foreach (var assemblyFile in assembliesToExamine)
{
var assm = mlc.LoadFromAssemblyPath(assemblyFile);
if (ContainsCustomAttr(assm))
{
var assm2 = Assembly.LoadFrom(assemblyFile);
AddMimicAssemblyInfo(assm2);
}
}
}
}
I'm writing a WinForms program that uses MEF to load assemblies. Those assemblies are not located in the same folder than the executable.
As I need to perform some file maintenance, I implemented some code in the file Program.cs, before loading the actual WinForm, so the files (even if assemblies) are not loaded (or shouldn't if they are) by the program.
I'm performing two operations:
- Moving a folder from one location to an other one
- Unzipping files from an archive and overwrite dll files from the folder moved (if file from the archive is newer than the one moved)
The problem is that after moving the folder, files in it are locked and cannot be overwritten. I also tried to move files one by one by disposing them when the move is finished.
Can someone explain me why the files are blocked and how I could avoid that
Thanks
private static void InitializePluginsFolder()
{
if (!Directory.Exists(Paths.PluginsPath))
{
Directory.CreateDirectory(Paths.PluginsPath);
}
// Find archive that contains plugins to deploy
var assembly = Assembly.GetExecutingAssembly();
if (assembly.Location == null)
{
throw new NullReferenceException("Executing assembly is null!");
}
var currentDirectory = new FileInfo(assembly.Location).DirectoryName;
if (currentDirectory == null)
{
throw new NullReferenceException("Current folder is null!");
}
// Check if previous installation contains a "Plugins" folder
var currentPluginsPath = Path.Combine(currentDirectory, "Plugins");
if (Directory.Exists(currentPluginsPath))
{
foreach (FileInfo fi in new DirectoryInfo(currentPluginsPath).GetFiles())
{
using (FileStream sourceStream = new FileStream(fi.FullName, FileMode.Open))
{
using (FileStream destStream = new FileStream(Path.Combine(Paths.PluginsPath, fi.Name), FileMode.Create))
{
destStream.Lock(0, sourceStream.Length);
sourceStream.CopyTo(destStream);
}
}
}
Directory.Delete(currentPluginsPath, true);
}
// Then updates plugins with latest version of plugins (zipped)
var pluginsZipFilePath = Path.Combine(currentDirectory, "Plugins.zip");
// Extract content of plugins archive to a temporary folder
var tempPath = string.Format("{0}_Temp", Paths.PluginsPath);
if (Directory.Exists(tempPath))
{
Directory.Delete(tempPath, true);
}
ZipFile.ExtractToDirectory(pluginsZipFilePath, tempPath);
// Moves all plugins to appropriate folder if version is greater
// to the version in place
foreach (var fi in new DirectoryInfo(tempPath).GetFiles())
{
if (fi.Extension.ToLower() != ".dll")
{
continue;
}
var targetFile = Path.Combine(Paths.PluginsPath, fi.Name);
if (File.Exists(targetFile))
{
if (fi.GetAssemblyVersion() > new FileInfo(targetFile).GetAssemblyVersion())
{
// If version to deploy is newer than current version
// Delete current version and copy the new one
// FAILS HERE
File.Copy(fi.FullName, targetFile, true);
}
}
else
{
File.Move(fi.FullName, targetFile);
}
}
// Delete temporary folder
Directory.Delete(tempPath, true);
}
Check the implementation of the GetAssemblyVersion() method used in this part of code:
if (File.Exists(targetFile))
{
if (fi.GetAssemblyVersion() > new FileInfo(targetFile).GetAssemblyVersion())
{
// If version to deploy is newer than current version
// Delete current version and copy the new one
// FAILS HERE
File.Copy(fi.FullName, targetFile, true);
}
}
fi variable has type FileInfo, GetAssemblyVersion() looks like an extension method. You should check how assembly version is retrieved from the file. If this method loads an assembly it should also unload it to release the file.
The separate AppDomain is helpful if you need to load the assembly, do the job and after that unload it. Here is the GetAssemblyVersion method implementation:
public static Version GetAssemblyVersion(this FileInfo fi)
{
AppDomain checkFileDomain = AppDomain.CreateDomain("DomainToCheckFileVersion");
Assembly assembly = checkFileDomain.Load(new AssemblyName {CodeBase = fi.FullName});
Version fileVersion = assembly.GetName().Version;
AppDomain.Unload(checkFileDomain);
return fileVersion;
}
The following implementation of the GetAssemblyVersion() could retrieve the assembly version without loading assembly into your AppDomain. Thnx #usterdev for the hint. It also allows you to get the version without assembly references resolve:
public static Version GetAssemblyVersion(this FileInfo fi)
{
return AssemblyName.GetAssemblyName(fi.FullName).Version;
}
You have to make sure that you are not loading the Assembly into your domain to get the Version from it, otherwise the file gets locked.
By using the AssemblyName.GetAssemblyName() static method (see MSDN), the assembly file is loaded, version is read and then unloaded but not added to your domain.
Here an extension for FileInfo doing so:
public static Version GetAssemblyVersion(this FileInfo fi)
{
AssemblyName an = AssemblyName.GetAssemblyName(fi.FullName);
return an.Version;
}
The below statement locks the file
destStream.Lock(0, sourceStream.Length);
but after that you havent unlocked the file. Perhaps that is the cause of your problem.
I would start checking if you program has actually already loaded the assembly.
two suggestions:
1 - Call a method like this before calling your InitializePluginsFolder
static void DumpLoadedAssemblies()
{
var ads = AppDomain.CurrentDomain.GetAssemblies();
Console.WriteLine(ads.Length);
foreach (var ad in ads)
{
Console.WriteLine(ad.FullName);
// maybe this can be helpful as well
foreach (var f in ad.GetFiles())
Console.WriteLine(f.Name);
Console.WriteLine("*******");
}
}
2 - In the first line of Main, register for AssemblyLoad Event and dump Loaded Assembly in the event handler
public static void Main()
{
AppDomain.CurrentDomain.AssemblyLoad += OnAssemlyLoad;
...
}
static void OnAssemlyLoad(object sender, AssemblyLoadEventArgs args)
{
Console.WriteLine("Assembly Loaded: " + args.LoadedAssembly.FullName);
}
You definitely load assembly using AssemblyName.GetAssemblyName, unfortunately .NET has no conventional ways of checking assembly metadata without loading assembly. To avoid this you can:
Load assembly in separated AppDomain as Nikita suggested, I can add: load it with ReflectionOnlyLoad
Or get assembly version using Mono.Cecil library as Reflector does
Just for completeness: actually you can load assembly into same AppDomain without locking assembly file in two stage: read file contents into byte[] and using Assembly.Load(byte[] rawAssembly) but this way has serious "Loading Context" issues and what will you do with several loaded assemblies :)
I used to have some code which scanned the bin directory of my application for assemblies which weren't loaded in the AppDomain yet and loaded them. It basically looked like:
foreach (var assemblyPath in Directory.GetFiles("path\to\bin", "*.dll"))
{
var inspected = Assembly.ReflectionOnlyLoadFrom(assemblyPath);
Assembly.Load(inspected.GetName());
}
I skipped the try/catch clauses, etc for brevity.
This allowed me to drop assemblies in the bin folder at run-time with implementations for certain interfaces and let the IoC container pick them up automatically. Now with the new Roslyn magic, there are no physical DLL's anymore when debugging. Is there any way to retrieve assembly names, project names or dependency names (in project.json) dynamically.
I guess I have to implement something like this example in the Entropy repo, but I don't know how to implement it for my scenario.
You can use the IAssemblyLoadContextAccessor interface to load ASP.NET 5 class library (.xproj) projects dynamically. The following example code works with Beta 4:
public class Startup
{
public void Configure(IApplicationBuilder app)
{
var assemblyLoadContextAccessor = app.ApplicationServices.GetService<IAssemblyLoadContextAccessor>();
var loadContext = assemblyLoadContextAccessor.Default;
var loadedAssembly = loadContext.Load("NameOfYourLibrary");
}
}
What you are looking for is ILibraryManager implementation which provides access to the complete graph of dependencies for the application. This is already flowed through the ASP.NET 5 DI system. So, you can reach out to it from there.
Sample usage can be found inside RoslynCompilationService.
I solved this issue partly using the ILibraryManager as suggested by #tugberk. I changed the approach a bit which dropped the need of scanning the bin folder for new assemblies. I just want all the loaded assemblies in the current AppDomain.
I injected an instance of the ILibraryManager interface in my type finder class and used the GetReferencingLibraries() method with the name of the core assembly, which is referenced by all the other assemblies in the application.
A sample implementation can be found here, where this is the important part:
public IEnumerable<Assembly> GetLoadedAssemblies()
{
return _libraryManager.GetReferencingLibraries(_coreAssemblyName.Name)
.SelectMany(info => info.Assemblies)
.Select(info => Assembly.Load(new AssemblyName(info.Name)));
}
For .net core users, here is my code for loading assemblies from a specific path. I had to use directives, as it's slightly different for .Net Framework and .Net Core.
In your class header you'll need to declare the using something similar to:
#if NET46
#else
using System.Runtime.Loader;
#endif
And in your function something similar to the following:
string assemblyPath = "c:\temp\assmebly.dll";
#if NET46
Assembly assembly = Assembly.LoadFrom(assemblyPath);
#else
AssemblyLoadContext context = AssemblyLoadContext.Default;
Assembly assembly = context.LoadFromAssemblyPath(assemblyPath);
#endif
Its not ASP.NET but it can be converted easily to asp.net.
bellow if function for loading an assembly, and invoke a method inside a class on that assembly.
private static FormCustomized loadLayout(global::System.String layoutFilename, global::System.String layoutNameSpace)
{
FormCustomized mainForm = default;
Type typeMainLayout = default;
FileInfo layoutFile;
layoutFile = new FileInfo(layoutFilename);
layoutFile.Refresh();
if (!layoutFile.Exists)
{
MessageBox.Show("Layout file not found. You need to reinstall the program");
return default;
}
try
{
Assembly assemblyRaw = Assembly.LoadFrom(layoutFilename);
AssemblyLoadContext context = AssemblyLoadContext.Default;
Assembly assembly = context.LoadFromAssemblyPath(layoutFilename);
Type typeMainLayoutIni = assembly.GetType(layoutNameSpace + ".initializeLayoutClass");
Object iniClass = Activator.CreateInstance(typeMainLayoutIni, true);
MethodInfo methodInfo = typeMainLayoutIni.GetMethod("AssembliesToLoadAtStart");
enVars.assemblies = (Dictionary<string, Environment.environmentAssembliesClass>)methodInfo.Invoke(iniClass, default);
typeMainLayout = assembly.GetType(layoutNameSpace + ".mainAppLayoutForm");
mainForm = Activator.CreateInstance(typeMainLayout, enVars) as FormCustomized;
}
catch (Exception ex)
{
return default;
}
return default;
}
I have a huge application where one project of my solution makes reports.
I want to add new report (update report) without building my project, just add .dll files. I read about Assembly and
AppDomain, but I don't know is it really good way to add new dll for new report and how to update old report in runtime?
Here's my example, it takes my first dll, but second time it doesn't. First dll - sum, second - deducted.
static void Main(string[] args)
{
try
{
//first domain
AppDomain domain = AppDomain.CreateDomain("MyDomain");
AssemblyDll asb1 = new AssemblyDll();
Console.WriteLine(asb1.AssemblyMethod(1));
AppDomain.Unload(domain);
Console.ReadKey();
//second domain
AppDomain newDomain = AppDomain.CreateDomain("myNewDomain");
AssemblyDll asb2 = new AssemblyDll();
Console.WriteLine(asb2.AssemblyMethod(2));
AppDomain.Unload(newDomain);
Console.ReadKey();
}
catch (Exception ex)
{
Console.WriteLine(ex.Message);
}
}
}
public class AssemblyDll
{
public string AssemblyMethod(int version)
{
//loading .dll
Assembly assembly = Assembly.LoadFrom(#"../../../../Assembly/DynamicDLL" + version + ".dll");
Type type = assembly.GetType("DynamicDLL.Dynamic");
object instance = Activator.CreateInstance(type);
MethodInfo[] methods = type.GetMethods();
//invoke method
object result = methods[0].Invoke(instance, new object[] { 5, 3 });
return result.ToString();
}
}
My .dll file comes from:
namespace DynamicDLL
{
public class Dynamic
{
public int DynamicMethod(int a, int b)
{
return a + b;
//return a - b;
}
}
}
If you want to write something like plugins and like the plugin approach, you should take a look at MEF http://msdn.microsoft.com/en/library/vstudio/dd460648.aspx
MEF allows you to use any assembly dynamically and even drop dlls into a folder and build a MEF catalog out of it.
Actually Visual Studio and uses MEF internally for extensiblility (Plugins...)
Assemblies are generally loaded into an AppDomain once and you cannot unload them once loaded.
You can create a new AppDomain and load your assemblies into this and when you release this the assemblies will be unloaded. However the caveat here is you cannot directly communicate between two AppDomain you have to marshal between the two using some other method like remoting.
There's been much wrote on this in terms of plugins and making plugins unloadable, a quick Google search presented these:
http://www.brad-smith.info/blog/archives/500
http://adrianvintu.com/blogengine/post/Unloadable-plugins.aspx
Hopefully these will aid you.
I have written a small piece of code regarding the dynamic loading of assemblies and creating class instances from those assemblies, including an executable, a test lib to be dynamically loaded and a loader library to load dynamic assembly into a new Appdomain. Loader library is referenced by both executable and the dynamic library.
//executable
[System.STAThreadAttribute()]
[System.LoaderOptimization(LoaderOptimization.MultiDomain)]
static void Main(string[] args)
{
AppDomainSetup domainSetup = new AppDomainSetup()
{
ApplicationBase = AppDomain.CurrentDomain.SetupInformation.ApplicationBase,
ConfigurationFile = AppDomain.CurrentDomain.SetupInformation.ConfigurationFile,
ApplicationName = AppDomain.CurrentDomain.SetupInformation.ApplicationName,
LoaderOptimization = LoaderOptimization.MultiDomain
};
AppDomain childDomain = AppDomain.CreateDomain("MyDomain", null, domainSetup);
Console.WriteLine(AppDomain.CurrentDomain.SetupInformation.LoaderOptimization.ToString());
Console.WriteLine(childDomain.SetupInformation.LoaderOptimization.ToString());
byte[] assembly = null;
string assemblyName = "CSTestLib";
using (FileStream fs = new FileStream(assemblyName+".dll",FileMode.Open))
{
byte[] byt = new byte[fs.Length];
fs.Read(byt,0,(int)fs.Length);
assembly = byt;
}
object[] pararmeters = {assemblyName,assembly};
string LoaderAssemblyName = typeof(AssemblyLoader).Assembly.FullName;
string LoaderClassName = typeof(AssemblyLoader).FullName;
AssemblyLoader assloader = (AssemblyLoader)childDomain.CreateInstanceAndUnwrap(LoaderAssemblyName,LoaderClassName , true, BindingFlags.CreateInstance, null, parameters, null, null);
object obj = assloader.Load("CSTestLib.Class1");
object obj2 = assloader.Load("CSTestLib.Class2");
AppDomain.Unload(childDomain);
Console.ReadKey();
}
//Dynamic Lib
using System;
namespace CSTestLib
{
public class Class1 :MarshalByRefObject
{
public Class1() { }
}
public class Class2 : MarshalByRefObject
{
public Class2() { }
}
}
//Loader Library
using System;
namespace LoaderLibrary
{
public class AssemblyLoader : MarshalByRefObject
{
string assemblyName;
public AssemblyLoader(string assName, byte[] ass)
{
assemblyName = assName;
AppDomain.CurrentDomain.Load(ass);
Console.WriteLine(AppDomain.CurrentDomain.FriendlyName + " " + AppDomain.CurrentDomain.SetupInformation.LoaderOptimization.ToString());
}
public object Load(string className)
{
object ret = null;
try
{
ret = AppDomain.CurrentDomain.CreateInstanceAndUnwrap(assemblyName, className);
}
catch (System.Exception ex)
{
Console.WriteLine(ex.Message);
}
return ret;
}
}
}
Here I set LoaderOptimizationAttribute on main() method but AppDomain.CurrentDomain.SetupInformation.LoaderOptimization.ToString(); says it is NotSpecified Why?
The differences between MultiDomain and MultiDomainHost is not so clear to me. Is MultiDomainHost for only GAC assemblies? For my situation which is more suitable?
According to this
JIT-compiled code cannot be shared for
assemblies loaded into the load-from
context, using the LoadFrom method of
the Assembly class, or loaded from
images using overloads of the Load
method that specify byte arrays.
So how can I detect if an assembly is loaded domain-neutral or not? How can assure I it is loaded domain-neutral?
This attribute has only an effect if you precompile your assemblies with NGen to speed up a warm start of your application. When you specify MultiDomain or MultiDomainHost you enable the usage of precompiled (ngenned) assemblies. You can verify this with Process Explorer where you can look at the list of loaded modules.
This is one of the biggest startup time savers if your application consists of several executable instances which share assemblies. This enables .NET to share the code pages between processes which in turn saves real memory (one assembly exists only once in the physical memory but it is shared between one or more processes) and prevents JITing the same code over and over again in each process which takes time at the cost that the generated code is a little less efficient as it could be when it would be compiled with the regular JIT which can use more dynamic data to generate the most efficient code.
In your example you load the assembly into a byte array which is located in the managed heap and increases your private byte count. This makes it impossible to share data between processes. Only read only pages which have a counterpart on your hard disc can be shared between processes. This is the reason why the attribute has no effect. If you are after a factor 2 of warm startup performance this is the attribute you were seeking for. For anything else it is not relevant.
Now back to your original question:
It is set but when you start your application under a debugger this MultiDomain attribute is ignored. When you start it outside of a debugger you will get the expected results.
Yes MultiDomainHost does enable AppDomain neutrality only for signed assemblies all others are not shared.
Code sharing can only happen when it is precompiled. The real question is: How to check if the assembly is precompiled? I do it with Process Explorer by looking at the list of loaded modules. When my loaded assembly shows up with a path to the Native Image cache and an .ni extension I am sure the precompiled image is beeing used. You can check this also with fuslogvw when you set the radio button to Native Images to check why a native images was not used by the runtime.