Assembly Loading Extension Points

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This demo uses the extensions points available for affecting managed assembly loading in .NET and shows when they are called by the runtime. The application (AssemblyLoading) loads:

• an assembly that is part of the Microsoft.NETCore.App framework and thus one of the known application assemblies
• an assembly (MyLibrary) that is not referenced by the application and thus requires handling in one of the available extension points to be successfully loaded

The following hooks into the managed assembly loading algorithm are included in this demo:

• AssemblyLoadContext.Load
• AssemblyLoadContext.Resolving
• AppDomain.AssemblyResolve

Build and Run

1. Install .NET 8.0 SDK or later

2. Build the solution with dotnet build

3. Run the generated binary - for example, AssemblyLoading/bin/Debug/net5.0/AssemblyLoading

   • The program will print information about its usage syntax

     • AssemblyLoading <context> [<extension-point>]

   • Example: AssemblyLoading default

     • The default AssemblyLoadContext is used. The extension points are implemented, but none of them load the MyLibrary assembly. The expected output will show each extension point being called:

       === Loading 'System.Xml' ===
       
       Successfully loaded assembly:
       - Assembly: System.Xml, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089
       - Load context: "Default" System.Runtime.Loader.DefaultAssemblyLoadContext #0
       
       === Loading 'MyLibrary' ===
       
       AssemblyLoadContext.Resolving event handler
       - Name: MyLibrary, Culture=neutral, PublicKeyToken=null;
       - Load context: "Default" System.Runtime.Loader.DefaultAssemblyLoadContext #0
       
       AppDomain.AssemblyResolve event handler
       - Name: MyLibrary, Culture=neutral, PublicKeyToken=null
       
       System.IO.FileNotFoundException: Could not load file or assembly 'MyLibrary, Culture=neutral, PublicKeyToken=null'. The system cannot find the file specified.
       File name: 'MyLibrary, Culture=neutral, PublicKeyToken=null'
       

   • Example: AssemblyLoading custom alc-resolving

     • A new custom AssemblyLoadContext is used. The extension points are implemented and the handler for the Resolving event on the custom AssemblyLoadContext loads the MyLibrary assembly. The expected output will show each extension point being called:

       === Loading 'System.Xml' ===
       
       AssemblyLoadContext.Load
       - Name: System.Xml, Culture=neutral, PublicKeyToken=null
       - Load context: "CustomALC" AssemblyLoading.Program+CustomALC #0
       
       Successfully loaded assembly:
       - Assembly: System.Xml, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089
       - Load context: "Default" System.Runtime.Loader.DefaultAssemblyLoadContext #1
       
       === Loading 'MyLibrary' ===
       
       AssemblyLoadContext.Load
       - Name: MyLibrary, Culture=neutral, PublicKeyToken=null
       - Load context: "CustomALC" AssemblyLoading.Program+CustomALC #0
       
       AssemblyLoadContext.Resolving event handler
       - Name: MyLibrary, Culture=neutral, PublicKeyToken=null;
       - Load context: "Default" System.Runtime.Loader.DefaultAssemblyLoadContext #1
       
       AssemblyLoadContext.Resolving event handler
       - Name: MyLibrary, Culture=neutral, PublicKeyToken=null;
       - Load context: "CustomALC" AssemblyLoading.Program+CustomALC #0
       
       Successfully loaded assembly:
       - Assembly: MyLibrary, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null
       - Load context: "CustomALC" AssemblyLoading.Program+CustomALC #0