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Module structure

The SampleModule has the following folder structure:

└───SampleModule
    │   Greeting.Commands.dll
    │   LocalDependency.dll
    │   SampleModule.psd1
    │
    └───Dependencies
            SharedDependency.dll

SampleModule.psd1 declares a nested module: NestedModules = @('Greeting.Commands.dll').

Greeting.Commands.dll references 2 dependencies: SharedDependency.dll and LocalDependency.dll. It contains:

  1. CustomALC.cs - A custom implementation of AssemblyLoadContext and the code that registers a handler to AssemblyLoadContext.Default.Resolving event when the module is loaded (of course, unregister when the module is removed).
  2. Command.cs - The real business logic of the module that exposes the Get-Greeting cmdlet.

LocalDependency.dll contains the real business logic of the module, which acts like a utility assembly needed by Greeting.Commands.dll. It also references SharedDependency.dll. This utility assembly is added to this sample intentionally, to demonstrate the behaviors when a module needs to request for loading the same assembly more than once.

SharedDependency.dll is the conflicting dependency assembly. The version referenced by SampleModule is 1.0.0.0.

How it works

During the loading of the nested module Greeting.Commands.dll, its OnImport implementation will be called, which will register a handler to the AssemblyLoadContext.Default.Resolving event.

The handler only reacts to the loading request of the 1.0.0.0 version of SharedDependency.dll, because that's the version this module depends on. The handler uses a singleton instance of the custom AssemblyLoadContext to serve all loading requests, so that it's guaranteed to return the same assembly instance for all loading requests it serves. The custom AssemblyLoadContext looks for the requested assembly from the Dependencies folder under the module base, and that's why SharedDependency.dll is placed there.

The syntax of Get-Greeting is

Get-Greeting -UseSharedDependency [<CommonParameters>]

Get-Greeting -UseLocalDependency [<CommonParameters>]

When -UseSharedDependency is specified, the loading of SharedDependency.dll will be triggered. When -UseLocalDependency is specified, the loading of LocalDependency.dll will be triggered, which will then trigger another loading request of SharedDependency.dll.