WeakReferenceMessenger automatic cleanup

[Sergio0694]

PR Type

What kind of change does this PR introduce?

• Improvements
• Optimizations

What is the current behavior?

The WeakReferenceMessenger requires users to manually call Cleanup() to perform trimming of internal structures. This is inconvenient for consumers (When should they call this method? Why should they have to worry about this?), or at least, it would be more convenient if the whole behavior was just automatic.

What is the new behavior?

This PR introduces automatic trimming, by leveraging a customized version of the Gen2GcCallback class to register a cleanup callback that will take care of trimming the messenger data structures if needed. Additionally this PR contains some improvements to nullability annotations, as well as one more minor performance improvements still within WeakReferenceMessenger.

PR Checklist

Please check if your PR fulfills the following requirements:

• Tested code with current supported SDKs
• Pull Request has been submitted to the documentation repository instructions. Link:
• Sample in sample app has been added / updated (for bug fixes / features)
  • Icon has been created (if new sample) following the Thumbnail Style Guide and templates
• New major technical changes in the toolkit have or will be added to the Wiki e.g. build changes, source generators, testing infrastructure, sample creation changes, etc...
• Tests for the changes have been added (for bug fixes / features) (if applicable)
• Header has been added to all new source files (run build/UpdateHeaders.bat)
• Contains NO breaking changes

Other information

[ghost]

Thanks Sergio0694 for opening a Pull Request! The reviewers will test the PR and highlight if there is any conflict or changes required. If the PR is approved we will proceed to merge the pull request 🙌

[Sergio0694]

Marking this as ready for review - even if we managed to get dotnet/runtime#53296 approved, that'd still be a separate improvement for WeakReferenceMessenger that we can do in another PR to add .NET 6 support as well (and branched off from #3998). The new auto-cleanup callback looks good on its own in the meantime, so worth taking this in already 🙂

[michael-hawker]

Assuming all the internal changes are covered by the existing unit tests.

Assume that devs still calling Cleanup are also still fine, this change is also now that it's OK if they don't?

[michael-hawker]

wondering if we want to make this a permalink or pin to a certain release for historical reference/comparison in the future?

Otherwise since it's just .NET Foundation code as well, we should be fine with just a link from a license perspective. Though wonder if we want a separate thing to call out other .NET Foundation code we've been using somewhere... 🤔

@clairernovotny do other projects do this somehow that we can refer to? Since we're all the same organization under the same license I don't think there's a legal attribution we need to follow, but was just thinking it could be nice from an evangelism perspective.

[Sergio0694]

"Assuming all the internal changes are covered by the existing unit tests."

Yup, though I've also just added one more test specifically for the automatic cleanup in d326912 just to be extra careful 😄

"Assume that devs still calling Cleanup are also still fine, this change is also now that it's OK if they don't?"

Exactly - it's not a breaking change and calling Cleanup() manually will still work just as fine, but with this PR it'll just no longer be needed and the messenger will take care of automatically trimming all its internal data whenever there's memory pressure 👍

[ghost]

Hello @michael-hawker!

Because this pull request has the auto merge :zap: label, I will be glad to assist with helping to merge this pull request once all check-in policies pass.

p.s. you can customize the way I help with merging this pull request, such as holding this pull request until a specific person approves. Simply @mention me (@msftbot) and give me an instruction to get started! Learn more here.

[michael-hawker]

@Sergio0694 there's a conflict here now. You want to resolve?

[Sergio0694]

@michael-hawker Done, should be good to review! 😄