fix(storage): Prevent duplicate observer registration in TransferWorkerObserver to mitigate OOM issues

[onseok]

• PR title and description conform to Pull Request guidelines.

Issue #, if available:
Issue #2840

Description of changes:
The error appears on devices with limited heap (for example, some tablets or set-top boxes running Android 7.1.2/OS 14) when many pending transfers trigger multiple LiveData observer registrations in the TransferWorkerObserver. These duplicate observer registrations may lead to excessive internal allocations (via Room’s InvalidationTracker, MapBuilder, and SetBuilder), eventually causing OOM.

To address this, the PR introduces a thread-safe set (observedTags) that tracks which transfer tags have already been observed. In the attachObserver() method, we now check if the tag is already present in observedTags and return early if so; otherwise, the observer is registered and the tag is added to the set. Similarly, in removeObserver(), we first verify that the tag exists in observedTags before unregistering the observer and then remove the tag. This change prevents the same transfer from being observed multiple times, reducing memory pressure and mitigating OOM issues without impacting the core functionality of transfer monitoring.

How did you test these changes?
Due to the internal and private visibility of several classes and methods in this module, direct testing of these functions is challenging.

Documentation update required?

• No
• Yes (Please include a PR link for the documentation update)

General Checklist

• Added Unit Tests
• Added Integration Tests
• Security oriented best practices and standards are followed (e.g. using input sanitization, principle of least privilege, etc)

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[tylerjroach]

Thank you for the PR, someone on our team will take a look and get back to you if we have any questions!

[mattcreaser]

Hi @onseok. The idea of the change looks good to me but you missed adding the tag to the set in attachObserver. We can also take advantage of the return values of add/remove.

[mattcreaser]

Once the above updates are made we can run tests and get this merged. Thanks for the contribution! 🚀

[onseok]

Hi @mattcreaser, thank you for the feedback! I've updated the PR to use the return values of add() and remove() for the observedTags set to control observer registration and removal. Please let me know if there are any further suggestions.

[mattcreaser]

Looks good to me. I've started running tests and once we get passes we can merge this to include in our next release.

[mattcreaser]

Hi @onseok the PR is failing lint check. Please run this command and ensure it passes: ./gradlew :aws-storage-s3:ktlintCheck

[onseok]

Hi @mattcreaser, I’ve fixed it by reordering the imports. It should pass ./gradlew :aws-storage-s3:ktlintCheck now!

[mattcreaser]

@onseok this PR has been merged and will be included in our next release. Thanks again!