Adding a close event to MessagePort API

[nononokam]

こんにちは TAG-さん!

I'm requesting a TAG review of a close event of MessagePort API.

This is a proposal to add a close event which notifies one of the MessagePorts that the other port has been disentangled (i.e., close() is called, an owning document is destroyed, or the port is garbage collected).

• Explainer¹ (minimally containing user needs and example code): https://github.com/fergald/explainer-messageport-close
• Specification URL: MessagePort API:add a close event whatwg/html#9933
• Tests: https://chromium-review.googlesource.com/c/chromium/src/+/5083156
• User research: Add onclose event to MessagePort whatwg/html#1766 (comment)
• Security and Privacy self-review²: https://github.com/fergald/explainer-messageport-close?tab=readme-ov-file#tag-security--privacy-questionnaire-answers
• GitHub repo (if you prefer feedback filed there): [url]
• Primary contacts (and their relationship to the specification):
  • Nonoka Muraki(@nononokam, Google)
  • Rakina Zata Amni(@rakina, Google)
  • Fergal Daly(@fergald, Google)
• Organization(s)/project(s) driving the specification: Google
• Key pieces of existing multi-stakeholder review or discussion of this specification: Add onclose event to MessagePort whatwg/html#1766
• External status/issue trackers for this specification (publicly visible, e.g. Chrome Status):https://chromestatus.com/feature/5086799659794432

Further details:

• [x] I have reviewed the TAG's Web Platform Design Principles
• Relevant time constraints or deadlines: My intern term will end on 1/19, so It would greatly benefit our efforts if we could receive reviews as soon as possible.
• The group where the work on this specification is currently being done: WHATWG
• The group where standardization of this work is intended to be done (if current group is a community group or other incubation venue): WHATWG
• Major unresolved issues with or opposition to this specification: N/A
• This work is being funded by: Google

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[hober]

Hi @nononokam!

@torgo @LeaVerou @matatk and I looked at this today and we think this looks pretty good! I'm a little worried about this sort-of exposing GC timing sometimes, but you've already considered that and have ended up in a reasonable place.