Handle garbage collection

[marcoscaceres]

The following tasks have been completed:

• Modified Web platform tests (link to pull request)

Implementation commitment:

• Chromium
• Gecko (https://bugzilla.mozilla.org/show_bug.cgi?id=)
• WebKit - Not participating in this working group.

Handles this case:

async function run() {
  const sentinel = await navigator.wakeLock.request("screen");
  sentinel.addEvenListener("release", function() {
       // do stuff
       console.log("Sentinel released!");
  }, { once: true });
  return; 
  // `sentinel` shouldn't get CG here, because we have an event registered
  // "once" removes the listener, allowing the object to be GC'ed.
}

run(); 

I don't know if we have the means to test the above via WPT... can folks think of a way of doing it without a manual test?

Presumedly, Chrome already implements the right thing here.

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Preview | Diff

[marcoscaceres]

Checked Chrome manually. It's implemented. I checked it by switching tabs and forcing the release event to fire, without manually releasing it.

[reillyeon]

Looks good with one comment. I'm also curious if there's a general guide to adding these kinds of considerations to specifications. It's come up occasionally in other APIs and I've never been sure if it is considered implementation-specific behavior.

[marcoscaceres]

for other folks that are interested, I filed a bug on the DOM spec about garbage collection + constructed objects on which events can be registered:
whatwg/dom#1003

@kenchris, maybe something the TAG might take up and add to the "the guide".

[rakuco]

(for completeness, the current Chromium code was added in https://chromium-review.googlesource.com/c/chromium/src/+/1868875 with some unit tests that basically check this behavior. I couldn't find a way to write a web test for it back then, even if I made it Chromium-specific and used self.gc())

[marcoscaceres]

For a little bit of a giggle, this what I did for permissions:

web-platform-tests/wpt#30190

We could do the same here… it’s not 100% assured to work, but might be good enough.

The main thing that we want to check is that the event actually fires.