Layout queries on elements in disconnected frames panics

[jdm]

<iframe></iframe>
<script>
  var i = document.querySelector('iframe');
  var d = i.contentDocument;
  var e = d.createElement('div');
  d.body.appendChild(e);
  i.remove();
  setTimeout(function() { e.getBoundingClientRect(); }, 10);
</script>

When we remove an iframe, we shut down its browsing context and layout thread. Layout queries assume that the layout thread always exists, however.

[jdm]

Previously found in #19170.

[jdm]

One way of fixing this would be to merge the script and layout threads.

[jdm]

I think we should fix this by removing this expect call and returning false if the send operation fails instead.

[jdm]

Then we can add an automated test based on the code I provided earlier. We will want to assert that the returned rectangle is zero-sized.

[soniasingla]

@highfive : assign me

[highfive]

Hey @soniasingla! Thanks for your interest in working on this issue. It's now assigned to you!

[highfive]

Hi! If you have any questions regarding this issue, feel free to make a comment here, or ask it in the #servo channel in Matrix.

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[gterzian]

I propose a slightly different solution to this, where at the top of force_reflow we'd add:

if !self.is_alive() {
            warn!("Reflow attempted on zombie window.");
            return false;
}

That way we narrow down the cases where we don't panic to iframes that have been removed from the document, instead of removing the panic entirely, which I think could simply hide other problems.

[jdm]

That sounds reasonable.

[gterzian]

Ok I think it would be even better to make:

servo/components/script/dom/window.rs

Line 2105 in fde47f8

pub fn layout_chan(&self) -> &Sender<Msg> {

return Option<&Sender<Msg>>,

where None would be returned if !self.is_alive()

and make every use of the layout chan go through this function, including inside window.rs.

[alarsyo]

@highfive: assign me

[highfive]

Hey @alarsyo! Thanks for your interest in working on this issue. It's now assigned to you!