One layout thread per script thread?

[asajeffrey]

At the moment, every document gets its own layout thread, which is wasteful as most of them are frozen. Can we have one layout thread per script thread instead?

This is related to #14719. cc @emilio

[emilio]

I think yes, also, that's the only way to properly handle iframe resizes from layout's point of view.

[asajeffrey]

It may be a bit tricky to do iframe resizes this way, since the iframe's parent may be in a different process. The constellation is probably going to need to mediate, which may cause issues for synchronous size queries.

[emilio]

Yeah, but visible effects are only on same-origin iframes, check out boris's comment in the other issue.

[asajeffrey]

True, but we might have an A:B:A situation, where the root document and its grandchild are same-origin, but the grandchild is in a cross-origin iframe, so its size depends on a layout thread in another process.

[emilio]

Yeah, but in that case the two same-origin iframes can't have any relationship right? (You can't reach via script the contentDocument of the other, for example, right?)

[jdm]

window.frames[0].contentDocument is totally valid.

[emilio]

Even cross-origin? huh

[asajeffrey]

It allows a grandchild to access it's same-origin grandparent even if it's parent is cross-origin.

[nox]

@asajeffrey Are you actually still working on this?

[asajeffrey]

Not actively. @emilio?

[emilio]

This would be nice, but requires significant rework I'm not actively looking into.