Allow scrolling tree nodes to exist in a detached state

• Component: Layout and Rendering
• Status: RESOLVED FIXED

[Simon Fraser (smfr)]

To avoid tricky ordering dependencies between compositing/scrolling tree updates in child and parent frames, we need to make it possible to create ScrollingStateNodes in a detached state (basically calling ScrollingCoordinator::attachToStateTree() with no parent node). This will allow subframes to have a detached subtree of scrolling nodes, then attach this subtree when the iframe layers are hooked up by RenderLayerCompositor.

[Simon Fraser (smfr)]

This is really a consequence of scrolling tree nodes being hidden behind the ScrollingCoordinator interface; a client can't hang on to a scrolling tree node; all it has to hang onto is a ScrollingNodeID.

[Simon Fraser (smfr)]

Created attachment 360248 [details]
Patch

[Radar WebKit Bug Importer]

<rdar://problem/47577565>

[Simon Fraser (smfr)]

https://trac.webkit.org/changeset/240551/webkit

[Shawn Roberts]

It appears that the changes in https://trac.webkit.org/changeset/240551/webkit

Has caused this test css3/filters/blur-filter-page-scroll-self.html

To become a flaky crash on Mac Debug WK2

History https://webkit-test-results.webkit.org/dashboards/flakiness_dashboard.html#showAllRuns=true&tests=css3%2Ffilters%2Fblur-filter-page-scroll-self.html

I reproduce this with run-webkit-tests --root debug-240551 css3/filters/blur-filter-page-scroll-self.html --iterations 500 -f --debug

I was able to reproduce crashes on 240551, but unable to reproduce crashes on 240550

[Frédéric Wang (:fredw)]

(In reply to Shawn Roberts from comment #5)
> It appears that the changes in
> https://trac.webkit.org/changeset/240551/webkit
> 
> Has caused this test css3/filters/blur-filter-page-scroll-self.html
> 
> To become a flaky crash on Mac Debug WK2
> 
> History
> https://webkit-test-results.webkit.org/dashboards/flakiness_dashboard.
> html#showAllRuns=true&tests=css3%2Ffilters%2Fblur-filter-page-scroll-self.
> html
> 
> I reproduce this with run-webkit-tests --root debug-240551
> css3/filters/blur-filter-page-scroll-self.html --iterations 500 -f --debug
> 
> I was able to reproduce crashes on 240551, but unable to reproduce crashes
> on 240550

That seems to be bug 193925, do you still see it after r240609?

[Frédéric Wang (:fredw)]

Comment on attachment 360248 [details]
Patch

View in context: https://bugs.webkit.org/attachment.cgi?id=360248&action=review

> Source/WebCore/page/scrolling/ScrollingStateTree.cpp:222
> +        for (auto child : *children) {

This was modified later r240610 (bug 193930 but I don't have access to it). And the children variable is no longer used.

[Frédéric Wang (:fredw)]

Committed r240651: <https://trac.webkit.org/changeset/240651>

[Shawn Roberts]

(In reply to Frédéric Wang (:fredw) from comment #8)
> Committed r240651: <https://trac.webkit.org/changeset/240651>

It appears it has been resolved. Thank you!