[Webkit-unassigned] [Bug 74111] New: Some overlay scrollbar API calls in ScrollAnimatorMac can lead to an assertion in RenderBox::mapAbsoluteToLocalPoint

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=74111

           Summary: Some overlay scrollbar API calls in ScrollAnimatorMac
                    can lead to an assertion in
                    RenderBox::mapAbsoluteToLocalPoint
           Product: WebKit
           Version: 528+ (Nightly build)
          Platform: Unspecified
        OS/Version: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Layout and Rendering
        AssignedTo: webkit-unassigned at lists.webkit.org
        ReportedBy: bdakin at apple.com


https://bugs.webkit.org/show_bug.cgi?id=73348 Fixed an extremely reproducible case of this bug, but it is still possible to encounter the assertion. (Sample backtrace below.) Basically, if we call into AppKit to update overlay scrollbar information during layout, then AppKit may call back into WebKit while a layout is still happening via our delegates, and do stuff that we would rather not happen during layout. Sam, Simon, and I discussed this extensively yesterday, and we think that a good way to fix this would be to add zero-delay timer for all of the AppKit calls that can be called during layout. Specifically, that would be the calls in:

ScrollAnimatorMac::notifyPositionChanged()
ScrollAnimatorMac::contentsResized()
…and possibly the add/remove scrollbar functions. (Those functions can definitely be called during a layout, but I don't think the AppKit-related work they do is troublesome.)

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