WKQCA::CAView::contextDidChangeCallback should do nothing when called on a background thread because it triggers WebCore rendering.
Created attachment 89051 [details]
It would be nice to have a little more information in the bug and ChangeLog about when this could happen and why it's OK to ignore the callback in that case.
It is safe to ignore the contextDidChangeCallback callback from background threads because in that case no changes have actually been committed to the context, so there is no chance animations will have started, etc.
Thanks, Eric. To be even more specific, IIRC, we expect to receive this notification on a background thread due to a CAImageQueue being modified. But in that case, as Eric said, there are no real changes to the context; we just need to render again (which WKCACFView will take care of on its own).
Eric, I think WebKit2 needs the same fix applied in LayerTreeHostCAWin.
http://trac.webkit.org/changeset/83497 for the WK1 part.
http://trac.webkit.org/changeset/83508 for the WK2 portion.