Avoid updating UI-side layer positions for no-op transactions#63293
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webkit-commit-queue merged 1 commit intoApr 23, 2026
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| m_needsApplyLayerPositions = false; | ||
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| Locker locker { m_treeLock }; |
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Do we need to lock before the check? Otherwise won't we have potentially multiple applyLayerPositions() queued that will still think they need to apply later positions even after the first one goes through?
djg
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Apr 22, 2026
| @@ -125,6 +125,8 @@ class ScrollingTree : public ThreadSafeRefCountedAndCanMakeThreadSafeWeakPtr<Scr | |||
| bool commitTreeStateInternal(std::unique_ptr<ScrollingStateTree>&&, std::optional<LayerHostingContextIdentifier>) WTF_REQUIRES_LOCK(m_treeLock); | |||
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| WEBCORE_EXPORT virtual void applyLayerPositions(); | |||
| void setNeedsApplyLayerPositions() { m_needsApplyLayerPositions = true; } | |||
| bool needsApplyLayerPositions() const { return m_needsApplyLayerPositions; } | |||
djg
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Apr 22, 2026
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| if (!m_needsApplyLayerPositions) | ||
| return; | ||
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| m_needsApplyLayerPositions = false; |
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Since std::atomic<bool> m_needsApplyLayerPositions, shouldn't you atomically, get and reset m_needsApplyLayerPositions to false? Then the winning thread can proceed.
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Updated to use m_needsApplyLayerPositions.exchange()
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https://bugs.webkit.org/show_bug.cgi?id=312959 rdar://175308880 Reviewed by Brent Fulgham. Currently, after every RemoteLayerTree commit that is received by the UI process, we call `applyScrollingTreeLayerPositionsAfterCommit()`, which traverses the scrolling tree and updates CALayer positions. If the transaction contains no scrolling tree changes, then this is not necessary; `applyLayerPositions()` only needs to be called after a scrolling tree state change, or after a user scroll. Track this state via `ScrollingTree::m_needsApplyLayerPositions()`, and set the flag under `commitTreeState()` and `scrollingTreeNodeDidScroll()`. It's the `commitTreeState(()` call that's skipped when `stateTree->hasChangedProperties()` is false. This should be a minor power saving. * Source/WebCore/page/scrolling/ScrollingTree.cpp: (WebCore::ScrollingTree::scrollingTreeNodeDidScroll): (WebCore::ScrollingTree::commitTreeStateInternal): (WebCore::ScrollingTree::applyLayerPositions): * Source/WebCore/page/scrolling/ScrollingTree.h: (WebCore::ScrollingTree::setNeedsApplyLayerPositions): Canonical link: https://commits.webkit.org/311816@main
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Committed 311816@main (8ff9ee2): https://commits.webkit.org/311816@main Reviewed commits have been landed. Closing PR #63293 and removing active labels. |
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