Changeset 286411 in webkit

Timestamp:

Dec 1, 2021, 8:58:54 PM (5 years ago)

Author:

Simon Fraser

Message:

Scrolling complex websites can stutter: scrolling thread frame can fail to process wheel events
​https://bugs.webkit.org/show_bug.cgi?id=233739
rdar://85946176

Reviewed by Tim Horton.

While the scrolling thread is chilling in
ThreadedScrollingTree::waitForRenderingUpdateCompletionOrTimeout(), waiting up to half a
frame to allow the main thread to handle the commit (for scroll synchronization), wheel
events may have been dispatched to the scrolling thread.

If we blow the timeout and commit anyway, we need to make sure we've handled these wheel
events first, so that the current frame can commit some layer movement. We can achieve this
by dispatching the applyLayerPositions(), which will enqueue it behind any waiting wheel
event dispatch from EventDispatcher::internalWheelEvent().

• page/scrolling/ScrollingTree.cpp:

(WebCore::ScrollingTree::applyLayerPositions):

• page/scrolling/ThreadedScrollingTree.cpp:

(WebCore::ThreadedScrollingTree::waitForRenderingUpdateCompletionOrTimeout):

Location:

trunk/Source/WebCore

Files:

• ChangeLog (modified) (1 diff)
• page/scrolling/ScrollingTree.cpp (modified) (1 diff)
• page/scrolling/ThreadedScrollingTree.cpp (modified) (1 diff)

trunk/Source/WebCore/ChangeLog

@@ +1 @@
+2021-12-01  Simon Fraser  <simon.fraser@apple.com>
+
+        Scrolling complex websites can stutter: scrolling thread frame can fail to process wheel events
+        https://bugs.webkit.org/show_bug.cgi?id=233739
+        rdar://85946176
+
+        Reviewed by Tim Horton.
+
+        While the scrolling thread is chilling in
+        ThreadedScrollingTree::waitForRenderingUpdateCompletionOrTimeout(), waiting up to half a
+        frame to allow the main thread to handle the commit (for scroll synchronization), wheel
+        events may have been dispatched to the scrolling thread.
+
+        If we blow the timeout and commit anyway, we need to make sure we've handled these wheel
+        events first, so that the current frame can commit some layer movement. We can achieve this
+        by dispatching the applyLayerPositions(), which will enqueue it behind any waiting wheel
+        event dispatch from EventDispatcher::internalWheelEvent().
+
+        * page/scrolling/ScrollingTree.cpp:
+        (WebCore::ScrollingTree::applyLayerPositions):
+        * page/scrolling/ThreadedScrollingTree.cpp:
+        (WebCore::ThreadedScrollingTree::waitForRenderingUpdateCompletionOrTimeout):
+
 2021-12-01  Simon Fraser  <simon.fraser@apple.com>
 

trunk/Source/WebCore/page/scrolling/ScrollingTree.cpp

@@ -438 +438 @@
 void ScrollingTree::applyLayerPositions()
 {
-    ASSERT(isMainThread());
     Locker locker { m_treeLock };
 

trunk/Source/WebCore/page/scrolling/ThreadedScrollingTree.cpp

@@ -418 +418 @@
         // At this point we know the main thread is taking too long in the rendering update,
         // so we give up trying to sync with the main thread and update layers here on the scrolling thread.
-        if (canUpdateLayersOnScrollingThread())
-            applyLayerPositionsInternal();
+        if (canUpdateLayersOnScrollingThread()) {
+            // Dispatch to allow for the scrolling thread to handle any outstanding wheel events before we commit layers.
+            ScrollingThread::dispatch([protectedThis = Ref { *this }]() {
+                protectedThis->applyLayerPositions();
+            });
+        }
         tracePoint(ScrollingThreadRenderUpdateSyncEnd, 1);
     } else