Check DisplayItemCient aliveness in cached subsequences

third_party/WebKit/Source/platform/graphics/paint/PaintController.cpp

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "platform/graphics/paint/PaintController.h"
 
 #include "platform/TraceEvent.h"
 #include "platform/graphics/GraphicsLayer.h"
 #include "platform/graphics/paint/DrawingDisplayItem.h"
 #include "third_party/skia/include/core/SkPictureAnalyzer.h"
@@ skipping 48 matching lines @@
     if (RuntimeEnabledFeatures::slimmingPaintV2Enabled())
         m_newPaintChunks.decrementDisplayItemIndex();
 }
 
 void PaintController::processNewItem(DisplayItem& displayItem)
 {
     DCHECK(!m_constructionDisabled);
     DCHECK(!skippingCache() || !displayItem.isCached());
 
 #if CHECK_DISPLAY_ITEM_CLIENT_ALIVENESS
-    if (!skippingCache() && (displayItem.isCacheable() || displayItem.isCached()))
-        displayItem.client().beginShouldKeepAlive(this);
+    if (!skippingCache()) {
+        if (displayItem.isCacheable() || displayItem.isCached()) {
+            displayItem.client().beginShouldKeepAlive(this);
+            if (!m_subsequenceClients.isEmpty())
+                displayItem.client().beginShouldKeepAlive(m_subsequenceClients.last());

[chrishtr, 2016/06/18 08:49:57]

What does this do exactly? beginShouldKeepAlive for the begin-subsequence marker
when processing something within the subsequence?
I don't fully understand this yet.

[Xianzhu, 2016/06/18 17:41:30]

Yes, this is to mark the new display item shouldKeepAlive under the current
subsequence. The shouldKeepAlive status will end when the subsequence owner is
invalidated or deleted, which is handled in DisplayItemClient.cpp.

Added comments.

+        }
+
+        if (displayItem.getType() == DisplayItem::Subsequence) {
+            m_subsequenceClients.append(&displayItem.client());
+        } else if (displayItem.getType() == DisplayItem::EndSubsequence) {
+            CHECK(m_subsequenceClients.last() == &displayItem.client());
+            m_subsequenceClients.removeLast();
+        }
+    }
 #endif
 
     if (displayItem.isCached())
         ++m_numCachedNewItems;
 
 #if DCHECK_IS_ON()
     // Verify noop begin/end pairs have been removed.
     if (m_newDisplayItemList.size() >= 2 && displayItem.isEnd()) {
         const auto& beginDisplayItem = m_newDisplayItemList[m_newDisplayItemList.size() - 2];
         if (beginDisplayItem.isBegin() && beginDisplayItem.getType() != DisplayItem::Subsequence && !beginDisplayItem.drawsContent())
@@ skipping 315 matching lines @@
 
 void PaintController::updateCacheGeneration()
 {
     m_currentCacheGeneration = DisplayItemCacheGeneration::next();
     for (const DisplayItem& displayItem : m_currentPaintArtifact.getDisplayItemList()) {
         if (!displayItem.isCacheable())
             continue;
         displayItem.client().setDisplayItemsCached(m_currentCacheGeneration);
     }
 #if CHECK_DISPLAY_ITEM_CLIENT_ALIVENESS
+    CHECK(m_subsequenceClients.isEmpty());
     DisplayItemClient::endShouldKeepAliveAllClients(this);
 #endif
 }
 
 void PaintController::appendDebugDrawingAfterCommit(const DisplayItemClient& displayItemClient, PassRefPtr<SkPicture> picture, const LayoutSize& offsetFromLayoutObject)
 {
     DCHECK(m_newDisplayItemList.isEmpty());
     DrawingDisplayItem& displayItem = m_currentPaintArtifact.getDisplayItemList().allocateAndConstruct<DrawingDisplayItem>(displayItemClient, DisplayItem::DebugDrawing, picture);
     displayItem.setSkippedCache();
     m_currentPaintArtifact.getDisplayItemList().appendVisualRect(visualRectForDisplayItem(displayItem, offsetFromLayoutObject));
@@ skipping 111 matching lines @@
 
 void PaintController::showDebugData() const
 {
     WTFLogAlways("current display item list: [%s]\n", displayItemListAsDebugString(m_currentPaintArtifact.getDisplayItemList()).utf8().data());
     WTFLogAlways("new display item list: [%s]\n", displayItemListAsDebugString(m_newDisplayItemList).utf8().data());
 }
 
 #endif // ifndef NDEBUG
 
 } // namespace blink