Oilpan: move LiveNodeList collections to the heap.

Source/core/dom/NodeRareData.cpp

 /*
  * Copyright (C) 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 40 matching lines @@
         it->value->invalidateCacheForAttribute(attrName);
 
     if (attrName)
         return;
 
     TagCollectionCacheNS::iterator tagCacheEnd = m_tagCollectionCacheNS.end();
     for (TagCollectionCacheNS::iterator it = m_tagCollectionCacheNS.begin(); it != tagCacheEnd; ++it)
         it->value->invalidateCache();
 }
 
+#if ENABLE(OILPAN)
+void NodeListsNodeData::clearWeakMembers(Visitor* visitor)
+{
+    if (m_childNodeList && !visitor->isAlive(m_childNodeList))

[haraken, 2014/05/20 09:27:33]

Nit: You don't need to check m_childNodeList.

+        m_childNodeList.clear();
+    if (!m_childNodeList && !m_atomicNameCaches.size() && !m_tagCollectionCacheNS.size())
+        m_owner->clearNodeLists();
+}
+#endif
+
+void NodeListsNodeData::trace(Visitor* visitor)
+{
+#if ENABLE(OILPAN)

[Erik Corry, 2014/05/20 09:09:48]

An alternative (I think simpler) way to do this would be to just have
m_childNodeList be a weak pointer and call trace on in normally.  In the trace
method of the NodeRareData you check whether the NodeListsNodeData is empty and
if it is you zero the pointer instead of tracing it.  This way there are no
explicitly registered weak callbacks.  The NodeListsNodeData is deleted one GC
later than the rest, but I don't think that's a big deal.

[sof, 2014/05/20 09:54:57]

I like this,it just fits better all around to move the is-empty checking out of
NodeListsNodeData to the object holding the reference. Done.

+    visitor->trace(m_atomicNameCaches);
+    visitor->trace(m_tagCollectionCacheNS);
+    visitor->trace(m_owner);
+    // NOTE: The m_childNodeList weak member is manually updated in
+    // clearWeakMembers() above hence not traced as a weak member
+    // here.
+    visitor->registerWeakMembers<NodeListsNodeData, &NodeListsNodeData::clearWeakMembers>(this);
+#endif
+}
+
 void NodeRareData::traceAfterDispatch(Visitor* visitor)
 {
     visitor->trace(m_mutationObserverData);
+    visitor->trace(m_nodeLists);
 }
 
 void NodeRareData::trace(Visitor* visitor)
 {
     if (m_isElementRareData)
         static_cast<ElementRareData*>(this)->traceAfterDispatch(visitor);
     else
         traceAfterDispatch(visitor);
 }
 
 void NodeRareData::finalizeGarbageCollectedObject()
 {
     RELEASE_ASSERT(!renderer());
     if (m_isElementRareData)
         static_cast<ElementRareData*>(this)->~ElementRareData();
     else
         this->~NodeRareData();
 }
 
 // Ensure the 10 bits reserved for the m_connectedFrameCount cannot overflow
 COMPILE_ASSERT(Page::maxNumberOfFrames < (1 << NodeRareData::ConnectedFrameCountBits), Frame_limit_should_fit_in_rare_data_count);
 
 } // namespace WebCore