[WeakMemoryCache] Remove Resource from MemoryCache just before destructed

third_party/WebKit/Source/core/fetch/MemoryCache.cpp

 /*
     Copyright (C) 1998 Lars Knoll (knoll@mpi-hd.mpg.de)
     Copyright (C) 2001 Dirk Mueller (mueller@kde.org)
     Copyright (C) 2002 Waldo Bastian (bastian@kde.org)
     Copyright (C) 2004, 2005, 2006, 2007, 2008 Apple Inc. All rights reserved.
 
     This library is free software; you can redistribute it and/or
     modify it under the terms of the GNU Library General Public
     License as published by the Free Software Foundation; either
     version 2 of the License, or (at your option) any later version.
@@ skipping 61 matching lines @@
 {
     if (RuntimeEnabledFeatures::weakMemoryCacheEnabled())
         m_resourceWeak = resource;
     else
         m_resource = resource;
 }
 
 DEFINE_TRACE(MemoryCacheEntry)
 {
     visitor->trace(m_resource);
-    visitor->trace(m_resourceWeak);
+    visitor->template registerWeakMembers<MemoryCacheEntry, &MemoryCacheEntry::clearResourceWeak>(this);

[Nate Chapin, 2016/06/20 21:54:17]

I don't speak templates, and it stuns me that this is valid syntax. :D

     visitor->trace(m_previousInLiveResourcesList);
     visitor->trace(m_nextInLiveResourcesList);
     visitor->trace(m_previousInAllResourcesList);
     visitor->trace(m_nextInAllResourcesList);
 }
 
+void MemoryCacheEntry::clearResourceWeak(Visitor* visitor)

[haraken, 2016/06/15 08:21:05]

This is not called when the MemoryCacheEntry is dead (i.e., clearResourceWeak is
called only when the MemoryCacheEntry was traced (i.e., alive)). Is it okay?

[hiroshige, 2016/06/15 11:53:41]

It's OK (because MemoryCacheEntry is alive unless it is evicted from 
MemoryCache).

+{
+    if (!m_resourceWeak || ThreadHeap::isHeapObjectAlive(m_resourceWeak))
+        return;
+    memoryCache()->remove(m_resourceWeak.get());
+    m_resourceWeak.clear();
+}
+
 void MemoryCacheEntry::dispose()
 {
     m_resource.clear();
     m_resourceWeak.clear();
 }
 
 Resource* MemoryCacheEntry::resource()
 {
     if (RuntimeEnabledFeatures::weakMemoryCacheEnabled())
         return m_resourceWeak.get();
@@ skipping 716 matching lines @@
                 printf("(%.1fK, %.1fK, %uA, %dR, %d); ", currentResource->decodedSize() / 1024.0f, (currentResource->encodedSize() + currentResource->overheadSize()) / 1024.0f, current->m_accessCount, currentResource->hasClientsOrObservers(), currentResource->isPurgeable());
 
             current = current->m_previousInAllResourcesList;
         }
     }
 }
 
 #endif // MEMORY_CACHE_STATS
 
 } // namespace blink