Simple BlinkGC heap compaction.

third_party/WebKit/Source/wtf/HashTable.h

 /*
  * Copyright (C) 2005, 2006, 2007, 2008, 2011, 2012 Apple Inc. All rights
  * reserved.
  * Copyright (C) 2008 David Levin <levin@chromium.org>
  *
  * 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 2063 matching lines @@
   // the backing is found in any other way than through its HashTable (ie from
   // an iterator) then the mark bit will be set and the pointers will be
   // marked strongly, avoiding problems with iterating over things that
   // disappear due to weak processing while we are iterating over them. We
   // register the backing store pointer for delayed marking which will take
   // place after we know if the backing is reachable from elsewhere. We also
   // register a weakProcessing callback which will perform weak processing if
   // needed.
   if (Traits::weakHandlingFlag == NoWeakHandlingInCollections) {
     Allocator::markNoTracing(visitor, m_table);
+    // If the backing store will be moved by sweep compaction, register the
+    // table reference pointing to the backing store object, so that the
+    // reference is updated upon object relocation.
+    Allocator::registerBackingStoreReference(visitor, &m_table);
   } else {
-    Allocator::registerDelayedMarkNoTracing(visitor, m_table);
+    Allocator::registerDelayedMarkNoTracing(visitor, &m_table);

[haraken, 2016/11/30 06:29:53]

Why don't we need to register the backing store of weak hash tables?

[sof, 2016/11/30 06:52:44]

See above answer.

     // Since we're delaying marking this HashTable, it is possible that the
     // registerWeakMembers is called multiple times (in rare
     // cases). However, it shouldn't cause any issue.
     Allocator::registerWeakMembers(
         visitor, this, m_table,
         WeakProcessingHashTableHelper<Traits::weakHandlingFlag, Key, Value,
                                       Extractor, HashFunctions, Traits,
                                       KeyTraits, Allocator>::process);
   }
   if (!IsTraceableInCollectionTrait<Traits>::value)
@@ skipping 164 matching lines @@
   CollectionIterator end(toBeRemoved.end());
   for (CollectionIterator it(toBeRemoved.begin()); it != end; ++it)
     collection.remove(*it);
 }
 
 }  // namespace WTF
 
 #include "wtf/HashIterators.h"
 
 #endif  // WTF_HashTable_h