Simple BlinkGC heap compaction.

third_party/WebKit/Source/platform/heap/Heap.h

 /*
  * Copyright (C) 2013 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 63 matching lines @@
     if (UNLIKELY(!!freeHook))
       freeHook(address);
   }
 
  private:
   static AllocationHook* m_allocationHook;
   static FreeHook* m_freeHook;
 };
 
 class CrossThreadPersistentRegion;
+class HeapCompact;
 template <typename T>
 class Member;
 template <typename T>
 class WeakMember;
 template <typename T>
 class UntracedMember;
 
 template <typename T, bool = NeedsAdjustAndMark<T>::value>
 class ObjectAliveTrait;
 
@@ skipping 280 matching lines @@
   bool popAndInvokeGlobalWeakCallback(Visitor*);
 
   // Register an ephemeron table for fixed-point iteration.
   void registerWeakTable(void* containerObject,
                          EphemeronCallback,
                          EphemeronCallback);
 #if ENABLE(ASSERT)
   bool weakTableRegistered(const void*);
 #endif
 
+  // Heap compaction registration methods:
+
+  // Register |slot| as containing a reference to a movable heap object.
+  //
+  // When compaction moves the object pointed to by |*slot| to |newAddress|,
+  // |*slot| must be updated to hold |newAddress| instead.
+  void registerMovingObjectReference(MovableReference*);
+
+  // Register a callback to be invoked upon moving the object starting at
+  // |reference|; see |MovingObjectCallback| documentation for details.
+  //
+  // This callback mechanism is needed to account for backing store objects
+  // containing intra-object pointers, all of which must be relocated/rebased
+  // to be done wrt the moved-to location.
+  //
+  // For Blink, |LinkedHashSet<>| is currently the only abstraction which
+  // relies on this feature.
+  void registerMovingObjectCallback(MovableReference,
+                                    MovingObjectCallback,
+                                    void* callbackData);
+
+  // Register a relocation; when |*slot| is compacted and moved,
+  // |slot| must be updated to point to |*slot|'s new location.
+  void registerRelocation(MovableReference* slot);

[haraken, 2016/11/30 06:29:52]

What's a difference between registerMovingObjectReference and
registerRelocation?

Also I cannot find any call site of registerRelocation...?

[sof, 2016/11/30 06:52:43]

Have a look at the documentation of HeapCompact::registerRelocation().

(registerRelocation() is currently not needed for Blink.)

+
   BlinkGC::GCReason lastGCReason() { return m_lastGCReason; }
   RegionTree* getRegionTree() { return m_regionTree.get(); }
 
   static inline size_t allocationSizeFromSize(size_t size) {
     // Add space for header.
     size_t allocationSize = size + sizeof(HeapObjectHeader);
     // The allocation size calculation can overflow for large sizes.
     RELEASE_ASSERT(allocationSize > size);
     // Align size with allocation granularity.
     allocationSize = (allocationSize + allocationMask) & ~allocationMask;
@@ skipping 37 matching lines @@
     ASSERT(gcInfoIndex < GCInfoTable::maxIndex);
     ASSERT(s_gcInfoTable);
     const GCInfo* info = s_gcInfoTable[gcInfoIndex];
     ASSERT(info);
     return info;
   }
 
   static void reportMemoryUsageHistogram();
   static void reportMemoryUsageForTracing();
 
+  HeapCompact* compaction();
+
  private:
   // Reset counters that track live and allocated-since-last-GC sizes.
   void resetHeapCounters();
 
   static int arenaIndexForObjectSize(size_t);
   static bool isNormalArenaIndex(int);
 
   void commitCallbackStacks();
   void decommitCallbackStacks();
 
   RecursiveMutex m_threadAttachMutex;
   ThreadStateSet m_threads;
   ThreadHeapStats m_stats;
   std::unique_ptr<RegionTree> m_regionTree;
   std::unique_ptr<HeapDoesNotContainCache> m_heapDoesNotContainCache;
   std::unique_ptr<SafePointBarrier> m_safePointBarrier;
   std::unique_ptr<FreePagePool> m_freePagePool;
   std::unique_ptr<OrphanedPagePool> m_orphanedPagePool;
   std::unique_ptr<CallbackStack> m_markingStack;
   std::unique_ptr<CallbackStack> m_postMarkingCallbackStack;
   std::unique_ptr<CallbackStack> m_globalWeakCallbackStack;
   std::unique_ptr<CallbackStack> m_ephemeronStack;
   BlinkGC::GCReason m_lastGCReason;
   StackFrameDepth m_stackFrameDepth;
 
+  std::unique_ptr<HeapCompact> m_compaction;
+
   static ThreadHeap* s_mainThreadHeap;
 
   friend class ThreadState;
 };
 
 template <typename T>
 struct IsEagerlyFinalizedType {
   STATIC_ONLY(IsEagerlyFinalizedType);
 
  private:
@@ skipping 194 matching lines @@
 template <typename T>
 void VisitorHelper<Derived>::handleWeakCell(Visitor* self, void* object) {
   T** cell = reinterpret_cast<T**>(object);
   if (*cell && !ObjectAliveTrait<T>::isHeapObjectAlive(*cell))
     *cell = nullptr;
 }
 
 }  // namespace blink
 
 #endif  // Heap_h