Simple BlinkGC heap compaction.

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

 // 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.
 
 #ifndef MarkingVisitorImpl_h
 #define MarkingVisitorImpl_h
 
 #include "platform/heap/Heap.h"
 #include "platform/heap/ThreadState.h"
 #include "platform/heap/Visitor.h"
@@ skipping 39 matching lines @@
                                             callback);
   }
 
   inline void mark(const void* objectPointer, TraceCallback callback) {
     if (!objectPointer)
       return;
     HeapObjectHeader* header = HeapObjectHeader::fromPayload(objectPointer);
     markHeader(header, header->payload(), callback);
   }
 
-  inline void registerDelayedMarkNoTracing(const void* objectPointer) {
+  inline void registerDelayedMarkNoTracing(void** objectPointer) {
     ASSERT(toDerived()->getMarkingMode() != Visitor::WeakProcessing);
     toDerived()->heap().pushPostMarkingCallback(
-        const_cast<void*>(objectPointer), &markNoTracingCallback);
+        reinterpret_cast<void*>(objectPointer), &markNoTracingCallback);
   }
 
   inline void registerWeakMembers(const void* closure,
                                   const void* objectPointer,
                                   WeakCallback callback) {
     ASSERT(toDerived()->getMarkingMode() != Visitor::WeakProcessing);
     // We don't want to run weak processings when taking a snapshot.
     if (toDerived()->getMarkingMode() == Visitor::SnapshotMarking)
       return;
     toDerived()->heap().pushThreadLocalWeakCallback(
         const_cast<void*>(closure), const_cast<void*>(objectPointer), callback);
   }
 
   inline void registerWeakTable(const void* closure,
                                 EphemeronCallback iterationCallback,
                                 EphemeronCallback iterationDoneCallback) {
     ASSERT(toDerived()->getMarkingMode() != Visitor::WeakProcessing);
     toDerived()->heap().registerWeakTable(
         const_cast<void*>(closure), iterationCallback, iterationDoneCallback);
   }
 
 #if ENABLE(ASSERT)
   inline bool weakTableRegistered(const void* closure) {
     return toDerived()->heap().weakTableRegistered(closure);
   }
 #endif
 
+  inline void registerMovingObjectReference(MovableReference* slot) {
+    if (toDerived()->getMarkingMode() != Visitor::GlobalMarkCompacting)
+      return;
+    toDerived()->heap().registerMovingObjectReference(slot);
+  }
+
+  inline void registerMovingObjectCallback(MovableReference reference,
+                                           MovingObjectCallback callback,
+                                           void* callbackData) {
+    if (toDerived()->getMarkingMode() != Visitor::GlobalMarkCompacting)
+      return;
+    toDerived()->heap().registerMovingObjectCallback(reference, callback,
+                                                     callbackData);
+  }
+
   inline bool ensureMarked(const void* objectPointer) {
     if (!objectPointer)
       return false;
     if (!toDerived()->shouldMarkObject(objectPointer))
       return false;
 #if ENABLE(ASSERT)
     if (HeapObjectHeader::fromPayload(objectPointer)->isMarked())
       return false;
 
     toDerived()->markNoTracing(objectPointer);
@@ skipping 13 matching lines @@
     // We don't want to run weak processings when taking a snapshot.
     if (toDerived()->getMarkingMode() == Visitor::SnapshotMarking)
       return;
     toDerived()->heap().pushGlobalWeakCallback(cell, callback);
   }
 
   Derived* toDerived() { return static_cast<Derived*>(this); }
 
  private:
   static void markNoTracingCallback(Visitor* visitor, void* object) {
-    visitor->markNoTracing(object);
+    // |object| is really the hash table's slot pointing
+    // to the backing store table. Adjust types accordingly..
+    void** reference = reinterpret_cast<void**>(object);
+    visitor->markNoTracing(*reference);
+    visitor->registerBackingStoreReference(reference);

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

What is this change for? Aren't we registering all backing stores in wtf/XXX.h?

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

Not the weakly-held backing stores, which is what this handles. 

[haraken, 2016/11/30 07:09:49]

What's a reason you need to handle weak backing stores specially?

[sof, 2016/11/30 07:26:38]

Keeping their marking and fixup registration together, a property worth
maintaining.

   }
 };
 
 }  // namespace blink
 
 #endif