Simple BlinkGC heap compaction.

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

 // Copyright 2015 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 BlinkGC_h
 #define BlinkGC_h
 
 // BlinkGC.h is a file that defines common things used by Blink GC.
 
 #include "platform/PlatformExport.h"
 #include "wtf/Allocator.h"
 
 namespace blink {
 
 class Visitor;
 
 #define PRINT_HEAP_STATS 0  // Enable this macro to print heap stats to stderr.
 
 using Address = uint8_t*;
 
 using FinalizationCallback = void (*)(void*);
 using VisitorCallback = void (*)(Visitor*, void* self);
 using TraceCallback = VisitorCallback;
 using WeakCallback = VisitorCallback;
 using EphemeronCallback = VisitorCallback;
 using PreFinalizerCallback = bool (*)(void*);
 
+// Simple alias to avoid heap compaction type signatures turning into
+// a sea of generic |void*|s.
+using MovableReference = void*;
+
+// Heap compaction supports registering callbacks that are to be invoked
+// when an object is moved during compaction. This is to support internal
+// location fixups that need to happen as a result.
+//
+// i.e., when the object residing at |from| is moved to |to| by the compaction
+// pass, invoke the callback to adjust any internal references that now need
+// to be |to|-relative.
+using MovingObjectCallback = void (*)(void* callbackData,
+                                      MovableReference from,
+                                      MovableReference to,
+                                      size_t);
+
 // List of typed arenas. The list is used to generate the implementation
 // of typed arena related methods.
 //
 // To create a new typed arena add a H(<ClassName>) to the
 // FOR_EACH_TYPED_ARENA macro below.
 #define FOR_EACH_TYPED_ARENA(H) \
   H(Node)                       \
   H(CSSValue)
 
 #define TypedArenaEnumName(Type) Type##ArenaIndex,
 
 class PLATFORM_EXPORT BlinkGC final {
   STATIC_ONLY(BlinkGC);
 
  public:
   // When garbage collecting we need to know whether or not there
   // can be pointers to Blink GC managed objects on the stack for
   // each thread. When threads reach a safe point they record
   // whether or not they have pointers on the stack.
   enum StackState { NoHeapPointersOnStack, HeapPointersOnStack };
 
   enum GCType {
     // Both of the marking task and the sweeping task run in
     // ThreadHeap::collectGarbage().
     GCWithSweep,
     // Only the marking task runs in ThreadHeap::collectGarbage().
     // The sweeping task is split into chunks and scheduled lazily.
     GCWithoutSweep,
+    // After the marking task has run in ThreadHeap::collectGarbage(),
+    // sweep compaction of some heap arenas is performed. The sweeping
+    // of the remaining arenas is split into chunks and scheduled lazily.
+    GCWithSweepCompaction,
     // Only the marking task runs just to take a heap snapshot.
     // The sweeping task doesn't run. The marks added in the marking task
     // are just cleared.
     TakeSnapshot,
     // The marking task does not mark objects outside the heap of the GCing
     // thread.
     ThreadTerminationGC,
     // Just run thread-local weak processing. The weak processing may trace
     // already marked objects but it must not trace any unmarked object.
     // It's unfortunate that the thread-local weak processing requires
     // a marking visitor. See TODO in HashTable::process.
     ThreadLocalWeakProcessing,
   };
 
   enum GCReason {
     IdleGC,
     PreciseGC,
     ConservativeGC,
     ForcedGC,
     MemoryPressureGC,
     PageNavigationGC,
     NumberOfGCReason,
   };
 
-  enum HeapIndices {
+  enum ArenaIndices {
     EagerSweepArenaIndex = 0,
     NormalPage1ArenaIndex,
     NormalPage2ArenaIndex,
     NormalPage3ArenaIndex,
     NormalPage4ArenaIndex,
     Vector1ArenaIndex,
     Vector2ArenaIndex,
     Vector3ArenaIndex,
     Vector4ArenaIndex,
     InlineVectorArenaIndex,
@@ skipping 10 matching lines @@
 
   enum ThreadHeapMode {
     MainThreadHeapMode,
     PerThreadHeapMode,
   };
 };
 
 }  // namespace blink
 
 #endif