[wrapper-tracing] Simplify tracing by forbidding tracing from within mixins

third_party/WebKit/Source/platform/heap/GarbageCollected.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 GarbageCollected_h
 #define GarbageCollected_h
 
 #include "platform/heap/ThreadState.h"
 #include "wtf/Allocator.h"
 #include "wtf/Assertions.h"
 #include "wtf/TypeTraits.h"
 
 namespace blink {
 
 template <typename T>
 class GarbageCollected;
-class HeapObjectHeader;
 class InlinedGlobalMarkingVisitor;
 class TraceWrapperBase;
-class WrapperVisitor;
 
 // GC_PLUGIN_IGNORE is used to make the plugin ignore a particular class or
 // field when checking for proper usage.  When using GC_PLUGIN_IGNORE
 // a bug-number should be provided as an argument where the bug describes
 // what needs to happen to remove the GC_PLUGIN_IGNORE again.
 #if COMPILER(CLANG)
 #define GC_PLUGIN_IGNORE(bug) \
   __attribute__((annotate("blink_gc_plugin_ignore")))
 #else
 #define GC_PLUGIN_IGNORE(bug)
@@ skipping 39 matching lines @@
 // Note that this is only enabled for Member<B>. For Member<A> which we can
 // compute the object header addr statically, this dynamic dispatch is not used.
 //
 class PLATFORM_EXPORT GarbageCollectedMixin {
  public:
   typedef int IsGarbageCollectedMixinMarker;
   virtual void adjustAndMark(Visitor*) const = 0;
   virtual void trace(Visitor*) {}
   virtual void adjustAndMark(InlinedGlobalMarkingVisitor) const = 0;
   virtual void trace(InlinedGlobalMarkingVisitor);
-  virtual void adjustAndMarkAndTraceWrapper(const WrapperVisitor*) const = 0;
-  virtual void adjustAndMarkWrapperNoTracing(const WrapperVisitor*) const = 0;
-  virtual void adjustAndTraceMarkedWrapper(const WrapperVisitor*) const = 0;
   virtual bool isHeapObjectAlive() const = 0;
-  virtual HeapObjectHeader* adjustAndGetHeapObjectHeader() const = 0;
 };
 
 #define DEFINE_GARBAGE_COLLECTED_MIXIN_METHODS(VISITOR, TYPE)                 \
  public:                                                                      \
   void adjustAndMark(VISITOR visitor) const override {                        \
     typedef WTF::IsSubclassOfTemplate<typename std::remove_const<TYPE>::type, \
                                       blink::GarbageCollected>                \
         IsSubclassOfGarbageCollected;                                         \
     static_assert(                                                            \
         IsSubclassOfGarbageCollected::value,                                  \
         "only garbage collected objects can have garbage collected mixins");  \
     if (TraceEagerlyTrait<TYPE>::value) {                                     \
       if (visitor->ensureMarked(static_cast<const TYPE*>(this)))              \
         TraceTrait<TYPE>::trace(visitor, const_cast<TYPE*>(this));            \
       return;                                                                 \
     }                                                                         \
     visitor->mark(static_cast<const TYPE*>(this),                             \
                   &blink::TraceTrait<TYPE>::trace);                           \
   }                                                                           \
                                                                               \
  private:
 
-#define DEFINE_GARBAGE_COLLECTED_MIXIN_WRAPPER_METHODS(TYPE)                 \
- private:                                                                    \
-  typedef WTF::IsSubclassOfTemplate<typename std::remove_const<TYPE>::type,  \
-                                    blink::GarbageCollected>                 \
-      IsSubclassOfGarbageCollected;                                          \
-                                                                             \
- public:                                                                     \
-  void adjustAndMarkAndTraceWrapper(const WrapperVisitor* visitor)           \
-      const override {                                                       \
-    static_assert(                                                           \
-        IsSubclassOfGarbageCollected::value,                                 \
-        "only garbage collected objects can have garbage collected mixins"); \
-    return AdjustAndMarkTrait<TYPE>::markAndTraceWrapper(                    \
-        visitor, static_cast<const TYPE*>(this));                            \
-  }                                                                          \
-  void adjustAndMarkWrapperNoTracing(const WrapperVisitor* visitor)          \
-      const override {                                                       \
-    static_assert(                                                           \
-        IsSubclassOfGarbageCollected::value,                                 \
-        "only garbage collected objects can have garbage collected mixins"); \
-    return AdjustAndMarkTrait<TYPE>::markWrapperNoTracing(                   \
-        visitor, static_cast<const TYPE*>(this));                            \
-  }                                                                          \
-  void adjustAndTraceMarkedWrapper(const WrapperVisitor* visitor)            \
-      const override {                                                       \
-    static_assert(                                                           \
-        IsSubclassOfGarbageCollected::value,                                 \
-        "only garbage collected objects can have garbage collected mixins"); \
-    AdjustAndMarkTrait<TYPE>::traceMarkedWrapper(                            \
-        visitor, static_cast<const TYPE*>(this));                            \
-  }                                                                          \
-  HeapObjectHeader* adjustAndGetHeapObjectHeader() const override {          \
-    static_assert(                                                           \
-        IsSubclassOfGarbageCollected::value,                                 \
-        "only garbage collected objects can have garbage collected mixins"); \
-    return AdjustAndMarkTrait<TYPE>::heapObjectHeader(                       \
-        static_cast<const TYPE*>(this));                                     \
-  }                                                                          \
-                                                                             \
- private:
-
 // A C++ object's vptr will be initialized to its leftmost base's vtable after
 // the constructors of all its subclasses have run, so if a subclass constructor
 // tries to access any of the vtbl entries of its leftmost base prematurely,
 // it'll find an as-yet incorrect vptr and fail. Which is exactly what a
 // garbage collector will try to do if it tries to access the leftmost base
 // while one of the subclass constructors of a GC mixin object triggers a GC.
 // It is consequently not safe to allow any GCs while these objects are under
 // (sub constructor) construction.
 //
 // To prevent GCs in that restricted window of a mixin object's construction:
@@ skipping 39 matching lines @@
 // the second one should leave the forbidden GC scope. This is realized by
 // recording the address of B's GarbageCollectedMixinConstructorMarker
 // when the "operator new" for B runs, and leaving the forbidden GC scope
 // when the constructor of the recorded GarbageCollectedMixinConstructorMarker
 // runs.
 #define USING_GARBAGE_COLLECTED_MIXIN(TYPE)                                  \
   IS_GARBAGE_COLLECTED_TYPE();                                               \
   DEFINE_GARBAGE_COLLECTED_MIXIN_METHODS(blink::Visitor*, TYPE)              \
   DEFINE_GARBAGE_COLLECTED_MIXIN_METHODS(blink::InlinedGlobalMarkingVisitor, \
                                          TYPE)                               \
-  DEFINE_GARBAGE_COLLECTED_MIXIN_WRAPPER_METHODS(TYPE)                       \
   DEFINE_GARBAGE_COLLECTED_MIXIN_CONSTRUCTOR_MARKER(TYPE)                    \
  public:                                                                     \
   bool isHeapObjectAlive() const override {                                  \
     return ThreadHeap::isHeapObjectAlive(this);                              \
   }                                                                          \
                                                                              \
  private:
 
 // An empty class with a constructor that's arranged invoked when all derived
 // constructors of a mixin instance have completed and it is safe to allow GCs
@@ skipping 124 matching lines @@
   static FalseType isSizeofKnown(...);
   static T& t;
 
  public:
   static const bool value = sizeof(TrueType) == sizeof(isSizeofKnown(&t));
 };
 
 }  // namespace blink
 
 #endif