// Copyright 2018 the V8 project 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 V8_OBJECTS_MAYBE_OBJECT_H_ #define V8_OBJECTS_MAYBE_OBJECT_H_ #include "src/execution/local-isolate-wrapper.h" #include "src/objects/tagged-impl.h" namespace v8 { namespace internal { // A MaybeObject is either a SMI, a strong reference to a HeapObject, a weak // reference to a HeapObject, or a cleared weak reference. It's used for // implementing in-place weak references (see design doc: goo.gl/j6SdcK ) class MaybeObject : public TaggedImpl<HeapObjectReferenceType::WEAK, Address> { public: constexpr MaybeObject() : TaggedImpl(kNullAddress) {} constexpr explicit MaybeObject(Address ptr) : TaggedImpl(ptr) {} // These operator->() overloads are required for handlified code. constexpr const MaybeObject* operator->() const { return this; } V8_INLINE static MaybeObject FromSmi(Smi smi); V8_INLINE static MaybeObject FromObject(Object object); V8_INLINE static MaybeObject MakeWeak(MaybeObject object); #ifdef VERIFY_HEAP static void VerifyMaybeObjectPointer(Isolate* isolate, MaybeObject p); #endif private: template <typename TFieldType, int kFieldOffset> friend class TaggedField; }; // A HeapObjectReference is either a strong reference to a HeapObject, a weak // reference to a HeapObject, or a cleared weak reference. class HeapObjectReference : public MaybeObject { public: explicit HeapObjectReference(Address address) : MaybeObject(address) {} V8_INLINE explicit HeapObjectReference(Object object); V8_INLINE static HeapObjectReference Strong(Object object); V8_INLINE static HeapObjectReference Weak(Object object); V8_INLINE static HeapObjectReference ClearedValue(const Isolate* isolate); V8_INLINE static HeapObjectReference ClearedValue( const OffThreadIsolate* isolate); V8_INLINE static HeapObjectReference ClearedValue( LocalIsolateWrapper isolate); template <typename THeapObjectSlot> V8_INLINE static void Update(THeapObjectSlot slot, HeapObject value); }; } // namespace internal } // namespace v8 #endif // V8_OBJECTS_MAYBE_OBJECT_H_