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// 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 "include/v8-internal.h"
#include "include/v8.h"
#include "src/globals.h"
#include "src/objects.h"
#include "src/objects/slots.h"
#include "src/objects/smi.h"
namespace v8 {
namespace internal {
class HeapObject;
class Isolate;
class StringStream;
// 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:
MaybeObject() : ptr_(kNullAddress) {}
explicit MaybeObject(Address ptr) : ptr_(ptr) {}
bool operator==(const MaybeObject& other) const { return ptr_ == other.ptr_; }
bool operator!=(const MaybeObject& other) const { return ptr_ != other.ptr_; }
Address ptr() const { return ptr_; }
// Enable incremental transition of client code.
MaybeObject* operator->() { return this; }
const MaybeObject* operator->() const { return this; }
bool IsSmi() const { return HAS_SMI_TAG(ptr_); }
inline bool ToSmi(Smi* value);
inline Smi ToSmi() const;
bool IsCleared() const {
return static_cast<uint32_t>(ptr_) == kClearedWeakHeapObjectLower32;
}
inline bool IsStrongOrWeak() const;
inline bool IsStrong() const;
// If this MaybeObject is a strong pointer to a HeapObject, returns true and
// sets *result. Otherwise returns false.
inline bool GetHeapObjectIfStrong(HeapObject* result) const;
// DCHECKs that this MaybeObject is a strong pointer to a HeapObject and
// returns the HeapObject.
inline HeapObject GetHeapObjectAssumeStrong() const;
inline bool IsWeak() const;
inline bool IsWeakOrCleared() const;
// If this MaybeObject is a weak pointer to a HeapObject, returns true and
// sets *result. Otherwise returns false.
inline bool GetHeapObjectIfWeak(HeapObject* result) const;
// DCHECKs that this MaybeObject is a weak pointer to a HeapObject and
// returns the HeapObject.
inline HeapObject GetHeapObjectAssumeWeak() const;
// If this MaybeObject is a strong or weak pointer to a HeapObject, returns
// true and sets *result. Otherwise returns false.
inline bool GetHeapObject(HeapObject* result) const;
inline bool GetHeapObject(HeapObject* result,
HeapObjectReferenceType* reference_type) const;
// DCHECKs that this MaybeObject is a strong or a weak pointer to a HeapObject
// and returns the HeapObject.
inline HeapObject GetHeapObject() const;
// DCHECKs that this MaybeObject is a strong or a weak pointer to a HeapObject
// or a SMI and returns the HeapObject or SMI.
inline Object GetHeapObjectOrSmi() const;
inline bool IsObject() const;
template <typename T>
T cast() const {
DCHECK(!HasWeakHeapObjectTag(ptr_));
return T::cast(Object(ptr_));
}
static MaybeObject FromSmi(Smi smi) {
DCHECK(HAS_SMI_TAG(smi->ptr()));
return MaybeObject(smi->ptr());
}
static MaybeObject FromObject(Object object) {
DCHECK(!HasWeakHeapObjectTag(object.ptr()));
return MaybeObject(object.ptr());
}
static inline MaybeObject MakeWeak(MaybeObject object);
#ifdef VERIFY_HEAP
static void VerifyMaybeObjectPointer(Isolate* isolate, MaybeObject p);
#endif
// Prints this object without details.
void ShortPrint(FILE* out = stdout);
// Prints this object without details to a message accumulator.
void ShortPrint(StringStream* accumulator);
void ShortPrint(std::ostream& os);
#ifdef OBJECT_PRINT
void Print();
void Print(std::ostream& os);
#else
void Print() { ShortPrint(); }
void Print(std::ostream& os) { ShortPrint(os); }
#endif
private:
Address ptr_;
};
// 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) {}
explicit HeapObjectReference(Object object) : MaybeObject(object->ptr()) {}
static HeapObjectReference Strong(Object object) {
DCHECK(!object->IsSmi());
DCHECK(!HasWeakHeapObjectTag(object));
return HeapObjectReference(object);
}
static HeapObjectReference Weak(Object object) {
DCHECK(!object->IsSmi());
DCHECK(!HasWeakHeapObjectTag(object));
return HeapObjectReference(object->ptr() | kWeakHeapObjectMask);
}
V8_INLINE static HeapObjectReference ClearedValue(Isolate* isolate);
template <typename THeapObjectSlot>
V8_INLINE static void Update(THeapObjectSlot slot, HeapObject value);
};
} // namespace internal
} // namespace v8
#endif // V8_OBJECTS_MAYBE_OBJECT_H_
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