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// Copyright 2023 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 INCLUDE_V8_HANDLE_BASE_H_
#define INCLUDE_V8_HANDLE_BASE_H_
#include "v8-internal.h" // NOLINT(build/include_directory)
namespace v8 {
namespace internal {
// Helper functions about values contained in handles.
// A value is either an indirect pointer or a direct pointer, depending on
// whether direct local support is enabled.
class ValueHelper final {
public:
#ifdef V8_ENABLE_DIRECT_LOCAL
static constexpr Address kTaggedNullAddress = 1;
static constexpr Address kEmpty = kTaggedNullAddress;
#else
static constexpr Address kEmpty = kNullAddress;
#endif // V8_ENABLE_DIRECT_LOCAL
template <typename T>
V8_INLINE static bool IsEmpty(T* value) {
return reinterpret_cast<Address>(value) == kEmpty;
}
// Returns a handle's "value" for all kinds of abstract handles. For Local,
// it is equivalent to `*handle`. The variadic parameters support handle
// types with extra type parameters, like `Persistent<T, M>`.
template <template <typename T, typename... Ms> typename H, typename T,
typename... Ms>
V8_INLINE static T* HandleAsValue(const H<T, Ms...>& handle) {
return handle.template value<T>();
}
#ifdef V8_ENABLE_DIRECT_LOCAL
template <typename T>
V8_INLINE static Address ValueAsAddress(const T* value) {
return reinterpret_cast<Address>(value);
}
template <typename T, bool check_null = true, typename S>
V8_INLINE static T* SlotAsValue(S* slot) {
if (check_null && slot == nullptr) {
return reinterpret_cast<T*>(kTaggedNullAddress);
}
return *reinterpret_cast<T**>(slot);
}
#else // !V8_ENABLE_DIRECT_LOCAL
template <typename T>
V8_INLINE static Address ValueAsAddress(const T* value) {
return *reinterpret_cast<const Address*>(value);
}
template <typename T, bool check_null = true, typename S>
V8_INLINE static T* SlotAsValue(S* slot) {
return reinterpret_cast<T*>(slot);
}
#endif // V8_ENABLE_DIRECT_LOCAL
};
/**
* Helper functions about handles.
*/
class HandleHelper final {
public:
/**
* Checks whether two handles are equal.
* They are equal iff they are both empty or they are both non-empty and the
* objects to which they refer are physically equal.
*
* If both handles refer to JS objects, this is the same as strict equality.
* For primitives, such as numbers or strings, a `false` return value does not
* indicate that the values aren't equal in the JavaScript sense.
* Use `Value::StrictEquals()` to check primitives for equality.
*/
template <typename T1, typename T2>
V8_INLINE static bool EqualHandles(const T1& lhs, const T2& rhs) {
if (lhs.IsEmpty()) return rhs.IsEmpty();
if (rhs.IsEmpty()) return false;
return lhs.ptr() == rhs.ptr();
}
static V8_EXPORT void VerifyOnStack(const void* ptr);
};
} // namespace internal
/**
* A base class for abstract handles containing indirect pointers.
* These are useful regardless of whether direct local support is enabled.
*/
class IndirectHandleBase {
public:
// Returns true if the handle is empty.
V8_INLINE bool IsEmpty() const { return location_ == nullptr; }
// Sets the handle to be empty. IsEmpty() will then return true.
V8_INLINE void Clear() { location_ = nullptr; }
protected:
friend class internal::ValueHelper;
friend class internal::HandleHelper;
V8_INLINE IndirectHandleBase() = default;
V8_INLINE IndirectHandleBase(const IndirectHandleBase& other) = default;
V8_INLINE IndirectHandleBase& operator=(const IndirectHandleBase& that) =
default;
V8_INLINE explicit IndirectHandleBase(internal::Address* location)
: location_(location) {}
// Returns the address of the actual heap object (tagged).
// This method must be called only if the handle is not empty, otherwise it
// will crash.
V8_INLINE internal::Address ptr() const { return *location_; }
// Returns a reference to the slot (indirect pointer).
V8_INLINE internal::Address* const& slot() const { return location_; }
V8_INLINE internal::Address*& slot() { return location_; }
// Returns the handler's "value" (direct or indirect pointer, depending on
// whether direct local support is enabled).
template <typename T>
V8_INLINE T* value() const {
return internal::ValueHelper::SlotAsValue<T, false>(slot());
}
private:
internal::Address* location_ = nullptr;
};
#ifdef V8_ENABLE_DIRECT_LOCAL
/**
* A base class for abstract handles containing direct pointers.
* These are only possible when conservative stack scanning is enabled.
*/
class DirectHandleBase {
public:
// Returns true if the handle is empty.
V8_INLINE bool IsEmpty() const {
return ptr_ == internal::ValueHelper::kEmpty;
}
// Sets the handle to be empty. IsEmpty() will then return true.
V8_INLINE void Clear() { ptr_ = internal::ValueHelper::kEmpty; }
protected:
friend class internal::ValueHelper;
friend class internal::HandleHelper;
V8_INLINE DirectHandleBase() = default;
V8_INLINE DirectHandleBase(const DirectHandleBase& other) = default;
V8_INLINE DirectHandleBase& operator=(const DirectHandleBase& that) = default;
V8_INLINE explicit DirectHandleBase(internal::Address ptr) : ptr_(ptr) {}
// Returns the address of the referenced object.
V8_INLINE internal::Address ptr() const { return ptr_; }
// Returns the handler's "value" (direct pointer, as direct local support
// is guaranteed to be enabled here).
template <typename T>
V8_INLINE T* value() const {
return reinterpret_cast<T*>(ptr_);
}
private:
internal::Address ptr_ = internal::ValueHelper::kEmpty;
};
#endif // V8_ENABLE_DIRECT_LOCAL
} // namespace v8
#endif // INCLUDE_V8_HANDLE_BASE_H_
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