v8-traced-handle.h

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// Copyright 2021 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_TRACED_HANDLE_H_
#define INCLUDE_V8_TRACED_HANDLE_H_
 
#include <stddef.h>
#include <stdint.h>
#include <stdio.h>
 
#include <atomic>
#include <memory>
#include <type_traits>
#include <utility>
 
#include "v8-internal.h"            // NOLINT(build/include_directory)
#include "v8-local-handle.h"        // NOLINT(build/include_directory)
#include "v8-weak-callback-info.h"  // NOLINT(build/include_directory)
#include "v8config.h"               // NOLINT(build/include_directory)
 
namespace v8 {
 
class Value;
 
namespace internal {
 
class BasicTracedReferenceExtractor;
 
enum class GlobalHandleStoreMode {
  kInitializingStore,
  kAssigningStore,
};
 
V8_EXPORT internal::Address* GlobalizeTracedReference(
    internal::Isolate* isolate, internal::Address* handle,
    internal::Address* slot, GlobalHandleStoreMode store_mode);
V8_EXPORT void MoveTracedReference(internal::Address** from,
                                   internal::Address** to);
V8_EXPORT void CopyTracedReference(const internal::Address* const* from,
                                   internal::Address** to);
V8_EXPORT void DisposeTracedReference(internal::Address* global_handle);
 
}  // namespace internal
 
class TracedReferenceBase {
 public:
  bool IsEmpty() const { return val_ == nullptr; }
 
  V8_INLINE void Reset();
 
  V8_INLINE v8::Local<v8::Value> Get(v8::Isolate* isolate) const {
    if (IsEmpty()) return Local<Value>();
    return Local<Value>::New(isolate, reinterpret_cast<Value*>(val_));
  }
 
  bool IsEmptyThreadSafe() const {
    return this->GetSlotThreadSafe() == nullptr;
  }
 
  V8_INLINE void SetWrapperClassId(uint16_t class_id);
 
  V8_INLINE uint16_t WrapperClassId() const;
 
 protected:
  void SetSlotThreadSafe(void* new_val) {
    reinterpret_cast<std::atomic<void*>*>(&val_)->store(
        new_val, std::memory_order_relaxed);
  }
 
  const void* GetSlotThreadSafe() const {
    return reinterpret_cast<std::atomic<const void*> const*>(&val_)->load(
        std::memory_order_relaxed);
  }
 
  V8_EXPORT void CheckValue() const;
 
  // val_ points to a GlobalHandles node.
  internal::Address* val_ = nullptr;
 
  friend class internal::BasicTracedReferenceExtractor;
  template <typename F>
  friend class Local;
  template <typename U>
  friend bool operator==(const TracedReferenceBase&, const Local<U>&);
  friend bool operator==(const TracedReferenceBase&,
                         const TracedReferenceBase&);
};
 
template <typename T>
class BasicTracedReference : public TracedReferenceBase {
 public:
  Local<T> Get(Isolate* isolate) const { return Local<T>::New(isolate, *this); }
 
  template <class S>
  V8_INLINE BasicTracedReference<S>& As() const {
    return reinterpret_cast<BasicTracedReference<S>&>(
        const_cast<BasicTracedReference<T>&>(*this));
  }
 
  T* operator->() const {
#ifdef V8_ENABLE_CHECKS
    CheckValue();
#endif  // V8_ENABLE_CHECKS
    return reinterpret_cast<T*>(val_);
  }
  T* operator*() const {
#ifdef V8_ENABLE_CHECKS
    CheckValue();
#endif  // V8_ENABLE_CHECKS
    return reinterpret_cast<T*>(val_);
  }
 
 private:
  BasicTracedReference() = default;
 
  V8_INLINE static internal::Address* New(
      Isolate* isolate, T* that, void* slot,
      internal::GlobalHandleStoreMode store_mode);
 
  friend class EmbedderHeapTracer;
  template <typename F>
  friend class Local;
  friend class Object;
  template <typename F>
  friend class TracedReference;
  template <typename F>
  friend class BasicTracedReference;
  template <typename F>
  friend class ReturnValue;
};
 
template <typename T>
class TracedReference : public BasicTracedReference<T> {
 public:
  using BasicTracedReference<T>::Reset;
 
  TracedReference() : BasicTracedReference<T>() {}
 
  template <class S>
  TracedReference(Isolate* isolate, Local<S> that) : BasicTracedReference<T>() {
    this->val_ = this->New(isolate, that.val_, &this->val_,
                           internal::GlobalHandleStoreMode::kInitializingStore);
    static_assert(std::is_base_of<T, S>::value, "type check");
  }
 
  V8_INLINE TracedReference(TracedReference&& other) noexcept {
    // Forward to operator=.
    *this = std::move(other);
  }
 
  template <typename S>
  V8_INLINE TracedReference(TracedReference<S>&& other) noexcept {
    // Forward to operator=.
    *this = std::move(other);
  }
 
  V8_INLINE TracedReference(const TracedReference& other) {
    // Forward to operator=;
    *this = other;
  }
 
  template <typename S>
  V8_INLINE TracedReference(const TracedReference<S>& other) {
    // Forward to operator=;
    *this = other;
  }
 
  V8_INLINE TracedReference& operator=(TracedReference&& rhs) noexcept;
 
  template <class S>
  V8_INLINE TracedReference& operator=(TracedReference<S>&& rhs) noexcept;
 
  V8_INLINE TracedReference& operator=(const TracedReference& rhs);
 
  template <class S>
  V8_INLINE TracedReference& operator=(const TracedReference<S>& rhs);
 
  template <class S>
  V8_INLINE void Reset(Isolate* isolate, const Local<S>& other);
 
  template <class S>
  V8_INLINE TracedReference<S>& As() const {
    return reinterpret_cast<TracedReference<S>&>(
        const_cast<TracedReference<T>&>(*this));
  }
};
 
// --- Implementation ---
template <class T>
internal::Address* BasicTracedReference<T>::New(
    Isolate* isolate, T* that, void* slot,
    internal::GlobalHandleStoreMode store_mode) {
  if (that == nullptr) return nullptr;
  internal::Address* p = reinterpret_cast<internal::Address*>(that);
  return internal::GlobalizeTracedReference(
      reinterpret_cast<internal::Isolate*>(isolate), p,
      reinterpret_cast<internal::Address*>(slot), store_mode);
}
 
void TracedReferenceBase::Reset() {
  if (IsEmpty()) return;
  internal::DisposeTracedReference(reinterpret_cast<internal::Address*>(val_));
  SetSlotThreadSafe(nullptr);
}
 
V8_INLINE bool operator==(const TracedReferenceBase& lhs,
                          const TracedReferenceBase& rhs) {
  v8::internal::Address* a = reinterpret_cast<v8::internal::Address*>(lhs.val_);
  v8::internal::Address* b = reinterpret_cast<v8::internal::Address*>(rhs.val_);
  if (a == nullptr) return b == nullptr;
  if (b == nullptr) return false;
  return *a == *b;
}
 
template <typename U>
V8_INLINE bool operator==(const TracedReferenceBase& lhs,
                          const v8::Local<U>& rhs) {
  v8::internal::Address* a = reinterpret_cast<v8::internal::Address*>(lhs.val_);
  v8::internal::Address* b = reinterpret_cast<v8::internal::Address*>(*rhs);
  if (a == nullptr) return b == nullptr;
  if (b == nullptr) return false;
  return *a == *b;
}
 
template <typename U>
V8_INLINE bool operator==(const v8::Local<U>& lhs,
                          const TracedReferenceBase& rhs) {
  return rhs == lhs;
}
 
V8_INLINE bool operator!=(const TracedReferenceBase& lhs,
                          const TracedReferenceBase& rhs) {
  return !(lhs == rhs);
}
 
template <typename U>
V8_INLINE bool operator!=(const TracedReferenceBase& lhs,
                          const v8::Local<U>& rhs) {
  return !(lhs == rhs);
}
 
template <typename U>
V8_INLINE bool operator!=(const v8::Local<U>& lhs,
                          const TracedReferenceBase& rhs) {
  return !(rhs == lhs);
}
 
template <class T>
template <class S>
void TracedReference<T>::Reset(Isolate* isolate, const Local<S>& other) {
  static_assert(std::is_base_of<T, S>::value, "type check");
  this->Reset();
  if (other.IsEmpty()) return;
  this->SetSlotThreadSafe(
      this->New(isolate, other.val_, &this->val_,
                internal::GlobalHandleStoreMode::kAssigningStore));
}
 
template <class T>
template <class S>
TracedReference<T>& TracedReference<T>::operator=(
    TracedReference<S>&& rhs) noexcept {
  static_assert(std::is_base_of<T, S>::value, "type check");
  *this = std::move(rhs.template As<T>());
  return *this;
}
 
template <class T>
template <class S>
TracedReference<T>& TracedReference<T>::operator=(
    const TracedReference<S>& rhs) {
  static_assert(std::is_base_of<T, S>::value, "type check");
  *this = rhs.template As<T>();
  return *this;
}
 
template <class T>
TracedReference<T>& TracedReference<T>::operator=(
    TracedReference&& rhs) noexcept {
  if (this != &rhs) {
    internal::MoveTracedReference(
        reinterpret_cast<internal::Address**>(&rhs.val_),
        reinterpret_cast<internal::Address**>(&this->val_));
  }
  return *this;
}
 
template <class T>
TracedReference<T>& TracedReference<T>::operator=(const TracedReference& rhs) {
  if (this != &rhs) {
    this->Reset();
    if (rhs.val_ != nullptr) {
      internal::CopyTracedReference(
          reinterpret_cast<const internal::Address* const*>(&rhs.val_),
          reinterpret_cast<internal::Address**>(&this->val_));
    }
  }
  return *this;
}
 
void TracedReferenceBase::SetWrapperClassId(uint16_t class_id) {
  using I = internal::Internals;
  if (IsEmpty()) return;
  internal::Address* obj = reinterpret_cast<internal::Address*>(val_);
  uint8_t* addr = reinterpret_cast<uint8_t*>(obj) + I::kNodeClassIdOffset;
  *reinterpret_cast<uint16_t*>(addr) = class_id;
}
 
uint16_t TracedReferenceBase::WrapperClassId() const {
  using I = internal::Internals;
  if (IsEmpty()) return 0;
  internal::Address* obj = reinterpret_cast<internal::Address*>(val_);
  uint8_t* addr = reinterpret_cast<uint8_t*>(obj) + I::kNodeClassIdOffset;
  return *reinterpret_cast<uint16_t*>(addr);
}
 
}  // namespace v8
 
#endif  // INCLUDE_V8_TRACED_HANDLE_H_