electron/shell/common/gin_helper/trackable_object.h

// Copyright (c) 2015 GitHub, Inc.
// Use of this source code is governed by the MIT license that can be
// found in the LICENSE file.

#ifndef ELECTRON_SHELL_COMMON_GIN_HELPER_TRACKABLE_OBJECT_H_
#define ELECTRON_SHELL_COMMON_GIN_HELPER_TRACKABLE_OBJECT_H_

#include <vector>

#include "base/memory/weak_ptr.h"
#include "shell/common/gin_helper/cleaned_up_at_exit.h"
#include "shell/common/gin_helper/event_emitter.h"
#include "shell/common/key_weak_map.h"

namespace base {
class SupportsUserData;
}

namespace gin_helper {

// Users should use TrackableObject instead.
class TrackableObjectBase : public CleanedUpAtExit {
 public:
  TrackableObjectBase();

  // disable copy
  TrackableObjectBase(const TrackableObjectBase&) = delete;
  TrackableObjectBase& operator=(const TrackableObjectBase&) = delete;

  // The ID in weak map.
  [[nodiscard]] constexpr int32_t weak_map_id() const { return weak_map_id_; }

  // Wrap TrackableObject into a class that SupportsUserData.
  void AttachAsUserData(base::SupportsUserData* wrapped);

  // Get the weak_map_id from SupportsUserData.
  static int32_t GetIDFromWrappedClass(base::SupportsUserData* wrapped);

 protected:
  ~TrackableObjectBase() override;

  // Returns a closure that can destroy the native class.
  base::OnceClosure GetDestroyClosure();

 private:
  void Destroy();

  static inline int32_t next_id_ = 0;
  const int32_t weak_map_id_ = ++next_id_;

  base::WeakPtrFactory<TrackableObjectBase> weak_factory_{this};
};

// All instances of TrackableObject will be kept in a weak map and can be got
// from its ID.
template <typename T>
class TrackableObject : public TrackableObjectBase, public EventEmitter<T> {
 public:
  // Mark the JS object as destroyed.
  void MarkDestroyed() {
    v8::HandleScope scope(gin_helper::Wrappable<T>::isolate());
    v8::Local<v8::Object> wrapper = gin_helper::Wrappable<T>::GetWrapper();
    if (!wrapper.IsEmpty()) {
      wrapper->SetAlignedPointerInInternalField(
          0, nullptr, v8::kEmbedderDataTypeTagDefault);
      gin_helper::WrappableBase::wrapper_.ClearWeak();
    }
  }

  bool IsDestroyed() {
    v8::HandleScope scope(gin_helper::Wrappable<T>::isolate());
    v8::Local<v8::Object> wrapper = gin_helper::Wrappable<T>::GetWrapper();
    return wrapper->InternalFieldCount() == 0 ||
           wrapper->GetAlignedPointerFromInternalField(
               0, v8::kEmbedderDataTypeTagDefault) == nullptr;
  }

  // Finds out the TrackableObject from its ID in weak map.
  static T* FromWeakMapID(v8::Isolate* isolate, int32_t id) {
    if (!weak_map_)
      return nullptr;

    v8::HandleScope scope(isolate);
    v8::MaybeLocal<v8::Object> object = weak_map_->Get(isolate, id);
    if (object.IsEmpty())
      return nullptr;

    T* self = nullptr;
    gin::ConvertFromV8(isolate, object.ToLocalChecked(), &self);
    return self;
  }

  // Finds out the TrackableObject from the class it wraps.
  static T* FromWrappedClass(v8::Isolate* isolate,
                             base::SupportsUserData* wrapped) {
    int32_t id = GetIDFromWrappedClass(wrapped);
    if (!id)
      return nullptr;
    return FromWeakMapID(isolate, id);
  }

  // Returns all objects in this class's weak map.
  static std::vector<v8::Local<v8::Object>> GetAll(v8::Isolate* isolate) {
    if (weak_map_)
      return weak_map_->Values(isolate);
    else
      return {};
  }

  // Removes this instance from the weak map.
  void RemoveFromWeakMap() {
    if (weak_map_)
      weak_map_->Remove(weak_map_id());
  }

 protected:
  TrackableObject() = default;
  ~TrackableObject() override { RemoveFromWeakMap(); }

  void InitWith(v8::Isolate* isolate, v8::Local<v8::Object> wrapper) override {
    if (!weak_map_) {
      weak_map_ = new electron::KeyWeakMap<int32_t>;
    }
    weak_map_->Set(isolate, weak_map_id(), wrapper);
    gin_helper::WrappableBase::InitWith(isolate, wrapper);
  }

 private:
  static electron::KeyWeakMap<int32_t>* weak_map_;  // leaked on purpose
};

template <typename T>
electron::KeyWeakMap<int32_t>* TrackableObject<T>::weak_map_ = nullptr;

}  // namespace gin_helper

#endif  // ELECTRON_SHELL_COMMON_GIN_HELPER_TRACKABLE_OBJECT_H_