electron/shell/common/key_weak_map.h

// Copyright (c) 2016 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_KEY_WEAK_MAP_H_
#define ELECTRON_SHELL_COMMON_KEY_WEAK_MAP_H_

#include <unordered_map>
#include <utility>
#include <vector>

#include "base/memory/raw_ptr.h"
#include "v8/include/v8-forward.h"

namespace electron {

// Like ES6's WeakMap, with a K key and Weak Pointer value.
template <typename K>
class KeyWeakMap {
 public:
  KeyWeakMap() {}
  ~KeyWeakMap() {
    for (auto& p : map_)
      p.second.second.ClearWeak();
  }

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

  // Sets the object to WeakMap with the given |key|.
  void Set(v8::Isolate* isolate, const K& key, v8::Local<v8::Object> object) {
    KeyObject key_object = {key, this};
    auto& p = map_[key] =
        std::make_pair(key_object, v8::Global<v8::Object>(isolate, object));
    p.second.SetWeak(&(p.first), OnObjectGC, v8::WeakCallbackType::kParameter);
  }

  // Gets the object from WeakMap by its |key|.
  v8::MaybeLocal<v8::Object> Get(v8::Isolate* isolate, const K& key) {
    if (auto iter = map_.find(key); iter != map_.end())
      return v8::Local<v8::Object>::New(isolate, iter->second.second);
    return {};
  }

  // Returns all objects.
  std::vector<v8::Local<v8::Object>> Values(v8::Isolate* isolate) const {
    std::vector<v8::Local<v8::Object>> values;
    values.reserve(map_.size());
    for (const auto& it : map_)
      values.emplace_back(
          v8::Local<v8::Object>::New(isolate, it.second.second));
    return values;
  }

  // Remove object with |key| in the WeakMap.
  void Remove(const K& key) {
    auto iter = map_.find(key);
    if (iter == map_.end())
      return;

    iter->second.second.ClearWeak();
    map_.erase(iter);
  }

 private:
  // Records the key and self, used by SetWeak.
  struct KeyObject {
    K key;
    raw_ptr<KeyWeakMap> self;
  };

  static void OnObjectGC(
      const v8::WeakCallbackInfo<typename KeyWeakMap<K>::KeyObject>& data) {
    KeyWeakMap<K>::KeyObject* key_object = data.GetParameter();
    key_object->self->Remove(key_object->key);
  }

  // Map of stored objects.
  std::unordered_map<K, std::pair<KeyObject, v8::Global<v8::Object>>> map_;
};

}  // namespace electron

#endif  // ELECTRON_SHELL_COMMON_KEY_WEAK_MAP_H_