content/browser/cache_storage/cache_storage_ref.h

// Copyright 2018 The Chromium 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 CONTENT_BROWSER_CACHE_STORAGE_CACHE_STORAGE_REF_H_
#define CONTENT_BROWSER_CACHE_STORAGE_CACHE_STORAGE_REF_H_

#include "base/memory/weak_ptr.h"

namespace content {

// Define a templated type to track references to a parameterized target type.
// The target type must provide AddHandleRef() methods and DropHandleRef()
// methods that will be called when the CacheStorageRef<> object is created
// and destroyed.
//
// Note, the reference being tracked by CacheStorageRef is intended to
// represent high level references from DOM objects exposed to javascript
// and does not correspond to typical smart pointer reference counts.
// Internally this class uses a WeakPtr<> to the target and cache_storage
// must manager the target life cycle through other mechanisms.
//
// Currently this is only used to track references to CacheStorageCache
// target objects, but will soon be used to track references to CacheStorage
// targets as well.
template <typename TargetType>
class CacheStorageRef {
 public:
  CacheStorageRef() = default;

  explicit CacheStorageRef(base::WeakPtr<TargetType> target)
      : target_(std::move(target)) {
    target_->AddHandleRef();
  }

  CacheStorageRef(CacheStorageRef&& rhs) noexcept
      : target_(std::move(rhs.target_)) {}

  CacheStorageRef& operator=(CacheStorageRef&& rhs) {
    if (target_)
      target_->DropHandleRef();
    target_ = std::move(rhs.target_);
    return *this;
  }

  ~CacheStorageRef() {
    if (target_)
      target_->DropHandleRef();
  }

  TargetType* value() { return target_.get(); }

  CacheStorageRef Clone() const { return CacheStorageRef(target_); }

 private:
  base::WeakPtr<TargetType> target_;

  DISALLOW_COPY_AND_ASSIGN(CacheStorageRef);
};

}  // namespace content

#endif  // CONTENT_BROWSER_CACHE_STORAGE_CACHE_STORAGE_REF_H_