chromium/third_party/pdfium/core/fxcrt/weak_ptr.h

// Copyright 2016 The PDFium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

// Original code copyright 2014 Foxit Software Inc. http://www.foxitsoftware.com

#ifndef CORE_FXCRT_WEAK_PTR_H_
#define CORE_FXCRT_WEAK_PTR_H_

#include <stdint.h>

#include <memory>
#include <utility>

#include "core/fxcrt/retain_ptr.h"

namespace fxcrt {

template <class T, class D = std::default_delete<T>>
class WeakPtr {
 public:
  WeakPtr() = default;
  WeakPtr(const WeakPtr& that) : … { … }
  WeakPtr(WeakPtr&& that) noexcept { … }
  explicit WeakPtr(std::unique_ptr<T, D> pObj)
      : … { … }

  // Deliberately implicit to allow passing nullptr.
  // NOLINTNEXTLINE(runtime/explicit)
  WeakPtr(std::nullptr_t arg) { … }

  explicit operator bool() const { return m_pHandle && !!m_pHandle->Get(); }
  bool HasOneRef() const { … }
  T* operator->() { … }
  const T* operator->() const { … }
  WeakPtr& operator=(const WeakPtr& that) { … }
  bool operator==(const WeakPtr& that) const { … }
  bool operator!=(const WeakPtr& that) const { … }

  T* Get() const { … }
  void DeleteObject() { … }
  void Reset() { … }
  void Reset(std::unique_ptr<T, D> pObj) { … }
  void Swap(WeakPtr& that) { … }

 private:
  class Handle {
   public:
    explicit Handle(std::unique_ptr<T, D> ptr) : m_pObj(std::move(ptr)) {}

    void Reset(std::unique_ptr<T, D> ptr) { m_pObj = std::move(ptr); }
    void Clear() {     // Now you're all weak ptrs ...
      m_pObj.reset();  // unique_ptr nulls first before invoking delete.
    }
    T* Get() const { return m_pObj.get(); }
    T* Retain() {
      ++m_nCount;
      return m_pObj.get();
    }
    void Release() {
      if (--m_nCount == 0)
        delete this;
    }
    bool HasOneRef() const { return m_nCount == 1; }

   private:
    ~Handle() = default;

    intptr_t m_nCount = 0;
    std::unique_ptr<T, D> m_pObj;
  };

  RetainPtr<Handle> m_pHandle;
};

}  // namespace fxcrt

WeakPtr;

#endif  // CORE_FXCRT_WEAK_PTR_H_