Implement weak pointers

core/fxcrt/include/cfx_weak_ptr.h

+// Copyright 2016 PDFium Authors. All rights reserved.
+// 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_INCLUDE_CFX_WEAK_PTR_H_
+#define CORE_FXCRT_INCLUDE_CFX_WEAK_PTR_H_
+
+#include <memory>
+
+#include "core/fxcrt/include/cfx_retain_ptr.h"
+#include "core/fxcrt/include/fx_system.h"
+
+template <class T, class D = std::default_delete<T>>
+class CFX_WeakPtr {
+ public:
+  CFX_WeakPtr() {}
+  CFX_WeakPtr(const CFX_WeakPtr& that) : m_pHandle(that.m_pHandle) {}
+  CFX_WeakPtr(CFX_WeakPtr&& that) { Swap(that); }
+  CFX_WeakPtr(std::unique_ptr<T, D> pObj)
+      : m_pHandle(new Handle(std::move(pObj))) {}
+
+  explicit operator bool() const { return m_pHandle && !!m_pHandle->Get(); }
+  bool HasOneRef() const { return m_pHandle && m_pHandle->HasOneRef(); }
+  T* operator->() { return m_pHandle->Get(); }
+  const T* operator->() const { return m_pHandle->Get(); }
+  CFX_WeakPtr& operator=(const CFX_WeakPtr& that) {
+    m_pHandle = that.m_pHandle;
+    return *this;
+  }
+  bool operator==(const CFX_WeakPtr& that) const {
+    return m_pHandle == that.m_pHandle;
+  }
+  bool operator!=(const CFX_WeakPtr& that) const { return !(*this == that); }
+
+  T* Get() const { return m_pHandle ? m_pHandle->Get() : nullptr; }
+  void Clear() {
+    if (m_pHandle) {
+      m_pHandle->Clear();
+      m_pHandle.Reset();
+    }
+  }
+  void Reset() { m_pHandle.Reset(); }
+  void Reset(std::unique_ptr<T, D> pObj) {
+    m_pHandle.Reset(new Handle(std::move(pObj)));
+  }
+  void Swap(CFX_WeakPtr& that) { m_pHandle.Swap(that.m_pHandle); }
+
+ private:
+  class Handle {
+   public:
+    explicit Handle(std::unique_ptr<T, D> ptr)
+        : m_nCount(0), 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() {}
+
+    intptr_t m_nCount;
+    std::unique_ptr<T, D> m_pObj;
+  };
+
+  CFX_RetainPtr<Handle> m_pHandle;
+};
+
+#endif  // CORE_FXCRT_INCLUDE_CFX_WEAK_PTR_H_