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diff --git a/core/fxcrt/weak_ptr.h b/core/fxcrt/weak_ptr.h
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+// 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_WEAK_PTR_H_
+#define CORE_FXCRT_WEAK_PTR_H_
+
+#include <cstddef>
+#include <memory>
+#include <utility>
+
+#include "core/fxcrt/fx_system.h"
+#include "core/fxcrt/retain_ptr.h"
+
+namespace fxcrt {
+
+template <class T, class D = std::default_delete<T>>
+class WeakPtr {
+ public:
+ WeakPtr() {}
+ WeakPtr(const WeakPtr& that) : m_pHandle(that.m_pHandle) {}
+ WeakPtr(WeakPtr&& that) noexcept { Swap(that); }
+ explicit WeakPtr(std::unique_ptr<T, D> pObj)
+ : m_pHandle(new Handle(std::move(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 { return m_pHandle && m_pHandle->HasOneRef(); }
+ T* operator->() { return m_pHandle->Get(); }
+ const T* operator->() const { return m_pHandle->Get(); }
+ WeakPtr& operator=(const WeakPtr& that) {
+ m_pHandle = that.m_pHandle;
+ return *this;
+ }
+ bool operator==(const WeakPtr& that) const {
+ return m_pHandle == that.m_pHandle;
+ }
+ bool operator!=(const WeakPtr& that) const { return !(*this == that); }
+
+ T* Get() const { return m_pHandle ? m_pHandle->Get() : nullptr; }
+ void DeleteObject() {
+ 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(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;
+ };
+
+ RetainPtr<Handle> m_pHandle;
+};
+
+} // namespace fxcrt
+
+using fxcrt::WeakPtr;
+
+#endif // CORE_FXCRT_WEAK_PTR_H_