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      1 // Copyright 2016 PDFium Authors. All rights reserved.
      2 // Use of this source code is governed by a BSD-style license that can be
      3 // found in the LICENSE file.
      4 
      5 // Original code copyright 2014 Foxit Software Inc. http://www.foxitsoftware.com
      6 
      7 #ifndef CORE_FXCRT_CFX_WEAK_PTR_H_
      8 #define CORE_FXCRT_CFX_WEAK_PTR_H_
      9 
     10 #include <cstddef>
     11 #include <memory>
     12 #include <utility>
     13 
     14 #include "core/fxcrt/cfx_retain_ptr.h"
     15 #include "core/fxcrt/fx_system.h"
     16 
     17 template <class T, class D = std::default_delete<T>>
     18 class CFX_WeakPtr {
     19  public:
     20   CFX_WeakPtr() {}
     21   CFX_WeakPtr(const CFX_WeakPtr& that) : m_pHandle(that.m_pHandle) {}
     22   CFX_WeakPtr(CFX_WeakPtr&& that) { Swap(that); }
     23   explicit CFX_WeakPtr(std::unique_ptr<T, D> pObj)
     24       : m_pHandle(new Handle(std::move(pObj))) {}
     25 
     26   // Deliberately implicit to allow passing nullptr.
     27   // NOLINTNEXTLINE(runtime/explicit)
     28   CFX_WeakPtr(std::nullptr_t arg) {}
     29 
     30   explicit operator bool() const { return m_pHandle && !!m_pHandle->Get(); }
     31   bool HasOneRef() const { return m_pHandle && m_pHandle->HasOneRef(); }
     32   T* operator->() { return m_pHandle->Get(); }
     33   const T* operator->() const { return m_pHandle->Get(); }
     34   CFX_WeakPtr& operator=(const CFX_WeakPtr& that) {
     35     m_pHandle = that.m_pHandle;
     36     return *this;
     37   }
     38   bool operator==(const CFX_WeakPtr& that) const {
     39     return m_pHandle == that.m_pHandle;
     40   }
     41   bool operator!=(const CFX_WeakPtr& that) const { return !(*this == that); }
     42 
     43   T* Get() const { return m_pHandle ? m_pHandle->Get() : nullptr; }
     44   void DeleteObject() {
     45     if (m_pHandle) {
     46       m_pHandle->Clear();
     47       m_pHandle.Reset();
     48     }
     49   }
     50   void Reset() { m_pHandle.Reset(); }
     51   void Reset(std::unique_ptr<T, D> pObj) {
     52     m_pHandle.Reset(new Handle(std::move(pObj)));
     53   }
     54   void Swap(CFX_WeakPtr& that) { m_pHandle.Swap(that.m_pHandle); }
     55 
     56  private:
     57   class Handle {
     58    public:
     59     explicit Handle(std::unique_ptr<T, D> ptr)
     60         : m_nCount(0), m_pObj(std::move(ptr)) {}
     61     void Reset(std::unique_ptr<T, D> ptr) { m_pObj = std::move(ptr); }
     62     void Clear() {     // Now you're all weak ptrs ...
     63       m_pObj.reset();  // unique_ptr nulls first before invoking delete.
     64     }
     65     T* Get() const { return m_pObj.get(); }
     66     T* Retain() {
     67       ++m_nCount;
     68       return m_pObj.get();
     69     }
     70     void Release() {
     71       if (--m_nCount == 0)
     72         delete this;
     73     }
     74     bool HasOneRef() const { return m_nCount == 1; }
     75 
     76    private:
     77     ~Handle() {}
     78 
     79     intptr_t m_nCount;
     80     std::unique_ptr<T, D> m_pObj;
     81   };
     82 
     83   CFX_RetainPtr<Handle> m_pHandle;
     84 };
     85 
     86 #endif  // CORE_FXCRT_CFX_WEAK_PTR_H_
     87