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_SHARED_COPY_ON_WRITE_H_ 8 #define CORE_FXCRT_CFX_SHARED_COPY_ON_WRITE_H_ 9 10 #include "core/fxcrt/cfx_retain_ptr.h" 11 #include "core/fxcrt/fx_system.h" 12 13 // A shared object with Copy on Write semantics that makes it appear as 14 // if each one were independent. 15 template <class ObjClass> 16 class CFX_SharedCopyOnWrite { 17 public: CFX_SharedCopyOnWrite()18 CFX_SharedCopyOnWrite() {} CFX_SharedCopyOnWrite(const CFX_SharedCopyOnWrite & other)19 CFX_SharedCopyOnWrite(const CFX_SharedCopyOnWrite& other) 20 : m_pObject(other.m_pObject) {} ~CFX_SharedCopyOnWrite()21 ~CFX_SharedCopyOnWrite() {} 22 23 template <typename... Args> Emplace(Args...params)24 ObjClass* Emplace(Args... params) { 25 m_pObject.Reset(new CountedObj(params...)); 26 return m_pObject.Get(); 27 } 28 29 CFX_SharedCopyOnWrite& operator=(const CFX_SharedCopyOnWrite& that) { 30 if (*this != that) 31 m_pObject = that.m_pObject; 32 return *this; 33 } 34 SetNull()35 void SetNull() { m_pObject.Reset(); } GetObject()36 const ObjClass* GetObject() const { return m_pObject.Get(); } 37 38 template <typename... Args> GetPrivateCopy(Args...params)39 ObjClass* GetPrivateCopy(Args... params) { 40 if (!m_pObject) 41 return Emplace(params...); 42 if (!m_pObject->HasOneRef()) 43 m_pObject.Reset(new CountedObj(*m_pObject)); 44 return m_pObject.Get(); 45 } 46 47 bool operator==(const CFX_SharedCopyOnWrite& that) const { 48 return m_pObject == that.m_pObject; 49 } 50 bool operator!=(const CFX_SharedCopyOnWrite& that) const { 51 return !(*this == that); 52 } 53 explicit operator bool() const { return !!m_pObject; } 54 55 private: 56 class CountedObj : public ObjClass { 57 public: 58 template <typename... Args> 59 // NOLINTNEXTLINE(runtime/explicit) CountedObj(Args...params)60 CountedObj(Args... params) : ObjClass(params...), m_RefCount(0) {} 61 CountedObj(const CountedObj & src)62 CountedObj(const CountedObj& src) : ObjClass(src), m_RefCount(0) {} ~CountedObj()63 ~CountedObj() { m_RefCount = 0; } 64 HasOneRef()65 bool HasOneRef() const { return m_RefCount == 1; } Retain()66 void Retain() { m_RefCount++; } Release()67 void Release() { 68 ASSERT(m_RefCount); 69 if (--m_RefCount == 0) 70 delete this; 71 } 72 73 private: 74 // To ensure ref counts do not overflow, consider the worst possible case: 75 // the entire address space contains nothing but pointers to this object. 76 // Since the count increments with each new pointer, the largest value is 77 // the number of pointers that can fit into the address space. The size of 78 // the address space itself is a good upper bound on it. 79 intptr_t m_RefCount; 80 }; 81 82 CFX_RetainPtr<CountedObj> m_pObject; 83 }; 84 85 #endif // CORE_FXCRT_CFX_SHARED_COPY_ON_WRITE_H_ 86