117 lines
4.0 KiB
C++
117 lines
4.0 KiB
C++
/*******************************************************************
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* Copyright (c) 2022~2023 XMuli All rights reserved.
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* GitHub: https://github.com/XMuli
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* Description: C++ 实现一个核心的 shared_ptr 智能指针模板类；实现了引用计数是线程安全的，但访问管理的资源不是线程安全的。
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* Note: 书写测试时，若使用默认构造函数, 成员变量 _ptr、_refCount、_pMutex 在 release() 中容易崩溃；推荐带参的构造函数，无错
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* Ref: https://juejin.cn/post/7111726931301072910#heading-8
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* https://cloud.tencent.com/developer/article/1688444
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* https://blog.csdn.net/Z_Stand/article/details/98512756
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******************************************************************/
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#pragma once
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#include <iostream>
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#include <mutex>
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using namespace std;
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template <typename T>
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class SharedPtr
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{
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public:
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SharedPtr() : _ptr(nullptr), _refCount(nullptr), _pMutex(nullptr) { cout << "default constructor" << endl; };
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SharedPtr(T* obj) : _ptr(obj), _refCount(new int(1)), _pMutex(new mutex) { cout << "no default constructor" << endl; };
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SharedPtr(const SharedPtr<T>& obj) // 其 _refCount 可以通过另外一个指针来修改，指向的是同一个地址
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: _ptr(obj._ptr)
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, _refCount(obj._refCount)
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, _pMutex(obj._pMutex)
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{
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cout << "copy constructor" << endl;
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addRefCount();
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};
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SharedPtr<T>& operator=(const SharedPtr<T>& obj)
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{
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cout << "copy assignment constructor" << endl;
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if (&obj != this) {
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if (_ptr != obj._ptr) {
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release(); // 先释放旧的资源
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_ptr = obj._ptr;
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_refCount = obj._refCount;
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_pMutex = obj._pMutex;
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addRefCount(); // 再技计数 +1
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}
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}
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return *this;
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}
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//SharedPtr(SharedPtr<T>&& obj) noexcept;
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//SharedPtr<T>& operator=(SharedPtr<T>&& obj)noexcept;
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~SharedPtr() { cout << "destructor" << endl; release(); }
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T& operator*() { return *_ptr; }
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T* operator->() { return _ptr; }
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int useCount() { return *_refCount; }
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T* get() { return _ptr; }
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private:
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void addRefCount()
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{
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cout << "addRefCount" << endl;
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_pMutex->lock();
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++*_refCount;
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_pMutex->unlock();
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}
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void release()
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{
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cout << "release" << endl;
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bool bDelMutex = false;
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_pMutex->lock();
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if (_ptr && --*_refCount == 0) { // 先校验是否存在，及计数为 0 才释放
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delete _ptr;
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delete _refCount;
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_ptr = nullptr;
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_refCount = nullptr;
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bDelMutex = true;
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}
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_pMutex->unlock();
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if (bDelMutex)
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delete _pMutex;
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}
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private: // 需在构造函数中初始化
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T* _ptr;
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int* _refCount;
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mutex* _pMutex; // 计数自增非原子操作，加锁解决多线程
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};
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int main()
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{
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SharedPtr<int> sp1(new int(10));
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SharedPtr<int> sp2(sp1);
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*sp2 = 20;
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//sp1 与 sp2 在管理这部分资源，引用计数为 2
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cout << sp1.useCount() << " *ptr:" << *sp1 << endl; //2 20
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cout << sp2.useCount() << " *ptr:" << *sp2 << endl; //2 20
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SharedPtr<int> sp3(new int(30));
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sp2 = sp3; //sp3 赋值给它，释放管理的旧资源，引用计数-1，
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cout << sp1.useCount() << " *ptr:" << *sp1 << endl; //1 20
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cout << sp2.useCount() << " *ptr:" << *sp2 << endl; //2 30
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cout << sp3.useCount() << " *ptr:" << *sp3 << endl; //2 30
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sp1 = sp3;
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cout << sp1.useCount() << " *ptr:" << *sp1 << endl; //3 30
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cout << sp2.useCount() << " *ptr:" << *sp2 << endl; //3 30
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cout << sp3.useCount() << " *ptr:" << *sp3 << endl; //3 30
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std::cout << "Hello World!\n";
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return 0;
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} |