懒汉式单例类
#include <iostream>#include <thread>#include <mutex>using namespace std;class Singleton{public: static Singleton* getInstance(); Singleton(const Singleton&) = delete; Singleton& operator=(const Singleton&) = delete;private: Singleton() = default; static Singleton* instance; static mutex mtx;};Singleton *Singleton::instance = nullptr;mutex Singleton::mtx;Singleton* Singleton::getInstance(){ if (instance == nullptr) { lock_guard<mutex> lck(mtx); // 留神这里 ！！！ if (instance == nullptr) { instance = new Singleton(); } } return instance;}void thread_func(){ Singleton* p = Singleton::getInstance(); // p-> do something ...}int main(){ thread th1(thread_func); thread th2(thread_func); th1.join(); th2.join(); return 0;}
饿汉式单例类
#include <iostream>#include <thread>using namespace std;class Singleton{public: static Singleton* getInstance(); Singleton(const Singleton&) = delete; Singleton& operator=(const Singleton&) = delete;private: Singleton() = default; static Singleton* instance;};Singleton *Singleton::instance = new Singleton(); // 留神这里 ！！！Singleton* Singleton::getInstance(){ return instance;}void thread_func(){ Singleton* p = Singleton::getInstance(); // p-> do something ...}int main(){ thread th1(thread_func); thread th2(thread_func); th1.join(); th2.join(); return 0;}
懒汉式的 call_once 实现
template <class Fn, class... Args> void call_once (once_flag& flag, Fn&& fn, Args&&... args);
- 精确执行一次可调用对象 fn ，即便同时从多个线程调用。
#include <iostream>#include <thread>#include <mutex>using namespace std;class Singleton{public: static Singleton* getInstance(); Singleton(const Singleton&) = delete; Singleton& operator=(const Singleton&) = delete;private: Singleton() = default; static void createInstance(); static Singleton* instance; static once_flag onceFlag;};void Singleton::createInstance(){ instance = new Singleton();}Singleton *Singleton::instance = nullptr;once_flag Singleton::onceFlag;Singleton* Singleton::getInstance(){ call_once(onceFlag, createInstance); // 留神这里 ！！！ return instance;}void thread_func(){ Singleton* p = Singleton::getInstance(); // p-> do something ...}int main(){ thread th1(thread_func); thread th2(thread_func); th1.join(); th2.join(); return 0;}
单例类的资源清理【饿、懒同理】
#include <iostream>#include <thread>#include <mutex>using namespace std;class Singleton{ struct Recycle { ~Recycle() // 留神这里 ！！！ { if (instance != nullptr) { delete instance; instance = nullptr; } } };public: static Singleton* getInstance(); Singleton(const Singleton&) = delete; Singleton& operator=(const Singleton&) = delete;private: Singleton() = default; ~Singleton(); static Singleton* instance; static mutex mtx;};Singleton *Singleton::instance = nullptr;mutex Singleton::mtx;Singleton* Singleton::getInstance(){ if (instance == nullptr) { lock_guard<mutex> lck(mtx); if (instance == nullptr) { instance = new Singleton(); static Recycle recycle; } } return instance;}Singleton::~Singleton() // 留神这里 ！！！{ // 单例类资源清理}void thread_func(){ Singleton* p = Singleton::getInstance(); // p-> do something ...}int main(){ thread th1(thread_func); thread th2(thread_func); th1.join(); th2.join(); return 0;}