C++單例模式實(shí)現(xiàn)（線程安全&支持多參數(shù)構(gòu)造）
線程安全版本
#include <<mutex>>
template <class T> class ThreadSafeSingleton {
public:
static T& get() {
std::call_once(ThreadSafeSingleton<T>::create_once_, &ThreadSafeSingleton<T>::Create);
return *ThreadSafeSingleton<T>::instance_;
}
protected:
static void Create() { instance_ = new T(); }
static std::once_flag create_once_;
static T* instance_;
};
template <class T> std::once_flag ThreadSafeSingleton<T>::create_once_;
template <class T> T* ThreadSafeSingleton<T>::instance_ = nullptr;
支持多參數(shù)版本的單例類
#include <iostream>
#include <mutex>
#include <cassert>
template<class T>
class ThreadSafeSingleton {
public:
template<typename...Args>
static T& Getinstance(Args&&... args) {
std::call_once(ThreadSafeSingleton<T>::_call_once_flag,
std::forward<void(Args&&...)>(&ThreadSafeSingleton<T>::init),
std::forward<Args>(args)...);
return *ThreadSafeSingleton<T>::m_instance;
}
private:
ThreadSafeSingleton() = default;
~ThreadSafeSingleton() {
delete ThreadSafeSingleton<T>::m_instance;
ThreadSafeSingleton<T>::m_instance = nullptr;
}
ThreadSafeSingleton(const ThreadSafeSingleton& o) = delete;
ThreadSafeSingleton& operator=(const ThreadSafeSingleton& o) = delete;
template<typename...Args>
static void init(Args&&...args) {
m_instance = new T(std::forward<Args>(args)...);
}
private:
static std::once_flag _call_once_flag;
static T* m_instance;
};
template<class T> T* ThreadSafeSingleton<T>::m_instance = nullptr;
template<class T> std::once_flag ThreadSafeSingleton<T>::_call_once_flag;
遇到問題點(diǎn)：
std::call_once中模板傳參時(shí)候需要注意點(diǎn)： 第二個(gè)參數(shù)為函數(shù)參數(shù)
std::forward<函數(shù)類型>(具體值)
std::forward<void(Args&&...)>(&ThreadSafeSingleton<T>::init),
最后調(diào)用：
std::call_once(ThreadSafeSingleton<T>::_call_once_flag,
? std::forward<void(Args&&...)>(&ThreadSafeSingleton<T>::init),
? std::forward<Args>(args)...);
測(cè)試代碼：
class TestSingleton1 {
public:
TestSingleton1(const std::string&){ std::cout << "lvalue" << std::endl;}
TestSingleton1(std::string&&){ std::cout << "rvalue" << std::endl;}
~TestSingleton1() = default;
void testFunc() {
std::cout << "test function 1" << "\n";
}
};
class TestSingleton2 {
public:
TestSingleton2(const std::string&){ std::cout << "lvalue" << std::endl;}
TestSingleton2(std::string&&){ std::cout << "rvalue" << std::endl;}
~TestSingleton2() = default;
void testFunc() {
std::cout << "test function 2" << "\n";
}
};
class TestSingleton3 {
public:
TestSingleton3(const std::string&,int i,double k){ std::cout << "lvalue" << std::endl;}
~TestSingleton3() = default;
void testFunc() {
std::cout << "test function 3" << "\n";
}
};
int main(int argc, char **argv) {
std::string str = "bb";
ThreadSafeSingleton<TestSingleton1>::Getinstance(str).testFunc();
ThreadSafeSingleton<TestSingleton2>::Getinstance(std::move(std::string("xxxx"))).testFunc();
ThreadSafeSingleton<TestSingleton3>::Getinstance("yyyy",1,2.0).testFunc();
return 0
}
本文代碼參考
《深入應(yīng)用C++11》
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