1 #include <iostream>
2 #include <mutex>
3
4 std::mutex mtx;
5 class Singleton {
6 private:
7 Singleton() {}
8 Singleton(const Singleton& a);
9 Singleton& operator=(const Singleton&);
10 static Singleton * instance;
11 public:
12 static Singleton* getInstance() {
13 if (instance == nullptr) {
14 mtx.lock();
15 if((instance == nullptr)){
16 instance = new Singleton();
17 }
18 mtx.unlock();
19 }
20 return instance;
21 }
22 };
23 Singleton* Singleton::instance = nullptr;
24
25 int main(){
26 Singleton* instance1 = Singleton::getInstance();
27 Singleton* instance2 = Singleton::getInstance();
28 if(instance1 == instance2){
29 std::cout << "singleton" << std::endl;
30 }
31 return 0;
32 }
