C++ Singleton + MultiThread

C++ Singleton + MultiThread

#include 
#include 
using namespace std;

template 
class Singleton {
public:
	static T *instance() {
		if (object == NULL) {
			mtx.lock();
			if (object == NULL) object = new T;
			mtx.unlock();
		}
		return object;
	}

private:
	Singleton() {}  // be here? necessary?
	static T *object;
	static mutex mtx;
};

template 
T* Singleton::object = NULL;

template 
mutex Singleton::mtx;

class Foo {
};

int main() {
	Foo *singletonFoo = Singleton::instance();
	return 0;
}