C++ and The Perils of Double-Checked Locking: Part I

1 // from the header file
2 class Singleton {
3 public:
4 static Singleton* instance();
5    ...
6 private:
7    static Singleton* pInstance;
8 };

9
10 // from the implementation file
11 Singleton* Singleton::pInstance = 0;
12
13 Singleton* Singleton::instance() {
14    if (pInstance == 0) {
15       pInstance = new Singleton;
16    }
17    return pInstance;
18 }

Example 1: In single-threaded environments, this code generally works okay.