C++ and the Perils of Double-Checked Locking: Part II

Singleton* Singleton::instance () {
   Singleton* tmp = pInstance;
   ... // insert memory barrier
   if (tmp == 0) {
      Lock lock;
      tmp = pInstance;
      if (tmp == 0) {
         tmp = new Singleton;
         ... // insert memory barrier
         pInstance = tmp;
      }
   }
   return tmp;
}

Example 12: Pseudocode that follows an example presented by David Bacon.