Implementing a thread-safe singleton

Singleton is probably one of the most well-known design patterns. It restricts the instantiation of a single object of a class, something that is necessary in some cases, although many times the use of a singleton is rather an anti-pattern that can be avoided with other design choices.

Since a singleton means a single instance of a class is available to an entire program, it is likely that such a unique instance might be accessible from different threads. Therefore, when you implement a singleton, you should also make it thread-safe.

Before C++11, doing that was not an easy job, and a double-checked locking technique was the typical approach. However, Scott Meyers and Andrei Alexandrescu showed, in a paper called C++ and the Perils of Double-Checked Locking, that using this pattern did not guarantee a thread-safe singleton implementation in portable C++. Fortunately, this changed in C++11, and this recipe shows how to write a thread-safe...