Is Meyers' implementation of the Singleton pattern thread safe?

Question

Is the following implementation, using lazy initialization, of Singleton (Meyers\' Singleton) thread safe?

static Singleton& instance()
{
           


        

Answer 1

Is the following implementation [...] thread safe?

On most platforms, this is not thread-safe. (Append the usual disclaimer explaining that the C++ standard doesn't know about threads, so, legally, it doesn't say whether it is or not.)

If not, why [...]?

The reason it isn't is that nothing prevents more than one thread from simultaneously executing s' constructor.

how to make it thread safe?

"C++ and the Perils of Double-Checked Locking" by Scott Meyers and Andrei Alexandrescu is a pretty good treatise on the subject of thread-safe singletons.