Thread-safe initialization of function-local static const objects

Question

This question made me question a practice I had been following for years.

For thread-safe initialization of function-local static const objects I protect t

Answer 1

Just call the function before you start creating threads, thus guaranteeing the reference and the object. Alternatively, don't use such a truly terrible design pattern. I mean, why on earth have a static reference to a static object? Why even have static objects? There's no benefit to this. Singletons are a terrible idea.

Answer 2

Here is my take (if really you can't initialize it before threads are launched):

I've seen (and used) something like this to protect static initialization, using boost::once

#include <boost/thread/once.hpp>

boost::once_flag flag;

// get thingy
const Thingy & get()
{
    static Thingy thingy;

    return thingy;
}

// create function
void create()
{
     get();
}

void use()
{
    // Ensure only one thread get to create first before all other
    boost::call_once( &create, flag );

    // get a constructed thingy
    const Thingy & thingy = get(); 

    // use it
    thingy.etc..()          
}

In my understanding, this way all threads wait on boost::call_once except one that will create the static variable. It will be created only once and then will never be called again. And then you have no lock any more.