Thread safe lazy construction of a singleton in C++

Question

Is there a way to implement a singleton object in C++ that is:

1. Lazily constructed in a thread safe manner (two threads might simultaneously be the first user o

Answer 1

1. read on weak memory model. It can break double-checked locks and spinlocks. Intel is strong memory model (yet), so on Intel it's easier

2. carefully use "volatile" to avoid caching of parts the object in registers, otherwise you'll have initialized the object pointer, but not the object itself, and the other thread will crash

3. the order of static variables initialization versus shared code loading is sometimes not trivial. I've seen cases when the code to destruct an object was already unloaded, so the program crashed on exit

4. such objects are hard to destroy properly

In general singletons are hard to do right and hard to debug. It's better to avoid them altogether.