pullValue should not return a value

[jcelerier]

It is entirely unsafe, since it can return a value that will then be deleted from another thread, before the one who called pullValue has the time to clone it.
Hence one should always do :

address->pullValue();
auto theValue = address->cloneValue();

For the same reasons, getValue() should not be used (maybe cloneValue should become getValue ?).
Another safe option would be to store the value in a shared_ptr and change the API to return it as a shared_ptr, but I don't know what would be the best performance-wise between these two options.