Hi, on the current Future (N2561) library proposal the promise protect the value setting/getting from multiple threads using a lock, but the lock do not protect the future initialization (lazy_init()). void set_value(typename detail::future_traits<R>::source_reference_type r) { lazy_init(); boost::lock_guard<boost::mutex> lock(future->mutex); if(future->done) { throw promise_already_satisfied(); } future->mark_finished_with_result_internal(r); } I'm wondering if we don't need to extend the protection or avoid the lazy initialization? I'm missing something? BTW, Is it safe to take the address of a promise? If not, why not delete the operator&()? Best, Vicente