void close(F& f) noexcept(noexcept(f(std::declval<pointer>()))) {
node_pointer ptr = take_head(stack_closed_tag());
while (ptr != nullptr) {
auto next = ptr->next;
f(promote(ptr));
ptr = next;
}
}
/// Sets the head to `stack_empty_tag()` and returns the previous head if
/// the queue was not empty.
pointer take_head() noexcept {
return take_head(stack_empty_tag());
}
/**
* @warning call only from the reader (owner)
*/
pointer try_pop() {
return take_head();
}
