void set_new_tail(counted_node_ptr &old_tail, counted_node_ptr const &new_tail) {
node * const current_tail_ptr = old_tail.get();
while (!tail.compare_exchange_weak(old_tail, new_tail) && old_tail.get() == current_tail_ptr) {}
if (old_tail.get() == current_tail_ptr) {
free_external_counter(old_tail);
return;
}
if (!current_tail_ptr->release_ref())
deallocate_node(current_tail_ptr);
}
stored_ptr pop() {
counted_node_ptr old_head = head.load(std::memory_order_relaxed);
for (;;) {
increase_external_count(head, old_head);
node * const ptr = old_head.get();
if (ptr == tail.load().get())
return nullptr;
counted_node_ptr next = ptr->next.load();
if (head.compare_exchange_strong(old_head, next)) {
T * const res = ptr->data.exchange(nullptr);
free_external_counter(old_head);
return stored_ptr(res);
}
if (!ptr->release_ref())
deallocate_node(ptr);
}
}
std::unique_ptr<T> pop()
{
counted_node_ptr old_head=head.load(std::memory_order_relaxed);
for(;;)
{
increase_external_count(head,old_head);
node* const ptr=old_head.ptr;
if(ptr==tail.load().ptr)
{
return std::unique_ptr<T>();
}
counted_node_ptr next=ptr->next.load();
if(head.compare_exchange_strong(old_head,next))
{
T* const res=ptr->data.exchange(nullptr);
free_external_counter(old_head);
return std::unique_ptr<T>(res);
}
ptr->release_ref();
}
}
