在this file中，deallocate_impl类用于使用free list管理无锁数据结构（例如，队列）的存储。
void deallocate_impl (index_t index)
{
freelist_node * new_pool_node =
reinterpret_cast<freelist_node*>(NodeStorage::nodes() + index);
// Shouldn't this line be placed inside the loop?
// The loop continues as long as the compare-and-exchange fails,
// which happens if the pool head has been concurrently updated.
// In that case, we MUST reload the new value of "pool_" to
// reuse its tag, link the new free-list head to it and
// compare against in the compare_and_exchange call.
tagged_index old_pool = pool_.load(memory_order_consume);
for(;;) {
// The old pool head tag is reused here without causing
// any ABA problems. However, if "index" is the same as
// old_pool.get_index(), a self-reference is written.
tagged_index new_pool (index, old_pool.get_tag());
new_pool_node->next.set_index(old_pool.get_index());
if (pool_.compare_exchange_weak(old_pool, new_pool))
return;
}
}
方法用于通过将节点链接回空闲列表来释放节点（释放的节点成为空闲列表的新头，取代旧头）。该方法应该是线程安全且无锁定的。一个实例的原始源代码在这里重复，我的注释注释指出可疑代码（潜在的错误？）：
{{1}}
我在Boost 1.62.0中也看到了相同的实现
答案 0 :(得分：2)
每次通话后，只要比较和交换失败，循环就会继续，如果池头已同时更新，则会发生这种情况。在这种情况下，我们必须重新加载“pool_”的新值以重用其标记...
compare_exchange_weak()会将pool_的先前值写入old_pool。 Documentation for compare_exchange_weak()
但是，如果“index”与old_pool.get_index（）...
相同
这可能不会发生，因为具有该索引的节点尚未移动到空闲列表。