kvs_data *kvs = _kvs.load(memory_order_acquire);
slot *res = putIfMatch(this, kvs, key_slot, value_slot, old_val);
// Only when copy_slot() call putIfMatch() will it return NULL
kvs_data *kvs = _kvs.load(memory_order_acquire);
slot *res = putIfMatch(this, kvs, key_slot, value_slot, old_val);
// Only when copy_slot() call putIfMatch() will it return NULL