The authors consider lock-free synchronization for dynamic embedded real-time systems that are subject to resource overloads and arbitrary activity arrivals. They model activity arrival behaviors using the Uni-modal Arbitrary arrival Model (or UAM). UAM embodies a stronger \"Adversary\" than most traditional arrival models. They derive the upper bound on lock-free retries under the UAM with utility accrual scheduling - the first such result. They establish the tradeoffs between lock-free and lock-based sharing under UAM. These include conditions under which activities' accrued timeliness utility is greater under lock-free than lock-based, and the consequent upper bound on the increase in accrued utility that is possible with lock-free.