On Lock-Free Synchronization for Dynamic Embedded Real-Time Software∗

We consider non-blocking synchronization for dynamic embedded real-time systems such as those that are subject to resource overloads and arbitrary activity arrivals. The multi-writer/multi-reader problem inherently occurs in such systems, when their activities must concurrently and mutually exclusive share data objects. We consider lock-free synchronization for this problem under the unimodal arbitrary arrival model (or UAM). UAM embodies a “stronger” adversary than most traditional arrival models. We establish the fundamental tradeoffs between lock-free and lock-based object sharing under UAM — the first such result. Our tradeoffs include analytical 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. Our implementation experience on a POSIX RTOS reveals that the lock-free scheduling algorithm yields higher accrued utility, by as much as 65%, and critical time satisfactions, by as much as 80%, over lock-based.