A Lock-Free Approach to Object Sharing in Real-Time Systems

This work aims to establish the viability of lock-free object sharing in uniprocessor real-time systems. Naive usage of conventional lock-based object-sharing schemes in realtime systems leads to unbounded priority inversion. A priority inversion occurs when a task is blocked by a lower-priority task that is inside a critical section. Mechanisms that bound priority inversion usually entail kernel overhead that is sometimes excessive. We propose that lock-free objects o er an attractive alternative to lock-based schemes because they eliminate priority inversion and its associated problems. On the surface, lock-free objects may seem to be unsuitable for hard real-time systems because accesses to such objects are not guaranteed to complete in bounded time. Nonetheless, we present scheduling conditions that demonstrate the applicability of lock-free objects in hard real-time systems. Our scheduling conditions are applicable to schemes such as rate-monotonic scheduling and earliest-deadlinerst scheduling. Previously known lock-free constructions are targeted towards asynchronous systems; such constructions require hardware support for strong synchronization primitives such as compare-and-swap. We show that constructions for uniprocessor real-time systems can be signi cantly simpli ed | and the need for strong primitives eliminated | by exploiting certain characteristics of real-time scheduling schemes.