Interruptible Critical Sections for Real-time Systems

In this paper, we present a new approach to synchronization in real-time systems. Existing methods for synchronization in real-time systems are pessimistic, and use blocking to enforce concurrency control. Protocols such as the priority ceiling protocol have been proposed to reduce the priority inversion that occurs when low priority tasks block high priority tasks. However, the priority ceiling protocol still allows a low priority task to block a high priority task, and requires the use of a static-priority scheduler. We propose optimistic synchronization methods as an alternative to pessimistic synchronization methods. Our synchronization algorithms never allow a low priority task to block a high priority task, and can be used with dynamic-priority schedulers. We show how the current research in non-blocking concurrent objects and in low-overhead uniprocessor synchronization can be synthesized to implement low-overhead optimistic synchronization.