Lock-Free Transactions for Real-Time Systems

Lock-free objects are an alternative to lock-based object sharing protocols such as the priority ceiling protocol [17, 21] in preemptive real-time uniprocessor systems. An object implementation is lock-free iff it guarantees the following: if several tasks concurrently perform operations on the object, and if some proper subset of these tasks stop taking steps, then at least one of the remaining tasks must complete its operation in a finite number of its own steps. This definition precludes the use of critical sections, because if a task stops taking steps while within a critical section, then other tasks are prevented from accessing that critical section. In several related papers, we have presented general techniques that can be used to implement lock-free objects in real-time uniprocessor systems [3, 18] and to schedule tasks that share such objects [3, 4]. Related research includes work on techniques for implementing specific lock-free objects (such as read/write buffers) [13, 19, 20], and work on synchronization mechanisms that are similar to lock-free objects but are implemented using kernel support [12, 19, 20].