Toward a non-atomic era: l-exclusion as a test case

Most of the research in concurrency control has been based on the existence of strong synchronization primitives such as test and set. Following Lamport, recent research promoting the use of weaker primitives, “safe” rather than “atomic,” has resulted in construction of atomic registers from safe ones, in the belief that they would be useful tools for process synchronization. We argue that the properties provided by atomic operations may be too powerful, masking core difficulties of problems and leading to inefficiency. We therefore advocate a different approach, to skip the intermediate step of achieving atomicity, and solve problems directly from safe registers. Though it has been shown that “test and set” cannot be implemented from safe registers, we show how to achieve a fair solution to l-exclusion, a classical concurrency control problem previously solved assuming a very powerful form of atomic “test and set”. We do so using safe registers alone and without introducing atomicity. The solution is based on the construction of a simple novel non-atomic synchronization primitive.