Lazy buffer semantics for partial order scenarios

Abstract

There exists a unique minimal generalisation of a UML sequence diagram (SD) that is race free, known as the inherent causal scenario. However, practitioners sometimes regard this solution as invalid since it is a purely mathematical construct that apparently does not describe a concrete software engineering solution for resolving race conditions. Practitioners often implement SDs with random access input buffers. Messages are then consumed correctly regardless of the order or time at which they arrive, which appears to avoid race conditions altogether. However, this approach changes the observable system behaviour from that specified. We refer to this approach as the lazy buffer realization of a SD. We introduce an operational semantics for the lazy buffer realization. We prove the inherent causal scenario global behaviour is bisimulation equivalent to the global behaviour of lazy buffer semantics. Hence, in this sense, the practitioners solution is theoretically the best possible. Also this proves that the inherent causal scenario does represent a `real-world' software solution.