Section: New Results

Models for reliability

Participants : Ivan Lanese, Michael Lienhardt, Gianluigi Zavattaro.

We have continued the study of reversibility started in the past years, aimed at developing programming abstractions for reliable distributed systems. In [38] we present croll-pi, a concurrent calculus extending roll-pi – an higher-order pi-calculus featuring a rollback operator – allowing the specification of alternatives to a computation to be used upon rollback. Alternatives in croll-pi are attached to messages. We show the robustness of this mechanism by encoding more complex idioms for specifying alternatives. We illustrate the expressiveness of our approach by encoding a calculus of communicating transactions and by modeling the 8-queens problem. We also formally prove that croll-pi is strictly more expressive than roll-pi.

We have continued the study of the expressive power of primitives for specifying compensations in long running transactions. Dynamic compensation installation allows for easier specification of fault handling in complex interactive systems since it enables to update the compensation policies according to run-time information. In [40] we show that in a simple pi-like calculus with static compensations the termination of a process is decidable, but it is undecidable in one with dynamic compensations. We then consider three commonly used patterns for dynamic compensations: parallel compensations, where new compensation items can only be added in parallel, replacing compensations, where old compensations are replaced, and nested compensations, where old compensations can be used (linearly) to build new ones. We show that termination is decidable in the first two cases and undecidable in the last one.