OSL: An Algorithmic Skeleton Library with Exceptions

Exception handling is a traditional and natural mechanism to manage errors and events that disrupt the normal flow of program instructions. In most concurrent or parallel systems, exception handling is done locally or sequentially, and cannot guarantee the global coherence of the system after an exception is caught. Working with a structured parallel model is an advantage in this respect. Algorithmic skeletons, that are patterns of parallel algorithms on distributed data structures, offer such a structured model. However very few algorithmic skeleton libraries provide a specific parallel exception mechanism, and no C++-based library. In this paper we propose the design of an exception mechanism for the C++ Orléans Skeleton Library that ensures the global coherence of the system after exceptions are caught. We explain our design choices, experiment on the performance penalty of its use, and we illustrate how to purposefully use this mechanism to extract the results in the course of some algorithms.