Debugging Parallel DEVS

Abstract

To this day, debugging support for the DEVS formalism has been provided, at best, in an ad-hoc way. The intricacies of dealing with the interplay of different notions of (simulated) time, formalism semantics, and user input have not been thoroughly investigated. This paper presents a visual modeling, simulation, and debugging environment for Parallel DEVS, which builds on a theoretical foundation for debugging DEVS models. We take inspiration from both code debugging and the simulation world to model our environment; we transpose a set of useful code debugging concepts onto Parallel DEVS, and combine those with simulation-specific operations, such as as-fast-as-possible simulation and (scaled) real-time execution. Apart from these common debugging operations, we introduce new features to the debugging of Parallel DEVS models, such as “god events,” which can alter the model state during simulation, and reversible debugging, which allows one to go back in time. To achieve this, the PythonPDEVS simulator is deconstructed and reconstructed: the modal part of the simulator–debugger, as well as the debugging operations, are modeled using the Statecharts formalism. These models are combined, resulting in a model of the timed, reactive behavior of a debuggable simulator for Parallel DEVS. The code for the simulator is automatically synthesized from this model. To improve usability, we combine the simulator with a visual modeling environment, allowing for visual and interactive live debugging.