Coqcots & Pycots: non-stopping components for safe dynamic reconfiguration

Software systems have to face evolutions of their running context and users. Therefore, the so-called dynamic reconfiguration has been commonly adopted for modifying some components and/or the architecture at runtime. Traditional approaches typically stop the needed components, apply the changes, and restart the components. However, this scheme is not suitable for critical systems and degrades user experience. This paper proposes to switch from the stop/restart scheme to dynamic software updating (DSU) techniques. Instead of stopping a component, its implementation is replaced by another one specifically built to apply the modifications while maintaining the best quality of service possible. The major contributions of this work are: (i) the integration of DSU techniques in a component model, and; (ii) a reconfiguration development process including specification, proof of correctness using Coq, and a systematic method to produce the executable script. In this perspective, the use of DSU techniques brings higher quality of service when reconfiguring component-based software and the formalization allows ensuring the safety and consistency of the reconfiguration process.