Implementing mode changes with shared resources in Ada

The ability to support mode changes is a desirable feature for many real-time systems in which the functionality provided may vary as the mission progresses. The addition and deletion of tasks, the change of task profiles, the coherent management of resources and, at the same time, the required timeliness guarantee is an exercise of coordination of activities in a real-time system. In this paper we suggest how to safely implement mode changes in Ada, taking resource management into account. We consider the hypothesis of Ada allowing dynamic ceilings for protected objects and then show how to plan the mode change so that during the transition, tasks do not use the resources inconsistently.