A heuristic search algorithm based on hybrid-tasks system model for scheduling tasks of NC system

NC system is a hybrid-tasks system, which is made up of periodic real-time tasks, nonperiodic real-time tasks and non-real-time tasks. Furthermore, tasks of NC system are not independent for the existence of precedence order and resource hazard. The traditional scheduling algorithms for real-time system are not suitable for these characteristics. A new hybrid-tasks system model is presented in this paper and the heuristic best-first search (BFS) algorithm is introduced to schedule tasks of this model. The BFS algorithm searches the state node matching all constraint conditions and minimizing (maximizing) the value of heuristic evaluation function in the state-space tree, so it solves the schedule problem with an optimal solution. The case study and computation complexity analysis prove that BFS algorithm can schedule tasks in NC system effectively.