Simultaneous Re-Planning and Plan Execution for Online Job Arrival

Anonymous

Keywords: Heuristic Search, Search in Planning and Scheduling, Online Planning

Abstract: In many AI planning applications, an agent receives new jobs (additional non-conflicting goals) while plan execution is still ongoing. Vanilla solutions are to (a) finish execution before tackling the new job, or to (b) interrupt execution and re-plan immediately. Option (a) misses opportunities to smoothly integrate the new job into the plan, while (b) leaves the agent idle during re-planning. We introduce simultaneous re-planning and execution (SRE), a planning algorithm that avoids both disadvantages. SRE re-plans for both the old and new jobs while the current plan is still being executed. The key difficulty is that, then, the initial state for the revised plan -- the state in which plan execution is at the end of re-planning -- depends on the time taken for re-planning. We address this through a variant of A* that starts with several speculative initial states, and incorporates time-aware search information to differentiate between these. On a collection of extended planning competition benchmarks, our algorithm consistently outperforms both (a) and (b).