Towards optimal priority assignments for the transactional event handlers of P-FRP

Priority-based Functional Reactive Programming (P-FRP) is a new functional programming formalism for real-time systems. P-FRP allows static priority assignment and guarantees real-time response by preempting lower priority tasks. Due to the state-less nature, preempted tasks are aborted and restarted after higher priority tasks have completed execution. Therefore, the rate-monotonic (RM) priority assignment is not optimal in P-FRP, and it has been unknown whether an optimal fixed priority assignment can even exist for such an execution model. In this paper, we first present the priority assignment characteristics of P-FRP. We then discuss the priority assignment in a task set with two tasks. We derive the conditions when the RM priority assignment is optimal and show that at least one of RM or utilization-monotonic (UM) is the optimal for the task set with two tasks. We prove the optimal priority assignment for a general P-FRP system having more than two tasks exists when the period of the task is a multiple of others. Experimental results using task sets of different sizes are also presented.