Library prosa.model.schedule.priority_driven

Priority-Driven Uniprocessor Schedules

We now define what it means for a uniprocessor schedule to respect a priority in the presence of jobs with non-preemptive segments. The main definition is stated for JLDP policies. For JLFP and FP policies, we provide thin wrappers on top of the JLDP definition because JLFP and FP policies can be used with this definition through the canonical conversions (see model.priority.coercion).
NB: This definition is useful only for uniprocessor models (but not necessarily ideal ones). A similar, more general definition could be stated for multiprocessor models, but this remains future work at this point.

Section Priority.

Consider any type of tasks ...
  Context {Task : TaskType}.

... and any type of jobs associated with these tasks.
  Context {Job : JobType}.
  Context `{JobTask Job Task}.

Suppose jobs have an arrival time, a cost, ...
  Context `{JobArrival Job}.
  Context `{JobCost Job}.

... and consider any processor model, preemption model, and notion of readiness.
  Context {PState : ProcessorState Job}.
  Context `{JobPreemptable Job}.
  Context {jr : JobReady Job PState}.

Given any job arrival sequence...
  Variable arr_seq : arrival_sequence Job.

...and any schedule of these jobs,
  Variable sched : schedule PState.

we say that a priority policy is respected by the schedule iff, at every preemption point, the priority of the scheduled job is higher than or equal to the priority of any backlogged job. We define three separate notions of priority policy compliance based on the three types of scheduling policies : JLDP...
  Definition respects_JLDP_policy_at_preemption_point (policy: JLDP_policy Job) :=
     j j_hp t,
      arrives_in arr_seq j
      preemption_time arr_seq sched t
      backlogged sched j t
      scheduled_at sched j_hp t
      hep_job_at t j_hp j.

... JLFP, and...