Library rt.restructuring.analysis.basic_facts.arrivals

Require Export rt.restructuring.behavior.all.
Require Export rt.util.all.

In this section, we relate job readiness to has_arrived.

Section Arrived.

Consider any kinds of jobs and any kind of processor state.

Context {Job : JobType} {PState : Type}.
Context `{ProcessorState Job PState}.

Consider any schedule...

...and suppose that jobs have a cost, an arrival time, and a notion of readiness.

  Context `{JobCost Job}.
  Context `{JobArrival Job}.
  (* We give the readiness typeclass instance a name here because we rely on it
     explicitly in proofs. *)
  Context {ReadyParam : JobReady Job PState}.

First, we note that readiness models are by definition consistent w.r.t. pending.

  Lemma any_ready_job_is_pending:
    ∀ j t,
      job_ready sched j t → pending sched j t.
  Proof.
    move: ReadyParam ⇒ [is_ready CONSISTENT].
    move⇒ j t READY.
    apply CONSISTENT.
    by exact READY.
  Qed.

Next, we observe that a given job must have arrived to be ready...

  Lemma ready_implies_arrived:
    ∀ j t, job_ready sched j t → has_arrived j t.
  Proof.
    move⇒ j t READY.
    move: (any_ready_job_is_pending j t READY).
    by rewrite /pending ⇒ /andP [ARR _].
  Qed.

...and lift this observation also to the level of whole schedules.

  Lemma jobs_must_arrive_to_be_ready:
    jobs_must_be_ready_to_execute sched →
    jobs_must_arrive_to_execute sched.
  Proof.
    rewrite /jobs_must_be_ready_to_execute /jobs_must_arrive_to_execute.
    move⇒ READY_IF_SCHED j t SCHED.
    move: (READY_IF_SCHED j t SCHED) ⇒ READY.
    by apply ready_implies_arrived.
  Qed.

End Arrived.

In this section, we establish useful facts about arrival sequence prefixes.

Section ArrivalSequencePrefix.

Assume that job arrival times are known.

Context {Job: JobType}.
Context `{JobArrival Job}.

Consider any job arrival sequence.

Variable arr_seq: arrival_sequence Job.

In this section, we prove some lemmas about arrival sequence prefixes.

Section Lemmas.

We begin with basic lemmas for manipulating the sequences.

Section Composition.

First, we show that the set of arriving jobs can be split into disjoint intervals.

      Lemma arrivals_between_cat:
        ∀ t1 t t2,
          t1 ≤ t →
          t ≤ t2 →
          arrivals_between arr_seq t1 t2 = arrivals_between arr_seq t1 t ++ arrivals_between arr_seq t t2.
      Proof.
        unfold arrivals_between; intros t1 t t2 GE LE.
          by rewrite (@big_cat_nat _ _ _ t).
      Qed.

Second, the same observation applies to membership in the set of arrived jobs.

      Lemma arrivals_between_mem_cat:
        ∀ j t1 t t2,
          t1 ≤ t →
          t ≤ t2 →
          j \in arrivals_between arr_seq t1 t2 =
                (j \in arrivals_between arr_seq t1 t ++ arrivals_between arr_seq t t2 ).
      Proof.
          by intros j t1 t t2 GE LE; rewrite (arrivals_between_cat _ t).
      Qed.

Third, we observe that we can grow the considered interval without "losing" any arrived jobs, i.e., membership in the set of arrived jobs is monotonic.

      Lemma arrivals_between_sub:
        ∀ j t1 t1' t2 t2',
          t1' ≤ t1 →
          t2 ≤ t2' →
          j \in arrivals_between arr_seq t1 t2 →
          j \in arrivals_between arr_seq t1' t2'.
      Proof.
        intros j t1 t1' t2 t2' GE1 LE2 IN.
        move: (leq_total t1 t2) ⇒ /orP [BEFORE | AFTER];
                                   last by rewrite /arrivals_between big_geq // in IN.
        rewrite /arrivals_between.
        rewrite → big_cat_nat with (n := t1); [simpl | by done | by apply: (leq_trans BEFORE)].
        rewrite mem_cat; apply/orP; right.
        rewrite → big_cat_nat with (n := t2); [simpl | by done | by done].
          by rewrite mem_cat; apply/orP; left.
      Qed.

    End Composition.

Next, we relate the arrival prefixes with job arrival times.

Section ArrivalTimes.

Assume that job arrival times are consistent.

Hypothesis H_consistent_arrival_times:
consistent_arrival_times arr_seq.

First, we prove that if a job belongs to the prefix (jobs_arrived_before t), then it arrives in the arrival sequence.

      Lemma in_arrivals_implies_arrived:
        ∀ j t1 t2,
          j \in arrivals_between arr_seq t1 t2 →
          arrives_in arr_seq j.
      Proof.
        rename H_consistent_arrival_times into CONS.
        intros j t1 t2 IN.
        apply mem_bigcat_nat_exists in IN.
        move: IN ⇒ [arr [IN _]].
          by ∃ arr.
      Qed.

Next, we prove that if a job belongs to the prefix (jobs_arrived_between t1 t2), then it indeed arrives between t1 and t2.

      Lemma in_arrivals_implies_arrived_between:
        ∀ j t1 t2,
          j \in arrivals_between arr_seq t1 t2 →
                arrived_between j t1 t2.
      Proof.
        rename H_consistent_arrival_times into CONS.
        intros j t1 t2 IN.
        apply mem_bigcat_nat_exists in IN.
        move: IN ⇒ [t0 [IN /= LT]].
          by apply CONS in IN; rewrite /arrived_between IN.
      Qed.

Similarly, if a job belongs to the prefix (jobs_arrived_before t), then it indeed arrives before time t.

      Lemma in_arrivals_implies_arrived_before:
        ∀ j t,
          j \in arrivals_before arr_seq t →
                arrived_before j t.
      Proof.
        intros j t IN.
        have: arrived_between j 0 t by apply in_arrivals_implies_arrived_between.
          by rewrite /arrived_between /=.
      Qed.

Similarly, we prove that if a job from the arrival sequence arrives before t, then it belongs to the sequence (jobs_arrived_before t).

      Lemma arrived_between_implies_in_arrivals:
        ∀ j t1 t2,
          arrives_in arr_seq j →
          arrived_between j t1 t2 →
          j \in arrivals_between arr_seq t1 t2.
      Proof.
        rename H_consistent_arrival_times into CONS.
        move ⇒ j t1 t2 [a_j ARRj] BEFORE.
        have SAME := ARRj; apply CONS in SAME; subst a_j.
          by apply mem_bigcat_nat with (j := (job_arrival j)).
      Qed.

Next, we prove that if the arrival sequence doesn't contain duplicate jobs, the same applies for any of its prefixes.

      Lemma arrivals_uniq :
        arrival_sequence_uniq arr_seq →
        ∀ t1 t2, uniq (arrivals_between arr_seq t1 t2).
      Proof.
        rename H_consistent_arrival_times into CONS.
        unfold arrivals_up_to; intros SET t1 t2.
        apply bigcat_nat_uniq; first by done.
        intros x t t' IN1 IN2.
          by apply CONS in IN1; apply CONS in IN2; subst.
      Qed.

Also note there can't by any arrivals in an empty time interval.

      Lemma arrivals_between_geq:
        ∀ t1 t2,
          t1 ≥ t2 →
          arrivals_between arr_seq t1 t2 = [::].
      Proof.
          by intros ? ? GE; rewrite /arrivals_between big_geq.
      Qed.

    End ArrivalTimes.

  End Lemmas.

End ArrivalSequencePrefix.