Library prosa.model.priority.coercion

Require Export prosa.model.priority.definitions.

Automatic FP ➔ JLFP ➔ JLDP Conversion

Since there are natural interpretations of FP and JLFP policies as JLFP and JLDP policies, respectively, we define conversions that express these generalizations. In practice, this means that Coq will be able to automatically satisfy a JLDP assumption if a JLFP or FP policy is in scope.

First, any FP policy can be interpreted as an JLFP policy by comparing jobs according to the priorities of their respective tasks. The priority is lowered to 10 in order to avoid conflict with other instances of JLFP policies which take FP policies as argument.

#[global]
Instance FP_to_JLFP {Job : JobType} {Task : TaskType} {tasks : JobTask Job Task}
(FP : FP_policy Task) : JLFP_policy Job | 10 :=
fun j1 j2 ⇒ hep_task (job_task j1) (job_task j2).

Second, any JLFP policy implies a JLDP policy that simply ignores the time parameter. Analogously, priority is lowered to 10 in order to avoid conflict with other instances of JLDP policies which take JLFP policies as argument.

#[global]
Instance JLFP_to_JLDP {Job : JobType}
(JLFP : JLFP_policy Job) : JLDP_policy Job | 10 :=
fun _ j1 j2 ⇒ hep_job j1 j2.

We add coercions to enable automatic conversion from JLFP to JLDP...

Coercion JLFP_to_JLDP : JLFP_policy >-> JLDP_policy.

...and from FP to JLFP.

#[warning="-uniform-inheritance"]
Coercion FP_to_JLFP : FP_policy >-> JLFP_policy.

We now prove lemmas about conversions between the properties of these priority classes.

Section PriorityRelationsConversion.

Consider any type of tasks ...

Context {Task : TaskType}.

... and any type of jobs associated with these tasks.

Context {Job : JobType}.
Context `{JobTask Job Task}.

To simplify later proofs, we make two trivial remarks on the FP->JLFP->JLDP coercion.

First, when considering a JLFP policy, hep_job_at and hep_job are by definition equivalent.

  Remark hep_job_at_jlfp :
    ∀ `{JLFP_policy Job} j j' t,
      hep_job_at t j j' = hep_job j j'.

Second, when considering an FP policy, hep_job_at and hep_task are by definition equivalent.

  Remark hep_job_at_fp :
    ∀ `{FP_policy Task} j j' t,
      hep_job_at t j j' = hep_task (job_task j) (job_task j').

We observe that lifting an FP_policy to a JLFP_policy trivially maintains reflexivity,...

  Lemma reflexive_priorities_FP_implies_JLFP :
    ∀ (fp: FP_policy Task),
      reflexive_task_priorities fp →
        reflexive_job_priorities (FP_to_JLFP fp).

...transitivity,...

  Lemma transitive_priorities_FP_implies_JLFP :
    ∀ (fp: FP_policy Task),
      transitive_task_priorities fp →
        transitive_job_priorities (FP_to_JLFP fp).

...and totality of priorities.

  Lemma total_priorities_FP_implies_JLFP :
    ∀ (fp: FP_policy Task),
      total_task_priorities fp →
        total_job_priorities (FP_to_JLFP fp).

Analogously, lifting a JLFP_policy to a JLDP_policy also maintains reflexivity,...

  Lemma reflexive_priorities_JLFP_implies_JLDP :
    ∀ (jlfp: JLFP_policy Job),
      reflexive_job_priorities jlfp →
        reflexive_priorities (JLFP_to_JLDP jlfp).

...transitivity,...

  Lemma transitive_priorities_JLFP_implies_JLDP :
  ∀ (jlfp : JLFP_policy Job),
    transitive_job_priorities jlfp →
      transitive_priorities (JLFP_to_JLDP jlfp).

...and totality of priorities.

  Lemma total_priorities_JLFP_implies_JLDP :
    ∀ (jlfp : JLFP_policy Job),
      total_job_priorities jlfp →
        total_priorities (JLFP_to_JLDP jlfp).

End PriorityRelationsConversion.

We add the above lemmas into the "Hint Database" basic_rt_facts, so Coq will be able to apply them automatically.

Global Hint Resolve
    reflexive_priorities_FP_implies_JLFP
    reflexive_priorities_JLFP_implies_JLDP
    transitive_priorities_FP_implies_JLFP
    transitive_priorities_JLFP_implies_JLDP
    total_priorities_FP_implies_JLFP
    total_priorities_JLFP_implies_JLDP
  : basic_rt_facts.