barrier.v 10.6 KB
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From algebra Require Export upred_big_op.
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From program_logic Require Export sts saved_prop.
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From heap_lang Require Export derived heap wp_tactics notation.
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Import uPred.
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Definition newchan := (λ: "", ref '0)%L.
Definition signal := (λ: "x", "x" <- '1)%L.
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Definition wait := (rec: "wait" "x" :=if: !"x" = '1 then '() else "wait" "x")%L.
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(** The STS describing the main barrier protocol. Every state has an index-set
    associated with it. These indices are actually [gname], because we use them
    with saved propositions. *)
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Module barrier_proto.
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  Inductive phase := Low | High.
  Record stateT := State { state_phase : phase; state_I : gset gname }.
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  Inductive token := Change (i : gname) | Send.

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  Global Instance stateT_inhabited: Inhabited stateT.
  Proof. split. exact (State Low ). Qed.

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  Definition change_tokens (I : gset gname) : set token :=
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    mkSet (λ t, match t with Change i => i  I | Send => False end).
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  Inductive trans : relation stateT :=
  | ChangeI p I2 I1 : trans (State p I1) (State p I2)
  | ChangePhase I : trans (State Low I) (State High I).
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  Definition tok (s : stateT) : set token :=
      change_tokens (state_I s)
     match state_phase s with Low =>  | High => {[ Send ]} end.
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  Canonical Structure sts := sts.STS trans tok.
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  (* The set of states containing some particular i *)
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  Definition i_states (i : gname) : set stateT :=
    mkSet (λ s, i  state_I s).

  Lemma i_states_closed i :
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    sts.closed (i_states i) {[ Change i ]}.
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  Proof.
    split.
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    - apply (non_empty_inhabited(State Low {[ i ]})). rewrite !mkSet_elem_of /=.
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      apply lookup_singleton.
    - move=>[p I]. rewrite /= /tok !mkSet_elem_of /= =>HI.
      move=>s' /elem_of_intersection. rewrite !mkSet_elem_of /=.
      move=>[[Htok|Htok] ? ]; subst s'; first done.
      destruct p; done.
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    - (* If we do the destruct of the states early, and then inversion
         on the proof of a transition, it doesn't work - we do not obtain
         the equalities we need. So we destruct the states late, because this
         means we can use "destruct" instead of "inversion". *)
      move=>s1 s2. rewrite !mkSet_elem_of /==> Hs1 Hstep.
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      (* We probably want some helper lemmas for this... *)
      inversion_clear Hstep as [T1 T2 Hdisj Hstep'].
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      inversion_clear Hstep' as [? ? ? ? Htrans _ _ Htok].
      destruct Htrans; last done; move:Hs1 Hdisj Htok.
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      rewrite /= /tok /=.
      intros. apply dec_stable. 
      assert (Change i  change_tokens I1) as HI1
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        by (rewrite mkSet_not_elem_of; set_solver +Hs1).
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      assert (Change i  change_tokens I2) as HI2.
      { destruct p.
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        - set_solver +Htok Hdisj HI1.
        - set_solver +Htok Hdisj HI1 / discriminate. }
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      done.
  Qed.
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  (* The set of low states *)
  Definition low_states : set stateT :=
    mkSet (λ s, if state_phase s is Low then True else False).
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  Lemma low_states_closed : sts.closed low_states {[ Send ]}.
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  Proof.
    split.
    - apply (non_empty_inhabited(State Low )). by rewrite !mkSet_elem_of /=.
    - move=>[p I]. rewrite /= /tok !mkSet_elem_of /= =>HI.
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      destruct p; last done. set_solver.
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    - move=>s1 s2. rewrite !mkSet_elem_of /==> Hs1 Hstep.
      inversion_clear Hstep as [T1 T2 Hdisj Hstep'].
      inversion_clear Hstep' as [? ? ? ? Htrans _ _ Htok].
      destruct Htrans; move:Hs1 Hdisj Htok =>/=;
                                first by destruct p.
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      rewrite /= /tok /=. intros. set_solver +Hdisj Htok.
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  Qed.

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End barrier_proto.
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(* I am too lazy to type the full module name all the time. But then
   why did we even put this into a module? Because some of the names 
   are so general.
   What we'd really like here is to import *some* of the names from
   the module into our namespaces. But Coq doesn't seem to support that...?? *)
Import barrier_proto.
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(** Now we come to the Iris part of the proof. *)
Section proof.
  Context {Σ : iFunctorG} (N : namespace).
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  Context `{heapG Σ} (heapN : namespace).
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  Context `{stsG heap_lang Σ sts}.
  Context `{savedPropG heap_lang Σ}.
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  Local Hint Immediate i_states_closed low_states_closed.

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  Local Notation iProp := (iPropG heap_lang Σ).
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  Definition waiting (P : iProp) (I : gset gname) : iProp :=
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    ( R : gname  iProp, (P - Π★{set I} (λ i, R i)) 
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                             Π★{set I} (λ i, saved_prop_own i (R i)))%I.
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  Definition ress (I : gset gname) : iProp :=
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    (Π★{set I} (λ i,  R, saved_prop_own i R  R))%I.
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  Local Notation state_to_val s :=
    (match s with State Low _ => 0 | State High _ => 1 end).
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  Definition barrier_inv (l : loc) (P : iProp) (s : stateT) : iProp :=
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    (l  '(state_to_val s) 
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     match s with State Low I' => waiting P I' | State High I' => ress I' end
    )%I.
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  Definition barrier_ctx (γ : gname) (l : loc) (P : iProp) : iProp :=
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    (heap_ctx heapN  sts_ctx γ N (barrier_inv l P))%I.
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  Definition send (l : loc) (P : iProp) : iProp :=
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    ( γ, barrier_ctx γ l P  sts_ownS γ low_states {[ Send ]})%I.
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  Definition recv (l : loc) (R : iProp) : iProp :=
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    ( γ P Q i, barrier_ctx γ l P  sts_ownS γ (i_states i) {[ Change i ]} 
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        saved_prop_own i Q  (Q - R))%I.

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  Lemma newchan_spec (P : iProp) (Φ : val  iProp) :
    (heap_ctx heapN   l, recv l P  send l P - Φ (LocV l))
     wp  (newchan '()) Φ.
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  Proof.
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    rewrite /newchan. wp_rec. (* TODO: wp_seq. *)
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    rewrite -wp_pvs. wp> eapply wp_alloc; eauto with I ndisj.
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    apply forall_intro=>l. rewrite (forall_elim l). apply wand_intro_l.
    rewrite !assoc. apply pvs_wand_r.
    (* The core of this proof: Allocating the STS and the saved prop. *)
    eapply sep_elim_True_r.
    { by eapply (saved_prop_alloc _ P). }
    rewrite pvs_frame_l. apply pvs_strip_pvs. rewrite sep_exist_l.
    apply exist_elim=>i.
    transitivity (pvs   (heap_ctx heapN   (barrier_inv l P (State Low {[ i ]}))   saved_prop_own i P)).
    - rewrite -pvs_intro. rewrite [(_  heap_ctx _)%I]comm -!assoc. apply sep_mono_r.
      rewrite {1}[saved_prop_own _ _]always_sep_dup !assoc. apply sep_mono_l.
      rewrite /barrier_inv /waiting -later_intro. apply sep_mono_r.
      rewrite -(exist_intro (const P)) /=. rewrite -[saved_prop_own _ _](left_id True%I ()%I).
      apply sep_mono.
      + rewrite -later_intro. apply wand_intro_l. rewrite right_id.
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        by rewrite big_sepS_singleton.
      + by rewrite big_sepS_singleton.
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    - rewrite (sts_alloc (barrier_inv l P)  N); last by eauto. rewrite !pvs_frame_r !pvs_frame_l. 
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      rewrite pvs_trans'. apply pvs_strip_pvs. rewrite sep_exist_r sep_exist_l. apply exist_elim=>γ.
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      (* TODO: The record notation is rather annoying here *)
      rewrite /recv /send. rewrite -(exist_intro γ) -(exist_intro P).
      rewrite -(exist_intro P) -(exist_intro i) -(exist_intro γ).
      (* This is even more annoying than usually, since rewrite sometimes unfolds stuff... *)
      rewrite [barrier_ctx _ _ _]lock !assoc [(_  locked _)%I]comm !assoc -lock.
      rewrite -always_sep_dup.
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      rewrite [barrier_ctx _ _ _]lock always_and_sep_l -!assoc assoc -lock.
      rewrite -pvs_frame_l. apply sep_mono_r.
      rewrite [(saved_prop_own _ _  _)%I]comm !assoc. rewrite -pvs_frame_r. apply sep_mono_l.
      rewrite -assoc [( _  _)%I]comm assoc -pvs_frame_r.
      eapply sep_elim_True_r; last eapply sep_mono_l.
      { rewrite -later_intro. apply wand_intro_l. by rewrite right_id. }
      rewrite (sts_own_weaken  _ _ (i_states i  low_states) _ ({[ Change i ]}  {[ Send ]})).
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      + apply pvs_mono. rewrite sts_ownS_op; eauto; []. set_solver.
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      + rewrite /= /tok /=. apply elem_of_equiv=>t. rewrite elem_of_difference elem_of_union.
        rewrite !mkSet_elem_of /change_tokens.
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        (* TODO: destruct t; set_solver does not work. What is the best way to do on? *)
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        destruct t as [i'|]; last by naive_solver. split.
        * move=>[_ Hn]. left. destruct (decide (i = i')); first by subst i.
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          exfalso. apply Hn. left. set_solver.
        * move=>[[EQ]|?]; last discriminate. set_solver. 
      + apply elem_of_intersection. rewrite !mkSet_elem_of /=. set_solver.
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      + apply sts.closed_op; eauto; first set_solver; [].
        apply (non_empty_inhabited (State Low {[ i ]})). apply elem_of_intersection.
        rewrite !mkSet_elem_of /=. set_solver.
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  Qed.
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  Lemma signal_spec l P (Φ : val  iProp) :
    heapN  N  (send l P  P  Φ '())  wp  (signal (LocV l)) Φ.
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  Proof.
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    intros Hdisj. rewrite /signal /send /barrier_ctx. rewrite sep_exist_r.
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    apply exist_elim=>γ. wp_rec. (* FIXME wp_let *)
    (* I think some evars here are better than repeating *everything* *)
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    eapply (sts_fsaS _ (wp_fsa _)) with (N0:=N) (γ0:=γ); simpl;
      eauto with I ndisj.
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    rewrite [(_  sts_ownS _ _ _)%I]comm -!assoc /wp_fsa. apply sep_mono_r.
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    apply forall_intro=>-[p I]. apply wand_intro_l. rewrite -!assoc.
    apply const_elim_sep_l=>Hs. destruct p; last done.
    rewrite {1}/barrier_inv =>/={Hs}. rewrite later_sep.
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    eapply wp_store; eauto with I ndisj.
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    rewrite -!assoc. apply sep_mono_r. etransitivity; last eapply later_mono.
    { (* Is this really the best way to strip the later? *)
      erewrite later_sep. apply sep_mono_r. apply later_intro. }
    apply wand_intro_l. rewrite -(exist_intro (State High I)).
    rewrite -(exist_intro ). rewrite const_equiv /=; last first.
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    { constructor; first constructor; rewrite /= /tok /=; set_solver. }
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    rewrite left_id -later_intro {2}/barrier_inv -!assoc. apply sep_mono_r.
    rewrite !assoc [(_  P)%I]comm !assoc -2!assoc.
    apply sep_mono; last first.
    { apply wand_intro_l. eauto with I. }
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    (* Now we come to the core of the proof: Updating from waiting to ress. *)
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    rewrite /waiting /ress sep_exist_l. apply exist_elim=>{Φ} Φ.
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    rewrite later_wand {1}(later_intro P) !assoc wand_elim_r.
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    rewrite big_sepS_later -big_sepS_sepS. apply big_sepS_mono'=>i.
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    rewrite -(exist_intro (Φ i)) comm. done.
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  Qed.
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  Lemma wait_spec l P (Φ : val  iProp) :
    heapN  N  (recv l P  (P - Φ '()))  wp  (wait (LocV l)) Φ.
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  Proof.
  Abort.

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  Lemma split_spec l P1 P2 Φ :
    (recv l (P1  P2)  (recv l P1  recv l P2 - Φ '()))  wp  Skip Φ.
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  Proof.
  Abort.

  Lemma recv_strengthen l P1 P2 :
    (P1 - P2)  (recv l P1 - recv l P2).
  Proof.
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    apply wand_intro_l. rewrite /recv. rewrite sep_exist_r. apply exist_mono=>γ.
    rewrite sep_exist_r. apply exist_mono=>P. rewrite sep_exist_r.
    apply exist_mono=>Q. rewrite sep_exist_r. apply exist_mono=>i.
    rewrite -!assoc. apply sep_mono_r, sep_mono_r, sep_mono_r, sep_mono_r.
    rewrite (later_intro (P1 - _)%I) -later_sep. apply later_mono.
    apply wand_intro_l. rewrite !assoc wand_elim_r wand_elim_r. done.
  Qed.
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End proof.