ticket_lock.v 12.9 KB
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From iris.proofmode Require Import tactics.
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From iris.algebra Require Export auth gset excl.
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From iris.base_logic Require Import auth.
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From iris_logrel Require Export logrel examples.lock examples.counter.
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Definition wait_loop: val :=
  rec: "wait_loop" "x" "lk" :=
    if: "x" = !(Fst "lk")
      then #() (* my turn *)
      else "wait_loop" "x" "lk".

Definition newlock : val :=
  λ: <>, ((* owner *) ref #0, (* next *) ref #0).

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Definition acquire : val := λ: "lk",
  let: "n" := FG_increment (Snd "lk") #() in
  wait_loop "n" "lk".
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Definition release : val :=
  λ: "lk", (Fst "lk") <- !(Fst "lk") + #1.

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Definition LockType : type := ref TNat × ref TNat.
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Hint Unfold LockType : typeable.

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Lemma newlock_type Γ : typed Γ newlock (Unit  LockType).
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Proof. solve_typed. Qed.

Hint Resolve newlock_type : typeable.

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Lemma acquire_type Γ : typed Γ acquire (LockType  TUnit).
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Proof.
  unlock acquire wait_loop.
  econstructor; cbn; solve_typed.
  econstructor; cbn; solve_typed.
  econstructor; cbn; solve_typed.
  econstructor; cbn; solve_typed.
Qed.
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Hint Resolve acquire_type : typeable.

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Lemma release_type Γ : typed Γ release (LockType  TUnit).
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Proof. solve_typed. Qed.

Hint Resolve release_type : typeable.

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Definition lockT : type := : (Unit  TVar 0) × (TVar 0  Unit) × (TVar 0  Unit).
Lemma ticket_lock_typed Γ : typed Γ (Pack (newlock, acquire, release)) lockT.
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Proof.
  apply TPack with LockType.
  asimpl. solve_typed.
Qed.

Class tlockG Σ :=
  tlock_G :> authG Σ (gset_disjUR nat).
Definition tlockΣ : gFunctors :=
  #[ authΣ (gset_disjUR nat) ].

Definition lockPool := gset ((loc * loc * gname) * loc).
Definition lockPoolR := gsetUR ((loc * loc * gname) * loc).

Class lockPoolG Σ :=
  lockPool_inG :> authG Σ lockPoolR.
Section refinement.
  Context `{logrelG Σ, tlockG Σ, lockPoolG Σ}.

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  (** * Basic abstractions around the concrete RA *)
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  (** ticket with the id `n` *)
  Definition ticket (γ : gname) (n : nat) := own γ ( GSet {[ n ]}).
  (** total number of issued tickets is `n` *)
  Definition issuedTickets (γ : gname) (n : nat) := own γ ( GSet (seq_set 0 n)).
  (** the locks `(ln, lo)` and `l'` are linked together in the pool P` *)
  Definition inPool (γP : gname) (lo ln : loc) (γ : gname) (l' : loc) := own γP ( {[(lo, ln, γ), l']}).
  (** the set `P` is in fact the lock pool associated with P` *)
  Definition isPool (γP : gname) (P : lockPool) := own γP ( P).
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  Lemma ticket_nondup γ n : ticket γ n - ticket γ n - False.
  Proof.
    iIntros "Ht1 Ht2".
    iDestruct (own_valid_2 with "Ht1 Ht2") as %?%gset_disj_valid_op.
    set_solver.
  Qed.
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  Lemma newIssuedTickets : (|==>  γ, issuedTickets γ 0)%I.
  Proof. iMod (own_alloc ( (GSet ))) as (γ) "Hγ"; [done|eauto]. Qed.
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  Lemma issueNewTicket γ m :
    issuedTickets γ m ==
    issuedTickets γ (S m)  ticket γ m.
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  Proof.
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    iIntros "Hseq".
    iMod (own_update with "Hseq") as "[Hseq Hticket]".
    { eapply auth_update_alloc.
      eapply (gset_disj_alloc_empty_local_update _ {[ m ]}).
      apply (seq_set_S_disjoint 0). }
    rewrite -(seq_set_S_union_L 0).
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    by iFrame.
  Qed.

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  Instance inPool_persistent γP lo ln γ l' : Persistent (inPool γP lo ln γ l').
  Proof. apply _. Qed.

  Lemma inPool_lookup γP lo ln γ l' P :
    inPool γP lo ln γ l' - isPool γP P -
    (lo, ln, γ, l')  P.
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  Proof.
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    iIntros "Hrs Ho".
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    iDestruct (own_valid_2 with "Ho Hrs") as %Hfoo.
    iPureIntro.
    apply auth_valid_discrete in Hfoo.
    simpl in Hfoo. destruct Hfoo as [Hfoo _].
    revert Hfoo. rewrite left_id.
    by rewrite gset_included elem_of_subseteq_singleton.
  Qed.

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  Lemma isPool_insert γP lo ln γ l' P :
    isPool γP P ==
    inPool γP lo ln γ l'  isPool γP ({[(lo, ln, γ, l')]}  P).
  Proof.
    iIntros "HP".
    iMod (own_update with "HP") as "[HP Hls]".
    { eapply auth_update_alloc.
      eapply (gset_local_update _ _ ({[(lo, ln, γ, l')]}  P)).
      apply union_subseteq_r. }
    iFrame "HP".
    rewrite -gset_op_union.
    by iDestruct "Hls" as "[#Hls _]".
  Qed.

  Lemma newIsPool (P : lockPool) : (|==>  γP, isPool γP P)%I.
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  Proof.
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    apply (own_alloc ( (P : lockPoolR))).
    by apply auth_auth_valid.
  Qed.

  Instance isPool_timeless γP P : Timeless (isPool γP P).
  Proof. apply _. Qed.
  Instance inPool_timeless γP lo ln γ l' : Timeless (inPool γP lo ln γ l').
  Proof. apply _. Qed.
  Instance ticket_timeless γ n : Timeless (ticket γ n).
  Proof. apply _. Qed.
  Instance issuedTickets_timeless γ n : Timeless (issuedTickets γ n).
  Proof. apply _. Qed.

  Opaque ticket issuedTickets inPool isPool.

  (** * Invariants and abstracts for them *)
  Definition lockInv (lo ln : loc) (γ : gname) (l' : loc) : iProp Σ :=
    ( (o n : nat) (b : bool), lo ↦ᵢ #o  ln ↦ᵢ #n
    issuedTickets γ n  l' ↦ₛ #b
    if b then ticket γ o else True)%I.

  Instance ifticket_timeless (b : bool) γ o : Timeless (if b then ticket γ o else True%I).
  Proof. destruct b; apply _. Qed.
  Instance lockInv_timeless lo ln γ l' : Timeless (lockInv lo ln γ l').
  Proof. apply _. Qed.

  Definition lockPoolInv (P : lockPool) : iProp Σ :=
    ([ set] rs  P, match rs with
                     | ((lo, ln, γ), l') => lockInv lo ln γ l'
                     end)%I.

  Instance lockPoolInv_timeless P : Timeless (lockPoolInv P).
  Proof.
    apply big_sepS_timeless.
    intros [[[? ?] ?] ?]. apply _.
  Qed.

  Lemma lockPoolInv_empty : lockPoolInv .
  Proof. by rewrite /lockPoolInv big_sepS_empty. Qed.

  Lemma lockPool_open γP (P : lockPool) (lo ln : loc) (γ : gname) (l' : loc) :
    isPool γP P -
    inPool γP lo ln γ l' -
    lockPoolInv P -
    isPool γP P  (lockInv lo ln γ l')  (lockInv lo ln γ l' - lockPoolInv P).
  Proof.
    iIntros "HP #Hin HPinv".
    iDestruct (inPool_lookup with "Hin HP") as %Hin.
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    rewrite /lockPoolInv.
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    iDestruct (big_sepS_elem_of_acc _ P _ with "HPinv") as "[Hrs Hreg]"; first apply Hin.
    by iFrame.
  Qed.

  Lemma lockPool_insert γP (P : lockPool) (lo ln : loc) γ l' :
    isPool γP P -
    lockPoolInv P -
    lockInv lo ln γ l' ==
    isPool γP ({[(lo, ln, γ, l')]}  P)
     lockPoolInv ({[(lo, ln, γ, l')]}  P)
     inPool γP lo ln γ l'.
  Proof.
    iIntros "HP HPinv".
    iDestruct 1 as (n o b) "(Hlo & Hln & Hissued & Hl' & Hticket)".
    iMod (isPool_insert γP lo ln γ l' P with "HP") as "[$ $]".
    rewrite /lockInv.
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    iAssert ((lo, ln, γ, l')  P  False)%I as %Hbaz.
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    { iIntros (HP).
      rewrite /lockPoolInv.
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      rewrite (big_sepS_elem_of _ P _ HP).
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      iDestruct "HPinv" as (? ? ?) "(Hlo' & Hln' & ?)".
      iDestruct (mapsto_valid_2 with "Hlo' Hlo") as %Hfoo.
      compute in Hfoo; contradiction. }
    rewrite /lockPoolInv.
    rewrite big_sepS_insert; last assumption.
    iFrame. iExists _,_,_. by iFrame.
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  Qed.

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  Opaque lockPoolInv.

  Definition moduleInv γp : iProp Σ :=
    ( (P : lockPool), isPool γp P  lockPoolInv P)%I.

  Program Definition lockInt (γp : gname) := λne vv,
    ( (lo ln : loc) (γ : gname) (l' : loc),
        vv.1 = (#lo, #ln)%V  vv.2 = #l'⌝
       inPool γp lo ln γ l')%I.
  Next Obligation. solve_proper. Qed.

  Instance lockInt_persistent γp ww : Persistent (lockInt γp ww).
  Proof. apply _. Qed.

  (** * Refinement proofs *)  
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  Definition N := logrelN.@"locked".

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  Local Ltac openI N := iInv N as (P) ">[HP HPinv]" "Hcl".
  Local Ltac closeI := iMod ("Hcl" with "[-]") as "_";
    first by (iNext; iExists _; iFrame).

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  (* Allocating a new lock *)
  Lemma newlock_refinement Δ Γ γp:
    inv N (moduleInv γp) -
    {(lockInt γp :: Δ); ⤉Γ}  newlock log lock.newlock : (Unit  TVar 0).
  Proof.
    iIntros "#Hinv".
    unlock newlock.
    iApply bin_log_related_arrow_val; eauto.
    { by unlock lock.newlock. }
    iAlways. iIntros (? ?) "/= [% %]"; simplify_eq.
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    (* Reducing to a value on the LHS *)
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    rel_let_l.
    rel_alloc_l as lo "Hlo".
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    rel_alloc_l as ln "Hln".
    (* Reducing to a value on the RHS *)
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    rel_apply_r bin_log_related_newlock_r.
    { solve_ndisj. }
    iIntros (l') "Hl'".
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    (* Establishing the invariant *)
    openI N.
    iMod newIssuedTickets as (γ) "Hγ".
    iMod (lockPool_insert _ _ lo ln with "HP HPinv [Hlo Hln Hl' Hγ]") as "(HP & HPinv & #Hin)".
    { iExists _,_,_; by iFrame. }
    closeI.
    rel_vals; iModIntro; iAlways.
    iExists _,_,_,_. by iFrame "Hin".
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  Qed.

  (* Acquiring a lock *)
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  (* helper lemma *)
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  Lemma wait_loop_refinement Δ Γ γp (lo ln : loc) γ (l' : loc) (m : nat) :
    inv N (moduleInv γp) -
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    inPool γp lo ln γ l' - (* two locks are linked *)
    ticket γ m -
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    {(lockInt γp :: Δ); ⤉Γ} 
      wait_loop #m (#lo, #ln) log lock.acquire #l' : TUnit.
  Proof.
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    iIntros "#Hinv #Hin Hticket".
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    rel_rec_l.
    iLöb as "IH".
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    unlock {2}wait_loop. simpl.
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    rel_let_l. rel_proj_l.
    rel_load_l_atomic.
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    openI N.
    iDestruct (lockPool_open with "HP Hin HPinv") as "(HP & Hls & HPinv)".
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    rewrite {1}/lockInv.
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    iDestruct "Hls" as (o n b) "(Hlo & Hln & Hissued & Hl' & Hrest)".
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    iModIntro. iExists _; iFrame; iNext.
    iIntros "Hlo".
    rel_op_l.
    case_decide; subst; rel_if_l.
    (* Whether the ticket is called out *)
    - destruct b.
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      { iDestruct (ticket_nondup with "Hticket Hrest") as %[]. }
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      rel_apply_r (bin_log_related_acquire_r with "Hl'").
      { solve_ndisj. }
      iIntros "Hl'".
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      iSpecialize ("HPinv" with "[Hlo Hln Hl' Hissued Hticket]").
      { iExists _,_,_. by iFrame. }
      closeI.
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      iApply bin_log_related_unit.
    - iMod ("Hcl" with "[-Hticket]") as "_".
      { iNext. iExists P; iFrame.
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        iApply "HPinv". iExists _,_,_; by iFrame. }
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      rel_rec_l.
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      unlock wait_loop. simpl_subst/=. by iApply "IH".
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  Qed.

  Lemma acquire_refinement Δ Γ γp :
    inv N (moduleInv γp) -
    {(lockInt γp :: Δ); ⤉Γ}  acquire log lock.acquire : (TVar 0  Unit).
  Proof.
    iIntros "#Hinv".
    unlock acquire; simpl.
    iApply bin_log_related_arrow_val; eauto.
    { by unlock lock.acquire. }
    iAlways. iIntros (? ?) "/= #Hl".
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    iDestruct "Hl" as (lo ln γ l') "(% & % & Hin)". simplify_eq.
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    rel_let_l. repeat rel_proj_l.
    (* rel_rec_l. (* TODO: cannot find the reduct *) *)
    rel_bind_l (FG_increment _ #()).
    rel_rec_l.
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    rel_apply_l (bin_log_FG_increment_logatomic _ (issuedTickets γ)%I True%I); first done.
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    iAlways.
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    openI N.
    iDestruct (lockPool_open with "HP Hin HPinv") as "(HP & Hls & HPinv)".
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    rewrite {1}/lockInv.
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    iDestruct "Hls" as (o n b) "(Hlo & Hln & Hissued & Hl' & Hticket)".
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    iModIntro. iExists _; iFrame.
    iSplit.
    - iDestruct 1 as (m) "[Hln ?]".
      iApply ("Hcl" with "[-]").
      iNext. iExists P; iFrame.
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      iApply "HPinv". iExists _,_,_; by iFrame.
    - iIntros (m) "[Hln Hissued] _".
      iMod (issueNewTicket with "Hissued") as "[Hissued Hm]".
      iMod ("Hcl" with "[-Hm]") as "_".
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      { iNext. iExists P; iFrame.
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        iApply "HPinv". iExists _,_,_; by iFrame. }
      rel_let_l.
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      by iApply wait_loop_refinement.
  Qed.

  (* Releasing the lock *)
  Lemma release_refinement Δ Γ γp :
    inv N (moduleInv γp) -
    {(lockInt γp :: Δ); ⤉Γ}  release log lock.release : (TVar 0  Unit).
  Proof.
    iIntros "#Hinv".
    unlock release.
    iApply bin_log_related_arrow_val; eauto.
    { by unlock lock.release. }
    iAlways. iIntros (? ?) "/= #Hl".
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    iDestruct "Hl" as (lo ln γ l') "(% & % & Hin)". simplify_eq.
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    rel_let_l. repeat rel_proj_l.
    rel_load_l_atomic.
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    openI N.
    iDestruct (lockPool_open with "HP Hin HPinv") as "(HP & Hls & HPinv)".
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    rewrite {1}/lockInv.
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    iDestruct "Hls" as (o n b) "(Hlo & Hln & Hissued & Hl' & Hticket)".
    iModIntro. iExists _; iFrame.
    iNext. iIntros "Hlo".
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    iMod ("Hcl" with "[-]") as "_".
    { iNext. iExists P; iFrame.
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      iApply "HPinv". iExists _,_,_; by iFrame. }
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    rel_op_l.
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    rel_store_l_atomic. clear n b P.
    openI N.
    iDestruct (lockPool_open with "HP Hin HPinv") as "(HP & Hls & HPinv)".
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    rewrite {1}/lockInv.
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    iDestruct "Hls" as (o' n b) "(Hlo & Hln & Hissued & Hl' & Hticket)".
    iModIntro. iExists _; iFrame.
    iNext. iIntros "Hlo".

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    rel_apply_r (bin_log_related_release_r with "Hl'").
    { solve_ndisj. }
    iIntros "Hl'".
    iMod ("Hcl" with "[-]") as "_".
    { iNext. iExists P; iFrame.
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      iApply "HPinv". iExists _,_,_. by iFrame. }
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    iApply bin_log_related_unit.
  Qed.

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  Lemma ticket_lock_refinement Γ :
    Γ  Pack (newlock, acquire, release)
      log
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        Pack (lock.newlock, lock.acquire, lock.release) : lockT.
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  Proof.
    iIntros (Δ).
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    iMod (newIsPool ) as (γp) "HP".
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    iMod (inv_alloc N _ (moduleInv γp) with "[HP]") as "#Hinv".
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    { iNext. iExists _; iFrame. iApply lockPoolInv_empty. }
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    iApply (bin_log_related_pack _ (lockInt γp)).
    repeat iApply bin_log_related_pair.
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    - by iApply newlock_refinement.
    - by iApply acquire_refinement.
    - by iApply release_refinement.
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  Qed.
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End refinement.