Commit 7de018e3 authored by Ralf Jung's avatar Ralf Jung

logically atomic increment on physical heap

parent da045e6b
......@@ -8,12 +8,41 @@ Set Default Proof Using "Type".
(** Show that implementing fetch-and-add on top of CAS preserves logical
atomicity. *)
(** First: logically atomic increment directly on top of the physical heap. *)
Section increment_physical.
Context `{!heapG Σ}.
Definition incr_phy : val :=
rec: "incr" "l" :=
let: "oldv" := !"l" in
if: CAS "l" "oldv" ("oldv" + #1)
then "oldv" (* return old value if success *)
else "incr" "l".
Lemma incr_phy_spec (l: loc) :
<<< (v : Z), l #v >>> incr_phy #l @ <<< l #(v + 1), RET #v >>>.
Proof.
iApply wp_atomic_intro. iIntros (Φ) "AU". iLöb as "IH". wp_lam.
wp_bind (!_)%E. iMod "AU" as (v) "[Hl [Hclose _]]".
wp_load. iMod ("Hclose" with "Hl") as "AU". iModIntro.
wp_pures. wp_bind (CAS _ _ _)%E. iMod "AU" as (w) "[Hl Hclose]".
destruct (decide (#v = #w)) as [[= ->]|Hx].
- wp_cas_suc. iDestruct "Hclose" as "[_ Hclose]". iMod ("Hclose" with "Hl") as "HΦ".
iModIntro. wp_if. done.
- wp_cas_fail. iDestruct "Hclose" as "[Hclose _]". iMod ("Hclose" with "Hl") as "AU".
iModIntro. wp_if. iApply "IH". done.
Qed.
End increment_physical.
(** Next: logically atomic increment on top of an arbitrary logically atomic heap *)
Section increment.
Context `{!heapG Σ} {aheap: atomic_heap Σ}.
Import atomic_heap.notation.
Definition incr: val :=
Definition incr : val :=
rec: "incr" "l" :=
let: "oldv" := !"l" in
if: CAS "l" "oldv" ("oldv" + #1)
......@@ -42,12 +71,15 @@ Section increment.
wp_if. iApply "IH". done.
Qed.
(** A "weak increment": assumes that there is no race *)
Definition weak_incr: val :=
rec: "weak_incr" "l" :=
let: "oldv" := !"l" in
"l" <- ("oldv" + #1);;
"oldv" (* return old value *).
(** Logically atomic spec for weak increment. Also an example for what TaDA
calls "private precondition". *)
(* TODO: Generalize to q and 1-q, based on some theory for a "maybe-mapsto"
connective that works on [option Qp] (the type of 1-q). *)
Lemma weak_incr_spec (l: loc) (v : Z) :
......
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