Commit 43199eff authored by Ralf Jung's avatar Ralf Jung
Browse files

Start with logically atomic stack: Write the code

parent f6521223
......@@ -19,3 +19,6 @@ logrel: $(filter theories/logrel/%,$(VOFILES))
hocap: $(filter theories/hocap/%,$(VOFILES))
.PHONY: hocap
logatom_stack: $(filter theories/logatom_stack/%,$(VOFILES))
.PHONY: logrel
......@@ -80,3 +80,5 @@ theories/hocap/contrib_bag.v
......@@ -9,6 +9,6 @@ build: [make "-j%{jobs}%"]
install: [make "install"]
remove: ["rm" "-rf" "%{lib}%/coq/user-contrib/iris_examples"]
depends: [
"coq-iris" { (= "dev.2018-07-13.0.cbf73155") | (= "dev") }
"coq-iris" { (= "dev.2018-07-13.2.af5611c8") | (= "dev") }
"coq-autosubst" { = "dev.coq86" }
From iris.algebra Require Import excl.
From iris.base_logic.lib Require Import invariants.
From iris.program_logic Require Import atomic.
From iris.proofmode Require Import tactics.
From iris.heap_lang Require Import lifting proofmode notation atomic_heap par.
From Require Import fractional.
Set Default Proof Using "Type".
(** * Implement a concurrent stack with helping on top of an arbitrary atomic
heap. *)
(** The CMRA & functor we need. *)
(* Not bundling heapG, as it may be shared with other users. *)
Class stackG Σ := StackG { stack_tokG :> inG Σ (exclR unitC) }.
Definition stackΣ : gFunctors := #[GFunctor (exclR unitC)].
Instance subG_stackΣ {Σ} : subG stackΣ Σ stackG Σ.
Proof. solve_inG. Qed.
Section stack.
Context `{!heapG Σ, stackG Σ} {aheap: atomic_heap Σ}.
Import atomic_heap.notation.
(** Code. A stack is a pair of two option pointers-to-pointers, one for the
head element (if the stack is non-empty) and for the current offer (if it
exists). A stack element is a pair of a value an an optional pointer to the
next element. *)
Definition new_stack : val :=
λ: <>,
let: "head" := ref NONE in
let: "offer" := ref NONE in
("head", "offer").
Definition push : val :=
rec: "push" "args" :=
let: "stack" := Fst "args" in
let: "val" := Snd "args" in
let: "head_old" := !(Fst "stack") in
let: "head_new" := ref ("val", "head_old") in
if: CAS (Fst "stack") "head_old" (SOME "head_new") then #() else
(* the CAS failed due to a race, let's try an offer on the side-channel *)
let: "state" := ref #0 in
let: "offer" := ("val", "state") in
(Snd "stack") <- SOME "offer" ;;
(* wait to see if anyone takes it *)
(* okay, enough waiting *)
(Snd "stack") <- NONE ;;
if: CAS "state" #0 #2 then
(* We retracted the offer. Just try the entire thing again. *)
"push" "args"
(* Someone took the offer. We are done. *)
Definition pop : val :=
rec: "pop" "stack" :=
match: !(Fst "stack") with
NONE => NONE (* stack empty *)
| SOME "head_old" =>
let: "head_old_data" := !"head_old" in
(* See if we can change the master head pointer *)
if: CAS (Fst "stack") (SOME "head_old") (Snd "head_old_data") then
(* That worked! We are done. Return the value. *)
Fst "head_old_data"
(* See if there is an offer on the side-channel *)
match: !(Snd "stack") with
(* Nope, no offer. Just try again. *)
"pop" "stack"
| SOME "offer" =>
(* Try to accept the offer. *)
if: CAS (Snd "offer") #0 #1 then
(* Success! We are done. Return the offered value. *)
Fst "offer"
(* Someone else was faster. Just try again. *)
"pop" "stack"
End stack.
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