Add bounded blocking Stack

Author: polytypic

Diff for: bench/bench_stack.ml

@@ -0,0 +1,86 @@
+open Multicore_bench
+open Picos_std_sync
+
+let run_one_domain ~budgetf ?(n_msgs = 50 * Util.iter_factor) () =
+  let t = Stack.create ~padded:true () in
+
+  let op push =
+    if push then Stack.push t 101
+    else match Stack.pop_exn t with _ -> () | exception Stack.Empty -> ()
+  in
+
+  let init _ =
+    assert (
+      match Stack.pop_exn t with _ -> false | exception Stack.Empty -> true);
+    Util.generate_push_and_pop_sequence n_msgs
+  in
+  let work _ bits = Util.Bits.iter op bits in
+
+  Times.record ~budgetf ~n_domains:1 ~init ~work ()
+  |> Times.to_thruput_metrics ~n:n_msgs ~singular:"message" ~config:"one domain"
+
+let run_one ~budgetf ~n_adders ~n_takers () =
+  let n_domains = n_adders + n_takers in
+
+  let n_msgs = 50 * Util.iter_factor in
+
+  let t = Stack.create ~padded:true () in
+
+  let n_msgs_to_add = Countdown.create ~n_domains:n_adders () in
+  let n_msgs_to_take = Countdown.create ~n_domains:n_takers () in
+
+  let init _ =
+    assert (
+      match Stack.pop_exn t with _ -> false | exception Stack.Empty -> true);
+    Countdown.non_atomic_set n_msgs_to_add n_msgs;
+    Countdown.non_atomic_set n_msgs_to_take n_msgs
+  in
+  let work i () =
+    if i < n_adders then
+      let rec work () =
+        let n = Countdown.alloc n_msgs_to_add ~domain_index:i ~batch:1000 in
+        if 0 < n then begin
+          for i = 1 to n do
+            Stack.push t i
+          done;
+          work ()
+        end
+      in
+      work ()
+    else
+      let i = i - n_adders in
+      let rec work () =
+        let n = Countdown.alloc n_msgs_to_take ~domain_index:i ~batch:1000 in
+        if 0 < n then
+          let rec loop n =
+            if 0 < n then begin
+              match Stack.pop_exn t with
+              | _ -> loop (n - 1)
+              | exception Stack.Empty ->
+                  Backoff.once Backoff.default |> ignore;
+                  loop n
+            end
+            else work ()
+          in
+          loop n
+      in
+      work ()
+  in
+
+  let config =
+    let format role n =
+      Printf.sprintf "%d %s%s" n role (if n = 1 then "" else "s")
+    in
+    Printf.sprintf "%s, %s"
+      (format "nb adder" n_adders)
+      (format "nb taker" n_takers)
+  in
+  Times.record ~budgetf ~n_domains ~init ~work ()
+  |> Times.to_thruput_metrics ~n:n_msgs ~singular:"message" ~config
+
+let run_suite ~budgetf =
+  run_one_domain ~budgetf ()
+  @ (Util.cross [ 1; 2; 4 ] [ 1; 2; 4 ]
+    |> List.concat_map @@ fun (n_adders, n_takers) ->
+       if Picos_domain.recommended_domain_count () < n_adders + n_takers then []
+       else run_one ~budgetf ~n_adders ~n_takers ())

Diff for: bench/dune

@@ -23,6 +23,7 @@
    (run %{test} -brief "Picos binaries")
    (run %{test} -brief "Bounded_q with Picos_std_sync")
    (run %{test} -brief "Memory usage")
+   (run %{test} -brief "Stack")
    ;;
    ))
  (foreign_stubs

Diff for: bench/main.ml

@@ -22,6 +22,7 @@ let benchmarks =
     ("Picos binaries", Bench_binaries.run_suite);
     ("Bounded_q with Picos_std_sync", Bench_bounded_q.run_suite);
     ("Memory usage", Bench_memory.run_suite);
+    ("Stack", Bench_stack.run_suite);
   ]
 
 let () = Multicore_bench.Cmd.run ~benchmarks ()

Diff for: lib/picos_std.sync/picos_std_sync.ml

@@ -9,3 +9,4 @@ module Latch = Latch
 module Barrier = Barrier
 module Ivar = Ivar
 module Stream = Stream
+module Stack = Stack

Diff for: lib/picos_std.sync/picos_std_sync.mli

@@ -753,6 +753,25 @@ module Stream : sig
       the [cursor] position. *)
 end
 
+module Stack : sig
+  (** *)
+
+  type !'a t
+  (** *)
+
+  val create : ?padded:bool -> ?capacity:int -> unit -> 'a t
+  (** *)
+
+  val push : 'a t -> 'a -> unit
+  (** *)
+
+  exception Empty
+  (** *)
+
+  val pop_exn : 'a t -> 'a
+  (** *)
+end
+
 (** {1 Examples}
 
     {2 A simple bounded queue}

Diff for: lib/picos_std.sync/stack.ml

@@ -0,0 +1,60 @@
+open Picos_std_awaitable
+
+type 'a state =
+  | Nil of { mutable capacity : int }
+  | Cons of { mutable capacity : int; value : 'a; rest : 'a state }
+
+type 'a t = 'a state Awaitable.t
+
+exception Empty
+
+let one = 0b10
+let busy_bit = 0b01
+
+let create ?padded ?capacity () =
+  let capacity =
+    match capacity with
+    | None -> Int.max_int land lnot busy_bit
+    | Some capacity -> capacity * one
+  in
+  Awaitable.make ?padded (Nil { capacity })
+
+let rec push t value backoff =
+  match Awaitable.get t with
+  | Nil r as before ->
+      let capacity = r.capacity land lnot busy_bit in
+      if
+        Awaitable.compare_and_set t before
+          (Cons { capacity = capacity - one; value; rest = Nil { capacity } })
+      then begin
+        if r.capacity land busy_bit <> 0 then Awaitable.broadcast t
+      end
+      else push t value (Backoff.once backoff)
+  | Cons r as before ->
+      let capacity = r.capacity in
+      if one <= capacity then begin
+        if
+          not
+            (Awaitable.compare_and_set t before
+               (Cons { capacity = capacity - one; value; rest = before }))
+        then push t value (Backoff.once backoff)
+      end
+      else begin
+        if capacity <> capacity lor busy_bit then
+          r.capacity <- capacity lor busy_bit;
+        Awaitable.await t before;
+        push t value Backoff.default
+      end
+
+let rec pop_exn t backoff =
+  match Awaitable.get t with
+  | Nil _ -> raise_notrace Empty
+  | Cons r as before ->
+      if Awaitable.compare_and_set t before r.rest then begin
+        if r.capacity land busy_bit <> 0 then Awaitable.broadcast t;
+        r.value
+      end
+      else pop_exn t (Backoff.once backoff)
+
+let[@inline] push t value = push t value Backoff.default
+let[@inline] pop_exn t = pop_exn t Backoff.default