wip: use picos computations

src/core/exn_bt.mli

@@ -4,8 +4,10 @@
 
     @since 0.6 *)
 
-include module type of Picos_exn_bt
 (** An exception bundled with a backtrace *)
+include module type of struct
+  include Picos_exn_bt
+end
 
 val exn : t -> exn
 val bt : t -> Printexc.raw_backtrace

src/core/fut.ml

@@ -1,118 +1,105 @@
 module A = Atomic_
+module C = Picos.Computation
 
 type 'a or_error = ('a, Exn_bt.t) result
 type 'a waiter = 'a or_error -> unit
-
-type 'a state =
-  | Done of 'a or_error
-  | Waiting of { waiters: 'a waiter list }
-
-type 'a t = { st: 'a state A.t } [@@unboxed]
+type 'a t = { st: 'a C.t } [@@unboxed]
 type 'a promise = 'a t
 
+let[@inline] make_ () : _ t =
+  let fut = { st = C.create ~mode:`LIFO () } in
+  fut
+
 let make () =
-  let fut = { st = A.make (Waiting { waiters = [] }) } in
+  let fut = make_ () in
   fut, fut
 
-let[@inline] of_result x : _ t = { st = A.make (Done x) }
-let[@inline] return x : _ t = of_result (Ok x)
-let[@inline] fail exn bt : _ t = of_result (Error { Exn_bt.exn; bt })
-let[@inline] fail_exn_bt ebt = of_result (Error ebt)
+let[@inline] return x : _ t = { st = C.returned x }
 
-let[@inline] is_resolved self : bool =
-  match A.get self.st with
-  | Done _ -> true
-  | Waiting _ -> false
+let[@inline] fail_exn_bt ebt =
+  let st = C.create () in
+  C.cancel st ebt;
+  { st }
 
-let[@inline] peek self : _ option =
-  match A.get self.st with
-  | Done x -> Some x
-  | Waiting _ -> None
+let[@inline] fail exn bt : _ t = fail_exn_bt { Exn_bt.exn; bt }
 
-let[@inline] raise_if_failed self : unit =
-  match A.get self.st with
-  | Done (Error ebt) -> Exn_bt.raise ebt
-  | _ -> ()
+let[@inline] of_result = function
+  | Ok x -> return x
+  | Error ebt -> fail_exn_bt ebt
 
-let[@inline] is_done self : bool =
-  match A.get self.st with
-  | Done _ -> true
-  | Waiting _ -> false
+let[@inline] is_resolved self : bool = not (C.is_running self.st)
+let is_done = is_resolved
+let[@inline] peek self : _ option = C.peek self.st
+let[@inline] raise_if_failed self : unit = C.check self.st
 
 let[@inline] is_success self =
-  match A.get self.st with
-  | Done (Ok _) -> true
+  match C.peek self.st with
+  | Some (Ok _) -> true
   | _ -> false
 
-let[@inline] is_failed self =
-  match A.get self.st with
-  | Done (Error _) -> true
-  | _ -> false
+let[@inline] is_failed self = C.is_canceled self.st
 
 exception Not_ready
 
 let[@inline] get_or_fail self =
-  match A.get self.st with
-  | Done x -> x
-  | Waiting _ -> raise Not_ready
+  match C.peek self.st with
+  | Some x -> x
+  | None -> raise Not_ready
 
 let[@inline] get_or_fail_exn self =
-  match A.get self.st with
-  | Done (Ok x) -> x
-  | Done (Error { exn; bt }) -> Printexc.raise_with_backtrace exn bt
-  | Waiting _ -> raise Not_ready
+  match C.peek self.st with
+  | Some (Ok x) -> x
+  | Some (Error ebt) -> Exn_bt.raise ebt
+  | None -> raise Not_ready
+
+let[@inline] peek_ok_assert_ (self : 'a t) : 'a =
+  if C.is_running self.st then assert false;
+  (* cannot block *)
+  C.await self.st
+
+let on_result_cb_ _tr f self : unit =
+  let res =
+    try Ok (peek_ok_assert_ self)
+    with exn ->
+      let ebt = Exn_bt.get exn in
+      Error ebt
+  in
+  f res
 
 let on_result (self : _ t) (f : _ waiter) : unit =
-  while
-    let st = A.get self.st in
-    match st with
-    | Done x ->
-      f x;
-      false
-    | Waiting { waiters = l } ->
-      not (A.compare_and_set self.st st (Waiting { waiters = f :: l }))
-  do
-    Domain_.relax ()
-  done
+  let trigger =
+    (Trigger.from_action f self on_result_cb_ [@alert "-handler"])
+  in
+  ignore (C.try_attach self.st trigger : bool)
+
+let[@inline] fulfill_idempotent self r =
+  match r with
+  | Ok x -> C.return self.st x
+  | Error ebt -> C.cancel self.st ebt
 
 exception Already_fulfilled
 
 let fulfill (self : _ t) (r : _ result) : unit =
-  let fs = ref [] in
-  while
-    let st = A.get self.st in
-    match st with
-    | Done _ -> raise Already_fulfilled
-    | Waiting { waiters = l } ->
-      let did_swap = A.compare_and_set self.st st (Done r) in
-      if did_swap then (
-        (* success, now call all the waiters *)
-        fs := l;
-        false
-      ) else
-        true
-  do
-    Domain_.relax ()
-  done;
-  List.iter (fun f -> try f r with _ -> ()) !fs;
-  ()
-
-let[@inline] fulfill_idempotent self r =
-  try fulfill self r with Already_fulfilled -> ()
+  let ok =
+    match r with
+    | Ok x -> C.try_return self.st x
+    | Error ebt -> C.try_cancel self.st ebt
+  in
+  if not ok then raise Already_fulfilled
 
 (* ### combinators ### *)
 
 let spawn ~on f : _ t =
-  let fut, promise = make () in
+  let fut = make_ () in
 
   let task () =
-    let res =
-      try Ok (f ())
-      with exn ->
-        let bt = Printexc.get_raw_backtrace () in
-        Error { Exn_bt.exn; bt }
-    in
-    fulfill promise res
+    try
+      let res = f () in
+      C.return fut.st res
+    with exn ->
+      let bt = Printexc.get_raw_backtrace () in
+      let ebt = { Exn_bt.exn; bt } in
+      C.cancel fut.st ebt
   in
 
   Runner.run_async on task;
@@ -127,8 +114,8 @@ let reify_error (f : 'a t) : 'a or_error t =
   match peek f with
   | Some res -> return res
   | None ->
-    let fut, promise = make () in
-    on_result f (fun r -> fulfill promise (Ok r));
+    let fut = make_ () in
+    on_result f (fun r -> fulfill fut (Ok r));
     fut
 
 let[@inline] get_runner_ ?on () : Runner.t option =
@@ -299,11 +286,6 @@ let choose_same a b : _ t =
       | Ok y -> fulfill_idempotent promise (Ok y));
     fut
 
-let peek_ok_assert_ (self : 'a t) : 'a =
-  match A.get self.st with
-  | Done (Ok x) -> x
-  | _ -> assert false
-
 let barrier_on_abstract_container_of_futures ~iter ~len ~aggregate_results cont
     : _ t =
   let n_items = len cont in
@@ -387,6 +369,7 @@ let for_list ~on l f : unit t =
 
 (* ### blocking ### *)
 
+(* TODO: use a trigger directly? *)
 let wait_block (self : 'a t) : 'a or_error =
   match A.get self.st with
   | Done x -> x (* fast path *)

src/core/trigger.ml

@@ -0,0 +1,4 @@
+(** Triggers from picos
+    @since NEXT_RELEASE *)
+
+include Picos.Trigger

src/core/types_.ml

@@ -1,6 +1,7 @@
 module TLS = Thread_local_storage
 module Domain_pool_ = Moonpool_dpool
 
+(* TODO: replace with Picos.Fiber.FLS *)
 type ls_value = ..
 
 (** Key for task local storage *)