Fiber.any: combine as we go

lib_eio/core/fiber.ml

@@ -90,18 +90,18 @@ let await_cancel () =
 type 'a any_status =
   | New
   | Ex of (exn * Printexc.raw_backtrace)
-  | OK of 'a list
+  | OK of 'a
 
-let rev_any fs =
+let any_gen ~return ~combine fs =
   let r = ref New in
   let parent_c =
     Cancel.sub_unchecked Any (fun cc ->
         let wrap h =
           match h () with
           | x ->
             begin match !r with
-              | New   -> r := OK [x]; Cancel.cancel cc Not_first
-              | OK ll -> r := OK (x :: ll)
+              | New -> r := OK (return x); Cancel.cancel cc Not_first
+              | OK prev -> r := OK (combine prev x)
               | Ex _ -> ()
             end
           | exception Cancel.Cancelled _ when not (Cancel.is_on cc) ->
@@ -111,7 +111,7 @@ let rev_any fs =
             ()
           | exception ex ->
             begin match !r with
-              | New  -> r := Ex (ex, Printexc.get_raw_backtrace ()); Cancel.cancel cc ex
+              | New -> r := Ex (ex, Printexc.get_raw_backtrace ()); Cancel.cancel cc ex
               | OK _ -> r := Ex (ex, Printexc.get_raw_backtrace ())
               | Ex prev ->
                 let bt = Printexc.get_raw_backtrace () in
@@ -137,7 +137,7 @@ let rev_any fs =
       )
   in
   match !r, Cancel.get_error parent_c with
-  | OK ll, None -> ll
+  | OK r, None -> r
   | (OK _ | New), Some ex -> raise ex
   | Ex (ex, bt), None -> Printexc.raise_with_backtrace ex bt
   | Ex ex1, Some ex2 ->
@@ -146,18 +146,10 @@ let rev_any fs =
     Printexc.raise_with_backtrace ex bt
   | New, None -> assert false
 
-let n_any ll = List.rev (rev_any ll)
+let n_any fs =
+  List.rev (any_gen fs ~return:(fun x -> [x]) ~combine:(fun xs x -> x :: xs))
 
-let any ?(combine = (fun x _ -> x)) ll =
-  (* The results are backwards *)
-  let rec reduce_right = function
-    | [y; x] -> combine x y
-    | x :: rest -> combine (reduce_right rest) x
-    | [] -> assert false
-  in
-  match rev_any ll with
-  | [x] -> x
-  | ll -> reduce_right ll
+let any ?(combine=(fun x _ -> x)) fs = any_gen fs ~return:Fun.id ~combine
 
 let first ?combine f g = any ?combine [f; g]