Remove obsolete second wakeup_paused

CHANGES

@@ -39,6 +39,10 @@
 
   * Fix marshall header size in Lwt_io.read_value. (Simmo Saan, #995)
 
+====== Misc ======
+
+  * Resolve paused promises only once in main loop. This lets Lwt.pause behave identical to Lwt_unix.yield. (#917, Christopher Zimmermann)
+
 
 ===== 5.6.1 =====
 

src/unix/lwt_main.ml

@@ -16,18 +16,14 @@ open Lwt.Infix
 
 let enter_iter_hooks = Lwt_sequence.create ()
 let leave_iter_hooks = Lwt_sequence.create ()
-let yielded = Lwt_sequence.create ()
 
-let yield () = (Lwt.add_task_r [@ocaml.warning "-3"]) yielded
+let yield () = Lwt.pause ()
 
 let abandon_yielded_and_paused () =
-  Lwt_sequence.clear yielded;
   Lwt.abandon_paused ()
 
 let run p =
   let rec run_loop () =
-    (* Fulfill paused promises now. *)
-    Lwt.wakeup_paused ();
     match Lwt.poll p with
     | Some x ->
       x
@@ -36,20 +32,12 @@ let run p =
       Lwt_sequence.iter_l (fun f -> f ()) enter_iter_hooks;
 
       (* Do the main loop call. *)
-      let should_block_waiting_for_io =
-        Lwt.paused_count () = 0 && Lwt_sequence.is_empty yielded in
+      let should_block_waiting_for_io = Lwt.paused_count () = 0 in
       Lwt_engine.iter should_block_waiting_for_io;
 
-      (* Fulfill paused promises again. *)
+      (* Fulfill paused promises. *)
       Lwt.wakeup_paused ();
 
-      (* Fulfill yield promises. *)
-      if not (Lwt_sequence.is_empty yielded) then begin
-        let tmp = Lwt_sequence.create () in
-        Lwt_sequence.transfer_r yielded tmp;
-        Lwt_sequence.iter_l (fun resolver -> Lwt.wakeup resolver ()) tmp
-      end;
-
       (* Call leave hooks. *)
       Lwt_sequence.iter_l (fun f -> f ()) leave_iter_hooks;
 

src/unix/lwt_main.mli

@@ -49,22 +49,19 @@ val yield : unit -> unit Lwt.t [@@deprecated "Use Lwt.pause instead"]
 
       @deprecated Since 5.5.0 [yield] is deprecated in favor of the more general
       {!Lwt.pause} in order to avoid discrepancies in resolution (see below) and
-      stay compatible with other execution environments such as js_of_ocaml.
+      stay compatible with other execution environments such as js_of_ocaml. *)
 
-      Currently, paused promises are resolved more frequently than yielded promises.
-      The difference is unintended but existing applications could depend on it.
-      Unifying the two pools of promises into one in the future would eliminate
-      possible discrepancies and simplify the code. *)
-
-val abandon_yielded_and_paused : unit -> unit
+val abandon_yielded_and_paused : unit -> unit [@@deprecated "Use Lwt.abandon_paused instead"]
 (** Causes promises created with {!Lwt.pause} and {!Lwt_main.yield} to remain
     forever pending.
 
-    [yield] is now deprecated in favor of the more general {!Lwt.pause}.
-    Once [yield] is phased out, this function will be deprecated as well.
+    (Note that [yield] is deprecated in favor of the more general {!Lwt.pause}.)
 
     This is meant for use with {!Lwt_unix.fork}, as a way to “abandon” more
-    promise chains that are pending in your process. *)
+    promise chains that are pending in your process.
+
+    @deprecated Since 5.7 [abandon_yielded_and_paused] is deprecated in favour
+    of [Lwt.abandon_paused]. *)
 
 
 

src/unix/lwt_unix.cppo.ml

@@ -123,7 +123,7 @@ let sleep delay =
   Lwt.on_cancel waiter (fun () -> Lwt_engine.stop_event ev);
   waiter
 
-let yield = (Lwt_main.yield [@warning "-3"])
+let yield = Lwt.pause
 
 let auto_yield timeout =
   let limit = ref (Unix.gettimeofday () +. timeout) in