From 6c4fb69d23b9020553de62a8f8c828f6fb192ed3 Mon Sep 17 00:00:00 2001
From: Simon Cruanes <simon.cruanes.2007@m4x.org>
Date: Wed, 9 Jul 2025 18:31:24 -0400
Subject: [PATCH] wip: lwt

---
 src/lwt/moonpool_lwt.ml | 79 +++++++++++++++++++++++++++++++++--------
 1 file changed, 65 insertions(+), 14 deletions(-)

diff --git a/src/lwt/moonpool_lwt.ml b/src/lwt/moonpool_lwt.ml
index e2a9e393..29f73c6a 100644
--- a/src/lwt/moonpool_lwt.ml
+++ b/src/lwt/moonpool_lwt.ml
@@ -16,44 +16,72 @@ let on_uncaught_exn : (Moonpool.Exn_bt.t -> unit) ref =
 
 module Scheduler_state = struct
   type st = {
-    tasks: WL.task_full BQ.t;
+    tasks: WL.task_full Queue.t;
+    actions_from_other_threads: (unit -> unit) BQ.t;
+        (** Other threads ask us to run closures in the lwt thread *)
+    mutable thread: int;
+    mutable closed: bool;
     mutable as_runner: Moonpool.Runner.t;
     mutable enter_hook: Lwt_main.Enter_iter_hooks.hook option;
     mutable leave_hook: Lwt_main.Leave_iter_hooks.hook option;
+    mutable notification: int;
+        (** A lwt_unix notification to wake up the event loop *)
+    has_notified: bool Atomic.t;
   }
 
   let st : st =
     {
-      tasks = BQ.create ();
+      tasks = Queue.create ();
+      actions_from_other_threads = BQ.create ();
+      thread = Thread.self () |> Thread.id;
+      closed = false;
       as_runner = Moonpool.Runner.dummy;
       enter_hook = None;
       leave_hook = None;
+      notification = 0;
+      has_notified = Atomic.make false;
     }
+end
+
+module Ops = struct
+  type st = Scheduler_state.st
 
   let around_task _ = default_around_task_
 
-  (* FIXME: need to wakeup lwt if needed! *)
-  let schedule (self : st) t = BQ.push self.tasks t
+  let add_action_from_another_thread_ (self : st) f : unit =
+    BQ.push self.actions_from_other_threads f;
+    if not (Atomic.exchange self.has_notified true) then
+      Lwt_unix.send_notification self.notification
+
+  let schedule (self : st) t =
+    if Thread.id (Thread.self ()) = self.thread then
+      Queue.push t self.tasks
+    else
+      add_action_from_another_thread_ self (fun () -> Queue.push t self.tasks)
 
   let get_next_task (self : st) =
-    try BQ.pop self.tasks with BQ.Closed -> raise WL.No_more_tasks
+    if self.closed then raise WL.No_more_tasks;
+    try Queue.pop self.tasks with Queue.Empty -> raise WL.No_more_tasks
 
   let on_exn _ ebt = !on_uncaught_exn ebt
-  let runner self = self.as_runner
+  let runner (self : st) = self.as_runner
 
   let as_runner (self : st) : Moonpool.Runner.t =
     Moonpool.Runner.For_runner_implementors.create
       ~size:(fun () -> 1)
-      ~num_tasks:(fun () -> BQ.size self.tasks)
+      ~num_tasks:(fun () ->
+        (* FIXME: thread safety. use an atomic?? *)
+        Queue.length self.tasks)
       ~run_async:(fun ~fiber f -> schedule self @@ WL.T_start { fiber; f })
-      ~shutdown:(fun ~wait:_ () -> BQ.close self.tasks)
+      ~shutdown:(fun ~wait:_ () -> self.closed <- true)
       ()
 
-  let before_start self : unit =
+  let before_start (self : st) : unit =
     self.as_runner <- as_runner self;
     ()
 
-  let cleanup self =
+  let cleanup (self : st) =
+    self.closed <- true;
     Option.iter Lwt_main.Enter_iter_hooks.remove self.enter_hook;
     Option.iter Lwt_main.Leave_iter_hooks.remove self.leave_hook;
     ()
@@ -71,7 +99,14 @@ module Scheduler_state = struct
 end
 
 open struct
-  module FG = WL.Fine_grained (Scheduler_state) ()
+  module FG =
+    WL.Fine_grained
+      (struct
+        include Scheduler_state
+
+        let ops = Ops.ops
+      end)
+      ()
 end
 
 let _dummy_exn_bt : Exn_bt.t =
@@ -110,9 +145,22 @@ let fut_of_lwt (lwt_fut : _ Lwt.t) : _ M.Fut.t =
     fut
 
 let run_in_hook () =
+  Printf.eprintf "AT %s\n%!" __LOC__;
+
+  (* execute actions sent from other threads *)
+  let local_acts = Queue.create () in
+  BQ.transfer Scheduler_state.st.actions_from_other_threads local_acts;
+  Queue.iter (fun f -> f ()) local_acts;
+
+  (* run tasks *)
+  Printf.eprintf "AT %s\n%!" __LOC__;
   FG.run ~max_tasks:1000 ();
-  if BQ.size Scheduler_state.st.tasks > 0 then
-    ignore (Lwt.pause () : unit Lwt.t)
+  Printf.eprintf "AT %s\n%!" __LOC__;
+
+  if not (Queue.is_empty Scheduler_state.st.tasks) then
+    ignore (Lwt.pause () : unit Lwt.t);
+  Printf.eprintf "AT %s\n%!" __LOC__;
+  ()
 
 let is_setup_ = ref false
 
@@ -123,7 +171,9 @@ let setup () =
     Scheduler_state.st.enter_hook <-
       Some (Lwt_main.Enter_iter_hooks.add_last run_in_hook);
     Scheduler_state.st.leave_hook <-
-      Some (Lwt_main.Leave_iter_hooks.add_last run_in_hook)
+      Some (Lwt_main.Leave_iter_hooks.add_last run_in_hook);
+    Scheduler_state.st.notification <-
+      Lwt_unix.make_notification ~once:false run_in_hook
   )
 
 let spawn_lwt f : _ Lwt.t =
@@ -138,5 +188,6 @@ let spawn_lwt f : _ Lwt.t =
 
 let lwt_main (f : _ -> 'a) : 'a =
   setup ();
+  Scheduler_state.st.thread <- Thread.self () |> Thread.id;
   let fut = spawn_lwt (fun () -> f Scheduler_state.st.as_runner) in
   Lwt_main.run fut