From 24eac75c69b3d74388bbbc8ee2b6792e7590e4c6 Mon Sep 17 00:00:00 2001
From: polwex <polwex@sortug.com>
Date: Mon, 6 Oct 2025 04:03:14 +0700
Subject: did this madman really implement parallelism on urbit

---
 ocaml/lib/io/behn.ml | 137 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 137 insertions(+)
 create mode 100644 ocaml/lib/io/behn.ml

(limited to 'ocaml/lib/io/behn.ml')

diff --git a/ocaml/lib/io/behn.ml b/ocaml/lib/io/behn.ml
new file mode 100644
index 0000000..95e1d02
--- /dev/null
+++ b/ocaml/lib/io/behn.ml
@@ -0,0 +1,137 @@
+(* Behn - Timer Driver using Eio.Time
+ *
+ * This is the first I/O driver - demonstrates the fiber-per-driver pattern!
+ *
+ * Behn manages timers:
+ * - SetTimer effects: schedule a timer
+ * - CancelTimer effects: cancel a timer
+ * - When timer fires: produce an ovum back to Arvo
+ *
+ * Key innovation: Uses Eio.Time.sleep for non-blocking waits!
+ * Multiple timers can run concurrently in separate fibers.
+ *)
+
+(* Timer state *)
+type timer = {
+  id: int64;
+  fire_time: float;        (* Unix timestamp *)
+  mutable cancelled: bool;
+}
+
+(* Behn driver state *)
+type t = {
+  timers: (int64, timer) Hashtbl.t;  (* Active timers by ID *)
+  lock: Mutex.t;
+}
+
+(* Create behn driver *)
+let create () = {
+  timers = Hashtbl.create 64;
+  lock = Mutex.create ();
+}
+
+(* Set a timer *)
+let set_timer behn ~id ~fire_time =
+  Mutex.lock behn.lock;
+  let timer = { id; fire_time; cancelled = false } in
+  Hashtbl.replace behn.timers id timer;
+  Mutex.unlock behn.lock;
+  Printf.printf "[Behn] Set timer %Ld for %f\n%!" id fire_time
+
+(* Cancel a timer *)
+let cancel_timer behn ~id =
+  Mutex.lock behn.lock;
+  (match Hashtbl.find_opt behn.timers id with
+  | Some timer ->
+      timer.cancelled <- true;
+      Printf.printf "[Behn] Cancelled timer %Ld\n%!" id
+  | None ->
+      Printf.printf "[Behn] Timer %Ld not found (already fired?)\n%!" id
+  );
+  Mutex.unlock behn.lock
+
+(* Timer fiber - waits for a timer to fire
+ *
+ * This runs as a separate fiber for each timer!
+ * Uses Eio.Time.sleep for non-blocking wait.
+ *)
+let timer_fiber behn ~env ~event_stream timer =
+  let clock = Eio.Stdenv.clock env in
+  let now = Unix.gettimeofday () in
+  let wait_time = max 0.0 (timer.fire_time -. now) in
+
+  Printf.printf "[Behn] Timer %Ld: waiting %.3f seconds\n%!" timer.id wait_time;
+
+  (* Non-blocking sleep using Eio! *)
+  Eio.Time.sleep clock wait_time;
+
+  (* Check if cancelled *)
+  Mutex.lock behn.lock;
+  let is_cancelled = timer.cancelled in
+  Hashtbl.remove behn.timers timer.id;
+  Mutex.unlock behn.lock;
+
+  if not is_cancelled then begin
+    Printf.printf "[Behn] Timer %Ld: FIRED! 🔥\n%!" timer.id;
+
+    (* Create timer ovum and send to event stream *)
+    let ovum_noun = Nock_lib.Effects.timer_ovum ~id:timer.id ~fire_time:timer.fire_time in
+    let event = Nock_lib.Noun.cell ovum_noun.wire ovum_noun.card in
+
+    (* Send to runtime event stream *)
+    Eio.Stream.add event_stream event;
+    Printf.printf "[Behn] Timer %Ld: event sent to runtime\n%!" timer.id
+  end else begin
+    Printf.printf "[Behn] Timer %Ld: cancelled, not firing\n%!" timer.id
+  end
+
+(* Behn driver fiber - processes timer effects
+ *
+ * This is the main fiber for the Behn driver.
+ * It reads SetTimer/CancelTimer effects and spawns timer fibers.
+ *)
+let driver_fiber behn ~sw ~env ~effect_queue ~event_stream =
+  Printf.printf "[Behn] Driver fiber started 🕐\n%!";
+
+  let rec loop () =
+    (* Get next effect from queue *)
+    match Nock_lib.Effects.try_dequeue effect_queue with
+    | None ->
+        (* No effects, sleep briefly *)
+        Eio.Time.sleep (Eio.Stdenv.clock env) 0.01;
+        loop ()
+
+    | Some eff ->
+        (match eff with
+        | Nock_lib.Effects.SetTimer { id; time } ->
+            set_timer behn ~id ~fire_time:time;
+
+            (* Spawn a fiber for this timer *)
+            let timer = Hashtbl.find behn.timers id in
+            Eio.Fiber.fork ~sw (fun () ->
+              timer_fiber behn ~env ~event_stream timer
+            );
+            loop ()
+
+        | Nock_lib.Effects.CancelTimer { id } ->
+            cancel_timer behn ~id;
+            loop ()
+
+        | _ ->
+            (* Not a behn effect, ignore *)
+            loop ()
+        )
+  in
+
+  try
+    loop ()
+  with
+  | End_of_file ->
+      Printf.printf "[Behn] Driver shutting down\n%!"
+
+(* Get active timer count *)
+let active_timers behn =
+  Mutex.lock behn.lock;
+  let count = Hashtbl.length behn.timers in
+  Mutex.unlock behn.lock;
+  count
-- 
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