From dc4d171d398abdbe67b126c26851a11985b599ff Mon Sep 17 00:00:00 2001
From: Simon Cruanes <simon.cruanes.2007@m4x.org>
Date: Wed, 25 Mar 2026 09:18:32 -0400
Subject: [PATCH] add regression test for #45

---
 test/dune               |  6 +++++
 test/t_fib_await_mem.ml | 54 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 60 insertions(+)
 create mode 100644 test/t_fib_await_mem.ml

diff --git a/test/dune b/test/dune
index 38b6a9c8..ef84406a 100644
--- a/test/dune
+++ b/test/dune
@@ -20,3 +20,9 @@
   unix
   trace-tef
   trace))
+
+(test
+ (name t_fib_await_mem)
+ (package moonpool)
+ (enabled_if (= %{system} linux))
+ (libraries moonpool))
diff --git a/test/t_fib_await_mem.ml b/test/t_fib_await_mem.ml
new file mode 100644
index 00000000..f255fdac
--- /dev/null
+++ b/test/t_fib_await_mem.ml
@@ -0,0 +1,54 @@
+(* regression test for #45 *)
+
+open Moonpool
+
+let ( let@ ) = ( @@ )
+
+let rec fib_direct x =
+  if x <= 1 then
+    1
+  else
+    fib_direct (x - 1) + fib_direct (x - 2)
+
+let cutoff = 8
+
+let rec fib_await ~on x : int Fut.t =
+  if x <= cutoff then
+    Fut.spawn ~on (fun () -> fib_direct x)
+  else
+    Fut.spawn ~on (fun () ->
+        let n1 = fib_await ~on (x - 1) in
+        let n2 = fib_await ~on (x - 2) in
+        let n1 = Fut.await n1 in
+        let n2 = Fut.await n2 in
+        n1 + n2)
+
+(** Read VmHWM (peak RSS in kB) from /proc/self/status. *)
+let get_vmhwm_kb () : int option =
+  let path = "/proc/self/status" in
+  match In_channel.with_open_bin path In_channel.input_all with
+  | exception Sys_error _ -> None
+  | content ->
+    let lines = String.split_on_char '\n' content in
+    List.find_map
+      (fun line -> Scanf.sscanf_opt line "VmHWM: %d kB" Fun.id)
+      lines
+
+let max_rss_bytes = 150_000_000
+
+let () =
+  let@ pool = Ws_pool.with_ ~num_threads:4 () in
+  let result = fib_await ~on:pool 40 |> Fut.wait_block_exn in
+  assert (result = 165580141);
+  match get_vmhwm_kb () with
+  | None ->
+    Printf.printf "fib 40 = %d (skip RSS check: no /proc/self/status)\n%!"
+      result
+  | Some hwm_kb ->
+    let hwm_bytes = hwm_kb * 1024 in
+    Printf.printf "fib 40 = %d, peak RSS = %d bytes\n%!" result hwm_bytes;
+    if hwm_bytes > max_rss_bytes then (
+      Printf.eprintf "FAIL: peak RSS %d bytes exceeds limit %d bytes\n%!"
+        hwm_bytes max_rss_bytes;
+      exit 1
+    )