From 8bd79c70b57276d3ad834b73ba6bb43290e72754 Mon Sep 17 00:00:00 2001
From: Simon Cruanes <simon.cruanes.2007@m4x.org>
Date: Mon, 8 Sep 2025 15:46:26 -0400
Subject: [PATCH] add Moonpool_lwt.on_lwt_thread

---
 src/lwt/moonpool_lwt.ml  | 1 +
 src/lwt/moonpool_lwt.mli | 5 +++++
 2 files changed, 6 insertions(+)

diff --git a/src/lwt/moonpool_lwt.ml b/src/lwt/moonpool_lwt.ml
index 4838a3fb..8338c009 100644
--- a/src/lwt/moonpool_lwt.ml
+++ b/src/lwt/moonpool_lwt.ml
@@ -307,6 +307,7 @@ let spawn_lwt f : _ Lwt.t =
   lwt_fut
 
 let spawn_lwt_ignore f = ignore (spawn_lwt f : unit Lwt.t)
+let on_lwt_thread = Main_state.on_lwt_thread
 
 let lwt_main (f : _ -> 'a) : 'a =
   let st = setup () in
diff --git a/src/lwt/moonpool_lwt.mli b/src/lwt/moonpool_lwt.mli
index 63fb97c7..2d8c9645 100644
--- a/src/lwt/moonpool_lwt.mli
+++ b/src/lwt/moonpool_lwt.mli
@@ -45,6 +45,11 @@ val lwt_main : (Moonpool.Runner.t -> 'a) -> 'a
 (** [lwt_main f] sets the moonpool-lwt bridge up, runs lwt main, calls [f],
     destroys the bridge, and return the result of [f()]. *)
 
+val on_lwt_thread : unit -> bool
+(** [on_lwt_thread ()] is true if the current thread is the one currently
+    running {!lwt_main}.
+    @raise Failure if {!lwt_main} was not called. *)
+
 val lwt_main_runner : unit -> Moonpool.Runner.t
 (** The runner from {!lwt_main}. The runner is only going to work if {!lwt_main}
     is currently running in some thread.