From a3e1fcc36299c1fdc629a99a2d7ee27b7c5cc09e Mon Sep 17 00:00:00 2001
From: Simon Cruanes <simon.cruanes.2007@m4x.org>
Date: Wed, 17 Dec 2025 11:07:12 -0500
Subject: [PATCH] add clock

---
 src/core/clock.ml | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)
 create mode 100644 src/core/clock.ml

diff --git a/src/core/clock.ml b/src/core/clock.ml
new file mode 100644
index 00000000..a9282522
--- /dev/null
+++ b/src/core/clock.ml
@@ -0,0 +1,26 @@
+open Opentelemetry_atomic
+
+type t = { now: unit -> Timestamp_ns.t } [@@unboxed]
+(** A clock: can get the current timestamp, with nanoseconds precision *)
+
+let[@inline] now (self : t) : Timestamp_ns.t = self.now ()
+
+(** Clock using {!Unix.gettimeofday} *)
+let unix : t =
+  { now = (fun () -> Int64.of_float (Unix.gettimeofday () *. 1e9)) }
+
+module Main = struct
+  open struct
+    let main : t Atomic.t = Atomic.make unix
+  end
+
+  let[@inline] get () = Atomic.get main
+
+  let set t : unit = Util_atomic.update_cas main (fun _ -> (), t)
+
+  (** Clock that always defers to the current main clock *)
+  let dynamic_main : t = { now = (fun () -> now (get ())) }
+end
+
+(** Timestamp using the main clock *)
+let[@inline] now_main () = now (Main.get ())