From 092b9a5d2e9304a482f779a198d3905212c96530 Mon Sep 17 00:00:00 2001
From: Simon Cruanes <simon.cruanes.2007@m4x.org>
Date: Wed, 17 Dec 2025 11:18:55 -0500
Subject: [PATCH] have a clock in exporter, pass a mtime in `tick`

---
 .../opentelemetry_client_cohttp_eio.ml        |  2 +-
 .../opentelemetry_client_cohttp_lwt.ml        |  2 +-
 .../opentelemetry_client_ocurl_lwt.ml         |  2 +-
 .../opentelemetry_client_ocurl.ml             |  3 ++-
 src/client/bounded_queue.ml                   |  2 +-
 src/client/consumer.ml                        |  5 +++--
 src/client/emitter_combine.ml                 |  2 +-
 src/client/exporter_add_batching.ml           |  3 +++
 src/client/exporter_combine.ml                |  3 ++-
 src/client/exporter_debug.ml                  |  4 +++-
 src/client/exporter_queued.ml                 | 13 +++++++------
 src/client/exporter_stdout.ml                 |  5 +++--
 src/client/generic_consumer.ml                |  6 +++---
 src/client/generic_consumer_exporter.ml       | 11 ++++-------
 src/client/lwt/util_ticker.ml                 |  3 ++-
 src/client/sampler.ml                         |  2 +-
 src/client/util_thread.ml                     |  5 ++++-
 src/core/event.ml                             |  4 ++--
 src/core/exporter.ml                          | 11 ++++++-----
 src/core/log_record.ml                        | 19 +++++++++----------
 src/core/metrics.ml                           | 19 +++++++------------
 src/emitter/emitter.ml                        | 10 +++++-----
 src/emitter/to_list.ml                        |  2 +-
 src/lib/gc_metrics.ml                         |  2 +-
 src/lib/main_exporter.ml                      |  8 +++++---
 src/lib/opentelemetry.ml                      |  3 ++-
 26 files changed, 80 insertions(+), 71 deletions(-)

diff --git a/src/client-cohttp-eio/opentelemetry_client_cohttp_eio.ml b/src/client-cohttp-eio/opentelemetry_client_cohttp_eio.ml
index 9788a057..d726e82e 100644
--- a/src/client-cohttp-eio/opentelemetry_client_cohttp_eio.ml
+++ b/src/client-cohttp-eio/opentelemetry_client_cohttp_eio.ml
@@ -174,7 +174,7 @@ let create_exporter ?(config = Config.make ()) ~sw ~env () =
     Bounded_queue_sync.create
       ~high_watermark:Bounded_queue.Defaults.high_watermark ()
   in
-  Exporter_queued.create ~q:bq ~consumer ()
+  Exporter_queued.create ~clock:Opentelemetry_ptime.clock ~q:bq ~consumer ()
   |> Exporter_add_batching.add_batching ~config
 
 let create_backend = create_exporter
diff --git a/src/client-cohttp-lwt/opentelemetry_client_cohttp_lwt.ml b/src/client-cohttp-lwt/opentelemetry_client_cohttp_lwt.ml
index cab5fc3d..149c272a 100644
--- a/src/client-cohttp-lwt/opentelemetry_client_cohttp_lwt.ml
+++ b/src/client-cohttp-lwt/opentelemetry_client_cohttp_lwt.ml
@@ -114,7 +114,7 @@ let create_exporter ?(config = Config.make ()) () =
     Bounded_queue_sync.create
       ~high_watermark:Bounded_queue.Defaults.high_watermark ()
   in
-  Exporter_queued.create ~q:bq ~consumer ()
+  Exporter_queued.create ~clock:Opentelemetry_ptime.clock ~q:bq ~consumer ()
   |> Exporter_add_batching.add_batching ~config
 
 let create_backend = create_exporter
diff --git a/src/client-ocurl-lwt/opentelemetry_client_ocurl_lwt.ml b/src/client-ocurl-lwt/opentelemetry_client_ocurl_lwt.ml
index fd8ff28e..f062d8dd 100644
--- a/src/client-ocurl-lwt/opentelemetry_client_ocurl_lwt.ml
+++ b/src/client-ocurl-lwt/opentelemetry_client_ocurl_lwt.ml
@@ -85,7 +85,7 @@ let create_exporter ?(config = Config.make ()) () =
     Bounded_queue_sync.create
       ~high_watermark:Bounded_queue.Defaults.high_watermark ()
   in
-  Exporter_queued.create ~q:bq ~consumer ()
+  Exporter_queued.create ~clock:Opentelemetry_ptime.clock ~q:bq ~consumer ()
   |> Exporter_add_batching.add_batching ~config
 
 let create_backend = create_exporter
diff --git a/src/client-ocurl/opentelemetry_client_ocurl.ml b/src/client-ocurl/opentelemetry_client_ocurl.ml
index 0d5c0d6d..9980e22a 100644
--- a/src/client-ocurl/opentelemetry_client_ocurl.ml
+++ b/src/client-ocurl/opentelemetry_client_ocurl.ml
@@ -92,7 +92,8 @@ let create_exporter ?(config = Config.make ()) () : OTEL.Exporter.t =
       ~high_watermark:OTELC.Bounded_queue.Defaults.high_watermark ()
   in
 
-  OTELC.Exporter_queued.create ~q:bq ~consumer ()
+  OTELC.Exporter_queued.create ~clock:Opentelemetry_ptime.clock ~q:bq ~consumer
+    ()
   |> OTELC.Exporter_add_batching.add_batching ~config:config.common
 
 let create_backend = create_exporter
diff --git a/src/client/bounded_queue.ml b/src/client/bounded_queue.ml
index 4c60d967..89a0ff30 100644
--- a/src/client/bounded_queue.ml
+++ b/src/client/bounded_queue.ml
@@ -111,7 +111,7 @@ module Send = struct
     let closed () = closed self in
     let enabled () = not (closed ()) in
     let emit x = if x <> [] then push self x in
-    let tick ~now:_ = () in
+    let tick ~mtime:_ = () in
 
     (* NOTE: we cannot actually flush, only close. Emptying the queue is
      fundamentally asynchronous because it's done by consumers *)
diff --git a/src/client/consumer.ml b/src/client/consumer.ml
index 48b5008f..1f416bba 100644
--- a/src/client/consumer.ml
+++ b/src/client/consumer.ml
@@ -10,7 +10,8 @@ type t = {
   tick: unit -> unit;
       (** Regularly called, eg to emit metrics, check timeouts, etc. Must be
           thread safe. *)
-  self_metrics: unit -> OTEL.Metrics.t list;  (** Self observing metrics *)
+  self_metrics: clock:OTEL.Clock.t -> unit -> OTEL.Metrics.t list;
+      (** Self observing metrics *)
 }
 (** A consumer for signals of type ['a] *)
 
@@ -20,7 +21,7 @@ let[@inline] active (self : t) : Aswitch.t = self.active ()
 
 let[@inline] shutdown (self : t) : unit = self.shutdown ()
 
-let[@inline] self_metrics self : _ list = self.self_metrics ()
+let[@inline] self_metrics ~clock self : _ list = self.self_metrics ~clock ()
 
 (** [on_stop e f] calls [f()] when [e] stops, or now if it's already stopped *)
 let on_stop self f = Aswitch.on_turn_off (self.active ()) f
diff --git a/src/client/emitter_combine.ml b/src/client/emitter_combine.ml
index 398b98be..c35fe4dc 100644
--- a/src/client/emitter_combine.ml
+++ b/src/client/emitter_combine.ml
@@ -26,7 +26,7 @@ let combine_l ?(closing : closing_behavior = `Close_when_all_closed)
   in
   let enabled () = not (closed ()) in
   let emit x = if x <> [] then List.iter (fun e -> emit e x) es in
-  let tick ~now = List.iter (tick ~now) es in
+  let tick ~mtime = List.iter (tick ~mtime) es in
   let flush_and_close () = List.iter flush_and_close es in
   { closed; enabled; emit; tick; flush_and_close }
 
diff --git a/src/client/exporter_add_batching.ml b/src/client/exporter_add_batching.ml
index 0f2f68ca..41ff7086 100644
--- a/src/client/exporter_add_batching.ml
+++ b/src/client/exporter_add_batching.ml
@@ -26,6 +26,8 @@ let add_batching ~(config : Http_config.t) (exp : OTEL.Exporter.t) :
   let active = exp.active in
   let tick = exp.tick in
   let on_tick = exp.on_tick in
+  let clock = exp.clock in
+
   let self_metrics () = exp.self_metrics () in
   let shutdown () =
     let open Opentelemetry_emitter in
@@ -38,6 +40,7 @@ let add_batching ~(config : Http_config.t) (exp : OTEL.Exporter.t) :
 
   {
     OTEL.Exporter.active;
+    clock;
     emit_spans;
     emit_metrics;
     emit_logs;
diff --git a/src/client/exporter_combine.ml b/src/client/exporter_combine.ml
index 0c2dbbc9..78bf84dc 100644
--- a/src/client/exporter_combine.ml
+++ b/src/client/exporter_combine.ml
@@ -22,13 +22,14 @@ let combine_l (es : OTEL.Exporter.t list) : OTEL.Exporter.t =
     let active, trigger = Aswitch.create () in
     {
       active = (fun () -> active);
+      clock = (List.hd es).clock;
       emit_spans =
         Emitter_combine.combine_l (List.map (fun e -> e.emit_spans) es);
       emit_logs = Emitter_combine.combine_l (List.map (fun e -> e.emit_logs) es);
       emit_metrics =
         Emitter_combine.combine_l (List.map (fun e -> e.emit_metrics) es);
       on_tick = (fun f -> List.iter (fun e -> e.on_tick f) es);
-      tick = (fun () -> List.iter tick es);
+      tick = (fun () -> List.iter (fun e -> e.tick ()) es);
       shutdown = (fun () -> shutdown_l es ~trigger);
       self_metrics =
         (fun () -> List.fold_left (fun acc e -> e.self_metrics () @ acc) [] es);
diff --git a/src/client/exporter_debug.ml b/src/client/exporter_debug.ml
index 946e1af4..dedc8659 100644
--- a/src/client/exporter_debug.ml
+++ b/src/client/exporter_debug.ml
@@ -3,12 +3,14 @@ open Opentelemetry_emitter
 
 (** [debug ?out ()] is an exporter that pretty-prints signals on [out].
     @param out the formatter into which to print, default [stderr]. *)
-let debug ?(out = Format.err_formatter) () : OTEL.Exporter.t =
+let debug ?(clock = OTEL.Clock.Main.dynamic_main) ?(out = Format.err_formatter)
+    () : OTEL.Exporter.t =
   let open Proto in
   let active, trigger = Aswitch.create () in
   let ticker = Cb_set.create () in
   {
     active = (fun () -> active);
+    clock;
     emit_spans =
       Emitter.make_simple () ~emit:(fun sp ->
           List.iter (Format.fprintf out "SPAN: %a@." Trace.pp_span) sp);
diff --git a/src/client/exporter_queued.ml b/src/client/exporter_queued.ml
index 883bef48..c8ab2043 100644
--- a/src/client/exporter_queued.ml
+++ b/src/client/exporter_queued.ml
@@ -9,18 +9,18 @@ module BQ_emitters = struct
      The bounded queue is a shared resource. *)
 
   let logs_emitter_of_bq (q : OTEL.Any_signal_l.t Bounded_queue.Send.t) :
-      OTEL.Logger.t =
+      _ OTEL.Emitter.t =
     Bounded_queue.Send.to_emitter q ~close_queue_on_close:false
     |> Opentelemetry_emitter.Emitter.flat_map OTEL.Any_signal_l.of_logs_or_empty
 
   let spans_emitter_of_bq (q : OTEL.Any_signal_l.t Bounded_queue.Send.t) :
-      OTEL.Tracer.t =
+      _ OTEL.Emitter.t =
     Bounded_queue.Send.to_emitter q ~close_queue_on_close:false
     |> Opentelemetry_emitter.Emitter.flat_map
          OTEL.Any_signal_l.of_spans_or_empty
 
   let metrics_emitter_of_bq (q : OTEL.Any_signal_l.t Bounded_queue.Send.t) :
-      OTEL.Metrics_emitter.t =
+      _ OTEL.Emitter.t =
     Bounded_queue.Send.to_emitter q ~close_queue_on_close:false
     |> Opentelemetry_emitter.Emitter.flat_map
          OTEL.Any_signal_l.of_metrics_or_empty
@@ -32,7 +32,7 @@ end
     bounded queue; while the consumer takes them from the queue to forward them
     somewhere else, store them, etc.
     @param resource_attributes attributes added to every "resource" batch *)
-let create ~(q : OTEL.Any_signal_l.t Bounded_queue.t)
+let create ~clock ~(q : OTEL.Any_signal_l.t Bounded_queue.t)
     ~(consumer : Consumer.any_signal_l_builder) () : OTEL.Exporter.t =
   let open Opentelemetry_emitter in
   let shutdown_started = Atomic.make false in
@@ -48,7 +48,7 @@ let create ~(q : OTEL.Any_signal_l.t Bounded_queue.t)
   let on_tick f = Cb_set.register tick_set f in
 
   let self_metrics () : _ list =
-    let now = OTEL.Timestamp_ns.now_unix_ns () in
+    let now = OTEL.Clock.now clock in
     let m_size =
       OTEL.Metrics.gauge ~name:"otel.sdk.exporter.queue.size"
         [ OTEL.Metrics.int ~now (Bounded_queue.Recv.size q.recv) ]
@@ -60,7 +60,7 @@ let create ~(q : OTEL.Any_signal_l.t Bounded_queue.t)
         ~name:"otel_ocaml.exporter_queue.discarded"
         [ OTEL.Metrics.int ~now (Bounded_queue.Recv.num_discarded q.recv) ]
     in
-    m_size :: m_cap :: m_discarded :: Consumer.self_metrics consumer
+    m_size :: m_cap :: m_discarded :: Consumer.self_metrics consumer ~clock
   in
 
   let shutdown () =
@@ -86,6 +86,7 @@ let create ~(q : OTEL.Any_signal_l.t Bounded_queue.t)
   let active () = active in
   {
     active;
+    clock;
     emit_logs;
     emit_metrics;
     emit_spans;
diff --git a/src/client/exporter_stdout.ml b/src/client/exporter_stdout.ml
index 0613c07b..551a5f4f 100644
--- a/src/client/exporter_stdout.ml
+++ b/src/client/exporter_stdout.ml
@@ -34,7 +34,7 @@ open struct
     )
 end
 
-let stdout : OTEL.Exporter.t =
+let stdout ?(clock = OTEL.Clock.Main.dynamic_main) () : OTEL.Exporter.t =
   let open Opentelemetry_util in
   let out = Format.std_formatter in
   let mutex = Mutex.create () in
@@ -49,7 +49,7 @@ let stdout : OTEL.Exporter.t =
       pp_vlist mutex pp_signal out l
     in
     let enabled () = Aswitch.is_on active in
-    let tick ~now:_ = () in
+    let tick ~mtime:_ = () in
     let flush_and_close () =
       if Aswitch.is_on active then
         let@ () = Util_mutex.protect mutex in
@@ -73,6 +73,7 @@ let stdout : OTEL.Exporter.t =
 
   {
     active = (fun () -> active);
+    clock;
     emit_spans;
     emit_logs;
     emit_metrics;
diff --git a/src/client/generic_consumer.ml b/src/client/generic_consumer.ml
index afa5ad99..f3951909 100644
--- a/src/client/generic_consumer.ml
+++ b/src/client/generic_consumer.ml
@@ -204,9 +204,9 @@ end = struct
 
     self
 
-  let self_metrics (self : state) : OTEL.Metrics.t list =
+  let self_metrics ~clock (self : state) : OTEL.Metrics.t list =
     let open OTEL.Metrics in
-    let now = OTEL.Timestamp_ns.now_unix_ns () in
+    let now = OTEL.Clock.now clock in
     let attrs = [ "otel.component.name", `String "otel_ocaml" ] in
     [
       sum ~name:"otel.sdk.exporter.errors" ~is_monotonic:true
@@ -220,7 +220,7 @@ end = struct
   let to_consumer (self : state) : Consumer.t =
     let shutdown () = shutdown self in
     let tick () = tick self in
-    let self_metrics () = self_metrics self in
+    let self_metrics ~clock () = self_metrics self ~clock in
     { active = (fun () -> self.active); tick; shutdown; self_metrics }
 
   let consumer ~sender_config ~n_workers ~ticker_task () :
diff --git a/src/client/generic_consumer_exporter.ml b/src/client/generic_consumer_exporter.ml
index 178864dd..cbbae6eb 100644
--- a/src/client/generic_consumer_exporter.ml
+++ b/src/client/generic_consumer_exporter.ml
@@ -113,22 +113,19 @@ end = struct
     start_worker self;
     self
 
-  let self_metrics (self : state) : OTEL.Metrics.t list =
+  let self_metrics (self : state) ~clock : OTEL.Metrics.t list =
     let open OTEL.Metrics in
-    let now = Mtime_clock.now () in
+    let now = OTEL.Clock.now clock in
     [
       sum ~name:"otel_ocaml.export.batches_discarded_by_bounded_queue"
         ~is_monotonic:true
-        [
-          int ~now:(Mtime.to_uint64_ns now)
-            (Bounded_queue.Recv.num_discarded self.q);
-        ];
+        [ int ~now (Bounded_queue.Recv.num_discarded self.q) ];
     ]
 
   let to_consumer (self : state) : Consumer.t =
     let shutdown () = shutdown self in
     let tick () = tick self in
-    let self_metrics () = self_metrics self in
+    let self_metrics ~clock () = self_metrics self ~clock in
     { active = (fun () -> self.active); tick; shutdown; self_metrics }
 
   let consumer exporter : _ Consumer.Builder.t =
diff --git a/src/client/lwt/util_ticker.ml b/src/client/lwt/util_ticker.ml
index 64c26da8..95aed6ad 100644
--- a/src/client/lwt/util_ticker.ml
+++ b/src/client/lwt/util_ticker.ml
@@ -12,7 +12,8 @@ let start_ticker_thread ?(finally = ignore) ~(stop : bool Atomic.t)
       Lwt.return ()
     ) else
       let* () = Lwt_unix.sleep frequency_s in
-      OTEL.Exporter.tick exp;
+      let mtime = Mtime_clock.now () in
+      OTEL.Exporter.tick exp ~mtime;
       tick_loop ()
   in
   Lwt.async tick_loop
diff --git a/src/client/sampler.ml b/src/client/sampler.ml
index 9ae63e0d..671eaf81 100644
--- a/src/client/sampler.ml
+++ b/src/client/sampler.ml
@@ -37,7 +37,7 @@ let wrap_emitter (self : t) (e : _ Emitter.t) : _ Emitter.t =
   let enabled () = e.enabled () in
   let closed () = Emitter.closed e in
   let flush_and_close () = Emitter.flush_and_close e in
-  let tick ~now = Emitter.tick e ~now in
+  let tick ~mtime = Emitter.tick e ~mtime in
 
   let emit l =
     if l <> [] && e.enabled () then (
diff --git a/src/client/util_thread.ml b/src/client/util_thread.ml
index dfbe61ac..9fad94e5 100644
--- a/src/client/util_thread.ml
+++ b/src/client/util_thread.ml
@@ -34,7 +34,10 @@ let setup_ticker_thread ~(active : Aswitch.t) ~sleep_ms (exp : OTEL.Exporter.t)
       while Aswitch.is_on active do
         Thread.delay sleep_s;
 
-        if Aswitch.is_on active then OTEL.Exporter.tick exp
+        if Aswitch.is_on active then (
+          let mtime = Mtime_clock.now () in
+          OTEL.Exporter.tick exp ~mtime
+        )
       done
     with
     | Sync_queue.Closed -> ()
diff --git a/src/core/event.ml b/src/core/event.ml
index 3d632a4d..34915e2e 100644
--- a/src/core/event.ml
+++ b/src/core/event.ml
@@ -3,7 +3,7 @@ open Proto.Trace
 
 type t = span_event
 
-let make ?(time_unix_nano = Timestamp_ns.now_unix_ns ()) ?(attrs = [])
-    (name : string) : t =
+let make ?(time_unix_nano = Clock.now_main ()) ?(attrs = []) (name : string) : t
+    =
   let attrs = List.map Key_value.conv attrs in
   make_span_event ~time_unix_nano ~name ~attributes:attrs ()
diff --git a/src/core/exporter.ml b/src/core/exporter.ml
index d4630173..bc7514a5 100644
--- a/src/core/exporter.ml
+++ b/src/core/exporter.ml
@@ -12,6 +12,7 @@ open Opentelemetry_emitter
 type t = {
   active: unit -> Aswitch.t;
       (** Is the exporer currently active? After shutdown this is turned off. *)
+  clock: Clock.t;
   emit_spans: Proto.Trace.span Emitter.t;
   emit_metrics: Proto.Metrics.metric Emitter.t;
   emit_logs: Proto.Logs.log_record Emitter.t;
@@ -34,6 +35,7 @@ let dummy () : t =
   let active, trigger = Aswitch.create () in
   {
     active = (fun () -> active);
+    clock = Clock.unix;
     emit_spans = Emitter.dummy;
     emit_metrics = Emitter.dummy;
     emit_logs = Emitter.dummy;
@@ -56,12 +58,11 @@ let[@inline] on_tick (self : t) f = self.on_tick f
 
 (** Do background work. Call this regularly if the collector doesn't already
     have a ticker thread or internal timer. *)
-let tick (self : t) =
+let tick ~mtime (self : t) =
   (* make sure emitters get the chance to check timeouts, flush, etc. *)
-  let now = Mtime_clock.now () in
-  Emitter.tick ~now self.emit_spans;
-  Emitter.tick ~now self.emit_metrics;
-  Emitter.tick ~now self.emit_logs;
+  Emitter.tick ~mtime self.emit_spans;
+  Emitter.tick ~mtime self.emit_metrics;
+  Emitter.tick ~mtime self.emit_logs;
 
   (* call the callbacks *)
   self.tick ();
diff --git a/src/core/log_record.ml b/src/core/log_record.ml
index 8d9e7a0f..57e6bfed 100644
--- a/src/core/log_record.ml
+++ b/src/core/log_record.ml
@@ -47,10 +47,9 @@ let pp_flags = Proto.Logs.pp_log_record_flags
 
 let pp = Proto.Logs.pp_log_record
 
-(** Make a single log entry *)
-let make ?time ?(observed_time_unix_nano = Timestamp_ns.now_unix_ns ())
-    ?severity ?log_level ?flags ?trace_id ?span_id ?(attrs = [])
-    (body : Value.t) : t =
+(** Make a single log entry. *)
+let make ?time ?severity ?log_level ?flags ?trace_id ?span_id ?(attrs = [])
+    ~(observed_time_unix_nano : Timestamp_ns.t) (body : Value.t) : t =
   let time_unix_nano =
     match time with
     | None -> observed_time_unix_nano
@@ -65,16 +64,16 @@ let make ?time ?(observed_time_unix_nano = Timestamp_ns.now_unix_ns ())
     ~attributes ?body ()
 
 (** Make a log entry whose body is a string *)
-let make_str ?time ?observed_time_unix_nano ?severity ?log_level ?flags
-    ?trace_id ?span_id ?attrs (body : string) : t =
-  make ?time ?observed_time_unix_nano ?severity ?log_level ?flags ?trace_id
+let make_str ?time ?severity ?log_level ?flags ?trace_id ?span_id ?attrs
+    ~observed_time_unix_nano (body : string) : t =
+  make ?time ~observed_time_unix_nano ?severity ?log_level ?flags ?trace_id
     ?span_id ?attrs (`String body)
 
 (** Make a log entry with format *)
-let make_strf ?time ?observed_time_unix_nano ?severity ?log_level ?flags
-    ?trace_id ?span_id ?attrs fmt =
+let make_strf ?time ?severity ?log_level ?flags ?trace_id ?span_id ?attrs
+    ~observed_time_unix_nano fmt =
   Format.kasprintf
     (fun bod ->
-      make_str ?time ?observed_time_unix_nano ?severity ?log_level ?flags
+      make_str ?time ~observed_time_unix_nano ?severity ?log_level ?flags
         ?trace_id ?span_id ?attrs bod)
     fmt
diff --git a/src/core/metrics.ml b/src/core/metrics.ml
index 988b7bd6..7298aefb 100644
--- a/src/core/metrics.ml
+++ b/src/core/metrics.ml
@@ -15,20 +15,16 @@ type t = Metrics.metric
 
 let pp = Proto.Metrics.pp_metric
 
-open struct
-  let _program_start = Timestamp_ns.now_unix_ns ()
-end
-
 (** Number data point, as a float *)
-let float ?start_time_unix_nano ?(now = Timestamp_ns.now_unix_ns ())
-    ?(attrs = []) (d : float) : number_data_point =
+let float ?start_time_unix_nano ?(now = Clock.now_main ()) ?(attrs = [])
+    (d : float) : number_data_point =
   let attributes = attrs |> List.map Key_value.conv in
   make_number_data_point ?start_time_unix_nano ~time_unix_nano:now ~attributes
     ~value:(As_double d) ()
 
 (** Number data point, as an int *)
-let int ?start_time_unix_nano ?(now = Timestamp_ns.now_unix_ns ()) ?(attrs = [])
-    (i : int) : number_data_point =
+let int ?start_time_unix_nano ?(now = Clock.now_main ()) ?(attrs = []) (i : int)
+    : number_data_point =
   let attributes = attrs |> List.map Key_value.conv in
   make_number_data_point ?start_time_unix_nano ~time_unix_nano:now ~attributes
     ~value:(As_int (Int64.of_int i))
@@ -60,10 +56,9 @@ let sum ~name ?description ?unit_
       count value of histogram for each bucket. Sum of the counts must be equal
       to [count]. length must be [1+length explicit_bounds]
     @param explicit_bounds strictly increasing list of bounds for the buckets *)
-let histogram_data_point ?start_time_unix_nano
-    ?(now = Timestamp_ns.now_unix_ns ()) ?(attrs = []) ?(exemplars = [])
-    ?(explicit_bounds = []) ?sum ~bucket_counts ~count () : histogram_data_point
-    =
+let histogram_data_point ?start_time_unix_nano ?(now = Clock.now_main ())
+    ?(attrs = []) ?(exemplars = []) ?(explicit_bounds = []) ?sum ~bucket_counts
+    ~count () : histogram_data_point =
   let attributes = attrs |> List.map Key_value.conv in
   make_histogram_data_point ?start_time_unix_nano ~time_unix_nano:now
     ~attributes ~exemplars ~bucket_counts ~explicit_bounds ~count ?sum ()
diff --git a/src/emitter/emitter.ml b/src/emitter/emitter.ml
index f0a23248..a3fc0f67 100644
--- a/src/emitter/emitter.ml
+++ b/src/emitter/emitter.ml
@@ -13,9 +13,9 @@ type -'a t = {
           signals it's given. *)
   emit: 'a list -> unit;
       (** Emit signals. @raise Closed if the emitter is closed. *)
-  tick: now:Mtime.t -> unit;
+  tick: mtime:Mtime.t -> unit;
       (** Call regularly to ensure background work is done. The current
-          timestamp is passed to improve testability. *)
+          monotonic timestamp is passed to improve testability. *)
   closed: unit -> bool;
       (** True if the emitter is already closed. Beware TOCTOU bugs. *)
   flush_and_close: unit -> unit;
@@ -27,7 +27,7 @@ let[@inline] enabled self : bool = self.enabled ()
 
 let[@inline] emit (self : _ t) l : unit = if l <> [] then self.emit l
 
-let[@inline] tick (self : _ t) ~now : unit = self.tick ~now
+let[@inline] tick (self : _ t) ~mtime : unit = self.tick ~mtime
 
 let[@inline] closed self : bool = self.closed ()
 
@@ -61,7 +61,7 @@ let make_simple ?tick ?closed ?enabled ?(flush_and_close = ignore) ~emit () :
     _ t =
   let tick =
     match tick with
-    | None -> fun ~now:_ -> ()
+    | None -> fun ~mtime:_ -> ()
     | Some f -> f
   in
   let closed, enabled =
@@ -78,7 +78,7 @@ let dummy : _ t =
   {
     enabled = (fun () -> false);
     emit = ignore;
-    tick = (fun ~now:_ -> ());
+    tick = (fun ~mtime:_ -> ());
     closed = (fun () -> true);
     flush_and_close = ignore;
   }
diff --git a/src/emitter/to_list.ml b/src/emitter/to_list.ml
index 04e228ca..e1601132 100644
--- a/src/emitter/to_list.ml
+++ b/src/emitter/to_list.ml
@@ -8,7 +8,7 @@ let to_list (l : 'a list ref) : 'a Emitter.t =
       (fun sigs ->
         if Atomic.get closed then raise Emitter.Closed;
         l := List.rev_append sigs !l);
-    tick = (fun ~now:_ -> ());
+    tick = (fun ~mtime:_ -> ());
     closed = (fun () -> Atomic.get closed);
     flush_and_close = (fun () -> Atomic.set closed true);
   }
diff --git a/src/lib/gc_metrics.ml b/src/lib/gc_metrics.ml
index 42dacac6..2c909de5 100644
--- a/src/lib/gc_metrics.ml
+++ b/src/lib/gc_metrics.ml
@@ -10,7 +10,7 @@ end
 
 let get_metrics () : Metrics.t list =
   let gc = Gc.quick_stat () in
-  let now = Timestamp_ns.now_unix_ns () in
+  let now = Clock.now_main () in
   let open Metrics in
   let open Conventions.Metrics in
   [
diff --git a/src/lib/main_exporter.ml b/src/lib/main_exporter.ml
index e35035f3..24c71974 100644
--- a/src/lib/main_exporter.ml
+++ b/src/lib/main_exporter.ml
@@ -21,7 +21,8 @@ let remove ~on_done () : unit =
   | None -> on_done ()
   | Some exp ->
     Aswitch.on_turn_off (Exporter.active exp) on_done;
-    tick exp;
+    let mtime = Mtime_clock.now () in
+    tick exp ~mtime;
     shutdown exp
 
 (** Is there a configured exporter? *)
@@ -42,10 +43,10 @@ module Util = struct
     let enabled () = present () in
     let closed () = not (enabled ()) in
     let flush_and_close () = () in
-    let tick ~now:_ =
+    let tick ~mtime =
       match get () with
       | None -> ()
-      | Some exp -> Exporter.tick exp
+      | Some exp -> Exporter.tick exp ~mtime
     in
     let emit signals =
       if signals <> [] then (
@@ -100,6 +101,7 @@ let dynamic_forward_to_main_exporter : Exporter.t =
   let shutdown () = () in
   {
     Exporter.active;
+    clock = Clock.Main.dynamic_main;
     emit_metrics;
     emit_spans;
     emit_logs;
diff --git a/src/lib/opentelemetry.ml b/src/lib/opentelemetry.ml
index b1af8234..615a3a6b 100644
--- a/src/lib/opentelemetry.ml
+++ b/src/lib/opentelemetry.ml
@@ -14,8 +14,9 @@ module Proto = Opentelemetry_proto
 
     This is mostly useful internally. Users should not need to touch it. *)
 
-(** {2 Timestamps} *)
+(** {2 Time} *)
 
+module Clock = Clock
 module Timestamp_ns = Timestamp_ns
 
 (** {2 Export signals to some external collector.} *)