emitter: add self_metrics, track batch n_dropped, sampler rate

src/client/bounded_queue.ml

@@ -106,17 +106,20 @@ module Send = struct
   (** Turn the writing end of the queue into an emitter.
       @param close_queue_on_close
         if true, closing the emitter will close the queue *)
-  let to_emitter ~close_queue_on_close (self : 'a t) :
+  let to_emitter ~signal_name ~close_queue_on_close (self : 'a t) :
       'a Opentelemetry_emitter.Emitter.t =
     let closed () = closed self in
     let enabled () = not (closed ()) in
     let emit x = if x <> [] then push self x in
     let tick ~mtime:_ = () in
 
+    (* the exporter will emit these, the queue is shared *)
+    let self_metrics ~now:_ () = [] in
+
     (* NOTE: we cannot actually flush, only close. Emptying the queue is
      fundamentally asynchronous because it's done by consumers *)
     let flush_and_close () = if close_queue_on_close then close self in
-    { closed; enabled; emit; tick; flush_and_close }
+    { signal_name; closed; enabled; emit; tick; flush_and_close; self_metrics }
 end
 
 type 'a t = {

src/client/emitter_batch.ml

@@ -12,8 +12,18 @@ let wrap_emitter_with_batch (self : _ Batch.t) (e : _ Emitter.t) : _ Emitter.t =
      then [e] itself will be closed. *)
   let closed_here = Atomic.make false in
 
+  let signal_name = e.signal_name in
   let enabled () = (not (Atomic.get closed_here)) && e.enabled () in
   let closed () = Atomic.get closed_here || e.closed () in
+
+  let dropped_name = Printf.sprintf "otel.sdk.%s.batch.dropped" signal_name in
+  let self_metrics ~now () =
+    let m =
+      Opentelemetry_core.Metrics.(
+        sum ~name:dropped_name [ int ~now (Batch.n_dropped self) ])
+    in
+    m :: e.self_metrics ~now ()
+  in
   let flush_and_close () =
     if not (Atomic.exchange closed_here true) then (
       (* NOTE: we need to close this wrapping emitter first, to prevent
@@ -52,7 +62,15 @@ let wrap_emitter_with_batch (self : _ Batch.t) (e : _ Emitter.t) : _ Emitter.t =
     )
   in
 
-  { Emitter.closed; enabled; flush_and_close; tick; emit }
+  {
+    Emitter.closed;
+    signal_name;
+    self_metrics;
+    enabled;
+    flush_and_close;
+    tick;
+    emit;
+  }
 
 let add_batching ~timeout ~batch_size (emitter : 'a Emitter.t) : 'a Emitter.t =
   let b = Batch.make ~batch:batch_size ~timeout () in

src/client/emitter_combine.ml

@@ -18,16 +18,26 @@ type closing_behavior =
       when is this emitter closing. Default [`Close_when_all_closed]. *)
 let combine_l ?(closing : closing_behavior = `Close_when_all_closed)
     (es : 'a t list) : 'a t =
+  assert (es <> []);
+  let signal_name = (List.hd es).signal_name in
   let closed =
    fun () ->
     match closing with
     | `Close_when_all_closed -> List.for_all closed es
     | `Close_when_one_closed -> List.exists closed es
   in
+  let self_metrics ~now () =
+    List.flatten @@ List.map (fun e -> e.self_metrics ~now ()) es
+  in
   let enabled () = not (closed ()) in
   let emit x = if x <> [] then List.iter (fun e -> emit e x) 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 }
+  { signal_name; self_metrics; closed; enabled; emit; tick; flush_and_close }
+
+let combine_l ?closing es : _ t =
+  match es with
+  | [] -> dummy
+  | _ -> combine_l ?closing es
 
 let combine e1 e2 : _ t = combine_l [ e1; e2 ]

src/client/emitter_sample.ml

@@ -1,11 +1,19 @@
 open Opentelemetry_emitter
 
 let add_sampler (self : Sampler.t) (e : _ Emitter.t) : _ Emitter.t =
+  let signal_name = e.signal_name in
   let enabled () = e.enabled () in
   let closed () = Emitter.closed e in
   let flush_and_close () = Emitter.flush_and_close e in
   let tick ~mtime = Emitter.tick e ~mtime in
 
+  let m_rate = Printf.sprintf "otel.sdk.%s.sampler.actual-rate" signal_name in
+  let self_metrics ~now () =
+    Opentelemetry_core.Metrics.(
+      gauge ~name:m_rate [ float ~now (Sampler.actual_rate self) ])
+    :: e.self_metrics ~now ()
+  in
+
   let emit l =
     if l <> [] && e.enabled () then (
       let accepted = List.filter (fun _x -> Sampler.accept self) l in
@@ -13,6 +21,14 @@ let add_sampler (self : Sampler.t) (e : _ Emitter.t) : _ Emitter.t =
     )
   in
 
-  { Emitter.closed; enabled; flush_and_close; tick; emit }
+  {
+    Emitter.closed;
+    self_metrics;
+    signal_name;
+    enabled;
+    flush_and_close;
+    tick;
+    emit;
+  }
 
 let sample ~proba_accept e = add_sampler (Sampler.create ~proba_accept ()) e

src/client/exporter_debug.ml

@@ -17,15 +17,15 @@ let debug ?(clock = OTEL.Clock.ptime_clock) ?(out = Format.err_formatter) () :
     active = (fun () -> active);
     clock;
     emit_spans =
-      Emitter.make_simple () ~emit:(fun sp ->
+      Emitter.make ~signal_name:"spans" () ~emit:(fun sp ->
           List.iter (Format.fprintf out "SPAN: %a@." Trace.pp_span) sp);
     emit_logs =
-      Emitter.make_simple () ~emit:(fun log ->
+      Emitter.make ~signal_name:"logs" () ~emit:(fun log ->
           List.iter
             (Format.fprintf out "LOG: %a@." Proto.Logs.pp_log_record)
             log);
     emit_metrics =
-      Emitter.make_simple () ~emit:(fun m ->
+      Emitter.make ~signal_name:"metrics" () ~emit:(fun m ->
           List.iter (Format.fprintf out "METRIC: %a@." Metrics.pp_metric) m);
     on_tick = Cb_set.register ticker;
     tick = (fun () -> Cb_set.trigger ticker);

src/client/exporter_queued.ml

@@ -17,18 +17,21 @@ module BQ_emitters = struct
 
   let logs_emitter_of_bq (q : OTEL.Any_signal_l.t Bounded_queue.Send.t) :
       _ OTEL.Emitter.t =
-    Bounded_queue.Send.to_emitter q ~close_queue_on_close:false
+    Bounded_queue.Send.to_emitter q ~signal_name:"logs"
+      ~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.Emitter.t =
-    Bounded_queue.Send.to_emitter q ~close_queue_on_close:false
+    Bounded_queue.Send.to_emitter q ~signal_name:"spans"
+      ~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.Emitter.t =
-    Bounded_queue.Send.to_emitter q ~close_queue_on_close:false
+    Bounded_queue.Send.to_emitter q ~signal_name:"metrics"
+      ~close_queue_on_close:false
     |> Opentelemetry_emitter.Emitter.flat_map
          OTEL.Any_signal_l.of_metrics_or_empty
 end
@@ -64,7 +67,7 @@ let create ~clock ~(q : OTEL.Any_signal_l.t Bounded_queue.t)
         [ OTEL.Metrics.int ~now (Bounded_queue.Recv.high_watermark q.recv) ]
     and m_discarded =
       OTEL.Metrics.sum ~is_monotonic:true
-        ~name:"otel_ocaml.exporter_queue.discarded"
+        ~name:"otel.sdk.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 ~clock

src/client/exporter_stdout.ml

@@ -47,12 +47,13 @@ let stdout ?(clock = OTEL.Clock.ptime_clock) () : OTEL.Exporter.t =
   let active, trigger = Aswitch.create () in
   let tick () = Cb_set.trigger ticker in
 
-  let mk_emitter pp_signal =
+  let mk_emitter ~signal_name pp_signal =
     let emit l =
       if Aswitch.is_off active then raise Emitter.Closed;
       pp_vlist mutex pp_signal out l
     in
     let enabled () = Aswitch.is_on active in
+    let self_metrics ~now:_ () = [] in
     let tick ~mtime:_ = () in
     let flush_and_close () =
       if Aswitch.is_on active then
@@ -60,12 +61,20 @@ let stdout ?(clock = OTEL.Clock.ptime_clock) () : OTEL.Exporter.t =
         Format.pp_print_flush out ()
     in
     let closed () = Aswitch.is_off active in
-    { Emitter.emit; closed; enabled; tick; flush_and_close }
+    {
+      Emitter.emit;
+      signal_name;
+      self_metrics;
+      closed;
+      enabled;
+      tick;
+      flush_and_close;
+    }
   in
 
-  let emit_spans = mk_emitter pp_span in
-  let emit_logs = mk_emitter pp_log in
-  let emit_metrics = mk_emitter pp_metric in
+  let emit_spans = mk_emitter ~signal_name:"spans" pp_span in
+  let emit_logs = mk_emitter ~signal_name:"logs" pp_log in
+  let emit_metrics = mk_emitter ~signal_name:"metrics" pp_metric in
 
   let self_metrics () = [] in
   let shutdown () =

src/client/http_config.mli

@@ -1,4 +1,5 @@
 (** @deprecated Use {!Exporter_config} instead *)
 
+[@@@deprecated "use Exporter_config instead"]
+
 include module type of Exporter_config
-[@@deprecated "use Exporter_config instead"]

src/core/exporter.ml

@@ -77,4 +77,12 @@ let[@inline] shutdown (self : t) : unit = self.shutdown ()
 
 let (cleanup [@deprecated "use shutdown instead"]) = shutdown
 
-let[@inline] self_metrics (self : t) : _ list = self.self_metrics ()
+let self_metrics (self : t) : _ list =
+  let now = Clock.now self.clock in
+  List.flatten
+    [
+      self.self_metrics ();
+      self.emit_spans.self_metrics ~now ();
+      self.emit_logs.self_metrics ~now ();
+      self.emit_metrics.self_metrics ~now ();
+    ]

src/emitter/dune

@@ -2,6 +2,8 @@
  (name opentelemetry_emitter)
  (public_name opentelemetry.emitter)
  (libraries
+  (re_export opentelemetry.proto)
+  (re_export opentelemetry.util)
   (re_export opentelemetry.atomic)
   (re_export mtime))
  (flags :standard -open Opentelemetry_atomic)

src/emitter/emitter.ml

@@ -8,6 +8,7 @@
 exception Closed
 
 type -'a t = {
+  signal_name: string;  (** Description of what signal is emitted *)
   enabled: unit -> bool;
       (** Return [true] if [emit] has a chance of doing something with the
           signals it's given. *)
@@ -20,6 +21,11 @@ type -'a t = {
       (** True if the emitter is already closed. Beware TOCTOU bugs. *)
   flush_and_close: unit -> unit;
       (** Flush internally buffered signals, then close. *)
+  self_metrics:
+    now:Opentelemetry_util.Timestamp_ns.t ->
+    unit ->
+    Opentelemetry_proto.Metrics.metric list;
+      (** metrics about the emitter itself. *)
 }
 (** An emitter for values of type ['a]. *)
 
@@ -33,6 +39,8 @@ let[@inline] closed self : bool = self.closed ()
 
 let[@inline] flush_and_close (self : _ t) : unit = self.flush_and_close ()
 
+let[@inline] self_metrics self ~now : _ list = self.self_metrics ~now ()
+
 (** [map f emitter] returns a new emitter that applies [f] to signals item-wise
     before passing them to [emitter] *)
 let map (f : 'a -> 'b) (self : 'b t) : 'a t =
@@ -56,9 +64,9 @@ let tap (f : 'a -> unit) (self : 'a t) : 'a t =
   in
   { self with emit }
 
-(** [make_simple ~emit ()] is an emitter that calls [emit]. *)
-let make_simple ?tick ?closed ?enabled ?(flush_and_close = ignore) ~emit () :
-    _ t =
+(** [make ~emit ()] is an emitter that calls [emit]. *)
+let make ?tick ?closed ?enabled ?(flush_and_close = ignore)
+    ?(self_metrics = fun ~now:_ () -> []) ~signal_name ~emit () : _ t =
   let tick =
     match tick with
     | None -> fun ~mtime:_ -> ()
@@ -71,14 +79,16 @@ let make_simple ?tick ?closed ?enabled ?(flush_and_close = ignore) ~emit () :
     | None, Some f -> (fun () -> not (f ())), f
     | Some f1, Some f2 -> f1, f2
   in
-  { tick; emit; flush_and_close; closed; enabled }
+  { signal_name; tick; emit; flush_and_close; closed; enabled; self_metrics }
 
 (** Dummy emitter, doesn't accept or emit anything. *)
 let dummy : _ t =
   {
+    signal_name = "dummy";
     enabled = (fun () -> false);
     emit = ignore;
     tick = (fun ~mtime:_ -> ());
     closed = (fun () -> true);
     flush_and_close = ignore;
+    self_metrics = (fun ~now:_ () -> []);
   }

src/emitter/to_list.ml

@@ -1,14 +1,13 @@
 (** Emitter that stores signals into a list, in reverse order (most recent
     signals first). *)
-let to_list (l : 'a list ref) : 'a Emitter.t =
-  let closed = Atomic.make false in
-  {
-    enabled = (fun () -> not (Atomic.get closed));
-    emit =
-      (fun sigs ->
-        if Atomic.get closed then raise Emitter.Closed;
-        l := List.rev_append sigs !l);
-    tick = (fun ~mtime:_ -> ());
-    closed = (fun () -> Atomic.get closed);
-    flush_and_close = (fun () -> Atomic.set closed true);
-  }
+let to_list ~signal_name (l : 'a list ref) : 'a Emitter.t =
+  let closed_ = Atomic.make false in
+  let enabled = fun () -> not (Atomic.get closed_) in
+  let emit =
+   fun sigs ->
+    if Atomic.get closed_ then raise Emitter.Closed;
+    l := List.rev_append sigs !l
+  in
+  let closed () = Atomic.get closed_ in
+  let flush_and_close = fun () -> Atomic.set closed_ true in
+  Emitter.make ~signal_name ~emit ~enabled ~closed ~flush_and_close ()

src/lib/main_exporter.ml

@@ -44,7 +44,8 @@ module Util = struct
       exporter. When this emitter is used to [emit signals], the current
       exporter is looked up, [get_emitter exporter] is then used to locate the
       relevant emitter [e'], and [signals] is in turn emitted in [e']. *)
-  let dynamic_forward_emitter_to_main_exporter ~get_emitter () : _ Emitter.t =
+  let dynamic_forward_emitter_to_main_exporter ~signal_name
+      ~(get_emitter : Exporter.t -> _ Emitter.t) () : _ Emitter.t =
     let enabled () = present () in
     let closed () = not (enabled ()) in
     let flush_and_close () = () in
@@ -53,6 +54,11 @@ module Util = struct
       | None -> ()
       | Some exp -> Exporter.tick exp ~mtime
     in
+    let self_metrics ~now () =
+      match get () with
+      | None -> []
+      | Some exp -> (get_emitter exp).self_metrics ~now ()
+    in
     let emit signals =
       if signals <> [] then (
         match get () with
@@ -62,7 +68,8 @@ module Util = struct
           Emitter.emit emitter signals
       )
     in
-    { Emitter.enabled; closed; emit; tick; flush_and_close }
+    Emitter.make ~signal_name ~enabled ~closed ~self_metrics ~flush_and_close
+      ~tick ~emit ()
 end
 
 (** Aswitch of the current exporter, or {!Aswitch.dummy} *)
@@ -77,15 +84,15 @@ let[@inline] active () : Aswitch.t =
     @since NEXT_RELEASE *)
 let dynamic_forward_to_main_exporter : Exporter.t =
   let emit_logs =
-    Util.dynamic_forward_emitter_to_main_exporter ()
+    Util.dynamic_forward_emitter_to_main_exporter () ~signal_name:"logs"
       ~get_emitter:Exporter.(fun e -> e.emit_logs)
   in
   let emit_metrics =
-    Util.dynamic_forward_emitter_to_main_exporter ()
+    Util.dynamic_forward_emitter_to_main_exporter () ~signal_name:"metrics"
       ~get_emitter:Exporter.(fun e -> e.emit_metrics)
   in
   let emit_spans =
-    Util.dynamic_forward_emitter_to_main_exporter ()
+    Util.dynamic_forward_emitter_to_main_exporter () ~signal_name:"spans"
       ~get_emitter:Exporter.(fun e -> e.emit_spans)
   in
   let on_tick f =

tests/implicit_scope/sync/test_implicit_scope_sync.ml

@@ -7,7 +7,8 @@ let test_exporter : Otel.Exporter.t =
   let open Otel.Exporter in
   {
     (dummy ()) with
-    emit_spans = Opentelemetry_emitter.To_list.to_list spans_emitted;
+    emit_spans =
+      Opentelemetry_emitter.To_list.to_list ~signal_name:"spans" spans_emitted;
   }
 
 let with_test_exporter f =