add Emitter_limit_interval

src/client/emitter_add_batching.mli

@@ -1,3 +1,12 @@
+(** Add a batch in front of an emitter.
+
+    The batch accumulates signals until it's full or too old, at which points
+    all the accumulated signals are emitted at once. Pushing into a batch is
+    generally very fast (amortized), in most cases; the slow path is only when
+    the batch needs to be emitted.
+
+    @since NEXT_RELEASE *)
+
 open Opentelemetry_emitter
 
 val wrap_emitter_with_batch : 'a Batch.t -> 'a Emitter.t -> 'a Emitter.t

src/client/emitter_limit_interval.ml

@@ -0,0 +1,8 @@
+open Common_.OTEL
+
+let add_interval_limiter il (e : _ Emitter.t) : _ Emitter.t =
+  let emit xs = if Interval_limiter.make_attempt il then Emitter.emit e xs in
+  { e with emit }
+
+let limit_interval ~min_interval (e : _ Emitter.t) : _ Emitter.t =
+  add_interval_limiter (Interval_limiter.create ~min_interval ()) e

src/client/emitter_limit_interval.mli

@@ -0,0 +1,25 @@
+(** Limit frequency at which the emitter emits.
+
+    This puts a hard floor on the interval between two consecutive successful
+    [emit]. Attempts to emit too early are simply discarded.
+
+    The use case for this is metrics: it's possible, for a gauge, to just drop
+    some entries if we've been emitting them too frequently.
+
+    {b NOTE}: it's better to do [limit_interval ~min_interval (add_batching e)]
+    than [add_batching (limit_interval ~min_interval e)], because in the later
+    case we might be dismissing a whole large batch at ine
+
+    @since NEXT_RELEASE *)
+
+open Common_.OTEL
+
+val add_interval_limiter : Interval_limiter.t -> 'a Emitter.t -> 'a Emitter.t
+(** [add_interval_limiter il e] is a new emitter [e'] that can only emit signals
+    less frequently than [Interval_limiter.min_interval il].
+
+    Trying to emit too early will simply drop the signal. *)
+
+val limit_interval : min_interval:Mtime.span -> 'a Emitter.t -> 'a Emitter.t
+(** [limit_interval ~min_interval e] is
+    [add_interval_limiter (Interval_limiter.create ~min_interval ()) e] *)