add high watermark to ocurl client

src/client/opentelemetry_client_ocurl.ml

@@ -170,12 +170,14 @@ end = struct
     mutable size: int;
     mutable q: 'a list;
     batch: int option;
+    high_watermark: int;
     timeout: Mtime.span option;
     mutable start: Mtime.t;
   }
 
   let make ?batch ?timeout () : _ t =
     Option.iter (fun b -> assert (b > 0)) batch;
+    let high_watermark = Option.fold ~none:100 ~some:(fun x -> x * 10) batch in
     {
       lock = Mutex.create ();
       size = 0;
@@ -183,6 +185,7 @@ end = struct
       q = [];
       batch;
       timeout;
+      high_watermark;
     }
 
   let is_empty_ self = self.size = 0
@@ -219,11 +222,19 @@ end = struct
   let push (self : _ t) x : bool =
     let@ () = with_mutex_ self.lock in
     if self.size = 0 && Option.is_some self.timeout then
+      (* current batch starts now *)
       self.start <- Mtime_clock.now ();
-    self.size <- 1 + self.size;
+    if self.size >= self.high_watermark then (
-    self.q <- x :: self.q;
+      (* drop this to prevent queue from growing too fast *)
-    let ready = is_full_ self in
+      Atomic.incr n_dropped;
-    ready
+      true
+    ) else (
+      (* add to queue *)
+      self.size <- 1 + self.size;
+      self.q <- x :: self.q;
+      let ready = is_full_ self in
+      ready
+    )
 
   let push' self x = ignore (push self x : bool)
 end