add Pool.num_tasks

src/pool.ml

@@ -51,7 +51,12 @@ let run (self : t) (f : task) : unit =
   | Exit -> ()
   | Bb_queue.Closed -> raise Shutdown
 
-let size self = Array.length self.threads
+let[@inline] size self = Array.length self.threads
+
+let num_tasks (self : t) : int =
+  let n = ref 0 in
+  Array.iter (fun q -> n := !n + Bb_queue.size q) self.qs;
+  !n
 
 exception Got_task of task
 

src/pool.mli

@@ -52,6 +52,11 @@ val create :
 val size : t -> int
 (** Number of threads *)
 
+val num_tasks : t -> int
+(** Current number of tasks. This is at best a snapshot, useful for metrics
+    and debugging.
+    @since 0.2 *)
+
 val shutdown : t -> unit
 (** Shutdown the pool and wait for it to terminate. Idempotent. *)