feat: Pool.run_wait_block can return a value now

src/pool.ml

@@ -63,17 +63,17 @@ let run_async (self : t) (task : task) : unit =
 
 let run = run_async
 
-let run_wait_block self task : unit =
+let run_wait_block self (f : unit -> 'a) : 'a =
   let q = Bb_queue.create () in
   run_async self (fun () ->
       try
-        task ();
+        let x = f () in
-        Bb_queue.push q (Ok ())
+        Bb_queue.push q (Ok x)
       with exn ->
         let bt = Printexc.get_raw_backtrace () in
         Bb_queue.push q (Error (exn, bt)));
   match Bb_queue.pop q with
-  | Ok () -> ()
+  | Ok x -> x
   | Error (exn, bt) -> Printexc.raise_with_backtrace exn bt
 
 let[@inline] size self = Array.length self.threads

src/pool.mli

@@ -82,10 +82,12 @@ val run : t -> (unit -> unit) -> unit
   [@@deprecated "use run_async"]
 (** deprecated alias to {!run_async} *)
 
-val run_wait_block : t -> (unit -> unit) -> unit
+val run_wait_block : t -> (unit -> 'a) -> 'a
 (** [run_wait_block pool f] schedules [f] for later execution
     on the pool, like {!run_async}.
-    It then blocks the current thread until [f()] is done executing.
+    It then blocks the current thread until [f()] is done executing,
+    and returns its result. If [f()] raises an exception, then [run_wait_block pool f]
+    will raise it as well.
 
     {b NOTE} be careful with deadlocks (see notes in {!Fut.wait_block}).
     @since 0.3 *)