add Bb_queue.to_{iter,gen,seq}

src/bb_queue.ml

@@ -93,3 +93,26 @@ let size (self : _ t) : int =
   let n = Queue.length self.q in
   Mutex.unlock self.mutex;
   n
+
+type 'a gen = unit -> 'a option
+type 'a iter = ('a -> unit) -> unit
+
+let to_iter self k =
+  try
+    while true do
+      let x = pop self in
+      k x
+    done
+  with Closed -> ()
+
+let to_gen self : _ gen =
+ fun () ->
+  match pop self with
+  | exception Closed -> None
+  | x -> Some x
+
+let rec to_seq self : _ Seq.t =
+ fun () ->
+  match pop self with
+  | exception Closed -> Seq.Nil
+  | x -> Seq.Cons (x, to_seq self)

src/bb_queue.mli

@@ -34,3 +34,19 @@ val try_push : 'a t -> 'a -> bool
 
 val close : _ t -> unit
 (** Close the queue, meaning there won't be any more [push] allowed. *)
+
+type 'a gen = unit -> 'a option
+type 'a iter = ('a -> unit) -> unit
+
+val to_iter : 'a t -> 'a iter
+(** [to_iter q] returns an iterator over all items in the queue.
+    This might not terminate if [q] is never closed.
+    @since NEXT_RELEASE *)
+
+val to_gen : 'a t -> 'a gen
+(** [to_gen q] returns a generator from the queue.
+    @since NEXT_RELEASE *)
+
+val to_seq : 'a t -> 'a Seq.t
+(** [to_gen q] returns a (transient) sequence from the queue.
+    @since NEXT_RELEASE *)