diff --git a/src/nanoev.ml b/src/nanoev.ml
index 4bf425a..00989e9 100644
--- a/src/nanoev.ml
+++ b/src/nanoev.ml
@@ -32,3 +32,13 @@ let[@inline] run_after_s (Ev (ops, st)) time x y f : unit =
   ops.run_after_s st time x y f
 
 let[@inline] step (Ev (ops, st)) : unit = ops.step st
+
+(*
+let rec read (self:t) fd buf i len : int =
+  match Unix.read fd buf i len with
+    | n -> n
+  | exception Unix.Unix_error (Unix, _, _) ->
+    read self fd buf i len
+*)
+
+
diff --git a/src/unix/nanoev_unix.ml b/src/unix/nanoev_unix.ml
index 3d54a5a..5c29cf6 100644
--- a/src/unix/nanoev_unix.ml
+++ b/src/unix/nanoev_unix.ml
@@ -34,18 +34,29 @@ type st = {
   mutable sub_w: Unix.file_descr list;
   mutable sub_up_to_date: bool;
       (** are [sub_r] and [sub_w] faithful reflections of [fds]? *)
+  wakeup_rd: Unix.file_descr;
+  wakeup_wr: Unix.file_descr;
+  wakeup_triggered: bool Atomic.t;
+      (** Make [wakeup_from_outside] idempotent within an iteration of [step] *)
+  in_select: bool Atomic.t;
   lock: Mutex.t;
 }
 
 let leq_timer (Timer a) (Timer b) = a.deadline <= b.deadline
 
 let create_st () : st =
+  let wakeup_rd, wakeup_wr = Unix.pipe () in
+  Unix.set_nonblock wakeup_rd;
   {
     timer = Heap.create ~leq:leq_timer ();
     fds = Hashtbl.create 16;
     sub_r = [];
     sub_w = [];
     sub_up_to_date = true;
+    wakeup_rd;
+    wakeup_wr;
+    wakeup_triggered = Atomic.make false;
+    in_select = Atomic.make false;
     lock = Mutex.create ();
   }
 
@@ -68,8 +79,11 @@ let clear (self : st) =
   self.sub_up_to_date <- true;
   ()
 
-(* TODO: *)
-let wakeup_from_outside _self : unit = ()
+let wakeup_from_outside (self : st) : unit =
+  if not (Atomic.exchange self.wakeup_triggered true) then (
+    let b = Bytes.make 1 '!' in
+    ignore (Unix.write self.wakeup_wr b 0 1 : int)
+  )
 
 let get_fd_ (self : st) fd : per_fd =
   match Hashtbl.find self.fds fd with
@@ -82,17 +96,22 @@ let get_fd_ (self : st) fd : per_fd =
 let on_readable self fd x y f : unit =
   let@ self = with_lock_ self in
   let per_fd = get_fd_ self fd in
-  per_fd.r <- Sub (x, y, f, per_fd.r)
+  per_fd.r <- Sub (x, y, f, per_fd.r);
+  self.sub_up_to_date <- false;
+  if Atomic.get self.in_select then wakeup_from_outside self
 
 let on_writable self fd x y f : unit =
   let@ self = with_lock_ self in
   let per_fd = get_fd_ self fd in
-  per_fd.w <- Sub (x, y, f, per_fd.w)
+  per_fd.w <- Sub (x, y, f, per_fd.w);
+  self.sub_up_to_date <- false;
+  if Atomic.get self.in_select then wakeup_from_outside self
 
 let run_after_s self time x y f : unit =
   let@ self = with_lock_ self in
   let deadline = now_ () +. time in
-  Heap.insert self.timer (Timer { deadline; x; y; f })
+  Heap.insert self.timer (Timer { deadline; x; y; f });
+  if Atomic.get self.in_select then wakeup_from_outside self
 
 let recompute_if_needed (self : st) =
   if not self.sub_up_to_date then (
@@ -108,16 +127,6 @@ let recompute_if_needed (self : st) =
       self.fds
   )
 
-(*
-    let set fd (ev : Event.t) : unit =
-      needs_recompute := true;
-      match Hashtbl.find subs fd with
-      | exception Not_found -> Hashtbl.add subs fd (ref ev)
-      | old_ev -> old_ev := Event.(!old_ev lor ev)
-
-    let iter_ready f : unit = List.iter (fun (fd, ev) -> f fd ev) !ready_fds
-*)
-
 let next_deadline_ (self : st) : float option =
   match Heap.peek_min_exn self.timer with
   | exception Heap.Empty -> None
@@ -136,18 +145,26 @@ let step (self : st) : unit =
     recompute_if_needed self;
     let timeout =
       match next_deadline_ self with
-      | None ->
-        let has_waiters = self.sub_r != [] || self.sub_w != [] in
-        if has_waiters then
-          1e9
-        else
-          0.
+      | None -> 30.
       | Some d -> max 0. (d -. now_ ())
     in
     timeout, self.sub_r, self.sub_w
   in
 
-  let r_reads, r_writes, _ = Unix.select sub_r sub_w [] timeout in
+  (* enter [select] *)
+  Atomic.set self.in_select true;
+  let r_reads, r_writes, _ =
+    Unix.select (self.wakeup_rd :: sub_r) sub_w [] timeout
+  in
+  Atomic.set self.in_select false;
+
+  (* drain pipe *)
+  if Atomic.exchange self.wakeup_triggered false then (
+    let b1 = Bytes.create 1 in
+    while try Unix.read self.wakeup_rd b1 0 1 > 0 with _ -> false do
+      ()
+    done
+  );
 
   (* gather the [per_fd] that are ready *)
   let ready_r = ref [] in