Use a single poll.

src/duppy.ml

@@ -24,27 +24,32 @@ module Pcre = Re.Pcre
 
 type fd = Unix.file_descr
 
-let poll r w timeout =
-  let timeout =
-    match timeout with
-      | x when x < 0. -> Poll.Timeout.never
-      | 0. -> Poll.Timeout.immediate
-      | x ->
-          let frac, int = modf x in
-          let int = Int64.mul (Int64.of_float int) 1_000_000_000L in
-          let frac = Int64.of_float (frac *. 1_000_000_000.) in
-          let timeout = Int64.add int frac in
-          Poll.Timeout.after timeout
-  in
+let poll =
   let poll = Poll.create () in
-  List.iter (fun fd -> Poll.set poll fd Poll.Event.read) r;
-  List.iter (fun fd -> Poll.set poll fd Poll.Event.write) w;
-  ignore (Poll.wait poll timeout);
-  let r = ref [] in
-  let w = ref [] in
-  Poll.iter_ready poll ~f:(fun fd -> function
-    | { Poll.Event.readable = true; _ } -> r := fd :: !r | _ -> w := fd :: !w);
-  (!r, !w)
+  fun r w timeout ->
+    let timeout =
+      match timeout with
+        | x when x < 0. -> Poll.Timeout.never
+        | 0. -> Poll.Timeout.immediate
+        | x ->
+            let frac, int = modf x in
+            let int = Int64.mul (Int64.of_float int) 1_000_000_000L in
+            let frac = Int64.of_float (frac *. 1_000_000_000.) in
+            let timeout = Int64.add int frac in
+            Poll.Timeout.after timeout
+    in
+    List.iter (fun fd -> Poll.set poll fd Poll.Event.read) r;
+    List.iter (fun fd -> Poll.set poll fd Poll.Event.write) w;
+    Fun.protect
+      (fun () ->
+        ignore (Poll.wait poll timeout);
+        let r = ref [] in
+        let w = ref [] in
+        Poll.iter_ready poll ~f:(fun fd -> function
+          | { Poll.Event.readable = true; _ } -> r := fd :: !r
+          | _ -> w := fd :: !w);
+        (!r, !w))
+      ~finally:(fun () -> Poll.clear poll)
 
 (** [remove f l] is like [List.find f l] but also returns the result of removing
   * the found element from the original list. *)