Lwt_stream.get leaks on cancel

[ygrek]

let mem_usage v =
  let open Objsize in
  let x = objsize v in
  show_info ~map:string_of_int x

let () =
  let (stream,_) = Lwt_stream.create () in
  let rec loop () =
    lwt _ = Lwt.pick [
      (lwt () = Lwt_unix.sleep 0.1 in Lwt.return ());
      (lwt _ = Lwt_stream.get stream in Lwt.return ());
    ] in
    loop ()
  in
  let tasks = Array.to_list (Array.init 10_000 (fun _ -> loop ())) in
  let nr = ref 0 in
  let rec memory () =
    lwt () = Lwt_unix.sleep 0.05 in
    Gc.compact ();
    let st = Gc.stat () in
    Printf.printf "%d) heap live %d, tasks %s\n%!" !nr st.Gc.live_words (mem_usage tasks);
    incr nr;
    memory ()
  in
  Lwt_main.run (Lwt.join (memory () :: tasks))

mem_usage requires objsize, you can remove it's usage and just observe heap growth.
Build with ocamlbuild -use-ocamlfind -tags 'syntax_camlp4o, package(lwt.syntax)' -pkgs lwt.unix,objsize lwt_leak.native

[aantron]

Thanks for the very nice report. This is fixed in the attached commit. The underlying problem was in Lwt.protected, used internally by Lwt_stream.get. If interested, please see the commit message for details.