Resource temporarily unavailable (EAGAIN) on recv

[rizo]

Running a simple Lwt-based example that uses Nanomsg_lwt.recv_string fails with the following error:

Fatal error: exception Nanomsg_lwt.Error("", "Resource temporarily unavailable")
Raised at file "src/core/lwt.ml", line 2719, characters 24-25
Called from file "src/unix/lwt_main.ml", line 33, characters 8-18

Here is the minimum program that can be used to reproduce the issue:

(* ocamlbuild -pkg lwt -pkg nanomsg.lwt tmp/nn_recv_lwt.native *)

let bind_pull addr =
  let addr = Nanomsg.Addr.bind_of_string addr in
  let socket = Nanomsg.socket_exn Nanomsg.Pull in
  let _eid = Nanomsg.bind_exn socket addr in
  socket

open Lwt.Infix

let () =
  let socket = bind_pull "tcp://127.0.0.1:9090" in
  Lwt_main.run begin
    Nanomsg_lwt.recv_string socket >>= fun str ->
    Lwt_io.printl str
  end

The equivalent blocking call to recv does work:

let () =
  let socket = bind_pull "tcp://127.0.0.1:9090" in
  Lwt_main.run begin
    match Nanomsg.recv_string socket with
    | Ok str -> Lwt_io.printl str
    | Error e -> Lwt_io.printl "err"
  end

I suspect it is related to the fact that the calls to bind and connect are natively asynchronous (related issue in nanomsg).