logs_eio.ml

let reporter ~env ~sw =
  let stdout = Eio.Stdenv.stdout env in
  let report (type a b) _src _level ~over (k : unit -> b) (msgf : (a, b) Logs.msgf) : b =
    let res = Atomic.make None in
    let k () =
      match Atomic.get res with
      | Some v -> v
      | None ->
        let v = k () in
        Atomic.set res (Some v);
        v
    in
    let () =
      Eio.Fiber.fork ~sw @@ fun () ->
      Eio.Buf_write.with_flow ~initial_size:512 stdout @@ fun v ->
      ignore
      @@ msgf
      @@ fun ?header ?tags fmt ->
      let f = Eio.Buf_write.make_formatter v in
      ignore header;
      ignore tags;
      Format.kfprintf (fun f -> Format.pp_print_flush f () |> over |> k) f fmt
    in
    k ()
  in
  { Logs.report }
;;

let () =
  Eio_main.run @@ fun env ->
  Eio.Switch.run @@ fun sw ->
  let clock = Eio.Stdenv.clock env in
  Logs.set_reporter @@ reporter ~env ~sw;
  Logs.err (fun m ->
    Eio.Time.sleep clock 2.;
    m "hello");
  Logs.err (fun m ->
    Eio.Time.sleep clock 0.01;
    m "world")
;;