Re: [Caml-list] [lwt] multiplexing several threads

[Mauricio Fernandez <mfp@acm.org>]

On Thu, Jan 31, 2013 at 10:53:31AM +0100, Mauricio Fernandez wrote:
> On Thu, Jan 31, 2013 at 09:37:29AM +0400, Ivan Gotovchits wrote:
> > The following solution
> > 
> >    let rec loop sc =
> >      let cmd = read_from_user () <?> read_event () in
> >      cmd >>= (process state)
> > 
> >    and process sc = function
> >      | Exit -> return sc
> >      | cmd  -> (* modify sc*) loop sc
> > 
> >    let r = Lwt_main.run (loop state)
> > 
> > doesn't work when the event thread wakes up first. In that case the next
> > step of the loop will call Lwt_read_line.read_line before the previous
> > invocation finishes and it breaks user input.
> > 
> > Please, help me to find a feasible solution to my problem!
> 

Just remembered that you might want to cancel the other thread before
returning too:

> let process s = function
>     Exit -> return (`Exit s)
>   | cmd -> let s = ... in return (`State s)
> 
> let rec loop state user_cmd event =
>   match_lwt
>     Lwt.choose
>       [ (lwt x = user_cmd in return (`User x));
>         (lwt x = event in return (`Event x));
>     ]
>   with
>     `User cmd -> begin match_lwt process state cmd with
>                    `Exit s -> return s

                      ===================

                      `Exit s -> Lwt.cancel event; return s

>                  | `State s -> loop s (read_from_user ()) event
>                  end
>   | `Event cmd -> begin match_lwt process state cmd with
>                    `Exit s -> return s
                                Lwt.cancel user_cmd; return s

>                  | `State s -> loop s user_cmd (read_event ())
>                  end
-- 
Mauricio Fernandez