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Date: Thu, 31 Jan 2013 10:53:31 +0100
From: Mauricio Fernandez <mfp@acm.org>
To: caml-list@inria.fr
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User-Agent: Mutt/1.5.17+20080114 (2008-01-14)
Subject: Re: [Caml-list] [lwt] multiplexing several threads

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!


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

-- 
Mauricio Fernandez