Re: [Caml-list] threads, signals, and timeout

[Philippe Wang <philippe.wang.lists@gmail.com>]

Considering that posix signals are not real-time *anyway*, using them
to programme specific treatments per-thread is hmmm... say a nightmare
! Plus I don't quite see how you could eventually have a non-broken
implementation. Gerd Stolpmann emphasized it if I understood well.

One solution would be to use state variables to check every once in a while.

Or maybe to use "fairthreads" instead, but I guess that the problem is
actually much more complicated than just that.

Well, I thought I had more interesting things to say. I was wrong,
then just my two cents.
Anyways, good luck!

Cheers,

Philippe Wang


On Mon, Oct 26, 2009 at 7:08 PM, yoann padioleau <pad.aryx@gmail.com> wrote:
> Hi,
>
> I would like to create different threads where each thread do some
> computation and are subject to different
> timeout. Without threads I usually use Unix.alarm with a SIGALARM
> handler that just raise a Timeout exception
> and everything works fine, but when I try to do something similar with
> threads it does not work
> because apparently the Unix.alarm done in one thread override the
> Unix.alarm done in another
> thread. I had a look at thread.mli but was not able to find anything
> related to timeout.
> Is there a way to have multiple timeout and multiple threads at the same time ?
>
> Here is a program that unforunately get the first timeout, but not the second :(
>
>
> (*
> ocamlc -g -thread unix.cma threads.cma signals_and_threads.ml
> *)
>
> exception Timeout
>
> let mytid () =
>  let t = Thread.self () in
>  let i = Thread.id t in
>  i
>
> let set_timeout () =
>
>  Sys.set_signal Sys.sigalrm
>    (Sys.Signal_handle (fun _ ->
>      prerr_endline "Time is up!";
>      print_string (Printf.sprintf "id: %d\n" (mytid()));
>      raise Timeout
>    ));
>
>  ignore(Unix.alarm 1);
>  ()
>
>
> let main =
>  let t1 =
>    Thread.create (fun () ->
>      set_timeout ();
>      print_string (Printf.sprintf "t1 id: %d\n" (mytid()));
>
>      let xs = [1;2;3] in
>      while(true) do
>        let _ = List.map (fun x -> x + 1) xs in
>        ()
>      done;
>      ()
>    ) ()
>  in
>
>  let t2 =
>    Thread.create (fun () ->
>      set_timeout ();
>      print_string (Printf.sprintf "t2 id: %d\n" (mytid()));
>
>      let xs = [1;2;3] in
>      while(true) do
>        let _ = List.map (fun x -> x + 1) xs in
>        ()
>      done;
>      ()
>    ) ()
>  in
>  Thread.join t1;
>  Thread.join t2;
>  ()
>
> ------------------
>
>
>
>
> Here is the output
> Time is up!
> t2 id: 2
> t1 id: 1
> id: 1
> Thread 1 killed on uncaught exception Signals_and_threads.Timeout
> .... <the program loops, meaning the second thread never received its timeout
>