(*
 * Copyright (C) 2003:
 *    Stefano Zacchiroli <zack@cs.unibo.it>
 *    for the HELM Team http://helm.cs.unibo.it/
 *
 *  This file is part of HELM, an Hypertextual, Electronic
 *  Library of Mathematics, developed at the Computer Science
 *  Department, University of Bologna, Italy.
 *
 *  HELM is free software; you can redistribute it and/or
 *  modify it under the terms of the GNU General Public License
 *  as published by the Free Software Foundation; either version 2
 *  of the License, or (at your option) any later version.
 *
 *  HELM is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with HELM; if not, write to the Free Software
 *  Foundation, Inc., 59 Temple Place - Suite 330, Boston,
 *  MA  02111-1307, USA.
 *
 *  For details, see the HELM World-Wide-Web page,
 *  http://helm.cs.unibo.it/
 *)

exception Can_t_kill of int * string ;; (* pid, reason *)

 (* perform an action inside a critical section controlled by given mutex *)
let do_critical mutex =
  fun action ->
    try
      Mutex.lock mutex;
      let res = Lazy.force action in
      Mutex.unlock mutex;
      res 
    with e -> Mutex.unlock mutex; raise e
;;

let kill_signal = Sys.sigusr2 ;;    (* signal used to kill children *)
let chan = Event.new_channel () ;;  (* communication channel between threads *)

  (* functions mangling "must die" PID list *)
let (add_to_dead_threads_walking, remove_from_dead_threads_walking, must_die) =
  let dead_threads_walking = ref [] in
  let mutex = Mutex.create () in
  let add pid = do_critical mutex (lazy (
      dead_threads_walking := pid :: !dead_threads_walking;
  )) in
  let remove pid = do_critical mutex (lazy (
      dead_threads_walking := List.filter ((<>) pid) !dead_threads_walking
  )) in
  let is_in pid = do_critical mutex (lazy (
      List.exists ((=) pid) !dead_threads_walking
  )) in
  (add, remove, is_in)
;;

  (* "kill_signal" handler, check if current process must die, if this is the
  case exits with Thread.exit *)
ignore (Sys.signal kill_signal (Sys.Signal_handle
  (fun signal ->
    let myself = Unix.getpid () in
    match signal with
    | sg when (sg = kill_signal) && (must_die myself) ->
        remove_from_dead_threads_walking myself;
        prerr_endline "AYEEEEH!";
        Thread.exit ()
    | _ -> ())))
;;

  (* given a thread body (i.e. first argument of a Thread.create invocation)
  return a new thread body which unblock the kill signal and send its pid to
  parent over "chan" *)
let wrap_thread body =
  fun arg ->
    ignore (Unix.sigprocmask Unix.SIG_UNBLOCK [ kill_signal ]);
    Event.sync (Event.send chan (Unix.getpid ()));
    body arg
;;

let creation_mutex = Mutex.create () ;;

(* REAL IMPLEMENTATION NOT YET WORKING --ZACK
let create body arg =
  do_critical creation_mutex (lazy (
      ignore (Thread.create (wrap_thread body) arg);
      Event.sync (Event.receive chan)
  ))
;;

let kill pid =
  add_to_dead_threads_walking pid;
  try
    Unix.kill pid kill_signal
  with e -> raise (Can_t_kill (pid, Printexc.to_string e))
;;
*)

(* FAKE IMPLEMENTATION *)
let create x y = let _ = Thread.create x y in ~-1 ;;
let kill _ = () ;;

  (* block kill signal in main process *)
ignore (Unix.sigprocmask Unix.SIG_BLOCK [ kill_signal ]) ;;