(*  Title:      Pure/ML-Systems/multithreading_polyml.ML

    ID:         $Id$

    Author:     Makarius

Multithreading in Poly/ML 5.1 (cf. polyml/basis/Thread.sml).

*)

open Thread;

signature MULTITHREADING_POLYML =

sig

  val ignore_interrupt: ('a -> 'b) -> 'a -> 'b

  val raise_interrupt: ('a -> 'b) -> 'a -> 'b

  structure TimeLimit: TIME_LIMIT

end;

signature BASIC_MULTITHREADING =

sig

  include BASIC_MULTITHREADING

  include MULTITHREADING_POLYML

end;

signature MULTITHREADING =

sig

  include MULTITHREADING

  include MULTITHREADING_POLYML

end;

structure Multithreading: MULTITHREADING =

struct

(* options *)

val trace = ref 0;

fun tracing level msg =

  if level <= ! trace

  then (TextIO.output (TextIO.stdErr, (">>> " ^ msg () ^ "\n")); TextIO.flushOut TextIO.stdErr)

  else ();

val available = true;

val max_threads = ref 1;

(* misc utils *)

fun cons x xs = x :: xs;

fun change r f = r := f (! r);

fun inc i = (i := ! i + 1; ! i);

fun dec i = (i := ! i - 1; ! i);

fun show "" = "" | show name = " " ^ name;

fun show' "" = "" | show' name = " [" ^ name ^ "]";

(* thread attributes *)

fun with_attributes new_atts f x =

  let

    val orig_atts = Thread.getAttributes ();

    fun restore () = Thread.setAttributes orig_atts;

  in

    Exn.release

    (*RACE for fully asynchronous interrupts!*)

    (let

        val _ = Thread.setAttributes new_atts;

        val result = Exn.capture (f orig_atts) x;

        val _ = restore ();

      in result end

      handle Interrupt => (restore (); Exn.Exn Interrupt))

  end;

(* interrupt handling *)

fun uninterruptible f x = with_attributes

  [Thread.EnableBroadcastInterrupt false, Thread.InterruptState Thread.InterruptDefer] f x;

fun interruptible f x = with_attributes

  [Thread.EnableBroadcastInterrupt true, Thread.InterruptState Thread.InterruptAsynchOnce] f x;

fun ignore_interrupt f = uninterruptible (fn _ => f);

fun raise_interrupt f = interruptible (fn _ => f);

(* execution with time limit *)

structure TimeLimit =

struct

exception TimeOut;

fun timeLimit time f x =

  uninterruptible (fn atts => fn () =>

    let

      val worker = Thread.self ();

      val timeout = ref false;

      val watchdog = Thread.fork (interruptible (fn _ => fn () =>

        (OS.Process.sleep time; timeout := true; Thread.interrupt worker)), []);

      (*RACE! timeout signal vs. external Interrupt*)

      val result = Exn.capture (with_attributes atts (fn _ => f)) x;

      val was_timeout = (case result of Exn.Exn Interrupt => ! timeout | _ => false);

      val _ = Thread.interrupt watchdog handle Thread _ => ();

    in if was_timeout then raise TimeOut else Exn.release result end) ();

end;

(* critical section -- may be nested within the same thread *)

local

val critical_lock = Mutex.mutex ();

val critical_thread = ref (NONE: Thread.thread option);

val critical_name = ref "";

in

fun self_critical () =

  (case ! critical_thread of

    NONE => false

  | SOME id => Thread.equal (id, Thread.self ()));

fun NAMED_CRITICAL name e =

  if self_critical () then e ()

  else

    uninterruptible (fn atts => fn () =>

      let

        val name' = ! critical_name;

        val _ =

          if Mutex.trylock critical_lock then ()

          else

            let

              val timer = Timer.startRealTimer ();

              val _ = tracing 4 (fn () => "CRITICAL" ^ show name ^ show' name' ^ ": waiting");

              val _ = Mutex.lock critical_lock;

              val time = Timer.checkRealTimer timer;

              val _ = tracing (if Time.> (time, Time.fromMilliseconds 10) then 3 else 4) (fn () =>

                "CRITICAL" ^ show name ^ show' name' ^ ": passed after " ^ Time.toString time);

            in () end;

        val _ = critical_thread := SOME (Thread.self ());

        val _ = critical_name := name;

        val result = Exn.capture (with_attributes atts (fn _ => e)) ();

        val _ = critical_name := "";

        val _ = critical_thread := NONE;

        val _ = Mutex.unlock critical_lock;

      in Exn.release result end) ();

fun CRITICAL e = NAMED_CRITICAL "" e;

end;

(* scheduling -- multiple threads working on a queue of tasks *)

datatype 'a task =

  Task of {body: unit -> unit, cont: 'a -> 'a, fail: 'a -> 'a} | Wait | Terminate;

fun schedule n next_task = uninterruptible (fn _ => fn tasks =>

  let

    (*protected execution*)

    val lock = Mutex.mutex ();

    val protected_name = ref "";

    fun PROTECTED name e =

      let

        val name' = ! protected_name;

        val _ =

          if Mutex.trylock lock then ()

          else

            let

              val _ = tracing 2 (fn () => "PROTECTED" ^ show name ^ show' name' ^ ": waiting");

              val _ = Mutex.lock lock;

              val _ = tracing 2 (fn () => "PROTECTED" ^ show name ^ show' name' ^ ": passed");

            in () end;

        val _ = protected_name := name;

        val res = Exn.capture e ();

        val _ = protected_name := "";

        val _ = Mutex.unlock lock;

      in Exn.release res end;

    (*wakeup condition*)

    val wakeup = ConditionVar.conditionVar ();

    fun wakeup_all () = ConditionVar.broadcast wakeup;

    fun wait () = ConditionVar.wait (wakeup, lock);

    fun wait_timeout () = ConditionVar.waitUntil (wakeup, lock, Time.now () + Time.fromSeconds 1);

    (*queue of tasks*)

    val queue = ref tasks;

    val active = ref 0;

    fun trace_active () = tracing 1 (fn () => "SCHEDULE: " ^ Int.toString (! active) ^ " active");

    fun dequeue () =

      let

        val (next, tasks') = next_task (! queue);

        val _ = queue := tasks';

      in

        (case next of Wait =>

          (dec active; trace_active ();

            wait ();

            inc active; trace_active ();

            dequeue ())

        | _ => next)

      end;

    (*pool of running threads*)

    val status = ref ([]: exn list);

    val running = ref ([]: Thread.thread list);

    fun start f =

      (inc active;

       change running (cons (Thread.fork (f, [Thread.InterruptState Thread.InterruptDefer]))));

    fun stop () =

      (dec active;

       change running (List.filter (fn t => not (Thread.equal (t, Thread.self ())))));

   (*worker thread*)

    fun worker () =

      (case PROTECTED "dequeue" dequeue of

        Task {body, cont, fail} =>

          (case Exn.capture (interruptible (fn _ => body)) () of

            Exn.Result () =>

              (PROTECTED "cont" (fn () => (change queue cont; wakeup_all ())); worker ())

          | Exn.Exn exn =>

              PROTECTED "fail" (fn () =>

                (change status (cons exn); change queue fail; stop (); wakeup_all ())))

      | Terminate => PROTECTED "terminate" (fn () => (stop (); wakeup_all ())));

    (*main control: fork and wait*)

    fun fork 0 = ()

      | fork k = (start worker; fork (k - 1));

    val _ = PROTECTED "main" (fn () =>

     (fork (Int.max (n, 1));

      while not (List.null (! running)) do

      (trace_active ();

       if not (List.null (! status)) then (List.app Thread.interrupt (! running)) else ();

       wait_timeout ())));

  in ! status end);

(* serial numbers *)

local

val serial_lock = Mutex.mutex ();

val serial_count = ref 0;

in

val serial = uninterruptible (fn _ => fn () =>

  let

    val _ = Mutex.lock serial_lock;

    val res = inc serial_count;

    val _ = Mutex.unlock serial_lock;

  in res end);

end;

end;

structure BasicMultithreading: BASIC_MULTITHREADING = Multithreading;

open BasicMultithreading;