(*  Title:      Pure/Concurrent/task_queue.ML

    ID:         $Id$

    Author:     Makarius

Ordered queue of grouped tasks.

*)

signature TASK_QUEUE =

sig

  eqtype task

  eqtype group

  val new_group: unit -> group

  val str_of_task: task -> string

  val str_of_group: group -> string

  type queue

  val empty: queue

  val enqueue: group -> task list -> (bool -> bool) -> queue -> task * queue

  val depend: task list -> task -> queue -> queue

  val dequeue: queue -> (task * group * (unit -> bool)) option * queue

  val dequeue_towards: task list -> queue -> (task * group * (unit -> bool)) option * queue

  val interrupt: queue -> task -> unit

  val interrupt_external: queue -> string -> unit

  val finish: task -> queue -> queue

  val cancel: queue -> group -> bool

end;

structure TaskQueue: TASK_QUEUE =

struct

(* identifiers *)

datatype task = Task of serial;

fun str_of_task (Task i) = string_of_int i;

datatype group = Group of serial * bool ref;

fun new_group () = Group (serial (), ref true);

fun str_of_group (Group (i, ref ok)) =

  if ok then string_of_int i else enclose "(" ")" (string_of_int i);

(* jobs *)

datatype job =

  Job of bool -> bool |

  Running of Thread.thread;

type jobs = (group * job) IntGraph.T;

fun defined_job (jobs: jobs) (Task id) = can (IntGraph.get_node jobs) id;

fun get_group (jobs: jobs) (Task id) = #1 (IntGraph.get_node jobs id);

fun get_job (jobs: jobs) (Task id) = #2 (IntGraph.get_node jobs id);

fun map_job (Task id) f (jobs: jobs) = IntGraph.map_node id (apsnd f) jobs;

fun add_job (Task id) (Task dep) (jobs: jobs) =

  IntGraph.add_edge_acyclic (dep, id) jobs handle IntGraph.UNDEF _ => jobs;

(* queue of grouped jobs *)

datatype queue = Queue of

 {groups: task list Inttab.table,   (*groups with presently active members*)

  jobs: jobs};                      (*job dependency graph*)

fun make_queue groups jobs = Queue {groups = groups, jobs = jobs};

val empty = make_queue Inttab.empty IntGraph.empty;

(* enqueue *)

fun enqueue (group as Group (gid, _)) deps job (Queue {groups, jobs}) =

  let

    val id = serial ();

    val task = Task id;

    val groups' = Inttab.cons_list (gid, task) groups;

    val jobs' = jobs

      |> IntGraph.new_node (id, (group, Job job)) |> fold (add_job task) deps;

  in (task, make_queue groups' jobs') end;

fun depend deps task (Queue {groups, jobs}) =

  make_queue groups (fold (add_job task) deps jobs);

(* dequeue *)

fun dequeue_if P (queue as Queue {groups, jobs}) =

  let

    fun ready (id, ((group as Group (_, ref ok), Job job), ([], _))) =

          if P id then SOME (Task id, group, (fn () => job ok)) else NONE

      | ready _ = NONE;

  in

    (case IntGraph.get_first ready jobs of

      NONE => (NONE, queue)

    | SOME result =>

        let val jobs' = map_job (#1 result) (K (Running (Thread.self ()))) jobs

        in (SOME result, make_queue groups jobs') end)

  end;

val dequeue = dequeue_if (K true);

fun dequeue_towards tasks (queue as Queue {jobs, ...}) =

  let val ids = tasks

    |> map_filter (fn task as Task id => if defined_job jobs task then SOME id else NONE)

  in dequeue_if (member (op =) (IntGraph.all_preds jobs ids)) queue end;

(* sporadic interrupts *)

fun interrupt_thread thread = Thread.interrupt thread handle Thread _ => ();

fun interrupt (Queue {jobs, ...}) task =

  (case try (get_job jobs) task of SOME (Running thread) => interrupt_thread thread | _ => ());

fun interrupt_external queue str =

  (case Int.fromString str of SOME id => interrupt queue (Task id) | NONE => ());

(* termination *)

fun cancel (Queue {groups, jobs}) (group as Group (gid, ok)) =

  let

    val _ = ok := false;  (*invalidate any future group members*)

    val tasks = Inttab.lookup_list groups gid;

    val running = fold (get_job jobs #> (fn Running thread => cons thread | _ => I)) tasks [];

    val _ = List.app interrupt_thread running;

  in null running end;

fun finish (task as Task id) (Queue {groups, jobs}) =

  let

    val Group (gid, _) = get_group jobs task;

    val groups' = Inttab.remove_list (op =) (gid, task) groups;

    val jobs' = IntGraph.del_nodes [id] jobs;

  in make_queue groups' jobs' end;

end;