(*  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 dequeue: Thread.thread -> queue -> (task * group * (unit -> bool)) option * queue

  val cancel: group -> queue -> Thread.thread list * queue

  val finish: task -> queue -> queue

end;

structure TaskQueue: TASK_QUEUE =

struct

(* identifiers *)

datatype task = Task of serial;

datatype group = Group of serial;

fun new_group () = Group (serial ());

fun str_of_task (Task i) = string_of_int i;

fun str_of_group (Group i) = string_of_int i;

(* jobs *)

datatype job =

  Job of bool * (bool -> bool) |

  Running of Thread.thread;

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

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;

(* queue of grouped jobs *)

datatype queue = Queue of

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

  jobs: jobs,                                             (*job dependency graph*)

  cache: (task * group * (unit -> bool)) Queue.T option}; (*cache of ready tasks*)

fun make_queue groups jobs cache =

  Queue {groups = groups, jobs = jobs, cache = cache};

val empty = make_queue Inttab.empty IntGraph.empty NONE;

(* queue operations *)

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;

    fun add_dep (Task dep) G = IntGraph.add_edge_acyclic (dep, id) G

      handle IntGraph.UNDEF _ => G;

    val jobs' = jobs |> IntGraph.new_node (id, (group, Job (true, job))) |> fold add_dep deps;

  in (task, make_queue groups' jobs' NONE) end;

fun dequeue thread (queue as Queue {groups, jobs, cache}) =

  let

    fun add_ready (id, ((group, Job (ok, job)), ([], _))) =

          Queue.enqueue (Task id, group, (fn () => job ok))

      | add_ready _ = I;

    val ready =

      (case cache of

        SOME ready => ready

      | NONE => IntGraph.fold add_ready jobs Queue.empty);

  in

    (case try Queue.dequeue ready of

      NONE => (NONE, make_queue groups jobs (SOME ready))

    | SOME (result, ready') =>

        let val jobs' = map_job (#1 result) (K (Running thread)) jobs

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

  end;

(* termination *)

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

  let

    val tasks = Inttab.lookup_list groups gid;

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

    val jobs' = fold (fn task =>

        (case get_job jobs task of

          Job (true, job) => map_job task (K (Job (false, job)))

        | _ => I)) tasks jobs;

  in (running, make_queue groups jobs' NONE) 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' NONE end;

end;