src/Pure/Concurrent/task_queue.ML

tuned message_text;

(*  Title:      Pure/Concurrent/task_queue.ML
    Author:     Makarius

Ordered queue of grouped tasks.
*)

signature TASK_QUEUE =
sig
  eqtype task
  val new_task: int -> task
  val pri_of_task: task -> int
  val str_of_task: task -> string
  eqtype group
  val new_group: unit -> group
  val invalidate_group: group -> unit
  val str_of_group: group -> string
  type queue
  val empty: queue
  val is_empty: queue -> bool
  val enqueue: group -> task list -> int -> (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)) * task list) 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 Task_Queue: TASK_QUEUE =
struct

(* tasks *)

datatype task = Task of int * serial;
fun new_task pri = Task (pri, serial ());

fun pri_of_task (Task (pri, _)) = pri;
fun str_of_task (Task (_, i)) = string_of_int i;

fun task_ord (Task t1, Task t2) = prod_ord (rev_order o int_ord) int_ord (t1, t2);
structure Task_Graph = GraphFun(type key = task val ord = task_ord);


(* groups *)

datatype group = Group of serial * bool ref;

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

fun invalidate_group (Group (_, ok)) = ok := false;

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) Task_Graph.T;

fun get_group (jobs: jobs) task = #1 (Task_Graph.get_node jobs task);
fun get_job (jobs: jobs) task = #2 (Task_Graph.get_node jobs task);
fun map_job task f (jobs: jobs) = Task_Graph.map_node task (apsnd f) jobs;

fun add_job task dep (jobs: jobs) =
  Task_Graph.add_edge (dep, task) jobs handle Task_Graph.UNDEF _ => jobs;

fun add_job_acyclic task dep (jobs: jobs) =
  Task_Graph.add_edge_acyclic (dep, task) jobs handle Task_Graph.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 Task_Graph.empty;
fun is_empty (Queue {jobs, ...}) = Task_Graph.is_empty jobs;


(* enqueue *)

fun enqueue (group as Group (gid, _)) deps pri job (Queue {groups, jobs}) =
  let
    val task = new_task pri;
    val groups' = Inttab.cons_list (gid, task) groups;
    val jobs' = jobs
      |> Task_Graph.new_node (task, (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_acyclic task) deps jobs);


(* dequeue *)

local

fun dequeue_result NONE queue = (NONE, queue)
  | dequeue_result (SOME (result as (task, _, _))) (Queue {groups, jobs}) =
      (SOME result, make_queue groups (map_job task (K (Running (Thread.self ()))) jobs));

in

fun dequeue (queue as Queue {jobs, ...}) =
  let
    fun ready (task, ((group as Group (_, ref ok), Job job), ([], _))) =
          SOME (task, group, (fn () => job ok))
      | ready _ = NONE;
  in dequeue_result (Task_Graph.get_first ready jobs) queue end;

fun dequeue_towards tasks (queue as Queue {jobs, ...}) =
  let
    val tasks' = filter (can (Task_Graph.get_node jobs)) tasks;

    fun ready task =
      (case Task_Graph.get_node jobs task of
        (group as Group (_, ref ok), Job job) =>
          if null (Task_Graph.imm_preds jobs task) then SOME (task, group, (fn () => job ok))
          else NONE
      | _ => NONE);
  in
    (case dequeue_result (get_first ready (Task_Graph.all_preds jobs tasks')) queue of
      (NONE, queue') => (NONE, queue')
    | (SOME work, queue') => (SOME (work, tasks'), queue'))
  end;

end;


(* sporadic interrupts *)

fun interrupt (Queue {jobs, ...}) task =
  (case try (get_job jobs) task of SOME (Running thread) => SimpleThread.interrupt thread | _ => ());

fun interrupt_external (queue as Queue {jobs, ...}) str =
  (case Int.fromString str of
    SOME i =>
      (case Task_Graph.get_first
          (fn (task as Task (_, j), _) => if i = j then SOME task else NONE) jobs
        of SOME task => interrupt queue task | NONE => ())
  | NONE => ());


(* misc operations *)

fun cancel (Queue {groups, jobs, ...}) (group as Group (gid, _)) =
  let
    val _ = invalidate_group group;
    val tasks = Inttab.lookup_list groups gid;
    val running = fold (get_job jobs #> (fn Running thread => cons thread | _ => I)) tasks [];
    val _ = List.app SimpleThread.interrupt running;
  in null running end;

fun finish task (Queue {groups, jobs}) =
  let
    val Group (gid, _) = get_group jobs task;
    val groups' = Inttab.remove_list (op =) (gid, task) groups;
    val jobs' = Task_Graph.del_node task jobs;
  in make_queue groups' jobs' end;

end;