wenzelm@28156
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(* Title: Pure/Concurrent/future.ML
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wenzelm@28156
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Author: Makarius
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wenzelm@32250
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Future values, see also
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http://www4.in.tum.de/~wenzelm/papers/parallel-isabelle.pdf
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wenzelm@28201
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Notes:
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* Futures are similar to delayed evaluation, i.e. delay/force is
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wenzelm@28201
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generalized to fork/join (and variants). The idea is to model
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wenzelm@28201
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parallel value-oriented computations, but *not* communicating
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processes.
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wenzelm@28201
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* Futures are grouped; failure of one group member causes the whole
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wenzelm@32220
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group to be interrupted eventually. Groups are block-structured.
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wenzelm@28201
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wenzelm@28201
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* Forked futures are evaluated spontaneously by a farm of worker
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threads in the background; join resynchronizes the computation and
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delivers results (values or exceptions).
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wenzelm@28201
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wenzelm@28201
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* The pool of worker threads is limited, usually in correlation with
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wenzelm@28201
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the number of physical cores on the machine. Note that allocation
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of runtime resources is distorted either if workers yield CPU time
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(e.g. via system sleep or wait operations), or if non-worker
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threads contend for significant runtime resources independently.
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*)
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signature FUTURE =
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sig
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wenzelm@29120
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type task = Task_Queue.task
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type group = Task_Queue.group
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wenzelm@32074
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val is_worker: unit -> bool
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val worker_group: unit -> Task_Queue.group option
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type 'a future
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val task_of: 'a future -> task
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val group_of: 'a future -> group
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val peek: 'a future -> 'a Exn.result option
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val is_finished: 'a future -> bool
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wenzelm@29002
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val value: 'a -> 'a future
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wenzelm@28979
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val fork_group: group -> (unit -> 'a) -> 'a future
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wenzelm@32729
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val fork_deps_pri: 'b future list -> int -> (unit -> 'a) -> 'a future
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wenzelm@28979
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val fork_deps: 'b future list -> (unit -> 'a) -> 'a future
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val fork_pri: int -> (unit -> 'a) -> 'a future
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val fork: (unit -> 'a) -> 'a future
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val join_results: 'a future list -> 'a Exn.result list
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val join_result: 'a future -> 'a Exn.result
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val join: 'a future -> 'a
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val map: ('a -> 'b) -> 'a future -> 'b future
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wenzelm@30621
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val interruptible_task: ('a -> 'b) -> 'a -> 'b
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wenzelm@29431
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val cancel_group: group -> unit
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val cancel: 'a future -> unit
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val shutdown: unit -> unit
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end;
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structure Future: FUTURE =
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struct
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(** future values **)
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(* identifiers *)
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type task = Task_Queue.task;
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type group = Task_Queue.group;
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local
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val tag = Universal.tag () : (string * task * group) option Universal.tag;
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in
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fun thread_data () = the_default NONE (Thread.getLocal tag);
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fun setmp_thread_data data f x =
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Library.setmp_thread_data tag (thread_data ()) (SOME data) f x;
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end;
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val is_worker = is_some o thread_data;
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val worker_group = Option.map #3 o thread_data;
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(* datatype future *)
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datatype 'a future = Future of
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{task: task,
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group: group,
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result: 'a Exn.result option Synchronized.var};
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fun task_of (Future {task, ...}) = task;
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fun group_of (Future {group, ...}) = group;
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fun result_of (Future {result, ...}) = result;
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wenzelm@32592
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fun peek x = Synchronized.value (result_of x);
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wenzelm@28558
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fun is_finished x = is_some (peek x);
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wenzelm@28320
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fun value x = Future
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{task = Task_Queue.new_task 0,
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group = Task_Queue.new_group NONE,
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result = Synchronized.var "future" (SOME (Exn.Result x))};
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wenzelm@29002
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wenzelm@28177
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(** scheduling **)
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(* global state *)
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val queue = Unsynchronized.ref Task_Queue.empty;
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val next = Unsynchronized.ref 0;
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val workers = Unsynchronized.ref ([]: (Thread.thread * bool) list);
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val scheduler = Unsynchronized.ref (NONE: Thread.thread option);
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val excessive = Unsynchronized.ref 0;
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val canceled = Unsynchronized.ref ([]: Task_Queue.group list);
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val do_shutdown = Unsynchronized.ref false;
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(* synchronization *)
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val scheduler_event = ConditionVar.conditionVar ();
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val work_available = ConditionVar.conditionVar ();
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val work_finished = ConditionVar.conditionVar ();
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local
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val lock = Mutex.mutex ();
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in
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wenzelm@28575
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fun SYNCHRONIZED name = SimpleThread.synchronized name lock;
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fun wait cond = (*requires SYNCHRONIZED*)
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Multithreading.sync_wait NONE NONE cond lock;
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wenzelm@28206
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wenzelm@32298
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fun wait_timeout timeout cond = (*requires SYNCHRONIZED*)
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Multithreading.sync_wait NONE (SOME (Time.+ (Time.now (), timeout))) cond lock;
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wenzelm@32219
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fun signal cond = (*requires SYNCHRONIZED*)
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ConditionVar.signal cond;
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fun broadcast cond = (*requires SYNCHRONIZED*)
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ConditionVar.broadcast cond;
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fun broadcast_work () = (*requires SYNCHRONIZED*)
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(ConditionVar.broadcast work_available;
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ConditionVar.broadcast work_finished);
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end;
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wenzelm@32119
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(* execute future jobs *)
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wenzelm@32119
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wenzelm@32119
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fun future_job group (e: unit -> 'a) =
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let
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val result = Synchronized.var "future" (NONE: 'a Exn.result option);
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fun job ok =
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let
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val res =
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if ok then
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Exn.capture (fn () =>
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Multithreading.with_attributes Multithreading.private_interrupts (fn _ => e ())) ()
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else Exn.Exn Exn.Interrupt;
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val _ = Synchronized.change result
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(fn NONE => SOME res
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| SOME _ => raise Fail "Duplicate assignment of future value");
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in
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(case res of
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Exn.Exn exn => (Task_Queue.cancel_group group exn; false)
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| Exn.Result _ => true)
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end;
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in (result, job) end;
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fun do_cancel group = (*requires SYNCHRONIZED*)
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wenzelm@32738
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(Unsynchronized.change canceled (insert Task_Queue.eq_group group);
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broadcast scheduler_event);
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wenzelm@29341
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wenzelm@29370
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fun execute name (task, group, jobs) =
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let
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val valid = not (Task_Queue.is_canceled group);
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val ok = setmp_thread_data (name, task, group) (fn () =>
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wenzelm@29384
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fold (fn job => fn ok => job valid andalso ok) jobs true) ();
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val _ = SYNCHRONIZED "finish" (fn () =>
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wenzelm@32219
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let
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val maximal = Unsynchronized.change_result queue (Task_Queue.finish task);
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wenzelm@32219
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val _ =
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if ok then ()
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else if Task_Queue.cancel (! queue) group then ()
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wenzelm@32219
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else do_cancel group;
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wenzelm@32219
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val _ = broadcast work_finished;
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wenzelm@32219
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val _ = if maximal then () else broadcast work_available;
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in () end);
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in () end;
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wenzelm@28167
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wenzelm@32250
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(* worker activity *)
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wenzelm@32250
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fun count_active () = (*requires SYNCHRONIZED*)
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fold (fn (_, active) => fn i => if active then i + 1 else i) (! workers) 0;
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wenzelm@32250
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wenzelm@32250
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fun change_active active = (*requires SYNCHRONIZED*)
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wenzelm@32738
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Unsynchronized.change workers
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wenzelm@32738
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(AList.update Thread.equal (Thread.self (), active));
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wenzelm@28167
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(* worker threads *)
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fun worker_wait cond = (*requires SYNCHRONIZED*)
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wenzelm@32290
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(change_active false; wait cond; change_active true);
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wenzelm@28162
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wenzelm@29120
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fun worker_next () = (*requires SYNCHRONIZED*)
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wenzelm@28167
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if ! excessive > 0 then
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wenzelm@32738
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(Unsynchronized.dec excessive;
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wenzelm@32738
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Unsynchronized.change workers
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wenzelm@32738
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(filter_out (fn (thread, _) => Thread.equal (thread, Thread.self ())));
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wenzelm@32219
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broadcast scheduler_event;
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NONE)
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wenzelm@32250
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else if count_active () > Multithreading.max_threads_value () then
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wenzelm@32250
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(worker_wait scheduler_event; worker_next ())
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else
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wenzelm@32738
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(case Unsynchronized.change_result queue (Task_Queue.dequeue (Thread.self ())) of
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wenzelm@32219
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NONE => (worker_wait work_available; worker_next ())
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wenzelm@28166
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| some => some);
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wenzelm@28167
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fun worker_loop name =
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wenzelm@32127
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(case SYNCHRONIZED name (fn () => worker_next ()) of
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wenzelm@29120
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NONE => ()
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wenzelm@28167
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| SOME work => (execute name work; worker_loop name));
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wenzelm@28156
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wenzelm@28167
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fun worker_start name = (*requires SYNCHRONIZED*)
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wenzelm@32738
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Unsynchronized.change workers (cons (SimpleThread.fork false (fn () =>
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wenzelm@32252
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(broadcast scheduler_event; worker_loop name)), true));
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wenzelm@28156
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wenzelm@28156
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wenzelm@28156
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(* scheduler *)
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wenzelm@28156
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wenzelm@32738
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val last_status = Unsynchronized.ref Time.zeroTime;
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wenzelm@32252
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val next_status = Time.fromMilliseconds 500;
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wenzelm@32252
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val next_round = Time.fromMilliseconds 50;
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wenzelm@32226
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wenzelm@28206
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fun scheduler_next () = (*requires SYNCHRONIZED*)
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wenzelm@28156
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let
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wenzelm@32226
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(*queue and worker status*)
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wenzelm@32226
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val _ =
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wenzelm@32226
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let val now = Time.now () in
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wenzelm@32226
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if Time.> (Time.+ (! last_status, next_status), now) then ()
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wenzelm@32226
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else
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wenzelm@32226
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(last_status := now; Multithreading.tracing 1 (fn () =>
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wenzelm@32226
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let
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wenzelm@32226
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val {ready, pending, running} = Task_Queue.status (! queue);
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wenzelm@32226
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val total = length (! workers);
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wenzelm@32250
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val active = count_active ();
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wenzelm@32226
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in
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wenzelm@32617
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"SCHEDULE " ^ Time.toString now ^ ": " ^
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wenzelm@32226
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string_of_int ready ^ " ready, " ^
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wenzelm@32226
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string_of_int pending ^ " pending, " ^
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wenzelm@32226
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string_of_int running ^ " running; " ^
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wenzelm@32226
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string_of_int total ^ " workers, " ^
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wenzelm@32226
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string_of_int active ^ " active"
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wenzelm@32226
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end))
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wenzelm@32226
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end;
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wenzelm@32053
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wenzelm@28206
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(*worker threads*)
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wenzelm@28191
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val _ =
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wenzelm@32219
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if forall (Thread.isActive o #1) (! workers) then ()
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wenzelm@32115
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else
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wenzelm@32219
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(case List.partition (Thread.isActive o #1) (! workers) of
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wenzelm@32115
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(_, []) => ()
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wenzelm@32220
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| (alive, dead) =>
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wenzelm@32220
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(workers := alive; Multithreading.tracing 0 (fn () =>
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wenzelm@32220
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"SCHEDULE: disposed " ^ string_of_int (length dead) ^ " dead worker threads")));
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wenzelm@28191
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wenzelm@28206
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val m = if ! do_shutdown then 0 else Multithreading.max_threads_value ();
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wenzelm@32644
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val mm = if m = 9999 then 1 else m * 2;
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wenzelm@32219
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val l = length (! workers);
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wenzelm@32115
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val _ = excessive := l - mm;
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wenzelm@28203
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val _ =
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wenzelm@32115
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if mm > l then
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wenzelm@32738
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funpow (mm - l) (fn () =>
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wenzelm@32738
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worker_start ("worker " ^ string_of_int (Unsynchronized.inc next))) ()
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wenzelm@28203
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else ();
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wenzelm@28206
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wenzelm@28206
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(*canceled groups*)
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wenzelm@32225
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val _ =
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wenzelm@32225
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if null (! canceled) then ()
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wenzelm@32293
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else
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wenzelm@32293
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(Multithreading.tracing 1 (fn () =>
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wenzelm@32293
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string_of_int (length (! canceled)) ^ " canceled groups");
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wenzelm@32738
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Unsynchronized.change canceled (filter_out (Task_Queue.cancel (! queue)));
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wenzelm@32293
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broadcast_work ());
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wenzelm@28206
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wenzelm@32228
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(*delay loop*)
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wenzelm@32298
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val _ = Exn.release (wait_timeout next_round scheduler_event);
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wenzelm@32219
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wenzelm@28206
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(*shutdown*)
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wenzelm@32228
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val _ = if Task_Queue.is_empty (! queue) then do_shutdown := true else ();
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wenzelm@32219
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val continue = not (! do_shutdown andalso null (! workers));
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wenzelm@28206
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val _ = if continue then () else scheduler := NONE;
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wenzelm@32219
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val _ = broadcast scheduler_event;
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wenzelm@32298
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in continue end
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wenzelm@32298
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handle Exn.Interrupt =>
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wenzelm@32298
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(Multithreading.tracing 1 (fn () => "Interrupt");
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wenzelm@32299
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293 |
uninterruptible (fn _ => fn () => List.app do_cancel (Task_Queue.cancel_all (! queue))) ();
|
wenzelm@32298
|
294 |
scheduler_next ());
|
wenzelm@32298
|
295 |
|
wenzelm@28206
|
296 |
fun scheduler_loop () =
|
wenzelm@32298
|
297 |
Multithreading.with_attributes
|
wenzelm@32298
|
298 |
(Multithreading.sync_interrupts Multithreading.public_interrupts)
|
wenzelm@32298
|
299 |
(fn _ => while SYNCHRONIZED "scheduler" (fn () => scheduler_next ()) do ());
|
wenzelm@28191
|
300 |
|
wenzelm@28203
|
301 |
fun scheduler_active () = (*requires SYNCHRONIZED*)
|
wenzelm@28203
|
302 |
(case ! scheduler of NONE => false | SOME thread => Thread.isActive thread);
|
wenzelm@28203
|
303 |
|
wenzelm@32228
|
304 |
fun scheduler_check () = (*requires SYNCHRONIZED*)
|
wenzelm@32228
|
305 |
(do_shutdown := false;
|
wenzelm@32252
|
306 |
if scheduler_active () then ()
|
wenzelm@32252
|
307 |
else scheduler := SOME (SimpleThread.fork false scheduler_loop));
|
wenzelm@28191
|
308 |
|
wenzelm@28191
|
309 |
|
wenzelm@28191
|
310 |
|
wenzelm@29370
|
311 |
(** futures **)
|
wenzelm@29370
|
312 |
|
wenzelm@29370
|
313 |
(* fork *)
|
wenzelm@29370
|
314 |
|
wenzelm@29370
|
315 |
fun fork_future opt_group deps pri e =
|
wenzelm@29370
|
316 |
let
|
wenzelm@32122
|
317 |
val group =
|
wenzelm@32122
|
318 |
(case opt_group of
|
wenzelm@32122
|
319 |
SOME group => group
|
wenzelm@32122
|
320 |
| NONE => Task_Queue.new_group (worker_group ()));
|
wenzelm@29370
|
321 |
val (result, job) = future_job group e;
|
wenzelm@32250
|
322 |
val task = SYNCHRONIZED "enqueue" (fn () =>
|
wenzelm@32219
|
323 |
let
|
wenzelm@32738
|
324 |
val (task, minimal) =
|
wenzelm@32738
|
325 |
Unsynchronized.change_result queue (Task_Queue.enqueue group deps pri job);
|
wenzelm@32219
|
326 |
val _ = if minimal then signal work_available else ();
|
wenzelm@32228
|
327 |
val _ = scheduler_check ();
|
wenzelm@32219
|
328 |
in task end);
|
wenzelm@28166
|
329 |
in Future {task = task, group = group, result = result} end;
|
wenzelm@28162
|
330 |
|
wenzelm@29370
|
331 |
fun fork_group group e = fork_future (SOME group) [] 0 e;
|
wenzelm@32729
|
332 |
fun fork_deps_pri deps pri e = fork_future NONE (map task_of deps) pri e;
|
wenzelm@32729
|
333 |
fun fork_deps deps e = fork_deps_pri deps 0 e;
|
wenzelm@32729
|
334 |
fun fork_pri pri e = fork_deps_pri [] pri e;
|
wenzelm@32729
|
335 |
fun fork e = fork_deps [] e;
|
wenzelm@28162
|
336 |
|
wenzelm@28186
|
337 |
|
wenzelm@29370
|
338 |
(* join *)
|
wenzelm@28186
|
339 |
|
wenzelm@29551
|
340 |
local
|
wenzelm@29551
|
341 |
|
wenzelm@32119
|
342 |
fun get_result x =
|
wenzelm@32119
|
343 |
(case peek x of
|
wenzelm@32122
|
344 |
NONE => Exn.Exn (SYS_ERROR "unfinished future")
|
wenzelm@32122
|
345 |
| SOME (Exn.Exn Exn.Interrupt) =>
|
wenzelm@32122
|
346 |
Exn.Exn (Exn.EXCEPTIONS (Exn.flatten_list (Task_Queue.group_status (group_of x))))
|
wenzelm@32122
|
347 |
| SOME res => res);
|
wenzelm@28177
|
348 |
|
wenzelm@32224
|
349 |
fun join_wait x =
|
wenzelm@32257
|
350 |
Synchronized.guarded_access (result_of x) (fn NONE => NONE | some => SOME ((), some));
|
wenzelm@32224
|
351 |
|
wenzelm@32115
|
352 |
fun join_next deps = (*requires SYNCHRONIZED*)
|
wenzelm@32224
|
353 |
if null deps then NONE
|
wenzelm@32224
|
354 |
else
|
wenzelm@32738
|
355 |
(case Unsynchronized.change_result queue (Task_Queue.dequeue_towards (Thread.self ()) deps) of
|
wenzelm@32224
|
356 |
(NONE, []) => NONE
|
wenzelm@32224
|
357 |
| (NONE, deps') => (worker_wait work_finished; join_next deps')
|
wenzelm@32224
|
358 |
| (SOME work, deps') => SOME (work, deps'));
|
wenzelm@32115
|
359 |
|
wenzelm@32224
|
360 |
fun join_work deps =
|
wenzelm@32115
|
361 |
(case SYNCHRONIZED "join" (fn () => join_next deps) of
|
wenzelm@29551
|
362 |
NONE => ()
|
wenzelm@32224
|
363 |
| SOME (work, deps') => (execute "join" work; join_work deps'));
|
wenzelm@29551
|
364 |
|
wenzelm@29551
|
365 |
in
|
wenzelm@29551
|
366 |
|
wenzelm@29370
|
367 |
fun join_results xs =
|
wenzelm@29370
|
368 |
if forall is_finished xs then map get_result xs
|
wenzelm@32250
|
369 |
else if Multithreading.self_critical () then
|
wenzelm@32250
|
370 |
error "Cannot join future values within critical section"
|
wenzelm@29370
|
371 |
else uninterruptible (fn _ => fn () =>
|
wenzelm@32250
|
372 |
(if is_worker ()
|
wenzelm@32250
|
373 |
then join_work (map task_of xs)
|
wenzelm@32250
|
374 |
else List.app join_wait xs;
|
wenzelm@32250
|
375 |
map get_result xs)) ();
|
wenzelm@28186
|
376 |
|
wenzelm@29551
|
377 |
end;
|
wenzelm@29551
|
378 |
|
wenzelm@28647
|
379 |
fun join_result x = singleton join_results x;
|
wenzelm@28647
|
380 |
fun join x = Exn.release (join_result x);
|
wenzelm@28156
|
381 |
|
wenzelm@28979
|
382 |
|
wenzelm@29370
|
383 |
(* map *)
|
wenzelm@28191
|
384 |
|
wenzelm@29384
|
385 |
fun map_future f x =
|
wenzelm@29370
|
386 |
let
|
wenzelm@29384
|
387 |
val task = task_of x;
|
wenzelm@32122
|
388 |
val group = Task_Queue.new_group (SOME (group_of x));
|
wenzelm@29384
|
389 |
val (result, job) = future_job group (fn () => f (join x));
|
wenzelm@29384
|
390 |
|
wenzelm@32250
|
391 |
val extended = SYNCHRONIZED "extend" (fn () =>
|
wenzelm@29370
|
392 |
(case Task_Queue.extend task job (! queue) of
|
wenzelm@29370
|
393 |
SOME queue' => (queue := queue'; true)
|
wenzelm@29370
|
394 |
| NONE => false));
|
wenzelm@29370
|
395 |
in
|
wenzelm@29384
|
396 |
if extended then Future {task = task, group = group, result = result}
|
wenzelm@32119
|
397 |
else fork_future (SOME group) [task] (Task_Queue.pri_of_task task) (fn () => f (join x))
|
wenzelm@29370
|
398 |
end;
|
wenzelm@29370
|
399 |
|
wenzelm@29370
|
400 |
|
wenzelm@29431
|
401 |
(* cancellation *)
|
wenzelm@28202
|
402 |
|
wenzelm@30621
|
403 |
fun interruptible_task f x =
|
wenzelm@30621
|
404 |
if Multithreading.available then
|
wenzelm@30621
|
405 |
Multithreading.with_attributes
|
wenzelm@32074
|
406 |
(if is_worker ()
|
wenzelm@32298
|
407 |
then Multithreading.private_interrupts
|
wenzelm@32298
|
408 |
else Multithreading.public_interrupts)
|
wenzelm@32298
|
409 |
(fn _ => f x)
|
wenzelm@30621
|
410 |
else interruptible f x;
|
wenzelm@30621
|
411 |
|
wenzelm@32228
|
412 |
(*cancel: present and future group members will be interrupted eventually*)
|
wenzelm@32228
|
413 |
fun cancel_group group = SYNCHRONIZED "cancel" (fn () => do_cancel group);
|
wenzelm@29431
|
414 |
fun cancel x = cancel_group (group_of x);
|
wenzelm@28206
|
415 |
|
wenzelm@29370
|
416 |
|
wenzelm@32228
|
417 |
(* shutdown *)
|
wenzelm@29370
|
418 |
|
wenzelm@28203
|
419 |
fun shutdown () =
|
wenzelm@28276
|
420 |
if Multithreading.available then
|
wenzelm@28276
|
421 |
SYNCHRONIZED "shutdown" (fn () =>
|
wenzelm@32228
|
422 |
while scheduler_active () do
|
wenzelm@32252
|
423 |
(wait scheduler_event; broadcast_work ()))
|
wenzelm@28276
|
424 |
else ();
|
wenzelm@28203
|
425 |
|
wenzelm@29370
|
426 |
|
wenzelm@29370
|
427 |
(*final declarations of this structure!*)
|
wenzelm@29370
|
428 |
val map = map_future;
|
wenzelm@29370
|
429 |
|
wenzelm@28156
|
430 |
end;
|
wenzelm@28972
|
431 |
|
wenzelm@28972
|
432 |
type 'a future = 'a Future.future;
|
wenzelm@28972
|
433 |
|