src/Pure/Concurrent/par_list.ML
author haftmann
Thu Oct 22 13:48:06 2009 +0200 (2009-10-22)
changeset 33063 4d462963a7db
parent 32614 fef7022dc5ab
child 35393 2f83aa48d696
permissions -rw-r--r--
map_range (and map_index) combinator
     1 (*  Title:      Pure/Concurrent/par_list.ML
     2     Author:     Makarius
     3 
     4 Parallel list combinators.
     5 
     6 Notes:
     7 
     8   * These combinators only make sense if the operator (function or
     9     predicate) applied to the list of operands takes considerable
    10     time.  The overhead of scheduling is significantly higher than
    11     just traversing the list of operands sequentially.
    12 
    13   * The order of operator application is non-deterministic.  Watch out
    14     for operators that have side-effects or raise exceptions!
    15 *)
    16 
    17 signature PAR_LIST =
    18 sig
    19   val map: ('a -> 'b) -> 'a list -> 'b list
    20   val get_some: ('a -> 'b option) -> 'a list -> 'b option
    21   val find_some: ('a -> bool) -> 'a list -> 'a option
    22   val exists: ('a -> bool) -> 'a list -> bool
    23   val forall: ('a -> bool) -> 'a list -> bool
    24 end;
    25 
    26 structure Par_List: PAR_LIST =
    27 struct
    28 
    29 fun raw_map f xs =
    30   if Multithreading.enabled () then
    31     let val group = Task_Queue.new_group (Future.worker_group ())
    32     in Future.join_results (map (fn x => Future.fork_group group (fn () => f x)) xs) end
    33   else map (Exn.capture f) xs;
    34 
    35 fun map f xs = Exn.release_first (raw_map f xs);
    36 
    37 fun get_some f xs =
    38   let
    39     exception FOUND of 'b option;
    40     fun found (Exn.Exn (FOUND some)) = some
    41       | found _ = NONE;
    42     val results = raw_map (fn x => (case f x of NONE => () | some => raise FOUND some)) xs;
    43   in
    44     (case get_first found results of
    45       SOME y => SOME y
    46     | NONE => (Exn.release_first results; NONE))
    47   end;
    48 
    49 fun find_some P = get_some (fn x => if P x then SOME x else NONE);
    50 
    51 fun exists P = is_some o get_some (fn x => if P x then SOME () else NONE);
    52 fun forall P = not o exists (not o P);
    53 
    54 end;