src/Pure/Concurrent/par_list.scala

tuned signature;

/*  Title:      Pure/Concurrent/par_list.scala
    Author:     Makarius

Parallel list combinators.
*/


package isabelle


object Par_List {
  def managed_results[A, B](
    f: A => B,
    xs: List[A],
    sequential: Boolean = false
  ) : List[Exn.Result[B]] = {
    if (sequential || xs.isEmpty || xs.tail.isEmpty) xs.map(x => Exn.capture { f(x) })
    else {
      val state = Synchronized[(List[Future[B]], Boolean)]((Nil, false))

      def cancel_other(self: Int = -1): Unit =
        state.change { case (futures, canceled) =>
          if (!canceled) {
            for ((future, i) <- futures.iterator.zipWithIndex if i != self)
              future.cancel()
          }
          (futures, true)
        }

      try {
        state.change(_ =>
          (xs.iterator.zipWithIndex.map({ case (x, self) =>
            Future.fork {
              Exn.capture { f(x) } match {
                case Exn.Exn(exn) => cancel_other(self); throw exn
                case Exn.Res(res) => res
              }
            }
          }).toList, false))

        state.value._1.map(_.join_result)
      }
      finally { cancel_other() }
    }
  }

  def map[A, B](f: A => B, xs: List[A], sequential: Boolean = false): List[B] =
    Exn.release_first(managed_results(f, xs, sequential = sequential))

  private class Found(val res: Any) extends Exception

  def get_some[A, B](f: A => Option[B], xs: List[A]): Option[B] = {
    val results =
      managed_results(
        (x: A) => f(x) match { case None => () case Some(y) => throw new Found(y) }, xs)
    results.collectFirst({
      case Exn.Exn(found) if found.isInstanceOf[Found] =>
        found.asInstanceOf[Found].res.asInstanceOf[B]
    }) match {
      case None => Exn.release_first(results); None
      case some => some
    }
  }

  def find_some[A](P: A => Boolean, xs: List[A]): Option[A] =
    get_some((x: A) => if (P(x)) Some(x) else None, xs)

  def exists[A](P: A => Boolean, xs: List[A]): Boolean = find_some(P, xs).isDefined
  def forall[A](P: A => Boolean, xs: List[A]): Boolean = !exists((x: A) => !P(x), xs)
}