Scala example source code file (ResizableParArrayCombiner.scala)

This example Scala source code file (ResizableParArrayCombiner.scala) is included in my "Source Code Warehouse" project. The intent of this project is to help you more easily find Scala source code examples by using tags.

All credit for the original source code belongs to scala-lang.org; I'm just trying to make examples easier to find. (For my Scala work, see my Scala examples and tutorials.)

Scala tags/keywords

array, arraybuffer, collection, copychaintoarray, environmentpassingcombiner, exposedarraybuffer, generics, int, lazycombiner, list, mutable, parallel, pararray, resizablepararraycombiner

The ResizableParArrayCombiner.scala Scala example source code

/*                     __                                               *\
**     ________ ___   / /  ___     Scala API                            **
**    / __/ __// _ | / /  / _ |    (c) 2003-2013, LAMP/EPFL             **
**  __\ \/ /__/ __ |/ /__/ __ |    http://scala-lang.org/               **
** /____/\___/_/ |_/____/_/ | |                                         **
**                          |/                                          **
\*                                                                      */

package scala
package collection.parallel.mutable



import scala.collection.generic.Sizing
import scala.collection.mutable.ArraySeq
import scala.collection.mutable.ArrayBuffer
import scala.collection.parallel.TaskSupport
import scala.collection.parallel.unsupportedop
import scala.collection.parallel.Combiner
import scala.collection.parallel.Task



/** An array combiner that uses a chain of arraybuffers to store elements. */
trait ResizableParArrayCombiner[T] extends LazyCombiner[T, ParArray[T], ExposedArrayBuffer[T]] {

  override def sizeHint(sz: Int) = if (chain.length == 1) chain(0).sizeHint(sz)

  // public method with private[mutable] type ExposedArrayBuffer in parameter type; cannot be overridden.
  final def newLazyCombiner(c: ArrayBuffer[ExposedArrayBuffer[T]]) = ResizableParArrayCombiner(c)

  def allocateAndCopy = if (chain.size > 1) {
    val arrayseq = new ArraySeq[T](size)
    val array = arrayseq.array.asInstanceOf[Array[Any]]

    combinerTaskSupport.executeAndWaitResult(new CopyChainToArray(array, 0, size))

    new ParArray(arrayseq)
  } else { // optimisation if there is only 1 array
    new ParArray(new ExposedArraySeq[T](chain(0).internalArray, size))
  }

  override def toString = "ResizableParArrayCombiner(" + size + "): " //+ chain

  /* tasks */

  class CopyChainToArray(array: Array[Any], offset: Int, howmany: Int) extends Task[Unit, CopyChainToArray] {
    var result = ()
    def leaf(prev: Option[Unit]) = if (howmany > 0) {
      var totalleft = howmany
      val (stbuff, stind) = findStart(offset)
      var buffind = stbuff
      var ind = stind
      var arrayIndex = offset
      while (totalleft > 0) {
        val currbuff = chain(buffind)
        val chunksize = if (totalleft < (currbuff.size - ind)) totalleft else currbuff.size - ind
        val until = ind + chunksize

        copyChunk(currbuff.internalArray, ind, array, arrayIndex, until)
        arrayIndex += chunksize
        ind += chunksize

        totalleft -= chunksize
        buffind += 1
        ind = 0
      }
    }
    private def copyChunk(buffarr: Array[AnyRef], buffStart: Int, ra: Array[Any], arrayStart: Int, until: Int) {
      Array.copy(buffarr, buffStart, ra, arrayStart, until - buffStart)
    }
    private def findStart(pos: Int) = {
      var left = pos
      var buffind = 0
      while (left >= chain(buffind).size) {
        left -= chain(buffind).size
        buffind += 1
      }
      (buffind, left)
    }
    def split = {
      val fp = howmany / 2
      List(new CopyChainToArray(array, offset, fp), new CopyChainToArray(array, offset + fp, howmany - fp))
    }
    def shouldSplitFurther = howmany > scala.collection.parallel.thresholdFromSize(size, combinerTaskSupport.parallelismLevel)
  }
}

object ResizableParArrayCombiner {
  def apply[T](c: ArrayBuffer[ExposedArrayBuffer[T]]): ResizableParArrayCombiner[T] = {
    new { val chain = c } with ResizableParArrayCombiner[T] // was: with EnvironmentPassingCombiner[T, ParArray[T]]
  }
  def apply[T](): ResizableParArrayCombiner[T] = apply(new ArrayBuffer[ExposedArrayBuffer[T]] += new ExposedArrayBuffer[T])
}