benchmark-iterator.scala

import java.util.concurrent.TimeUnit
import org.openjdk.jmh.annotations._
import scala.util.Random

@State(Scope.Thread)
@BenchmarkMode(Array(Mode.Throughput))
@OutputTimeUnit(TimeUnit.SECONDS)
class IteratorBenchmark {
  @Param(Array("8"))
  var cycles = 0

  @Param(Array("8192"))
  var size = 0

  var arrayRef: Array[Int] = null
  var listRef: List[Int] = null

  @Setup
  def setup(): Unit = {
    arrayRef = (0 until size).map(_ => Random.nextInt()).toArray
    listRef = (0 until size).map(_ => Random.nextInt()).toList
  }

  @Benchmark
  def array: Option[Long] = {
    var sum = 0
    var cycle = 0
    while (cycle < cycles) {
      var idx = 0
      while (idx < arrayRef.length) {
        sum += arrayRef(idx)
        idx += 1
      }
      cycle += 1
    }
    Option(sum)
  }

  @Benchmark
  def arrayIter: Option[Long] = {
    var sum = 0
    var cycle = 0
    while (cycle < cycles) {
      val cursor = arrayRef.iterator
      while (cursor.hasNext) sum += cursor.next()
      cycle += 1
    }
    Option(sum)
  }

  @Benchmark
  def list: Option[Long] = {
    var sum = 0
    var cycle = 0
    while (cycle < cycles) {
      var cursor = listRef
      while (cursor ne Nil) {
        sum += cursor.head
        cursor = cursor.tail
      }
      cycle += 1
    }
    Option(sum)
  }

  @Benchmark
  def listIter: Option[Long] = {
    var sum = 0
    var cycle = 0
    while (cycle < cycles) {
      val cursor = listRef.iterator
      while (cursor.hasNext) sum += cursor.next()
      cycle += 1
    }
    Option(sum)
  }
}