scala - 第一次调用 scala 函数比控制台上的后续调用花费更长的时间

Question

功能定义：

 import java.time.LocalDateTime
  import java.time.temporal._
  import java.time.ZoneId

  def iterateList(A: List[Int]) {
    val utcZone = ZoneId.of("UTC")
    val startTime = LocalDateTime.now().atZone(utcZone).toInstant
    val B = A.foreach(row => row)
    val endTime = LocalDateTime.now().atZone(utcZone).toInstant

    println(
      s"total time to iterate in micro-seconds :  ${startTime.until(endTime, ChronoUnit.MICROS)}")
  }




  scala> val aList = List.range(1,1000000)
aList: List[Int] = List(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119, 120, 121, 122, 123, 124, 125, 126, 127, 128, 129, 130, 131, 132, 133, 134, 135, 136, 137, 138, 139, 140, 141, 142, 143, 144, 145, 146, 147, 148, 149, 150, 151, 152, 153, 154, 155, 156, 157, 158, 159, 160, 161, 162, 163, 164, 165, 166, 167, 168, 169, 170, 171, ...

为什么第一次调用函数需要很长时间，而后续调用在 sbt-console 中需要 <50% 的时间？

scala> iterateList(aList)
total time to iterate in micro-seconds :  29000

scala> iterateList(aList)
total time to iterate in micro-seconds :  12000

scala> iterateList(aList)
total time to iterate in micro-seconds :  13000

标签： scalatime-complexity