关于jvm：为什么独立代码块的执行时间取决于Scala中的执行顺序？

Why do the execution time of independent code blocks depend on execution order in Scala?

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我有一个用scala编写的程序。我想测量不同独立代码块的执行时间。当我以明显的方式(即在每个块之前和之后插入System.nanoTime())时，我观察到执行时间取决于块的顺序。前几个街区的时间总是比其他街区多。

我创造了一个复制这种行为的最低限度的例子。所有代码块都是相同的，为了简单起见，对于整数数组调用hashCode()。

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package experiments

import scala.util.Random

/**
* Measuring execution time of a code block
*
* Minimalistic example
*/
object CodeBlockMeasurement {

def main(args: Array[String]): Unit = {
val numRecords = args(0).toInt
// number of independent measurements
val iterations = args(1).toInt

// Changes results a little bit, but not too much
// val records2 = Array.fill[Int](1)(0)
// records2.foreach(x => {})

for (_ <- 1 to iterations) {
measure(numRecords)
}
}

def measure(numRecords: Int): Unit = {
// using a new array every time
val records = Array.fill[Int](numRecords)(new Random().nextInt())
// block of code to be measured
def doSomething(): Unit = {
records.foreach(k => k.hashCode())
}
// measure execution time of the code-block
elapsedTime(doSomething(),"HashCodeExperiment")
}

def elapsedTime(block: => Unit, name: String): Unit = {
val t0 = System.nanoTime()
val result = block
val t1 = System.nanoTime()
// print out elapsed time in milliseconds
println(s"$name took ${(t1 - t0).toDouble / 1000000} ms")
}
}

在用numRecords = 100000和iterations = 10运行程序之后，我的控制台如下所示：

HashCodeExperiment took 14.630283 ms
HashCodeExperiment took 7.125693 ms
HashCodeExperiment took 0.368151 ms
HashCodeExperiment took 0.431628 ms
HashCodeExperiment took 0.086455 ms
HashCodeExperiment took 0.056458 ms
HashCodeExperiment took 0.055138 ms
HashCodeExperiment took 0.062997 ms
HashCodeExperiment took 0.063736 ms
HashCodeExperiment took 0.056682 ms

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有人能解释为什么吗？不应该都是一样的吗？哪个是真正的执行时间？

谢谢，彼得

Environment parameters:
OS: ubuntu 14.04 LTS (64 bit)
IDE: IntelliJ IDEA 2016.1.1 (IU-145.597)
Scala: 2.11.7

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