Scala shell中的垃圾收集

Question

import scala.util.Random

def uuid = java.util.UUID.randomUUID.toString

def generateRandomList(size: Int): List[Float] = {
    List.fill(size)(Random.nextFloat)
}

val numDimensions = 1000
val numberToWrite = 20000

val out = for ( i <- 1 to numberToWrite) yield {
      val randomList = generateRandomList(numDimensions)
      (uuid, randomList)  // trying tuples insread
}

java.lang.OutOfMemoryError: GC overhead limit exceeded
  at java.lang.Float.valueOf(Float.java:433)
  at scala.runtime.BoxesRunTime.boxToFloat(BoxesRunTime.java:73)
  at $anonfun$generateRandomArray$1.apply(<console>:14)
  at scala.collection.generic.GenTraversableFactory.fill(GenTraversableFactory.scala:90)
  at .generateRandomArray(<console>:14)
  at $anonfun$1.apply(<console>:17)
  at $anonfun$1.apply(<console>:16)
  at scala.collection.TraversableLike$$anonfun$map$1.apply(TraversableLike.scala:234)
  at scala.collection.TraversableLike$$anonfun$map$1.apply(TraversableLike.scala:234)
  at scala.collection.immutable.Range.foreach(Range.scala:160)
  at scala.collection.TraversableLike$class.map(TraversableLike.scala:234)
  at scala.collection.AbstractTraversable.map(Traversable.scala:104)
  ... 20 elided

scala> val heapSize = Runtime.getRuntime().totalMemory(); // Get current size of heap in bytes
heapSize: Long = 212860928

scala> val heapMaxSize = Runtime.getRuntime().maxMemory(); // Get maximum size of heap in bytes. The heap cannot     grow beyond this size.// Any attempt will result in an OutOfMemoryException.

heapMaxSize: Long = 239075328

scala> val heapFreeSize = Runtime.getRuntime().freeMemory();  // Get amount of free memory within the heap in bytes.     This size will increase // after garbage collection and decrease as new objects are created.

heapFreeSize: Long = 152842176

尽管我的最大可用堆大小似乎大于我认为我需要的粗略内存量，但我还是尝试通过./scala-j-xmx2g来增加堆大小([4])。虽然这解决了我的问题，但最好知道是否有更好的方法来创建这种随机数据，从而避免我不得不增加JVM可用的内存？因此，我有以下三个问题，如果有人能回答，我将不胜感激：

>

在Scala中，尤其是在Scala shell中，垃圾回收何时发生？在上面的命令中，有什么可以收集，那么为什么要调用GC（对不起，第二部分可能表明我对GC缺乏了解）？

我对占用的内存量的粗略计算是否有效（当然，我预计列表和元组的开销会更大一些，但假设相对来说不会那么多）？如果是这样，为什么我的最大堆大小(239e6字节）应该涵盖内存不足？如果没有，我使用了什么额外的内存？

1. 错误java.lang.OutofMemoryError：超出GC开销限制
2. 在Java 8中字符串使用多少内存？
3. 如何查看应用程序正在使用的当前堆大小？
4. 增加Scala的JVM堆大小？

Answer 1

为了回答REPL特定的部分：

https://issues.scala-lang.org/browse/si-4331

进行大量分配的人通常更喜欢array和buffer。

scala> var x = new Array[Byte](20000000 * 4)
x: Array[Byte] = Array(0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, ...
scala> x = null
x: Array[Byte] = null

scala> x = new Array[Byte](20000000 * 4)
x: Array[Byte] = [B@475530b9

scala> x = null
x: Array[Byte] = null

scala> x = new Array[Byte](20000000 * 4)
java.lang.OutOfMemoryError: Java heap space
  ... 32 elided