scala – 奇怪的并行收集行为

我想抽象出这个问题的方式如下：

// just measures time a block of code runs
def time(block: => Unit) : Long = {
  val start = System.currentTimeMillis
  block
  val stop = System.currentTimeMillis
  stop - start
}

// "lengthy" task
def work = {
  Thread.sleep(100)
  println("done")
  1
}

import scala.collection.GenSeq


abstract class ContextTransform {
  def apply[T](genSeq: GenSeq[T]): GenSeq[T]
}

object ParContextTransform extends ContextTransform {
  override def apply[T](genSeq: GenSeq[T]): GenSeq[T] = genSeq.par
}

// this works as expected
def callingParDirectly = {
  val range = (1 to 10).par

  // make sure we really got a ParSeq
  println(range) 
  for (i <- range) yield work
}

// this doesn't 
def callingParWithContextTransform(contextTransform: ContextTransform) = {
  val range = contextTransform(1 to 10)

  // make sure we really got a ParSeq
  println(range)
  for (i <- range) yield work
}

解释器的结果：

scala> time(callingParDirectly)
ParRange(1,2,3,4,5,6,7,8,9,10)
done
// ...
done
res20: Long = 503

scala> time(callingParWithContextTransform(ParContextTransform))
ParRange(1,10)
done
// ...
done
res21: Long = 1002

我的第一个赌注是该系列没有正确拆分和println的
“完成”确实表明……但如果我不屈服,上面的代码效果很好
任何事情(只需运行工作方法).

我无法理解为什么callingParWithContextTransform方法不起作用
比如callingParDirectly;我错过了什么？