斯卡拉期货基础知识

发布时间：2020-12-16 18:01:33 所属栏目：安全来源：网络整理

导读：我在 Scala中有以下代码： case class Water(temp: Int)case class Milk(temp: Int)def heatWaterFor(minutes: Int,water: Water) = Future { Thread.sleep(1000) Water(82)}def boilMilkFor(minutes: Int,milk: Milk) = Future { Thread.sleep(1000) Milk(9

我在 Scala中有以下代码：

case class Water(temp: Int)

case class Milk(temp: Int)

def heatWaterFor(minutes: Int,water: Water) = Future {
  Thread.sleep(1000)
  Water(82)
}

def boilMilkFor(minutes: Int,milk: Milk) = Future {
  Thread.sleep(1000)
  Milk(90)
}

def frothMilk(hotwater: Water,hotmilk: Milk) = Future {
  Thread.sleep(1000)
  hotmilk
}

val start = System.currentTimeMillis()

val milkMaker = for {
   water <- heatWaterFor(10,Water(10))
   milk <- boilMilkFor(5,Milk(10))
   frothed = frothMilk(water,milk)
   hotMilk <- frothed
 } yield (hotMilk)

Await.ready(milkMaker,Duration.Inf)
val end = System.currentTimeMillis() - start
println(milkMaker.value + ",Time taken: "+((end/1000))+" seconds.")

我的目的是将heatWaterFor(…)和boilMilkFor(…)并行化,因为它们是独立的.但我觉得上面的代码是连续的,根本没有利用期货的力量.显然,运行需要3000毫秒(这是一个额外的证据).

我在这里缺少什么基本的东西？

解决方法

for表达式被简化为一系列map,flatMap和withFilter操作.您具体的表达式减少到这样：

heatWaterFor(10,Water(10))
        .flatMap(water => boilMilkFor(5,Milk(10))
                             .flatMap(milk => frothMilk(water,milk))

正如您在此处所看到的,下一个未来的执行是在上一个完成时开始的.因此,如果要并行执行它们,则需要执行以下操作：

val heatWater = heatWaterFor(10,Water(10))
val boilMilk = boilMilkFor(5,Milk(10))

val milkMaker = for {
   water <- heatWater
   milk <- boilMilk
   hotMilk <- frothMilk(water,milk)
} yield (hotMilk)

这将同时启动heatWaterFor和boilMilkFor,然后在这两个完成时启动frothMilk(因为它取决于其他两个期货的结果).

（编辑：李大同）

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