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).
