我面临着一个小问题，Scala的Future的行为不一致。下面是我有的代码
package TryFuture
import scala.concurrent.Future
import scala.concurrent.future
import scala.concurrent.ExecutionContext.Implicits.global
import scala.concurrent.duration._
import scala.util.Random
class FutureCappuccino {
// Some type aliases, just for getting more meaningful method signatures:
type CoffeeBeans = String
type GroundCoffee = String
case class Water(temperature: Int)
type Milk = String
type FrothedMilk = String
type Espresso = String
type Cappuccino = String
// some exceptions for things that might go wrong in the individual steps
// (we'll need some of them later, use the others when experimenting
// with the code):
case class GrindingException(msg: String) extends Exception(msg)
case class FrothingException(msg: String) extends Exception(msg)
case class WaterBoilingException(msg: String) extends Exception(msg)
case class BrewingException(msg: String) extends Exception(msg)
def grind(beans: CoffeeBeans): Future[GroundCoffee] = future {
println("Start grinding with thread: " + Thread.currentThread().getId())
//Thread.sleep(10)
if (beans == "baked beans") throw GrindingException("are you joking?")
println("Finished grinding..")
s"ground coffee of $beans"
}
def heatWater(water: Water): Future[Water] = future {
println("Heating the water with thread: " + Thread.currentThread().getId())
//Thread.sleep(10)
println("It's hot!!")
water.copy(temperature = 85)
}
def frothMilk(milk: Milk): Future[FrothedMilk] = future {
println("milk frothing system engaged! with thread: " + Thread.currentThread().getId())
//Thread.sleep(Random.nextInt(10))
println("shutting down milk frothing system")
s"frothed $milk"
}
def brew(coffee: GroundCoffee, heatedWater: Water): Future[Espresso] = future {
println("happy brewing :) with thread: " + Thread.currentThread().getId())
//Thread.sleep(Random.nextInt(10))
println("it's brewed!")
s"espresso"
}
def combine(espresso: Espresso, frothedMilk: FrothedMilk): Future[String] = future {
println("Combine starting with thread: " + Thread.currentThread().getId())
"Your Cappuccino is ready"
}
// going through these steps sequentially:
def prepareCappuccino() = {
val brewed = for {
coffee <- grind("not baked beans")
water <- heatWater(Water(25))
brewed <- brew(coffee, water)
} yield brewed
brewed
}
}
现在我所期待的是，水会等待研磨完成，然后酿造会等待研磨和加热水完成。但是当我在我的MacBook中运行这个程序时，我只得到下面的o/p用螺纹开始研磨：8，然后执行完成。它不是在等待剩下的东西。找不到我在这里缺少的东西，为什么它不在等待？有什么帮助吗？
def grind(beans: CoffeeBeans): Future[GroundCoffee] = future {
println("Start grinding with thread: " + Thread.currentThread().getId())
if (beans == "baked beans") throw GrindingException("are you joking?")
...
}
def prepareCappuccino() = {
val brewed = for {
coffee <- grind("baked beans")
water <- heatWater(Water(25))
brewed <- brew(coffee, water)
} yield brewed
brewed
}
grind方法正在引发异常，导致for表达式导致失败将来
当grind被传递为"未烘焙的豆子"时，它会按预期工作。
你的主线程退出得太早了。
使用Thread.sleep或Await.result
最终通过以下更改明确了概念：
package TryFuture
import scala.concurrent.Future
import scala.concurrent.future
import scala.util.{Success,Failure}
import scala.concurrent.ExecutionContext.Implicits.global
import scala.concurrent.duration._
import scala.util.Random
class FutureCappuccino {
// Some type aliases, just for getting more meaningful method signatures:
type CoffeeBeans = String
type GroundCoffee = String
case class Water(temperature: Int)
type Milk = String
type FrothedMilk = String
type Espresso = String
type Cappuccino = String
// some exceptions for things that might go wrong in the individual steps
// (we'll need some of them later, use the others when experimenting
// with the code):
case class GrindingException(msg: String) extends Exception(msg)
case class FrothingException(msg: String) extends Exception(msg)
case class WaterBoilingException(msg: String) extends Exception(msg)
case class BrewingException(msg: String) extends Exception(msg)
def grind(beans: CoffeeBeans): Future[GroundCoffee] = {
println("Start grinding with thread: " + Thread.currentThread().getId())
Thread.sleep(200)
if (beans == "baked beans") throw GrindingException("are you joking?")
future {
Thread.sleep(200)
s"ground coffee of $beans"
}
}
def heatWater(water: Water): Future[Water] = {
println("Heating the water with thread: " + Thread.currentThread().getId())
Thread.sleep(200)
future {
water.copy(temperature = 85)
}
}
def frothMilk(milk: Milk): Future[FrothedMilk] = {
println("milk frothing system engaged! with thread: " + Thread.currentThread().getId())
Thread.sleep(200)
future {
s"frothed $milk"
}
}
def brew(coffee: GroundCoffee, heatedWater: Water): Future[Espresso] = {
println("happy brewing :) with thread: " + Thread.currentThread().getId())
Thread.sleep(200)
future {
s"espresso"
}
}
def combine(espresso: Espresso, frothedMilk: FrothedMilk): Future[String] = {
println("Combine starting with thread: " + Thread.currentThread().getId())
Thread.sleep(200)
future {
Thread.sleep(20)
"Your Cappuccino is ready"
}
}
// going through these steps sequentially:
def prepareCappuccino() = {
val coffees = grind("not baked beans")
val waters = heatWater(Water(25))
val milks = frothMilk("milk")
val combined = for {
coffee <- coffees
water <- waters
brewed <- brew(coffee, water)
milk <- milks
combined <- combine(brewed, milk)
} yield combined
combined onComplete {
case Success(t) => println("combined is done")
case Failure(t) => t
}
coffees onComplete {
case Success(t) => println("Coffee is done")
case Failure(t) => t
}
combined
}
}
最后======>
val myFutureCappuccino = new FutureCappuccino()
val myCoffee = myFutureCappuccino.prepareCappuccino
Thread.sleep(2000)
myCoffee onComplete{
case Success(t) => println(t)
case Failure(p) => println(p.getMessage())
}
现在对输出感到满意：
Start grinding with thread: 1
Heating the water with thread: 1
milk frothing system engaged! with thread: 1
happy brewing :) with thread: 8
Coffee is done
Combine starting with thread: 8
combined is done
Your Cappuccino is ready
在这里分享答案，希望它能帮助到别人。谢谢