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如何立即执行未来

scala

0

user79074 · 技术社区 · 11 月前

假设我的未来定义如下

val fut = Future {
  println("Doing some work")
  Thread.sleep(5000)
  println("Work done")
}

我稍后会访问这个未来,但希望在启动时执行它,而不是在我引用fut时执行

我在某个地方读到,通过执行以下操作可以立即执行:

scala.concurrent.ExecutionContext.Implicits.global.execute(fut)

然而,这不会编译,因为execute只需要一个Runnable。有没有一种方法可以在不同的线程中立即执行这个未来?

1 回复 | 直到 11 月前

1

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sarveshseri 11 月前

Scala Future s使用创建 Future.apply 被热切地执行。

对于非急切执行,您必须定义自己的类来间接创建 未来 使用 Promise .

import scala.concurrent.{Future, Promise}
import scala.util.{Failure, Success, Try}

class NonEagerFuture[A](computation: => A) extends Runnable {
  private val promise = Promise[A]

  override def run(): Unit = {
    Try(computation) match {
      case Success(result)    => promise.success(result)
      case Failure(exception) => promise.failure(exception)
    }
  }

  def isFutureCompleted(): Boolean =
    promise.isCompleted

  def getResult(): A =
    if (!promise.isCompleted) {
      throw new IllegalStateException("Future is not completed yet")
    } else {
      promise.future.value.get.get
    }

  def getScalaFuture(): Future[A] =
    promise.future

}

它可以如下使用,

println("creating the future")

val nonEagerFuture = new NonEagerFuture({
  println("Doing some work")
  Thread.sleep(5000)
  println("Work done")
  println("returning 5 as result")
  5
})

println("running for the future")
scala.concurrent.ExecutionContext.Implicits.global.execute(nonEagerFuture)

// can also get the internal scala future and use it
// this scala future will not have the eager problem 
println("get the scala future") 
val scalaFuture = nonEagerFuture.getScalaFuture()
println("printing scalaFuture" + scalaFuture)

// or block for completion using isFutureCompleted
println("checking for the future")
while (!nonEagerFuture.isFutureCompleted()) {
  Thread.sleep(1000)
  println("Checking completed: " + nonEagerFuture.isFutureCompleted())
}

println("getting result for the future")
println("Result: " + nonEagerFuture.getResult())