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user79074
Asked: 2024-12-30 22:20:54 +0800 CST

如何立即执行未来

  • 772

假设我有一个定义如下的未来

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

我稍后会访问这个未来，但希望它在启动时执行，而不是在我引用 fut 时执行

我在某处读到过，可以通过执行以下操作立即执行：

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

但是这不会编译，因为执行仅需要一个 Runnable。有没有办法可以在另一个线程中立即执行这个未来？

scala

1 个回答

  1. Best Answer

    使用ScalaFuture创建的Future.apply将被急切执行。

    对于非急切执行，您必须定义自己的类来间接Future使用创建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

}

    它可以按以下方式使用，

    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())
    • 1

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