如何在没有java.util.Timer的情况下实现延迟的将来? [英] How to implement a delayed future without java.util.Timer?

问题描述

我正在编写一个简单的函数来返回 Future [Unit] ，该延迟在给定的延迟后完成.

I am writing a simple function to return a Future[Unit] that completes after a given delay.

def delayedFuture(delay: FiniteDuration): Future[Unit] = {
  val promise = Promise[Unit]()
  val timerTask = new java.util.TimerTask {
    override def run(): Unit = promise.complete(Success(()))
  }
  new java.util.Timer().schedule(timerTask, delay.toMillis)
  promise.future
}

此实现可能可以工作，但我不喜欢为每次调用创建新的 Timer ，因为每个 Timer 实例都会创建一个线程.我可以将 Timer 实例作为参数传递给 delayedFuture ，但我不希望客户端代码了解 Timer .所以我想我根本不能使用 java.util.Timer .

This implementation can probably work but I don't like creating a new Timer for each invocation because each Timer instance creates a thread. I can pass a Timer instance to delayedFuture as an argument but I don't want client code to know about Timer. So I guess I cannot use java.util.Timer at all.

我想使用 ExecutionContext 进行任务调度，并可能像这样定义 delayedFuture :

I would like to use ExecutionContext for task scheduling and maybe define delayedFuture like this:

def delayedFuture(delay: FiniteDuration)
                 (implicit ec: ExecutoionContext): Future[Unit] = ???

在没有 java.util.Timer 的情况下实现这样的 delayedFuture 的最简单方法是什么?

What is the simplest way to implement delayedFuture like this without java.util.Timer ?

推荐答案

您无需为每次调用创建新的 Timer .只需创建一个全局的.

You don't need to create a new Timer for each invocation. Just make one global one.

object Delayed {
  private val timer = new Timer
  def apply[T](delay: Duration)(task: => T): Future[T] = {
    val promise = Promise[T]()
    val tt = new TimerTask {
      override def run(): Unit = promise.success(task)
    }
    timer.schedule(tt, delay.toMillis)
    promise.future
  }

  def unit(delay: Duration) = apply[Unit](delay) { () }
}

然后， Delayed.unit(10秒)为您提供一个可以在10秒内满足的未来单位.

Then, Delayed.unit(10 seconds) gives you a future unit that satisfies in 10 seconds.

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