您将如何使用 Scala 的异步超时多个异步请求？

Question

我不知道 Scala，但我很好奇它的异步功能（类似于 C# 的）。你如何将这个 go 代码翻译成 Scala 异步？http://talks.golang.org/2012/concurrency.slide#47c := make(chan Result)go func() { c <- Web(query) } ()go func() { c <- Image(query) } ()go func() { c <- Video(query) } ()timeout := time.After(80 * time.Millisecond)for i := 0; i < 3; i++ {    select {    case result := <-c:        results = append(results, result)    case <-timeout:        fmt.Println("timed out")        return    }}return

Answer 1

这是如何完成的草图（未经测试；我不声称这是最好的解决方案）：

// I assume that the Web/Image/Video functions return instances of Future[Result]

val f1 = Web(query)

val f2 = Image(query)

val f3 = Video(query)

val t = timeout(80.milliseconds)

// using Scala's Future API

val results: Future[Seq[Result]] = for {

  r1 <- or(f1)(t)

  r2 <- or(f2)(t)

  r3 <- or(f3)(t)

} yield (r1.toSeq ++ r2.toSeq ++ r3.toSeq)

// OR using async

val results: Future[Seq[Result]] = async {

  val r1 = or(f1)(t)

  val r2 = or(f2)(t)

  val r3 = or(f3)(t)

  await(r1).toSeq ++ await(r2).toSeq ++ await(r3).toSeq

}

// or and timeout are utility/library functions defined below

def or[T](f1: Future[T])(f2: Future[Option[Nothing]]): Future[Option[T]] =

  Future.firstCompletedOf(f1 map Some.apply, f2)

// create a future that will complete successfully with None

// after the given duration passes

def timeout(d: Duration): Future[Option[Nothing]] = {

  val p = Promise[Option[Nothing]]

  Scheduler.after(d) { p success None }

  p.future

}