slow-fast-futures.sc

import scala.concurrent.ExecutionContext.Implicits.global
import scala.concurrent.*

def delay(delay: Long)(id: String) = Future {
  Thread.sleep(delay)
  println(s"$id done")
  id
}

def fast(id: String) = delay(500)(id)
def slow(id: String) = delay(1000)(id)

def firstA = List(fast("A"), slow("B"), slow("C"))
def lastA  = List(slow("B"), slow("C"), fast("A"))

Future.firstCompletedOf(firstA).foreach(x => println(s"### $x"))
Future.firstCompletedOf(lastA).foreach(x => println(s"### $x"))


/*

  final def firstCompletedOf[T](futures: IterableOnce[Future[T]])(implicit executor: ExecutionContext): Future[T] = {
    val i = futures.iterator
    if (!i.hasNext) Future.never
    else {
      val p = Promise[T]()
      val firstCompleteHandler = new AtomicReference[Promise[T]](p) with (Try[T] => Unit) {
        override final def apply(v1: Try[T]): Unit =  {
          val r = getAndSet(null)
          if (r ne null)
            r tryComplete v1 // tryComplete is likely to be cheaper than complete
        }
      }
      while(i.hasNext && firstCompleteHandler.get != null) // exit early if possible
        i.next().onComplete(firstCompleteHandler)
      p.future
    }
  }
 */

// https://www.politico.com/news/magazine/2024/05/03/college-campus-protests-israel-gaza-student-journalists-00155672?utm_medium=10today.us.sat.rd.20240504.436.1&utm_source=email&utm_content=article&utm_campaign=email-2022