arrow-fx / arrow.fx.typeclasses / Concurrent / racePair

racePair

abstract fun <A, B> CoroutineContext.racePair(fa: Kind<F, A>, fb: Kind<F, B>): Kind<F, RacePair<F, A, B>>

Race two tasks concurrently within a new F. Race results in a winner and the other, yet to finish task running in a Fiber.

import arrow.Kind
import arrow.fx.*
import arrow.fx.extensions.io.concurrent.concurrent
import arrow.fx.typeclasses.*
import kotlinx.coroutines.Dispatchers

fun main(args: Array<String>) {
  fun <F> Concurrent<F>.example(): Kind<F, String> =
    //sampleStart
    fx.concurrent {
      val racePair = !Dispatchers.Default.racePair(never<Int>(), just("Hello World!"))
      racePair.fold(
        { _, _ -> "never cannot win race" },
        { _, winner -> winner }
      )
  }
  //sampleEnd

  val r = IO.concurrent().example().fix().unsafeRunSync()
  println("Race winner result is: $r")
}

Parameters

this - @racePair CoroutineContext to execute the source F on.

fa - task to participate in the race

fb - task to participate in the race

Return F either Left with product of the winner’s result fa and still running task fb, or Right with product of running task fa and the winner’s result fb.

See Also

raceN