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Future Composition with Scala and Akka
import scala.concurrent._
import scala.concurrent.duration._
import scala.concurrent.ExecutionContext.Implicits._
import scala.util.{ Success, Failure }
import akka.actor._
import akka.pattern.{ after, ask, pipe }
import akka.util.Timeout
object LogSearch extends App {
println("Starting actor system")
val system = ActorSystem("futures")
println("Starting log search")
try {
// timeout for each search task
val fallbackTimeout = 2 seconds
// timeout use with akka.patterns.ask
implicit val timeout = new Timeout(5 seconds)
require(fallbackTimeout < timeout.duration)
// Create SearchActor
val search = system.actorOf(Props[LogSearchActor])
// Test worktimes for search
val worktimes = List(1000, 1500, 1200, 800, 2000, 600, 3500, 8000, 250)
// Asking for results
val futureResults = (search ? Search(worktimes, fallbackTimeout))
// Cast to correct type
.mapTo[List[String]]
// In case something went wrong
.recover {
case e: TimeoutException => List("timeout")
case e: Exception => List(e getMessage)
}
// Callback (non-blocking)
.onComplete {
case Success(results) =>
println(":: Results ::")
results foreach (r => println(s" $r"))
system shutdown ()
case Failure(t) =>
t printStackTrace ()
system shutdown ()
}
} catch {
case t: Throwable =>
t printStackTrace ()
system shutdown ()
}
// Await end of programm
system awaitTermination (20 seconds)
}
class LogSearchActor extends Actor {
def receive = {
case Search(worktimes, timeout) =>
// Doing all the work in one actor using futures
val searchFutures = worktimes map { worktime =>
val searchFuture = search(worktime)
val fallback = after(timeout, context.system.scheduler) { Future successful s"$worktime ms > $timeout" }
Future firstCompletedOf Seq(searchFuture, fallback)
}
// Pipe future results to sender
(Future sequence searchFutures) pipeTo sender
case _ =>
}
def search(worktime: Int): Future[String] = future {
Thread sleep worktime
s"found something in $worktime ms"
}
}
case class Search(worktime: List[Int], timeout: FiniteDuration)
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