Scheduler

import akka.actor.Actor
import akka.actor.Props
import scala.concurrent.duration._
 
    //Use the system's dispatcher as ExecutionContext
    import system.dispatcher
 
    //Schedules to send the "foo"-message to the testActor after 50ms
    system.scheduler.scheduleOnce(50 milliseconds, testActor, "foo")

//Schedules a function to be executed (send a message to the testActor) after 50ms
system.scheduler.scheduleOnce(50 milliseconds) {
  testActor ! System.currentTimeMillis
}

val Tick = "tick"
class TickActor extends Actor {
  def receive = {
    case Tick => //Do something
  }
}
val tickActor = system.actorOf(Props(classOf[TickActor], this))
//Use system's dispatcher as ExecutionContext
import system.dispatcher
 
//This will schedule to send the Tick-message
//to the tickActor after 0ms repeating every 50ms
val cancellable =
  system.scheduler.schedule(
    0 milliseconds,
    50 milliseconds,
    tickActor,
    Tick)
 
//This cancels further Ticks to be sent
cancellable.cancel()

/**
 * Light-weight scheduler for running asynchronous tasks after some deadline
 * in the future. Not terribly precise but cheap.
 */
def scheduler: Scheduler

/**
 * An Akka scheduler service. This one needs one special behavior: if
 * Closeable, it MUST execute all outstanding tasks upon .close() in order
 * to properly shutdown all dispatchers.
 *
 * Furthermore, this timer service MUST throw IllegalStateException if it
 * cannot schedule a task. Once scheduled, the task MUST be executed. If
 * executed upon close(), the task may execute before its timeout.
 *
 * Scheduler implementation are loaded reflectively at ActorSystem start-up
 * with the following constructor arguments:
 *  1) the system’s com.typesafe.config.Config (from system.settings.config)
 *  2) a akka.event.LoggingAdapter
 *  3) a java.util.concurrent.ThreadFactory
 */
trait Scheduler {
  /**
   * Schedules a message to be sent repeatedly with an initial delay and
   * frequency. E.g. if you would like a message to be sent immediately and
   * thereafter every 500ms you would set delay=Duration.Zero and
   * interval=Duration(500, TimeUnit.MILLISECONDS)
   *
   * Java & Scala API
   */
  final def schedule(
    initialDelay: FiniteDuration,
    interval:     FiniteDuration,
    receiver:     ActorRef,
    message:      Any)(implicit
    executor: ExecutionContext,
                       sender: ActorRef = Actor.noSender): Cancellable =
    schedule(initialDelay, interval, new Runnable {
      def run = {
        receiver ! message
        if (receiver.isTerminated)
          throw new SchedulerException("timer active for terminated actor")
      }
    })
 
  /**
   * Schedules a function to be run repeatedly with an initial delay and a
   * frequency. E.g. if you would like the function to be run after 2 seconds
   * and thereafter every 100ms you would set delay = Duration(2, TimeUnit.SECONDS)
   * and interval = Duration(100, TimeUnit.MILLISECONDS). If the execution of
   * the function takes longer than the interval, the subsequent execution will
   * start immediately after the prior one completes (there will be no overlap
   * of the function executions). In such cases, the actual execution interval
   * will differ from the interval passed to this method.
   *
   * If the function throws an exception the repeated scheduling is aborted,
   * i.e. the function will not be invoked any more.
   *
   * Scala API
   */
  final def schedule(
    initialDelay: FiniteDuration,
    interval:     FiniteDuration)(f: ⇒ Unit)(
    implicit
    executor: ExecutionContext): Cancellable =
    schedule(initialDelay, interval, new Runnable { override def run = f })
 
  /**
   * Schedules a `Runnable` to be run repeatedly with an initial delay and
   * a frequency. E.g. if you would like the function to be run after 2
   * seconds and thereafter every 100ms you would set delay = Duration(2,
   * TimeUnit.SECONDS) and interval = Duration(100, TimeUnit.MILLISECONDS). If
   * the execution of the runnable takes longer than the interval, the
   * subsequent execution will start immediately after the prior one completes
   * (there will be no overlap of executions of the runnable). In such cases,
   * the actual execution interval will differ from the interval passed to this
   * method.
   *
   * If the `Runnable` throws an exception the repeated scheduling is aborted,
   * i.e. the function will not be invoked any more.
   *
   * Java API
   */
  def schedule(
    initialDelay: FiniteDuration,
    interval:     FiniteDuration,
    runnable:     Runnable)(implicit executor: ExecutionContext): Cancellable
 
  /**
   * Schedules a message to be sent once with a delay, i.e. a time period that has
   * to pass before the message is sent.
   *
   * Java & Scala API
   */
  final def scheduleOnce(
    delay:    FiniteDuration,
    receiver: ActorRef,
    message:  Any)(implicit
    executor: ExecutionContext,
                   sender: ActorRef = Actor.noSender): Cancellable =
    scheduleOnce(delay, new Runnable {
      override def run = receiver ! message
    })
 
  /**
   * Schedules a function to be run once with a delay, i.e. a time period that has
   * to pass before the function is run.
   *
   * Scala API
   */
  final def scheduleOnce(delay: FiniteDuration)(f: ⇒ Unit)(
    implicit
    executor: ExecutionContext): Cancellable =
    scheduleOnce(delay, new Runnable { override def run = f })
 
  /**
   * Schedules a Runnable to be run once with a delay, i.e. a time period that
   * has to pass before the runnable is executed.
   *
   * Java & Scala API
   */
  def scheduleOnce(
    delay:    FiniteDuration,
    runnable: Runnable)(implicit executor: ExecutionContext): Cancellable
 
  /**
   * The maximum supported task frequency of this scheduler, i.e. the inverse
   * of the minimum time interval between executions of a recurring task, in Hz.
   */
  def maxFrequency: Double
 
}

/**
 * Signifies something that can be cancelled
 * There is no strict guarantee that the implementation is thread-safe,
 * but it should be good practice to make it so.
 */
trait Cancellable {
  /**
   * Cancels this Cancellable and returns true if that was successful.
   * If this cancellable was (concurrently) cancelled already, then this method
   * will return false although isCancelled will return true.
   *
   * Java & Scala API
   */
  def cancel(): Boolean
 
  /**
   * Returns true if and only if this Cancellable has been successfully cancelled
   *
   * Java & Scala API
   */
  def isCancelled: Boolean
}