akka

pattern

package pattern

Commonly Used Patterns With Akka

This package is used as a collection point for usage patterns which involve actors, futures, etc. but are loosely enough coupled to (multiple of) them to present them separately from the core implementation. Currently supported are:

In Scala the recommended usage is to import the pattern from the package object:

import akka.pattern.ask

ask(actor, message) // use it directly
actor ask message   // use it by implicit conversion

For Java the patterns are available as static methods of the akka.pattern.Patterns class:

import static akka.pattern.Patterns.ask;

ask(actor, message);
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package.scala
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  1. pattern
  2. FutureTimeoutSupport
  3. GracefulStopSupport
  4. AskSupport
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Type Members

  1. trait AskSupport extends AnyRef

    This object contains implementation details of the “ask” pattern.

  2. class AskTimeoutException extends TimeoutException

    This is what is used to complete a Future that is returned from an ask/? call, when it times out.

  3. final class AskableActorRef extends AnyVal

  4. final class AskableActorSelection extends AnyVal

  5. class CircuitBreaker extends AbstractCircuitBreaker

    Provides circuit breaker functionality to provide stability when working with "dangerous" operations, e.

  6. class CircuitBreakerOpenException extends AkkaException with NoStackTrace

    Exception thrown when Circuit Breaker is open.

  7. trait FutureTimeoutSupport extends AnyRef

  8. trait GracefulStopSupport extends AnyRef

  9. trait PipeToSupport extends AnyRef

  10. final class PipeableFuture[T] extends AnyRef

    Definition Classes
    PipeToSupport

Value Members

  1. object CircuitBreaker

    Companion object providing factory methods for Circuit Breaker which runs callbacks in caller's thread

  2. object Patterns

  3. def after[T](duration: FiniteDuration, using: Scheduler)(value: ⇒ Future[T])(implicit ec: ExecutionContext): Future[T]

    Returns a scala.concurrent.Future that will be completed with the success or failure of the provided value after the specified duration.

    Returns a scala.concurrent.Future that will be completed with the success or failure of the provided value after the specified duration.

    Definition Classes
    FutureTimeoutSupport
  4. def ask(actorSelection: ActorSelection, message: Any)(implicit timeout: Timeout): Future[Any]

    Sends a message asynchronously and returns a scala.concurrent.Future holding the eventual reply message; this means that the target actor needs to send the result to the sender reference provided.

    Sends a message asynchronously and returns a scala.concurrent.Future holding the eventual reply message; this means that the target actor needs to send the result to the sender reference provided. The Future will be completed with an akka.pattern.AskTimeoutException after the given timeout has expired; this is independent from any timeout applied while awaiting a result for this future (i.e. in Await.result(..., timeout)).

    Warning: When using future callbacks, inside actors you need to carefully avoid closing over the containing actor’s object, i.e. do not call methods or access mutable state on the enclosing actor from within the callback. This would break the actor encapsulation and may introduce synchronization bugs and race conditions because the callback will be scheduled concurrently to the enclosing actor. Unfortunately there is not yet a way to detect these illegal accesses at compile time.

    Recommended usage:

    val f = ask(worker, request)(timeout)
    f.map { response =>
      EnrichedMessage(response)
    } pipeTo nextActor
    Definition Classes
    AskSupport
  5. implicit def ask(actorSelection: ActorSelection): AskableActorSelection

    Import this implicit conversion to gain ? and ask methods on akka.actor.ActorSelection, which will defer to the ask(actorSelection, message)(timeout) method defined here.

    Import this implicit conversion to gain ? and ask methods on akka.actor.ActorSelection, which will defer to the ask(actorSelection, message)(timeout) method defined here.

    import akka.pattern.ask
    
    val future = selection ? message             // => ask(selection, message)
    val future = selection ask message           // => ask(selection, message)
    val future = selection.ask(message)(timeout) // => ask(selection, message)(timeout)

    All of the above use an implicit akka.util.Timeout.

    Definition Classes
    AskSupport
  6. def ask(actorRef: ActorRef, message: Any)(implicit timeout: Timeout): Future[Any]

    Sends a message asynchronously and returns a scala.concurrent.Future holding the eventual reply message; this means that the target actor needs to send the result to the sender reference provided.

    Sends a message asynchronously and returns a scala.concurrent.Future holding the eventual reply message; this means that the target actor needs to send the result to the sender reference provided. The Future will be completed with an akka.pattern.AskTimeoutException after the given timeout has expired; this is independent from any timeout applied while awaiting a result for this future (i.e. in Await.result(..., timeout)).

    Warning: When using future callbacks, inside actors you need to carefully avoid closing over the containing actor’s object, i.e. do not call methods or access mutable state on the enclosing actor from within the callback. This would break the actor encapsulation and may introduce synchronization bugs and race conditions because the callback will be scheduled concurrently to the enclosing actor. Unfortunately there is not yet a way to detect these illegal accesses at compile time.

    Recommended usage:

    val f = ask(worker, request)(timeout)
    f.map { response =>
      EnrichedMessage(response)
    } pipeTo nextActor
    Definition Classes
    AskSupport
  7. implicit def ask(actorRef: ActorRef): AskableActorRef

    Import this implicit conversion to gain ? and ask methods on akka.actor.ActorRef, which will defer to the ask(actorRef, message)(timeout) method defined here.

    Import this implicit conversion to gain ? and ask methods on akka.actor.ActorRef, which will defer to the ask(actorRef, message)(timeout) method defined here.

    import akka.pattern.ask
    
    val future = actor ? message             // => ask(actor, message)
    val future = actor ask message           // => ask(actor, message)
    val future = actor.ask(message)(timeout) // => ask(actor, message)(timeout)

    All of the above use an implicit akka.util.Timeout.

    Definition Classes
    AskSupport
  8. def gracefulStop(target: ActorRef, timeout: FiniteDuration, stopMessage: Any = PoisonPill): Future[Boolean]

    Returns a scala.concurrent.Future that will be completed with success (value true) when existing messages of the target actor has been processed and the actor has been terminated.

    Returns a scala.concurrent.Future that will be completed with success (value true) when existing messages of the target actor has been processed and the actor has been terminated.

    Useful when you need to wait for termination or compose ordered termination of several actors, which should only be done outside of the ActorSystem as blocking inside Actors is discouraged.

    IMPORTANT NOTICE: the actor being terminated and its supervisor being informed of the availability of the deceased actor’s name are two distinct operations, which do not obey any reliable ordering. Especially the following will NOT work:

    def receive = {
    case msg =>
      Await.result(gracefulStop(someChild, timeout), timeout)
      context.actorOf(Props(...), "someChild") // assuming that that was someChildᅰs name, this will NOT work
    }

    If the target actor isn't terminated within the timeout the scala.concurrent.Future is completed with failure akka.pattern.AskTimeoutException.

    If you want to invoke specialized stopping logic on your target actor instead of PoisonPill, you can pass your stop command as a parameter:

    gracefulStop(someChild, timeout, MyStopGracefullyMessage).onComplete {
    // Do something after someChild being stopped
    }
    Definition Classes
    GracefulStopSupport
  9. implicit def pipe[T](future: Future[T])(implicit executionContext: ExecutionContext): PipeableFuture[T]

    Import this implicit conversion to gain the pipeTo method on scala.concurrent.Future:

    Import this implicit conversion to gain the pipeTo method on scala.concurrent.Future:

    import akka.pattern.pipe
    
    Future { doExpensiveCalc() } pipeTo nextActor
    
    or
    
    pipe(someFuture) to nextActor

    The successful result of the future is sent as a message to the recipient, or the failure is sent in a akka.actor.Status.Failure to the recipient.

    Definition Classes
    PipeToSupport

Inherited from FutureTimeoutSupport

Inherited from GracefulStopSupport

Inherited from AskSupport

Inherited from PipeToSupport

Inherited from AnyRef

Inherited from Any

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