Packages

p

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:

  • ask: create a temporary one-off actor for receiving a reply to a message and complete a scala.concurrent.Future with it; returns said Future.
  • pipeTo: feed eventually computed value of a future to an akka.actor.ActorRef as a message.
  • pipeToSelection: feed eventually computed value of a future to an akka.actor.ActorSelection as a message.

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);
Source
package.scala
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  1. pattern
  2. RetrySupport
  3. FutureTimeoutSupport
  4. GracefulStopSupport
  5. AskSupport
  6. PipeToSupport
  7. AnyRef
  8. Any
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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.

    This is what is used to complete a Future that is returned from an ask/? call, when it times out. A typical reason for AskTimeoutException is that the recipient actor didn't send a reply.

  3. final class AskableActorRef extends AnyVal
  4. final class AskableActorSelection extends AnyVal
  5. sealed trait BackoffOnFailureOptions extends ExtendedBackoffOptions[BackoffOnFailureOptions]
    Annotations
    @DoNotInherit()
  6. sealed trait BackoffOnStopOptions extends ExtendedBackoffOptions[BackoffOnStopOptions]
    Annotations
    @DoNotInherit()
  7. final class BackoffSupervisor extends BackoffOnStopSupervisor
  8. class CircuitBreaker extends AbstractCircuitBreaker

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

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

    Transitions through three states: - In *Closed* state, calls pass through until the maxFailures count is reached. This causes the circuit breaker to open. Both exceptions and calls exceeding callTimeout are considered failures. - In *Open* state, calls fail-fast with an exception. After resetTimeout, circuit breaker transitions to half-open state. - In *Half-Open* state, the first call will be allowed through, if it succeeds the circuit breaker will reset to closed state. If it fails, the circuit breaker will re-open to open state. All calls beyond the first that execute while the first is running will fail-fast with an exception.

  9. class CircuitBreakerOpenException extends AkkaException with NoStackTrace

    Exception thrown when Circuit Breaker is open.

  10. trait ExplicitAskSupport extends AnyRef

    This object contains implementation details of the “ask” pattern, which can be combined with "replyTo" pattern.

  11. final class ExplicitlyAskableActorRef extends AnyVal
  12. final class ExplicitlyAskableActorSelection extends AnyVal
  13. trait FutureRef[T] extends AnyRef

    A combination of a Future and an ActorRef associated with it, which points to an actor performing a task which will eventually resolve the Future.

  14. trait FutureTimeoutSupport extends AnyRef
  15. trait GracefulStopSupport extends AnyRef
  16. trait PipeToSupport extends AnyRef
  17. final class PipeableCompletionStage[T] extends AnyRef
    Definition Classes
    PipeToSupport
  18. final class PipeableFuture[T] extends AnyRef
    Definition Classes
    PipeToSupport
  19. trait PromiseRef[T] extends AnyRef

    A combination of a Promise and an ActorRef associated with it, which points to an actor performing a task which will eventually resolve the Promise.

  20. trait RetrySupport extends AnyRef

    This trait provides the retry utility function

  21. trait BackoffOptions extends AnyRef

    Configures a back-off supervisor actor.

    Configures a back-off supervisor actor. Start with Backoff.onStop or Backoff.onFailure. BackoffOptions is immutable, so be sure to chain methods like:

    val options = Backoff.onFailure(childProps, childName, minBackoff, maxBackoff, randomFactor)
                  .withManualReset
    context.actorOf(BackoffSupervisor.props(options), name)
    Annotations
    @DoNotInherit() @Deprecated @deprecated
    Deprecated

    (Since version 2.5.22) Use new API from BackoffOpts object instead

Value Members

  1. 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
  2. def afterCompletionStage[T](duration: FiniteDuration, using: Scheduler)(value: ⇒ CompletionStage[T])(implicit ec: ExecutionContext): CompletionStage[T]

    Returns a java.util.concurrent.CompletionStage that will be completed with the success or failure of the provided value after the specified duration.

    Returns a java.util.concurrent.CompletionStage that will be completed with the success or failure of the provided value after the specified duration.

    Definition Classes
    FutureTimeoutSupport
  3. def ask(actorSelection: ActorSelection, message: Any, sender: ActorRef)(implicit timeout: Timeout): Future[Any]
    Definition Classes
    AskSupport
  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)). A typical reason for AskTimeoutException is that the recipient actor didn't send a reply.

    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, sender: ActorRef)(implicit timeout: Timeout): Future[Any]
    Definition Classes
    AskSupport
  7. 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)). A typical reason for AskTimeoutException is that the recipient actor didn't send a reply.

    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
  8. 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
  9. 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 someChild’s 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
  10. 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
    // requires implicit ExecutionContext, e.g. by importing `context.dispatcher` inside an Actor
    
    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
  11. implicit def pipeCompletionStage[T](future: CompletionStage[T])(implicit executionContext: ExecutionContext): PipeableCompletionStage[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
    // requires implicit ExecutionContext, e.g. by importing `context.dispatcher` inside an Actor
    
    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
  12. def retry[T](attempt: () ⇒ Future[T], attempts: Int, delay: FiniteDuration)(implicit ec: ExecutionContext, scheduler: Scheduler): Future[T]

    Given a function from Unit to Future, returns an internally retrying Future The first attempt will be made immediately, each subsequent attempt will be made after 'delay' A scheduler (eg context.system.scheduler) must be provided to delay each retry If attempts are exhausted the returned future is simply the result of invoking attempt.

    Given a function from Unit to Future, returns an internally retrying Future The first attempt will be made immediately, each subsequent attempt will be made after 'delay' A scheduler (eg context.system.scheduler) must be provided to delay each retry If attempts are exhausted the returned future is simply the result of invoking attempt. Note that the attempt function will be invoked on the given execution context for subsequent tries and therefore must be thread safe (not touch unsafe mutable state).

    Example usage:

    protected val sendAndReceive: HttpRequest => Future[HttpResponse]
    private val sendReceiveRetry: HttpRequest => Future[HttpResponse] = (req: HttpRequest) => retry[HttpResponse](
      attempt = () => sendAndReceive(req),
      attempts = 10,
      delay = 2 seconds,
      scheduler = context.system.scheduler
    )
    Definition Classes
    RetrySupport
  13. object AskableActorRef
  14. object AskableActorSelection
  15. object BackoffOpts

    Backoff options allow to specify a number of properties for backoff supervisors.

  16. object BackoffSupervisor
  17. object CircuitBreaker

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

  18. object FutureRef
  19. object Patterns

    Java API: for Akka patterns such as ask, pipe and others which work with java.util.concurrent.CompletionStage.

  20. object PromiseRef
  21. object RetrySupport extends RetrySupport

Deprecated Value Members

  1. object Backoff

    Annotations
    @Deprecated @deprecated
    Deprecated

    (Since version 2.5.22) Use new API from BackoffOpts object instead

  2. object PatternsCS

    Java 8+ API for Akka patterns such as ask, pipe and others which work with java.util.concurrent.CompletionStage.

    Java 8+ API for Akka patterns such as ask, pipe and others which work with java.util.concurrent.CompletionStage.

    For working with Scala scala.concurrent.Future from Java you may want to use akka.pattern.Patterns instead.

    Annotations
    @deprecated
    Deprecated

    (Since version 2.5.19) Use Patterns instead.

Inherited from RetrySupport

Inherited from FutureTimeoutSupport

Inherited from GracefulStopSupport

Inherited from AskSupport

Inherited from PipeToSupport

Inherited from AnyRef

Inherited from Any

Ungrouped