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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
Linear Supertypes
RetrySupport, FutureTimeoutSupport, GracefulStopSupport, AskSupport, PipeToSupport, AnyRef, Any
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  1. pattern
  2. RetrySupport
  3. FutureTimeoutSupport
  4. GracefulStopSupport
  5. AskSupport
  6. PipeToSupport
  7. AnyRef
  8. Any
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Package Members

  1. package internal

Type Members

  1. trait AskSupport extends AnyRef

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

  2. class AskTimeoutException extends TimeoutException with NoStackTrace

    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. class CircuitBreaker extends AbstractCircuitBreaker

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

    Provides circuit breaker functionality for 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.

  8. class CircuitBreakerOpenException extends AkkaException with NoStackTrace

    Exception thrown when Circuit Breaker is open.

  9. final class CircuitBreakersRegistry extends Extension

    A CircuitBreakersPanel is a central point collecting all circuit breakers in Akka.

  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. final class StatusReply[+T] extends AnyRef

    Generic top-level message type for replies that signal failure or success.

    Generic top-level message type for replies that signal failure or success. Convenient to use together with the askWithStatus ask variants.

    Create using the factory methods StatusReply#success and StatusReply#error.

    Akka contains predefined serializers for the wrapper type and the textual error messages.

    T

    the type of value a successful reply would have

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 after[T](duration: FiniteDuration)(value: => Future[T])(implicit system: ClassicActorSystemProvider): 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
  3. 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
  4. def afterCompletionStage[T](duration: FiniteDuration)(value: => CompletionStage[T])(implicit system: ClassicActorSystemProvider): 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
  5. def ask(actorSelection: ActorSelection, message: Any, sender: ActorRef)(implicit timeout: Timeout): Future[Any]
    Definition Classes
    AskSupport
  6. 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
  7. 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
  8. def ask(actorRef: ActorRef, message: Any, sender: ActorRef)(implicit timeout: Timeout): Future[Any]
    Definition Classes
    AskSupport
  9. 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
  10. 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
  11. def askWithStatus(actorRef: ActorRef, message: Any, sender: ActorRef)(implicit timeout: Timeout): Future[Any]

    Use for messages whose response is known to be a akka.pattern.StatusReply.

    Use for messages whose response is known to be a akka.pattern.StatusReply. When a akka.pattern.StatusReply.Success response arrives the future is completed with the wrapped value, if a akka.pattern.StatusReply.Error arrives the future is instead failed.

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

    Use for messages whose response is known to be a akka.pattern.StatusReply.

    Use for messages whose response is known to be a akka.pattern.StatusReply. When a akka.pattern.StatusReply.Success response arrives the future is completed with the wrapped value, if a akka.pattern.StatusReply.Error arrives the future is instead failed.

    Definition Classes
    AskSupport
  13. 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
  14. 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
  15. 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
  16. def retry[T](attempt: () => Future[T], shouldRetry: (Throwable) => Boolean, attempts: Int, delayFunction: (Int) => Option[FiniteDuration])(implicit ec: ExecutionContext, scheduler: Scheduler): Future[T]

    Given a function from Unit to Future, returns an internally retrying Future.

    Given a function from Unit to Future, returns an internally retrying Future. The first attempt will be made immediately, any subsequent attempt will be made after the 'delay' return by delayFunction(the input next attempt count start from 1). Returns None for no delay. A scheduler (eg context.system.scheduler) must be provided to delay each retry. You could provide a function to generate the next delay duration after first attempt, this function should never return null, otherwise an IllegalArgumentException will be thrown.

    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).

    If an attempt fails, the exception from the failure will be passed to the 'shouldRetry' predicate; if the predicate evaluates 'true', a retry will be attempted. This allows for short-circuiting in situations where the retries cannot be expected to succeed (e.g. in a situation where the legality of arguments can only be determined asynchronously).

    Example usage:

    // retry with backoff

    protected val sendAndReceive: HttpRequest => Future[HttpResponse] = { (req) => ??? }
private val sendReceiveRetry: HttpRequest => Future[HttpResponse] = (req: HttpRequest) => retry[HttpResponse](
  attempt = () => sendAndReceive(req),
  attempts = 10,
  delayFunction = attempted => Option(2.seconds * attempted),
  shouldRetry = ex => !ex.isInstanceOf[IllegalArgumentException]
)
    Definition Classes
    RetrySupport
  17. def retry[T](attempt: () => Future[T], attempts: Int, delayFunction: (Int) => Option[FiniteDuration])(implicit ec: ExecutionContext, scheduler: Scheduler): Future[T]

    Given a function from Unit to Future, returns an internally retrying Future.

    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 the 'delay' return by delayFunction(the input next attempt count start from 1). Returns None for no delay. A scheduler (eg context.system.scheduler) must be provided to delay each retry. You could provide a function to generate the next delay duration after first attempt, this function should never return null, otherwise an IllegalArgumentException will be thrown.

    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:

    //retry with back off

    protected val sendAndReceive: HttpRequest => Future[HttpResponse]
private val sendReceiveRetry: HttpRequest => Future[HttpResponse] = (req: HttpRequest) => retry[HttpResponse](
  attempt = () => sendAndReceive(req),
  attempts = 10,
  delayFunction = attempted => Option(2.seconds * attempted)
)
    Definition Classes
    RetrySupport
  18. 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.

    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
)
    Definition Classes
    RetrySupport
  19. def retry[T](attempt: () => Future[T], shouldRetry: (Throwable) => Boolean, attempts: Int, minBackoff: FiniteDuration, maxBackoff: FiniteDuration, randomFactor: Double)(implicit ec: ExecutionContext, scheduler: Scheduler): Future[T]

    Given a function from Unit to Future, returns an internally retrying Future.

    Given a function from Unit to Future, returns an internally retrying Future. The first attempt will be made immediately, each subsequent attempt will made with a backoff time if the preceding attempt failed and the 'shouldRetry' predicate, when applied to the failure's exception evaluates to 'true'. If the predicate evaluates to 'false', the failed attempt will be returned. This allows for short-circuiting in situations where the retries cannot be expected to succeed (e.g. in a situation where the legality of arguments can only be determined asynchronously).

    If attempts are exhausted, the returned future is that of the last 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 def sendAndReceive(req: HttpRequest): Future[HttpResponse]
private val sendReceiveRetry: HttpRequest => Future[HttpResponse] = (req: HttpRequest) => retry[HttpResponse](
  attempt = () => sendAndReceive(req),
  attempts = 10,
  minBackoff = 1.second,
  maxBackoff = 10.seconds,
  randomFactor = 0.2,
  shouldRetry = ex => !ex.isInstanceOf[IllegalArgumentException])
    Definition Classes
    RetrySupport
  20. def retry[T](attempt: () => Future[T], attempts: Int, minBackoff: FiniteDuration, maxBackoff: FiniteDuration, randomFactor: Double)(implicit ec: ExecutionContext, scheduler: Scheduler): Future[T]

    Given a function from Unit to Future, returns an internally retrying Future.

    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 with a backoff time, if the previous attempt failed.

    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,
  minBackoff = 1.seconds,
  maxBackoff = 2.seconds,
  randomFactor = 0.5
)
    minBackoff

    minimum (initial) duration until the child actor will started again, if it is terminated

    maxBackoff

    the exponential back-off is capped to this duration

    randomFactor

    after calculation of the exponential back-off an additional random delay based on this factor is added, e.g. 0.2 adds up to 20% delay. In order to skip this additional delay pass in 0.

    Definition Classes
    RetrySupport
  21. def retry[T](attempt: () => Future[T], shouldRetry: (Throwable) => Boolean, attempts: Int)(implicit ec: ExecutionContext): Future[T]

    Given a function from Unit to Future, returns an internally retrying Future.

    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 immediately if the preceding attempt failed and the 'shouldRetry' predicate, when applied to the failure's exception evaluates to 'true'. If the predicate evaluates to 'false', the failed attempt will be returned. This allows for short-circuiting in situations where the retries cannot be expected to succeed (e.g. in a situation where the legality of arguments can only be determined asynchronously).

    If attempts are exhausted, the returned future is the that of the last 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

    def possiblyFailing(): Future[Something] = ???
val withRetry: Future[Something] = retry(
  attempt = possiblyFailing,
  attempts = 10,
  shouldRetry = { (ex) => ex.isInstanceOf[IllegalArgumentException] })
    Definition Classes
    RetrySupport
  22. def retry[T](attempt: () => Future[T], attempts: Int)(implicit ec: ExecutionContext): Future[T]

    Given a function from Unit to Future, returns an internally retrying Future.

    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 immediately if the previous attempt failed.

    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:

    def possiblyFailing(): Future[Something] = ???
val withRetry: Future[Something] = retry(attempt = possiblyFailing, attempts = 10)
    Definition Classes
    RetrySupport
  23. object AskableActorRef
  24. object BackoffOpts

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

  25. object BackoffSupervisor
  26. object CircuitBreaker

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

  27. object CircuitBreakersRegistry extends ExtensionId[CircuitBreakersRegistry] with ExtensionIdProvider

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

  28. object FutureRef
  29. object Patterns

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

  30. object PromiseRef
  31. object RetrySupport extends RetrySupport
  32. object StatusReply

Inherited from RetrySupport

Inherited from FutureTimeoutSupport

Inherited from GracefulStopSupport

Inherited from AskSupport

Inherited from PipeToSupport

Inherited from AnyRef

Inherited from Any

Ungrouped