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 org.apache.pekko.actor.ActorRef as a message.
- pipeToSelection: feed eventually computed value of a future to an org.apache.pekko.actor.ActorSelection as a message.
In Scala the recommended usage is to import the pattern from the package object:
import org.apache.pekko.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 org.apache.pekko.pattern.Patterns class:
import static org.apache.pekko.pattern.Patterns.ask;
ask(actor, message);
- Source
- package.scala
- Alphabetic
- By Inheritance
- pattern
- RetrySupport
- FutureTimeoutSupport
- GracefulStopSupport
- AskSupport
- PipeToSupport
- AnyRef
- Any
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- Public
- Protected
Type Members
- trait AskSupport extends AnyRef
This object contains implementation details of the “ask” pattern.
- 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. - final class AskableActorRef extends AnyVal
- final class AskableActorSelection extends AnyVal
- sealed trait BackoffOnFailureOptions extends ExtendedBackoffOptions[BackoffOnFailureOptions]
- Annotations
- @DoNotInherit()
- sealed trait BackoffOnStopOptions extends ExtendedBackoffOptions[BackoffOnStopOptions]
- Annotations
- @DoNotInherit()
- final class BackoffSupervisor extends BackoffOnStopSupervisor
- 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 exceedingcallTimeout
are considered failures. - In *Open* state, calls fail-fast with an exception. AfterresetTimeout
, 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. - class CircuitBreakerOpenException extends PekkoException with NoStackTrace
Exception thrown when Circuit Breaker is open.
- final class CircuitBreakersRegistry extends Extension
A CircuitBreakersPanel is a central point collecting all circuit breakers in Akka.
- trait ExplicitAskSupport extends AnyRef
This object contains implementation details of the “ask” pattern, which can be combined with "replyTo" pattern.
- final class ExplicitlyAskableActorRef extends AnyVal
- final class ExplicitlyAskableActorSelection extends AnyVal
- 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.
- trait FutureTimeoutSupport extends AnyRef
- trait GracefulStopSupport extends AnyRef
- trait PipeToSupport extends AnyRef
- final class PipeableCompletionStage[T] extends AnyRef
- Definition Classes
- PipeToSupport
- final class PipeableFuture[T] extends AnyRef
- Definition Classes
- PipeToSupport
- 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.
- trait RetrySupport extends AnyRef
This trait provides the retry utility function
- 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.
Pekko contains predefined serializers for the wrapper type and the textual error messages.
- T
the type of value a successful reply would have
Deprecated Type Members
- trait BackoffOptions extends AnyRef
Configures a back-off supervisor actor.
Configures a back-off supervisor actor. Start with
Backoff.onStop
orBackoff.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
(Since version Akka 2.5.22) Use new API from BackoffOpts object instead
Value Members
- 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
- 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
- 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
- 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
- def ask(actorSelection: ActorSelection, message: Any, sender: ActorRef)(implicit timeout: Timeout): Future[Any]
- Definition Classes
- AskSupport
- 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 pekko.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 forAskTimeoutException
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
- implicit def ask(actorSelection: ActorSelection): AskableActorSelection
Import this implicit conversion to gain
?
andask
methods on pekko.actor.ActorSelection, which will defer to theask(actorSelection, message)(timeout)
method defined here.Import this implicit conversion to gain
?
andask
methods on pekko.actor.ActorSelection, which will defer to theask(actorSelection, message)(timeout)
method defined here.import org.apache.pekko.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 pekko.util.Timeout.
- Definition Classes
- AskSupport
- def ask(actorRef: ActorRef, message: Any, sender: ActorRef)(implicit timeout: Timeout): Future[Any]
- Definition Classes
- AskSupport
- 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 pekko.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 forAskTimeoutException
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
- implicit def ask(actorRef: ActorRef): AskableActorRef
Import this implicit conversion to gain
?
andask
methods on pekko.actor.ActorRef, which will defer to theask(actorRef, message)(timeout)
method defined here.Import this implicit conversion to gain
?
andask
methods on pekko.actor.ActorRef, which will defer to theask(actorRef, message)(timeout)
method defined here.import org.apache.pekko.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 pekko.util.Timeout.
- Definition Classes
- AskSupport
- def askWithStatus(actorRef: ActorRef, message: Any, sender: ActorRef)(implicit timeout: Timeout): Future[Any]
Use for messages whose response is known to be a pekko.pattern.StatusReply.
Use for messages whose response is known to be a pekko.pattern.StatusReply. When a pekko.pattern.StatusReply.Success response arrives the future is completed with the wrapped value, if a pekko.pattern.StatusReply.Error arrives the future is instead failed.
- Definition Classes
- AskSupport
- def askWithStatus(actorRef: ActorRef, message: Any)(implicit timeout: Timeout): Future[Any]
Use for messages whose response is known to be a pekko.pattern.StatusReply.
Use for messages whose response is known to be a pekko.pattern.StatusReply. When a pekko.pattern.StatusReply.Success response arrives the future is completed with the wrapped value, if a pekko.pattern.StatusReply.Error arrives the future is instead failed.
- Definition Classes
- AskSupport
- 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 pekko.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
- 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 org.apache.pekko.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 pekko.actor.Status.Failure to the recipient.
- Definition Classes
- PipeToSupport
- 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 org.apache.pekko.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 pekko.actor.Status.Failure to the recipient.
- Definition Classes
- PipeToSupport
- 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 returnnull
, otherwise an IllegalArgumentException will be through.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
- 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
- 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 to20%
delay. In order to skip this additional delay pass in0
.
- Definition Classes
- RetrySupport
- 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
- object AskableActorRef
- object BackoffOpts
Backoff options allow to specify a number of properties for backoff supervisors.
- object BackoffSupervisor
- object CircuitBreaker
Companion object providing factory methods for Circuit Breaker which runs callbacks in caller's thread
- object CircuitBreakersRegistry extends ExtensionId[CircuitBreakersRegistry] with ExtensionIdProvider
Companion object providing factory methods for Circuit Breaker which runs callbacks in caller's thread
- object FutureRef
- object Patterns
Java API: for Pekko patterns such as
ask
,pipe
and others which work with java.util.concurrent.CompletionStage. - object PromiseRef
- object RetrySupport extends RetrySupport
- object StatusReply
Deprecated Value Members
- object Backoff
- Annotations
- @deprecated
- Deprecated
(Since version Akka 2.5.22) Use new API from BackoffOpts object instead
- object PatternsCS
Java 8+ API for Pekko patterns such as
ask
,pipe
and others which work with java.util.concurrent.CompletionStage.Java 8+ API for Pekko 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 pekko.pattern.Patterns instead.
- Annotations
- @deprecated
- Deprecated
(Since version Akka 2.5.19) Use Patterns instead.