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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- By Inheritance
- pattern
- FutureTimeoutSupport
- GracefulStopSupport
- AskSupport
- PipeToSupport
- AnyRef
- Any
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Type Members
-
trait
AskSupport
extends AnyRef
This object contains implementation details of the “ask” pattern.
-
class
AskTimeoutException
extends TimeoutException
This is what is used to complete a Future that is returned from an ask/? call, when it times out.
- final class AskableActorRef extends AnyVal
- final class AskableActorSelection extends AnyVal
-
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)
-
final
class
BackoffSupervisor
extends Actor with HandleBackoff
Back-off supervisor that stops and starts a child actor using a back-off algorithm when the child actor stops.
Back-off supervisor that stops and starts a child actor using a back-off algorithm when the child actor stops. This back-off supervisor is created by using
akka.pattern.BackoffSupervisor.props
withBackoff.onStop
. -
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 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 AkkaException with NoStackTrace
Exception thrown when Circuit Breaker is open.
-
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.
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
afterCompletionStage[T](duration: FiniteDuration, using: Scheduler)(value: ⇒ CompletionStage[T])(implicit ec: ExecutionContext): CompletionStage[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
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 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. inAwait.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
-
implicit
def
ask(actorSelection: ActorSelection): AskableActorSelection
Import this implicit conversion to gain
?
andask
methods on akka.actor.ActorSelection, which will defer to theask(actorSelection, message)(timeout)
method defined here.Import this implicit conversion to gain
?
andask
methods on akka.actor.ActorSelection, which will defer to theask(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
-
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 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. inAwait.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
-
implicit
def
ask(actorRef: ActorRef): AskableActorRef
Import this implicit conversion to gain
?
andask
methods on akka.actor.ActorRef, which will defer to theask(actorRef, message)(timeout)
method defined here.Import this implicit conversion to gain
?
andask
methods on akka.actor.ActorRef, which will defer to theask(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
-
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
-
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
-
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 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
- object AskableActorRef
- object AskableActorSelection
-
object
Backoff
Builds back-off options for creating a back-off supervisor.
Builds back-off options for creating a back-off supervisor. You can pass
BackoffOptions
toakka.pattern.BackoffSupervisor.props
. An example of creating back-off options:Backoff.onFailure(childProps, childName, minBackoff, maxBackoff, randomFactor) .withManualReset .withSupervisorStrategy( OneforOneStrategy(){ case e: GivingUpException => Stop case e: RetryableException => Restart } )
- object BackoffSupervisor
-
object
CircuitBreaker
Companion object providing factory methods for Circuit Breaker which runs callbacks in caller's thread
- object FutureRef
- object Patterns
- object PatternsCS
- object PromiseRef