pattern
This object contains implementation details of the “ask” pattern.
This is what is used to complete a Future that is returned from an ask/? call, when it times out.
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)
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
with Backoff.onStop.
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.
Exception thrown when Circuit Breaker is open.
This object contains implementation details of the “ask” pattern, which can be combined with "replyTo" pattern.
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.
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.
Builds back-off options for creating a back-off supervisor.
Builds back-off options for creating a back-off supervisor.
You can pass BackoffOptions to akka.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
}
)
.withReplyWhileStopped(TheSystemIsDown)
Companion object providing factory methods for Circuit Breaker which runs callbacks in caller's thread
"Pre Java 8" Java API for Akka patterns such as ask, pipe and others.
"Pre Java 8" Java API for Akka patterns such as ask, pipe and others.
These methods are possible to call from Java however work with the Scala scala.concurrent.Future, due to the lack of non-blocking reactive Future implementation before Java 8.
For Java applications developed with Java 8 and later, you might want to use akka.pattern.PatternsCS instead, which provide alternatives for these patterns 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.
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.
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.
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.
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
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.
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
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.
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
}
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 nextActorThe 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.
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 nextActorThe 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.
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:
For Java the patterns are available as static methods of the akka.pattern.Patterns class:
import static akka.pattern.Patterns.ask; ask(actor, message);