Apache Pekko/org.apache.pekko/org.apache.pekko.pattern

org.apache.pekko.pattern

== Commonly Used Patterns With Pekko ==

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 a org.apache.pekko.actor.ActorRef as a message.
pipeToSelection: feed eventually computed value of a future to a 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);

Attributes

Members list

Packages

== Extended Versions Of Pekko Patterns ==

This subpackage contains extended versions of Apache Pekko patterns.

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. a message.

In Scala the recommended usage is to import the pattern from the package object:

import org.apache.pekko.pattern.extended.ask

ask(actor, askSender => Request(askSender)) // use it directly
actor ask (Request(_))   // 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, new org.apache.pekko.japi.function.Function<ActorRef, Object> {
 Object apply(ActorRef askSender) {
   return new Request(askSender);
 }
});

Attributes

Type members

Classlikes

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

Attributes

Source: AskSupport.scala
Supertypes: class Object

trait Matchable

class Any

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.

Attributes

Source: AskSupport.scala
Supertypes: trait NoStackTrace

class TimeoutException

class Exception

class Throwable

trait Serializable

class Object

trait Matchable

class Any
Show all

Attributes

Companion: class
Source: AskSupport.scala
Supertypes: class Object

trait Matchable

class Any
Self type: AskableActorRef.type

Attributes

Companion: object
Source: AskSupport.scala
Supertypes: class AnyVal

trait Matchable

class Any

Attributes

Source: AskSupport.scala
Supertypes: class AnyVal

trait Matchable

class Any

@DoNotInherit

Attributes

Source: BackoffOptions.scala
Supertypes: class Object

trait Matchable

class Any

@DoNotInherit

Attributes

Source: BackoffOptions.scala
Supertypes: class Object

trait Matchable

class Any

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

Attributes

Source: BackoffOptions.scala
Supertypes: class Object

trait Matchable

class Any
Self type: BackoffOpts.type

Attributes

Source: BackoffSupervisor.scala
Supertypes: class Object

trait Matchable

class Any
Self type: BackoffSupervisor.type

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

Attributes

Companion: class
Source: CircuitBreaker.scala
Supertypes: class Object

trait Matchable

class Any
Self type: CircuitBreaker.type

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.

Value parameters

callTimeout: scala.concurrent.duration.FiniteDuration of time after which to consider a call a failure
executor: scala.concurrent.ExecutionContext used for execution of state transition listeners
maxFailures: Maximum number of failures before opening the circuit
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. randomFactor should be in range 0.0 (inclusive) and 1.0 (inclusive). In order to skip this additional delay pass in 0.
resetTimeout: scala.concurrent.duration.FiniteDuration of time after which to attempt to close the circuit
scheduler: Reference to Pekko scheduler

Attributes

Companion: object
Source: CircuitBreaker.scala
Supertypes: class Object

trait Matchable

class Any

Exception thrown when Circuit Breaker is open.

Value parameters

message: Defaults to "Circuit Breaker is open; calls are failing fast"
remainingDuration: Stores remaining time before attempting a reset. Zero duration means the breaker is currently in half-open state.

Attributes

Source: CircuitBreaker.scala
Supertypes: trait NoStackTrace

class PekkoException

class RuntimeException

class Exception

class Throwable

trait Serializable

class Object

trait Matchable

class Any
Show all

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

Attributes

Companion: class
Source: CircuitBreakersRegistry.scala
Supertypes: trait ExtensionIdProvider

trait ExtensionId[CircuitBreakersRegistry]

class Object

trait Matchable

class Any
Self type: CircuitBreakersRegistry.type

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

Attributes

Companion: object
Source: CircuitBreakersRegistry.scala
Supertypes: trait Extension

class Object

trait Matchable

class Any

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

Attributes

Source: AskSupport.scala
Supertypes: class Object

trait Matchable

class Any

Attributes

Source: AskSupport.scala
Supertypes: class AnyVal

trait Matchable

class Any

Attributes

Source: AskSupport.scala
Supertypes: class AnyVal

trait Matchable

class Any

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.

Attributes

Companion: object
Source: PromiseRef.scala
Supertypes: class Object

trait Matchable

class Any

Attributes

Companion: trait
Source: PromiseRef.scala
Supertypes: class Object

trait Matchable

class Any
Self type: FutureRef.type

Attributes

Source: FutureTimeoutSupport.scala
Supertypes: class Object

trait Matchable

class Any

Attributes

Source: GracefulStopSupport.scala
Supertypes: class Object

trait Matchable

class Any

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

Attributes

Source: Patterns.scala
Supertypes: class Object

trait Matchable

class Any
Self type: Patterns.type

Attributes

Source: PipeToSupport.scala
Supertypes: class Object

trait Matchable

class Any

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.

Attributes

Companion: object
Source: PromiseRef.scala
Supertypes: class Object

trait Matchable

class Any
Self type: FutureRef[T]

Attributes

Companion: trait
Source: PromiseRef.scala
Supertypes: class Object

trait Matchable

class Any
Self type: PromiseRef.type

This trait provides the retry utility function

Attributes

Companion: object
Source: RetrySupport.scala
Supertypes: class Object

trait Matchable

class Any
Known subtypes: object RetrySupport

Attributes

Companion: trait
Source: RetrySupport.scala
Supertypes: trait RetrySupport

class Object

trait Matchable

class Any
Self type: RetrySupport.type

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.

Type parameters

T: the type of value a successful reply would have

Attributes

Companion: object
Source: StatusReply.scala
Supertypes: class Object

trait Matchable

class Any

Attributes

Companion: class
Source: StatusReply.scala
Supertypes: class Object

trait Matchable

class Any
Self type: StatusReply.type

Inherited classlikes

Attributes

Inherited from:: PipeToSupport
Source: PipeToSupport.scala
Supertypes: class Object

trait Matchable

class Any

Attributes

Inherited from:: PipeToSupport
Source: PipeToSupport.scala
Supertypes: class Object

trait Matchable

class Any

Value members

Inherited methods

Returns a scala.concurrent.Future that will be completed with the success or failure of the provided value after the specified duration.

Attributes

Inherited from:: FutureTimeoutSupport
Source: FutureTimeoutSupport.scala

Returns a scala.concurrent.Future that will be completed with the success or failure of the provided value after the specified duration.

Attributes

Inherited from:: FutureTimeoutSupport
Source: FutureTimeoutSupport.scala

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

Attributes

Inherited from:: FutureTimeoutSupport
Source: FutureTimeoutSupport.scala

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

Attributes

Inherited from:: FutureTimeoutSupport
Source: FutureTimeoutSupport.scala

Attributes

Inherited from:: AskSupport
Source: AskSupport.scala

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 a 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 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

Attributes

Inherited from:: AskSupport
Source: AskSupport.scala

Attributes

Inherited from:: AskSupport
Source: AskSupport.scala

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.

Recommended usage:

 val f = ask(worker, request)(timeout)
 f.map { response =>
   EnrichedMessage(response)
 } pipeTo nextActor

Attributes

Inherited from:: AskSupport
Source: AskSupport.scala

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.

Attributes

Inherited from:: AskSupport
Source: AskSupport.scala

Attributes

Inherited from:: AskSupport
Source: AskSupport.scala

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
 }

Attributes

Inherited from:: GracefulStopSupport
Source: GracefulStopSupport.scala

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

When the future is completed, the shouldRetry predicate is always been invoked with the result (or null if none) and the exception (or null if none). If the shouldRetry predicate returns true, then a new attempt is made, each subsequent attempt will be made after the 'delay' return by delayFunction (the input next attempt count start from 1). Returns scala.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 a java.lang.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 (i.e. not touch unsafe mutable state).

Example usage:

//retry with back off

protected val sendAndReceive: HttpRequest => Future[HttpResponse]
protected val shouldRetry: (HttpResponse, Throwable) => throwable ne null
private val sendReceiveRetry: HttpRequest => Future[HttpResponse] = (req: HttpRequest) => retry[HttpResponse](
 attempt = () => sendAndReceive(req),
 shouldRetry,
 attempts = 10,
 delayFunction = attempted => Option(2.seconds * attempted)
)

Value parameters

attempt: the function to be attempted
attempts: the maximum number of attempts
delayFunction: the function to generate the next delay duration, None for no delay
ec: the execution context
scheduler: the scheduler for scheduling a delay
shouldRetry: the predicate to determine if the attempt should be retried

Attributes

Returns: the result future which maybe retried
Since: 1.1.0
Inherited from:: RetrySupport
Source: RetrySupport.scala

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 scala.None for no delay.

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)
)

Attributes

Inherited from:: RetrySupport
Source: RetrySupport.scala

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

Example usage:

protected val sendAndReceive: HttpRequest => Future[HttpResponse]
protected val shouldRetry: (HttpResponse, Throwable) => throwable ne null
private val sendReceiveRetry: HttpRequest => Future[HttpResponse] = (req: HttpRequest) => retry[HttpResponse](
 attempt = () => sendAndReceive(req),
 shouldRetry,
 attempts = 10,
 delay = 2.seconds
)

Value parameters

attempt: the function to be attempted
attempts: the maximum number of attempts
delay: the delay duration
ec: the execution context
scheduler: the scheduler for scheduling a delay
shouldRetry: the predicate to determine if the attempt should be retried

Attributes

Returns: the result future which maybe retried
Since: 1.1.0
Inherited from:: RetrySupport
Source: RetrySupport.scala

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.

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
)

Attributes

Inherited from:: RetrySupport
Source: RetrySupport.scala

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

Example usage:

protected val sendAndReceive: HttpRequest => Future[HttpResponse]
protected val shouldRetry: (HttpResponse, Throwable) => throwable ne null
private val sendReceiveRetry: HttpRequest => Future[HttpResponse] = (req: HttpRequest) => retry[HttpResponse](
 attempt = () => sendAndReceive(req),
 shouldRetry,
 attempts = 10,
 minBackoff = 1.seconds,
 maxBackoff = 2.seconds,
 randomFactor = 0.5
)

Value parameters

attempt: the function to be attempted
attempts: the maximum number of attempts
ec: the execution context
maxBackoff: the exponential back-off is capped to this duration
minBackoff: minimum (initial) duration until the child actor will started again, if it is terminated
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.
scheduler: the scheduler for scheduling a delay
shouldRetry: the predicate to determine if the attempt should be retried

Attributes

Returns: the result future which maybe retried
Since: 1.1.0
Inherited from:: RetrySupport
Source: RetrySupport.scala

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.

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
)

Value parameters

maxBackoff: the exponential back-off is capped to this duration
minBackoff: minimum (initial) duration until the child actor will started again, if it is terminated
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.

Attributes

Inherited from:: RetrySupport
Source: RetrySupport.scala

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

Example usage:

def possiblyFailing(): Future[Something] = ???
val shouldRetry: (Something, Throwable) => throwable ne null
val withRetry: Future[Something] = retry(attempt = possiblyFailing, shouldRetry, attempts = 10)

Value parameters

attempt: the function to be attempted
attempts: the maximum number of attempts
ec: the execution context
shouldRetry: the predicate to determine if the attempt should be retried

Attributes

Returns: the result future which maybe retried
Since: 1.1.0
Inherited from:: RetrySupport
Source: RetrySupport.scala

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.

Example usage:

def possiblyFailing(): Future[Something] = ???
val withRetry: Future[Something] = retry(attempt = possiblyFailing, attempts = 10)

Attributes

Inherited from:: RetrySupport
Source: RetrySupport.scala

Returns a scala.concurrent.Future that will be completed with a TimeoutException if the provided value is not completed within the specified duration.

Attributes

Since: 1.2.0
Inherited from:: FutureTimeoutSupport
Source: FutureTimeoutSupport.scala

Deprecated and Inherited methods

Returns a java.util.concurrent.CompletionStage that will be completed with a TimeoutException if the provided value is not completed within the specified duration.

Attributes

Since: 1.2.0
Deprecated: [Since version 2.0.0] Use `CompletableFuture#orTimeout instead.
Inherited from:: FutureTimeoutSupport
Source: FutureTimeoutSupport.scala

Implicits

Inherited implicits

Import this implicit conversion to gain ? and ask methods on pekko.actor.ActorSelection, which will defer to the ask(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.

Attributes

Inherited from:: AskSupport
Source: AskSupport.scala

Import this implicit conversion to gain ? and ask methods on pekko.actor.ActorRef, which will defer to the ask(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.

Attributes

Inherited from:: AskSupport
Source: AskSupport.scala

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.

Attributes

Inherited from:: PipeToSupport
Source: PipeToSupport.scala

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.

Attributes

Inherited from:: PipeToSupport
Source: PipeToSupport.scala

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