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/**
* Copyright (C) 2009-2014 Typesafe Inc.
*/
package akka.pattern
import java.util.concurrent.TimeoutException
import akka.actor._
import akka.dispatch.sysmsg._
import akka.util.{ Timeout, Unsafe }
import scala.annotation.tailrec
import scala.concurrent.{ ExecutionContext, Future, Promise }
import scala.language.implicitConversions
import scala.util.{ Failure, Success }
/**
* This is what is used to complete a Future that is returned from an ask/? call,
* when it times out.
*/
class AskTimeoutException(message: String, cause: Throwable) extends TimeoutException(message) {
def this(message: String) = this(message, null: Throwable)
override def getCause(): Throwable = cause
}
/**
* This object contains implementation details of the “ask” pattern.
*/
trait AskSupport {
/**
* 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]].
*/
implicit def ask(actorRef: ActorRef): AskableActorRef = new AskableActorRef(actorRef)
/**
* 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
* }}}
*
*/
def ask(actorRef: ActorRef, message: Any)(implicit timeout: Timeout): Future[Any] = actorRef ? message
/**
* 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]].
*/
implicit def ask(actorSelection: ActorSelection): AskableActorSelection = new AskableActorSelection(actorSelection)
/**
* 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
* }}}
*
*/
def ask(actorSelection: ActorSelection, message: Any)(implicit timeout: Timeout): Future[Any] = actorSelection ? message
}
/*
* Implementation class of the “ask” pattern enrichment of ActorRef
*/
final class AskableActorRef(val actorRef: ActorRef) extends AnyVal {
def ask(message: Any)(implicit timeout: Timeout): Future[Any] = actorRef match {
case ref: InternalActorRef if ref.isTerminated ⇒
actorRef ! message
Future.failed[Any](new AskTimeoutException(s"Recipient[$actorRef] had already been terminated."))
case ref: InternalActorRef ⇒
if (timeout.duration.length <= 0)
Future.failed[Any](new IllegalArgumentException(s"Timeout length must not be negative, question not sent to [$actorRef]"))
else {
val a = PromiseActorRef(ref.provider, timeout, targetName = actorRef.toString)
actorRef.tell(message, a)
a.result.future
}
case _ ⇒ Future.failed[Any](new IllegalArgumentException(s"Unsupported recipient ActorRef type, question not sent to [$actorRef]"))
}
def ?(message: Any)(implicit timeout: Timeout): Future[Any] = ask(message)(timeout)
}
/*
* Implementation class of the “ask” pattern enrichment of ActorSelection
*/
final class AskableActorSelection(val actorSel: ActorSelection) extends AnyVal {
def ask(message: Any)(implicit timeout: Timeout): Future[Any] = actorSel.anchor match {
case ref: InternalActorRef ⇒
if (timeout.duration.length <= 0)
Future.failed[Any](
new IllegalArgumentException(s"Timeout length must not be negative, question not sent to [$actorSel]"))
else {
val a = PromiseActorRef(ref.provider, timeout, targetName = actorSel.toString)
actorSel.tell(message, a)
a.result.future
}
case _ ⇒ Future.failed[Any](new IllegalArgumentException(s"Unsupported recipient ActorRef type, question not sent to [$actorSel]"))
}
def ?(message: Any)(implicit timeout: Timeout): Future[Any] = ask(message)(timeout)
}
/**
* Akka private optimized representation of the temporary actor spawned to
* receive the reply to an "ask" operation.
*
* INTERNAL API
*/
private[akka] final class PromiseActorRef private (val provider: ActorRefProvider, val result: Promise[Any])
extends MinimalActorRef {
import AbstractPromiseActorRef.{ stateOffset, watchedByOffset }
import PromiseActorRef._
/**
* As an optimization for the common (local) case we only register this PromiseActorRef
* with the provider when the `path` member is actually queried, which happens during
* serialization (but also during a simple call to `toString`, `equals` or `hashCode`!).
*
* Defined states:
* null => started, path not yet created
* Registering => currently creating temp path and registering it
* path: ActorPath => path is available and was registered
* StoppedWithPath(path) => stopped, path available
* Stopped => stopped, path not yet created
*/
@volatile
private[this] var _stateDoNotCallMeDirectly: AnyRef = _
@volatile
private[this] var _watchedByDoNotCallMeDirectly: Set[ActorRef] = ActorCell.emptyActorRefSet
@inline
private[this] def watchedBy: Set[ActorRef] = Unsafe.instance.getObjectVolatile(this, watchedByOffset).asInstanceOf[Set[ActorRef]]
@inline
private[this] def updateWatchedBy(oldWatchedBy: Set[ActorRef], newWatchedBy: Set[ActorRef]): Boolean =
Unsafe.instance.compareAndSwapObject(this, watchedByOffset, oldWatchedBy, newWatchedBy)
@tailrec // Returns false if the Promise is already completed
private[this] final def addWatcher(watcher: ActorRef): Boolean = watchedBy match {
case null ⇒ false
case other ⇒ updateWatchedBy(other, other + watcher) || addWatcher(watcher)
}
@tailrec
private[this] final def remWatcher(watcher: ActorRef): Unit = watchedBy match {
case null ⇒ ()
case other ⇒ if (!updateWatchedBy(other, other - watcher)) remWatcher(watcher)
}
@tailrec
private[this] final def clearWatchers(): Set[ActorRef] = watchedBy match {
case null ⇒ ActorCell.emptyActorRefSet
case other ⇒ if (!updateWatchedBy(other, null)) clearWatchers() else other
}
@inline
private[this] def state: AnyRef = Unsafe.instance.getObjectVolatile(this, stateOffset)
@inline
private[this] def updateState(oldState: AnyRef, newState: AnyRef): Boolean =
Unsafe.instance.compareAndSwapObject(this, stateOffset, oldState, newState)
@inline
private[this] def setState(newState: AnyRef): Unit = Unsafe.instance.putObjectVolatile(this, stateOffset, newState)
override def getParent: InternalActorRef = provider.tempContainer
def internalCallingThreadExecutionContext: ExecutionContext =
provider.guardian.underlying.systemImpl.internalCallingThreadExecutionContext
/**
* Contract of this method:
* Must always return the same ActorPath, which must have
* been registered if we haven't been stopped yet.
*/
@tailrec
def path: ActorPath = state match {
case null ⇒
if (updateState(null, Registering)) {
var p: ActorPath = null
try {
p = provider.tempPath()
provider.registerTempActor(this, p)
p
} finally { setState(p) }
} else path
case p: ActorPath ⇒ p
case StoppedWithPath(p) ⇒ p
case Stopped ⇒
// even if we are already stopped we still need to produce a proper path
updateState(Stopped, StoppedWithPath(provider.tempPath()))
path
case Registering ⇒ path // spin until registration is completed
}
override def !(message: Any)(implicit sender: ActorRef = Actor.noSender): Unit = state match {
case Stopped | _: StoppedWithPath ⇒ provider.deadLetters ! message
case _ ⇒
if (message == null) throw new InvalidMessageException("Message is null")
if (!(result.tryComplete(
message match {
case Status.Success(r) ⇒ Success(r)
case Status.Failure(f) ⇒ Failure(f)
case other ⇒ Success(other)
}))) provider.deadLetters ! message
}
override def sendSystemMessage(message: SystemMessage): Unit = message match {
case _: Terminate ⇒ stop()
case DeathWatchNotification(a, ec, at) ⇒ this.!(Terminated(a)(existenceConfirmed = ec, addressTerminated = at))
case Watch(watchee, watcher) ⇒
if (watchee == this && watcher != this) {
if (!addWatcher(watcher))
// ➡➡➡ NEVER SEND THE SAME SYSTEM MESSAGE OBJECT TO TWO ACTORS ⬅⬅⬅
watcher.sendSystemMessage(DeathWatchNotification(watchee, existenceConfirmed = true, addressTerminated = false))
} else System.err.println("BUG: illegal Watch(%s,%s) for %s".format(watchee, watcher, this))
case Unwatch(watchee, watcher) ⇒
if (watchee == this && watcher != this) remWatcher(watcher)
else System.err.println("BUG: illegal Unwatch(%s,%s) for %s".format(watchee, watcher, this))
case _ ⇒
}
@deprecated("Use context.watch(actor) and receive Terminated(actor)", "2.2") override def isTerminated: Boolean = state match {
case Stopped | _: StoppedWithPath ⇒ true
case _ ⇒ false
}
@tailrec
override def stop(): Unit = {
def ensureCompleted(): Unit = {
result tryComplete ActorStopResult
val watchers = clearWatchers()
if (!watchers.isEmpty) {
watchers foreach { watcher ⇒
// ➡➡➡ NEVER SEND THE SAME SYSTEM MESSAGE OBJECT TO TWO ACTORS ⬅⬅⬅
watcher.asInstanceOf[InternalActorRef]
.sendSystemMessage(DeathWatchNotification(this, existenceConfirmed = true, addressTerminated = false))
}
}
}
state match {
case null ⇒ // if path was never queried nobody can possibly be watching us, so we don't have to publish termination either
if (updateState(null, Stopped)) ensureCompleted() else stop()
case p: ActorPath ⇒
if (updateState(p, StoppedWithPath(p))) { try ensureCompleted() finally provider.unregisterTempActor(p) } else stop()
case Stopped | _: StoppedWithPath ⇒ // already stopped
case Registering ⇒ stop() // spin until registration is completed before stopping
}
}
}
/**
* INTERNAL API
*/
private[akka] object PromiseActorRef {
private case object Registering
private case object Stopped
private case class StoppedWithPath(path: ActorPath)
private val ActorStopResult = Failure(new ActorKilledException("Stopped"))
def apply(provider: ActorRefProvider, timeout: Timeout, targetName: String): PromiseActorRef = {
val result = Promise[Any]()
val scheduler = provider.guardian.underlying.system.scheduler
val a = new PromiseActorRef(provider, result)
implicit val ec = a.internalCallingThreadExecutionContext
val f = scheduler.scheduleOnce(timeout.duration) {
result tryComplete Failure(new AskTimeoutException(s"Ask timed out on [$targetName] after [${timeout.duration.toMillis} ms]"))
}
result.future onComplete { _ ⇒ try a.stop() finally f.cancel() }
a
}
}
