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/*
* Copyright (C) 2009-2020 Lightbend Inc.
*/
package akka.actor
import scala.collection.immutable
import scala.util.control.NoStackTrace
import akka.AkkaException
import akka.annotation.InternalStableApi
import akka.dispatch.{
DequeBasedMessageQueueSemantics,
Envelope,
RequiresMessageQueue,
UnboundedDequeBasedMessageQueueSemantics
}
/**
* The `Stash` trait enables an actor to temporarily stash away messages that can not or
* should not be handled using the actor's current behavior.
*
* Example:
*
* class ActorWithProtocol extends Actor with Stash {
* def receive = {
* case "open" =>
* unstashAll()
* context.become({
* case "write" => // do writing...
* case "close" =>
* unstashAll()
* context.unbecome()
* case msg => stash()
* }, discardOld = false)
* case "done" => // done
* case msg => stash()
* }
* }
*
*
* Note that the `Stash` trait can only be used together with actors that have a deque-based
* mailbox. By default Stash based actors request a Deque based mailbox since the stash
* trait extends `RequiresMessageQueue[DequeBasedMessageQueueSemantics]`.
* You can override the default mailbox provided when `DequeBasedMessageQueueSemantics` are requested via config:
*
* Alternatively, you can add your own requirement marker to the actor and configure a mailbox type to be used
* for your marker.
*
* For a `Stash` that also enforces unboundedness of the deque see [[akka.actor.UnboundedStash]]. For a `Stash`
* that does not enforce any mailbox type see [[akka.actor.UnrestrictedStash]].
*
* Note that the `Stash` trait must be mixed into (a subclass of) the `Actor` trait before
* any trait/class that overrides the `preRestart` callback. This means it's not possible to write
* `Actor with MyActor with Stash` if `MyActor` overrides `preRestart`.
*/
trait Stash extends UnrestrictedStash with RequiresMessageQueue[DequeBasedMessageQueueSemantics]
/**
* The `UnboundedStash` trait is a version of [[akka.actor.Stash]] that enforces an unbounded stash for you actor.
*/
trait UnboundedStash extends UnrestrictedStash with RequiresMessageQueue[UnboundedDequeBasedMessageQueueSemantics]
/**
* A version of [[akka.actor.Stash]] that does not enforce any mailbox type. The proper mailbox has to be configured
* manually, and the mailbox should extend the [[akka.dispatch.DequeBasedMessageQueueSemantics]] marker trait.
*/
trait UnrestrictedStash extends Actor with StashSupport {
/**
* Overridden callback. Prepends all messages in the stash to the mailbox,
* clears the stash, stops all children and invokes the postStop() callback.
*/
@throws(classOf[Exception])
override def preRestart(reason: Throwable, message: Option[Any]): Unit = {
try unstashAll()
finally super.preRestart(reason, message)
}
/**
* Overridden callback. Prepends all messages in the stash to the mailbox and clears the stash.
* Must be called when overriding this method, otherwise stashed messages won't be propagated to DeadLetters
* when actor stops.
*/
@throws(classOf[Exception])
override def postStop(): Unit =
try unstashAll()
finally super.postStop()
}
/**
* INTERNAL API.
*
* A factory for creating stashes for an actor instance.
*
* @see [[StashSupport]]
*/
private[akka] trait StashFactory { this: Actor =>
private[akka] def createStash()(implicit ctx: ActorContext, ref: ActorRef): StashSupport = new StashSupport {
def context: ActorContext = ctx
def self: ActorRef = ref
}
}
/**
* INTERNAL API.
*
* Support trait for implementing a stash for an actor instance. A default stash per actor (= user stash)
* is maintained by [[UnrestrictedStash]] by extending this trait. Actors that explicitly need other stashes
* (optionally in addition to and isolated from the user stash) can create new stashes via [[StashFactory]].
*/
private[akka] trait StashSupport {
/**
* INTERNAL API.
*
* Context of the actor that uses this stash.
*/
private[akka] def context: ActorContext
/**
* INTERNAL API.
*
* Self reference of the actor that uses this stash.
*/
private[akka] def self: ActorRef
/* The private stash of the actor. It is only accessible using `stash()` and
* `unstashAll()`.
*/
private var theStash = Vector.empty[Envelope]
private def actorCell = context.asInstanceOf[ActorCell]
/* The capacity of the stash. Configured in the actor's mailbox or dispatcher config.
*/
private val capacity: Int =
context.system.mailboxes.stashCapacity(context.props.dispatcher, context.props.mailbox)
/**
* INTERNAL API.
*
* The actor's deque-based message queue.
* `mailbox.queue` is the underlying `Deque`.
*/
private[akka] val mailbox: DequeBasedMessageQueueSemantics = {
actorCell.mailbox.messageQueue match {
case queue: DequeBasedMessageQueueSemantics => queue
case other =>
throw ActorInitializationException(
self,
s"DequeBasedMailbox required, got: ${other.getClass.getName}\n" +
"""An (unbounded) deque-based mailbox can be configured as follows:
| my-custom-mailbox {
| mailbox-type = "akka.dispatch.UnboundedDequeBasedMailbox"
| }
|""".stripMargin)
}
}
/**
* Adds the current message (the message that the actor received last) to the
* actor's stash.
*
* @throws StashOverflowException in case of a stash capacity violation
* @throws IllegalStateException if the same message is stashed more than once
*/
def stash(): Unit = {
val currMsg = actorCell.currentMessage
if (theStash.nonEmpty && (currMsg eq theStash.last))
throw new IllegalStateException(s"Can't stash the same message $currMsg more than once")
if (capacity <= 0 || theStash.size < capacity) theStash :+= currMsg
else
throw new StashOverflowException(
s"Couldn't enqueue message ${currMsg.message.getClass.getName} from ${currMsg.sender} to stash of $self")
}
/**
* Prepends `others` to this stash. This method is optimized for a large stash and
* small `others`.
*/
private[akka] def prepend(others: immutable.Seq[Envelope]): Unit =
theStash = others.foldRight(theStash)((e, s) => e +: s)
/**
* Prepends the oldest message in the stash to the mailbox, and then removes that
* message from the stash.
*
* Messages from the stash are enqueued to the mailbox until the capacity of the
* mailbox (if any) has been reached. In case a bounded mailbox overflows, a
* `MessageQueueAppendFailedException` is thrown.
*
* The unstashed message is guaranteed to be removed from the stash regardless
* if the `unstash()` call successfully returns or throws an exception.
*/
private[akka] def unstash(): Unit =
if (theStash.nonEmpty) try {
enqueueFirst(theStash.head)
} finally {
theStash = theStash.tail
}
/**
* Prepends all messages in the stash to the mailbox, and then clears the stash.
*
* Messages from the stash are enqueued to the mailbox until the capacity of the
* mailbox (if any) has been reached. In case a bounded mailbox overflows, a
* `MessageQueueAppendFailedException` is thrown.
*
* The stash is guaranteed to be empty after calling `unstashAll()`.
*/
def unstashAll(): Unit = unstashAll(_ => true)
/**
* INTERNAL API.
*
* Prepends selected messages in the stash, applying `filterPredicate`, to the
* mailbox, and then clears the stash.
*
* Messages from the stash are enqueued to the mailbox until the capacity of the
* mailbox (if any) has been reached. In case a bounded mailbox overflows, a
* `MessageQueueAppendFailedException` is thrown.
*
* The stash is guaranteed to be empty after calling `unstashAll(Any => Boolean)`.
*
* @param filterPredicate only stashed messages selected by this predicate are
* prepended to the mailbox.
*/
@InternalStableApi
private[akka] def unstashAll(filterPredicate: Any => Boolean): Unit = {
try {
val i = theStash.reverseIterator.filter(envelope => filterPredicate(envelope.message))
while (i.hasNext) enqueueFirst(i.next())
} finally {
theStash = Vector.empty[Envelope]
}
}
/**
* INTERNAL API.
*
* Clears the stash and and returns all envelopes that have not been unstashed.
*/
@InternalStableApi
private[akka] def clearStash(): Vector[Envelope] = {
val stashed = theStash
theStash = Vector.empty[Envelope]
stashed
}
/**
* Enqueues `envelope` at the first position in the mailbox. If the message contained in
* the envelope is a `Terminated` message, it will be ensured that it can be re-received
* by the actor.
*/
private def enqueueFirst(envelope: Envelope): Unit = {
mailbox.enqueueFirst(self, envelope)
envelope.message match {
case Terminated(ref) => actorCell.terminatedQueuedFor(ref, None)
case _ =>
}
}
}
/**
* Is thrown when the size of the Stash exceeds the capacity of the Stash
*/
class StashOverflowException(message: String, cause: Throwable = null)
extends AkkaException(message, cause)
with NoStackTrace
