akka.routing.SmallestMailbox.scala Maven / Gradle / Ivy
/*
* Copyright (C) 2009-2019 Lightbend Inc.
*/
package akka.routing
import scala.annotation.tailrec
import scala.collection.immutable
import java.util.concurrent.ThreadLocalRandom
import com.typesafe.config.Config
import akka.actor.ActorCell
import akka.actor.ActorRefWithCell
import akka.actor.SupervisorStrategy
import akka.dispatch.Dispatchers
import akka.actor.ActorSystem
import com.github.ghik.silencer.silent
object SmallestMailboxRoutingLogic {
def apply(): SmallestMailboxRoutingLogic = new SmallestMailboxRoutingLogic
}
/**
* Tries to send to the non-suspended routee with fewest messages in mailbox.
* The selection is done in this order:
*
* - pick any idle routee (not processing message) with empty mailbox
* - pick any routee with empty mailbox
* - pick routee with fewest pending messages in mailbox
* - pick any remote routee, remote actors are consider lowest priority,
* since their mailbox size is unknown
*
*/
@silent
@SerialVersionUID(1L)
class SmallestMailboxRoutingLogic extends RoutingLogic {
override def select(message: Any, routees: immutable.IndexedSeq[Routee]): Routee =
if (routees.isEmpty) NoRoutee
else selectNext(routees)
// Worst-case a 2-pass inspection with mailbox size checking done on second pass, and only until no one empty is found.
// Lowest score wins, score 0 is autowin
// If no actor with score 0 is found, it will return that, or if it is terminated, a random of the entire set.
// Why? Well, in case we had 0 viable actors and all we got was the default, which is the DeadLetters, anything else is better.
// Order of interest, in ascending priority:
// 1. The NoRoutee
// 2. A Suspended ActorRef
// 3. An ActorRef with unknown mailbox size but with one message being processed
// 4. An ActorRef with unknown mailbox size that isn't processing anything
// 5. An ActorRef with a known mailbox size
// 6. An ActorRef without any messages
@tailrec private def selectNext(
targets: immutable.IndexedSeq[Routee],
proposedTarget: Routee = NoRoutee,
currentScore: Long = Long.MaxValue,
at: Int = 0,
deep: Boolean = false): Routee = {
if (targets.isEmpty)
NoRoutee
else if (at >= targets.size) {
if (deep) {
if (isTerminated(proposedTarget)) targets(ThreadLocalRandom.current.nextInt(targets.size)) else proposedTarget
} else selectNext(targets, proposedTarget, currentScore, 0, deep = true)
} else {
val target = targets(at)
val newScore: Long =
if (isSuspended(target)) Long.MaxValue - 1
else { //Just about better than the DeadLetters
(if (isProcessingMessage(target)) 1L else 0L) +
(if (!hasMessages(target)) 0L
else { //Race between hasMessages and numberOfMessages here, unfortunate the numberOfMessages returns 0 if unknown
val noOfMsgs: Long = if (deep) numberOfMessages(target) else 0
if (noOfMsgs > 0) noOfMsgs else Long.MaxValue - 3 //Just better than a suspended actorref
})
}
if (newScore == 0) target
else if (newScore < 0 || newScore >= currentScore) selectNext(targets, proposedTarget, currentScore, at + 1, deep)
else selectNext(targets, target, newScore, at + 1, deep)
}
}
// TODO should we rewrite this not to use isTerminated?
@silent
protected def isTerminated(a: Routee): Boolean = a match {
case ActorRefRoutee(ref) => ref.isTerminated
case _ => false
}
/**
* Returns true if the actor is currently processing a message.
* It will always return false for remote actors.
* Method is exposed to subclasses to be able to implement custom
* routers based on mailbox and actor internal state.
*/
protected def isProcessingMessage(a: Routee): Boolean = a match {
case ActorRefRoutee(x: ActorRefWithCell) =>
x.underlying match {
case cell: ActorCell => cell.mailbox.isScheduled && cell.currentMessage != null
case _ => false
}
case _ => false
}
/**
* Returns true if the actor currently has any pending messages
* in the mailbox, i.e. the mailbox is not empty.
* It will always return false for remote actors.
* Method is exposed to subclasses to be able to implement custom
* routers based on mailbox and actor internal state.
*/
protected def hasMessages(a: Routee): Boolean = a match {
case ActorRefRoutee(x: ActorRefWithCell) => x.underlying.hasMessages
case _ => false
}
/**
* Returns true if the actor is currently suspended.
* It will always return false for remote actors.
* Method is exposed to subclasses to be able to implement custom
* routers based on mailbox and actor internal state.
*/
protected def isSuspended(a: Routee): Boolean = a match {
case ActorRefRoutee(x: ActorRefWithCell) =>
x.underlying match {
case cell: ActorCell => cell.mailbox.isSuspended
case _ => true
}
case _ => false
}
/**
* Returns the number of pending messages in the mailbox of the actor.
* It will always return 0 for remote actors.
* Method is exposed to subclasses to be able to implement custom
* routers based on mailbox and actor internal state.
*/
protected def numberOfMessages(a: Routee): Int = a match {
case ActorRefRoutee(x: ActorRefWithCell) => x.underlying.numberOfMessages
case _ => 0
}
}
/**
* A router pool that tries to send to the non-suspended routee with fewest messages in mailbox.
* The selection is done in this order:
*
* - pick any idle routee (not processing message) with empty mailbox
* - pick any routee with empty mailbox
* - pick routee with fewest pending messages in mailbox
* - pick any remote routee, remote actors are consider lowest priority,
* since their mailbox size is unknown
*
*
* The configuration parameter trumps the constructor arguments. This means that
* if you provide `nrOfInstances` during instantiation they will be ignored if
* the router is defined in the configuration file for the actor being used.
*
* Supervision Setup
*
* Any routees that are created by a router will be created as the router's children.
* The router is therefore also the children's supervisor.
*
* The supervision strategy of the router actor can be configured with
* [[#withSupervisorStrategy]]. If no strategy is provided, routers default to
* a strategy of “always escalate”. This means that errors are passed up to the
* router's supervisor for handling.
*
* The router's supervisor will treat the error as an error with the router itself.
* Therefore a directive to stop or restart will cause the router itself to stop or
* restart. The router, in turn, will cause its children to stop and restart.
*
* @param nrOfInstances initial number of routees in the pool
*
* @param resizer optional resizer that dynamically adjust the pool size
*
* @param supervisorStrategy strategy for supervising the routees, see 'Supervision Setup'
*
* @param routerDispatcher dispatcher to use for the router head actor, which handles
* supervision, death watch and router management messages
*/
@silent
@SerialVersionUID(1L)
final case class SmallestMailboxPool(
val nrOfInstances: Int,
override val resizer: Option[Resizer] = None,
override val supervisorStrategy: SupervisorStrategy = Pool.defaultSupervisorStrategy,
override val routerDispatcher: String = Dispatchers.DefaultDispatcherId,
override val usePoolDispatcher: Boolean = false)
extends Pool
with PoolOverrideUnsetConfig[SmallestMailboxPool] {
def this(config: Config) =
this(
nrOfInstances = config.getInt("nr-of-instances"),
resizer = Resizer.fromConfig(config),
usePoolDispatcher = config.hasPath("pool-dispatcher"))
/**
* Java API
* @param nr initial number of routees in the pool
*/
def this(nr: Int) = this(nrOfInstances = nr)
override def createRouter(system: ActorSystem): Router = new Router(SmallestMailboxRoutingLogic())
override def nrOfInstances(sys: ActorSystem) = this.nrOfInstances
/**
* Setting the supervisor strategy to be used for the “head” Router actor.
*/
def withSupervisorStrategy(strategy: SupervisorStrategy): SmallestMailboxPool = copy(supervisorStrategy = strategy)
/**
* Setting the resizer to be used.
*/
def withResizer(resizer: Resizer): SmallestMailboxPool = copy(resizer = Some(resizer))
/**
* Setting the dispatcher to be used for the router head actor, which handles
* supervision, death watch and router management messages.
*/
def withDispatcher(dispatcherId: String): SmallestMailboxPool = copy(routerDispatcher = dispatcherId)
/**
* Uses the resizer and/or the supervisor strategy of the given RouterConfig
* if this RouterConfig doesn't have one, i.e. the resizer defined in code is used if
* resizer was not defined in config.
*/
override def withFallback(other: RouterConfig): RouterConfig = this.overrideUnsetConfig(other)
}
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