Adding high-performance MPSC queue based mailbox to Akka

akka-actor/src/main/scala/akka/dispatch/Mailbox.scala

@@ -10,10 +10,10 @@ import akka.actor.{ ActorCell, ActorRef, Cell, ActorSystem, InternalActorRef, De
 import akka.util.{ Unsafe, BoundedBlockingQueue }
 import akka.event.Logging.Error
 import scala.concurrent.duration.Duration
+import scala.concurrent.duration.FiniteDuration
 import scala.annotation.tailrec
 import scala.util.control.NonFatal
 import com.typesafe.config.Config
-import scala.concurrent.duration.FiniteDuration
 
 /**
  * INTERNAL API
@@ -193,9 +193,6 @@ private[akka] abstract class Mailbox(val messageQueue: MessageQueue)
     updateStatus(s, s & ~Scheduled) || setAsIdle()
   }
 
-  /*
-   * AtomicReferenceFieldUpdater for system queue.
-   */
   protected final def systemQueueGet: SystemMessage =
     Unsafe.instance.getObjectVolatile(this, AbstractMailbox.systemMessageOffset).asInstanceOf[SystemMessage]
 
@@ -343,6 +340,28 @@ trait MessageQueue {
   def cleanUp(owner: ActorRef, deadLetters: MessageQueue): Unit
 }
 
+class NodeMessageQueue extends AbstractNodeQueue[Envelope] with MessageQueue {
+
+  final def enqueue(receiver: ActorRef, handle: Envelope): Unit = add(handle)
+
+  final def dequeue(): Envelope = poll()
+
+  final def numberOfMessages: Int = {
+    @tailrec def count(node: AbstractNodeQueue.Node[Envelope], c: Int): Int = if (node eq null) c else count(node.next(), c + 1)
+    count(peek(), 0)
+  }
+
+  final def hasMessages: Boolean = peek() ne null
+
+  @tailrec final def cleanUp(owner: ActorRef, deadLetters: MessageQueue): Unit = {
+    val envelope = dequeue()
+    if (envelope ne null) {
+      deadLetters.enqueue(owner, envelope)
+      cleanUp(owner, deadLetters)
+    }
+  }
+}
+
 /**
  * INTERNAL API
  */
@@ -518,6 +537,18 @@ case class UnboundedMailbox() extends MailboxType {
     }
 }
 
+/**
+ * MPSCUnboundedMailbox is a high-performance unbounded MailboxType,
+ * the only drawback is that you can't have multiple consumers,
+ * which rules out using it with BalancingDispatcher for instance.
+ */
+case class MPSCUnboundedMailbox() extends MailboxType {
+
+  def this(settings: ActorSystem.Settings, config: Config) = this()
+
+  final override def create(owner: Option[ActorRef], system: Option[ActorSystem]): MessageQueue = new NodeMessageQueue()
+}
+
 /**
  * BoundedMailbox is the default bounded MailboxType used by Akka Actors.
  */