diff --git a/akka-actor-tests/src/test/scala/akka/actor/dispatch/ActorModelSpec.scala b/akka-actor-tests/src/test/scala/akka/actor/dispatch/ActorModelSpec.scala
index 46bf609c7a..deafb9cdc1 100644
--- a/akka-actor-tests/src/test/scala/akka/actor/dispatch/ActorModelSpec.scala
+++ b/akka-actor-tests/src/test/scala/akka/actor/dispatch/ActorModelSpec.scala
@@ -110,8 +110,9 @@ object ActorModelSpec {
     val stops = new AtomicLong(0)
 
     def getStats(actorRef: ActorRef) = {
-      stats.putIfAbsent(actorRef, new InterceptorStats) match {
-        case null  ⇒ stats.get(actorRef)
+      val is = new InterceptorStats
+      stats.putIfAbsent(actorRef, is) match {
+        case null  ⇒ is
         case other ⇒ other
       }
     }
@@ -127,12 +128,12 @@ object ActorModelSpec {
     }
 
     protected[akka] abstract override def register(actor: ActorCell) {
-      getStats(actor.self).registers.incrementAndGet()
+      assert(getStats(actor.self).registers.incrementAndGet() == 1)
       super.register(actor)
     }
 
     protected[akka] abstract override def unregister(actor: ActorCell) {
-      getStats(actor.self).unregisters.incrementAndGet()
+      assert(getStats(actor.self).unregisters.incrementAndGet() == 1)
       super.unregister(actor)
     }
 
@@ -368,13 +369,18 @@ abstract class ActorModelSpec(config: String) extends AkkaSpec(config) with Defa
                 val buddies = dispatcher.buddies
                 val mq = dispatcher.messageQueue
 
-                System.err.println("Buddies left: ")
-                buddies.toArray foreach {
+                System.err.println("Buddies left: " + buddies.size + " stopLatch: " + stopLatch.getCount + " inhab:" + dispatcher.inhabitants)
+                buddies.toArray sorted new Ordering[AnyRef] {
+                  def compare(l: AnyRef, r: AnyRef) = (l, r) match {
+                    case (ll: ActorCell, rr: ActorCell) ⇒ ll.self.path.toString.compareTo(rr.self.path.toString)
+                  }
+                } foreach {
                   case cell: ActorCell ⇒
                     System.err.println(" - " + cell.self.path + " " + cell.isTerminated + " " + cell.mailbox.status + " " + cell.mailbox.numberOfMessages + " " + SystemMessage.size(cell.mailbox.systemDrain()))
                 }
 
-                System.err.println("Mailbox: " + mq.numberOfMessages + " " + mq.hasMessages + " ")
+                System.err.println("Mailbox: " + mq.numberOfMessages + " " + mq.hasMessages)
+                Iterator.continually(mq.dequeue) takeWhile (_ ne null) foreach System.err.println
               case _ ⇒
             }
 
@@ -540,7 +546,8 @@ object BalancingDispatcherModelSpec {
         Duration(config.getNanoseconds("throughput-deadline-time"), TimeUnit.NANOSECONDS),
         mailboxType,
         configureExecutor(),
-        Duration(config.getMilliseconds("shutdown-timeout"), TimeUnit.MILLISECONDS)) with MessageDispatcherInterceptor
+        Duration(config.getMilliseconds("shutdown-timeout"), TimeUnit.MILLISECONDS),
+        config.getBoolean("attempt-teamwork")) with MessageDispatcherInterceptor
 
     override def dispatcher(): MessageDispatcher = instance
   }
diff --git a/akka-actor-tests/src/test/scala/akka/config/ConfigSpec.scala b/akka-actor-tests/src/test/scala/akka/config/ConfigSpec.scala
index dd5149ad8e..127907412e 100644
--- a/akka-actor-tests/src/test/scala/akka/config/ConfigSpec.scala
+++ b/akka-actor-tests/src/test/scala/akka/config/ConfigSpec.scala
@@ -53,6 +53,7 @@ class ConfigSpec extends AkkaSpec(ConfigFactory.defaultReference) {
           c.getMilliseconds("shutdown-timeout") must equal(1 * 1000)
           c.getInt("throughput") must equal(5)
           c.getMilliseconds("throughput-deadline-time") must equal(0)
+          c.getBoolean("attempt-teamwork") must equal(true)
         }
 
         //Fork join executor config
diff --git a/akka-actor-tests/src/test/scala/akka/routing/ResizerSpec.scala b/akka-actor-tests/src/test/scala/akka/routing/ResizerSpec.scala
index 2130afe107..1f78c64edf 100644
--- a/akka-actor-tests/src/test/scala/akka/routing/ResizerSpec.scala
+++ b/akka-actor-tests/src/test/scala/akka/routing/ResizerSpec.scala
@@ -11,6 +11,7 @@ import akka.util.duration._
 import akka.actor.ActorRef
 import java.util.concurrent.atomic.AtomicInteger
 import akka.pattern.ask
+import akka.util.Duration
 
 object ResizerSpec {
 
@@ -160,53 +161,48 @@ class ResizerSpec extends AkkaSpec(ResizerSpec.config) with DefaultTimeout with
       // as influenced by the backlog of blocking pooled actors
 
       val resizer = DefaultResizer(
-        lowerBound = 2,
-        upperBound = 4,
+        lowerBound = 3,
+        upperBound = 5,
         rampupRate = 0.1,
+        backoffRate = 0.0,
         pressureThreshold = 1,
         messagesPerResize = 1,
         backoffThreshold = 0.0)
 
       val router = system.actorOf(Props(new Actor {
         def receive = {
-          case (n: Int, latch: TestLatch, count: AtomicInteger) ⇒
-            (n millis).dilated.sleep
-            count.incrementAndGet
-            latch.countDown()
+          case d: Duration ⇒ d.dilated.sleep; sender ! "done"
+          case "echo"      ⇒ sender ! "reply"
         }
       }).withRouter(RoundRobinRouter(resizer = Some(resizer))))
 
       // first message should create the minimum number of routees
-      router ! 1
+      router ! "echo"
+      expectMsg("reply")
 
-      Await.result(router ? CurrentRoutees, 5 seconds).asInstanceOf[RouterRoutees].routees.size must be(2)
+      def routees(r: ActorRef): Int = {
+        r ! CurrentRoutees
+        expectMsgType[RouterRoutees].routees.size
+      }
 
-      def loop(loops: Int, t: Int, latch: TestLatch, count: AtomicInteger) = {
-        (100 millis).dilated.sleep
-        for (m ← 0 until loops) {
-          router.!((t, latch, count))
-          (100 millis).dilated.sleep
-        }
+      routees(router) must be(3)
+
+      def loop(loops: Int, d: Duration) = {
+        for (m ← 0 until loops) router ! d
+        for (m ← 0 until loops) expectMsg(d * 3, "done")
       }
 
       // 2 more should go thru without triggering more
-      val count1 = new AtomicInteger
-      val latch1 = TestLatch(2)
-      loop(2, 200, latch1, count1)
-      Await.ready(latch1, TestLatch.DefaultTimeout)
-      count1.get must be(2)
+      loop(2, 200 millis)
 
-      Await.result(router ? CurrentRoutees, 5 seconds).asInstanceOf[RouterRoutees].routees.size must be(2)
+      routees(router) must be(3)
 
       // a whole bunch should max it out
-      val count2 = new AtomicInteger
-      val latch2 = TestLatch(10)
-      loop(10, 500, latch2, count2)
-      Await.ready(latch2, TestLatch.DefaultTimeout)
-      count2.get must be(10)
-
-      Await.result(router ? CurrentRoutees, 5 seconds).asInstanceOf[RouterRoutees].routees.size must be(4)
+      loop(10, 500 millis)
+      awaitCond(routees(router) > 3)
 
+      loop(10, 500 millis)
+      awaitCond(routees(router) == 5)
     }
 
     "backoff" in {
@@ -239,7 +235,7 @@ class ResizerSpec extends AkkaSpec(ResizerSpec.config) with DefaultTimeout with
       (300 millis).dilated.sleep
 
       // let it cool down
-      for (m ← 0 to 3) {
+      for (m ← 0 to 5) {
         router ! 1
         (500 millis).dilated.sleep
       }
diff --git a/akka-actor/src/main/resources/reference.conf b/akka-actor/src/main/resources/reference.conf
index 62d49d61cd..8240aee4d7 100644
--- a/akka-actor/src/main/resources/reference.conf
+++ b/akka-actor/src/main/resources/reference.conf
@@ -245,6 +245,11 @@ akka {
       # mailbox is used. The Class of the FQCN must have a constructor with a
       # com.typesafe.config.Config parameter.
       mailbox-type = ""
+
+      # For BalancingDispatcher: If the balancing dispatcher should attempt to
+      # schedule idle actors using the same dispatcher when a message comes in,
+      # and the dispatchers ExecutorService is not fully busy already.
+      attempt-teamwork = on
     }
 
     debug {
diff --git a/akka-actor/src/main/scala/akka/actor/ActorCell.scala b/akka-actor/src/main/scala/akka/actor/ActorCell.scala
index aa718e12c8..c22529b2c8 100644
--- a/akka-actor/src/main/scala/akka/actor/ActorCell.scala
+++ b/akka-actor/src/main/scala/akka/actor/ActorCell.scala
@@ -285,14 +285,18 @@ private[akka] class ActorCell(
   final def isTerminated: Boolean = mailbox.isClosed
 
   final def start(): Unit = {
+    /*
+     * Create the mailbox and enqueue the Create() message to ensure that 
+     * this is processed before anything else.
+     */
     mailbox = dispatcher.createMailbox(this)
+    // ➡➡➡ NEVER SEND THE SAME SYSTEM MESSAGE OBJECT TO TWO ACTORS ⬅⬅⬅
+    mailbox.systemEnqueue(self, Create())
 
     // ➡➡➡ NEVER SEND THE SAME SYSTEM MESSAGE OBJECT TO TWO ACTORS ⬅⬅⬅
     parent.sendSystemMessage(akka.dispatch.Supervise(self))
 
-    // ➡➡➡ NEVER SEND THE SAME SYSTEM MESSAGE OBJECT TO TWO ACTORS ⬅⬅⬅
-    dispatcher.systemDispatch(this, Create())
-
+    // This call is expected to start off the actor by scheduling its mailbox.
     dispatcher.attach(this)
   }
 
diff --git a/akka-actor/src/main/scala/akka/dispatch/AbstractDispatcher.scala b/akka-actor/src/main/scala/akka/dispatch/AbstractDispatcher.scala
index 1b31be630c..6046e249af 100644
--- a/akka-actor/src/main/scala/akka/dispatch/AbstractDispatcher.scala
+++ b/akka-actor/src/main/scala/akka/dispatch/AbstractDispatcher.scala
@@ -156,7 +156,10 @@ trait ExecutionContext {
    * log the problem or whatever is appropriate for the implementation.
    */
   def reportFailure(t: Throwable): Unit
+}
 
+private[akka] trait LoadMetrics { self: Executor ⇒
+  def atFullThrottle(): Boolean
 }
 
 object MessageDispatcher {
@@ -185,9 +188,14 @@ abstract class MessageDispatcher(val prerequisites: DispatcherPrerequisites) ext
   def id: String
 
   /**
-   * Attaches the specified actor instance to this dispatcher
+   * Attaches the specified actor instance to this dispatcher, which includes
+   * scheduling it to run for the first time (Create() is expected to have
+   * been enqueued by the ActorCell upon mailbox creation).
    */
-  final def attach(actor: ActorCell): Unit = register(actor)
+  final def attach(actor: ActorCell): Unit = {
+    register(actor)
+    registerForExecution(actor.mailbox, false, true)
+  }
 
   /**
    * Detaches the specified actor instance from this dispatcher
@@ -243,7 +251,7 @@ abstract class MessageDispatcher(val prerequisites: DispatcherPrerequisites) ext
     () ⇒ if (inhabitantsUpdater.decrementAndGet(this) == 0) ifSensibleToDoSoThenScheduleShutdown()
 
   /**
-   * If you override it, you must call it. But only ever once. See "attach" for only invocation
+   * If you override it, you must call it. But only ever once. See "attach" for only invocation.
    */
   protected[akka] def register(actor: ActorCell) {
     inhabitantsUpdater.incrementAndGet(this)
@@ -260,6 +268,8 @@ abstract class MessageDispatcher(val prerequisites: DispatcherPrerequisites) ext
     mailBox.cleanUp()
   }
 
+  def inhabitants: Long = inhabitantsUpdater.get(this)
+
   private val shutdownAction = new Runnable {
     @tailrec
     final def run() {
@@ -440,11 +450,13 @@ object ForkJoinExecutorConfigurator {
   final class AkkaForkJoinPool(parallelism: Int,
                                threadFactory: ForkJoinPool.ForkJoinWorkerThreadFactory,
                                unhandledExceptionHandler: Thread.UncaughtExceptionHandler)
-    extends ForkJoinPool(parallelism, threadFactory, unhandledExceptionHandler, true) {
+    extends ForkJoinPool(parallelism, threadFactory, unhandledExceptionHandler, true) with LoadMetrics {
     override def execute(r: Runnable): Unit = r match {
       case m: Mailbox ⇒ super.execute(new MailboxExecutionTask(m))
       case other      ⇒ super.execute(other)
     }
+
+    def atFullThrottle(): Boolean = this.getActiveThreadCount() >= this.getParallelism()
   }
 
   /**
diff --git a/akka-actor/src/main/scala/akka/dispatch/BalancingDispatcher.scala b/akka-actor/src/main/scala/akka/dispatch/BalancingDispatcher.scala
index 8542ac69c8..d2d978341c 100644
--- a/akka-actor/src/main/scala/akka/dispatch/BalancingDispatcher.scala
+++ b/akka-actor/src/main/scala/akka/dispatch/BalancingDispatcher.scala
@@ -4,12 +4,11 @@
 
 package akka.dispatch
 
-import util.DynamicVariable
 import akka.actor.{ ActorCell, ActorRef }
-import java.util.concurrent.{ LinkedBlockingQueue, ConcurrentLinkedQueue, ConcurrentSkipListSet }
 import annotation.tailrec
-import java.util.concurrent.atomic.AtomicBoolean
-import akka.util.Duration
+import akka.util.{ Duration, Helpers }
+import java.util.{ Comparator, Iterator }
+import java.util.concurrent.{ Executor, LinkedBlockingQueue, ConcurrentLinkedQueue, ConcurrentSkipListSet }
 
 /**
  * An executor based event driven dispatcher which will try to redistribute work from busy actors to idle actors. It is assumed
@@ -32,20 +31,27 @@ class BalancingDispatcher(
   throughputDeadlineTime: Duration,
   mailboxType: MailboxType,
   _executorServiceFactoryProvider: ExecutorServiceFactoryProvider,
-  _shutdownTimeout: Duration)
+  _shutdownTimeout: Duration,
+  attemptTeamWork: Boolean)
   extends Dispatcher(_prerequisites, _id, throughput, throughputDeadlineTime, mailboxType, _executorServiceFactoryProvider, _shutdownTimeout) {
 
-  val buddies = new ConcurrentSkipListSet[ActorCell](akka.util.Helpers.IdentityHashComparator)
-  val rebalance = new AtomicBoolean(false)
+  val buddies = new ConcurrentSkipListSet[ActorCell](
+    Helpers.identityHashComparator(new Comparator[ActorCell] {
+      def compare(l: ActorCell, r: ActorCell) = l.self.path compareTo r.self.path
+    }))
 
   val messageQueue: MessageQueue = mailboxType match {
-    case u: UnboundedMailbox ⇒ new QueueBasedMessageQueue with UnboundedMessageQueueSemantics {
-      final val queue = new ConcurrentLinkedQueue[Envelope]
-    }
-    case BoundedMailbox(cap, timeout) ⇒ new QueueBasedMessageQueue with BoundedMessageQueueSemantics {
-      final val queue = new LinkedBlockingQueue[Envelope](cap)
-      final val pushTimeOut = timeout
-    }
+    case UnboundedMailbox() ⇒
+      new QueueBasedMessageQueue with UnboundedMessageQueueSemantics {
+        final val queue = new ConcurrentLinkedQueue[Envelope]
+      }
+
+    case BoundedMailbox(cap, timeout) ⇒
+      new QueueBasedMessageQueue with BoundedMessageQueueSemantics {
+        final val queue = new LinkedBlockingQueue[Envelope](cap)
+        final val pushTimeOut = timeout
+      }
+
     case other ⇒ throw new IllegalArgumentException("Only handles BoundedMailbox and UnboundedMailbox, but you specified [" + other + "]")
   }
 
@@ -84,30 +90,20 @@ class BalancingDispatcher(
   protected[akka] override def unregister(actor: ActorCell) = {
     buddies.remove(actor)
     super.unregister(actor)
-    intoTheFray(except = actor) //When someone leaves, he tosses a friend into the fray
+    if (messageQueue.hasMessages) scheduleOne()
   }
 
-  def intoTheFray(except: ActorCell): Unit =
-    if (rebalance.compareAndSet(false, true)) {
-      try {
-        val i = buddies.iterator()
-
-        @tailrec
-        def throwIn(): Unit = {
-          val n = if (i.hasNext) i.next() else null
-          if (n eq null) ()
-          else if ((n ne except) && registerForExecution(n.mailbox, false, false)) ()
-          else throwIn()
-        }
-        throwIn()
-      } finally {
-        rebalance.set(false)
-      }
-    }
-
   override protected[akka] def dispatch(receiver: ActorCell, invocation: Envelope) = {
     messageQueue.enqueue(receiver.self, invocation)
-    registerForExecution(receiver.mailbox, false, false)
-    intoTheFray(except = receiver)
+    if (!registerForExecution(receiver.mailbox, false, false) && doTeamWork) scheduleOne()
   }
-}
+
+  protected def doTeamWork(): Boolean =
+    attemptTeamWork && (executorService.get().executor match {
+      case lm: LoadMetrics ⇒ lm.atFullThrottle == false
+      case other           ⇒ true
+    })
+
+  @tailrec private def scheduleOne(i: Iterator[ActorCell] = buddies.iterator): Unit =
+    if (i.hasNext && !registerForExecution(i.next.mailbox, false, false)) scheduleOne(i)
+}
\ No newline at end of file
diff --git a/akka-actor/src/main/scala/akka/dispatch/Dispatcher.scala b/akka-actor/src/main/scala/akka/dispatch/Dispatcher.scala
index a735ea367e..2046f02286 100644
--- a/akka-actor/src/main/scala/akka/dispatch/Dispatcher.scala
+++ b/akka-actor/src/main/scala/akka/dispatch/Dispatcher.scala
@@ -32,12 +32,11 @@ class Dispatcher(
   val shutdownTimeout: Duration)
   extends MessageDispatcher(_prerequisites) {
 
-  protected[akka] val executorServiceFactory: ExecutorServiceFactory =
+  protected val executorServiceFactory: ExecutorServiceFactory =
     executorServiceFactoryProvider.createExecutorServiceFactory(id, prerequisites.threadFactory)
 
-  protected[akka] val executorService = new AtomicReference[ExecutorService](new ExecutorServiceDelegate {
-    lazy val executor = executorServiceFactory.createExecutorService
-  })
+  protected val executorService = new AtomicReference[ExecutorServiceDelegate](
+    new ExecutorServiceDelegate { lazy val executor = executorServiceFactory.createExecutorService })
 
   protected[akka] def dispatch(receiver: ActorCell, invocation: Envelope) = {
     val mbox = receiver.mailbox
diff --git a/akka-actor/src/main/scala/akka/dispatch/Dispatchers.scala b/akka-actor/src/main/scala/akka/dispatch/Dispatchers.scala
index 8e99e05b06..5f4528146d 100644
--- a/akka-actor/src/main/scala/akka/dispatch/Dispatchers.scala
+++ b/akka-actor/src/main/scala/akka/dispatch/Dispatchers.scala
@@ -189,7 +189,8 @@ class BalancingDispatcherConfigurator(config: Config, prerequisites: DispatcherP
     config.getInt("throughput"),
     Duration(config.getNanoseconds("throughput-deadline-time"), TimeUnit.NANOSECONDS),
     mailboxType, configureExecutor(),
-    Duration(config.getMilliseconds("shutdown-timeout"), TimeUnit.MILLISECONDS))
+    Duration(config.getMilliseconds("shutdown-timeout"), TimeUnit.MILLISECONDS),
+    config.getBoolean("attempt-teamwork"))
 
   /**
    * Returns the same dispatcher instance for each invocation
diff --git a/akka-actor/src/main/scala/akka/dispatch/Mailbox.scala b/akka-actor/src/main/scala/akka/dispatch/Mailbox.scala
index cc15ae2173..4c50cb5c8d 100644
--- a/akka-actor/src/main/scala/akka/dispatch/Mailbox.scala
+++ b/akka-actor/src/main/scala/akka/dispatch/Mailbox.scala
@@ -190,7 +190,10 @@ private[akka] abstract class Mailbox(val actor: ActorCell) extends MessageQueue
     var nextMessage = systemDrain()
     try {
       while ((nextMessage ne null) && !isClosed) {
-        if (debug) println(actor.self + " processing system message " + nextMessage + " with children " + actor.childrenRefs)
+        if (debug) println(actor.self + " processing system message " + nextMessage + " with " +
+          (if (actor.childrenRefs.isEmpty) "no children"
+          else if (actor.childrenRefs.size > 20) actor.childrenRefs.size + " children"
+          else actor.childrenRefs.mkString("children:\n    ", "\n    ", "")))
         actor systemInvoke nextMessage
         nextMessage = nextMessage.next
         // don’t ever execute normal message when system message present!
@@ -236,15 +239,26 @@ private[akka] abstract class Mailbox(val actor: ActorCell) extends MessageQueue
 }
 
 trait MessageQueue {
-  /*
-   * These method need to be implemented in subclasses; they should not rely on the internal stuff above.
+  /**
+   * Try to enqueue the message to this queue, or throw an exception.
    */
-  def enqueue(receiver: ActorRef, handle: Envelope)
+  def enqueue(receiver: ActorRef, handle: Envelope): Unit // NOTE: receiver is used only in two places, but cannot be removed
 
+  /**
+   * Try to dequeue the next message from this queue, return null failing that.
+   */
   def dequeue(): Envelope
 
+  /**
+   * Should return the current number of messages held in this queue; may
+   * always return 0 if no other value is available efficiently. Do not use
+   * this for testing for presence of messages, use `hasMessages` instead.
+   */
   def numberOfMessages: Int
 
+  /**
+   * Indicates whether this queue is non-empty.
+   */
   def hasMessages: Boolean
 }
 
@@ -292,15 +306,15 @@ trait DefaultSystemMessageQueue { self: Mailbox ⇒
 }
 
 trait UnboundedMessageQueueSemantics extends QueueBasedMessageQueue {
-  final def enqueue(receiver: ActorRef, handle: Envelope): Unit = queue add handle
-  final def dequeue(): Envelope = queue.poll()
+  def enqueue(receiver: ActorRef, handle: Envelope): Unit = queue add handle
+  def dequeue(): Envelope = queue.poll()
 }
 
 trait BoundedMessageQueueSemantics extends QueueBasedMessageQueue {
   def pushTimeOut: Duration
   override def queue: BlockingQueue[Envelope]
 
-  final def enqueue(receiver: ActorRef, handle: Envelope) {
+  def enqueue(receiver: ActorRef, handle: Envelope) {
     if (pushTimeOut.length > 0) {
       queue.offer(handle, pushTimeOut.length, pushTimeOut.unit) || {
         throw new MessageQueueAppendFailedException("Couldn't enqueue message " + handle + " to " + receiver)
@@ -308,13 +322,13 @@ trait BoundedMessageQueueSemantics extends QueueBasedMessageQueue {
     } else queue put handle
   }
 
-  final def dequeue(): Envelope = queue.poll()
+  def dequeue(): Envelope = queue.poll()
 }
 
 trait QueueBasedMessageQueue extends MessageQueue {
   def queue: Queue[Envelope]
-  final def numberOfMessages = queue.size
-  final def hasMessages = !queue.isEmpty
+  def numberOfMessages = queue.size
+  def hasMessages = !queue.isEmpty
 }
 
 /**
diff --git a/akka-actor/src/main/scala/akka/dispatch/ThreadPoolBuilder.scala b/akka-actor/src/main/scala/akka/dispatch/ThreadPoolBuilder.scala
index 1c63831013..b6fd432296 100644
--- a/akka-actor/src/main/scala/akka/dispatch/ThreadPoolBuilder.scala
+++ b/akka-actor/src/main/scala/akka/dispatch/ThreadPoolBuilder.scala
@@ -81,14 +81,16 @@ case class ThreadPoolConfig(allowCorePoolTimeout: Boolean = ThreadPoolConfig.def
   extends ExecutorServiceFactoryProvider {
   class ThreadPoolExecutorServiceFactory(val threadFactory: ThreadFactory) extends ExecutorServiceFactory {
     def createExecutorService: ExecutorService = {
-      val service = new ThreadPoolExecutor(
+      val service: ThreadPoolExecutor = new ThreadPoolExecutor(
         corePoolSize,
         maxPoolSize,
         threadTimeout.length,
         threadTimeout.unit,
         queueFactory(),
         threadFactory,
-        rejectionPolicy)
+        rejectionPolicy) with LoadMetrics {
+        def atFullThrottle(): Boolean = this.getActiveCount >= this.getPoolSize
+      }
       service.allowCoreThreadTimeOut(allowCorePoolTimeout)
       service
     }
@@ -182,7 +184,7 @@ case class MonitorableThreadFactory(name: String,
   protected def wire[T <: Thread](t: T): T = {
     t.setUncaughtExceptionHandler(exceptionHandler)
     t.setDaemon(daemonic)
-    contextClassLoader foreach (t.setContextClassLoader(_))
+    contextClassLoader foreach t.setContextClassLoader
     t
   }
 }
diff --git a/akka-actor/src/main/scala/akka/routing/Routing.scala b/akka-actor/src/main/scala/akka/routing/Routing.scala
index da2c81d1a7..4ff6609255 100644
--- a/akka-actor/src/main/scala/akka/routing/Routing.scala
+++ b/akka-actor/src/main/scala/akka/routing/Routing.scala
@@ -1028,7 +1028,8 @@ case class DefaultResizer(
    */
   def capacity(routees: IndexedSeq[ActorRef]): Int = {
     val currentSize = routees.size
-    val delta = filter(pressure(routees), currentSize)
+    val press = pressure(routees)
+    val delta = filter(press, currentSize)
     val proposed = currentSize + delta
 
     if (proposed < lowerBound) delta + (lowerBound - proposed)
@@ -1058,7 +1059,7 @@ case class DefaultResizer(
       case a: LocalActorRef ⇒
         val cell = a.underlying
         pressureThreshold match {
-          case 1          ⇒ cell.mailbox.isScheduled && cell.currentMessage != null
+          case 1          ⇒ cell.mailbox.isScheduled && cell.mailbox.hasMessages
           case i if i < 1 ⇒ cell.mailbox.isScheduled && cell.currentMessage != null
           case threshold  ⇒ cell.mailbox.numberOfMessages >= threshold
         }
diff --git a/akka-actor/src/main/scala/akka/util/Helpers.scala b/akka-actor/src/main/scala/akka/util/Helpers.scala
index 60e6be8b65..25cb279f2e 100644
--- a/akka-actor/src/main/scala/akka/util/Helpers.scala
+++ b/akka-actor/src/main/scala/akka/util/Helpers.scala
@@ -21,8 +21,18 @@ object Helpers {
     if (diff > 0) 1 else if (diff < 0) -1 else 0
   }
 
-  val IdentityHashComparator = new Comparator[AnyRef] {
-    def compare(a: AnyRef, b: AnyRef): Int = compareIdentityHash(a, b)
+  /**
+   * Create a comparator which will efficiently use `System.identityHashCode`,
+   * unless that happens to be the same for two non-equals objects, in which
+   * case the supplied “real” comparator is used; the comparator must be
+   * consistent with equals, otherwise it would not be an enhancement over
+   * the identityHashCode.
+   */
+  def identityHashComparator[T <: AnyRef](comp: Comparator[T]): Comparator[T] = new Comparator[T] {
+    def compare(a: T, b: T): Int = compareIdentityHash(a, b) match {
+      case 0 if a != b ⇒ comp.compare(a, b)
+      case x           ⇒ x
+    }
   }
 
   final val base64chars = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789+~"
diff --git a/akka-testkit/src/main/scala/akka/testkit/CallingThreadDispatcher.scala b/akka-testkit/src/main/scala/akka/testkit/CallingThreadDispatcher.scala
index 8282ee58f5..8b2d15a079 100644
--- a/akka-testkit/src/main/scala/akka/testkit/CallingThreadDispatcher.scala
+++ b/akka-testkit/src/main/scala/akka/testkit/CallingThreadDispatcher.scala
@@ -8,7 +8,7 @@ import java.util.concurrent.locks.ReentrantLock
 import java.util.LinkedList
 import scala.annotation.tailrec
 import com.typesafe.config.Config
-import akka.actor.{ ExtensionIdProvider, ExtensionId, Extension, ExtendedActorSystem, ActorRef, ActorCell }
+import akka.actor.{ ActorInitializationException, ExtensionIdProvider, ExtensionId, Extension, ExtendedActorSystem, ActorRef, ActorCell }
 import akka.dispatch.{ TaskInvocation, SystemMessage, Suspend, Resume, MessageDispatcherConfigurator, MessageDispatcher, Mailbox, Envelope, DispatcherPrerequisites, DefaultSystemMessageQueue }
 import akka.util.duration.intToDurationInt
 import akka.util.{ Switch, Duration }
@@ -132,6 +132,17 @@ class CallingThreadDispatcher(
 
   protected[akka] override def shutdownTimeout = 1 second
 
+  protected[akka] override def register(actor: ActorCell): Unit = {
+    super.register(actor)
+    actor.mailbox match {
+      case mbox: CallingThreadMailbox ⇒
+        val queue = mbox.queue
+        queue.enter
+        runQueue(mbox, queue)
+      case x ⇒ throw new ActorInitializationException("expected CallingThreadMailbox, got " + x.getClass)
+    }
+  }
+
   override def suspend(actor: ActorCell) {
     actor.mailbox match {
       case m: CallingThreadMailbox ⇒ m.suspendSwitch.switchOn