Removing uuid tracking in MessageDispatcher, isn't needed and will be reducing the overall memory footprint per actor

akka-actor-tests/src/test/scala/akka/actor/dispatch/ActorModelSpec.scala

@@ -120,17 +120,11 @@ object ActorModelSpec {
     protected[akka] abstract override def register(actor: ActorCell) {
       getStats(actor.ref).registers.incrementAndGet()
       super.register(actor)
-      //printMembers("after registering " + actor)
     }
 
     protected[akka] abstract override def unregister(actor: ActorCell) {
       getStats(actor.ref).unregisters.incrementAndGet()
       super.unregister(actor)
-      //printMembers("after unregistering " + actor)
-    }
-
-    def printMembers(when: String) {
-      System.err.println(when + " then " + uuids.toArray.toList.map(_.toString.split("-")(0)).mkString("==> ", ", ", "<=="))
     }
 
     protected[akka] abstract override def dispatch(invocation: Envelope) {

akka-actor-tests/src/test/scala/akka/actor/dispatch/DispatcherActorSpec.scala

@@ -81,7 +81,7 @@ class DispatcherActorSpec extends AkkaSpec {
       (1 to 100) foreach { _ ⇒ slowOne ! "ping" }
       fastOne ! "sabotage"
       start.countDown()
-      val result = latch.await(5, TimeUnit.SECONDS)
+      val result = latch.await(10, TimeUnit.SECONDS)
       fastOne.stop()
       slowOne.stop()
       assert(result === true)

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

@@ -70,8 +70,8 @@ object MessageDispatcher {
 abstract class MessageDispatcher(val app: AkkaApplication) extends Serializable {
   import MessageDispatcher._
 
-  protected val uuids = new ConcurrentSkipListSet[Uuid]
   protected val _tasks = new AtomicLong(0L)
+  protected val _actors = new AtomicLong(0L)
   protected val guard = new ReentrantGuard
   protected val active = new Switch(false)
 
@@ -123,7 +123,7 @@ abstract class MessageDispatcher(val app: AkkaApplication) extends Serializable
   final def detach(actor: ActorCell) {
     guard withGuard {
       unregister(actor)
-      if (uuids.isEmpty && _tasks.get == 0) {
+      if (_tasks.get == 0 && _actors.get == 0) {
         shutdownSchedule match {
           case UNSCHEDULED ⇒
             shutdownSchedule = SCHEDULED
@@ -155,7 +155,7 @@ abstract class MessageDispatcher(val app: AkkaApplication) extends Serializable
   private val taskCleanup: () ⇒ Unit =
     () ⇒ if (_tasks.decrementAndGet() == 0) {
       guard withGuard {
-        if (_tasks.get == 0 && uuids.isEmpty) {
+        if (_tasks.get == 0 && _actors.get == 0) {
           shutdownSchedule match {
             case UNSCHEDULED ⇒
               shutdownSchedule = SCHEDULED
@@ -173,9 +173,8 @@ abstract class MessageDispatcher(val app: AkkaApplication) extends Serializable
    * and only call it under the dispatcher-guard, see "attach" for the only invocation
    */
   protected[akka] def register(actor: ActorCell) {
-    if (uuids add actor.uuid) {
+    _actors.incrementAndGet()
-      systemDispatch(SystemEnvelope(actor, Create, NullChannel)) //FIXME should this be here or moved into ActorCell.start perhaps?
+    systemDispatch(SystemEnvelope(actor, Create, NullChannel)) //FIXME should this be here or moved into ActorCell.start perhaps?
-    } else System.err.println("Couldn't register: " + actor)
   }
 
   /**
@@ -183,12 +182,11 @@ abstract class MessageDispatcher(val app: AkkaApplication) extends Serializable
    * and only call it under the dispatcher-guard, see "detach" for the only invocation
    */
   protected[akka] def unregister(actor: ActorCell) {
-    if (uuids remove actor.uuid) {
+    _actors.decrementAndGet()
-      val mailBox = actor.mailbox
+    val mailBox = actor.mailbox
-      mailBox.becomeClosed()
+    mailBox.becomeClosed()
-      actor.mailbox = deadLetterMailbox //FIXME getAndSet would be preferrable here
+    actor.mailbox = deadLetterMailbox //FIXME getAndSet would be preferrable here
-      cleanUpMailboxFor(actor, mailBox)
+    cleanUpMailboxFor(actor, mailBox)
-    } else System.err.println("Couldn't unregister: " + actor)
   }
 
   /**
@@ -222,7 +220,7 @@ abstract class MessageDispatcher(val app: AkkaApplication) extends Serializable
             shutdownSchedule = SCHEDULED
             app.scheduler.scheduleOnce(this, timeoutMs, TimeUnit.MILLISECONDS)
           case SCHEDULED ⇒
-            if (uuids.isEmpty && _tasks.get == 0) {
+            if (_tasks.get == 0) {
               active switchOff {
                 shutdown() // shut down in the dispatcher's references is zero
               }
@@ -243,16 +241,21 @@ abstract class MessageDispatcher(val app: AkkaApplication) extends Serializable
   /**
    * After the call to this method, the dispatcher mustn't begin any new message processing for the specified reference
    */
-  def suspend(actor: ActorCell): Unit =
+  def suspend(actor: ActorCell): Unit = {
-    if (uuids.contains(actor.uuid)) actor.mailbox.becomeSuspended()
+    val mbox = actor.mailbox
+    if (mbox.dispatcher eq this)
+      mbox.becomeSuspended()
+  }
 
   /*
    * After the call to this method, the dispatcher must begin any new message processing for the specified reference
    */
-  def resume(actor: ActorCell): Unit = if (uuids.contains(actor.uuid)) {
+  def resume(actor: ActorCell): Unit = {
     val mbox = actor.mailbox
-    mbox.becomeOpen()
+    if (mbox.dispatcher eq this) {
-    registerForExecution(mbox, false, false)
+      mbox.becomeOpen()
+      registerForExecution(mbox, false, false)
+    }
   }
 
   /**