Add UID to RemoteActorRef, see #3072

* Sending to a previous incarnation of an actor shall fail,
  to make remote actors work the same way as local ones (in
  the sense that after Terminated() the ref is not working anymore)
* Changed equality of ActorRef to take the uid into account
* Parse uid fragment in RelativeActorPath and ActorPathExtractor
* Handle uid in getChild and in RemoteSystemDaemon
* Use toSerializationFormat and toSerializationFormatWithAddress
  in serialization
* Replaced var uid in ActorCell and ChildRestartStats with
  constructor parameters (path)
* Create the uid in one single place, in makeChild in parent
* Handle ActorRef with and without uid in DeathWatch
* Optimize ActorPath.toString and friends
* Update documentation and migration guide

akka-actor-tests/src/test/scala/akka/actor/ActorDSLSpec.scala

@@ -208,14 +208,14 @@ class ActorDSLSpec extends AkkaSpec {
       // here we pass in the ActorRefFactory explicitly as an example
       val a = actor(system, "fred")(new Act {
         val b = actor("barney")(new Act {
-          whenStarting { context.parent ! ("hello from " + self) }
+          whenStarting { context.parent ! ("hello from " + self.path) }
         })
         become {
           case x ⇒ testActor ! x
         }
       })
       //#nested-actor
-      expectMsg("hello from Actor[akka://ActorDSLSpec/user/fred/barney]")
+      expectMsg("hello from akka://ActorDSLSpec/user/fred/barney")
       lastSender must be(a)
     }
 

akka-actor-tests/src/test/scala/akka/actor/ActorLookupSpec.scala

@@ -71,11 +71,33 @@ class ActorLookupSpec extends AkkaSpec with DefaultTimeout {
     }
 
     "find actors by looking up their string representation" in {
+      // this is only true for local actor references
       system.actorFor(c1.path.toString) must be === c1
       system.actorFor(c2.path.toString) must be === c2
       system.actorFor(c21.path.toString) must be === c21
     }
 
+    "take actor incarnation into account when comparing actor references" in {
+      val name = "abcdefg"
+      val a1 = system.actorOf(p, name)
+      watch(a1)
+      a1 ! PoisonPill
+      expectMsgType[Terminated].actor must be === a1
+
+      // not equal because it's terminated
+      system.actorFor(a1.path.toString) must not be (a1)
+
+      val a2 = system.actorOf(p, name)
+      a2.path must be(a1.path)
+      a2.path.toString must be(a1.path.toString)
+      a2 must not be (a1)
+      a2.toString must not be (a1.toString)
+
+      watch(a2)
+      a2 ! PoisonPill
+      expectMsgType[Terminated].actor must be === a2
+    }
+
     "find actors by looking up their root-anchored relative path" in {
       system.actorFor(c1.path.elements.mkString("/", "/", "")) must be === c1
       system.actorFor(c2.path.elements.mkString("/", "/", "")) must be === c2
@@ -163,6 +185,9 @@ class ActorLookupSpec extends AkkaSpec with DefaultTimeout {
     "find actors by looking up their string representation" in {
       def check(looker: ActorRef, pathOf: ActorRef, result: ActorRef) {
         Await.result(looker ? LookupString(pathOf.path.toString), timeout.duration) must be === result
+        // with uid
+        Await.result(looker ? LookupString(pathOf.path.toSerializationFormat), timeout.duration) must be === result
+        // with trailing /
         Await.result(looker ? LookupString(pathOf.path.toString + "/"), timeout.duration) must be === result
       }
       for {

akka-actor-tests/src/test/scala/akka/actor/ActorPathSpec.scala

@@ -0,0 +1,46 @@
+/**
+ * Copyright (C) 2009-2013 Typesafe Inc. <http://www.typesafe.com>
+ */
+package akka.actor
+
+import org.scalatest.WordSpec
+import org.scalatest.matchers.MustMatchers
+
+class ActorPathSpec extends WordSpec with MustMatchers {
+
+  "ActorPath" must {
+
+    "create correct toString" in {
+      val a = Address("akka.tcp", "mysys")
+      RootActorPath(a).toString must be("akka.tcp://mysys/")
+      (RootActorPath(a) / "user").toString must be("akka.tcp://mysys/user")
+      (RootActorPath(a) / "user" / "foo").toString must be("akka.tcp://mysys/user/foo")
+      (RootActorPath(a) / "user" / "foo" / "bar").toString must be("akka.tcp://mysys/user/foo/bar")
+    }
+
+    "create correct toStringWithAddress" in {
+      val local = Address("akka.tcp", "mysys")
+      val a = local.copy(host = Some("aaa"), port = Some(2552))
+      val b = a.copy(host = Some("bb"))
+      val c = a.copy(host = Some("cccc"))
+      val root = RootActorPath(local)
+      root.toStringWithAddress(a) must be("akka.tcp://mysys@aaa:2552/")
+      (root / "user").toStringWithAddress(a) must be("akka.tcp://mysys@aaa:2552/user")
+      (root / "user" / "foo").toStringWithAddress(a) must be("akka.tcp://mysys@aaa:2552/user/foo")
+
+      //      root.toStringWithAddress(b) must be("akka.tcp://mysys@bb:2552/")
+      (root / "user").toStringWithAddress(b) must be("akka.tcp://mysys@bb:2552/user")
+      (root / "user" / "foo").toStringWithAddress(b) must be("akka.tcp://mysys@bb:2552/user/foo")
+
+      root.toStringWithAddress(c) must be("akka.tcp://mysys@cccc:2552/")
+      (root / "user").toStringWithAddress(c) must be("akka.tcp://mysys@cccc:2552/user")
+      (root / "user" / "foo").toStringWithAddress(c) must be("akka.tcp://mysys@cccc:2552/user/foo")
+
+      val rootA = RootActorPath(a)
+      rootA.toStringWithAddress(b) must be("akka.tcp://mysys@aaa:2552/")
+      (rootA / "user").toStringWithAddress(b) must be("akka.tcp://mysys@aaa:2552/user")
+      (rootA / "user" / "foo").toStringWithAddress(b) must be("akka.tcp://mysys@aaa:2552/user/foo")
+
+    }
+  }
+}

akka-actor-tests/src/test/scala/akka/actor/RelativeActorPathSpec.scala

@@ -23,5 +23,8 @@ class RelativeActorPathSpec extends WordSpec with MustMatchers {
       val name = URLEncoder.encode("akka://ClusterSystem@127.0.0.1:2552", "UTF-8")
       elements(name) must be(List(name))
     }
+    "match path with uid fragment" in {
+      elements("foo/bar/baz#1234") must be(List("foo", "bar", "baz#1234"))
+    }
   }
 }

akka-actor-tests/src/test/scala/akka/actor/SupervisorHierarchySpec.scala

@@ -54,7 +54,7 @@ object SupervisorHierarchySpec {
   }
 
   case class Ready(ref: ActorRef)
-  case class Died(ref: ActorRef)
+  case class Died(path: ActorPath)
   case object Abort
   case object PingOfDeath
   case object PongOfDeath
@@ -112,17 +112,17 @@ object SupervisorHierarchySpec {
    * upon Restart or would have to be managed by the highest supervisor (which
    * is undesirable).
    */
-  case class HierarchyState(log: Vector[Event], kids: Map[ActorRef, Int], failConstr: Failure)
+  case class HierarchyState(log: Vector[Event], kids: Map[ActorPath, Int], failConstr: Failure)
-  val stateCache = new ConcurrentHashMap[ActorRef, HierarchyState]()
+  val stateCache = new ConcurrentHashMap[ActorPath, HierarchyState]()
 
   class Hierarchy(size: Int, breadth: Int, listener: ActorRef, myLevel: Int) extends Actor {
 
     var log = Vector.empty[Event]
 
-    stateCache.get(self) match {
+    stateCache.get(self.path) match {
       case hs @ HierarchyState(l: Vector[Event], _, f: Failure) if f.failConstr > 0 ⇒
         val log = l :+ Event("Failed in constructor", identityHashCode(this))
-        stateCache.put(self, hs.copy(log = log, failConstr = f.copy(failConstr = f.failConstr - 1)))
+        stateCache.put(self.path, hs.copy(log = log, failConstr = f.copy(failConstr = f.failConstr - 1)))
         throw f
       case _ ⇒
     }
@@ -149,7 +149,7 @@ object SupervisorHierarchySpec {
       log :+= Event("started", identityHashCode(this))
       listener ! Ready(self)
       val s = size - 1 // subtract myself
-      val kidInfo: Map[ActorRef, Int] =
+      val kidInfo: Map[ActorPath, Int] =
         if (s > 0) {
           val kids = Random.nextInt(Math.min(breadth, s)) + 1
           val sizes = s / kids
@@ -158,10 +158,10 @@ object SupervisorHierarchySpec {
           (1 to kids).map { (id) ⇒
             val kidSize = if (rest > 0) { rest -= 1; sizes + 1 } else sizes
             val props = propsTemplate.withCreator(new Hierarchy(kidSize, breadth, listener, myLevel + 1))
-            (context.watch(context.actorOf(props, id.toString)), kidSize)
+            (context.watch(context.actorOf(props, id.toString)).path, kidSize)
           }(collection.breakOut)
         } else Map()
-      stateCache.put(self, HierarchyState(log, kidInfo, null))
+      stateCache.put(self.path, HierarchyState(log, kidInfo, null))
     }
 
     var preRestartCalled = false
@@ -178,12 +178,12 @@ object SupervisorHierarchySpec {
               context.unwatch(child)
               context.stop(child)
             }
-            stateCache.put(self, stateCache.get(self).copy(log = log))
+            stateCache.put(self.path, stateCache.get(self.path).copy(log = log))
             if (f.failPre > 0) {
               f.failPre -= 1
               throw f
             }
-          case _ ⇒ stateCache.put(self, stateCache.get(self).copy(log = log))
+          case _ ⇒ stateCache.put(self.path, stateCache.get(self.path).copy(log = log))
         }
       }
     }
@@ -217,14 +217,14 @@ object SupervisorHierarchySpec {
     })
 
     override def postRestart(cause: Throwable) {
-      val state = stateCache.get(self)
+      val state = stateCache.get(self.path)
       log = state.log
       log :+= Event("restarted " + suspendCount + " " + cause, identityHashCode(this))
       state.kids foreach {
-        case (child, kidSize) ⇒
+        case (childPath, kidSize) ⇒
-          val name = child.path.name
+          val name = childPath.name
-          if (context.actorFor(name).isTerminated) {
+          if (context.child(name).isEmpty) {
-            listener ! Died(child)
+            listener ! Died(childPath)
             val props = Props(new Hierarchy(kidSize, breadth, listener, myLevel + 1)).withDispatcher("hierarchy")
             context.watch(context.actorOf(props, name))
           }
@@ -243,7 +243,7 @@ object SupervisorHierarchySpec {
       if (failed || suspended) {
         listener ! ErrorLog("not resumed (" + failed + ", " + suspended + ")", log)
       } else {
-        stateCache.put(self, HierarchyState(log, Map(), null))
+        stateCache.put(self.path, HierarchyState(log, Map(), null))
       }
     }
 
@@ -270,7 +270,7 @@ object SupervisorHierarchySpec {
       val handler: Receive = {
         case f: Failure ⇒
           setFlags(f.directive)
-          stateCache.put(self, stateCache.get(self).copy(failConstr = f.copy()))
+          stateCache.put(self.path, stateCache.get(self.path).copy(failConstr = f.copy()))
           throw f
         case "ping"      ⇒ { Thread.sleep((Random.nextFloat * 1.03).toLong); sender ! "pong" }
         case Dump(0)     ⇒ abort("dump")
@@ -281,9 +281,9 @@ object SupervisorHierarchySpec {
            * (if the unwatch() came too late), so just ignore in this case.
            */
           val name = ref.path.name
-          if (pongsToGo == 0 && context.actorFor(name).isTerminated) {
+          if (pongsToGo == 0 && context.child(name).isEmpty) {
-            listener ! Died(ref)
+            listener ! Died(ref.path)
-            val kids = stateCache.get(self).kids(ref)
+            val kids = stateCache.get(self.path).kids(ref.path)
             val props = Props(new Hierarchy(kids, breadth, listener, myLevel + 1)).withDispatcher("hierarchy")
             context.watch(context.actorOf(props, name))
           } else {
@@ -469,8 +469,8 @@ object SupervisorHierarchySpec {
       case x if x > 0.03 ⇒ 1
       case _             ⇒ 2
     }
-    private def bury(ref: ActorRef): Unit = {
+    private def bury(path: ActorPath): Unit = {
-      val deadGuy = ref.path.elements
+      val deadGuy = path.elements
       val deadGuySize = deadGuy.size
       val isChild = (other: ActorRef) ⇒ other.path.elements.take(deadGuySize) == deadGuy
       idleChildren = idleChildren filterNot isChild
@@ -499,8 +499,8 @@ object SupervisorHierarchySpec {
         else context.system.scheduler.scheduleOnce(workSchedule, self, Work)(context.dispatcher)
         stay using (x - 1)
       case Event(Work, _) ⇒ if (pingChildren.isEmpty) goto(LastPing) else goto(Finishing)
-      case Event(Died(ref), _) ⇒
+      case Event(Died(path), _) ⇒
-        bury(ref)
+        bury(path)
         stay
       case Event("pong", _) ⇒
         pingChildren -= sender
@@ -631,7 +631,7 @@ object SupervisorHierarchySpec {
         case l: LocalActorRef ⇒
           l.underlying.actor match {
             case h: Hierarchy ⇒ errors :+= target -> ErrorLog("forced", h.log)
-            case _            ⇒ errors :+= target -> ErrorLog("fetched", stateCache.get(target).log)
+            case _            ⇒ errors :+= target -> ErrorLog("fetched", stateCache.get(target.path).log)
           }
           if (depth > 0) {
             l.underlying.children foreach (getErrors(_, depth - 1))
@@ -644,7 +644,7 @@ object SupervisorHierarchySpec {
         case l: LocalActorRef ⇒
           l.underlying.actor match {
             case h: Hierarchy ⇒ errors :+= target -> ErrorLog("forced", h.log)
-            case _            ⇒ errors :+= target -> ErrorLog("fetched", stateCache.get(target).log)
+            case _            ⇒ errors :+= target -> ErrorLog("fetched", stateCache.get(target.path).log)
           }
           if (target != hierarchy) getErrorsUp(l.getParent)
       }

akka-actor-tests/src/test/scala/akka/actor/SupervisorSpec.scala

@@ -393,10 +393,10 @@ class SupervisorSpec extends AkkaSpec with BeforeAndAfterEach with ImplicitSende
         override def postRestart(reason: Throwable): Unit = testActor ! "parent restarted"
 
         def receive = {
-          case t @ Terminated(`child`) ⇒ testActor ! "child terminated"
+          case Terminated(a) if a.path == child.path ⇒ testActor ! "child terminated" // FIXME case t @ Terminated(`child`) ticket #3156
-          case l: TestLatch            ⇒ child ! l
+          case l: TestLatch                          ⇒ child ! l
-          case "test"                  ⇒ sender ! "green"
+          case "test"                                ⇒ sender ! "green"
-          case "testchild"             ⇒ child forward "test"
+          case "testchild"                           ⇒ child forward "test"
         }
       }))
 

akka-actor-tests/src/test/scala/akka/serialization/SerializeSpec.scala

@@ -332,7 +332,7 @@ class SerializationCompatibilitySpec extends AkkaSpec(SerializationTests.mostlyR
       String.valueOf(encodeHex(ser.serialize(obj, obj.getClass).get)) must be(asExpected)
 
     "be preserved for the Create SystemMessage" in {
-      verify(Create(1234), "aced00057372000c7363616c612e5475706c6532bc7daadf46211a990200024c00025f317400124c6a6176612f6c616e672f4f626a6563743b4c00025f3271007e0001787073720014616b6b612e64697370617463682e437265617465bcdf9f7f2675038d0200014900037569647870000004d27671007e0003")
+      verify(Create(), "aced00057372000c7363616c612e5475706c6532bc7daadf46211a990200024c00025f317400124c6a6176612f6c616e672f4f626a6563743b4c00025f3271007e0001787073720014616b6b612e64697370617463682e437265617465000000000000000302000078707671007e0003")
     }
     "be preserved for the Recreate SystemMessage" in {
       verify(Recreate(null), "aced00057372000c7363616c612e5475706c6532bc7daadf46211a990200024c00025f317400124c6a6176612f6c616e672f4f626a6563743b4c00025f3271007e0001787073720016616b6b612e64697370617463682e52656372656174650987c65c8d378a800200014c000563617573657400154c6a6176612f6c616e672f5468726f7761626c653b7870707671007e0003")
@@ -347,7 +347,7 @@ class SerializationCompatibilitySpec extends AkkaSpec(SerializationTests.mostlyR
       verify(Terminate(), "aced00057372000c7363616c612e5475706c6532bc7daadf46211a990200024c00025f317400124c6a6176612f6c616e672f4f626a6563743b4c00025f3271007e0001787073720017616b6b612e64697370617463682e5465726d696e61746509d66ca68318700f02000078707671007e0003")
     }
     "be preserved for the Supervise SystemMessage" in {
-      verify(Supervise(FakeActorRef("child"), true, 2468), "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")
+      verify(Supervise(FakeActorRef("child"), true), "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")
     }
     "be preserved for the ChildTerminated SystemMessage" in {
       verify(ChildTerminated(FakeActorRef("child")), "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")

akka-actor/src/main/scala/akka/actor/ActorCell.scala

@@ -16,6 +16,7 @@ import akka.event.Logging.{ LogEvent, Debug, Error }
 import akka.japi.Procedure
 import akka.dispatch.NullMessage
 import scala.concurrent.ExecutionContext
+import scala.concurrent.forkjoin.ThreadLocalRandom
 
 /**
  * The actor context - the view of the actor cell from the actor.
@@ -304,8 +305,26 @@ private[akka] object ActorCell {
   final val emptyBehaviorStack: List[Actor.Receive] = Nil
 
   final val emptyActorRefSet: Set[ActorRef] = immutable.TreeSet.empty
+  final val emptyActorRefMap: Map[ActorPath, ActorRef] = immutable.TreeMap.empty
 
   final val terminatedProps: Props = Props(() ⇒ throw new IllegalActorStateException("This Actor has been terminated"))
+
+  final val undefinedUid = 0
+
+  @tailrec final def newUid(): Int = {
+    // Note that this uid is also used as hashCode in ActorRef, so be careful
+    // to not break hashing if you change the way uid is generated
+    val uid = ThreadLocalRandom.current.nextInt()
+    if (uid == undefinedUid) newUid
+    else uid
+  }
+
+  final def splitNameAndUid(name: String): (String, Int) = {
+    val i = name.indexOf('#')
+    if (i < 0) (name, undefinedUid)
+    else (name.substring(0, i), Integer.valueOf(name.substring(i + 1)))
+  }
+
 }
 
 //ACTORCELL IS 64bytes and should stay that way unless very good reason not to (machine sympathy, cache line fit)
@@ -337,7 +356,7 @@ private[akka] class ActorCell(
   protected final def lookupRoot = self
   final def provider = system.provider
 
-  protected var uid: Int = 0
+  protected def uid: Int = self.path.uid
   private[this] var _actor: Actor = _
   def actor: Actor = _actor
   protected def actor_=(a: Actor): Unit = _actor = a
@@ -361,7 +380,7 @@ private[akka] class ActorCell(
     var todo = message.next
     try {
       message match {
-        case Create(uid)               ⇒ create(uid)
+        case Create()                  ⇒ create()
         case Watch(watchee, watcher)   ⇒ addWatcher(watchee, watcher)
         case Unwatch(watchee, watcher) ⇒ remWatcher(watchee, watcher)
         case Recreate(cause) ⇒
@@ -379,10 +398,10 @@ private[akka] class ActorCell(
             case null                  ⇒ faultResume(inRespToFailure)
             case w: WaitingForChildren ⇒ w.enqueue(message)
           }
-        case Terminate()                  ⇒ terminate()
+        case Terminate()             ⇒ terminate()
-        case Supervise(child, async, uid) ⇒ supervise(child, async, uid)
+        case Supervise(child, async) ⇒ supervise(child, async)
-        case ChildTerminated(child)       ⇒ todo = handleChildTerminated(child)
+        case ChildTerminated(child)  ⇒ todo = handleChildTerminated(child)
-        case NoMessage                    ⇒ // only here to suppress warning
+        case NoMessage               ⇒ // only here to suppress warning
       }
     } catch handleNonFatalOrInterruptedException { e ⇒
       handleInvokeFailure(Nil, e)
@@ -473,7 +492,7 @@ private[akka] class ActorCell(
     }
   }
 
-  protected def create(uid: Int): Unit = {
+  protected def create(): Unit = {
     def clearOutActorIfNonNull(): Unit = {
       if (actor != null) {
         clearActorFields(actor)
@@ -481,7 +500,6 @@ private[akka] class ActorCell(
       }
     }
     try {
-      this.uid = uid
       val created = newActor()
       actor = created
       created.preStart()
@@ -505,12 +523,11 @@ private[akka] class ActorCell(
     }
   }
 
-  private def supervise(child: ActorRef, async: Boolean, uid: Int): Unit =
+  private def supervise(child: ActorRef, async: Boolean): Unit =
     if (!isTerminating) {
       // Supervise is the first thing we get from a new child, so store away the UID for later use in handleFailure()
       initChild(child) match {
         case Some(crs) ⇒
-          crs.uid = uid
           handleSupervise(child, async)
           if (system.settings.DebugLifecycle) publish(Debug(self.path.toString, clazz(actor), "now supervising " + child))
         case None ⇒ publish(Error(self.path.toString, clazz(actor), "received Supervise from unregistered child " + child + ", this will not end well"))

akka-actor/src/main/scala/akka/actor/ActorPath.scala

@@ -6,6 +6,7 @@ import scala.annotation.tailrec
 import scala.collection.immutable
 import akka.japi.Util.immutableSeq
 import java.net.MalformedURLException
+import java.lang.{ StringBuilder ⇒ JStringBuilder }
 
 object ActorPath {
   /**
@@ -35,6 +36,13 @@ object ActorPath {
  * as possible, which owing to the bottom-up recursive nature of ActorPath
  * is sorted by path elements FROM RIGHT TO LEFT, where RootActorPath >
  * ChildActorPath in case the number of elements is different.
+ *
+ * Two actor paths are compared equal when they have the same name and parent
+ * elements, including the root address information. That does not necessarily
+ * mean that they point to the same incarnation of the actor if the actor is
+ * re-created with the same path. In other words, in contrast to how actor
+ * references are compared the unique id of the actor is not taken into account
+ * when comparing actor paths.
  */
 @SerialVersionUID(1L)
 sealed trait ActorPath extends Comparable[ActorPath] with Serializable {
@@ -96,6 +104,37 @@ sealed trait ActorPath extends Comparable[ActorPath] with Serializable {
    * information.
    */
   def toStringWithAddress(address: Address): String
+
+  /**
+   * Generate full String representation including the
+   * uid for the actor cell instance as URI fragment.
+   * This representation should be used as serialized
+   * representation instead of `toString`.
+   */
+  def toSerializationFormat: String
+
+  /**
+   * Generate full String representation including the uid for the actor cell
+   * instance as URI fragment, replacing the Address in the RootActor Path
+   * with the given one unless this path’s address includes host and port
+   * information. This representation should be used as serialized
+   * representation instead of `toStringWithAddress`.
+   */
+  def toSerializationFormatWithAddress(address: Address): String
+
+  /**
+   * INTERNAL API
+   * Unique identifier of the actor. Used for distinguishing
+   * different incarnations of actors with same path (name elements).
+   */
+  private[akka] def uid: Int
+
+  /**
+   * INTERNAL API
+   * Creates a new ActorPath with same elements but with the specified `uid`.
+   */
+  private[akka] def withUid(uid: Int): ActorPath
+
 }
 
 /**
@@ -109,29 +148,55 @@ final case class RootActorPath(address: Address, name: String = "/") extends Act
 
   override def root: RootActorPath = this
 
-  override def /(child: String): ActorPath = new ChildActorPath(this, child)
+  override def /(child: String): ActorPath = {
+    val (childName, uid) = ActorCell.splitNameAndUid(child)
+    new ChildActorPath(this, childName, uid)
+  }
 
   override def elements: immutable.Iterable[String] = ActorPath.emptyActorPath
 
   override val toString: String = address + name
 
+  override val toSerializationFormat: String = toString
+
   override def toStringWithAddress(addr: Address): String =
     if (address.host.isDefined) address + name
     else addr + name
 
+  override def toSerializationFormatWithAddress(addr: Address): String = toStringWithAddress(addr)
+
   override def compareTo(other: ActorPath): Int = other match {
     case r: RootActorPath  ⇒ toString compareTo r.toString // FIXME make this cheaper by comparing address and name in isolation
     case c: ChildActorPath ⇒ 1
   }
+
+  /**
+   * INTERNAL API
+   */
+  private[akka] def uid: Int = ActorCell.undefinedUid
+
+  /**
+   * INTERNAL API
+   */
+  override private[akka] def withUid(uid: Int): ActorPath =
+    if (uid == ActorCell.undefinedUid) this
+    else throw new IllegalStateException("RootActorPath must not have uid")
+
 }
 
 @SerialVersionUID(1L)
-final class ChildActorPath(val parent: ActorPath, val name: String) extends ActorPath {
+final class ChildActorPath private[akka] (val parent: ActorPath, val name: String, override private[akka] val uid: Int) extends ActorPath {
   if (name.indexOf('/') != -1) throw new IllegalArgumentException("/ is a path separator and is not legal in ActorPath names: [%s]" format name)
+  if (name.indexOf('#') != -1) throw new IllegalArgumentException("# is a fragment separator and is not legal in ActorPath names: [%s]" format name)
+
+  def this(parent: ActorPath, name: String) = this(parent, name, ActorCell.undefinedUid)
 
   override def address: Address = root.address
 
-  override def /(child: String): ActorPath = new ChildActorPath(this, child)
+  override def /(child: String): ActorPath = {
+    val (childName, uid) = ActorCell.splitNameAndUid(child)
+    new ChildActorPath(this, childName, uid)
+  }
 
   override def elements: immutable.Iterable[String] = {
     @tailrec
@@ -151,28 +216,82 @@ final class ChildActorPath(val parent: ActorPath, val name: String) extends Acto
     rec(this)
   }
 
-  // TODO research whether this should be cached somehow (might be fast enough, but creates GC pressure)
+  /**
-  /*
+   * INTERNAL API
-   * idea: add one field which holds the total length (because that is known)
-   * so that only one String needs to be allocated before traversal; this is
-   * cheaper than any cache
    */
-  override def toString = {
+  override private[akka] def withUid(uid: Int): ActorPath =
-    @tailrec
+    if (uid == this.uid) this
-    def rec(p: ActorPath, s: StringBuilder): StringBuilder = p match {
+    else new ChildActorPath(parent, name, uid)
-      case r: RootActorPath ⇒ s.insert(0, r.toString)
+
-      case _                ⇒ rec(p.parent, s.insert(0, '/').insert(0, p.name))
+  override def toString: String = {
-    }
+    val length = toStringLength
-    rec(parent, new StringBuilder(32).append(name)).toString
+    buildToString(new JStringBuilder(length), length, 0, _.toString).toString
   }
 
-  override def toStringWithAddress(addr: Address) = {
+  override def toSerializationFormat: String = {
+    val length = toStringLength
+    val sb = buildToString(new JStringBuilder(length + 12), length, 0, _.toString)
+    appendUidFragment(sb).toString
+  }
+
+  private def toStringLength: Int = toStringOffset + name.length
+
+  private val toStringOffset: Int = parent match {
+    case r: RootActorPath  ⇒ r.address.toString.length + r.name.length
+    case c: ChildActorPath ⇒ c.toStringLength + 1
+  }
+
+  override def toStringWithAddress(addr: Address): String = {
+    val diff = addressStringLengthDiff(addr)
+    val length = toStringLength + diff
+    buildToString(new JStringBuilder(length), length, diff, _.toStringWithAddress(addr)).toString
+  }
+
+  override def toSerializationFormatWithAddress(addr: Address): String = {
+    val diff = addressStringLengthDiff(addr)
+    val length = toStringLength + diff
+    val sb = buildToString(new JStringBuilder(length + 12), length, diff, _.toStringWithAddress(addr))
+    appendUidFragment(sb).toString
+  }
+
+  private def addressStringLengthDiff(addr: Address): Int = {
+    val r = root
+    if (r.address.host.isDefined) 0
+    else (addr.toString.length - r.address.toString.length)
+  }
+
+  /**
+   * Optimized toString construction. Used by `toString`, `toSerializationFormat`,
+   * and friends `WithAddress`
+   * @param sb builder that will be modified (and same instance is returned)
+   * @param length pre-calculated length of the to be constructed String, not
+   *   necessarily same as sb.capacity because more things may be appended to the
+   *   sb afterwards
+   * @param diff difference in offset for each child element, due to different address
+   * @param rootString function to construct the root element string
+   */
+  private def buildToString(sb: JStringBuilder, length: Int, diff: Int, rootString: RootActorPath ⇒ String): JStringBuilder = {
     @tailrec
-    def rec(p: ActorPath, s: StringBuilder): StringBuilder = p match {
+    def rec(p: ActorPath): JStringBuilder = p match {
-      case r: RootActorPath ⇒ s.insert(0, r.toStringWithAddress(addr))
+      case r: RootActorPath ⇒
-      case _                ⇒ rec(p.parent, s.insert(0, '/').insert(0, p.name))
+        val rootStr = rootString(r)
+        sb.replace(0, rootStr.length, rootStr)
+      case c: ChildActorPath ⇒
+        val start = c.toStringOffset + diff
+        val end = start + c.name.length
+        sb.replace(start, end, c.name)
+        if (c ne this)
+          sb.replace(end, end + 1, "/")
+        rec(c.parent)
     }
-    rec(parent, new StringBuilder(32).append(name)).toString
+
+    sb.setLength(length)
+    rec(this)
+  }
+
+  private def appendUidFragment(sb: JStringBuilder): JStringBuilder = {
+    if (uid == ActorCell.undefinedUid) sb
+    else sb.append("#").append(uid)
   }
 
   override def equals(other: Any): Boolean = {

akka-actor/src/main/scala/akka/actor/ActorRef.scala

@@ -12,7 +12,6 @@ import akka.event.EventStream
 import scala.annotation.tailrec
 import java.util.concurrent.ConcurrentHashMap
 import akka.event.LoggingAdapter
-import scala.concurrent.forkjoin.ThreadLocalRandom
 import scala.collection.JavaConverters
 
 /**
@@ -73,6 +72,17 @@ import scala.collection.JavaConverters
  *
  * ActorRef does not have a method for terminating the actor it points to, use
  * [[akka.actor.ActorRefFactory]]`.stop(child)` for this purpose.
+ *
+ * Two actor references are compared equal when they have the same path and point to
+ * the same actor incarnation. A reference pointing to a terminated actor doesn't compare
+ * equal to a reference pointing to another (re-created) actor with the same path.
+ * Actor references acquired with `actorFor` do not always include the full information
+ * about the underlying actor identity and therefore such references do not always compare
+ * equal to references acquired with `actorOf`, `sender`, or `context.self`.
+ *
+ * If you need to keep track of actor references in a collection and do not care
+ * about the exact actor incarnation you can use the ``ActorPath`` as key because
+ * the unique id of the actor is not taken into account when comparing actor paths.
  */
 abstract class ActorRef extends java.lang.Comparable[ActorRef] with Serializable {
   scalaRef: InternalActorRef ⇒
@@ -83,9 +93,13 @@ abstract class ActorRef extends java.lang.Comparable[ActorRef] with Serializable
   def path: ActorPath
 
   /**
-   * Comparison only takes address into account.
+   * Comparison takes path and the unique id of the actor cell into account.
    */
-  final def compareTo(other: ActorRef) = this.path compareTo other.path
+  final def compareTo(other: ActorRef) = {
+    val x = this.path compareTo other.path
+    if (x == 0) this.path.uid compareTo other.path.uid
+    else x
+  }
 
   /**
    * Sends the specified message to the sender, i.e. fire-and-forget semantics.
@@ -122,15 +136,22 @@ abstract class ActorRef extends java.lang.Comparable[ActorRef] with Serializable
    */
   def isTerminated: Boolean
 
-  // FIXME RK check if we should scramble the bits or whether they can stay the same
+  final override def hashCode: Int = {
-  final override def hashCode: Int = path.hashCode
+    if (path.uid == ActorCell.undefinedUid) path.hashCode
+    else path.uid
+  }
 
+  /**
+   * Equals takes path and the unique id of the actor cell into account.
+   */
   final override def equals(that: Any): Boolean = that match {
-    case other: ActorRef ⇒ path == other.path
+    case other: ActorRef ⇒ path.uid == other.path.uid && path == other.path
     case _               ⇒ false
   }
 
-  override def toString = "Actor[%s]".format(path)
+  override def toString: String =
+    if (path.uid == ActorCell.undefinedUid) s"Actor[${path}]"
+    else s"Actor[${path}#${path.uid}]"
 }
 
 /**
@@ -270,7 +291,7 @@ private[akka] class LocalActorRef private[akka] (
    * object from another thread as soon as we run init.
    */
   private val actorCell: ActorCell = newActorCell(_system, this, _props, _supervisor)
-  actorCell.init(ThreadLocalRandom.current.nextInt(), sendSupervise = true)
+  actorCell.init(sendSupervise = true)
 
   protected def newActorCell(system: ActorSystemImpl, ref: InternalActorRef, props: Props, supervisor: InternalActorRef): ActorCell =
     new ActorCell(system, ref, props, supervisor)
@@ -316,11 +337,14 @@ private[akka] class LocalActorRef private[akka] (
    * Method for looking up a single child beneath this actor. Override in order
    * to inject “synthetic” actor paths like “/temp”.
    */
-  protected def getSingleChild(name: String): InternalActorRef =
+  protected def getSingleChild(name: String): InternalActorRef = {
-    actorCell.getChildByName(name) match {
+    val (childName, uid) = ActorCell.splitNameAndUid(name)
-      case Some(crs: ChildRestartStats) ⇒ crs.child.asInstanceOf[InternalActorRef]
+    actorCell.getChildByName(childName) match {
-      case _                            ⇒ Nobody
+      case Some(crs: ChildRestartStats) if uid == ActorCell.undefinedUid || uid == crs.uid ⇒
+        crs.child.asInstanceOf[InternalActorRef]
+      case _ ⇒ Nobody
     }
+  }
 
   override def getChild(names: Iterator[String]): InternalActorRef = {
     /*
@@ -384,8 +408,8 @@ private[akka] case class SerializedActorRef private (path: String) {
 private[akka] object SerializedActorRef {
   def apply(path: ActorPath): SerializedActorRef = {
     Serialization.currentTransportAddress.value match {
-      case null ⇒ new SerializedActorRef(path.toString)
+      case null ⇒ new SerializedActorRef(path.toSerializationFormat)
-      case addr ⇒ new SerializedActorRef(path.toStringWithAddress(addr))
+      case addr ⇒ new SerializedActorRef(path.toSerializationFormatWithAddress(addr))
     }
   }
 }

akka-actor/src/main/scala/akka/actor/ActorRefProvider.scala

@@ -396,7 +396,7 @@ class LocalActorRefProvider private[akka] (
 
     override def sendSystemMessage(message: SystemMessage): Unit = stopped ifOff {
       message match {
-        case Supervise(_, _, _) ⇒ // TODO register child in some map to keep track of it and enable shutdown after all dead
+        case Supervise(_, _)    ⇒ // TODO register child in some map to keep track of it and enable shutdown after all dead
         case ChildTerminated(_) ⇒ stop()
         case _                  ⇒ log.error(this + " received unexpected system message [" + message + "]")
       }

akka-actor/src/main/scala/akka/actor/Address.scala

@@ -47,7 +47,7 @@ final case class Address private (protocol: String, system: String, host: Option
    */
   @transient
   override lazy val toString: String = {
-    val sb = (new StringBuilder(protocol)).append("://").append(system)
+    val sb = (new java.lang.StringBuilder(protocol)).append("://").append(system)
 
     if (host.isDefined) sb.append('@').append(host.get)
     if (port.isDefined) sb.append(':').append(port.get)
@@ -76,12 +76,14 @@ object Address {
 }
 
 private[akka] trait PathUtils {
-  protected def split(s: String): List[String] = {
+  protected def split(s: String, fragment: String): List[String] = {
     @tailrec
     def rec(pos: Int, acc: List[String]): List[String] = {
       val from = s.lastIndexOf('/', pos - 1)
       val sub = s.substring(from + 1, pos)
-      val l = sub :: acc
+      val l =
+        if ((fragment ne null) && acc.isEmpty) sub + "#" + fragment :: acc
+        else sub :: acc
       if (from == -1) l else rec(from, l)
     }
     rec(s.length, Nil)
@@ -93,7 +95,7 @@ object RelativeActorPath extends PathUtils {
     try {
       val uri = new URI(addr)
       if (uri.isAbsolute) None
-      else Some(split(uri.getRawPath))
+      else Some(split(uri.getRawPath, uri.getRawFragment))
     } catch {
       case _: URISyntaxException ⇒ None
     }
@@ -142,7 +144,7 @@ object ActorPathExtractor extends PathUtils {
       val uri = new URI(addr)
       uri.getRawPath match {
         case null ⇒ None
-        case path ⇒ AddressFromURIString.unapply(uri).map((_, split(path).drop(1)))
+        case path ⇒ AddressFromURIString.unapply(uri).map((_, split(path, uri.getRawFragment).drop(1)))
       }
     } catch {
       case _: URISyntaxException ⇒ None

akka-actor/src/main/scala/akka/actor/FaultHandling.scala

@@ -32,7 +32,7 @@ private[akka] case object ChildNameReserved extends ChildStats
 case class ChildRestartStats(child: ActorRef, var maxNrOfRetriesCount: Int = 0, var restartTimeWindowStartNanos: Long = 0L)
   extends ChildStats {
 
-  var uid: Int = 0
+  def uid: Int = child.path.uid
 
   //FIXME How about making ChildRestartStats immutable and then move these methods into the actual supervisor strategies?
   def requestRestartPermission(retriesWindow: (Option[Int], Option[Int])): Boolean =

akka-actor/src/main/scala/akka/actor/RepointableActorRef.scala

@@ -10,7 +10,6 @@ import java.util.concurrent.TimeUnit
 import java.util.concurrent.locks.ReentrantLock
 
 import scala.annotation.tailrec
-import scala.concurrent.forkjoin.ThreadLocalRandom
 
 import akka.actor.dungeon.ChildrenContainer
 import akka.event.Logging.Warning
@@ -73,10 +72,9 @@ private[akka] class RepointableActorRef(
   def initialize(async: Boolean): this.type =
     underlying match {
       case null ⇒
-        val uid = ThreadLocalRandom.current.nextInt()
+        swapCell(new UnstartedCell(system, this, props, supervisor))
-        swapCell(new UnstartedCell(system, this, props, supervisor, uid))
         swapLookup(underlying)
-        supervisor.sendSystemMessage(Supervise(this, async, uid))
+        supervisor.sendSystemMessage(Supervise(this, async))
         if (!async) point()
         this
       case other ⇒ throw new IllegalStateException("initialize called more than once!")
@@ -112,7 +110,7 @@ private[akka] class RepointableActorRef(
    * unstarted cell. The cell must be fully functional.
    */
   def newCell(old: UnstartedCell): Cell =
-    new ActorCell(system, this, props, supervisor).init(old.uid, sendSupervise = false)
+    new ActorCell(system, this, props, supervisor).init(sendSupervise = false)
 
   def start(): Unit = ()
 
@@ -144,9 +142,11 @@ private[akka] class RepointableActorRef(
         case ".." ⇒ getParent.getChild(name)
         case ""   ⇒ getChild(name)
         case other ⇒
-          lookup.getChildByName(other) match {
+          val (childName, uid) = ActorCell.splitNameAndUid(other)
-            case Some(crs: ChildRestartStats) ⇒ crs.child.asInstanceOf[InternalActorRef].getChild(name)
+          lookup.getChildByName(childName) match {
-            case _                            ⇒ Nobody
+            case Some(crs: ChildRestartStats) if uid == ActorCell.undefinedUid || uid == crs.uid ⇒
+              crs.child.asInstanceOf[InternalActorRef].getChild(name)
+            case _ ⇒ Nobody
           }
       }
     } else this
@@ -162,8 +162,7 @@ private[akka] class RepointableActorRef(
 private[akka] class UnstartedCell(val systemImpl: ActorSystemImpl,
                                   val self: RepointableActorRef,
                                   val props: Props,
-                                  val supervisor: InternalActorRef,
+                                  val supervisor: InternalActorRef) extends Cell {
-                                  val uid: Int) extends Cell {
 
   /*
    * This lock protects all accesses to this cell’s queues. It also ensures

akka-actor/src/main/scala/akka/actor/dungeon/Children.scala

@@ -182,7 +182,8 @@ private[akka] trait Children { this: ActorCell ⇒
       // this name will either be unreserved or overwritten with a real child below
       val actor =
         try {
-          cell.provider.actorOf(cell.systemImpl, props, cell.self, cell.self.path / name,
+          val childPath = (cell.self.path / name).withUid(ActorCell.newUid())
+          cell.provider.actorOf(cell.systemImpl, props, cell.self, childPath,
             systemService = systemService, deploy = None, lookupDeploy = true, async = async)
         } catch {
           case e: InterruptedException ⇒

akka-actor/src/main/scala/akka/actor/dungeon/DeathWatch.scala

@@ -8,6 +8,7 @@ import akka.actor.{ Terminated, InternalActorRef, ActorRef, ActorRefScope, Actor
 import akka.dispatch.{ ChildTerminated, Watch, Unwatch }
 import akka.event.Logging.{ Warning, Error, Debug }
 import scala.util.control.NonFatal
+import akka.actor.MinimalActorRef
 
 private[akka] trait DeathWatch { this: ActorCell ⇒
 
@@ -16,7 +17,7 @@ private[akka] trait DeathWatch { this: ActorCell ⇒
 
   override final def watch(subject: ActorRef): ActorRef = subject match {
     case a: InternalActorRef ⇒
-      if (a != self && !watching.contains(a)) {
+      if (a != self && !watchingContains(a)) {
         maintainAddressTerminatedSubscription(a) {
           a.sendSystemMessage(Watch(a, self)) // ➡➡➡ NEVER SEND THE SAME SYSTEM MESSAGE OBJECT TO TWO ACTORS ⬅⬅⬅
           watching += a
@@ -27,10 +28,10 @@ private[akka] trait DeathWatch { this: ActorCell ⇒
 
   override final def unwatch(subject: ActorRef): ActorRef = subject match {
     case a: InternalActorRef ⇒
-      if (a != self && watching.contains(a)) {
+      if (a != self && watchingContains(a)) {
         maintainAddressTerminatedSubscription(a) {
           a.sendSystemMessage(Unwatch(a, self)) // ➡➡➡ NEVER SEND THE SAME SYSTEM MESSAGE OBJECT TO TWO ACTORS ⬅⬅⬅
-          watching -= a
+          removeWatching(a)
         }
       }
       a
@@ -41,13 +42,28 @@ private[akka] trait DeathWatch { this: ActorCell ⇒
    * it will be propagated to user's receive.
    */
   protected def watchedActorTerminated(t: Terminated): Unit =
-    if (watching.contains(t.actor)) {
+    if (watchingContains(t.actor)) {
       maintainAddressTerminatedSubscription(t.actor) {
-        watching -= t.actor
+        removeWatching(t.actor)
       }
       receiveMessage(t)
     }
 
+  // TODO this should be removed and be replaced with `watching.contains(subject)`
+  //   when all actor references have uid, i.e. actorFor is removed
+  private def watchingContains(subject: ActorRef): Boolean = {
+    watching.contains(subject) || (subject.path.uid != ActorCell.undefinedUid &&
+      watching.contains(new UndefinedUidActorRef(subject)))
+  }
+
+  // TODO this should be removed and be replaced with `watching -= subject`
+  //   when all actor references have uid, i.e. actorFor is removed
+  private def removeWatching(subject: ActorRef): Unit = {
+    watching -= subject
+    if (subject.path.uid != ActorCell.undefinedUid)
+      watching -= new UndefinedUidActorRef(subject)
+  }
+
   protected def tellWatchersWeDied(actor: Actor): Unit = {
     if (!watchedBy.isEmpty) {
       val terminated = Terminated(self)(existenceConfirmed = true, addressTerminated = false)
@@ -168,3 +184,8 @@ private[akka] trait DeathWatch { this: ActorCell ⇒
   private def subscribeAddressTerminated(): Unit = system.eventStream.subscribe(self, classOf[AddressTerminated])
 
 }
+
+private[akka] class UndefinedUidActorRef(ref: ActorRef) extends MinimalActorRef {
+  override val path = ref.path.withUid(ActorCell.undefinedUid)
+  override def provider = throw new UnsupportedOperationException("UndefinedUidActorRef does not provide")
+}

akka-actor/src/main/scala/akka/actor/dungeon/Dispatch.scala

@@ -40,7 +40,7 @@ private[akka] trait Dispatch { this: ActorCell ⇒
    * reasonably different from the previous UID of a possible actor with the same path,
    * which can be achieved by using ThreadLocalRandom.current.nextInt().
    */
-  final def init(uid: Int, sendSupervise: Boolean): this.type = {
+  final def init(sendSupervise: Boolean): this.type = {
     /*
      * Create the mailbox and enqueue the Create() message to ensure that
      * this is processed before anything else.
@@ -49,11 +49,11 @@ private[akka] trait Dispatch { this: ActorCell ⇒
     mailbox.setActor(this)
 
     // ➡➡➡ NEVER SEND THE SAME SYSTEM MESSAGE OBJECT TO TWO ACTORS ⬅⬅⬅
-    mailbox.systemEnqueue(self, Create(uid))
+    mailbox.systemEnqueue(self, Create())
 
     if (sendSupervise) {
       // ➡➡➡ NEVER SEND THE SAME SYSTEM MESSAGE OBJECT TO TWO ACTORS ⬅⬅⬅
-      parent.sendSystemMessage(akka.dispatch.Supervise(self, async = false, uid))
+      parent.sendSystemMessage(akka.dispatch.Supervise(self, async = false))
       parent ! NullMessage // read ScalaDoc of NullMessage to see why
     }
     this

akka-actor/src/main/scala/akka/actor/dungeon/FaultHandling.scala

@@ -134,7 +134,7 @@ private[akka] trait FaultHandling { this: ActorCell ⇒
   private def finishCreate(): Unit = {
     try resumeNonRecursive()
     finally clearFailed()
-    create(uid)
+    create()
   }
 
   protected def terminate() {

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

@@ -82,8 +82,8 @@ private[akka] sealed trait SystemMessage extends PossiblyHarmful with Serializab
 /**
  * INTERNAL API
  */
-@SerialVersionUID(-4836972106317757555L)
+@SerialVersionUID(3L)
-private[akka] case class Create(uid: Int) extends SystemMessage // send to self from Dispatcher.register
+private[akka] case class Create() extends SystemMessage // send to self from Dispatcher.register
 /**
  * INTERNAL API
  */
@@ -107,8 +107,8 @@ private[akka] case class Terminate() extends SystemMessage // sent to self from
 /**
  * INTERNAL API
  */
-@SerialVersionUID(3245747602115485675L)
+@SerialVersionUID(3L)
-private[akka] case class Supervise(child: ActorRef, async: Boolean, uid: Int) extends SystemMessage // sent to supervisor ActorRef from ActorCell.start
+private[akka] case class Supervise(child: ActorRef, async: Boolean) extends SystemMessage // sent to supervisor ActorRef from ActorCell.start
 /**
  * INTERNAL API
  */

akka-actor/src/main/scala/akka/event/Logging.scala

@@ -872,7 +872,7 @@ trait LoggingAdapter {
   }
 
   def format(t: String, arg: Any*): String = {
-    val sb = new StringBuilder(64)
+    val sb = new java.lang.StringBuilder(64)
     var p = 0
     var rest = t
     while (p < arg.length) {

akka-actor/src/main/scala/akka/pattern/GracefulStopSupport.scala

@@ -55,13 +55,13 @@ trait GracefulStopSupport {
         internalTarget.sendSystemMessage(Watch(target, ref))
         val f = ref.result.future
         f onComplete { // Just making sure we're not leaking here
-          case Success(Terminated(`target`)) ⇒ ()
+          case Success(Terminated(a)) if a.path == target.path ⇒ ()
-          case _                             ⇒ internalTarget.sendSystemMessage(Unwatch(target, ref))
+          case _ ⇒ internalTarget.sendSystemMessage(Unwatch(target, ref))
         }
         target ! stopMessage
         f map {
-          case Terminated(`target`) ⇒ true
+          case Terminated(a) if a.path == target.path ⇒ true
-          case _                    ⇒ false
+          case _                                      ⇒ false
         }
       case s ⇒ throw new IllegalArgumentException("Unknown ActorSystem implementation: '" + s + "'")
     }

akka-actor/src/main/scala/akka/routing/Routing.scala

@@ -35,7 +35,7 @@ private[akka] class RoutedActorRef(_system: ActorSystemImpl, _props: Props, _sup
         " is invalid - you can not use a 'BalancingDispatcher' as a Router's dispatcher, you can however use it for the routees.")
   } else _props.routerConfig.verifyConfig()
 
-  override def newCell(old: UnstartedCell): Cell = new RoutedActorCell(system, this, props, supervisor).init(old.uid, sendSupervise = false)
+  override def newCell(old: UnstartedCell): Cell = new RoutedActorCell(system, this, props, supervisor).init(sendSupervise = false)
 
 }
 
@@ -76,7 +76,7 @@ private[akka] class RoutedActorCell(_system: ActorSystemImpl, _ref: InternalActo
 
   def applyRoute(sender: ActorRef, message: Any): immutable.Iterable[Destination] = message match {
     case _: AutoReceivedMessage                ⇒ Destination(sender, self) :: Nil
-    case CurrentRoutees                        ⇒ sender ! RouterRoutees(_routees); Nil
+    case CurrentRoutees                        ⇒ { sender ! RouterRoutees(_routees); Nil }
     case msg if route.isDefinedAt(sender, msg) ⇒ route(sender, message)
     case _                                     ⇒ Nil
   }
@@ -94,13 +94,13 @@ private[akka] class RoutedActorCell(_system: ActorSystemImpl, _ref: InternalActo
   }
 
   /**
-   * Adds the routees to existing routees.
+   * Removes the abandoned routees from existing routees.
    * Removes death watch of the routees. Doesn't stop the routees.
    * Not thread safe, but intended to be called from protected points, such as
    * `Resizer.resize`
    */
   private[akka] def removeRoutees(abandonedRoutees: immutable.Iterable[ActorRef]): Unit = {
-    _routees = abandonedRoutees.foldLeft(_routees) { (xs, x) ⇒ unwatch(x); xs.filterNot(_ == x) }
+    _routees = abandonedRoutees.foldLeft(_routees) { (xs, x) ⇒ unwatch(x); xs.filterNot(_.path == x.path) }
   }
 
   /**

akka-actor/src/main/scala/akka/util/Crypt.scala

@@ -32,7 +32,7 @@ object Crypt {
   }
 
   def hexify(bytes: Array[Byte]): String = {
-    val builder = new StringBuilder(bytes.length * 2)
+    val builder = new java.lang.StringBuilder(bytes.length * 2)
     bytes.foreach { byte ⇒ builder.append(hex.charAt((byte & 0xF0) >> 4)).append(hex.charAt(byte & 0xF)) }
     builder.toString
   }

akka-actor/src/main/scala/akka/util/Helpers.scala

@@ -40,8 +40,8 @@ object Helpers {
   final val base64chars = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789+~"
 
   @tailrec
-  def base64(l: Long, sb: StringBuilder = new StringBuilder("$")): String = {
+  def base64(l: Long, sb: java.lang.StringBuilder = new java.lang.StringBuilder("$")): String = {
-    sb += base64chars.charAt(l.toInt & 63)
+    sb append base64chars.charAt(l.toInt & 63)
     val next = l >>> 6
     if (next == 0) sb.toString
     else base64(next, sb)

akka-cluster/src/multi-jvm/scala/akka/cluster/StressSpec.scala

@@ -254,7 +254,7 @@ object StressMultiJvmSpec extends MultiNodeConfig {
 
     def maxDuration = results.map(_.duration).max
 
-    def totalClusterStats = results.foldLeft(ClusterStats()){_ :+ _.clusterStats}
+    def totalClusterStats = results.foldLeft(ClusterStats()) { _ :+ _.clusterStats }
 
     def formatMetrics: String = {
       import akka.cluster.Member.addressOrdering
@@ -302,7 +302,7 @@ object StressMultiJvmSpec extends MultiNodeConfig {
       s"${monitor}\t${subject}\t${phi.count}\t${phi.countAboveOne}\t${phi.max.form}"
 
     def formatStats: String =
-      (clusterStatsObservedByNode map { case (monitor, stats) => s"${monitor}\t${stats}" }).
+      (clusterStatsObservedByNode map { case (monitor, stats) ⇒ s"${monitor}\t${stats}" }).
         mkString("ClusterStats\n", "\n", "")
   }
 
@@ -403,7 +403,7 @@ object StressMultiJvmSpec extends MultiNodeConfig {
     def receive = {
       case StatsTick ⇒
         val res = StatsResult(cluster.selfAddress, cluster.readView.latestStats :- startStats)
-        reportTo foreach { _ !  res }
+        reportTo foreach { _ ! res }
       case ReportTo(ref) ⇒
         reportTo = ref
       case Reset ⇒
@@ -553,7 +553,9 @@ object StressMultiJvmSpec extends MultiNodeConfig {
    * Used for remote death watch testing
    */
   class Watchee extends Actor {
-    def receive = Actor.emptyBehavior
+    def receive = {
+      case Ping ⇒ sender ! Pong
+    }
   }
 
   /**
@@ -621,6 +623,9 @@ object StressMultiJvmSpec extends MultiNodeConfig {
   case class ChildrenCount(numberOfChildren: Int, numberOfChildRestarts: Int)
   case object Reset
 
+  case object Ping
+  case object Pong
+
 }
 
 class StressMultiJvmNode1 extends StressSpec
@@ -700,7 +705,7 @@ abstract class StressSpec
     runOn(roles.head) {
       val r = clusterResultAggregator
       watch(r)
-      expectMsgPF(remaining) { case Terminated(`r`) ⇒ true }
+      expectMsgPF(remaining) { case Terminated(a) if a.path == r.path ⇒ true }
     }
     enterBarrier("cluster-result-done-" + step)
   }
@@ -773,7 +778,9 @@ abstract class StressSpec
     }
     enterBarrier("watchee-created-" + step)
     runOn(roles.head) {
-      watch(system.actorFor(node(removeRole) / "user" / "watchee"))
+      system.actorFor(node(removeRole) / "user" / "watchee") ! Ping
+      expectMsg(Pong)
+      watch(lastSender)
     }
     enterBarrier("watch-estabilished-" + step)
 
@@ -790,9 +797,9 @@ abstract class StressSpec
     }
 
     runOn(roles.head) {
-      val expectedRef = system.actorFor(RootActorPath(removeAddress) / "user" / "watchee")
+      val expectedPath = RootActorPath(removeAddress) / "user" / "watchee"
       expectMsgPF(remaining) {
-        case Terminated(`expectedRef`) ⇒ true
+        case Terminated(a) if a.path == expectedPath ⇒ true
       }
     }
     enterBarrier("watch-verified-" + step)
@@ -939,7 +946,7 @@ abstract class StressSpec
       workResult.jobsPerSecond.form,
       workResult.retryCount, workResult.sendCount)
     watch(m)
-    expectMsgPF(remaining) { case Terminated(`m`) ⇒ true }
+    expectMsgPF(remaining) { case Terminated(a) if a.path == m.path ⇒ true }
     workResult
   }
 
@@ -947,7 +954,7 @@ abstract class StressSpec
     within(duration + 10.seconds) {
       val rounds = (duration.toMillis / oneIteration.toMillis).max(1).toInt
       val supervisor = system.actorOf(Props[Supervisor], "supervisor")
-      for (count <- 0 until rounds) {
+      for (count ← 0 until rounds) {
         createResultAggregator(title, expectedResults = nbrUsedRoles, includeInHistory = false)
 
         reportResult {

akka-contrib/src/main/scala/akka/contrib/pattern/ReliableProxy.scala

@@ -26,7 +26,8 @@ object ReliableProxy {
         } else {
           log.debug("received msg of {} from {} with wrong serial", msg.asInstanceOf[AnyRef].getClass, snd)
         }
-      case Terminated(`target`) ⇒ context stop self
+      //TODO use exact match of target when all actor references have uid, i.e. actorFor has been removed
+      case Terminated(a) if a.path == target.path ⇒ context stop self
     }
   }
 

akka-docs/rst/general/addressing.rst

@@ -91,6 +91,26 @@ followed by the concatenation of the path elements, from root guardian to the
 designated actor; the path elements are the names of the traversed actors and
 are separated by slashes.
 
+What is the Difference Between Actor Reference and Path?
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+An actor reference designates a single actor and the life-cycle of the reference
+matches that actor’s life-cycle; an actor path represents a name which may or 
+may not be inhabited by an actor and the path itself does not have a life-cycle, 
+it never becomes invalid. You can create an actor path without creating an actor, 
+but you cannot create an actor reference without creating corresponding actor. 
+
+.. note::
+
+  That definition does not hold for ``actorFor``, which is one of the reasons why 
+  ``actorFor`` is deprecated in favor of ``actorSelection``.
+
+You can create an actor, terminate it, and then create a new actor with the same
+actor path. The newly created actor is a new incarnation of the actor. It is not
+the same actor. An actor reference to the old incarnation is not valid for the new
+incarnation. Messages sent to the old actor reference will not be delivered
+to the new incarnation even though they have the same path.
+
 Actor Path Anchors
 ^^^^^^^^^^^^^^^^^^
 
@@ -180,9 +200,9 @@ the whole lifetime of the actor. In the case of a local actor reference, the
 named actor needs to exist before the lookup, or else the acquired reference
 will be an :class:`EmptyLocalActorRef`. This will be true even if an actor with
 that exact path is created after acquiring the actor reference. For remote actor
-references the behaviour is different and sending messages to such a reference
+references acquired with `actorFor` the behaviour is different and sending messages 
-will under the hood look up the actor by path on the remote system for every
+to such a reference will under the hood look up the actor by path on the remote
-message send.
+system for every message send.
 
 Absolute vs. Relative Paths
 ```````````````````````````
@@ -246,18 +266,39 @@ Summary: ``actorOf`` vs. ``actorFor``
   - ``actorFor`` only ever looks up an existing actor, i.e. does not create
     one.
 
+Actor Reference and Path Equality
+---------------------------------
+
+Equality of ``ActorRef`` match the intention that an ``ActorRef`` corresponds to
+the target actor incarnation. Two actor references are compared equal when they have
+the same path and point to the same actor incarnation. A reference pointing to a
+terminated actor does not compare equal to a reference pointing to another (re-created)
+actor with the same path. Note that a restart of an actor caused by a failure still 
+means that it is the same actor incarnation, i.e. a restart is not visible for the 
+consumer of the ``ActorRef``.
+
+Remote actor references acquired with ``actorFor`` do not include the full
+information about the underlying actor identity and therefore such references 
+do not compare equal to references acquired with ``actorOf``, ``sender``, 
+or ``context.self``. Because of this ``actorFor`` is deprecated in favor of
+``actorSelection``.
+
+If you need to keep track of actor references in a collection and do not care about
+the exact actor incarnation you can use the ``ActorPath`` as key, because the identifier
+of the target actor is not taken into account when comparing actor paths.
+
 Reusing Actor Paths
 -------------------
 
-When an actor is terminated, its path will point to the dead letter mailbox,
+When an actor is terminated, its reference will point to the dead letter mailbox,
 DeathWatch will publish its final transition and in general it is not expected
 to come back to life again (since the actor life cycle does not allow this).
 While it is possible to create an actor at a later time with an identical
 path—simply due to it being impossible to enforce the opposite without keeping
 the set of all actors ever created available—this is not good practice: remote
-actor references which “died” suddenly start to work again, but without any
+actor references acquired with ``actorFor`` which “died” suddenly start to work
-guarantee of ordering between this transition and any other event, hence the
+again, but without any guarantee of ordering between this transition and any 
-new inhabitant of the path may receive messages which were destined for the
+other event, hence the new inhabitant of the path may receive messages which were destined for the
 previous tenant.
 
 It may be the right thing to do in very specific circumstances, but make sure

akka-docs/rst/java/code/docs/serialization/SerializationDocTestBase.java

@@ -67,8 +67,8 @@ public class SerializationDocTestBase {
     // within a piece of code that sets it,
     // so either you need to supply your own,
     // or simply use the local path.
-    if (transportAddress == null) identifier = theActorRef.path().toString();
+    if (transportAddress == null) identifier = theActorRef.path().toSerializationFormat();
-    else identifier = theActorRef.path().toStringWithAddress(transportAddress);
+    else identifier = theActorRef.path().toSerializationFormatWithAddress(transportAddress);
     // Then just serialize the identifier however you like
 
 

akka-docs/rst/java/serialization.rst

@@ -120,10 +120,18 @@ you might want to know how to serialize and deserialize them properly, here's th
 
 .. note::
   
-  ``ActorPath.toStringWithAddress`` only differs from ``toString`` if the
+  ``ActorPath.toSerializationFormatWithAddress`` differs from ``toString`` if the
   address does not already have ``host`` and ``port`` components, i.e. it only
   inserts address information for local addresses.
   
+  ``toSerializationFormatWithAddress`` also adds the unique id of the actor, which will
+  change when the actor is stopped and then created again with the same name.
+  Sending messages to a reference pointing the old actor will not be delivered
+  to the new actor. If you do not want this behavior, e.g. in case of long term
+  storage of the reference, you can use ``toStringWithAddress``, which does not
+  include the unique id.
+
+
 This assumes that serialization happens in the context of sending a message
 through the remote transport. There are other uses of serialization, though,
 e.g. storing actor references outside of an actor application (database,

akka-docs/rst/project/migration-guide-2.1.x-2.2.x.rst

@@ -152,4 +152,44 @@ available via the ``inbound`` boolean field of the event.
 
 New configuration settings are also available, see the remoting documentation for more detail: :ref:`remoting-scala`
 
+ActorRef equality and sending to remote actors
+==============================================
 
+Sending messages to an ``ActorRef`` must have the same semantics no matter if the target actor is located
+on a remote host or in the same ``ActorSystem`` in the same JVM. This was not always the case. For example
+when the target actor is terminated and created again under the same path. Sending to local references
+of the previous incarnation of the actor will not be delivered to the new incarnation, but that was the case
+for remote references. The reason was that the target actor was looked up by its path on every message 
+delivery and the path didn't distinguish between the two incarnations of the actor. This has been fixed, and
+sending messages to remote references that points to a terminated actor will not be delivered to a new 
+actor with the same path.
+
+Equality of ``ActorRef`` has been changed to match the intention that an ``ActorRef`` corresponds to the target
+actor instance. Two actor references are compared equal when they have the same path and point to the same
+actor incarnation. A reference pointing to a terminated actor does not compare equal to a reference pointing
+to another (re-created) actor with the same path. Note that a restart of an actor caused by a failure still 
+means that it's the same actor incarnation, i.e. a restart is not visible for the consumer of the ``ActorRef``.
+
+Equality in 2.1 was only based on the path of the ``ActorRef``. If you need to keep track of actor references
+in a collection and do not care about the exact actor incarnation you can use the ``ActorPath`` as key, because
+the identifier of the target actor is not taken into account when comparing actor paths.
+
+Remote actor references acquired with ``actorFor`` do not include the full information about the underlying actor
+identity and therefore such references do not compare equal to references acquired with ``actorOf``, 
+``sender``, or ``context.self``. Because of this ``actorFor`` is deprecated, as explained in 
+:ref:`migration_2.2_actorSelection`.
+
+Note that when a parent actor is restarted its children are by default stopped and re-created, i.e. the child
+after the restart will be a different incarnation than the child before the restart. This has always been the
+case, but in some situations you might not have noticed, e.g. when comparing such actor references or sending
+messages to remote deployed children of a restarted parent.
+
+This may also have implications if you compare the ``ActorRef`` received in a ``Terminated`` message
+with an expected ``ActorRef``.
+
+.. _migration_2.2_actorSelection:
+
+Use ``actorSelection`` instead of ``actorFor``
+==============================================
+
+FIXME: ticket #3074

akka-docs/rst/scala/code/docs/serialization/SerializationDocSpec.scala

@@ -171,8 +171,8 @@ package docs.serialization {
       // so either you need to supply your own,
       // or simply use the local path.
       val identifier: String = Serialization.currentTransportAddress.value match {
-        case null    ⇒ theActorRef.path.toString
+        case null    ⇒ theActorRef.path.toSerializationFormat
-        case address ⇒ theActorRef.path.toStringWithAddress(address)
+        case address ⇒ theActorRef.path.toSerializationFormatWithAddress(address)
       }
       // Then just serialize the identifier however you like
 
@@ -192,7 +192,7 @@ package docs.serialization {
       }
 
       def serializeTo(ref: ActorRef, remote: Address): String =
-        ref.path.toStringWithAddress(ExternalAddress(theActorSystem).addressFor(remote))
+        ref.path.toSerializationFormatWithAddress(ExternalAddress(theActorSystem).addressFor(remote))
       //#external-address
     }
 
@@ -207,7 +207,7 @@ package docs.serialization {
       }
 
       def serializeAkkaDefault(ref: ActorRef): String =
-        ref.path.toStringWithAddress(ExternalAddress(theActorSystem).addressForAkka)
+        ref.path.toSerializationFormatWithAddress(ExternalAddress(theActorSystem).addressForAkka)
       //#external-address-default
     }
   }

akka-docs/rst/scala/serialization.rst

@@ -109,10 +109,17 @@ you might want to know how to serialize and deserialize them properly, here's th
 
 .. note::
   
-  ``ActorPath.toStringWithAddress`` only differs from ``toString`` if the
+  ``ActorPath.toSerializationFormatWithAddress`` differs from ``toString`` if the
   address does not already have ``host`` and ``port`` components, i.e. it only
   inserts address information for local addresses. 
 
+  ``toSerializationFormatWithAddress`` also adds the unique id of the actor, which will
+  change when the actor is stopped and then created again with the same name.
+  Sending messages to a reference pointing the old actor will not be delivered
+  to the new actor. If you don't want this behavior, e.g. in case of long term
+  storage of the reference, you can use ``toStringWithAddress``, which doesn't
+  include the unique id.
+
 This assumes that serialization happens in the context of sending a message
 through the remote transport. There are other uses of serialization, though,
 e.g. storing actor references outside of an actor application (database,

akka-remote/src/main/scala/akka/remote/RemoteActorRefProvider.scala

@@ -241,7 +241,8 @@ private[akka] class RemoteActorRefProvider(
           } else {
             try {
               val localAddress = transport.localAddressForRemote(addr)
-              val rpath = RootActorPath(addr) / "remote" / localAddress.protocol / localAddress.hostPort / path.elements
+              val rpath = (RootActorPath(addr) / "remote" / localAddress.protocol / localAddress.hostPort / path.elements).
+                withUid(path.uid)
               new RemoteActorRef(transport, localAddress, rpath, supervisor, Some(props), Some(d))
             } catch {
               case NonFatal(e) ⇒
@@ -280,15 +281,19 @@ private[akka] class RemoteActorRefProvider(
    * Called in deserialization of incoming remote messages. In this case the correct local address is known, therefore
    * this method is faster than the actorFor above.
    */
-  def actorForWithLocalAddress(ref: InternalActorRef, path: String, localAddress: Address): InternalActorRef = path match {
+  def actorForWithLocalAddress(ref: InternalActorRef, path: String, localAddress: Address): InternalActorRef = {
-    case ActorPathExtractor(address, elems) ⇒
+    path match {
-      if (hasAddress(address)) actorFor(rootGuardian, elems)
+      case ActorPathExtractor(address, elems) ⇒
-      else new RemoteActorRef(transport, localAddress,
+        if (hasAddress(address)) actorFor(rootGuardian, elems)
-        new RootActorPath(address) / elems, Nobody, props = None, deploy = None)
+        else new RemoteActorRef(transport, localAddress,
-    case _ ⇒ local.actorFor(ref, path)
+          new RootActorPath(address) / elems, Nobody, props = None, deploy = None)
+      case _ ⇒
+        local.actorFor(ref, path)
+    }
   }
 
-  def actorFor(ref: InternalActorRef, path: Iterable[String]): InternalActorRef = local.actorFor(ref, path)
+  def actorFor(ref: InternalActorRef, path: Iterable[String]): InternalActorRef =
+    local.actorFor(ref, path)
 
   /**
    * Using (checking out) actor on a specific node.
@@ -297,7 +302,7 @@ private[akka] class RemoteActorRefProvider(
     log.debug("[{}] Instantiating Remote Actor [{}]", rootPath, path)
 
     // we don’t wait for the ACK, because the remote end will process this command before any other message to the new actor
-    actorFor(RootActorPath(path.address) / "remote") ! DaemonMsgCreate(props, deploy, path.toString, supervisor)
+    actorFor(RootActorPath(path.address) / "remote") ! DaemonMsgCreate(props, deploy, path.toSerializationFormat, supervisor)
   }
 
   def getExternalAddressFor(addr: Address): Option[Address] = {

akka-remote/src/main/scala/akka/remote/RemoteDaemon.scala

@@ -12,6 +12,7 @@ import akka.dispatch.Watch
 import akka.actor.ActorRefWithCell
 import akka.actor.ActorRefScope
 import akka.util.Switch
+import akka.actor.RootActorPath
 
 /**
  * INTERNAL API
@@ -54,11 +55,14 @@ private[akka] class RemoteSystemDaemon(
 
     @tailrec
     def rec(s: String, n: Int): (InternalActorRef, Int) = {
-      getChild(s) match {
+      import akka.actor.ActorCell._
+      val (childName, uid) = splitNameAndUid(s)
+      getChild(childName) match {
         case null ⇒
           val last = s.lastIndexOf('/')
           if (last == -1) (Nobody, n)
           else rec(s.substring(0, last), n + 1)
+        case ref if uid != undefinedUid && uid != ref.path.uid ⇒ (Nobody, n)
         case ref ⇒ (ref, n)
       }
     }
@@ -82,15 +86,21 @@ private[akka] class RemoteSystemDaemon(
               // TODO RK currently the extracted “address” is just ignored, is that okay?
               // TODO RK canonicalize path so as not to duplicate it always #1446
               val subpath = elems.drop(1)
-              val path = this.path / subpath
+              val p = this.path / subpath
+              val childName = {
+                val s = subpath.mkString("/")
+                val i = s.indexOf('#')
+                if (i < 0) s
+                else s.substring(0, i)
+              }
               val isTerminating = !terminating.whileOff {
                 val actor = system.provider.actorOf(system, props, supervisor.asInstanceOf[InternalActorRef],
-                  path, systemService = false, Some(deploy), lookupDeploy = true, async = false)
+                  p, systemService = false, Some(deploy), lookupDeploy = true, async = false)
-                addChild(subpath.mkString("/"), actor)
+                addChild(childName, actor)
                 actor.sendSystemMessage(Watch(actor, this))
                 actor.start()
               }
-              if (isTerminating) log.error("Skipping [{}] to RemoteSystemDaemon on [{}] while terminating", message, path.address)
+              if (isTerminating) log.error("Skipping [{}] to RemoteSystemDaemon on [{}] while terminating", message, p.address)
             case _ ⇒
               log.debug("remote path does not match path from message [{}]", message)
           }

akka-remote/src/main/scala/akka/remote/serialization/ProtobufSerializer.scala

@@ -19,8 +19,8 @@ object ProtobufSerializer {
    */
   def serializeActorRef(ref: ActorRef): ActorRefProtocol = {
     val identifier: String = Serialization.currentTransportAddress.value match {
-      case null    ⇒ ref.path.toString
+      case null    ⇒ ref.path.toSerializationFormat
-      case address ⇒ ref.path.toStringWithAddress(address)
+      case address ⇒ ref.path.toSerializationFormatWithAddress(address)
     }
     ActorRefProtocol.newBuilder.setPath(identifier).build
   }

akka-remote/src/main/scala/akka/remote/transport/AkkaPduCodec.scala

@@ -182,7 +182,7 @@ private[remote] object AkkaPduProtobufCodec extends AkkaPduCodec {
 
   private def serializeActorRef(defaultAddress: Address, ref: ActorRef): ActorRefProtocol = {
     ActorRefProtocol.newBuilder.setPath(
-      if (ref.path.address.host.isDefined) ref.path.toString else ref.path.toStringWithAddress(defaultAddress)).build()
+      if (ref.path.address.host.isDefined) ref.path.toSerializationFormat else ref.path.toSerializationFormatWithAddress(defaultAddress)).build()
   }
 
   private def serializeAddress(address: Address): Option[AddressProtocol] = {

akka-remote/src/test/scala/akka/remote/RemotingSpec.scala

@@ -119,14 +119,14 @@ class RemotingSpec extends AkkaSpec(RemotingSpec.cfg) with ImplicitSender with D
         test.local-address = "test://remote-sys@localhost:12346"
       }
     """).withFallback(system.settings.config).resolve()
-  val other = ActorSystem("remote-sys", conf)
+  val otherSystem = ActorSystem("remote-sys", conf)
 
   for (
     (name, proto) ← Seq(
       "/gonk" -> "tcp",
       "/zagzag" -> "udp",
       "/roghtaar" -> "ssl.tcp")
-  ) deploy(system, Deploy(name, scope = RemoteScope(addr(other, proto))))
+  ) deploy(system, Deploy(name, scope = RemoteScope(addr(otherSystem, proto))))
 
   def addr(sys: ActorSystem, proto: String) =
     sys.asInstanceOf[ExtendedActorSystem].provider.getExternalAddressFor(Address(s"akka.$proto", "", "", 0)).get
@@ -135,12 +135,12 @@ class RemotingSpec extends AkkaSpec(RemotingSpec.cfg) with ImplicitSender with D
     sys.asInstanceOf[ExtendedActorSystem].provider.asInstanceOf[RemoteActorRefProvider].deployer.deploy(d)
   }
 
-  val remote = other.actorOf(Props[Echo2], "echo")
+  val remote = otherSystem.actorOf(Props[Echo2], "echo")
 
   val here = system.actorFor("akka.test://remote-sys@localhost:12346/user/echo")
 
   override def afterTermination() {
-    other.shutdown()
+    otherSystem.shutdown()
     AssociationRegistry.clear()
   }
 
@@ -168,16 +168,16 @@ class RemotingSpec extends AkkaSpec(RemotingSpec.cfg) with ImplicitSender with D
     "send dead letters on remote if actor does not exist" in {
       EventFilter.warning(pattern = "dead.*buh", occurrences = 1).intercept {
         system.actorFor("akka.test://remote-sys@localhost:12346/does/not/exist") ! "buh"
-      }(other)
+      }(otherSystem)
     }
 
     "not be exhausted by sending to broken connections" in {
       val tcpOnlyConfig = ConfigFactory.parseString("""akka.remote.enabled-transports = ["akka.remote.netty.tcp"]""").
-        withFallback(other.settings.config)
+        withFallback(otherSystem.settings.config)
-      val moreSystems = Vector.fill(5)(ActorSystem(other.name, tcpOnlyConfig))
+      val moreSystems = Vector.fill(5)(ActorSystem(otherSystem.name, tcpOnlyConfig))
       moreSystems foreach (_.actorOf(Props[Echo2], name = "echo"))
       val moreRefs = moreSystems map (sys ⇒ system.actorFor(RootActorPath(addr(sys, "tcp")) / "user" / "echo"))
-      val aliveEcho = system.actorFor(RootActorPath(addr(other, "tcp")) / "user" / "echo")
+      val aliveEcho = system.actorFor(RootActorPath(addr(otherSystem, "tcp")) / "user" / "echo")
       val n = 100
 
       // first everything is up and running
@@ -223,6 +223,30 @@ class RemotingSpec extends AkkaSpec(RemotingSpec.cfg) with ImplicitSender with D
       expectMsg("postStop")
     }
 
+    "not send to remote re-created actor with same name" in {
+      val echo = otherSystem.actorOf(Props[Echo1], "otherEcho1")
+      echo ! 71
+      expectMsg(71)
+      echo ! PoisonPill
+      expectMsg("postStop")
+      echo ! 72
+      expectNoMsg(1.second)
+
+      val echo2 = otherSystem.actorOf(Props[Echo1], "otherEcho1")
+      echo2 ! 73
+      expectMsg(73)
+      // msg to old ActorRef (different uid) should not get through
+      echo2.path.uid must not be (echo.path.uid)
+      echo ! 74
+      expectNoMsg(1.second)
+
+      otherSystem.actorFor("/user/otherEcho1") ! 75
+      expectMsg(75)
+
+      system.actorFor("akka.test://remote-sys@localhost:12346/user/otherEcho1") ! 76
+      expectMsg(76)
+    }
+
     "look-up actors across node boundaries" in {
       val l = system.actorOf(Props(new Actor {
         def receive = {
@@ -230,20 +254,41 @@ class RemotingSpec extends AkkaSpec(RemotingSpec.cfg) with ImplicitSender with D
           case s: String             ⇒ sender ! context.actorFor(s)
         }
       }), "looker")
+      // child is configured to be deployed on remote-sys (otherSystem)
       l ! (Props[Echo1], "child")
-      val r = expectMsgType[ActorRef]
+      val child = expectMsgType[ActorRef]
-      r ! (Props[Echo1], "grandchild")
+      // grandchild is configured to be deployed on RemotingSpec (system)
-      val remref = expectMsgType[ActorRef]
+      child ! (Props[Echo1], "grandchild")
-      remref.asInstanceOf[ActorRefScope].isLocal must be(true)
+      val grandchild = expectMsgType[ActorRef]
+      grandchild.asInstanceOf[ActorRefScope].isLocal must be(true)
+      grandchild ! 43
+      expectMsg(43)
       val myref = system.actorFor(system / "looker" / "child" / "grandchild")
       myref.isInstanceOf[RemoteActorRef] must be(true)
-      myref ! 43
+      myref ! 44
-      expectMsg(43)
+      expectMsg(44)
-      lastSender must be theSameInstanceAs remref
+      lastSender must be(grandchild)
-      r.asInstanceOf[RemoteActorRef].getParent must be(l)
+      lastSender must be theSameInstanceAs grandchild
-      system.actorFor("/user/looker/child") must be theSameInstanceAs r
+      child.asInstanceOf[RemoteActorRef].getParent must be(l)
+      system.actorFor("/user/looker/child") must be theSameInstanceAs child
       Await.result(l ? "child/..", timeout.duration).asInstanceOf[AnyRef] must be theSameInstanceAs l
       Await.result(system.actorFor(system / "looker" / "child") ? "..", timeout.duration).asInstanceOf[AnyRef] must be theSameInstanceAs l
+
+      watch(child)
+      child ! PoisonPill
+      expectMsg("postStop")
+      expectMsgType[Terminated].actor must be === child
+      l ! (Props[Echo1], "child")
+      val child2 = expectMsgType[ActorRef]
+      child2 ! 45
+      expectMsg(45)
+      // msg to old ActorRef (different uid) should not get through
+      child2.path.uid must not be (child.path.uid)
+      child ! 46
+      expectNoMsg(1.second)
+      system.actorFor(system / "looker" / "child") ! 47
+      expectMsg(47)
+
     }
 
     "not fail ask across node boundaries" in {
@@ -255,7 +300,7 @@ class RemotingSpec extends AkkaSpec(RemotingSpec.cfg) with ImplicitSender with D
     "be able to use multiple transports and use the appropriate one (TCP)" in {
       val r = system.actorOf(Props[Echo1], "gonk")
       r.path.toString must be ===
-        s"akka.tcp://remote-sys@localhost:${port(other, "tcp")}/remote/akka.tcp/RemotingSpec@localhost:${port(system, "tcp")}/user/gonk"
+        s"akka.tcp://remote-sys@localhost:${port(otherSystem, "tcp")}/remote/akka.tcp/RemotingSpec@localhost:${port(system, "tcp")}/user/gonk"
       r ! 42
       expectMsg(42)
       EventFilter[Exception]("crash", occurrences = 1).intercept {
@@ -271,7 +316,7 @@ class RemotingSpec extends AkkaSpec(RemotingSpec.cfg) with ImplicitSender with D
     "be able to use multiple transports and use the appropriate one (UDP)" in {
       val r = system.actorOf(Props[Echo1], "zagzag")
       r.path.toString must be ===
-        s"akka.udp://remote-sys@localhost:${port(other, "udp")}/remote/akka.udp/RemotingSpec@localhost:${port(system, "udp")}/user/zagzag"
+        s"akka.udp://remote-sys@localhost:${port(otherSystem, "udp")}/remote/akka.udp/RemotingSpec@localhost:${port(system, "udp")}/user/zagzag"
       r ! 42
       expectMsg(10.seconds, 42)
       EventFilter[Exception]("crash", occurrences = 1).intercept {
@@ -287,7 +332,7 @@ class RemotingSpec extends AkkaSpec(RemotingSpec.cfg) with ImplicitSender with D
     "be able to use multiple transports and use the appropriate one (SSL)" in {
       val r = system.actorOf(Props[Echo1], "roghtaar")
       r.path.toString must be ===
-        s"akka.ssl.tcp://remote-sys@localhost:${port(other, "ssl.tcp")}/remote/akka.ssl.tcp/RemotingSpec@localhost:${port(system, "ssl.tcp")}/user/roghtaar"
+        s"akka.ssl.tcp://remote-sys@localhost:${port(otherSystem, "ssl.tcp")}/remote/akka.ssl.tcp/RemotingSpec@localhost:${port(system, "ssl.tcp")}/user/roghtaar"
       r ! 42
       expectMsg(10.seconds, 42)
       EventFilter[Exception]("crash", occurrences = 1).intercept {
@@ -305,7 +350,7 @@ class RemotingSpec extends AkkaSpec(RemotingSpec.cfg) with ImplicitSender with D
   override def beforeTermination() {
     system.eventStream.publish(TestEvent.Mute(
       EventFilter.warning(pattern = "received dead letter.*(InboundPayload|Disassociate)")))
-    other.eventStream.publish(TestEvent.Mute(
+    otherSystem.eventStream.publish(TestEvent.Mute(
       EventFilter[EndpointException](),
       EventFilter.error(start = "AssociationError"),
       EventFilter.warning(pattern = "received dead letter.*(InboundPayload|Disassociate|HandleListener)")))