incorporate review comments

- fix some code formatting & docs
- make ActorCell.parent a volatile var

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

@@ -7,5 +7,6 @@ class Supervisor extends Actor {
   def receive = {
     case x: Props ⇒ sender ! context.actorOf(x)
   }
+  // need to override the default of stopping all children upon restart, tests rely on keeping them around
   override def preRestart(cause: Throwable, msg: Option[Any]) {}
 }

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

@@ -15,6 +15,7 @@ object SupervisorHierarchySpec {
     protected def receive = {
       case p: Props ⇒ sender ! context.actorOf(p)
     }
+    // test relies on keeping children around during restart
     override def preRestart(cause: Throwable, msg: Option[Any]) {}
     override def postRestart(reason: Throwable) = {
       countDown.countDown()

akka-actor/src/main/resources/reference.conf

@@ -37,7 +37,7 @@ akka {
   actor {
     provider = "akka.actor.LocalActorRefProvider"
     creation-timeout = 20s           # Timeout for ActorSystem.actorOf
-    reaper-period = 5s               # frequency with which stopping actors are prodded in case they had to be removed from their parents
+    reaper-interval = 5s             # frequency with which stopping actors are prodded in case they had to be removed from their parents
     timeout = 5s                     # Default timeout for Future based invocations
                                      #    - Actor:        ask && ?
                                      #    - UntypedActor: ask

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

@@ -185,7 +185,7 @@ private[akka] class ActorCell(
   val system: ActorSystemImpl,
   val self: InternalActorRef,
   val props: Props,
-  final val parent: InternalActorRef,
+  @volatile var parent: InternalActorRef,
   /*no member*/ _receiveTimeout: Option[Duration],
   var hotswap: Stack[PartialFunction[Any, Unit]]) extends UntypedActorContext {
 

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

@@ -240,6 +240,10 @@ trait ActorRefFactory {
    * an asynchronous operation, i.e. involves a message send, but if invoked
    * on an [[akka.actor.ActorContext]] if operating on a child of that
    * context it will free up the name for immediate reuse.
+   *
+   * When invoked on [[akka.actor.ActorSystem]] for a top-level actor, this
+   * method sends a message to the guardian actor and blocks waiting for a reply,
+   * see `akka.actor.creation-timeout` in the `reference.conf`.
    */
   def stop(actor: ActorRef): Unit
 }

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

@@ -73,7 +73,7 @@ object ActorSystem {
     val ProviderClass = getString("akka.actor.provider")
 
     val CreationTimeout = Timeout(Duration(getMilliseconds("akka.actor.creation-timeout"), MILLISECONDS))
-    val ReaperPeriod = Duration(getMilliseconds("akka.actor.reaper-period"), MILLISECONDS)
+    val ReaperInterval = Duration(getMilliseconds("akka.actor.reaper-interval"), MILLISECONDS)
     val ActorTimeout = Timeout(Duration(getMilliseconds("akka.actor.timeout"), MILLISECONDS))
     val SerializeAllMessages = getBoolean("akka.actor.serialize-messages")
 
@@ -441,7 +441,7 @@ class ActorSystemImpl(val name: String, applicationConfig: Config) extends Actor
     this
   }
 
-  lazy val locker: Locker = new Locker(scheduler, ReaperPeriod, lookupRoot.path / "locker", deathWatch)
+  lazy val locker: Locker = new Locker(scheduler, ReaperInterval, lookupRoot.path / "locker", deathWatch)
 
   def start() = _start
 

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

@@ -15,7 +15,7 @@ class Locker(scheduler: Scheduler, period: Duration, val path: ActorPath, val de
     def run = {
       val iter = heap.entrySet.iterator
       while (iter.hasNext) {
-        val soul = iter.next();
+        val soul = iter.next()
         deathWatch.subscribe(Locker.this, soul.getKey) // in case Terminated got lost somewhere
         soul.getKey match {
           case _: LocalActorRef ⇒ // nothing to do, they know what they signed up for
@@ -41,24 +41,10 @@ class Locker(scheduler: Scheduler, period: Duration, val path: ActorPath, val de
       soul match {
         case local: LocalActorRef ⇒
           val cell = local.underlying
-          rebind(cell, cell.getClass)
+          cell.parent = this
         case _ ⇒
       }
     case _ ⇒ // ignore
   }
 
-  @scala.annotation.tailrec
-  final private def rebind(cell: ActorCell, clazz: Class[_]): Unit = {
-    try {
-      val heart = clazz.getDeclaredField("parent")
-      heart.setAccessible(true)
-      heart.set(cell, this)
-      return
-    } catch {
-      case _: NoSuchFieldException ⇒
-    }
-    val sc = clazz.getSuperclass
-    if (sc != null) rebind(cell, sc)
-  }
-
 }