Improve performance on IActorRef.Child API

src/benchmark/Akka.Benchmarks/Actor/GetChildBenchmark.cs

@@ -96,7 +96,7 @@ protected override void OnReceive(object message)
         private ActorWithChild.Get _getMessage = new ActorWithChild.Get("food");
         private ActorWithChild.Create _createMessage = new ActorWithChild.Create("food");
 
-        private ActorCell _cell;
+        private IActorContext _cell;
         private RepointableActorRef _repointableActorRef;
         private LocalActorRef _localActorRef;
         private VirtualPathContainer _virtualPathContainer;
@@ -129,7 +129,7 @@ public async Task Setup()
         [Benchmark]
         public void ResolveChild()
         {
-            _cell.TryGetSingleChild(_getMessage.Name, out var child);
+            _cell.Child(_getMessage.Name);
         }
 
         [Benchmark]

src/core/Akka.API.Tests/CoreAPISpec.ApproveCore.approved.txt

@@ -1081,7 +1081,7 @@ namespace Akka.Actor
         bool IsTerminated { get; }
         Akka.Actor.IInternalActorRef Parent { get; }
         Akka.Actor.IActorRefProvider Provider { get; }
-        Akka.Actor.IActorRef GetChild(System.Collections.Generic.IEnumerable<string> name);
+        Akka.Actor.IActorRef GetChild(System.Collections.Generic.IReadOnlyList<string> name);
         void Restart(System.Exception cause);
         void Resume(System.Exception causedByFailure = null);
         [System.ObsoleteAttribute("Use SendSystemMessage(message) [1.1.0]")]
@@ -1202,7 +1202,7 @@ namespace Akka.Actor
         public abstract bool IsTerminated { get; }
         public abstract Akka.Actor.IInternalActorRef Parent { get; }
         public abstract Akka.Actor.IActorRefProvider Provider { get; }
-        public abstract Akka.Actor.IActorRef GetChild(System.Collections.Generic.IEnumerable<string> name);
+        public abstract Akka.Actor.IActorRef GetChild(System.Collections.Generic.IReadOnlyList<string> name);
         public abstract void Restart(System.Exception cause);
         public abstract void Resume(System.Exception causedByFailure = null);
         [System.ObsoleteAttribute("Use SendSystemMessage(message) instead [1.1.0]")]
@@ -1245,7 +1245,7 @@ namespace Akka.Actor
         protected Akka.Actor.IInternalActorRef Supervisor { get; }
         protected Akka.Actor.ActorSystem System { get; }
         public override Akka.Actor.ICell Underlying { get; }
-        public override Akka.Actor.IActorRef GetChild(System.Collections.Generic.IEnumerable<string> name) { }
+        public override Akka.Actor.IActorRef GetChild(System.Collections.Generic.IReadOnlyList<string> name) { }
         public override Akka.Actor.IInternalActorRef GetSingleChild(string name) { }
         protected virtual Akka.Actor.ActorCell NewActorCell(Akka.Actor.Internal.ActorSystemImpl system, Akka.Actor.IInternalActorRef self, Akka.Actor.Props props, Akka.Dispatch.MessageDispatcher dispatcher, Akka.Actor.IInternalActorRef supervisor) { }
         public override void Restart(System.Exception cause) { }
@@ -1317,7 +1317,7 @@ namespace Akka.Actor
         [System.ObsoleteAttribute("Use Context.Watch and Receive<Terminated> [1.1.0]")]
         public override bool IsTerminated { get; }
         public override Akka.Actor.IInternalActorRef Parent { get; }
-        public override Akka.Actor.IActorRef GetChild(System.Collections.Generic.IEnumerable<string> name) { }
+        public override Akka.Actor.IActorRef GetChild(System.Collections.Generic.IReadOnlyList<string> name) { }
         public override void Restart(System.Exception cause) { }
         public override void Resume(System.Exception causedByFailure = null) { }
         public override void SendSystemMessage(Akka.Dispatch.SysMsg.ISystemMessage message) { }
@@ -1533,7 +1533,7 @@ namespace Akka.Actor
         public override Akka.Actor.ActorPath Path { get; }
         public override Akka.Actor.IActorRefProvider Provider { get; }
         public override Akka.Actor.ICell Underlying { get; }
-        public override Akka.Actor.IActorRef GetChild(System.Collections.Generic.IEnumerable<string> name) { }
+        public override Akka.Actor.IActorRef GetChild(System.Collections.Generic.IReadOnlyList<string> name) { }
         public override Akka.Actor.IInternalActorRef GetSingleChild(string name) { }
         public Akka.Actor.RepointableActorRef Initialize(bool async) { }
         protected virtual Akka.Actor.ActorCell NewCell() { }

src/core/Akka.API.Tests/CoreAPISpec.ApproveRemote.approved.txt

@@ -171,7 +171,7 @@ namespace Akka.Remote
         public override Akka.Actor.IInternalActorRef Parent { get; }
         public override Akka.Actor.ActorPath Path { get; }
         public override Akka.Actor.IActorRefProvider Provider { get; }
-        public override Akka.Actor.IActorRef GetChild(System.Collections.Generic.IEnumerable<string> name) { }
+        public override Akka.Actor.IActorRef GetChild(System.Collections.Generic.IReadOnlyList<string> name) { }
         public bool IsWatchIntercepted(Akka.Actor.IActorRef watchee, Akka.Actor.IActorRef watcher) { }
         public override void Restart(System.Exception cause) { }
         public override void Resume(System.Exception causedByFailure = null) { }

src/core/Akka.Remote/RemoteActorRef.cs

@@ -12,6 +12,7 @@
 using Akka.Annotations;
 using Akka.Dispatch.SysMsg;
 using Akka.Event;
+using Akka.Util.Internal.Collections;
 
 namespace Akka.Remote
 {
@@ -106,17 +107,16 @@ public RemoteActorRef(RemoteTransport remote, Address localAddressToUse, ActorPa
         /// <param name="name">The name.</param>
         /// <returns>ActorRef.</returns>
         /// <exception cref="System.NotImplementedException">TBD</exception>
-        public override IActorRef GetChild(IEnumerable<string> name)
+        public override IActorRef GetChild(IReadOnlyList<string> name)
         {
-            var items = name.ToList();
-            switch (items.FirstOrDefault())
+            switch (name.FirstOrDefault())
             {
                 case null:
                     return this;
                 case "..":
-                    return Parent.GetChild(items.Skip(1));
+                    return Parent.GetChild(name.NoCopySlice(1));
                 default:
-                    return new RemoteActorRef(Remote, LocalAddressToUse, Path / items, ActorRefs.Nobody, Props.None, Deploy.None);
+                    return new RemoteActorRef(Remote, LocalAddressToUse, Path / name, ActorRefs.Nobody, Props.None, Deploy.None);
             }
         }
 

src/core/Akka.Remote/RemoteSystemDaemon.cs

@@ -156,11 +156,9 @@ protected override void TellInternal(object message, IActorRef sender)
                     }
                 }
 
-                var t = Rec(ImmutableList<string>.Empty);
-                var concatenatedChildNames = t.Item1;
-                var m = t.Item2;
+                var (concatenatedChildNames, m) = Rec(ImmutableList<string>.Empty);
 
-                var child = GetChild(concatenatedChildNames);
+                var child = GetChild(concatenatedChildNames.ToList());
                 if (child.IsNobody())
                 {
                     var emptyRef = new EmptyLocalActorRef(_system.Provider,
@@ -302,7 +300,7 @@ private void HandleDaemonMsgCreate(DaemonMsgCreate message)
         /// </summary>
         /// <param name="name">The name.</param>
         /// <returns>ActorRef.</returns>
-        public override IActorRef GetChild(IEnumerable<string> name)
+        public override IActorRef GetChild(IReadOnlyList<string> name)
         {
             var path = name.Join("/");
             var n = 0;
@@ -313,7 +311,7 @@ public override IActorRef GetChild(IEnumerable<string> name)
                 {
                     if (uid != ActorCell.UndefinedUid && uid != child.Path.Uid)
                         return Nobody.Instance;
-                    return n == 0 ? child : child.GetChild(name.TakeRight(n));
+                    return n == 0 ? child : child.GetChild(name.TakeRight(n).ToList());
                 }
 
                 var last = path.LastIndexOf("/", StringComparison.Ordinal);

src/core/Akka.TestKit/TestActorRefBase.cs

@@ -258,7 +258,7 @@ ISurrogate ISurrogated.ToSurrogate(ActorSystem system)
 
         bool IInternalActorRef.IsTerminated { get { return _internalRef.IsTerminated; } }
 
-        IActorRef IInternalActorRef.GetChild(IEnumerable<string> name)
+        IActorRef IInternalActorRef.GetChild(IReadOnlyList<string> name)
         {
             return _internalRef.GetChild(name);
         }

src/core/Akka.TestKit/TestProbe.cs

@@ -124,7 +124,7 @@ ISurrogate ISurrogated.ToSurrogate(ActorSystem system)
 
         bool IInternalActorRef.IsTerminated { get { return ((IInternalActorRef)TestActor).IsTerminated; } }
 
-        IActorRef IInternalActorRef.GetChild(IEnumerable<string> name)
+        IActorRef IInternalActorRef.GetChild(IReadOnlyList<string> name)
         {
             return ((IInternalActorRef)TestActor).GetChild(name);
         }

src/core/Akka/Actor/ActorCell.Children.cs

@@ -265,8 +265,7 @@ protected void SetTerminated()
         {
             get
             {
-                var terminating = ChildrenContainer as TerminatingChildrenContainer;
-                return terminating != null && terminating.Reason is SuspendReason.IWaitingForChildren;
+                return ChildrenContainer is TerminatingChildrenContainer terminating && terminating.Reason is SuspendReason.IWaitingForChildren;
             }
         }
 
@@ -325,8 +324,7 @@ public bool TryGetChildStatsByName(string name, out IChildStats child)   //This
         /// </summary>
         private bool TryGetChildRestartStatsByName(string name, out ChildRestartStats child)
         {
-            IChildStats stats;
-            if (ChildrenContainer.TryGetByName(name, out stats))
+            if (ChildrenContainer.TryGetByName(name, out var stats))
             {
                 child = stats as ChildRestartStats;
                 if (child != null)
@@ -358,10 +356,11 @@ protected bool TryGetChildStatsByRef(IActorRef actor, out ChildRestartStats chil
         [Obsolete("Use TryGetSingleChild [0.7.1]")]
         public IInternalActorRef GetSingleChild(string name)
         {
-            IInternalActorRef child;
-            return TryGetSingleChild(name, out child) ? child : ActorRefs.Nobody;
+            return TryGetSingleChild(name, out var child) ? child : ActorRefs.Nobody;
         }
 
+
+
         /// <summary>
         /// TBD
         /// </summary>

src/core/Akka/Actor/ActorCell.cs

@@ -241,7 +241,10 @@ public void Init(bool sendSupervise, MailboxType mailboxType)
 
         IActorRef IActorContext.Child(string name)
         {
-            return TryGetSingleChild(name, out var child) ? child : ActorRefs.Nobody;
+            if (TryGetChildStatsByName(name, out var child) && child is ChildRestartStats s)
+                return s.Child;
+
+            return ActorRefs.Nobody;
         }
 
         /// <summary>

src/core/Akka/Actor/ActorRef.cs

@@ -19,6 +19,7 @@
 using Akka.Event;
 using Akka.Util;
 using Akka.Util.Internal;
+using Akka.Util.Internal.Collections;
 
 namespace Akka.Actor
 {
@@ -422,7 +423,7 @@ public interface IInternalActorRef : IActorRef, IActorRefScope
         /// </summary>
         /// <param name="name">The path elements.</param>
         /// <returns>The <see cref="IActorRef"/>, or if the requested path does not exist, returns <see cref="Nobody"/>.</returns>
-        IActorRef GetChild(IEnumerable<string> name);
+        IActorRef GetChild(IReadOnlyList<string> name);
 
         /// <summary>
         /// Resumes an actor if it has been suspended.
@@ -481,7 +482,7 @@ public abstract class InternalActorRefBase : ActorRefBase, IInternalActorRef
         public abstract IActorRefProvider Provider { get; }
 
         /// <inheritdoc cref="IInternalActorRef"/>
-        public abstract IActorRef GetChild(IEnumerable<string> name);    //TODO: Refactor this to use an IEnumerator instead as this will be faster instead of enumerating multiple times over name, as the implementations currently do.
+        public abstract IActorRef GetChild(IReadOnlyList<string> name);    //TODO: Refactor this to use an IEnumerator instead as this will be faster instead of enumerating multiple times over name, as the implementations currently do.
 
         /// <inheritdoc cref="IInternalActorRef"/>
         public abstract void Resume(Exception causedByFailure = null);
@@ -530,9 +531,9 @@ public override IInternalActorRef Parent
         }
 
         /// <inheritdoc cref="InternalActorRefBase"/>
-        public override IActorRef GetChild(IEnumerable<string> name)
+        public override IActorRef GetChild(IReadOnlyList<string> name)
         {
-            if (name.All(string.IsNullOrEmpty))
+            if (name.All(x => string.IsNullOrEmpty(x)))
                 return this;
             return ActorRefs.Nobody;
         }
@@ -874,20 +875,17 @@ override def getChild(name: Iterator[String]): InternalActorRef = {
         /// </summary>
         /// <param name="name">TBD</param>
         /// <returns>TBD</returns>
-        public override IActorRef GetChild(IEnumerable<string> name)
+        public override IActorRef GetChild(IReadOnlyList<string> name)
         {
             //Using enumerator to avoid multiple enumerations of name.
-            var enumerator = name.GetEnumerator();
-            if (!enumerator.MoveNext())
-            {
-                //name was empty
+            if (name.Count == 0)
                 return this;
-            }
-            var firstName = enumerator.Current;
+
+            var firstName = name[0];
             if (string.IsNullOrEmpty(firstName))
                 return this;
             if (_children.TryGetValue(firstName, out var child))
-                return child.GetChild(new Enumerable<string>(enumerator));
+                return child.GetChild(name.NoCopySlice(1));
             return ActorRefs.Nobody;
         }
 

src/core/Akka/Actor/ActorRefProvider.cs

@@ -462,7 +462,7 @@ public IActorRef ResolveActorRef(ActorPath path)
         /// <param name="actorRef">TBD</param>
         /// <param name="pathElements">TBD</param>
         /// <returns>TBD</returns>
-        internal IInternalActorRef ResolveActorRef(IInternalActorRef actorRef, IReadOnlyCollection<string> pathElements)
+        internal IInternalActorRef ResolveActorRef(IInternalActorRef actorRef, IReadOnlyList<string> pathElements)
         {
             if (pathElements.Count == 0)
             {

src/core/Akka/Actor/LocalActorRef.cs

@@ -12,6 +12,7 @@
 using Akka.Dispatch;
 using Akka.Dispatch.SysMsg;
 using Akka.Util.Internal;
+using Akka.Util.Internal.Collections;
 
 namespace Akka.Actor
 {
@@ -52,7 +53,8 @@ public class LocalActorRef : ActorRefWithCell, ILocalRef
         /// <param name="mailboxType">TBD</param>
         /// <param name="supervisor">TBD</param>
         /// <param name="path">TBD</param>
-        public LocalActorRef(ActorSystemImpl system, Props props, MessageDispatcher dispatcher, MailboxType mailboxType, IInternalActorRef supervisor, ActorPath path) 
+        public LocalActorRef(ActorSystemImpl system, Props props, MessageDispatcher dispatcher, MailboxType mailboxType,
+            IInternalActorRef supervisor, ActorPath path)
         {
             _system = system;
             _props = props;
@@ -61,18 +63,19 @@ public LocalActorRef(ActorSystemImpl system, Props props, MessageDispatcher disp
             _supervisor = supervisor;
             _path = path;
 
-           /*
-            * Safe publication of this class’s fields is guaranteed by Mailbox.SetActor()
-            * which is called indirectly from ActorCell.init() (if you’re wondering why
-            * this is at all important, remember that under the CLR readonly fields are only
-            * frozen at the _end_ of the constructor, but we are publishing "this" before
-            * that is reached).
-            * This means that the result of NewActorCell needs to be written to the field
-            * _cell before we call init and start, since we can start using "this"
-            * object from another thread as soon as we run init.
-            */
+            /*
+             * Safe publication of this class’s fields is guaranteed by Mailbox.SetActor()
+             * which is called indirectly from ActorCell.init() (if you’re wondering why
+             * this is at all important, remember that under the CLR readonly fields are only
+             * frozen at the _end_ of the constructor, but we are publishing "this" before
+             * that is reached).
+             * This means that the result of NewActorCell needs to be written to the field
+             * _cell before we call init and start, since we can start using "this"
+             * object from another thread as soon as we run init.
+             */
             // ReSharper disable once VirtualMemberCallInConstructor 
-            _cell = NewActorCell(_system, this, _props, _dispatcher, _supervisor); // _cell needs to be assigned before Init is called. 
+            _cell = NewActorCell(_system, this, _props, _dispatcher,
+                _supervisor); // _cell needs to be assigned before Init is called. 
             _cell.Init(true, MailboxType);
         }
 
@@ -211,14 +214,13 @@ public override IInternalActorRef GetSingleChild(string name)
         }
 
         /// <inheritdoc/>
-        public override IActorRef GetChild(IEnumerable<string> name)
+        public override IActorRef GetChild(IReadOnlyList<string> name)
         {
-            var current = (IActorRef)this;
+            IActorRef current = this;
             int index = 0;
-            foreach (string element in name)
+            foreach (var element in name)
             {
-                var currentLocalActorRef = current as LocalActorRef;
-                if (currentLocalActorRef != null)
+                if (current is LocalActorRef currentLocalActorRef)
                 {
                     switch (element)
                     {
@@ -232,20 +234,21 @@ public override IActorRef GetChild(IEnumerable<string> name)
                             break;
                     }
                 }
-                else
+                else if (current is IInternalActorRef internalActorRef)
                 {
                     //Current is not a LocalActorRef
-                    if (current != null)
-                    {
-                        var rest = name.Skip(index).ToList();
-                        return current.AsInstanceOf<IInternalActorRef>().GetChild(rest);
-                    }
+                    var rest = name.NoCopySlice(index);
+                    return internalActorRef.GetChild(rest);
+                }
+                else // not a LocalActorRef or an IInternalActorRef
+                {
                     throw new NotSupportedException("Bug, we should not get here");
                 }
+
                 index++;
             }
+
             return current;
         }
     }
-}
-
+}