Added an UnboundStablePriorityMailbox (akkadotnet#3536)

* Added an UnboundStablePriorityMailbox, sending messages according to priority. Messages with the same priority will be send using the same order as they appear. akkadotnet#2652 is the related issue.

* added PropertyTest for StableListPriorityQueue

* forgot to add spec

* verified that the UnboundedStablePriorityMailbox can be loaded and used

* validate4d that UnboundedStablePriorityMailbox supports stashing

* added API approval for core

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

@@ -2612,6 +2612,14 @@ namespace Akka.Dispatch
         public virtual Akka.Dispatch.MessageQueues.IMessageQueue Create(Akka.Actor.IActorRef owner, Akka.Actor.ActorSystem system) { }
         protected abstract int PriorityGenerator(object message);
     }
+    public abstract class UnboundedStablePriorityMailbox : Akka.Dispatch.MailboxType, Akka.Dispatch.IProducesMessageQueue<Akka.Dispatch.MessageQueues.UnboundedStablePriorityMessageQueue>
+    {
+        public const int DefaultCapacity = 11;
+        protected UnboundedStablePriorityMailbox(Akka.Actor.Settings settings, Akka.Configuration.Config config) { }
+        public int InitialCapacity { get; }
+        public virtual Akka.Dispatch.MessageQueues.IMessageQueue Create(Akka.Actor.IActorRef owner, Akka.Actor.ActorSystem system) { }
+        protected abstract int PriorityGenerator(object message);
+    }
 }
 namespace Akka.Dispatch.MessageQueues
 {
@@ -2687,6 +2695,14 @@ namespace Akka.Dispatch.MessageQueues
         protected override void LockedEnqueue(Akka.Actor.Envelope envelope) { }
         protected override bool LockedTryDequeue(out Akka.Actor.Envelope envelope) { }
     }
+    public class UnboundedStablePriorityMessageQueue : Akka.Dispatch.MessageQueues.BlockingMessageQueue, Akka.Dispatch.IDequeBasedMessageQueueSemantics, Akka.Dispatch.ISemantics, Akka.Dispatch.IUnboundedDequeBasedMessageQueueSemantics, Akka.Dispatch.IUnboundedMessageQueueSemantics
+    {
+        public UnboundedStablePriorityMessageQueue(System.Func<object, int> priorityGenerator, int initialCapacity) { }
+        protected override int LockedCount { get; }
+        public void EnqueueFirst(Akka.Actor.Envelope envelope) { }
+        protected override void LockedEnqueue(Akka.Actor.Envelope envelope) { }
+        protected override bool LockedTryDequeue(out Akka.Actor.Envelope envelope) { }
+    }
 }
 namespace Akka.Dispatch.SysMsg
 {
@@ -4773,6 +4789,16 @@ namespace Akka.Util
         public static readonly bool IsMono;
         public static readonly bool IsWindows;
     }
+    public sealed class StableListPriorityQueue
+    {
+        public StableListPriorityQueue(int initialCapacity, System.Func<object, int> priorityCalculator) { }
+        public int Count() { }
+        public Akka.Actor.Envelope Dequeue() { }
+        public void Enqueue(Akka.Actor.Envelope item) { }
+        public bool IsConsistent() { }
+        public Akka.Actor.Envelope Peek() { }
+        public override string ToString() { }
+    }
     public class static StandardOutWriter
     {
         public static void Write(string message, System.Nullable<System.ConsoleColor> foregroundColor = null, System.Nullable<System.ConsoleColor> backgroundColor = null) { }

src/core/Akka.Tests/Dispatch/MailboxesSpec.cs

@@ -47,6 +47,27 @@ public TestPriorityMailbox(Settings settings, Config config) : base(settings, co
         }
     }
 
+    public class TestStablePriorityMailbox : UnboundedStablePriorityMailbox
+    {
+        protected override int PriorityGenerator(object message)
+        {
+            if (message is string)
+                return 1;
+            if (message is bool)
+                return 2;
+            if (message is int)
+                return 3;
+            if (message is double)
+                return 4;
+
+            return 5;
+        }
+
+        public TestStablePriorityMailbox(Settings settings, Config config) : base(settings, config)
+        {
+        }
+    }
+
     public class IntPriorityMailbox : UnboundedPriorityMailbox
     {
         protected override int PriorityGenerator(object message)
@@ -138,6 +159,9 @@ private static string GetConfig()
 int-prio-mailbox {
     mailbox-type : """ + typeof(IntPriorityMailbox).AssemblyQualifiedName + @"""
 }
+stable-prio-mailbox{
+    mailbox-type : """ + typeof(TestStablePriorityMailbox).AssemblyQualifiedName + @"""
+}
 ";
         }
 
@@ -204,7 +228,45 @@ public void Can_use_unbounded_priority_mailbox()
             ExpectMsg(2.0);
 
             ExpectNoMsg(TimeSpan.FromSeconds(0.3));
-        }       
+        }
+
+        [Fact]
+        public void Can_use_unbounded_stable_priority_mailbox()
+        {
+            var actor = (IInternalActorRef)Sys.ActorOf(EchoActor.Props(this).WithMailbox("stable-prio-mailbox"), "echo");
+
+            //pause mailbox until all messages have been told
+            actor.SendSystemMessage(new Suspend());
+
+            // wait until we can confirm that the mailbox is suspended before we begin sending messages
+            AwaitCondition(() => (((ActorRefWithCell)actor).Underlying is ActorCell) && ((ActorRefWithCell)actor).Underlying.AsInstanceOf<ActorCell>().Mailbox.IsSuspended());
+
+            actor.Tell(true);
+            for (var i = 0; i < 30; i++)
+            {
+                actor.Tell(i);
+            }
+            actor.Tell("a");
+            actor.Tell(2.0);
+            for (var i = 0; i < 30; i++)
+            {
+                actor.Tell(i + 30);
+            }
+            actor.SendSystemMessage(new Resume(null));
+
+            //resume mailbox, this prevents the mailbox from running to early
+            //priority mailbox is best effort only
+
+            ExpectMsg("a");
+            ExpectMsg(true);
+            for (var i = 0; i < 60; i++)
+            {
+                ExpectMsg(i);
+            }
+            ExpectMsg(2.0);
+
+            ExpectNoMsg(TimeSpan.FromSeconds(0.3));
+        }
 
         [Fact]
         public void Priority_mailbox_keeps_ordering_with_many_priority_values()
@@ -286,6 +348,49 @@ public void Unbounded_Priority_Mailbox_Supports_Unbounded_Stashing()
 
             ExpectNoMsg(TimeSpan.FromSeconds(0.3));
         }
+
+        [Fact]
+        public void Unbounded_Stable_Priority_Mailbox_Supports_Unbounded_Stashing()
+        {
+            var actor = (IInternalActorRef)Sys.ActorOf(StashingActor.Props(this).WithMailbox("stable-prio-mailbox"), "echo");
+
+            //pause mailbox until all messages have been told
+            actor.SendSystemMessage(new Suspend());
+
+            AwaitCondition(() => (((ActorRefWithCell)actor).Underlying is ActorCell) && ((ActorRefWithCell)actor).Underlying.AsInstanceOf<ActorCell>().Mailbox.IsSuspended());
+
+            var values = new int[10];
+            var increment = (int)(UInt32.MaxValue / values.Length);
+
+            for (var i = 0; i < values.Length; i++)
+                values[i] = Int32.MinValue + increment * i;
+
+            // tell the actor in order
+            foreach (var value in values)
+            {
+                actor.Tell(value);
+                actor.Tell(value);
+                actor.Tell(value);
+            }
+
+            actor.Tell(new StashingActor.Start());
+
+            //resume mailbox, this prevents the mailbox from running to early
+            actor.SendSystemMessage(new Resume(null));
+
+            this.Within(5.Seconds(), () =>
+            {
+                // expect the messages in the original order
+                foreach (var value in values)
+                {
+                    ExpectMsg(value);
+                    ExpectMsg(value);
+                    ExpectMsg(value);
+                }
+            });
+
+            ExpectNoMsg(TimeSpan.FromSeconds(0.3));
+        }
     }
 }
 

src/core/Akka.Tests/Util/StableListPriorityQueueSpec.cs

@@ -0,0 +1,55 @@
+// //-----------------------------------------------------------------------
+// // <copyright file="StableListPriorityQueueSpec.cs" company="Akka.NET Project">
+// //     Copyright (C) 2009-2019 Lightbend Inc. <http://www.lightbend.com>
+// //     Copyright (C) 2013-2019 .NET Foundation <https://github.com/akkadotnet/akka.net>
+// // </copyright>
+// //-----------------------------------------------------------------------
+
+using System.Collections.Generic;
+using System.Linq;
+using Akka.Actor;
+using Akka.Util;
+using FsCheck;
+using FsCheck.Xunit;
+
+namespace Akka.Tests.Util
+{
+    public class StableListPriorityQueueSpec
+    {
+        public static int Priority(object obj)
+        {
+            switch (obj)
+            {
+                case int i:
+                    return i;
+                case string str:
+                    return str.Length;
+                default:
+                    return 1;
+            }
+        }
+
+        [Property(MaxTest = 1000)]
+        public Property StableListPriorityQueue_must_be_stable(NonEmptyString[] values)
+        {
+            var sortedValues = values
+                .Select(x => x.Item)
+                .GroupBy(x => x.Length)
+                .OrderBy(x => x.Key)
+                .SelectMany(x => x).ToList();
+            var pq = new StableListPriorityQueue(10, Priority);
+
+            foreach (var i in values.Select(x => x.Item)) pq.Enqueue(new Envelope(i, ActorRefs.NoSender));
+
+            var isConsistent = pq.IsConsistent().ToProperty().Label("Expected queue to be consistent, but was not.");
+
+            var queueValues = new List<string>();
+            while (pq.Count() > 0) queueValues.Add((string)pq.Dequeue().Message);
+
+            var sequenceEqual = queueValues.SequenceEqual(sortedValues).ToProperty().Label(
+                $"Expected output to be [{string.Join(",", sortedValues)}] but was [{string.Join(",", queueValues)}]");
+
+            return sequenceEqual.And(isConsistent);
+        }
+    }
+}

src/core/Akka/Dispatch/Mailbox.cs

@@ -682,7 +682,7 @@ public override IMessageQueue Create(IActorRef owner, ActorSystem system)
     /// Priority mailbox base class; unbounded mailbox that allows for prioritization of its contents.
     /// Extend this class and implement the <see cref="PriorityGenerator"/> method with your own prioritization.
     /// The value returned by the <see cref="PriorityGenerator"/> method will be used to order the message in the mailbox.
-    /// Lower values will be delivered first. Messages ordered by the same number will remain in delivery order.
+    /// Lower values will be delivered first. Messages ordered by the same number will remain in delivered in undefined order.
     /// </summary>
     public abstract class UnboundedPriorityMailbox : MailboxType, IProducesMessageQueue<UnboundedPriorityMessageQueue>
     {
@@ -716,7 +716,45 @@ protected UnboundedPriorityMailbox(Settings settings, Config config) : base(sett
         }
     }
 
-    //todo: bounded priority mailbox; stable priority mailboxes
+    //todo: bounded priority mailbox;
+
+    /// <summary>
+    /// Priority mailbox - an unbounded mailbox that allows for prioritization of its contents.
+    /// Extend this class and implement the <see cref="PriorityGenerator"/> method with your own prioritization.
+    /// The value returned by the <see cref="PriorityGenerator"/> method will be used to order the message in the mailbox.
+    /// Lower values will be delivered first. Messages ordered by the same number will remain in delivery order.
+    /// </summary>
+    public abstract class UnboundedStablePriorityMailbox : MailboxType, IProducesMessageQueue<UnboundedStablePriorityMessageQueue>
+    {
+        /// <summary>
+        /// Function responsible for generating the priority value of a message based on its type and content.
+        /// </summary>
+        /// <param name="message">The message to inspect.</param>
+        /// <returns>An integer. The lower the value, the higher the priority.</returns>
+        protected abstract int PriorityGenerator(object message);
+
+        /// <summary>
+        /// The initial capacity of the unbounded mailbox.
+        /// </summary>
+        public int InitialCapacity { get; }
+
+        /// <summary>
+        /// The default capacity of an unbounded priority mailbox.
+        /// </summary>
+        public const int DefaultCapacity = 11;
+
+        /// <inheritdoc cref="MailboxType"/>
+        public sealed override IMessageQueue Create(IActorRef owner, ActorSystem system)
+        {
+            return new UnboundedStablePriorityMessageQueue(PriorityGenerator, InitialCapacity);
+        }
+
+        /// <inheritdoc cref="MailboxType"/>
+        protected UnboundedStablePriorityMailbox(Settings settings, Config config) : base(settings, config)
+        {
+            InitialCapacity = DefaultCapacity;
+        }
+    }
 
     /// <summary>
     /// UnboundedDequeBasedMailbox is an unbounded <see cref="MailboxType"/> backed by a double-ended queue. Used for stashing.

src/core/Akka/Dispatch/MessageQueues/UnboundedPriorityMessageQueue.cs

@@ -94,5 +94,4 @@ public void EnqueueFirst(Envelope envelope)
             _prependBuffer.Push(envelope);
         }
     }
-}
-
+}

src/core/Akka/Dispatch/MessageQueues/UnboundedStablePriorityMessageQueue.cs

@@ -0,0 +1,89 @@
+//-----------------------------------------------------------------------
+// <copyright file="UnboundedPriorityMessageQueue.cs" company="Akka.NET Project">
+//     Copyright (C) 2009-2018 Lightbend Inc. <http://www.lightbend.com>
+//     Copyright (C) 2013-2018 .NET Foundation <https://github.com/akkadotnet/akka.net>
+// </copyright>
+//-----------------------------------------------------------------------
+
+using System;
+using System.Collections.Generic;
+using Akka.Actor;
+using Akka.Util;
+
+namespace Akka.Dispatch.MessageQueues
+{
+    /// <summary> 
+    /// Base class for a message queue that uses a priority generator for messages 
+    /// </summary>
+    public class UnboundedStablePriorityMessageQueue : BlockingMessageQueue, IUnboundedDequeBasedMessageQueueSemantics
+    {
+        private readonly StableListPriorityQueue _prioQueue;
+        // doesn't need to be threadsafe - only called from within actor
+        private readonly Stack<Envelope> _prependBuffer = new Stack<Envelope>();
+
+
+        /// <summary>
+        /// Creates a new unbounded priority message queue.
+        /// </summary>
+        /// <param name="priorityGenerator">The calculator function for determining the priority of inbound messages.</param>
+        /// <param name="initialCapacity">The initial capacity of the queue.</param>
+        public UnboundedStablePriorityMessageQueue(Func<object, int> priorityGenerator, int initialCapacity)
+        {
+            _prioQueue = new StableListPriorityQueue(initialCapacity, priorityGenerator);
+        }
+
+        /// <summary>
+        /// Unsafe method for computing the underlying message count. 
+        /// </summary>
+        /// <remarks>
+        /// Called from within a synchronization mechanism.
+        /// </remarks>
+        protected override int LockedCount
+        {
+            get { return _prioQueue.Count(); }
+        }
+
+        /// <summary>
+        /// Unsafe method for enqueuing a new message to the queue.
+        /// </summary>
+        /// <param name="envelope">The message to enqueue.</param>
+        /// <remarks>
+        /// Called from within a synchronization mechanism.
+        /// </remarks>
+        protected override void LockedEnqueue(Envelope envelope)
+        {
+            _prioQueue.Enqueue(envelope);
+        }
+
+        /// <summary>
+        /// Unsafe method for attempting to dequeue a message.
+        /// </summary>
+        /// <param name="envelope">The message that might be dequeued.</param>
+        /// <returns><c>true</c> if a message was available to be dequeued, <c>false</c> otherwise.</returns>
+        /// <remarks>
+        /// Called from within a synchronization mechanism.
+        /// </remarks>
+        protected override bool LockedTryDequeue(out Envelope envelope)
+        {
+            if (_prependBuffer.Count > 0)
+            {
+                envelope = _prependBuffer.Pop();
+                return true;
+            }
+
+            if (_prioQueue.Count() > 0)
+            {
+                envelope = _prioQueue.Dequeue();
+                return true;
+            }
+            envelope = default(Envelope);
+            return false;
+        }
+
+        public void EnqueueFirst(Envelope envelope)
+        {
+            _prependBuffer.Push(envelope);
+        }
+    }
+}
+