Work on ConsumerController deadlock

src/core/Akka.API.Tests/verify/CoreAPISpec.ApproveCore.DotNet.verified.txt

@@ -2559,6 +2559,7 @@ namespace Akka.Delivery
             public bool OnlyFlowControl { get; set; }
             public System.TimeSpan ResendIntervalMax { get; set; }
             public System.TimeSpan ResendIntervalMin { get; set; }
+            public bool RetryConfirmation { get; set; }
             public static Akka.Delivery.ConsumerController.Settings Create(Akka.Actor.ActorSystem actorSystem) { }
             public static Akka.Delivery.ConsumerController.Settings Create(Akka.Configuration.Config config) { }
             public override string ToString() { }

src/core/Akka.API.Tests/verify/CoreAPISpec.ApproveCore.Net.verified.txt

@@ -2557,6 +2557,7 @@ namespace Akka.Delivery
             public bool OnlyFlowControl { get; set; }
             public System.TimeSpan ResendIntervalMax { get; set; }
             public System.TimeSpan ResendIntervalMin { get; set; }
+            public bool RetryConfirmation { get; set; }
             public static Akka.Delivery.ConsumerController.Settings Create(Akka.Actor.ActorSystem actorSystem) { }
             public static Akka.Delivery.ConsumerController.Settings Create(Akka.Configuration.Config config) { }
             public override string ToString() { }

src/core/Akka.Tests/Delivery/ConsumerControllerRetryConfirmSpecs.cs

@@ -0,0 +1,75 @@
+// -----------------------------------------------------------------------
+//  <copyright file="ConsumerControllerRetryConfirmSpecs.cs" company="Akka.NET Project">
+//      Copyright (C) 2009-2024 Lightbend Inc. <http://www.lightbend.com>
+//      Copyright (C) 2013-2024 .NET Foundation <https://github.com/akkadotnet/akka.net>
+//  </copyright>
+// -----------------------------------------------------------------------
+
+using System.Threading.Tasks;
+using Akka.Actor;
+using Akka.Configuration;
+using Akka.Delivery;
+using Akka.Util;
+using FluentAssertions;
+using FluentAssertions.Extensions;
+using Xunit;
+using Xunit.Abstractions;
+using static Akka.Tests.Delivery.TestConsumer;
+
+namespace Akka.Tests.Delivery;
+
+public class ConsumerControllerRetryConfirmSpecs : TestKit.Xunit2.TestKit
+{
+    public static readonly Config Config = @"
+        akka.reliable-delivery.consumer-controller {
+        flow-control-window = 20
+        resend-interval-min = 1s
+        retry-confirmation = true
+    }";
+
+    public ConsumerControllerRetryConfirmSpecs(ITestOutputHelper outputHelper) : base(
+        Config.WithFallback(TestSerializer.Config).WithFallback(ZeroLengthSerializer.Config), output: outputHelper)
+    {
+    }
+
+    private int _idCount = 0;
+    private int NextId() => _idCount++;
+    private string ProducerId => $"p-{_idCount}";
+
+    [Fact]
+    public void ConsumerController_Settings_confirmation_retry_must_not_be_set_by_default()
+    {
+        var config = ConfigurationFactory.Default();
+        var settings = ConsumerController.Settings.Create(config.GetConfig("akka.reliable-delivery.consumer-controller"));
+        settings.RetryConfirmation.Should().BeFalse();
+    }
+
+    [Fact]
+    public void ConsumerController_Settings_confirmation_retry_must_be_set()
+    {
+        var settings = ConsumerController.Settings.Create(Sys);
+        settings.RetryConfirmation.Should().BeTrue();
+    }
+
+    [Fact]
+    public async Task ConsumerController_must_resend_Delivery_on_confirmation_retry()
+    {
+        var id = NextId();
+        var consumerProbe = CreateTestProbe();
+        var consumerController = Sys.ActorOf(ConsumerController.Create<Job>(Sys, Option<IActorRef>.None),
+            $"consumerController-{id}");
+        var producerControllerProbe = CreateTestProbe();
+
+        consumerController.Tell(new ConsumerController.Start<Job>(consumerProbe.Ref));
+        consumerController.Tell(new ConsumerController.RegisterToProducerController<Job>(producerControllerProbe.Ref));
+        await producerControllerProbe.ExpectMsgAsync<ProducerController.RegisterConsumer<Job>>();
+
+        consumerController.Tell(SequencedMessage(ProducerId, 1, producerControllerProbe.Ref));
+
+        await consumerProbe.ExpectMsgAsync<ConsumerController.Delivery<Job>>();
+
+        // expected resend
+        await consumerProbe.ExpectMsgAsync<ConsumerController.Delivery<Job>>(1.5.Seconds());
+    }
+
+}

src/core/Akka.Tests/Delivery/ConsumerControllerSpecs.cs

@@ -7,6 +7,7 @@
 using Akka.Delivery.Internal;
 using Akka.Util;
 using FluentAssertions;
+using FluentAssertions.Extensions;
 using Xunit;
 using Xunit.Abstractions;
 using static Akka.Tests.Delivery.TestConsumer;
@@ -672,4 +673,26 @@ public async Task ConsumerController_can_process_zero_length_Chunk()
         consumerController.Tell(seqMessages1.First());
         (await consumerProbe.ExpectMsgAsync<ConsumerController.Delivery<ZeroLengthSerializer.TestMsg>>()).Message.Should().Be(ZeroLengthSerializer.TestMsg.Instance);
     }
+
+    [Fact]
+    public async Task ConsumerController_must_not_resend_Delivery()
+    {
+        var id = NextId();
+        var consumerProbe = CreateTestProbe();
+        var consumerController = Sys.ActorOf(ConsumerController.Create<Job>(Sys, Option<IActorRef>.None),
+            $"consumerController-{id}");
+        var producerControllerProbe = CreateTestProbe();
+
+        consumerController.Tell(new ConsumerController.Start<Job>(consumerProbe.Ref));
+        consumerController.Tell(new ConsumerController.RegisterToProducerController<Job>(producerControllerProbe.Ref));
+        await producerControllerProbe.ExpectMsgAsync<ProducerController.RegisterConsumer<Job>>();
+
+        consumerController.Tell(SequencedMessage(ProducerId, 1, producerControllerProbe.Ref));
+
+        await consumerProbe.ExpectMsgAsync<ConsumerController.Delivery<Job>>();
+
+        // expects no resend
+        await consumerProbe.ExpectNoMsgAsync(1.5.Seconds());
+    }
+
 }

src/core/Akka/Configuration/akka.conf

@@ -664,6 +664,12 @@ akka {
       # kept in memory in the `ProducerController` until they have been
       # confirmed, but the drawback is that lost messages will not be delivered.
       only-flow-control = false
+
+      # When disabled, the <see cref="ConsumerController"/> will discard any <c>Retry</c> messages when it is
+      # waiting for a message delivery confirmation.
+      #
+      # When enabled, timed-out message delivery will be subject to the same retry mechanism as all other message types. 
+      retry-confirmation = false
     }
 
     work-pulling {

src/core/Akka/Delivery/ConsumerController.cs

@@ -229,26 +229,59 @@ public static Settings Create(ActorSystem actorSystem)
 
         public static Settings Create(Config config)
         {
-            return new Settings(config.GetInt("flow-control-window"), config.GetTimeSpan("resend-interval-min"),
-                config.GetTimeSpan("resend-interval-max"), config.GetBoolean("only-flow-control"));
+            return new Settings(
+                flowControlWindow: config.GetInt("flow-control-window"), 
+                resendIntervalMin: config.GetTimeSpan("resend-interval-min"),
+                resendIntervalMax: config.GetTimeSpan("resend-interval-max"), 
+                onlyFlowControl: config.GetBoolean("only-flow-control"),
+                retryConfirmation: config.GetBoolean("retry-confirmation"));
         }
 
         private Settings(int flowControlWindow, TimeSpan resendIntervalMin, TimeSpan resendIntervalMax,
-            bool onlyFlowControl)
+            bool onlyFlowControl, bool retryConfirmation)
         {
             FlowControlWindow = flowControlWindow;
             ResendIntervalMin = resendIntervalMin;
             ResendIntervalMax = resendIntervalMax;
             OnlyFlowControl = onlyFlowControl;
+            RetryConfirmation = retryConfirmation;
         }
 
+        /// <summary>
+        /// Number of messages in flight between <see cref="ProducerController"/> and <see cref="ConsumerController"/>.
+        ///
+        /// The <see cref="ConsumerController"/> requests for more message when half of the window has been used.
+        /// </summary>
         public int FlowControlWindow { get; init; }
 
+        /// <summary>
+        /// The ConsumerController resends flow control messages to the ProducerController with the <see cref="ResendIntervalMin"/>,
+        /// and increasing it gradually to <see cref="ResendIntervalMax"/> when idle.
+        /// </summary>
         public TimeSpan ResendIntervalMin { get; init; }
 
+        /// <summary>
+        /// The ConsumerController resends flow control messages to the ProducerController with the <see cref="ResendIntervalMin"/>,
+        /// and increasing it gradually to <see cref="ResendIntervalMax"/> when idle.
+        /// </summary>
         public TimeSpan ResendIntervalMax { get; init; }
 
+        /// <summary>
+        /// If this is enabled lost messages will not be resent, but flow control is used.
+        ///
+        /// This can be more efficient since messages don't have to be kept in memory in the
+        /// <see cref="ProducerController"/> until they have been confirmed, but the drawback is that lost messages
+        /// will not be delivered.
+        /// </summary>
         public bool OnlyFlowControl { get; init; }
+
+        /// <summary>
+        /// When disabled, the <see cref="ConsumerController"/> will discard any <c>Retry</c> messages when it is
+        /// waiting for a message delivery confirmation.
+        ///
+        /// When enabled, timed-out message delivery will be subject to the same retry mechanism as all other message types. 
+        /// </summary>
+        public bool RetryConfirmation { get; init; }
 
         public override string ToString()
         {

src/core/Akka/Delivery/Internal/ConsumerControllerImpl.cs

@@ -386,6 +386,17 @@ long ComputeNextSeqNr()
         Receive<Retry>(_ =>
         {
             // no retries when WaitingForConfirmation, will be performed from (idle) active
+            if (!Settings.RetryConfirmation)
+                return;
+
+            _log.Debug("Consumer received Retry while waiting for confirmation.");
+            ReceiveRetry(() =>
+            {
+                _log.Debug("Retry sending SequencedMessage [{0}].", sequencedMessage.SeqNr);
+                CurrentState.Consumer.Tell(new Delivery<T>(sequencedMessage.Message.Message!, Context.Self,
+                    sequencedMessage.ProducerId, sequencedMessage.SeqNr));
+                Become(() => WaitingForConfirmation(sequencedMessage));
+            });
         });
 
         Receive<ConsumerController.Start<T>>(start =>