Akka.IO: fix TcpListener connection queue problem

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

@@ -3995,7 +3995,7 @@ namespace Akka.IO
         }
         public class Bind : Akka.IO.Tcp.Command
         {
-            public Bind(Akka.Actor.IActorRef handler, System.Net.EndPoint localAddress, int backlog = 100, System.Collections.Generic.IEnumerable<Akka.IO.Inet.SocketOption> options = null, bool pullMode = False) { }
+            public Bind(Akka.Actor.IActorRef handler, System.Net.EndPoint localAddress, int backlog = 1024, System.Collections.Generic.IEnumerable<Akka.IO.Inet.SocketOption> options = null, bool pullMode = False) { }
             public int Backlog { get; }
             public Akka.Actor.IActorRef Handler { get; }
             public System.Net.EndPoint LocalAddress { get; }

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

@@ -3985,7 +3985,7 @@ namespace Akka.IO
         }
         public class Bind : Akka.IO.Tcp.Command
         {
-            public Bind(Akka.Actor.IActorRef handler, System.Net.EndPoint localAddress, int backlog = 100, System.Collections.Generic.IEnumerable<Akka.IO.Inet.SocketOption> options = null, bool pullMode = False) { }
+            public Bind(Akka.Actor.IActorRef handler, System.Net.EndPoint localAddress, int backlog = 1024, System.Collections.Generic.IEnumerable<Akka.IO.Inet.SocketOption> options = null, bool pullMode = False) { }
             public int Backlog { get; }
             public Akka.Actor.IActorRef Handler { get; }
             public System.Net.EndPoint LocalAddress { get; }

src/core/Akka.Tests/IO/TcpListenerSpec.cs

@@ -75,7 +75,6 @@ class TestSetup
             private readonly IActorRef _handlerRef;
             private readonly TestProbe _bindCommander;
             private readonly TestProbe _parent;
-            private readonly TestProbe _selectorRouter;
             private readonly TestActorRef<ListenerParent> _parentRef;
 
             public TestSetup(TestKitBase kit, bool pullMode)
@@ -87,7 +86,7 @@ public TestSetup(TestKitBase kit, bool pullMode)
                 _handlerRef = _handler.Ref;
                 _bindCommander = kit.CreateTestProbe();
                 _parent = kit.CreateTestProbe();
-                _selectorRouter = kit.CreateTestProbe();
+                SelectorRouter = kit.CreateTestProbe();
 
                 _parentRef = new TestActorRef<ListenerParent>(kit.Sys, Props.Create(() => new ListenerParent(this, pullMode)));
             }
@@ -115,10 +114,7 @@ public async Task AttemptConnectionToEndpoint()
 
             public IActorRef Listener { get { return _parentRef.UnderlyingActor.Listener; } }
 
-            public TestProbe SelectorRouter
-            {
-                get { return _selectorRouter; }
-            }
+            public TestProbe SelectorRouter { get; }
 
             public TestProbe BindCommander { get { return _bindCommander; } }
             public TestProbe Parent { get { return _parent; } }
@@ -128,7 +124,7 @@ public TestProbe SelectorRouter
             internal void AfterBind(Socket socket)
                 => LocalEndPoint = (IPEndPoint)socket.LocalEndPoint;
 
-            class ListenerParent : ActorBase
+            private class ListenerParent : ActorBase
             {
                 private readonly TestSetup _test;
                 private readonly bool _pullMode;

src/core/Akka.Tests/IO/TcpSettingsSpec.cs

@@ -0,0 +1,42 @@
+//-----------------------------------------------------------------------
+// <copyright file="TcpSettingsSpec.cs" company="Akka.NET Project">
+//     Copyright (C) 2009-2022 Lightbend Inc. <http://www.lightbend.com>
+//     Copyright (C) 2013-2025 .NET Foundation <https://github.com/akkadotnet/akka.net>
+// </copyright>
+//-----------------------------------------------------------------------
+
+using System;
+using Akka.Actor;
+using Akka.Configuration;
+using Akka.IO;
+using FluentAssertions;
+using Xunit;
+
+namespace Akka.Tests.IO
+{
+    public class TcpSettingsSpec
+    {
+        [Fact]
+        public void TcpSettings_should_parse_all_akka_io_tcp_config_values_correctly()
+        {
+            // Arrange: load the default reference config
+            var config = ConfigurationFactory.Default();
+            var tcpConfig = config.GetConfig("akka.io.tcp");
+            var settings = TcpSettings.Create(tcpConfig);
+
+            // Assert: all values match akka.conf reference
+            settings.BufferPoolConfigPath.Should().Be("akka.io.tcp.disabled-buffer-pool");
+            settings.InitialSocketAsyncEventArgs.Should().Be(32);
+            settings.TraceLogging.Should().BeFalse();
+            settings.BatchAcceptLimit.Should().Be(Environment.ProcessorCount * 2);
+            settings.RegisterTimeout.Should().Be(TimeSpan.FromSeconds(5));
+            settings.ReceivedMessageSizeLimit.Should().Be(int.MaxValue);
+            settings.ManagementDispatcher.Should().Be("akka.actor.internal-dispatcher");
+            settings.FileIODispatcher.Should().Be("akka.actor.default-blocking-io-dispatcher");
+            settings.TransferToLimit.Should().Be(524288); // 512 KiB
+            settings.FinishConnectRetries.Should().Be(5);
+            settings.OutgoingSocketForceIpv4.Should().BeFalse();
+            settings.WriteCommandsQueueMaxSize.Should().Be(-1);
+        }
+    }
+} 

src/core/Akka/Configuration/akka.conf

@@ -763,8 +763,11 @@ akka {
 
       # The maximum number of connection that are accepted in one go,
       # higher numbers decrease latency, lower numbers increase fairness on
-      # the worker-dispatcher
-      batch-accept-limit = 10
+      # the worker-dispatcher.
+      #
+      # By default we scale to logical CPUs * 2, but you can set this to an
+      # integer value greater than 0.
+      batch-accept-limit = scale-to-cpus
 
       # The duration a connection actor waits for a `Register` message from
       # its commander before aborting the connection.

src/core/Akka/IO/Tcp.cs

@@ -156,12 +156,12 @@ public class Bind : Command
             /// </summary>
             /// <param name="handler">The actor who will be handling the TCP listener.</param>
             /// <param name="localAddress">The local endpoint we are binding to.</param>
-            /// <param name="backlog">TCP backlog - the number of pending connections that the queue will hold.</param>
+            /// <param name="backlog">TCP backlog - the number of pending connections that the queue will hold. Defaults to 1024.</param>
             /// <param name="options">A set of socket options.</param>
             /// <param name="pullMode">Specifies whether we're running in "pull mode" or not.</param>
             public Bind(IActorRef handler,
                 EndPoint localAddress,
-                int backlog = 100,
+                int backlog = 1024,
                 IEnumerable<Inet.SocketOption> options = null,
                 bool pullMode = false)
             {