Add fix and update tests

global.json

@@ -1,6 +1,5 @@
 {
   "sdk": {
-    "version": "9.0.100-preview.7.24407.12",
-    "rollForward": "latestFeature"
+    "version": "9.0.100-rc.1.24452.12"
   }
 }

src/Grpc.Net.Client/Balancer/SubchannelsLoadBalancer.cs

@@ -122,6 +122,7 @@ public override void UpdateChannelState(ChannelState state)
 
         var allUpdatedSubchannels = new List<AddressSubchannel>();
         var newSubchannels = new List<Subchannel>();
+        var modifiedSubchannelsCount = 0;
         var currentSubchannels = _addressSubchannels.ToList();
 
         // The state's addresses is the new authoritative list of addresses.
@@ -150,6 +151,8 @@ public override void UpdateChannelState(ChannelState state)
                         address,
                         newOrCurrentSubchannel.LastKnownState);
                     newOrCurrentSubchannel.Subchannel.UpdateAddresses(new[] { address });
+
+                    modifiedSubchannelsCount++;
                 }
 
                 SubchannelLog.SubchannelPreserved(_logger, newOrCurrentSubchannel.Subchannel.Id, address);
@@ -171,7 +174,7 @@ public override void UpdateChannelState(ChannelState state)
         // This can all be removed.
         var removedSubConnections = currentSubchannels;
 
-        if (removedSubConnections.Count == 0 && newSubchannels.Count == 0)
+        if (removedSubConnections.Count == 0 && newSubchannels.Count == 0 && modifiedSubchannelsCount == 0)
         {
             SubchannelsLoadBalancerLog.ConnectionsUnchanged(_logger);
             return;

test/Grpc.Net.Client.Tests/Balancer/SubchannelsLoadBalancerTests.cs

@@ -0,0 +1,199 @@
+#region Copyright notice and license
+
+// Copyright 2019 The gRPC Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#endregion
+
+#if SUPPORT_LOAD_BALANCING
+using System.Net;
+using Grpc.Core;
+using Grpc.Net.Client.Balancer;
+using Grpc.Net.Client.Balancer.Internal;
+using Grpc.Tests.Shared;
+using Microsoft.Extensions.Logging;
+using Microsoft.Extensions.Logging.Abstractions;
+
+namespace Grpc.Net.Client.Tests.Infrastructure.Balancer;
+
+[TestFixture]
+public class SubchannelsLoadBalancerTests
+{
+    [Test]
+    public void UpdateChannelState_AddressMatchAndAttributesDifferent_UpdateState()
+    {
+        // Arrange
+        const string host1 = "127.0.0.1";
+        const string host2 = "127.0.0.2";
+        const int port = 80;
+
+        const string attributeKey = "key1";
+
+        var controller = new CustomChannelControlHelper();
+        var balancer = new CustomBalancer(controller, NullLoggerFactory.Instance);
+
+        // create 2 addresses with some attributes
+        var address1 = new BalancerAddress(host1, port);
+        address1.Attributes.TryAdd(attributeKey, 20); // <-- difference
+
+        var address2 = new BalancerAddress(host2, port);
+        address2.Attributes.TryAdd(attributeKey, 80); // <-- difference
+
+        var state1 = new ChannelState(
+            status: new Status(),
+            addresses: [address1, address2],
+            loadBalancingConfig: null,
+            attributes: new BalancerAttributes());
+
+        // create 2 addresses with the same hosts and ports as previous but with other attribute values
+        var address3 = new BalancerAddress(host1, port);
+        address3.Attributes.TryAdd(attributeKey, 40); // <-- difference
+
+        var address4 = new BalancerAddress(host2, port);
+        address4.Attributes.TryAdd(attributeKey, 60); // <-- difference
+
+        var state2 = new ChannelState(
+            status: new Status(),
+            addresses: [address3, address4],
+            loadBalancingConfig: null,
+            attributes: new BalancerAttributes());
+
+        // Act
+        // first update with `address1` and `address2`
+        balancer.UpdateChannelState(state1);
+
+        // remember count of `IChannelControlHelper.UpdateState()` calls
+        var updateStateCallsCount1 = controller.UpdateStateCallsCount;
+
+        // second update with `address3` and `address4`
+        // which differs from `address1` and `address2` _only_ in attributes values
+        balancer.UpdateChannelState(state2);
+
+        // get count of `IChannelControlHelper.UpdateState()` calls after second update
+        var updateStateCallsCount2 = controller.UpdateStateCallsCount;
+
+        // Assert
+        Assert.True(
+            updateStateCallsCount2 > updateStateCallsCount1,
+            "`IChannelControlHelper.UpdateState()` was not called from `SubchannelsLoadBalancer.UpdateChannelState()`");
+    }
+}
+
+file class CustomBalancer(
+    IChannelControlHelper controller,
+    ILoggerFactory loggerFactory)
+    : SubchannelsLoadBalancer(controller, loggerFactory)
+{
+    protected override SubchannelPicker CreatePicker(IReadOnlyList<Subchannel> readySubchannels)
+    {
+        return new CustomPicker(readySubchannels);
+    }
+}
+
+file class CustomPicker : SubchannelPicker
+{
+    private IReadOnlyList<Subchannel> readySubchannels;
+
+    public CustomPicker(IReadOnlyList<Subchannel> readySubchannels)
+    {
+        this.readySubchannels = readySubchannels;
+    }
+
+    public override PickResult Pick(PickContext context)
+    {
+        return PickResult.ForSubchannel(readySubchannels[0]);
+    }
+}
+
+file class CustomChannelControlHelper : IChannelControlHelper
+{
+    public int UpdateStateCallsCount { get; private set; }
+
+    public Subchannel CreateSubchannel(SubchannelOptions options)
+    {
+        var subchannelTransportFactory = new CustomSubchannelTransportFactory();
+
+        var manager = new ConnectionManager(
+            new CustomResolver(),
+            true,
+            NullLoggerFactory.Instance,
+            new CustomBackoffPolicyFactory(),
+            subchannelTransportFactory,
+            []);
+
+        return ((IChannelControlHelper)manager).CreateSubchannel(options);
+    }
+
+    public void UpdateState(BalancerState state)
+    {
+        UpdateStateCallsCount++;
+    }
+
+    public void RefreshResolver() { }
+}
+
+file class CustomResolver() : PollingResolver(NullLoggerFactory.Instance)
+{
+    protected override Task ResolveAsync(CancellationToken cancellationToken)
+    {
+        return Task.CompletedTask;
+    }
+}
+
+file class CustomBackoffPolicyFactory : IBackoffPolicyFactory
+{
+    public IBackoffPolicy Create()
+    {
+        return new CustomBackoffPolicy();
+    }
+}
+
+file class CustomBackoffPolicy : IBackoffPolicy
+{
+    public TimeSpan NextBackoff()
+    {
+        return TimeSpan.Zero;
+    }
+}
+
+file class CustomSubchannelTransportFactory : ISubchannelTransportFactory
+{
+    public ISubchannelTransport Create(Subchannel subchannel)
+    {
+        return new CustomSubchannelTransport();
+    }
+}
+
+file class CustomSubchannelTransport : ISubchannelTransport
+{
+    public void Dispose() { }
+
+    public DnsEndPoint? CurrentEndPoint { get; }
+    public TimeSpan? ConnectTimeout { get; }
+    public TransportStatus TransportStatus { get; }
+
+    public ValueTask<Stream> GetStreamAsync(DnsEndPoint endPoint, CancellationToken cancellationToken)
+    {
+        return ValueTask.FromResult<Stream>(new MemoryStream());
+    }
+
+    public ValueTask<ConnectResult> TryConnectAsync(ConnectContext context, int attempt)
+    {
+        return ValueTask.FromResult(ConnectResult.Success);
+    }
+
+    public void Disconnect() { }
+}
+
+#endif