Interrupt existing subchannel connect attempt when reconnect is requested

src/Grpc.Net.Client/Balancer/Internal/ISubchannelTransport.cs

@@ -34,7 +34,7 @@ internal interface ISubchannelTransport : IDisposable
     TransportStatus TransportStatus { get; }
 
     ValueTask<Stream> GetStreamAsync(DnsEndPoint endPoint, CancellationToken cancellationToken);
-    ValueTask<ConnectResult> TryConnectAsync(ConnectContext context);
+    ValueTask<ConnectResult> TryConnectAsync(ConnectContext context, int attempt);
 
     void Disconnect();
 }

src/Grpc.Net.Client/Balancer/Internal/PassiveSubchannelTransport.cs

@@ -52,7 +52,7 @@ public void Disconnect()
         _subchannel.UpdateConnectivityState(ConnectivityState.Idle, "Disconnected.");
     }
 
-    public ValueTask<ConnectResult> TryConnectAsync(ConnectContext context)
+    public ValueTask<ConnectResult> TryConnectAsync(ConnectContext context, int attempt)
     {
         Debug.Assert(_subchannel._addresses.Count == 1);
         Debug.Assert(CurrentEndPoint == null);

src/Grpc.Net.Client/Balancer/Internal/SocketConnectivitySubchannelTransport.cs

@@ -144,7 +144,7 @@ private void DisconnectUnsynchronized()
         _currentEndPoint = null;
     }
 
-    public async ValueTask<ConnectResult> TryConnectAsync(ConnectContext context)
+    public async ValueTask<ConnectResult> TryConnectAsync(ConnectContext context, int attempt)
     {
         Debug.Assert(CurrentEndPoint == null);
 

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

@@ -165,6 +165,8 @@ public void Dispose()
     /// <param name="addresses"></param>
     public void UpdateAddresses(IReadOnlyList<BalancerAddress> addresses)
     {
+        SubchannelLog.AddressesUpdated(_logger, Id, addresses);
+
         var requireReconnect = false;
         lock (Lock)
         {
@@ -278,6 +280,8 @@ private void CancelInProgressConnect()
                 _connectContext.CancelConnect();
                 _connectContext.Dispose();
             }
+
+            _delayInterruptTcs?.TrySetResult(null);
         }
     }
 
@@ -313,7 +317,7 @@ private async Task ConnectTransportAsync()
                     }
                 }
 
-                switch (await _transport.TryConnectAsync(connectContext).ConfigureAwait(false))
+                switch (await _transport.TryConnectAsync(connectContext, attempt).ConfigureAwait(false))
                 {
                     case ConnectResult.Success:
                         return;
@@ -345,17 +349,21 @@ private async Task ConnectTransportAsync()
                 {
                     // Task.Delay won. Check CTS to see if it won because of cancellation.
                     delayCts.Token.ThrowIfCancellationRequested();
+                    SubchannelLog.ConnectBackoffComplete(_logger, Id);
                 }
                 else
                 {
                     SubchannelLog.ConnectBackoffInterrupted(_logger, Id);
 
-                    // Delay interrupt was triggered. Reset back-off.
-                    backoffPolicy = _manager.BackoffPolicyFactory.Create();
-
                     // Cancel the Task.Delay that's no longer needed.
                     // https://github.com/davidfowl/AspNetCoreDiagnosticScenarios/blob/519ef7d231c01116f02bc04354816a735f2a36b6/AsyncGuidance.md#using-a-timeout
                     delayCts.Cancel();
+
+                    // Check to connect context token to see if the delay was interrupted because of a connect cancellation.
+                    connectContext.CancellationToken.ThrowIfCancellationRequested();
+
+                    // Delay interrupt was triggered. Reset back-off.
+                    backoffPolicy = _manager.BackoffPolicyFactory.Create();
                 }
             }
         }
@@ -532,6 +540,12 @@ internal static class SubchannelLog
     private static readonly Action<ILogger, string, Exception?> _cancelingConnect =
         LoggerMessage.Define<string>(LogLevel.Debug, new EventId(17, "CancelingConnect"), "Subchannel id '{SubchannelId}' canceling connect.");
 
+    private static readonly Action<ILogger, string, Exception?> _connectBackoffComplete =
+        LoggerMessage.Define<string>(LogLevel.Trace, new EventId(18, "ConnectBackoffComplete"), "Subchannel id '{SubchannelId}' connect backoff complete.");
+
+    private static readonly Action<ILogger, string, string, Exception?> _addressesUpdated =
+        LoggerMessage.Define<string, string>(LogLevel.Trace, new EventId(19, "AddressesUpdated"), "Subchannel id '{SubchannelId}' updated with addresses: {Addresses}");
+
     public static void SubchannelCreated(ILogger logger, string subchannelId, IReadOnlyList<BalancerAddress> addresses)
     {
         if (logger.IsEnabled(LogLevel.Debug))
@@ -620,5 +634,19 @@ public static void CancelingConnect(ILogger logger, string subchannelId)
     {
         _cancelingConnect(logger, subchannelId, null);
     }
+
+    public static void ConnectBackoffComplete(ILogger logger, string subchannelId)
+    {
+        _connectBackoffComplete(logger, subchannelId, null);
+    }
+
+    public static void AddressesUpdated(ILogger logger, string subchannelId, IReadOnlyList<BalancerAddress> addresses)
+    {
+        if (logger.IsEnabled(LogLevel.Trace))
+        {
+            var addressesText = string.Join(", ", addresses.Select(a => a.EndPoint.Host + ":" + a.EndPoint.Port));
+            _addressesUpdated(logger, subchannelId, addressesText, null);
+        }
+    }
 }
 #endif

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

@@ -188,7 +188,7 @@ public async Task PickAsync_ErrorConnectingToSubchannel_ThrowsError()
             new BalancerAddress("localhost", 80)
         });
 
-        var transportFactory = new TestSubchannelTransportFactory((s, c) =>
+        var transportFactory = TestSubchannelTransportFactory.Create((s, c) =>
         {
             return Task.FromException<TryConnectResult>(new Exception("Test error!"));
         });
@@ -357,7 +357,7 @@ public async Task UpdateAddresses_ConnectIsInProgress_InProgressConnectIsCancele
 
         var syncPoint = new SyncPoint(runContinuationsAsynchronously: true);
 
-        var transportFactory = new TestSubchannelTransportFactory(async (s, c) =>
+        var transportFactory = TestSubchannelTransportFactory.Create(async (s, c) =>
         {
             c.Register(state => ((SyncPoint)state!).Continue(), syncPoint);
 
@@ -548,7 +548,7 @@ public async Task PickAsync_ExecutionContext_DoesNotCaptureAsyncLocalsInConnect(
 
         var callbackAsyncLocalValues = new List<object>();
 
-        var transportFactory = new TestSubchannelTransportFactory((subchannel, cancellationToken) =>
+        var transportFactory = TestSubchannelTransportFactory.Create((subchannel, cancellationToken) =>
         {
             callbackAsyncLocalValues.Add(asyncLocal.Value);
             if (callbackAsyncLocalValues.Count >= 2)

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

@@ -58,7 +58,7 @@ public async Task ChangeAddresses_HasReadySubchannel_OldSubchannelShutdown()
         services.AddSingleton<ResolverFactory>(new TestResolverFactory(resolver));
 
         var subChannelConnections = new List<Subchannel>();
-        var transportFactory = new TestSubchannelTransportFactory((s, c) =>
+        var transportFactory = TestSubchannelTransportFactory.Create((s, c) =>
         {
             lock (subChannelConnections)
             {
@@ -176,7 +176,7 @@ public async Task ResolverError_HasFailedSubchannel_SubchannelShutdown()
             new BalancerAddress("localhost", 80)
         });
 
-        var transportFactory = new TestSubchannelTransportFactory((s, c) => Task.FromResult(new TryConnectResult(ConnectivityState.TransientFailure)));
+        var transportFactory = TestSubchannelTransportFactory.Create((s, c) => Task.FromResult(new TryConnectResult(ConnectivityState.TransientFailure)));
         services.AddSingleton<ResolverFactory>(new TestResolverFactory(resolver));
         services.AddSingleton<ISubchannelTransportFactory>(transportFactory);
         var serviceProvider = services.BuildServiceProvider();
@@ -234,7 +234,7 @@ public async Task RequestConnection_InitialConnectionFails_ExponentialBackoff()
         var connectivityState = ConnectivityState.TransientFailure;
 
         services.AddSingleton<ResolverFactory>(new TestResolverFactory(resolver));
-        services.AddSingleton<ISubchannelTransportFactory>(new TestSubchannelTransportFactory(async (s, c) =>
+        services.AddSingleton<ISubchannelTransportFactory>(TestSubchannelTransportFactory.Create(async (s, c) =>
         {
             await syncPoint.WaitToContinue();
             return new TryConnectResult(connectivityState);
@@ -290,7 +290,7 @@ public async Task RequestConnection_InitialConnectionEnds_EntersIdleState()
         });
 
         var transportConnectCount = 0;
-        var transportFactory = new TestSubchannelTransportFactory((s, c) =>
+        var transportFactory = TestSubchannelTransportFactory.Create((s, c) =>
         {
             transportConnectCount++;
             return Task.FromResult(new TryConnectResult(ConnectivityState.Ready));
@@ -340,7 +340,7 @@ public async Task RequestConnection_IdleConnectionConnectAsync_StateToReady()
         resolver.UpdateAddresses(new List<BalancerAddress> { new BalancerAddress("localhost", 80) });
 
         var transportConnectCount = 0;
-        var transportFactory = new TestSubchannelTransportFactory((s, c) =>
+        var transportFactory = TestSubchannelTransportFactory.Create((s, c) =>
         {
             transportConnectCount++;
             return Task.FromResult(new TryConnectResult(ConnectivityState.Ready));
@@ -385,7 +385,7 @@ public async Task RequestConnection_IdleConnectionPick_StateToReady()
         resolver.UpdateAddresses(new List<BalancerAddress> { new BalancerAddress("localhost", 80) });
 
         var transportConnectCount = 0;
-        var transportFactory = new TestSubchannelTransportFactory((s, c) =>
+        var transportFactory = TestSubchannelTransportFactory.Create((s, c) =>
         {
             transportConnectCount++;
             return Task.FromResult(new TryConnectResult(ConnectivityState.Ready));
@@ -448,7 +448,7 @@ public async Task UnaryCall_TransportConnecting_OnePickStarted()
 
         var tcs = new TaskCompletionSource<object?>(TaskCreationOptions.RunContinuationsAsynchronously);
         var transportConnectCount = 0;
-        var transportFactory = new TestSubchannelTransportFactory((s, c) =>
+        var transportFactory = TestSubchannelTransportFactory.Create((s, c) =>
         {
             transportConnectCount++;
 
@@ -510,7 +510,7 @@ public async Task UnaryCall_TransportConnecting_ErrorAfterTransientFailure()
 
         var tcs = new TaskCompletionSource<object?>(TaskCreationOptions.RunContinuationsAsynchronously);
         var transportConnectCount = 0;
-        var transportFactory = new TestSubchannelTransportFactory((s, c) =>
+        var transportFactory = TestSubchannelTransportFactory.Create((s, c) =>
         {
             transportConnectCount++;
 
@@ -576,7 +576,7 @@ public async Task DeadlineExceeded_MultipleCalls_CallsWaitForDeadline()
         var resolver = new TestResolver();
         resolver.UpdateAddresses(new List<BalancerAddress> { new BalancerAddress("localhost", 80) });
 
-        var transportFactory = new TestSubchannelTransportFactory((s, c) =>
+        var transportFactory = TestSubchannelTransportFactory.Create((s, c) =>
         {
             return Task.FromResult(new TryConnectResult(ConnectivityState.Connecting));
         });
@@ -640,7 +640,7 @@ public async Task ConnectTimeout_MultipleCalls_AttemptReconnect()
         resolver.UpdateAddresses(new List<BalancerAddress> { new BalancerAddress("localhost", 80) });
 
         var tryConnectTcs = new TaskCompletionSource<TryConnectResult>(TaskCreationOptions.RunContinuationsAsynchronously);
-        var transportFactory = new TestSubchannelTransportFactory((s, ct) =>
+        var transportFactory = TestSubchannelTransportFactory.Create((s, ct) =>
         {
             return tryConnectTcs.Task;
         });

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

@@ -19,6 +19,7 @@
 #if SUPPORT_LOAD_BALANCING
 using System;
 using System.Collections.Generic;
+using System.Diagnostics;
 using System.Linq;
 using System.Net;
 using System.Threading;
@@ -298,7 +299,7 @@ public async Task Resolver_ServiceConfigInResult()
         var currentConnectivityState = ConnectivityState.Ready;
 
         services.AddSingleton<ResolverFactory>(new TestResolverFactory(resolver));
-        services.AddSingleton<ISubchannelTransportFactory>(new TestSubchannelTransportFactory(async (s, c) =>
+        services.AddSingleton<ISubchannelTransportFactory>(TestSubchannelTransportFactory.Create(async (s, i, c) =>
         {
             await syncPoint.WaitToContinue();
             return new TryConnectResult(currentConnectivityState);
@@ -551,5 +552,134 @@ public async Task ResolveServiceConfig_ErrorOnSecondResolve_PickSuccess()
         var balancer = (ChildHandlerLoadBalancer)channel.ConnectionManager._balancer!;
         return (T?)balancer._current?.LoadBalancer;
     }
+
+    internal class TestBackoffPolicyFactory : IBackoffPolicyFactory
+    {
+        private readonly TimeSpan _backoff;
+
+        public TestBackoffPolicyFactory() : this(TimeSpan.FromSeconds(20))
+        {
+        }
+
+        public TestBackoffPolicyFactory(TimeSpan backoff)
+        {
+            _backoff = backoff;
+        }
+
+        public IBackoffPolicy Create()
+        {
+            return new TestBackoffPolicy(_backoff);
+        }
+
+        private class TestBackoffPolicy : IBackoffPolicy
+        {
+            private readonly TimeSpan _backoff;
+
+            public TestBackoffPolicy(TimeSpan backoff)
+            {
+                _backoff = backoff;
+            }
+
+            public TimeSpan NextBackoff()
+            {
+                return _backoff;
+            }
+        }
+    }
+
+    [Test]
+    public async Task Resolver_UpdateResultsAfterPreviousConnect_InterruptConnect()
+    {
+        // Arrange
+        var services = new ServiceCollection();
+
+        // add logger
+        services.AddNUnitLogger();
+        var loggerFactory = services.BuildServiceProvider().GetRequiredService<ILoggerFactory>();
+        var logger = loggerFactory.CreateLogger<ResolverTests>();
+
+        // add resolver and balancer
+        var resolver = new TestResolver(loggerFactory);
+        var result = ResolverResult.ForResult(new List<BalancerAddress> { new BalancerAddress("localhost", 80) }, serviceConfig: null, serviceConfigStatus: null);
+        resolver.UpdateResult(result);
+
+        services.AddSingleton<ResolverFactory>(new TestResolverFactory(resolver));
+        services.AddSingleton<IBackoffPolicyFactory>(new TestBackoffPolicyFactory(TimeSpan.FromSeconds(0.2)));
+
+        var tryConnectData = new List<(IReadOnlyList<BalancerAddress> BalancerAddresses, int Attempt, bool IsCancellationRequested)>();
+
+        var tryConnectCount = 0;
+        services.AddSingleton<ISubchannelTransportFactory>(
+            TestSubchannelTransportFactory.Create((subchannel, attempt, cancellationToken) =>
+            {
+                var addresses = subchannel.GetAddresses();
+                var isCancellationRequested = cancellationToken.IsCancellationRequested;
+                ConnectivityState state;
+
+                var i = Interlocked.Increment(ref tryConnectCount);
+                if (i == 1)
+                {
+                    state = ConnectivityState.Ready;
+                }
+                else
+                {
+                    state = attempt >= 2 ? ConnectivityState.Ready : ConnectivityState.TransientFailure;
+                }
+
+                logger.LogInformation("TryConnect attempt {Attempt} to addresses {Addresses}. State: {ConnectivityState}, IsCancellationRequested: {IsCancellationRequested}", attempt, string.Join(", ", addresses), state, isCancellationRequested);
+
+                lock (tryConnectData)
+                {
+                    tryConnectData.Add((addresses, attempt, isCancellationRequested));
+                }
+
+                return Task.FromResult(new TryConnectResult(state));
+            }));
+
+        var channelOptions = new GrpcChannelOptions
+        {
+            Credentials = ChannelCredentials.Insecure,
+            ServiceProvider = services.BuildServiceProvider(),
+        };
+
+        // Act
+        var channel = GrpcChannel.ForAddress("test:///test_addr", channelOptions);
+
+        logger.LogInformation("Client connecting.");
+        await channel.ConnectionManager.ConnectAsync(waitForReady: true, CancellationToken.None);
+
+        logger.LogInformation("Client updating resolver.");
+        result = ResolverResult.ForResult(new List<BalancerAddress> { new BalancerAddress("localhost", 81) }, serviceConfig: null, serviceConfigStatus: null);
+        resolver.UpdateResult(result);
+
+        logger.LogInformation("Client picking.");
+        await ExceptionAssert.ThrowsAsync<RpcException>(async () => await channel.ConnectionManager.PickAsync(
+            new PickContext(),
+            waitForReady: false,
+            CancellationToken.None));
+
+        logger.LogInformation("Client updating Resolver.");
+        result = ResolverResult.ForResult(new List<BalancerAddress> { new BalancerAddress("localhost", 82) }, serviceConfig: null, serviceConfigStatus: null);
+        resolver.UpdateResult(result);
+
+        logger.LogInformation("Client picking and waiting for ready.");
+        await channel.ConnectionManager.PickAsync(
+            new PickContext(),
+            waitForReady: true,
+            CancellationToken.None);
+
+        // Assert
+        logger.LogInformation("TryConnectData count: {Count}", tryConnectData.Count);
+        foreach (var data in tryConnectData)
+        {
+            logger.LogInformation("Attempt: {Attempt}, BalancerAddresses: {BalancerAddresses}, IsCancellationRequested: {IsCancellationRequested}", data.Attempt, string.Join(", ", data.BalancerAddresses), data.IsCancellationRequested);
+        }
+
+        var duplicate = tryConnectData.GroupBy(d => new { Address = d.BalancerAddresses.Single(), d.Attempt }).FirstOrDefault(g => g.Count() >= 2);
+        if (duplicate != null)
+        {
+            Assert.Fail($"Duplicate attempts to address. Count: {duplicate.Count()}, Address: {duplicate.Key.Address}");
+        }
+    }
 }
 #endif