improve channel behavior in shutdown situations

src/csharp/Grpc.Core.Tests/ChannelTest.cs

@@ -32,6 +32,7 @@
 #endregion
 
 using System;
+using System.Threading.Tasks;
 using Grpc.Core;
 using Grpc.Core.Internal;
 using Grpc.Core.Utils;
@@ -89,5 +90,43 @@ namespace Grpc.Core.Tests
             channel.ShutdownAsync().Wait();
             Assert.ThrowsAsync(typeof(InvalidOperationException), async () => await channel.ShutdownAsync());
         }
+
+        [Test]
+        public async Task ShutdownTokenCancelledAfterShutdown()
+        {
+            var channel = new Channel("localhost", ChannelCredentials.Insecure);
+            Assert.IsFalse(channel.ShutdownToken.IsCancellationRequested);
+            var shutdownTask = channel.ShutdownAsync();
+            Assert.IsTrue(channel.ShutdownToken.IsCancellationRequested);
+            await shutdownTask;
+        }
+
+        [Test]
+        public async Task StateIsFatalFailureAfterShutdown()
+        {
+            var channel = new Channel("localhost", ChannelCredentials.Insecure);
+            await channel.ShutdownAsync();
+            Assert.AreEqual(ChannelState.FatalFailure, channel.State);
+        }
+
+        [Test]
+        public async Task ShutdownFinishesWaitForStateChangedAsync()
+        {
+            var channel = new Channel("localhost", ChannelCredentials.Insecure);
+            var stateChangedTask = channel.WaitForStateChangedAsync(ChannelState.Idle);
+            var shutdownTask = channel.ShutdownAsync();
+            await stateChangedTask;
+            await shutdownTask;
+        }
+
+        [Test]
+        public async Task OperationsThrowAfterShutdown()
+        {
+            var channel = new Channel("localhost", ChannelCredentials.Insecure);
+            await channel.ShutdownAsync();
+            Assert.ThrowsAsync(typeof(ObjectDisposedException), async () => await channel.WaitForStateChangedAsync(ChannelState.Idle));
+            Assert.Throws(typeof(ObjectDisposedException), () => { var x = channel.ResolvedTarget; });
+            Assert.ThrowsAsync(typeof(TaskCanceledException), async () => await channel.ConnectAsync());
+        }
     }
 }

src/csharp/Grpc.Core/Channel.cs

@@ -32,6 +32,7 @@
 using System;
 using System.Collections.Generic;
 using System.Linq;
+using System.Threading;
 using System.Threading.Tasks;
 
 using Grpc.Core.Internal;
@@ -51,6 +52,7 @@ namespace Grpc.Core
 
         readonly object myLock = new object();
         readonly AtomicCounter activeCallCounter = new AtomicCounter();
+        readonly CancellationTokenSource shutdownTokenSource = new CancellationTokenSource();
 
         readonly string target;
         readonly GrpcEnvironment environment;
@@ -101,12 +103,13 @@ namespace Grpc.Core
 
         /// <summary>
         /// Gets current connectivity state of this channel.
+        /// After channel is has been shutdown, <c>ChannelState.FatalFailure</c> will be returned.
         /// </summary>
         public ChannelState State
         {
             get
             {
-                return handle.CheckConnectivityState(false);        
+                return GetConnectivityState(false);
             }
         }
 
@@ -154,6 +157,17 @@ namespace Grpc.Core
             }
         }
 
+        /// <summary>
+        /// Returns a token that gets cancelled once <c>ShutdownAsync</c> is invoked.
+        /// </summary>
+        public CancellationToken ShutdownToken
+        {
+            get
+            {
+                return this.shutdownTokenSource.Token;
+            }
+        }
+
         /// <summary>
         /// Allows explicitly requesting channel to connect without starting an RPC.
         /// Returned task completes once state Ready was seen. If the deadline is reached,
@@ -164,7 +178,7 @@ namespace Grpc.Core
         /// <param name="deadline">The deadline. <c>null</c> indicates no deadline.</param>
         public async Task ConnectAsync(DateTime? deadline = null)
         {
-            var currentState = handle.CheckConnectivityState(true);
+            var currentState = GetConnectivityState(true);
             while (currentState != ChannelState.Ready)
             {
                 if (currentState == ChannelState.FatalFailure)
@@ -172,7 +186,7 @@ namespace Grpc.Core
                     throw new OperationCanceledException("Channel has reached FatalFailure state.");
                 }
                 await WaitForStateChangedAsync(currentState, deadline).ConfigureAwait(false);
-                currentState = handle.CheckConnectivityState(false);
+                currentState = GetConnectivityState(false);
             }
         }
 
@@ -188,6 +202,8 @@ namespace Grpc.Core
                 shutdownRequested = true;
             }
 
+            shutdownTokenSource.Cancel();
+
             var activeCallCount = activeCallCounter.Count;
             if (activeCallCount > 0)
             {
@@ -231,6 +247,18 @@ namespace Grpc.Core
             activeCallCounter.Decrement();
         }
 
+        private ChannelState GetConnectivityState(bool tryToConnect)
+        {
+            try
+            {
+                return handle.CheckConnectivityState(tryToConnect);
+            }
+            catch (ObjectDisposedException)
+            {
+                return ChannelState.FatalFailure;
+            }
+        }
+
         private static void EnsureUserAgentChannelOption(Dictionary<string, ChannelOption> options)
         {
             var key = ChannelOptions.PrimaryUserAgentString;