Fix task cancellation exception on shut down (#93)

Author: jamarino

src/Winton.Extensions.Configuration.Consul/ConsulConfigurationProvider.cs

@@ -45,7 +45,6 @@ public ConsulConfigurationProvider(
         public void Dispose()
         {
             _cancellationTokenSource.Cancel();
-            _pollTask?.Wait(500);
             _cancellationTokenSource.Dispose();
         }
 
@@ -57,20 +56,22 @@ public override void Load()
                 return;
             }
 
-            DoLoad().GetAwaiter().GetResult();
+            var cancellationToken = _cancellationTokenSource.Token;
+
+            DoLoad(cancellationToken).GetAwaiter().GetResult();
 
             // Polling starts after the initial load to ensure no concurrent access to the key from this instance
             if (_source.ReloadOnChange)
             {
-                _pollTask = Task.Run(PollingLoop);
+                _pollTask = Task.Run(() => PollingLoop(cancellationToken), cancellationToken);
             }
         }
 
-        private async Task DoLoad()
+        private async Task DoLoad(CancellationToken cancellationToken)
         {
             try
             {
-                var result = await GetKvPairs(false).ConfigureAwait(false);
+                var result = await GetKvPairs(false, cancellationToken).ConfigureAwait(false);
 
                 if (result.HasValue())
                 {
@@ -94,7 +95,7 @@ private async Task DoLoad()
             }
         }
 
-        private async Task<QueryResult<KVPair[]>> GetKvPairs(bool waitForChange)
+        private async Task<QueryResult<KVPair[]>> GetKvPairs(bool waitForChange, CancellationToken cancellationToken)
         {
             using var consulClient = _consulClientFactory.Create();
             var queryOptions = new QueryOptions
@@ -106,27 +107,25 @@ private async Task<QueryResult<KVPair[]>> GetKvPairs(bool waitForChange)
             var result =
                 await consulClient
                     .KV
-                    .List(_source.Key, queryOptions, _cancellationTokenSource.Token)
+                    .List(_source.Key, queryOptions, cancellationToken)
                     .ConfigureAwait(false);
 
             return result.StatusCode switch
             {
                 HttpStatusCode.OK => result,
                 HttpStatusCode.NotFound => result,
-                _ =>
-                    throw
-                        new Exception($"Error loading configuration from consul. Status code: {result.StatusCode}.")
-                };
+                _ => throw new Exception($"Error loading configuration from consul. Status code: {result.StatusCode}.")
+            };
         }
 
-        private async Task PollingLoop()
+        private async Task PollingLoop(CancellationToken cancellationToken)
         {
             var consecutiveFailureCount = 0;
-            while (!_cancellationTokenSource.Token.IsCancellationRequested)
+            while (!cancellationToken.IsCancellationRequested)
             {
                 try
                 {
-                    var result = await GetKvPairs(true).ConfigureAwait(false);
+                    var result = await GetKvPairs(true, cancellationToken).ConfigureAwait(false);
 
                     if (result.HasValue() && result.LastIndex > _lastIndex)
                     {
@@ -143,7 +142,7 @@ private async Task PollingLoop()
                         _source.OnWatchException?.Invoke(
                             new ConsulWatchExceptionContext(exception, ++consecutiveFailureCount, _source)) ??
                         TimeSpan.FromSeconds(5);
-                    await Task.Delay(wait, _cancellationTokenSource.Token);
+                    await Task.Delay(wait, cancellationToken);
                 }
             }
         }

test/Winton.Extensions.Configuration.Consul.Test/ConsulConfigurationProviderTests.cs

@@ -72,8 +72,8 @@ public sealed class Dispose : ConsulConfigurationProviderTests
             private async Task ShouldCancelPollingTaskWhenReloading()
             {
                 var expectedKvCalls = 0;
-                var pollingCancelled = new TaskCompletionSource<CancellationToken>();
-                CancellationToken cancellationToken = default;
+                var pollingCancelled = new TaskCompletionSource<bool>();
+
                 _source.ReloadOnChange = true;
                 _source.Optional = true;
                 _kvEndpoint
@@ -87,18 +87,21 @@ private async Task ShouldCancelPollingTaskWhenReloading()
                             }
 
                             expectedKvCalls++;
-                            if (cancellationToken == default)
+                            if (token.CanBeCanceled)
                             {
-                                cancellationToken = token;
+                                token.Register(() => pollingCancelled.TrySetResult(true));
                             }
                         })
-                    .Returns(
-                        pollingCancelled.Task.IsCompleted
-                            ? Task.FromCanceled<QueryResult<KVPair[]>>(pollingCancelled.Task.Result)
-                            : Task.FromResult(new QueryResult<KVPair[]> { StatusCode = HttpStatusCode.OK }));
+                    .Returns<string, QueryOptions, CancellationToken>(
+                        (_, __, token) =>
+                            token.IsCancellationRequested
+                                ? Task.FromCanceled<QueryResult<KVPair[]>>(token)
+                                : Task.Delay(5).ContinueWith(t => new QueryResult<KVPair[]> { StatusCode = HttpStatusCode.OK }));
 
                 _provider.Load();
-                cancellationToken.Register(() => pollingCancelled.SetResult(cancellationToken));
+
+                // allow polling loop to spin up
+                await Task.Delay(25);
 
                 _provider.Dispose();