Merge pull request #393 from dotnet-maestro-bot/merge/release/2.2-to-master

[automated] Merge branch 'release/2.2' => 'master'

Author: rynowak

build/dependencies.props

@@ -31,4 +31,5 @@
   </PropertyGroup>
   <PropertyGroup Label="Package Versions: Pinned" />
   <Import Project="$(DotNetPackageVersionPropsPath)" Condition=" '$(DotNetPackageVersionPropsPath)' != '' " />
+  <PropertyGroup Label="Package Versions: Pinned" />
 </Project>

korebuild-lock.txt

@@ -1,2 +1,2 @@
 version:3.0.0-alpha1-20180907.9
-commithash:f997365a8832ff0a3cbd9a98df45734ac2723fa0
+commithash:f997365a8832ff0a3cbd9a98df45734ac2723fa0

src/Microsoft.Extensions.Primitives/CancellationChangeToken.cs

@@ -31,6 +31,14 @@ public CancellationChangeToken(CancellationToken cancellationToken)
         /// <inheritdoc />
         public IDisposable RegisterChangeCallback(Action<object> callback, object state)
         {
+            // Don't capture the current ExecutionContext and its AsyncLocals onto the token registration causing them to live forever
+            var restoreFlow = false;
+            if (!ExecutionContext.IsFlowSuppressed())
+            {
+                ExecutionContext.SuppressFlow();
+                restoreFlow = true;
+            }
+
             try
             {
                 return Token.Register(callback, state);
@@ -40,6 +48,14 @@ public IDisposable RegisterChangeCallback(Action<object> callback, object state)
                 // Reset the flag so that we can indicate to future callers that this wouldn't work.
                 ActiveChangeCallbacks = false;
             }
+            finally
+            {
+                // Restore the current ExecutionContext
+                if (restoreFlow)
+                {
+                    ExecutionContext.RestoreFlow();
+                }
+            }
 
             return NullDisposable.Instance;
         }

test/Microsoft.Extensions.Primitives.Tests/ChangeTokenTest.cs

@@ -2,6 +2,7 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
+using System.Threading;
 using Xunit;
 
 namespace Microsoft.Extensions.Primitives
@@ -87,5 +88,40 @@ public void ChangesFireAfterExceptionsWithState()
             Assert.Equal(2, count);
             Assert.NotNull(callbackState);
         }
+
+        [Fact]
+        public void AsyncLocalsNotCapturedAndRestored()
+        {
+            // Capture clean context
+            var executionContext = ExecutionContext.Capture();
+
+            var cancellationTokenSource = new CancellationTokenSource();
+            var cancellationToken = cancellationTokenSource.Token;
+            var cancellationChangeToken = new CancellationChangeToken(cancellationToken);
+            var executed = false;
+
+            // Set AsyncLocal
+            var asyncLocal = new AsyncLocal<int>();
+            asyncLocal.Value = 1;
+
+            // Register Callback
+            cancellationChangeToken.RegisterChangeCallback(al =>
+            {
+                // AsyncLocal not set, when run on clean context
+                // A suppressed flow runs in current context, rather than restoring the captured context
+                Assert.Equal(0, ((AsyncLocal<int>) al).Value);
+                executed = true;
+            }, asyncLocal);
+
+            // AsyncLocal should still be set
+            Assert.Equal(1, asyncLocal.Value);
+
+            // Check AsyncLocal is not restored by running on clean context
+            ExecutionContext.Run(executionContext, cts => ((CancellationTokenSource)cts).Cancel(), cancellationTokenSource);
+
+            // AsyncLocal should still be set
+            Assert.Equal(1, asyncLocal.Value);
+            Assert.True(executed);
+        }
     }
 }