Use DispatcherPriority.Background for JoinableTaskFactory in tests

Author: sharwell

THIRD-PARTY-NOTICES.txt

@@ -21,3 +21,30 @@ 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.
+
+License notice for Microsoft.VisualStudio.Threading
+---------------------------------------------------
+
+Microsoft.VisualStudio.Threading
+Copyright (c) Microsoft Corporation
+All rights reserved. 
+
+MIT License
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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+SOFTWARE.

Tvl.VisualStudio.MouseFastScroll.IntegrationTests/AbstractIdeIntegrationTest.cs

@@ -6,8 +6,10 @@ namespace Tvl.VisualStudio.MouseFastScroll.IntegrationTests
     using System;
     using System.Threading.Tasks;
     using System.Windows;
+    using System.Windows.Threading;
     using Microsoft.VisualStudio.Shell.Interop;
     using Microsoft.VisualStudio.Threading;
+    using Tvl.VisualStudio.MouseFastScroll.IntegrationTests.Threading;
     using Xunit;
 
     [VsTestSettings(UIThread = true)]
@@ -57,7 +59,7 @@ private set
                 {
                     _joinableTaskContext = value;
                     _joinableTaskCollection = value.CreateCollection();
-                    _joinableTaskFactory = value.CreateFactory(_joinableTaskCollection);
+                    _joinableTaskFactory = value.CreateFactory(_joinableTaskCollection).WithPriority(Application.Current.Dispatcher, DispatcherPriority.Background);
                 }
             }
         }

Tvl.VisualStudio.MouseFastScroll.IntegrationTests/Threading/JoinableTaskFactoryExtensions.cs

@@ -0,0 +1,42 @@
+// Copyright (c) Tunnel Vision Laboratories, LLC. All Rights Reserved.
+// Licensed under the Apache License, Version 2.0. See LICENSE.txt in the project root for license information.
+
+namespace Tvl.VisualStudio.MouseFastScroll.IntegrationTests.Threading
+{
+    using System.Threading;
+    using System.Windows.Threading;
+    using Microsoft;
+    using Microsoft.VisualStudio.Threading;
+
+    // JoinableTaskFactory.WithPriority is available in later releases of vs-threading, but we reference 1.2.0.0 for
+    // compatibility with Visual Studio 2013.
+    // https://github.com/Microsoft/vs-threading/pull/142
+    internal static class JoinableTaskFactoryExtensions
+    {
+        internal static JoinableTaskFactory WithPriority(this JoinableTaskFactory joinableTaskFactory, Dispatcher dispatcher, DispatcherPriority priority)
+        {
+            Requires.NotNull(joinableTaskFactory, nameof(joinableTaskFactory));
+            Requires.NotNull(dispatcher, nameof(dispatcher));
+
+            return new DispatcherJoinableTaskFactory(joinableTaskFactory, dispatcher, priority);
+        }
+
+        private class DispatcherJoinableTaskFactory : DelegatingJoinableTaskFactory
+        {
+            private readonly Dispatcher _dispatcher;
+            private readonly DispatcherPriority _priority;
+
+            public DispatcherJoinableTaskFactory(JoinableTaskFactory innerFactory, Dispatcher dispatcher, DispatcherPriority priority)
+                : base(innerFactory)
+            {
+                _dispatcher = dispatcher;
+                _priority = priority;
+            }
+
+            protected override void PostToUnderlyingSynchronizationContext(SendOrPostCallback callback, object state)
+            {
+                _dispatcher.BeginInvoke(_priority, callback, state);
+            }
+        }
+    }
+}