Imported Upstream version 4.3.2.467

Former-commit-id: 9c2cb47f45fa221e661ab616387c9cda183f283d

mcs/class/System.Threading.Tasks.Dataflow/CoreFxSources/Internal/Threading.cs

@@ -0,0 +1,52 @@
+// Copyright (c) Microsoft. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+using System;
+using System.Collections.Generic;
+using System.Diagnostics;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace System.Threading.Tasks.Dataflow.Internal.Threading
+{
+    internal delegate void TimerCallback(object state);
+
+    internal sealed class Timer : CancellationTokenSource, IDisposable
+    {
+        internal Timer(TimerCallback callback, object state, int dueTime, int period)
+        {
+            Debug.Assert(period == -1, "This stub implementation only supports dueTime.");
+            Task.Delay(dueTime, Token).ContinueWith((t, s) =>
+            {
+                var tuple = (Tuple<TimerCallback, object>)s;
+                tuple.Item1(tuple.Item2);
+            }, Tuple.Create(callback, state), CancellationToken.None,
+                TaskContinuationOptions.ExecuteSynchronously | TaskContinuationOptions.OnlyOnRanToCompletion,
+                TaskScheduler.Default);
+        }
+
+        public new void Dispose() { base.Cancel(); }
+    }
+
+    internal sealed class Thread
+    {
+        internal static bool Yield() { return true; }
+    }
+
+    internal delegate void WaitCallback(object state);
+
+    internal sealed class ThreadPool
+    {
+        private static readonly SynchronizationContext _ctx = new SynchronizationContext();
+
+        internal static void QueueUserWorkItem(WaitCallback callback, object state)
+        {
+            _ctx.Post(s =>
+            {
+                var tuple = (Tuple<WaitCallback, object>)s;
+                tuple.Item1(tuple.Item2);
+            }, Tuple.Create(callback, state));
+        }
+    }
+}