Imported Upstream version 4.0.0~alpha1

Former-commit-id: 806294f5ded97629b74c85c09952f2a74fe182d9

external/referencesource/System.ServiceModel/System/ServiceModel/Channels/LockHelper.cs

@@ -0,0 +1,62 @@
+// <copyright>
+// Copyright (c) Microsoft Corporation.  All rights reserved.
+// </copyright>
+
+namespace System.ServiceModel.Channels
+{
+    using System.Runtime;
+    using System.Threading;
+
+    // IMPORTANT: Only meant to be used within a using statement.
+    struct LockHelper : IDisposable
+    {
+        ReaderWriterLockSlim readerWriterLock;
+        bool isReaderLock;
+        bool isLockHeld;
+
+        LockHelper(ReaderWriterLockSlim readerWriterLock, bool isReaderLock)
+        {
+            this.readerWriterLock = readerWriterLock;
+            this.isReaderLock = isReaderLock;
+
+            if (isReaderLock)
+            {
+                this.readerWriterLock.EnterReadLock();
+            }
+            else
+            {
+                this.readerWriterLock.EnterWriteLock();
+            }
+
+            this.isLockHeld = true;
+        }
+
+        public void Dispose()
+        {
+            if (this.isLockHeld)
+            {
+                this.isLockHeld = false;
+                if (this.isReaderLock)
+                {
+                    this.readerWriterLock.ExitReadLock();
+                }
+                else
+                {
+                    this.readerWriterLock.ExitWriteLock();
+                }
+            }
+        }
+
+        internal static IDisposable TakeWriterLock(ReaderWriterLockSlim readerWriterLock)
+        {
+            Fx.Assert(readerWriterLock != null, "The readerWriterLock cannot be null.");
+            return new LockHelper(readerWriterLock, false);
+        }
+
+        internal static IDisposable TakeReaderLock(ReaderWriterLockSlim readerWriterLock)
+        {
+            Fx.Assert(readerWriterLock != null, "The readerWriterLock cannot be null.");
+            return new LockHelper(readerWriterLock, true);
+        }
+    }
+}