Merge pull request #408 from benaadams/CancellationTokenSource

Remove CreateLinkedTokenSource

Author: davidfowl

src/Microsoft.AspNet.Server.Kestrel/Http/Frame.cs

@@ -53,8 +53,8 @@ public partial class Frame : FrameContext, IFrameControl
         private Task _requestProcessingTask;
         private volatile bool _requestProcessingStopping; // volatile, see: https://msdn.microsoft.com/en-us/library/x13ttww7.aspx
         private volatile bool _requestAborted;
-        private CancellationTokenSource _disconnectCts = new CancellationTokenSource();
-        private CancellationTokenSource _requestAbortCts;
+        private CancellationTokenSource _abortedCts;
+        private CancellationToken? _manuallySetRequestAbortToken;
 
         private FrameRequestStream _requestBody;
         private FrameResponseStream _responseBody;
@@ -135,8 +135,47 @@ public string HttpVersion
 
         public Stream DuplexStream { get; set; }
 
-        public CancellationToken RequestAborted { get; set; }
+        public CancellationToken RequestAborted
+        {
+            get
+            {
+                // If a request abort token was previously explicitly set, return it.
+                if (_manuallySetRequestAbortToken.HasValue)
+                    return _manuallySetRequestAbortToken.Value;
+
+                // Otherwise, get the abort CTS.  If we have one, which would mean that someone previously
+                // asked for the RequestAborted token, simply return its token.  If we don't,
+                // check to see whether we've already aborted, in which case just return an
+                // already canceled token.  Finally, force a source into existence if we still
+                // don't have one, and return its token.
+                var cts = _abortedCts;
+                return
+                    cts != null ? cts.Token :
+                    _requestAborted ? new CancellationToken(true) :
+                    RequestAbortedSource.Token;
+            }
+            set
+            {
+                // Set an abort token, overriding one we create internally.  This setter and associated
+                // field exist purely to support IHttpRequestLifetimeFeature.set_RequestAborted.
+                _manuallySetRequestAbortToken = value;
+            }
+        }
 
+        private CancellationTokenSource RequestAbortedSource
+        {
+            get
+            {
+                // Get the abort token, lazily-initializing it if necessary.
+                // Make sure it's canceled if an abort request already came in.
+                var cts = LazyInitializer.EnsureInitialized(ref _abortedCts, () => new CancellationTokenSource());
+                if (_requestAborted)
+                {
+                    cts.Cancel();
+                }
+                return cts;
+            }
+        }
         public bool HasResponseStarted
         {
             get { return _responseStarted; }
@@ -188,7 +227,8 @@ public void Reset()
 
             _prepareRequest?.Invoke(this);
 
-            _requestAbortCts?.Dispose();
+            _manuallySetRequestAbortToken = null;
+            _abortedCts = null;
         }
 
         public void ResetResponseHeaders()
@@ -244,13 +284,16 @@ public void Abort()
             {
                 ConnectionControl.End(ProduceEndType.SocketDisconnect);
                 SocketInput.AbortAwaiting();
-
-                _disconnectCts.Cancel();
+                RequestAbortedSource.Cancel();
             }
             catch (Exception ex)
             {
                 Log.LogError("Abort", ex);
             }
+            finally
+            {
+                _abortedCts = null;
+            }
         }
 
         /// <summary>
@@ -294,8 +337,8 @@ public async Task RequestProcessingAsync()
                         ResponseBody = _responseBody;
                         DuplexStream = new FrameDuplexStream(RequestBody, ResponseBody);
 
-                        _requestAbortCts = CancellationTokenSource.CreateLinkedTokenSource(_disconnectCts.Token);
-                        RequestAborted = _requestAbortCts.Token;
+                        _abortedCts = null;
+                        _manuallySetRequestAbortToken = null;
 
                         var httpContext = HttpContextFactory.Create(this);
                         try
@@ -351,7 +394,7 @@ public async Task RequestProcessingAsync()
             {
                 try
                 {
-                    _disconnectCts.Dispose();
+                    _abortedCts = null;
 
                     // If _requestAborted is set, the connection has already been closed.
                     if (!_requestAborted)