Imported Upstream version 4.6.0.165

Former-commit-id: d509131f71da404210981e7263b375675928eea7

mcs/class/System/System.Net/SimpleAsyncResult.cs

@@ -81,14 +81,14 @@ namespace System.Net
 				return running;
 			}, inner => {
 				if (inner.GotException) {
-					if (inner.CompletedSynchronously)
+					if (inner.synch)
 						Monitor.Exit (locker);
 					callback (inner);
 					return;
 				}
 
 				try {
-					if (!inner.CompletedSynchronously)
+					if (!inner.synch)
 						Monitor.Enter (locker);
 
 					callback (inner);
@@ -186,8 +186,30 @@ namespace System.Net
 			}
 		}
 
+		bool? user_read_synch;
+
 		public bool CompletedSynchronously {
-			get { return synch; }
+			get {
+				//
+				// CompletedSynchronously (for System.Net networking stack) means "was the operation completed before the first time
+				// that somebody asked if it was completed synchronously"? They do this because some of their asynchronous operations
+				// (particularly those in the Socket class) will avoid the cost of capturing and transferring the ExecutionContext
+				// to the callback thread by checking CompletedSynchronously, and calling the callback from within BeginXxx instead of
+				// on the completion port thread if the native winsock call completes quickly.
+				//
+				// TODO: racy
+				if (user_read_synch != null)
+					return user_read_synch.Value;
+
+				user_read_synch	= synch;
+				return user_read_synch.Value;
+			}
+		}
+
+		internal bool CompletedSynchronouslyPeek {
+			get {
+				return synch;
+			}
 		}
 
 		public bool IsCompleted {