More Race Condition Fixes (#28)

Author: viceroypenguin

src/Immediate.Cache.Shared/ApplicationCacheBase.cs

@@ -137,35 +137,32 @@ private Task<TResponse> GetHandlerTask()
 				if (_responseSource is { Task: { Status: not (TaskStatus.Faulted or TaskStatus.Canceled) } task })
 					return task;
 
+				task = (_responseSource = new()).Task;
+				var cancellationTokenSource = _tokenSource = new();
+
 				// escape current sync context
 				_ = Task.Factory.StartNew(
-					RunHandler,
+					o => RunHandler((CancellationTokenSource)o!),
+					cancellationTokenSource,
 					CancellationToken.None,
 					TaskCreationOptions.PreferFairness,
 					TaskScheduler.Current
 				);
 
-				return (_responseSource = new()).Task;
+				return task;
 			}
 		}
 
-		private async Task RunHandler()
+		private async Task RunHandler(CancellationTokenSource tokenSource)
 		{
-			while (true)
+			lock (_lock)
 			{
-				CancellationTokenSource tokenSource;
-
-				lock (_lock)
-				{
-					if (_responseSource?.Task is { IsCompletedSuccessfully: true })
-						return;
-
-					if (_tokenSource is null or { IsCancellationRequested: true })
-						_tokenSource = new();
-
-					tokenSource = _tokenSource;
-				}
+				if (_responseSource?.Task is { IsCompletedSuccessfully: true })
+					return;
+			}
 
+			while (true)
+			{
 				try
 				{
 					var token = tokenSource.Token;
@@ -202,6 +199,17 @@ private async Task RunHandler()
 						return;
 					}
 				}
+
+				lock (_lock)
+				{
+					if (_responseSource is null or { Task.IsCompleted: true })
+						return;
+
+					if (_tokenSource is null or { IsCancellationRequested: true })
+						_tokenSource = new();
+
+					tokenSource = _tokenSource;
+				}
 			}
 		}