Merge pull request dotnet#19255 from sharwell/asynclazy-fast-path

Use a wait-free fast path in AsyncLazy<T>.GetValueAsync

src/Workspaces/Core/Portable/Utilities/AsyncLazy`1.cs

@@ -179,6 +179,12 @@ public override T GetValue(CancellationToken cancellationToken)
         {
             cancellationToken.ThrowIfCancellationRequested();
 
+            // If the value is already available, return it immediately
+            if (TryGetValue(out T value))
+            {
+                return value;
+            }
+
             Request request = null;
             AsynchronousComputationToStart? newAsynchronousComputation = null;
 
@@ -297,7 +303,14 @@ public override Task<T> GetValueAsync(CancellationToken cancellationToken)
             // Optimization: if we're already cancelled, do not pass go
             if (cancellationToken.IsCancellationRequested)
             {
-                return new Task<T>(() => default(T), cancellationToken);
+                return Task.FromCanceled<T>(cancellationToken);
+            }
+
+            // Avoid taking the lock if a cached value is available
+            var cachedResult = _cachedResult;
+            if (cachedResult != null)
+            {
+                return cachedResult;
             }
 
             Request request;