AsyncAtomicFactory.Initializer: do not call SetException on TCS to avoid unobserved task exception when garbage collecting TCS

Author: advdotnet

BitFaster.Caching.UnitTests/Atomic/AsyncAtomicFactoryTests.cs

@@ -75,6 +75,44 @@ public async Task WhenValueCreateThrowsValueIsNotStored()
             (await a.GetValueAsync(1, k => Task.FromResult(3))).Should().Be(3);
         }
 
+        [Fact]
+        public async Task WhenValueCreateThrowsDoesNotCauseUnobservedTaskException()
+        {
+            bool unobservedExceptionThrown = false;
+
+            TaskScheduler.UnobservedTaskException += OnUnobservedTaskException;
+            try
+            {
+                await AsyncAtomicFactoryGetValueAsync();
+
+                GC.Collect();
+                GC.WaitForPendingFinalizers();
+            }
+            finally
+            {
+                TaskScheduler.UnobservedTaskException -= OnUnobservedTaskException;
+            }
+            unobservedExceptionThrown.Should().BeFalse();
+
+            void OnUnobservedTaskException(object sender, UnobservedTaskExceptionEventArgs e)
+            {
+                unobservedExceptionThrown = true;
+                e.SetObserved();
+            }
+
+            static async Task AsyncAtomicFactoryGetValueAsync()
+            {
+                var a = new AsyncAtomicFactory<int, int>();
+                try
+                {
+                    _ = await a.GetValueAsync(12, (i) => throw new ArithmeticException());
+                }
+                catch (ArithmeticException)
+                {
+                }
+            }
+        }
+
         [Fact]
         public async Task WhenCallersRunConcurrentlyResultIsFromWinner()
         {

BitFaster.Caching/Atomic/AsyncAtomicFactory.cs

@@ -155,10 +155,9 @@ public async ValueTask<V> CreateValueAsync<TFactory>(K key, TFactory valueFactor
 
                         return value;
                     }
-                    catch (Exception ex)
+                    catch (Exception)
                     {
                         Volatile.Write(ref isInitialized, false);
-                        tcs.SetException(ex);
                         throw;
                     }
                 }